Accuracy Assessment of Immediate and Delayed Implant Placements Using CAD/CAM Surgical Guides

Oral rehabilitation with implant-supported prostheses is considered to be a reliable and predictable procedure. The high reliability of this procedure permits dental implants to be placed according to the restorative demands.^1–3  The general agreement is that detailed presurgical treatment planning is the foundation for future implant success, leading to the concept of restoratively driven implant treatment. This concept is now considered to be the primary goal in implant dentistry, enabling reverse planning of the desired restorative plan to the surgical field with the aid of recent advances in the field of radiology, digital imaging, and 3D printing.⁴ 

In implant treatment, 3D cone beam computerized tomography (CBCT) images have gradually replaced conventional 2D imaging techniques that do not provide complete spatial information of the patient's anatomy,¹ such as bone topography, or exact locations of vital structures, such as nerves and arteries.³  Furthermore, CBCT-driven implant planning has become more popular due to the increased availability and lower costs.⁵ 

The introduction of 3D imaging technology has been revolutionary in the field of CAD/CAM surgical guide fabrication.²  The digital data acquired from CBCT images can be used to create a virtual 3D model. This provides the clinician with a realistic view of the patient's anatomy, permitting a virtual execution of the surgery in a precise, restoratively driven manner prior to surgery using an implant treatment planning software.^1,2,5  With the aid of a radiographic stent or a virtual restoration designed by the software, the clinician is able to position the implants in the most appropriate location from a restorative standpoint. Furthermore, this technology can assist clinicians in measuring and evaluating local anatomy,²  and enhance communication between clinicians regarding restorative and surgical matters. Such software is now available from a number of manufacturers, such as Anatomage, Astra Facilitate, in2guide, SimPlant/Materialize, and NobelClinician.

Until recently, this method of virtual treatment planning was limited only to computer monitors for visualization purposes and was difficult to translate to the surgical field. Today, surgical guides can be fabricated with computer assisted manufacturing (CAM) to allow for the transfer of this computer assisted design (CAD) and the 3D virtual planned treatment decisions to the actual surgical field.²  This CAD/CAM process uses rapid prototyping (RP) to create 3D stereolithographic (SLA) models¹  on which the guides are made. The SLA models are made by continuously incorporating layers of photosensitive resin based on the data provided.^4,6,7  RP technology—better known as 3D printing—creates surgical guides by incorporating implant system-specific metal sleeves in the resin for each planned implant location.⁴ 

Today, the increased demand for immediate implant placements is accompanied by increased challenges to successfully execute the procedure. Due to the local anatomy of the socket after extraction, osteotomy drills may deflect from the intended site of preparation due to the palatal bony slope of the socket, resulting in a suboptimal implant position. Furthermore, space limitations, high esthetic demands, and the desire to have an immediate temporary restoration after extraction and implant placement require a very high level of accuracy for esthetic success. Computer-aided methods of implant placements have been proposed to minimize the significantly higher positioning errors associated with freehand methods in delayed placements.⁵  The hypothesis proposed in this study is that a CAD/CAM-guided approach in immediate placement cases can be as reliable and accurate as delayed placement using this guided approach. Furthermore, immediate temporization procedures can also be facilitated.

Although accuracy assessments of multiple CAD/CAM surgical guides have been reported in previous studies,^1,2  investigations regarding the use of such tools for immediate implant placements have not yet been widely reported. The purpose of this study is to assess the accuracy of immediately placed implants using Anatomage Invivo5 CAD/CAM surgical guides and compare their use to delayed implant placement protocol.

Patients who had implants placed using Anatomage Invivo5 (Anatomage, San Jose, Calif) CAD/CAM surgical guides during the period of 2012–2015 were evaluated retrospectively. Then, patients who received immediate implant placements and delayed implant placements replacing 1–2 teeth were included in this study. Two experienced surgeons with extensive knowledge and skills regarding guided surgeries were involved. One surgeon placed all the immediate cases and the other surgeon placed all the delayed cases.

For immediate implant cases, the position of the teeth to be extracted were considered as a reference for the desired position of the final restoration and served as radiographic templates. As for the delayed implant cases, a pre-operative CBCT scan was made with a radiographic guide in place.

Using the software, the implants were virtually placed in the desired position, P0 (Figure 1). Using a digital intra-oral scanner (iTero, Align Technologies, San Jose, Calif), STL data files were obtained to provide the dental and soft-tissue information. This STL data was sent to Anatomage for merging with presurgical CBCT DICOM data files, which represent the data of the planned implant position. In the cases where an intra-oral digital scanner was not available, a polyvinyl siloxane impression of the patient was taken, and a stone model was created. This stone model was then later digitally scanned.

After confirming the desired restorative outcome, the virtual implants were saved in the software and uploaded to the Anatomage website to fabricate CAD/CAM surgical guides (Figure 2). After obtaining the surgical guide(s), the implants were placed accordingly, using the prescription provided by the manufacturer (Figure 3). If an immediate temporary crown was desired at the time of implant placement, Anatomage created a 3D printed SLA model with the implant analog in place. This 3D model was then sent to a dental lab to prefabricate the temporary crown prior to surgery.

After completion of the surgery for the immediately placed implants, a postsurgical CBCT was obtained to superimpose with the presurgical CBCT and the simulated implant in the software Position P0. The position of the actual implant placed is referred to as P1 (Figure 4). Deviations in the dimensions of the simulated implant and the actual implant position were evaluated in the following manner: deviation at crest (point C), deviation at apex (point A), and deviation of the axis (angle A) (Figures 4 and 5).

As for the delayed implant placement cases, the master casts that were used for fabrication of the final restoration were gathered, and a scanning healing abutment was placed in the implant analog. The master casts with the scanning abutment were then scanned using a digital scanner, which then allowed us to deduce the final position of the placed implant. This data was then superimposed onto the virtually planned implant position (P0) in the pre-operative CBCT, as described in Figure 6.

For statistical analysis, the Statistical Package for the Social Sciences (SPSS Inc, Chicago, Ill) was used. Descriptive data was presented in the form of mean, range, and standard deviation. Furthermore, to test differences between the two methods of postoperative evaluations, a nonparametric analysis using a Mann-Whitney U test was used since data are not equally distributed. Finally, to compare the immediate and delayed groups, a nonparametric analysis using a Mann-Whitney U test was also used since data are also not equally distributed. Differences were considered to be statistically significant if P < .05.

A total of 29 patients were included in this study, with a total of 40 implants placed. All patients were partially edentulous (missing 1–2 teeth) and hence had tooth-supported surgical guides. Nine of the patients had 15 implants placed using a delayed method. Twenty of the patients had 25 implants placed immediately at the time of the extraction. Implants used in the immediate placement group were Nobel Biocare conical connection (Nobel Biocare, Göteborg, Sweden). Implants placed in the delayed placement group were Biomet 3i (Implant Innovations, West Palm Beach, Fla). All patients in the immediate placement group had their implants temporized at the time of surgery. Within the delayed group, 3 implants were placed in the anterior region and 12 were placed in the posterior region. Within the immediate group, 8 were placed in the anterior region and 17 were placed in the posterior region.

To test differences between the two different postoperative assessment methods comparing the immediate and delayed groups, a random sample of 9 postoperative implants in casts were collected from the immediate placement group and compared to the results achieved using postoperative CBCT scans for the same group (immediate group). A nonparametric Mann Whitney test was performed. No significant differences were found between results achieved from different postoperative methods of assessments within the 3 variables tested, as shown in Table 1 (P = .05).

In this study, two different postsurgical methods were used to determine the final position of the implants. The use of postsurgical CBCT scan in the immediate group was justified to evaluate the integrity of the buccal wall after extraction and implant placement. However, the use of postsurgical CBCT scans for the delayed group was not justified per the ALARA principle. In this study, a new method for postsurgical evaluation of implant placement was used with the final master cast as a reference for implant position. To confirm standard methods of evaluation, a Mann-Whitney test was performed between both methods of evaluation, and there was no statistically significant difference between measures obtained from both methods (Table 1). Hence, both postsurgical methods of evaluation were considered relatively similar.

In this study, the overall means measured for crestal, apical, and angle deviations were 0.86 mm, 1.25 mm, and 3.79°, respectively, as shown in Table 2. The means for the immediate group deviations were as follows: crestal = 0.85 mm, apex = 1.10, and angle = 3.49°. The means for the delayed group deviations were as follows: crestal = 0.88 mm, apex = 1.59, and angle = 4.29°. No statistically significant difference was found at the crest and angle; however, there was a statistically significant difference between the immediate and delayed group at point A, apex, with the immediate group (mean 1.10 mm), presenting more accurate placement at the apical point than the delayed group (1.59 mm) (P < .05), as shown in Table 3.

Deviations between planned and actual positions of implants placed with a CAD/CAM guided approach has been reported in the literature for a number of systems and approaches.^8–10  A meta-regression analysis reported by Schneider et al¹  revealed a mean deviation at the entry point (crest) of 1.07 mm, at the apex of 1.63, and an overall mean error in angulation of 5.261. Arisan et al⁵  compared the incidence of implant positioning deviations related to the use of freehand and computer-aided treatment methods. The results showed that interproximal emergence, insufficient interimplant distance, and improper parallelism errors were significantly higher in implants placed with the use of the freehand method as compared to computer-aided methods of treatment. Al Harbi & Sun¹¹  used interactive SimPlant software (SimPlant 8.0, Materialise Medical, Glen Burnie, Md) to create surgical guides for 40 implants and assess for accuracy. According to the study, 88% and 91% of the implants recorded a <7° angle deviation for the mesiodistal and buccolingual plane angle, respectively. No statistical significant difference was found for the angle deviation. The mean difference of the entrance point was within 0.2 ± 0.72 mm, 85% of the implants were within <1 mm from the intended position, whereas a difference of >1 mm was recorded for 5 maxillary implants (15%). A statistically significant difference was shown for the entrance point deviation.¹¹  Behneke et al¹²  used implant 3D software (med3D GmbH, Heidelberg, Germany) to compare the planned and actual positions and axes, and they found linear deviations in the median at the neck and apex of 0.27 mm (range 0.01–0.97 mm), and of 0.46 mm (range 0.03–1.38 mm), respectively. The angle deviation was 1.841 in median, with a range of 0.07–6.261 mm.¹²  Ozan et al¹³  evaluated the angular and linear deviations at the implant neck and apex between planned and placed implants using SLA surgical guides with planning software Stent Cad (Media Lab Software, LaSpezia, Italy). The mean angular deviation of all placed implants was 4.1–2.3°, whereas mean linear deviation was 1.11– 0.7 mm at the implant neck and 1.41– 0.9 mm at the implant apex compared with the planned implants. The angular deviations of the placed implants compared with the planned implants were 2.91° ± 1.3°, 4.63° ± 2.6°, and 4.51° ± 2.1° for the tooth-supported, bone-supported, and mucosa-supported surgical guides, respectively.¹³  Reasons of such deviations and inaccuracies can be multifactorial. Vercruyssen et al¹⁴  described several causes of such inaccuracies to be at the examination, planning, and execution phases of such treatment. Furthermore, D'haese et al¹⁵  suggested that connecting abutments for immediate load protocols may cause additional deviations due to the torque applied during abutment fixation in less stable implants. Furthermore, it was suggested by Ozan et al¹³  that SLA surgical guides may be reliable in implant placement, and tooth-supported SLA surgical guides were more accurate than bone- or mucosa-supported SLA surgical guides.

An additional potential of using this CAD/CAM method of immediate implant placement and temporization is the possible fabrication and delivery of a final abutment placed at the time of surgery, hence, avoiding replacing multiple abutments during treatment. This final abutment can support a temporary crown immediately after surgery, then a final crown after healing without being replaced.¹⁶  This is significant since multiple insults to soft tissue around implants caused by frequent replacement of abutments during healing might have a negative influence on crestal bone, possibly resulting in compromised structural and esthetic outcomes.¹⁶  Furthermore, the impact of soft tissue health and stability on implant therapy outcomes has been investigated heavily by multiple investigators.^17–19 

Although authors in this study propose that CAD/CAM surgical guides might facilitate immediate implant placement and temporization, still of paramount importance is following conventional criteria proposed for case selection for immediate implant placement and temporization as described in the literature,^18–28  and using this CAD/CAM method as an additional tool that might facilitate the procedure.

Further investigations are needed to critically evaluate CAD/CAM methods of implant installation in immediate placements to assess their full potential in improving outcomes in such cases. Furthermore, authors recommend addressing limitations in this study, mainly by increasing the implant numbers involved, which might lead to more accurate data reflecting smaller standard deviations.

Within the limitations of this study, CAD/CAM surgical guides can be reliable tools to accurately place implants immediately and/or in a delayed fashion. Additionally, due to the accuracy of the implants at the time of placement, it is also possible to prefabricate temporary crowns before the placement of the implant, which can be delivered to the patient at the time of surgery. No statistically significant differences were found between the delayed and the immediate group at the crest and angle; however, apical position was more accurate in the immediate group.

Abbreviations

3D

three dimensional

2D

two dimensional

CAD/CAM

computer-assisted design/computer-assisted manufacturing

CBCT

cone beam computerized tomography

RP

rapid prototyping

SLA

Stereolithographic