d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/dema
Laboratory tests for assessing adaptability and stickiness of dental composites Martin Rosentritt ∗ , Sebastian Buczovsky, Michael Behr, Verena Preis Department of Prosthetic Dentistry, Regensburg University Medical Center, Germany
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objective. Handling (stickiness, adaptability) of a dental composite does strongly influence
Received 4 March 2013
quality and success of a dental restoration. The purpose was to develop an in vitro test,
Received in revised form
which allows for evaluating adaptability and stickiness.
7 March 2014
Methods. 15 dentists were asked for providing individual assessment (school scores 1–6)
Accepted 21 May 2014
of five dental composites addressing adaptability and stickiness. Composites were applied with a dental plugger (d = 1.8 mm) in a class I cavity (human tooth 17). The tooth was fixed on a force gauge for simultaneous determination of application forces with varying storage
Keywords:
(6/25 ◦ C) and application temperatures (6/25 ◦ C). On basis of these data tensile tests were per-
Composite
formed with a dental plugger (application force 1 N/2 N; v = 35 mm/min) on PMMA- or human
Handling
tooth plates. Composite was dosed onto the tip of the plugger and applied. Application and
Stickiness
unplugging was performed once and unplugging forces (UF) and length of the adhesive flags
Adaptability
(LAF) were determined at different storage (6/25 ◦ C) and application temperatures (25/37 ◦ C).
Rheology
Unplugging work (UW) was calculated from area of UF and LAF data.
Flow
Results. The individual assessment revealed significantly different temperature-dependent
Application
application forces between 0.58 N and 2.23 N. Adaptability was assessed between 2.1 and 2.8 school scores. Stickiness varied significantly between the materials (scores: 2–3.2). UW differed significantly between the materials with values between 3.20 N mm and 37.83 N mm. Between PMMA substrate or tooth slides and between 1 N or 2 N application force only small UW differences were found. Significance. The presented in vitro unplugging work allows for an in vitro estimation of the handling parameters adaptability and stickiness. © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Light curing dental composites are state of the art for clinical restorations. The development of these composites is strongly orientated on clinical requirements. Therefore
various materials with different viscosities, application forms and with optimized properties are available [1]. Nevertheless the clinical success of a composite is strongly influenced by handling opportunities. For example insufficient condensation may result in voids or porosities and may reduce stability, marginal integrity or wear resistance. Because handling may
∗ Corresponding author at: Department of Prosthetic Dentistry, Regensburg University Medical Center, D-93042 Regensburg, Germany. Tel.: +49 941 944 6054; fax: +49 941 944 6171. E-mail address: [email protected] (M. Rosentritt). http://dx.doi.org/10.1016/j.dental.2014.05.014 0109-5641/© 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
964
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
2.
Materials and methods
Five different commercially available composite materials were investigated: Admira, Arabesk Top, Grandio, Polofil Molar L (all Voco, Cuxhafen, Germany) and Tetric Evo Ceram (IvoclarVivadent, Schaan, Liechtenstein).
2.1.
Part 1
For a praxis-orientated estimation, 15 dentists evaluated the subjective handling properties of the composite materials (estimated power > 0.9, G*Power 3.1.3, Kiel, Germany). The dentists were asked to address to “adaptability” and “stickiness” using school grades from 1 (good/high) to 6 (bad/low). For simulating clinical conditions, the dentists applied the materials with a dental plugger (flat d = 1.8 mm, DE 295R, Aesculap, Melsungen, Germany) in a class I cavity (height 5 mm, diameter: 4 mm), which was prepared in a human tooth (tooth 17). Composite was applied in about 2 mm increments. Teeth and plugger were cleaned with chlorhexidine and teeth were kept in water between the tests. Materials were stored and applied at 25 ◦ C. With a force gauge (Type 8435-6001, resolution 0.01 N, Burster, Gernsbach, Germany), which was located under the teeth, the plugging force was determined. Further on plugging forces were measured at two different storage temperatures (6 ◦ C, 25 ◦ C) and two application temperatures (6 ◦ C, 25 ◦ C). Tooth temperatures were regulated using a selfassembled heating module.
-
Force (AF) [N]
2.5
Force (UF) [N]
not be fully described by individual parameters like stiffness, viscosity (rheology) [2], adhesive behavior, visco-elastic behavior [3] or the filler components [4], it is practise to ask dentists for their distinct impression of unset composites. Parameters are the ease to adapt a composite in the cavity (adaptability), how the composite sticks to the cavity or instrument (stickiness) or how firm the composite appears (firmness). Often a high number of dentists is questioned, which results in high expenditure and costs. Therefore, a standardized laboratory test seems necessary, which allows for estimating handling of composites. Already performed tests are tensile tests or profilometry, examining the influence of different speed, testing temperatures or different substrate surfaces. Work for probe separation, maximum force [4] or coefficients of variation [5] were defined as parameters for characterization of composite properties, temperature influence and unplugging speed. Partly the length of the adhesive flag was determined by polymerizing the material during tensile testing [6]. But in conclusion no test seems available representing the clinical situation. Therefore, the idea was to ask a representative number of dentists for the evaluation of different composites and relate these results to in vitro tensile tests. Clinical parameters such as human tooth tissue, storage conditions or cavity temperatures should be considered. Undetermined application force should be evaluated. The hypothesis of this investigation was that unplugging work might provide an opportunity for evaluating adaptability and stickiness of dental composites. The purpose of this study was to develop a simplified test, which allows for standardizing adaptability and stickiness.
2.0 1.5 1.0 0.5 0.0 0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
-0.5
-1.0
Length (LAF) [cm]
Fig. 1 – Force [N]/length [mm] diagram with application force (AF, positive) and unplugging force (UF, negative) (example, 25 ◦ C/25 ◦ C).
2.2.
Part 2
A dental plugger was fixed to a universal testing machine (Zwick 1446, resolution 0.001 N, Zwick, Ulm, Germany), which allows applying standardized application forces (1 N or 2 N as a result of part 1) and speed (35 mm/min). After a number of pre-tests with standard cavities (tooth, PMMA) and for simplification of the testing protocol, we decided to carry out the tests on PMMA- or human tooth plates (thickness 1.5 mm). Plates were cut with an inner whole saw (SP 1600, Leica, Wetzlar, Germany) under water cooling and, in case of tooth plates, in root-crown direction. Composite was dosed (1.5 mm × 2 mm, Composite-gun tubes 1915, KerrHawe, Bioggio, Switzerland) and fixed to the tip of the plugger. Application and unplugging was performed one time and the unplugging forces (UF) and the length of the adhesive flags (LAF [mm]) were determined. For detailed optical information on LAF, the tests were recorded with video (Handycam DCR-DVD450E, Sony, Tokio, Japan). Unplugging work (UW) was calculated from area of UF and LAF (integrated) data (UW [N mm] = UF [N] × LAF [mm]). Tests were performed with two different storage temperatures (6 ◦ C, 25 ◦ C) and two application temperatures (25 ◦ C, 37 ◦ C). To hinder an uncontrolled polymerization of the applied materials, all tests were performed under yellow light (Fig. 1). Mean and standard deviation were calculated. Statistical analysis was performed with SPSS 19 (IBM, New York, USA) using one-way ANOVA and linear uni/multi-variant comparison (Bonferroni Post Hoc). The level of significance was set to 0.05.
3.
Results
3.1.
Part 1
Stickiness of Arabesk and Admira were determined “3.1–3.2”, whereas Grandio, Polofil and Tetric were characterized as less sticky (“2–2.5”). A comparable ranking was found for adaptability: Arabesk and Admira were evaluated 2.8, whereas Grandio, Polofil and Tetric got grades between 2.1 and 2.4 (good
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
Table 1 – Individual evaluation of stickiness and adaptability (school grades from 1 (good/high) to 6 (bad/low); mean ± STD; n = 15 dentists; identical letters indicate significant differences). Material Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
Stickiness 1 = not sticky 3.1 3.2 2.1 2.0 2.5
± ± ± ± ±
1.0a 1.1bc 1.1b 0.8ac 0.8
Adaptability 1 = very good 2.8 2.8 2.1 2.2 2.4
± ± ± ± ±
0.9 0.7 0.8 0.8 0.7
applicable) (Table 1; Bonferroni comparison). One-way ANOVA test revealed significant differences for stickiness (p = 0.003), whereas no differences were found for adaptability (p = 0.055). Plugging forces varied between 0.58 ± 0.31 N (Polofil Molar 25 ◦ C/37 ◦ C) and 2.23 N (Admira 25 ◦ C/25 ◦ C). Highest plugging forces were found for the materials when stored and applied at 25 ◦ C. Lowest results were determined at a storage temperature of 25 ◦ C and application temperature of 37 ◦ C. Group comparison showed significant force differences between both application temperatures at storage temperatures of 6 ◦ C and 25 ◦ C (p < 0.001). At cavity temperatures of 25 ◦ C (p = 0.006) and 37 ◦ C (p = 0.003) significant force differences were found for the influence of storage temperatures. Details are provided in Table 2.
3.2.
Part 2
3.2.1.
1 N application
Unplugging work (UW) varied between 32.81 ± 2.51 N mm (Arabest Top, 25 ◦ C/37 ◦ C) and 4.27 ± 1.10 N mm (Tetric EvoCeram 6 ◦ C/37 ◦ C) on PMMA and 37.83 ± 10.09 N mm (Arabest Top, 6 ◦ C/37 ◦ C) and 4.87 ± 0.46 N mm (Grandio (6 ◦ C/25 ◦ C) on tooth slides. The multi-parameter tests provided significant UW differences (p < 0.001) for different materials and application temperature, but not for storage temperature (p > 0.0710). A uni-variant comparison showed that UW allowed a significant (p < 0.032) differentiation between the materials for different temperature combinations. Only for 6 ◦ C/37 ◦ C no significant (p = 0.106) different UW between the materials was found. No significant (p > 0.289) UW differences could be determined between identical materials on PMMA or tooth slides.
3.2.2.
2 N application
Unplugging work (UW) varied between 21.33 ± 4.27 N mm (Arabest Top, 6 ◦ C/25 ◦ C) and 3.20 ± 0.32 N mm (Grandio 25 ◦ C/25 ◦ C) on PMMA and 26.58 ± 1.77 N mm (Arabest Top, 6 ◦ C/37 ◦ C) and 3.49 ± 0.55 N mm (Tetric Evo Ceram 6 ◦ C/37 ◦ C) on tooth slides. The multi-parameter tests showed significant UW differences (p < 0.001) with different materials, storage temperature and application temperature. A uni-variant comparison displayed that UW allowed a significant (p < 0.008) differentiation between the materials for different temperature combinations. No significant (p > 0.226) UW differences were found between materials on PMMA or tooth slides. Unplugging work was highest for Admira and Arabest top under all application and storage conditions. Statistical analysis provided significant (p < 0.001) differences in unplugging
965
work, which allows grouping of the materials: (#1) Admira, Arabesk top and (#2) Grandio, Polofil Molar L, Tetric Evo Ceram. UW allowed a significant differentiation of the materials with 1 N or 2 N application force on tooth slides (p < 0.001) or PMMA (p < 0.001), with the exception on PMMA at 25 ◦ C/37 ◦ C (p = 0.065). Results see Table 3.
4.
Discussion
The hypothesis of this investigation that unplugging work might provide an opportunity for evaluating adaptability and stickiness of dental composites could be confirmed. Individual correlations between clinical assessment and in vitro unplugging work could be confirmed. The evaluation revealed maximum application forces of about 0.58–2.23 N, without differences between the investigated materials at identical temperature conditions. Results in similar force range were found by Kaleem et al. [7], although we found different ranking of tested materials. A force gauge with sufficient resolution was used, but generally the low application forces may allow only for limited differentiation between the materials. Here the use of a thicker, but unfortunately clinically unrealistic “plugger” may contribute to achieve higher forces (due to higher area), which might allow for a better differentiation of the results. An influence of temperature was found for different storage or application conditions: with higher application temperature and with increased storage temperature at an application temperature of 37 ◦ C, generally smaller forces were applied for all materials. This represents the decreased viscosity with increasing temperature. With higher temperature the movability of the polymer chains is increased and viscoelasticity is decreased [2,3]. A stronger influence on the individual results was found for the application temperature instead of storage temperature. With higher application temperature the wetting effect of the substrate surface should increase [8]. Effects like surface roughness, surface energy or even the speed of testing may influence the results. Beyond this, warming of the individual materials and constant temperature conditions during testing situation should be guaranteed. The warm-up period for a typical syringe (∼4 g) for example from 6 ◦ C to 25 ◦ C is about 10 min and further up to 30 ◦ C is about 20 min, whereas the tests normally last less than 5 min. In case of the 25 ◦ C-application, application force was unexpectedly higher with increased storage temperature. This may be attributed to constant temperature conditions without temperature differences between storage (25 ◦ C) and application (25 ◦ C). With these settings the strongest differentiation between the materials was found, which allows for a grouping of the composites comparable with the individual assessment of stickiness and adaptability. Regarding the individual assessment we found maximum differences of 1.2 school scores for stickiness. The individual assignment revealed significant differences variances between the composites. Stickiness may be correlated with the adaptation of the material at the plugger/cavity and may therefore be defined by tensile forces which develop during pulling out the plugger [4]. A soft material in tendency is evaluated stickier and a hard composite is assessed worse
966
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
Table 2 – Plugging forces of different composites at different storage (ST) and application temperatures (AT) (no significant differences indicated by identical: letters (row)/indices (column); mean ± STD). Material
Force ± STD [N]
Admira
1.29 0.81 2.23 0.67
± ± ± ±
Arabesk Top
0.41a# 0.24b* 1.24c# 0.21d*
1.26 0.80 2.11 0.72
± ± ± ±
0.34a# 0.30b* 0.93c# 0.30d*
Grandio
1.18 0.92 1.88 0.87
± ± ± ±
0.54a# 0.33b* 1.00c# 0.33d*
adaptable. Stickiness depends on both, the condition and type of substrate and plugger, therefore effects like clinical dentin etching and application of bonding agents [5] and different plugger forms and materials should be investigated in more detail. Adaptability may be regarded as a combination of individual parameters such as firmness, hardness or stickiness. Although 15 dentists participated only small differences of about 0.7 school scores were found. Therefore, the data should be interpreted with care and, against expectations of the power analysis, for a more detailed verification a higher number of dentists should contribute to the evaluation. On basis of a number of preliminary tests it was possible to reduce side effects of a repeated local application (only one impression) and the geometry of the cavity (tests on slides). Unplugging work provided good differentiation between the materials and similar ranking of the composites according to stickiness and adaptability. “Work” combines the energy which is necessary to separate composite and substrate as well as the coherence of the composite, which may depend on molecular cohesion and crosslinking status [7,9]. PMMA surfaces allowed comparable ranking of the materials as seen for tooth hard tissue, and therefore PMMA may
Polofil Molar L
1.40 0.80 1.93 0.58
± ± ± ±
0.42a 0.25b* 0.93c 0.31d*
Temperature [◦ C] storage/application
Tetric EvoCeram 1.29 1.01 1.69 0.78
± ± ± ±
0.39a 0.32b* 0.62c 0.20d*
6/25 6/37 25/25 25/37
be used as an easy-to-use alternative for further tests. This confirms data from Ertl et al. [5] showing similar ranking of the composites on different substrata. Comparable roughness (prepared teeth: Ra about 0.4 m, bonded: 0.1 m) may be achieved with sandblasted (0.3 m) or untreated (0.05 m) PMMA. Both application forces (1 N/2 N) allowed for a significant evaluation of the influence of storage- or application temperatures. The 2 N-application showed that the materials might be applied in thicker layers for achieving sufficient data, which certainly stands in contrast to a clinical application. With deeper impression into the composite, results may be influenced by some material which additionally wets the sides of the plugger, instead only of wetting the facial side. Complex adhesion effects were reduced by resigning on the application in a cavity, but it was difficult to dose the materials for the application; therefore additional efforts should be made to guarantee comparable mass of the applied composites. Further efforts have to be made improving the constancy of the tests and reduce standard deviations. The investigation showed that it is difficult to describe the complex visco-elastic behavior and rheological performance of the composite with a simple test design, especially when
Table 3 – Unplugging work (UW [N mm]) at different storage and application temperatures; PMMA or tooth slice; application force 1 N/2 N (mean ± STD). Material
PMMA-slice UW [N mm]
Temperature [◦ C] Storage/application
1 N application
Tooth-slice UW [N mm]
2 N application
1 N application
2 N application
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
6/25
14.43 22.00 6.07 7.96 7.67
± ± ± ± ±
1.20 5.32 0.68 0.40 0.27
20.40 21.33 4.92 4.52 7.00
± ± ± ± ±
3.01 4.27 0.76 0.41 0.59
24.72 25.98 4.87 8.51 7.02
± ± ± ± ±
1.98 0.49 0.46 1.53 1.05
19.21 20.12 5.56 4.75 4.77
± ± ± ± ±
1.92 3.27 0.55 0.53 0.52
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
25/25
14.73 20.04 6.23 7.96 8.19
± ± ± ± ±
1.60 2.04 3.25 1.16 0.46
15.65 19.65 3.20 5.68 6.66
± ± ± ± ±
3.23 2.45 0.32 0.90 0.42
26.60 23.70 5.63 7.98 7.49
± ± ± ± ±
4.86 2.82 0.95 0.63 0.46
12.50 23.51 3.66 6.33 3.78
± ± ± ± ±
1.89 6.63 2.46 1.05 047
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
6/37
22.67 16.28 6.21 12.63 4.27
± ± ± ± ±
1.63 1.59 2.52 1.08 1.10
17.97 17.98 8.25 5.42 3.64
± ± ± ± ±
2.94 5.11 3.2 0.71 0.90
24.10 37.83 10.10 8.56 7.02
± ± ± ± ±
2.43 10.09 4.80 0.35 0.62
23.23 26.58 7.13 5.50 3.49
± ± ± ± ±
2.68 1.77 0.51 1.57 0.55
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
25/37
26.92 32.81 6.91 9.64 10.42
± ± ± ± ±
1.27 2.51 1.87 0.83 2.52
10.00 20.71 8.13 7.64 4.60
± ± ± ± ±
2.31 3.51 0.89 1.04 0.17
20.08 34.64 6.22 12.30 5.70
± ± ± ± ±
1.47 4.53 0.96 1.81 0.33
13.29 21.75 4.00 6.00 3.80
± ± ± ± ±
2.30 0.75 0.68 0.82 0.47
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
complex properties are further influenced by aging of pastes or pre-polymerized materials [10]. The tests provided an “overall” stickiness, which does not allow for the differentiation between stickiness in the cavity or on the plugger.
5.
Conclusion
Within the limitations of this study unplugging work might provide an opportunity for evaluating adaptability and stickiness of dental composites. The data show a good relationship between in vitro data and clinical evaluation.
references
[1] Schultz S, Rosentritt M, Behr M, Handel G. Mechanical properties and three-body wear of dental restoratives and their comparative flowable materials. Quint Inter 2010;41:e1–10. [2] Silikas N, Watts DC. Rheology of urethane di-methacrylate and diluent formulations. Dent Mater 1999;15:257–61.
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[3] Mesquita RV, Geis-Gerstorfer J. Influence of temperature on visco-elastic properties of direct and indirect dental composite resins. Dent Mater 2008;24:623–32. [4] Kalemm M, Satterthwaite JD, Watts DC. Effect of filler particle size and morphology on force/work parameters for stickiness of unset resin-composites. Dent Mater 2009;25:1585–92. [5] Ertl K, Graf A, Watts D, Schedle A. Stickiness prior to setting of some light cured resin-composites. Dent Mater 2010;26:59–66. [6] Al-Sharaa KA, Watts DC. Stickiness of dental resin composite materials to steel, dentin and bonded dentin. Dent Mater 2003;19:182–7. [7] Kaleem M, Satterthwaite JD, Watts DC. A method for assessing force/work parameters for stickiness of unset resin-composites. Dent Mater 2011;27:805–10. [8] De Gennes PG, Hua X, Levinson P. Dynamics of wetting. Local contact angles. J Fluid Mech 1990;215:55–63. [9] Chuang HK, Chiu C, Paniagua R. Avery adhesive test yields more performance data than traditional probe. Adhes Age 1997;40:18–23. [10] Hahnel S, Henrich A, Bürgers R, Handel G, Rosentritt M. Investigation of mechanical properties of modern dental composites after artificial aging for one year. Oper Dent 2010;35:412–9.
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/dema
Laboratory tests for assessing adaptability and stickiness of dental composites Martin Rosentritt ∗ , Sebastian Buczovsky, Michael Behr, Verena Preis Department of Prosthetic Dentistry, Regensburg University Medical Center, Germany
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objective. Handling (stickiness, adaptability) of a dental composite does strongly influence
Received 4 March 2013
quality and success of a dental restoration. The purpose was to develop an in vitro test,
Received in revised form
which allows for evaluating adaptability and stickiness.
7 March 2014
Methods. 15 dentists were asked for providing individual assessment (school scores 1–6)
Accepted 21 May 2014
of five dental composites addressing adaptability and stickiness. Composites were applied with a dental plugger (d = 1.8 mm) in a class I cavity (human tooth 17). The tooth was fixed on a force gauge for simultaneous determination of application forces with varying storage
Keywords:
(6/25 ◦ C) and application temperatures (6/25 ◦ C). On basis of these data tensile tests were per-
Composite
formed with a dental plugger (application force 1 N/2 N; v = 35 mm/min) on PMMA- or human
Handling
tooth plates. Composite was dosed onto the tip of the plugger and applied. Application and
Stickiness
unplugging was performed once and unplugging forces (UF) and length of the adhesive flags
Adaptability
(LAF) were determined at different storage (6/25 ◦ C) and application temperatures (25/37 ◦ C).
Rheology
Unplugging work (UW) was calculated from area of UF and LAF data.
Flow
Results. The individual assessment revealed significantly different temperature-dependent
Application
application forces between 0.58 N and 2.23 N. Adaptability was assessed between 2.1 and 2.8 school scores. Stickiness varied significantly between the materials (scores: 2–3.2). UW differed significantly between the materials with values between 3.20 N mm and 37.83 N mm. Between PMMA substrate or tooth slides and between 1 N or 2 N application force only small UW differences were found. Significance. The presented in vitro unplugging work allows for an in vitro estimation of the handling parameters adaptability and stickiness. © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Light curing dental composites are state of the art for clinical restorations. The development of these composites is strongly orientated on clinical requirements. Therefore
various materials with different viscosities, application forms and with optimized properties are available [1]. Nevertheless the clinical success of a composite is strongly influenced by handling opportunities. For example insufficient condensation may result in voids or porosities and may reduce stability, marginal integrity or wear resistance. Because handling may
∗ Corresponding author at: Department of Prosthetic Dentistry, Regensburg University Medical Center, D-93042 Regensburg, Germany. Tel.: +49 941 944 6054; fax: +49 941 944 6171. E-mail address: [email protected] (M. Rosentritt). http://dx.doi.org/10.1016/j.dental.2014.05.014 0109-5641/© 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
964
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
2.
Materials and methods
Five different commercially available composite materials were investigated: Admira, Arabesk Top, Grandio, Polofil Molar L (all Voco, Cuxhafen, Germany) and Tetric Evo Ceram (IvoclarVivadent, Schaan, Liechtenstein).
2.1.
Part 1
For a praxis-orientated estimation, 15 dentists evaluated the subjective handling properties of the composite materials (estimated power > 0.9, G*Power 3.1.3, Kiel, Germany). The dentists were asked to address to “adaptability” and “stickiness” using school grades from 1 (good/high) to 6 (bad/low). For simulating clinical conditions, the dentists applied the materials with a dental plugger (flat d = 1.8 mm, DE 295R, Aesculap, Melsungen, Germany) in a class I cavity (height 5 mm, diameter: 4 mm), which was prepared in a human tooth (tooth 17). Composite was applied in about 2 mm increments. Teeth and plugger were cleaned with chlorhexidine and teeth were kept in water between the tests. Materials were stored and applied at 25 ◦ C. With a force gauge (Type 8435-6001, resolution 0.01 N, Burster, Gernsbach, Germany), which was located under the teeth, the plugging force was determined. Further on plugging forces were measured at two different storage temperatures (6 ◦ C, 25 ◦ C) and two application temperatures (6 ◦ C, 25 ◦ C). Tooth temperatures were regulated using a selfassembled heating module.
-
Force (AF) [N]
2.5
Force (UF) [N]
not be fully described by individual parameters like stiffness, viscosity (rheology) [2], adhesive behavior, visco-elastic behavior [3] or the filler components [4], it is practise to ask dentists for their distinct impression of unset composites. Parameters are the ease to adapt a composite in the cavity (adaptability), how the composite sticks to the cavity or instrument (stickiness) or how firm the composite appears (firmness). Often a high number of dentists is questioned, which results in high expenditure and costs. Therefore, a standardized laboratory test seems necessary, which allows for estimating handling of composites. Already performed tests are tensile tests or profilometry, examining the influence of different speed, testing temperatures or different substrate surfaces. Work for probe separation, maximum force [4] or coefficients of variation [5] were defined as parameters for characterization of composite properties, temperature influence and unplugging speed. Partly the length of the adhesive flag was determined by polymerizing the material during tensile testing [6]. But in conclusion no test seems available representing the clinical situation. Therefore, the idea was to ask a representative number of dentists for the evaluation of different composites and relate these results to in vitro tensile tests. Clinical parameters such as human tooth tissue, storage conditions or cavity temperatures should be considered. Undetermined application force should be evaluated. The hypothesis of this investigation was that unplugging work might provide an opportunity for evaluating adaptability and stickiness of dental composites. The purpose of this study was to develop a simplified test, which allows for standardizing adaptability and stickiness.
2.0 1.5 1.0 0.5 0.0 0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
-0.5
-1.0
Length (LAF) [cm]
Fig. 1 – Force [N]/length [mm] diagram with application force (AF, positive) and unplugging force (UF, negative) (example, 25 ◦ C/25 ◦ C).
2.2.
Part 2
A dental plugger was fixed to a universal testing machine (Zwick 1446, resolution 0.001 N, Zwick, Ulm, Germany), which allows applying standardized application forces (1 N or 2 N as a result of part 1) and speed (35 mm/min). After a number of pre-tests with standard cavities (tooth, PMMA) and for simplification of the testing protocol, we decided to carry out the tests on PMMA- or human tooth plates (thickness 1.5 mm). Plates were cut with an inner whole saw (SP 1600, Leica, Wetzlar, Germany) under water cooling and, in case of tooth plates, in root-crown direction. Composite was dosed (1.5 mm × 2 mm, Composite-gun tubes 1915, KerrHawe, Bioggio, Switzerland) and fixed to the tip of the plugger. Application and unplugging was performed one time and the unplugging forces (UF) and the length of the adhesive flags (LAF [mm]) were determined. For detailed optical information on LAF, the tests were recorded with video (Handycam DCR-DVD450E, Sony, Tokio, Japan). Unplugging work (UW) was calculated from area of UF and LAF (integrated) data (UW [N mm] = UF [N] × LAF [mm]). Tests were performed with two different storage temperatures (6 ◦ C, 25 ◦ C) and two application temperatures (25 ◦ C, 37 ◦ C). To hinder an uncontrolled polymerization of the applied materials, all tests were performed under yellow light (Fig. 1). Mean and standard deviation were calculated. Statistical analysis was performed with SPSS 19 (IBM, New York, USA) using one-way ANOVA and linear uni/multi-variant comparison (Bonferroni Post Hoc). The level of significance was set to 0.05.
3.
Results
3.1.
Part 1
Stickiness of Arabesk and Admira were determined “3.1–3.2”, whereas Grandio, Polofil and Tetric were characterized as less sticky (“2–2.5”). A comparable ranking was found for adaptability: Arabesk and Admira were evaluated 2.8, whereas Grandio, Polofil and Tetric got grades between 2.1 and 2.4 (good
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
Table 1 – Individual evaluation of stickiness and adaptability (school grades from 1 (good/high) to 6 (bad/low); mean ± STD; n = 15 dentists; identical letters indicate significant differences). Material Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
Stickiness 1 = not sticky 3.1 3.2 2.1 2.0 2.5
± ± ± ± ±
1.0a 1.1bc 1.1b 0.8ac 0.8
Adaptability 1 = very good 2.8 2.8 2.1 2.2 2.4
± ± ± ± ±
0.9 0.7 0.8 0.8 0.7
applicable) (Table 1; Bonferroni comparison). One-way ANOVA test revealed significant differences for stickiness (p = 0.003), whereas no differences were found for adaptability (p = 0.055). Plugging forces varied between 0.58 ± 0.31 N (Polofil Molar 25 ◦ C/37 ◦ C) and 2.23 N (Admira 25 ◦ C/25 ◦ C). Highest plugging forces were found for the materials when stored and applied at 25 ◦ C. Lowest results were determined at a storage temperature of 25 ◦ C and application temperature of 37 ◦ C. Group comparison showed significant force differences between both application temperatures at storage temperatures of 6 ◦ C and 25 ◦ C (p < 0.001). At cavity temperatures of 25 ◦ C (p = 0.006) and 37 ◦ C (p = 0.003) significant force differences were found for the influence of storage temperatures. Details are provided in Table 2.
3.2.
Part 2
3.2.1.
1 N application
Unplugging work (UW) varied between 32.81 ± 2.51 N mm (Arabest Top, 25 ◦ C/37 ◦ C) and 4.27 ± 1.10 N mm (Tetric EvoCeram 6 ◦ C/37 ◦ C) on PMMA and 37.83 ± 10.09 N mm (Arabest Top, 6 ◦ C/37 ◦ C) and 4.87 ± 0.46 N mm (Grandio (6 ◦ C/25 ◦ C) on tooth slides. The multi-parameter tests provided significant UW differences (p < 0.001) for different materials and application temperature, but not for storage temperature (p > 0.0710). A uni-variant comparison showed that UW allowed a significant (p < 0.032) differentiation between the materials for different temperature combinations. Only for 6 ◦ C/37 ◦ C no significant (p = 0.106) different UW between the materials was found. No significant (p > 0.289) UW differences could be determined between identical materials on PMMA or tooth slides.
3.2.2.
2 N application
Unplugging work (UW) varied between 21.33 ± 4.27 N mm (Arabest Top, 6 ◦ C/25 ◦ C) and 3.20 ± 0.32 N mm (Grandio 25 ◦ C/25 ◦ C) on PMMA and 26.58 ± 1.77 N mm (Arabest Top, 6 ◦ C/37 ◦ C) and 3.49 ± 0.55 N mm (Tetric Evo Ceram 6 ◦ C/37 ◦ C) on tooth slides. The multi-parameter tests showed significant UW differences (p < 0.001) with different materials, storage temperature and application temperature. A uni-variant comparison displayed that UW allowed a significant (p < 0.008) differentiation between the materials for different temperature combinations. No significant (p > 0.226) UW differences were found between materials on PMMA or tooth slides. Unplugging work was highest for Admira and Arabest top under all application and storage conditions. Statistical analysis provided significant (p < 0.001) differences in unplugging
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work, which allows grouping of the materials: (#1) Admira, Arabesk top and (#2) Grandio, Polofil Molar L, Tetric Evo Ceram. UW allowed a significant differentiation of the materials with 1 N or 2 N application force on tooth slides (p < 0.001) or PMMA (p < 0.001), with the exception on PMMA at 25 ◦ C/37 ◦ C (p = 0.065). Results see Table 3.
4.
Discussion
The hypothesis of this investigation that unplugging work might provide an opportunity for evaluating adaptability and stickiness of dental composites could be confirmed. Individual correlations between clinical assessment and in vitro unplugging work could be confirmed. The evaluation revealed maximum application forces of about 0.58–2.23 N, without differences between the investigated materials at identical temperature conditions. Results in similar force range were found by Kaleem et al. [7], although we found different ranking of tested materials. A force gauge with sufficient resolution was used, but generally the low application forces may allow only for limited differentiation between the materials. Here the use of a thicker, but unfortunately clinically unrealistic “plugger” may contribute to achieve higher forces (due to higher area), which might allow for a better differentiation of the results. An influence of temperature was found for different storage or application conditions: with higher application temperature and with increased storage temperature at an application temperature of 37 ◦ C, generally smaller forces were applied for all materials. This represents the decreased viscosity with increasing temperature. With higher temperature the movability of the polymer chains is increased and viscoelasticity is decreased [2,3]. A stronger influence on the individual results was found for the application temperature instead of storage temperature. With higher application temperature the wetting effect of the substrate surface should increase [8]. Effects like surface roughness, surface energy or even the speed of testing may influence the results. Beyond this, warming of the individual materials and constant temperature conditions during testing situation should be guaranteed. The warm-up period for a typical syringe (∼4 g) for example from 6 ◦ C to 25 ◦ C is about 10 min and further up to 30 ◦ C is about 20 min, whereas the tests normally last less than 5 min. In case of the 25 ◦ C-application, application force was unexpectedly higher with increased storage temperature. This may be attributed to constant temperature conditions without temperature differences between storage (25 ◦ C) and application (25 ◦ C). With these settings the strongest differentiation between the materials was found, which allows for a grouping of the composites comparable with the individual assessment of stickiness and adaptability. Regarding the individual assessment we found maximum differences of 1.2 school scores for stickiness. The individual assignment revealed significant differences variances between the composites. Stickiness may be correlated with the adaptation of the material at the plugger/cavity and may therefore be defined by tensile forces which develop during pulling out the plugger [4]. A soft material in tendency is evaluated stickier and a hard composite is assessed worse
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d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
Table 2 – Plugging forces of different composites at different storage (ST) and application temperatures (AT) (no significant differences indicated by identical: letters (row)/indices (column); mean ± STD). Material
Force ± STD [N]
Admira
1.29 0.81 2.23 0.67
± ± ± ±
Arabesk Top
0.41a# 0.24b* 1.24c# 0.21d*
1.26 0.80 2.11 0.72
± ± ± ±
0.34a# 0.30b* 0.93c# 0.30d*
Grandio
1.18 0.92 1.88 0.87
± ± ± ±
0.54a# 0.33b* 1.00c# 0.33d*
adaptable. Stickiness depends on both, the condition and type of substrate and plugger, therefore effects like clinical dentin etching and application of bonding agents [5] and different plugger forms and materials should be investigated in more detail. Adaptability may be regarded as a combination of individual parameters such as firmness, hardness or stickiness. Although 15 dentists participated only small differences of about 0.7 school scores were found. Therefore, the data should be interpreted with care and, against expectations of the power analysis, for a more detailed verification a higher number of dentists should contribute to the evaluation. On basis of a number of preliminary tests it was possible to reduce side effects of a repeated local application (only one impression) and the geometry of the cavity (tests on slides). Unplugging work provided good differentiation between the materials and similar ranking of the composites according to stickiness and adaptability. “Work” combines the energy which is necessary to separate composite and substrate as well as the coherence of the composite, which may depend on molecular cohesion and crosslinking status [7,9]. PMMA surfaces allowed comparable ranking of the materials as seen for tooth hard tissue, and therefore PMMA may
Polofil Molar L
1.40 0.80 1.93 0.58
± ± ± ±
0.42a 0.25b* 0.93c 0.31d*
Temperature [◦ C] storage/application
Tetric EvoCeram 1.29 1.01 1.69 0.78
± ± ± ±
0.39a 0.32b* 0.62c 0.20d*
6/25 6/37 25/25 25/37
be used as an easy-to-use alternative for further tests. This confirms data from Ertl et al. [5] showing similar ranking of the composites on different substrata. Comparable roughness (prepared teeth: Ra about 0.4 m, bonded: 0.1 m) may be achieved with sandblasted (0.3 m) or untreated (0.05 m) PMMA. Both application forces (1 N/2 N) allowed for a significant evaluation of the influence of storage- or application temperatures. The 2 N-application showed that the materials might be applied in thicker layers for achieving sufficient data, which certainly stands in contrast to a clinical application. With deeper impression into the composite, results may be influenced by some material which additionally wets the sides of the plugger, instead only of wetting the facial side. Complex adhesion effects were reduced by resigning on the application in a cavity, but it was difficult to dose the materials for the application; therefore additional efforts should be made to guarantee comparable mass of the applied composites. Further efforts have to be made improving the constancy of the tests and reduce standard deviations. The investigation showed that it is difficult to describe the complex visco-elastic behavior and rheological performance of the composite with a simple test design, especially when
Table 3 – Unplugging work (UW [N mm]) at different storage and application temperatures; PMMA or tooth slice; application force 1 N/2 N (mean ± STD). Material
PMMA-slice UW [N mm]
Temperature [◦ C] Storage/application
1 N application
Tooth-slice UW [N mm]
2 N application
1 N application
2 N application
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
6/25
14.43 22.00 6.07 7.96 7.67
± ± ± ± ±
1.20 5.32 0.68 0.40 0.27
20.40 21.33 4.92 4.52 7.00
± ± ± ± ±
3.01 4.27 0.76 0.41 0.59
24.72 25.98 4.87 8.51 7.02
± ± ± ± ±
1.98 0.49 0.46 1.53 1.05
19.21 20.12 5.56 4.75 4.77
± ± ± ± ±
1.92 3.27 0.55 0.53 0.52
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
25/25
14.73 20.04 6.23 7.96 8.19
± ± ± ± ±
1.60 2.04 3.25 1.16 0.46
15.65 19.65 3.20 5.68 6.66
± ± ± ± ±
3.23 2.45 0.32 0.90 0.42
26.60 23.70 5.63 7.98 7.49
± ± ± ± ±
4.86 2.82 0.95 0.63 0.46
12.50 23.51 3.66 6.33 3.78
± ± ± ± ±
1.89 6.63 2.46 1.05 047
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
6/37
22.67 16.28 6.21 12.63 4.27
± ± ± ± ±
1.63 1.59 2.52 1.08 1.10
17.97 17.98 8.25 5.42 3.64
± ± ± ± ±
2.94 5.11 3.2 0.71 0.90
24.10 37.83 10.10 8.56 7.02
± ± ± ± ±
2.43 10.09 4.80 0.35 0.62
23.23 26.58 7.13 5.50 3.49
± ± ± ± ±
2.68 1.77 0.51 1.57 0.55
Admira Arabesk Top Grandio Polofil Molar L Tetric EvoCeram
25/37
26.92 32.81 6.91 9.64 10.42
± ± ± ± ±
1.27 2.51 1.87 0.83 2.52
10.00 20.71 8.13 7.64 4.60
± ± ± ± ±
2.31 3.51 0.89 1.04 0.17
20.08 34.64 6.22 12.30 5.70
± ± ± ± ±
1.47 4.53 0.96 1.81 0.33
13.29 21.75 4.00 6.00 3.80
± ± ± ± ±
2.30 0.75 0.68 0.82 0.47
d e n t a l m a t e r i a l s 3 0 ( 2 0 1 4 ) 963–967
complex properties are further influenced by aging of pastes or pre-polymerized materials [10]. The tests provided an “overall” stickiness, which does not allow for the differentiation between stickiness in the cavity or on the plugger.
5.
Conclusion
Within the limitations of this study unplugging work might provide an opportunity for evaluating adaptability and stickiness of dental composites. The data show a good relationship between in vitro data and clinical evaluation.
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