Abstract: Objective Using clinical observation questionnaires, imaging methods and other detections, to compare marginal bone loss (MBL), mechanical complications and patient satisfaction of mandibular ball cap overdenture supported by narrow neck and regular neck implant. Methods The over denture design for edentulous mandible was to implant two implants, while the upper attachment was no-splint cap structure. All cases were divided into 2 groups: ①26 cases of narrow neck implants (? = 3.3mm) , 52 implants in total; ②28 cases of regular neck implants (?= 4.1 mm), totally 54 implants. The implant surrounding soft tissue (pocket depth, gingival bleeding index, plaque index and dental calculus index), MBL, repair complications, were observed by clinical examination and imaging after implanting denture 6 months, 1 year and 3 years respectively. The patients' degree of satisfaction through questionnaire was also surveyed in these periods. Results In the three-year follow-up period, all of 108 implants did not loosen and fall out. The average values of marginal bone absorption (MBL) for narrow neck and regular neck implant group were (2.1±0.4) mm, (1.4±0.3)mm respectively, the difference was statistically significant. Repair complications of narrow neck implant and regular neck implant groups were 0.26 and 0.27 (per year/per person) respectively. Patient satisfaction of the latter was slightly higher than the former, which had no significant difference. Conclusion The 3-year retrospective study shows that implant diameter may have impact on the edge of bone absorption during the use of two implants categories. Marginal bone absorption in conventional implant neck is less than narrow neck, while mechanical complications and patient satisfaction in both of them have no significant difference.

Key words: diameter implants, mandibular overdentures, marginal bone loss, retrospective study