Stability, Micromotion, and Microstrain in Short Implants with High Crown-to-Implant Ratios: Combined in Vitro and...

To evaluate the biomechanical behavior, implant stability, micromotion under loading, and peri-implant bone microstrain of short dental implants (4 mm) compared with longer implants (6, 8, and 10 mm), particularly in high crownto- implant (C/I) ratio scenarios, and to assess the effect of prosthetic splinting as a biomechanical strategy.

A total of 50 implants with internal connections (4-, 6-, 8-, and 10-mm implants) were placed in 9 fresh bovine ribs and restored with standardized polymethyl methacrylate (PMMA) crowns to achieve C/I ratios of 1.22 for 10-mm implants, 1.77 for 8-mm implants, 2.7 for 6-mm implants, and 4.55 for 4-mm implants. A maximum of six implants were placed in each rib, with a 6-mm distance between implants in all cases. Using resonance frequency analysis (RFA) and controlled loading (50 N, 6-degree angulation), implant stability and micromotion were evaluated via image-based analysis. Subsequently, a subset of 4-mm implants was tested with a splinted PMMA bridge. Finite element analysis (FEA) using models consistent with the in vitro setup was performed to evaluate bone microstrain, von Mises stress, and displacement.

Implant stability (implant stability quotient [ISQ] values) increased significantly with implant length, with the 10-mm group having the highest values (mean ISQ = 68.4) (P < .05). Micromotion and FEA displacement were inversely correlated with implant length and positively correlated with the C/I ratio. The 4-mm implants had significantly higher micromotion and microstrain values, but splinting significantly reduced both parameters and achieved a performance comparable to that of longer implants. Von Mises stress values in the peri-implant bone and abutments were highest in the 4-mm group.

Short dental implants correlate with poorer values for implant stability than conventional implants. High C/I ratios in short implants are associated with increased micromovement and microloading of the bone, but splinting improves biomechanical performance and may be advisable when using short implants, especially when implementing immediate loading protocols.