Effect of preparation design on fracture strength of compromised molars restored with direct composite resin restorations: An in vitro and finite element analysis study.

STATEMENT OF PROBLEM: More data are needed on the influence of preparation design on the fracture strength, failure type, repairability, and polymerization-induced cracks of molar teeth restored with direct composite resin restorations. PURPOSE: This in vitro and finite element analysis study investigated the effect of different preparation designs on fracture strength, failure type, repairability, tooth deformation, and the formation of polymerization-induced cracks of compromised molars restored with direct composite resin restorations. MATERIAL AND METHODS: Human molars (n=64) were randomly assigned to 4 different preparation designs: undermined inlay (UI), extended inlay (EI), restricted overlay (RO), and extended overlay (EO). The teeth were restored using direct composite resin and subjected to artificial thermomechanical aging in a mastication simulator, followed by load-to-failure testing. Three-dimensional (3D) finite element analysis was conducted to assess tooth deformation. Polymerization-induced cracks were evaluated using optical microscopy and transillumination. The fracture strength data were analyzed using a Kruskal-Wallis test, while the failure mode, repairability, and polymerization cracks were analyzed using the Fisher exact test (α=.05). RESULTS: All specimens withstood thermomechanical aging, and no statistically significant difference in fracture strength was observed among the 4 preparation designs (P>.05). The finite element analysis showed differences in tooth deformation, but no correlation was observed with in vitro fracture resistance. The RO and EO groups presented significantly more destructive failures compared with the UI and EI groups (P<.01). The RO group had significantly fewer repairable failures than the UI and EI groups (P=.024). A correlation was found between higher frequencies of repairability and higher tooth deformation. A significant correlation between the increase in microfractures and preparation design was observed (P<.01), with the UI group exhibiting a higher increase in microfracture size compared with the EO group (P<.05). CONCLUSIONS: No influence of preparation design on the fracture strength of compromised molars restored with direct composite resin restorations was evident in this study, but the failure mode of cusp coverage restorations was more destructive and often less repairable. The finite element analysis showed more tooth deformation in inlay preparations, with lower stresses within the root, leading to more reparable fractures. Since cusp coverage direct composite resin restorations fractured in a more destructive manner, this study suggests that even a tooth with undermined cusps should be restored without cusp coverage.

Partial glass-ceramic posterior restorations with margins beyond or above the cemento-enamel junction: An observational retrospective clinical study.

PURPOSE: This observational retrospective clinical study aimed to investigate the survival and success rates of partial indirect lithium disilicate restorations with margins extending above or beyond the cementoenamel junction (CEJ). METHODS: The study included patients who underwent partial indirect lithium disilicate restorations with immediate dentin sealing (IDS) between January 2008 and October 2018. All the restorations were placed in a single general dental practice following a standardized protocol. The impact of various predictive variables on the survival rates was assessed. Moreover, modified United States Public Health Service (USPHS) criteria were used to evaluate the survival quality. RESULTS: Totally 1146 partial indirect lithium disilicate restorations in 260 patients were evaluated over an average period of 7.5 years. The cumulative survival and success rates were 97.3% and 95.3%, respectively. Margins extending beyond the cemento-enamel junction did not increase the risk of success or survival failure (P > 0.05). Patients with a high risk of caries, male sex, or non-vital teeth had a significantly higher risk of restoration failure (P < 0.05). Restorations with longer clinical service times exhibited marginally lower clinical quality (P < 0.001). CONCLUSIONS: Partial indirect glass-ceramic restorations demonstrated survival and success rates of 97.3% and 95.3%, respectively, over an extended period. However, a higher risk of restoration failure existed in patients with a high caries risk for (pre)molars that had undergone endodontic treatment and in males. In terms of the risk of success or survival failure, comparable results were obtained for the positions of the restoration margin in relation to the cemento-enamel junction.

Clinical performance of bonded partial lithium disilicate restorations: The influence of preparation characteristics on survival and success.

OBJECTIVES: The aim of this study was to investigate the influence of preparation characteristics on the survival, success, and clinical performance of partial indirect lithium disilicate restorations with immediate dentin sealing. METHODS: This retrospective clinical study evaluated partial indirect lithium disilicate restorations placed in conjunction with Immediate Dentin Sealing (IDS) in (pre)molar teeth between March 2018 and May 2021. The restorations were luted using pre-heated composite. The study focused on survival, success, and clinical performance, which was evaluated using the modified United States Public Health Service (USPHS) criteria. Results were analyzed using the Kaplan-Meier estimates, log-rank tests, and Fisher exact tests. RESULTS: Partial indirect lithium disilicate restorations (N = 454) were evaluated in 214 patients. The mean evaluation time was 37 months, with a cumulative survival rate of 99.2 % and a cumulative success rate of 97.6 %. Fourteen failures occurred, with endodontic pathology as the predominant failure mode, followed by secondary caries, debonding, and tooth fracture. No statistically significant influence of the preparation variables on survival and success was observed (p > .05). The short-term clinical performance was clinically acceptable in > 90 % of the evaluations. CONCLUSIONS: This retrospective study on partial indirect lithium disilicate restorations in conjunction with IDS demonstrates survival and success rates of 99.2 and 96.7 % over a mean evaluation period of 37 months. A marked influence of the studied preparation characteristics on the survival, success and clinical performance of lithium disilicate partial restorations could not be demonstrated. Partial lithium disilicate restorations exhibit good clinical performance in >90 % of the cases. CLINICAL SIGNIFICANCE: The results of this study suggest that preparation characteristics had no significant impact on the survival, success, and clinical performance of partial lithium disilicate restorations in conjunction with IDS. Results show good clinical performance and high survival and success rates, regardless of preparation characteristics.

Effect of preparation design on fracture strength of compromised molars restored with lithium disilicate inlay and overlay restorations: An in vitro and in silico study.

PURPOSE: The objective of this study was to determine the influence of different preparation designs on the fracture strength, failure type, repairability, formation of polymerization-induced cracks, and tooth deformation of structurally compromised molars restored with lithium disilicate inlays and overlays in combination with Immediate Dentin Sealing (IDS). MATERIAL AND METHODS: Human molars (N = 64) were randomly assigned to four different preparation designs: Undermined Inlay (UI), Extended Inlay (EI), Restricted Overlay (RO), and Extended Overlay (EO). The teeth were restored using lithium disilicate partial restorations and subjected to thermomechanical fatigue in a chewing simulator (1,2 × 10 (Mondelli et al., 2007) cycles on 50 N, 8000x 5-55 °C), followed by load to failure testing. In silico finite element analysis was conducted to assess tooth deformation. Polymerization-induced cracks were evaluated using optical microscopy and transillumination. Fracture strengths were statistically analyzed using a Kruskal-Wallis test, while the failure mode, repairability, and polymerization cracks were analyzed using Fisher exact test. RESULTS: The propagation of polymerization-induced cracks did not significantly differ among preparation designs. All specimens withstood chewing simulator fatigue, with no visible cracks in teeth or restorations. Fracture strength was significantly influenced by preparation design, with restricted overlay (RO) showing higher fracture strength compared to extended inlay (EI) (p = .042). Tooth deformation and fracture resistance correlated between in vitro and in silico analyses). UI exhibited a statistically less destructive failure pattern than EO (p < .01) and RO (p = .036). No statistically significant influence of the preparation design on repairability was observed. Groups with higher repairability rates experienced increased tooth deformation, leading to less catastrophic failures. CONCLUSIONS: The preparation design affected the fracture strength of compromised molars restored with lithium disilicate inlays and overlays, with significantly lower fracture strength for an extended inlay. The failure pattern of lithium disilicate overlays is significantly more destructive than that of undermined and extended inlays. The finite element analysis showed more tooth deformation in the inlay restorations, with lower forces in the roots, leading to less destructive fractures. Since cusp coverage restorations fracture in a more destructive manner, this study suggests the undermined inlay preparation design as a viable option for restoring weakened cusps.

Clinical longevity of extensive direct resin composite restorations after amalgam replacement with a mean follow-up of 15 years.

OBJECTIVES: The aim of this retrospective clinical study was to determine the survival of extensive direct resin composite restorations after amalgam replacement on vital molars and premolars after a mean observation period of 15 years. METHODS: Between January 2007 and September 2013, a total of 117 extensive cusp replacing direct resin composite restorations were placed in 88 patients in a general dental practice. These were indicated for replacement of existing amalgam restorations. Tooth vitality, the absence of at least one cusp in premolars, and at least two cusps in molars were considered for inclusion. The long-term follow-up of the restorations, re-evaluated after up to 17 years using the original evaluation criteria is reported. RESULTS: 81 of 88 patients (92.1%) and 106 of 117 restorations (90.6%) were available for follow-up. The cumulative success rate was 62.0% (95% CI: 47.3-76.2, AFR 2.79%) after a mean observation time of 163.4 months, the cumulative survival rate was 74.7% (95% CI: 59.8-89.6%, AFR: 1.70%) after a mean observation time of 179.1 months. The number of cusps replaced in premolars had a statistically significant influence on the success and survival rate of the restorations (HR of respectively, 2.974 and 3.175, p = <0.0005). Premolars with two cusps replaced had 297% more chance of failure than premolars with one cusp replaced. CONCLUSIONS: Extensive direct resin composite restorations placed after amalgam replacement showed good survival after a mean observation period of 15 years. The number of cusps involved had a statistically significant influence on the longevity of the restorations in premolars. CLINICAL SIGNIFICANCE: With good survival and low annual failure rates, direct resin composite restorations are a suitable treatment for repairing extensive defects in posterior teeth involving multiple cusps and surfaces, provided that they are placed by a dentist who has long experience and is skilled in the placement of direct composite materials.

Effect of immediate dentine sealing on the aging and fracture strength of lithium disilicate inlays and overlays.

OBJECTIVES: The objectives of this study were to compare the in vitro, laboratory aging, fracture strength, failure mode and reparability of molars restored with lithium disilicate inlays and overlays in conjunction with or without immediate dentin sealing (IDS). METHODS: Forty extracted, sound human molars were selected and divided into four groups: 1) Inlays with IDS; 2) Inlays without IDS; 3) Overlays with IDS; 4) Overlays without IDS. Standard MOD preparations were made (3 mm wide, 5 mm deep) and in groups 2 and 4, all the cusps were reduced by 2 mm. Directly following tooth preparation, IDS was applied in specimens belonging to groups 1 and 3. The indirect restorations were luted with a heated composite. The restored teeth were subsequently challenged during aging (1.2 million cycles) and thermocycling loading (8000 cycles, 5-55 degrees C). Subsequently, the fracture strength was tested by a load to failure test at 45°. A failure analysis was performed using light- and scanning electron microscopy. The results were analyzed using two-way ANOVA and a Fisher exact test. RESULTS: Mean fracture load + SD (N) were: Group 1 (n = 12): 1610 ± 419; Group 2 (n = 12): 1115 ± 487; Group 3 (n = 12): 2011 ± 496; Group 4 (n = 12): 1837 ± 406. Teeth restored with an onlay were stronger than those restored with an inlay restoration (p < .001). Teeth with IDS were stronger overall than those without IDS (p = .026). The interaction between preparation type and the mode of dentin conditioning had no statistically significant influence on fracture strength (p = .272). Subsequently, custom hypothesis tests showed that there was no statistically significant difference in fracture strength between inlays with IDS and overlays without IDS (p = .27). Overlays tend to fail in a more destructive, non-reparable way (p = .003). SIGNIFICANCE: Both variables IDS and overlay preparation improve overall fracture strength. Inlays with IDS and overlays without IDS didn't differ in fracture strength. Both inlays and overlays are strong enough to withstand physiological chewing forces.