clinical and anatomy study of the human mental …

Abstract

The great diffusion of the surgical techniques in jaws sur-gery and the progress of the radiological imagining proce-dures expressed many interest in clinical anatomy of themental foramen (MF). The study goal was to determine theprecise location of the MF and the surrounding anatomicallandmarks. Measurements of the MF position relative tothe surgical landmarks and related posterior teeth weremade on 20 dry mandibles with complete dentition and in-tact alveolar bridge obtained from the Institute of Anato-my, School of Medicine, University in Sarajevo. Themeasurements were made by anthropometric methods onthe booth sides of the mandible, and compared with meas-urement made on the orthopantomogram radiographs ofthe same mandibles. The most common position of the MFwas in line with the longitudinal axis of the second premo-lar. In the vertical plane on the skulls the MF lays in themidpoint of the distance between the lower border of themandible and the alveolar margin, however on the ortho-pantomogram MF appeared slightly bellow the midpoint.In the horizontal plane it lays approximately one third ofthe distance between the mandibular symphysis and theposterior border of the ramus of the mandible measure-ment from A-P projection and one quarter of that distancemeasurement from the profile projection. There were nosignificant differences between distances MF from poster-ior border of the ramus of the mandible measurement fromA-P and profile projection and the one obtained on ortho-pantomogram and their ratio is constant value determinedas 1,065. The MF was on average 25 mm lateral to themandibular skeletal midline and symmetrical, and symme-try was preserved on the orthopantomogram. The measure-ment showed significant differences in distances of MFfrom superior border mandible measurement on dry man-dible and orthopantomogram radiographs while distancebellow the MF was not significantly different. The con-stant values of MF distance to the posterior border of theramus of the mandible measured as 1,065 and the distanceto the medial skeletal line of 2,11 made it possible to alsodetermine average angle of 43 degrees stream of the cor-pus of the mandible behind MF. These values in combina-tion with ratios of MF to the different anatomic landmarksdesignated as relative horizontal and relative vertical posi-tion, would be of importance not only from anatomical butalso from practical point of view for estimation of alveo-lar bridge resorption and preoperative analysis in orthog-nat postresection or implant surgery in the mandible.

Introduction

Although a lot of research was performed in order to eval-uate the appearance and location of anatomical landmarkson panoramic radiographs, there seems to be no system-atic study of the appearance of the mental foramen fromeither, clinical or experimental viewpoint. Knowing theposition of the mental foramen is important for clinicianswhen administering regional anesthesia and performingsurgery in the mental region of the mandible. Recent de-velopment of the mandibular implants technique and theincreasing frequency of orthognathic surgery have in-creased the possibility of surgical procedures near themental foramina, also. Although it is often possible to identify the mental fora-men by palpation and radiographically, knowing the nor-mal range of possible locations is essential. Standard an-atomic texts contain data collections from dried skullswhich are often of unknown origin or from an ethnicgroup that does not represent the Bosnian population.Sto{i} (1) described anatomical features of mental fora-men on 150 dry mandibles and reported that the mostcommon position of the foramen was in the center of thecorpus of the mandible in the vertical plane and betweenthe lower premolar. Two different approaches to the studyof mental foramina are available: evaluation and analysisof radiographs and procedures carried out on dry skulls.Both approaches are essential for the thorough under-standing of the location and appearance of this importantanatomical landmark. This article considers both, theanalysis of experimental procedures on the dry skulls andtheir radiograph appearance. The study, in addition to themeasurements that define it, review anatomical facts sig-nificant for preoperative planning of either, implant pro-cedures of the mandible or reconstructive procedures aft-er mandibular resection surgery and posttraumatic defects. Furthermore, the difference in size and morphology of pa-tient jaws makes the use of absolute measurements frompanoramic radiographs of little value. Expressing the ra-tio of the different anatomic features of the mandible to ameasurable distance by using consistent anatomic land-marks is probably a better method. Only a few articlesbased on this approach appear in the literature. Wical andSwope studied mandibular alveolar bone height in pano-ramic radiographs of 130 fully dentulous adults with min-imal or no evidence of resorbtion using the ratio of the al-veolar bone height and distance from the mental foramen.The authors used ratios of measured values with mean

15BOSNIAN JOURNAL OF BASIC MEDICAL SCIENCES 2004; 4 (3): 15-23

CLINICAL AND ANATOMY STUDYOF THE HUMAN MENTAL FORAMENAmer Smajilagi}1*, Faruk Dilberovi}2

1 Clinics for Maxillofacial Surgery, University Clinics Center Sarajevo, Sarajevo, Bosnia and Herzegovina2 Institute of Anatomy "Prof.dr. Hajrudin Hadjiselimovic", School of Medicine, University of Sarajevo, Sarajevo* Corresponding author

value of 2,9 and believed that the calculation of these val-ues would enable classification of the alveolar resorbtion.Other authors studied the radiographic appearance of fo-ramen mental such as Yoshua and LeBrook (3,4) whoshowed that vertical position of the mental foramen wasdifferent in dentelous and edentulous patients as a resultof alveolar resorbtion. Alantar at al. (5) compared the ap-pearance of the mental foramen by different radiographytechniques using Panorex, Orthopantomograms and Pan-elipses and concluded that Orthopantomogram and Pano-rex were more precise for identification (above 80%) thanPanelipse (60%)

Aims

The aims of this research were:

1. To determine the most common position of the men-tal foramen in Bosnian population in relation to thelower teeth and compare the results with those report-ed for other populations.

2. To determining the position of the mental foramen inrelation to the mandibular symphysis, the posteriorborder ramus of the mandible, the lower border of themandible and the alveolar crest on dry adult dentelousmandibles

3. To compare the results with those obtained on the or-thopantomogram radiographs of mandibles and to es-tablish some standards based on the achieved resultsin order to expand these studies in some areas ofmandible reconstructive surgery in various clinicalsituations.

Materials And Methods

Twenty sculls obtained from the Institute of Anatomy,School of Medicine, University of Sarajevo with dente-lous mandibles and intact alveolar bridges were used instudy. The measurements were made by anthropometricalmethods on the both sides of every mandible. Everymeasurement was reported, with its specific variation in-terval. All measurements were done with high standardand accuracy.

The position of the mental foramen inrelation to lower posterior teeth.

The position of the mental foramen with respect to teethwas investigated in a sample of Bosnian population, ofunknown age or sex. The position of the mental foramenin relation to the mandibular teeth was recorded as lyingin line with long axis of a posterior tooth or their interden-tal spaces in one of five position as shown in Figure 1.The position was assessed by holding a transparent flexi-

ble plastic sheet with a T-mark against the lateral aspectof the occlusal plane and vertical line used to locate theposition of the foramen. The relation between the foramenand the body of the mandible in horizontal and verticalplanes was determined when the mandible was placed ona horizontal surface and held by vertical pressure on thesecond molar tooth. This is defined by Morrant (6) as thestandard horizontal plane and shown in Figure 2.

The horizontal position of the mental foramen

Horizontal positions of the mental foramen on dry skullswere determined in two visual projections, antero-posteri-or and profile, on drowned horizontal line parallel with oc-clusion surface that went through the center of the mentalforamen cutting the mandible in the most anterior and themost distal point as shown in Figure 3. On the projected

16 BOSNIAN JOURNAL OF BASIC MEDICAL SCIENCES 2004; 4 (3): 15-23

Amer Smajilagi} et al.: CLINICAL AND ANATOMY STUDY OF THE HUMAN MENTAL FORAMEN

Figure 1. Picture for the numeric expression of the mentalforamen position relative to the mandibular teeth. (1.posi-tion of FM as lying in line with long axis of the first pre-molar tooth, 2.interdental spaces between premolars, 3.line with long axis of the second premolar teeth, 4. inter-dental spaces between second premolar and first molar,5. line with long axis of the first molar root)

Figure 2. Measurement plane and the relation of themental foramen on mandibla. Oclusal surface is parallelto the horizontal plane of the floor.

horizontal line, the distance from the foramen mental to theanterior point on mandibular symphysis was designated asPd, and the distance from the mental foramen to the poster-ior border of the ramus of the mandible was designated asZd. In sagital plane, the distance from the mental foramento the middle line of the mandible was designated as Ps,and distance from the distal point of the mandible to themiddle line was designated as Zs as shown on Figure 4.

The vertical position of the mental foramen

The technique used for vertical measurement was virtuallythe same as the Wical and Swope's. These measurementswere done on the drown vertical line perpendicular to theocclusive surface cutting the center of the mental foramen.The distance from the upper edge of the mental foramen tothe alveolar crest was designated as Gv, and the distancefrom the lover edge of the mental foramen to the inferiorborder of mandible was designated as Dv as shown in Fig-ure 5. These signs were different to those used by Wicaland Swoope (2) to designate similar measurements.

The position of the mental foramen on orthopantomo-gram radiographs

Using this method and distances, appearances and posi-tion of the mental foramen from horizontal and verticalplanes on the ortopantomogram radiographs was deter-mined. Every mandible was placed in identical positionon the orthopantomogram machine, fixed in the machinetube with occlusion surface parallel to the horizontal sur-face of room floor during recording. Figure 6. showsstandard mandible radiographs obtained in this study.Contrast BaSO4 was injected in each mental foramen be-cause of precise identification on X-ray.Figure 7. shows measurements done from horizontal po-sition and distance of the mental foramen from the ante-rior point of corpus mandible (Pd), and distance of themental foramen from the distal point of the ramus of themandible (Zd), on determined horizontal line. Figure 8.shows measurements done from vertical position and thedistance of the mental foramen from the alveolar crest(Gv), and distance of the mental foramen from the inferi-



Figure 3. Measurement plane and relationship of the mental foramen to the sumphysis menti (Pd) and posterior borderof the ramus of the mandible (Zd).A. Anterioposterior projection; B. Profile projection.

Figure 4. Plane of the measurement and relationship ofthe mental foramen to the medial skeletal line (Ps), andposterior border of the ramus of the mandible to themedial skeletal line(Zs).

Figure 5.Plane of measurement and relation of the mentalforamen to the alveolar crest (Gv) and inferior border ofmandible ( Dv).

or mandible border (Dv) on drown vertical line.The result obtained on dry skulls and on ortopantomo-gram radiographs were compared.

Results

For the clinical and diagnostic imaging purposes the me-dium values of the anatomical measurements can be con-sidered sufficient. For anthropometric, anesthesiologicaland surgical aims knowing the maximum and the mini-mum values and the variation interval is also necessary.The measurements, in this study, were made by anthropo-metric methods and are reported in the tables with meanvalues and their specific variation intervals.The means and standard deviations for the horizontal po-sition of the mental foramen measurements of dry skullsfrom different projections are shown in Table 1.Using these values the ratios between measures from dif-ferent projections Pd (a-p/profile) and Zd (a-p/profile) andratios between Zd/Pd from the same projection designatedas relative horizontal position were determined . The means and standard deviations for those ratios andrelative horizontal position measures on dry skulls areshown in Table 2.The position of the mental foramen in the dry skulls withrespect to teeth is shown in Table 3.The mean values and standard deviations for the distanceof the mental foramen from alveolar crest and inferiorborder of the mandible and their ratio determined as rela-tive vertical position are shown in Table 4.Mean values and standard deviations for the ortopantomo-gram measurements from horizontal and vertical projec-tions are shown in Table 5.Comparison of mean values of measures on ortopantomo-gram and dry skulls are shown in Table 6.

Discusion

The present investigation is unique, because it was basedon the material from Bosnian ethnic group. The most common position of the mental foramen was inline with longitudinal axis of the second premolar fol-lowed closely by the location between the first and second



Figure 6. Radiographic images of mandible with oclusalsurface parallel with the horizontal surface of the roomfloor when picture was recorded.

Figure 7. Distances measured on radiographic images ofmandibles: (Pd) from foramen mental to the sumphysis,(Zd) from foramen mental to the posterior border of theramus of the mandible.

Figure 8. Distances measured on radiographic images ofmandibles: (Dv) from inferior border of mandible to loweredge of mental foramen, (Gv) from upper edge of fora-men mental to the alveolar crest.

Figure 9. Relative vertical position (R.V.P.) and Dv as constant value, method for estimation of alveolar resorption. (A. radi-ograph mandible with intact alveolar bridge B. radiograph mandible with total resorbtion of alveolar bridge and R.V.P. ? 0)

premolars (Table 3). The mental foramen was not posi-tioned symmetrically. These results concur with the re-search done by Moiseiwitsch (7) which conclud that fora-men was generally found on average between premolars,determined on North American Caucasian population.Similar study was done on other ethnic groups and ityielded different results. Shankland (8) showed, in hisstudy, that the mental foramen on Asian Indians mandi-bles was located in 75,36% of 138 total mandibular sidesdirectly bellow the second premolar. Oguz (9), in his re-search, showed that the mental foramen was positioned in61,7% of 34 of total Turkish adults on dry skulls belowthe root of the second premolar on the right and in 50 %on the left. Mbajiorgu (10) presented the most commonposition of the mental foramen between the lower premo-lars on Black Zimbabwean populations. These results, as

other previous similar studies indicated ethnic and racialdifferences in most common positions of the mental fora-men. In white population the mental foramen was posi-tioned more distal than in black or Asian population. Theresults in the study confirmed these conclusions. Santini(11) compared positions of the mental foramen in Chineseand British population, and found that modal position ofthe mental foramen was relative to the standing mandibleteeth in the British sample and lay in line with the longitu-dinal axis of the second premolar tooth whereas the mo-dal position in the Chinese sample was in line between thefirst and second premolar teeth. The standard anatomytextbook notion that the foramen always lies between thefirst and second premolars cannot be accepted now. Racialdifferences occur and it is clear that in Asian and Chinesepeople, the most common position is between first andsecond premolar teeth whereas the result of this study alsoagree that in white Bosnian population the mental foramenwas most commonly positioned in the long axis of the sec-ond premolar tooth. Clinicians should expect to find themental foramen mostly in line between premolar in blackor Asian population and more distal in white population.According to the anatomy texts by Sicher (12) and Shil-ler (13), the mental foramen lies midway between the al-veolar border and the inferior border of the mandible orcloser to the latter. As can be seen in this study (Table 4),the mental foramen is positioned in the middle of the dis-tance from the inferior border of the mandible to the alve-olar crest on projected perpendicular line. These valuesare accordingly compared with the results of Oguz (9) thatshow that the distance of the mental foramen to the inferi-or border of the mandible is 14,61 mm and 14,29 mm tothe right and left, then to the superior border was 13,62mm to the right and 14,62 mm to the left. Mbajiorgu (10)showed that in the Black Zimbabweans population, invertical plane, the mental foramen lays slightly below themidpoint of the distance between the lover border of the



Figure 10. Scheme for the assessment of average anglestrength of the corpus of mandible behind mental foramenunder the angle of 43 degrees to the skeletal middle lineusing values ratios Zd / Pd = 2,115., and ratios Zd from A-P and profile projection Zd/Zd 1,065.

Figure 11. A) Average angle of strength of the mandible corpus behind foramen mental 43 degree.B) Average angle deformation strength of the mandible corpus behind the mental foramen on the orthopanthmogram ofnormal mandibles. It was possible to affirm that surrender in normal average values measurements on orthopantomo-grams radiograph images; R.H.P. (2,83 - 2,73), R.V.P. (1,16 - 1,19) and angle of 47 degrees suggested an anomaly.

mandible and the alveolar margin in 41% of 32 mandiblesright and 45,5% for the left sides. When these results arecompared with the results of our study done on whiteBosnian population no ethnic differences in the positionof the mental foramen in the vertical plane are found.Although the true vertical position of the mental foramenas measured on skulls is approximately centered in the al-veolar bone, the majority of ortopantomogram radio-

graphs showed the mental foramen significantly closer tothe inferior border of the mandible than it actually is (Ta-ble 5). The distance of the mental foramen from the infe-rior mandible border was not significantly different com-pared with the measurements on dry skulls. The highermean values of the relative vertical position in orthopan-tomogram of 1,19-0,20 right and 1,19-0,23 left confirmthe lower positioned foramina on the radiographs and weconclude that orthopantomogram changes true values invertical plane. Packota at al. (14) compared absolute radi-ographic measurements of marginal bone loss on ortho-pantomograms and intraoral radiographs with actualmeasurements on dry skulls. They concluded that all ra-diographic measurements overestimated the amount ofbony support present and that in assessing marginal boneloss pantomographs gave results that deviated less fromactual measurements on dry skulls than those obtainedfrom intraoral radiographs. In studies of the mandible themental foramen was used as a constant anatomic land-mark based on the relative constancy of the relation of theforamen to the inferior border of the mandible in spite ofresorbtion of the edentulous alveolar process (14). Wicaland Swoope (2) believed that the lower edge of the men-tal foramen was used as a reference mark in panoramic ra-diographs for estimating the amount of alveolar bone loss.



Figure 12. The scheme for adequate preoperative recon-struction of corpus mandible defect using values desig-nated in this study; Relative horizontal position designat-ed as ratio Zd/Pd, relationship of distal point of mandibleand foramen mental in accordance with medial skeletalmidline Zs/Ps determined as 2,1, and angle of corpusmandible behind mental foramen is 43 degree

Alveolar ridge height determined in their study was ex-pressed as ratio instead of absolute measurements, be-cause differences in patient size and the position maymake absolute measurements less meaningful for clinicaluse. The basic method used in this investigation for themandibular analyses was virtually the same as the one usedby Wical and Swoope. Studies of the mandible in presentstudy have used the mental foramen as a constant anatom-ical landmark based on the relative constancy of the rela-tion of the foramen to the inferior border of the mandible inspite of resorption of the alveolar process. We believed thatthe lower edge of the mental foramen is to be used as a ref-erence mark in orthopantomogram radiographs for estimat-ing the amount of alveolar bone loss. We rationalized thatthe bone below the foramen consists of predictable propor-tion of the total bone height in most of normal patients andis not significantly affected by resorption until extreme at-rophy occurs. One of the criteria used in our study was theposition of the mandible in Orthopantomogram machineand clearly visible mental foramen (Figure 9). The distance of the mental foramen from symphysismeasured from A-P projection were 25,7 mm for rightside and 24,8 mm for left side which coincides with re-search of Santini A., who compared the position of themental foramen in different ethnic groups and showed de-pendence of the position of the mental foramen from eth-nic and racial groups. The author showed distally posi-tioned mental foramen in Chinese population compared tothe British. The mean distance of the foramen from sym-physis in the British was 25,2 mm and not significantly different when comparedwith our study. In Chinese that distance was 27,6 mm.The result of our study confirm that the mental foramen

in Asian population is positioned more distally than in thewhite one. The ratio between the distances of the mentalforamen from anterior point Pd and the distances of themental foramen from distal point of the ramus of the man-dible Zd designated as relative horizontal position weremean 2,44 right and 2,66 left for A-P projection. Fromthat profile the values were right 4,06 and left 4,83 (Table2). Comparing mean values between distances of themental foramen from symphysis of the mandible (Pd)from different projections, we showed significant differ-ences. The mean distances of the mental foramen from thedistal point of the ramus of the mandibles showed no sig-nificant differences (Table 2), and their ratio had constantvalue of 1,065. Mean value of distances of the mental fo-ramen from the middle line of the mandible was symmet-rical and distances of the distal point of the mandible fromthe middle line was symmetrical also. Using the results inthis study ratio of these distances has a constant value of2,115 (Table 2). Using these results it was possible to de-termine the average angle corpus of the mandible behindthe mental foramen in relation with the middle line. Us-ing that ratio and the ratio above pointed that the corpusof the mandible behind the foramen is always a straightline that spreads out under the angle of 43 degrees to themiddle line in normal mandible. (Figure 10, 11). It waspossible to affirm that the ortopanthomogram twisted nor-mal angle corpus of the mandible behind the mental fora-men, 47 degrees to the normal mandible (Figure 12).These results using the mental foramen as a constant an-atomic landmark and its relation with other parts of themandible may be used in preoperative schedules and plan-ning of reconstructive procedures on the mandible afterresection, surgery or posttraumatic defects.



Knowledge of the distances from surgically encounteredanatomic landmarks may be of assistance in locating theseimportant maxillofacial neurologic structures duringmany procedures. This information may play an evenmore important role in new techniques for minimally in-vasive surgery that are developed. Understanding the lo-cation of these foramina will also assist the clinicians inperforming local anesthetic blocks procedures.

Conclusions

- The most common position of the mental foramen inrelation to the mandibular teeth was in line with thesecond premolar teeth in 47,06 % right and 64,71%left, and in the line between first and second premo-lar teeth in 41,18 % right 29,41 % left.

- In the sagital plane, mean value of the distance fromthe mental foramen to the middle line of the mandi-ble was 24,05 mm right and 24,15 mm left, and themean distance from the distal point of the mandibleto the middle line was 50,35 mm right and 51,20 mmleft.

- The mean distance in the horizontal plane on theskulls from the foramen mental to the anterior pointon the mandibular symphysis from A-P projectionwas 29,41 mm right , 24,80 mm left and 15,15 mmright and 12,85 mm left from the profile projection.

- The mean distance from the mental foramen to theposterior border of the ramus of the mandible was63,7 mm right and 64,45 mm left measured from A-P projection, and 59,40 mm right and 60,65 mm left,measured from the profile projection.

- On the ortopantomogram mean distance measuredfrom the foramen mental to the medial point of thecorpus mandible was 22,56 mm right and 22,17 mmleft and was significantly different when comparedwith the values determined on the skulls

- The mean distance from the foramen mental to theposterior border of the ramus of the mandible was64,29 mm right and 60,67 mm left measured on theortopantomogram and there were no significant dif-ferences compared with the measurements deter-mined on the skulls.

- The mean distance from the upper edge of the mentalforamen to the alveolar crest measured on the skullswas 14,37 mm right and 14,47 mm left and the meandistance from the lover edge of the mental foramen tothe inferior border of mandible was 13,27 mm rightand 13,95 mm left.

- The mean distance from the upper edge of the mentalforamen to the alveolar crest measured on the orto-pantomogram was 17,62 mm right and 17,53 mm leftand was significantly different when compared withthis values determined on the skulls

- The mean distance from the lover edge of the mentalforamen to the inferior border of mandible on the or-topantomogram was 15,22 mm right and 14,61 mmleft and there were no significant differences com-pared with the measurements determined on theskulls.

- Ratio of these values determined as relative verticalposition and relative horizontal position measured onthe ortopantomogram may be used in preoperativeplanning of reconstructive procedures on the mandible





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