Primary implant stability of two implant macro-designs in different alveolar ridge morphologies: an in vitro study

The primary aim of this in vitro study was to investigate the primary implant stability obtained in immediate and late implant placement scenarios. Secondary aims evaluated the effect of two distinct implant macro-designs and examined the correlation between resonance frequency analysis (RFA) and final insertion torque.

Partially edentulous maxillary models including six single sites simulating extraction sockets and healed alveolar ridges were used. Virtual implant planning facilitated static computer-assisted implant placement of bone level implants with either a shallow-threaded and cylindrical (BL), or deep-threaded and tapered implant macro-design (BLX). The insertion torque was continuously measured during implant placement, and RFA was performed after final implant positioning.

One-hundred and forty-four implants were equally distributed to two alveolar ridge morphologies and implant designs. Higher final insertion torque and RFA values were observed for implants placed in healed ridges compared to extraction sockets (40.8 ± 13.5 vs. 20.6 ± 8.4 Ncm, and RFA 70.7 ± 2.8 vs. 59.6 ± 6.5, both p < 0.001), and for BL implants compared to BLX implants (35.7 ± 13.0 vs. 25.7 ± 8.9 Ncm, and RFA 66.7 ± 4.4 vs. 63.6 ± 4.9, both p < 0.001). Insertion torque and mean RFA values positively correlated (r = 0.742; p < 0.001).

Primary implant stability is significantly affected by the alveolar ridge morphology and the implant macro-design, demonstrating higher values in healed sites and shallow-threaded, cylindrical implants. Therefore, a tailored selection of the implant design depending on the implant placement and loading protocol is recommended.