Download Evaluation of Distances between the Mandibular Teeth and the

10.5005/jp-journals-10021-1110
RESEARCH ARTICLE
Vikrant Bhandari et al
Evaluation of Distances between the
Mandibular Teeth and the Alveolar Process in
Himachali Population with Normal Occlusion
1
Vikrant Bhandari, 2Anil Singla, 3Vivek Mahajan, 4Harupinder Singh Jaj, 5Vishal Seth
ABSTRACT
Introduction: The aim of this study was to evaluate the distances between the mandibular permanent teeth and the alveolar process in
Himachali population with normal occlusion.
Materials and methods: Fifty mandibular casts from untreated subjects of Himachal population were selected who had permanent dentition. A
computer program was used to calculate the distances between the dental reference points and the alveolar process for each tooth. The mean
values were then compared to the normal values by applying the Student t-test at a significance level of 0.05.
Results: The results showed a progressive increase of these distances from the anterior region (incisors) to the posterior region (molars), from
0.00 to 2.46 mm.
Conclusion: Himachali population with normal occlusion have more lingual crown positions for the incisors, premolars and molars compared
with Americans with normal occlusion.
Keywords: WALA ridge, FA point, Glass beads.
How to cite this article: Bhandari V, Singla A, Mahajan V, Jaj HS, Seth V. Evaluation of Distances between the Mandibular Teeth and the
Alveolar Process in Himachali Population with Normal Occlusion. J Ind Orthod Soc 2012;46(4):300-303.
INTRODUCTION
The form of the mandibular dental arch is considered one of
the main references during treatment, as it is an important
factor for the stability of orthodontic treatment.1 Andrews and
Andrews2 described an anatomic ridge on the mandibular
alveolar process that delimited the soft tissue band
immediately superior to the mucogingival junction. This
structure was called the WALA ridge, so that the teeth must
be aligned according to the appropriate distance between the
dental crowns (FA point) and WALA ridge. Thus, preservation
of the form and dimensions of the dental arches must be one
of the first object of orthodontic treatment.
MATERIALS AND METHODS
Fifty mandibular dental casts of Himachal population with
age group from 13 to 21 years. were selected with teeth in
1
Postgraduate Student, 2Professor and Head, 3,5Senior Lecturer, 4Reader
Department of Orthodontics, Himachal Dental College, Mandi
Himachal Pradesh, India
1-5
Corresponding Author: Vikrant Bhandari, Postgraduate Student
Department of Orthodontics, Himachal Dental College, Mandi, Himachal
Pradesh, India, e-mail: [email protected]
Received on: 22/2/12
Accepted after Revision: 18/7/12
300
occlusion except for third molars as the following inclusion
criteria:
1. All the patients had the permanent dentition.
2. All the patients had the natural occlusion.
3. All the patients had no previous history of orthodontic
treatment.
According to the method used by Trivino et al3 a red glass
bead was glued to the buccal aspect of each tooth, simulating
the FA point at the center of the clinical crowns of the incisors,
canines, and premolars and at the buccal groove of the molars
(Fig. 1). Then, a black glass bead was glued and positioned on
the anatomic line of the WALA ridge (Will Andrews and Larry
Andrews), adjacent to the FA point.
After bonding the glass beads, the dental casts were
digitized on a scanner (Scanjet 6100C, Hewlett-Packard, Palo
Alto, Calif), and images with 300-dpi resolution in TIFF
(Tagged Image File Format) format were obtained (Fig. 2).
The correct position of the dental cast on the scanner was
established with millimeter paper. The dental cast was placed
in the rectangle’s center, so that the posterior edge of the
models would be parallel to the horizontal lines and the middle
dental line parallel to the vertical lines. The arch images of
the 50 mandibular dental casts were divided into right and left
sides, obtaining 100 semiarches that were projected on a flat
computer screen with the software Image J (Java, Sun
Microsystems, Palo Alto, California). With this software, the
distances between the red and black glass beads could be
calculated, indicating the linear measurements between the
FA points and the WALA ridge, and establishing the horizontal
JAYPEE
JIOS
Evaluation of Distances between the Mandibular Teeth and the Alveolar Process in Himachali Population with Normal Occlusion
relationship of the clinical crowns to the alveolar bone. This
distance was measured from a point determined on the inner
border of the red glass bead (the border nearest to the buccal
aspect of the tooth) to a specific point of the black bead, which
was the next glass bead border to the alveolar ridge for the
first and second molars and the second premolar. For the first
premolars, canines and incisors, the most external border of
the black bead was selected. After obtaining these measurements for the first premolars, canines and incisors, 2 mm was
subtracted from these values, since the measurements included
the black glass bead image on these teeth.
RESULTS
The mean values of the distance between the FA point of the
mandibular teeth and the WALA ridge progressively increased
from the central incisor to the second permanent molar, from
0.00 to 2.46 mm respectively (Fig. 3).
No statistically significant difference was found between
the mean values of our sample and Andrews2 values for the
distance of first permanent molar (Table 1).
Fig. 2: Red and black glass beads showing FA points and
WALA ridge respectively
DISCUSSION
Discovering the nature of equilibrium of the natural dentition
is of primary importance to orthodontists whose concern is
Fig. 3: Digital image of the dental cast on the grid
Fig. 1: Mean values of the distance between the FA points and WALA
ridge from central incisor to second molar
achieving ideal and stable dental arches. Considering the
relative stability observed in dental arch form, even during
growth, the anatomic position of the dental arch stabilized
between the tongue and the circumoral musculature, and the
experiences encountered in moving teeth and stabilizing them
following such movement, all strongly supporting the concept
that the teeth reside in equilibrium in the undisturbed state.3
After eruption, the crowns of the permanent teeth are subject
Table 1: Comparison of mean values of distance between the FA point of mandibular teeth and
WALA ridge (mm) with Andrew’s values2 by the student t-test
Tooth
7
6
5
4
3
2
1
Mean (n = 50)
2.46
2.04
1.53
1.17
0.95
0.19
0.00
SD
±0.52
±0.64
±0.50
±0.47
±0.43
±0.29
±0.00
Andrews (n = 50)
2.20
2.00
1.30
0.80
0.60
0.30
0.10
Difference
t
0.26
0.04
0.23
0.37
0.35
0.11
0.10
3.585
0.465
3.233
5.585
5.831
– 2.430
0.000
p
0.001*
0.644 NS
0.002*
0.000*
0.000*
0.019*
0.000*
NS: Statistically nonsignificant, *Statistically significant
The Journal of Indian Orthodontic Society, October-December 2012;46(4):300-303
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Vikrant Bhandari et al
to alterations as a result of ‘environmental’ forces. These
forces may tip the teeth around their centers of rotation. Even
though most patients with a malocclusion have an altered dental
arch form, the alterations achieved with mechanics during
orthodontic treatment should not affect the balance between
bone , dental and muscular structures. The arrangement of these
structures adjacent to teeth and jaws should be considered the
limit for orthodontic movement.4-7 Hypothetically, when this
occurs, the centers of rotation of the mandibular teeth, which
remain in the center of the basal bone, do not alter, however,
the crowns and root apex may be altered.3
According to some authors,8-15 the dental arch can be
described by diagrams constructed from patients. Measurements or diagrams that describe mean curves are determined
by mathematical equations. Other studies have shown wide
variations in dental arch shapes between subjects; this caused
author to search for universal landmarks that might establish
an individualized shape for each patient.16-19
Andrews and Andrews2 suggested the use of an anatomic
reference, such as a parameter with the object of centralizing
the roots of teeth in the basal bone, which they denominated
via the WALA ridge (named after Will Andrews and Larry
Andrews). The WALA ridge is the strip of soft tissue
immediately above the mucogingival junction of the mandible,
at the level of the line that passes through the centers of
rotation of the teeth or close to it, and is exclusive to the
mandible. Therefore, the center line of rotation (hypothetical
line that passes through the horizontal center of rotation of
each tooth) would be the line that best conserves the original
and ideal form of the dental arch. Thus, the ideal form of the
maxillary and mandibular dental arches would be dictated by
the form of the basal bone of the mandible. When the form of
the mandibular dental arch is correct, the wire that unites the
bracket slots of ‘straightwire’ brackets should have the same
shape as that of the WALA ridge.3 The mandibular alveolar
process is selected because its shape would be minimally
effected by faciolingual tipping of the teeth, this would happen
because of the shape of the underlying basal bone.3 By taking
it as a base of the study, i.e. relation between teeth and the
WALA ridge, standard distances were established between FA
points and the WALA ridge which would influence the
treatment plan.
In this study, dental casts with normal occlusion of
Himachali patient were taken and distance between FA point
and WALA ridge were calculated. The mean values of the
distance between FA point and WALA ridge were 0.00 mm
for central incisors, 0.19 mm for lateral incisors, 0.95 mm
for canines, 1.17 mm for first premolar, 1.53 mm for second
premolar, 2.04 mm for first molar and 2.46 mm for second
molar. A gradual increase was observed from anterior to
posterior region. So it was concluded that the mandibular teeth
were more lingually placed in Himachali population as
compared to study conducted by Andrews and Andrews2 on
Caucasians except for central and lateral incisors (Table 1).
No statistically significant difference was observed at first
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molars after applying the Student t-test to compare our
numbers to the values of Andrews and Andrews.2 The results
of our study are in concordance with the study conducted by
Tarcila Trivino, Danilo Furquim3 in Brazillian with normal
occlusion.
Ronay et al20 conducted a study which shows the distal to
the mandibular canines, the average distance between FA and
WALA points describing the same tooth changes
buccolingually. In this posterior area, the FA points are more
lingually located than the WALA points. They also reported
only positive values between FA and WALA points and
projected that the points at the mucogingival junction were
always more buccally positioned than the most prominent part
of the tooth crown.
The results of our study disagree with the results of study
conducted by Kanashiro and Vigorito21 who found lower mean
values for the central incisors (–0.38 mm), lateral incisors (–
0.12 mm) and canines (0.24 mm), and higher mean values for
first premolars (1.49 mm), second premolars (2.67 mm), first
molars (3.00 mm) and second molars (3.51 mm), indicating
more lingually placed posterior teeth as compared to Himachal
population.
The discrepancy between the mean values of the FA points
and the WALA ridge distances in this study and the results of
other authors can be attributed to the different methodologies
and the differences in their samples. In our study, we chose to
bond glass beads because of the difficulty in visualizing the
distances between the FA points and the WALA ridge in the
mandibular incisor region. Evaluation of the method error
showed no systematic and casual error, demonstrating the
accuracy of this methodology.3
On the contrary, this study suggests that all basal and dental
arches should be individually derived. Furthermore, the basal
arch, represented by WALA points, can be used as a clinical
guide in fabricating individualized archwire templates.20
CONCLUSION
It was concluded from our study that Himachali population
with normal occlusion, there are standardized distances
between the FA points and the WALA ridge, decreasing from
the posterior to the anterior regions of the dental arch,
indicating a progressively lingual position of the mandibular
teeth.
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