How does an error in positioning the template affect the accuracy of implants inserted using a single fixed mucosa-supported stereolithographic surgical guide?


Computer-aided implantology using a single fixed stereolithographic surgical guide involves a sequence of diagnostic and therapeutic events, and errors can creep in at different stages. Taken together, these can be termed the ‘total error’. A positioning of the surgical guide on the support surface different to that of the diagnostic template may generate an error that reoccurs with all the implants inserted, and this error can be termed the ‘guide positioning error’. The aim of the present study was to measure the deviation between the planned and inserted implants due to this guide positioning error, to evaluate if this error was statistically significant, and concurrently, to assess the influence of the type of arch (upper vs lower jaw) and mucosal thickness on the guide positioning error. Twenty-four subjects were treated and 172 implants inserted. Preoperative and postoperative computed tomography images were compared using Mimics software to determine the total error and guide positioning error. Quantitative data were described; the t -test and Pearson correlation coefficient were used. The guide positioning error was found to affect the accuracy, but was statistically significant only for global coronal deviation ( P = 0.038). Arch of support and mucosa thickness did not affect the guide positioning error.

The use of computer-aided implantology (CAI) for the placement of dental implants is designed to reduce errors, provide better control, and eliminate the aesthetic and biomechanical risks that are involved in standard implant surgery. One way in which CAI is applied in a clinical setting is through single-type stereolithographic guided systems; this constitutes the focus of the present study. The single-type guide consists of a stereolithographic surgical template with guide sleeves for fixture installation, additional guide sleeves for fixation screw installation, and depth calibrated drills to prepare osteotomies ( Fig. 1 ). The stereolithographic guided surgery system involves a sequence of diagnostic and therapeutic events, and errors can arise at different stages. In line with the literature, the accuracy of the entire procedure is defined in this paper as the deviation between the position of the implant in the planning (or planned implant position) and the position of the implant postoperatively (or inserted implant position). In this paper we term this deviation the ‘total error’.

Fig. 1
Surgical components and instruments used in a single stereolithographic guided surgery system (External Hex Safe; Materialise Dental, Leuven, Belgium): (A) stereolithographic surgical guide; (B) internal tube; (C) fixation screw drill; (D) fixation screw; (E) mucotome for flap-less surgery; (F) and (G) diameter and depth calibrated drills for guided osteotomy; (H) implant holder for guided implant insertion. *Guide sleeve for fixation screw installation. **Internal tube inserted in the guide sleeves to guide the drilling procedure.

Although the literature describes different types of error that have occurred in real clinical situations, the clinical significance of each individual type of error has not as yet been determined. However, most sources of error can lead to an error that affects every single implant randomly. In this paper we term this the ‘random error’.

Stereolithographic guided surgery systems use a diagnostic template, called a scanno-guide, to determine the prosthesis-driven implant position. The scanno-guide is either a radiopaque replica of the patient’s temporary prosthesis, or it is the patient’s actual denture (double-scan technique).

The position of the diagnostic template during the computed tomography (CT) scan is taken as a reference guide during the planning phase and must be exactly reproduced by the surgical guide during the surgery. A positioning of the surgical guide on the support surface that is different to that of the diagnostic template may generate an error that reoccurs on each implant inserted with the same surgical guide ( Fig. 2 ). In this paper we term this reoccurring error a ‘systematic error’.

Fig. 2
How the systematic error may occur. Implants are planned using the diagnostic template (in red), but if the surgical guide (in blue) is not placed in the same position as the diagnostic template, the inserted implants (in blue) deviate from the planned implants (in red). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

It is also to be noted that during the drilling sequence and/or implant insertion for each single implant, the surgical guide itself may slightly rotate or move, and this movement may differ from site to site, resulting in a random error. With the above considerations in mind, the aims of this study were: (1) to measure the systematic error that arises from the positioning of the surgical guide on the support surface if different to that of the diagnostic template, when using a single fixed mucosa-supported stereolithographic surgical template (External Hex Safe; Materialise Dental, Leuven, Belgium) in completely edentulous patients, and its clinical significance when compared to the total error; (2) to measure whether the variables of type of arch operated on (upper vs lower arch) and mucosal thickness result in statistically significant differences with regard to systematic error.

Materials and methods

An observational, retrospective study of 24 subjects (18 male and six female) with a completely edentulous jaw (any remaining dental elements had been extracted at least 3 months prior to the implant–prosthetic rehabilitation) was conducted. Subjects and treatment characteristics are summarized in Table 1 . Regular smokers (defined as a habit of 10 or more cigarettes a day) were not excluded. Subjects with systemic health problems, parafunctional habits, poor oral hygiene, severe alveolar bone deficiencies, uncontrolled diabetes, current irradiation to the head or neck, psychological disorders, and alcohol or drug addiction were excluded.

Table 1
Characteristics of the study subjects.
Number of subjects 24
Male 18 (75%)
Female 6 (25%)
Maxilla 13 (54%)
Mandible 11 (46%)
Mean age (years) 58

For each subject, a radiopaque diagnostic template (scanno-guide) was initially created. A CT scan of each subject’s arch was performed with a spiral CT device (Asteion Multi; Toshiba Medical Systems, Rome, Italy). CT parameters used were: 0° gantry tilt, high resolution bone kernel, 0.5 nominal slice thickness, 0.5 mm interval, 0.5 mm pitch. The scans, which included the scanno-guide to integrate the anatomical data with the functional and aesthetic requirements, were taken without inter-arch contact, using a bite index to prevent overlapping between the images of the opposite arch and the scanno-guide and to prevent positioning error. The potential locations for implant placement and the corresponding implant length and width were planned using SimPlant software (Materialise Dental, Leuven, Belgium) ( Fig. 3 ).

Fig. 3
The computer planning program employed in the present study (SimPlant; Materialise, Leuven, Belgium) allows visualization of the project from a multitude of 2D and 3D points of view. Axial, 3D, panoramic, and cross-sectional images are visible at the same time on a computer monitor; the practitioner can interactively change the position of the planned implant in each plane until the result is satisfactory. (A) Cross-sectional view of the proposed implant positioning relative to the optimal final tooth positioning (maxillary left canine); the implants are fine-tuned based on bone volume and optimal emergence profiles of the prosthetic restoration. (B) Axial view. (C) Panoramic view of the SimPlant analysis of the subject’s maxillary CT scan; the scanno-guide is in place, demonstrating a differential barium concentration gradient in the denture base versus the teeth. (D) A view of the 3D reconstruction allows visual verification of implant placement.

Using this software, the implants were virtually-placed according to bone anatomy and prosthetic designs, and a surgical template was developed (External Hex Safe; Materialise Dental, Leuven, Belgium) ( Fig. 4 ). In each case, after checking for perfect adaptation to the mucosa of the edentulous arch and the stability of the template, the surgical guide was fixed to the bone with at least three osteosynthesis screws (mean diameter of 2 mm and mean length of 12 mm), placed in a tripod formation. Cylindrical implants (Prime System, IMPLADENT, Formia, Latina, Italy), with an external hexagon (diameter 3.75 mm and lengths ranging from 10 mm to 15 mm) were inserted in the upper and lower completely edentulous arches using a stereolithographic surgical template. The surgical guide allowed control of the implant site preparation and guided implant insertion, using osteotomy site-specific drills with vertical stops to control the depth of the implant site preparation and specific delivery mounts (implant holder, diameter 4.00 mm, length from 4 mm to 15 mm).

Jan 19, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on How does an error in positioning the template affect the accuracy of implants inserted using a single fixed mucosa-supported stereolithographic surgical guide?
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