Stability of connected micro-implants and miniplates for skeletal anchorage

Abstract

AIM: Use of skeletal anchorage in orthodontics has gained increasing popularity in both clinical applications and research. The indications for skeletal anchorage range from intrusion of an individual tooth to retraction of the whole dentition, and even orthopaedic movement. However, no study has examined the stability of connected micro-implants. The aim of this investigation was to examine the stability of the connected micro-implants and miniplates. MATERIALS AND METHOD: Three different skeletal anchorage systems were investigated; 1) two 1.5 mm diameter cylindrical micro-implants connected with a 0.021 × 0.025 inch stainless steel (SS) wire, 2) two 1.6 mm diameter tapered micro-implants connected with a 0.021 × 0.025 inch SS wire and 3) two 2 mm diameter cylindrical micro-implants connected by a titanium locking miniplate. The connected micro-implants were fi xed on standardized bovine bone specimens. The connected systems underwent uniaxial pull-out tests at the midpoint of the connecting wire/miniplate by a mechanical testing machine (Instron, model 1185). Statistical analysis, one-way ANOVA, was used to determine differences in the pullout test results between the different groups. RESULTS: Both the connecting titanium miniplate and SS wire connection systems showed severe deformation causing damage at the screw head which broke before the micro-implants failed. The titanium locking miniplate system showed the highest pullout force (529 N) compared with the other two wire connection systems (P < 0.001). The threads in the screw head and the plate holes in the miniplate locking system were advantageous in transmitting force to microimplants compared with using SS archwire and composite resin, as the latter fractured at lower force. The 2 mm miniplate connected micro-implants were also stiffer than the 1.6 and 1.5 mm systems (P < 0.001). The yield force of the 2-mm miniplate (153 N) was signifi cantly higher than the 1.5 mm (88 N) and 1.6 mm (76 N) systems (P < 0.001). The high yield force and stiffness of the miniplate system might well withstand intraoral masticatory and orthodontic force without any deformation. CONCLUSION: This in vitro study demonstrated that connecting two micro-implants with a miniplate results in greater stiffness and yield force. This aids resistance to force and deformation, thus providing a more stable system for orthodontic skeletal anchorage.