Original study - ZZI 04/2009

Clinical assessment of the reliability of a computer-aided implant planning concept using laboratory-fabricated templates based on cone beam computed tomography

A. Behneke1, M. Burwinkel1, B. d’Hoedt1, N. Behneke2

The purpose of this prospective study was to assess the reliability of computer-aided implant planning based on cone beam computed tomography and mechanical transfer using laboratory-fabricated surgical templates. A total of 131 implants were placed with the aid of 3D-based transfer templates in forty consecutive partially or fully edentulous patients between September 2006 and November 2008. After individual adaptation of the scan templates and cone beam CT scanning, the acquired data for virtual implant planning and simulation was processed using the med3D and coDiagnostiX software programs. Following spatial alignment using the references and positioning table, the scan templates were converted for the transfer of the planning results to the actual surgical situation by inserting guide tubes for cavity preparation. The data recorded intraoperatively and the preoperative planning data were assessed using descriptive statistics, scattergrams and the Spearman correlation coefficient to compare the planned and actual situation. Agreement between the planned and actual implant sizes was 97.7 % for length and 96.2 % for diameter. The Spearman correlation coefficient indicated a high relationship between planned and achieved outcome with 0.99 for the length, 0.95 for the diameter, 0.90 for the width of buccal bone wall and 0.80 for the width of oral bone wall and dehiscence. On average, the differences in width between the planned and intraoperative situation were 0.15 ± 0.45 mm for the buccal bone wall, and 0.1 ± 0.39 mm for the oral bone wall. The maximal overestimation of the width of bone wall was –1.5 mm for the buccal aspect and –0.7 mm for the oral aspect. Underestimations of the actual bone availability were a maximum of 1.0 and 1.5 mm respectively. Differences between planned and achieved outcome were more frequent in completely edentulous patients with mucosa-supported templates and the maximum overestimation for the width of the buccal bone wall increased to –1.5 mm (mean 0.2 mm). If natural teeth were used to support the template in partially edentulous patients, the bone width was overestimated by a maximum of –0.5 mm (mean 0.1 mm) indicating very accurate transference of data.

Keywords: Computer-aided implant planning, dental implants, surgical templates, transfer, cone beam computed tomography

Introduction

3D-based pre-implantological diagnosis has become considerably more widespread in dentistry with the introduction of cone beam computed tomography. Using a safe level of radiation exposure, CBCT technology allows a detailed view of the three-dimensional bone architecture and adjacent anatomically relevant structures. Acquisition of 3D image data, however, is only one component in the complex overall system of a prosthetically orientated implant planning concept. In addition to a suitable software program for virtual planning and simulation of the superstructure, it is essential to have transfer techniques that can transfer the planning data acquired from the computer simulation to the actual surgical site. Apart from dynamic navigation for transferring the virtual plan to the intraoperative field, mechanical transfer techniques are also available that require less investment in logistics and equipment, which according to the latest findings produce comparable results [7] and accuracy [9, 12].

The mechanical transfer technique is based on templates that can be produced in two ways. Rapid prototyping technology produces templates using the CAD/CAM and steriolithographic (SimPlant/Materialise, NobelGuide/Biocare) technique. The bases of the templates are generated directly from the 3D image data and their accuracy of fit therefore greatly depends on the quality of the 3D image data [5]. The second option for 3D-based templates is to fabricate a template on a dental stone model in the dental laboratory. In this case the radiological template is converted into a surgical template. The template is used for visualizing the subsequent idealized superstructure and the accurate fit of this template can be checked and finely adjusted occlusally before producing the CBCT images. Particularly in the case of patients with a partial or residual dentition this method should ensure reproducible positioning of the template, which ultimately has a crucial effect on the quality of the transfer of planning between the virtual reality and actual surgical situation.

The purpose of this study was to assess the reliability of a CBCT-based, computer-aided implant planning concept using laboratory-fabricated templates. The reliability was evaluated by comparing the preoperative planning data with the intraoperative findings.

Materials and methods

In a prospective monocentric study between 1 September 2006 and 15 November 2008 a total of 131 implants were placed in 40 consecutive patients following CBCT diagnostics with the aid of 3D-based templates. Mucosa-borne, tooth-borne or tooth-mucosa-borne templates were fabricated on stone models depending on the indication. The template bases were made of clear acrylic and the missing teeth were fabricated in the ideal prosthetic position using radiopaque acrylic. The missing teeth were fabricated using either methacrylate with a 30 % barium sulphate powder additive or Acryline (anax dent GmbH, Stuttgart) radiopaque acrylic. Depending on the planning software used, Lego bricks or titanium pins were used as references for transfer of the virtual implant planning to the templates.

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