A study used three methods to measure the anterior loop of the mental nerve on 12 human cadavers: cone-beam CT (CBCT), a 3D stereolithographic model (STL), and anatomy. The researchers sought to determine the accuracy of CBCT and STL in identifying and measuring the anterior loop.
While CBCT was found to be accurate and reliable, the STL was found to significantly both overestimate and underestimate the anterior loop.
The mental nerve follows a looping course around the jaw, communicates with the facial nerve and provides sensory innervation to areas of the chin and lower lip. Injury to the anterior loop of the mental nerve can cause numbness or altered sensory perception.
Reports on the length and location of the mental nerve vary widely between patients. One study found the anterior loop in 28% of the patients. However, another study reported it to be present 88% of the time. Some clinicians recommend maintaining a safety margin of 1 mm between implants and the nerve; others suggest as much as a 6-mm distance.
Because of conflicting reports, various methods have been used to detect and measure the anterior loop. It has been determined that panoramic and periapical radiographs do not provide information about the loop that is reliable enough for clinicians to use in placing implants.
The authors recommend that CBCT should be a prerequisite in identifying and measuring the anterior loop of the mental nerve for implant surgery. Additionally, a fixed distance from the mental foramen should not be used as a safety guideline; rather, the anterior loop itself should be located, they noted. And a safety distance of at least 2 mm from the anterior-most portion of the loop should be observed in implant placement.
The STL model should be used with caution because the model has not been shown to be highly accurate in estimating the anterior loop, the researchers concluded.