Evaluation of the correlation between insertion torque and primary stability of dental implants using a block bone test

PURPOSE: Implant stability at the time of surgery is crucial for the long-term success of dental implants. Primary stability is considered of paramount importance to achieve osseointegration. The purpose of the present study was to investigate the correlation between the insertion torque and primary stability of dental implants using artificial bone blocks with different bone densities and compositions to mimic different circumstances that are encountered in routine daily clinical settings. METHODS: In order to validate the objectives, various sized holes were made in bone blocks with different bone densities (#10, #20, #30, #40, and #50) using a surgical drill and insertion torque together with implant stability quotient (ISQ) values that were measured using the Osstell Mentor. The experimental groups under evaluation were subdivided into 5 subgroups according to the circumstances. RESULTS: In group 1, the mean insertion torque and ISQ values increased as the density of the bone blocks increased. For group 2, the mean insertion torque values decreased as the final drill size expanded, but this was not the case for the ISQ values. The mean insertion torque values in group 3 increased with the thickness of the cortical bone, and the same was true for the ISQ values. For group 4, the mean insertion torque values increased as the cancellous bone density increased, but the correlation with the ISQ values was weak. Finally, in group 5, the mean insertion torque decreased as the final drill size increased, but the correlation with the ISQ value was weak. CONCLUSIONS: Within the limitations of the study, it was concluded that primary stability does not simply depend on the insertion torque, but also on the bone quality.

Effect of microthreads on removal torque and bone-to-implant contact: an experimental study in miniature pigs

PURPOSE: The objective of this study was to evaluate the effect of microthreads on removal torque and bone-to-implant contact (BIC). METHODS: Twelve miniature pigs for each experiment, a total of 24 animals, were used. In the removal torque analysis, each animal received 2 types of implants in each tibia, which were treated with sandblasting and acid etching but with or without microthreads at the marginal portion. The animals were sacrificed after 4, 8, or 12 weeks of healing. Each subgroup consisted of 4 animals, and the tibias were extracted and removal torque was measured. In the BIC analysis, each animal received 3 types of implants. Two types of implants were used for the removal torque test and another type of implant served as the control. The BIC experiment was conducted in the mandible of the animals. The P1-M1 teeth were extracted, and after a 4-month healing period, 3 each of the 2 types of implants were placed, with one type on each side of the mandible, for a total of 6 implants per animal. The animals were sacrificed after a 2-, 4-, or 8-week healing period. Each subgroup consisted of 4 animals. The mandibles were extracted, specimens were processed, and BIC was analyzed. RESULTS: No significant difference in removal torque value or BIC was found between implants with and without microthreads. The removal torque value increased between 4 and 8 weeks of healing for both types of implants, but there was no significant difference between 8 and 12 weeks. The percentage of BIC increased between 2 and 4 weeks for all types of implants, but there was no significant difference between 4 and 8 weeks. CONCLUSIONS: The existence of microthreads was not a significant factor in mechanical and histological stability.

A Finite Element Analysis on the Effectiveness and Ideal Positions of the Tansfixators in Pedicle Screw Instrumentation / 대한정형외과연구학회지

Recent studies suggest that addition of transfixators to pedicle screw instrumentation enhances rotational stability of the constructs. However, the effectiveness of the transfixators along with their ideal numbers and positions still remains unclear. In this study, finite element analysis was performed to suggest the most effective positions of the transfixators based on their numbers. For this purpose, a finite element model of a spinal segment(L3-5) with total vertebrectomy at L4 and pedicle screw instrumentation was developed. The finite element model was made with 3-D 8 node solid elements so that they are more realistic and closer to the actual human vertebrae than the preciously published models. On this model, the transfixator(s) were placed along the pre-determined position(s) along the rod while its number was varied between 1 and 2. Appropriate boundary conditions were designated and rotational moment of 6.4 Nm was applied both in axial rotation and lateral bending. Improvement in rotational stability due to addition of the transfixator(s) was calculated as the percent decrease in motion relative to the case without. Results suggested that with one transfixator the rotational stability increased by the average of 19.0% and 6.1% against axial rotation and lateral bending, respectively. With two, the corresponding improvements were 32.3% and 10.7%. Against axial rotation, it was most effective when transfixator was placed at the middle of the rod(22.9%) for one transfixator and at the 1/3 and 2/3 sites along the rod(35.8%) for two. Against lateral bending, the ideal position(s) were at the proximal end(10.7%) for one transfixator and at the proximal and distal ends of the construct(17.7%) for two. It was also found that adding of a transfixator was more sensitive against lateral bending than against axial rotation(78% versus 64%). In conclusion, base on our biomechanical results, it can be suggested that the ideal positions for the ators are located at the equidistance from the both ends of the rod against axial rotation and at the both ends against lateral bending.