Anterior Loop of the Mental Nerve

Anterior loop of the mental nerve: amorphological and radiographic study

Dusan V KuzmanovicAlan GT PayneJules A KieserGeorge J Dias

Authors’ affiliations:Dusan V Kuzmanovic, Alan GT Payne,Department of Oral Rehabilitation, School ofDentistry, University of Otago, New ZealandJules A Kieser, Department of Oral Sciences,School of Dentistry, University of Otago,New ZealandGeorge J Dias, Department of Anatomy andStructural Biology, Medical School,University of Otago,New Zealand

Correspondence to:Dr Alan GT PayneDepartment of Oral Rehabilitation School ofDentistry PO Box 647University of OtagoDunedinNew ZealandFaxþ þ64 3 479 5079e-mail: [email protected]

Key words: anterior loop of mental nerve, implant treatment planning, anatomical

dissection, radiography

Abstract: Treatment planning for dental implant patients is often complicated by the

unknown extent of the anterior loop of the mental neurovascular bundle. The aim of this

study was to determine the correlation between the visual interpretation of the panoramic

radiographs and the anatomical dissection findings in a cadaveric sample. Panoramic

radiographs of the 22 randomly selected coronally sectioned human head specimens were

taken using the Scanoras (Soridex, Orinon Corporation Ltd, Helsinki, Finland) radiographic

unit jaw panorama (Programme 001, magnification 1.3) and dental panorama (Programme

003, magnification 1.7) and interpreted by two calibrated observers. Bilateral anatomical

dissection was then performed on all specimens. The anterior loop of the mental canal was

only identified in six panoramic radiographs (27%) (range 0.5–3mm). Therewas a significant

positive correlation between both observers of the radiographs and between the two

radiographic programmes used. Anatomical measurements of the anterior loop of the

mental neurovascular bundle revealed its presence in eight dissected specimens (range 0.11–

3.31 mm;mean 1.20, ± 0.90). Fifty percent of the radiographically observed anterior loops of

themental canal weremisinterpreted by observers with both radiographic programmes and

62% of the anatomically identified loops were not observed radiographically. Clinicians

should not rely on panoramic radiographs for identifying the anterior loop of the mental

nerve during implant treatment planning. However, a safe guideline of 4mm, from themost

anterior point of the mental foramen, is recommended for implant treatment planning, on

the basis of our anatomical findings.

Treatment concepts for the edentulous

mandible using removable implant over-

dentures or fixed implant bridges identify

surgical requests for two to five inter-

foraminal implants, regardless of super-

structure design (Batenburg et al. 1998;

Merickse-Stern et al. 2000). When two

implants are used, for removable over-

dentures, there is lack of consensus on the

inter-abutment distance (12–35mm) with

variation within reports (Naert et al. 1997;

Watson et al. 1997; Wright &Watson 1998;

Naert et al. 1999; Payne& Solomons 2000).

When three, four or five implants are

used for fixed or removable prosthodontic

solutions, the crucial position of the distal

two implants is determined by the essential

surgical reference point of the mental

foramina, and particularly the extent of

the anterior loop of the mental neurovas-

cular bundle (Solar et al. 1994; Rosenquist

1996; Misch 1998). The cantilever length

of the fixed implant bridge, distal to the last

implant, is also dictated by, to a greater

extent, the position of the distal implant

closest to the mental foramen. Addition-

ally, in partially dentate patients, who have

lost mandibular premolar and molar teeth,

themental foramen andmental nerve or its

anterior loop is also the critical surgicalISSN 0905-7161

Copyright r Blackwell Munksgaard 2003

Date:Accepted 24 June 2002

To cite this article:Kuzmanovic DV, Payne AGT, Kieser JA, Dias GJ.Anterior loop of the mental nerve: a morphological andradiographic studyClin. Oral Impl. Res. 14, 2003; 464–471

464

landmark and essential reference point

during treatment planning.

It is acknowledged that surgical trauma

or injury to the mental nerve is possible

during implant surgery in the interforam-

inal area of themandible (Ellies 1992; Ellies

& Hawker 1993). As a result, a number of

studies have reported an incidence of

transient altered sensation from 8.5% to

24% during periods of up to 3–16 months

postoperatively following implant surgery

(Wismeijer et al. 1997; Dao&Mellor 1998;

Bartling et al. 1999; Walton 2000).

There is considerable variation among

researchers of the incidence and extent of


cular bundle. The reported length of the

anterior loop ranged as little as 0.5 mm in

some patients (Rosenquist 1996) and as

much as 10mm in others (Rothman 1998).

Several methods and techniques for identi-

fying the extent of the anterior loop of the

mental neurovascular bundle have been

proposed using panoramic radiographs,

computed tomography, and determination

of the anterior loop during surgery using a

curved explorer (Rothman 1998; Misch

1999). While intraoral (periapical) radio-

graphs have not been recommended for

preoperative assessment of the extent of the

anterior loop, there have been some at-

tempts by researchers to correlate visuali-

zation of these radiographs with anatomic

reality (Bavitz et al. 1993; Mardinger et al.

2000). Bavitz et al. (1993) investigated the

path of the mental nerve in a cadaveric

sample and compared its anatomywith this

type of radiographic interpretation. They

reported that the maximum length of the

anterior loop based on anatomicalmeasure-

ments was 1mm. In contrast, the average

radiographic loop was 2.5mm for a dentate

group and 0.6 mm for an edentulous group.

Itwas apparent that therewas a tendency to

overestimate the extent of the anterior loop

during these radiographic examinations.

Mardinger et al. (2000) concluded that

there was no correlation between the

anatomical intraosseous path of the mental

nerve in 46 hemisected cadaveric mand-

ibles and the radiographic interpretation of

periapical radiographs. These authors re-

ported the presence of the anterior loop in

28% of dissected specimens (range 0.4–

2.19mm), and concluded that the periapi-

cal radiographs of the anterior loop of the

mental nerve in cadaver mandibles do not

disclose the true ramification of the inferior

alveolar nerve to the mental and incisive

nerve.

Panoramic radiography has been sug-

gested and used for diagnostic purposes

in implantology (Lekholm & Zarb 1985;

Schwartz et al. 1992; Truhlar et al. 1993;

Misch 1999; Bartling et al. 1999; Walton

2000). However, there is paucity in docu-

mented research attempting to correlate

anatomical dissection findings with these

radiographic views. The only study that has

attempted to correlate anatomic measure-

ments of the extent of the anterior loop of

the mental neurovascular bundle with

actual panoramic radiographic measure-

ments was by Arzouman et al. (1993).

The extent of the anterior loop was

measured directly on 25 skulls, using

polyethylene tubing that was ‘placed into

the anterior loop and the distance the tube

extended beyond the anterior border of the

mental foramen was recorded’’. An average

length of the anterior loop was 6.95mm

identified on these anatomical measure-

ments. On the other hand, in radiographic

measurements, without radiographic mar-

kers, the average length of the loop was

2.69mm (Panelipse) and 2.75mm (Orthor-

alix). The mean anterior loop lengths,

identified in radiographs with radiopaque

markers, were 4.17mm (Panelipse) and

4.64mm (Orthoralix). There have been

no reports published to date evaluating

the predictability of panoramic views using

Scanoras (Soridex, Orinon Corporation

Ltd. Helsinki, Finland) jaw or dental

panoramas for identifying the anterior loop

of the mental neurovascular bundle.

The aim of the present study was to

determine if a correlation existed between

the anatomically dissected path of the

mental neurovascular bundle in a cadaver

sample and the radiographically estimated

path of the mental canal using a rotational,

narrow-beampanoramic imaging Scanoras

radiographic unit.

Materials and methods

Twenty-two coronally sectioned human

head specimens, fixed in formalin, were

randomly selected from the collection of

the Department of Anatomy and Structural

Biology, University of Otago, Dunedin,

New Zealand. The specimens were all

from people of Caucasian descent.

Characteristics of the study sample are

shown in Table 1. The mandibular residual

ridge morphology of the edentulous speci-

mens was classified (Cawood & Howell

1988) during anatomical dissection.

Radiographic evaluation

The specimens were placed on a custom-

made plastic platform secured to the chin

brace of the Scanoras machine. The speci-

mens were accurately positioned with the

guidance of light lines for the mid-sagittal,

frontal, and horizontal planes, correctly

placed relative to the anatomical land-

marks. Jaw panorama using Scanora Ima-

ging Programme 001 (1.3 magnification),

and dental panorama using Scanora Ima-

ging Programme 003 (1.7 magnification)

were taken with the recommended techni-

que. The specimens were exposed with

Kodak T.Mat G/RA Panoramic (Eastman

Kodak Company, Rochester, NY, USA)

films and with the use of a single Lanex

Fine screen installed in the back of the

cassette. The Scanoras X-ray machine was

operated at 66kVp, 10mA, for 13 s. The

films were processed in the ALL PRO 100-

L (ALL PRO Imaging Corporation, New

York, NY, USA) automatic processor.

These radiographs were observed, prior to

anatomical dissection, by two independent

observers under standard viewing condi-

tions. Observers classified the radiologic

appearance of themental foramina into four

types (Yosue & Brooks 1989): Type I, a

continuous type in which the mental canal

was connected to the mandibular canal;

Table 1. Characteristics of the study sample

Number ofspecimens

Gender (%) Age range Mean age

F M

Edentulous 14 50 50 71–93 80 (SD 7.79)Partially edentulous 8 37.5 62.5 64–88 71 (SD 8.15)

Total 22 45.45 54.54 64–93 77 (SD 8.86)

Kuzmanovic et al . Anterior loop of the mental nerve

465 | Clin. Oral Impl. Res. 14, 2003 / 464–471

Type II, a separated type in which the

mental canal does not show continuity

with the mandibular canal; Type III, a

diffuse type in which the foramina could

be identified but with indistinct borders;

Type IV, an unidentified type in which the

mental foramina could not be identified on

the panoramic radiographs. The extent of

the anterior loop of themental canal of each

radiograph was estimated by each observer

by measuring the shortest distance from

the two lines passing through the most

anterior point of the mental foramen and

the most anterior point of the mental canal

to the nearest 0.5mm (Fig. 1). A Scanoras

Soredex-Finndent ruler with graduated

measurements, according to the respective

magnification, was used.

Anatomical evaluation

The mandibles of all specimens were

excised from the specimen heads by sec-

tioning the ramus. The canines and pre-

molars were extracted in the partially

edentulous specimens. The soft tissue of

each mandible was dissected and the

mental foramen and mental neurovascular

bundle were identified. An osteotomy with

a radius of 2 cm was made on each

mandible. Firstly, using a round bur No.

1, holes were drilled through the cortex.

Subsequently, these holes were connected

with a fissure bur No. 2 and the cortex was

removed ‘‘en block’’. The osteotomy was

extended 1 cm anteriorly, from 0.5mm

above the point of most anterior concavity

of themental foramen, parallel to the lower

border of the mandible, and 1 cm poster-

iorly, from the point of deepest posterior

concavity of the mental foramen. The

cancellous bone was then curetted using a

scaler and, in some difficult cases, a No. 2

round bur was used. The bone quality in

the edentulous mandibles was classified

during these procedures (Lekholm & Zarb

1985). After exposure of the incisive and

the inferior neurovascular bundles, photo-

graphs with scales in place were takenwith

a Nikon E2S digital camera. The images

were taken from the superior lingual side of

the mandibles at a 451 angle. This orienta-

tion was maintained for imaging of every

specimen. The rationale for the lingual

approach was to maintain the accurate

three-dimensional anatomical relationship

between the neurovascular bundle and the

bone. The Scion Image, Beta 4.0.2 (Scion

Corporation, Frederick, Maryland, USA)

programme was used to draw two lines,

x and y line (Fig. 2). The x line was

constructed through point a (point of

deepest anterior concavity of the mental

foramen), parallel to the outer cortex of the

mandible. The y line was also drawn

through point a. The value of the angle

formed by the two lines (x and y) drawn

through the a point was 90o. The length of


cular bundle was obtained by measuring

the nearest distance from the reference

point b (point of the ramification between

the incisive and mental branches) to the

line y (reference point c). The diameter of

the incisive neurovascular bundle was

measured as close to the ramification as

Fig. 1. Reference points of measurement for the anterior loop of the mental canal. a – point of deepest anterior

concavity of the mental foramen; b – point of the most anterior point of the mental canal : x line and y drawn

through point a and point b.

Fig. 2. Reference points of measurement for the anterior loop of the mental neurovascular bundle. a – point of

deepest anterior concavity of the mental foramen; x line and y drawn through point a; b – point of the

ramification between the incisive and mental branches; c – nearest point on y line from the point b; d – the

mental neurovascular bundle; e – the mental nerve; f – the incisive nerve.



possible also using the Scion Image, Beta

4.0.2 programme.

Data and statistical analysis

All calculations were performed with SPSS

statistical software. The degree of agree-

ment between the different examiners and

programmes readings was examined using

the Kappa statistics for categorical mea-

sures, and the Pearson correlation coeffi-

cient test for continuous measures.

Results

The most common radiographic appear-

ance of the mental foramen (Yosue &

Brooks 1989 classification), as determined

on both panoramic radiographs jaw pano-

rama (Programme 001) and dental pano-

rama (Programme 003) by the two

observers, was continuous type (Type I)

with an overall prevalence of 44%, fol-

lowed by the separated type (Type II, 31%).

The mental foramen was not able to be

identified in 12% of radiographs, while the

diffuse type (Type III) was found in 13% of

radiographs (Table 2). Intraobserver agree-

ment for each of the two observers using

the two radiographic programmes (Pro-

gramme 001 and Programme 003) showed

almost perfect agreement (observer 1: 0.967

(P<0.01) and observer 2: 0.890 (P<0.01).

Agreement between the two radiographic

programmes was moderate to substantial

(Programme 001 and 003, 0.575 and 0.650

respectively (P<0.01).

A comparison of the extent of the

anterior loops of the mental neurovascular

bundle revealed by the radiographic mea-

surements and anatomical dissection is

presented in Fig. 3. The anterior loop of

themental canalwas observed to be present

in six radiographs (27%) by both observers

and ranged from 0.5 to 3mm in length

(mean 1.50;þ 0.09). The length of the

anterior loop of themental canal was either

over- or underestimated in all radiographs.

A significant positive correlationwas found

between the two observers and between the

two radiographic programmes (Table 3).

Following anatomical dissection of the

cadaver specimens, measurements of the

anterior loop of the mental neurovascular

bundle revealed its presence on both the left

and right sides in eight dissected specimens

(37%) (Fig. 3). The extent of the anterior

loop ranged from 0.11 to 3.31mm (mean

1.20;þ 0.90). The Pearson correlation

coefficient between the measurements of

the left and right sides of the mandible

indicated significant agreement (0.954,

P<0.01). The results of Kappa statistics

Table 2. Radiographic appearance of the mental foramina (classification according to Yosue& Brooks, 1989)

Observer 1Programme001 (%)




Overallprevalence

(%)

Type I 32 32 57 54 44Type II 43 40 23 18 31Type III 14 14 11 14 13Type IV 11 14 9 14 12

Fig. 3. The individual values (by specimen) of the extent of the anterior loop of the mental neurovascular bundle obtained from the panoramic measurements and

anatomical dissection.



showed only slight agreement between

radiographic interpretation of the anterior

loop and measurements of the anatomical

dissection (0.101).

The most common bone quality with

Lekholm&Zarb classificationwas Type III

(36%), followed by type II (32%). Type I

and Type IV were less common, 9% and

23%, respectively. With the Cawood &

Howell classification bone quantity, Type

6 was observed in 16 specimens (57%),

followed by Type 5 found in eight cadavers

(29%) and Type 4 in four cadavers (14%).

Pearson correlation analyses showed a

negative correlation between both the bone

quality and quantity and the radiographic

extent of the anterior loop (Table 4).

Anatomical dissection also revealed that

themean diameter of the incisive nervewas

1.80,þ0.46 (range 0.9–2.53mm).

Discussion

Our study has shown that the reliability of

the panoramic radiographs, when planning

for implant placement in the interforaminal

region of the mandible, may be limited.

The radiographic length of the anterior loop

of themental canal can only bemeasured in

radiographs where the entire course of the

mental canal is visualized, from the man-

dibular canal through the mental foramen

(Type I, or continuous Type, Yosue &

Brooks classification (1989)). The results

of our study show that on respective

panoramic radiographs, Type I was identi-

fied in average of 44% of the specimens

(Table 2). These findings confirm the

previous ones of Yosue & Brooks (1989).

Furthermore, our findings showed that the

anterior loop of the mental canal was

observed in six radiographs (27%), inwhich

the mental foramen was identified as Type

I, in both radiographic images (range 0.5–

3mm in length).

It is of interest that the length of the

anterior loop of the mental canal, when

identified radiographically and confirmed

anatomically, was either over- or under-

estimated. One of the disadvantages of

panoramic images is its geometric distor-

tion of the anatomical structures (Grondahl

et al. 1996). Distortions of the panoramic

images in the horizontal and vertical plane,

especially in the anterior region, depend on

the anatomical variations between arch

curvatures and on accurate patient posi-

tioning in the radiographic machine (Schiff

et al. 1986; Truhlar et al. 1993). Therefore,

difficulty with positioning the specimens

accurately probably resulted in either over-

or underestimation of the length of the

anterior loop of the mental canal. In

contrast to our results, Arzouman et al.

(1993) showed a clear tendency to under-

estimate the extent of the anterior loop in

radiographic examinations without radio-

paque markers. The differences may be

explained by the fact that Arzouman et al.

(1993) used dry human mandibles and

radiopaquemarkers to determine the length

of the anterior loop of the mental canal.

Radiopaque markers could penetrate the

mental canal or enter the incisive canal,

resulting in overestimation of the length of

the mental canal.

The true diagnostic accuracy of the jaw

panorama and dental panorama was eval-

uated in our dissection of cadaveric speci-

mens. The mean anatomical incidence of


cular bundle in our study was 37% (range

0.11–3.31mm). This is similar to those of

Mardinger et al. (2000), who reported the

presence of the anterior loop in 28% of

dissected specimens (length range 0.4–

2.19mm). Although a low incidence of

the anterior loop reported by Bavitz et al.

(1993) and Rosenquist (1996) was in

accordance with our study, the results

of the anatomical measurements were

somewhat different. Bavitz et al. (1993)

reported the maximum length of the

anterior loop, based on anatomical mea-

surements in a cadaveric sample, to be 1

mm. In a study performed unilaterally in

58 patients, Rosenquist (1996) reported the

maximum length of the anterior loop to

be 1mm. Differences in the length of the

anterior loop reported in these studies

and the present study can be explained by

different experimental techniques. The

main advantage of our ‘lingual-approach’

technique is that the three-dimensional

anatomy of the mental neurovascular

bundle and mental foramen is maintained

and inaccuracies of anatomical measure-

ments are minimized. Our results do

however differ widely from those reported

by Arzouman et al. (1993). A critical

review of that work showed that the

authors estimated that the average dia-

meter of the incisive canal was 2mm;

hence they used radiopaque markers and

flexible tubing that were ‘approximately

2mm in diameter’. They also suggested

that the incisive canal was thinner than the

inferior alveolar canal. Our study shows

that the incisive neurovascular bundle, near

the ramification, can in fact be as wide as

2.53mm in diameter. Furthermore, our

observation was that the walls of the

mental canal can be very porous and

thin in specimens with advanced bone

resorption. Therefore, the marker inserted

Table 3. Inter - and intraobserver correlation of the radiographic measurements; (P001) Scanora Programme 001; (P 003) Scanora Programme003

Observer 1–P 001Observer 1–P 0 03

Observer 2–P 001Observer 2–P 003



Radiographic interpretation of the anterior loop 0.991 (P<0.01) 0.981 (P<0.01) 0.943 (P<0.01) 0.917 (P<0.01)

Table 4. Bone quality and bone quantity, with radiographic interpretation analysed usingthe Pearson correlation test; (P 001) Scanora programme 001; (P 003) Scanora programme003

Observer1–P 001

Observer1–P 003

Observer2–P 001

Observer2–P 003

Bone quality with radiographic interpretationof the anterior loop

� 0.416 � 0.416 � 0.416 � 0.416

Bone quantity with radiographic interpretationof the anterior loop

� 0.303 � 0.307 � 0. 304 � 0.304



into the mental canal can easily penetrate

the mental canal or enter the incisive

canal. Consequently, other anatomical

structures can be accidentally measured

rather than the anterior loop of the mental

canal. The significance of their findings

may be questionable.

There are undoubtedly clear differences

between the anatomical and panoramic

measurements of the anterior loop. Data

analyses showed that 50% of the radio-

graphically observed anterior loops of the

mental canal were misinterpreted in both

radiographic programmes and by both ob-

servers, and 62% of the anatomically

identified loops was not observed radio-

graphically. The same inaccuracy of radio-

graphic measurements was found when

using both jaw panorama (Scanora

Programme 001) and dental panorama

(Scanora Programme 003). Therefore, these

findings indicated low specificity and

low sensitivity of both panoramic pro-

grammes regardless of their magnification.

Poor bone quality and bone quantity in the

edentulous specimens had negative correla-

tion with both radiographic and anatomical

extent of the mental canal or mental

neurovascular bundle. Radiographic visua-

lization of the anterior loop of the mental

canal, especially in edentulous patients,

may be adversely affected by poor

bone quality. This is of significance to

clinicians during implant treatment plan-

ning. The negative correlation between

the radiographic interpretations of the

mental canal in specimens could be due

to the decreased porosity of the mental

canal walls due to poor bone quality.

Furthermore, resorption of the residual

alveolar ridges in edentulous patients

may have progressed to such an extent

causing resorption of the mental canal

and exposure of the mental neurovascular

bundle. This may explain the negative

correlation between the poor bone quantity

and anatomical presence of the mental

nerve.

Intraoral and panoramic radiographs of

the area for edentulous and partially eden-

tulous patients give two-dimensional views

(Jacobs & van Steenberghe 1998; Serhal

et al. 2001). It is acknowledged that there

are proposals of advantages in the use of

computerized tomography to clarify the

mandibular canal and the anterior loop of

the mental neurovascular bundle (Roth-

man 1998; Serhal et al. 2001). One surgical

approach that has been proposed, aided by

preoperative panoramic radiographs during

treatment planning, can be the tilting of the

posteriormandibular implants (Krekmanov

et al. 2000). If the mandibular implants are

tilted approximately 25–351 in the area of

the anterior loop of the mental nerve, then

the prospective research has indicated, at

least in edentulous patients that the

patients, can gain a mean distance of

6.5mm of prosthesis support (Krekmanov

et al. 2000). This described surgical tech-

nique of his suggests that the implant can

be placed ‘close’ to the anterior wall of the

mental neurovascular bundle and parallel

to it, and then tilted mesially by 25–351 to

accommodate the anterior loop. The results

of our study indicated that Scanoras

panoramic radiographsmay not be accurate

in determining the tilt of the implants

because of its low sensitivity and specifi-

city. Therefore, tilting could only be

determined clinically or with the aid of CT.

Conclusions

Clinicians should not rely on panoramic

radiographs for identifying the anterior loop

of the mental nerve during implant treat-

ment planning. However, a safe guideline

of 4mm, from the most anterior point of

the mental foramen, is recommended for

implant treatment planning on the basis of

our anatomical findings.

Acknowledgements: The authors

wish to acknowledge the assistance

of the staff of the Clinical Overdenture

Research Project (CORP), School

of Dentistry, and the Department of

Anatomy and Structural Biology, School

of Medicine, University of Otago,

Dunedin, New Zealand. Radiographic

Supplies Ltd, Christchurch, New

Zealand are thanked for their

generous supply of radiographic

films for our study. We also thank

Professor Brian Monteith for allowing

the project to be conducted within the

Department of Oral Rehabilitation,

University of Otago, Dunedin, New

Zealand, in partial fulfilment of a

Master of Dental Surgery

(Prosthodontics).

Resume

Le plan de traitement pour les patients desirant des

implants est souvent complique par la meconnais-

sance de l’emplacement de la boucle anterieure du

nerf dentaire inferieur. Le but de cette etude a ete de

determiner la relation entre l’interpretation visuelle

de radiographies panoramiques et les decouvertes

effectuees par dissection anatomique sur cadavres.

Des radiographies panoramiques de 22 humains ont

ete prises par Scanoras, panoramique machoire

(programme 001, grandissement 1,3) et panoramique

dentaire (programme 0,03, grandissement 1,7) et

interpretees par deux observateurs calibres. La

dissection anatomique bilaterale a ensuite ete effec-

tuee. La boucle anterieure du canal n’a seulement ete

identifiee que dans six radiographies panoramiques

(27%)(de 0,5 a 3 mm). Il y avait une relation positive

significative entre les deux observateurs des radio-

graphies et entre les deux programmes de radio-

graphies utilisees. Les mesures anatomiques de la

boucle anterieure ont montre leur presence dans six

specimens disseques ( de 0,11 a 3,31 mm; moyenne

1,20±0,90). Cinquante % des boucles anterieures

observees radiographiquement etaient mal interpre-

tees par les observateurs avec les deux programmes

de radiographies, et 62 % des boucles identifiees

anatomiquement n’etaient pas decelables radiogra-

phiquement. Les cliniciens ne devraient pas trop se

baser sur les radiographies panoramiques pour

identifier la boucle anterieure du nerf mentonnier

durant le plan de traitement implantaire. Cependant,

une conduite raisonnable et preventive serait de

laisser 4 mm a partir du point le plus anterieure du

foramen mentonnier lors du plan de traitement

implantaire.

Zusammenfassung

Die Schleife des Nervus mentalis: Eine morpholo-

gische und radiologische Studie.

Die Behandlungsplanung mit Zahnimplantaten

wird am Patienten wegen dem unbekannten Verlauf

und der variablen Ausdehnung des Nervgefassbun-

dels vom Nervus mentalis oft erschwert. Das Ziel

dieser Studie war, eine Korrelation zu finden

zwischen der visuellen Interpretation des Panora-

marontgenbildes und den effektiven anatomischen

Verhaltnissen auf Schnitten von Leichenpraparaten.

Man stelltemit dem Rontgengerat Scanoras von 22

zufallig ausgewahlten menschlichen Schadelprapar-

aten nach zwei verschiedenen Programmen (Pro-

gramm 001, Vergrosserung 1.3 und Programm 003,

Vergrosserung 1.7) Panoramaaufnahmen her und

liess sie von zwei kalibrierten Untersuchern inter-

pretieren. Anschliessend stellte man beidseits der

Schadel ein anatomisches Schnittpraparat her. Die

vordere Schleife des Mentalkanals konnte nur auf 6

Panoramarontgenbildern (27%) (Bandbreite 0.5–

3mm) bestimmtwerden. Man fand eine signifikante

positive Korrelation zwischen den beiden Untersu-

chern der Rontgenaufnahmen und auch zwischen

den zwei verschiedenen verwendeten Rontgenpro-

grammen.Die anatomische Vermessung des vorderen

Bogens des Gefassnervenbundels vom N. mentalis



gelang in 8 Praparaten (Bandbreite 0.11-3.31mm;

Mittelwert 1.20þ 0.90). 50% der radiologisch beo-

bachteten vorderen Bogen desMentalkanaleswurden

von den Untersuchern mit beiden Rontgenprogram-

men falsch interpretiert, und 62% der anatomisch

freigelegten Bogen konnten rontgenologisch nicht

nachgewiesen werden. Der Kliniker sollte sich also

bei der Implantatplanung und der Identifikation des

vorderen Bogens des N. mentalis nicht auf Panor-

amarontgenbilder verlassen. Man empfahl jedoch fur

die Implantatplanung auf Grund dieser anato-

mischen Erkenntnisse ein Sicherheitsabstand von

4mm vom vordersten Punkt des Foramen mentale.

Resumen

La planificacion de los pacientes de implantes

dentales es a veces complicada por el desconoci-

miento de la extension de la curva del paquete

neurovascular del nervio mentoniano. La intencion

de este estudio fue determinar la correlacion entre la

interpretacion de las radiografıas panoramicas y los

hallazgos en la diseccion anatomica en muestras

cadavericas. Se tomaron radiografıas panoramicas

de los 22 especımenes seleccionados de cabezas

humanas seccionadas coronalmente usando la uni-

dad radiografica Scanoras, panorama mandibular

(Programa 001, magnificacion 1.3) y panorama

dental (Programa 003, magnificacion 1.7) y se

interpretaron por dos observadores calibrados. La

curva anterior del canal mentoniano fue identificado

solo en 6 radiografıas panoramicas (27%) (rango 0.5 –

3 mm). Hubo una correlacion positiva entre los dos

programas radiograficos usados. Las mediciones

anatomicas de la curva anterior del paquete neuro-

vascular mentoniano revelaron su presencia en 8

especımenes diseccionados (rango 0.11 – 3.31 mm;

media 1.20 ± 0.90). Se malinterpretaron por los

observadores el 50% de las curvas anteriores

observadas radiograficamente con ambos programas

radiograficos y el 62% de las curvas identificadas

anatomicamente no se observaron radiografica-

mente. Los clınicos no pueden confiar en las

radiografıas panoramicas para identificar la curva

anterior del nervio mentoniano durante la planifica-

cion del tratamiento de implantes. De todos modos,

se recomienda un margen seguro de 4 mm, desde el

puntomas anterior del foramen dental, basandose en

nuestros hallazgos anatomicos.

References

Arzouman, J.M., Otis, L., Kipnis, V. & Levine, D.

(1993) Observation of the anterior loop of

the inferior alveolar canal. International

Journal of Oral and Maxillofacial Implants 8:

295–300.

Bartling, R., Freemand, K. & Kraut, R.A. (1999) The

incidence of altered sensation of the mental nerve

after mandibular implant placement. Interna-

tional Journal of Oral Maxillofacial Surgery 14:

1408–1410.

Batenburg, R.H.K., Meijer, H.J.A., Raghoebar,

G.M., Raghoebar, G.M. & Vissink, A. (1998)

Treatment concept for mandibular overdentures

supported by endosseous implants: a literature

review. International Journal of Oral and Max-

illofacial Implants 13: 539–545.

Bavitz, B.J., Harn, D.S., Hansen, A.C. & Lang, M.

(1993) An anatomical study of mental neurovas-

cular bundle–implant relationship. International

Journal of Oral and Maxillofacial Implants 8:

563–567.

Cawood, J. &Howell, R.A. (1988) A classification of

the edentulous jaws. International Journal of Oral

Maxillofacial Surgery 17: 232–236.

Dao, T.T. & Mellor, A. (1998) Sensory disturbances

associated with implant surgery. International

Journal of Prosthodontics 11: 462–469.

Ellies, L. (1992) Altered sensation following

mandibular implant surgery: a retrospective study.

Journal of Prosthetic Dentistry 68: 664–671.

Ellies, L.G. & Hawker, P.B. (1993) The prevalence

of altered sensation associated with implant

surgery. International Journal of Oral and Max-

illofacial Implants 8: 674–679.

Grondahl, K., Ekestubbe, A. & Grondahl, H.-G.

(1996) Radiography in Oral Endosseous Pros-

theses. Goteborg, Sweden: Nobel Biocare.

Jacobs, R. & van, Steenberghe D. (1998) The guide

for radiographic planning and assessment of

implants. Belgium: Catholic University, Leuven

Press.

Krekmanov, L., Kahn,M., Rangert, B.& Lindstrom,H.

(2000) Tilting of posterior mandibular and max-

illary implants for improved prosthesis support.

International Journal of Oral and Maxillofacial

Implants 15: 405–414.

Lekholm, U. & Zarb, G.A. (1985) Patient selection

and preparation. In: Branemark, P.I., Zarb, G.A.

& Albrektsson, T., eds. Tissue Integrated Pros-

theses – Osseointegration in Clinical Dentistry,

199–209. Chicago, USA: Quintessence Publish-

ing Co., Inc.

Mardinger, O., Chaushu, G., Arensburg, B., Taicher,

S. & Kaffe, I. (2000) Anterior loop of the mental

canal: an anatomical–radiologic study. Implant

Dentistry 9: 120–123.

Mericske-Stern, RD. (1998) Treatment outcomes

with implant-supported overdentures: Clinical

consideration. Journal of Prosthetic Dentistry 79:

66–73.

Mericske-Stern, R.D., Taylor, T.D.& Belser, U. (2000)

Management of the edentulous patient. Clinical

Oral Implant Research 11 (Suppl.): 108–125.

Misch, C.E. (1999) Contemporary implant dentis-

try. In: Misch, C.E., ed. Root form surgery in

the edentulous mandible: stage I implant inser-

tion, 2nd edition, 349–350. St Louis, USA: CV

Mosby Co.

Naert, I.E., Gizani, S., Vuylsteke, M. & van

Steenberghe, D. (1999) A 5-year prospective

randomised clinical trial on the influence of

splinted and unsplinted oral implants retaining a

mandibular overdenture: prosthetic aspects and

patient satisfaction. Journal of Oral Rehabilita-

tion 26: 195–202.

Naert, I.E., Hooge, M., Quirynen, M. & van

Steenberghe, D. (1997) The reliability of im-

plant-retained hinging overdentures for the fully

edentulousmandible. Anup to 9-year longitudinal

study. Clinical Oral Investigations 1: 119–124.

Payne, A.G.T. & Solomons F, Y. (2000) Mandibular

implant-supported overdentures: a prospective eva-

luation of theburdenof prosthodonticmaintenance

with 3 different attachment systems. Interna-

tional Journal of Prosthodontics 13: 246–253.

Rosenquist, B. (1996) Is there an anterior loop of the

inferior alveolar nerve? International Journal of

Periodontics and Restorative Dentistry 16: 41–45.

Rothman, S.L.G. (1998) Dental applications of

computerized tomography: surgical planning for

implant placement. In: Rothman, S.L.G., ed.

Computerized tomography of the mandible, 1st

edition, 43–47. Chicago: Quintessence Publishing

Co., Inc.

Schiff, T., D’Ambrosio, J., Glass, B.J., Langlais, R.P.

& McDavid, W.D. (1986) Common positioning

and technical errors in the panoramic radiography.

Journal of American Dental Association 113:

422–426.

Serhal, C.B., van Steenberghe, D., Quirynen, M. &

Jacobs, R. (2001) Localisation of the mandibular

canal using conventional spiral tomography: a



human cadaver study. Clinical Oral Implant

Research 12: 230–236.

Schwartz, M.S., Rothman, S.L.G., Chafetz, N. &

Stauts, B. (1992) Preoperative diagnostic radiology

for the tissue integrated prosthesis. In: W.R.,

Laney & D.E., Tolman, eds. Tissue integration

oral, orthopedic, and maxillofacial reconstruc-

tion, 68–79. Chicago: Quintessence Publication

Co., Inc.

Solar, P., Ulm, C., Fre, G., Frey, G. & Matejka, M.

(1994) A classification of the intraosseous paths of

the mental nerve. International Journal of Oral

and Maxillofacial Implants 9: 339–344.

Truhlar, R.S., Morris, H.F. & Ochi, S. (1993) A

review of panoramic radiography and its potential

use in implant dentistry. Implant Dentistry 2:

122–130.

Walton, J.N. (2000) Altered sensation associated

with implants in the anterior mandible: a pro-

spective study. Journal of Prosthetic Dentistry 83:

443–449.

Watson, R.M., Jemt, T., Chai, J., Harnett, J., Heath,

M.R. & Hutton, J.E., et al. (1997) Prosthodontic

treatment, patient response, and the need for

maintenance of complete implant-supported over-

dentures: an appraisal of 5 years of prospective

study. International Journal of Prosthodontics 10:

345–354.

Wismeijer, D., van Waas, M.A., Vermeeren, J.I. &

Kalk, W. (1997) Patient’s perception of sensory

disturbances of the mental nerve before and after

implant surgery: a prospective study of 110

patients. British Journal of Oral andMaxillofacial

Surgery 35: 254–259.

Wright, P.S. & Watson, R.M. (1998) Effect of

prefabricated bar design with implant-stabilized

prostheses on ridge resorption: a clinical report.

International Journal of Oral and Maxillofacial

Implants 13: 77–81.

Yosue, T. & Brooks, L.S. (1989) The appearance of

mental foramina on panoramic radiographs. I.

Evaluation of patients. Oral Surgery Oral Medi-

cine Oral Pathology 68: 360–364.



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Anterior Loop of the Mental Nerve