This was my first contribution to an Orthodontic article. With Dr. Dhirawat of the Chiang Mai Orthodontic faculty, we measured many models of Northern Thai's with good occlusion and facial profile with our NEW instrument the T.A.D. or Torque Angulation Device. This instrument was the first digital instrument able to measure Tip and Torque accurately and easily from Orthodontic study models. As all previous studies were probably done on a particular population and geographical location, then we wanted to compare the values derived with previous studies such as Andrews, Hilgers, Bennet, Roth, MBT, etc.. having a new instrument also meant that the readings were more in tune with the related tooth morphology Conclusions, should bracket prescriptions differ for different races, facial types, etc?.

1. Dhirawat Jotikasthira, BSc,
DDS, MDSc1 CROWN ANGULATION AND INCLINATION
Peter Sheffield, BSc, MS 2 OF NORTHERN THAIS WITH GOOD
Anmol Kalha, OSRE, BSc,
BDS, MDS3
OCCLUSION
When patients of differing ethnicities are treated with one bracket
Zameer Syed, BDS, MDS4
system, negative consequences for the occlusion can result. This
study investigated the crown angulation and inclination on study
casts of 60 Northern Thais (30 males and 30 females) with a good
occlusion. In all study casts, each tooth (except the third molars) was
evaluated with the orthodontic Torque Angulation Device (TAD) twice
on the right side; this was also performed twice on the left side. The
mean of the two evaluations was used for the statistical analysis. The
means of the males and females were compared with the indepen-
dent Student t test. The results were that the crown angulation of the
mandibular first and second molars was significantly higher in
females (P <.01) and that the crown inclination of all teeth did not dif-
fer between the two sexes. World J Orthod 2010:71–74.
Key words: crown inclination, crown angulation, Northern Thais, normal
occlusion, Torque Angulation Device
ccurate bracket positioning is of The or thodontic Torque Angulation
A critical importance for biomechan-
ics and the realization of the potential
Device (TAD) is a device that measures
crown angulation and inclination in a
of preadjusted edgewise appliances. precise and objective fashion.
Precise measurements of crown angu-
lation and inclination are crucial for the
construction of brackets for a specific MATERIALS AND METHODS
1Associate
population.
Professor, Department of
The advent of sophisticated appli- The materials comprised 60 plaster
Orthodontics, Faculty of Dentistry,
Chiang Mai University, Chiang Mai, ances and materials has helped raise casts and facial and intraoral pho-
Thailand. the standard of orthodontic treatment. tographs of Northern Thais (30 males
2Manager, TAD Concept & Dental
As a result, achieving an ideal occlusion and 30 females) from the Department of
Laboratory, Hexa Ceram, Chiang has become a realistic aim. The current Orthodontics, Faculty of Dentistry, Chi-
Mai, Thailand.
3Dean and Head, Department of
concepts of ideal static occlusion are ang Mai University, Thailand. The age
Orthodontics, Institute Of Dental based on Andrews’ keys of normal occlu- distribution by sex and the number of
Studies and Technology, Dehli, sion, of which crown angulation and teeth are shown in Table 1.
India. inclination are important features. 1
4Tutor, Department of Orthodontics,
Andrews stated that if these key factors Inclusion criteria were:
Govt. Dental College, J&K, India.
are not achieved, there will be a space
CORRESPONDENCE discrepancy in the dental arch or the • Excellent or good occlusion with nor-
Dr Zameer Syed occlusion will be compromised.1 Crown mal overjet and overbite
Faculty of Dentistry angulation and inclination vary among • No or only slight incisor crowding
Department of Orthodontics populations. Only one study to date has • Pleasing profile
Government Dental College and Hospital
Karan Nagar
described these parameters in Northern • No interproximal caries or extensive
Srinagar 190010 Thais. The measuring device used in this restorations
India investigation was a modified protractor.2 • No previous orthodontic intervention
71
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2. Jotikasthira et al WORLD JOURNAL OF ORTHODONTICS
Table 1 Mean age (y), standard deviation (SD), minimum, maximum, and
sample size separately and combined for both sexes
Total
Age SD Minimum Maximum subjects
Males 20.18 1.60 16.30 25.90 30
Females 19.19 2.62 15.60 28.80 30
Combined 20.00 2.30 15.60 28.80 60
Fig 1 (right) The orthodontic Torque Angulation Device (TAD). The blade was set to
lie along to long axis of the clinical crown by adjusting the fine angulation knob.
The crown angulation was read from a digital screen.
Seven orthodontists evaluated all curvature of the blade fitted optimally the
records to exclude any subject with an vestibular surface of the tooth being
unacceptable occlusion or facial appear- measured. After this adjustment, the
ance. crown inclination was displayed.
On all casts, all teeth (except the third
molars) on the right side were evaluated
twice with the orthodontic Torque Angula- Statistical methods
tion Device (TAD). The evaluation was also
performed twice on the left side. The The mean of the first and the second
study casts were fixated on an adjustable measurement was used for the statistical
table with the horizontal occlusal line analysis. If the independent Student t test
(HOL) parallel to the TAD platform (Fig 1). showed no significant difference between
The HOL is an imaginary line connecting the right and left side, the values from
the right and left midcrown molar points both sides were combined. The indepen-
and the average of the clinical midcrown dent Student t test was also used to com-
points of both central incisors. pare the means of the males and
The crown angulation was measured females. To test the reliability of the mea-
according to Andrews1: The long axis of surements, the intraobserver difference
clinical crown (LACC) was drawn on the was calculated on six randomly selected
labial surface of the clinical crown of models. Pearson correlation coefficient (r)
every tooth (Fig 2). On the LACC of each was 0.978.
tooth, the midpoint of the clinical crown
(L A point) was marked. It was con-
structed by bisecting the height of the RESULTS
clinical crown (with 1.0 mm added for the
gingival sulcus) on the LACC. Box plots of the crown angulation of all
The model was then moved toward the teeth (right and left sides combined) of
blade of the TAD. At the same time, the ta - both sexes are shown in Fig 3. The crown
ble was adjusted in height. When the blade angulation of the mandibular first and
was running along the LACC, the crown second molars was significantly higher
angulation could be read on the display. (P < .01) in females.
The crown inclination was recorded by Box plots of the crown inclination of all
moving the model until the middle of the teeth (right and left sides combined) of
blade coincided with the LA point and the both sexes are shown in Fig 4.
72
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3. VOLUME 11, NUMBER 1, 2010 Jotikasthira et al
Male maxillary arch Female maxillary arch
1.88 (0.34) 2.79 (0.34)
LACC
3.18 (0.48) 4.61 (0.42)
A LACC
3.72 (0.54) 3.81 (0.52)
0.07 (0.44) 0.67 (0.50)
I
0.42 (0,43) 1.57 (0.49)
0.96 (0,37) 0.74 (0.61)
LA point
Occlusal
plane –1.89 (1.09) –5.17 (1.15)
–30 –20 –10 0 10 20 20 10 0 –10 –20 –30
Fig 2 Construction of the long axis of the
Degrees Degrees
clinical crown (LACC) and the midpoint of
the clinical crown (LA point) to evaluate Central incisor Lateral incisor Canine First premolar
crown angulation (A) and inclination (I). By
connecting the average of the LA-points of Second premolar
First molar Second molar
the two central incisors with the mid-crown Degrees Degrees
molar points, the horizontal occlusal line –30 –20 –10 0 10 20 20 10 0 –10 –20 –30
(HOL) is established as a reference line.
7.92 (0.81) 11.17 (0.74)
3.29 (0.52) 6.15 (0.52)
2.18 (0.59) 3.00 (0.52)
0.28 (0.52) 1.66 (0.57)
0.33 (0.52) –0.26 (0.56)
0.05 (0.48) –0.12 (0.49)
0.05 (0.40) –0.19 (0.45)
Fig 3 Box plot graphs of the crown angula- Male mandibular arch Female mandibular arch
tion of all teeth in both sexes (right and left
sides combined). * = significant difference Outlying data P < .01
(P < .01) between male and female.
DISCUSSION CONCLUSION
The values of crown inclination and angu- This study investigated the crown angula-
lation measured in this study were simi- tions and inclination of Northern Thais with
lar to those of a previous study.2 In the good occlusion. Measurements of each
maxillary and mandibular arch, the crown tooth (except third molars) from the study
angulations in the present study were casts of 60 subjects (30 males and 30
smaller than those of Andrews,1 except females) were performed twice by using
for the first and second molars. the Orthodontic Torque Angulation Device
The crown angulation of the central (TAD). The means of both measurements
and lateral incisors in the present study were used for statistical analysis. The
was greater than that of studies by Vardi- respective values of the two sexes were
mon and Lambertz3 and Dellinger.4 compared with the independent Student
73
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4. Jotikasthira et al WORLD JOURNAL OF ORTHODONTICS
Fig 4 Box plot graphs of the crown incli-
Male maxillary arch Female maxillary arch
7.32 (0.51) 8.22(0.63)
nation of all teeth in both sexes (right and
left sides combined).
5.52 (0.61) 6.65 (0.64)
–5.50 (0.67) –6.79 (0.65)
–7.88 (0.67) –8.33 (0.76)
–9.29 (0.62) –9.25 (0.71)
–8.39 (0.70) –7.83 (0.72)
–11.97 (0.86) –11.90 (0.77)
–30 –20 –10 0 10 20 20 10 0 –10 –20 –30
Degrees Degrees
Central incisor Lateral incisor Canine First premolar
Second premolar First molar Second molar
Degrees Degrees
–30 –20 –10 0 10 20 20 10 0 –10 –20 –30
–29.15 (0.69) –28.88(0.71)
–20.38 (0.95) –20.23 (0.94)
–18.38 (0.84) –16.48 (1.04)
–14.73 (0.89) –11.52 (0.88)
–0.51 (0.85) –2.89 (0.70)
1.16 (0.82) 2.69(0.57)
4.32(0.82) 5.24 (0.66)
Male mandibular arch Female mandibular arch
Outlying data
t test. The results were that females have a REFERENCES
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The authors are grateful to Hexa Ceram, Chiang 4. Dellinger EL. A scientific assessment of the
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74
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