Macrogeometry and Bone Density Control Over the Primary Stability of 6-mm Implants: An In Vitro Study

Purpose: Short implants are used in clinical conditions of insufficient vertical b: one availability. This study aimed to compare the primary stability of short implants with different macrodesigns placed in different bone densities in vitro. Materials and Methods: One hundred twenty short (6-mm) implants (20/group) were placed at the bone level in commercially available polyurethane blocks representing type I and IV bone quality. The groups were as follows: test A group (4.6-mm diameter with tapered body), test B group (4.8-mm diameter/cylindric microthreaded neck), and test C group (4.8-mm diameter, cylindric body with polished collar, three threads at the intraosseous portion). Implant primary stability was assessed using insertion torque and implant stability quotient (ISQ) values. A blinded calibrated clinician recorded all measurements. Statistical comparisons were completed using a one-way analysis of variance (ANOVA) and Bonferroni posttests. Results: The insertion torque values (mean ± SD) for groups A, B, and C in type I bone were 52.50 ± 5.25, 49.00 ± 5.98, and 46.25 ± 3.93, and in type IV bone, the values were 14.00 ± 2.05, 15.50 ± 2.76, and 9.75 ± 1.11, respectively. Also, the ISQ values were 67.25 ± 2.760, 69.25 ± 1.67, and 61.80 ± 5.68 (type I bone); and 53.27 ± 1.99, 60.65 ± 2.11, and 51.97 ± 4.51 (type IV bone), respectively. The comparison showed statistical differences in ISQ (Bonferroni adjusted P <.0001) for the A and B groups but also for the A and C groups (type I bone), in soft bone between the A and B groups and between the B and C groups, and also for the insertion torque values for the A and C groups and between the B and C groups in type IV bone. Conclusion: Short implant macrogeometry defines primary stability. Short implants with 6-mm length and multiple threads can achieve good primary stability in vitro in type I and IV artificial bone. Int J Oral Maxillofac Implants 2021;36:322–326. doi: 10.11607/jomi.8804