Single implants with different neck designs in the aesthetic zone: a randomized clinical trial

Objectives: To compare single implants in the aesthetic zone with different neck designs for marginal bone-level changes and clinical outcome measures. Materials and methods: Ninety-three patients with a missing anterior tooth in the maxilla were randomly assigned to be treated with an implant with a 1.5 mm smooth neck (‘‘smooth group’’), a moderately rough neck with grooves (‘‘rough group’’) or a scalloped moderately rough neck with grooves (‘‘scalloped-group’’). Implants were installed in healed sites and were loaded after 3 months. Follow-up visits were conducted at 6 and 18 months after implant placement. Results: The scalloped group showed significantly more radiographic bone loss from implant placement to 18 months (2.01 0.77 mm) compared with the smooth group (1.19 0.82mm) and rough group (0.9 0.57 mm). Furthermore the scalloped group showed significantly deeper pocket depths and a higher bleeding score. There were no between-group differences in soft tissue levels. Survival rates were 97% for the smooth group and 100% for the rough and scalloped groups (P40.05). No significant differences in outcome were found between the smooth group and rough group. Conclusion: For anterior tooth replacements, implants with a scalloped neck showed more marginal bone loss and less favourable clinical outcome compared with implants with a 1.5 mm smooth neck or implants with a rough neck. A lost or congenitally missing tooth in the anterior region usually requires prosthetic replacement for functional and aesthetic reasons. The aesthetic outcome is determined by the appearance of the crown and the surrounding soft tissues, which should be harmonious with the adjacent dentition. Currently, dental implants are widely used for dental rehabilitation, even in aesthetically delicate areas as the anterior maxilla. The level of the periimplant marginal bone is strongly related to the level of the peri-implant mucosa (Bengazi et al. 1996; Hermann et al. 1997, 2000, 2001; Chang et al. 1999) which, in turn, is commonly considered a major factor determining the aesthetic outcome (Furhauser et al. 2005; Meijer et al. 2005). Loss of peri-implant marginal bone could therefore affect the level of the peri-implant mucosa, and hence, the final aesthetic outcome. Furthermore, marginal bone loss may induce pocket formation, which could be unfavourable for the long-term health of the peri-implant tissues (Rams et al. 1984; Heydenrijk et al. 2002). There is evidence that the design of the implant neck influences the amount of marginal peri-implant bone loss (Shin et al. 2006; Lee et al. 2007; McAllister 2007; Bratu et al. 2009; Nickenig et al. 2009). Although the traditional smooth implant neck is accompanied by the least accumulation of plaque (Teughels et al. 2006; Baldi et al. 2009), several studies have shown more marginal bone loss around these implants compared with implants with a rough surface topography at the implant neck (Shin et al. 2006; Bratu et al. 2009; Nickenig et al. 2009). Furthermore, it has been reported that retention elements at the implant neck, such as grooves or microthreads, favour the preservation of marginal bone (Palmer et al. 2000; Shin et al. 2006; Lee et al. 2007). In addition, it has been suggested that an implant neck with a scalloped implant platform might preserve proximal marginal bone (Wohrle 2003; Kan et al. 2007; McAllister 2007). A scalloped implant neck would mirror the natural alveolar ridge curvature, particularly in the anterior zone, and consequently a more Date: Accepted 18 October 2010 To cite this article: den Hartog L, Meijer HJA, Stegenga B, Tymstra N, Vissink A, Raghoebar GM. Single implants with different neck designs in the aesthetic zone: a randomized clinical trial. Clin. Oral Impl. Res. 22, 2011; 1289–1297. doi: 10.1111/j.1600-0501.2010. 02109.x c 2011 John Wiley & Sons A/S 1289 non-violent position of the implant–abutment interface could be realized compared with common flat-platform implant designs. There is however, a paucity of well-designed trials addressing the influence of the implant neck design on bone and soft tissue parameters in single-implant cases in the aesthetic zone (den Hartog et al. 2008). Therefore, the main objective of our study was to compare the marginal bone level change around single implants in the maxillary aesthetic zone with a 1.5 mm smooth neck, a moderately rough neck with grooves and a scalloped moderately rough neck with grooves. In addition, the influence of the implant neck architecture on soft tissue levels and clinical outcome variables was taken into consideration. Material and methods Patients Patients referred to the department of Oral and Maxillofacial Surgery (University Medical Center Groningen, University of Groningen, Groningen, the Netherlands) for single-implant treatment in the maxillary anterior region were considered for inclusion if they fulfilled the following criteria: at least 18 years of age; one missing tooth being an incisor, canine or first premolar in the maxilla with adjacent natural teeth; adequate oral hygiene, i.e. modified plaque index score and modified sulcus bleeding index score 1 (Mombelli et al. 1987); mesial–distal width of diastema at least 6 mm. Exclusion criteria were: ASA score III (Smeets et al. 1998); presence of clinically active periodontal disease as expressed by probing pocket depths 4 mm and bleeding on probing (index score 41); presence of peri-apical lesions or any other abnormalities in the anterior region as detected on a radiograph; smoking; a history of radiotherapy to the head and neck region. Study design This prospective, randomized clinical trial was approved by the Medical Ethical Committee of the University Medical Center Groningen. Patients were included between January 2005 and February 2008. A written informed consent was obtained from all eligible patients before enrolment. A specifically designed locked computer software program was used to randomly assign patients to one of three study groups to be treated with: a 1.5 mm smooth (‘‘machined’’) implant neck (Replace Select Tapered, Nobel Biocare AB, Göteborg, Sweden) – ‘‘smooth group’’ (Fig. 1a); a moderately rough implant neck with grooves (NobelReplace Tapered Groovy, Nobel Biocare AB) – ‘‘rough group’’ (Fig. 1b); a scalloped moderately rough implant neck with grooves (NobelPerfect Groovy, Nobel Biocare AB) – ‘‘scalloped group’’ (Fig. 1c). Randomization by minimization (Altman 1991) was used to balance possible prognostic variables between the three treatment groups. Minimization was used for the variables age ( 30, 431 60 , 460 years), location of the implant site (central or lateral incisor, canine or first premolar) and whether or not a pre-implant augmentation procedure was indicated based on a clinical and diagnostic cast assessment. The allocation result was kept in a locked computer file that was not accessible for the examiner and the practitioners. The surgeon who inserted the implants was informed about the allocation on the day of surgery. Intervention procedure All implants were placed in healed sites. A minimal period of 3 months after tooth removal was adopted allowing the extraction site to heal. When bone volume was insufficient for implant placement, a bone augmentation procedure was carried out. As a grafting material, autogenous bone from the retromolar-ramus or maxillary tuberosity area was used together with anorganic bovine bone (Geistlich Bio-Oss, Geistlich Pharma AG, Wolhusen, Switzerland) covered with a Geistlich Bio-Gide membrane (Geistlich Pharma AG). Implants were inserted 3 months after the augmentation procedure. One day before implant surgery, patients started taking antibiotics (amoxicillin 500 mg, three times daily for 7 days or clindamycin 300 mg, four times daily for 7 days in case of amoxicillin allergy) and using a 0.2% chlorhexidine mouthwash (two times daily for 7 days) for oral disinfection. Following local anaesthesia, a slightly palatal crest-incision was made with extensions through the buccal and palatal sulcus of the adjacent teeth and a divergent reliving incision at the distal tooth. A minimal mucoperiosteal flap was prepared to expose the alveolar ridge. The implant site was prepared by using a surgical template that was fabricated in the dental laboratory, based on the prospective implant