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ET AL
Retentive Strength of Implant-Supported Base Metal Copings Over Short Metal Abutments Using Different Luting Agents and Surface Treatments Farahnaz Nejatidanesh, DDS, MS,* Omid Savabi, DDS, MS,† Maziar Ebrahimi, DDS, MS,‡ and Ghazal Savabi, DDS§
oss of retention is the most common complication with cement-retained implant-supported prostheses,1,2 especially on short abutments.3 The retention of cement-retained restorations can be affected by the geometry of the abutment, surface roughness of the abutment and restoration, and the type of luting agent.4,5 The height of abutment is a determining factor that affects the surface area, resistance, and retention properties. The use of short abutments in limited interarch space can jeopardize the retention and resistance of the restorations.6,7 In these situations, retentive characteristics of the luting agent are more important for retention of the restoration. Many studies have shown that definitive cements provide more retention than provisional cements.8–10 The retention of conventional cements derived from the micromechanical retention of abutment and the intaglio surface of restoration.10–12
L
*Professor, Dental Materials Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran; Biomaterials Research Group, Isfahan University of Technology, Isfahan, Iran. †Professor, Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran; Biomaterials Research Group, Isfahan University of Technology, Isfahan, Iran. ‡Assistant Professor, Department of Endodontics, School of Dentistry, Khorasgan Islamic Azad University, Isfahan, Iran. §Dental Student, Dental Students’ Research Committee, School of Dentistry, Khorasgan Islamic Azad University, Isfahan, Iran.
Reprint requests and correspondence to: Omid Savabi, DDS, MS, 400 Sheikhsadoogh Shomali Street, Sheikhsadoogh Cross Road, Isfahan 81648-13315, Iran, Phone: 0098311-6614059/0098311-7922890, Fax: 0098311-6687080, E-mail: [email protected] ISSN 1056-6163/14/02302-162 Implant Dentistry Volume 23 Number 2 Copyright © 2014 by Lippincott Williams & Wilkins DOI: 10.1097/ID.0000000000000049
Purpose: To evaluate the effect of surface treatments on retention of implant-supported restorations over short abutments. Materials and Methods: One hundred twenty metal copings were made on Straumann solid abutments (3 mm length). The copings were divided into 2 groups: control and air abraded (50 mm Al2O3). The copings were luted using Fleck’s, Poly F, Panavia F, and Fuji Plus. In resin cements groups, 2 subgroups were studied base on the application of Alloy Primer (n ¼ 10). After conditioning in saliva and 5000 thermal cycles, retentive strengths of specimens were measured. Data were analyzed by 1-way ANOVA and Tukey honestly significant difference tests (a ¼ 0.05).
Results: Panavia F 2.0 combined with Alloy Primer showed the most retentive values. In control and air abraded groups, there was no significant difference between the studied luting agents. Alloy Primer significantly increased the retention of copings luted with Panavia F 2.0. Conclusion: Within the limitations of this study, the retentive strength of metal copings over short implant abutments was not improved by airborne-particle abrasion. However, Alloy primer enhanced the retention of metal copings that were luted using Panavia F 2.0. (Implant Dent 2014;23:162–167) Key Words: dental implants, dental restoration failure, surface properties, dental prosthesis retention
However, the resin cements exhibit chemical bonding to the restoration and are advocated to enhance retention.13–16 Zinc phosphate,17 zinc polycarboxylate,18,19 and resin cements9,20 have been the most retentive definitive luting agents for cementation of implant-supported restorations. Surface treatment of the intaglio surface of the restoration before cementation can enhance the bond strength of the luting agent to the restoration. Different studies evaluated the effect of mechanical surface treatment of casting such as oxide layer formed
during porcelain firing and airborneparticle abrasion on the bond and retentive strength of castings.15,16,20,21 Most dental schools in the United States recommended either no treatment or abrasion of the internal surface of implantsupported restorations, before definitive cementation.22 Airborne-particle abrasion with aluminum oxide particles is an inexpensive technique that removes debris, roughens the surface of the casting, and also increases the surface area of restoration.15,23 Although in some studies, air abrasion treatment significantly enhances the retention of implant-supported
IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014
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Table 1. Luting Agents Studied Product Name Fleck’s Poly F Fuji Plus Panavia F 2.0
Manufacturer
Lot Number
Mizzy Co., Cherry Hill, NJ Dentsply, Weybridge, England GC Co., Tokyo, Japan
Powder: L-77; Liquid: R3LYB 0905001485
Kuraray Co., Kurashiki, Japan
crowns,24,25 others reported no benefits of this surface treatment in bond strength to the base metal alloys.15,16,20,26 Furthermore, results of some studies showed an interaction between luting agent type and surface roughness. In fact, air abrasion could interfere the retention of some types of luting agents.20,27 In addition, the surface of restorations can be chemically treated using tin plating, silicoating, or the application of metal primers to improve the cement’s bonding strength to the metal substructure.16,23,28–30 Although improvement of the bond strength with Alloy Primers has been reported,16,30,31 some studies found a decrease in bond strength with the use of metal primers when compared with different surface treatments.29,32
0905261
Type of Luting Agent Zinc phosphate Zinc polycarboxylate Resin-modified glass ionomer Resin-based
51291
The purpose of this study was to evaluate the effect of different surface treatments on the retention of implantsupported restorations over short abutments using 4 permanent luting agents. The null hypothesis was that the different surface treatment methods would not affect the retention of implant-supported copings over short abutments.
MATERIALS
AND
METHODS
One hundred twenty solid abutments with 5.5 mm length and 8-degree taper (048.541, ITI Dental Implant System; Straumann AG, Basel, Switzerland) and 120 implant analogs (048.124; Straumann AG) were used. The abutments were tightened to implant analogs at 35 N$cm of torque. The implant-
Fig. 1. The metal copings were divided into 2 groups: control group with no surface treatment and group with airborne-particle abrasion. For resin cements, the control group and group with airborne-particle abrasion treatment were divided into 2 subgroups: (1) subgroup with no chemical treatment and (2) subgroup in which both abutment and intaglio surfaces of copings were treated by Alloy Primer.
Mixing Method and Ratio Hand mix, 8 g of powder with 0.3 mL of liquid Hand mix, 1 scoop powder with 2 drops of distilled water Automix capsule, 10 s mixing at 4000 rpm Hand mix, equal length of base and catalyst, light cured for 40 s
abutment complex were embedded vertically in a T-shaped block of autopolymerizing acrylic resin (Meliodent; Heraeus Kulzer, Hanau, Germany) using a dental surveyor for precise alignment. The height of the abutments were reduced to 3 mm using diamond rotary cutting instrument secured in a milling machine (Harnisch + Reith; Winterbach, Germany) under copious water irrigation to ensure the same preparation for the abutments. One hundred twenty copings were made using an autopolymerizing resin (Pattern resin; GC Co., Tokyo, Japan) with a loop on the occlusal surface for the retention test. The resin patterns were invested in a phosphate-bonded investment (Ceravest Quick; GC Co.) and cast in a base metal alloy (Rexillium III; Pentron, Wallingford, CT). After divesting and cleaning with an ultrasonic cleaner and hydrofluoric acid, the inner surface of the castings was inspected under magnification (34), and surface irregularities were removed with a small round carbide bur. The metal copings were checked for fitness using a silicon disclosing medium (Fit Checker; GC Co.), and further potential interferences of the castings were evaluated and adjusted if necessary. All castings were then subjected to a single, simulated porcelain degas firing cycle in a porcelain furnace (Programat P300/G2; Ivoclar Vivadent AG, Schaan, Liechtenstein) to form an oxide layer (from 649 to 1038°C with the vacuum on). The castings were divided into 2 groups: group 1 consists of 60 castings with no surface modification (control), group 2 underwent airborne-particle abrasion using 50 mm Al2O3 particles at 3.0 bar pressure perpendicular to each surface from a distance of 10 mm for
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METAL COPINGS
NEJATIDANESH
ET AL
Table 2. Mean (SD) Dislodging Forces of the Studied Groups (N) Control Fleck’s Poly F Fuji Plus Panavia F2.0
248.33 246.41 191.50 178.16
Alloy Primer
Airborne-Particle Abrasion + Alloy Primer
d d 130.80 (34.36)A,a 290.13 (53.08)A,a
d d 57.53 (34.35)B,b 177.30 (51.16)B,a
Airborne-Particle Abrasion
(44.87)A,a (36.32)A,a (34.93)A,a (59.15)B,a
181.03 129.76 144.96 172.79
(54.91)A,a (36.00)B,a (51.69)A,a (49.95)B,a
Significant differences between the means in raw (uppercase letter) and column (lowercase letter) are characterized by different letters (P , 0.05).
Table 3. One-Way ANOVA Source Between groups Within groups Total
Sum of Square
df
Mean Square
F
Sig.
426423.310 210168.086 636591.397
11 99 110
38,765.755 2122.910
18.261
0.000
10 seconds. Then, the castings were cleaned ultrasonically in 96% isopropyl alcohol for 5 minutes. Two different types of luting agents were evaluated in this study (Table 1): resin cements (Panavia F2.0, Fuji Plus) and conventional cements (Fleck’s, Poly F). In each group, 10 copings were cemented with the conventional cements. For resin cements, the control group and group with airborne-particle abrasion treatment were divided into 2 subgroups: in the first subgroup, no chemical treatment was made, and in the second subgroup, the abutment surface and the intaglio surface of copings were treated by Alloy Primer (Kuraray Co., Kurashiki, Japan) (n ¼ 10). Figure 1 reveals the studied groups. Each cement was mixed according to the manufacturer’s instruction and applied to the intaglio surface of copings.
The copings were gently seated on the abutments and held in place under a 5-kg load for 10 minutes. After initial setting of the cement, excess cement was removed with an explorer. For Panavia F.2.0, the restorations were light polymerized using a polymerization unit (blue phase C8; Ivoclar Vivadent AG, Schaan, Liechtenstein) for 10 seconds. After removing the excess cement, the copings were light polymerized for 30 seconds on each side. All samples were incubated at 37° C for 24 hours and conditioned in artificial saliva for the following 7 days and finally were subjected to 5000 thermal cycling, 5 to 55°C with 30-second dwell time. The copings of all groups were dislodged along the long axis of the abutment-implant analog complex with a universal testing machine (Instron 4302; Instron, Bucks, United Kingdom)
Fig. 2. Percentage of types of failure mode for each studied groups. S: sandblasting, AP: Alloy Primer.
at a crosshead speed of 5 mm/min. The dislodgment force and the failure mode were recorded. The failure modes were as follows33: (1) cement remained mainly on the coping surface (more than 75%), (2) cement remained on both coping and abutment surface (between 25% and 75%), (3) cement remained mainly on abutment surfaces (more than 75%). The dislodging forces were statistically analyzed using 1-way ANOVA, and Tukey honestly significant difference (HSD) (a ¼ 0.05). No statistical analysis was performed on the failure mode of the studied cements.
RESULTS Mean retentive values and SD of the studied groups are shown in Table 2. Panavia F 2.0 combined with Alloy Primer showed the most retentive strength while Fuji Plus with Alloy Primer and airborne-particle abrasion had the least. In control group, the retentive strengths of the conventional luting agents were higher than the resin ones. After mechanical treatment, Panavia F 2.0 and Fleck’s showed the highest retentive values. But the differences between different luting agents were not statistically different in control group and after airborne-particle abrasion (P ¼ 0.06 for control group and P , 0.12 after airborne-particle abrasion) (Table 2). One-way ANOVA showed that there was significant difference between the studied groups (Table 3). Airborne-particle abrasion resulted in reduction of the luting agents’ retention. Tukey post hoc test revealed that there was no significant difference between control groups and after airborne-particle abrasion among studied luting agents (P ¼ 0.07 for Fleck’s, P ¼ 1.00 for Panavia F, and P ¼ 0.66 for Fuji Plus) except Poly F,
IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014 for which this reduction was significant (P , 0.001) (Table 2). Regarding Alloy Primer, the retention of the copings significantly increased when Panavia F 2.0 was used as the luting agent (P , 0.001) while it reduced the retention in Fuji Plus without statistically significant difference (P ¼ 0.10) (Table 2). The failure mode in all groups was mostly adhesive such a way that the cement remained mainly in the intaglio surface of the copings (91.59%), which means that bond between luting agents and intaglio surface of copings was higher than adhesion of cement to abutment. In few specimens in the control groups, which were luted using Fleck’s and Poly F, and in the group that were luted with Panavia F 2.0 combined with Alloy Primer, cement remained on both the coping and abutment surfaces. In none of the experimental groups cement remained mainly on the abutment surface (Fig. 2).
DISCUSSION The null hypothesis of this study that the different surface treatment methods have no effect on the retention of implantsupported copings over short abutments could only be partially rejected. By the results of this study, airborne-particle abrasion of the copings could not improve the retentive strength of metal copings over short implant abutments; however, application of Alloy Primer significantly increased the retention of copings that were luted with Panavia F 2.0. The retentive strength of cementretained restorations is affected by the abutment characteristics, such as height and convergence angle and surface roughness.24,34 Comparing the results of the current study with our previous study using a similar methodology on 5.5-mm-height ITI abutments showed that the retention of copings decreased after reduction of the abutment height to 3 mm.10 In previous study, the retentive values of luted copings without any surface treatment were as follows: Fleck’s 267.62, Poly F 247.07, Fuji Plus 320.97, and Panavia F2 194.36 Newton, with no statistical significance difference.10 Although newly developed cements were introduced to implant dentistry, the cements evaluated in the current study
are still among the most commonly used luting agents. The results of current study showed that the retentive strength of studied luting agents in the control group with no pretreatment was not significantly different (P ¼ 0.06). Some studies indicated that the retentive strength of resinous luting agents was superior to that of resin-modified glass ionomer, zinc phosphate, and zinc polycarboxylate luting agents.5,9,35 The retentive strength of the resin cements can be achieved by application of adhesive system.11 In control group of this study, no bonding agent was used for Panavia F 2.0 and the different results can be related to this fact. However, there are some studies that demonstrated same retentive values for different type of definitive cements.10,24,36 Some authors showed that zinc polycarboxylate luting agent is one of the most retentive luting agents for cementation of implantretained castings.18–20 This can be related to adhesion of polycarboxylate cement to the fairly smooth machined abutment surfaces.9,19 In addition, there was no difference in retention of the copings after airborne-particle abrasion. Regarding the effect of airborne-particle abrasion on the bond strength of luting agents to metallic substructure, previous studies have conflicting results.15,16,20,21,24,37–39 Airborne-particle abrasion with 50-mm aluminum oxide particles increases the surface area, micromechanical retention, and wetting surface.26 However, non-sandblasted surface of base metal alloys is highly reactive with high freesurface energy due to a thick oxide layer. These oxides provide potential locations for bonding and increase micromechanical retention of the metal surface.15,16,37 In addition, in the current study, no prefabricated burn out cap was used for wax up, which could increase adaptation and roughness of the intaglio surface of metal copings, but sandblasting can prepare a homogeneous roughness that can reduce overall irregularities. Airborne-particle abrasion of restorations with large size particles and repeated sandblasting can remove significant amounts of material and affect clinical adaptation of the restorations,23 which was not used in this study. It has been shown that after
165
airborne-particle abrasion, loose alumina particles remain on the surface layer of metal and cannot be removed even by ultrasonic cleaning,23,40 which can jeopardize the bonding. Swartz et al26 also observed no improvement in retention of implant-supported prostheses luted with resin-modified glass ionomers after sandblasting and related this result to weak wettability of this luting agent. In the present study, the retentive values of copings decreased after sandblasting although it was not significant. According to the results of the current study, application of an Alloy Primer can enhance the retentive strength of metal copings luted with Panavia F 2.0 but had no significant effect on Fuji Plus. Two components in Alloy Primer can increase bonding of resin to the metal surface. The 6-(4vinylbenzyl-n-propyl) amino-1,3,5-triazine-2,4-dithione enhances bonding to the noble metals.31 Phosphoric acid monomer (10-methacryloyloxydecyl dihydrogen phosphate [MDP]) enhances the retention of resins to the base metal alloys.31,41 Yanagida et al42 stated that the MDP monomer, which presents in both the Alloy Primer and Panavia F, consists of 3 components that function differently: the methacryloyl, dihydrogen phosphate, and decyl groups. The methacryloyl group is necessary for copolymerizing the MDP monomers in the primer and the matrix monomers of luting agent. The dihydrogen phosphate group has the key role in chemical adherence of cement to the metal oxide. The decyl group prevents penetration of water into the adhesive interface. The results of the present study are similar to the other studies that showed that metal primers enhance the retention of implant-supported crowns when the resin cements were used.16,30,31 Our results conflict with the findings of a similar study on short ITI solid abutments, in which the most retentive strength was obtained when the copings were luted with Panavia 21 after sandblasting in combination with the application of an Alloy Primer.24 However, in this study, titanium alloy was used for casting and the copings were made using burn out caps. In addition, both the castings and the abutments were
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sandblasted, and no thermal cycling and conditioning were performed.24 It was reported that Panavia and titanium alloys exhibit higher bond strength than the other alloys.24,43 As the results of this study showed, the use of an Alloy Primer did not affect the retention of metal copings that were luted using Fuji Plus. Resin-modified glass ionomer cements have a hydrophilic nature44 but the phosphate monomer component (MDP) has hydrophobic properties.45 When the metal primer is applied to the surface of the casting, this hydrophobic part can interfere with the proper bonding of a hydrophilic resinmodified glass ionomer.46 In addition, the water sorption of a resin-modified glass ionomer is much higher than other cements that can cause crack formation in the cement and result in lower resistance to tensile forces.47 The failure mode of the Panavia F2.0 and Fuji Plus with no surface treatment was completely adhesive, which means the cement remained mainly in the intaglio surface of the copings. However, the luting agent remained on both the casting and the abutment surfaces after application of the Alloy Primer combined with Panavia F2.0. This can be supported by the higher retentive strength of this group. In the control group, zinc phosphate and zinc polycarboxylate cements adhered mainly to the castings surfaces. After airborne-particle abrasion, the luting agent remained completely on the casting surface in all groups. This may be explained by the effect of airborneparticle abrasion in increasing the surface area, mechanical retention, and wetting surface.26 There was no specimen where the luting agent remained mainly on the abutment surface because the abutment surface is relatively smooth and titanium is an inert material. One of the limitations of this study is that other factors, such as pH changes and dynamic fatigue loading, that can affect the clinical behavior of studied luting agents and surface treatments and possibly decrease the retention force of implant-supported restorations were not evaluated in the present study. Therefore, careful interpretation in the clinical application of the results is suggested.
METAL COPINGS
NEJATIDANESH
However, in this study, a base metal alloy was used for fabrication of copings, but in implantology, most prosthetic components are Ti, Ti alloy, and superstructures mostly made by noble metals alloys. Although the use of base metal alloys may increase the risk of galvanic corrosion, the alloy type has no effect on crown retention strength.15
CONCLUSIONS Within the limitations of this study, these conclusions can be drawn: 1. The airborne-particle abrasion did not improve the retention of base metal alloy copings over short implant abutments. 2. Alloy Primer can enhance the retention of metal copings when Panavia F 2.0 is used as the luting agent.
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
ACKNOWLEDGMENTS This study was supported by Isfahan University of Medical Sciences Research Grant # 288108.
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IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014 crowns. Int J Oral Maxillofac Implants. 2002;17:536–542. 19. Mehl C, Harder S, Wolfart M, et al. Retrievability of implant-retained crowns following cementation. Clin Oral Implants Res. 2008;19:1304–1311. 20. Wolfart M, Wolfart S, Kern M. Retention forces and seating discrepancies of implant-retained castings after cementation. Int J Oral Maxillofac Implants. 2006;21:519–525. 21. Gurbuz A, Inan O, Kaplan R, et al. Effect of airborne-particle abrasion on retentive strength in overtapered fixed prosthodontic restorations. Quintessence Int. 2008;39:e134–e138. 22. Tarica DY, Alvarado VM, Truong ST. Survey of United States dental schools on cementation protocols for implant crown restorations. J Prosthet Dent. 2010;103:68–79. 23. Kern M, Thompson VP. Sandblasting and silica-coating of dental alloys: volume loss, morphology and changes in the surface composition. Dent Mater. 1993;9: 151–161. 24. Sadig WM, Al Harbi MW. Effects of surface conditioning on the retentiveness of titanium crowns over short implant abutments. Implant Dent. 2007;16:387–396. 25. de Campos TN, Adachi LK, Miashiro K, et al. Effect of surface topography of implant abutments on retention of cemented single-tooth crowns. Int J Periodontics Restorative Dent. 2010;30:409–413. 26. Swartz JM, Davis RD, Overton JD. Tensile bond strength of resin-modified glass-ionomer cement to microabraded and silica-coated or tin-plated high noble ceramic alloy. J Prosthodont. 2000;9:195–200. 27. Kim Y, Yamashita J, Shotwell JL, et al. The comparison of provisional luting agents and abutment surface roughness on the retention of provisional implantsupported crowns. J Prosthet Dent. 2006;95:450–455.
28. Laufer BZ, Nicholls JI, Townsend JD. SiOx-C coating: A composite-to-metal bonding mechanism. J Prosthet Dent. 1988;60:320–327. 29. Parsa RZ, Goldstein GR, Barrack GM, et al. An in vitro comparison of tensile bond strengths of noble and base metal alloys to enamel. J Prosthet Dent. 2003; 90:175–183. 30. Antoniadou M, Kern M, Strub JR. Effect of a new metal primer on the bond strength between a resin cement and two high-noble alloys. J Prosthet Dent. 2000; 84:554–560. 31. Yoshida K, Kamada K, Atsuta M. Adhesive primers for bonding cobaltchromium alloy to resin. J Oral Rehabil. 1999;26:475–478. 32. Fonseca RG, de Almeida JG, Haneda IG, et al. Effect of metal primers on bond strength of resin cements to base metals. J Prosthet Dent. 2009;101:262–268. 33. Palacios RP, Johnson GH, Phillips KM, et al. Retention of zirconium oxide ceramic crowns with three types of cement. J Prosthet Dent. 2006;96:104–114. 34. Bresciano M, Schierano G, Manzella C, et al. Retention of luting agents on implant abutments of different height and taper. Clin Oral Implants Res. 2005;16:594–598. 35. Maeyama H, Sawase T, Jimbo R, et al. Retentive strength of metal copings on prefabricated abutments with five different cements. Clin Implant Dent Relat Res. 2005;7:229–234. 36. Montenegro AC, Machado AN, Depes Gouvea CV. Tensile strength of cementing agents on the CeraOne system of dental prosthesis on implants. Implant Dent. 2008;17:451–460. 37. Breeding LC, Dixon DL. The effect of metal surface treatment on the shear bond strengths of base and noble metals bonded to enamel. J Prosthet Dent. 1996; 76:390–393.
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38. Dixon DL, Breeding LC, Hughie ML, et al. Comparison of shear bond strengths of two resin luting systems for a base and a high noble metal alloy bonded to enamel. J Prosthet Dent. 1994;72:457–461. 39. Sen D, Nayir E, Pamuk S. Comparison of the tensile bond strength of highnoble, noble, and base metal alloys bonded to enamel. J Prosthet Dent. 2000;84:561–566. 40. Papadopoulos T, Tsetsekou A, Eliades G. Effect of aluminium oxide sandblasting on cast commercially pure titanium surfaces. Eur J Prosthodont Restor Dent. 1999;7:15–21. 41. Yoshida K, Taira Y, Matsumura H, et al. Effect of adhesive metal primers on bonding a prosthetic composite resin to metals. J Prosthet Dent. 1993;69:357–362. 42. Yanagida H, Matsumura H, Taira Y, et al. Adhesive bonding of composite material to cast titanium with varying surface preparations. J Oral Rehabil. 2002; 29:121–126. 43. Kern M, Thompson VP. Durability of resin bonds to pure titanium. J Prosthodont. 1995;4:16–22. 44. Gerdolle DA, Mortier E, Jacquot B, et al. Water sorption and water solubility of current luting cements: An in vitro study. Quintessence Int. 2008;39:e107–e114. 45. Matsumura H, Shimoe S, Nagano K, et al. Effect of noble metal conditioners on bonding between prosthetic composite material and silver-palladium-copper-gold alloy. J Prosthet Dent. 1999;81:710–714. 46. Furuchi M, Oshima A, Ishikawa Y, et al. Effect of metal priming agents on bond strength of resin-modified glass ionomers joined to gold alloy. Dent Mater J. 2007;26:728–732. 47. Burgess J, Norling B, Summitt J. Resin ionomer restorative materials: The new generation. J Esthet Dent. 1994;6: 207–215.
RETENTIVENESS
OF IMPLANT-SUPPORTED
METAL COPINGS
NEJATIDANESH
ET AL
Retentive Strength of Implant-Supported Base Metal Copings Over Short Metal Abutments Using Different Luting Agents and Surface Treatments Farahnaz Nejatidanesh, DDS, MS,* Omid Savabi, DDS, MS,† Maziar Ebrahimi, DDS, MS,‡ and Ghazal Savabi, DDS§
oss of retention is the most common complication with cement-retained implant-supported prostheses,1,2 especially on short abutments.3 The retention of cement-retained restorations can be affected by the geometry of the abutment, surface roughness of the abutment and restoration, and the type of luting agent.4,5 The height of abutment is a determining factor that affects the surface area, resistance, and retention properties. The use of short abutments in limited interarch space can jeopardize the retention and resistance of the restorations.6,7 In these situations, retentive characteristics of the luting agent are more important for retention of the restoration. Many studies have shown that definitive cements provide more retention than provisional cements.8–10 The retention of conventional cements derived from the micromechanical retention of abutment and the intaglio surface of restoration.10–12
L
*Professor, Dental Materials Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran; Biomaterials Research Group, Isfahan University of Technology, Isfahan, Iran. †Professor, Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran; Biomaterials Research Group, Isfahan University of Technology, Isfahan, Iran. ‡Assistant Professor, Department of Endodontics, School of Dentistry, Khorasgan Islamic Azad University, Isfahan, Iran. §Dental Student, Dental Students’ Research Committee, School of Dentistry, Khorasgan Islamic Azad University, Isfahan, Iran.
Reprint requests and correspondence to: Omid Savabi, DDS, MS, 400 Sheikhsadoogh Shomali Street, Sheikhsadoogh Cross Road, Isfahan 81648-13315, Iran, Phone: 0098311-6614059/0098311-7922890, Fax: 0098311-6687080, E-mail: [email protected] ISSN 1056-6163/14/02302-162 Implant Dentistry Volume 23 Number 2 Copyright © 2014 by Lippincott Williams & Wilkins DOI: 10.1097/ID.0000000000000049
Purpose: To evaluate the effect of surface treatments on retention of implant-supported restorations over short abutments. Materials and Methods: One hundred twenty metal copings were made on Straumann solid abutments (3 mm length). The copings were divided into 2 groups: control and air abraded (50 mm Al2O3). The copings were luted using Fleck’s, Poly F, Panavia F, and Fuji Plus. In resin cements groups, 2 subgroups were studied base on the application of Alloy Primer (n ¼ 10). After conditioning in saliva and 5000 thermal cycles, retentive strengths of specimens were measured. Data were analyzed by 1-way ANOVA and Tukey honestly significant difference tests (a ¼ 0.05).
Results: Panavia F 2.0 combined with Alloy Primer showed the most retentive values. In control and air abraded groups, there was no significant difference between the studied luting agents. Alloy Primer significantly increased the retention of copings luted with Panavia F 2.0. Conclusion: Within the limitations of this study, the retentive strength of metal copings over short implant abutments was not improved by airborne-particle abrasion. However, Alloy primer enhanced the retention of metal copings that were luted using Panavia F 2.0. (Implant Dent 2014;23:162–167) Key Words: dental implants, dental restoration failure, surface properties, dental prosthesis retention
However, the resin cements exhibit chemical bonding to the restoration and are advocated to enhance retention.13–16 Zinc phosphate,17 zinc polycarboxylate,18,19 and resin cements9,20 have been the most retentive definitive luting agents for cementation of implant-supported restorations. Surface treatment of the intaglio surface of the restoration before cementation can enhance the bond strength of the luting agent to the restoration. Different studies evaluated the effect of mechanical surface treatment of casting such as oxide layer formed
during porcelain firing and airborneparticle abrasion on the bond and retentive strength of castings.15,16,20,21 Most dental schools in the United States recommended either no treatment or abrasion of the internal surface of implantsupported restorations, before definitive cementation.22 Airborne-particle abrasion with aluminum oxide particles is an inexpensive technique that removes debris, roughens the surface of the casting, and also increases the surface area of restoration.15,23 Although in some studies, air abrasion treatment significantly enhances the retention of implant-supported
IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014
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Table 1. Luting Agents Studied Product Name Fleck’s Poly F Fuji Plus Panavia F 2.0
Manufacturer
Lot Number
Mizzy Co., Cherry Hill, NJ Dentsply, Weybridge, England GC Co., Tokyo, Japan
Powder: L-77; Liquid: R3LYB 0905001485
Kuraray Co., Kurashiki, Japan
crowns,24,25 others reported no benefits of this surface treatment in bond strength to the base metal alloys.15,16,20,26 Furthermore, results of some studies showed an interaction between luting agent type and surface roughness. In fact, air abrasion could interfere the retention of some types of luting agents.20,27 In addition, the surface of restorations can be chemically treated using tin plating, silicoating, or the application of metal primers to improve the cement’s bonding strength to the metal substructure.16,23,28–30 Although improvement of the bond strength with Alloy Primers has been reported,16,30,31 some studies found a decrease in bond strength with the use of metal primers when compared with different surface treatments.29,32
0905261
Type of Luting Agent Zinc phosphate Zinc polycarboxylate Resin-modified glass ionomer Resin-based
51291
The purpose of this study was to evaluate the effect of different surface treatments on the retention of implantsupported restorations over short abutments using 4 permanent luting agents. The null hypothesis was that the different surface treatment methods would not affect the retention of implant-supported copings over short abutments.
MATERIALS
AND
METHODS
One hundred twenty solid abutments with 5.5 mm length and 8-degree taper (048.541, ITI Dental Implant System; Straumann AG, Basel, Switzerland) and 120 implant analogs (048.124; Straumann AG) were used. The abutments were tightened to implant analogs at 35 N$cm of torque. The implant-
Fig. 1. The metal copings were divided into 2 groups: control group with no surface treatment and group with airborne-particle abrasion. For resin cements, the control group and group with airborne-particle abrasion treatment were divided into 2 subgroups: (1) subgroup with no chemical treatment and (2) subgroup in which both abutment and intaglio surfaces of copings were treated by Alloy Primer.
Mixing Method and Ratio Hand mix, 8 g of powder with 0.3 mL of liquid Hand mix, 1 scoop powder with 2 drops of distilled water Automix capsule, 10 s mixing at 4000 rpm Hand mix, equal length of base and catalyst, light cured for 40 s
abutment complex were embedded vertically in a T-shaped block of autopolymerizing acrylic resin (Meliodent; Heraeus Kulzer, Hanau, Germany) using a dental surveyor for precise alignment. The height of the abutments were reduced to 3 mm using diamond rotary cutting instrument secured in a milling machine (Harnisch + Reith; Winterbach, Germany) under copious water irrigation to ensure the same preparation for the abutments. One hundred twenty copings were made using an autopolymerizing resin (Pattern resin; GC Co., Tokyo, Japan) with a loop on the occlusal surface for the retention test. The resin patterns were invested in a phosphate-bonded investment (Ceravest Quick; GC Co.) and cast in a base metal alloy (Rexillium III; Pentron, Wallingford, CT). After divesting and cleaning with an ultrasonic cleaner and hydrofluoric acid, the inner surface of the castings was inspected under magnification (34), and surface irregularities were removed with a small round carbide bur. The metal copings were checked for fitness using a silicon disclosing medium (Fit Checker; GC Co.), and further potential interferences of the castings were evaluated and adjusted if necessary. All castings were then subjected to a single, simulated porcelain degas firing cycle in a porcelain furnace (Programat P300/G2; Ivoclar Vivadent AG, Schaan, Liechtenstein) to form an oxide layer (from 649 to 1038°C with the vacuum on). The castings were divided into 2 groups: group 1 consists of 60 castings with no surface modification (control), group 2 underwent airborne-particle abrasion using 50 mm Al2O3 particles at 3.0 bar pressure perpendicular to each surface from a distance of 10 mm for
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RETENTIVENESS
OF IMPLANT-SUPPORTED
METAL COPINGS
NEJATIDANESH
ET AL
Table 2. Mean (SD) Dislodging Forces of the Studied Groups (N) Control Fleck’s Poly F Fuji Plus Panavia F2.0
248.33 246.41 191.50 178.16
Alloy Primer
Airborne-Particle Abrasion + Alloy Primer
d d 130.80 (34.36)A,a 290.13 (53.08)A,a
d d 57.53 (34.35)B,b 177.30 (51.16)B,a
Airborne-Particle Abrasion
(44.87)A,a (36.32)A,a (34.93)A,a (59.15)B,a
181.03 129.76 144.96 172.79
(54.91)A,a (36.00)B,a (51.69)A,a (49.95)B,a
Significant differences between the means in raw (uppercase letter) and column (lowercase letter) are characterized by different letters (P , 0.05).
Table 3. One-Way ANOVA Source Between groups Within groups Total
Sum of Square
df
Mean Square
F
Sig.
426423.310 210168.086 636591.397
11 99 110
38,765.755 2122.910
18.261
0.000
10 seconds. Then, the castings were cleaned ultrasonically in 96% isopropyl alcohol for 5 minutes. Two different types of luting agents were evaluated in this study (Table 1): resin cements (Panavia F2.0, Fuji Plus) and conventional cements (Fleck’s, Poly F). In each group, 10 copings were cemented with the conventional cements. For resin cements, the control group and group with airborne-particle abrasion treatment were divided into 2 subgroups: in the first subgroup, no chemical treatment was made, and in the second subgroup, the abutment surface and the intaglio surface of copings were treated by Alloy Primer (Kuraray Co., Kurashiki, Japan) (n ¼ 10). Figure 1 reveals the studied groups. Each cement was mixed according to the manufacturer’s instruction and applied to the intaglio surface of copings.
The copings were gently seated on the abutments and held in place under a 5-kg load for 10 minutes. After initial setting of the cement, excess cement was removed with an explorer. For Panavia F.2.0, the restorations were light polymerized using a polymerization unit (blue phase C8; Ivoclar Vivadent AG, Schaan, Liechtenstein) for 10 seconds. After removing the excess cement, the copings were light polymerized for 30 seconds on each side. All samples were incubated at 37° C for 24 hours and conditioned in artificial saliva for the following 7 days and finally were subjected to 5000 thermal cycling, 5 to 55°C with 30-second dwell time. The copings of all groups were dislodged along the long axis of the abutment-implant analog complex with a universal testing machine (Instron 4302; Instron, Bucks, United Kingdom)
Fig. 2. Percentage of types of failure mode for each studied groups. S: sandblasting, AP: Alloy Primer.
at a crosshead speed of 5 mm/min. The dislodgment force and the failure mode were recorded. The failure modes were as follows33: (1) cement remained mainly on the coping surface (more than 75%), (2) cement remained on both coping and abutment surface (between 25% and 75%), (3) cement remained mainly on abutment surfaces (more than 75%). The dislodging forces were statistically analyzed using 1-way ANOVA, and Tukey honestly significant difference (HSD) (a ¼ 0.05). No statistical analysis was performed on the failure mode of the studied cements.
RESULTS Mean retentive values and SD of the studied groups are shown in Table 2. Panavia F 2.0 combined with Alloy Primer showed the most retentive strength while Fuji Plus with Alloy Primer and airborne-particle abrasion had the least. In control group, the retentive strengths of the conventional luting agents were higher than the resin ones. After mechanical treatment, Panavia F 2.0 and Fleck’s showed the highest retentive values. But the differences between different luting agents were not statistically different in control group and after airborne-particle abrasion (P ¼ 0.06 for control group and P , 0.12 after airborne-particle abrasion) (Table 2). One-way ANOVA showed that there was significant difference between the studied groups (Table 3). Airborne-particle abrasion resulted in reduction of the luting agents’ retention. Tukey post hoc test revealed that there was no significant difference between control groups and after airborne-particle abrasion among studied luting agents (P ¼ 0.07 for Fleck’s, P ¼ 1.00 for Panavia F, and P ¼ 0.66 for Fuji Plus) except Poly F,
IMPLANT DENTISTRY / VOLUME 23, NUMBER 2 2014 for which this reduction was significant (P , 0.001) (Table 2). Regarding Alloy Primer, the retention of the copings significantly increased when Panavia F 2.0 was used as the luting agent (P , 0.001) while it reduced the retention in Fuji Plus without statistically significant difference (P ¼ 0.10) (Table 2). The failure mode in all groups was mostly adhesive such a way that the cement remained mainly in the intaglio surface of the copings (91.59%), which means that bond between luting agents and intaglio surface of copings was higher than adhesion of cement to abutment. In few specimens in the control groups, which were luted using Fleck’s and Poly F, and in the group that were luted with Panavia F 2.0 combined with Alloy Primer, cement remained on both the coping and abutment surfaces. In none of the experimental groups cement remained mainly on the abutment surface (Fig. 2).
DISCUSSION The null hypothesis of this study that the different surface treatment methods have no effect on the retention of implantsupported copings over short abutments could only be partially rejected. By the results of this study, airborne-particle abrasion of the copings could not improve the retentive strength of metal copings over short implant abutments; however, application of Alloy Primer significantly increased the retention of copings that were luted with Panavia F 2.0. The retentive strength of cementretained restorations is affected by the abutment characteristics, such as height and convergence angle and surface roughness.24,34 Comparing the results of the current study with our previous study using a similar methodology on 5.5-mm-height ITI abutments showed that the retention of copings decreased after reduction of the abutment height to 3 mm.10 In previous study, the retentive values of luted copings without any surface treatment were as follows: Fleck’s 267.62, Poly F 247.07, Fuji Plus 320.97, and Panavia F2 194.36 Newton, with no statistical significance difference.10 Although newly developed cements were introduced to implant dentistry, the cements evaluated in the current study
are still among the most commonly used luting agents. The results of current study showed that the retentive strength of studied luting agents in the control group with no pretreatment was not significantly different (P ¼ 0.06). Some studies indicated that the retentive strength of resinous luting agents was superior to that of resin-modified glass ionomer, zinc phosphate, and zinc polycarboxylate luting agents.5,9,35 The retentive strength of the resin cements can be achieved by application of adhesive system.11 In control group of this study, no bonding agent was used for Panavia F 2.0 and the different results can be related to this fact. However, there are some studies that demonstrated same retentive values for different type of definitive cements.10,24,36 Some authors showed that zinc polycarboxylate luting agent is one of the most retentive luting agents for cementation of implantretained castings.18–20 This can be related to adhesion of polycarboxylate cement to the fairly smooth machined abutment surfaces.9,19 In addition, there was no difference in retention of the copings after airborne-particle abrasion. Regarding the effect of airborne-particle abrasion on the bond strength of luting agents to metallic substructure, previous studies have conflicting results.15,16,20,21,24,37–39 Airborne-particle abrasion with 50-mm aluminum oxide particles increases the surface area, micromechanical retention, and wetting surface.26 However, non-sandblasted surface of base metal alloys is highly reactive with high freesurface energy due to a thick oxide layer. These oxides provide potential locations for bonding and increase micromechanical retention of the metal surface.15,16,37 In addition, in the current study, no prefabricated burn out cap was used for wax up, which could increase adaptation and roughness of the intaglio surface of metal copings, but sandblasting can prepare a homogeneous roughness that can reduce overall irregularities. Airborne-particle abrasion of restorations with large size particles and repeated sandblasting can remove significant amounts of material and affect clinical adaptation of the restorations,23 which was not used in this study. It has been shown that after
165
airborne-particle abrasion, loose alumina particles remain on the surface layer of metal and cannot be removed even by ultrasonic cleaning,23,40 which can jeopardize the bonding. Swartz et al26 also observed no improvement in retention of implant-supported prostheses luted with resin-modified glass ionomers after sandblasting and related this result to weak wettability of this luting agent. In the present study, the retentive values of copings decreased after sandblasting although it was not significant. According to the results of the current study, application of an Alloy Primer can enhance the retentive strength of metal copings luted with Panavia F 2.0 but had no significant effect on Fuji Plus. Two components in Alloy Primer can increase bonding of resin to the metal surface. The 6-(4vinylbenzyl-n-propyl) amino-1,3,5-triazine-2,4-dithione enhances bonding to the noble metals.31 Phosphoric acid monomer (10-methacryloyloxydecyl dihydrogen phosphate [MDP]) enhances the retention of resins to the base metal alloys.31,41 Yanagida et al42 stated that the MDP monomer, which presents in both the Alloy Primer and Panavia F, consists of 3 components that function differently: the methacryloyl, dihydrogen phosphate, and decyl groups. The methacryloyl group is necessary for copolymerizing the MDP monomers in the primer and the matrix monomers of luting agent. The dihydrogen phosphate group has the key role in chemical adherence of cement to the metal oxide. The decyl group prevents penetration of water into the adhesive interface. The results of the present study are similar to the other studies that showed that metal primers enhance the retention of implant-supported crowns when the resin cements were used.16,30,31 Our results conflict with the findings of a similar study on short ITI solid abutments, in which the most retentive strength was obtained when the copings were luted with Panavia 21 after sandblasting in combination with the application of an Alloy Primer.24 However, in this study, titanium alloy was used for casting and the copings were made using burn out caps. In addition, both the castings and the abutments were
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OF IMPLANT-SUPPORTED
sandblasted, and no thermal cycling and conditioning were performed.24 It was reported that Panavia and titanium alloys exhibit higher bond strength than the other alloys.24,43 As the results of this study showed, the use of an Alloy Primer did not affect the retention of metal copings that were luted using Fuji Plus. Resin-modified glass ionomer cements have a hydrophilic nature44 but the phosphate monomer component (MDP) has hydrophobic properties.45 When the metal primer is applied to the surface of the casting, this hydrophobic part can interfere with the proper bonding of a hydrophilic resinmodified glass ionomer.46 In addition, the water sorption of a resin-modified glass ionomer is much higher than other cements that can cause crack formation in the cement and result in lower resistance to tensile forces.47 The failure mode of the Panavia F2.0 and Fuji Plus with no surface treatment was completely adhesive, which means the cement remained mainly in the intaglio surface of the copings. However, the luting agent remained on both the casting and the abutment surfaces after application of the Alloy Primer combined with Panavia F2.0. This can be supported by the higher retentive strength of this group. In the control group, zinc phosphate and zinc polycarboxylate cements adhered mainly to the castings surfaces. After airborne-particle abrasion, the luting agent remained completely on the casting surface in all groups. This may be explained by the effect of airborneparticle abrasion in increasing the surface area, mechanical retention, and wetting surface.26 There was no specimen where the luting agent remained mainly on the abutment surface because the abutment surface is relatively smooth and titanium is an inert material. One of the limitations of this study is that other factors, such as pH changes and dynamic fatigue loading, that can affect the clinical behavior of studied luting agents and surface treatments and possibly decrease the retention force of implant-supported restorations were not evaluated in the present study. Therefore, careful interpretation in the clinical application of the results is suggested.
METAL COPINGS
NEJATIDANESH
However, in this study, a base metal alloy was used for fabrication of copings, but in implantology, most prosthetic components are Ti, Ti alloy, and superstructures mostly made by noble metals alloys. Although the use of base metal alloys may increase the risk of galvanic corrosion, the alloy type has no effect on crown retention strength.15
CONCLUSIONS Within the limitations of this study, these conclusions can be drawn: 1. The airborne-particle abrasion did not improve the retention of base metal alloy copings over short implant abutments. 2. Alloy Primer can enhance the retention of metal copings when Panavia F 2.0 is used as the luting agent.
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
ACKNOWLEDGMENTS This study was supported by Isfahan University of Medical Sciences Research Grant # 288108.
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