Influence of Implant Macrodesign on the ISQ Values of Implants Placed in Bone Defects with Different Configurations:...

To evaluate the variations in implant stability quotient (ISQ) values of parallel-walled (PW) and tapered-walled (TW) implants subjected to simulated peri-implant bone defects of different depths and configurations in two different bone densities (Type 2 [D2] and Type 3 [D3]).

A total of 80 implants (40 PW and 40 TW) (width of 4.25 mm, length of 11.5 mm; GMI Dental) were placed in polyurethane blocks simulating D2 and D3 bone densities. The following eight peri-implant defect scenarios were created: (1) bone loss of 1/3 the implant height involving one wall; (2) bone loss of 1/3 the implant height involving two walls; (3) bone loss of 1/3 the implant height involving three walls; (4) bone loss of 1/3 the implant height with circumferential involvement; (5) bone loss of 2/3 the implant height involving one wall; (6) bone loss of 2/3 the implant height involving two walls; (7) bone loss of 2/3 the implant height involving three walls; (8) bone loss of 2/3 the implant height with circumferential involvement. ISQ values were measured with the Osstell Beacon device in two directions (buccolingual and mesiodistal), and mean values were recorded. Statistical analyses included Student's t test, Mann-Whitney U test, chi-square, Fisher's exact test, Friedman test, and linear regression models.

Initial ISQ values (at placement [M0]) indicated high stability (> 70) for both implant designs (PW and TW) in D2 and D3 bone blocks. Progressive bone loss significantly reduced ISQ values (P < .001). In D2 bone, TW implants showed greater stability in some 1/3 bone loss scenarios (two wall [M2]), but PW implants outperformed TW implants in deeper (2/3 bone loss) defects affecting multiple walls (M2, three wall [M3], and four wall [M4]). In D3 bone, PW implants consistently showed superior stability under 2/3 bone loss conditions (single wall [M1], M3, and M4). Multivariate regression confirmed that bone density and extent of bone loss were the strongest predictors of ISQ reduction, while implant design became significant in the presence of advanced circumferential loss.

Bone density and the extent of peri-implant bone loss are key determinants of implant stability. Implant macrodesign plays a relevant role as bone support decreases; moreover, TW implants were more negatively affected than PW implants under advanced bone loss. While ISQ values remained above the low stability threshold (< 60) with 1/3 bone loss, stability dropped markedly when 2/3 of the implant length was compromised.