The Influence of Dentin Wall Thickness and Adhesive Surface in Post and Core Crown and Endocrown Restorations on Central and Lateral Incisors

Purpose: The main purpose of this study was to determine the influence of dentin wall thickness (DWT) and adhesive surface on the fracture strength and failure mode in maxillary incisors restored with post and core crowns or endocrowns. Methods and Materials: Forty-eight sound maxillary incisors were selected and randomly divided into four groups (n=12): lateral incisor endocrown, lateral incisor post and core, central incisor endocrown, and central incisor post and core. All specimens obtained an endodontic treatment and were decoronated (2 mm ferrule remained). Chamfer outlines ended at the cementoenamel junction (outline in dentin). Dentin wall thickness (mm) was measured on 12 points per sample using a modified digital calliper. Fiber posts and cores were placed in two groups, and an immediate dentin sealing was applied on exposed dentin in all groups before taking digital impressions. Digital impressions were analyzed and the adhesive surface (mm(2)) was measured. Indirect restorations were made of lithium disilicate (IPS e.max, computer-aided design/computer-aided manufacturing). The restorations were luted after surface conditioning the crowns and teeth. Thermocyclic aging was performed (10,000 times in baths of 5 degrees C and 55 degrees C) and the specimens were loaded until fracture. Fractures were specified on failure mode and repairability, and they were analyzed with one-way ANOVA, chi(2)-test, and linear regression analysis in SPSS (alpha=0.05). Results: There was no significant difference in fracture strength and failure mode between all groups. Endocrown restorations on central incisors had significantly more repairable fractures than the post and core crowns. Regression analyses showed a statistically significant positive correlation between DWT/adhesive surface and fracture strength in the post and core groups. Conclusions: Both endocrowns and post and core crowns on the central and lateral incisors obtained clinically applicable fracture strengths. In the central incisor groups, the endocrown restorations had significantly more repairable failures. When the walls were thicker, or when the adhesive surface was larger, higher fracture strengths were obtained in the post and core groups

Influence of Preparation Design and Restorative Material on Fatigue and Fracture Strength of Restored Maxillary Premolars

Statement of Problem: Extensive carious lesions and/or large preexisting restorations possibly contribute to crack formation, ultimately resulting in a fracture that may lead to the loss of a tooth cusp. Hence, preparation design strategy in conjunction with the restorative material selected could be influential in the occurrence of a cuspal fracture. Purpose: The purpose of this in vitro study was to evaluate the fatigue behavior and fracture strength of maxillary premolars restored with direct composite and indirect ceramic inlays and overlays, with different preparation depths in the presence or absence of cuspal coverage, and analyze their failure types. Methods and Materials: Sound maxillary premolars (N=90; n=10) were divided into nine groups: group C: control; group DCI3: direct composite inlay 3 mm; group DCI5: direct composite inlay 5 mm; group ICI3: indirect ceramic inlay 3 mm; group ICI5: indirect ceramic inlay 5 mm; group DCO3: direct composite overlay 3 mm; group DCO5: direct composite overlay 5 mm; group ICO3: indirect ceramic overlay 3 mm; group ICO5: indirect ceramic overlay 5 mm. In indirect ceramic, lithium disilicate restoration groups, immediate dentin sealing was applied. After restoration, all specimens were tested in fatigue (1,200,000 cycles, 50 N, 1.7 Hz). Samples were critically appraised, and the specimens without failure were subjected to a load to failure test. Failure types were classified and the data analyzed. Results: Zero failures were observed in the fatigue testing. The following mean load to failure strengths (N) were recorded: group ICO5: 858 N; group DCI3: 829 N; group ICO3: 816 N; group C: 804 N; group ICI3: 681 N; group DCO5: 635 N; group DCI5: 528 N; group DCO3: 507 N; group ICI5: 482 N. Zero interaction was found between design-depth-material (p=0.468). However, significant interactions were found for the design-depth (p=0.012) and design-material (p=0.006). Within restorations at preparation depth of 3 mm, direct composite overlays obtained a significantly lower fracture strength in comparison to indirect ceramic onlays (p=0.013) and direct composite inlays (p=0.028). In restorations at depth 5 mm, significantly higher fracture load values were observed in indirect ceramic overlays compared with the inlays (p=0.018). Indirect ceramic overlays on 3 mm were significantly stronger than the deep inlays in ceramic (p=0.002) and tended to be stronger than the deep direct composite inlays. Severe, nonreparable fractures were observed with preparation depth of 5 mm within ceramic groups. Conclusions: The preparation depth significantly affected the fracture strength of tooth when restored with either composite or ceramic materials. Upon deep cavity preparations, cuspal coverage proved to be beneficial when a glass ceramic was used as the restorative material. Upon shallow cavity preparations, a minimally invasive approach regarding preparation design used in conjunction with a direct composite material was favorable

Fracture Strength of Various Types of Large Direct Composite and Indirect Glass Ceramic Restorations

Introduction: The objective of this study was to investigate the mechanical behavior of severely compromised endodontically treated molars restored by means of various types of composite buildups, full-contour lithium disilicate crowns (with or without post) or a lithium disilicate endocrown. Methods and Materials: One hundred five sound molars were endodontically treated and randomly assigned to 1 control group (endodontic access cavity only) and 6 experimental groups (n=15): glass fiber reinforced composite (GFRC group), direct microhybrid composite (C group), direct microhybrid composite restoration with glass fiber post (CP group), composite buildup and full-contour lithium disilicate crown (LDS group), additional glass fiber post (P-LDS group), and endocrown (EC group). Molar crowns in the treatment groups were removed 1 mm above the cementoenamel junction and restored. All specimens were thermomechanically aged (1.2x10(6) cycles at 1.7 Hz/50N, 8000 cycles 5 degrees C to 55 degrees C) and axially loaded until failure. Data were analyzed using analysis of variance and Tukey post hoc test (alpha=0.05). Results: Fracture strength was significantly affected by the type of restoration (p=0.000; statistically similar groups identified with superscript letters): LDSB (3217 +/- 1052 N), P-LDSAB (2697 +/- 665 N), ECAB (2425 +/- 993 N), C-A (2192 +/- 752), control(A) (1890 +/- 774 N), CPA (1830 +/- 590 N), and GFRC(A) (1823 +/- 911 N). Group GFRC obtained significantly more repairable fractures than the other groups. Conclusions: Significant differences in fracture strength were obtained between LDS, the composite restorations, and control group. Direct composite restorations showed similar fracture strength as P-LDS and EC. Incorporating a glass fiber reinforced composite resulted in significantly more repairable failures

Effect of Immediate Dentin Sealing and Surface Conditioning on the Microtensile Bond Strength of Resin-based Composite to Dentin

This study evaluated the microtensile bond strength (μTBS) of resin-based composite (RBC) to dentin after different immediate dentin sealing (IDS) strategies and surface-conditioning (SC) methods and on two water storage times. Human molars (n=48) were randomly divided into eight experimental groups involving four different IDS strategies-IDS-1L with one layer of adhesive, IDS-2L with two layers of adhesive, IDS-F with one layer of adhesive and one layer of flowable RBC, and DDS (delayed dentin sealing) with no layer of adhesive (control)-and two different SC methods-SC-P with pumice rubbing and SC-PC with pumice rubbing followed by tribochemical silica coating. The μTBS test was performed after one week and after six months of water storage, being recorded as the "immediate" and "aged" μTBS, respectively. Composite-adhesive-dentin microspecimens (0.9×0.9×8-9 mm) were stressed in tension until failure to determine the μTBS. Failure mode and location of failure were categorized. Two-way analysis of variance was applied to analyze the data for statistically significant differences between the experimental groups (p<0.05). Two-way analysis of variance revealed no significant differences between the one-week μTBS specimens for IDS strategy (p=0.087) and SC methods (p=0.806). However, the interaction of IDS strategy and SC methods appeared statistically significant (p=0.016). The six-month specimen evaluation showed no significant difference in μTBS for SC (p=0.297) and SC/IDS interaction (p=0.055), but the μTBS of the IDS strategies differed significantly among them (p=0.003). For tribochemical silica-coated IDS, no significant effect of aging on μTBS was recorded (p=0.465), but there was a highly significant difference in μTBS depending on the IDS strategy (p<0.001). In addition, the interaction of IDS and aging was borderline statistically significant (p=0.045). The specimens failed mainly at the adhesive-dentin interface for all experimental groups. Dentin exposure during clinical procedures for indirect restorations benefits from the application of IDS, which was shown to result in higher bond strength. No significant differences were found between cleaning with solely pumice or pumice followed by tribochemical silica coating.status: publishe