Identification of Specific Panoramic High-Risk Signs in Impacted Third Molar Cases in Which Cone Beam Computed Tomography Changes the Treatment Decision

Characterizations of three-dimensional root morphology and topological location of mandibular third molars by cone-beam computed tomography

PURPOSE

This study aimed to delineate three-dimensional (3D) root morphology and topological locations of mandibular third molars (MTMs) by cone-beam computed tomography (CBCT) in a Chinese adult dental population.

METHODS

Adult patients with MTMs were retrospectively screened based on CBCT images at our institution between January 2018 and December 2019. Root morphology and spatial locations of these teeth were defined based on CBCT 3D images. Potential associations with epidemiological and clinical/radiological parameters were analyzed using Chi-square or Fisher exact test. Two-tailed P values less than 0.05 were considered statistically significant.

RESULTS

A total number of 2680 eligible patients (male/female:0.74; 35 ± 10 years old) with 4180 MTMs were enrolled. The majority of MTMs had 2 roots 3064 (73.30%), followed by 800 (19.14%) 1 root, 302 (7.22%) 3 roots, and 14 (0.33%) 4 roots. More than half of one-rooted MTMs were convergent, followed by club-shaped and C-shaped. Among MTMs with 2 roots, 2860 (93.34%) were M-D (mesio-distal) types. Most MTMs with 3 roots were M-2D (one root in mesial, two roots in distal) types, followed by 2M-D (two roots in mesial, one root in distal) types, and B-2L (one root in buccal, two roots in lingual) types. The presence of root configurations was significantly associated with the angulation, depth, and width classification in two-rooted MTMs (P < 0.05).

CONCLUSIONS

Although the morphology and spatial locations of MTMs vary greatly, our results from a large dental population reconfirm that most MTMs have two roots with mesial-distal type of spatial distribution.

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.

Current thinking in lower third molar surgery

The removal of lower third molar teeth is one of the most common surgical procedures performed worldwide, but many concepts in this surgery have been unclear and have engendered different opinions. This paper aims to review current thinking in certain pertinent aspects of this surgery to update the reader on the most current research and synthesise it to make clinical recommendations. Topics covered include preoperative imaging, timing of removal, flap design, lingual retraction, coronectomy, lingual split, closure techniques, and use of antibiotics, steroids, and drains.

Deep learning-based evaluation of the relationship between mandibular third molar and mandibular canal on CBCT

OBJECTIVES

The objective of our study was to develop and validate a deep learning approach based on convolutional neural networks (CNNs) for automatic detection of the mandibular third molar (M3) and the mandibular canal (MC) and evaluation of the relationship between them on CBCT.

MATERIALS AND METHODS

A dataset of 254 CBCT scans with annotations by radiologists was used for the training, the validation, and the test. The proposed approach consisted of two modules: (1) detection and pixel-wise segmentation of M3 and MC based on U-Nets; (2) M3-MC relation classification based on ResNet-34. The performances were evaluated with the test set. The classification performance of our approach was compared with two residents in oral and maxillofacial radiology.

RESULTS

For segmentation performance, the M3 had a mean Dice similarity coefficient (mDSC) of 0.9730 and a mean intersection over union (mIoU) of 0.9606; the MC had a mDSC of 0.9248 and a mIoU of 0.9003. The classification models achieved a mean sensitivity of 90.2%, a mean specificity of 95.0%, and a mean accuracy of 93.3%, which was on par with the residents.

CONCLUSIONS

Our approach based on CNNs demonstrated an encouraging performance for the automatic detection and evaluation of the M3 and MC on CBCT. Clinical relevance An automated approach based on CNNs for detection and evaluation of M3 and MC on CBCT has been established, which can be utilized to improve diagnostic efficiency and facilitate the precision diagnosis and treatment of M3.

Is it possible to filter third molar cases with panoramic radiography in which roots surround the inferior alveolar canal? A comparison using cone-beam computed tomography

Inferior alveolar nerve (IAN) entrapment in third molar (M3) roots bears a significant risk for nerve injury. The aim of this study was to identify specific panoramic radiographic (PR) signs that can reliably identify IAN entrapment (IANE) root conformations. In a retrospective case-control study, 10 IANE and 218 non-IANE third molar risk cases were examined by PR and CBCT. The collected data included "classic" specific high-risk panoramic signs, number of M3 roots, extent of inferior alveolar canal (IAC)-root tip overlap, rotated position of M3 and impaction pattern. After bivariate analysis, sensitivity, specificity, positive and negative predictive values, positive likelihood ratios (LR+) and accuracy (area under the curve [AUC]) were calculated for the most significant predictive variables. Interruption of both cortical lines (LR⁺: 43.6; AUC: 96.0%) and upward diversion of the IAC (LR⁺: 36.3; AUC: 96.5%) were the most accurate single signs indicating IANE. Upward diversion combined with root darkening and interruption of the IAC (AUC: 97.4%) and the combination of darkening with interruption and with a rotated M3 (LR⁺:130.8; AUC: 97.8%) were the most accurate combinations predicting IANE. IANE may be correctly filtered with PR when focusing on the signs of upward diversion, darkening, interruption and rotated M3 position, especially in cases involving their multiple (≥3) presence. CBCT evaluation is highly recommended in these cases before partial and total tooth removals.

Delayed-onset infections after lower third molar surgery: a Hungarian case-control study

OBJECTIVE

Delayed-onset infection is defined as infectious swelling and trismus accompanied by pain or the presence of suppuration starting approximately 30 days after surgery. This study aimed to describe the occurrence and potential predisposing factors of delayed-onset infection.

STUDY DESIGN

A retrospective case-control study of 223 lower third molar surgeries was performed. Participants were selected from among 1102 outpatients who underwent surgery between January 2013 and June 2018 at Semmelweis University. The inclusion criterion for the case group was inflammation of the operated area after suture removal. Patients in the control group were healthy nonsmokers <26 years old who healed without complication. Statistical analysis was performed using the Shapiro-Wilk test, the Mann-Whitney U test, and Fisher's exact test.

RESULTS

Complications occurred only in patients <26 years old approximately 29.5 days after surgery. A significantly higher risk was observed for younger age, total soft tissue coverage, deeper impaction, lower Nolla stage (P < .001), mesioangular direction (P = .002), and full bone coverage (P < .05). Distal space was inversely correlated with complications (P < .001).

CONCLUSIONS

Lower Nolla stage, total soft tissue coverage, lack of distal space, deeper impaction, or mesioangular tilt may promote delayed-onset infection. Follow-up of at-risk patients and the maintenance of oral hygiene are recommended.