Maria Helvatjoglu-Antoniades

A preliminary evaluation of the structural integrity and fracture mode of minimally prepared resin bonded CAD/CAM crowns

PURPOSE This study was a preliminary evaluation of two minimal preparation designs proposed for ceramic and composite resin bonded CAD/CAM crowns. It compared the structural integrity and fracture mode of teeth restored with traditionally and minimally prepared resin bonded CAD/CAM crowns fabricated from the same material hypothesizing that teeth restored with minimal resin bonded crowns would demonstrate the same fracture strength to teeth restored with traditional resin bonded crowns. MATERIALS AND METHODS Forty intact maxillary molar teeth were used and divided in four groups. Two groups were prepared according to a traditional crown preparation design and two groups were prepared according to minimal preparation designs. A resin composite (Paradigm MZ100, 3M ESPE) and a leucite glass-ceramic (ProCAD, Ivoclar Vivadent) were used for the fabrication of the crowns using CEREC Scan. Crowns of ceramic were cemented using Variolink II (Ivoclar Vivadent) and crowns of composite with Rely X Unicem Aplicap (3M ESPE) and loaded until fracture. Load data was analysed using ANOVA comparing crowns of the same restorative material. The mode of fracture was also recorded and analysed (Kruskal-Wallis). RESULTS For the composite system the mean fracture load and SD was 1682N (+/-315) for the traditional and 1751N (+/-338) for the minimal crowns. For the ceramic system the mean fracture load and SD was 1512N (+/-373) for the traditional and 1837 (+/-356) for the minimal crowns. No statistically significant difference was found between the two designs for each system. Nonparametric analysis (Kruskal-Wallis) of the fracture mode showed no statistical significant difference between designs for either material (p>.05). CONCLUSION Within the limitations of this experimental design, it was found that minimally prepared resin bonded CEREC crowns demonstrated equal fracture resistance and mode of fracture to that of crowns bonded to traditionally prepared teeth.

Effects of Dentin Bonding Agents on the Cell Cycle of Fibroblasts

The aim of this study was to evaluate the effects of 3 dentin bonding agents on cell survival and proliferation and on cell cycle progression of cultured cells. The experiments were performed on RPC-C2A and L929 cells. Specimens of the 3 dentin bonding agents (Clearfil Tri-S, AdheSE, and XP BOND) were placed in culture medium, and the extraction media were applied to cells as experimental material. The effect of the bonding materials on cell survival and proliferation was assessed by a modified sulforhodamine B staining assay, and the effect on DNA synthesis was assessed by bromodeoxyuridine uptake. Flow cytometry was used for cell cycle analysis. Cell viability and proliferation decreased in a dose-dependent manner after exposure of cells to the tested materials. XP BOND expressed the highest activity of all tested bonding agents (P < .05). The self-etch bonding agents tested did not produce any significant effects on cell cycle distribution. However, exposure of cells to the total-etch agent XP BOND induced a G(2)-phase arrest in both cell lines, and this effect was more evident in L929 cells than in RPC-C2A cells.

Effect of in-office bleaching agents on physical properties of dental composite resins.

OBJECTIVES The physical properties of dental restorative materials have a crucial effect on the longevity of restorations and moreover on the esthetic demands of patients, but they may be compromised by bleaching treatments. The purpose of this study was to evaluate the effects of in-office bleaching agents on the physical properties of three composite resin restorative materials. METHOD AND MATERIALS The bleaching agents used were hydrogen peroxide and carbamide peroxide at high concentrations. Specimens of each material were prepared, cured, and polished. Measurements of color difference, microhardness, and surface roughness were recorded before and after bleaching and data were examined statistically by analysis of variance (ANOVA) and Tukey HSD post-hoc test at P < .05. RESULTS The measurements showed that hue and chroma of silorane-based composite resin altered after the bleaching procedure (P < .05). No statistically significant differences were found when testing the microhardness and surface roughness of composite resins tested (P > .05). CONCLUSION The silorane-based composite resin tested showed some color alteration after bleaching procedures. The bleaching procedure did not alter the microhardness and the surface roughness of all composite resins tested.

Dynamic viscoelastic behavior of resin cements measured by torsional resonance

OBJECTIVE The purpose of the study was to measure the viscoelastic properties of four dental resin composite cements using a dynamic mechanical analysis technique. METHODS Dynamic torsional loading was conducted in the frequency range from 1 to 80 Hz. Cement specimens were tested after storage in 37 degrees C water for 24 h. One group was thermal cycled prior to testing. Measurements were taken at 21, 37, and 50 degrees C. Storage modulus, loss tangent and other viscoelastic parameters were determined from the amplitude/frequency curves. RESULTS Storage moduli of the cements ranged from 2.9 to 4.1 GPa at 37 degrees C. Loss tangents ranged from 0.054 to 0.084. Storage moduli decreased in a regular way with increasing temperature, whereas, loss tangents increased. Thermal cycling caused small decreases in storage moduli. SIGNIFICANCE Resin cements with higher filler loading were found to have higher storage moduli and lower loss tangents. Since these properties have been associated with better clinical performance in the areas of retention and prevention of fracture of porcelain and resin restorations, the more highly filled cements may be recommended. Temperature variations influenced viscoelastic behavior of the cements. However, within the temperature range studied no sharp drop in modulus was seen, so the materials should function satisfactorily in the oral cavity.

Pulp response to dentine adhesives: A study on mature human pulps

Objective: To clinically investigate the antibacterial effects of a commercially available self-etch 12-methacryloyloxy- dodecylpyridinium bromide (MDPB)-containing adhesive system in comparison with its respective non-MDPB-containing adhesive and to evaluate the pulp responses when in use on human teeth. Materials and Methods: Sixty-two viable human teeth scheduled for extraction were used. Class V cavities were prepared on the buccal surfaces of the teeth and filled with the tested materials (Protect Bond/Clearfil AP-X, SE Bond/Clearfil AP-X and Dycal/Ketac Fill Plus) as a control group, according to manufacturers recommendations. Randomly divided to two groups teeth remained intra-orally for 4 and 8 weeks. After extraction, teeth were decalcified, sectioned and stained using the Mayers hematoxylin and eosin, and modified Brown-Brenns technique. Pulp responses were evaluated microscopically under a microscope and remaining dentine thickness measured under a stereomicroscope. Results: No statistically significant differences regarding pulp inflammation or bacterial infiltration were found either for the materials tested or for periods of post-operative evaluation. Conclusions: The results suggested that for a short period of evaluation there are no quantitative differences, regardless to restoring material used.

In vitro fluoride uptake by bovine enamel from aesthetic restorative materials.

OBJECTIVES The purposes of this in vitro study were to determine whether different types of fluoride-containing restoratives produce differing levels of fluoride uptake by bovine enamel, and to determine the effect of time on this uptake. METHODS Seven aesthetic restorative materials were evaluated. Forty bovine enamel slabs were prepared for each tested material, five of which were used to determine baseline fluoride concentrations. Each slab was attached to a disc of the tested material and suspended in synthetic saliva for up to 64 days. After removal, the specimens were acid etched with perchloric acid, and the dissolved enamel was analysed for fluoride and calcium. Fluoride was determined by direct potensiometric analysis, whereas the amount of calcium was evaluated by means of atomic absorption spectrophotometry. RESULTS Higher values of fluoride uptake, not significantly different, were recorded in the first two groups. A statistically significant difference was found in fluoride uptake between Fuji II LC and the three compomers in all test intervals. No significant differences were found in the amounts of fluoride uptake between the three compomers. The highest fluoride uptake from all compomers was recorded by F2000. CONCLUSION Enamel acquired significant amounts of fluoride from all materials with variations during the test intervals.

Color match of resin composites to intact tooth structure

Introduction The optical properties of dental restorative materials have a dramatic effect on patient esthetics, which may be compromised by the poor blending effect of composites resins at the composite–tooth interface. Objective The objective of this study was to evaluate the color-matching ability and the blending effects of 3 different composite resins when restoring natural teeth. Methods Three commercially available composites and 60 central incisors were used for this experiment. Each tooth was sectioned horizontally at the level of the cementum–enamel junction, and the crown was then bisected along the long axis of the tooth. One half of each tooth was restored individually with composite resin, after matching with the corresponding tooth shade. The tooth color was evaluated preoperatively and postoperatively using an intraoral spectrophotometer and a scientific spectrophotometer. Color differences were then evaluated by the CIEDE2000 color difference formula. Results The results showed the existence of color differences between the intact and the restored sections of the teeth. However, these differences were considered acceptable, since the ΔΕ value ranged below 3.3. The ΔE, Δa and Δb parameters showed no statistically significant differences between the groups (p>0.05). Conclusions The 3 composites tested were able to mimic natural teeth and produce acceptable restorations. However, the color of the resin composites needs to be evaluated over the long term, because it is subject to alterations in the oral environment over time.