The effect of zirconia thickness on the biaxial flexural strength of zirconiaceramic bilayered discs.

The aim of this study was to assess the effect of zirconia core thickness on the biaxial flexural strength values of zirconia-porcelain bilayered discs. A total of 60 discs with 0.3, 0.4, and 0.5 mm thickness were obtained from a fully sintered zirconia block. A 1.5-mm thick layer of veneer porcelain was fired on the zirconia specimens and biaxial flexural strength tests were performed on the bilayered discs. In each group, the loading surface was the veneer porcelain in half of the specimens (core in tension) and the zirconia core surface in the other half (core in compression). The zirconia core thickness had no effect on the biaxial flexural strength of zirconiaporcelain bilayered discs when the core was in tension (p>0.05). Whereas, when the core was in compression, an increase in the zirconia core thickness resulted in an increase in the biaxial flexural strength (p<0.05).

In vitro effect of cavity disinfectants on the bond strength of dentin bonding systems.

OBJECTIVE: To evaluate the effect of two cavity disinfectants, a 2% chlorhexidine and a 1% benzalkonium chloride solution, on the shear and tensile bond strengths of dentin bonding systems to dentin. METHOD AND MATERIALS: Superficial dentin was exposed from 84 freshly extracted human third molars. The teeth were randomly assigned to two main groups according to the bonding agent used, either One Step or Optibond Solo. Each dentin bonding system had six test groups (three for shear, three for tensile testing), and each test group had a control and two cavity disinfectant groups. In the control groups, dentin bonding systems were applied after etching the dentin, whereas in the cavity disinfectant groups, dentin was conditioned and treated for 20 seconds with the disinfectants before applying the dentin bonding systems. A hybrid resin composite then was applied to all treated samples. After storage in distilled water at 37 degrees C for 24 hours, shear and tensile tests were performed. Data were analyzed using Kruskall-Wallis and Mann-Whitney U tests. RESULTS: The mean shear and tensile bond strengths of One Step and Optibond Solo were not significantly different from each other, and the cavity disinfectants also had no significant effects on shear and tensile bond strength values versus the controls. CONCLUSION: The results indicate that the use of 2% chlorhexidine and 1% benzalkonium chloride solutions as cavity disinfectants after etching the dentin did not affect the shear and tensile bond strengths of One Step and Optibond Solo.

Oral toxicity of pefloxacin, norfloxacin, ofloxacin and ciprofloxacin: comparison of biomechanical and histopathological effects on Achilles tendon in rats.

Four fluoroquinolones (pefloxacin, norfloxacin, ofloxacin and ciprofloxacin) were compared according to their biomechanical and histopathological effects on rat Achilles tendon. Wistar rats were divided into one untreated control and four treatment groups in parallel. Pefloxacin mesylate dihydrate (40 mg/kg), norfloxacin (40 mg/kg), ofloxacin (20 mg/kg) and ciprofloxacin (50 mg/kg) were administered by gavage twice daily for three consecutive weeks. 6 weeks after treatment, the test animals were euthanised and Achilles tendon specimens were collected. A computer monitored tensile testing machine was utilised for biomechanical testing. The mean elastic modulus of the control group was significantly higher than that of the norfloxacin and pefloxacin groups (p<0.05 and p<0.01, respectively). The mean yield force (YF) of the control group was significantly higher than those of ciprofloxacin, norfloxacin and pefloxacin groups (p<0.001, p<0.05 and p<0.01, respectively). The mean ultimate tensile force (UTF) of the control group was significantly higher than of the ciprofloxacin, norfloxacin, and pefloxacin groups (p<0.001, p<0.05 and p<0.01, respectively). Hyaline degeneration and fibre disarrangement were observed in the tendons of the ciprofloxacin, pefloxacin, and ofloxacin treated-groups, whereas myxomatous degeneration was observed only in the ciprofloxacin and pefloxacin groups. In conclusion, these findings in our rat model reveal significant deterioration of biomechanical parameters following fluoroquinolone exposure, and indicate significantly higher biomechanical toxicity for ciprofloxacin and pefloxacin.

Effects of calcitonin on the biomechanics, histopathology, and radiography of callus formation in rats.

BACKGROUND: This study was designed to examine the effect of salmon calcitonin on fracture repair. METHODS: A transverse middiaphyseal fracture of the right tibia was surgically induced, and stabilized by an intramedullary Kirschner wire. Eighty male Wistar rats were arbitrarily assigned to four groups of 20 animals each. Groups I and II were the controls and did not receive any medication but did receive placebo injections. The other two groups received 5 IU/kg/day salmon calcitonin intramuscularly for 6 weeks (Group III) or for 10 weeks (Group IV) postoperatively. The formation and healing of the bones were determined by radiographic and histopathological analyses and by biomechanical tests. RESULTS: In radiographic examinations, there were no statistically significant differences between groups I and III at week 6 or between groups II and IV at week 10. However, the histopathological evaluation scores were higher in the calcitonin group at the early stage (6 weeks) of fracture healing, which indicates a more mature callus formation (P < 0.05). The values for maximum torsional moment during fracture were higher in the calcitonin group in both stages of fracture healing (P < 0.01). CONCLUSIONS: This study could have two important clinical implications. (1) Higher scores for the histopathological evaluation and a greater resistance to moment force applied at an early stage (week 6) of fracture healing imply that calcitonin intake might enable us to allow earlier mobilization and weight-bearing in clinical cases with rigid fixation. (2) At a late stage of fracture healing (week 10), the significantly better (P < 0.0001) results obtained in the biomechanical parameters used might imply that calcitonin intake could enable us to perform early implant removal, and strongly suggest that the strength and quality of the callus formation could be improved by administering calcitonin following a fracture.

Resistance to fracture of endodontically treated teeth restored with different post systems.

STATEMENT OF PROBLEM: Very little is known about the resistance to fracture of endodontically treated teeth restored with newly developed esthetic post systems. Purpose. This in vitro study compared the effect of 1 titanium and 3 esthetic post systems on the fracture resistance and fracture patterns of crowned, endodontically treated teeth. MATERIAL AND METHODS: A total of 40 recently extracted human maxillary canines with their crowns removed were endodontically treated. Four groups of 10 specimens were formed. Teeth were restored with titanium, quartz fiber, glass fiber, and zirconia posts and numbered as groups 1, 2, 3, and 4, respectively. All posts were cemented with Single Bond dental adhesive system and dual-polymerizing RelyX ARC adhesive resin cement. All teeth were restored with composite cores, and metal crowns were fabricated and cemented with glass ionomer cement. Each specimen was embedded in acrylic resin and then secured in a universal load-testing machine. A compressive load was applied at a 130-degree angle to the long axis of the tooth until fracture, at a crosshead speed of 1 mm/min. One-way analysis of variance and a Tukey test were used to determine the significance of the failure loads between groups (P<.001). A non-parametric chi(2) test was conducted for evaluation of the mode of failure (P<.001). RESULTS: The mean failure loads (kg) were 66.95, 91.20, 75.90, and 78.91 for groups 1 to 4, respectively. Teeth restored with quartz fiber posts (group 2) exhibited significantly higher resistance to fracture (P<.001) than the other 3 groups. Teeth restored with glass fiber and zirconia posts (groups 3 and 4) were statistically similar (P>.05). Fractures that would allow repair of the tooth were observed in groups 2 and 3, whereas unrestorable, catastrophic fractures were observed in groups 1 and 4 (P<.001). CONCLUSION: Within the limitations of this study, significantly higher failure loads were recorded for root canal treated teeth restored with quartz fiber posts. Fractures that would allow repeated repair were observed in teeth restored with quartz fiber and glass fiber posts.