Immediate placement of regular diameter implants in molar post-extraction sites of the maxilla and mandible resulted in a high implant failure rate during a 1-year follow-up period.

The implant survival rate was 73.3% after 1 year in function. The performance of immediate placements in post-extraction sites was also analysed in the Cafiero et al., Atieh et al., Tallarico et al., and Checchi et al. prospective 1-year studies [15, 20,21,22]. They reported a 1-year implant survival rate of 100%, 66.7%, 100%, and 89.4%, respectively. In the present study, an implant diameter of 4.3 mm was used in all the patients; the aforementioned studies used implant diameters of 4.8 mm, 8–9 mm, 7 mm, and 6–8 mm, respectively. The Atieh et al. [15] implant survival rate was the lowest (66.7%) and comparable with the survival rate in the present study, but it must be mentioned that the implant placement was combined with immediate provisionalization, whereas in the other studies, the implants were restored after 3–6 months. It was reported that implant stability in healed bone in the early postoperative period is positively influenced by the macro-thread design. A large thread depth with sharp thread edges and a small thread pitch (distance between two threads) gives higher implant stability than a small thread depth with v-shaped edges and large thread pitch [23, 24]. Finding enough primary stability in molar post-extraction sites may be difficult because of the thin interradicular bony septum. However, it is claimed that wide and ultra-wide diameter implants can be used in post-extraction molar sites to overcome this lack of primary stability [14]. All the failed implants of the present study became mobile within 6 months after functional loading. It can be assumed that, notwithstanding the initial primary stability of more than 45 Ncm, impaired healing with too less initial contact between implant and bone was the main reason for the failures. In the present study, implants were used implants with a large thread depth, sharp thread edges, but with a regular thread pitch and a regular diameter. The Cafiero et al., Tallarico et al., and Checchi et al. prospective 1-year delayed loading studies [20,21,22] used wide or ultra-wide diameter implants with a small thread pitch. This difference might be the reason for the much lower implant survival rate in the present study.