The influence of the clinical crown-implant ratio on crestal bone loss around ITI dental implants placed in the posterior jaw: A 10-year retrospective study

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The influence of the clinical crown-implant ratio on crestal bone loss around ITI dental implants placed in the posterior jaw: A 10-year retrospective study
March 2003
Blanes, Rafael J.
Palma de Mallorca, Spain
Implant Dentistry: Volume 12(1) March 2003 p 99
Lippincott Williams & Wilkins
Abstract
Introduction.
The posterior region of partially edentulous patients offers a demanding clinical scenario for the rehabilitation of missing teeth with dental implants. The inferior alveolar nerve, the resorption of the alveolar ridge, and the presence of high occlusal loads may lead to implant-born prostheses with short fixtures and long clinical crowns, causing an unfavorable clinical crown-implant ratio (C/I ratio) of the implant restoration. This clinical situation may cause bending moments, which may affect implant survival and crestal bone levels around dental implants.
Purpose.
The aim of this presentation is to evaluate the long-term effect of the clinical C/I ratio, various clinical parameters, and different prosthetic treatment modalities on implant success and radiographic crestal bone loss around ITI dental implant restorations.
Materials and Methods.
In the period between October 1989 and January 1994, 247 ITI dental implants were consecutively placed in the premolar and molar locations of 109 partially edentulous patients admitted for treatment in the University of Geneva. All implants were restored by means of ceramic-to-metal fused fixed partial dentures and single crowns. Patients were followed as part of a prospective longitudinal study focusing on implant success. Surgical, radiographic clinical, and prosthetic variables were collected at the 1-year recall after implant placement and at the latest clinical evaluation. Radiographic parameters were evaluated on periapical radiographs taken with a standardized long-cone paralleling technique. Radiographic measurements were taken twice-two weeks apart-on a screen projection of the periapical film. Clinical C/I ratio was calculated dividing the clinical crown length (linear distance in millimeters from the occlusal surface to the most apical bone-to-implant contact) by the clinical implant length (linear distance in millimeters from the implant apex to the most apical bone-to-implant contact). Implant restorations were divided into three groups, according to their respective clinical C/I ratios: a: 0-0.99; b: 1-1.99; c: = 2.
Results.
The mean observation time was 6 years (ranging from 5 to 10 years). Four implants failed, giving a 10-year cumulative survival rate of 98.3%. Mean annual crestal bone loss was -0.039 ¨± 0.200 mm. Annual crestal bone loss in nonsmokers and smokers were -0.028 ¨± 0.182 mm and -0.091 ¨± 0.267 mm, respectively. Differences between both groups were not statistically significant (ANOVA:P = 0.454). Mean clinical C/I ratio was 1.769 ¨± 0.56 mm., with 39 (20.3%) implants displaying clinical C/I ratios = 2. Annual crestal bone loss in groups a, b, c was -0.339 ¨± 0.273 mm; -0.029 ¨± 0.153 mm; and -0.018 ¨± 0.256 mm, respectively. Differences between groups were statistically significant (ANOVA:P = 0.009). Clinical parameters such as: age, gender, implant length, bone quality, cantilever extensions, splinting, or cemented restorations did not affect crestal bone levels.
Conclusions.
ITI dental implants placed in the posterior jaw show an excellent long-term implant survival rate and an acceptable annual crestal bone loss. Smoking seems not to influence crestal bone loss around ITI dental implants. Finally, higher clinical C/I ratios seem to induce less crestal bone loss than lower clinical C/I ratios.