The Journal of Adhesive Dentistry, 06/2007

Purpose: To assess the effect of the composite surface conditioning on the microtensile bond strength of a resin cement to a composite used for inlay/onlay restorations. Materials and Methods: Forty-two blocks (6 x 6 x 4 mm) of a microfilled composite (Vita VMLC) were produced and divided into 3 groups (N = 14) by composite surface conditioning methods: Gr1 - etching with 37% phosphoric acid, washing, drying, silanization; Gr2 - air abrasion with 50-Ìm Al2O3 particles, silanization; Gr3 - chairside tribochemical silica coating (CoJet System), silanization. Single-Bond (one-step adhesive) was applied on the conditioned surfaces and the two resin blocks treated with the same method were cemented using RelyX ARC (dual-curing resin cement). The specimens were stored for 7 days in water at 37°C and then sectioned to produce nontrimmed beam samples, which were submitted to microtensile bond strength testing (µTBS). For statistical analysis (one-way ANOVA and Tukey's test, · = 0.05), the means of the beam samples from each luted specimen were calculated (n = 7). Results: µTBS values (MPa) of Gr2 (62.0 ± 3.9a) and Gr3 (60.5 ± 7.9a) were statistically similar to each other and higher than Gr1 (38.2 ± 8.9b). The analysis of the fractured surfaces revealed that all failures occurred at the adhesive zone. Conclusion: Conditioning methods with 50-Ìm Al2O3 or tribochemical silica coating allowed bonding between resin and composite that was statistically similar and stronger than conditioning with acid etching. Keywords: composite, inlay, surface conditioning, microtensile bond strength, tribochemical silica coating

Purpose: Using finite element analysis (FEA), to determine the nominal shrinkage stress of a composite under different restriction conditions defined by the longitudinal compliance (LC) and C-factor (C) of the testing system, and by the elastic modulus of the bonding substrate (E). Materials and Methods: Eight axisymmetric models representing an experimental setup used to determine composite shrinkage stress were simulated. Composite thicknesses of 0.5 mm and 4 mm were tested, defining different C and volumes (C = 6 and vol = 14 mm3 or C = 0.8 and vol = 113 mm3, respectively). The E of the substrate was tested in two levels, 12 GPa and 207 GPa. Two LC values (1x10-6 or 28x10-6 mm/N) were defined for each E value by varying the length of the rods used as bonding substrate (0.3 mm and 9.5 mm for E = 12 GPa; 6.0 mm and 163.9 mm for E = 207 GPa). Materials were considered elastic, homogeneous, and isotropic. Shrinkage was simulated by thermal analogy. Nominal stress (nodal force/cross-sectional area) was calculated for each condition. Results were analyzed using Taguchi's method. Results: Nominal stress values varied between 1.7 MPa and 30.3 MPa. The main variables were statistically significant (LC: p = 0.0046; C: p = 0.0153; E: p = 0.0155), as well as the LC x E interaction (p = 0.0354). Stress reduction between low and high LC was more pronounced for E = 207 GPa compared to E = 12 GPa. Stress was lower for the high C conditions for both compliance levels. Conclusion: Not only the C-factor of the testing assembly, but also its LC and the E of the bonding substrate influence stresses generated by composite shrinkage. Keywords: C-factor, shrinkage stress, finite element analysis, compliance, elastic modulus

Purpose: To test the effects of sequential application of potassium oxalate gel/adhesive agent on in vitro dentin permeability. Materials and Methods: Full crown preparations were made in extracted human molars to expose deep coronal dentin. The roots and pulp were removed and the resulting crown segments were connected to a special device (Flodec) to permit the measurement of the permeability of the specimens before and after treatments. Minimum and maximum permeability were recorded after smear layer and phosphoric acid treatment. A new smear layer was created and the permeability measured after the crowns were bonded with Single Bond (3M ESPE), One-Up Bond F (Tokuyama), and AdheSE (Ivoclar Vivadent), either according to manufacturer's instructions or after treating the acid-etched dentin with a 3 wt% potassium oxalate gel. The results were expressed as a percentage of maximum permeability values. Impressions and epoxy resin replicas from the crown segments were produced for SEM examination. Results: None of the adhesives were able to eliminate the fluid flow through dentin. Two-way ANOVA revealed that the application of potassium oxalate prior to the bonding procedures was the most effective technique in reducing the dentin permeability (p 0.05), regardless of the adhesive used. SEM micrographs showed that transudation of dentinal fluid could be identified on the surfaces of all replicas. Conclusion: The use of potassium oxalate gel was effective in reducing the permeability of bonded dentin. Keywords: dentin bonding, dentin permeability, oxalate treatment

Purpose: The aim of this study was to evaluate the effect of Er:YAG laser ablation on the microstructure of the dentin/adhesive interface after acid-base challenge in vitro. Materials and Methods: Thirty-two extracted third molars were used. One pair of disk-shaped specimens was obtained from the midcoronal dentin of each tooth. One surface in each pair was subjected to Er:YAG laser irradiation, while the other was ground using 600-grit SiC abrasive paper. The specimens were assigned to 4 groups with 8 pairs in each group. A self-etching primer (Clearfil SE-Bond), a bonding adhesive (Clearfil SE-Bond), and a photocuring composite (Clearfil APX) were applied according to manufacturer's instructions to create dentin-resin "sandwiches" of each pair, except in group IV, where no primer was applied. The specimens were stored in demineralizing solution for 20 min in groups I and IV, 60 min in group II, and 120 min in group III. After immersion in 5% NaOCl, all the specimens were polished and argon-ion etched. Finally, the interfaces between the dentin and bonding agent were observed under a scanning electron microscope. Results: All specimens in groups I to III showed an acid-base resistant zone, except those of group IV, which debonded completely. A statistically significant difference was found in the thickness of the acid-base resistant zone between group I vs groups II and III for both abraded and Er:YAG-irradiated surfaces. There was no statistically significant difference in the thickness of the acid-base resistant zone between groups II and III for both conventionally prepared and Er:YAG-irradiated surfaces. Conclusion: The existence of an acid-base resistant zone following the application of the SE Bond system on both abraded and Er:YAG-lased human dentin, regardless of the acid-base challenge duration, was confirmed. Keywords: Er:YAG laser, acid-base resistant zone, self-etching primer, dentin, acid-base challenge

Purpose: To evaluate the influence of the brush type as a carrier of priming adhesive solutions and the use of paper points as a remover of the excess of these solutions on the push-out bond strength of resin cement to bovine root dentin. The null hypotheses were that brush type and the use of paper points do not affect the bond strength. Materials and Methods: The canals of 80 single-root bovine roots (16 mm in length) were prepared at 12 mm using the preparation drill (FRC Postec Plus, Ivoclar). Half of each root was embedded in acrylic resin and the specimens were divided into 8 groups, considering the factors "brush type" (4 levels) and "paper point" (2 levels) (n = 10): Gr 1: small microbrush (Cavi-Tip, SDI); Gr 2: Microbrush (Dentsply); Gr 3: Endobrush (Bisco); Gr 4: conventional brush (Bisco); Gr 5: Cavi-Tip (SDI) + paper points; Gr 6: Microbrush (Dentsply) + paper points; Gr 7: Endobrush (Bisco) + paper points; Gr 8: conventional brush (Bisco) + paper points. The root dentin was treated with a multistep total-etch adhesive system (All Bond 2). The adhesive system was applied using each microbrush, with and without using paper points. One fiber post was molded with addition silicon and 80 posts were made of resin cement (Duolink). The resin posts were luted (Duolink resin cement), and the specimens were stored for 24 h in water at 37°C. Each specimen was cut into 4 disk-shaped samples (1.8 mm in thickness), which were submitted to the push-out test. Results: The brush type (p 0.0001) (small microbrush > microbrush = endobrush = conventional brush) and the use of paper points (p = 0.0001) (with > without) influenced the bond strength significantly (two-way ANOVA). The null hypotheses were rejected. Conclusion: The smallest brush (Cavi-Tip) and the use of paper points significantly improved the resin bond to bovine root dentin. Keywords: push-out test, bond strength, root canal dentin, resin cement, microbrush, paper point

Purpose: To estimate which combination of restorative materials resulted in the most homogeneous stress and strain distributions in post-and-core treated teeth. Materials and Methods: Eight experimental finite element models with different material configurations were simulated; both indirect and direct restorations were considered. An arbitrary load of 50 N was applied on the palatal surface of the crown at a 60-degree angle to the tooth's longitudinal axis to simulate tearing function. Results: In all the models, the values of both strain and stress recorded in the middle third of the buccal aspect of the root surface were off the scale. In contrast, the minimum values were noticed at the level of both the apical portion of the post and the root apex. Conclusion: The mechanical properties of the crown and core materials influenced both the position of concentration areas and the level of stress and strain along the dentin/cement/post interfaces. Keywords: post, composite, adhesive, endodontically treated teeth, finite element analysis

Purpose: To examine the etching efficacy of three self-etching systems to unconditioned enamel and to phosphoricacid conditioned enamel using scanning electron microscopy (SEM), and to investigate the microtensile bond strength (µTBS) of three self-etching adhesives to unconditioned enamel used according to the manufacturers' instructions, on phosphoric-acid conditioned enamel, and when their different adhesives were replaced with a control resin after etching. Materials and Methods: Clearfil SE Bond (CSE), Tyrian SPE/One-Step Plus (TY), and Adper Prompt L-Pop (AD) were employed. Scotchbond Multi-Purpose Plus (SBMP), an etch-and-rinse adhesive, was used as control. For µTBS evaluation, the buccal or lingual mid-coronal enamel of 30 molars was used. In the first group, self-etching adhesives were applied conventionally, according to manufacturers' directions (group C). A second group of specimens was etched with 35% phosphoric acid before application of the self-etching adhesives (group PA), and the third group of specimens was etched with the self-etching adhesives, rinsed, but bonded using a control bonding resin (group CR). Following restoration with Z250, they were sectioned into beams (0.8 mm2), and stressed to failure. Data were subjected to two-way ANOVA and Tukey's test. The etching efficacy of the self-etching adhesives, phosphoric acid, and prior phosphoric acid + SE application was evaluated under SEM. Results: All self-etching adhesives applied as recommended by the manufacturers showed lower µTBS values than those obtained in PA and CR groups, although this difference was only significant for TY and AD. The means of all self-etching adhesives under PA and CR groups were similar to SBMP. The enamel conditioned with self-etching adhesive showed a less distinct pattern. CSE exhibited the mildest etching pattern. All self-etching adhesives applied after phosphoric acid exhibited a more retentive etching pattern. Conclusion: The bond strength values of low-pH self-etching adhesives can be improved by the adjunctive use of phosphoric acid or replacement of the bonding resin. Keywords: self-etching, adhesives, cohesive strength, unconditioned enamel, etching pattern

Purpose: This study evaluated the five-year clinical performance of Dyract AP, a polyacid-modified resin composite, in restorations of Class I carious lesions. Materials and Methods: One hundred eight Class I carious lesions in 21 patients were restored with Dyract AP. The lesions, which were macroscopically diagnosed with a probe, involved fissures. The average buccolingual width of the cavities was equal to or less than one-third of the intercuspal width. Restorations were clinically evaluated by two experienced, calibrated examiners at baseline and at 1, 2, 3, 4, and 5 years, utilizing the modified Ryge criteria. The evaluation criteria included color match, marginal discoloration, wear or loss of anatomical form, caries, marginal adaptation, and surface texture. Results: At the end of the 5-year period, a total of 13 restorations had failed, and the cumulative rate of success was 93.37%. By the 5-year recall, 12 restorations had carious lesions adjacent to the margins, and 1 restoration had discoloration that was rated as Charlie. Color changes, marginal discoloration, wear or loss of anatomical form, caries, marginal adaptation, and change in surface texture were found to be statistically significant (p 0.001) after 5 years. Aside from the thirteen failed restorations, the degrees of color matching, marginal discoloration, wear or loss of anatomical form, caries, marginal adaptation, and surface texture were clinically acceptable at 5 years after treatment. Conclusion: At the end of 5 years, Dyract AP exhibited acceptable clinical performance in the treatment of Class I carious lesions. Therefore, it can be considered an alternative material for the restoration of Class I cavities. Keywords: Dyract AP, polyacid-modified resin composite, Class I carious lesions, clinical performance