Paulo Henrique Orlato Rossetti

Correlation between margin fit and microleakage in complete crowns cemented with three luting agents

Microleakage can be related to margin misfit. Also, traditional microleakage techniques are time-consuming. This study evaluated the existence of correlation between in vitro margin fit and a new microleakage technique for complete crowns cemented with 3 different luting agents. Thirty human premolars were prepared for full-coverage crowns with a convergence angle of 6 degrees, chamfer margin of 1.2 mm circumferentially, and occlusal reduction of 1.5 mm. Ni-Cr cast crowns were cemented with either zinc phosphate (ZP) (S.S. White), resin-modified glass-ionomer (RMGI) (Rely X Luting Cement) or a resin-based luting agent (RC) (Enforce). Margin fit (seating discrepancy and margin gap) was evaluated according to criteria in the literature under microscope with 0.001 mm accuracy. After thermal cycling, crowns were longitudinally sectioned and microleakage scores at tooth-cement interface were obtained and recorded at x100 magnification. Margin fit parameters were compared with the one-way ANOVA test and microleakage scores with Kruskal-Wallis and Dunns tests (α=0.05). Correlation between margin fit and microleakage was analyzed with the Spearmans test (α=0.05). Seating discrepancy and marginal gap values ranged from 81.82 μm to 137.22 μm (p=0.117), and from 75.42 μm to 78.49 μm (p=0.940), respectively. Marginal microleakage scores were ZP=3.02, RMGI=0.35 and RC=0.12 (p<0.001), with no differences between RMGI and RC scores. The correlation coefficient values ranged from -0.27 to 0.30 (p>0.05). Conclusion: Margin fit parameters and microleakage showed no strong correlations; cast crowns cemented with RMGI and RC had lower microleakage scores than ZP cement.

Association Between Sleep Bruxism and Temporomandibular Disorders: A Polysomnographic Pilot Study

Abstract The aim of this study was to verify the association between sleep bruxism (SB) and temporomandibular disorders (TMD) in a sample of 14 TMD patients and 12 healthy control subjects. All participants were evaluated using a clinical questionnaire, visual analog scale (VAS) for TMJ/muscle palpation, and by functional examination. The experimental group was divided into three TMD subgroups: joint sounds and pain, muscular tenderness, and mixed diagnosis. All participants underwent polysomnographic recording (PSG). A second clinical examination was then carried out to verify the relationship between rhythmic masticatory muscle activity and pain/tenderness on the following morning. The experimental and control groups presented VAS mean scores of 36.85±23.73 mm and 0 mm, respectively. The presence of SB was neither associated with TMD (p>0.05) nor with pain on palpation (p>0.05). Further research with a more representative sample of each TMD subgroup is necessary to elucidate its interaction with SB.

THE INFLUENCE OF SCREW TYPE, ALLOY AND CYLINDER POSITION ON THE MARGINAL FIT OF IMPLANT FRAMEWORKS BEFORE AND AFTER LASER WELDING

Misfit at the abutment-prosthetic cylinder interface can cause loss of preload, leading to loosening or fracture of gold and titanium screws. Objectives: To evaluate the influence of screw type, alloy, and cylinder position on marginal fit of implant frameworks before and after laser welding. Methods: After Estheticone-like abutments were screwed to the implants, thirty plastic prosthetic cylinders were mounted and waxed-up to fifteen cylindrical bars. Each specimen had three interconnected prosthetic components. Five specimens were one-piece cast in titanium and five in cobalt-chromium alloy. On each specimen, tests were conducted with hexagonal titanium and slotted gold screws separately, performing a total of thirty tested screws. Measurements at the interfaces were performed using an optical microscope with 5 μm accuracy. After sectioning, specimens were laser welded and new measurements were obtained. Data were submitted to a four-way ANOVA and Tukeys multiple comparisons test (α =0.05). Results: Slotted and hexagonal screws did not present significant differences regarding to the fit of cylinders cast in titanium, either in one-piece casting framework or after laser welding. When slotted and hexagonal screws were tested on the cobalt-chromium specimens, statistically significant differences were found for the one-piece casting condition, with the slotted screws presenting better fit (24.13μm) than the hexagonal screws (27.93 μm). Besides, no statistically significant differences were found after laser welding. Conclusions: 1) The use of different metal alloys do exert influence on the marginal fit, 2) The slotted and hexagonal screws play the exclusive role of fixing the prosthesis, and did not improve the fit of cylinders, and 3) cylinder position did not affect marginal fit values.

Marginal fit at cylinder-abutment interface before and after overcasting procedure.

The aim of this study was to measure marginal fit at cylinder-abutment interface, before and after overcasting procedure. A hexagonal implant was fixed to a stainless steel base and a Estheticone-like abutment used during all the experiment. Before casting procedure, gold (Group I) and Ni-Cr-Be (Group II) premachined cylinders were tightened to the abutment with gold and titanium screws (in both groups), with 10Ncm and 20Ncm torque values for the same screw type. Vertical measures were taken at the light microscope (Mitutoyo 5050, Tokyo, Japan) three times in six different parts along the abutment-cylinder interface for each torque value. Cylinders were overcast with Ag-Pd (Group I) or Ni-Cr-Be (Group II) alloy. After casting, the same measures and torque values were repeated. Intragroup differences (10 or 20Ncm torque values, before and after casting) and intergroup differences (10 and 20Ncm torque values, before or after casting) were analyzed by the Paired t Test; (p<0.05). Intragroup differences were observed for G-I (gold, 20Ncm, titanium screw, p=0.044) and for G-II (Ni-Cr-Be, 10Ncm, gold screw, p=0.002). Intergroup differences only were not observed in the G-II group (Ni-Cr-Be, 10 and 20Ncm, titanium screw, p=0.534). Within the limits of this study, the following conclusions can be drawn: 1) Regardless of screw type, marginal misfit was higher for Ni-Cr-Be cylinders after casting, but within acceptable levels of fit; 2) The combination of gold cylinders with gold or titanium screws was the most effective to reduce marginal misfit; 3) Both screw types did not improve marginal fit of Ni-Cr-Be cylinders after overcastting, and 4) Although a 20Ncm torque improved marginal fit in all situations, its use is not recommended due to the increased risk of prosthesis failure. Ni-Cr-Be alloys may be successfully used in single-tooth implant restorations, with no damage to the fit between abutment and prosthetic cylinder.