One of the most important aspects of behavior management in pediatric dentistry
is pain control (McDonald et al., 2004). Local
anesthesia is still the main technique for pain control in pediatric dental
treatments, when deep operative or surgical procedures are undertaken for the
mandibular primary or permanent teeth, the Inferior Alveolar Nerve (IANB) should
be blocked (McDonald et al., 2004). However, there
is no consensus on the position of the mandibular foramen (MF) in relation to
the occlusal plane in children to realize where the needle tip should be placed
in the standard IANB. Olsen recommended inserting the needle tip below the occlusal
plane for mandibular primary teeth (Olsen, 1956). Benham
(1976) conversely, recommended administering anesthesia to the MF either
at or slightly above the occlusal plane in primary dentition.Benham. Also Hwang
et al. (1990) showed that the position of foramen in children is
more inferoanterior compared with adults (Hwang et al.,
1990). Various researches have been conducted on cephalometric and panoramic
radiographs regarding the position of Tsai (2002, 2004)
and Kanno et al. (2005). Basically, in order
to have a rapid, deep and safe local anesthesia, location of MF in relation
to the occlusal plane should be acquired. As the child grows up, the position
of MF changes. Hence, for a successful mandibular local anesthesia, consideration
to such changes is imperative. Bishara et al. (1990)
showed that dento-facial parameters are bound to ethnic origins.
The objective(s) of this study was to locate the MF relative to the occlusal plane on the panoramic radiographs related to 7-10 year-old children, who were referred to the Mashhad School of Dentistry, Iran, for taking radiography.
MATERIALS AND METHODS
This study was conducted on 200 panoramic radiographs and 200 dental casts related to a total of 200 children (106 girls and 94 boys), who were referred to the Mashhad School of Dentistry, Iran during 2005 through 2007. The subjects were divided into four groups of 7, 8, 9 and 10-year-old children.
|| Calibration of a panoramic image using Planmeca dimaxis classic
||Points of study
Point 1: The most superior anterior point of mandibular canal
Point 2: The deepest point on the anterior border of the ramus
Point 3: The most prominent point on the canine crown
Point 4: The most prominent point on the end-most fully erupted tooth
Point 5: The most prominent inferior point at the angle of mandible
Point 6: The most prominent posterior point on condyle
Point 7: The most prominent posterior point at the angle of mandible
|| Hypothetical Lines
P1:occlusal plane connecting points 3 and 4
P2:perpendicular line to point 2
P3:ramus posterior plane connecting points 6 and 7
P4:mandibular plane tangent to point 5
L:perpendicular line from point 1 to P1
L1:perpendicular line from point 1 to P2
L2:perpendicular line from point 1 to P3
L3:perpendicular line from point 1 to P4
A:internal angle between P3 and P4
To follow ethics, the subjects were selected among the patients who had already referred to the School of Dentistry for radiography; that is, they were not recommended for radiography just for the study. The age range was 7 to 10 years. The criteria that every individual had to meet to be involved in this investigation were listed as normal facial morphology, presence of all posterior teeth in the mouth. Based on the study standard for radiographs, horizontal Frankfort plane was paralleled with the earth-horizon during radiography to avoid chin tilt, and only one technician took all the radiographs. Radiographs with gross distortion and children under orthodontic treatment were excluded from the study.
Radiographic records were obtained using a dental radiography instrument (Orthopantomograph Apparatus, Planmeca 2002, Model cc, Finland) at the Mashhad School of Dentistry. Then the informative consent was obtained from the parents.
Panoramic radiographs were scanned by a high-resolution scanner (600 dpi resolution) (Umax Powerlook, Model 2100, Taiwan) by magnification of 1:1 and the inputs were saved in related files.
In order to have a precise linear measurement of anterior superior point of mandibular canal to the occlusal plane and also for calibration of radiograph magnification, we used the software Planmeca Dimaxis Classic which measures the variables in pixels as default but there is also a capability of conversion into millimeters.
Mesiodistal width of the most posterior mandibular tooth on both sides of each
dental cast was measured in millimeter using a caliper. Thus, two distances
were acquired on both left and right sides to calculate linear measurements
and to calibrate the magnification in the software (RVG Planmeca 2002, Dimaxis
3 2 2) (Fig. 1). The points and the lines of study (Fig.
2, 3) were drawn by the software, with the accuracy of
100th millimeter. The mandibular gonial angles were also calculated on the radiographs
All the quantities were obtained in millimeters and by a single calibrated examiner, examining only five panoramic radiographs daily for prevention of any eye error. In a pilot study on the scans of five panoramic radiographs, the mean and standard deviation were set as 0.5±0.1 mm for duplicate measurements of intra-examiner and it considered being a reflection of intra-examiner reliability.
To evaluate the validity of the method, four skulls were placed in panoramic
head holder (MF and occlusal plane, identified by steel wire, placed at the
lingual and buccal cusp of mandibular posterior teeth, respectively). Then images
were acquired when Frankfort plane of each skull was parallel with the earth-horizon.
The mean and standard deviation were not found to be significantly different
in duplicate vertical and horizontal measurements of lines in the skulls and
on the panoramic radiographs.
The distances from the most anterior superior point of mandibular canal to above, at and below the occlusal plane were recorded as positive, zero and negative whole numbers, respectively. Then, data were analyzed using SPSS (11.5, SPSS Inc., Chicago Ill, USA) and the means were compared with each other by Bivariate-ANOVA and Pearson tests.
A total of 200 children (106 girls and 94 boys) were evaluated in the study described herein. The findings for the left and right sides were compared; consistent with no significant difference in the means of variables (p>0.05).
The distance between the most anterosuperior points of mandibular canal (point 1) to the occlusal plane (L) showed significant difference with both age and sex (p<0.001). The mean of L based on the age and sex have come in Fig. 4 and Table 1.
Also, among the 10-year-old children, MF was observed above and at the occlusal
plane in about 86% and 4%, in that order.
||Distance between point 1 (mandibuar foramen) and occlusal
plane in millimeter (mean values of left side)
||Graphic demonstration compares average distances of L1 and
L2. Vertical line: Average distance (mm), Horizontal line: Age (years old)
||Graphic demonstration compares average distances of L3 based
on sex, Vertical line: Average distances (mm), Horizontal line: Age (years
|| Pearson correlation test
|*Correlation is significant in 0.05 levels, • Correlation
is significant in 0.01 levels, NS: Not significant
The distance from point 1 to the anterior border of ramus (L1) represented
significant difference with age (p<0.01), however, no sex-specific trends
were identified (p>0.05).
In addition, there was a statistical difference between age (p<0.001) and sex (p<0.01) with the distance from point 1 to the posterior border of ramus (L2). Also a significant difference was found between both age and sex with the distance from point 1 to the inferior border of ramus (L3) (p<0.001).
The findings revealed L1 to be greater than L2 in all age-range and both sexes
Fig. 5. The Mean of L3 in 7-10 years old children increased
by 2.8 mm and 4.1 mm in boys and girls, respectively Fig. 6.
Moreover, gonial angle (A) showed significant difference with age (p<0.01)
and no significant difference between the gonial angle and sex was found (p>0.05).
||Graphic demonstration compares average distances of L3 based
on sex, Vertical line: Average distances (mm), Horizontal line: Age (years
The means and the standard deviation of linear and angular measurements and
the results of Analysis of Variance (ANOVA) have come in Table
1. Furthermore, all measurements were tested by Pearson to find the correlations
The position of the mandibular foramen and its importance for a successful inferior alveolar anesthesia has been well documented. The aim of this study was to locate the position of the mandibular foramen in relation to the occlusal plane on the panoramic radiographs of 7-10-year-old Iranian children.
Basically, there are some limitations in the study of mandibular foramen position
on dry skull, such as unknown age and sex, indefinite anatomic landmarks and
mandibular tooth loss. Moreover, distortion of mandibular foramen area on panoramic
radiographs is a primary concern. Afsar et al. (1998)
showed that panoramic radiography was as good as oblique cephalometry for the
location of mandibular foramen. Unlike Harrison (1948)
but similar to Tsai (2004) investigation. The difference
between the location of MF on the left and right sides was not statistically
significant in the present study. However, there was a significant difference
in distance from point 1 to the occlusal plane (L) with age and sex.
We recommend placing the needle tip below the occlusal plane for 7-8-year-old children although in one 8-year-old boy (1% of 7-8-year-olds) point 1 was +4.4 mm (above the occlusal plane), which was probably related to the specific anatomical characteristic of the boy.
We also recommended inserting the needle below the occlusal plane in 9-year-old
boys while the needle tip in 9-year-old girls suggested to be placed slightly
above the occlusal plane, as a result of pre-pubertal growth.
Furthermore, anesthesia should be administered above the occlusal plane in 10-year-old children as MF was observed above and at the occlusal plane in about 86 and 4%, respectively. We found that if the injection is administered below the occlusal plane only 10% of 10 year-old children undergo mandibular teeth anesthesia.
Kanno et al. (2005) found a gradual increase
in distance between the lingual and the occlusal plane in both sexes aged 7
to 10 years. They also recommended inserting the needle tip at least 6 mm above
the occlusal plane for this age range.
Benham (1976) analyzed the distance between the mandibular
foramen and the occlusal plane on lateral cephalometric radiographs in 5-7,
7-9 and 9-11-year-olds, concluded in no significant difference in 7 to 9 years
of age. However, in 9-11-year-olds there was an upward increase in the distance
between the mandibular foramen and the occlusal plane, which was attributed
to the eruption of canines and premolars. In an investigation by Afsar
et al. (1998) no difference was found in linear measurements of the
mandibular foramen and the occlusal plane with age and sex, as opposed to this
In horizontal measurements, L1 was greater than L2 in the four groups of the study.
Mandibular foramen, in our study, maintained a more posterior position to mid-ramus
that was related to the growth of ramus in various directions, agreed with some
other investigations (Benham, 1976; Enlow,
In addition, we found a significant difference between L2 and sex in the four groups, which can be explained by the growth and bone mineralization in the posterior border of the ramus due to genital hormones. There was also a growth spurt in the posterior border of the ramus in girls after the age of 8.
However, Kanno et al. (2005) found no statistical
differences in the distance of foramen to anterior and posterior borders. Tsai
(2004) showed that growth of anterior border of ramus was stable whereas
posterior border of mandible showed growth spurt after the third stage of hellman.
The greatest mean for increase in L1 was observed in 8-9-year-old girls by 1 mm and the least mean in 9-10-year-old boys by 0.05 mm. The growth in the anterior border of the ramus found to be almost constant; however, the posterior border underwent a sudden growth after the age of 8 and 9 in boys and girls, respectively, which might be due to growth of condyle and apposition of the bone in the posterior border of the mandibular ramus and the gonial angle.
The mean of perpendicular distance from point 1 to the lower border of the mandible increased by 2.82 mm in boys and 4.10 mm in girls aged 7-10 years and the greatest increase found to be about 2.05 mm and 2.2 mm in 9-year-old girls and 10-year-old boys, respectively.
The positional changes in vertical direction might be referring to the growth of the ramus and the apposition of the bone in the lower mandibular border.
Mandibular growth is partly associated with the gonial angle. Moreover, growth and development of nasomaxillary complex is related to the vertical growth of ramus resulting in downward rotation of the mandible. Such inclination may lead to anterior open bite which will be compensated compensate with anterior development of the jaws.
Basically, mandibular anterior teeth show more upward trend than canine and
premolar teeth which is followed by alveolar process growth (Enlow,
1982). Simultaneously, gonial angle decreases during transition from mixed
dentition to permanent dention (Tsai, 2002). This pattern
eventually causes posterior downward inclination of the occlusal plane.
In our study, decrease of the gonial angle in 8 to 9-year-olds was as a result of distance increase between foramen and occlusal plane, particularly at the age of 9 years, which caused L to be positive. There was also more posterior downward inclination of occlusal plane in 9 year-old girls than boys.
Increase of gonial angle in this study was observed in 9 to 10-year-olds which
can be associated with vertical growth of the condyle during this age period,
as Bjork (1963).
In general, gonial angle increases and decreases by vertical and sagittal growth
of the condyle, respectively. This study resulted in a negative relationship
between gonial angle and the distances between the most anterosuperior points
of the mandibular canal to each mandibular border. That is, more obtuse gonial
angle more mandibular growth potential is, as Tsia agrees with Tsai
The position of the most superior anterior point of the mandibular foramen on the ramus changes horizontally and vertically which is related to the age and sex. IANB should be administered below and above the occlusal plane in 7-9 and 10-year-old boys, respectively. Also, IANB should be administered below and above the occlusal plane in 7-8 and 9-10-year-old girls, in that order.
We acknowledge gratefully the financial support of the Research vice Deputy at the School of Dentistry, Mashhad University of Medical Sciences.