J Orofac Orthop DOI 10.1007/s00056-016-0011-y
ORIGINAL ARTICLE
Shear bond strength of brackets on restorative materials Comparison on various dental restorative materials using the universal primer MonobondÒ Plus
Scherhaftfestigkeit von kieferorthopa¨dischen Metall- und Keramikbrackets Vergleich auf unterschiedlichen zahna¨rztlichen Restaurationsmaterialien unter Verwendung des Universal-Primers MonobondÒ Plus Thomas Ebert1,2 • Laura Elsner1 • Ursula Hirschfelder1 • Sebastian Hanke1 Received: 24 July 2014 / Accepted: 7 May 2015 Ó Springer-Verlag Berlin Heidelberg 2016
Abstract Objective The purpose of this work was to analyze surfaces consisting of different restorative materials for shear bond strength (SBS) and failure patterns of metal and ceramic brackets. Bonding involved the use of a universal primer (MonobondÒ Plus, Ivoclar Vivadent). Materials and methods Six restorative materials were tested, including one composite resin (Clearfil MajestyTM Posterior, Kuraray Noritake Dental), one glass–ceramic material (IPS EmpressÒ Esthetic, Ivoclar Vivadent), one oxide-ceramic material (CORiTEC Zr transpa Disc, imesicore), two base-metal alloys (remaniumÒ star, Dentaurum; ColadoÒ CC, Ivoclar Vivadent), and one palladium-based alloy (CallistoÒ 75 Pd, Ivoclar Vivadent). Bovine incisors served as controls. Both metal and ceramic brackets (discoveryÒ/discoveryÒ pearl; Dentaurum) were bonded to the restorative surfaces after sandblasting and pretreatment with MonobondÒ Plus. A setup modified from DIN 13990-2 was used for SBS testing and adhesive remnant index (ARI)-based analysis of failure patterns.
Results The metal brackets showed the highest mean SBS values on the glass–ceramic material (68.61 N/mm2) and the composite resin (67.58 N/mm2) and the lowest mean SBS on one of the base-metal alloys (ColadoÒ CC; 14.01 N/mm2). The ceramic brackets showed the highest mean SBS on the glass–ceramic material (63.36 N/mm2) and the lowest mean SBS on the palladium-based alloy (38.48 N/mm2). Significant differences between the metal and ceramic brackets were observed in terms of both SBS values and ARI scores (p \ 0.05). Under both bracket types, fractures of the composite-resin and the glass–ceramic samples were observed upon debonding. Opaque restorative materials under metal brackets were found to involve undercuring of the adhesive. Conclusions MonobondÒ Plus succeeded in generating high bond strengths of both bracket types on all restorative surfaces. Given our observations of cohesive fracture (including cases of surface avulsion) of the composite-resin and the glass–ceramic samples, we recommend against using these material combinations in clinical practice. Keywords Orthodontics Shear bond strength Orthodontic brackets Universal primer DIN 13990-2
Dr. Thomas Ebert. & Thomas Ebert [email protected] 1
Department of Orthodontics, University of Erlangen Medical School, Erlangen, Germany
2
Department of Orthodontics and Orofacial Orthopedics, Zahnklinik 3-Kieferorthopa¨die, Universita¨tsklinikum Erlangen, Glu¨ckstrasse 11, 91054 Erlangen, Germany
Zusammenfassung Ziel Ziel unserer Untersuchung war es, die Scherhaftfestigkeit und das Abscherverhalten von Metall- und Keramikbrackets auf verschiedenen Restaurationsmaterialien unter Verwendung des Universal-Primers MonobondÒ Plus zu untersuchen. Material und Methodik Es wurden 6 verschiedene Restaurationsmaterialien untersucht: Komposit (Clearfil MajestyTM
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Posterior, Kuraray Noritake Dental, Hattersheim am Main, Deutschland), Glaskeramik (IPS EmpressÒ Esthetic, Ivoclar Vivadent, Ellwangen, Deutschland), Oxidkeramik (CORiTEC Zr transpa Disc, imes-icore, Eiterfeld, Deutschland), 2 NEM(Nichtedelmetall)-Legierungen (remaniumÒ star, Dentaurum, Ispringen, Deutschland und ColadoÒ CC, Ivoclar Vivadent, Ellwangen, Deutschland) und eine Edelmetall-Palladium-Legierung (CallistoÒ 75 Pd, Ivoclar Vivadent, Ellwangen, Deutschland). Als Kontrollgruppe dienten extrahierte Rinderschneideza¨hne. Es wurden Metall- (discoveryÒ) und Keramikbrackets (discoveryÒ pearl, beide Dentaurum) verwendet. Die Oberfla¨chen der Restaurationsmaterialien wurden sandgestrahlt und mit dem Universal-Primer MonobondÒ Plus (Ivoclar Vivadent, Liechtenstein) vorbehandelt. In Anlehnung an die DIN 13990-2 erfolgten die Scherhaftfestigkeitspru¨fung und die Analyse des Bruchverhaltens (ARI). Ergebnisse Fu¨r Metallbrackets wurden die ho¨chsten mittleren Scherhaftfestigkeitswerte bei den Gruppen Glaskeramik (68,61 N/mm2) und Komposit (67,58 N/mm2) erreicht. Der niedrigste Mittelwert zeigte sich hingegen bei der NEMLegierung ColadoÒ CC (14,01 N/mm2). Bei Betrachtung der Keramikbrackets ergaben sich die ho¨chsten Mittelwerte bei der Gruppe Glaskeramik (63,36 N/mm2), der geringste Wert bei der Palladiumlegierung (38,48 N/mm2). Sowohl hinsichtlich der Scherfestigkeit als auch des ARI (,,adhesive remnant index‘‘) konnten signifikante Unterschiede zwischen Metall- und Keramikbrackets (p \ 0,05) festgestellt werden. Bei den Gruppen Komposit und Glaskeramik kam es wa¨hrend des Abschervorgangs bei beiden Brackettypen zur Fraktur der Probeko¨rper. In Kombination mit Metallbrackets konnte bei lichtundurchla¨ssigen Restaurationsmaterialien eine nur unvollsta¨ndige Polymerisation des Adha¨sivs nachgewiesen werden. Schlussfolgerung Der Universal-Primer MonobondÒ Plus konnte auf allen Restaurationsmaterialien fu¨r beide Brackettypen hohe Scherhaftfestigkeitswerte erzeugen. Bei der Komposit- und Glaskeramikgruppe kam es beim Schervorgang zur Fraktur der Probeko¨rper und teilweise zu koha¨siven Ausrissen, weshalb der klinische Einsatz auf diesen Materialien nicht empfohlen werden kann. Schlu¨sselwo¨rter Kieferorthopa¨die Scherhaftfestigkeit Bracket Universal-Primer Restaurationsmaterialien DIN 13990-2
Introduction The first step in initiating treatment with a fixed orthodontic appliance is to bond orthodontic attachments to the vestibular or lingual tooth surfaces. In most ado-
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lescent patients, adhesive bonding preceded by acid etching to condition the enamel is the approach of choice, as these patients will usually present with more or less ‘‘virgin’’ natural dentitions [7]. However, fixed appliances are today increasingly used in adult patients as well. Orthodontists are therefore no longer exclusively dealing with sound natural dentitions but also with dental restorations [4]. These surfaces, in turn, may consist of different materials, notably including alloys (of precious or base metals), ceramics (glass or oxide), and composite resins [1]. For a smooth and time-saving treatment process, modified techniques and materials are required to establish reliable bonds on surfaces consisting of these various types of restorative materials. In prosthetic dentistry, special primers are used to establish a durable bond following pretreatment of the bonding surface, but few studies have been devoted specifically to the adhesive union achieved by orthodontic brackets bonded to common restorative materials. While shear bond strengths (SBS) in the range of 4–10 N/mm2 have been demanded for bonding to enamel [12], no recommendations are currently available for bonding to restorative materials. From a clinical viewpoint, bond strengths at least as high as on enamel should also be achieved on restorative materials to avoid high rates of bracket loss. On the other hand, excessive strengths must be avoided to allow for smooth debonding without damaging, let alone destroying, the restorative surface [17]. Ideally, a single primer would be available that could be used in bonding orthodontic brackets to any restorative material while being neither technique-sensitive nor associated with material-specific differences in pretreatment. MonobondÒ Plus (Ivoclar Vivadent, Schaan, Liechtenstein) universal primer is stated by its manufacturer to be suitable for all types of restorative materials. The product consists of a highly diluted ethanolic solution that includes three active reagents: a silane, a phosphoric acid reagent, and a disulfide. Thus, it offers the advantage of containing several primers in one flask whose content can be applied to different restorative materials in exactly the same way. Once applied to the surface, a layer with the appropriate active monomer is formed, which causes the hydrophilic surface to become hydrophobic for optimal wetting of the restorative surface with the adhesive. After formation of this layer, an air blower is used to remove the excessive monomer together with the solvent. The purpose of this study was to investigate whether MonobondÒ Plus can result in adequate bond strengths for metal or ceramic attachments on a number of dental restorative materials and whether its use can be recommended in orthodontics.
Shear bond strength of brackets on restorative materials
Materials and methods
Bonding substrates
Brackets
Table 1 and Fig. 1 also convey an overview of the restorative materials (used in prosthetic and conservative dentistry) we included as bonding substrates. As composite resin, we used a highly filled nanocomposite (ClearfilTM Majesty Posterior; Kuraray Noritake, Hattersheim am Main, Germany). As ceramics, we used a glass–ceramic veneering material (IPS EmpressÒ Esthetic; Ivoclar Vivadent) and a high-strength zirconia (Coritec Zr Transpa Disc; Imes-Icore, Eiterfeld, Germany). As base-metal alloys, we used two materials with cobalt–chromium as their main constituent (remaniumÒ star, Dentaurum, Ispringen, Germany; ColadoÒ CC; Ivoclar Vivadent). As a precious-metal alloy, we used a palladium-
Details on the two (conventionally ligated) types of brackets included are provided in Table 1 and Fig. 1. Only brackets for upper central incisors were used. The first design was an esthetic ceramic bracket (DiscoveryÒ Pearl; Dentaurum, Ispringen, Germany) manufactured by ceramic injection molding (CIM) technology and featuring a laser-structured base (surface: 11.88 mm2). The second design was a conventional metal bracket (DiscoveryÒ; Dentaurum) manufactured by metal injection molding (MIM) technology and also featuring a laser-structured base (surface 11.82 mm2).
Tab. 1 Brackets and restorative materials used in this study Tab. 1 In der Studie eingesetzte Brackets und Restaurationsmaterialien
Trade name
Type
Manufacturer
DiscoveryÒ
Metal bracket
Dentaurum
DiscoveryÒ Pearl ClearfilTM Majesty Posterior
Ceramic bracket Nano-filled composite resin
Dentaurum Kuraray Noritake
IPS EmpressÒ Esthetic
Glass ceramic for veneers
Ivoclar Vivadent
Coritec Zr Transpa Disc
Zirconia (Zr2O3) ceramic
Imes-Icore
RemaniumÒ star
Base-metal (CoCr) alloy
Dentaurum
ColadoÒ CC
Base-metal (CoCr) alloy
Ivoclar Vivadent
CallistoÒ 75 Pd
Noble-metal (Pd-based) alloy
Ivoclar Vivadent
Fig. 1 Restorative materials and brackets investigated. Top to bottom on the left ClearfilTM Majesty Posterior; IPS EmpressÒ Esthetic. Top to bottom in the cente Coritec Zr Transpa Disc; remaniumÒ star; ColadoÒ CC; CallistoÒ 75 Pd. Top to bottom on the right bovine control tooth; metal bracket (DiscoveryÒ); ceramic bracket (DiscoveryÒ Pearl)
Abb. 1 Untersuchte Restaurationsmaterialen und Brackets. Links, von oben nach unten ClearfilTM Majesty Posterior, IPS EmpressÒ Esthetic; Mitte, von oben nach unten CORiTEC Zr transpa Disc, remaniumÒ star, ColadoÒ CC, CallistoÒ 75 Pd; rechts, von oben nach unten Rinderschneidezahn (Kontrolle), Metallbracket (discoveryÒ), Keramikbracket (discoveryÒ pearl)
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based alloy (CallistoÒ 75 Pd; Ivoclar Vivadent). Permanent bovine incisors that had been freshly extracted served as control group. Each group (six experimental groups and one control group) included 30 samples, to which either ceramic (n = 15) or metal (n = 15) brackets were bonded. An exception was the ColadoÒ CC group, which included metal brackets on only 10 samples. Thus a total of 205 samples were available for debonding. Primers and adhesive The primers employed included MonobondÒ Plus in all groups of restorative materials and TransbondTM XT Light Cure Adhesive Primer (3 M Unitek, Neuss, Germany) in the control group. In all groups, the metal and ceramic brackets were bonded with TransbondTM XT Light Cure Adhesive (3 M Unitek). Sample preparation The CallistoÒ 75 Pd precious-metal alloy was supplied in the form of plates; due to their torsional stiffness and dimensional stability, the dimensions of these plates (12.8 9 7.8 9 1.0 mm) were used as a blueprint for all samples in all experimental groups. The ColadoÒ CC base-metal samples were cast and polished to high gloss in the laboratory. The zirconia samples were milled from blanks and compacted in a sintering furnace. The remaniumÒ star base-metal alloy, again, was available from the manufacturer as plates not requiring further processing. The IPS EmpressÒ Esthetic glass–ceramic material is normally pressed to shape; it is supplied in the form of cylindrical blanks (length 13.4 mm; diameter 11.4 mm), which were longitudinally halved with a diamond saw and embedded in resin (Technovit 4004; Heraeus Kulzer, Wehrheim, Germany) as per DIN 13990-2 [10] such that the prospective bonding surface was not in contact with the resin. The composite-resin samples were created by layering ClearfilTM Majesty into a mold of addition-type silicone (Lab-Silicone; Henry Schein, Melville, NY, USA) created from the previously prepared, halved glass–ceramic cylinders; the composite-resin cylinders resulting from the subsequent light curing were then embedded in resin, using the same steps outlined above for the glass–ceramic samples. The bovine teeth were embedded in Technovit 4004 as well. In accordance with DIN 13990-2, all samples were oriented such that the shear blade used for debonding made perpendicular contact with the bracket base. Bonding procedure The surfaces of the restorative materials were degreased with alcohol and roughened with 50-lm alumina particles
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using an intraoral sandblaster (MicroEtcher; Danville Materials, San Ramon, CA, USA) applied from a distance of approximately 50 mm for 10 s, followed by rinsing with a water spray for 10 s and drying with oil-free compressed air. MonobondÒ Plus universal primer was applied, in accordance with the manufacturer’s instructions, as a thin layer and allowed to rest for 60 s. Then excess material was removed from the surface with an air blower. The bracket bases were covered with TransbondTM XT adhesive and, as per DIN 13990-2, placed onto the samples using gentle pressure, followed by careful removal of excessive resin. Finally a curing light (Valo Ortho; Opal Orthodontics, South Jordan, UT, USA) was applied to the mesial, distal, occlusal and gingival aspects of the bracket at 1200 mW/cm2 for 10 s each. Shear bond strength test The experimental setup was devised with reference to DIN 13990-2. After the samples had been stored in distilled water at 37 °C inside an incubator for 24 h, we conducted the SBS test using a universal testing machine (Zwick/ Roell, Ulm, Germany). In the groups remaniumÒ star, ColadoÒ CC, CallistoÒ 75 Pd, and Coritec Zr Transpa Disc, stable positioning of the samples during debonding was ensured by mounting them in the testing machine with a special aluminum block. All samples were positioned and mounted such that the debonding force was applied perpendicular to the bracket base. Departing from DIN 13990-2, which describes the use of a wire loop, we employed an apparatus with a shear blade that ruled out any contact with structures other than the bracket base during debonding (Fig. 2). This modification reliably prevented the applied force from sliding off the bracket base, considering the very flat base designs employed. Using a load cell (output 1 kN) to measure the force levels applied, the shear blade was lowered at a rate of 1.0 mm/min until the bond failed. Then, dividing the maximum load (N) applied by the surface area of the bonding site (mm2), the SBS was calculated and expressed in N/mm2. Failure patterns After debonding, both the surfaces of the samples and the bracket bases were analyzed at 109 magnification (Stemi SV6; Zeiss, Oberkochen, Germany) for the patterns by which the bonds had failed. Four patterns were distinguished—via ARI (Adhesive Remnant Index) scores as described by Artu˚n and Bergand [2]—depending on how much adhesive was left on the samples and on the bracket base: ARI 0 (0 % on sample, 100 % on bracket), ARI 1 (\50 % on sample, [50 % on bracket), ARI 2 ([50 % on
Shear bond strength of brackets on restorative materials
sample, \50 % on bracket), or ARI 3 (100 % on sample, 0 % on bracket). Statistical analysis The data of our evaluations were transferred to spreadsheet software (Excel 2010; Microsoft, Redmond, WA, USA) and analyzed using a statistical add-in (XLStat2013; Addinsoft, Paris, France). The values from the measurements were descriptively prepared and subjected to a Shapiro–Wilk test for normal distribution, a nonparametric Mann–Whitney U test and Kruskal–Wallis (analysis of variance by ranks) test for intergroup differences, and a Brunner–Dette–Munk (analysis of variance by ranks) test for two factors. A v2 test was used to analyze the distribution of ARI scores. Bonferroni correction was applied to arrive at statistically predictive significances. All tests were based on p B 0.05 as probability of error.
Results Dataset
Fig. 2 As an example for all material combinations tested, this photograph shows a Coritec Zr Transpa Disc sample mounted in the shear apparatus with a DiscoveryÒ metal bracket bonded to its surface. The shear blade is lowered such that it makes precisely perpendicular contact with the bracket base Abb. 2 Exemplarisch fu¨r alle untersuchten Materialkombinationen ist eine Probe der Gruppe CORiTEC Zr transpa Disc in Kombination mit dem discoveryÒ Metall-Bracket in der Abschervorrichtung eingespannt. Der Abscherstempel trifft senkrecht von oben exakt auf die Bracketbasis
The dataset of values measured in this study originally included 205 results (corresponding to the number of samples subjected to SBS testing). After correction for outliers, 202 results were available for statistical analysis. Descriptive statistics were calculated for each of the restorative materials, including the mean SBS and its standard deviation, as well as its median value and range. These values were calculated separately for metal (Table 2) and for ceramic (Table 3) brackets. The SBS values measured with either bracket type in box plots are shown in Figs. 3 and 4. Nonparametric tests were used for analysis, since a normal distribution was not present.
Tab. 2 Shear bond strengths obtained with metal brackets Tab. 2 Scherhaftfestigkeit bei Metallbrackets n
Mean ± SD (N)
Median (N)
Min|max (N)
Mean ± SD (N/mm2)
Median (N/mm2)
Min|max (N/mm2)
ClearfilTM Majesty Posterior
15
798.80 ± 89.60
784.49
641.35|951.86
67.58 ± 7.58
66.37
54.26|80.53
IPS EmpressÒ Esthetic
15
810.97 ± 69.74
800.92
717.12|960.97
68.61 ± 5.90
67.76
60.67|81.30
Coritec Zr Transpa Disc
15
434.03 ± 23.88
440.18
387.34|468.54
36.72 ± 2.02
37.24
32.77|39.64
RemaniumÒ star
15
305.78 ± 71.98
311.10
165.13|443.60
25.87 ± 6.09
26.32
13.97|37.53
9
165.60 ± 29.55
159.57
127.30|227.30
14.01 ± 2.50
13.50
10.77|19.23
CallistoÒ 75 Pd
15
185.93 ± 36.88
178.01
130.49|257.79
15.73 ± 3.12
15.06
11.04|21.81
Control group
15
705.65 ± 138.06
705.65
425.05|910.84
59.70 ± 11.68
59.70
35.96|77.06
ColadoÒ CC
Data expressed as two separate sets of values (N and N/mm2) obtained after exclusion of outliers
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E. Thomas et al. Tab. 3 Shear bond strengths obtained with ceramic brackets Tab. 3 Scherhaftfestigkeit bei Keramikbrackets n
Mean ± SD (N)
Median (N)
Min|max (N)
Mean ± SD (N/mm2)
Median (N/mm2)
Min|max (N/mm2)
ClearfilTM Majesty Posterior
15
491.00 ± 105.14
495.87
321.95|746.30
41.33 ± 8.85
41.74
27.10|62.82
IPS EmpressÒ Esthetic
14
752.72 ± 110.60
753.55
633.09|950.04
63.36 ± 9.31
63.43
53.29|79.97
Coritec Zr Transpa Disc RemaniumÒ star
15 15
531.99 ± 138.16 640.69 ± 124.62
533.53 631.42
337.99|781.70 392.40|819.60
44.78 ± 11.63 53.93 ± 10.49
44.91 53.15
28.45|65.80 33.03|68.99
ColadoÒ CC
15
583.07 ± 148.74
600.06
333.23|832.79
49.08 ± 12.52
50.51
28.05|70.10
CallistoÒ 75 Pd
15
457.14 ± 69.02
449.06
354.14|560.74
38.48 ± 5.81
37.80
29.81|47.20
Control group
14
589.25 ± 142.68
615.50
441.58|783.60
49.60 ± 12.01
51.81
37.17|65.96
Data expressed as two separate sets of values (N and N/mm2) obtained after exclusion of outliers
Fig. 3 Box-plot diagram of shear bond strengths under metal brackets. Lines and crosses inside the boxes indicate median and mean values, respectively Abb. 3 Boxplot-Darstellung der Scherhaftfestigkeitswerte unter Metallbrackets. Horizontale Linien Medianwerte, Kreuze Mittelwerte
Fig. 4 Box-plot diagram of shear bond strengths under ceramic brackets. Lines and crosses inside the boxes indicate median and mean values, respectively Abb. 4 Boxplot-Darstellung der Scherhaftfestigkeitswerte unter Keramikbrackets. Horizontale Linien Medianwerte, Kreuze Mittelwerte
Shear bond strength
the ClearfilTM Majesty Posterior, remaniumÒ star, ColadoÒ CC, CallistoÒ 75 Pd and control groups, but not in the IPS EmpressÒ Esthetic and Coritec Zr Transpa Disc groups (data not shown). Two-way ANOVA by ranks (Brunner–Dette– Munk test) disclosed that the most important modifier of results was restorative material, followed by interaction and bracket type. Incomplete curing of the adhesive was noted with the metal brackets in the remaniumÒ star, ColadoÒ CC, and CallistoÒ 75 Pd groups. We shall elaborate on this finding in the ‘‘Discussion’’.
The metal brackets (Table 2; Fig. 3) yielded the highest mean SBS values (68.61 and 67.58 N/mm2) in the IPS EmpressÒ Esthetic and ClearfilTM Majesty Posterior groups and the lowest mean SBS (14.01 N/mm2) in the ColadoÒ CC group. With the ceramic brackets (Table 3; Fig. 4), the highest mean values (63.36 and 53.93 N/mm2) were observed in the IPS EmpressÒ Esthetic and remaniumÒ star groups and the lowest mean value (38.48 N/mm2) in the CallistoÒ 75 Pd group. ANOVA by ranks revealed some significant differences between restorative materials under both the metal and the ceramic brackets. Pairwise comparisons of these intergroup differences are given in Tables 4 and 5. Significant (p B 0.05) within-group differences in SBS between the metal and the ceramic brackets emerged in
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Failure patterns Debonding of the metal brackets (Fig. 5) overwhelmingly resulted in scores of ARI 0 across all groups (n = 69). Scores of ARI 1 (n = 9) or 2 (n = 2) were noted
Shear bond strength of brackets on restorative materials Tab. 4 Pairwise intergroup comparison of shear bond strengths under metal brackets Tab. 4 Paarweiser Intergruppen-Vergleich der Scherhaftfestigkeit unter Metallbrackets p ClearfilTM ClearfilTM Majesty Posterior
1
IPS
Coritec
RemaniumÒ
ColadoÒ
CallistoÒ
Control
*
IPS EmpressÒ Esthetic
\0.0001
1
*
Coritec Zr Transpa Disc RemaniumÒ star
0.456 0.005
0.000 0.063
1 0.040
1
ColadoÒ CC
0.096
0.003
0.358
0.257
1
CallistoÒ 75 Pd
0.449
\0.0001
0.133
0.000
0.015
1
Control group
0.040
0.012
0.186
0.487
0.676
0.005
1
ColadoÒ
CallistoÒ
Control
* *
* Significant differences based on a significance level of 0.0024 after Bonferroni correction
Tab. 5 Pairwise intergroup comparison of shear bond strengths under ceramic brackets Tab. 5 Paarweiser Intergruppen-Vergleich der Scherhaftfestigkeit unter Keramikbrackets p ClearfilTM
IPS
ClearfilTM Majesty Posterior
1
IPS EmpressÒ Esthetic
0.896
1
Coritec Zr Transpa Disc
0.007
0.004
Coritec
RemaniumÒ *
*
*
*
*
*
1
Ò
Remanium star
\0.0001
\0.0001
0.194
1
ColadoÒ CC
\0.0001
\0.0001
0.004
0.081
1
CallistoÒ 75 Pd
\0.0001
\0.0001
0.004
0.123
0.682
0.435
0.362
0.054
0.001
\0.0001
Control group
* * 1 \0.0001
* 1
* Significant differences based on a significance level of 0.0018 after Bonferroni correction
Fig. 5 Distribution of ARI scores after debonding of metal brackets Abb. 5 Verteilung der ARI-Werte nach Debonding der Metallbrackets
considerably less often. Findings of ARI 3 were confined to sporadic cases within the remaniumÒ star (n = 3) und ClearfilTM Majesty Posterior (n = 1) groups. A different distribution of failure patterns was seen with the ceramic brackets (Fig. 6). Here ARI 3 was the dominant score in all groups other than the control group (n = 53), followed by
ARI 2 (n = 19) and ARI 1 (n = 13). The only groups to exhibit any scores of ARI 0 were CallistoÒ 75 Pd (n = 4), Coritec Zr Transpa Disc (n = 1), and the controls (n = 1). The v2 test showed that most of these within-group differences between metal and ceramic brackets in terms of ARI-score distribution were significant, remaniumÒ star being the only group to show no significant bracket-specific difference in this regard. All samples in the ClearfilTM Majesty Posterior and IPS EmpressÒ Esthetic groups, used with either bracket type, showed internal fractures after debonding (Figs. 7, 8, 9, 10). In the control group, the high shear forces induced enamel cracks in 2 of the 15 teeth used under ceramic brackets and in 10 of the 15 teeth used under metal brackets.
Discussion The aim of this in vitro study was to determine whether a commercially available primer was capable of generating bond strengths between metal or ceramic brackets and dental restorative materials that would be sufficiently high
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E. Thomas et al. Fig. 6 Distribution of ARI scores after debonding of ceramic brackets Abb. 6 Verteilung der ARIWerte nach Debonding der Keramikbrackets
Fig. 7 Cohesive fractures inside a composite-resin sample (ClearfilTM Majesty) after debonding of a metal bracket. ARI score is 0. The resin fractures even include superficial avulsion Abb. 7 Koha¨sive Frakturen innerhalb der Probe ClearfilTM MajestyTM nach Abscherung eines Metallbrackets. Der ARI-Score betra¨gt 0, deutlich sichtbar sind oberfla¨chliche Ausrisse von Komposit
for orthodontic treatment. As reference, we adopted the range of 5.9–7.8 N/mm2 demanded by Reynolds [20] for attachments on enamel. While over 30 years old, this is still a useful recommendation, as this range is below the cohesive strength of enamel (10.3 N/mm2) [6] to avoid or minimize avulsion-type enamel fractures upon debonding [11, 19, 22]. While debonding from restored tooth surfaces will not damage enamel, there is nevertheless a risk of inducing defects or initiating cracks on veneers or other types of restored surfaces [16, 17]. Pertinent reference values are currently not available in the literature. To judge the clinical effectiveness of the primer used in this study, it was important that the pretreatment applied to
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Fig. 8 Cohesive fractures inside a composite-resin sample (ClearfilTM Majesty) after debonding of a ceramic bracket. ARI score is 3. The entire adhesive is retained on the resin sample; note the visible impression of the bracket base Abb. 8 Koha¨sive Frakturen innerhalb der Probe ClearfilTM MajestyTM nach Abscherung eines Keramikbrackets. Der ARI-Score betra¨gt 3, das Adha¨siv mit Abdruck der Bracketbasis ist vollsta¨ndig auf der Probe verblieben
the surfaces would be neither technique-sensitive nor timeconsuming and, most importantly, would not vary with different restorative materials. The latter requirement of uniform pretreatment was met, since the only pretreatment applied to the restorative surfaces was sandblasting with alumina particles as per the manufacturer’s recommendations. The exposure time required for the universal primer of 60 s was consistent with the duration of enamel etching [7] and had to be followed by removal of excessive material with an air blower.
Shear bond strength of brackets on restorative materials
Fig. 9 Cohesive fractures inside a glass–ceramic sample (IPS EmpressÒ Esthetic) sample after debonding of a metal bracket. ARI score is 0. The ceramic fractures even include superficial avulsion Abb. 9 Koha¨sive Frakturen innerhalb der Probe IPS EmpressÒ Esthetic nach Abscherung eines Metallbrackets. Der ARI-Score betra¨gt 0, sichtbar sind oberfla¨chliche Ausrisse von Glaskeramik
as a diluted ethanolic solution that consists of three mutually stable bonding monomers (silane, phosphoricacid agent, disulfide). As a rule, glass–ceramic materials are either etched with hydrofluoric acid or blasted with alumina particles to generate a microretentive surface [13, 26], followed by a step known as ‘‘silanization’’ enabling the ceramic surface to enter a chemical bond [18]. MonobondÒ Plus achieves this task via a functional trihydroxysilane group of a methacrylate monomer binding to the silicate surface of the restoration as part of a condensation reaction. As zirconia and base metals possess a high affinity to phosphoric acid and form poorly soluble phosphates [25], MonobondÒ Plus contains methacrylate monomers with a functional phosphoric-acid group for chemical bonding, resulting in a strong and hydrolysisproof bond to zirconia or base-metal surfaces. Bonding to precious metals is achieved via a cyclic disulfide group with a ring structure, which will open as the reaction is taking place on the metal surface and, via a sulfur atom, will bind to the surface forming a light sulfide layer. In any of these scenarios, only the reagent chemically matching the restorative material will actively react, while the excessive monomer can subsequently be removed together with the solvent by applying an air blower. What remains is a hydrophobic surface which, in turn, can enter a bond with a composite resin. Shear apparatus
Fig. 10 Cohesive fractures inside a glass–ceramic sample (IPS EmpressÒ Esthetic) after debonding of a ceramic bracket. ARI score is 3. The entire adhesive is retained on the resin sample; note the visible impression of the bracket base Abb. 10 Koha¨sive Fraktur innerhalb der Probe IPS EmpressÒ Esthetic nach Abscherung eines Keramikbrackets. Der ARI-Score betra¨gt 3, das Adha¨siv mit Abdruck der Bracketbasis ist vollsta¨ndig auf der Probe verblieben
MonobondÒ Plus No specialized products are currently available to bond orthodontic brackets to restorative materials. Yet MonobondÒ Plus is stated by its manufacturer to generate reliable bonds in this context, even though its intended use is primarily for permanent indirect restorations in prosthetic and conservative dentistry [25]. This primer comes
Departing from DIN 13990-2, which describes the use of a wire loop, we employed an apparatus featuring a shear blade for debonding (Fig. 2). This setup allowed the shear force to be applied from a perpendicular direction directly to the bracket base. In this way, pure shear force without moment components could be maintained. We regarded a wire loop as unfavorable due to the considerable flatness of the bracket bases, which would have prevented secure retention of the loop under the base during debonding. This use of a specific shear apparatus might explain our finding of some high SBS values compared to the literature. Composite resin ClearfilTM Majesty Posterior, representing the class of dental filling resins among the restorative materials here tested, reached a mean SBS of 67.58 N/mm2 under metal brackets—which was the second-highest overall value in this study—and 41.33 N/mm2 under ceramic brackets. As illustrated by Figs. 7 and 8, cohesive fractures inside the samples were noted both under the metal and under the ceramic brackets in spite of different failure patterns involved (ARI 0 versus 3). In 2010, Viwattanatipa et al. [24], by contrast, reported a mean SBS of just 6.9 N/mm2
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for brackets bonded to nano-filled composite resin; however, they initially stored the samples in distilled water for 1 month and exposed them to thermocycling after pretreatment with a special resin primer. In 2013, Daratsianos et al. [9] reported decreases down to 23.1 % of initial SBS values after fatigue simulation. Ribeiro et al. [21] recorded a mean of 6.82 N/mm2 on composite-resin samples after surface roughening with a diamond bur in the absence of artificial aging. This is in contrast to data on composite repairs involving silane, which resulted in SBS values [50 N/mm2 despite artificial aging [14]. Overall, very heterogeneous results are documented in the literature, due to different pretreatment and storage protocols and properties of the materials tested. Regrettably, this makes a direct comparison virtually impossible.
Oxide ceramic Coritec Zr Transpa Disc, representing the category of highstrength zirconia ceramics among the restorative materials tested here, reached a mean SBS of 36.72 N/mm2 under metal brackets and 44.78 N/mm2 under ceramic brackets. As expected, due to the high strength of zirconia ceramics, we observed no fractures on evaluating the failure patterns. Attia et al. [3] and Kern and Thompson [16] published a study on MonobondÒ Plus based on a similar experimental setup, which resulted in a comparable SBS of 42.5 N/mm2. Thus MonobondÒ Plus universal primer does seem to be usable in orthodontic bonding procedures to zirconia restorations. Base-metal alloys
Glass ceramic Very high mean SBS values were also noted with IPS EmpressÒ Esthetic both on the metal (68.61 N/mm2) and on the ceramic (63.36 N/mm2) brackets. Again, these similar SBS data were obtained even though both bracket types were associated with clearly different failure modes (Figs. 5, 6; ARI 0 versus 2–3). Likewise, much the same pattern as in the ClearfilTM Majesty Posterior group emerged in that almost all samples showed cohesive fractures (Figs. 9, 10). Cochran et al. [8], in a 1997 study involving different protocols of glass–ceramic pretreatment, achieved SBS levels of 41 N/mm2 after sandblasting and silanization, associated with an increased rate of ceramic fractures. After sandblasting or hydrofluoric-acid etching only, they observed 6.5 or 18.0 N/mm2 and lower fracture rates. In 2012, Girish et al. [13] confirmed that sandblasting and silanization was associated with the highest SBS values. Bourke and Rock [5] recommended a pretreatment for feldspathic ceramics that includes etching with 37 % phosphoric acid for 60 s and additional silanization to reach clinically adequate bond strengths while reducing the risk of ceramic fracture. Unfortunately, no survival rates are currently documented for ceramic restorations after debonding of brackets. In vitro data on record, however, do suggest that rather moderate SBS levels gentle on the restorations should be favored for temporary orthodontic use. Our result of metal versus ceramic brackets resulting in contrasting failure patterns is presumably due to their differences in elastic modulus and retentive strength. Given our findings of high SBS values and resultant sample fractures in the ClearfilTM Majesty Posterior and IPS EmpressÒ Esthetic groups, bonding of brackets to glass ceramics or composite resins is not a suitable application for MonobondÒ Plus universal primer.
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With remaniumÒ star und ColadoÒ CC, we evaluated two materials falling into this category. Under metal brackets, these achieved a mean SBS value of 25.87 and 14.01 N/ mm2, respectively. Sanokhan et al. [23], in a 2012 study comparing the SBS of composite resin to a cobalt–chromium alloy used with different primers, reported a mean of 13.87 N/mm2 for MonobondÒ Plus after sandblasting (significance level 95 %). The failure patterns we observed in both groups were mainly characterized by ARI scores 0 and 1; in other words, absence of residual adhesive on the samples was the predominant finding. Under ceramic brackets, both materials achieved clearly higher mean SBS values of 53.93 N/mm2 (remaniumÒ star) or 49.08 N/mm2 (ColadoÒ CC) than under metal brackets, which was associated with a distinct shift of failure patterns toward higher percentages (up to 100 %) of residual adhesive being left on the samples, as reflected by a predominance of ARI scores 2 and 3. Precious-metal alloy CallistoÒ 75 Pd, being a palladium-based alloy and representing the class of precious-metal alloys among the restorative materials tested here, reached a mean SBS of 15.73 N/mm2 under metal brackets, which ranks between the values for the two base-metal alloys. The bracket–adhesive–metal interface predominantly failed between the adhesive and the alloy (ARI 0). In 2013, Jung et al. [15] evaluated the SBS of metal brackets on gold restorations depending on how long the silane applied after sandblasting was allowed to rest on the surface; they observed a mean value of 11.86 N/mm2. In most instances, however, more than 90 % of the adhesive remained on the samples. Similar to both of the base-metal alloys under ceramic brackets, the mean SBS value achieved by CallistoÒ 75 Pd was distinctly higher under ceramic brackets (38.48 N/
Shear bond strength of brackets on restorative materials
mm2). Again, ARI score 3 was the predominant failure pattern in this group. 5. Metal versus ceramic brackets The marked differences in SBS between metal and ceramic brackets in the groups remaniumÒ star, ColadoÒ CC, and CallistoÒ 75 Pd may be attributed to incomplete polymerization of the adhesive on the metal brackets. Despite 40 s of light curing, our post-debonding analysis of fracture behavior did reveal undercured adhesive on the material combinations that involved metal brackets: while complete polymerization was present in the marginal bracket areas close to the light, undercured sites (scratchable with a probe) were found in the central base areas. Thus, it is advisable, whenever materials of this type are combined in clinical practice, to optimize the bond by resorting to a chemically curing adhesive.
Other considerations The results of this in vitro study reflect early situations of bond strength achieved on samples that had been stored for 24 h. Since the adhesive may theoretically undergo some continued polymerization during these 24 h, relevantly smaller levels of bond strength may actually be present immediately after bonding of brackets in clinical practice. Recent data have shown that fatigue simulation performed on bracket–adhesive–enamel complexes involving TransbondTM XT induced a decrease in SBS down to 23.1 % of the initial situations depending on the number of loading cycles [9]. Our comparison between the restorative materials tested in the present study is permissible because the same adhesive was used in all groups. Given the current paucity of data in the literature about bond strengths on dental restorative materials, there is an urgent need for more experimental and clinical studies.
Conclusion 1. 2.
3.
4.
MonobondÒ Plus generated high SBS levels on all restorative materials tested. The composite-resin and glass–ceramic samples were found to fracture during debonding, even including avulsion-type surface fractures in some cases. The failure patterns observed (expressed as ARI scores) revealed a number of statistically significant differences between metal and ceramic brackets. Temporary clinical bonding of brackets to compositeresin or glass–ceramic surfaces is not a recommended application for MonobondÒ Plus, considering the
6.
fracture risk of these materials in the presence of high bond strengths. Undercuring of the adhesive may result when metal brackets are bonded to opaque restorative materials. In clinical practice, a chemically curing adhesive should be used whenever materials of this type are combined. Prior to any bonding of brackets to restorative surfaces, patient information needs to be provided about the risk of damaging or destroying the restoration.
Acknowledgments The authors are indebted to Dentaurum, Ivoclar Vivadent, and Ortho Service Germany for their kind support and provision of the materials used in this study. They also wish to thank the staff members of the Materials Science Laboratory of the First Department of Dentistry (Zahnklinik 1) at University of Erlangen and Mr. Lo¨w for technical support. Financial support for the project was received from the German Orthodontic Society. Compliance with ethical guidelines Conflict of interest Thomas Ebert, Laura Elsner, Ursula Hirschfelder, Sebastian Hanke stat that there are no conflicts of interest. The accompanying manuscript does not include studies on humans or animals.
References 1. Abu Alhaija ES, Abu AlReesh IA, AlWahadni AM (2010) Factors affecting the shear bond strength of metal and ceramic brackets bonded to different ceramic surfaces. Eur J Orthod 32(3):274–280 2. Artun J, Bergland S (1984) Clinical trials with crystal growth conditioning as an alternative to acid-etch enamel pretreatment. Am J Orthod 85(4):333–340 3. Attia A, Lehmann F, Kern M (2011) Influence of surface conditioning and cleaning methods on resin bonding to zirconia ceramic. Dental Mater 27(3):207–213 4. Blakey R, Mah J (2010) Effects of surface conditioning on the shear bond strength of orthodontic brackets bonded to temporary polycarbonate crowns. Am J Orthod Dentofac Orthoped 138(1):72–78 5. Bourke BM, Rock WP (1999) Factors affecting the shear bond strength of orthodontic brackets to porcelain. Br J Orthod 26(4):285–290 6. Bowen RL, Rodriguez MS (1962) Tensile strength and modulus of elasticity of tooth structure and several restorative materials. J Am Dent Assoc 64:378–387 7. Buonocore MG (1955) A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 34(6):849–853 8. Cochran D, O’Keefe KL, Turner DT, Powers JM (1997) Bond strength of orthodontic composite cement to treated porcelain. Am J Orthod Dentofac Orthoped 111(3):297–300 9. Daratsianos N, Musabegovic E, Reimann S, Gruner M, Jager A, Bourauel C (2013) The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study. Dental Mater 29(5):506–513 10. DIN13990-2 (2009) Zahnheilkunde - Pru¨fverfahren fu¨r die Scherhaftfestigkeit von Adha¨siven fu¨r kieferorthopa¨dische Befestigungselemente - Teil 2: Gesamtverbund Befestigungselement-Adha¨siv-Zahnschmelz. Beuth Verlag, Berlin
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E. Thomas et al. 11. Ferreira FG, Nouer DF, Silva NP, Garbui IU, Correr-Sobrinho L, Nouer PR (2013) Qualitative and quantitative evaluation of human dental enamel after bracket debonding: a noncontact three-dimensional optical profilometry analysis. Clinical oral investigations 12. Gillis I, Redlich M (1998) The effect of different porcelain conditioning techniques on shear bond strength of stainless steel brackets. Am J Orthod Dentofac Orthoped 114(4):387–392 13. Girish PV, Dinesh U, Bhat CS, Shetty PC (2012) Comparison of shear bond strength of metal brackets bonded to porcelain surface using different surface conditioning methods: an in vitro study. J Contemp Dent Pract 13(4):487–493 14. Jafarzadeh Kashi TS, Erfan M, Rakhshan V, Aghabaigi N, Tabatabaei FS (2011) An in vitro assessment of the effects of three surface treatments on repair bond strength of aged composites. Oper Dent 36(6):608–617 15. Jung MH, Shon WJ, Park YS, Chung SH (2013) Effects of silanation time on shear bond strength between a gold alloy surface and metal bracket. Kor J Orthod 43(3):127–133 16. Kern M, Thompson VP (1994) Sandblasting and silica coating of a glass-infiltrated alumina ceramic: volume loss, morphology, and changes in the surface composition. J Prosthet Dent 71(5):453–461 17. Lee-Knight CT, Wylie SG, Major PW, Glover KE, Grace M (1997) Mechanical and electrothermal debonding: effect on ceramic veneers and dental pulp. Am J Orthod Dentofac Orthoped 112(3):263–270 18. Lu R, Harcourt JK, Tyas MJ, Alexander B (1992) An investigation of the composite resin/porcelain interface. Aust Dent J 37(1):12–19
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19. Pont HB, Ozcan M, Bagis B, Ren Y (2010) Loss of surface enamel after bracket debonding: an in vivo and ex vivo evaluation. Am J Orthod Dentofac Orthoped 138(4):387, e381–389 (discussion 387–389) 20. Reynolds IR (1975) A review of direct orthodontic bonding. Br J Orthod 2:171–178 21. Ribeiro AA, de Morais AV, Brunetto DP, Ruellas AC, de Araujo MT (2013) Comparison of shear bond strength of orthodontics brackets on composite resin restorations with different surface treatments. Dental Press J Orthod 18(4):98–103 22. Ryf S, Flury S, Palaniappan S, Lussi A, van Meerbeek B, Zimmerli B (2012) Enamel loss and adhesive remnants following bracket removal and various clean-up procedures in vitro. Eur J Orthod 34(1):25–32 23. Sanohkan S, Urapepon S, Harnirattisai C, Sirisinha C, Sunintaboon P (2012) Shear bond strength between autopolymerizing acrylic resin and Co–Cr alloy using different primers. Dent Mater J 31(5):765–771 24. Viwattanatipa N, Jermwiwatkul W, Chintavalakorn R, Nanthavanich N (2010) The effect of different surface preparation techniques on the survival probabilities of orthodontic brackets bonded to nanofill composite resin. J Orthod 37(3):162–173 25. Vo¨lkel T (2011) Wissenschaftliche Dokumentation Monobond Plus. In. Wissenschaflicher Dienst Ivoclar Vivadent AG, Liechtenstein 26. Wolf DM, Powers JM, O’Keefe KL (1993) Bond strength of composite to etched and sandblasted porcelain. Am J Dent 6(3):155–158
ORIGINAL ARTICLE
Shear bond strength of brackets on restorative materials Comparison on various dental restorative materials using the universal primer MonobondÒ Plus
Scherhaftfestigkeit von kieferorthopa¨dischen Metall- und Keramikbrackets Vergleich auf unterschiedlichen zahna¨rztlichen Restaurationsmaterialien unter Verwendung des Universal-Primers MonobondÒ Plus Thomas Ebert1,2 • Laura Elsner1 • Ursula Hirschfelder1 • Sebastian Hanke1 Received: 24 July 2014 / Accepted: 7 May 2015 Ó Springer-Verlag Berlin Heidelberg 2016
Abstract Objective The purpose of this work was to analyze surfaces consisting of different restorative materials for shear bond strength (SBS) and failure patterns of metal and ceramic brackets. Bonding involved the use of a universal primer (MonobondÒ Plus, Ivoclar Vivadent). Materials and methods Six restorative materials were tested, including one composite resin (Clearfil MajestyTM Posterior, Kuraray Noritake Dental), one glass–ceramic material (IPS EmpressÒ Esthetic, Ivoclar Vivadent), one oxide-ceramic material (CORiTEC Zr transpa Disc, imesicore), two base-metal alloys (remaniumÒ star, Dentaurum; ColadoÒ CC, Ivoclar Vivadent), and one palladium-based alloy (CallistoÒ 75 Pd, Ivoclar Vivadent). Bovine incisors served as controls. Both metal and ceramic brackets (discoveryÒ/discoveryÒ pearl; Dentaurum) were bonded to the restorative surfaces after sandblasting and pretreatment with MonobondÒ Plus. A setup modified from DIN 13990-2 was used for SBS testing and adhesive remnant index (ARI)-based analysis of failure patterns.
Results The metal brackets showed the highest mean SBS values on the glass–ceramic material (68.61 N/mm2) and the composite resin (67.58 N/mm2) and the lowest mean SBS on one of the base-metal alloys (ColadoÒ CC; 14.01 N/mm2). The ceramic brackets showed the highest mean SBS on the glass–ceramic material (63.36 N/mm2) and the lowest mean SBS on the palladium-based alloy (38.48 N/mm2). Significant differences between the metal and ceramic brackets were observed in terms of both SBS values and ARI scores (p \ 0.05). Under both bracket types, fractures of the composite-resin and the glass–ceramic samples were observed upon debonding. Opaque restorative materials under metal brackets were found to involve undercuring of the adhesive. Conclusions MonobondÒ Plus succeeded in generating high bond strengths of both bracket types on all restorative surfaces. Given our observations of cohesive fracture (including cases of surface avulsion) of the composite-resin and the glass–ceramic samples, we recommend against using these material combinations in clinical practice. Keywords Orthodontics Shear bond strength Orthodontic brackets Universal primer DIN 13990-2
Dr. Thomas Ebert. & Thomas Ebert [email protected] 1
Department of Orthodontics, University of Erlangen Medical School, Erlangen, Germany
2
Department of Orthodontics and Orofacial Orthopedics, Zahnklinik 3-Kieferorthopa¨die, Universita¨tsklinikum Erlangen, Glu¨ckstrasse 11, 91054 Erlangen, Germany
Zusammenfassung Ziel Ziel unserer Untersuchung war es, die Scherhaftfestigkeit und das Abscherverhalten von Metall- und Keramikbrackets auf verschiedenen Restaurationsmaterialien unter Verwendung des Universal-Primers MonobondÒ Plus zu untersuchen. Material und Methodik Es wurden 6 verschiedene Restaurationsmaterialien untersucht: Komposit (Clearfil MajestyTM
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Posterior, Kuraray Noritake Dental, Hattersheim am Main, Deutschland), Glaskeramik (IPS EmpressÒ Esthetic, Ivoclar Vivadent, Ellwangen, Deutschland), Oxidkeramik (CORiTEC Zr transpa Disc, imes-icore, Eiterfeld, Deutschland), 2 NEM(Nichtedelmetall)-Legierungen (remaniumÒ star, Dentaurum, Ispringen, Deutschland und ColadoÒ CC, Ivoclar Vivadent, Ellwangen, Deutschland) und eine Edelmetall-Palladium-Legierung (CallistoÒ 75 Pd, Ivoclar Vivadent, Ellwangen, Deutschland). Als Kontrollgruppe dienten extrahierte Rinderschneideza¨hne. Es wurden Metall- (discoveryÒ) und Keramikbrackets (discoveryÒ pearl, beide Dentaurum) verwendet. Die Oberfla¨chen der Restaurationsmaterialien wurden sandgestrahlt und mit dem Universal-Primer MonobondÒ Plus (Ivoclar Vivadent, Liechtenstein) vorbehandelt. In Anlehnung an die DIN 13990-2 erfolgten die Scherhaftfestigkeitspru¨fung und die Analyse des Bruchverhaltens (ARI). Ergebnisse Fu¨r Metallbrackets wurden die ho¨chsten mittleren Scherhaftfestigkeitswerte bei den Gruppen Glaskeramik (68,61 N/mm2) und Komposit (67,58 N/mm2) erreicht. Der niedrigste Mittelwert zeigte sich hingegen bei der NEMLegierung ColadoÒ CC (14,01 N/mm2). Bei Betrachtung der Keramikbrackets ergaben sich die ho¨chsten Mittelwerte bei der Gruppe Glaskeramik (63,36 N/mm2), der geringste Wert bei der Palladiumlegierung (38,48 N/mm2). Sowohl hinsichtlich der Scherfestigkeit als auch des ARI (,,adhesive remnant index‘‘) konnten signifikante Unterschiede zwischen Metall- und Keramikbrackets (p \ 0,05) festgestellt werden. Bei den Gruppen Komposit und Glaskeramik kam es wa¨hrend des Abschervorgangs bei beiden Brackettypen zur Fraktur der Probeko¨rper. In Kombination mit Metallbrackets konnte bei lichtundurchla¨ssigen Restaurationsmaterialien eine nur unvollsta¨ndige Polymerisation des Adha¨sivs nachgewiesen werden. Schlussfolgerung Der Universal-Primer MonobondÒ Plus konnte auf allen Restaurationsmaterialien fu¨r beide Brackettypen hohe Scherhaftfestigkeitswerte erzeugen. Bei der Komposit- und Glaskeramikgruppe kam es beim Schervorgang zur Fraktur der Probeko¨rper und teilweise zu koha¨siven Ausrissen, weshalb der klinische Einsatz auf diesen Materialien nicht empfohlen werden kann. Schlu¨sselwo¨rter Kieferorthopa¨die Scherhaftfestigkeit Bracket Universal-Primer Restaurationsmaterialien DIN 13990-2
Introduction The first step in initiating treatment with a fixed orthodontic appliance is to bond orthodontic attachments to the vestibular or lingual tooth surfaces. In most ado-
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lescent patients, adhesive bonding preceded by acid etching to condition the enamel is the approach of choice, as these patients will usually present with more or less ‘‘virgin’’ natural dentitions [7]. However, fixed appliances are today increasingly used in adult patients as well. Orthodontists are therefore no longer exclusively dealing with sound natural dentitions but also with dental restorations [4]. These surfaces, in turn, may consist of different materials, notably including alloys (of precious or base metals), ceramics (glass or oxide), and composite resins [1]. For a smooth and time-saving treatment process, modified techniques and materials are required to establish reliable bonds on surfaces consisting of these various types of restorative materials. In prosthetic dentistry, special primers are used to establish a durable bond following pretreatment of the bonding surface, but few studies have been devoted specifically to the adhesive union achieved by orthodontic brackets bonded to common restorative materials. While shear bond strengths (SBS) in the range of 4–10 N/mm2 have been demanded for bonding to enamel [12], no recommendations are currently available for bonding to restorative materials. From a clinical viewpoint, bond strengths at least as high as on enamel should also be achieved on restorative materials to avoid high rates of bracket loss. On the other hand, excessive strengths must be avoided to allow for smooth debonding without damaging, let alone destroying, the restorative surface [17]. Ideally, a single primer would be available that could be used in bonding orthodontic brackets to any restorative material while being neither technique-sensitive nor associated with material-specific differences in pretreatment. MonobondÒ Plus (Ivoclar Vivadent, Schaan, Liechtenstein) universal primer is stated by its manufacturer to be suitable for all types of restorative materials. The product consists of a highly diluted ethanolic solution that includes three active reagents: a silane, a phosphoric acid reagent, and a disulfide. Thus, it offers the advantage of containing several primers in one flask whose content can be applied to different restorative materials in exactly the same way. Once applied to the surface, a layer with the appropriate active monomer is formed, which causes the hydrophilic surface to become hydrophobic for optimal wetting of the restorative surface with the adhesive. After formation of this layer, an air blower is used to remove the excessive monomer together with the solvent. The purpose of this study was to investigate whether MonobondÒ Plus can result in adequate bond strengths for metal or ceramic attachments on a number of dental restorative materials and whether its use can be recommended in orthodontics.
Shear bond strength of brackets on restorative materials
Materials and methods
Bonding substrates
Brackets
Table 1 and Fig. 1 also convey an overview of the restorative materials (used in prosthetic and conservative dentistry) we included as bonding substrates. As composite resin, we used a highly filled nanocomposite (ClearfilTM Majesty Posterior; Kuraray Noritake, Hattersheim am Main, Germany). As ceramics, we used a glass–ceramic veneering material (IPS EmpressÒ Esthetic; Ivoclar Vivadent) and a high-strength zirconia (Coritec Zr Transpa Disc; Imes-Icore, Eiterfeld, Germany). As base-metal alloys, we used two materials with cobalt–chromium as their main constituent (remaniumÒ star, Dentaurum, Ispringen, Germany; ColadoÒ CC; Ivoclar Vivadent). As a precious-metal alloy, we used a palladium-
Details on the two (conventionally ligated) types of brackets included are provided in Table 1 and Fig. 1. Only brackets for upper central incisors were used. The first design was an esthetic ceramic bracket (DiscoveryÒ Pearl; Dentaurum, Ispringen, Germany) manufactured by ceramic injection molding (CIM) technology and featuring a laser-structured base (surface: 11.88 mm2). The second design was a conventional metal bracket (DiscoveryÒ; Dentaurum) manufactured by metal injection molding (MIM) technology and also featuring a laser-structured base (surface 11.82 mm2).
Tab. 1 Brackets and restorative materials used in this study Tab. 1 In der Studie eingesetzte Brackets und Restaurationsmaterialien
Trade name
Type
Manufacturer
DiscoveryÒ
Metal bracket
Dentaurum
DiscoveryÒ Pearl ClearfilTM Majesty Posterior
Ceramic bracket Nano-filled composite resin
Dentaurum Kuraray Noritake
IPS EmpressÒ Esthetic
Glass ceramic for veneers
Ivoclar Vivadent
Coritec Zr Transpa Disc
Zirconia (Zr2O3) ceramic
Imes-Icore
RemaniumÒ star
Base-metal (CoCr) alloy
Dentaurum
ColadoÒ CC
Base-metal (CoCr) alloy
Ivoclar Vivadent
CallistoÒ 75 Pd
Noble-metal (Pd-based) alloy
Ivoclar Vivadent
Fig. 1 Restorative materials and brackets investigated. Top to bottom on the left ClearfilTM Majesty Posterior; IPS EmpressÒ Esthetic. Top to bottom in the cente Coritec Zr Transpa Disc; remaniumÒ star; ColadoÒ CC; CallistoÒ 75 Pd. Top to bottom on the right bovine control tooth; metal bracket (DiscoveryÒ); ceramic bracket (DiscoveryÒ Pearl)
Abb. 1 Untersuchte Restaurationsmaterialen und Brackets. Links, von oben nach unten ClearfilTM Majesty Posterior, IPS EmpressÒ Esthetic; Mitte, von oben nach unten CORiTEC Zr transpa Disc, remaniumÒ star, ColadoÒ CC, CallistoÒ 75 Pd; rechts, von oben nach unten Rinderschneidezahn (Kontrolle), Metallbracket (discoveryÒ), Keramikbracket (discoveryÒ pearl)
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based alloy (CallistoÒ 75 Pd; Ivoclar Vivadent). Permanent bovine incisors that had been freshly extracted served as control group. Each group (six experimental groups and one control group) included 30 samples, to which either ceramic (n = 15) or metal (n = 15) brackets were bonded. An exception was the ColadoÒ CC group, which included metal brackets on only 10 samples. Thus a total of 205 samples were available for debonding. Primers and adhesive The primers employed included MonobondÒ Plus in all groups of restorative materials and TransbondTM XT Light Cure Adhesive Primer (3 M Unitek, Neuss, Germany) in the control group. In all groups, the metal and ceramic brackets were bonded with TransbondTM XT Light Cure Adhesive (3 M Unitek). Sample preparation The CallistoÒ 75 Pd precious-metal alloy was supplied in the form of plates; due to their torsional stiffness and dimensional stability, the dimensions of these plates (12.8 9 7.8 9 1.0 mm) were used as a blueprint for all samples in all experimental groups. The ColadoÒ CC base-metal samples were cast and polished to high gloss in the laboratory. The zirconia samples were milled from blanks and compacted in a sintering furnace. The remaniumÒ star base-metal alloy, again, was available from the manufacturer as plates not requiring further processing. The IPS EmpressÒ Esthetic glass–ceramic material is normally pressed to shape; it is supplied in the form of cylindrical blanks (length 13.4 mm; diameter 11.4 mm), which were longitudinally halved with a diamond saw and embedded in resin (Technovit 4004; Heraeus Kulzer, Wehrheim, Germany) as per DIN 13990-2 [10] such that the prospective bonding surface was not in contact with the resin. The composite-resin samples were created by layering ClearfilTM Majesty into a mold of addition-type silicone (Lab-Silicone; Henry Schein, Melville, NY, USA) created from the previously prepared, halved glass–ceramic cylinders; the composite-resin cylinders resulting from the subsequent light curing were then embedded in resin, using the same steps outlined above for the glass–ceramic samples. The bovine teeth were embedded in Technovit 4004 as well. In accordance with DIN 13990-2, all samples were oriented such that the shear blade used for debonding made perpendicular contact with the bracket base. Bonding procedure The surfaces of the restorative materials were degreased with alcohol and roughened with 50-lm alumina particles
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using an intraoral sandblaster (MicroEtcher; Danville Materials, San Ramon, CA, USA) applied from a distance of approximately 50 mm for 10 s, followed by rinsing with a water spray for 10 s and drying with oil-free compressed air. MonobondÒ Plus universal primer was applied, in accordance with the manufacturer’s instructions, as a thin layer and allowed to rest for 60 s. Then excess material was removed from the surface with an air blower. The bracket bases were covered with TransbondTM XT adhesive and, as per DIN 13990-2, placed onto the samples using gentle pressure, followed by careful removal of excessive resin. Finally a curing light (Valo Ortho; Opal Orthodontics, South Jordan, UT, USA) was applied to the mesial, distal, occlusal and gingival aspects of the bracket at 1200 mW/cm2 for 10 s each. Shear bond strength test The experimental setup was devised with reference to DIN 13990-2. After the samples had been stored in distilled water at 37 °C inside an incubator for 24 h, we conducted the SBS test using a universal testing machine (Zwick/ Roell, Ulm, Germany). In the groups remaniumÒ star, ColadoÒ CC, CallistoÒ 75 Pd, and Coritec Zr Transpa Disc, stable positioning of the samples during debonding was ensured by mounting them in the testing machine with a special aluminum block. All samples were positioned and mounted such that the debonding force was applied perpendicular to the bracket base. Departing from DIN 13990-2, which describes the use of a wire loop, we employed an apparatus with a shear blade that ruled out any contact with structures other than the bracket base during debonding (Fig. 2). This modification reliably prevented the applied force from sliding off the bracket base, considering the very flat base designs employed. Using a load cell (output 1 kN) to measure the force levels applied, the shear blade was lowered at a rate of 1.0 mm/min until the bond failed. Then, dividing the maximum load (N) applied by the surface area of the bonding site (mm2), the SBS was calculated and expressed in N/mm2. Failure patterns After debonding, both the surfaces of the samples and the bracket bases were analyzed at 109 magnification (Stemi SV6; Zeiss, Oberkochen, Germany) for the patterns by which the bonds had failed. Four patterns were distinguished—via ARI (Adhesive Remnant Index) scores as described by Artu˚n and Bergand [2]—depending on how much adhesive was left on the samples and on the bracket base: ARI 0 (0 % on sample, 100 % on bracket), ARI 1 (\50 % on sample, [50 % on bracket), ARI 2 ([50 % on
Shear bond strength of brackets on restorative materials
sample, \50 % on bracket), or ARI 3 (100 % on sample, 0 % on bracket). Statistical analysis The data of our evaluations were transferred to spreadsheet software (Excel 2010; Microsoft, Redmond, WA, USA) and analyzed using a statistical add-in (XLStat2013; Addinsoft, Paris, France). The values from the measurements were descriptively prepared and subjected to a Shapiro–Wilk test for normal distribution, a nonparametric Mann–Whitney U test and Kruskal–Wallis (analysis of variance by ranks) test for intergroup differences, and a Brunner–Dette–Munk (analysis of variance by ranks) test for two factors. A v2 test was used to analyze the distribution of ARI scores. Bonferroni correction was applied to arrive at statistically predictive significances. All tests were based on p B 0.05 as probability of error.
Results Dataset
Fig. 2 As an example for all material combinations tested, this photograph shows a Coritec Zr Transpa Disc sample mounted in the shear apparatus with a DiscoveryÒ metal bracket bonded to its surface. The shear blade is lowered such that it makes precisely perpendicular contact with the bracket base Abb. 2 Exemplarisch fu¨r alle untersuchten Materialkombinationen ist eine Probe der Gruppe CORiTEC Zr transpa Disc in Kombination mit dem discoveryÒ Metall-Bracket in der Abschervorrichtung eingespannt. Der Abscherstempel trifft senkrecht von oben exakt auf die Bracketbasis
The dataset of values measured in this study originally included 205 results (corresponding to the number of samples subjected to SBS testing). After correction for outliers, 202 results were available for statistical analysis. Descriptive statistics were calculated for each of the restorative materials, including the mean SBS and its standard deviation, as well as its median value and range. These values were calculated separately for metal (Table 2) and for ceramic (Table 3) brackets. The SBS values measured with either bracket type in box plots are shown in Figs. 3 and 4. Nonparametric tests were used for analysis, since a normal distribution was not present.
Tab. 2 Shear bond strengths obtained with metal brackets Tab. 2 Scherhaftfestigkeit bei Metallbrackets n
Mean ± SD (N)
Median (N)
Min|max (N)
Mean ± SD (N/mm2)
Median (N/mm2)
Min|max (N/mm2)
ClearfilTM Majesty Posterior
15
798.80 ± 89.60
784.49
641.35|951.86
67.58 ± 7.58
66.37
54.26|80.53
IPS EmpressÒ Esthetic
15
810.97 ± 69.74
800.92
717.12|960.97
68.61 ± 5.90
67.76
60.67|81.30
Coritec Zr Transpa Disc
15
434.03 ± 23.88
440.18
387.34|468.54
36.72 ± 2.02
37.24
32.77|39.64
RemaniumÒ star
15
305.78 ± 71.98
311.10
165.13|443.60
25.87 ± 6.09
26.32
13.97|37.53
9
165.60 ± 29.55
159.57
127.30|227.30
14.01 ± 2.50
13.50
10.77|19.23
CallistoÒ 75 Pd
15
185.93 ± 36.88
178.01
130.49|257.79
15.73 ± 3.12
15.06
11.04|21.81
Control group
15
705.65 ± 138.06
705.65
425.05|910.84
59.70 ± 11.68
59.70
35.96|77.06
ColadoÒ CC
Data expressed as two separate sets of values (N and N/mm2) obtained after exclusion of outliers
123
E. Thomas et al. Tab. 3 Shear bond strengths obtained with ceramic brackets Tab. 3 Scherhaftfestigkeit bei Keramikbrackets n
Mean ± SD (N)
Median (N)
Min|max (N)
Mean ± SD (N/mm2)
Median (N/mm2)
Min|max (N/mm2)
ClearfilTM Majesty Posterior
15
491.00 ± 105.14
495.87
321.95|746.30
41.33 ± 8.85
41.74
27.10|62.82
IPS EmpressÒ Esthetic
14
752.72 ± 110.60
753.55
633.09|950.04
63.36 ± 9.31
63.43
53.29|79.97
Coritec Zr Transpa Disc RemaniumÒ star
15 15
531.99 ± 138.16 640.69 ± 124.62
533.53 631.42
337.99|781.70 392.40|819.60
44.78 ± 11.63 53.93 ± 10.49
44.91 53.15
28.45|65.80 33.03|68.99
ColadoÒ CC
15
583.07 ± 148.74
600.06
333.23|832.79
49.08 ± 12.52
50.51
28.05|70.10
CallistoÒ 75 Pd
15
457.14 ± 69.02
449.06
354.14|560.74
38.48 ± 5.81
37.80
29.81|47.20
Control group
14
589.25 ± 142.68
615.50
441.58|783.60
49.60 ± 12.01
51.81
37.17|65.96
Data expressed as two separate sets of values (N and N/mm2) obtained after exclusion of outliers
Fig. 3 Box-plot diagram of shear bond strengths under metal brackets. Lines and crosses inside the boxes indicate median and mean values, respectively Abb. 3 Boxplot-Darstellung der Scherhaftfestigkeitswerte unter Metallbrackets. Horizontale Linien Medianwerte, Kreuze Mittelwerte
Fig. 4 Box-plot diagram of shear bond strengths under ceramic brackets. Lines and crosses inside the boxes indicate median and mean values, respectively Abb. 4 Boxplot-Darstellung der Scherhaftfestigkeitswerte unter Keramikbrackets. Horizontale Linien Medianwerte, Kreuze Mittelwerte
Shear bond strength
the ClearfilTM Majesty Posterior, remaniumÒ star, ColadoÒ CC, CallistoÒ 75 Pd and control groups, but not in the IPS EmpressÒ Esthetic and Coritec Zr Transpa Disc groups (data not shown). Two-way ANOVA by ranks (Brunner–Dette– Munk test) disclosed that the most important modifier of results was restorative material, followed by interaction and bracket type. Incomplete curing of the adhesive was noted with the metal brackets in the remaniumÒ star, ColadoÒ CC, and CallistoÒ 75 Pd groups. We shall elaborate on this finding in the ‘‘Discussion’’.
The metal brackets (Table 2; Fig. 3) yielded the highest mean SBS values (68.61 and 67.58 N/mm2) in the IPS EmpressÒ Esthetic and ClearfilTM Majesty Posterior groups and the lowest mean SBS (14.01 N/mm2) in the ColadoÒ CC group. With the ceramic brackets (Table 3; Fig. 4), the highest mean values (63.36 and 53.93 N/mm2) were observed in the IPS EmpressÒ Esthetic and remaniumÒ star groups and the lowest mean value (38.48 N/mm2) in the CallistoÒ 75 Pd group. ANOVA by ranks revealed some significant differences between restorative materials under both the metal and the ceramic brackets. Pairwise comparisons of these intergroup differences are given in Tables 4 and 5. Significant (p B 0.05) within-group differences in SBS between the metal and the ceramic brackets emerged in
123
Failure patterns Debonding of the metal brackets (Fig. 5) overwhelmingly resulted in scores of ARI 0 across all groups (n = 69). Scores of ARI 1 (n = 9) or 2 (n = 2) were noted
Shear bond strength of brackets on restorative materials Tab. 4 Pairwise intergroup comparison of shear bond strengths under metal brackets Tab. 4 Paarweiser Intergruppen-Vergleich der Scherhaftfestigkeit unter Metallbrackets p ClearfilTM ClearfilTM Majesty Posterior
1
IPS
Coritec
RemaniumÒ
ColadoÒ
CallistoÒ
Control
*
IPS EmpressÒ Esthetic
\0.0001
1
*
Coritec Zr Transpa Disc RemaniumÒ star
0.456 0.005
0.000 0.063
1 0.040
1
ColadoÒ CC
0.096
0.003
0.358
0.257
1
CallistoÒ 75 Pd
0.449
\0.0001
0.133
0.000
0.015
1
Control group
0.040
0.012
0.186
0.487
0.676
0.005
1
ColadoÒ
CallistoÒ
Control
* *
* Significant differences based on a significance level of 0.0024 after Bonferroni correction
Tab. 5 Pairwise intergroup comparison of shear bond strengths under ceramic brackets Tab. 5 Paarweiser Intergruppen-Vergleich der Scherhaftfestigkeit unter Keramikbrackets p ClearfilTM
IPS
ClearfilTM Majesty Posterior
1
IPS EmpressÒ Esthetic
0.896
1
Coritec Zr Transpa Disc
0.007
0.004
Coritec
RemaniumÒ *
*
*
*
*
*
1
Ò
Remanium star
\0.0001
\0.0001
0.194
1
ColadoÒ CC
\0.0001
\0.0001
0.004
0.081
1
CallistoÒ 75 Pd
\0.0001
\0.0001
0.004
0.123
0.682
0.435
0.362
0.054
0.001
\0.0001
Control group
* * 1 \0.0001
* 1
* Significant differences based on a significance level of 0.0018 after Bonferroni correction
Fig. 5 Distribution of ARI scores after debonding of metal brackets Abb. 5 Verteilung der ARI-Werte nach Debonding der Metallbrackets
considerably less often. Findings of ARI 3 were confined to sporadic cases within the remaniumÒ star (n = 3) und ClearfilTM Majesty Posterior (n = 1) groups. A different distribution of failure patterns was seen with the ceramic brackets (Fig. 6). Here ARI 3 was the dominant score in all groups other than the control group (n = 53), followed by
ARI 2 (n = 19) and ARI 1 (n = 13). The only groups to exhibit any scores of ARI 0 were CallistoÒ 75 Pd (n = 4), Coritec Zr Transpa Disc (n = 1), and the controls (n = 1). The v2 test showed that most of these within-group differences between metal and ceramic brackets in terms of ARI-score distribution were significant, remaniumÒ star being the only group to show no significant bracket-specific difference in this regard. All samples in the ClearfilTM Majesty Posterior and IPS EmpressÒ Esthetic groups, used with either bracket type, showed internal fractures after debonding (Figs. 7, 8, 9, 10). In the control group, the high shear forces induced enamel cracks in 2 of the 15 teeth used under ceramic brackets and in 10 of the 15 teeth used under metal brackets.
Discussion The aim of this in vitro study was to determine whether a commercially available primer was capable of generating bond strengths between metal or ceramic brackets and dental restorative materials that would be sufficiently high
123
E. Thomas et al. Fig. 6 Distribution of ARI scores after debonding of ceramic brackets Abb. 6 Verteilung der ARIWerte nach Debonding der Keramikbrackets
Fig. 7 Cohesive fractures inside a composite-resin sample (ClearfilTM Majesty) after debonding of a metal bracket. ARI score is 0. The resin fractures even include superficial avulsion Abb. 7 Koha¨sive Frakturen innerhalb der Probe ClearfilTM MajestyTM nach Abscherung eines Metallbrackets. Der ARI-Score betra¨gt 0, deutlich sichtbar sind oberfla¨chliche Ausrisse von Komposit
for orthodontic treatment. As reference, we adopted the range of 5.9–7.8 N/mm2 demanded by Reynolds [20] for attachments on enamel. While over 30 years old, this is still a useful recommendation, as this range is below the cohesive strength of enamel (10.3 N/mm2) [6] to avoid or minimize avulsion-type enamel fractures upon debonding [11, 19, 22]. While debonding from restored tooth surfaces will not damage enamel, there is nevertheless a risk of inducing defects or initiating cracks on veneers or other types of restored surfaces [16, 17]. Pertinent reference values are currently not available in the literature. To judge the clinical effectiveness of the primer used in this study, it was important that the pretreatment applied to
123
Fig. 8 Cohesive fractures inside a composite-resin sample (ClearfilTM Majesty) after debonding of a ceramic bracket. ARI score is 3. The entire adhesive is retained on the resin sample; note the visible impression of the bracket base Abb. 8 Koha¨sive Frakturen innerhalb der Probe ClearfilTM MajestyTM nach Abscherung eines Keramikbrackets. Der ARI-Score betra¨gt 3, das Adha¨siv mit Abdruck der Bracketbasis ist vollsta¨ndig auf der Probe verblieben
the surfaces would be neither technique-sensitive nor timeconsuming and, most importantly, would not vary with different restorative materials. The latter requirement of uniform pretreatment was met, since the only pretreatment applied to the restorative surfaces was sandblasting with alumina particles as per the manufacturer’s recommendations. The exposure time required for the universal primer of 60 s was consistent with the duration of enamel etching [7] and had to be followed by removal of excessive material with an air blower.
Shear bond strength of brackets on restorative materials
Fig. 9 Cohesive fractures inside a glass–ceramic sample (IPS EmpressÒ Esthetic) sample after debonding of a metal bracket. ARI score is 0. The ceramic fractures even include superficial avulsion Abb. 9 Koha¨sive Frakturen innerhalb der Probe IPS EmpressÒ Esthetic nach Abscherung eines Metallbrackets. Der ARI-Score betra¨gt 0, sichtbar sind oberfla¨chliche Ausrisse von Glaskeramik
as a diluted ethanolic solution that consists of three mutually stable bonding monomers (silane, phosphoricacid agent, disulfide). As a rule, glass–ceramic materials are either etched with hydrofluoric acid or blasted with alumina particles to generate a microretentive surface [13, 26], followed by a step known as ‘‘silanization’’ enabling the ceramic surface to enter a chemical bond [18]. MonobondÒ Plus achieves this task via a functional trihydroxysilane group of a methacrylate monomer binding to the silicate surface of the restoration as part of a condensation reaction. As zirconia and base metals possess a high affinity to phosphoric acid and form poorly soluble phosphates [25], MonobondÒ Plus contains methacrylate monomers with a functional phosphoric-acid group for chemical bonding, resulting in a strong and hydrolysisproof bond to zirconia or base-metal surfaces. Bonding to precious metals is achieved via a cyclic disulfide group with a ring structure, which will open as the reaction is taking place on the metal surface and, via a sulfur atom, will bind to the surface forming a light sulfide layer. In any of these scenarios, only the reagent chemically matching the restorative material will actively react, while the excessive monomer can subsequently be removed together with the solvent by applying an air blower. What remains is a hydrophobic surface which, in turn, can enter a bond with a composite resin. Shear apparatus
Fig. 10 Cohesive fractures inside a glass–ceramic sample (IPS EmpressÒ Esthetic) after debonding of a ceramic bracket. ARI score is 3. The entire adhesive is retained on the resin sample; note the visible impression of the bracket base Abb. 10 Koha¨sive Fraktur innerhalb der Probe IPS EmpressÒ Esthetic nach Abscherung eines Keramikbrackets. Der ARI-Score betra¨gt 3, das Adha¨siv mit Abdruck der Bracketbasis ist vollsta¨ndig auf der Probe verblieben
MonobondÒ Plus No specialized products are currently available to bond orthodontic brackets to restorative materials. Yet MonobondÒ Plus is stated by its manufacturer to generate reliable bonds in this context, even though its intended use is primarily for permanent indirect restorations in prosthetic and conservative dentistry [25]. This primer comes
Departing from DIN 13990-2, which describes the use of a wire loop, we employed an apparatus featuring a shear blade for debonding (Fig. 2). This setup allowed the shear force to be applied from a perpendicular direction directly to the bracket base. In this way, pure shear force without moment components could be maintained. We regarded a wire loop as unfavorable due to the considerable flatness of the bracket bases, which would have prevented secure retention of the loop under the base during debonding. This use of a specific shear apparatus might explain our finding of some high SBS values compared to the literature. Composite resin ClearfilTM Majesty Posterior, representing the class of dental filling resins among the restorative materials here tested, reached a mean SBS of 67.58 N/mm2 under metal brackets—which was the second-highest overall value in this study—and 41.33 N/mm2 under ceramic brackets. As illustrated by Figs. 7 and 8, cohesive fractures inside the samples were noted both under the metal and under the ceramic brackets in spite of different failure patterns involved (ARI 0 versus 3). In 2010, Viwattanatipa et al. [24], by contrast, reported a mean SBS of just 6.9 N/mm2
123
E. Thomas et al.
for brackets bonded to nano-filled composite resin; however, they initially stored the samples in distilled water for 1 month and exposed them to thermocycling after pretreatment with a special resin primer. In 2013, Daratsianos et al. [9] reported decreases down to 23.1 % of initial SBS values after fatigue simulation. Ribeiro et al. [21] recorded a mean of 6.82 N/mm2 on composite-resin samples after surface roughening with a diamond bur in the absence of artificial aging. This is in contrast to data on composite repairs involving silane, which resulted in SBS values [50 N/mm2 despite artificial aging [14]. Overall, very heterogeneous results are documented in the literature, due to different pretreatment and storage protocols and properties of the materials tested. Regrettably, this makes a direct comparison virtually impossible.
Oxide ceramic Coritec Zr Transpa Disc, representing the category of highstrength zirconia ceramics among the restorative materials tested here, reached a mean SBS of 36.72 N/mm2 under metal brackets and 44.78 N/mm2 under ceramic brackets. As expected, due to the high strength of zirconia ceramics, we observed no fractures on evaluating the failure patterns. Attia et al. [3] and Kern and Thompson [16] published a study on MonobondÒ Plus based on a similar experimental setup, which resulted in a comparable SBS of 42.5 N/mm2. Thus MonobondÒ Plus universal primer does seem to be usable in orthodontic bonding procedures to zirconia restorations. Base-metal alloys
Glass ceramic Very high mean SBS values were also noted with IPS EmpressÒ Esthetic both on the metal (68.61 N/mm2) and on the ceramic (63.36 N/mm2) brackets. Again, these similar SBS data were obtained even though both bracket types were associated with clearly different failure modes (Figs. 5, 6; ARI 0 versus 2–3). Likewise, much the same pattern as in the ClearfilTM Majesty Posterior group emerged in that almost all samples showed cohesive fractures (Figs. 9, 10). Cochran et al. [8], in a 1997 study involving different protocols of glass–ceramic pretreatment, achieved SBS levels of 41 N/mm2 after sandblasting and silanization, associated with an increased rate of ceramic fractures. After sandblasting or hydrofluoric-acid etching only, they observed 6.5 or 18.0 N/mm2 and lower fracture rates. In 2012, Girish et al. [13] confirmed that sandblasting and silanization was associated with the highest SBS values. Bourke and Rock [5] recommended a pretreatment for feldspathic ceramics that includes etching with 37 % phosphoric acid for 60 s and additional silanization to reach clinically adequate bond strengths while reducing the risk of ceramic fracture. Unfortunately, no survival rates are currently documented for ceramic restorations after debonding of brackets. In vitro data on record, however, do suggest that rather moderate SBS levels gentle on the restorations should be favored for temporary orthodontic use. Our result of metal versus ceramic brackets resulting in contrasting failure patterns is presumably due to their differences in elastic modulus and retentive strength. Given our findings of high SBS values and resultant sample fractures in the ClearfilTM Majesty Posterior and IPS EmpressÒ Esthetic groups, bonding of brackets to glass ceramics or composite resins is not a suitable application for MonobondÒ Plus universal primer.
123
With remaniumÒ star und ColadoÒ CC, we evaluated two materials falling into this category. Under metal brackets, these achieved a mean SBS value of 25.87 and 14.01 N/ mm2, respectively. Sanokhan et al. [23], in a 2012 study comparing the SBS of composite resin to a cobalt–chromium alloy used with different primers, reported a mean of 13.87 N/mm2 for MonobondÒ Plus after sandblasting (significance level 95 %). The failure patterns we observed in both groups were mainly characterized by ARI scores 0 and 1; in other words, absence of residual adhesive on the samples was the predominant finding. Under ceramic brackets, both materials achieved clearly higher mean SBS values of 53.93 N/mm2 (remaniumÒ star) or 49.08 N/mm2 (ColadoÒ CC) than under metal brackets, which was associated with a distinct shift of failure patterns toward higher percentages (up to 100 %) of residual adhesive being left on the samples, as reflected by a predominance of ARI scores 2 and 3. Precious-metal alloy CallistoÒ 75 Pd, being a palladium-based alloy and representing the class of precious-metal alloys among the restorative materials tested here, reached a mean SBS of 15.73 N/mm2 under metal brackets, which ranks between the values for the two base-metal alloys. The bracket–adhesive–metal interface predominantly failed between the adhesive and the alloy (ARI 0). In 2013, Jung et al. [15] evaluated the SBS of metal brackets on gold restorations depending on how long the silane applied after sandblasting was allowed to rest on the surface; they observed a mean value of 11.86 N/mm2. In most instances, however, more than 90 % of the adhesive remained on the samples. Similar to both of the base-metal alloys under ceramic brackets, the mean SBS value achieved by CallistoÒ 75 Pd was distinctly higher under ceramic brackets (38.48 N/
Shear bond strength of brackets on restorative materials
mm2). Again, ARI score 3 was the predominant failure pattern in this group. 5. Metal versus ceramic brackets The marked differences in SBS between metal and ceramic brackets in the groups remaniumÒ star, ColadoÒ CC, and CallistoÒ 75 Pd may be attributed to incomplete polymerization of the adhesive on the metal brackets. Despite 40 s of light curing, our post-debonding analysis of fracture behavior did reveal undercured adhesive on the material combinations that involved metal brackets: while complete polymerization was present in the marginal bracket areas close to the light, undercured sites (scratchable with a probe) were found in the central base areas. Thus, it is advisable, whenever materials of this type are combined in clinical practice, to optimize the bond by resorting to a chemically curing adhesive.
Other considerations The results of this in vitro study reflect early situations of bond strength achieved on samples that had been stored for 24 h. Since the adhesive may theoretically undergo some continued polymerization during these 24 h, relevantly smaller levels of bond strength may actually be present immediately after bonding of brackets in clinical practice. Recent data have shown that fatigue simulation performed on bracket–adhesive–enamel complexes involving TransbondTM XT induced a decrease in SBS down to 23.1 % of the initial situations depending on the number of loading cycles [9]. Our comparison between the restorative materials tested in the present study is permissible because the same adhesive was used in all groups. Given the current paucity of data in the literature about bond strengths on dental restorative materials, there is an urgent need for more experimental and clinical studies.
Conclusion 1. 2.
3.
4.
MonobondÒ Plus generated high SBS levels on all restorative materials tested. The composite-resin and glass–ceramic samples were found to fracture during debonding, even including avulsion-type surface fractures in some cases. The failure patterns observed (expressed as ARI scores) revealed a number of statistically significant differences between metal and ceramic brackets. Temporary clinical bonding of brackets to compositeresin or glass–ceramic surfaces is not a recommended application for MonobondÒ Plus, considering the
6.
fracture risk of these materials in the presence of high bond strengths. Undercuring of the adhesive may result when metal brackets are bonded to opaque restorative materials. In clinical practice, a chemically curing adhesive should be used whenever materials of this type are combined. Prior to any bonding of brackets to restorative surfaces, patient information needs to be provided about the risk of damaging or destroying the restoration.
Acknowledgments The authors are indebted to Dentaurum, Ivoclar Vivadent, and Ortho Service Germany for their kind support and provision of the materials used in this study. They also wish to thank the staff members of the Materials Science Laboratory of the First Department of Dentistry (Zahnklinik 1) at University of Erlangen and Mr. Lo¨w for technical support. Financial support for the project was received from the German Orthodontic Society. Compliance with ethical guidelines Conflict of interest Thomas Ebert, Laura Elsner, Ursula Hirschfelder, Sebastian Hanke stat that there are no conflicts of interest. The accompanying manuscript does not include studies on humans or animals.
References 1. Abu Alhaija ES, Abu AlReesh IA, AlWahadni AM (2010) Factors affecting the shear bond strength of metal and ceramic brackets bonded to different ceramic surfaces. Eur J Orthod 32(3):274–280 2. Artun J, Bergland S (1984) Clinical trials with crystal growth conditioning as an alternative to acid-etch enamel pretreatment. Am J Orthod 85(4):333–340 3. Attia A, Lehmann F, Kern M (2011) Influence of surface conditioning and cleaning methods on resin bonding to zirconia ceramic. Dental Mater 27(3):207–213 4. Blakey R, Mah J (2010) Effects of surface conditioning on the shear bond strength of orthodontic brackets bonded to temporary polycarbonate crowns. Am J Orthod Dentofac Orthoped 138(1):72–78 5. Bourke BM, Rock WP (1999) Factors affecting the shear bond strength of orthodontic brackets to porcelain. Br J Orthod 26(4):285–290 6. Bowen RL, Rodriguez MS (1962) Tensile strength and modulus of elasticity of tooth structure and several restorative materials. J Am Dent Assoc 64:378–387 7. Buonocore MG (1955) A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 34(6):849–853 8. Cochran D, O’Keefe KL, Turner DT, Powers JM (1997) Bond strength of orthodontic composite cement to treated porcelain. Am J Orthod Dentofac Orthoped 111(3):297–300 9. Daratsianos N, Musabegovic E, Reimann S, Gruner M, Jager A, Bourauel C (2013) The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study. Dental Mater 29(5):506–513 10. DIN13990-2 (2009) Zahnheilkunde - Pru¨fverfahren fu¨r die Scherhaftfestigkeit von Adha¨siven fu¨r kieferorthopa¨dische Befestigungselemente - Teil 2: Gesamtverbund Befestigungselement-Adha¨siv-Zahnschmelz. Beuth Verlag, Berlin
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E. Thomas et al. 11. Ferreira FG, Nouer DF, Silva NP, Garbui IU, Correr-Sobrinho L, Nouer PR (2013) Qualitative and quantitative evaluation of human dental enamel after bracket debonding: a noncontact three-dimensional optical profilometry analysis. Clinical oral investigations 12. Gillis I, Redlich M (1998) The effect of different porcelain conditioning techniques on shear bond strength of stainless steel brackets. Am J Orthod Dentofac Orthoped 114(4):387–392 13. Girish PV, Dinesh U, Bhat CS, Shetty PC (2012) Comparison of shear bond strength of metal brackets bonded to porcelain surface using different surface conditioning methods: an in vitro study. J Contemp Dent Pract 13(4):487–493 14. Jafarzadeh Kashi TS, Erfan M, Rakhshan V, Aghabaigi N, Tabatabaei FS (2011) An in vitro assessment of the effects of three surface treatments on repair bond strength of aged composites. Oper Dent 36(6):608–617 15. Jung MH, Shon WJ, Park YS, Chung SH (2013) Effects of silanation time on shear bond strength between a gold alloy surface and metal bracket. Kor J Orthod 43(3):127–133 16. Kern M, Thompson VP (1994) Sandblasting and silica coating of a glass-infiltrated alumina ceramic: volume loss, morphology, and changes in the surface composition. J Prosthet Dent 71(5):453–461 17. Lee-Knight CT, Wylie SG, Major PW, Glover KE, Grace M (1997) Mechanical and electrothermal debonding: effect on ceramic veneers and dental pulp. Am J Orthod Dentofac Orthoped 112(3):263–270 18. Lu R, Harcourt JK, Tyas MJ, Alexander B (1992) An investigation of the composite resin/porcelain interface. Aust Dent J 37(1):12–19
123
19. Pont HB, Ozcan M, Bagis B, Ren Y (2010) Loss of surface enamel after bracket debonding: an in vivo and ex vivo evaluation. Am J Orthod Dentofac Orthoped 138(4):387, e381–389 (discussion 387–389) 20. Reynolds IR (1975) A review of direct orthodontic bonding. Br J Orthod 2:171–178 21. Ribeiro AA, de Morais AV, Brunetto DP, Ruellas AC, de Araujo MT (2013) Comparison of shear bond strength of orthodontics brackets on composite resin restorations with different surface treatments. Dental Press J Orthod 18(4):98–103 22. Ryf S, Flury S, Palaniappan S, Lussi A, van Meerbeek B, Zimmerli B (2012) Enamel loss and adhesive remnants following bracket removal and various clean-up procedures in vitro. Eur J Orthod 34(1):25–32 23. Sanohkan S, Urapepon S, Harnirattisai C, Sirisinha C, Sunintaboon P (2012) Shear bond strength between autopolymerizing acrylic resin and Co–Cr alloy using different primers. Dent Mater J 31(5):765–771 24. Viwattanatipa N, Jermwiwatkul W, Chintavalakorn R, Nanthavanich N (2010) The effect of different surface preparation techniques on the survival probabilities of orthodontic brackets bonded to nanofill composite resin. J Orthod 37(3):162–173 25. Vo¨lkel T (2011) Wissenschaftliche Dokumentation Monobond Plus. In. Wissenschaflicher Dienst Ivoclar Vivadent AG, Liechtenstein 26. Wolf DM, Powers JM, O’Keefe KL (1993) Bond strength of composite to etched and sandblasted porcelain. Am J Dent 6(3):155–158
