Finite Element Analysis of Bone Stress in the Posterior Mandible Using Regular and Short Implants, in the Same Context, with Splinted and Nonsplinted Prostheses.

PURPOSE: The aim of this study was to compare the bone stress generated by rehabilitation using regular and short-length Morse taper implants (11 and 5 mm, respectively) in the same context and allied with splinted (SP) and nonsplinted (NSP) prostheses in the posterior area of the mandible using finite element analysis. MATERIALS AND METHODS: Three-dimensional geometric models using regular implants (Ø4 × 11 mm) and short implants (Ø4 × 5 mm) were simulated with a left posterior mandible that had the first premolar tooth and all teeth posterior to that premolar removed. The four experimental groups were as follows: Group 1 NSP (two regular implants and one short implant rehabilitated with nonsplinted prostheses), Group 1 SP (two regular implants and one short implant rehabilitated with splinted prostheses), Group 2 NSP (one regular implant and two short implants rehabilitated with nonsplinted prostheses), and Group 2 SP (one regular implant and two short implants rehabilitated with splinted prostheses). Oblique forces were simulated in molars (365 N) and premolars (200 N). Qualitative and quantitative analyses of the minimum principal stress in bone were performed using the ANSYS Workbench software, version 10.0. RESULTS: The splinted prostheses decreased the stress to the surrounding bone of short implants. Moreover, they also decreased the stress on the surrounding bone adjacent to the tooth. However, the splinted prostheses generated higher stress in the coverage of the surrounding bone for regular intermediate implants and prominently in the bone at the implant cervical region, at the edge crest, compared with the individualized groups. CONCLUSION: The benefits in the use of splinted prostheses are notable for the preservation of the bone surrounding the short implants and tooth; however, it is necessary to evaluate each clinical situation because, in this context, the regular implants are at higher stress than the individualized implants.

Loss of preload in screwed implant joints as a function of time and tightening/untightening sequences.

PURPOSE: The purpose of this study was to determine whether abutment screw tightening and untightening influenced loss of preload in three different implant/abutment interfaces, or on the implant body. MATERIALS AND METHODS: Five custom-fabricated machined titanium implants were used, each with its respective abutment, with different connection types, retention screws, and torque values (external hexagon with titanium screw/32 Ncm, external hexagon with coated screw/32 Ncm, internal hexagon/20 Ncm and internal conical/20 and 32 Ncm). Each implant tested had two strain gauges attached and was submitted to five tightening/untightening sequences. RESULTS: External hexagons resulted in the lowest preload values generated in the implant cervical third (mean of 27.75 N), while the internal hexagon had the highest values (mean of 219.61 N). CONCLUSIONS: There was no immediate significant loss of preload after screw tightening. Tightening/untightening sequences, regardless of the implant/abutment interface design or type of screw used in the study, did not result in any significant loss of initial preload. Conical implant connections demonstrated greater structural reinforcement within the internal connections.

Evaluation of radiographic technique using a new customized film holder for dental implant assessment.

PURPOSE: The aim was to evaluate the reproducibility of a radiographic technique using a new customized film holder in the follow-up of screwed single-tooth implants. MATERIALS AND METHODS: Ten implants placed in the mandible (n = 6) and maxilla (n = 4) of 8 patients were submitted to radiographic assessments. Radiographs were taken using a customized film holder adapted to implant abutment after 4 (T0) and 8 (T1) months of implant placement. Quantitative evaluations were performed through horizontal and vertical measurements to analyze radiographic standardization. RESULTS: No differences were detected after comparison of implant and abutment diameter measurements between radiographs after 4 and 8 months. No significant variations were detected in vertical measurements (implant and abutment length) between radiographs obtained in T0 and T1. CONCLUSIONS: The use of customized film holder adapted to the implant abutment seems to contribute to the standardization of radiographs at different times of screwed single-tooth implants.

Wear resistance of experimental titanium alloys for dental applications.

The present study evaluated microstructure, microhardness and wear resistance of experimental titanium alloys containing zirconium and tantalum. Alloys were melted in arc melting furnace according to the following compositions: Ti-5Zr, Ti-5Ta and Ti-5Ta-5Zr (%wt). Hemispheres and disks were obtained from wax patterns that were invested and cast by plasma. Microstructures were evaluated using optical microscopy and X-ray diffraction (XRD) analysis and also Vickers microhardness was measured. Hemispherical samples and disks were used for 2-body wear tests, performed by repeated grinding of the samples. Wear resistance was assessed as height loss after 40,000 cycles. The data were compared using ANOVA and post-hoc Tukey test. Ti-5Zr presented a Widmanstätten structure and the identified phases were α and α' while Ti-5Ta and Ti-5Ta-5Zr presented α, ß, α' and α" phases, but the former presented a lamellar structure, and the other, acicular. The microhardness of Ti-5Zr was significantly greater than other materials and cp Ti presented wear resistance significantly lower than experimental alloys. It was concluded that wear resistance was improved when adding Ta and Zr to titanium and Zr increased microhardness of Ti-5Zr alloy.