Apical fracture of one-piece titanium-zirconium mini-implant for mandibular overdenture: a prospective 3-year follow-up

Abstract

Objectives: To assess the 3-year clinic-radiographic features and risk factors for apical fracture of mini-implants for mandibular overdentures. Material and Methods: Participants in a clinical trial (n = 74) were assessed for post-insertion identification of apical fractures of one-piece titanium–zirconium mini-implants (Straumann Mini-Implant System). Fractures were identified during implant insertion or in follow-up imaging exams. Cases were clinically and radiographically monitored up to the 3-year follow-up. Results: Five implants in five patients had apical fractures (1.69% of the 296 inserted implants). No clinical signs of peri-implant complications were found, and overall treatment outcomes were positive for all patients. Satisfactory osseointegration was achieved, and no evidence of periapical pathology was noted on panoramic radiographs. The patients were notified about the apical implant fracture at the time of the surgery, and during follow-up appointments, they were reassured about the absence of further complications in the long term. It was hypothesized that the increased risk of fracture was associated with high insertion torques (around 80 N cm) and implant insertion in areas where the tip engages into a hard basal cortical bone (Types I–II) with an inclined cortical surface in the lingual aspect of the alveolar bone. Conclusions: The incidence of apical fracture was low and did not result in any clinically relevant complications and may be detected during the surgery or in follow-up radiographs. Although the intraosseous implant tip fragment may not be of major concern, additional caution to prevent excessive insertion torque and to avoid anatomical regions of higher risk may be advisable.