Influence of Thread Design on Dental Implant Osseointegration Assayed Using the Lan-Yu Mini-Pig Model

The primary success of implantation is according to osseointegration. The bone-to-implant contact (BIC) % is one of the methods to evaluate the osseointergation. In our study, the mini-pig animal model was used to study the osseointegration in different implant macro-design in early implantation period. Eight mini-pigs were divided into 2 groups and implanted with 2 thread profiles (trapezoidal and square) and 5 thread pitches (0.6, 0.8, 1.0, 1.2, and 1.4 mm) into their jaws. After 8 and 16 weeks, the mini-pigs were sacrificed and the specimen of implant surrounded bone were harvested. The implant surface was detected under scanning electron microscopy (SEM), Masson-Goldner staining (MGS) and immunohistochemical staining (IHC). BIC were obtained under SEM and MGS. Bone formation and maturation were assessed using IHC to detect bone morphogenetic protein-2 (BMP-2) and osteocalcin (OC). The BIC measured for trapezoidal-thread implants with a pitch of 0.8 mm was higher than that of square-thread implants in both the 8- and 16-week groups. The BIC values of the trapezoidal thread profile with a pitch range of 0.6-1.4 mm were not significantly different (P > 0.05) in the 8- and 16-week groups. BMP-2 and OC were detected in both cases, but BMP-2 and OC in the trapezoidal thread group was more regular than the square thread group. The bone in the trapezoidal thread group was more mature. In conclusion, the trapezoidal thread profile with 0.8 mm pitch is the most ideal macro-design for osseointegration.