Insertion Torque Value and Implant Stability Quotient: Separate Evaluation and Correlation for Different Clinical Parameters.

PURPOSE: To observe whether the initial implant stability, evaluated by two different methods-the insertion torque value (ITV) and implant stability quotient (ISQ)-may be influenced by different clinical conditions as well as to understand whether it is possible to establish an overall positive correlation between both methods and whether the obtained correlation is maintained for each clinical variable under scope. MATERIALS AND METHODS: The initial implant stability was evaluated by assessing and recording the ITV and the ISQ for each implant included in the study. The independent evolution of each method was observed considering clinical conditions grouped by gender (male or female), age (≤ 60 or > 60 years), arch (mandible or maxilla), location (incisors, canines and premolars, or molars), implant geometry (aggressive tapered or traditional parallel), diameter (3.5, 3.75, 4.3, or 5 mm), length (≥ 10 or < 10 mm), and immediate implantation (yes or no). The Mann-Whitney-Wilcoxon and Kruskal-Wallis localization tests were used to identify intragroup differences. To determine the level of correlation between both methods, the Spearman rank correlation was used. RESULTS: The intragroup comparisons showed that the mandible (P = .03), short implants (P = .03), and delayed implantation (P = .07) subgroups exhibited higher ITVs. The other groups did not show significant differences. The higher ISQ measurements were obtained in the mandible (P = .0002), younger patients (P = .02), diameters of 3.75 mm and 4.3 mm (P = .04), and delayed implantation (P < .0001) subgroups. No differences were found for the other groups. A strong overall correlation (rho = 0.541; P = 8.023e-06) was found between both methods for ITVs up to 40 Ncm once they were accompanied by a linear increase in the ISQ to a value up to 78. From this value, the overall correlation decreased (rho = 0.237; P = .0055). Regarding the clinical conditions, different levels of significant correlations were found for both genders, older patients, maxilla, molar area, aggressive tapered implant geometries, diameters of 4.3 mm, diameters of 5 mm, lengths ≥ 10 mm, and implants placed in healed bone. The other clinical conditions under scope did not exhibit an important correlation between both methods. CONCLUSION: When analyzed separately, clinical conditions such as the arch, implant length and diameter, patient age, and timing of implantation showed an influence on the ITV and the ISQ. An important overall correlation between both methods was found for ITVs of ≤ 40 Ncm. This correlation was maintained for several of the clinical conditions studied.

Effect of crown-to-implant ratio and crown height space on marginal bone stress: a finite element analysis.

BACKGROUND: Crown-to-implant ratio and crown height space, associated with the use of short implants, have been related with marginal bone loss. However, it is unclear which of the two entities would play the most important role on the bone remodelling process. Using a finite element analysis, the present work aims to help clarifying how those two factors contribute for the stress generation at the marginal bone level. A numerical model (reference model), with a crown-to-implant ratio of 4, was double validated and submitted to a numerical calculation. Then, it was modified in two different ways: (a) by decreasing the prosthetic height obtaining crown-to-implant ratios of 3, 2.5 and 2 and (b) by increasing the implants length obtaining a crown-to-implant ratio of 2.08. The new models were also submitted to numerical calculations. RESULTS: The reference model showed a marginal bone stress of 96.9 MPa. The increase in the implants' length did not show statistically significant differences in the marginal bone stress (p-value = 0.2364). The decrease in the prosthetic height was accompanied with a statistically significant decrease in the marginal bone stresses (p-value = 2.2e- 16). CONCLUSIONS: The results represent a paradigm change as the crown height space appears to be more responsible for marginal bone stress than the high crown-to-implant ratios or the implants' length. New prosthetic designs should be attempted to decrease the stress generated at the marginal bone level.