|Year : 2020 | Volume
| Issue : 3 | Page : 47-55
Key factors for a successful surgical guide: A prospective pilot study
Rami Abou Khalil, Nabil Ghosn, Nadim Mokbel, Carole Chakar, Nada Naaman
Department of Periodontology, Saint-Joseph University, Achrafieh, Beirut, Lebanon
|Date of Submission||24-Oct-2020|
|Date of Decision||29-Nov-2020|
|Date of Acceptance||24-Dec-2020|
|Date of Web Publication||26-Feb-2021|
Rami Abou Khalil
Department of Periodontology, Saint-Joseph University, Achrafieh, Beirut
Source of Support: None, Conflict of Interest: None
Aims: The aim of this prospective pilot study was to assess the effect of the variation factors starting from the impression technique to the surgery itself in the accuracy of the dental-supported stereolithographic surgical template in implant surgery. Methods and Materials: Eighteen tapered bone level Straumann implants were inserted in 12 partially edentulous patients. The pre- and post-operative cone-beam computed tomography scans were matched allowing comparison of the planned implants with the inserted ones, considering the coronal, apical, and the angular deviation values, according to different surgeons and different implant length. Results: A mean coronal variation of 1.15 ± 0.616 mm, an apical variation of 1.43 ± 0.77, mm and the angular variation of 2.90 ± 1.41were shown. These deviations were within the range reported by several systematic reviews with lower standard deviation from the mean values. Conclusion: Within the limitations of this study, the control of the variation key factors shows better results in guided surgery and with a higher consistency in the results even with different operators.
Keywords: Cone-beam computed tomography, guided surgery, intraoral scan, stereolithography, tooth-supported guide
|How to cite this article:|
Khalil RA, Ghosn N, Mokbel N, Chakar C, Naaman N. Key factors for a successful surgical guide: A prospective pilot study. J Oral Maxillofac Radiol 2020;8:47-55
|How to cite this URL:|
Khalil RA, Ghosn N, Mokbel N, Chakar C, Naaman N. Key factors for a successful surgical guide: A prospective pilot study. J Oral Maxillofac Radiol [serial online] 2020 [cited 2021 Apr 17];8:47-55. Available from: https://www.joomr.org/text.asp?2020/8/3/47/310381
| Introduction|| |
Since the introduction of osseointegrated implants in oral rehabilitation, the medical field has undergone a remarkable advancement in dental implants, till the osseointegration became a predictable outcome.
The anatomical structures that could be at risk during surgery,,, the biomechanical factors, and the increasing esthetic demands which could compromise the treatment outcome, encouraged the surgeon to gain more precision in implant positioning. This could be achieved if implant placement is driven by bone quality, bone quantity, and the planned prosthetic treatment.
In usual cases, mucoperiosteal flap is raised; bone surface is inspected and cleaned. Implants are positioned and their angulation is adapted according to the radiological planning and the intraoperative findings.
In that matter, implant insertion has been and continues to be intuitively guided for most clinicians, and this may lead to suboptimal implant positioning.
The impact of the discrepancy between the placed and the optimal implant positioning, and the difficulty to obtain an optimal prosthetic result can lead to an unsatisfactory outcome. Therefore, prosthetically driven implant surgery has become a subject of interest. In fact, correct implant positioning has obvious advantages such as favorable esthetic and prosthetic outcomes, long-term stability of peri-implant hard and soft tissues as a result of simple oral hygiene, and the potential to ensure optimal occlusion and loading.,
The transfer from the presurgical planning to the operative field became possible using a three-dimensional surgical guide. Its main purpose is to transfer the exact information by guiding the osteotomy in the orientation and the location of the implant as in the presurgical planning.
However, the rapid development of the technology has led to unrealistic clinical expectations for its efficacy and ease of use, while the risk of deviation (transfer error from the software-planning stage to the surgical field) remains substantial, due to several factors that could influence the accuracy of this technique, compromising its safety and effectiveness.
Because of that, most analysis of the literature yields heterogeneous results. Those distortions are due to imperfections that can occur at each of the building steps, but the contribution of each of these steps to the overall error remains unclear.
The surgical guide biomodeling can be divided into three steps starting with the data image acquisition that includes the digital impression by intraoral scanning and the cone-beam computed tomography (CBCT). The second step consists of three main points: image merging, implant simulation, and surgical guide design. And the last step before the surgery itself includes model manufacturing.
The type of support can affect the efficacy and the precision of the guide. To the best of our knowledge, the transfer error of the three-dimensional (3D) guides by inexperienced surgeons to the surgical field, using a tooth-supported guide has not yet been assessed because the overall available clinical evidence on the anatomical precision and its consequence on the prosthetic field is scarce.
In the present study, our primary outcome was to evaluate the accuracy of a dental-supported surgical guide used by two different operators using CBCT images once all the variation factors of the biomodeling are taken into consideration. Our secondary outcomes were to determine the relationship between the planned and inserted implant and to compare the timing of the surgery and the postoperative patient satisfaction between experienced and inexperienced operators.
| Materials and Methods|| |
A total of 11 dental-supported stereolithographic surgical guides were used for 11 patients (5 males and 6 females with ages ranging from 22 to 68 years who visited the Department of Periodontology, Faculty of Dental Medicine, Saint-Joseph University (Beirut, Lebanon) for dental implant surgeries from November 2017 to October 2018. This study was conducted in accordance with the Ethics Committee of Saint-Joseph University School of Medicine (USJ-2016-49). The inclusion and exclusion criteria are presented in [Table 1].
The surgical interventions were performed by either one of the two designated operators; a 3rd-year postgraduate student (RA) and an experienced specialist (NM) decided by a coin toss before each surgery.
The protocol employed consisted of a treatment sequence that involved the following steps: first, an intraoral scan (3 shape TRIOS 3) of the surgical site was taken, using a specific scanning strategy to have the optimal accuracy, starting with the occlusal surface, then the buccal and finalizing with the palatal/lingual, to reduce the number of successive images taken and minimize the point clouds, resulting in a digital model of the surgical site [Figure 1]. Second, all patients underwent preoperative radiological scanning using the Newtom VGI CBCT machine (under the imaging conditions: 110 kV tube voltage, 2.2–8.30 mA tube current, 12 cm × 8 cm field of view, and 0.15 mm voxel size, over a total acquisition time of 18 s), in an open bite position to reduce interarch teeth superposition. Scan data were saved in Digital Imaging and Communications in Medicine (DICOM format). Third, digital 3D surgical planning was undertaken in the 3shape implant studio software. The Intra Oral Scan data were aligned with the CBCT data, and the alignment was verified through the specific software algorithm and manually on the 2D slices. A virtual waxup was made and served as a prosthetic guide for the ideal implant placement. Implants were then virtually placed according to bone anatomy and prosthetic design. Different implant lengths (8, 10, and 12 mm) were used according to bone height. Finally, the surgical guide design was created with a bar added to connect both distal parts to reduce the lateral distortion during the printing [Figure 2]. The design was then exported as an STL file for 3D printing (PROJET MP-3500, 3D Systems).
|Figure 2: Surgical guide simulation with a bar joining the two lateral parts|
Click here to view
Once the guide was printed and finalized, the fitting was checked by positioning the template in the mouth and applying a manual pressure on each side. In case of a misfit or an absence of stability, the IOS and the guide were redone.
Eighteen Straumann tapered bone level implants (BLT: 4.1 mm or 4.8 mm diameter and 8, 10, or 12 mm length) were inserted, in partially edentulous patients, using stereolithographic templates.
The same surgical protocol was followed by both operators: an initial incision at the ridge crest was made, followed by an intrasulcular incision at the adjacent teeth; a full-thickness mucoperiosteal flap was elevated to have a correct fit of the guide; proceeding to the degranulation of the ridge crest with a Rhodes back action and a root planning of the adjacent teeth using a manual scaler. Progressive osteotomies from the pilot to the final drill using drill keys were made under continuous irrigation following the manufacturer recommendations.
After completion of the osteotomies, the implants were placed through the guide with the corresponding implant holder, followed by the placement of healing abutments. Finally, the flap was adapted and sutures were made.
The timing of each surgery was recorded from the first incision to the last suture. The patient satisfaction and comfort levels were also measured using a visual analog scale (VAS- from 1 to 10 – 10 being most satisfied) directly after the surgery (t0) and 1 week later (t7). Following the surgery, all patients underwent a second CBCT under the same imaging conditions.
For a precise calculation, the surface scan and the guide model, both in STL format, were imported into a 3D-system software (Mesh-mixer, Autodesk.Inc) and grouped to make one single model. Using the same software, the guide was then cut, conserving only the guide hole with the sleeve in place. Finally, the total surface scan with the sleeve of the guide was obtained as a single model [Figure 3] in STL format (Simulation model). The postoperative CBCT data in DICOM format were imported into the Blue Sky Plan® (Blue Sky Bio, LLC, Grayslake, IL, USA) software. The simulation model was imported and aligned with the postoperative DICOM data. The final result obtained was the CBCT with the placed implant and the sleeve position of the guide used [Figure 4]. Simulating a new implant, using the sleeve position, a “3D superimposition” of the simulated implant and the placed implant was done. A blind calibrated examiner (NG) made all the deviation measurements, following specific parameters [Figure 5]:
|Figure 3: Initial model and the sleeve guide in place after cutting out the guide for superimposition for postsurgical superposition|
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|Figure 4: A1/A2-simulated implant position acquired from a superimposition of the sleeve position with the STL of the surgical guide at the implant location using the same surgical offset of the originally planned implant. B1/B2: Real implant position was acquired by a superimposition of a new implant on top of the real implant on the postoperative cone-beam computed tomography. Note that the exposure was reduced in two-dimensional to minimize the distortion/artifacts of the real implant. C1/C2: The result was two accurate three-dimensional models of the planned (red) and real (gray) implant|
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|Figure 5: Schematic representation of the three-dimensional angular (α), coronal (MN-M planned implant head; N placed implant head) and apical (OP-O planned implant apex; P placed implant apex) deviation between the planned and placed implant|
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- Angular deviation (α) calculated as the 3D angle between the longitudinal axis of the planned and placed implants [Figure 5].
- Linear deviation defined as the distance between the coronal (M) and the apical center of the planned implant (O) and those of the placed implant [MN and OP in [Figure 5].
In addition, each implant survival rate was measured at 1-year follow-up.
The statistical package software for social sciences (SPSS for Windows, Chicago, IL, USA, version 24.0) was used for statistical analysis of the data. The level of significance was set at P < 0.05. Percentage and frequency were used to describe categorical variables. Mean, standard deviation, and minimum–maximum were used to describe continuous variables.
- The Kolmogorov–Smirnov tests were used to assess the normality distribution of the continuous variables. Parametric tests were executed when variables were normally distributed. Nonparametric tests were executed when variables were not normally distributed
- Student's t-tests and Mann–Whitney tests were used to compare the continuous variables within the two groups
- Analysis of variance and Kruskal–Wallis tests were used for the comparison of continuous variables between two groups
- One-sample t-tests were performed to compare the mean deviation in each group with the theoretical value 0 (absence of deviation)
- Paired Student's t-tests and Wilcoxon tests were used to compare the continuous variables within groups
- 95% confidence interval was calculated for the mean outcomes to assess the precision of the measurements.
| Results|| |
The measurements of the apical, coronal, and angular deviations according to two surgeons and to implant length are presented in [Table 2].
|Table 2: Mean, standard deviation, minimum and maximum values of the apical, coronal, and angular deviations according to surgeons, and implant length (* Statistically significant compared to 0 variations)|
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Our study revealed that the mean apical, coronal, and angular deviations were not significantly different between operators. The mean apical deviation increased with the implant length (8, 10, and 12 mm), but the difference was not significant (P = 0.314), as well as the angular deviation (P = 0.602).
The mean coronal deviation (1.15 ± 0.616) in the whole sample was significantly lower compared to the apical deviation. The mean deviation increased with the implant length (P = 0.479). The mean angular deviation (2.907 ± 1.417) was significantly different from the theoretical value 0.
On the other hand, patient satisfaction was high, with no significant difference between operators at baseline (t0) and at (t7). Regarding the operation time, there is no significant difference between the operators with means of 15.50 ± 4.370 min for operator 1 and 11.71 ± 2.984 min for operator 2 [Table 3]. In addition, intraoperator variation showed that the operation time decreased throughout the study for both surgeons, starting with a mean of 20 min for the first surgeries and finishing with a mean of 12 min for the same number of implants.
All placed implants were prosthetically finalized after 2 months of the surgery. All implants showed a survival rate of 100% after a 1-year follow-up period.
| Discussion|| |
In the present study, we proposed the use of a dental-supported surgical guide followed by a radiological analysis to determine the accuracy and the relation between the planned and placed implant, considering each variation factor and minimizing its effect.
As stated by Vercruyssen et al., the use of stereolithographic guides offers a significant advantage by reducing surgery time and its difficulty.
In an in vitro study, Sarment et al. tried to evaluate the accuracy of computer-generated and conventional surgical guides. They showed an average distance deviation of 1.5 mm at the coronal part of the implant and 2.1 mm at the apex with the conventional template, and 0.9 and 1.0 mm with the stereolithographic guide. They concluded that using 3D-guides provided greater accuracy than conventional guides.
Moreover, the use of dedicated implant planning software and guided surgery could sometimes avoid bone augmentation procedures. Several published articles concluded that it was possible to insert implants with guided surgical protocols in atrophic areas. Fortin in 2008 reported 98% implant survival rate after 4 years in partially edentulous cases with severely resorbed posterior maxilla avoiding sinus augmentation. Implants have been inserted with a CAD/CAM surgical template, based on digital planning, exploiting anterior or posterior wall or the septa of the sinus as well as the palatal curvature. During the 4-year observation period, no complications were recorded, and no implants were lost.
In our study, the accuracy of the guide was evaluated by dissecting the bio-modeling and taking each of its 8 points into consideration to reduce the global variation.
The intraoral scanners (IOS), similar to any 3D scanners, project a light source onto the object. The images captured by sensors are processed by the software, which generates point clouds triangulated, creating a 3D surface model (mesh), then processed to obtain the final 3D model. Imburgia et al., 2017, concluded that the 3shape TRIOS-IOS showed a 24.5 μm and a 31.5 μm precision, respectively, for the partial and full edentulous model. To minimize the variations, between the obtained STL data and the real scanned surface, a scanning strategy should be followed always starting with the occlusal surface, then the buccal and finalizing the scan with the palatal/lingual, to reduce the number of successive images taken and minimize the point clouds.
In addition, CBCT machines perform differently from one to another, and the image quality depends on each machine specification and on the presence of metal in the field of view.
In 2012, Primo concluded that the maximum dimensional error is 0.74% when using the CBCT with a voxel size of 0.25 mm, and 0.82% when the voxel size is 0.40 mm.
The acquisition of tomographic images and incorrect processing of the CBCT data can result in a cumulative variation of a maximum rate of 0.5 mm that should be considered during the simulation. All CBCTs should be taken in an open bite position, to avoid interarch teeth superposition, which facilitates the matching with the surface scan and reduces the matching error to a minimum. As for the patient with multiple metal reconstructions, the use of a radiological guide is recommended.
After the import of the surface scan and the CBCT images into the software (3Shape Implant Studio), the first step of the image processing is the superposition. It implies the overlay of the surface scan over the conjunctive bone and teeth structures. The superimposition is done first automatically and checked/adjusted manually before confirmation. This technique is user sensitive; hence, any variation of the CBCT or error during the surface scanning or the matching will cause variation during this stage that could reach an order of 300 μm. This variation could negatively modify the following readings and placement of the implant. In the present study, the data superposition was done by an experienced operator (NG) in dental imaging to reduce the variation.
A study published by Cassetta et al. in 2013 concluded that 62.6% of the total error is attributed to intrinsic errors. They implied that by reducing the offset of the master tube and the implant height, the variation error (apical and angular variation) would be theoretically reduced. Thus, the apical deviation is proportionally influenced by the offset, the mucosa thickness, and implant length. Minimizing these three points will decrease the apical and lateral variation. For that reason, in this study, a flap was opened to compensate the thickness of the mucosa and to minimize the offset to a minimum. In addition, the usage of a shorter implant limited the linear apical variation. Eight millimeters implants showed less apical and angular deviation compared to longer implants (10 and 12 mm).
Bone types can also be a source of error. Colombo et al. in 2017 concluded that with greater density, the guide is more likely to rotate due to the friction inside the drilling site. Using the software estimation of the bone density before the surgery allows an implant simulation in a more favorable site, thus reducing any probable microdislodgment of the guide.
When the simulation is finalized, the guide in STL format is sent for printing. Camardella et al. compared the precision of three different printed models. Models with the regular base and the horseshoe-shaped base (with and without a bar); the horseshoe-shaped base with a bar had smaller values (−0.702 mm) compared with the other two types of model base. That means adding a stabilization bar to the guide helps decrease the printing variations.
In 2018, Kim published an article where they assessed the precision of dental models printed with 3D printers. The stereolithography showed the least variations of all, with a significant difference in the overall buccolingual width and vertical crown height of 176 ± 73 μm and 141 ± 35 μm, respectively. In the present study, stereolithography was the only printing technique used, and all guides were finalized with the addition of distal stabilization bars.
Another variation factor is the guide support type; various surgical guide designs are described in the literature based on the supporting surface:
- Tooth-supported guide: placed entirely on teeth
- Mucosa-supported guide: positioned directly on the mucosa
- Bone-supported guide: placed on the bone after raising a mucoperiosteal flap
- Special supported: attached to implants inserted before or during the actual implant surgery).
Ozan in 2009 evaluating 110 implants using tooth, bone, and mucosal supported guides, found that tooth-supported guides showed significant smaller deviations compared to mucosal and bone-supported guides. In addition, he observed that accuracy improves with a greater supporting surface (maxilla vs. mandibula) or with the fixation of the surgical guide.
In addition, Cassetta et al. in 2013 concluded that computer-aided implant placement is a useful complement to conventional surgery, but it only offers a guide and does not replace surgical experience and knowledge. Vasak et al. in 2011 also reported a clear learning curve regarding the accuracy of implants placed with NobelGuide templates (that could limit the surgical complications). The level of experience plays an important role in the variations including patient selection, drilling technique, and heat management.
Furthermore, Gerlinde et al. published an article in 2014 investigating the accuracy of stereolithographic guides executed by inexperienced surgeons (in both implant and guided surgery) and comparing these data with data of an experienced implant surgeon assuming that with less experience, problems frequency such as excessive heat during drilling, and nonstabilization of the implant may increase. Results showed that the level of experience had no influence on the implant placement when all steps were supervised by experienced dentists. In the present study, two different operators did the surgeries. The results showed the lack of significant difference between the two operators regarding the duration of the surgery, patient satisfaction, and implant precision. These findings could be attributed to the fact that both operators had a certain level of knowledge in implant surgery. However, a clear learning curve was apparent, emerging from the fact that surgical timing was reduced through the study for both operators, starting with a mean of 20 min for the first surgeries and finishing with a mean of 12 min. That is in accordance with multiple studies.,,
Theoretically, all errors could have a cumulative effect even if, in most instances, they compensate each other. To our knowledge, there is no published study taking into consideration all the variation key factors together and proposing ways to minimize their effect.
In Cassetta's study, evaluating the accuracy of a surgical guide comparing 3D positions of planned and placed implants, they compared images of 129 implants in 28 subjects. They observed a deviation at the coronal and apical portions of implants, and at the angulation, respectively, of 1.59 ± 0.68 mm, 2.07 ± 0.88 mm, and 4.11° ± 2.4°. Even without a clinical significance, they concluded that keeping a safety zone of 2 mm is necessary to avoid critical anatomical structure injuries. They assessed the influence of intrinsic factors on the precision of the surgical guide. They observed that, in the maxilla, the accuracy of the guides was improved due to a greater supporting surface and also with the fixation of the guide. In the present study, variations were slightly lower: the mean coronal variation was 1.15 ± 0.616 mm, the apical variation was 1.43 ± 0.77 mm, and the angular variation was 2.90° ± 1.41°. This difference is mostly attributed to the fact that, in the study of Cassetta et al., the authors took into consideration the intrinsic and clinical factors, and the guides used were mostly mucosa/bone supported. In our study, the intrinsic factors were taken into consideration to reduce the variation in addition to other factors.
In a systematic review published by Tahmaseb in 2014, including 38 articles, the average deviation at the implant entry point was 1.12 mm, with a maximum deviation of 4.5 mm, 1.39 mm at the apex, with the maximum of 7.1 mm; and the average angular deviation of 3.89° with a maximum of 21.16°. From these data, we deduce that guided surgery has a good accuracy level and allows applying these protocols in complex cases such as severe bone atrophy. However, it is crucial to take the variations into consideration.
In the present study, the mean results were similar to the results stated by Tahmaseb showing that some deviations between the planned and inserted implants exist. However, the main difference is in the variations from the mean value, which are 0.61 mm, 0.77 mm, and 1.4°, respectively, for the coronal, apical, and angular deviation that shows a consistency in the results obtained even with different operators.
Regarding variation related to bone type, multiple studies have already proven that the greater the bone density, the higher is the variation.,,,,,,, In the present study, type II bone showed the highest variation. However, this is attributed to the fact that most of the placed implant was in a type II bone, and only two implants were placed in type I bone.
3D-guide is often associated with flapless surgery. Even though the literature is lacking long-term studies comparing directly the success rate of conventional and flapless implant placement, many authors seem to agree that implant survival rates are comparable regardless of the protocol chosen. In the present study, an open flap procedure was used, but the visual analog scale noted by each patient showed high satisfaction with minimal discomfort with both operators. Furthermore, all implants placed showed a 100% survival rate after a 1-year period.
However, many articles highlighted an important number of complications. It included surgical complications such as guide fractures or prosthetic complications such as misfits and prosthetic fractures. The rate of complications seemed to be closely related to the technique learning curve. From the present study, no conclusions could be drawn concerning the prosthetic complications value because there was no immediate temporization. None of the cases have shown any guide fracture due to the stabilization bar and the reduced rotational force applied to the guide.
Due to the limited number of implants placed in this study, further studies should be done with a bigger number of implants and a longer observational period, taking into consideration all the variation parameters and the ways prescribed to minimize their effects.
An important fact to consider in future studies is bone temperature control while an external irrigation system is used in conjunction with the surgical guide.
On the other hand, a clear description of the postsurgical superposition is missing from the literature. For that reason, a detailed (step-by-step) superposition technique was described in this article.
| Conclusion|| |
As observed in the study, the accuracy of the guided surgery depends on all the cumulative and interactive errors involved, from the dataset acquisition to the surgical procedure.
Some recommendations should be followed to reduce the variations:
- Respecting the recommendation for the impression technique
- Open bite position during the scanning and repetitive evaluation of the CBCT machine
- Reducing the offset to the minimum and using shorter implants
- Adding a stabilization bar to the guides and maximizing its support area
- Respecting the learning curve and the knowledge for the overall implant surgery and the digital guide system more specifically.
The authors would like to express their gratitude to Dr. Nada OSTA for performing the statistical measurements.
All surgical costs were supported directly by the patients. All necessary equipment were already available at the university.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]