Implant dentures have substantially higher financial costs than conventional complete dentures (MacEntee and Walton, 1998), although two consensus conferences concluded that a mandibular overdenture supported by two implants is the “minimum standard” of treatment for edentulous patients (Thomason et al., 2012). Others believe that this standard disregards those who cannot afford two implants, and implies that anything less is negligent care (Owen, 2009). Indeed, there is no evidence for a single standard of care for edentulous mandibles with or without implants (Fitzapatrick, 2006), or a link between the number of implants and complications or satisfaction with overdentures (Roccuzzo et al., 2012). Cordioli et al. (1997) monitored 15 patients for five years, each with a mandibular overdenture attached with a ball abutment and rubber o-ring to one midline implant, and the patients remained comfortable and without an implant failure. Liddelow and Henry (2007) reported similar success for 28 patients one year after most had immediate placement of mandibular overdentures on a single midline implant.
Walton et al. (2009) reported results from the first year of this randomized clinical trial, allocating one or two implants in the anterior mandible to retain overdentures with ball abutments and gold matrices about six weeks after implant placement. No implants in the 1-implant group failed; however, five failed in the 2-implant group, all before connecting the dentures to the implants. At one year most participants were satisfied in both groups, and there were no statistical differences in satisfaction or prosthetic maintenance, while the 1-implant group required significantly less time and financial costs for the initial treatment. Kronström et al. (2010) also allocated participants randomly to receive one or two mandibular anterior implants with ball patrices and O-ring matrices to connect overdentures immediately after placing the implants. Three (18%) participants in the 1-implant group and six (32%) in the 2-implant group lost implants during the first year. Others reported that time and costs are similar to maintain different attachment systems for implant overdentures (Cehreli et al., 2010), although the evidence remains inconclusive given the various ways that data have been reported (Bryant et al., 2007). We conclude from the available evidence that implant survival, participant satisfaction, and ongoing maintenance of overdentures on one or two implants are similar for at least one year, and the single-implant has lower initial costs.
We now aim to test the null hypothesis that there is no significant difference in participant satisfaction after 5 years between the one-implant and two-implant mandibular overdenture groups. Our secondary aims are to assess changes in satisfaction between and within each group over five years, and differences in implant survival and prosthetic maintenance between groups.