Accuracy of a Newly Developed Cone-Beam Computerized Tomography-Aided Surgical Guidance System for Dental Implant Placement: An Ex Vivo Study

Presurgical implant planning is of paramount importance for the successful outcome of dental implant treatment. To enable appropriate placement of implants, planning should include the identification of critical anatomical landmarks, a bone-quality assessment, and prosthetic considerations.^1–3  Data obtained by computed tomography (CT) and cone-beam computed tomography (CBCT) can be processed in commercially available implant simulation software to provide a preoperative view of anatomical structures in the jaw bone.⁴  Transferring preoperative plans to the surgical field requires the use of stereolithographic guides^5–8  to ensure surgical safety and accurate transference of preoperative planning.

Initially, stereolithographic guides were used to provide alveolar bone support after flap exposure; however, this method failed to provide depth control for osteotomy drills.⁹  For this reason, tooth- and mucosa-supported guides, which provided depth control and eliminated the need for flap elevation, came into use for implant insertion.^10,11  The main advantage of flapless implant surgery is that it drastically reduces postoperative discomfort.¹²  However, it has the disadvantage of a lack of visibility of anatomical features and critical structures, such as nerves and blood vessels, and hence, it requires a safety zone of at least 1–2 mm to avoid critical anatomical structures.⁴ 

Methods for measuring implant placement accuracy have involved specially designed surgical guide templates, milling machines, and superimposition software.¹³  Although superimposition software is useful for comparing preoperative and postoperative CT views using anatomical or radiopaque markers, this requires a second CT scan, thus exposing the patient to additional radiation and additional expense.¹⁴ 

In comparison to traditional medical CT systems, dental CBCT units offer reduced effective radiation doses, shorter acquisition scan times, easier imaging, and lower costs. Thus, CBCT is now commonly used for a variety of purposes in implantology, dento-maxillofacial surgery, image-guided surgical procedures, orthodontics, periodontics, and endodontics.^15–17 

The aim of this study was to measure the precision of StentCad Beyond (Ay Tasarim Ltd, Ankara, Turkey), a newly developed CBCT-aided surgical guidance system, in placing dental implants ex vivo.

The study was conducted using 5 cadaver mandibles. A radiopaque scan prosthesis was manufactured for each mandible to provide accurate implant planning. Mandibles were then scanned using an Iluma CBCT (3M Imtec, Ardmore, Oklahoma) scanner set at 120 kvP and 3.8 mA for 40 seconds, and DICOM slices of 0.3 mm thickness were transferred to the StentCad Beyond implant simulation software, which was used to plan implant locations and angles in line with anatomical limitations and prosthetic considerations.

The StentCad Beyond surgical implant system is a 2-part system consisting of a base plate and a handpiece apparatus, both of which are created from biocompatible material using stereolithography. The StentCad Beyond surgical implant system was used to provide depth, location, and angle control throughout the implant insertion process (Figure 1). Using this guiding system, 20 implant locations were drilled (MIS, Implants Technologies Ltd, Shlomi, Israel) according to a preoperative plan. Of these, 9 drills were inserted using a bone-supported guidance system and 11 using a tooth/bone-supported guidance system. After final drilling, mandibles were scanned again using the same CBCT unit and the same settings.

To assess the precision of the StentCad Beyond system, postoperatively scanned data were transferred to the StentCad Beyond software to virtually superimpose pre- and postoperative implant positions. Images of the final drills were exported in .stl format with pins showing the depth, angle, and location of the implants. The .stl data for both preoperative and postoperative plans were imported to the Rhinoceros version 4 software program (McNeel Ins, Seattle, WA), which was used to superimpose the postoperative and preoperative models (Figures 2 and 3). After extracting bone structures from the images, deviations in horizontal position, depth, and angle between planned and actual positions drilled were calculated for each implant, and differences between bone-supported and tooth/bone-supported guidance systems were analyzed using t-tests, with a significance level of P < .05.

Linear parameters were measured at both the coronal and the apical center. Angular, depth, and horizontal (coronal and apical) deviations are presented in Table 1.

For bone-supported guidance systems, deviations at the apical depth ranged from 1.54 mm to 0.79 mm, whereas deviations at the coronal depth ranged from 1.67 mm to 0.54 mm. In addition, deviations at the horizontal apical ranged from 2.20 mm to 0.15 mm, deviations at the horizontal coronal ranged from 1.80 mm to 0.11 mm, and angular deviations ranged from 6.21° to 1.23°.

For tooth/bone-supported guidance systems, deviations at the apical depth ranged from 1.92 mm to 1.06 mm, whereas deviations at the coronal depth ranged from 1.87 mm to 1.00 mm. Also, deviations at the horizontal apical ranged from 2.16 mm to 0.29 mm, deviations at the horizontal coronal ranged from 1.70 mm to 0.69 mm, and angular deviations ranged from 7.57° to 2.50°.

Table 2 shows the mean deviations obtained from bone-supported and tooth/bone-supported guidance systems. Data analysis showed a mean coronal deviation of 1.2 ± 0.3 mm and 0.6 ± 0.6 mm, mean apical deviation of 1.3 ± 0.6 mm and 0.7 ± 0.6 mm, mean apical and coronal depth deviation of 1.4 ± 0.3 mm and 1.3 ± 0.3 mm, and mean angular deviation of 4.2° ± 2.0° and 3.0° ± 1.5° for the tooth/bone-supported and the bone-supported guides, respectively.

When the results for the 2 systems were compared, no statistically significant differences were found in coronal depth deviation, apical depth deviation, or angular deviation (P > .05). However, significant differences were found in mean horizontal coronal deviation (P = .016) and mean horizontal apical deviation (P = .047).

Surgical and prosthodontic treatment plans can be visualized through the virtual placement of an implant of a specific length and diameter at a desired horizontal position, angulation, and depth.^18,19  Transferring treatment plan information using a surgical template is critical to the success of implant restoration; however, accurate transference remains difficult to achieve.^13,20 

Deviations between planned and actual implant positions can result from errors at the planning and/or operative stages. With manual implantation, the implant follows the trajectory of least resistance, which can lead to substantial deviations, especially in patients with comparatively soft bone tissue. For this reason, guided implant placement tends to result in smaller deviations than manual placement.⁴  However, with guided placement, large angular deviations have been observed as a result of a poor fit between the tissue and the surgical guide.¹³  The precision of the entire implantation procedure depends largely upon the ability to accurately position the drill guide on top of the bone and to maintain a stable position throughout the procedure.¹³  During surgery, if the template is not fixed horizontally to the bone with small pins, the template may not remain properly seated, which will result in misalignment of the implant.^10,21 

The accuracy of placement using guided surgery can be evaluated by examining the deviations between virtual planning and postoperative implant positions, which can be achieved through the superimposition of pre- and postoperative CBCT scans.⁴  Previous studies analyzing the accuracy of implant guidance systems have been conducted by measuring implants or by measuring drill holes only. This study measured the positions of the final drills provided by MIS implants (Implants Technologies Ltd, Shlomi, Israel).

This study is the first to assess the use of bone-supported and tooth/bone-supported StentCad Beyond ex vivo. The deviation values reported in this study are consistent with those of previous reports for bone-supported guides. However, unlike the guidance systems examined in these earlier reports, the StentCad Beyond system reported on here offers the unique advantage of a depth-control mechanism without the need for multiple guides. Previous studies have suggested that the use of a single guide throughout the osteotomy procedure, along with a depth-control mechanism, may help reduce deviations in placement.^22,23 

A meta-analysis of in vitro, cadaver, and clinical studies of guided implant surgery accuracy found mean horizontal deviations of 1.1 mm and 1.6 mm, respectively, at the implant crown and apex, a mean deviation of 0.5 mm in depth, and a mean angular deviation of 5°-6°.²⁴  In vitro studies are free of confounding clinical factors that cause movement of the surgical guide and restrict access during surgery, causing greater deviation. Although the greater control over patient-related factors provided by in vitro studies makes the direct comparison of data from in vitro and cadaver studies difficult, the data obtained from the present ex vivo cadaver study is comparable with that of previous in vitro,²⁵  cadaver,^26,27  and clinical studies.^23,28 

One in vitro study²⁵  compared the accuracy of conventional acrylic and stereolithographic surgical guides by drilling holes in 5 edentulous epoxy mandibles—5 holes in each right (control) side using conventional surgical guides and 5 holes in each left (experimental) side using a stereolithographic surgical guide—and comparing pre- and postoperative jaw scans to identify deviations. Mean deviations at both the entrance point and implant apex were significantly lower using the sterolithographic guide (0.9 ± 0.5 mm and 0.1 ± 0.6 mm, respectively) compared with the conventional guide (1.5 ± 0.7 mm and 2.1 ± 0.97 mm, respectively).

Another study examined the use of a bone-supported stereolithographic guide in the placement of implants in 2 cadavers after raising a mucoperiostal flap.²⁶  An image-volume registration technique used to compare planned and placed implant locations found mean deviations of 0.8 ± 0.3 mm at the implant crown and 0.9 ± 0.3 mm at the implant apex and a mean angular deviation of 1.8°. The greatest deviations were found in the longitudinal direction of implants, supporting the assumption that shorter implants can be placed with greater accuracy than longer implants.²⁶ 

An ex vivo study²⁷  that evaluated the accuracy of 3different computer-aided surgery systems found the Simplant/SurgiGuidesystem (Materialise Dental, Leuven, Belgium), a computerized CT-assisted implant system that uses a stereolithographic surgical guide, produced a mean depth deviation of 0.6 ± 0.4 mm, mean coronal deviation of 1.5 ± 0.8 mm, and mean angular deviation of 7.9° ± 5°.²⁷  These results are analogous to our results for the StentCad Beyond system.

A study by Arisan et al²³  that evaluated the in vivo accuracy of 2 stereolithographic guidance systems from 2 commercial manufacturers (Stent-Cad, Kos-gep, ODTU, Ankara, Turkey; and Simplant, Materialise Dental, Leuven, Belgium) found that bone-supported multiple guides resulted in the highest mean deviations in implant placement (StentCad = 5° ± 1.66°, 1.70 ± 0.52 mm [horizontal-coronal], and 1.99 ± 0.64 mm [horizontal-apical]; Simplant = 4.73° ± 1.28°, 1.56 ± 0.25 mm [horizontal-coronal] and 1.86 ± 0.4 [horizontal-apical]).²³  In the present study, the mean horizontal coronal deviation was 0.61 ± 0.6 mm, the mean horizontal apical deviation was 0.7 ± 0.6 mm, and the mean angular deviation was 2.97 ± 1.5 mm for the bone-supported guidance system. The higher deviations found by Arisan et al compared with our study may be due to use of bone-supported multiple guides in the aforementioned study. Deviations for implants placed using single guides, whether tooth- or mucosa-supported, have been found to be significantly lower than those of implants placed using multiple bone-supported guides.²³  The higher deviations found with bone-supported guides may be related to the fact that, in some cases, the pilot drill slid out from the thin cortical plane when bone-supported guides were used. Changing guides after each drill can also cause deviations.

Several studies have reported that tooth-supported guides result in the smallest deviations.^8,23,28 These findings conflict with those of the present study, which found higher deviations for tooth/bone-supported guides than for bone-supported guides. The statistically significant difference in both coronal and apical linear deviation in the tooth/bone-supported group in our study may be related to the available teeth in the cadaver jaws, which may have inhibited stability of the stereolithographic guide surfaces.

This study used cadaver specimens to mimic the in vivo situation; however, the greater brittleness and lower resistance of cadaver bone prevent the full extrapolation of the findings of this experimental study to the actual situation in clinical practice. In spite of this limitation, the similarity of the results obtained in this study and previous studies support the accuracy of the stereolithographic StentCad Beyond system, and further in vivo research is currently being conducted to validate the system's actual clinical performance.

The use of the StentCad Beyond system for fully guided implant insertion, in combination with CBCT images, enabled the accurate placement of dental implants in line with preoperative plans. Although this study on cadavers adds valuable information about the accuracy of the StentCad Beyond system, the most useful assessment will be provided through its clinical use.

CBCT

cone-beam computerized tomography

CT

computerized tomography

The authors are grateful to Ayberk Yağız of Ay Tasarim Ltd, Ankara, Turkey and MIS, Implants Technologies Ltd, Shlomi, Israel.