Effect of restorative, endodontic, and fatigue treatments on the cuspal deflection of maxillary premolars subjected to different cyclic occlusal forces: an in vitro study.

This study aimed to determine the effect of adhesive direct composite restorations, endodontic treatments, and fatigue treatments on the cuspal deflection of maxillary premolars subjected to different cyclic occlusal forces. Thirty intact maxillary second premolars were selected. Ten teeth were left untreated (group IN), 10 teeth were subjected to endodontic and restorative treatment (group FL), and the remaining 10 teeth were subjected to endodontic, restorative, and fatigue treatments (group FT). All teeth were subjected to 5 occlusal compressive loading forces (98, 147, 196, 245, and 294 N) with a universal testing device. A total of 15 experimental groups were obtained with 3 tooth conditions (IN, FL, FT) and 5 different occlusal loading values. Deflection amounts (µm) were measured with laser sensors and recorded, and obtained data were statistically analyzed with one-way analysis of variance at a significance level of .05. Mean cuspal deflection values (µm) and SDs of experimental groups ranged as follows: IN-98 (24.4 ± 19.8), IN-147 (34.8 ± 28.9), IN-196 (43.8 ± 34.7), IN-245 (54.5 ± 46.4), IN-294 (60.3 ± 50.6), FL-98 (56 ± 49.1), FL-147 (62.6 ± 49.6), FL-196 (72.4 ± 52.1), FL-245 (81.3 ± 56), FL-294 (92.2 ± 60.9), FT-98 (77.2 ± 80.9), FT-147 (83.4 ± 81.3), FT-196 (92.6 ± 83.7), FT-245 (102.7 ± 85.4), and FT-294 (124.2 ± 89.5). Mean values of three main experimental groups were as follows: IN (43.5 µm), FL (72.9 µm) and FT (96.0 µm). Significant differences were found between the three main groups and relevant subgroups (P < .001). Highest cuspal deflection values (CDV) were obtained in FT groups. Lowest CDV were obtained in IN groups. FL groups showed higher deflection values than IN groups. CDV increased progressively as the teeth were restored and subjected to fatigue treatment.

Degree of conversion of dual-cure resins light-cured through glass-fiber posts.

PURPOSE: To evaluate the degree of conversion (DC) of dual-curing materials used to lute glass-fiber posts in a simulated root canal polymerized by two different modalities. METHODS: Artificial root canals were used to simulate a clinical condition to lute 45 posts by three different dual curing luting cements (Calibra, Multilink Automix and Variolink II). Two light cure modalities were chosen for each luting cement: standard (S group) 400 mW/cm2 for 120 seconds and high-power (H group) 1200 mW/cm2 for 40 seconds. Raman spectra were collected at different positions in the post surface (1, 3, 5 and 7 mm from the coronal-most portion of the post covered in cement) and the percentage degree of conversion was computed. The data were analyzed using ANOVA and post-hoc Student-Neuman-Keuls t-test (P = 0.05). RESULTS: The DC of the tested luting composites decreased progressively while increasing the distance from the light tip. Regardless of the polymerization modality (H or S) applied. Conversely, the curing modality significantly influenced the DC of the tested materials, evidencing different responses to the same energy density: Calibra seemed to be less dependent on light-curing than the other tested materials, showing a constant behavior. Multilink Automix reached the highest DCs in the S group compared to the H mode. Variolink II showed an interesting drawback in DC at 7 mm when cured in the H model. Dual-cure materials show adequate monomer conversion but when the distance from the curing light increased, a variable, but significant lowering in conversion rate was observed. In addition, the time and power of curing appeared to be material-dependent and should be calibrated individually.

Adhesive restoration of endodontically treated premolars: influence of posts on cuspal deflection.

PURPOSE: To determine, by means of a non-destructive experimental procedure, the effectiveness of adhesive restorations in reducing the cuspal deflection of endodontically treated premolars, with or without root canal fiber posts. MATERIALS AND METHODS: The cuspal deflection of ten sound, intact maxillary premolars was evaluated. A loading device induced deformation by axial force (ranging from 98 to 294 N) applied on the occlusal surface of teeth while laser sensors registered the amount of deflection. Once tested, teeth were endodontically treated and the marginal ridges were removed. The teeth were randomly divided into two groups and restored with: group 1) dual curing adhesive, flowable composite, and microhybrid composite; group 2) the same materials associated with root canal glass fiber post and composite cement. The cuspal deflection test was repeated with the same protocol after restorative procedures, allowing a direct comparison of the same samples. Statistical analysis was performed using ANOVA at a significance level of 0.05. RESULTS: Different average cuspal deflection was detected in the two groups: composite resin with post insertion resulted in lower deformation compared with composite alone. Mean deflection ranged from 3.43 to 12.17 µm in intact teeth, from 14.42 to 26.93 µm in group 1, and from 15.35 to 20.39 µm in group 2. ANOVA found significant differences (p = 0.02). CONCLUSION: Bonded composite restorations with fiber posts may be more effective than composite alone in reducing the cuspal deflection in endodontically treated premolars in which the marginal ridges have been lost.

Degree of conversion of three composite materials employed in the adhesive cementation of indirect restorations: a micro-Raman analysis.

OBJECTIVES: Adhesive luting of indirect restorations can be carried out employing dual- or light-curing materials. This in vitro study evaluated the degree of conversion (DC) of the materials employed in this procedure, seeking how the combination of time and power of curing applied during polymerisation, as well as the temperature of the light-curing composite, influenced the DC. MATERIALS AND METHODS: One hundred and eighty onlays of different thicknesses (2 mm, 3 mm, 4 mm) were luted with three different composites: two dual-curing cements (Variolink II and Calibra) and a light-curing composite (Venus). The same halogen lamp was used with three different modalities selected to provide a constant quantity of energy. The time/power combinations tested were 400 mW/cm(2) for 120 s, 800 mW/cm(2) for 60s and 1200 mW/cm(2) for 40 s. The light-curing composite was employed at room temperature and after preheating at 54 degrees C. Each sample was examined in three positions using the Micro-Raman Dilor HR LabRam spectrometer to evaluate the polymer conversion degree. The data were analysed using analysis of variance and the Student-Newman-Keuls test (p=0.05). RESULTS: The dual-curing materials showed average conversion percentages close to 64%, although onlays thickness clearly influence the degree of conversion, the light-curing composite showed satisfactory results only when onlays thickness was thin, however preheating significantly improved the performance of the light-curing composite under onlays of great thickness. CONCLUSIONS: Optimal luting of indirect restorations is clearly dependent from light source power, irradiation time and dual-cure luting cement or light-curing composite chosen. It should be calibrated for each material to acquire high DCs. Preheating of light-curing only composites allows for the materials to reach optimal conversion degrees.