The radiological prediction of inferior alveolar nerve injury during third molar surgery

Evaluation of the mandibular canal and the third mandibular molar relationship by CBCT with a deep learning approach

OBJECTIVE

The mandibular canal (MC) houses the inferior alveolar nerve. Extraction of the mandibular third molar (MM3) is a common dental surgery, often complicated by nerve damage. CBCT is the most effective imaging method to assess the relationship between MM3 and MC. With advancements in artificial intelligence, deep learning has shown promising results in dentistry. The aim of this study is to evaluate the MC-MM3 relationship using CBCT and a deep learning technique, as well as to automatically segment the mandibular impacted third molar, mandibular canal, mental and mandibular foramen.

METHODS

This retrospective study analyzed CBCT data from 300 patients. Segmentation was used for labeling, dividing the data into training (n = 270) and test (n = 30) sets. The nnU-NetV2 architecture was employed to develop an optimal deep learning model. The model's success was validated using the test set, with metrics including accuracy, sensitivity, precision, Dice score, Jaccard index, and AUC.

RESULTS

For the MM3 annotated on CBCT, the accuracy was 0.99, sensitivity 0.90, precision 0.85, Dice score 0.85, Jaccard index 0.78, AUC value 0.95. In MC evaluation, accuracy was 0.99, sensitivity 0.75, precision 0.78, Dice score 0.76, Jaccard index 0.62, AUC value 0.88. For the evaluation of mental foramen; accuracy 0.99, sensitivity 0.64, precision 0.66, Dice score 0.64, Jaccard index 0.57, AUC value 0.82. In the evaluation of mandibular foramen, accuracy was found to be 0.99, sensitivity 0.79, precision 0.68, Dice score 0.71, and AUC value 0.90. Evaluating the MM3-MC relationship, the model showed an 80% correlation with observer assessments.

CONCLUSION

The nnU-NetV2 deep learning architecture reliably identifies the MC-MM3 relationship in CBCT images, aiding in diagnosis, surgical planning, and complication prediction.

Radiographic characteristics of impacted teeth: A retrospective study of 2199 radiograph

OBJECTIVE

To analyze the radiological characteristics of impacted teeth in the population of Makkah in Saudi Arabia.

METHODS

A retrospective analysis was conducted on 2199 digital panoramic radiograph (OPG) scans collected from the database of the dental teaching hospital at Umm Al-Qura University, Makkah, KSA. Out of these, 1503 OPGs (749 males and 754 females) met the inclusion criteria, which required clear OPGs with high quality and good visibility of anatomic structures. The study included patients of both genders, aged between 13 and 70, with complete root formation of impacted teeth.

RESULTS

The analysis of 1,503 patients' radiographs revealed that 27.70% had impacted third molars, with mandibular molars being more commonly affected than maxillary molars. Additionally, other impacted teeth were observed, including maxillary canines, second premolars, second molars, and supernumerary teeth. Male patients had a slightly higher prevalence of impaction. The majority of impacted third molars were found in the age group of 18-30. The angulation and depth of impacted teeth differed between maxillary and mandibular arches. Most impacted mandibular third molars had a class I relation with the ramus.

CONCLUSION

The study provides valuable insights into impacted teeth in Makkah, Saudi Arabia. It highlights a significant occurrence of impacted third molars, as well as other teeth. These findings contribute to a better understanding of impacted teeth and provide important support for dental professionals in their efforts to improve patient outcomes.

Panoramic radiographic features for machine learning based detection of mandibular third molar root and inferior alveolar canal contact

This study uses machine learning (ML) to elucidate the contact relationship between the mandibular third molar (M3M) and the inferior alveolar canal (IAC), leading to three major contributions; (1) The first publicly accessible PR image dataset with semantic annotations for 1,478 IACs and M3Ms from 1,010 patients is introduced, which includes challenging cases, such as false positive contacts, with CBCT images as the gold standard, (2) Established radiological indicators for M3M-IAC contact were extracted as features using digital image processing, and these features were used as inputs for various ML methods. Eligibility was assessed through statistical analysis and radiologists evaluations. Clinical feedback from radiologists on these features provides insights for future improvements. (3) ANNs, two custom CNNs, seven established DL models, and their combinations were used for automatic M3M-IAC contact determination with extracted features, semantic annotations, and ROIs. The ANN configuration surpassed both radiologists and DL models in specificity (82%), F1 score (92%), and accuracy (85%), while maintaining a comparable sensitivity (86%) to the DL models. This indicates that ANNs can effectively predict M3M-IAC contact relations and are particularly effective at identifying cases with no contact relation between M3M and IAC compared to other ML methods. Future work should focus on developing automated segmentation algorithms for M3M and IAC on PRs, to identify relevant anatomical structures, thereby improving clinical usability. The dataset, feature extraction, and ML codes are available through the CONTACT grand challenge.

Coronectomy of mandibular third molars with dental pathology: a prospective cohort study of 121 molars

PURPOSE

Coronectomy is a valuable treatment proven safe for non-pathological mandibular third molars with an increased risk of inferior alveolar nerve injury. Coronectomy may also be useful for mandibular third molars with dentigerous cysts and caries, but this is not commonly performed due to the lack of well-designed, evidence-based studies. Here, we aim to investigate the safety of coronectomy for mandibular third molars with caries and dentigerous cysts.

METHODS

One hundred fifteen patients with an impacted mandibular third molar with a dentigerous cyst or caries underwent coronectomy or complete removal and received follow-up with clinical and radiographical examinations. We statistically compared the presence of postoperative complications after coronectomy versus complete removal.

RESULTS

Data from 121 molars were available for analysis. The results revealed no significant difference in the occurrence of postoperative complications (including persistent pain, inferior alveolar nerve injury, infection, alveolar osteitis, excessive bleeding, and the need for retreatment) between coronectomy and complete removal. Additionally, the incidence of postoperative complications was not related to any analyzed patient- or molar-related factors, including age, gender, health status, smoking, caries, dentigerous cyst extent, and impaction degree.

CONCLUSION

For pathological impacted mandibular third molars with dentigerous cysts and caries, coronectomy exhibited both short-term and long-term safety, showing no significant difference in postoperative complications compared to total removal. Our results suggest that coronectomy can be indicated for pathological mandibular third molars with proximity to the inferior alveolar nerve.

TRIAL REGISTRATION NUMBER

Not applicable.

Learning Curve in the Extraction of Impacted Lower Third Molars: A Prospective Cohort Study

INTRODUCTION

Third molar removal is one of the most common surgical procedures in dentistry. Therefore, it is important to evaluate the learning curve of dentists undergoing surgical training. Thus, the aims of this study were to assess the performance of oral surgery residents in third molar extractions based on operative time and the occurrence of incidents/complications, and to determine which variables are associated with surgical difficulty.

MATERIAL AND METHODS

A prospective cohort study was carried out in adults requiring an impacted lower third molar extraction. All procedures were performed by residents of a master's degree in Oral Surgery and Implantology. The outcome variables were operative time and surgeon-reported difficulty. A descriptive, bivariate and multivariate analysis was performed.

RESULTS

One hundred and 74 patients were operated on by six students. Similar performance was observed among the surgeons. Although a significant improvement in operative time was seen after 10 cases, a non-significant decreasing trend of incidents was also found. The multivariate analysis revealed an association between difficulty with crown/root sectioning and impaction against the second molar.

CONCLUSIONS

At least 10 lower impacted third molar extractions performed by postgraduate students with experience in tooth extractions are required to improve the operative time. Incidents seem to decrease slightly with the number of procedures performed. Surgical difficulty seems to be related to the need for crown/tooth sectioning and greater impaction against the second molar. Further studies are required to confirm these findings.

Radiographic Predictors of Postoperative Inferior Alveolar Nerve Injury in Mandibular Third Molar Surgery

BACKGROUND

Cone-beam computed tomography (CBCT) provides additional 3-dimensional information on the relationship between the mandibular third molar (M3M) and the inferior alveolar nerve (IAN). As such, CBCT is being increasingly utilized in preoperative M3M assessment.

PURPOSE

The purpose of the study was to compare the radiographic findings on panoramic and CBCT and their association with postoperative IAN paresthesia.

STUDY DESIGN, SETTING, SAMPLE

We conducted a retrospective cohort study in a sample of patients referred to the Department of Oral and Maxillofacial Surgery at the Royal Dental Hospital of Melbourne, for management of impacted M3Ms. Patients were included in this study if they had 1 or more high-risk findings on orthopantomogram (OPG), had both OPG and CBCT imaging taken and if at least 1 M3M had been extracted. Subjects were excluded from this study if their M3Ms were not extracted or if a CBCT was not indicated.

INDEPENDENT VARIABLE

The independent variable was radiographic features identified on OPG (Rood and Shehab's radiographic signs, root morphology, impaction type, Pell and Gregory classification) and CBCT (number and location of roots, severity of IAN compression and the presence of ankylosis).

MAIN OUTCOME VARIABLE

The outcome variable was postoperative neurosensory function defined as any reported paresthesia at 2-week postprocedural review.

COVARIATES

The covariates were patient demographic information (age, sex).

ANALYSES

Variables were initially assessed with univariate logistic regression analysis to determine factors related to developing postoperative paresthesia. Multivariate logistic regression analysis was then used to assess the association between positive univariate study variables and postoperative paresthesia, while adjusting for potential confounders. Covariates were assessed using an omnibus likelihood ratio test and included if they were statistically significant at the P < .05 level.

RESULTS

The study sample consisted of 257 subjects who underwent surgical removal of n = 386 M3Ms. The mean age was 25.9 (standard deviation = 7.05). The panoramic features of narrowing of canal, diversion of canal and dark and bifid roots were identified as statistically significant associations of postoperative paresthesia. No CBCT features were significantly associated of postoperative paresthesia.

CONCLUSION AND RELEVANCE

Certain panoramic features, along with patient age, are significant predictors of IAN paresthesia. CBCT findings were not significant predictors upon multivariate analysis, thus additional CBCT imaging did not significantly improve ability to predict paresthesia.

Treatment decision for impacted mandibular third molars: Effects of cone-beam computed tomography and level of surgeons' experience

The aim of this study was to analyse the effect of surgeons' experience and the benefit of using cone-beam computed tomography (CBCT) images, compared to the use of panoramic radiography (PAN) images, on their decisions with regard to mandibular third molar treatment modality. Panoramic radiographs and CBCTs from a total of 143 patients who had undergone impacted third molar surgery were randomly evaluated for treatment decision by 10 participants with differing clinical experience (5 novices and 5 experienced surgeons). The degree of agreement between the same type of participants was 'Substantial Agreement' (0.61-0.80) or 'Almost Perfect' (0.81-1.00). When the treatment modality decisions of the experienced and novice surgeons, using PAN and CBCT images, were compared, a statistically significant difference was found (p<0.01) between the variables. In 50 cases, experienced surgeons decided from CBCT images that total extraction was the best treatment method but opted for coronectomy when presented with PAN images of the same cases. In 164 cases novice surgeons decided on total extraction from CBCT images but chose coronectomy when presented with PAN images of the same cases. The results obtained from this study revealed that the degree of professional experience of the surgeon was a significant factor in determining the treatment decision. Moreover, the treatment choice of experienced surgeons was less affected by the change in imaging technique employed, when compared to novice surgeons.

Analysis of clinical and radiographic outcomes at least 5 years after coronectomy for deeply impacted mandibular third molars

OBJECTIVE

Coronectomy is an alternative to traditional mandibular third molar extraction when the inferior alveolar nerve (IAN) is closely associated with the roots of these molars. Given the paucity of research on the long-term outcomes after coronectomy, we conducted this study to evaluate clinical and radiographic outcomes at least 5 years post-coronectomy.

METHODS

This retrospective study enrolled all patients with impacted mandibular third molars treated with coronectomy at our institution who were willing to return for follow-up evaluation 5 years or more after their original procedure. Patient data were obtained retrospectively from hospital records and during oral examinations at the follow-up study appointment. We assessed the following postoperative clinical outcomes: injury to the IAN, root migration distance, root exposure in the oral cavity, non-healing sockets, pain or sensitivity in the coronectomy area, and the presence of periapical pathology.

RESULTS

Of the 196 patients invited to participate, 66 patients (male, 32 %; female, 68 %) who underwent a total of 75 coronectomies were included in this study. No persistent hypoesthesia of the lower lip were reported during follow-up. Two patients required reoperation because of root eruption into the oral cavity. Approximately two-thirds of residual roots migrated from their position on preoperative radiographs; the mean migration distance was 3.2 ± 1.3 mm. Two patients (2.6 %) had pain in the soft tissues around the coronectomy site.

CONCLUSION

Our findings confirm that coronectomy is an effective treatment option for preventing IAN injury when the nerve is in close proximity to the roots of these molars.

Stepwise multi-stage resection technique for surgical extraction of a partially erupted mandibular third molar with inferior alveolar nerve entrapment: a case report

The removal of lower third molars is one of the most common surgical procedures in routine dental practice. However, perforation of the mandibular third molars by the inferior alveolar nerve (IAN) is a rare occurrence. These cases are considered to carry a heightened risk of IAN injury due to the nerve being entrapped within the tooth. This case report details the experience of a 43-year-old female who visited the clinic for surgical removal of her lower third molar. She reported a six-month history of pain in area of tooth number 38, along with persistent hypersensitivity radiating through the lower lip and chin on the left side of her face, accompanied by abnormal sensations and numbness occurring alongside the pain. The case includes entrapment of IAN within the root of the partially erupted tooth, causing neurosensory disturbances. The associated lower third molar was extracted using a stepwise multi-stage resection technique in order to preserve the entrapped nerve. The patient's pain improved after surgery. This report contributes to current clinical knowledge and practices for extracting teeth with IAN entrapment. It addresses a gap in the limited and outdated literature on such cases.

Radiological and Surgical Assessment of Proximity of Roots of Mandibular Third Molar to the Inferior Alveolar Canal in Impacted Teeth

Background and Objective

A mandibular canal around the lower third molar roots house the inferior alveolar nerve (IAN). There is a risk of nerve injury during surgical tooth extraction.

Methods

The College of Dental Sciences at Davangere's Department of Oral and Maxillofacial Surgery served as the outpatient setting for this investigation. The study comprised one hundred participants who were going to have their mandibular third molars surgically extracted. The risk of IAN injury was evaluated by comparing the radiographic findings from preoperative orthopantomography and intraoral periapical radiographs with intraoperative observations.

Results

The study revealed that the patient's age did not have a significant correlation with the risk of nerve injury. However, cases involving bony impactions were found to have a higher risk of IAN damage. Additionally, mesioangular impactions and radiographic indicators, such as root deflection, were associated with an elevated risk of nerve injury.

Conclusion

To reduce the risk of IAN injury during the extraction of mandibular third molars, it is essential to have a detailed understanding of the relevant anatomical features and to plan the surgical procedure meticulously.

The success rates and outcomes of mandibular third molar coronectomy: 167 cases

PURPOSE

The purpose of this study was to assess success rates and to report complications of coronectomy of mandibular third molars (M3M), including intra-operative failure, pain, infection, dry socket, inferior dental alveolar (IAN) and lingual nerve (LN) injuries and re-operation rates.

METHODS

Retrospective analysis of 167 coronectomies completed between January 2017 to December 2022 was undertaken.

RESULTS

The success of coronectomy was 93%. Intra-operative failure was reported to be 3.6% (n = 8). Complications accounted for pain (15%, n = 24), infection (9%, n = 15) and dry socket (3.6%, n = 6). Three patients required removal of M3M root at 3 months (n = 2) and 24 months (n = 1), accounting for 1.8% re-operation rate. A total of number of patients who suffered a nerve injury was 12; three of these were permanent (LN - 1.2%, n = 2; IAN - 0.6%, n = 1), nine were temporary (IAN - 1.2%; n = 2, LN - 2.4%; n = 4; site not specified - 1.8%, n = 3). No patients with intra-operative failure and re-operation suffered IAN or LN injury post-operatively.

CONCLUSION

Coronectomy offers a successful strategy for management of high risk M3M. The treatment outcomes can be improved with careful case selection and adjusting surgical technique, including assessment of root morphology, incomplete crown sectioning technique and avoidance of lingual retraction. Reporting of coronectomy success as a factor of surgical outcome, presence or absence of permanent IAN injury, persistent symptoms or any other long-standing complications (such as LN injury), and the need for re-operation accounting for root migration status may be a useful tool to measure coronectomy outcomes.

Use of CBCT and panoramic radiography in the prediction of alterations in sensivity of the inferior alveolar nerve in third molars: A retrospective cross-sectional study

Objectives

We investigated which type of orthopantomography (OPG) was best able to predict neurological alterations of the inferior alveolar nerve (IAN) during extraction of a lower third molar (3 M).

Methods

We analysed cone beam computed tomographies (CBCTs) that were performed at a private dental clinic in Cartagena, Spain over five consecutive years. The CBCTs, together with their corresponding OPGs, had been prescribed for the surgical extraction of a lower 3 M.

Results

We analysed a total of 342 CBCTs and their corresponding OPGs. After explaining the risk of changes in the IAN sensitivity, 37 patients refused to undergo surgical extraction. The incidence of sensitivity alterations in the 332 dental extractions was 62 (19%): 44 were paraesthesias of the IAN, and 18 were associated with darkening of the root and interruption of the cortical line.

Conclusion

When an OPG revealed darkening of the root and interruption of the cortical line, the risk of contact between the lower 3 M and the IAN-that is, the probability of changes in IAN sensitivity-increased by over three-fold.

Protocol for Diagnostic Test Accuracy Study: Evaluation of Cone Beam Computed Tomography (CBCT) in Prediction of Inferior Alveolar Nerve Injury as Compared to Orthopantomography (OPG) Secondary to Surgical Removal of Impacted Mandibular Third Molars

Introduction Impairment of the inferior alveolar/dental nerve (IAN) is a relatively uncommon complication after lower wisdom tooth removal. Studies report varying incidences of IAN injury, with dysesthesia being noted as particularly distressing and 0-0.9% cases extending for a long duration. Neurosensory disruptions can severely impact speech, chewing, swallowing, and social interactions, leading to chronic pain and a lower quality of life. It also poses a risk of inadvertent injuries during meals. Although orthopantomogram (OPG) is primarily used for diagnosis, but when the lower wisdom tooth and nerve are in close approximation, cone beam computed tomography (CBCT) is recommended, despite its higher cost and radiation exposure. A white paper on third molar management necessitates further research on CBCT's role, citing conflicting evidence. Further in a multicentric trial, the difference between the OPG versus CBCT group was not statistically significant due to the low incidence of IAN injuries. They have emphasized the need for more well-designed studies to reach a statistically significant conclusion by meta-analyses. Hence, this study aims to provide additional evidence. Methods It is a two-arm, parallel, diagnostic study design involving individuals between the ages of 18 and 50 years, requiring lower wisdom tooth removal that is closely approximated with the nerve. Eligible adults, based on the specified inclusion/exclusion criteria, will be recruited into the study; informed consent will be obtained; then assigned randomly to the OPG or CBCT group using a random computer-generated sequence. Extractions will be done under local anesthesia using a standard surgical protocol with odontectomy. Surgical variables will include the experience of the surgeon, amongst others. The outcome variables will be recorded using patient interviews (subjective) and objective examinations from day one up to six months after surgery. The primary outcome will comprise the number of patients reporting abnormal sensations post-surgery. Secondary outcomes will include objectively confirmed IAN injuries and permanent IAN injuries (>6 months). Results will be analyzed statistically to look for significance and possible risk factors associated with it. Results If a statistically significant result is obtained, then we can deliberately reduce CBCT referrals and reserve them only for high-risk cases, wherein the risk of IAN injury cannot be predicted by OPG alone. If the experience of the surgeon proves to be an important risk factor, then it can also help refer high-risk patients to surgeons with more experience. Conclusion If CBCT proves to be statistically superior to OPG in the prediction of nerve injury, then we will be able to avoid significant morbidity and improve the quality of life of such patients by either modifying the surgical steps or by choosing other conservative treatment modalities. Further, this may reduce unnecessary CBCT referrals, thus reducing radiation exposure, the cost to patients, and, in turn, national healthcare expenditure. Besides, CBCT is not available at all centers, so a lot of low-risk patients can be managed safely at primary health centers, thus reducing the urban patient load.

Association of indications for mandibular third molar coronectomy and the Pell and Gregory and the Winter classification systems

PURPOSE

The purpose of this study was to determine how the surgeon's decision to perform a mandibular third molar coronectomy or surgical removal is associated with the impaction pattern as classified using Pell and Gregory or Winter's system.

METHODS

This observational, cross-sectional study was conducted on 813 mandibular third molars belonging to 565 patients. All patients were referred for removal of the mandibular third molar and had radiographic signs indicating a close relationship with the inferior alveolar nerve. Panoramic images were classified according to the impaction pattern.

RESULTS

A coronectomy was performed on 492 (60.5%) mandibular third molars. Most impacted mandibular third molars were class IIB with a mesioangular inclination. A significant association was found between the Pell and Gregory classification and the surgeon's choice (p = 0.002). Winter's classification was not significantly associated with surgeon choice (p = 0.425).

CONCLUSION

Mandibular third molar coronectomy is chosen more frequently than surgical removal if molars are class III and position B.

TRIAL REGISTRATION NUMBER

Not applicable.

Fully automated deep learning model for detecting proximity of mandibular third molar root to inferior alveolar canal using panoramic radiographs

OBJECTIVE

This study endeavored to develop a novel, fully automated deep-learning model to determine the topographic relationship between mandibular third molar (MM3) roots and the inferior alveolar canal (IAC) using panoramic radiographs (PRs).

STUDY DESIGN

A total of 1570 eligible subjects with MM3s who had paired PR and cone beam computed tomography (CBCT) from January 2019 to December 2020 were retrospectively collected and randomly grouped into training (80%), validation (10%), and testing (10%) cohorts. The spatial relationship of MM3/IAC was assessed by CBCT and set as the ground truth. MM3-IACnet, a modified deep learning network based on YOLOv5 (You only look once), was trained to detect MM3/IAC proximity using PR. Its diagnostic performance was further compared with dentists, AlexNet, GoogleNet, VGG-16, ResNet-50, and YOLOv5 in another independent cohort with 100 high-risk MM3 defined as root overlapping with IAC on PR.

RESULTS

The MM3-IACnet performed best in predicting the MM3/IAC proximity, as evidenced by the highest accuracy (0.885), precision (0.899), area under the curve value (0.95), and minimal time-spending compared with other models. Moreover, our MM3-IACnet outperformed other models in MM3/IAC risk prediction in high-risk cases.

CONCLUSION

MM3-IACnet model can assist clinicians in MM3s risk assessment and treatment planning by detecting MM3/IAC topographic relationship using PR.

Evaluation of anatomical relationships in the mandibular third molar region based on its angulation and depth of impaction: a CBCT-based study

PURPOSE

The aim of this study is to evaluate the relationship between the inclination/impaction depth and root proximity to the inferior alveolar canal/lingual plate on a millimeter scale using CBCT scans.

METHODS

340 CBCT scans of the mandibular third molar (M3) of 219 patients were evaluated for this cross-sectional study. After adjustment of the 3D orientation of the individual's jaws, the study variables including the angulation between M3 and second molar (M2)/occlusal plane (OP), and the distance of mesial (M)/distal (D) roots of M3 from the inferior alveolar canal (IAC) and lingual plate (LP) were measured. Winter's classification was used for the specification of teeth angulation. The vertical position of each M3 was then evaluated using the 3D view window (based on Pell & Gregory classification). The Spearman correlation coefficient was used for reporting the correlation between quantitative variables. The One-way ANOVA test and the Welch analysis were used for inter-group comparisons. Finally, a multivariant analysis of variances was performed.

RESULTS

Most third molars had a mesioangular inclination (52.1%), and vertical inclination (25.9%) was in second place. There was no significant correlation between angulation and age or the D/LP. A strong positive correlation between M3:M2 and M3:OP was observed (0.983). Furthermore, there was a weak negative correlation between M/IAC or M/LP and angulation (- 0.16 and - 0.13, respectively). Concerning Winter's classification, the relationship between D/IAC and angulation was statistically significant (P = 0.003). Furthermore, teeth in position A had lesser inclination compared to those with B or C positions. Multivariate analysis revealed that there was no statistically significant relationship between particular combinations of inclination-impaction depth and proximity of the M3 roots to the IAC or LP (P = 0.211).

CONCLUSIONS

The findings of the current study revealed that there is a strong correlation between M3:M2 and M3:OP. The D/IAC was the only variable that had a significant relationship with the angulation of these teeth. Moreover, the roots of horizontally inclined teeth with position A were the closest to the LP and the farthermost to the IAC.

Outcomes of Coronectomy and Total Odontectomy of Impacted Mandibular Third Molars

OBJECTIVE

The aim of this research was to evaluate the surgical complications and neurosensory deficits after coronectomy and the complete removal of mandibular third molars.

METHODS

The study sample included patients requiring surgical removal of mandibular third molars. A coronectomy was conducted on 220 teeth showing signs of close proximity to the inferior alveolar canal. A complete extraction was performed on 218 teeth with no risk signs. The patients were evaluated at 1 week and 1, 3, 6, 12, and 24 months after surgery for pain, swelling, neurologic deficit, dry socket, postoperative bleeding, infection, root migration, and eruption.

RESULTS

No significant difference was noted in pain and swelling; however, bleeding and dry socket were significantly higher in the odontectomy group (P = .017). The inferior alveolar nerve deficit was higher in the odontectomy group (3.7%) than the coronectomy group (0.5%) (P = .017). The percentage and distance of root migration of coronectomised teeth at 3, 6, and 12 months were 60% (2.37 ± 0.96 mm), 66% (3.35 ± 0.86 mm), and 74% (3.85 ± 0.93 mm), respectively.

CONCLUSIONS

Coronectomy is a safe procedure and should be performed when the roots are closely associated with the mandibular canal. Although root migration is common, the likelihood of root exposure is low and roots rarely need removal.

Risk factors for impacted lower third molar root perforation through the undercut-shaped lingual plate: preoperative insights from panoramic radiography

This study aimed to identify risk factors associated with perforation of the undercut (U)-shaped lingual plate (LP) by the lower third molar (LM3) root using panoramic radiography (PAN). We retrospectively examined 468 impacted LM3s from 468 individuals, categorizing LM3-LP associations and LP morphology in the coronal section of cone-beam computed tomography as perforation or nonperforation and U-type or non-U-type, respectively. The outcome was the combination of perforation and U-type, and study variables included patient demographics (age and sex) and PAN-associated features (Winter's classification, Pell-Gregory classification, and two major Rood signs). Multivariate logistic regression methods were used for analysis. Perforated and U-type LPs were observed in 205 (43.8%) and 212 (45.3%) cases, respectively. The double-positive outcome was observed in 126 LM3s (26.9%). In the multivariate model, age ≥ 26 years [odds ratio (OR), 2.66; p = 0.002], men (OR, 2.01; p = 0.002), mesioangular (OR, 2.74; p = 0.038) and horizontal impaction (OR, 3.05; p = 0.019), and root darkening (OR, 1.73; p = 0.039) were independently associated with the risk. Class III impaction (OR, 0.35; p = 0.021) and interruption of the white line (OR, 0.55; p = 0.017) were negatively correlated with the risk. In conclusion, this study highlights the importance of identifying the higher probability of U-type LP perforation by the LM3 root in men aged over their midtwenties with Class I/II impaction and mesioangularly or horizontally impacted LM3s, along with root darkening and no interruption of the white line on PAN.

Investigation of the relationship between the mandibular third molar teeth and the inferior alveolar nerve using posteroanterior radiographs: a pilot study

BACKGROUND

The most severe complication that can occur after mandibular third molar (MM3) surgery is inferior alveolar nerve (IAN) damage. It is crucial to have a comprehensive radiographic evaluation to reduce the possibility of nerve damage. The objective of this study is to assess the diagnostic accuracy of panoramic radiographs (PR) and posteroanterior (PA) radiographs in identifying the association between impacted MM3 roots and IAN.

METHODS

This study included individuals who had PR, PA radiographs, and cone beam computed tomography (CBCT) and who had at least one impacted MM3. A total of 141 impacted MM3s were evaluated on CBCT images, and the findings were considered gold standard. The relationship between impacted MM3 roots and IAN was also evaluated on PR and PA radiographies. The data was analyzed using the McNemar and Chi-squared tests. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of PR and PA radiographies were determined.

RESULTS

Considering CBCT the gold standard, the relationship between MM3 roots and IAN was found to be statistically significant between PR and CBCT (p = 0.00). However, there was no statistically significant relationship between PA radiography and CBCT (0.227). The study revealed that the most prevalent limitation of the PR in assessing the relationship between MM3 roots and IAN was the identification of false-positive relationship.

CONCLUSIONS

PA radiography may be a good alternative in developing countries to find out if there is a contact between MM3 roots and IAN because it is easier to get to, cheaper, and uses less radiation.

Relationship between Impacted Mandibular Third Molars and the Mandibular Canal on CBCT Scans

This study aimed to assess the relationship of impacted mandibular third molars with the mandibular canal on cone beam computed tomography (CBCT) scans. This cross-sectional study was conducted on CBCT scans of 137 patients with 204 impacted mandibular third molars. The relation of age, gender, class of impaction, anatomical position of canal relative to tooth (buccal, lingual, inferior, inter-radicular), tooth angulation (mesioangular, vertical, distoangular, horizontal), relationship of tooth with the mandibular canal (no contact, in contact, relation), relationship of tooth with the mandibular cortex, anatomical site of contact of tooth with the mandibular cortex (buccal, lingual, inferior), and the impression of canal (grooving, no effect) on impacted teeth were evaluated. Data were analyzed using one-way ANOVA, Chi-square test and Fisher's exact test. Class B of impaction (78.9%), inferior position of canal relative to the impacted tooth (53.9%) and mesioangular angulation (53.4%) had the highest frequency, respectively. The relationship of tooth with the mandibular canal was "relation" in most cases (53.4%) followed by no contact (26.9%) and in contact (19.6%). Significant associations were noted between depth of impaction (P < 0.001), tooth angulation (P = 0.024), anatomical position of canal relative to tooth (P < 0.001), relationship of tooth with the mandibular cortex (P = 0.032) and anatomical site of contact of tooth with the mandibular cortex (P = 0.013) with the impacted tooth-mandibular canal relationship. CBCT provides accurate information about the relationship of impacted third molars with the mandibular canal and can decrease the risk of traumatization of inferior alveolar nerve (IAN) during their surgical extraction.

Association of Radiographic Signs in Determining the Proximity of Mandibular Third Molar Roots to the Mandibular Canal and Postoperative Occurrence of Neurosensory Disorders: A Cohort Study

BACKGROUND

The routine oral and maxillofacial procedure involving the surgical removal of impacted mandibular third molars comes with inherent risks to nearby anatomical structures. Proximity of mandibular third molar roots to the inferior alveolar nerve (IAN) poses a significant risk for injury, prompting the need for reliable assessment methods. Radiographic indicators, particularly those observed on intraoral periapical radiographs (IOPARs), offer a dependable means to evaluate proximity.

OBJECTIVES

This study seeks to examine the closeness between the mandibular canal and the roots of mandibular third molars using IOPARs and to assess the incidence of postoperative neurosensory disorders.

METHODS

A cohort of 100 subjects aged 18 to 25, presenting for partially erupted/ impacted mandibular third molar removal, underwent IOPAR examinations. Data analysis employed IBM SPSS Statistics for Windows, Version 12 (Released 2004; IBM Corp., Armonk, New York, United States), calculating frequencies, percentages, means, standard deviations, and ranges. Radiographic signs of proximity were evaluated, and a standardized surgical procedure was performed under local anesthesia. Postoperative neurosensory disorders were assessed using various methods.

RESULTS

Of the evaluated subjects, darkening of the root (52%) was the most prevalent radiographic sign, followed by interruption of the white line of the canal (20%). The prevalence of radiographic signs varied, with none of the patients experiencing narrowing of the root. Postsurgical paraesthesia assessment revealed no nerve sensitivity alterations in any patient.

CONCLUSION

Preoperative radiographic examination is imperative for determining the relationship between mandibular third molar roots and the inferior alveolar canal, aiding in preventing IAN damage during extraction. Contrary to radiographic signs, there was no observed association between impacted mandibular third molar radiographic signs and the occurrence of postoperative neurosensory disorders.

Three-dimensional positional relationship between impacted mandibular third molars and the mandibular canal

OBJECTIVE

To observe the three-dimensional positional relationship between impacted mandibular third molars (IMTMs) and mandibular canal close contacts using cone beam computed tomography (CBCT).

METHODS

A total of 101 patients with IMTMs were selected who met the diagnostic criteria for 142 teeth (no bone wall imaging area between IMTMs and the mandibular canal, a high-density bone cortical imaging area only, or a ≦1 mm bone imaging area). The parameters of the rotating CBCT anode were set as follows: 110 kV, 40-50 mA; the focal point and exposure field were set as 0.3 mmh and a high-resolution zoom, respectively; the exposure time and image layer thickness were set as 5.4 s and 0.25 mm. Three-dimensional reconstruction was performed, and the position of the mandibular canal through the IMTM area was observed continuously from the coronal, horizontal and sagittal planes.

RESULTS

We found that the mandibular canal was interrupted below the third molar (TM) in 85 cases, accounting for 59.86% of all cases. The mandibular canal was located below the buccal and lingual curvatures in 33 and 19 cases, respectively, accounting for 23.23% and 19%. In addition, a small number of mandibular canals were also located on the buccal side of the mandibular molars (2.82%). We also found one case of direct insertion of the mandibular third molar (MTM) into the mandibular canal. In addition, the mandibular canal passed through the IMTM region with 125 close contacts at the roots (88.03%); 14 mandibular canals were in contact with all teeth and 3 were in contact with the crown.

CONCLUSION

The use of CBCT can provide a dynamic and comprehensive understanding of the three-dimensional positional relationship of the mandibular alveolar nerve canal passing through the IMTM area, providing a high clinical reference value when extracting IMTMs and reducing the risk of injury to the inferior alveolar nerve.

Radiographic evaluation of mandibular third molars: an ex vivo comparative study between multilayer and conventional panoramic radiography

OBJECTIVES

To compare the multilayer panoramic radiography (MPAN) and conventional panoramic radiography (CPAN) in the evaluation of mandibular third molars using cone-beam computed tomography (CBCT) as a reference.

METHODS

CPAN, MPAN, and CBCT scans from 33 dry human mandibles were acquired using the OP300 Maxio unit, totalizing 56 mandibular third molars to be evaluated. Three examiners evaluated each third molar according to their position, depth of impaction in the mandibular ramus, proximity between the dental root apexes and the mandibular canal, and the presence of radiographic signs of proximity to the mandibular canal. In addition, when there was a distance between the root apexes and the mandibular canal, it was measured. As a reference, these same parameters were assessed in the CBCT scans by a fourth examiner. For the statistical analysis, the weighted Kappa, Bland Altman, and Wilcoxon tests were performed (α = 0.05).

RESULTS

The agreement between the assessments performed in the panoramic modalities with the CBCT ranged from 66.1% to 100.0% for the categorical variables. Overall, the agreement values of CPAN and MPAN with CBCT were similar. The distances between the dental root apex and the mandibular canal for both CPAN and MPAN were significantly underestimated compared to CBCT (p < 0.05). The intra- and interexaminer agreements of the examiners ranged from poor to almost perfect; in general, the agreements were higher in the evaluation performed in the MPAN than in the CPAN.

CONCLUSIONS

The MPAN performs similarly to CPAN for evaluating mandibular third molars and their proximity relationship to the mandibular canal.

CLINICAL RELEVANCE

Preoperative evaluation of lower mandibular third molars is usually performed using CPAN. Recently, a new tool, MPAN, was developed, which has not yet been tested for the evaluation of mandibular third molars and showed similar performance to CPAN in the present study. Future studies using MPAN are encouraged to evaluate other diagnostic tasks.

Risk factors observed in 2-dimensional radiographs for permanent injury of the inferior alveolar nerve after removal of mandibular third molars: a case-control study

OBJECTIVE

To assess whether differences exist in signs observed in 2D radiographs of mandibular third molars between a case group of patients with and a control group without permanent sensory disturbance of the inferior alveolar nerve (IAN) after removal.

STUDY DESIGN

Three observers blinded to patient status assessed radiographs from the case group (n=162) and the control group (n=172). Two new signs, craniocaudal relation of the roots and the mandibular canal and position of the canal over the roots; and 4 "classic" signs, interruption of the white borders of the canal, darkening of the roots, narrowing of the canal lumen, and diversion of the canal over the roots were registered. Chi-square tests assessed differences in distribution of radiographic signs between the groups. Odds ratios expressed the association between radiographic signs and permanent sensory disturbance. Inter- and intraobserver reliability values were calculated.

RESULTS

We found significantly more teeth with roots positioned inferiorly to the canal borders (P<0.001; OR 4.1-5.3) and with the canal superimposed over the upper or middle third of the roots (P<0.001; OR 2.6-3.9) in the case group than in the control group. Inter- and intraobserver reproducibility was excellent for roots inferior to the canal borders and fair to good for canal superimposition.

CONCLUSIONS

Two radiographic signs are valid predictors of permanent sensory disturbance of the IAN in 2D radiographs.

Reproducibility analysis of automated deep learning based localisation of mandibular canals on a temporal CBCT dataset

Preoperative radiological identification of mandibular canals is essential for maxillofacial surgery. This study demonstrates the reproducibility of a deep learning system (DLS) by evaluating its localisation performance on 165 heterogeneous cone beam computed tomography (CBCT) scans from 72 patients in comparison to an experienced radiologist's annotations. We evaluated the performance of the DLS using the symmetric mean curve distance (SMCD), the average symmetric surface distance (ASSD), and the Dice similarity coefficient (DSC). The reproducibility of the SMCD was assessed using the within-subject coefficient of repeatability (RC). Three other experts rated the diagnostic validity twice using a 0-4 Likert scale. The reproducibility of the Likert scoring was assessed using the repeatability measure (RM). The RC of SMCD was 0.969 mm, the median (interquartile range) SMCD and ASSD were 0.643 (0.186) mm and 0.351 (0.135) mm, respectively, and the mean (standard deviation) DSC was 0.548 (0.138). The DLS performance was most affected by postoperative changes. The RM of the Likert scoring was 0.923 for the radiologist and 0.877 for the DLS. The mean (standard deviation) Likert score was 3.94 (0.27) for the radiologist and 3.84 (0.65) for the DLS. The DLS demonstrated proficient qualitative and quantitative reproducibility, temporal generalisability, and clinical validity.

Artificial Intelligence for Classifying the Relationship between Impacted Third Molar and Mandibular Canal on Panoramic Radiographs

The purpose of this investigation was to evaluate the diagnostic performance of two convolutional neural networks (CNNs), namely ResNet-152 and VGG-19, in analyzing, on panoramic images, the rapport that exists between the lower third molar (MM3) and the mandibular canal (MC), and to compare this performance with that of an inexperienced observer (a sixth year dental student). Utilizing the k-fold cross-validation technique, 142 MM3 images, cropped from 83 panoramic images, were split into 80% as training and validation data and 20% as test data. They were subsequently labeled by an experienced radiologist as the gold standard. In order to compare the diagnostic capabilities of CNN algorithms and the inexperienced observer, the diagnostic accuracy, sensitivity, specificity, and positive predictive value (PPV) were determined. ResNet-152 achieved a mean sensitivity, specificity, PPV, and accuracy, of 84.09%, 94.11%, 92.11%, and 88.86%, respectively. VGG-19 achieved 71.82%, 93.33%, 92.26%, and 85.28% regarding the aforementioned characteristics. The dental student's diagnostic performance was respectively 69.60%, 53.00%, 64.85%, and 62.53%. This work demonstrated the potential use of deep CNN architecture for the identification and evaluation of the contact between MM3 and MC in panoramic pictures. In addition, CNNs could be a useful tool to assist inexperienced observers in more accurately identifying contact relationships between MM3 and MC on panoramic images.

Positional assessment of lower third molar and mandibular canal using explainable artificial intelligence

OBJECTIVE

The aim of this study is to automatically assess the positional relationship between lower third molars (M3i) and the mandibular canal (MC) based on the panoramic radiograph(s) (PR(s)).

MATERIAL AND METHODS

A total of 1444 M3s were manually annotated and labeled on 863 PRs as a reference. A deep-learning approach, based on MobileNet-V2 combination with a skeletonization algorithm and a signed distance method, was trained and validated on 733 PRs with 1227 M3s to classify the positional relationship between M3i and MC into three categories. Subsequently, the trained algorithm was applied to a test set consisting of 130 PRs (217 M3s). Accuracy, precision, sensitivity, specificity, negative predictive value, and F1-score were calculated.

RESULTS

The proposed method achieved a weighted accuracy of 0.951, precision of 0.943, sensitivity of 0.941, specificity of 0.800, negative predictive value of 0.865 and an F1-score of 0.938.

CONCLUSION

AI-enhanced assessment of PRs can objectively, accurately, and reproducibly determine the positional relationship between M3i and MC.

CLINICAL SIGNIFICANCE

The use of such an explainable AI system can assist clinicians in the intuitive positional assessment of lower third molars and mandibular canals. Further research is required to automatically assess the risk of alveolar nerve injury on panoramic radiographs.

Application of Cone Beam Computed Tomography in Risk Assessment of Lower Third Molar Surgery

Risks of lower third molar surgery like the inferior alveolar nerve injury may result in permanent consequences. Risk assessment is important prior to the surgery and forms part of the informed consent process. Traditionally, plain radiographs like orthopantomogram have been used routinely for this purpose. Cone beam computed tomography (CBCT) has offered more information from the 3D images in the lower third molar surgery assessment. The proximity of the tooth root to the inferior alveolar canal, which harbours the inferior alveolar nerve, can be clearly identified on CBCT. It also allows the assessment of potential root resorption of the adjacent second molar as well as the bone loss at its distal aspect as a consequence of the third molar. This review summarized the application of CBCT in the risk assessment of lower third molar surgery and discussed how it could aid in the decision-making of high-risk cases to improve safety and treatment outcomes.

Neurosensory Deficits of Inferior Alveolar Nerve Following Impacted Mandibular Third Molar Extraction: Comparison of One-Stage Complete Extraction with Two-Stage Partial Coronectomy Surgical Technique

Objectives

Inferior alveolar nerve neurosensory deficit is a worrisome complication of surgical extraction of impacted mandibular third molars. A novel approach using two-stage partial coronectomy has been proposed as an alternative surgical procedure to reduce this complication. This study compared neurosensory deficits of inferior alveolar nerve following impacted mandibular third molar extraction using one-stage complete extraction with the two-stage partial coronectomy technique.

Material and Methods

Subjects with mesioangular or horizontal impacted mandibular third molar with an intimate relationship with inferior dental canal who met the inclusion criteria were recruited for the study. Subjects were divided into one-stage and two-stage partial coronectomy techniques. The subjects were evaluated for the presence of inferior alveolar neurosensory deficit, and the relationships of neurosensory nerve deficit with sex, age and type of impaction.

Results

Neurosensory deficit was observed in 5 subjects (7.8%), with all cases seen in the one-stage group. This difference was statistically significant (p = 0.03). The relationship between the incidence of neurosensory deficit and age, sex, type of impaction, surgical difficulty, operating time and root morphology was not statistically significant (p > 0.05).

Conclusion

Findings from this study suggest partial coronectomy compared to one-stage complete extraction reduces the incidence of Inferior alveolar nerve neurosensory deficit.

[Classification of lower impacted third molars position and their interrelationship with mandibular canal]

Classification of lower Impacted third molars position and their interrelationship with mandibular canal have a great scientific, theoretical and practical importance. An attempt to systematize and classify all anatomical impacted third molars position has been made by many authors. Based on our scientific literature search, we found: 8 impacted third molars classifications, 7 third molars and mandibular canal interposition classifications, as well as 5 classifications of mandibular canal anatomical branching variants. Most classifications are proposed by the author to predict third molar eruption perspective, determine level of operation complexity and prevent mandibular canal damage. New clinical classification development of impacted third molars interrelationship with mandibular canal, which combined the radiological PR, CBCT criteria, neurovascular bundle trauma prognosis, and operative technic choice can be actual.

External validation of cone-beam computed tomography- and panoramic radiography-featured prediction models for inferior alveolar nerve injury after lower third molar removal: proposal of a risk calculator

We previously developed basic and extended models to predict inferior alveolar nerve injuries (IANI) after lower third molar (LM3) removal based on cone-beam computed tomography (CBCT) images. Although these models comprised predictors, including increased age and inferior alveolar canal-related CBCT factors, external validations were lacking. Therefore, this study externally validated these models and compared them with other related models based on their performance. Original and newly validated samples included patients who underwent LM3 removal following CBCT. Subsequently, 39 and 25 patients with IANI, then 457 and 295 randomly selected patients without IANI were chosen of the observed 1573 and 1052 patients, respectively. CBCT- and panoramic radiograph (PAN)-featured models were validated. Then, models' discrimination and calibration abilities were assessed using C-statistics and calibration plots, respectively. Brier scores were also quantified, after which logistic recalibration was achieved to optimize calibration, and a risk calculator was developed. During the external validation, the extended model exhibited the best C-statistic (0.822) and Brier score (0.064), whereas two CBCT- and two PAN-featured models showed lower performances with C-statistics (0.764, 0.706, 0.584, and 0.627) and Brier scores (0.069, 0.074, 0.075, and 0.072). Besides, all models showed a tendency to overpredict its high-risk range. However, recalibration of the extended model resulted in excellent calibration performance. CBCT-featured models, especially the extended model, conclusively showed a superior predictive performance to PAN models. Therefore, the risk calculator on the extended CBCT model is proposed to be a clinical decision-aid tool that preoperatively predicts IANI risk.

Automatic visualization of the mandibular canal in relation to an impacted mandibular third molar on panoramic radiographs using deep learning segmentation and transfer learning techniques

OBJECTIVE

The aim of this study was to create and assess a deep learning model using segmentation and transfer learning methods to visualize the proximity of the mandibular canal to an impacted third molar on panoramic radiographs.

STUDY DESIGN

The panoramic radiographs containing the mandibular canal and impacted third molar were collected from 2 hospitals (Hospitals A and B). A total of 3200 areas were used for creating and evaluating learning models. A source model was created using the data from Hospital A, simulatively transferred to Hospital B, and trained using various amounts of data from Hospital B to create target models. The same data were then applied to the target models to calculate the Dice coefficient, Jaccard index, and sensitivity.

RESULTS

The performance of target models trained using 200 or more data sets was equivalent to that of the source model tested using data obtained from the same hospital (Hospital A).

CONCLUSIONS

Sufficiently qualified models could delineate the mandibular canal in relation to an impacted third molar on panoramic radiographs using a segmentation technique. Transfer learning appears to be an effective method for creating such models using a relatively small number of data sets.

Does the addition of cone-beam CT to panoral imaging reduce inferior dental nerve injuries resulting from third molar surgery? A systematic review

Objective

This systematic review aims to examine whether cone-beam CT (CBCT) assessment influences the incidence of nerve injury following high-risk mandibular third molar (MTM) surgery.

Study Design

Randomised controlled trials comparing two and three-dimensional imaging for assessing high-risk MTMs were included. MEDLINE, EMBASE, CENTRAL and the Dentistry and Oral Science Source (DOSS) were systematically searched along with extensive grey literature searches, hand searching of web sites, and detailed citation searching up to 3 September 2022. Risk of bias was assessed against the Cochrane Risk of Bias Tool (RoB 2.0). Certainty of the evidence was assessed using GRADE.

Results

Two authors independently screened 402 abstracts prior to full text screening of 27 articles, which culminated in seven RCTs for inclusion. Two studies were assessed as high risk of bias overall. The other five raised some concerns largely due to unblinded patients and lack of prior trial registration. Just one study reported significantly less nerve injuries following CBCT. The remaining six articles found no significant difference.

Conclusion

The seven RCTs included in this systematic review offered moderate quality evidence that CBCT does not routinely translate to reduced incidence of nerve injury in MTM removal. A single study provided low quality evidence for a consequent change in the surgical approach. Low quality evidence from 3 studies suggested CBCT does not influence the duration of third molar surgery.

Radiographic factors associated with inferior alveolar nerve exposure during mandibular third molar surgery and their influence on neurosensory deficit: A prospective study

Introduction

The inferior alveolar nerve (IAN) can occasionally be observed in the extraction socket of the mandibular third molar (M3M) intraoperatively. Exposure of inferior alveolar neurovascular bundle during surgery primarily depends upon the absence of bony cortex between the canal and root of impacted third molar or either by existence of a very thin cortical lining between two which gets broken during luxation of tooth. Accurate anatomical relationship of inferior alveolar canal with root apex of impacted (M3M) and the location of canal can be determined by Cone beam computed tomography (CBCT).

Material and methods

Initially 200 patients evaluated by Orthopantomogram (OPG) for anatomical relationship of IAN with impacted (M3M) and various radiographic risk factors for nerve injury. Among these 200, 75 showed the presence of two or more than two risk factors for IAN injury which then were further evaluated by using CBCT for presence or absence of cortex of canal and location of canal on buccal, lingual, inferior, and interradicular position.

Conclusion

Cortex of canal is an important barrier between the root apex and inferior alveolar neurovascular bundle. Interruption of cortex on CBCT, the interradicularly and lingually positioned neurovascular bundle become a strong affirmation for intra operative nerve exposure during (M3M) surgery. Although its exposure is affected by various factors such as bone density, sex and age of patient, surgeon's expertise, operative tissue damage, post operative edema, surgical procedure, but neurosensory deficit do not occur simply after the exposure of neurovascular bundle.

Pre-eruptive intracoronal resorption in "high-risk" impacted third molars: A report of four cases

Pre-eruptive intracoronal resorption (PEIR) is usually an incidental finding as a radiolucent lesion within the coronal dentin of unerupted teeth. Through the four cases reported here, authors would demonstrate deeply impacted "high-risk" third molars with PEIR defects, showing an increased risk of inferior alveolar nerve (IAN) injury. However, follow-up or coronectomy may eliminate or reduce the risk of neurosensory disturbances, in case of PEIR lesions this can be contradictory due to the unpredictable reactions of the third molar's pulp. Cases show the important role of preoperative imaging in the diagnostics and management of deeply impacted PEIR third molars and highlight the need for investigations regarding coronectomy in such cases.

When dental extractions go wrong: An overview of common complications and management

The extraction of teeth carries a risk of associated complications, some of which may be predicted, providing an opportunity for them to be prevented or their effects minimised. Prior to embarking on any extraction, the dentist must be confident that they are able to deal with any complication that may arise. This paper provides an overview of the complications of dental extraction which are commonly encountered, considers the factors which predispose to them arising, suggests how the risk of them occurring can be reduced, and describes how they should be managed.

Prevalence of and risk factors for postoperative complications after lower third molar extraction: A multicenter prospective observational study in Japan

Lower third molar extraction is the most common surgical treatment among routine dental and oral surgical procedures. while the surgical procedures for lower third molar extraction are well established, the difficulty of tooth extraction and the frequency of postoperative complications differ depending on the patient's background. To establish a management protocol for the lower third molars, the prevalence of and risk factors for postoperative complications after lower third molar extraction were investigated in a large number of Japanese patients in a multicenter prospective study. During 6 consecutive months in 2020, 1826 lower third molar extractions were performed at the 20 participating institutions. The medical records of the patients were reviewed, and relevant data were extracted. The prevalence of and risk factors for postoperative complications were analyzed. The prevalence of postoperative complications after lower third molar extraction was 10.0%. Multivariate analysis indicated that age (≤32 vs >32, odds ratio [OR]: 1.428, 95% confidence interval [95% CI]: 1.040-1.962, P < .05), the radiographic anatomical relationship between the tooth roots and mandibular canal (overlapping of the roots and canal vs no close anatomical relationship between the roots and the superior border of the canal, OR: 2.078, 95% CI: 1.333-3.238, P < .01; overlapping of the roots and canal vs roots impinging on the superior border of the canal, OR: 1.599, 95% CI: 1.050-2.435, P < .05), and impaction depth according to the Pell and Gregory classification (position C vs position A, OR: 3.7622, 95% CI: 2.079-6.310, P < .001; position C vs position B, OR: 2.574, 95% CI: 1.574-4.210, P < .001) are significant independent risk factors for postoperative complications after lower third molar extraction. These results suggested that higher age and a deeply impacted tooth might be significant independent risk factors for postoperative complications after lower third molar extraction.

The Radiological Evaluation of Mandibular Canal Related Variables in Mandibular Third Molar Region: a Retrospective Multicenter Study

OBJECTIVES

The aim of this retrospective study was to investigate anatomical structure of mandibular canal and the factors those increase the possibility of inferior alveolar nerve damage in mandibular third molar region of Turkish population.

MATERIAL AND METHODS

Overall 320 participants with 436 mandibular third molars were included from four different study centers. Following variables were measured: type and depth of third molar impaction, position of mandibular canal in relation to third molars, morphology of mandibular canal, cortication status of mandibular canal, possible contact between the third molars and mandibular canal, thickness and density of superior, buccal, and lingual mandibular canal wall, bucco-lingual and apico-coronal mandibular canal diameters on cone-beam computed tomography scans.

RESULTS

Lingual mandibular canal wall density and thickness were decreased significantly as the impaction depth of mandibular third molar was increased (P = 0.045, P = 0.001 respectively). Highest buccal mandibular canal wall density and thickness were observed in lingual position of mandibular canal in relation to mandibular third molar (P = 0.021, P = 0.034 respectively). Mandibular canal with oval/round morphology had higher apico-coronal diameter in comparison to tear drop and dumbbell morphologies (P = 0.018). Additionally, mandibular canals with observed cortication border and no contact with mandibular third molar had denser and thicker lingual mandibular canal wall (P = 0.003, P = 0.001 respectively).

CONCLUSIONS

Buccal and lingual mandibular canal wall density, thickness and mandibular canal diameter may be related with high-risk indicators of inferior alveolar nerve injury.

Automated Prediction of Extraction Difficulty and Inferior Alveolar Nerve Injury for Mandibular Third Molar Using a Deep Neural Network

Extraction of mandibular third molars is a common procedure in oral and maxillofacial surgery. There are studies that simultaneously predict the extraction difficulty of mandibular third molar and the complications that may occur. Thus, we propose a method of automatically detecting mandibular third molars in the panoramic radiographic images and predicting the extraction difficulty and likelihood of inferior alveolar nerve (IAN) injury. Our dataset consists of 4903 panoramic radiographic images acquired from various dental hospitals. Seven dentists annotated detection and classification labels. The detection model determines the mandibular third molar in the panoramic radiographic image. The region of interest (ROI) includes the detected mandibular third molar, adjacent teeth, and IAN, which is cropped in the panoramic radiographic image. The classification models use ROI as input to predict the extraction difficulty and likelihood of IAN injury. The achieved detection performance was 99.0% mAP over the intersection of union (IOU) 0.5. In addition, we achieved an 83.5% accuracy for the prediction of extraction difficulty and an 81.1% accuracy for the prediction of the likelihood of IAN injury. We demonstrated that a deep learning method can support the diagnosis for extracting the mandibular third molar.

The Effectiveness of Semi-Automated and Fully Automatic Segmentation for Inferior Alveolar Canal Localization on CBCT Scans: A Systematic Review

This systematic review aims to identify the available semi-automatic and fully automatic algorithms for inferior alveolar canal localization as well as to present their diagnostic accuracy. Articles related to inferior alveolar nerve/canal localization using methods based on artificial intelligence (semi-automated and fully automated) were collected electronically from five different databases (PubMed, Medline, Web of Science, Cochrane, and Scopus). Two independent reviewers screened the titles and abstracts of the collected data, stored in EndnoteX7, against the inclusion criteria. Afterward, the included articles have been critically appraised to assess the quality of the studies using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool. Seven studies were included following the deduplication and screening against exclusion criteria of the 990 initially collected articles. In total, 1288 human cone-beam computed tomography (CBCT) scans were investigated for inferior alveolar canal localization using different algorithms and compared to the results obtained from manual tracing executed by experts in the field. The reported values for diagnostic accuracy of the used algorithms were extracted. A wide range of testing measures was implemented in the analyzed studies, while some of the expected indexes were still missing in the results. Future studies should consider the new artificial intelligence guidelines to ensure proper methodology, reporting, results, and validation.

Comparison of Digital OPG and CBCT in Assessment of Risk Factors Associated with Inferior Nerve Injury during Mandibular Third Molar Surgery

Background: Pre-operative radiographic assessment of the anatomical relationship between the roots of the mandibular third molar and the inferior alveolar nerve (IAN) is a must to minimize the risk of IAN injury during surgery. Objectives: To compare the radiographic signs of digital orthopantomogram (OPG) and cone-beam computed tomography (CBCT). An additional objective was to assess the cortex status between the mandibular canal and third molar on CBCT images in relation to the demographic characteristics, region (right or left side), and angulation of mandibular molar. Methodology: In this retrospective study, a total of 350 impacted mandibular third molars with a close relationship between the inferior alveolar canal (IAC) and impacted mandibular third molars on digital OPG were further referred for CBCT imaging for assessment of the position of the mandibular canal. The study was conducted between August 2018 and February 2020. Digital OPGs were evaluated for radiographic signs like interruption of the mandibular canal wall, darkening of the roots, diversion of the mandibular canal, and narrowing of the mandibular canal. The age and sex of patients, site of impacted third molar, Winter’s classification of mandibular third molar, position of IAC relative to impacted molar, and the radiographic markers of OPG were assessed for cortical integrity using CBCT. Chi square testing was applied to study the values of difference and binomial logistic regression was done to assess the factors associated with cortication. Statistical significance was set at p ≤ 0.05. Results: Among 350 patients, 207 (59.1%) were male and 143 (40.9%) were female with a mean age of 36.8 years. The most common OPG sign was interruption of white line, seen in 179 (51.1%) cases. In total, 246 cases (70.3%) showed an absence of canal cortication between the mandibular canal and the impacted third molar on CBCT images. Cortication was observed in all cases with a combination of panoramic signs which was statistically significant (p = 0.047). Cortication was observed in 85 (50.6%) cases where IAC was positioned on the buccal side, 11 (16.9%) in cases of inferiorly positioned IAC, and just 8 (7.6%) for cases of lingually positioned IAC which was statistically significant (p = 0.003). Statistically insignificant (p > 0.05) results were noted for cortex status in CBCT images with regards to the age, sex, site, and angulation of impacted third molars. Conclusion: CBCT imaging is highly recommended for those cases where diversion of the mandibular canal is observed on OPG and when the roots are present between canals.

Prediction of neurosensory disorders after impacted third molar extraction based on cone beam CT Maglione's classification: A pilot study

Background

Surgical difficulty assessment in the extraction of impacted mandibular third molars is a constant challenge for oral surgeons.

Aim

The first aim was to apply Maglione's new classification on patients that needed surgical extraction of impacted mandibular third molars, and the second aim was to study the correlation of the classification classes with the occurrence of postoperative neurosensory disorders.

Materials & methods

The present prospective clinical trial pilot study was conducted on patients attending oral and maxillofacial surgery clinics from February 2017 until January 2018 for the surgical extraction of impacted lower third molars.

Results

Fifty-one out of sixty-nine patients made the surgical removal of one impacted mandibular third molar. The most common subclass was 1B (24.6%), followed by subclass 3B (23.2%). Subclass 3A and 4B showed an equal distribution of (11.6%) each, and then subclass 2B (10%). The most significant subclass was 4B with (5.9%) neurosensory disturbance. None of the patients had a permanent disturbance.

Conclusion

Maglione's classification offers unique detailed description of the buccolingual relationship of MTM with IAC that could be used as a future reliable radiographic guide to reduce the risk of post-operative neurosensory disturbances after MTM surgical removal.

Evaluation of the Outcomes of Coronectomy Procedure versus Surgical Extraction of Lower Third Molars Which Have a High Risk for Inferior Alveolar Nerve Injury: A Systematic Review

Results

No study reported permanent inferior alveolar nerve injury (p-IANI) regarding coronectomy; however, transient inferior alveolar nerve injury (t-IANI) was reported in 0–2.20% of successful coronectomy and 0–8% of failed coronectomy. Postextraction t-IANI ranged from 0% to 16.66% while p-IANI from 0% to 3.63%. In 5 studies, root migration occurred in 2% to 85.3% of cases and the distance rate was 2.33–3.43 mm at 6 months postoperatively; then the migration gradually decreased and stopped at 12 months.

Conclusion

This systematic review revealed that coronectomy is an efficient alternative for the management of impacted 3rd M with a high risk of IANI. Patients who got antibiotics postcoronectomy procedures had lower infection rates than those who did not receive antibiotic therapy. We recommend further research on coronectomy with longer follow-up periods to assess the retained roots' long-term outcomes and to assess the effect of antibiotics administration on postcoronectomy infection rate. This systematic review is registered under number CRD42020198394.

Correlation of Panoramic Radiological and Intra-Operative Findings of Impacted Mandibular 3rd Molar in Relation to Inferior Alveolar Canal: A Prospective Study

Aim

The objective of this study was to correlate the preoperative radiological findings and intraoperative surgical findings during removal of impacted mandibular 3rd molar with respect to the inferior alveolar canal.

Materials and Method

The prospective study design included 100 patients between the age group of 20 years and 50 years who visited the Department of Oral and Maxillofacial Surgery at Vydehi Institute of Dental Sciences and Research Centre, Whitefield, Bengaluru. A preoperative panoramic radiograph was taken and the parameters were assessed and a normal surgical protocol was followed to extract the impacted mandibular 3rd molar with intra-operative assessment as well.

Results

Out of the 100 patients with definitive radiological signs showing close relation of the third molar to the mandibular canal who underwent surgical removal, only 12 patients presented with definitive clinical findings of the association.

Conclusion

A true close relationship between the third molars and mandibular canal increases the risk of inferior alveolar nerve injury, and accurate evaluation of the relationship is essential to avoid the risk of surgery. The accuracy of the plain radiographs to diagnose an intimate relationship between the neurovascular bundle and the third molar root has its limitations, since only 12 of the 100 patients with positive radiological signs showed clinical evidence of involvement. Surgeons should be aware of the limitations of the radiographic markers of panoramic radiography and should consider more detailed imaging in more specific cases in which one or more radiographic marker is present.

Inferior alveolar nerve damage secondary to orthodontic treatment: A systematic scoping review

BACKGROUND

Neurosensory impairment is a common complication following inferior alveolar nerve (IAN) damage.

OBJECTIVE

To document and report the various causes, diagnosis, and management of IAN damage secondary to orthodontic treatment.

METHODS

An electronic search for studies that reported IAN damage in patients undergoing orthodontic treatment was performed up to July 15, 2020 using MEDLINE, Embase, and PubMed databases. Descriptive analyses and linear regression model were performed.

RESULTS

A total of 15 case reports were identified including 16 patients with an overall mean age of 23.3. All the included studies reported temporary sensory alterations which manifested as anesthesia (19%, n = 3), paresthesia (75%, n = 12), or combined (6%, n = 1). The majority of cases managed by stopping the orthodontic force (75%, n = 12), followed by appliance adjustments (19%, n = 3), providing a bite plate (13%, n = 2), and/or providing pharmacological management (38%, n = 6). Full recovery median duration reported in all cases following the aforementioned managements was 17.5 days.

CONCLUSIONS

IAN damage secondary to orthodontic treatment is emerging in the literature in recent years. Identifying high risk patients with close proximity to the IAN canal is a must to formulate a proper treatment plan to avoid such complications.

Comparison of Preoperative Cone-Beam Computed Tomography and 3D-Double Echo Steady-State MRI in Third Molar Surgery

We investigated the reliability of assessing a positional relationship between the inferior alveolar nerve (IAN) and mandibular third molar (MTM) based on CBCT, 3D-DESS MRI, and CBCT/MRI image fusion. Furthermore, we evaluated qualitative parameters such as inflammatory processes and imaging fusion patterns. Therefore, two raters prospectively assessed in 19 patients with high-risk MTM surgery cases several parameters for technical image quality and diagnostic ability using modified Likert rating scales. Inter- and intra-reader agreement was evaluated by performing weighted kappa analysis. The inter- and intra-reader agreement for the positional relationship was moderate (κ = 0.566, κ = 0.577). Regarding the detectability of inflammatory processes, the agreement was substantial (κ = 0.66, κ = 0.668), with MRI providing a superior diagnostic benefit regarding early inflammation detection. Independent of the readers’ experience, the agreement of judgment in 3D-DESS MRI was adequate. Black bone MRI sequences such as 3D-DESS MRI providing highly confidential preoperative assessment in MTM surgery have no significant limitations in diagnostic information. With improved cost and time efficiency, dental MRI has the potential to establish itself as a valid alternative in high-risk cases compared to CBCT in future clinical routine.

Prediction of post-traumatic neuropathy following impacted mandibular third molar removal

OBJECTIVES

The extraction of impacted mandibular third molars is a common surgical procedure often associated with complications including post-traumatic neuropathy. Previous work has focused on identifying confounding factors, but a robust preoperative risk prediction model remains elusive.

METHODS

Using a dataset of 648 patients and 812 impacted mandibular third molars, we used least absolute shrinkage and selection operator (LASSO) to fit prediction models based on risk factors assessed at both the tooth and patient levels. In addition, we fitted multivariable logistic regression models with the Firth correction for generalized estimating equations (GEE).

RESULTS

The LASSO model for post-traumatic neuropathy identified distoangular impaction of ≥ 45° (odds ratio [OR] = 2.9), proximity to the inferior alveolar nerve of ≤ 3 mm (OR = 1.9), disadvantageous curving (OR = 1.4), and psychiatric conditions (OR = 2.1) as predictors [area under the receiving operator characteristic curve (AUC) = 0.75]. Among other complications analyzed, the LASSO model for bleeding identified deep embedding or full impaction (OR = 1.8), psychiatric conditions (OR = 1.3), and age (OR = 0.9) as predictors (AUC = 0.64). These associations between predictors and postoperative complications were fundamentally reinforced by the corresponding GEE models.

CONCLUSIONS

Our findings point to the predictability of post-traumatic neuropathy and bleeding based on tooth anatomy and patient characteristics, overall suggesting that preoperatively identifiable factors can predict the risk of adverse outcomes in the extraction of impacted mandibular third molars.

CLINICAL SIGNIFICANCE

Mandibular third molar extraction is both a routine procedure and a leading cause of trigeminal neuropathy. Prevention of post-traumatic neuropathy, aided by individualized preoperative risk prediction, is of high clinical relevance.