Removal of third molars continues to be one of the most common surgical procedures completed by oral and maxillofacial surgeons with approximately 10 million wisdom teeth removed on 5 million individuals in the United States each year. One of the more concerning complications associated with third molar removal is injury to the inferior alveolar nerve (IAN) at a reported rate of 1-5%. A treatment modality that could further reduce the incidence of IAN injury is a coronectomy, during which the roots of the third molar are intentionally left within the mandible.
In this retrospective cohort study, we examined the success rate and morbidities of the coronectomy procedure for mandibular third molars. Additionally, we assessed the rate of root migration over time and factors associated with both success and root migration for study subjects.
The study population was drawn from patients who underwent coronectomy for mandibular third molars between 2013-2017 by a single oral surgeon (author M.A.K) as an outpatient in a private practice setting. Inclusion criteria included full patient records, minimum of seven-day follow-up, pre-operative panoramic radiograph and post-operative panoramic radiographs. Incomplete records and patients lost to follow up resulted in exclusion. Success was determined by successful completion of planned coronectomy and none of the following: re-operation; infection; or injury to either the lingual nerve or IAN. Root migration was measured using stored panoramic radiographs and the measurement tool within TigerView Professional software. This standardization measurement was completed by measuring the distance from the root apices of the mandibular third molar to the adjacent cemento-enamel junction of the mandibular second molar. Magnification was controlled for between radiographs by using the height of the second molar as a constant to adjust all measurements as needed.
One hundred and forty-nine patients who underwent 211 coronectomy procedures on mandibular third molars between 2013-2017 were evaluated and 117 patients who underwent 166 coronectomies met criteria and were included as study subjects. Subjects had a mean age of 23 years old and were 76% female. Overall, coronectomy for mandibular third molars was 97% successful (161/166 third molars). Case failures were due to root removal during surgery (1.2% total cases), remaining enamel prompting re-operation at one week (0.6%), post-operative infection (0.6%), and liver clot formation (0.6%). Mean follow up time for study subjects was 129 days (range 7 , 1,096 days). Total mean root migration for all study subjects was 4.10 mm (range 0.20, 15.39 mm). The rate of root migration was greatest between zero and six months, with movement plateauing at six to twelve months of follow-up. By twelve months, 95% of subjects’ remaining roots were fully covered with bone. Further, while root migration greater than 1 mm occurred in 89% of study subjects, zero cases required a second operation for root removal.
Only few papers exist in the literature comprehensively evaluating the results of the coronectomy in the United States limiting its widespread acceptance in the field. The results of this study demonstrate that coronectomy for mandibular third molars is an effective and predictable treatment option for high-risk molars associated with the IAN. Further, by tracking rates of root migration, appropriate follow-up can be evidence based and surgeons can properly educate patients on expectations given this data. Ultimately, coronectomy is a single treatment modality that should be offered to patients as a safe treatment and quality of care alternative for mandibular third molars in close proximity to the inferior alveolar nerve.
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