Do anatomical variations of the mandibular canal pose an increased risk of inferior alveolar nerve injury after third molar removal?

OBJECTIVES: The present study aimed to assess whether anatomical variations of the mandibular canal are associated with neurosensory disturbances of the inferior alveolar nerve (IAN) following mandibular third molar removal. METHODS: Two observers compared the detection of third molar root-nerve relations and bifurcations of the mandibular canal on panoramic radiographs and CBCT images of 201 patients undergoing removal of 357 mandibular third molars. Potential neurosensory disturbances of the IAN were surveyed ten days after surgery. Fisher's Exact was performed to correlate presence of canal variations to postoperative neurosensory disturbances. Positive and negative predictive values (PPV, NPV) and likelihood ratios (LR + , LR-) were calculated. RESULTS: Thirteen patients reported postoperative altered sensation of the lower lip, with 2 of them having mandibular canal bifurcations on the ipsilateral side of the injury. Fisher's Exact showed that the studied mandibular canal variations were not related to postoperative neurosensory disturbances. CBCT was superior in visualization of anatomical variations of the mandibular canal. Prevalence of bifurcations was 14% on CBCT and 7% on panoramic radiographs. In both imaging modalities and for all parameters, PPVs were low (0.04 - 0.06) and NPVs were high (0.92 - 0.98), with LR ranging around 1. CONCLUSION: In the present study, the assessed mandibular canal variations had limited predictive value for IAN neurosensory disturbances following third molar removal. CLINICAL RELEVANCE: While a close relation between the third molar and the mandibular canal remains a high risk factor, mandibular canal variations did not pose an increased risk of postoperative IAN injury after third molar removal.

Radiological risk indicators for persistent postoperative morbidity after third molar removal.

OBJECTIVES: Although panoramic radiographs are extensively studied for diagnosis and preoperative planning in third molar surgery, research on the predictive value of this radiographic information regarding the postoperative recovery of patients remains underexploited. This prospective cohort study aimed to assess the potential relationship between radiologic risk indicators and persistent postoperative morbidity, in 1009 patients undergoing 2825 third molar extractions in context of the M3BE study. METHODS: Two observers evaluated ten radiographic parameters: vertical and horizontal eruption status, third molar orientation, surgical difficulty, nerve relation, maxillary sinus relation, presence of periapical and pericoronal radiolucencies, caries, and third or second molar resorption. Patients' postoperative recovery was recorded 3 and 10 days after surgery. Univariate logistic regression was performed to assess potential associations between radiographic risk indicators and persistent postoperative morbidity. RESULTS: Deep impactions were significantly associated with the persistence of postoperative pain, trismus and swelling until 10 days after surgery, prolonged need for pain medication, and the inability to resume daily activities and work/studies. Pericoronal radiolucencies and resorption were significantly associated with persistent morbidity and a longer recovery time, whereas caries and periapical lesions were linked to a shorter recovery time. CONCLUSION: Based on the results of this study, clinicians may better inform patients at risk for persistent postoperative discomfort according to what was preoperatively diagnosed on the panoramic radiograph. CLINICAL RELEVANCE: Preoperative panoramic radiographs contain information about patients at risk of prolonged recovery after third molar removal. Several risk indicators for persistent postoperative morbidity were identified.

Artificial intelligence-driven novel tool for tooth detection and segmentation on panoramic radiographs.

OBJECTIVE: To evaluate the performance of a new artificial intelligence (AI)-driven tool for tooth detection and segmentation on panoramic radiographs. MATERIALS AND METHODS: In total, 153 radiographs were collected. A dentomaxillofacial radiologist labeled and segmented each tooth, serving as the ground truth. Class-agnostic crops with one tooth resulted in 3576 training teeth. The AI-driven tool combined two deep convolutional neural networks with expert refinement. Accuracy of the system to detect and segment teeth was the primary outcome, time analysis secondary. The Kruskal-Wallis test was used to evaluate differences of performance metrics among teeth groups and different devices and chi-square test to verify associations among the amount of corrections, presence of false positive and false negative, and crown and root parts of teeth with potential AI misinterpretations. RESULTS: The system achieved a sensitivity of 98.9% and a precision of 99.6% for tooth detection. For segmenting teeth, lower canines presented best results with the following values for intersection over union, precision, recall, F1-score, and Hausdorff distances: 95.3%, 96.9%, 98.3%, 97.5%, and 7.9, respectively. Although still above 90%, segmentation results for both upper and lower molars were somewhat lower. The method showed a clinically significant reduction of 67% of the time consumed for the manual. CONCLUSIONS: The AI tool yielded a highly accurate and fast performance for detecting and segmenting teeth, faster than the ground truth alone. CLINICAL SIGNIFICANCE: An innovative clinical AI-driven tool showed a faster and more accurate performance to detect and segment teeth on panoramic radiographs compared with manual segmentation.

Is third molar development affected by third molar impaction or impaction-related parameters?

OBJECTIVE: To evaluate the effect of third molar impaction and impaction-related parameters on third molar development. MATERIALS AND METHODS: Panoramic radiographs (N=3972) from 473 males and 558 females between 3.2 and 23.5 years old were analysed. Three parameters of impaction were examined: hindering contact between third and adjacent second molar, retromolar space availability (only in lower third molars), and angulation between the third and adjacent second molar. From the separate parameters, a definition for impaction was derived. Third molars' development was staged according to a modified Köhler et al. staging technique. A linear model was used to compare within-stage and overall age, as a function of hindering contact, retromolar space, and impaction. Furthermore, a quadratic function was used to study the correlation between age and angulation. RESULTS: Significant differences were found in mean age as a function of hindering contact and retromolar space, depending on third molar location and stage. There was a significant relation between angulation and age, depending on the stage, with all third molars evolving to a more upright position (closer to 0°). Mean ages of subjects with impacted third molars were significantly lower in certain third molar stages, but the differences were clinically small (absolute differences ≤0.65 years). Moreover, after correction for stage differences, no significant differences in age could be demonstrated. CONCLUSIONS: The development of impacted and non-impacted third molars can be considered clinically equal in our study population. CLINICAL RELEVANCE: There is no distinction required between impacted and non-impacted third molars for dental age estimation.

PROPHYLACTIC VS. SYMPTOMATIC THIRD MOLAR REMOVAL: EFFECTS ON PATIENT POSTOPERATIVE MORBIDITY.

PURPOSE: The present study aimed to assess differences in postoperative morbidity between prophylactic and symptomatic third molar removals, and to assess the effect of age on the recovery of the patient. METHODS: Patients admitted for third molar removal were prospectively followed up four times during treatment in context of the M3BE study. Data were collected through pre-, peri and postoperative surveys (days 3 and 10). Uni- and multivariable logistic regression was used to assess the probability of postoperative symptoms of discomfort on day 3 and day 10 according to several patient- and surgery-related predictive factors (age, gender, indication for removal, method of extraction, anesthesia and number of extracted maxillary and/or mandibular third molars). RESULTS: In total, 6010 patients with a mean age of 25.2 (± 11.2) underwent 6347 surgeries to have 15,357 third molars removed. Frequently observed symptoms of postoperative discomfort were pain, trismus and swelling, all of which were transient in nature with steep decreases from postoperative days 3 to 10. Increasing age was associated with an enhanced risk of persistent pain, trismus and swelling and a significantly higher risk of iatrogenic injury to the inferior alveolar nerve. Symptomatic indications for removal were more common in patients over age 25 years, but these pre-existing pathologies did not compromise the postoperative recovery process. Other factors related to postoperative morbidity were female gender, intraoperative osteotomy and the number of extractions. CONCLUSION: The results of this study suggest that there are convincing patient- and surgery-related factors that favor timely third molar removal, preferably before the age of 25, especially in order to avoid persistent morbidity and nerve complications.

Does Retaining Third Molars Result in the Development of Pathology Over Time? A Systematic Review.

PURPOSE: The present systematic review was conducted to assess the available literature on pathologies associated with third molar retention. MATERIALS AND METHODS: A systematic literature search was conducted in MEDLINE (PubMed), Embase, and Cochrane Library and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. Relevant reports were selected using predefined inclusion and exclusion criteria. Pathology related to third molar retention included caries, periodontal pathology, second molar external root resorption, and pathologic widening of the third molar pericoronal space. The methodologic quality of each study was reviewed using a pathology-specific tool to assess the risk of bias. RESULTS: A total of 37 studies were included for qualitative analysis. The available data showed that asymptomatic retained third molars frequently become diseased with increasing age of the patient and increased retention time. Caries and periodontal pathology were most frequently observed, especially in partially erupted third molars and mesially inclined mandibular third molars. Overall, the available data were regarded as medium to fair quality evidence. CONCLUSIONS: The available data have revealed that retained asymptomatic third molars rarely remain disease-free over time. Increasing age and, thus, increasing retention time seemed associated with greater disease prevalence. Well-designed, prospective follow-up studies are needed to substantiate the clinical management of asymptomatic disease-free third molars.

Radiographic prediction of mandibular third molar eruption and mandibular canal involvement based on angulation.

OBJECTIVES: The aim of our study was to identify and predict patients at risk of impeded mandibular third molar eruption and potential relation between the third molar roots and the mandibular canal, based on molar angulations in an early development stage. SETTING AND SAMPLE POPULATION: A total of 1011 adolescent orthodontic patients were included in this longitudinal study. MATERIALS AND METHODS: We analysed pre-eruptive rotational changes and root development of mandibular third molars on 2022 panoramic radiographs (two time-points). Five variables were evaluated: third molar eruption level, development stage, risk of relation between the third molar and the mandibular canal, the molar angulations and orthodontic treatment. The relation between early third molar angulation and mean annual angulation change was assessed using a linear mixed model. Logistic regression was applied to investigate a potential correlation of the radiographic variables with the eruption potential and risk of developing a relation between the third molar and the mandibular canal. RESULTS: Mandibular third molar follicles with an initial angulation exceeding 27.0° relative to the second molar tend to progressively increase their angulation during further development. A significant correlation was found between the hemimandibular molar angulations and the probability of eruption (P < 0.0001). The second to first molar angulation was predictive for potential development of a relation with the mandibular canal (P = 0.005). CONCLUSION: From the present data, it appears that severely angulated mandibular third molars (>27.0°) have a minimal chance of future eruption and a maximal risk of developing a relation with the mandibular canal.

A novel in vivo method to evaluate trueness of digital impressions.

BACKGROUND: Intraoral scanners are devices for capturing digital impressions in dentistry. Until now, several in vitro studies have assessed the trueness of digital impressions, but in vivo studies are missing. Therefore, the purpose of this study was to introduce a new method to assess trueness of intraoral scanners and digital impressions in an in vivo clinical set-up. METHODS: A digital impression using an intraoral scanner (Trios® 3 Cart wired, 3Shape, Copenhagen, Denmark) and a conventional alginate impression (Cavex Impressional®, Cavex, Haarlem, the Netherlands) as clinical reference were made for two patients assigned for full mouth extraction. A total of 30 teeth were collected upon surgery after impressions making. The gypsum model created from conventional impression and extracted teeth were then scanned in a lab scanner (Activity 885®, SmartOptics, Bochum, Germany). Digital model of the intraoral scanner (DM), digital model of the conventional gypsum cast (CM) and those of the extracted natural teeth (NT) were imported to a reverse engineering software (3-matic®, Materialise, Leuven, Belgium) in which the three models were registered then DM and CM were compared to their corresponding teeth in NT by distance map calculations. RESULTS: DM had statistically insignificant better trueness when compared to CM for total dataset (p = 0.15), statistically insignificant better trueness for CM when mandibular arches analyzed alone (p = 0.56), while a significantly better DM trueness (p = 0.013) was found when only maxillary arches were compared. CONCLUSIONS: Our results show that digital impression technique is clinically as good as or better than the current reference standard for study models of orthognathic surgery patients.

A retrospective longitudinal assessment of artificial intelligence-assisted radiographic prediction of lower third molar eruption.

Prediction of lower third molar eruption is crucial for its timely extraction. Therefore, the primary aim of this study was to investigate the prediction of lower third molar eruption and its uprighting with the assistance of an artificial intelligence (AI) tool. The secondary aim was identifying the incidence of fully erupted lower third molars with hygienic cleansability. In total, 771 patients having two panoramic radiographs were recruited, where the first radiograph was acquired at 8-15 years of age (T1) and the second acquisition was between 16 and 23 years (T2). The predictive model for third molar eruption could not be obtained as few teeth reached full eruption. However, uprighting model at T2 showed that in cases with sufficient retromolar space, an initial angulation of < 32° predicted uprighting. Full eruption was observed for 13.9% of the teeth, and only 1.7% showed hygienic cleansability. The predictions model of third molar uprighting could act as a valuable aid for guiding a clinician with the decision-making process of extracting third molars which fail to erupt in an upright fashion. In addition, a low incidence of fully erupted molars with hygienic cleansability suggest that a clinician might opt for prophylactic extraction.

Surgical experience and patient morbidity after third molar removal.

OBJECTIVES: The present study aimed to assess differences in patients' postoperative morbidity after third molar removal in relation to the surgeon's level of experience and other intraoperative factors. MATERIAL AND METHODS: Patients admitted for prophylactic removal of asymptomatic third molars were prospectively followed up on day 3 and 10 after surgery in the context of the M3BE-study. Uni- and multivariable logistic regression was performed to assess the associations between surgeon's (in)experience and postoperative discomfort. Other contributing factors were gender, age, extraction method (osteotomy or not), and number of extractions and involved jaws. RESULTS: In total, 7 senior surgeons and 28 surgical residents operated 2560 patients (8672 third molars). Differences in postoperative morbidity on day 3 and 10 after surgery were small. The results showed no significant associations between surgeon's inexperience and postoperative discomfort (pain, trismus, swelling), except for persistent pain (day 10; OR 1.468; p = 0.0016). No effect was observed on the occurrence of postoperative nerve complications. It was shown that postoperative morbidity was more dependent on factors like age, gender, number of extractions and intraoperative osteotomy. CONCLUSION: We may conclude that patient recovery following third molar removal is affected by other factors than surgical experience. However, surgical residents seemed to cause significantly more persisting pain problems 10 days after surgery.

A retrospective cohort study on reasons to retain third molars.

The primary goal of this study was to identify and quantify indications for retaining third molars. This retrospective cohort study included 1682 patients (818 male, 864 female; mean age 31 years) who were referred to the University Hospitals Leuven for third molar removal. Eight reasons for retaining the third molars were identified: (1) risk of damaging adjacent structures, (2) compromised health status, (3) adequate space for eruption, (4) third molar serves as abutment tooth, (5) orthodontic reasons, (6) eruption into proper occlusion, (7) symptomless third molars in patients >30 years old, and (8) patient preference. To compare these categories between sex and age groups, a generalized linear model for binary data was fitted with a logit link. A total of 1149 third molars in 548 patients were not extracted. The most frequent reasons for retaining third molar teeth were: eruption into proper occlusion (31.9%), patient preference (31.5%), and symptomless third molars in patients >30 years old (17.5%). Compromised health status and advanced age were often included in the decision regarding whether to retain the third molars. One third of the referred patients had reasons to retain one or more third molars. These findings might facilitate the future development of a consensus statement.

Artificial Intelligence (AI)-Driven Molar Angulation Measurements to Predict Third Molar Eruption on Panoramic Radiographs.

The purpose of the presented Artificial Intelligence (AI)-tool was to automatically segment the mandibular molars on panoramic radiographs and extract the molar orientations in order to predict the third molars' eruption potential. In total, 838 panoramic radiographs were used for training (n = 588) and validation (n = 250) of the network. A fully convolutional neural network with ResNet-101 backbone jointly predicted the molar segmentation maps and an estimate of the orientation lines, which was then iteratively refined by regression on the mesial and distal sides of the segmentation contours. Accuracy was quantified as the fraction of correct angulations (with predefined error intervals) compared to human reference measurements. Performance differences between the network and reference measurements were visually assessed using Bland-Altman plots. The quantitative analysis for automatic molar segmentation resulted in mean IoUs approximating 90%. Mean Hausdorff distances were lowest for first and second molars. The network angulation measurements reached accuracies of 79.7% [-2.5°; 2.5°] and 98.1% [-5°; 5°], combined with a clinically significant reduction in user-time of >53%. In conclusion, this study validated a new and unique AI-driven tool for fast, accurate, and consistent automated measurement of molar angulations on panoramic radiographs. Complementing the dental practitioner with accurate AI-tools will facilitate and optimize dental care and synergistically lead to ever-increasing diagnostic accuracies.

CBCT vs other imaging modalities to assess peri-implant bone and diagnose complications: a systematic review.

AIM: The objective of this systematic review was to evaluate the diagnostic value of CBCT compared with 2D imaging and clinical gold standard techniques in peri-implant bone defect detection and measurement. MATERIALS AND METHODS: Literature search was performed using MEDLINE, Embase and Web of Science databases up to July 2017. Clinical, ex vivo, in vitro and animal studies that assessed and measured peri-implant bone defects using different imaging modalities were included in this review. Two reviewers performed data extraction and qualitative analysis. The methodological quality of each study was reviewed using the QUADAS-2 tool. RESULTS: The initial search revealed 2849 unique papers. Full-text analysis was performed on 60 articles. For the present review, nine studies were considered eligible to be included for qualitative analysis. CBCT performed similar to intraoral radiography in mesiodistal defect detection and measurements. Additional buccolingual visualisation and volumetric and morphological assessment of peri-implant bone defects are major advantages of 3D visualisation with CBCT. Nevertheless, one must be aware of metal artefacts masking osseointegration, shallow bony defects and other peri-implant radiolucencies, thus impeding early diagnosis of intrabony lesions. CONCLUSIONS: The present review did not provide evidence to support the use of CBCT as standard postoperative procedure to evaluate peri-implant bone. Up to date, we are clinically forced to remain with intraoral radiography, notwithstanding the inherent limitations related to restricted field of view and two-dimensional overlap. A 3D imaging approach for postoperative implant evaluation is crucial, making further development of an optimised and artefact-free CBCT protocol indispensable.