Is it possible to improve the accuracy of implants inserted with a stereolithographic surgical guide by reducing the tolerance between mechanical components?

Abstract

When using a stereolithographic surgical guide, a potentially clinically relevant error may be the mechanical error caused by the bur guide cylinder gap due to the presence of a rotational allowance of drills in the tubes. The aim of the present study was to determine if it is possible to reduce the total error by limiting the tolerance among the mechanical components and to evaluate its clinical incidence. Sixty implants were inserted in eight totally edentate subjects using the External Hex Safe ® system with mechanical components modified to minimize the tolerance. Pre- and postoperative computed tomography images were compared, and the angular deviation was calculated between the planned and the placed implants. The mean angular deviation was 2.02° (range 0.81–3.48°; standard deviation 0.87). The results of the present study show that by limiting the error that originates from mechanical components, the total error could be significantly reduced.

Computer-aided oral implant surgery using a stereolithographic surgical guide involves a sequence of diagnostic and therapeutic events and errors can creep in at different stages. In this paper, and as widely described in the literature, the accuracy of the entire procedure is defined as the deviation between the position of the implant postoperatively (inserted implant position) and the position of the implant in the planning (planned implant position). We define this deviation as the total error.

Complications occurring in real clinical situations have been collected and investigated in order to reduce the level of error and to improve treatment, but it has yet to be determined which of the different steps of computer-aided implantology (CAI) may more frequently give rise to an error.

In the stereolithographic single-type surgical guide, dental implant positioning is totally guided; one guide is used for the osteotomy site preparation as well as the implant insertion. In these systems, one of the potentially clinically relevant errors may be the mechanical error caused by the bur guide cylinder gap due to the presence of a rotational allowance of the drills in the tubes, which can be defined as an intrinsic error of the surgical guide.

When evaluating the importance of intrinsic error in determining any discrepancy between the planned and the final position of the inserted implant, only the angular deviation must be considered, as in reality, the coronal deviation is affected by the distance between the bottom of the guide tube and the entry point of the drill in the alveolar ridge, while the apical deviation is additionally affected by the length of the implant. If the angular error that arises from the tolerance amongst the different mechanical components of a single stereolithographic surgical guide is considered, it results in a maximum theoretical angular error of 5.15°.

The aim of the present study was to determine if it is possible with a single-type stereolithographic surgical guide to reduce the total error through limiting the tolerance amongst the mechanical components (intrinsic error), and to evaluate the clinical incidence of the intrinsic error on the total error.

Materials and methods

A single-type stereolithographic surgical guide (External Hex Safe ® ; Materialise Dental, Leuven, Belgium) was used for totally edentate subjects who required an implant-prosthetic rehabilitation. All patients consecutively treated with CAI between June 2011 and June 2012 were included in this retrospective study.

The surgical interventions were performed by the same operator (MC) who also carried out the virtual surgical planning using implant planning software (SimPlant ® ; Materialise Dental, Leuven, Belgium). The implants were inserted using the External Hex Safe system, but with modified mechanical components that minimized the tolerance.

To reduce the total number of External Hex Safe system mechanical components, the guide tubes were connected directly to the head of the surgical handpiece ( Figs 1 and 2 ). Guide tubes of decreasing length were constructed in order to advance the surgical osteotomy with maximum control ( Fig. 3 ).

Fig. 1
CAD drawing of the metal shell, comprising an upper part (b) and a lower part (c), which are mounted on the head of the surgical handpiece (a), using two fixing screws (d). The guide tubes (e) are firmly screwed on to this shell.

Fig. 2
A guide tube directly screwed on to the head of the surgical handpiece.

Fig. 3
Guide tubes of decreasing length, used to advance the surgical osteotomy, screwed to the head of the surgical handpiece.

During osteotomy, increasingly longer guide tubes were inserted into the master tube and they progressed inside the master tube with only a vertical movement of entry and exit ( Fig. 4 ).

Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Is it possible to improve the accuracy of implants inserted with a stereolithographic surgical guide by reducing the tolerance between mechanical components?
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