Historically, implants have been used and documented mainly with diameters between 3.7 and 4.3 mm. Employing these diameters for numerous indications, scientifically substantiated treatment protocols with excellent long-term results have been established [1]. One disadvantage of a standard-diameter implant is the fact that, in clinical use, the available horizontal crestal dimensions of the alveolar ridge are sometimes too small. Although there is some discussion on the amount of bone (buccal and oral) necessary for a successful dental implant, most authors advise at least 1 mm residual bone present adjacent to the implant surface, which consequently requires a horizontal crestal alveolar width of 6 mm for a standard implant. However, the exact threshold for the residual buccal bone thickness has yet not been scientifically clarified and is still under discussion. When inadequate bone width is present for placement of standard-diameter implants, most practitioners have been taught to suggest bone grafting, using either autogenous bone or one of the many available bone substitutes. Bone grafting is a well-documented procedure to restore lost bone volume, but it is associated with increased morbidity and a prolonged treatment time, with the necessary graft-healing period when dentures cannot be worn [2]. While many additive techniques for the reconstruction of missing morphology are employed on a routine basis today, surgical intervention may not always lead to the desired outcome. Physiologically, some patients may be poor candidates for extensive grafting, or they may simply decline such treatment on emotional or financial grounds. Narrow-diameter implants (NDIs) would be beneficial to decrease the rate of augmentations necessary for implant insertion. NDI is an implant with a diameter less than 3.75 mm and is clinically indicated in specific conditions of rehabilitation such as a reduced interradicular bone, thin alveolar crest, or replacing teeth with a small cervical diameter [3]. The availability of residual bone width less than 5 mm is also indicative for the use of NDIs. Several studies have reported the use of narrow-diameter implants in different clinical situations and using different surgical techniques [4,5,6,7,8,9]. In most cases, satisfactory results have been obtained, achieving medium- and long-term cumulative survival rates equivalent to those obtained in restorations using larger diameter implants (between 94 and 100% survival rates). Until now, the use of NDIs has been restricted to certain defined indications with comparable low occlusal loading like incisors or as retaining elements for overdentures. Posterior regions of the jaws with reduced bone quantity make it challenging to rehabilitate without the use of complex reconstruction techniques.

The aim of this cohort study was to evaluate the outcome of narrow-diameter implants (2.75 and 3.25 mm diameter) used as definitive implants in patients with insufficient bone ridge thickness for placing standard-diameter implants in posterior regions of the mandible. The present study reports the clinical outcome up to 1 year after loading. It is planned to follow up this patients’ cohort to the fifth year of function in order to evaluate the success of the procedure over time. The present article is reported according to the STROBE statement for improving the quality of observational studies (http://www.strobe-statement.org).