Young-Il Kang* Dong-Won Lee* Kwang-Ho Park Ik-Sang Moon Effect of thread size on the implant neck area: preliminary results at 1 year of function Authors’ affiliations: Young-Il Kang*, Dong-Won Lee*, Ik-Sang Moon, Department of Periodontology, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, Korea Kwang-Ho Park, Department of Oral and Maxillofacial Surgery, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, Korea Corresponding author: Prof. Ik-Sang Moon Department of Periodontology, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University 146-92 Dogok-dong, Gangnam-gu, Seoul, Korea Tel.: +82 2 2019 3565 Fax: +82 2 3463 4052 e-mail: ismoon@yuhs.ac *Contributed equally. Key words: alveolar bone loss, dental implants, microthread, prospective study, thread size Abstract Objectives: To evaluate and compare the effect of the coronal thread size on the marginal bone loss around the fixtures, when both implants were provided with threads to the top of fixture. Materials and methods: Two groups of implants, one with a macro-thread to the top of the fixture (A) and the other with a micro-thread to the top of the fixture (B), were placed adjacent to each other in the partially edentulous areas of 20 patients. Bone loss around each implant was analyzed after 1 year of functional loading. The bone losses after loading were compared using Wilcoxon’s signed-rank test. Results: The mean marginal bone losses (A, 0.154 ± 0.144 mm; B, 0.125 ± 0.136 mm) were not statistically significant between the two groups (P = 0.669). Conclusions: There was no significant difference between implant with macro- and micro-neck thread in terms of marginal bone loss after 1 year of loading. Recent clinical studies by our group regarding the effect of micro-thread on the marginal bone level showed that (i) the use of micro- thread on the implant neck area can preserve the peri-implant marginal bone effectively, compared with the fixtures without micro- thread (Lee et al. 2007), (ii) the location of the micro-thread in the neck area plays an important role in peri-implant marginal bone stabilization (Song et al. 2009) and (iii) differ- ence in gross fixture design on the neck area did not result in significant difference of mar- ginal bone loss (Kim et al. 2010). Naturally, the sequel question arose regarding the effect of the thread size on the neck portion of the implant. The use of certain pitch distances of the threads was known to be a favorable element in preserving the peri-implant bone (Motoyo- shi et al. 2005). According to finite element analysis, very small threads with a favorable profile can affect the stress distribution in the bone as much as commonly sized threads (Hansson & Werke 2003). Adequate mechanical stimulation is an important requirement for the successful integration of load-bearing surfaces (Wiskott & Belser 1999). From a biomechanical per- spective, retention elements such as the threads on the implant neck area provide the mechanical stimulation required to maintain the marginal bone level (Hansson 1999). Stud- ies have verified the advantages of micro- thread on the coronal portion of fixture, com- pared with a smooth neck, in terms of the established bone-to-implant contact and marginal bone level maintenance (Berglundh et al. 2005; Abrahamsson & Berglundh 2006). The role of micro-threads in the neck portion has been researched in numerous studies (Hansson & Werke 2003; Berglundh et al. 2005; Abrahamsson & Berglundh 2006; Lee et al. 2007; Song et al. 2009; Kim et al. 2010). In contrast, few clinical studies have addressed the role of thread size, or thread pitch distance, on the maintenance of the peri-implant marginal bone, when the threads were positioned to the top of fixtures. Thus, the aim of this clinical investigation was to evaluate and to compare the effect of the coronal thread design on the marginal bone loss around the fixtures, when both implants were provided with threads to the top of fixture, but the size of the threads differs between the implants. Material and methods This study was approved by the Institutional Review Board of Gangnam Severance Hospi- tal, Yonsei University. Patients were Date: Accepted 3 July 2011 To cite this article: Kang Y-I, Lee D-W, Park K-H, Moon I-S. Effect of thread size on the implant neck area: preliminary results at 1 year of function. Clin. Oral Impl. Res. 23, 2012, 1147–1151 doi: 10.1111/j.1600-0501.2011.02298.x © 2011 John Wiley & Sons A/S 1147