Application Effects of Modified Coronectomy in Mandibular Third Molars with High-Risk Proximity to the Mandibular Canal and Characteristics of Residual Root Migration
This study demonstrates that modified coronectomy effectively prevents inferior alveolar nerve injury in high-risk mandibular third molar cases with minimal postoperative pain, despite requiring longer operative time, while revealing that residual root migration over 12 months is influenced by root length and morphology, with 5–10 mm roots showing the greatest stability.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Deep within the lower jawbone runs a vital highway of nerves, carrying sensation to the lower lip and chin. When a dentist needs to remove a wisdom tooth that is buried deep and tangled with this nerve, the procedure carries a significant risk: damaging the nerve can leave a patient with permanent numbness or a strange, tingling sensation. For decades, surgeons have faced a difficult choice. They could attempt to pull the entire tooth out, risking injury to the nerve, or they could leave the tooth behind entirely, leaving a potential source of infection. A middle path, known as a coronectomy, involves removing only the top part of the tooth, the crown, while leaving the roots safely buried in the bone. However, this technique has its own complications, such as the remaining roots moving or causing problems later. Researchers at the Army Medical University in China set out to refine this middle path, testing a modified version of the procedure to see if it could offer better protection for the nerve while keeping the remaining roots stable.
The study focused on seventy-three patients who had lower wisdom teeth that posed a high risk to the nearby nerve. Before any surgery, every patient received a detailed three-dimensional scan of their jaw. Based on these images, the team divided the patients into three groups. One group underwent a standard, complete extraction of the tooth. A second group received a traditional coronectomy, where the crown was removed but the roots were left as they were. The third group, the largest, received the new modified coronectomy. In this approach, the surgeons did not just snap off the top of the tooth; they carefully removed the entire outer enamel shell and then shaved down the remaining root structure under direct vision. They ensured the remaining root was short enough to stay below the gum line and the surrounding bone, but long enough to remain stable. The goal was to create a smooth, clean surface that would encourage the bone to heal over it, rather than leaving jagged edges that might irritate the tissue or the nerve.
The results showed a clear trade-off between safety and speed. The modified coronectomy took longer to perform, averaging about fifty-one minutes per tooth, compared to roughly thirty-three minutes for the standard extraction. It also involved slightly more bleeding during the procedure. However, the benefits for the patient were immediate and significant. On the third day after surgery, patients who had the modified procedure reported less pain than those who had their teeth fully removed. More importantly, the study found zero cases of nerve injury in the group that received the modified coronectomy. In contrast, nearly twelve percent of the patients who had a standard extraction experienced temporary numbness or tingling in their lower lip or chin. While the symptoms in the extraction group eventually faded, usually within three months, the modified approach completely avoided the risk of injury in this study.
The researchers also tracked what happened to the leftover roots over the course of a year. A major concern with leaving roots behind is that they might migrate, or move, through the bone, potentially causing pain or exposing themselves through the gum. The study found that these roots did move, but the amount of movement depended on how long the root was and what shape it had. Roots that were left between five and ten millimeters long showed the most stability, moving the least over the twelve-month period. Roots that were shorter than five millimeters or longer than ten millimeters tended to move more. The shape of the root mattered as well; teeth with a single, straight root stayed relatively put, while roots that were fused together or curved showed more movement as time went on. Interestingly, the roots that moved the most were the ones that were left very long, suggesting that leaving too much tooth behind might actually encourage it to shift.
This work suggests that for wisdom teeth that are dangerously close to the main nerve, a carefully performed modified coronectomy is a viable and safer alternative to a full extraction. It offers a way to protect the nerve from injury and reduce postoperative pain, even if it requires more time in the chair and a slightly more complex surgical technique. The findings also provide practical guidance for surgeons: if they choose to leave a root behind, cutting it to a length between five and ten millimeters and ensuring the root is single and straight may offer the best chance of it staying put. While the study was conducted at a single center and involved a specific group of patients, the results highlight that balancing the removal of the tooth with the preservation of the nerve is possible. The key lies in the precision of the cut and the management of the remaining root, turning a risky extraction into a controlled, protective procedure.
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