Download correlation between nasolabial angle and maxillary incisor inclination

Original Article
Nasolabial Angle & Maxillary Incisor Inclination
Pak Armed Forces Med J 2015; 65(Suppl-2): S236-39
CORRELATION BETWEEN NASOLABIAL ANGLE AND MAXILLARY INCISOR
INCLINATION
Abdullah Jan, Hamza Rehman, Nida Taifur, Azhar Ali Bangash
Armed Forces Institute of Dentistry Rawalpindi, Pakistan
ABSTRACT
Objective: To find out the relationship between nasolabial angle and maxillary incisor inclination
Study Design: Cross sectional study
Patients and Methods: On the basis of inclusion criteria; 208 good quality lateral cephalograms were traced.
Nasolabial angle and maxillary incisor to S-N plane were drawn. Correlation was done by using Pearson
correlation coefficient (r). Bivariate analysis was done. p value was also determined. A p value of less than 0.05
was considered to be statistically significant.
Results: Out of a total study sample (N=208) 41% were male where as 58.2% were female. Regarding the class
of occlusion, 40.4% of our population was Class I, 47% was class II and 12.5 % was Class III. The mean age of
patients in our sample was 17.15 years with a range between 11 to 35 years. The mean nasolabial angle (NLA)
was 102 degrees (50 to 148 degrees). The mean maxillary incisor to S-N plane (I –SN) angle was 105, with a
minimum of 57 and maximum of 138 degrees and standard deviation of 12.02. Pearson correlation coefficient
test (r=-0.97) showed that the relationship between pre-treatment nasolabial angle and pretreatment maxillary
incisor inclination was not present.
Conclusions: Pretreatment relationship between maxillary incisor inclination and nasolabial angle is
statistically insignificant.
Keywords: Maxillary Incisor inclination, Nasolabial angle, Relationship.
INTRODUCTION
Evaluation of the face in the profile view is
an integral part of comprehensive orthodontic
diagnosis. Different methods for evaluation of
profile have been proposed including
traditional cephalometrics and soft-tissue
analysis. Nasolabial angle gives an indication of
protrusion
of
upper
lip.
Traditional
cephalometrics uses internal osseous landmarks
to define points, lines, and/or planes, which in
turn are used to quantify anteroposterior (AP)
jaw and incisor positions1-3. One of the chief
concerns of patients reporting for orthodontic
treatment is unacceptable / abnormal maxillary
Incisor position in sagittal plane. Planned
Maxillary Incisor Position (PIP) is thus one of
the requirements to achieve ideal orthodontic
results4 .
Clinicians consider maxillary incisor
protrusion to be the prime reason for reduced
nasolabial angle but interestingly there is little
evidence both in international and local
literature about the relationship between
maxillary incisor inclination and nasolabial
angle, so there was a need to find out about this
relationship.
MATERIAL AND METHODS
This was a cross sectional study. All the
patients were randomly selected from
Orthodontics department, Armed Forces
Institute of Dentistry (AFID). The sampling was
based on convenience model. Pretreatment
lateral cephalometric radiographs of patients
reporting to AFID from January 2014 till
December 2014 were used.
The inclusion criteria of the patients for this
study were based on the fact that the patients
had never gone through orthognathic surgery
or orthodontic treatment. Our sample included
patients without any restorations in the anterior
teeth and patients without impacted, missing
teeth.
Correspondence: Dr Abdullah Jan, Classified
Orthodontist AFID, Rawalpindi, Pakistan
Email: [email protected]
Received: 07 Jul 2015; revised received: 21 Aug 2015;
accepted: 09 Oct 2015
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Nasolabial Angle & Maxillary Incisor Inclination
Pak Armed Forces Med J 2015; 65(Suppl-2): S236-39
Exclusion criteria included Patients with cleft
lip/ palate and patients with supernumerary
teeth.
were 84, 98 and 26 respectively. The mean age
of the patients in our sample was 17.15 years.
The range of age was between 11 to 35 years.
The Standard deviation for age was 3.94. In our
study population, the mean nasolabial angle
(NLA) range was 102 degrees. The range was
from 50 to 148 degrees. The standard deviation
for NLA was 16.45. The mean maxillary incisor
to S-N plane (I –SN) angle was 105, with a
minimum of 57 and maximum of 138 degrees.
The standard deviation for I-SN was 12.02.
This study used the pretreatment
cephalometric radiographs of 208 subjects.
Good quality cephalometric radiographs were
taken with patients lips in relaxed position
showing a more precise anatomy of the lip.
These were traced on 0.003 inch matte acetate
tracing paper5. The nasolabial angle was formed
by drawing a line tangent to the base of the
nose and a line tangent to the upper lip. To
evaluate the inclination of upper incisor, S-N
plane was drawn as a reference plane.
According to Steiner, the advantage of using
these two midline points (S and N point) is that
they are moved only a minimal amount
whenever the head deviates from the true
profile position and this plane remains true
even if the head is rotated in the cephalostat6.
In our sample the Bivariate analysis for
correlation was done. One would predict a
strong and one would indicate a weak
correlation. For p value the significance was
assumed at a value of < 0.05.
DISCUSSION
Clinicians are often of the opinion that
reducing the maxillary incisor inclination by
extractions can also increase the nasolabial
angle. This in turn will reduce the prominence
of upper lip in patients with protrusive lips. It is
rather well accepted by clinicians that the
extraction of four first premolars can be
effective in the treatment of bimaxillary
protrusion. Whether evidence based approach
to treatment is being followed is still
SPSS 22 was used for statistical analysis.
Frequencies and percentages were determined
for gender and class of occlusion. Minimum
and maximum value, mean and SD were
determined for age, nasolabial angle (NLA) and
Upper Incisor to S-N plane (I-SN). Pearson
correlation coefficient (r) was applied for
Table: Correlation between nasolabial angle and maxillary incisor SN plane.
Variable
Mean
SD
Coefficient of correlation (r)
NLA
102
16.45
-.097
I-SN
105
12.02
p value
0.165
comparison. To find the correlation, Bivariate
analysis was performed on Nasolabial angle
and Upper Incisor to S-N plane. The
significance was judged by a p value of < 0.05.
controversial. It is surprising that there is
relatively little in the literature providing
concrete evidence on the efficacy of extraction
of teeth for reducing the lip protrusion.
RESULTS
Scheideman et al7 reported a normal mean
nasolabial angle of 111.48 with a small decrease
in this angle expected with age, primarily
because of the downward growth of the nose.
Fitzgerald et al emphasized continued nasal
development in any analysis of nasolabial
angles. In this study, the mean pretreatment
values for the nasolabial and labial angles of
The results showed that 4.8% of our study
population was male and 58.2% were female.
The frequency was 87 and 121 between male
and female patients respectively. Regarding the
class of occlusion, 40.4% of our population was
class I, 47% was class II and 12.5 % was class III.
The frequency for class I, Class II and class III
237
Nasolabial Angle & Maxillary Incisor Inclination
Pak Armed Forces Med J 2015; 65(Suppl-2): S236-39
both groups were slightly less than the
normal8,9.
decrease in upper and lower incisor inclination
and a significant decrease in the anteroposterior
position of the upper and lower incisors
(p =.001). These findings suggest that this
treatment modality is effective in decreasing the
incisor proclination.
Angle suggested that the soft tissues would
assume a harmonious position, only when the
dentition was intact and arranged in an ideal
occlusion, while Tweed proposed the use of a
hard tissue diagnostic and treatment planning
with the assumption that an upright
mandibular incisor over the basal bone was
stable and esthetic10. Reidel stated that the
ultimate goal of orthodontics is magnificence,
which includes ideal form, function and
esthetics11.
In a study by Saxby15 and Freer it was
concluded that lip position may be affected by
incisor position and skeletal convexity at point
A, but this study did not try to find out a
statistical correlation.
Fida et al12 reported the skeletal and dental
characteristics of Pakistani population with lip
strain. Increased value of maxillary incisor
inclination (I-SN) were found, with a mean
value of 118 degrees. There were no statistical
significant correlation of skeletal convexity at
point A and maxillary incisor inclination with
upper lip inclination as evaluated by Pearson’s
correlations of point A to facial plane, I-FH and
ISN with upper lip inclination.
Changes in the nasolabial angle of the softtissue profile were assessed quantitatively in a
serial cephalometric study16 of fifty treated
subjects and forty-three untreated subjects, all
of whom had Class II, Division 1 malocclusions.
Correlations, simple and multiple regression
analysis and multifactorial analysis of variance
were used to examine the changes in the
nasolabial angle owing to incisor superius
retraction
and
associated
skeletal
displacements. There were no significant
changes in nasolabial angle because of growth.
However, the greater the maxillary incisor
retraction, the greater was the increase in
nasolabial angle. However another study
reported results in non-concordance with the
above studies17 . It was proved that there is no
correlation between the nasolabial angle and
upper incisor inclination and between the
upper
incisor
inclination
and
lower
compartment of nasolabial angle.
Similarly Chaudhry tried to find Upper
incisor to SN plane (I-SN) value for a Pakistani
population. I-SN value was found to be 118
degrees for patients with bimaxillary
protrusion 13. In this study however statistical
correlations between lip procumbency and
incisor inclination were not made.
There are some limitations of our study.
The patients selected did not go through any
orthodontic treatment. Only pretreatment
lateral cephalograms were traced. If there were
patients who had been treated solely by
extraction or non extraction the results may
have been different.
In another study14 patients were treated
with the extraction of four premolars and the
retraction of anterior teeth in an attempt to
correct their bimaxillary protrusion. The results
of this study demonstrated a significant
increase in interincisal angle, a significant
CONCLUSION
The results of our study show that the two
variables i.e. Nasolabial angle (NLA) and
Incisor to SN plane (I-SN) are weakly and
negatively correlated i.e. r = -.097. This confers
that when NLA increases, the S-N to maxillary
incisor angle will decrease. Similarly the p value
of 0.165 is not significant statistically. Our study
was different from the other local studies since
no treatment intervention was carried out.
There is a weak and negative correlation
between Nasolabial angle and maxillary incisor
inclination. However, the pre treatment
correlation between Nasolabial angle (NLA)
and upper incisor inclination to S-N plane (I238
Nasolabial Angle & Maxillary Incisor Inclination
Pak Armed Forces Med J 2015; 65(Suppl-2): S236-39
SN) is not statistically significant. Further
studies need to be done to assess the effects of
treatment (extraction or non extraction) on the
nasolabial angle and maxillary incisor
inclination.
6. Steiner CC. Cephalometrics for you and me. Am J Orthod. 1953; 39(10):
729-55.
7. Scheideman GB, Bell WH, Legan HL, Finn RA, Reisch JS.
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78(4): 404-20.
8. Fitzgerald JP, Nanda RS, Currier GF. An evaluation of the nasolabial
angle and the relative inclinations of the nose and upper lip. Am J
Orthod Dentofacial Orthop. 1992; 102(4): 328-34.
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1995; 107(5): 476-83.
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11. Riedel RA. Esthetics and its relation to orthodontic therapy. Angle
Orthod. 1950; 20(3): 168-78.
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proclination. PODJ. 2008; 22(2): 207-10.
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bimaxillary protrusion. PODJ. 2008; 22(2): 199-202.
14. Bills DA, Handelman CS, BeGole EA. Bimaxillary dentoalveolar
protrusion: traits and orthodontic correction. Angle Orthod. 2005;
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15. Saxby PJ, Freer TJ. Dentoskeletal determinants of soft tissue
morphology. Angle Orthod. 1985; 55(2): 147-54.
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incisor retraction. Am J Orthod. 1982; 82(5): 384-91.
17. Patrik G, Kalpesh P, Hina D, Nikunj P, Milind P, Viral H, et al. Effect
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values really matter? IJHS. 2014; 2(2): 217-20.
CONFLICT OF INTEREST
This study has no conflict of interest to
declare by any author.
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