Prevalence of bifid and trifid mandibular canals with unusual patterns of nerve branching using cone beam computed tomography

Lack of knowledge concerning the inferior alveolar canal anatomical variations had proven to increase the incidence of surgical complications, so the study aimed to assess the configuration and prevalence of bifid and trifid mandibular canals using cone beam CT in Egyptian subpopulation. Cone beam CT scans of 278 patients (530 hemi-mandibles) were included in the study, in which bifid and trifid mandibular canals or any other branching patterns were recorded and evaluated. Bifid canals were categorized following Naitoh classification, and the diameter of the main mandibular and accessory canals was measured. Bifid canals were detected in 181 canals (34%) while trifid canals in 46 canals (8.7%). Upon classifying the bifid canals, 78 canals showed forward type, 40 retromolar type, 33 dental type, and 7 canals showed buccolingual type. Two special bifid canals subtypes were reported in 23 canals and nine distinct patterns of trifid canals were reported in our study. In addition, unusual patterns of canal branching were reported in 5 cases. The mean diameter of the accessory canals was 1.18?±?.54 mm and the main canal was 3.98?±?1.31 mm. This study reported a high prevalence (54%) of canal branching, which reinforces the importance of cone beam CT in pre-surgical planning.

     

下颌管分支的锥形束CT观测研究

目的 基于锥形束CT（cone beam computed tomography，CBCT）研究下颌管分支的分布情况及相关数据，为临床实践提供指导和依据。方法 对400例（共800侧下颌骨）山西地区成年人，拍摄CBCT后对下颌管分支的出现情况及其长度、直径和角度进行测量分析，探究性别、左右侧及各年龄层对下颌管分支的影响。结果 400例患者中下颌管分支的发生率为40.75%（163/400），共发生于248侧（31.0%）下颌骨中。下颌管分支的分型中，磨牙后管、牙管、前行管和颊舌侧管的比例分别为45.97%、23.39%、28.63%和2.02%，下颌管分支的直径平均为（1.18±0.36）mm，长度平均为（12.58±4.72）mm，与下颌管主干的夹角平均为42.46°±18.14°。结论 山西地区成年人群的下颌管分支发生率较高，尤其在磨牙后区较常见，在行下颌后牙区外科手术前，建议拍摄CBCT预估风险，避免发生术中损伤导致严重的并发症。     

Bifid and trifid mandibular canal. A coincidental finding

A 26-year-old man was suffering from pericoronitis of his mandibular third molars. To determine the position of the mandibular canal in relation to the roots of the third molars, a panoramic radiograph was made. The radiograph revealed at the right side a bifid mandibular canal and the upper part of the canal seemed to be related to the third molar. Additionally, a cone beam CT was made, which revealed a bifid mandibular canal at the left side and a trifid mandibular canal at the right side. Anatomical anomalies of the mandibular canal may have clinical implications, such as an increased risk of injury to the inferior alveolar nerve in case of removing a mandibular third molar and inadequate local anesthetics.     

Failure to obtain adequate anaesthesia associated with a bifid mandibular canal: a case report

The inferior alveolar nerve (IAN) block is the most common method for obtaining mandibular anaesthesia in dental practice but it is estimated to have a success rate of only 80 to 85 per cent. Causes of failure include problems with operator technique and anatomical variation between individuals. This case report involves a patient who received IAN blocks on two separate occasions that resulted in only partial anaesthesia of the ipsilateral side of the mandible. Radiographic assessment disclosed the presence of bifid mandibular canals that were present bilaterally and that may have affected the outcomes of the local anaesthetic procedures. Previous studies of bifid mandibular canals are reviewed and suggestions provided that should enable clinicians to differentially diagnose, and then manage, cases where IAN blocks result in inadequate mandibular anaesthesia.     

A review of the intraosseous course of the nerves of the mandible.

A review of the literature revealed that a common feature of all human mandibles is a large nerve (inferior alveolar nerve, IAN) between the mandibular and mental foramina. This nerve sends branches directly to the teeth or contributes a variable number of branches to a plexus of nerves which does the same. The plexus originates from a separate nerve that enters the mandibular foramen. The nerve plexus has been demonstrated by dissections and not by radiology. The buccal-lingual and superior-inferior positions of the IAN were not consistent among mandibles. The intramandibular IAN frequently ran a concave curve with a posterior segment descending as it progressed anteriorly and an anterior segment that ascended to the mental foramen. A bony canal was not always observed between the mandibular and mental foramina. The canal frequently lacked definite walls, especially near the mental foramen. Bilateral symmetry (location of the canal in each half of the mandible) was common, whereas duplications of the canal were rare. Nutrient canals and other branches of the mandibular nerve have been observed within the mandible. These may have been confused for the IAN or may contribute to the plexus of nerves.     

Variations of the bony canal in the mandibular ramus using cone-beam computed tomography

The location and configuration of the mandibular canal are important in surgical procedures involving the mandible. Previously, we reported that bifid mandibular canals could be classified into four types: retromolar, dental, forward, and bucco-lingual canals, using cone-beam computed tomography (CBCT). Herein we report three Japanese patients with a bony canal in the mandibular ramus, which was independent of the mandibular canal, using CBCT images. A CBCT unit with a flat panel detector and exposure volume of 102 mm in diameter and 102 mm in height was used. Two-dimensional (2D) and three-dimensional (3D) images in the mandibular ramus region were reconstructed using 3D visualization and measurement software packages. Three bony canals in two patients were considered to correspond to a temporal crest canal, which was raised from the mandibular notch, and reached the antero-inferior region of the coronoid process. One bony canal in one patient, ran bucco-lingually in the mandibular ramus. It is important for variations in the mandibular and bony canals to be carefully observed, by use of CBCT images, in surgical procedures involving the mandible.     

基于CBCT的西南地区汉族人双下颌管形态学研究

目的：利用CBCT分析西南地区汉族人双下颌管发生的概率及各型双下颌管的形态学特征,为与之密切相关的口腔临床操作提供参考。方法：选择 2014-2016年期间于自贡市第四人民医院口腔科就诊拍摄CBCT的汉族患者300例,观察患者有无双下颌管,描述其形态学特征并进行统计学分析。结果：西南地区汉族人双下颌管的发生率为19.33%。其中,磨牙后管占比最高（58.75%）,其次为根尖管（23.75%）和前行管（15.00%）,颊舌向管最少（2.50%）。结论：基于CBCT的研究表明西南地区汉族人双下颌管有较高的发生率,并且各型分支存在形态学差异,临床工作中需重视其影响。     

Bifid mandibular canal in Japanese

The location and configuration of mandibular canal variations are important in surgical procedures involving the mandible, such as extraction of an impacted third molar, dental implant treatment, and sagittal split ramus osteotomy. We report 3 Japanese patients with bifid mandibular canals using panoramic radiograph and multi-slice helical computed tomography (CT) images. In 2 of the 5 sides, the bifid mandibular canal was suggested on panoramic radiograph. The bifid mandibular canal had a short and narrow upper canal toward the distal area of the second molar in 4 sides, and a short and narrow lower canal toward the distal area of second molar in 1 side, as revealed on reconstructed CT images. Since the location and configuration of mandibular canal variations are important in surgical procedures involving the mandible, they should be carefully observed using reconstructed CT images.     

Preoperative assessment of the relationship between the mandibular third molar and the mandibular canal by axial computed tomography with coronal and sagittal reconstruction

OBJECTIVE: We sought to evaluate the relationship between the mandibular third molar and the mandibular canal by using axial computed tomography with coronal and sagittal reconstruction for third molar surgery. STUDY DESIGN: Forty-seven impacted third molars in 41 patients were found in close association with the mandibular canal during a panoramic radiographic assessment. The relationship between the mandibular third molar and the mandibular canal was evaluated by using computed tomography and compared in terms of operative exposure of the inferior alveolar nerve and postoperative labial dysesthesia. RESULTS: Twenty-four (51%) mandibular canals were buccal relative to the third molar, 12 were lingual, 9 were inferior, and 2 were between roots. At the time of the surgical procedure, the inferior alveolar nerve was visible in 7 patients. Postoperative lower lip dysesthesia occurred in 1 patient whose mandibular canal was in the lingual position. CONCLUSIONS: Axial computed tomography with coronal and sagittal reconstruction provides useful information to surgeons regarding the relationship between the mandibular third molar and the mandibular canal.     

Evaluation of Dimensional Accuracy of Panoramic Cross‐Sectional Tomography,Its Ability to Identify the Inferior Alveolar Canal,and Its Impact on Estimation of Appropriate Implant Dimensions in the Mandibular Posterior Region

Objectives: To evaluate the dimensional accuracy of panoramic cross‐sectional tomography, its impact on implant size estimation and its ability in identifying the inferior alveolar canal in the mandibular posterior region. Material and Methods: Eight partially edentulous mandibles with 18 edentulous sites were obtained. Orthopantomograms and tomograms were made and the mandible's outline and the position of mandibular canals on tomograms were traced on a clear acetate paper. Horizontal and vertical magnification factors were calculated. The mandibular height, distance between mandibular canal and alveolar crest, maximum bucco‐lingual width, distance between buccal cortex and mandibular canal, and cortical thickness at the inferior border of the mandible were measured. Potential implant sites were identified and implant sizes were estimated. Location and visibility of mandibular canals were also evaluated. The mandibles were sectioned at each site and all the above mentioned parameters were assessed which served as gold standard. Results: Mean horizontal and vertical magnification factors were 1.47 ± 0.048 and 1.53 ± 0.038. Total height and maximum bucco‐lingual width were underestimated by 1.88% and 1.59%. Crest to canal distance, cortical thickness at the inferior border of the mandible and buccal cortex to mandibular canal were overestimated by 0.59%, 5.16%, and 3.64%. Implant sizes were estimated for 11 sites and changes were recorded at 2 sites between record 1 and record 2. However, there was no disagreement between record 2 and record 3. Of the canals, 61.11% were located lingually and the visibility of mandibular canals was poor in 44.44% of cases. Conclusions: The tomograms were found to be accurate for the measurements in both horizontal and vertical planes and reliable for implant size estimation, taking into consideration proper magnification factors. They were also found to be useful in assessing the location of mandibular canal but were not very effective in discerning it.     

Inferior alveolar nerve paresthesia relieved by microscopic endodontic treatment

We experienced two cases of inferior alveolar nerve paresthesia caused by root canal medicaments, which were successfully relieved by microscopic endodontic treatment. In the first case, the paresthesia might have been attributable to infiltration of calcium hydroxide into the mandibular canal through the root canals of the mandibular left second molar tooth. In the second case, the paresthesia might have been attributable to infiltration of paraformaldehyde through the root canals of the mandibular right second molar tooth. The paresthesia was relieved in both cases by repetitive microscopic endodontic irrigation using physiological saline solution in combination with oral vitamin B12 and adenosine triphosphate.     

A split ostectomy of mandibular body and angle reduction

Combined mandibular angle resection with angle-splitting ostectomy (ASO) is more effective than conventional simple or multistaged ostectomy. Removal of the outer cortex of the mandibular body by ASO lessens the protuberance of the masseter muscle. In this study, the anatomy of the mandibular canals in seven human cadavers was studied in detail, and a guideline for ASO and mandibular angle ostectomy was set up so as to avoid injury to the inferior alveolar nerve. The most vulnerable area of the inferior alveolar nerve is the line from the gonion (G) to the junction (O) of the intersecting vertical line along the anterior border of the ramus and the horizontal line on the alveolar crest because of the thin anterior distance (AD) between the buccal surface of the mandible and the outer wall of the mandibular canal. The resection line should not be above 17.5 mm at the GO line to ensure a safe inferior distance, the distance between the inferior border of the mandible and the floor of the mandibular canal (21.6 +/- 4.1 mm). The body of the mandible was less vulnerable to injury to the inferior alveolar nerve in ASO because of the relatively thicker AD at the second molar (8.3 mm) and first molar (6.8 mm). Pilot surgery was performed in five cadavers. The lateral cortex was safely split off, avoiding injury to the inferior alveolar nerve, and angle ostectomy was then done. This method was applied in two clinical cases without any complications. The "split ostectomy of mandibular body and angle reduction" is a new and safe method of avoiding the injury to the inferior alveolar nerve.     

Prospective study of dysesthesia following odontectomy of impacted mandibular third molars

Dysesthesia following odontectomy of impacted mandibular third molars is observed in some patients. This prospective study reports the clinical incidence of this untoward sequela to occur in 3.3% of patients. An analysis of possible etiologic factors reveals that development of dysesthesia of the inferior alveolar and lingual nerves is more likely to occur with: complete bony impacted mandibular third molars; mesioangular impacted third molars; impacted third molars with the crown at the cemento-enamel junction of the second molar; and when burs are used to remove bone and when the roots approximate the inferior alveolar canal.     

颏孔区域的解剖学研究

目的　研究国人下颌管前端的位置及其延续关系 ,为临床手术提供解剖学依据。方法　打磨 6 0侧湿下颌骨标本 ,暴露下颌管前端及其延续部分并直接观察和测量。结果　下颌管前端分出同一方向前行的切牙神经管和向后、上、外转弯的颏管。颏管开口于颏孔 ,其管径为 (2 .2 6± 0 .6 0 )mm ,管长 (4 .0 1± 1.2 0 )mm。切牙神经管的管径为 (1.76± 0 .2 6 )mm ,其下缘至下颌骨下缘的垂直距离为 (9.5 3± 1.43)mm ,其始端对应颏孔前缘的水平距离为 (3.5 4± 0 .72 )mm。下牙槽神经的终末支颏神经和切牙神经分别走行与上述两管内。结论　颏管和切牙神经管由下颌管发出 ,其内分别为同名神经。     

Mandibular premolar with three root canals—two case reports

The presence of three root canals in the mandibular premolar may sometimes be recognized when there is persistent postoperative discomfort following root canal therapy. This paper presents two cases of root canal treatment of mandibular premolars with three root canals including one mandibular first premolar and one mandibular second premolar. The possibility that there is more than one root canal in lower premolar teeth must be considered in the radiographic and clinical examination during root canal treatment.     

Strychnine-enhanced transsynaptic destruction of medullary dorsal horn neurones following transection of the trigeminal nerve in adult rats including evidence of involvement of the bony environment of the transection neuroma in the peripheral mechanism

Following transection of a nerve, strychnine (1 mg/kg per day) was intraperitoneally injected for 3-23 days at various post-transectional intervals and the medullary and spinal dorsal horns were histologically examined. Strychnine-enhanced transsynaptic destruction was seen when the inferior alveolar nerve was transected and the proximal stump was left in situ in the mandibular canal. Pyknotic neuronal cell bodies were observed in the dorsal half of the medullary dorsal horn ipsilateral to the nerve transection, an area which is known to receive dense innervation from the ipsilateral inferior alveolar nerve. Three days of strychnine treatment revealed pyknotic cells when the experiment was terminated between 18 and 30 days postoperatively. A longer period of strychnine treatment had a tendency to produce more pyknotic cells. Transection of neither mental, lingual, auriculotemporal nor infraorbital nerve induced strychnine-enhanced transsynaptic destruction in the medullary and spinal dorsal horns which are known to receive primary input from the severed nerves. Strychnine-enhanced transsynaptic destruction following transection of the inferior alveolar nerve was effectively prevented by placing the proximal stump outside the mandibular canal.     

Proximity of Impacted Mandibular Third Molars to the Inferior Alveolar Canal and Its Radiographic Predictors: A Panoramic Radiographic Study

Purpose

To assess the radiographic proximity of impacted mandibular third molars to the inferior alveolar canal on panoramic radiographs. The radiographic distance between the impacted mandibular third molars and inferior alveolar canal and the reliable radiographic risk predictor signs that indicate close proximity between these two structures were evaluated.

Methods

The study comprised of 64 subjects with 68 symptomatic impacted mandibular third molars for whom panoramic radiographs were made. The radiographs were interpreted for type of impaction, radiographic distance between impacted mandibular third molars to inferior alveolar canal and presence of one or more of the seven radiographic risk predictor signs. Further, these teeth were surgically removed and the proximity was assessed based on the exposure of inferior alveolar canal/nerve which was considered as Gold standard.

Results

The overall mean distance from the impacted mandibular third molars to inferior alveolar canal was −0.50 mm. Most of the samples (61.8 %) extended beyond the superior border of the inferior alveolar canal with a mean distance of −1.40 mm. Mesioangular impactions were found to be in the close proximity (−1.14 mm) to inferior alveolar canal than any other type. Interruption of the white line was the only statistically significant radiographic risk predictor sign p = 0.006 (< 0.05) that indicated close proximity of impacted mandibular third molars to inferior alveolar canal.

Conclusion

It can be concluded that panoramic radiographs are reliable in assessing the proximity of impacted mandibular third molars to inferior alveolar canal. Mesioangular impactions are more closely placed to inferior alveolar canal and interruption of the white line is the most reliable risk predictor sign on the panoramic radiographs.     

Traumatic neuroma of the inferior alveolar nerve: a case report

Traumatic neuromas are rare entities which characteristically arise subsequently to surgery and are usually accompanied by pain, typically neuralgic. We present an unusual case of an intraosseous traumatic neuroma of the inferior alveolar nerve following tooth extraction. A 56-year-old man consulted for paresthesias and hyperesthesia in the left mandibular region following extraction of the left mandibular third molar (#38). The panoramic radiograph revealed a radiolucent lesion in the inferior alveolar nerve canal, and CT demonstrated the existence of a mass within the canal, producing widening of the same. Nerve-sparing excisional biopsy was performed. Histopathology and immunohistochemistry were consistent with traumatic neuroma of the left inferior alveolar nerve. After 3 years of follow-up, the patient is asymptomatic and there are no signs of recurrence.     

下颌管的走行及解剖结构的研究

目的　研究下颌管的位置及解剖结构 ,为种植牙提供解剖依据。方法　选 15具成人有牙下颌骨标本在特定截面上测量下颌管纵横径和四壁厚度 ,观察 4具动脉灌注新鲜标本的下颌管内血管神经之间的关系。结果　下颌管在下颌骨体部走行中偏舌侧 ,并近下颌骨下缘 ;管内血管位于神经之上。结论　牙种植术中按正常解剖方位钻孔 ,可避免损伤下牙槽神经。如术中下颌管内突然涌出大量新鲜血 ,则提示继续手术可能损伤下牙槽神经