|Year : 2016 | Volume
| Issue : 3 | Page : 57-61
Cone beam computed tomography guided surgical stent: A preimplant planning procedure, a pilot study
Kritika Saxena, Bharat M Mody, Akshay Rathore
Department of Oral Medicine and Radiology, ITS Dental College, Muradnagar, Ghaziabad, Uttar Pradesh, India
|Date of Web Publication||21-Dec-2016|
Department of Oral Medicine and Radiology, ITS Dental College, Muradnagar, Ghaziabad, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The aim of the present study was to evaluate the efficacy of cone-beam computed tomography (CBCT)-based radiologic stent in guidance for preimplant placement procedures. Setting and Design: This study was a pilot study conducted among 5 patients who presented for dental implants and attending the department of Oral Medicine and Radiology, ITS Dental College, Muradnagar for CBCT volumetric scans. Materials and Methods: The dimensions of bone available for implants were measured from the scans. A radiologic stent was prepared on the study model using three radiopaque pins per implant site, which simulated the implant in the CBCT scan. The pin which was in the direction of the residual bone was identified and retained, and the remaining pins were removed. The retained pin was utilized and the final surgical stent was prepared. It was checked if the final implant placement could be accomplished surgically using the modified stent. Results: A total of 7 implants were inserted. The final implant placement was based on the CBCT data and was evaluated by postoperative radiographs. All the implant sites showed proper placement of the implants. Conclusion: The stent used in our study was cost effective and easy to fabricate. Apart from the anteroposterior direction, it was also possible to give buccolingual direction to the implant, reducing the chances of perforation.
Keywords: Cone beam computed tomography, implant planning, surgical stent
|How to cite this article:|
Saxena K, Mody BM, Rathore A. Cone beam computed tomography guided surgical stent: A preimplant planning procedure, a pilot study. J Oral Maxillofac Radiol 2016;4:57-61
|How to cite this URL:|
Saxena K, Mody BM, Rathore A. Cone beam computed tomography guided surgical stent: A preimplant planning procedure, a pilot study. J Oral Maxillofac Radiol [serial online] 2016 [cited 2020 Oct 30];4:57-61. Available from: https://www.joomr.org/text.asp?2016/4/3/57/196347
| Introduction|| |
Implant-supported prosthesis requires an estimation of the correct mesiodistal and buccolingual direction of implant placement in the treatment planning stage.  In the absence of easy availability of computer-aided design and computer-aided manufacturing (CAD-CAM) facility, a new manual method was devised for fabrication of radiologic stent with the guidance of cone-beam computed tomography (CBCT) scans. In this study, we fabricated a cost effective surgical stent with metal markers and evaluated its efficacy in determining the positioning and angulation of final implant placement through surgical stent.
The aim of the present study was to study the efficacy of CBCT-based radiologic stent in guidance for preimplant placement procedures. The study had the following objectives:
- To prepare a radiologic stent using radiopaque pins to guide the implant simulation in a CBCT scan of a patient going for dental implant placement
- To identify the pins which are in the direction of the residual bone and utilize the directions for the implant simulation
- To simulate implants on CBCT images in edentulous spaces with the help of radiopaque pins in the stent
- Remove the guiding pins and prepare the final surgical stent for implant placement and check if the final implant placement could be accomplished surgically.
| Materials and Methods|| |
The study included 5 patients who reported to the Department of Oral Medicine and Radiology, ITS Dental college, Muradnagar, for the replacement of their missing teeth and desired implant-supported prosthesis. After all the preliminary hematological and radiographic investigations, the patients were included in the study. A diagnostic impression was made of the maxillary and mandibular arches with an impression tray (Jabbar India), an irreversible hydrocolloid impression material. Study models were prepared using these impressions. The edentulous spaces for the placement of implants were identified. According to the patient's expectations, the number of implants to be placed and the number of final prosthesis were finalized. On the study model (with edentulous span), one point was marked at the crest of the ridge (reference point) at the site of the final prosthesis; this reference point was guided by the abutting natural tooth (point 1) [Figure 1]. If more than one implant were to be placed in the edentulous span, another point was marked on the crest for the second implant again at the crest of the ridge (point 2). These two points were marked 7 mm apart [Figure 1]. Two points were marked buccally and lingually at a distance of 1.5 mm on either side of points 1 and 2 [Figure 1]. On the study model, a self-cure acrylic resin custom tray (Rapid Repair, Pyrex) was fabricated [Figure 2]. All the marking on the cast were transferred to the acrylic custom tray using a permanent marking pen [Figure 2]. Holes were drilled along the points marked using a tapered fissure crosscut bur no. 701 (head diameter 1.2 mm) up to a depth of 3 mm [Figure 2]. On the three points marked previously along points 1 and 2, one metal post (Size 1; length 8 mm) each was inserted and stabilized by modeling wax (Hiflex). This resulted in a total of three posts at each respective point. The central post was in the direction of the abutting tooth. One was directed buccally by fanning it out 5° while the other one was similarly fanned out lingually [Figure 3].
|Figure 1: Points 1 and 2 marked 7 mm apart. Two markings on either side of points 1 and 2 at a distance of 1.5 mm|
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|Figure 2: Acrylic plate on the edentulous area with the markings. Metal posts: size 0, 8 mm in length|
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|Figure 3: Metal post inserted and stabilized by modeling wax at previously marked points; fanning 5° buccally and lingually|
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Before subjecting the patients to CBCT scan, an approval by the ethical committee of the institution was obtained. Patients were informed about the entire procedure before going for CBCT scans and an informed consent was taken from each patient. The entire assembly was placed inside the patient's mouth, and a CBCT Scan was taken using Newtom Giano (90 kVp, 10 mAs, 9 s exposure time, and 5 × 5 field of view).
The slice thickness was kept at 1.0 mm and cross-sections were generated along the arch. The scan data was interpreted in multiplanar reconstruction (MPR) mode and viewed in all the three orthogonal planes i.e., sagittal, coronal, and axial. Cross-sections were used to calculate the buccolingual dimension, superior-inferior bone dimensions i.e., bone width and height. The buccolingual dimension was measured from cortex-to-cortex and superior-inferior dimension was measured from the crest of the ridge till approximately 2.0 mm superior to the inferior alveolar canal [Figure 4] and [Table 1]. , Similar measurements were accomplished at each implant site. Implant simulation was done at each site, taking into consideration the available height, width, and the direction of the residual bone [Figure 4] and [Table 2]. The radiopaque pin which closely matched the implant simulation was earmarked [Figure 5].
|Figure 4: Measuring the buccolingual and supero‑inferior dimensions at the implant sites|
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According to Almong et al.,  "In the bucco-lingual plane the angle between the implant trajectory and residual bone trajectory should be less than 20 degrees to prevent unfavorable bending moment." Based on this assumption, out of the three metal markers, the marker with angulation less than 20° from the direction of the implant simulation was identified [Figure 5] and [Table 3]. The markers were selected for each implant site. After assessing the angulation, all the pins were removed. The holes which did not correspond to the direction of the simulation/metal marker in the acrylic base plate were closed using self-cure acrylic resin [Figure 6]. The holes corresponding to the selected metal marker were kept patent.
|Figure 6: Holes corresponding to the selected marker (marked with arrows). Assessment of the relative parallelism of the implants|
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|Table 3: Planned implant position in relation to buccolingual angulation (coronal view)|
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The final acrylic surgical stent was prepared such that it had sufficient thickness to create a channel for the unidirectional insertion of bur. During the surgical procedure, as the depth of bur increased, acrylic was selectively grinded to allow further insertion of drilling bur. This procedure was continued until half the bur was inserted in the bone. Stent was then removed and the remaining insertion was done. The final depth was achieved by the drilling bur.
| Results|| |
Implant simulations on volumetric data obtained by CBCT scans for all implant sites were accomplished. Radiologic stent and surgical stents were prepared; implants were placed. The relative parallelism was assessed by taking a postoperative radiograph of the implant site, which was found to be accurate when compared to the preoperative three-dimensional assessment done using CBCT [Figure 6] and [Table 4].
|Table 4: Achieved implant position in relation to mesiodistal parallelism (sagittal view)|
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The primary aim of the project was to check the right direction of the implant, which was accomplished. As this is a qualitative assessment, no statistics could be presented. The radiographs show the final result.
| Discussion|| |
For a successful implant supported definitive restoration, the implant must be placed at the correct and preplanned position and angulation. The mesiodistal placement of the implant should aid in the preservation of papilla and provide anesthetic implant restoration profile.  The implant should be placed at least 1.5 mm from the adjacent teeth with a minimum 3 mm interimplant distance. The distance of implant from buccal and lingual cortical plates should be greater than 0.5 mm. ,,] In the buccolingual plane, the angle between the implant trajectory and residual bone trajectory should be less than 20° to prevent unfavorable bending moment. 
The foremost advantage of the stent used in this study is its surgical ease, simplicity, precise accuracy, and low cost. It can be fabricated with minimum laboratory procedures which are used in routine dental practice. On the other hand, the fixed-type screw retained implant stents which are fabricated with the help of computed tomography and CAD/CAM technology are very costly and require more time and laboratory procedures. ,, The stents fabricated with the radiopaque metal markers provide radiographic as well as clinical ease for optimum implant installation. The drill holes can directly be made through the stent, and hence, the implant surgery may become less traumatic with decreased operative time, resulting in accelerated post-surgical healing, fewer postoperative complications, and increased comfort and satisfaction for the patient. In the present study, it was possible to determine both, buccolingual and mesiodistal, positions of the implants, thus increasing the accuracy in the final placement of the prosthesis.
Akca et al. suggested a method to fabricate stents with a 4-mm flat plate to achieve mesiodistal parallel placement of multiple implants, however, this stent could not determine the buccolingual orientation of the implant.  Another stent design for multiple implant placements was proposed by Takeshita et al., where they used an acrylic resin stent with silicone markers. In their design, the buccal/lingual half of the stent was removed at the time of the surgery to provide adequate visualization of the site. This can lead to compromised control of implant drill because it can deviate towards the unsupported site. In our stent, the drill channel is supported from all sides. 
In multiple implant situations, nonparallel implant placement is the primary cause of nonaxial loading and subsequent failure. , The implants placed using stents are more accurately positioned than those without the stent.  Recent ones though being very accurate are expensive require extensive laboratory set up for their fabrication. The stent used in our study is cost effective and easy to fabricate. Apart from the anteroposterior direction, it is also possible to provide buccolingual direction to the implant, reducing the chances of perforation. It provides adequate accuracy as well in terms of implant position and angulation.
On the other hand, our study had the following limitations:
- The study was done as a pilot study on a small sample size
- Qualitative assessment of ease both for patient and the implantologist needs to be evaluated
- The method should also be evaluated by different implantologists and radiologists on a larger sample for statistically valid effectiveness.
| Conclusion|| |
In conclusion, we could achieve an accurate position and angulation of implants in our study with the guidance of CBCT images. Hence, the use of dual purpose radiographic and surgical stents may be employed for treatment planning and placement of dental implants with further studies.
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], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4]