Fracture resistance of teeth with oval canal morphology restored using oval and circular posts.

The study aimed to evaluate the effects of different post morphologies and placement lengths on the fracture resistance of teeth with oval canal morphology that had been restored with crowns. Extracted mandibular premolars with similar dimensions were decoronated. After the root canal treatment, the teeth were mounted on acrylic blocks. Samples were randomly divided into four groups (n = 10 each). In groups C-10 and C-5, 10-mm- and 5-mm-long circular post spaces were created. In groups O-10 and O-5, 10-mm- and 5-mm-long oval post spaces were ultrasonically created. After post cementation, all specimens were restored with composite cores and prepared at height of 6 mm. Thereafter, all teeth were restored with crowns. After thermocycling, all specimens underwent fracture resistance testing. Oval posts and placement at 10-mm depth showed higher fracture resistance than circular posts and placement at 5-mm depth (P < 0.001). Increased post length and use of oval posts enhanced the fracture strength of teeth with oval canal morphology. Based on the results of this study, although the fracture resistance of teeth restored with crowns was enhanced by deep fiber post placement, the use of oval fiber post is recommended in cases where deep placement is impossible. (J Oral Sci 58, 339-345, 2016).

Effect of fluid contamination on reverse torque values in bone-level implants.

INTRODUCTION: Screw loosening is one of the most common mechanical complications within the prosthetic components of dental implants. Clinicians must know if reverse torque values (RTVs) are affected by contamination of the implant abutment screw hole with either blood, saliva or chlorhexidine. METHODS: Forty implants were divided into 4 groups (n = 10). Implants were embedded in epoxy resin and placed in a digital torque meter. Screw holes of 30 implants were contaminated with either chlorhexidine (CG), fresh human saliva (SG), or blood (BG), and the remaining noncontaminated screws served as a control group (NC). Abutment screws were tightened using a hand-held torque meter (25 N·cm). Thermocycling (1500 cycles) was performed, and abutment detorque values were calculated using the digital torque meter. RESULTS: RTVs were lower than insertion torque values for all groups. According to Tukey HSD Test, blood contamination of abutment screws resulted in significantly lower RTVs (18.950 ± 2.641 N·cm) when compared with controls. CONCLUSIONS: Blood contamination of abutment screw holes was shown to significantly decrease RTVs. Blood contamination may result in greater loosening of implant screws in clinical practice.

Infrared thermographic comparison of temperature increases on the root surface during dowel space preparations using circular versus oval fiber dowel systems.

PURPOSE: The purpose was to evaluate temperature increases during dowel space preparations with oval and circular fiber dowel systems. MATERIALS AND METHODS: This study included 42 single-rooted human mandibular premolars. Roots were scanned with cone-beam computerized tomography (CBCT) to determine the ovoid root canal morphology. Root canals were treated with Ni-Ti rotary instruments and obturated. A second CBCT was taken to determine the thinnest dentin thickness of each root. Roots were randomly divided into two groups (n = 21) according to the fiber dowel system used: group 1, circular fiber dowel system (D.T. Light-Post); group 2, oval fiber dowel system (Ellipson Post). Dowel spaces were prepared using a circular fiber dowel drill and a diamond-coated ultrasonic tip with an oval section under water cooling until 9 mm dowel spaces were obtained. Temperature changes were recorded from the thinnest root surfaces using a FLIR E60 thermal imaging camera. RESULTS: Temperature increases were significantly greater with the circular fiber dowel system than with the oval fiber dowel system (p < 0.05). CONCLUSIONS: Although both dowel systems generated high temperature increases on root surfaces, the relatively lower temperature increase associated with the use of oval fiber dowels in ovoid canals makes it preferable to the use of circular fiber dowels.