ABSTRACT
Background:
The precise location of the anterior loop is of utmost importance during implant surgery to avoid any postoperative complications. The aim of the institution-based study was to determine the prevalence of the anterior loop with respect to age and gender in the northeast population.
Materials and Methods:
Sixty outpatients opting for implant prostheses in the interforaminal region of the mandible were enrolled in this study based on the inclusion and exclusion criteria.
Results:
The anterior loop was identified in 18.3% of the total subjects, and the mean length of the anterior loop was found to be 3.37 ± 0.53 mm. Planning for prosthetic-driven the implant placement was possible in 54.5% of the subjects.
Conclusions:
Proper treatment planning using cone beam computed tomography (CBCT) with a radiographic stent is paramount important for the safe placement of implant in the presence of the anterior loop of the mental nerve.
KEYWORDS: Anterior loop, computed tomography, cone beam computed tomography, mental nerve
INTRODUCTION
The inferior alveolar nerve (IAN) is an important branch of the mandibular nerve that can extend in a few cases beyond the mental foramen and traverse upwards, outwards, and course again backward to exit through the mental foramen and is called the “anterior loop (AL) of the mental nerve.”[1] Proper knowledge of the AL is necessary during implant placement to avoid postoperative complications.
When the apico-coronal bone height and presence of an AL compromise parallel implant placement, the next consideration is through the placement of four implants which allows two axially placed anterior implants and two posteriorly tilted implants between 30° and 40° to maximize implant length and avoid inadvertent injury to anatomic structures (i.e., the mental nerve).[2]
A preoperative radiographic assessment like cone beam computed tomography (CBCT) plays an important role in developing a comprehensive treatment plan for the long-term clinical success of implant prosthesis.[3] For the planning of a prosthetically guided implant placement, the radiographic stent in conjunction with CBCT enables the clinician to determine the proper size, position, and angulation of the implant relative to the occlusal load. No such studies have been found in dental literature conducted on the northeast population of India. Thus, the study aimed to assess the anatomical variation of the mental nerve loop to estimate a safe zone for implant placement in the interforaminal region of the mandible in the northeast population.
MATERIALS AND METHODS
The present study was carried out on 60 volunteer outpatients reported to the department of prosthodontics between August 2021 and September 2022, opting for implant-supported prostheses. Subjects were selected following the undermentioned inclusion and exclusion criteria. Written consent was obtained from each subject. The ethical clearance No. RDC/29/2011/2044 was obtained from the institutional ethical committee.
Inclusion criteria
Patient aged 21 years and above.
Patients having edentulous areas in the interforaminal region of the mandible opting for implant prosthesis placement.
Exclusion criteria
The patient should be free of medical conditions such as uncontrolled diabetes, osteoporosis, Paget’s diseases, etc.
Any history of trauma and related mandibular fractures around the symphysis and parasymphysis region.
Presence of impacted canines or any odontogenic/cystic lesion in the interforaminal region.
The patient presented with anodontia/retained deciduous tooth in relation to mandibular cuspids and/or bicuspids.
All the statistics have been calculated and computed using the IBM Statistical Package for Social Sciences (SPSS) version 20. The Chi-square test is used to test the differences in distributions and associations among categorical variables. Mann-Whitney U test was used to test the differences in mean length and mean angulation between independent groups. Wilcoxon matched-pair test to test the differences in mean length pre and post change of orientation of implants. A P value < 0.05 was considered statistically significant.
RESULTS
The AL was identified in 18.3% of the total 60 subjects. The length of the AL was significantly longer on the right side (P = 0.042) than on the left side [Table 1]. In the presence of an AL, the length of the implant can be increased (2–4 mm) by changing in orientation and angulation from the prosthetic driven implant position (PDI) site implant distally by 30–32 degrees (P < 0.001) in 45.5% of the cases [Table 2].
Table 1.
Overall length (mm) and mean angulation (degree) of the AL with respect to side
| Length of the AL | Mean length of the AL | P | Mean angulation | P |
|---|---|---|---|---|
| Right side | 3.71±0.64 | 0.042, S | 57.7±14.1 | 0.80, NS |
| Left side | 3.03±0.42 | 60.4±24.5 | ||
| Overall | 3.37±0.53 | 59.1±19.3 |
Table 2.
Variations in orientation and angulation from PDI site implant in the presence of AL
| Cases with variation | Side | Orientation and angulation | Variation in orientation | Variation in angulation (degree) | Length of PDI implants (mm) | Length after changing the orientation of implant (mm) | |
|---|---|---|---|---|---|---|---|
|
| |||||||
| Mesial (degree) | Buccal (degree) | ||||||
| 1 | Right | Distal | 7 | 11 | |||
| Left | 7 | 6 | 30 | ||||
| 2 | Right | 6 | 6 | Distal | 30 | 7 | 11 |
| Left | |||||||
| 3 | Right | 6 | 7 | Distal | 32 | 7 | 11 |
| Left | 6 | 6 | 30 | 7 | 11 | ||
| 4 | Right | Buccal, lingual | 7 | 11 | |||
| Left | 7 | 8 | 30 | ||||
| 5 | Right | Distal | 9 | 11 | |||
| Left | 6 | 7 | 30 | ||||
| Mean | 6.33 | 6.67 | 7.33 | 11 | |||
| Standard deviation | 0.52 | 0.82 | 0.82 | 0 | |||
| P | 0.411, NS | P<0.001, S | |||||
DISCUSSION
Numerous studies have been conducted on the AL of the mental nerve in the past two decades.[3,4,5,6] The prevalence of the AL in the present study was found to be 18.3%. The present findings are similar to those of the study done by Sridhar et al.[7] However, Rodricks et al.[6] reported a higher prevalence of 57.5% than the present study.
The present study did not reveal significant variation in the prevalence of AL with respect to gender (P = 0.929). This is similar to the findings reported by Puri et al.[8] However, Gupta et al.[9] found a higher prevalence of ALs among the male subjects. In contrast, studies conducted by Suneetha et al.[10] reported that the AL was more common in females.
The mean length of the AL in the present study was 3.71 ± 0.64 mm on the right side and 3.03 ± 0.42 on the left side, exhibiting a statistically significant difference (P = 0.04 2S). The AL length of 0.89 mm in the Greek population was reported by Apostolakis et al.[11] using cross-sectional and parasagittal sections of CBCT, which were significantly longer on the right side than on the left side. On the contrary, Nascimento et al.[12] using consecutive coronal reconstructions on CBCT, found a mean length of 1.1 ± 0.8 mm in the Brazilian population with no significant side differences.
CONCLUSION
Within the limitations of the present study, the following conclusions can be drawn:
AL of the mental nerve is prevalent in 18.3% of the subjects with a mean length of 3.37 ± 0.53 mm.
Changes in the position, orientation, and angulation of implants may help in the prevention of unintentional damage to the neurovascular bundle in the premolar region and also increase the length of angulated implants.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Bavitz JB, Harn SD, Hansen CA, Lang M. An anatomical study of mental neurovascular bundle-implant relationships. Int J Oral Maxillofac Implants. 1993;8:563–7. [PubMed] [Google Scholar]
- 2.Krekmanov L, Kahn M, Rangert B, Lindström H. Tilting of posterior mandibular and maxillary implants for improved prosthesis support. Int J Oral Maxillofac Implants. 2000;15:405–14. [PubMed] [Google Scholar]
- 3.Kuzmanovic DV, Payne AG, Kieser JA, Dias GJ. Anterior loop of the mental nerve: A morphological and radiographic study. Clin Oral Impl Res. 2003;14:464–71. doi: 10.1034/j.1600-0501.2003.00869.x. [DOI] [PubMed] [Google Scholar]
- 4.Solar P, Ulm C, Frey G, Matejka M. Classification of the intraosseous paths of the mental nerve. Int J Oral Maxillofac. 1994;9:339–44. [Google Scholar]
- 5.Chaudhary A, Kaur G, Lalawat S. Locating the anterior loop of the inferior alveolar nerve on CBCT. EC Dent Sci. 2019;18:58–62. [Google Scholar]
- 6.Rodricks D, Phulambrikar T, Singh SK, Gupta A. Evaluation of incidence of mental nerve loop in Central India population using cone beam computed tomography. Indian J Dent Res. 2018;29:627–33. doi: 10.4103/ijdr.IJDR_50_17. [DOI] [PubMed] [Google Scholar]
- 7.Sridhar M, Dhanraj M, Thiyaneswaran N, Jain AR. A retrospective radiographic evaluation of incisive canal and anterior loop of mental nerve using cone beam computed tomography. Drug Invention Today. 2018;10((9)) [Google Scholar]
- 8.Puri A, Verma P, Mahajan P, Bansal A, Kohli S, Faraz SA. CBCT evaluation of the vital mandibular interforaminal anatomical structures. Ann Maxillofac Surg. 2020;10:149–57. doi: 10.4103/ams.ams_144_19. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Gupta A, Kumar S, Singh SK, Kumar A, Gupta A, Mehta P. Assessment of anterior loop of inferior alveolar nerve and its anatomic variations with age, gender, and dentition status in Indian population: A CBCT study. Int J Dent 2021. 2021 doi: 10.1155/2021/1813603. 1813603. doi: 10.1155/2021/1813603. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Suneetha JS, Samatha Y, Kiran AR, Naik NP, Kumar BN, Anoop G. Assessment of anterior loop of inferior alveolar nerve – A cone beam computed tomography study. J Orofac Sci. 2022;14:41–6. [Google Scholar]
- 11.Apostolakis D, Brown JE. The anterior loop of the inferior alveolar nerve: Prevalence, measurement of its length and a recommendation for interforaminal implant installation-based on cone beam CT imaging. Clin Oral Implants Res. 2012;23:1022–30. doi: 10.1111/j.1600-0501.2011.02261.x. [DOI] [PubMed] [Google Scholar]
- 12.do Nascimento EH, Dos Anjos Pontual ML, Dos Anjos Pontual A, da Cruz Perez DE, Figueiroa JN, Frazão MA, et al. Assessment of the anterior loop of the mandibular canal: A study using cone-beam computed tomography. Imaging Sci Dent. 2016;46:69–75. doi: 10.5624/isd.2016.46.2.69. [DOI] [PMC free article] [PubMed] [Google Scholar]