Analysis of Linear and Angular Deviations of Implants Installed With a Tomographic-Guided Surgery Technique: A Prospective Cohort Study

The search for less traumatic surgical procedures for the patient has been considered a trend in dental implantology.¹  The flapless surgical technique of implant placement has been proposed because of some advantages in the reduction of surgical site morbidity and bone resorption due to the periosteal detachments.^2–4  However, the absence of visualization of the bone tissue may induce deviations in the implant installation in relation to the original treatment planning, which may reduce the success of prosthetic rehabilitations.⁵ 

Because of this issue, it has been proposed that flapless surgical techniques for implant placement are required to be performed by means of surgical guides, made on the basis of the computerized tomography (CT) performed before the surgical procedure for implant installation.^1,6,7  It has been shown that the installation of implants by means of the CT-guided surgery technique presents smaller linear and angular deviations than implants installed with open flaps associated with conventional guides in cadavers,⁸  and the implants installed by free-hand techniques in jaw casts.⁹  In addition, compared with implants installed with conventional surgery, implants installed with the CT-guided surgery technique present similar clinical results in relation to the success and survival of implants and peri-implant tissue stability.^10–12  Furthermore, it has been described that the high accuracy of the implantation of the implant, close to what was planned, allows the preparation of prostheses with better biomechanical characteristics installed at an early stage,¹  which would promote a reduction in treatment time and increase patient comfort.¹ 

An important factor that may interfere with the accuracy of surgical guides in maintaining the planning of implants is the type of tissue used to fix the guide (bone, teeth, or mucosa). The tooth guides are considered the guides with the best accuracy.^6,13  However, in cases in which the patient has a fully edentulous maxilla or mandible, this type of guide cannot be used.¹⁴  Thus, one can expect that the surgical procedure performed in this type of patient presents greater linear and angular deviations between the implants installed and planned,¹³  which makes the surgical technique more prone to technical errors.⁵ 

Investigation of factors that interfere with deviations of the implants installed by the CT-guided surgery technique has been conducted with some frequency.^{3,6,8,9,15–19}  However, it has been emphasized in systematic reviews that there is a necessity for a specific description of these interference factors.^13,20  Thus, the objective of this study was to evaluate the linear and angular deviations of implants installed by the flapless CT-guided surgery technique in fully edentulous patients.

This study was approved by the Human Research Ethics Committee of our institution (protocol No. 1.089/10). All patients were informed about their participation in this study and signed a free and informed consent form. The ethical terms of the revised Helsinki Declaration in 2015 were followed in this study.

Eighteen patients were selected from the specialization course in implant dentistry from our institution between January and December 2015. To be included in this study, patients had to present with the following inclusion criteria: absence of systemic impairment, no smoking habits, no contraindication to the surgical procedure, and 1 fully edentulous arch. Of these patients, 10 presented a totally edentulous maxilla, while 8 presented a totally edentulous mandible. The patients received a total of 115 implants, of which 81 implants were installed in the upper arch while 34 implants were installed in the lower arch.

Tomographic guides were made with radiopaque markers of gutta percha in the region of the first molars and central incisors for tomographic examination in both the upper and lower arches (Figure 1a). Cone beam CT was performed with ICat Classic Tomography (Imaging Sciences International, Hatfield, Pa) with 0.25-mm cutoff thickness, 0.25-mm reconstruction interval, and 120 kV and 36.12 mAs as exposure factors. These examinations were performed with the tomographic guide in position and with the guide isolated, with the purpose of positioning the guide on the tomographic examination during the planning of the positioning of the implants, by means of the double tomography technique. After the acquisition of the image, the virtual planning for the positioning of the implants in relation to the previously made prosthesis was performed using Dental Slice software (Dental Slice Navegação Virtual, Bioparts prototipagem Biomédica, Brasília, Brazil; Figures 1b and c). The virtual planning was then sent for the preparation of the prototype surgical guides (Bioparts prototipagem Biomédica; Figure 2a).

The patients were initially submitted to intra- and extraoral asepsis of the operative field using a 0.2% chlorhexidine digluconate solution and submitted to a local anesthesia with 2% mepivacaine with 1:100 000 epinephrine (Mepiadre, DFL, Rio de Janeiro, Brazil). After stabilization of the surgical guide, the drilling procedure was started using a sequence of drills indicated by the manufacturer, until the installation of the Morse connection implants (Slice Guide, Conexão sistemas de prótese, Arujá, Brazil), without the opening of the flaps (Figure 2b and c). The selection of the diameter and height of the implants was based on the virtual planning. No sutures were required. For postoperative care, amoxicillin 500 mg for 7 days, nimesulid 100 mg for 3 days, sodium dipyrone 500 mg for 3 days, and mouthwash with chlorhexidine digluconate for 7 days were prescribed for the patients.

After the implant placement, micro-unit intermediate pillars were installed (Conexão Sistemas de Prótese). In the sequence, the transfer molding was carried out, followed by the execution of the occlusion record with the aid of the multifunctional guide. The metallic infrastructure and teeth were mounted in wax for clinical testing and subsequent acrylization of the prosthesis. The prosthesis was installed on the day after the surgery (Figure 3a through c). Then, a new tomographic examination was performed to measure the linear and angular deviations.

The measurement of the linear and angular deviations between the virtual planning and the final position of the implants was performed with the overlap of the planning and postoperative tomographies through the full version Dental Slice software (Bioparts, Brasília, Brazil). A central point was identified on each platform, one at the center and one at the apex of the implant, as well as a vector that passes at each point captured, to obtain the angle resulting from the deviation between the planned and the executed. The distance D1 was calculated considering the linear distance between the points at the apex of the implant, and the distance D2 was calculated considering the linear distance between the points at the center of the implant and D3 at the implant platform. The angle A1 was calculated in degrees between the vectors: vt planned and vt installed (Figure 4).

The normal distribution of the data was detected by the D'Agostino and Pearson test. Thus, the parametric test of repeated-measurements analysis of variance complemented by the Tukey test was applied to compare the linear deviations of the different regions of the implants. The paired t test was used to compare the mean values of linear or angular deviations for anterior and posterior regions, whereas the comparison between linear and angular deviations of implants installed in the maxilla and mandible was performed by means of the unpaired t test. To evaluate the examiner calibration, the measurements were repeated in 20 implants randomly selected, with an interval of 1 week, and these data were compared through the Pearson correlation. The software GraphPad Prism 6 (San Diego, Calif) was used to apply all the statistical tests of this study, with a significance level set as 5%. The statistical analysis was reviewed by an independent statistician.

All patients completed the study. There were no differences in the linear and angular deviations of the implants installed in the maxilla and mandible. Compared with the coronal region, there was a trend of greater linear deviations in the apical regions of the implants and a greater tendency toward deviations in the posterior regions than in the anterior regions; however, these differences were not significant. Table 1 shows the mean and standard deviation data for the linear and angular deviations in implants installed in the maxilla and mandible by the CT-guided surgery technique. Table 2 presents the mean and standard deviation data for the linear and angular deviations in implants installed in the anterior and posterior region of the maxilla and mandible.

Regarding the prosthetic predictability, no angled abutments were used. The angulation of the intermediate pillars was maintained in the final execution of the prostheses, as in virtual planning. Only 1 implant (1.61%) presented mobility at the time of oral rehabilitation and was not used in prosthetic rehabilitation, which did not interfere with the prosthetic rehabilitation. The reproducibility of the examiner evaluations presented a high correlation rate (r = 0.91).

This study showed that the use of the CT-guided surgery technique by means of prototyping guides based on the tomographic examinations presented high efficiency in the implant installations in a position close to that previously planned, which allowed the use of straight pillars and screwed prostheses that were installed early in all treated cases. In addition, only 1 implant was lost in the entire sample, and there was no need for flap opening in any of the patients.

It was shown that the linear deviation ranges of the implants placed in maxilla were 1.72–2.41 mm and 1.83–2.18 mm in the mandible, while the angular deviations were 2.41° in the maxilla and 2.50° in the mandible, without significant differences between the implants installed in the maxilla and mandible, as demonstrated in another clinical trial.¹⁶  The data on the deviation of the implants installed in this study are close to the range of detected deviations from clinical studies that evaluated the insertion of implants by a CT-guided surgery technique. A clinical study comparing the linear and angular deviations of the implants installed by fixed prototyped guides on mucosa or teeth showed that implants installed with the aid of the mucous guides had linear deviations of 0.94 mm at the apex and 0.69 mm at the platform of implants with angular deviations of 2.71°.⁶  Another clinical study that evaluated the linear and angular deviations of the implants installed in totally edentulous patients presented linear deviations of 1.68 mm at the implant platform and 2.19 mm at the apex of the dental implants, while the angular deviation was 4.67°.¹⁵ 

In this study, the type of surgical guide used was for mucosal fixation and total bed preparation, in which all the phases of the perforations until the implantation of the implant were made with the guide in position. It has been demonstrated in other studies that the mucosal surgical guides present worse accuracy than the tooth surgical guides^6,13 ; however, the fact that the target population in this study was totally edentulous in 1 jaw prevented the use of tooth guides. Despite this issue, the fixation of the mucosal guide by perforating screws, as performed in this study, reduces the possibility of linear and angular deviations.^3,15  Keeping the guide in a fixed position throughout the surgical procedure has also been indicated as a way to reduce the deviations of the position of the implants in relation to the initial planning.^1,20  Although studies have cited the use of fixed guides as a complicating factor for surgical bed irrigation, which could lead to excessive heating and necrosis of the bone around the implants, this complication has not been demonstrated in preclinical studies.^21–23 

A fact observed in this study was that all patients were submitted to early rehabilitation without the need for extensive flap opening. Previous clinical studies did not show clinical superiority of the CT-guided surgery compared with the opening flap techniques with or without the aid of guided surgeries,¹¹  which demonstrates that the great advantages of the flapless CT-guided surgery technique are the comfort provided to the patient,^1,2,24  the reduction in the time required for occlusal activation of the installed implants,¹  and the reduction in the need for bone grafting.²  In addition, it has been demonstrated that patients undergoing flapless and unguided surgery have lower rates of implant survival than patients undergoing conventional implant installation technique with open flaps.⁵  In fact, the opening of the flap facilitates the visualization of the surgical bed and reduces the possibility of the occurrence of dehiscence and fenestrations, which are common complications of unguided and flapless surgeries.^1,5,24  Thus, the positive effects related to the application of the flapless surgery can be achieved only if the prototyped guide is used, since it reduces the possibility of negative intercurrences during the implant installation procedure.

It this study, no statistical differences in the linear deviations were observed between the different portions of the implants or in the different regions where the implants were placed, and this finding was not in agreement with results described in previous studies that stated that the implants placed with the aid of CT-guided surgery presented more deviation at the apical portion of the implants, especially when the implants were placed in the posterior regions of the mounth.^16,17,25  Some factors, such as the greater difficulty in adapting the guide in the posterior regions of the mouth,²⁵  the size of the guides' washers and their distance to the top of the alveolar ridge,^17,25  and the fact that the augmentation of the distance of the tip of the drill to the guide can improve linear deviations, due to the eccentric movements that occur during the preparation of the surgical perforation,¹⁷  can explain the major deviations found in these regions of the mouth and implants. However, the absence of differences in our study may be related to the different protocols used, since the implants were placed with a fixed mucosal guide that was maintained in position during the total preparation of the surgical perforation used for the implant placement.

The design of the study, the good accuracy of the technique used, and the high reproducibility of the analysis promoted the acquisition of data with good internal validity. However, this study presents limitations that must be considered when analyzing the results obtained as they interfered with the external validity of our data. The limited sample size did not confirm the statistical trends of greater deviations in the posterior region of the maxilla and the apex of the implants. The absence of comparison with other implant insertion methods, such as insertion of the implants by free hand, open, or flapless techniques, did not allow for the assessment of the impact of deviations associated with the application of different techniques. Some other important comparisons are scarce in the literature, such as a comparison between fully and partially CT-guided surgery and a comparison of the CT-guided surgery flapless technique in association with intraoral scanning with the technique used in this study in more challenging clinical situations, such as immediately placed implants in postextraction alveolar sockets.

The insertion of implants using the CT-guided surgery technique promoted the installation of implants with accuracy and allowed the installation of straight pillars in all cases evaluated. The linear deviations were not different in the different regions of the mouth or in the different portions of the implants.

Abbreviation

CT

computerized tomography

The authors would like to thank Prof Dr Suzane Cristina Pigossi (assistant professor of periodontology of the Federal University of Alfenas, Brazil) for revision of the statistical analysis of this study.

The authors declare no conflicts of interest regarding this study.