JICDRO is a UGC approved journal (Journal no. 63927)

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CASE REPORT
Year : 2012  |  Volume : 4  |  Issue : 1  |  Page : 29-36

Significance of cone beam computed tomography based implant treatment planning and fabrication of stereolithographic surgical guides for implant therapy in the nasopalatine canal region


1 Department of Biomedical and Diagnostic Sciences, School of Dentistry, University of Detroit Mercy, 2700 Martin Luther King Jr. Blvd., Detroit, MI 48208, USA
2 Private Practice, Plymouth, Michigan, USA
3 Department of Periodontics and Oral Medicine, The University of Michigan, School of Dentistry, Ann Arbor, MI 48109-1078, USA
4 Department of Periodontics, Meharry Medical College, School of Dentistry, Nashville, TN 37221, USA
5 Department of Periodontology and Oral Implantology, Temple University Office of the Dean, Philadelphia, PA, USA
6 Restorative Dentistry, University of Detroit Mercy School of Dentistry, Detroit, MI 48208, USA

Date of Web Publication23-Apr-2014

Correspondence Address:
Ashok Balasundaram
Department of Biomedical and Diagnostic Sciences, School of Dentistry, University of Detroit Mercy, 2700 Martin Luther King Jr., Blvd., Detroit, MI 48208
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2231-0754.131400

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   Abstract 

Implants are being used in practice today with ever increasing types of implants and simple procedures through which dentists can place them. However, the chance for a complication to occur while placing implants has been largely under-estimated. This is primarily because emphasis is not placed in avoiding important neurovascular structures such as the nasopalatine canal during implant surgery. Cone beam computed tomography (CBCT) is being widely utilized in implant treatment planning. Third-party software is applied to CBCT data to enable treatment planning. Several of these treatment plans are used to fabricate stereo lithographic guides which will help with placement of the implant at the planned site with total precision. This case-review explains how CBCT can help in placing implants with the help of a surgical guide in anatomically challenged areas such as the nasopalatine canal.

Keywords: Cone beam computed tomography, implant treatment planning, nasopalatine canal, stereolithography, surgical guide


How to cite this article:
Balasundaram A, Seluk LW, Benavides E, Juluri R, Suzuki JB, Gurun D. Significance of cone beam computed tomography based implant treatment planning and fabrication of stereolithographic surgical guides for implant therapy in the nasopalatine canal region. J Int Clin Dent Res Organ 2012;4:29-36

How to cite this URL:
Balasundaram A, Seluk LW, Benavides E, Juluri R, Suzuki JB, Gurun D. Significance of cone beam computed tomography based implant treatment planning and fabrication of stereolithographic surgical guides for implant therapy in the nasopalatine canal region. J Int Clin Dent Res Organ [serial online] 2012 [cited 2019 Mar 21];4:29-36. Available from: http://www.jicdro.org/text.asp?2012/4/1/29/131400


   Introduction Top


Implant supported restorations have become a simple and cost-effective alternative for replacing missing teeth. [1],[2] Today, implant surgery has evolved from a specialist-based treatment modality to one performed by an increasing number of general dentists. With the ever-increasing number of implants being placed in practice, there is likely to be an overall increase in the chance for untoward incidents during implant placement. [3],[4],[5],[6] Complications arise mainly from direct surgical contact with important structures such as inferior alveolar nerve and vessels, mandibular incisive canal, mental foramen and nerve, lingual nerve and artery, mylohyoid nerve, submandibular and sublingual fossa, maxillary sinus and nasopalatine nerve and vessels. [7],[8],[9],[10],[11],[12],[13],[14],[15],[16] Due to the absence of adequate pre-operative implant treatment plan, there have been reports of exsanguinating life-threatening circumstances due to wrongful placement of implant injuring vital structures such as the lingual artery. [17]

The nasopalatine canal which transmits the nasopalatine nerve and sphenopalatine artery possesses strategic importance due to its anatomical position (seen on a radiograph as a pair of radiopaque lines, extending from the incisive foramen to the level of the nasal floor) in the maxillary midline. [18],[19],[20] The morphological, anatomical and dimensional variation of the nasopalatine canal may interfere with successful implant placement in the region. [21],[22] Therefore, acquiring additional information of the nasopalatine canal from sources such as radiographs has the potential to improve the outcome of implant placement in the maxillary midline region.

To date, the only proven method for pre-operative evaluation of the nasopalatine canal has been radiography. [23],[24] Conventional two-dimensional intra-oral radiographs have been traditionally used to assess structures of morphological and pathological interest such as the nasopalatine canal. However, the image of the canal is liable to distortion due to superimposition of other anatomical structures and also suffers from inherent geometric characteristics of an image produced as a result of transmission (conventional) radiography. Furthermore, true position and morphologic characteristics (size and shape) of the canal visualized on a two-dimensional radiograph can vary largely due to projection and angulation changes. [23]

Cone beam computed tomography (CBCT) is becoming widely utilized for dentomaxillofacial applications and appears to be replacing medical computed tomography (CT), especially for implant treatment planning. Approximately, 80% of patients referred to imaging centers for CBCT scans would later be treated with implants. [25] The spatial resolution of these CBCT images is comparable to that of medical CT images. It is also evident that the spatial resolution of CBCT images is adequate for diagnostic needs in the head and neck region, particularly for implant treatment planning.

Initially, controversies were raised about the role of CBCT in implant treatment planning. [26],[27] The advent of interactive computer software programs for implant treatment planning rendered the appropriate solution. [28],[29] Several software packages, e.g., Facilitate TM (Astra Tech Dental, Waltham, MA), Nobel Procera (Nobel Biocare USA), Keystone dental (Keystone Dental, Burlington, MA) provide a 3D image based platform for pre-operative implant treatment planning. The usefulness of scan data from both medical CT and dental CBCT, for accurate and predictable 3D computer-based planning has already been proven. [26],[30] It is important to understand that these software programs are not only used to gather pertinent information on the fixture size and orientation but also allow for virtual 3D positioning of the implant fixture to assess proximity to neurovascular structures such as the nasopalatine canal. [31],[32] Once the software-based treatment planning has been completed, the dataset would be used for the manufacturing of stereo lithographic surgical guides. [33],[34],[35]

Through this case series, we describe the significance of 3D radiographic assessment of the nasopalatine canal (including morphological and dimensional characteristics) prior to implant placement in the anterior maxilla. Further emphasis has been placed on the role of a 3D interactive software program utilizing CBCT data in making changes to the treatment plan to avoid this neurovascular structure and later fabricate a stereo-lithographic guide.


   Case Reports Top


Case 1

Dental history


In October 2008, a 44-year-old male was referred to a prosthodontist by his dentist for consultation regarding tooth replacement in the upper left anterior region, especially teeth #9, #10 and #11. History revealed the patient was in a car accident 3 weeks prior to reporting to a general dentist in which his car was hit by a moving train. There was no significant medical history. Clinical examination revealed the crown fracture on tooth #8 and palatally inclined fracture associated with tooth #9. Radiographic examination

(full mouth radiographic series) showed the fracture of the crown of tooth #8 exposing part of the restoration [Figure 1].
Figure 1: Full mouth radiographs for case 1

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Also, it was interesting to note that the nasopalatine canal was prominent and the canal diameter slightly increased (but within normal limits) on the radiograph. Also, tooth #10 and #11 were avulsed (lost as a result of the trauma). Tooth #12 demonstrated a fractured cusp. Teeth #10 and #11 were fully avulsed during the accident [Figure 2]. It was also evident from the radiographs that there was significant crestal bone loss (buccal and lingual) in the region of the avulsed teeth [Figure 1]. Tooth #12 showed evidence of cusp fracture, which was later confirmed to be vital and did not require endodontic treatment prior to crown preparation, as per the endodontist.
Figure 2: Clinical photograph (Initial) for case 1

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Treatment plan

The initial treatment plan included removal of fractured tooth #9 followed by implant placement in the region of teeth #9, #10 and #11. Tooth #12 would be restored at a later time. The final treatment plan would involve replacing teeth #9, #10 and #11 with endosseous implant fixtures and individual crowns involving teeth #8, #9, #10, #11 and #12. Since there was significant bone loss in #10 and #11 areas, bone grafting was necessary prior to implant placement. The patient was referred to an oral surgeon who successfully grafted the proposed sites with graft material and restored crestal bone volume and architecture in preparation to receive implant fixtures.

After preliminary analysis of the implant sites of teeth #9, #10 and #11 areas, including the bone loss pattern following trauma and the anatomy of the nasopalatine canal on the radiograph, the prosthodontist determined that free hand placement of three individual implants in the proposed sites would definitely pose a challenge. Therefore, he decided to obtain a CBCT scan of the proposed implant sites and later using a dental implant treatment planning software (Facilitate, Materialise Inc.) develop a stereo-lithographic surgical guide to place implants.

Cone beam computed tomography scan

The patient was referred to a local oral and maxillofacial imaging center for CBCT scan of the head to include the jaws and maxillofacial structures. A second (new) generation 17-19 Platinum I-CAT CBCT scanner (Imaging Sciences International, Hatfield, PA) was used to scan the patient's head. The scan resolution was set at 0.25 mm voxel size. The other scan parameters were 120 kv and 12 mA. The scan time was 8.9 s. The dataset acquired from the scan was saved in DICOM (Digital Imaging and Communication in Medicine) format to enable treatment planning using the Facilitate (Materialise) software.

Implant treatment planning

Three dimensional multiplanar images were reviewed from the entire data set including anatomy of interest, i.e., anterior maxilla. Virtual implant templates of various diameters and tapers were selected from the implant library embedded in the software and placement simulated at the proposed implant sites. Implant templates were tried at the #9, #10 and #11 sites. The prosthodontist had initially decided to use a 5.5 mm diameter implant in the tooth #9 site and

5.0 mm diameter implants in the tooth #10 and #11 implant site. However, when the placement of the implant templates of these sizes was virtually simulated in the anterior maxilla using the software, the anterior most implant template seemed to disrupt the cortical border of the nasopalatine canal and appeared to be lodged in the canal.

At this point, a maxillofacial radiologist was summoned to evaluate the proximity of the virtual implants to the nasopalatine canal. Upon reviewing the treatment plan already done with the virtual implants, the radiologist and the prosthodontist concluded that the diameter of the final implants had to be reduced in order to accommodate three implant fixtures at the proposed sites. It was crucial to confirm the intended position of the virtual implants since the final data set after effective treatment planning was planned to be sent to a lab outside of the US for fabrication of a stereo-lithographic surgical guide. After careful review of the treatment plan, it was decided to reduce the implant diameter to 5 mm, 4.5 mm and 4.5 mm in the #9, #10 and #11 areas respectively. At this time, the virtual implant radiographically cleared the nasopalatine canal and the anterior most implant template was only superficially in contact with the cortical border (left side) of the nasopalatine canal [Figure 3] and [Figure 4]. Upon confirmation of the treatment plan by the prosthodontist and the radiologist, the data set with the treatment plan was sent electronically for fabrication of the stereo lithographic surgical guide.
Figure 3: Facilitate software view (panoramic) final treatment plan sent to materialise for fabrication of surgical guide for case 1

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Figure 4: Facilitate software view (axial) final treatment plan sent to materialise for fabrication of surgical guide for case 1

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Implant surgery

With adequate pain control, tooth #9 was non-traumatically extracted and other implant sites in the region of #10 and #11 were also prepared for single-stage implant placement surgery. Implant fixture of sizes 5.0 mm and two 4.5 mm implants (Astra Tech Dental, MA, USA), were placed in the areas of teeth #9, #10 and 11, respectively with the help of the stereolithographic surgical guide. Implant fixtures were covered with the corresponding healing abutments. Healing was uneventful after one month following to implant placement [Figure 5]. The implant was later adequately restored [Figure 6]. Intra-oral periapical radiographs were taken during placement of each implant fixture followed by a panoramic radiograph upon completion of the entire procedure. Post-operative radiographs confirmed that all the implants were placed in their respective ideal site as planned when compared to the originally treatment planned images [Figure 7]. Measurements taken from the pre-operative treatment plan, and post-operative radiographic images seemed to correspond within a margin of ±0.5 mm.
Figure 5: Clinical photograph (1 month after implant placement) for case 1

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Figure 6: Clinical photograph with final restoration for case 1

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Figure 7: Post-operative radiograph (3 months after implant placement) for case 1

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Case 2

Dental history


In June 2008, a 79-year-old male patient reported to a prosthodontist for consultation regarding dental treatment in the upper anterior region, especially teeth #7 and #9. Dental history revealed that the patient was at high risk for caries and several teeth in the maxilla, and mandible were removed and replaced with endosseous implant fixtures and adequately restored. No relevant medical history was elicited. A full-mouth radiographic examination revealed that #7 was grossly carious and was fractured down to the root level. Tooth #8 was endodontically treated and restored. Tooth #9 was also completely fractured at the gingival level. Teeth #7 and #9 were therefore considered non-restorable. Tooth #10 and #11 were already replaced with implants and restored. Implant fixture replacing the tooth #10 appeared to be mesially tilted and appeared to impinge on the periodontal ligament space of the root of tooth #9 [Figure 8]. History also revealed that the patient had already consulted a periodontist who advised that due to the position of the mesially inclined implant fixture of tooth #10 and the presence of the nasopalatine canal, implant therapy was not an option for replacing the tooth #9. The nasopalatine canal was also identified and assessed on the two-dimensional periapical radiograph.
Figure 8: Initial periapical radiograph for case 2

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Initial treatment plan

The initial treatment plan included removal of tooth #7 and #9 followed by implant placement in the region of the extracted teeth. The final treatment plan would involve immediate implant placement of tooth #9 following removal of the root. The same procedure would later be followed for tooth #7. Later, the implants would be loaded occlusally by fabricating individual crowns for the implants in the area of teeth #7 and #9. At this point, it was decided to perform advanced imaging and obtain cross-sectional information of bone, especially in the region of teeth #7 and #9 to establish feasibility of implant placement due to space constraints.

Cone beam computed tomography scan

The patient initially had a two-dimensional advanced imaging procedure, i.e., linear tomography. The findings on the linear tomographic images confirmed the findings from initial intra-oral periapical radiographs. However, due to superimposition of adjacent structures into the slices of interest, anatomy such as the nasopalatine canal was not clearly discernable. Therefore, the patient was referred to a local oral and maxillofacial imaging center for CBCT scan of the maxilla and mandible. A second generation 17-19 Platinum I-CAT CBCT scanner (Imaging Sciences International, Hatfield, PA) was used to scan the patient's head. The scan resolution was set at 0.25 mm voxel size. The other scan parameters were 120 kv and 12 mA. The scan time was 8.9 s.

Three dimensional multiplanar images were reviewed from the entire data set including the region of interest, i.e., anterior maxilla. Upon initial review of the nasopalatine canal on the CBCT images, tooth #9 and the mesially tilted implant of tooth #10, it was decided that free-hand immediate implant placement to replace the tooth #9 would be difficult. In order to perform virtual treatment planning, the CBCT data set was converted into a DICOM format and analyzed through Facilitate TM (Astra Tech Dental, Waltham, MA).

Implant treatment planning with interactive software

A maxillofacial radiologist was consulted for the treatment planning phase. The treatment planning software Facilitate TM (Astra Tech Dental, Waltham, MA) allowed various implant templates to be placed virtually so that the appropriate implant fixture size could be confirmed due to the constricted space available between the nasopalatine canal and mesially angulated implant fixture #10. Further analysis of the case revealed that removal of existing tooth #9 would lead the way for a safe placement of a 5 mm diameter (15 mm length) tapered implant (Straumann) which would avoid the nasopalatine canal completely and occupy the space between implant at tooth #10 site and the nasopalatine canal. Upon confirmation of the treatment planning by the prosthodontist and the radiologist, the implant treatment planning data set was sent electronically for fabrication of the stereo-lithographic surgical guide.

Implant surgery

With adequate pain control, tooth #9 site was prepared for single-stage implant surgery immediately following extraction. Tooth #9 was non-traumatically extracted and an Astra Tech Dental Implant fixture (5.0 mm diameter, 13 mm length) was placed with the help of a surgical guide [Figure 9] immediately and covered with a healing abutment (Astra Tech, MA, USA). Soft tissue over the site was sutured after placing an adequate collagen plug around implant fixture. Patient did experience more than normal bleeding during the procedure. However, normal radiographic osseointegration was noticed one month following to implant placement [Figure 10]. The implant was later restored.
Figure 9: Stereolithographic surgical guide on model for case 2

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Figure 10: Clinical photograph (1 month post-operative) for case 2

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   Discussion Top


The increasing number of implants placed in today's dental practices proportionately increases the probability of iatrogenic injury to critical structures such as the neurovascular structures contained in the nasopalatine canal. [15],[19] Other structures such as maxillary sinus also gain importance when sinus grafting procedures are planned to place implants in a severely resorbed maxillary ridge. This case report emphasizes, in particular, the significance of the nasopalatine canal when implant therapy is considered in the maxillary incisor region. Furthermore, methods to avoid this important anatomical landmark by utilizing advanced 3D imaging modalities combined with pre-operative treatment planning have been elucidated with case examples. The fabrication of a surgical guide based on the treatment plan generated from CBCT data and the accuracy of such guides to avoid neurovascular structures during surgery has also been explained in this case report.

The reasons for revisiting the characteristics of the nasopalatine canal, in particular, in this paper, are multifold. Firstly, the nasopalatine canal shows considerable variation in location, size and shape. These variations need to be kept in mind when considering implants in the upper anterior region. The diameter of the canal is considered normal if it is less than 6 mm and pathology is considered if the diameter exceeds 10 mm. It is also imperative to make sure that there is adequate bucco-lingual width of bone anterior to the canal during implant placement. The average distance from the anterior cortical border of the canal to the buccal cortical plate of anterior maxilla is 5.9 mm, with a range between 2.9 mm to 13.6 mm. It has been reported that in 4% of cases, the size of the nasopalatine canal prevented implant placement. [18],[26] Secondly, the nasopalatine canal undergoes changes following extraction of teeth in the maxillary anterior region and subsequent resorption of alveolar bone. The canal becomes wider in these circumstances further increasing the probability of injury during implant placement. Furthermore, the canal widens as age advances. It is, therefore, difficult to ascertain at times if the canal widened due to factors such as age or following resorption of the ridge. Thirdly, the canal shows a variation among males and females. Males tend to have a wider nasopalatine canal. It has also been reported that there could be a correlation between the shape of the nasopalatine canal and race, and lastly, the presence of accessory canals, though uncommon, is important when considering implant placement in the maxillary incisor region.

Due to the anatomic variability in morphology and dimensions of the canal together with the variability in the content of the canal, we decided to explain through a case series, effective ways to investigate the canal and avoid it, through 3D cross-sectional imaging and the fabrication of surgical guides.

CBCT is a low-cost, low-dose procedure and is currently available at many dental institutions and imaging centers throughout the US. [36],[37],[38] CBCT is most commonly used to image the maxillofacial region for pre-operative evaluation of alveolar bone prior to implant placement. [39] The evaluation of bone with CBCT helps the implantologist to assess the quality and quantity of cortical and cancellous bone, especially in the bucco-lingual dimension. Important neurovascular structures and occult pathoses in the region of the proposed implant site can also be assessed. [40] There is no doubt that 3D imaging, particularly CBCT, has increased the success of implant therapy in modern times. [25],[40],[41] It is, however, difficult to quantify how much CBCT imaging alone contributes to the success of implant therapy.

Scientific literature is beginning to emerge on the various applications of CBCT in the head and neck region, with particular reference to dental implant therapy. [37],[42],[43] This includes reports on assessment of critical neurovascular structures at implant-bearing sites and the advantage of pre-surgical planning with CBCT data. [40],[44],[45] There have also been a few reports in literature describing the application of computer technology in implant treatment, including the ability to fabricate surgical guides using CBCT data.

As a wide variety of techniques in implant therapy become widely accepted and utilized, it is recommended that CBCT imaging be embraced as part of the implant treatment planning protocol. [29],[45],[46],[47] This involves utilizing CBCT in the diagnostic work up of a potential implant treatment plan and extending this to develop a confirmative treatment plan using appropriate software. [46],[48],[49],[50],[51] Using the treatment planning software ensures that implant placement is prosthetically-driven. [29],[45],[46],[47] The treatment plan concludes with the fabrication of surgical guides. The use of surgical guides decreases the complications that might arise due to free-hand placement of implants following incorrect orientation of the implant fixture and damage to neurovascular structures. [33],[52],[53] In this case series, the importance of an interdisciplinary approach during the treatment planning process is also stressed.

Concerning the successful treatment outcomes in this particular case report, the authors reviewed similar cases in literature citing complications to the nasopalatine canal area following implant placement. Though hard evidence, to that effect, could not be found, it is certain that negative outcomes such as paresthesia following nerve injury could have occurred and not reported. Future studies should look into the morbidity following implant placement in the nasopalatine canal region through the free-hand technique and compare it to techniques mentioned in this report.


   Conclusion Top


CBCT scans of the anterior maxilla are recommended prior to surgical placement of implant fixtures in the anterior maxilla. This would help avoid important anatomical structures such as the nasopalatine canal. Accuracy during implant placement leads, in turn, to an ideal restoration of the implant fixture to produce excellent functional and esthetic results. The purpose of this case review is to provide a framework in which the following essential elements of implant therapy were enmeshed.

  • Knowledge of variations in size and shape of important anatomical structures such as the nasopalatine canal and its significance in implant treatment planning. [18],[54]
  • Value of CBCT data and implant treatment planning software in avoiding the nasopalatine canal.
  • Stereolithographic surgical guides, which translate the implant treatment plan into accurate implant surgical placement of implants as compared to the free-hand method. [35],[52],[55],[56],[57],[58],[59],[60]


 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]



 

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