Clin Oral Invest DOI 10.1007/s00784-014-1209-2

ORIGINAL ARTICLE

Effect of tooth brush abrasion and thermo-mechanical loading on direct and indirect veneer restorations Martin Rosentritt & Alexander Sawaljanow & Michael Behr & Carola Kolbeck & Verena Preis

Received: 9 December 2013 / Accepted: 4 February 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract Objectives This study investigated toothbrush abrasion and in vitro aging on ceramic (indirect technique) and composite veneers (direct technique). Materials and methods Identical composite and individual human incisors were restored with industrially preformed composite veneers, indirectly produced ceramic veneers, and direct composite restorations. Surface roughness was determined before and after tooth brushing. A 5-year period of oral service was simulated by thermal cycling and mechanical loading (TCML). After TCML, all specimens were examined with microscopy and scanning electron microscopy. Specimens without failures during TCML were loaded until failure. Statistics: analysis of variance; Bonferroni’s post hoc analysis, Kaplan–Meier–Log Rank test (α=0.05). Results Tooth brushing yielded a non-significant increase (p= 0.560) in roughness in all materials (industrial veneer, 0.12+/ −0.07 μm, direct restoration, 0.18+/−0.14 μm, ceramic, 0.35+/−0.16 μm). No significant differences in roughness could be determined between the materials, neither before nor after testing (p20 MPa. b. Individual human anterior teeth: Twenty-four maxillary central caries-free human incisors stored in 0.5 % chloramine solution were randomly divided into three groups of eight specimens each (n=3×8). The individual teeth were prepared for the application of the veneer (Meisinger 806314 black, yellow; dimensions: 8–9×9.5–11×0.8– 0.9 mm) (Fig. 1). Sixteen veneers per material were produced from the following three systems: 1. Preformed composite veneer (Componeer, size L) luted with composite (Synergy D6) and coating (One Coat Bond) (all Coltène, CH), 2. Press-ceramic (e.max press, glazed, control) luted with dual curing composite cement (Variolink II, ceramic etching with etching gel 20s, Heliobond, Monobond S, Syntac classic) (all Ivoclar-Vivadent), and 3. Restorative composite (Filtek Supreme XTE, Adper Easy Bond, 3 M Espe) as a direct restoration. Adhesives and composites were polymerized for 4×40 s (Elipar Trilight, 3 M Espe, G, 1,000 mW/cm2). For simulating an artificial periodontium, the roots of all teeth (groups a and b) were covered with a polyether layer measuring 0.75 mm in thickness (Impregum, 3 M Espe, Seefeld, G). Teeth were fixed at a 45° angle to the horizontal line using PMMA resin (Palapress Vario, Kulzer, G) (Fig. 2). Thermal cycling and mechanical loading (TCML) was Fig. 1 Design of veneer preparation in composite and human teeth

Clin Oral Invest loading force veneer sample holder 45° simulated periodontium

PMMA resin

Fig. 2 Design of testing apparatus and loading situation

performed trying to simulate a 5-year period of oral service (parameters, 6,000 thermal cycles 5 °C/55 °C, 1.2×106 mastication cycles with 50 N, 8.3 days) using steatite sphere (d= 12 mm) antagonists [9, 10]. Loading was applied to the palatal Fig. 3 a–c Photographs and 3Dscans (magnification×10) after toothbrush abrasion: a preformed composite, b ceramic, c restorative composite

side, 2 mm below the incisal edge. During TCML, all specimens were investigated daily (light microscope SV8, magnification×10, Olympus, J) for any damage. After TCML, all specimens were examined in detail with a light microscope (reflection/transmission), laser-scanning microcopy (3D laserscanning microscope Keyence KJ, J, ×5–10), and scanning electron microscopy (SEM) (Phillips Quanta FEG 400, FEI, NL, low vacuum, 10KeV, magnifications×20, 100, 2,500, and 4,000). Specimens without any failures during TCML were subsequently loaded until failure using a testing machine (Zwick 1446, Ulm, Germany; v=1 mm/min). Force was applied with a round steel antagonist (d=12 mm), and a tin foil (0.25 mm) between crown and antagonist prevented force peaks. Specimens were optically examined after fracture testing, and the failure mode was divided into fracture of the tooth or fracture of the veneer.

Clin Oral Invest

Tooth brush abrasion

Results

Veneer specimens (n=8 per material) were fixed horizontally with the facial side up. Tooth brushing was simulated with a tooth brush (Oral B1-2-3 Indicator, Procter & Gamble, UK) and abrasive slurry of toothpaste (Colgate Total, Signal AntiCaries, 250 g per 1 l distilled water). For simulating 1 year of brushing, 7,200 circular cycles (d=10 mm, vertical loading 250 g, 40 mm/s, toothbrush-abrasion tester ZM-3, SD Mechatronik, G) were applied. Surface roughness (Perthometer SP6, Perthen, G, LT = 1.7/0.25, velocity 0.1 mm/s, 2 μm diamond indenter) was determined on three sites (incisal, central, cervical) before and after tooth brushing. Calculations and statistical analysis were carried out using SPSS 19.0 for Windows (SPSS Inc., IL, USA). Power calculation (G*Power 3.1.3, Kiel, G) provided an estimated power of >90 % using eight specimens per group. Distribution of the data was controlled with the Kolmogorov–Smirnov test. Means and standard deviations were calculated and analyzed with one-way analysis of variance and the Bonferroni test for post hoc analysis. Survival performance was calculated with the Kaplan–Meier–Log Rank test. The level of significance was set at α=0.05.

Tooth brush abrasion

Fig. 4 SEM pictures: preformed composite (magnifications, ×20, 100, 2,500, 4,000)

Surface roughness before testing varied from 0.09+/−0.03 μm (industrial composite), to 0.13+/−0.16 μm (direct composite), and 0.27+/−0.19 μm (ceramic). After the abrasion test, all materials showed a non-significant increase (p=0.560) to 0.12+/−0.07 μm (industrial composite, p=0.061), 0.18+/ −0.14 μm (direct composite, p=0.142), and 0.35+/−0.16 μm (ceramic, p=0.244). No significant differences were found between the individual materials (p0.172). The mean fracture force varied between 527.8+/−132.4 N (ceramic), 478.3+/−165.4 N (preformed composite), and 605.0+/−263.5 N (direct composite). No significant

different fracture forces were found between the individual groups (p>0.708) (Table 1). Because of the drop out during TCML, statistical power was reduced. The Kaplan–Meier– Log Rank test did not show any significant differences (p= 0.380) between the three groups.

Discussion The different veneers investigated showed comparable values for surface roughness before and after tooth brush abrasion. The three veneer groups yielded no significantly different drop out in artificial and human teeth and no significantly different fracture results in human teeth after TCML. Therefore, we have to reject the hypothesis that clinically proven ceramic veneers [2, 3] provide lower abrasion as well as improved in vitro survival performance and higher stability than direct or preformed composite veneers. Contrary to expectations, we did not find any large differences between the various veneer systems with regard to the influence of tooth brush abrasion on surface roughness. Based on the testing parameters, the small increase in surface roughness of all systems may indicate that no major changes in the

Clin Oral Invest Fig. 6 SEM pictures: direct restorative composite (magnification, ×20, 100, 2,500, 4,000)

appearance of the veneers might be found during the first years of application, but the increase in surface roughness may reduce color stability or gloss [11, 12]. Nevertheless, no direct correlation between gloss and surface roughness could be determined in earlier investigations [13]. Subjectively evaluated, ceramic veneers showed higher gloss, whereas composite veneers looked duller and had an apparently rougher surface (Fig. 3a–c). Limitations of the test might be expected because of the concave geometry of the veneer that may have influenced tooth brushing effects and individual assessment. Fig. 7 a, b Failure on artificial teeth: ceramic veneer (after TCML)

For all systems, a more complex layering, the use of optically adapted cements [14] or a stronger individualization of the veneer may help improve the esthetical outcome. Generally, patients seem to prefer direct composites over ceramic veneers [15]. Artificial aging combining thermal cycling and mechanical loading seems to sufficiently predict probable clinical failure [9], and this method has already been successfully applied in different anterior restorations [16–18]. Abutment mobility of the teeth was integrated into the testing design because it

Clin Oral Invest Table 1 Failure pattern and fracture force Artificial teeth Veneer type Ceramic Preformed composite

Failure during TCML 2× labial cracking 1× root fracture

Human teeth Fracture force [N] n.e.; facture of the teeth

Effect of tooth brush abrasion and thermo-mechanical loading on direct and indirect veneer restorations.

This study investigated toothbrush abrasion and in vitro aging on ceramic (indirect technique) and composite veneers (direct technique)...
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