Clinical application of a new cone-beam computerized tomography system to assess multiple two-dimensional images for the preoperative treatment planning of maxillary implants: case reports.

Accurate assessment of the location of the maxillary sinuses, incisive canal, and nasal cavity, as well as the height, width, and angulation of bone is essential for implant treatment planning. The purpose of this study was to introduce the clinical application of a cone-beam computerized tomography system (Ortho-CT) to assess multiple two-dimensional (2D) images for the preoperative treatment planning of maxillary implants. To evaluate the multiple 2D images scanned using the Ortho-CT system the maxillary region placed with radiopaque template in the maxilla. Ortho-CT images provided useful information for evaluating the morphology of the maxilla, for locating the incisive canal, maxillary sinuses, nasal cavity, and for showing the relationship of the template to the bone. It is concluded that the Ortho-CT system is a useful aid for diagnosis and treatment planning for maxillary implant treatment.     

Avoiding injury to the inferior alveolar nerve by routine use of intraoperative radiographs during implant placement

Injury to the inferior alveolar nerve during implant placement in the posterior atrophic mandible is a rare but serious complication. Although a preoperative computerized tomography scan can help determine the distance from the alveolar ridge to the nerve canal, variables such as magnification errors, ridge anatomy, and operator technique can increase the chance for complications. The routine use of intraoperative periapical radiographs during the drilling sequence is an inexpensive and reliable tool, allowing the operator to confidently adjust the direction and depth of the implant during placement. Most important, it helps avoid the risk of injury to the inferior alveolar nerve in cases in which there is limited vertical alveolar bone. Using this technique for 21 implants placed in the posterior atrophic mandible, with less than 10 mm of vertical bone to the inferior alveolar nerve canal, the authors observed no incidents of postoperative paresthesia.     

A retrospective radiographic evaluation of the anterior loop of the mental nerve: Comparison between panoramic radiography and cone beam computerized tomography

Objectives: To compare the prevalence and the length of mental loop, measured with panoramic radiography (PR) and cone beam computerized tomography (CBCT). Material and Methods: PG and CBCT images where analyzed by a single calibrated examiner to determine the presence and the position of the mental foramen (MF), its distance to the lower mandible border, the anterior length of the mental loop (ML) and the bone quality in 82 PR and 82 CBCT. Results: ML was identified in 36.6 % of PR and 48.8 % of CBCT. PR showed a magnification of 1.87 when compared to CBCT. The mean of anterior extension of the inferior alveolar nerve and the distance to the inferior border of the mandible was higher for PR (2.8 mm, sd 0.91 mm on the PR , range 1.5 to 4.7 mm and 1.59, sd 0.9 on the CBCT ,range 0.4 to 4.0 mm) Conclusions: There is a magnification in PR images with respect to those of CBCT. The differences between CBCT and PR with regards to the identification and length of the ML are not statistically significant. Identification and accuracy measurements of ML did not depend on the bone quality. Considering that two dimensional imaging provides less accurate and reliable information regarding the anterior loop, a CBCT scan could be recommended when planning implant placement in the anterior region. Key words:Mental loop, mental nerve, mental canal, preoperative implant planning, panoramic tomography, cone beam computerized tomography.     

Efficacy of panoramic radiographs in the preoperative planning of posterior mandibular implants: a prospective clinical study of 1527 consecutively treated patients

OBJECTIVES: Various imaging techniques, including conventional radiography and computed tomography, are proposed to localize the mandibular canal prior to implant surgery. The aim of this study is to determine the incidence of altered mental nerve sensation after implant placement in the posterior segment of the mandible when a panoramic radiograph is the only preoperative imaging technique used. MATERIAL AND METHODS: The study included 1527 partially and totally edentulous patients who had consecutively received 2584 implants in the posterior segment of the mandible. Preoperative bone height was evaluated from the top of the alveolar crest to the superior border of the mandibular canal on a standard panoramic radiograph. A graduated implant scale from the implant manufacturer was used and 2 mm were subtracted as a safety margin to determine the length of the implant to be inserted. RESULTS: No permanent sensory disturbances of the inferior alveolar nerve were observed. There were two cases of postoperative paresthesia, representing 2/2584 (0.08%) of implants inserted in the posterior segment of the mandible or 2/1527 (0.13%) of patients. These sensory disturbances were minor, lasted for 3 and 6 weeks and resolved spontaneously. CONCLUSIONS: Panoramic examination can be considered a safe preoperative evaluation procedure for routine posterior mandibular implant placement. Panoramic radiography is a quick, simple, low-cost and low-dose presurgical diagnostic tool. When a safety margin of at least 2 mm above the mandibular canal is respected, panoramic radiography appears to be sufficient to evaluate available bone height prior to insertion of posterior mandibular implants; cross-sectional imaging techniques may not be necessary.     

超声骨刀在下牙槽神经移位同期种植中的应用

目的:探讨超声骨刀辅助下对下牙槽嵴严重萎缩的患者行下牙槽神经移位术,并同期种植的临床应用效果。方法:对1例48岁牙槽嵴严重萎缩的女性患者,利用超声骨刀行右下牙槽神经移位术并同期植入种植体2枚。结果:该患者术后出现右下唇感觉障碍症状,3个月后恢复;术后4个月患者完成种植义齿的上部结构修复。经随访3月,修复完成后种植体无松动或脱落。结论:利用超声骨刀行下牙槽神经移位术并同期种植,能有效地减小下牙槽神经损伤的风险,解决下颌骨牙槽嵴严重萎缩患者的种植修复问题。     

螺旋CT结合Dentascan软件在种植牙术前颌骨评估中的应用

目的：评价螺旋CT结合Dentascan软件和定位模板在种植牙术前颌骨评估中的应用价值。方法：将用压模机制作的透明树脂定位模板戴入植牙患者口内,以0．5mm层厚螺旋CT扫描颌骨。扫描的数据传至CT工作站用Dentascan软件处理后显示侧断层图、曲面断层图及三维重建图。结果：所有25例病例重建图均能清晰的显示颌骨的形态、质地和重要的解剖结构,如上领窦、颏孔、下牙槽神经管,并且能精确的测量缺牙区可用骨的高度、厚度和宽度。结论：螺旋CT结合Dentascan软件和定位模板在种植牙治疗计划的设计中起关键作用,尤其像前牙美容区域,并有利于提高种植牙的成功率。     

Study of the inferior alveolar canal and mental foramen on digital panoramic images

Objectives: To study the radiographic location of the mental foramen and appearance of the inferior alveolar canal and the relationship between image gray values and the clarity of inferior alveolar canal on the digital panoramic images and to evaluate if the histogram equalization of the digital image would improve the visualization of the inferior alveolar canal outline on the digital panoramic images in the mandible. Methods: Five hundred digital panoramic images were evaluated by two examiners using a specific inclusion criteria. Only the right side of the mandible was studied. Chi-square analyses were used for comparisons of distributions. Mean and median pixel values were analyzed separately with a one-way analysis of variance. Also, percentages were calculated to report the usefulness of the histogram equalization for visualization of canal. Results: Results show variation in location of mental foramen. Most frequent location of the mental foramen was reported as first and second premolar region. Chi-square analysis showed that the frequency of occurrence of the mental foramen was equally probable for any of the three locations. The study did not find significant usefulness of the gray values obtained from the histogram equalization in predicting the clarity of inferior alveolar canal outlines. Clinical significance: Knowing the normal relationship and the anatomical variation of the maxillofacial structures for each patient is important for surgical implant treatment planning to avoid future complications. It is also important to be familiar with the advantages and limitations of diagnostic aids available before making treatment planning decisions based on such findings. Keywords: Digital imaging, Panoramic, Inferior alveolar canal, Mental foramen. How to cite this article: Pria CM, Masood F, Beckerley JM, Carson RE. Study of the Inferior Alveolar Canal and Mental Foramen on Digital Panoramic Images. J Contemp Dent Pract 2011;12(4):265-271. Source of support: Nil Conflict of interest: None declared.     

Neurosensory function and implant survival rate following implant placement with nerve transpositioning: a case study

In patients with extensive bone resorption, implant placement posterior to the mental foramen is a problematic surgical procedure. This paper reports the results in 6 patients (aged 20-61) with edentulous areas in the posterior part of the mandible, in whom 26 Nobelpharma implants were placed, including 17 with transposition of the inferior alveolar nerve allowing the use of implant fixtures of at least 10 mm in length. Subsequent neurosensory function, based on British Medical Research Council definitions, and implant survival rate were examined. In all cases, postoperative numbness occurred in the lower lip and mental area. Three years after surgery, while one patient had completely recovered neurosensory function, five patients still experienced partial numbness, although this was not perceived as a problem by those patients. The implant survival rate was 100% approximately three years after surgery. The results suggest that a higher implant survival rate is likely when longer fixtures are used, but this is also more likely to lead to slight long-term neurosensory dysfunction.     

Mandibular fracture as a complication of inferior alveolar nerve transposition and placement of endosseous implants: a case report

Placement of endosseous implants and inferior alveolar nerve transposition is a treatment option for patients with an edentulous posterior mandible with inadequate bone height superior to the inferior alveolar canal. Complications associated with these procedures include infection, prolonged neurosensory disturbances, and/or pathologic fracture. This report presents the surgical management of a patient with a mandible fracture after inferior alveolar nerve transposition with concurrent placement of two endosseous implants.     

Inferior alveolar nerve transposition with involvement of the mental foramen for implant placement

Inferior Alveolar Nerve (IAN) transposition is an option for prosthetic rehabilitation in cases of moderate or even severe bone reabsorption for patients that do not tolerate removable dentures. The aim of the present report is to describe an inferior alveolar nerve transposition with involvement of the mental foramen for implant placement. The surgical procedure was performed under local anesthesia, by the inferior alveolar, lingual and buccal nerve blocking technique. Centripetal osteotomy was performed, and bone tissue was removed, leaving the nerve tissue free in the foramen area. After that, transsection of the incisor nerve was performed, and lateral osteotomy was started from the buccal direction, toward the trajectory of the IAN. The procedure was concluded, by making use of a delicate resin spatula to manipulate the vascular-nervous bundle. The drilling sequence for placing the dental implants was performed, and autogenous bone was harvested using a bone collector attached to the surgical suction appliance. After the implants were placed, the bone tissue previously collected during the osteotomies and drilling processes was placed in order to protect the IAN from contact with the implants. The surgical protocol for inferior alveolar nerve transposition, followed by implant placement presented excellent results, with complete recovery of the sensitivity, seven months after the surgical procedure.     

A precise radiographic method to determine the location of the inferior alveolar canal in the posterior edentulous mandible: implications for dental implants. Part 2: Clinical application

An analysis of implant placement in the posterior region of eight edentulous cadaver mandibles was performed. The results demonstrated that the radiographic technique developed can be employed to safely place implants adjacent to the inferior alveolar nerve in the posterior mandible by using radiographic laminography and a specially designed intraoral reference splint.     

Surgical technique for achieving implant parallelism and measurement of the discrepancy in panoramic radiograph.

PURPOSE: This article describes a surgical technique for achieving implant placement parallelism and presents an equation concept to predict the bone depth available for implant placement by measuring the discrepancy of the panoramic radiograph compared with a clinical situation in cases in which a wide edentulous area is present. MATERIALS AND METHODS: A surgical template with tube technique in combination with measurement of the vertical dimension of the mandible bone available for implant placement was used to treat 2 patients in whom 7 and 3 implants, respectively, were inserted in the lower and upper jaws. RESULTS: All implants were successfully implanted into their reliable positions. In regard to the position of an important area such as the inferior alveolar nerve and maxillary sinus, this predictive equation can provide an extra margin of security. CONCLUSION: A partial denture surgical template technique with tube technique using a Coen's drill guide in combination with a mathematical equation to find the clinical-radiographic discrepancy can be used as an alternative method in placement guidance of dental implant insertions and its fixed prosthetic treatment planning in a wide edentulous area.     

A precise radiographic method to determine the location of the inferior alveolar canal in the posterior edentulous mandible: implications for dental implants. Part 1: Technique

In severely atrophic or osteoporotic mandibles, the location of the inferior alveolar nerve may vary considerably, both superoinferiorly and mediolaterally. A clinician's ability to reliably locate this nerve within the mandible would permit the surgical planning of implant placement in the posterior edentulous mandible. Eight edentulous cadaver mandibles were studied. A technique that precisely locates the inferior alveolar nerve within the mandible is described. The technique will aid the surgeon in planning a surgical approach to the posterior mandible with reduced risk of injury to the inferior alveolar nerve.     

Vulnerability of the inferior alveolar nerve and mental nerve during genioplasty: an anatomic study

Microgenia or "small chin" is corrected by various techniques, such as insertion of an alloplastic implant, cartilage or bone grafting, or horizontal advancement osteotomy. Horizontal recession osteotomy is used in macrogenia. Particularly in a microgenic mandible, the mental foramen is unexpectedly nearer to the inferior border of the body. During sliding horizontal osteotomy of the mentum, the inferior alveolar nerve (IAN) and mental nerve are vulnerable to an injury. Thirty fresh hemimandibles were used for a study of the IAN. The IAN course was traced by serial sections at intervals of 5 mm. In 50 dry specimens the direction of the mandibular canal was evaluated by the photographs with a stick put into the mental foramen. The IAN in mandibular canal runs above the lower one-third of the mandibular body. The terminal mandibular canal locates at an average of 4.5 mm under the mental foramen, advances 5.0 mm anteriorly, loops, and ends at the foramen. The direction of the mandibular canal at the mental foramen was 39.4 degrees lateral, 67.2 degrees superior, and 80.2 degrees posterior. It is advisable for surgeons to keep the level of sliding osteotomy of the mentum at least 4.5 mm below the mental foramen to spare the IAN.     

The use of vein grafts in the repair of the inferior alveolar nerve following surgery

Damage to the branches of the trigeminal nerve can occur as a result of a variety of causes. The most common damage to all divisions of this nerve occurs as a result of facial trauma. Unfortunately, iatrogenic damage to the inferior alveolar branch of the mandibular division of the trigeminal nerve is common because of its anatomical position within the mandible and its closeness to the teeth, particularly the third molar. It has been reported there is an incidence of approximately 0.5% of permanent damage to the inferior alveolar nerve following third molar removal. Extraction of other teeth within the mandible carries a lower incidence of permanent damage. However, damage can still occur in the premolar area, where the nerve exits the mandible via the mental foramen. Dental implants are a relatively new but increasing cause of damage to this nerve, particularly if the preoperative planning is inadequate. CT scanning is important for planning the placement of implants if this damage is to be reduced. Primary repair of the damaged nerve will offer the best chance of recovery. However, if there is a gap, and the nerve ends cannot be approximated without tension, a graft is required. Traditionally, nerve grafts have been used for this purpose but other conduits have also been used, including vein grafts. This article demonstrates the use of vein grafts in the reconstruction of the inferior dental branch of the mandibular division of the trigeminal nerve following injury, in this case due to difficulty in third molar removal, following sagittal split osteotomy and during the removal of a benign tumour from the mandible. In the five cases presented, this technique has demonstrated good success, with an acceptable return of function occurring in most patients.     

Analysis of short implants and lateralization of the inferior alveolar nerve with 2-stage dental implants by finite element method

There are difficulties for dental implant use in posterior mandible when there is little bone height for implant placement. Among the treatment alternatives available, there is no direct comparison between short implants and conventional implants placed with lateralization of the inferior alveolar nerve. The present study aimed to comparatively evaluate the risk of peri-implant bone loss of the above treatments. With this aim, computed tomography scans of mandibles were processed, and implants and prosthetic components were reverse engineered for reconstruction of three-dimensional models to simulate the biomechanical behavior of 3-element fixed partial dentures supported by 2 osseointegrated implants, using simulations with the finite element method. The models of implants were based on MK III implants (Nobel Biocare) of 5- and 4-mm diameter by 7-mm length, representing short implants, and 4- and 3.75-mm diameter by 15-mm length, representing implants used in lateralization of the inferior alveolar nerve. All models were simulated with prestress concerning the stresses generated by the torque of the screw. Axial and oblique occlusal loads at 45% were simulated, resulting in 8 different simulations. The results showed that the risk for bone loss in osseointegrated implants is greater for treatments with short implants.     

Inferior alveolar nerve repositioning in implant surgery

Severe resorption of the posterior mandible possesses one of the most difficult restorative challenges to the implant surgery today. This resorption may prevent the placement of dental implants without the potentially damage to the inferior alveolar nerve. To create the opportunity of insertion dental implants of adequately length in those cases, the technique of nerve repositioning has been advocated. The purpose of this article is to describe two cases of nerve repositioning combined with placement of dental implants. Both cases showed appropriate postoperative healing without damage to the inferior alveolar nerve. The inferior alveolar nerve repositioning technique seems to be an acceptable alternative to augmentation procedure prior to dental implants placement in cases exhibiting atrophic posterior mandibular ridges.     

The mental foramen and nerve: clinical and anatomical factors related to dental implant placement: a literature review

BACKGROUND: The mental foramen is a strategically important landmark during osteotomy procedures. Its location and the possibility that an anterior loop of the mental nerve may be present mesial to the mental foramen needs to be considered before implant surgery to avoid mental nerve injury. METHODS: Articles that addressed the position, number, and size of the mental foramen, mental nerve anatomy, and consequences of nerve damage were evaluated for information pertinent to clinicians performing implant dentistry. RESULTS: The mental foramen may be oval or round and is usually located apical to the second mandibular premolar or between apices of the premolars. However, its location can vary from the mandibular canine to the first molar. The foramen may not appear on conventional radiographs, and linear measurements need to be adjusted to account for radiographic distortion. Computerized tomography (CT) scans are more accurate for detecting the mental foramen than conventional radiographs. There are discrepancies between studies regarding the prevalence and length of the loop of the mental nerve mesial to the mental foramen. Furthermore, investigations that compared radiographic and cadaveric dissection data with respect to identifying the anterior loop reported that radiographic assessments result in a high percentage of false-positive and -negatives findings. Sensory dysfunction due to nerve damage in the foraminal area can occur if the inferior alveolar or mental nerve is damaged during preparation of an osteotomy. CONCLUSIONS: To avoid nerve injury during surgery in the foraminal area, guidelines were developed based on the literature with respect to verifying the position of the mental foramen and validating the presence of an anterior loop of the mental nerve. These guidelines included leaving a 2 mm zone of safety between an implant and the coronal aspect of the nerve; observation of the inferior alveolar nerve and mental foramen on panoramic and periapical films prior to implant placement; use of CT scans when these techniques do not provide clarity with respect to the position of the nerve; surgical corroboration of the mental foramen's position when an anterior loop of the mental foramen is suspected of being present or if it is unclear how much bone is present coronal to the foramen to establish a zone of safety (in millimeters) for implant placement; once a safety zone is identified, implants can be placed anterior to, posterior to, or above the mental foramen; and prior to placing an implant anterior to the mental foramen that is deeper than the safety zone, the foramen must be probed to exclude the possibility that an anterior loop is present. In general, altered lip sensations are preventable if the mental foramen is located and this knowledge is employed when performing surgical procedures in the foraminal area.     

Endosseous implant placement in conjunction with inferior alveolar nerve transposition: a report of an unusual complication and surgical management

Inferior alveolar nerve transposition and placement of endosseous implants is one of the treatment options for patients with an edentulous posterior mandible with inadequate bone height superior to the inferior alveolar canal. The possible complications associated with this technique include prolonged neurosensory disturbances, infection, and pathologic fracture. This report presents the surgical management of a patient who sustained a mandibular fracture after inferior alveolar nerve transposition for the placement of 3 endosseous implants.     

Lateralization of the inferior alveolar nerve with simultaneous implant placement: a modified technique

PURPOSE: Several nerve repositioning techniques have ben presented in the literature, each with limitations. This article presents a new technique involving the use of 2 osteotomies, with minimizes particularly the potential duration of sensory disruption and the risk of nerve paresthesia and inadvertent nerve transection or compression. MATERIALS AND METHODS: Ten patients ranging in age from 47 to 67 years were selected for nerve lateralization utilizing the modified technique. A total of 23 cylindrical implants were placed. An average follow-up period was 29.8 months. RESULTS: Of the 10 patients, 4 experienced total return of sensation within 3 to 4 weeks. One patient experienced complete recovery at 6 weeks. DISCUSSION: Creating 2 osteotomies as described minimizes the chances for postoperative neuropraxia and nerve paresthesia or anesthesia. CONCLUSION: When there is moderate-to-severe bone resorption of the mandible posterior to the mental foramen, repositioning the inferior alveolar nerve using both an anterior and posterior osteotomy allows for more bone to accommodate ideal placement and greater length of implant.