Purpose: The aim of this study was to investigate the prevalence and length of the anterior loop (AL), the distance from this landmark to the alveolar crest and its relation with the shape of the foramen and emergency pattern in the Spanish population on helical computed tomography scan (helical CT scan) through tridimensional reconstructions.
Methods: Helical CT scan images of 41 patients aged 65 or older were analyzed. A total of 82 human hemi-mandibles were examined in this study. A tridimensional reconstruction of each mandible and Inferior Alveolar Nerve canal was created in AMIRA® software (AMIRA, Mercury Computer Systems, Berlin, Germany). Prevalence, length and distance between the AL, mental foramen and alveolar ridge were measured. This retrospective observational study was performed according to the STROBE guidelines.
Results: Prevalence of the AL was 53.7 % (n = 44) and the mean length was 1.3 ± 0.64 mm. The mean distance from the highest point of the loop to the alveolar ridge was 13.4 ± 2.8 mm. The mean diameter of the mental foramen was 3.5 ± 0.65 mm and the proportion of the oval-shaped was 62.2 % (n = 51) and round-shaped was 37.8 % (n = 31). The study found that patients with type 1 pattern emergency pattern had a higher prevalence of the AL (p = 0.03).
Conclusions: Prevalence, location and length of the anterior loop can be overlooked if only two-dimensional pre-surgical studies are performed. Therefore, three-dimensional imaging and modeling of anatomic structures should be used for the pre-operative examination of the interforaminal area. Given the wide variability of the emergency pattern of the mental nerve and the prevalence and location of the anterior loop, it should be studied in every patient individually.
Keywords: Anterior loop; Computer-assisted three-dimensional imaging; Cross-sectional anatomy; Inferior alveolar nerve; Mental canal; Preoperative implant planning.