Effect of finishing instrumentation on the marginal integrity of resin-based composite restorations.

PURPOSE: This study evaluated the effect of the use of different finishing instruments on the marginal integrity of resin composite restorations. MATERIALS AND METHODS: Bovine incisors (N = 75) embedded in epoxy resin had the facial enamel ground and polished to 1200-grit. A standardized cavity (3 x 3 mm, 2 mm deep) was prepared on each specimen and restored with a 2-step total-etch adhesive (Single Bond, 3M ESPE, St. Paul, MN, USA) and a hybrid resin composite (Filtek Z250, 3M ESPE) in a single increment. The restorations were mechanically polished to 1200-grit. Specimens were randomized into different groups (N = 5) according to finishing technique: positive control (1200-grit paper), negative control (regular-grit diamond), fine cross-cut laminated burs, straight-cut laminated burs, spiral-cut laminated burs, and finishing diamonds. The straight-cut burs, spiral-cut burs, and finishing diamonds were tested individually as fine, extra-fine, and ultra-fine, as well as sequentially as a series. A high-speed, water-cooled handpiece under standardized pressure (0.5 N) and time (40 seconds) was used for all finishing procedures. Specimens were processed for scanning electron microscope, and margin gaps were systematically measured. Data were analyzed with one-way analysis of variance and Duncan test. RESULTS: The negative control specimens (course diamond) presented the largest gaps, whereas the positive control specimens (mechanically polished) generated the smallest gaps. No statistically significant difference was noted between the finishing diamonds and the positive control. The negative control exhibited significantly larger gaps when compared with the other finishing instruments. Intermediate results were observed for cross-cut, straight-cut, and spiral-cut laminated burs. Fine, extra-fine and ultra-fine finishing diamonds generated smaller gaps compared with laminated burs, but the differences were not always statistically significant. CONCLUSION: Fine, extra-fine and ultra-fine finishing diamonds used to finish composite restorations generated better marginal integrity when compared with carbides and regular-grit diamonds. CLINICAL SIGNIFICANCE When finishing composite restorations, finishing diamond burs result in better composite margins than carbide laminated burs.

Dentin and enamel bond strengths of dual-cure composite luting agents used with dual-cure dental adhesives.

OBJECTIVE: The purpose of this in vitro study was to evaluate and compare dentin and enamel bond strengths obtained with dual-cure composite luting agents when used with dual-cure dental adhesives. METHODS: Human molars were ground flat to expose enamel (n=80) or dentin (n=80). Specimens in each substrate group were randomly assigned to eight treatment sub-groups, according to four adhesive-luting agent combinations and two test conditions (with or without thermocycling). Pre-polymerized composite resin posts (TPH Spectrum) were luted to either the enamel or dentin surfaces with one of the following adhesive-luting agent combinations: (1) Xeno IV Dual Cure (dual-cure self-etch adhesive) and Calibra (dual-cure luting agent); (2) Prime & Bond NT Dual Cure (dual-cure total-etch adhesive) and Calibra; (3) OptiBond All-in-One Dual Cure (dual-cure self-etch adhesive) and Nexus 2 Dual Syringe (dual-cure luting agent); (4) OptiBond Solo Plus Dual Cure (dual-cure total-etch adhesive) and Nexus 2 Dual Syringe. For each treatment sub-group, half the specimens (n=10) were tested after 24h storage in water at 37 degrees C, and the other half (n=10) were tested after thermocycling for 1800 cycles between water baths held at 5 and 55 degrees C, with a dwell time in each bath of 30s, and a transfer time of 10s. Bond strengths were measured in shear mode, and expressed in MPa. The fracture mode (adhesive, cohesive, mixed) was examined. Data were analyzed for statistical significance with a factorial ANOVA and post hoc tests. RESULTS: Mean enamel bond strengths ranged from 8.4MPa for non-thermocycled OptiBond All-in-One|Nexus 2 to 35.5MPa for non-thermocycled Prime & Bond NT|Calibra. Mean dentin bond strengths ranged from 14.5MPa for non-thermocycled OptiBond Solo Plus|Nexus 2 to 30.9MPa for thermocycled Xeno IV|Calibra. The fracture mode was predominantly adhesive for all groups. CONCLUSIONS: On enamel, the total-etch adhesives performed better than their self-etch counterparts, while in dentin, the opposite was found, i.e., the self-etch adhesives performed better than their total-etch counterparts. Thermocycling for 1800 cycles did not affect the SBS of the materials tested to dentin and enamel.

Using extracted teeth for research: the effect of storage medium and sterilization on dentin bond strengths.

BACKGROUND: The Centers for Disease Control and Prevention has adopted guidelines for infection control of extracted teeth used for research and teaching, requiring that teeth be sterilized before use. The authors conducted a study to test the null hypothesis that the storage medium and sterilization method have no effect on composite-to-dentin bond strengths. MATERIALS AND METHODS: The authors collected 170 bovine incisors, cleaned them and placed them randomly into one of six storage media at 37 degrees C for 60 days: distilled water (dH(2)O), 0.9 percent sodium chloride, 0.5 percent chloramine-T, 5.25 percent sodium hypochlorite (NaClO), 2 percent glutaraldehyde and 10 percent formalin. For sterilization, they autoclaved a subset of 10 specimens from every sample, while they stored another subset of 10 specimens from every sample (except for the 10 percent formalin sample) in 10 percent formalin for 14 days. The authors then embedded the specimens in epoxy and ground flat the facial surface to expose middle-depth dentin, which they polished to 600 grit. They used a dental adhesive to apply composite to the exposed dentin. The authors tested the composite-to-dentin shear bond strength 24 hours after bonding. They analyzed the data using global analysis of variance and, when appropriate, multiple post hoc tests (P = .05). RESULTS: Storage in NaClO resulted in significantly lower bond strength than that of the other treatment specimens. Sterilization with the autoclave negatively affected the bond strength of specimens stored initially in dH(2)O or 10 percent formalin, while sterilization with formalin alone had no significant effect on bond strengths. CONCLUSIONS: Storing bovine teeth in 5.25 percent NaClO may negatively affect composite-to-dentin bond strengths. Immersion in 10 percent formalin might be the best option for storage and sterilization of bovine teeth that are to be used in dental bonding studies in vitro.

An in vitro microbial model for producing caries-like lesions on enamel

This study aimed to develop a low cost in vitro viable microbiological model to produce biofilms to be used in dental researches. Single and multi-species biofilms of S. mutans, S. sobrinus, S. mitis, S. salivarius, S. cricetus and S. sanguinis were grown on bovine enamel slabs during 10 days, in a sterile brain-heart infusion broth, containing 5% sucrose and incubated at 37ºC in an atmosphere of 10% CO2. The slabs were transferred to a fresh medium at every 6, 12 or 24 hours. After the experimental period, enamel volume percent mineral was determined by cross-sectional microhardness. Caries-like lesions were found in all bacterial groups when compared with the control group. No statistical significant differences were found between S. mutans and S. sobrinus with respect of their cariogenicity or among the periods of medium change. However, it was found a statistical significant difference among the cariogenicity of S. salivarius and S. sanguinis (ANOVA followed by Tukey test). This model has successfully developed caries-like lesion on enamel and the medium can be changed at every 24 hours utilizing either S. mutans or S. sobrinus.

Photosensitization of in vitro biofilms by toluidine blue O combined with a light-emitting diode.

In natural ecosystems, micro-organisms grow preferentially attached to surfaces, forming matrix-enclosed biofilms. The aim of this study was to determine photodestruction levels in biofilms after subjecting them to photodynamic therapy. Biofilms of Streptococcus mutans, S. sobrinus, and S. sanguinis were grown on enamel slabs for 3, 5 or 7 d. Both the number of viable micro-organisms and the concentration of water-insoluble polysaccharides were analysed, and mineral loss (DeltaZ) analyses were performed on the enamel slabs. The antimicrobial potential of toluidine blue O (0.1 mg ml(-1)), associated with 85.7 J cm(-2) of a light-emission diode, was evaluated on the viability of 5-d biofilms. Both the number of micro-organisms and the concentration of water-insoluble polysaccharide increased with the age of the biofilms. A significant reduction ( approximately 95%) in viability was observed for S. mutans and S. sobrinus biofilms following photosensitization, with a > 99.9% reduction in the viability of S. sanguinis biofilms. In conclusion, a biofilm model was shown to be suitable for studying changes in bacterial numbers and enamel mineralization and for demonstrating the potential value of photosensitization in the control of in vitro biofilms.