Fracture incidence in mandibular overdentures retained by one or two implants

Abstract

Statement of problem: While 2 to 4 implants are preferred to retain and stabilize an implant overdenture, some reports suggest a single implant is adequate to retain an overdenture. Denture fracture is one of the common complications with overdentures; however, there is no information on the incidence of fractures when dentures are retained by 1 implant.

Purpose: The purpose of this study was to compare the fracture incidence of mandibular overdentures retained by 1 and 2 implants.

Material and methods: The records of 85 subjects enrolled in the Vancouver Implant Prosthesis (VIP) clinical trial between 2003 and 2008 and followed up for at least 17 months were reviewed retrospectively. From the clinical records, subjects who had experienced a fractured overdenture were identified. A fracture was considered as either a visible crack in the acrylic resin or complete separation of the denture parts. The same clinical records listed 3 denture fracture sites: over the implant, elsewhere, or unknown. A chi-square test was used to compare the incidence of fracture (alpha=.05). Kaplan-Meier and log rank tests were used to compare the survival rate of overdenture or "time to fracture" (alpha=.05).

Results: Forty-two subjects received a single implant, and 43 received 2 implants. In total, there were 17 fractures recorded for 13 subjects. Nine single-implant subjects experienced 11 denture fractures, while 4 double-implant subjects experienced 6 fractures. There was no significant difference in the incidence of denture fractures in prostheses retained by 1 or 2 implants. When denture fractures did occur, they were found most frequently in areas adjacent to the implant(s).

Conclusions: The incidence of denture base fractures was not significantly different between overdentures retained by 1 implant and those retained by 2 implants. When fractures did occur, they tended to be in areas adjacent to implants.