Question: What is the incidence of lingual cortical bone perforation occurring before the extraction of the mandibular third molar?
Amin S*, Elsheikh A^, Meyer R, Bagheri S
- * Dr. Sara A. Amin, BDS, MSc, Dental Team Leader at 3Sixty.
- ^ Dr. Ahmad K. Elsheikh BDS, Chief Dental Officer at 3Sixty.
Retrospective study using previously-collected data.
The study population consisted of 100 patients aged between 18-65 years old who have at least one erupted or impacted mandibular third molar. CBCT scans of said patients were obtained and assessed using 3Sixty dps Dental Planning Software in the form of DICOM files.
The primary outcome measure was the incidence of lingual cortical bone perforation at the apex and the apical half of the root of teeth 17 and/or 32. Secondary outcome measure was a lingual bone thickness in cases where there was no perforation observed. Third outcome measure was the incidence of impacted lower third molars.
51.2% of the patients were found to have a perforated lingual cortical bone at the root apex of the lower third molar; 52.8% at the apical half of the root. In non-perforated instances, lingual bone was found to be 1.25 mm at the apex on average; while at most apical half, it was found to be 0.93 mm. Impacation rates were found to be statistically significant in the group where perforation was present both at the apex (p-value < 0.001, Effect size = 0.378), and at the apical half (p-value < 0.001, Effect size = 0.445).
The number of CBCT images where the lingual portion of cortical bone surrounding impacted or non-impacted third mandibular molars were observed to be perforated, was found to be statistically significant. The authors suggest that the incidence of perforated bone can be a pre-occurrence rather than a post-extraction complication.
The third molar, commonly known as the “wisdom tooth” is the last tooth to emerge in the mouth, usually during the period from 17 to 25 years of age. At the age of 7, the lower third molar begins developing within the mandibular ramus. Its eruption pattern largely depends on the available space beyond the already-erupted second molar, which in turn will be determined by several factors such as genetics, diet, bone and teeth size. Third molar impaction is a commonly observed clinical occurrence and is the cause of multiple complications. As a result, third molars are among the most frequently extracted teeth; both surgically and non-surgically.
Surgical extraction of the mandibular third molar can result in perforation of the thin lingual cortical bone endangering the lingual nerve. Therefore, preoperative radiographs are sometimes essential in the diagnosis and treatment planning phase. For a long time, the gold standard for radiographic findings has been panoramic and periapical x-rays. Both are often used in clinical investigations in order to determine the existence of any anatomical abnormalities as well as the type of impaction. However, cone-beam computed tomography (CBCT) is a more sophisticated diagnostic tool than panoramic and periapical radiographs when three-dimensional visualization of the surgical site is needed.
This retrospective study took advantage of the availability of previously collected routine data in the form of CBCT images of the mandibular third molar area. The aforementioned images belonged to implant-placement surgery patients aged between 18-65 and were collected during the period from 2018 to 2020. The inclusion criteria were:
- High-resolution CBCT images
- Impacted or non-impacted mandibular third molars that are wholly formed (i.e. apices are closed)
The exclusion criteria included:
- Poor quality CBCT images
- Mandibular third molars with incompletely-formed roots
- History of bone-affecting systemic conditions or presence of infections
100 CBCT images met the inclusion criteria and were imported into 360dps Dental Planning Software in DICOM file format. The authors measured two distances in cross-sectional view from the lingual cortical bone outer border, namely to the root apex of the most lingual root (i.e. if multiple roots were present), and to the apical half of the root. 127 mandibular third molars were analyzed; 62% of the patients were found to be male and 38% female. 70% of the study population fell within the age range of 41-65 years old. Impaction incidence was 18.1%, with 23 impacted teeth out of a total of 127.
In terms of perforation, 51.2% were lingually perforated at the level of the apical foramen, and 52.8% at the level of the apical half. Correlation between the prevalence of teeth impaction and lingual cortex bone perforation was found to be statistically significant both at the apex (p-value < 0.001, Effect size = 0.378), and at the apical half (p-value < 0.001, Effect size = 0.445). No other significant correlation was evident about either gender or age groups. On average, cortical bone was observed to be 1.25 mm thick at the apex, and 0.96 thick at the lower half of the root– lingually.
This radiographic study suggests that a significant number of single- or multi-rooted lower third molars can be demonstrated to have an existing lingual perforation in the cortex of the surrounding bone prior to surgical or non-surgical extraction. The authors assert that 3D CBCT imaging is superior to conventional 2D radiographs as a preoperative diagnostic tool considering the anatomical variations of the lower third molars. According to the findings of this study, patients who need their lower wisdom teeth removed may benefit more from CBCT scanning to avoid perforation-related surgical complications such as root displacement in the sublingual space or damage to the lingual nerve. Further investigation into this question is recommended by the researchers– increasing the study sample as well as including younger age groups. Evidently, the limitation of this study lies in the retrospective case-control design; hence it may be difficult to draw a causal association between the incidence of impaction about pre-existing perforation.