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Analysis of stresses during the polymerization shrinkage of self-curing resin cement in indirect restorations: A finite-element study
Adhesive cementation is essential for the longevity of indirect esthetic restorations. However, polymerization shrinkage of resin cement generates stress, which may cause failures in the tooth–restoration interface. Thus, understanding the biomechanics of resin cement is important for predicting the clinical behavior of an esthetic indirect restoration. This study analyzed the stresses generated during polymerization shrinkage of self-curing resin cement in ceramic and in indirect resin (IR) restorations, using the finite-element method (FEM). A 3-D model of a second molar restored with ceramic or IR onlay restoration was designed. The polymerization shrinkage of self-curing resin cement was simulated in FEM software using an analogy between the thermal stress and the resulting contraction of the resin cement. The localization and values of tensile stresses in the dental structure, cement, and adhesive layer were identified. RESULTS: The location and value of the tensile stresses were similar for the two restorative materials. High tensile stresses were identified in the axiopulpal wall and angles of the tooth preparation, with major stresses found in the cement located in the axiopulpal wall. The high stress values and their concentration in the angles of the prepared tooth emphasize the importance of round angles and the use of cements with lower rates of shrinkage.
Adhesion to zirconia used for dental restorations: a systematic review and meta-analysis
Currently, no consensus exists regarding the best adhesion protocol for zirconia used in dentistry; this is particularly important for restorations where mechanical retention is deficient. This systematic review analyzed the adhesion potential of resin-based and glass-ionomer luting cements to zirconia and aimed to highlight the possible dominant factors affecting the bond strength results to this substrate. Original scientific papers on adhesion to zirconia published in the MEDLINE (PubMed) database between 01/01/1995 and 01/06/2011 were included in this systematic review. Descriptive statistics were performed and the frequencies of the studied parameters, means, standard deviations, confidence intervals (95% CI; uncorrected and corrected), median values, and interquartile ranges (IQR) were calculated for the bond strength data reported for various factor levels. Based on the results of this systematic review, increased adhesion could be expected after physicochemical conditioning of zirconia. MDP-based resin cements tend to present higher results than those of other cement types when tested using macro- and microtensile tests. Adhesion studies on zirconia and reporting of data require more standardization.
Effects of solvent evaporation time on immediate adhesive properties of universal adhesives to dentin
The objective was to evaluate the microtensile bond strengths (μTBS) and nanoleakage (NL) of three universal or multi-mode adhesives, applied with increasing solvent evaporation times. One-hundred and forty caries-free extracted third molars were divided into 20 groups for bond strength testing, according to three factors: 1) Adhesive - All-Bond Universal (ABU, Bisco, Inc.), Prime&Bond Elect (PBE, DENTSPLY), and Scotchbond Universal Adhesive (SBU, 3M ESPE); 2) Bonding strategy - self-etch (SE) or etch-and-rinse (ER); and 3) Adhesive solvent evaporation time - 5 s, 15 s, and 25 s. Two extra groups were prepared with ABU because the respective manufacturer recommends a solvent evaporation time of 10 s. Resin-dentin beams (0.8 mm2) were tested at 0.5 mm/min (μTBS). For NL, 40 extracted molars were randomly assigned to each of the 20 groups. Dentin disks were restored, immersed in ammoniacal silver nitrate, sectioned, and processed for evaluation under a FESEM in backscattered mode. RESULTS: Increasing solvent evaporation time from 5 s to 25 s resulted in statistically higher mean μTBS for all adhesives when used in ER mode. Regarding NL, ER resulted in greater NL than SE for each of the evaporation times regardless of the adhesive used.