Fracture load of CAD/CAM ultrathin occlusal veneers luted to enamel or dentin.

OBJECTIVES: To evaluate, in vitro, the fracture load of IPS e.max CAD occlusal veneers at thicknesses of either 0.3 or 0.6 mm luted to enamel or dentin. MATERIALS AND METHODS: Fifty human molars were randomly distributed into five groups (n = 10): G1 - healthy teeth (control); G2-0.3-mm-thick veneers luted to enamel; G3-0.6-mm-thick veneers luted to enamel; G4-0.3-mm-thick veneers luted to dentin; and G5-0.6-mm-thick veneers luted to dentin. After the luting procedures, the specimens were immersed in distilled water at 37°C for 24 hours and then subjected to mechanical loading (106 cycles at 200 N load). The specimens were subjected to a fracture load test in a universal testing machine. Two-way ANOVA and Tukey's test (α = 0.05) were used to analyze data. RESULTS: Only the thickness factor was significant (P = .002). Values of fracture load followed by distinct letters represent significant differences (P < .05): G1 (3204 N ± 730)ab ; G2 (3144 N ± 729)ab ; G3 (2489 N ± 606)b ; G4 (3591 N ± 776)a ; and G5 (2770 N ± 598)ab . CONCLUSION: IPS e.max ultrathin occlusal veneers luted to enamel or dentin obtained fracture load comparable to that of the healthy tooth. CLINICAL SIGNIFICANCE: IPS e.max CAD ultrathin occlusal veneers at 0.3 or 0.6-mm-thick seem to provide good perspectives in relation to the clinical use.

Bone Strength in Growing Rats Treated with Fluoride: a Multi-dose Histomorphometric, Biomechanical and Densitometric Study.

Bone deformation and fragility are common signs of skeletal fluorosis. Disorganisation of bone tissue and presence of inflammatory foci were observed after fluoride (F-) administration. Most information about F- effects on bone has been obtained in adult individuals. However, in fluorosis areas, children are a population very exposed to F- and prone to develop not only dental but also skeletal fluoroses. The aim of this work was to evaluate the bone parameters responsible for the effect of different doses of F- on fracture load of the trabecular and cortical bones using multivariate analysis in growing rats. Twenty-four 21-day-old Sprague-Dawley rats were divided into four groups: F0, F20, F40 and F80, which received orally 0, 20, 40 or 80 µmol F-/100 g bw/day, respectively, for 30 days. After treatment, tibiae were used for measuring bone histomorphometric and connectivity parameters, bone mineral density (BMD) and bone cortical parameters. The femurs were used for biomechanical tests and bone F- content. Trabecular bone volume was significantly decreased by F-. Consistently, we observed a significant decrease in fracture load and Young's modulus (YM) of the trabecular bone in F--treated groups. However, cortical bone parameters were not significantly affected by F-. Moreover, there were no significant differences in cortical nor trabecular BMD. Multivariate analysis revealed a significant correlation between the trabecular fracture load and YM but not with bone volume or BMD. It is concluded that when F- is administered as a single daily dose, it produces significant decrease in trabecular bone strength by changing the elasticity of the trabecular bone.

Thickness of immediate dentin sealing materials and its effect on the fracture load of a reinforced all-ceramic crown.

OBJECTIVES: The objective of this study is to evaluate, in vitro, the thickness of immediate dentin sealing (IDS) materials on full crown preparations and its effect on the fracture load of a reinforced all-ceramic crown. MATERIALS AND METHODS: SIXTY PREMOLARS RECEIVED FULL CROWN PREPARATION AND WERE DIVIDED INTO THE FOLLOWING GROUPS ACCORDING TO THE IDS TECHNIQUE: G1-control; G2-Clearfil SE Bond; and G3-Clearfil SE Bond and Protect Liner F. After the impressions were taken, the preparations were temporized with acrylic resin crowns. IPS empress 2 restorations were fabricated and later cemented on the preparations with Panavia F. 10 specimens from each group were submitted to fracture load testing. The other 10 specimens were sectioned buccolingually before the thicknesses of Panavia F, Clearfil SE Bond and Protect Liner F were measured in 10 different positions using a microscope. RESULTS: According to analysis of variance and Tukey's test, the fracture load of Group 3 (1300 N) was significantly higher than that of Group 1 (1001 N) (P < 0.01). Group 2 (1189 N) was not significantly different from Groups 1 and 3. The higher thickness of Clearfil SE Bond was obtained in the concave part of the preparation. Protect Liner F presented a more uniform range of values at different positions. The thickness of Panavia F was higher in the occlusal portion of the preparation. CONCLUSIONS: The film thickness formed by the IDS materials is influenced by the position under the crown, suggesting its potential to increase the fracture load of the IPS empress 2 ceramic crowns.

Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns

OBJECTIVE: This study investigated the durability of repaired all-ceramic crowns after cyclic loading. MATERIAL AND METHODS: Eighty In-ceram zirconia crowns were fabricated to restore prepared maxillary premolars. Resin cement was used for cementation of crowns. Palatal cusps were removed to simulate fracture of veneering porcelain and divided into 4 groups (n = 20). Fracture site was treated before repair as follows: roughening with diamond bur, (DB); air abrasion using 50 µm Al2O3, (AA) and silica coating using Cojet system followed by silane application, (SC). Control group (CG) 20 specimens were left without fracture. Palatal cusps were repaired using composite resin. Specimens were stored in water bath at 37ºC for one week. Ten specimens of each group were subjected to cyclic loading. Fracture load (N) was recorded for each specimen using a universal testing machine. Two-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) test (a=.05) were used for statistical analysis. RESULTS: There was statistically significant difference between control and tested groups, (p<0.001). Post Hoc analysis with the Tukey HSD test showed that cyclic loading fatigue significantly decreased means fracture load of control and test groups as follows (CG, 950.4±62.6 / 872.3±87.4, P = 0.0004), (DB, 624.2 ±38 / 425.5± 31.7, P <.001), (AA, 711.5 ±15.5 / 490 ± 25.2, p <0.001) and (SC, 788.7 ± 18.1 / 610.2 ± 25.2, P <.001), while silica coating and silane application significantly increased fracture load of repaired crowns (p<0.05). CONCLUSION: Repair of fractured In-ceram zirconia crowns after chairside treatment of the fracture site by silica coating and silane application could improve longevity of repaired In-ceram zirconia crowns.