Radiographical Evaluation of the Gap at the Implant-Abutment Interface

Introduction: The detection of marginal gaps at the implant-abutment interface is a common clinical task in prosthodontic treatment. For the detection of the gap intraorally, especially under thick soft tissues the most common method is dental radiography. Objective: The objective of this experimental study was to investigate the accuracy of conservative dental radiography to detect marginal gaps at the implant-abutment interface. For these reasons radiographs were taken on internal and external hex implants with different experimental gaps and inclinations. Materials and Methods: The abutment (with a space created by plastic sheets 0.5 and 0.2 mm in thickness) was screwed on the implant, and the implant was placed into a box filled with silicone impression material. The X-ray film was placed parallel to the implant at the back of the box, the borders of the box were marked to the base and the box. A ruler of 10 cm was fixed at a long X-ray tube to ensure parallelism to the implant, X-ray film. Sets of radiographs were made at 0 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees (to the abutment) and -5 degrees, -10 degrees, -15 degrees, -20 degrees, -25 degrees, -30 degrees (to the implant) degrees. The X-ray images were observed with visual examination, under magnification, and in higher magnification in a slide projector. The phenomenal and the true gap at the implant-abutment interface were calculated in order to determine the distortion. Results: There were significant differences between the internal and external hex implants because of the different morphology of the implants. The detecting ability to diagnose a gap at the implant-abutment interface varied significantly with the angulation degree of the X-ray tube. At inclinations to the implant (- inclination) the gap diminished earlier than those inclinations to the prosthetic abutment (+ inclinations). In all examinations the gap was not detectable at angulations higher than 20 degrees. In visual examination at 25 degrees and 30 degrees an average clinician could diagnose the distortion. Conclusions: The X-ray diagnosis of gap at the interface can be significantly influenced by the inclination of the X-ray tube in relation to the long axis of the implant. To achieve accurate results, the use of a paralleling device is advocated in order to achieve greater detection ability. CLINICAL RELEVANCE Dental radiography is often used for detection of marginal gaps at the implant-abutment interface. The angulation of the X-ray beam may lead to inaccurate diagnosis in gap detection. The use of a paralleling device is indicated for evaluation of marginal accuracy. The geometry of the implant (internal or external hexagon) influences the gap evaluation. (J Esthet Restor Dent 22:235-251, 2010).