Objectives and Methods: The aim of this in vitro study was to evaluate the morphology of dentine ... more Objectives and Methods: The aim of this in vitro study was to evaluate the morphology of dentine in Class V and the Class II preparation walls in terms of tubule orientation, density and increase in surface area after conditioning. Six circular V-shaped preparations were cut at the cementum-enamel junction (CEJ) of anterior teeth and six Class II cavities with the
The CICERO method of crown fabrication consists of optically digitizing a gypsum die, designing t... more The CICERO method of crown fabrication consists of optically digitizing a gypsum die, designing the crown layer buildup, and subsequently pressing, sintering, and milling consecutive layers of a shaded high-strength alumina-based core material, a layer of dentin porcelain, and a final layer of incisal porcelain. Final finishing is performed in the dental laboratory. The CICERO method allows efficient production of
To evaluate the effects of dentin adhesives employed as resin sealers and provisional cementation... more To evaluate the effects of dentin adhesives employed as resin sealers and provisional cementation on the bond strengths of a resin cement to dentin. A two-step etch-and-rinse adhesive (Excite DSC--Group 1) and two-step self-etch adhesive (AdheSE--Group 2) were applied to exposed dentin surfaces prepared from human molars (N=4). Water was used instead of a resin sealer in control Groups 3 and 4. A eugenol-free provisional cement (except for Group 4) was applied to the treated surfaces. After storing in distilled water for 1 week, the provisional cement was removed and cylindrical composite blocks were luted with a resin cement (Variolink II). 0.9 x 0.9 mm sticks were produced from these luted specimens for microtensile bond testing and SEM examination. One-way ANOVA revealed that neither the resin sealer nor the temporary eugenol-free cement had a negative effect on the final bond strength (P> 0.05). Mixed failures were predominantly identified from SEM.
Dark-colored posts may negatively affect the esthetics of all-ceramic single unit crowns as the t... more Dark-colored posts may negatively affect the esthetics of all-ceramic single unit crowns as the thin layers of luting cement may not be sufficiently opaque. This in vitro study evaluated the influence of the color of 2 commercially available nonmetallic opaque posts (carbon fiber and zirconia) and an experimental esthetic post, and the shade and thickness of luting cements on the esthetics of all-ceramic restorations. Sample disks at several thickness values were made in glass-ceramic (IPS-Empress), an experimental ceramic, a zirconia, a carbon fiber post material, a resin composite material (Z100) as reference, and a luting cement (Variolink II). A laboratory procedure, with 3 possible combinations of stapling the disks, was used. This was performed for 4 substrates, 3 cement colors at 2 thickness values, and 3 heights of ceramic disks. For each combination, the shift in color was measured with a spectrophotometer. Readings were performed for 3 conditions: (1) ability of ceramic to mask the aspect of the abutment in relation to its thickness (1.0, 1.5, or 2.0 mm); (2) effect of a change in cement color (W, Y, or B) on the final color of the ceramic; and (3) influence of cement film thickness (0.1 or 0.2 mm) on the final color of the ceramic. When ceramic thickness was 1 mm, all other variables were visually appreciable. For ceramic thickness of 1.5 mm, color differences decreased and most differences were appreciable only with laboratory instruments. For ceramic thickness of 2.0 mm, there were no detectable, clinically relevant differences. The final esthetic result of the all-ceramic IPS-Empress glass-ceramic restoration was not affected by the presence of different substrates with different colors when the thickness was more than 2.0 mm. When ceramic thickness decreases to 1.5 mm, it is advised to take the substrate aspects into consideration. If the ceramic thickness is less than 1.0 mm, the use of a full ceramic crown is contraindicated because color matching of the abutment is required to ensure an acceptable esthetic result. Differences in cement thickness (0.1 or 0.2 mm) may slightly affect the final result. As this parameter can be controlled by the operator only to a certain extent, it cannot be considered as a procedure to correct color. Availability of different cement shades allows only minor esthetic corrections, which might be instrumentally detectable but are clinically not relevant.
The combination of diverse materials and complex geometry makes stress distribution analysis in t... more The combination of diverse materials and complex geometry makes stress distribution analysis in teeth very complicated. Simulation in a computerized model might enable a study of the simultaneous interaction of the many variables. A 3D solid model of a human maxillary premolar was prepared and exported into a 3D-finite element model (FEM). Additionally, a generic class II MOD cavity preparation and restoration was simulated in the FEM model by a proper choice of the mesh volumes. A validation procedure of the FEM model was executed based on a comparison of theoretical calculations and experimental data. Different rigidities were assigned to the adhesive system and restorative materials. Two different stress conditions were simulated: (a) stresses arising from the polymerization shrinkage and (b) stresses resulting from shrinkage stress in combination with vertical occlusal loading. Three different cases were analyzed: a sound tooth, a tooth with a class II MOD cavity, adhesively restored with a high (25 GPa) and one with a low (12.5GPa) elastic modulus composite. The cusp movements induced by polymerization stress and (over)-functional occlusal loading were evaluated. While cusp displacement was higher for the more rigid composites due to the pre-stressing from polymerization shrinkage, cusp movements turned out to be lower for the more flexible composites in case the restored tooth which was stressed by the occlusal loading. This preliminary study by 3D FEA on adhesively restored teeth with a class II MOD cavity indicated that Young's modulus values of the restorative materials play an essential role in the success of the restoration. Premature failure due to stresses arising from polymerization shrinkage and occlusal loading can be prevented by proper selection and combination of materials.
The purpose of this study was to investigate the effect of differences in the resin-cement elasti... more The purpose of this study was to investigate the effect of differences in the resin-cement elastic modulus on stress-transmission to ceramic or resin-based composite inlay-restored Class II MOD cavities during vertical occlusal loading. Three finite-element (FE) models of Class II MOD cavity restorations in an upper premolar were produced. Model A represented a glass-ceramic inlay in combination with an adhesive and a high Young's modulus resin-cement. Model B represented the same glass-ceramic inlay in combination with the same adhesive and a low Young's modulus resin-cement. Model C represented a heat-cured resin-composite inlay in combination with the same adhesive and the same low Young's modulus resin cement. Occlusal vertical loading of 400 N was simulated on the FE models of the restored teeth. Ansys FE software was used to compute the local von Mises stresses for each of the models and to compare the observed maximum intensities and distributions. Experimental validation of the FE models was conducted. Complex biomechanical behavior of the restored teeth became apparent, arising from the effects of the axial and lateral components of the constant occlusal vertical loading. In the ceramic-inlay models, the greatest von Mises stress was observed on the lateral walls, vestibular and lingual, of the cavity. Indirect resin-composite inlays performed better in terms of stress dissipation. Glass-ceramic inlays transferred stresses to the dental walls and, depending on its rigidity, to the resin-cement and the adhesive layers. For high cement layer modulus values, the ceramic restorations were not able to redistribute the stresses properly into the cavity. However, stress-redistribution did occur with the resin-composite inlays. Application of low modulus luting and restorative materials do partially absorb deformations under loading and limit the stress intensity, transmitted to the remaining tooth structures.
The purpose of this study was to measure the development of contraction stress of three composite... more The purpose of this study was to measure the development of contraction stress of three composite resin restorative materials during photo-polymerization: a micro-hybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA); a nano-filled composite (Filtek Supreme, 3M ESPE, St. Paul, MN, USA); and a low-shrinkage composite (AElite LS, Bisco Inc., Schaumburg, IL, USA). Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen-curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 150 s after photo-initiation. Contraction stress (MPa) was calculated at 20, 40, 60 and 150 s. Data were statistically analyzed. The low-shrinkage composite AElite LS exhibited the lowest stress values compared to other materials (p<0.05). Statistical analysis did not show significant differences between Filtek Z250 and Filtek Supreme. The low-shrinkage composite showed lower contraction stress than micro-hybrid and nano-filled composite. Ideally, non-shrinking resins would represent the ultimate solution to overcome polymerization contraction and stress-related problems.
Objectives and Methods: The aim of this in vitro study was to evaluate the morphology of dentine ... more Objectives and Methods: The aim of this in vitro study was to evaluate the morphology of dentine in Class V and the Class II preparation walls in terms of tubule orientation, density and increase in surface area after conditioning. Six circular V-shaped preparations were cut at the cementum-enamel junction (CEJ) of anterior teeth and six Class II cavities with the
The CICERO method of crown fabrication consists of optically digitizing a gypsum die, designing t... more The CICERO method of crown fabrication consists of optically digitizing a gypsum die, designing the crown layer buildup, and subsequently pressing, sintering, and milling consecutive layers of a shaded high-strength alumina-based core material, a layer of dentin porcelain, and a final layer of incisal porcelain. Final finishing is performed in the dental laboratory. The CICERO method allows efficient production of
To evaluate the effects of dentin adhesives employed as resin sealers and provisional cementation... more To evaluate the effects of dentin adhesives employed as resin sealers and provisional cementation on the bond strengths of a resin cement to dentin. A two-step etch-and-rinse adhesive (Excite DSC--Group 1) and two-step self-etch adhesive (AdheSE--Group 2) were applied to exposed dentin surfaces prepared from human molars (N=4). Water was used instead of a resin sealer in control Groups 3 and 4. A eugenol-free provisional cement (except for Group 4) was applied to the treated surfaces. After storing in distilled water for 1 week, the provisional cement was removed and cylindrical composite blocks were luted with a resin cement (Variolink II). 0.9 x 0.9 mm sticks were produced from these luted specimens for microtensile bond testing and SEM examination. One-way ANOVA revealed that neither the resin sealer nor the temporary eugenol-free cement had a negative effect on the final bond strength (P> 0.05). Mixed failures were predominantly identified from SEM.
Dark-colored posts may negatively affect the esthetics of all-ceramic single unit crowns as the t... more Dark-colored posts may negatively affect the esthetics of all-ceramic single unit crowns as the thin layers of luting cement may not be sufficiently opaque. This in vitro study evaluated the influence of the color of 2 commercially available nonmetallic opaque posts (carbon fiber and zirconia) and an experimental esthetic post, and the shade and thickness of luting cements on the esthetics of all-ceramic restorations. Sample disks at several thickness values were made in glass-ceramic (IPS-Empress), an experimental ceramic, a zirconia, a carbon fiber post material, a resin composite material (Z100) as reference, and a luting cement (Variolink II). A laboratory procedure, with 3 possible combinations of stapling the disks, was used. This was performed for 4 substrates, 3 cement colors at 2 thickness values, and 3 heights of ceramic disks. For each combination, the shift in color was measured with a spectrophotometer. Readings were performed for 3 conditions: (1) ability of ceramic to mask the aspect of the abutment in relation to its thickness (1.0, 1.5, or 2.0 mm); (2) effect of a change in cement color (W, Y, or B) on the final color of the ceramic; and (3) influence of cement film thickness (0.1 or 0.2 mm) on the final color of the ceramic. When ceramic thickness was 1 mm, all other variables were visually appreciable. For ceramic thickness of 1.5 mm, color differences decreased and most differences were appreciable only with laboratory instruments. For ceramic thickness of 2.0 mm, there were no detectable, clinically relevant differences. The final esthetic result of the all-ceramic IPS-Empress glass-ceramic restoration was not affected by the presence of different substrates with different colors when the thickness was more than 2.0 mm. When ceramic thickness decreases to 1.5 mm, it is advised to take the substrate aspects into consideration. If the ceramic thickness is less than 1.0 mm, the use of a full ceramic crown is contraindicated because color matching of the abutment is required to ensure an acceptable esthetic result. Differences in cement thickness (0.1 or 0.2 mm) may slightly affect the final result. As this parameter can be controlled by the operator only to a certain extent, it cannot be considered as a procedure to correct color. Availability of different cement shades allows only minor esthetic corrections, which might be instrumentally detectable but are clinically not relevant.
The combination of diverse materials and complex geometry makes stress distribution analysis in t... more The combination of diverse materials and complex geometry makes stress distribution analysis in teeth very complicated. Simulation in a computerized model might enable a study of the simultaneous interaction of the many variables. A 3D solid model of a human maxillary premolar was prepared and exported into a 3D-finite element model (FEM). Additionally, a generic class II MOD cavity preparation and restoration was simulated in the FEM model by a proper choice of the mesh volumes. A validation procedure of the FEM model was executed based on a comparison of theoretical calculations and experimental data. Different rigidities were assigned to the adhesive system and restorative materials. Two different stress conditions were simulated: (a) stresses arising from the polymerization shrinkage and (b) stresses resulting from shrinkage stress in combination with vertical occlusal loading. Three different cases were analyzed: a sound tooth, a tooth with a class II MOD cavity, adhesively restored with a high (25 GPa) and one with a low (12.5GPa) elastic modulus composite. The cusp movements induced by polymerization stress and (over)-functional occlusal loading were evaluated. While cusp displacement was higher for the more rigid composites due to the pre-stressing from polymerization shrinkage, cusp movements turned out to be lower for the more flexible composites in case the restored tooth which was stressed by the occlusal loading. This preliminary study by 3D FEA on adhesively restored teeth with a class II MOD cavity indicated that Young's modulus values of the restorative materials play an essential role in the success of the restoration. Premature failure due to stresses arising from polymerization shrinkage and occlusal loading can be prevented by proper selection and combination of materials.
The purpose of this study was to investigate the effect of differences in the resin-cement elasti... more The purpose of this study was to investigate the effect of differences in the resin-cement elastic modulus on stress-transmission to ceramic or resin-based composite inlay-restored Class II MOD cavities during vertical occlusal loading. Three finite-element (FE) models of Class II MOD cavity restorations in an upper premolar were produced. Model A represented a glass-ceramic inlay in combination with an adhesive and a high Young's modulus resin-cement. Model B represented the same glass-ceramic inlay in combination with the same adhesive and a low Young's modulus resin-cement. Model C represented a heat-cured resin-composite inlay in combination with the same adhesive and the same low Young's modulus resin cement. Occlusal vertical loading of 400 N was simulated on the FE models of the restored teeth. Ansys FE software was used to compute the local von Mises stresses for each of the models and to compare the observed maximum intensities and distributions. Experimental validation of the FE models was conducted. Complex biomechanical behavior of the restored teeth became apparent, arising from the effects of the axial and lateral components of the constant occlusal vertical loading. In the ceramic-inlay models, the greatest von Mises stress was observed on the lateral walls, vestibular and lingual, of the cavity. Indirect resin-composite inlays performed better in terms of stress dissipation. Glass-ceramic inlays transferred stresses to the dental walls and, depending on its rigidity, to the resin-cement and the adhesive layers. For high cement layer modulus values, the ceramic restorations were not able to redistribute the stresses properly into the cavity. However, stress-redistribution did occur with the resin-composite inlays. Application of low modulus luting and restorative materials do partially absorb deformations under loading and limit the stress intensity, transmitted to the remaining tooth structures.
The purpose of this study was to measure the development of contraction stress of three composite... more The purpose of this study was to measure the development of contraction stress of three composite resin restorative materials during photo-polymerization: a micro-hybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA); a nano-filled composite (Filtek Supreme, 3M ESPE, St. Paul, MN, USA); and a low-shrinkage composite (AElite LS, Bisco Inc., Schaumburg, IL, USA). Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen-curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 150 s after photo-initiation. Contraction stress (MPa) was calculated at 20, 40, 60 and 150 s. Data were statistically analyzed. The low-shrinkage composite AElite LS exhibited the lowest stress values compared to other materials (p<0.05). Statistical analysis did not show significant differences between Filtek Z250 and Filtek Supreme. The low-shrinkage composite showed lower contraction stress than micro-hybrid and nano-filled composite. Ideally, non-shrinking resins would represent the ultimate solution to overcome polymerization contraction and stress-related problems.
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Papers by David Moujaes