Predictive factors of the dimensions and location of mental foramen using cone beam computed tomography

RESEARCH ARTICLE Predictive factors of the dimensions and location of mental foramen using cone beam computed tomography Juan Muinelo-Lorenzo 1☯ , Ana Ferna ´ndez-Alonso 1 , Ernesto Smyth-Chamosa 2‡ , Juan Antonio Sua ´rez-Quintanilla 3 , Jesu ´s Varela-Mallou 4‡ , Marı ´a Mercedes Sua ´rezCunqueiro 5☯¤ * 1Department of Surgery and Surgical Medical Specialties, Santiago de Compostela University, Santiago de Compostela, A Coruña, Spain, 2Department of Psychiatry, Radiology and Public Health, Santiago de Compostela University, Santiago de Compostela, A Coruña, Spain, 3Department of Morphological Sciences, Santiago de Compostela University, Santiago de Compostela, A Coruña, Spain, 4Department of Organizational Psychology, Forensic Law, and Methodology of Behavioral Sciences, Santiago de Compostela University, Santiago de Compostela, A Coruña, Spain, 5Department of Surgery and Medical Surgical Specialties, Medicine and Dentistry School, University of Santiago de Compostela, Spain, Health Research Institute of Santiago (IDIS), Santiago de Compostela, Spain ☯These authors contributed equally to this work. ¤Current address: Medicine and Dentistry School, Santiago de Compostela University, Ru ´a Entrerrı ´os, Santiago de Compostela, A Coruña, Spain ‡ These authors also contributed equally to this work. *mariamercedes.suare[email protected] Abstract Objective The mental foramen (MF) hosts main neurovascular structures, making it of crucial importance for surgical procedures. This study aimed to analyze the factors influencing the dimensions and location of the MF. Materials and methods Cone beam computed tomography (CBCT) scans of 344 patients were examined for MF dimensions, as well as for the distances from the MF to the alveolar crest (MF-MSB), and to the inferior mandibular border (MF-MIB). Results Gender, mandibular side and presence of accessory mental foramina (AMF) significantly influence MF area. Males, left hemimandibles, and hemimandibles with no AMF had a higher rate of large MF areas (B = −0.60; p = 0.003, females; B = 0.55; p = 0.005; B = 0.85; p = 0.038). Age, gender and dental status significantly influence MF-MSB distance. The distance decreased as age increased (B = −0.054; p = 0.001), females showed a lower rate of long MF-MSB distances (B = −0.94, p = 0.001), and dentate patients showed a higher rate of long MF-MSB distances (B = 2.27; p = 0.001). Age, gender and emerging angle significantly influenced MF-MIB distance. The distance decreased as age and emerging angle PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 1 / 16 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Muinelo-Lorenzo J, Ferna ´ndez-Alonso A, Smyth-Chamosa E, Sua ´rez-Quintanilla JA, VarelaMallou J, Sua ´rez-Cunqueiro MM (2017) Predictive factors of the dimensions and location of mental foramen using cone beam computed tomography. PLoS ONE 12(8): e0179704. https://doi.org/ 10.1371/journal.pone.0179704 Editor: James J. Cray, Jr., Medical University of South Carolina, UNITED STATES Received: July 21, 2016 Accepted: May 8, 2017 Published: August 17, 2017 Copyright: ©2017 Muinelo-Lorenzo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its supporting information files Funding: The authors have no support or funding to report Competing interests: The authors have declared that no competing interests exist increased (B = −0.01; p = 0.001; B = −0.03; p = 0.001), and females had a lower rate of long MF-MIB distances (B = −1.94, p = 0.001). Conclusions General and local factors influence the dimensions and location of MF. MF dimensions are influenced by gender, mandibular side, anteroposterior position, and the presence of AMF. Distance from MF to alveolar crest is influenced by gender, age and dental status, while the relative MF position is influenced by age and dental status. CBCT images make it possible to analyze the MF in order to avoid complications during surgical procedures. Introduction The mental foramen (MF) is considered one of the main anatomic landmarks in the anterior region of the mandible because it constitutes the exit through which the terminal mandibular neurovascular branches pass. There are anatomical variations affecting the MF and mental nerve regarding location, size, emerging direction, number, and shape [1,2]. Since prehistoric times, the mandible of humans has undergone a decrease in its overall size compared to other primates [3,4]. The mental foramen (MF) has also varied its size and location. The MF has shifted from the molar region in Neolithic skulls to its current premolar position in modern humans. Moreover, the MF has increased in size since the Neolithic period [5]. The most common MF pattern of emergence in Caucasians and Maoris is the posterior direction, whereas right-angled emergence is predominant in Negro skulls [6]. There have been reports of subjects with double or multiple MFs [7]. The occurrence of these accessory mental foramina (AMF) has been explained by the early separation of the mental nerve prior to the complete formation of the MF [8], which does not occur until the twelfth week of intrauterine development [9]. The morphometric characteristics of MF are of special interest due to the clinical implications involved. MF can be injured during surgical procedures, resulting in paresthesia or anesthesia of the chin, lower lip, and gingiva from MF to midline [1,10]. It is critical for dental surgeons to accurately identify the MF prior to implant placement, orthognathic surgery, bone augmentation procedures and periapical surgery osteotomies [11–14]. An analysis of the factors having a possible influence on the size and position of the MF would allow for better understanding of MF variations prior to these procedures and help prevent vascular and nerve injuries. This study aimed to analyze the factors influencing MF dimensions and location. Material and methods Study population The overall sample consisted of 357 patients for whom pre-operative CBCT imaging was performed from July 2008 to June 2014 for various clinical indications, in the Radiology Unit of the Medicine and Dentistry School at the University of Santiago de Compostela, Spain. Ethical approval for the study was obtained from the Galician Ethics Committee of Clinical Research (Ref. 2012/272). Written informed consent was obtained from all participants in the study. The inclusion criteria were as follows: (1) whole mandibular body included in the CBCT volume; and (2) the CBCT voxel size was 0.3 mm or less. The exclusion criteria consisted of the following: (1) presence of any developmental or pathological conditions in the area of MF Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 2 / 16 (i.e., tumors, cysts, or malformations); (2) presence of incompletely erupted teeth in the anatomic region; (3) evidence of mandibular fractures or surgical interventions, such as repositioning of inferior alveolar nerve or orthognatic surgery, and (4) presence of any artifacts or blurring affecting image quality. Image adquisition CBCT exams were performed using i-CAT 1 Model 17–19 (Imaging Sciences International Inc., Pensilvania, USA), with a flat panel detector of cesium iodure (CsI) made of amorphous silicon (a-Si). The following exposure settings were used: tube voltaje peak of 120 kVp, current of 5 mAs, and exposure time of 14.7 s. The patient’s occlusal plane was set parallel to the floor. Multiplanar CBCT reconstructions were jointly analyzed by two experienced researchers to identify MF and AMF. The projection data in DICOM files were reconstructed on computer (Samsung 1 R522; Samsung Electronics, Seoul, South Korea) using Carestream 1 CS 3D v.3.2.12 software (Carestream Health Inc., Rochester, NY, USA.). CBCT-reconstruction slice thickness was 0.3 mm. Measurement procedure On cross-sectional slices, the position of MF in the mandibular body was determined by the distance from the alveolar bone crest to the MF superior border (MF-MSB), and the distance from the MF inferior border to the lower border of the mandible (MF-MIB). Mandibular vertical distance (MV) was calculated by the sum of the MF-MSB and MF-MIB distances. The crossing angle between the tangent to the vestibular mandibular surface and a parallel to the emerging direction of the mental nerve was considered the emerging angle (Fig 1). MF emergence was classified into four types according to its exit direction: I) superior, II) posterior, III) direct, and IV) anterior. The anteroposterior location of MF was classified with respect to mandibular teeth from the 1st premolar to 1st molar. Dental status was classified into three groups: dentate (6 or more remaining teeth), partially dentate (less than 6 remaining teeth) and edentulous. Long and short axes of each MF were measured on CBCT sagittal reconstructions; in addition, MF areas were calculated using the formula: oval area, A = abπ/4; [where a= long diameter and b= short diameter] (Fig 2). An AMF was defined as an ancillary buccal foramen presenting continuity with the mandibular canal. AMF had a smaller diameter than MFs. CBCT measurements were carried out by an experienced researcher under standard conditions (a 15.6 inch monitor in a dimly lit room). Intra-observer variability was analyzed by remeasuring 40 randomly selected CBCT images 1 month later. Statistical analysis Statistical analysis was performed using SPSS 1 (v. 21.0, IBM Corporation, NY, USA). Descriptive data included mean ±standard deviation (SD). Intra-observer and inter-observer agreement were assessed using the intraclass correlation coefficient. The t-test was used for paired comparisons in MF morphometric characteristics between gender and age groups. The oneway ANOVA and post hoc Bonferroni multiple comparison tests were used to compare MF characteristics in relation to dental status and MF position. A polar group strategy was used to obtain dichotomized variables. For each dependent variable two groups were established: the first group was 33 rd percentile, and the second group was 66 th percentile. A binary logistic regression analysis was performed to determine the factors influencing MF dimensions and location. Regression analysis was further performed to analyze the influence of age on MF-MSB distance in fully dentate patients. Statistical significance was set at p <0.05. Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 3 / 16 Results The final sample consisted of 344 CBCT scans selected from the initial 355. Three CBCTs were excluded from the initial sample due to partially erupted or included teeth in the region of interest, six scans presented pathology (four patients had radiolucident areas consistent with granulomas or cysts, one patient had lesions consistent with cherubism, and another had multiple dental inclusions and lesions suggesting cysts), and two CBCTs did not have adequate quality for analysis. The population consisted of 205 females (59.6%) and 139 males (40.4%) (mean age 47.44 ±15.52 years; range: 13–86). Of the total 688 MFs, the mean long diameter was 4.44 ±1.13 mm, the mean short diameter was 2.92 ±0.75 mm, and the mean area was 10.62 ±5.00 mm 2 . MF short diameter and MF area were significantly higher on the left side (p = 0.000, p = 0.013). The MF-MIB distance was 13.55 ±1.06 mm, and MF-MSB distance was 11.42 ±3.34 mm. The mean MF emerging angle from the mandible was 53.45 ±15.90˚. Male subjects presented statistically higher MF dimensions (long diameter, short diameter, and area) (p = 0.000, p = 0.000, p = 0.000, respectively), distances (MF-MIB and MF-MSB) (p = 0.000, p = 0.000, respectively), and MF emerging angle (p = 0.028). Younger subjects presented statistically higher MF-MSB distance (p = 0.000), while older subjects presented statistically higher MF emerging angle (p = 0.000). Differences were also found with respect to dental status. Dentate subjects had significantly higher MF dimensions (long diameter and area) than edentulous patients (p = 0.013, p = 0.038). Dentate patients also had statistically higher MF-MSB distance (p = 0.000), while MF emerging angle was statistically higher in edentulous patients (p = 0.000) (Table 1). The anteroposterior location of MF in relation to mandibular teeth presented the following distribution: 2.7% were below the 1 st molar, 9.1% between the 1 st and 2 nd molars, 57.9% below the 2 nd premolar, 25.3% between the 2 nd and 1 st premolar, and 5.0% were below the 1 st Fig 1. Location of the MF. (A) MF-MSB distance (1), MF-MIB distance (2), Emerging angle of the MF (3). (B) CBCT cross-sectional reconstructed slices of the mandible to show MF-MSB and MF-MIB distances, and emerging angle. https://doi.org/10.1371/journal.pone.0179704.g001 Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 4 / 16 premolar. MFs presented a statistically significant reduction in dimension (long diameter, short diameter, and area) as their position moved closer to the midline (Table 2) (Fig 3). The predominant type of MF emergence was superior direction, followed in frequency by direct, posterior and anterior types. No statistically significant differences were observed with regard to gender (p >0.05). However, there were statistical differences between age groups (p = 0.000). Patients under 50 years of age had superior emergence MFs more frequently than Fig 2. Dimensions of the MF. (A) Long diameter (1), Short diameter (2). (B) CBCT sagittal reconstructed slices of the mandible to show the long and short diameters of the MF. https://doi.org/10.1371/journal.pone.0179704.g002 Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 5 / 16 older patients. Conversely, patients over 50 had a higher number of direct-type MFs. Regarding the anteroposterior position, no statistically significant differences were found in emergence type. However, there were statistically significant differences according to dental status (p = 0.000). Dentate patients had mostly superior-direction MFs, while partially dentate and edentulous patients had mostly direct emergence. MF morphometric characteristics varied significantly depending on the type of emergence. Statistically significant differences in long diameter, MF-MSB and MF-MIB distances were observed. The MF-MIB distance was statistically higher in superior-type MFs as compared to direct-emergence MFs (p = 0.034). In addition, MF-MSB distance was statistically higher in superior-type MFs compared to direct-emergence MFs and anterior-emergence MFs (p = 0.005, p = 0.000). Furthermore, this distance was statistically higher in posterior-emergence MFs than anterior-emergence MFs (p = 0.042) (S1 Dataset). Inter-observer variability was an intraclass correlation mean value of 0.748, ranging from 0.62 to 0.85. Intra-observer variability was an intraclass correlation mean value of 0.799, ranging from 0.61 to 0.91 (S2 Dataset). Table 1. MF morphometric characteristics with respect to dental status. Dentate Partially dentate Edentulous MF CHARACTERISTICS (n = 614) (n = 28) (n = 46) P Long Diameter 2.93 ±0.76 2.96 ±0.60 2.67 ±0.79 0.075 Short Diameter 4.47 ±1.12*4.42 ±1.09 3.97 ±1.16*0.013 Area 10.71 ±5.07*10.57 ±4.15 8.75 ±4.56*0.038 MF-MIB 13.52 ±1.59 13.47 ±1.79 13.89 ±1.63 0.325 MF-MSB 11.84 ±3.02*9.68 ±3.13† 6.77 ±3.75*†0.000 Emerging Angle 52.07 ±14.68*54.54 ±18.35† 71.20 ±19.33*†0.000 MF characteristics are expressed as means ±standard deviation. The ANOVA was performed to compare MF characteristics with respect to dental status. Results in bold letters indicate statistical significance (p<0.05). *, and † indicates a significant difference after Bonferroni post-hoc multiple tests. MF, mental foramen; MF-MIB, distance from the alveolar crest to the MF; MF-MIB, distance from the MF to the inferior mandibular border. https://doi.org/10.1371/journal.pone.0179704.t001 Table 2. MF morphometric characteristics with respect to anteroposterior location. 1 st M 1 st M-2 nd PM 2 nd PM 2 nd PM-1 st PM 1 st PM CHARACTERISTICS (n = 17) (n = 58) (n = 370) (n = 161) (n = 32) P Long Diameter 4.54 ±1.19 4.77 ±1.14*4.49 ±1.03† 4.41 ±1.20 3.81 ±1.40*†0.003 Short Diameter 3.17 ±0.78*3.24 ±0.79†¶ 2.96 ±0.72R2.85 ±0.77† 2.45 ±0.79*¶R0.000 Area 11.64 ±5.03 12.46 ±5.44*10.75 ±4.77† 10.36 ±5.11 7.99 ±5.37*†0.001 MF-MIB 14.47 ±2.04 13.69 ±1.54 13.55 ±1.60 13.50 ±1.55 13.67 ±1.80 0.194 MF-MSB 12.15 ±3.36 11.23 ±3.60 11.58 ±3.12 12.18 ±2.53 12.15 ±3.49 0.144 Emerging Angle 47.12 ±12.04 55.22 ±16.28 52.21 ±15.13 52.73 ±14.03 52.66 ±15.77 0.365 MF characteristics are expressed as means ±standard deviation. The ANOVA was performed to compare MF characteristics with respect to MF anteroposterior location. Results in bold letters indicate statistical significance (p <0.05). *, †, ¶, and Rindicates a significant difference after Bonferroni post-hoc multiple tests. M, molar; PM, premolar; MF, mental foramen; MF-MIB, distance from the alveolar crest to the MF; MF-MIB, distance from the MF to the inferior mandibular border. https://doi.org/10.1371/journal.pone.0179704.t002 Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 6 / 16 Predicting the dimensions of the mental foramen The regression results indicated that gender, mandibular side, anteroposterior MF position and AMF presence significantly influence MF short diameter (p <0.05). Females had a significantly lower rate of large MF short diameters (B = −0.73; p = 0.001). Regarding mandibular side, there was a higher rate of large MF short diameters on the left side (B = 0.71; p = 0.001). In relation to the anteroposterior position, the MFs situated below the 1 st molar (B = 1.85; p = 0.026), between the 1 st molar and 2 nd premolar (B = 2.03; p = 0.001), and below the 2 nd premolar (B = 1.03; p = 0.038) had a higher rate of large MF short diameters in comparison to the MFs situated below the 1 st premolar. With respect to those located below the 1 st premolar, the rate of large MF short diameters was 6.3 times greater below the 1 st molar, 7.6 times greater between the 1 st molar and 2 nd premolar, 2.8 times greater below the 2 nd premolar, and 2.7 times greater between the 2 nd and 1 st premolar (Table 2) (Fig 3). In addition, hemimandibles with no AMF showed a higher rate of large MF short diameters (B = 0.90; p = 0.038). The rate of large MF short diameters was nearly 2.5 times higher in hemimandibles with no AMF presence. The regression analysis showed that gender and presence of AMF had a significant influence on MF long diameter (p <0.05). The regression analysis showed that gender, mandibular side and the presence of AMF significantly influence MF area (p <0.05). Females had a lower rate of large MF areas (B = −0.60; Fig 3. MF morphometric characteristics with respect to anteroposterior position. MFs presented a statistically significant reduction in dimensions (long diameter, short diameter, and area) as their position moved closer to the midline. The area and long diameter of the MFs located below the 2nd premolar and those located between 1st molar and 2nd premolar were significantly higher compared to the MFs located below 1st premolar. The short diameter of the MFs located below the 1st molar, between 1st molar and 2nd premolar, and below the 2nd premolar was significantly higher compared to the MFs located below the 1st premolar. In addition, the short diameter of the MFs located between the 1 st molar and 2 nd premolar was significantly higher compared to the MFs located between the 2 nd premolar and 1 st premolar. https://doi.org/10.1371/journal.pone.0179704.g003 Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 7 / 16 p = 0.003). The likelihood of presenting a large MF area was 1.8 times greater in males (1/0.54; OR in females = 0.54). Regarding side, left hemimandibles had a higher rate of large MF areas (B = 0.55; p = 0.005). The likelihood of having large MF area was 1.7 times greater in left hemimandibles. In addition, hemimandibles with no AMF had a higher rate of large MF areas (B = 0.85; p = 0.038). The likelihood of having large MF area was 2.3 times greater in hemimandibles with no AMF (Table 3) (Fig 4), (S3 Dataset). Predicting the location of the mental foramen The binary logistic regression showed that age, gender and dental status significantly influence MF-MSB distance (p <0.05). This distance decreased as age increased (B = −0.054; p = 0.001). In terms of gender, females had a lower rate of long MF-MSB distances (B = −0.94, p = 0.001). The likelihood of having a long MF-MSB distance was 2.56 times higher in males (1/0.39; OR in females = 0.39). In addition, dentate patients showed a 10-times higher rate of long MF-MSB distances in comparison with edentulous patients (B = 2.27; p = 0.001). Regarding completely dentate patients, the linear regression analysis revealed that age had an influence on MF-MSB distance (R = 0.26; B = −0.05; p = 0.02) and MF-MSB/MV ratio (R = 0.32; B = −0.001; p <0.01) (Fig 5). The binary logistic regression showed that age, gender and emerging angle significantly influenced the MF-MIB distance (p <0.05). The distance decreased as age increased (B = −0.01; p = 0.001). In terms of gender, females had a lower rate of long MF-MIB distances (B = −1.94, p = 0.001). The likelihood of having a long MF-MIB distance was 7.14 times higher in males (1/0.14; OR in females = 0.14). In addition, as emerging angle increased, the likelihood of presenting long MF-MIB distances decreased (B = −0.03; p = 0.001). The binary logistic regression showed that age, gender, dental status and emerging angle significantly influenced the MV distance (p <0.05). This distance decreased as age increased (B = −0.04; p = 0.000). In terms of gender, females had a lower rate of long MV distances (B = −1.96, p = 0.000). The likelihood of having a long MV distance was 7.14 times higher in Table 3. Determining factors of MF long diameter, short diameter and area. B P OR (95%CI) Long Diameter Gender (female) −0.50 0.01 0.60 (0.41,0.88) Presence of AMF −0.80 0.04 0.23 (1.02,4.84) Short Diameter Gender (female) −0.73 0.001 0.47 (0.31,0.72) Mandibular side (left)ft) 0.71 0.001 2.05 (1.34,3.12) Anteroposterior position of MF 1st M 1.85 0.026 6.35 (1.24,32.51) 1st M-2nd PM 2.03 0.001 7.61 (2.26,25.65) 2nd PM 1.03 0.038 2.82 (1.06,7.53) Absence of AMF 0.90 0.038 2.46 (1.05,5.76) Area Gender (female) −0.60 0.003 0,54 (1.00,1.03) Mandibular side (left) 0.55 0.005 1.74 (0.09,0.22) Presence of AMF 0.85 0.038 2.34 (0.95,0.98) Binary logistic regression to determine the general and local factors influencing MF dimensions: Results in bold letters indicate statistical significance (p <0.05). MF, mental foramen; AMF, accessory mental foramen; M, molar; PM, premolar; OR, odds ratio. https://doi.org/10.1371/journal.pone.0179704.t003 Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 8 / 16 males (1/0.14; OR in females = 0.14). In addition, dentate patients showed an almost 5 times higher rate of long MV distances as compared to edentulous patients (B = 1.59; p = 0.001). Regarding emerging angle, the higher the angle the lower the likelihood of presenting long MV distances (B = −0.03; p = 0.000). The binary logistic regression showed that age and dental status significantly influenced the MF-MSB/MV ratio (p <0.05). The ratio decreased as age increased (B = −0.05; p = 0.000). In addition, dentate patients showed a 10 times higher rate of long MF-MSB/MV ratios in comparison to edentulous patients (B = 2.37; p = 0.001) (Table 4), (S4 Dataset). Discussion This study has identified a number of factors influencing MF size. Gender, mandibular side, MF anteroposterior position, and the presence of AMF largely determine variations in MF Fig 4. Distribution of MF area. (A) Females had a lower rate of large MF areas (B = −0.60; p <0.01). Left hemimandibles had a higher rate of large MF areas (B = 0.55; p <0.01). (B) Hemimandibles with no AMF had a higher rate of large MF areas (B = 0.85; p <0.05). https://doi.org/10.1371/journal.pone.0179704.g004 Predictive factors of mental foramen morphometry PLOS ONE | https://doi.org/10.1371/journal.pone.0179704 August 17, 2017 9 / 16 37. Chandra A, Singh A, Badni M, Jaiswal R, Agnihotri A. Determination of sex by radiographic analysis of mental foramen in North Indian population. J Forensic Dent Sci. 2013; 5: 52–55. https://doi.org/10. 4103/0975-1475.114556 PMID: 23960416. 38. Chu RA, Nahas FX, Di Martino M, Soares FA, Novo NF, Smith RL, et al. 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