A Retrospective Study on Identification of Anterior Loop Pattern of Mental Nerve Entry into Mental Foramen in Digital Orthopantomography among South Indian Population

Background: In the premolar location of mandible, the mental nerve's entry into the mental foramen pattern is a significant landmark. Different patterns of mental nerve entrance have been discovered. The current experiment was attempted to detect the different entry routes of the mental nerve into the mandible using panoramic radiographs, which are employed in pre-surgical evaluation. Materials and Methods: The current study used a total of 200 panoramic radiographs collected for diagnostic purposes. The location and entrance pattern of the mental nerve on the both sides were noted on the radiographs. Straight, looping, and perpendicular entry patterns were identified in the data. The data is tabulated and statistically analysed in SPSS software using Chisquare. Results: The existence of an anterior loop was determined to be the most usual pattern of entry of the mental nerve, accounting for 79 percent of the total radiographs examined 21 percent , and a perpendicular pattern 6 percent. The p value is 0.432 and p value 0.309, with respect to age and gender respectively which is statistically not significant. Conclusion: The findings obtained from the study within the limits, it can be stated that the straight Original Research Article Srithika and Prathap; JPRI, 33(60B): 3306-3312, 2021; Article no.JPRI.78952 3307 pattern of anterior loop of mental nerve was the most common. A panoramic radiograph may be a viable radiological tool for detecting the existence of an anterior loop that should be confirmed in order to plan surgical treatments in the mandibular premolar region prior to surgery.


INTRODUCTION
The inferior alveolar nerve is a mandibular nerve branch that starts on the lingual side of the mandibular ramus and passes down to the mandibular canal, feeding teeth of mandible and adjoining gums [1]. One of the terminal branches of the inferior alveolar nerve is the mental nerve, which arises from the mental foramen and supplies the skin and mucous membrane of the buccal vestibule from the medial border of the masseter muscle to the midline [2].
Before the nerve emerges from the mental foramen, some authors documented an anterior loop [3]. The structure "where the inferior and anterior to the mental foramen has been crossed by mental neurovascular bundle then it doubles or loops back to exit the mental foramen" was first described by Bavitz and Misch. In around 11-60% of panoramic radiographs, this can be seen. More about the additional routes of the mental nerve as it escapes via the mental foramen has not been described. Some investigations classified the pattern as looped or non-looped, or defined it as posteriorly directed, anteriorly directed, or both [4]. The experience from our previous studies [5][6][7][8][9][10][11][12][13][14] have led us to focus on the current topic.
The most common problem during implant placement in the mandibular premolar region is neurosensory changes in the chin and lower lip. Complications can emerge when crucial critical structures like the mental foramen and anterior mental loop are not appropriately recognised and safeguarded [15]. Using proper radiography techniques, the exact location of the anatomical structures should be established prior to surgery to avoid harm to these essential structures [15,16]. Although a number of morphometric investigations have shown the mental nerve's entry pattern into the mental foramen, only a few radiography studies have been conducted in this regard [17]. To plan these surgical procedures, anatomic landmarks are commonly discovered utilising panoramic radiography.
The purpose of this study is to see if a OPG is enough to detect the appearance of an anterior loop pattern and other related variable patterns of mental nerve entrance, or if more advanced imaging techniques are required. Our research team has published high-quality papers in the past [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. The goal of this study is to use digital orthopantomography to discover the anterior loop pattern of the mental nerve's entry into the mental foramen.

MATERIALS AND METHODS
This is a retrospective study conducted in a private dental college hospital in chennai and the study was approved by the institutional reveal board. Total 200 panoramic radiographs obtained from records maintained in the Department of Oral Medicine and Radiology were randomly selected for the study. Only highquality radiographs with respect to geometric accuracy and contrast of image were selected for the study. Radiographs showing radiolucent or radiopaque lesions in the mental foramen region of mandible and evidence of fracture around the mental foramen and mandibular canal region, radiographs showing supernumerary or unerupted teeth in the mental foramen region and radiographs showing processing or exposure errors and artifacts obscuring visibility of structures in the mandible were excluded from the study. The radiographs were evaluated for the pattern of entry of the mental nerve into the mental foramen on either side of the mandible. The observations thus made were recorded as Anterior loop (AL), straight (S), or Perpendicular (P) and the total numbers of patterns observed on both sides were recorded. Inter-observer variability was assessed using the kappa test. Tabulations for the presence of each pattern were done for both sides and the percentages calculated and analyzed using the SPSS tool.

RESULTS
The most common pattern of mental nerve entry was found to be straight, accounting for seventy nine percent of all samples examined. The straight patterns is followed by the existence of an anterior loop (21%), and a perpendicular type of pattern. (6 percent). The p value is 0.432 and p value 0.309, with respect to age and gender respectively which is statistically not significant. (Figs 1,2).

DISCUSSION
Maximum samples account's for straight type of entrance of mental nerves into mental foramen, according to the findings of this study.
Few investigations in cadaveric mandibles have looked at the transitional section of the nerve, between the mandibular canal and the mental foramen is the inferior alveolar nerve. Solar and colleagues categorized their examples into loop and non-loop kinds [38]. The author looked at the real course of the mental nerve's emergence and classified it as with various patterns. An investigation of the origins of the mental nerve in a varied populations. A straight pattern of the mental canal entering into the mental foramen directly was discovered [39].
So yet, no radiographic tests have been conducted to see if such patterns are detectable on radiographs. Despite the fact that radiographic studies have not reported the numerous forms of the mental nerve's entrance into the mental foramen. Dissimilar diagnostic techniques, equipment, and poor radiography quality may explain the diversity in the radiographic assessment of the anterior loop when reported for the varied rule used to describe the anterior loop. The inability to tell it apart from normal trabecular patterns is the most probable explanation [40]. The appearance of the anterior loop pattern on three-dimensional cone beam tomography has been determined to be significantly better in studies [41].
The MF was nearer to the alveolar crest in the imaging with an anterior loop than in the radiographs with no loop, according to the current study. As a result of this discovery, It's possible that the mental nerve must loop back to enter the foramen when the mental foramen is little higher in the vertical planar line.
Finally, because of the existence of the anterior loop, the morphology of the premolar region of mandible has clinical relevance in preliminary assessment of surgical treatments. Neurosensory changes in the chin and lower lip may result from damage to this nerve bundle. The implantation of endosseous implants in the anterior inter-foraminal area has piqued researchers' curiosity. The most posterior implant should be positioned as near to the mental foramen as possible to maximise the space between implants [42].  1. The frequency distribution with respect to age. The X axis presents the age and the y axis presents the number of samples. Type I is anterior loop (blue), type ll is straight (green), type lll is perpendicular (yellow). Anterior loop pattern is observed in more frequency among age group 20-40 yrs. The Chi square test was observed with p value 0.432, which is not significant Fig. 2. The frequency distribution with respect to gender. In the X axis, 1 presents male and 2 represents female. In the y axis the numbers represent the number of samples. Type I is anterior (blue), type ll is straight (green), type lll is perpendicular (yellow), among which anterior loop and straight pattern are more in males than females. Chi square test was done with p value 0.309, which is statistically not significant The distal aspect of an implant in the mental region should be 1mm anterior to the anterior edge of the mental foramen, according to Bavitz et al. [43] However, some writers suggest that the MF and the most dorsal implant be separated by at least 6 mm. However, the study can be expanded to a larger scale in the future.

CONCLUSION
The findings obtained from the study within the limits, it can be stated that the straight pattern of anterior loop of mental nerve was the most common. A panoramic radiograph may be a viable imaging tool for detecting the existence of an anterior loop that needs to be confirmed in order to plan surgical treatments in the premolar region of mandible prior to surgery. The exact design of premolar region of mandible, which is crucial for planning any surgical operations in this region, may need studies involving a range of ethnic groups.

CONSENT
It is not applicable.

ETHICAL APPROVAL
As per international standard or university standard written ethical approval has been collected and preserved by the author(s).

ACKNOWLEDGEMENT
We thank Saveetha Dental College and Hospitals for the successful completion of the study.