Diederik Hentenaar

130 Chapter 6 MATERIAL AND METHODS Subjects Data used in the present study consisted of patient data from two studies previously performed at the department of Oral and Maxillofacial Surgery, University Medical Center Groningen (21,22). Both studies included non-smoking patients who needed one or more dental implants in the posterior region. Between 2005 and 2010, 122 implants were placed in a total of 96 patients. All patients received individually designed suprastructures. Up to 5 years after placement of the implant restoration patients were seen for clinical and radiographic follow-up examination. Inclusion criteria and results from clinical and radiographical analyses of both study populations were reported previously (21,22). Eligibility criteria used for the present study were as follows: patients with non-splinted, two-piece implants and platform-switched abutment connections, placed in posterior healed sites (i.e. 3 months healing of extraction sites after tooth removal) of maxilla and mandible, in between two natural teeth or adjacent to one natural tooth. Exclusion criteria were as follows; patients with two or more adjacent implants, implants in the anterior region (inter premolar region), implant-abutment matched connections (non-platform-switched), soft-tissue level implants or implants with a poor restoration connection (i.e. abutment-restoration gap), patients that were smokers. Implants that were not fully depicted or showed a buccal-lingual over- angulation on peri-apical radiographs were also excluded. Radiographic analysis Peri-apical radiographs (Planmeca Intra X-ray unit; Planmeca, Helsiniki, Finland) taken at one month (T1, baseline) and 5 years (T60) after placement of the final implant crown were used for radiographic assessment of the crown contour and marginal bone level. To standardize radiographs and assure perpendicularity (i.e. positioning of the film parallel to the long axis of the implant) an individualized X-ray holder and paralleling technique were used (23). Bone level change measurement Peri-implant bone level change was determined on radiographs taken on T1 and T60. The distance from the implant reference point (most outside point of implant neck) to the level of bone-to-implant contact was measured at both the mesial and distal aspect of the implant. Radiographs were calibrated using the known dimensions of the implant as reference values. Illustrator software (Illustrator CS; Adobe Systems Inc, San Jose, CA, USA) was used for calibration of the implants. The difference in bone level between one month and five years after crown placement was calculated and used for correlational analysis.