Variation of Facial Soft Tissue Thickness in Nepalese Adult Orthodontic Subjects

Introduction: Variations in facial soft tissue thickness have been established previously by studies conducted in different population. Hence, it is essential to obtain facial soft tissue thickness measurement data specific to a population and develop individual standards. The objective of this research is to obtain facial soft tissue thickness data of Nepalese adult male and female subjects seeking orthodontic treatment with different sagittal skeletal malocclusion and evaluate variations in facial soft tissue thickness. Materials & Method: Facial soft tissue thicknesses was measured manually on ninety pretreatment lateral cephalogram at eleven points (Glabella, Nasion, Rhinion, Subnasale, Labrale superius, Stomion, Labrale inferius, Labiomentale, Pogonion,Gnathion and Menton). One-way Analysis of variances [one-way ANOVA] followed by Least significant difference (LSD) post hoc test was used to determine difference in facial soft tissue thickness measurements among three sagittal skeletal group for both sexes. In addition, Student’s t-test was used to find difference in facial soft tissue thickness between the male and female subjects in each skeletal Class. Result: Statistically significant differences were found at points Rhinion, Subnasale, Labrale superius, Stomion and Gnathion in males and at Subnasale, Labrale superius, Stomion and Labrale inferius in females while comparing facial soft tissue thickness among three sagittal skeletal classes. Also, it was observed that mean facial soft tissue thickness was greater for males as compared to female subjects with significant differences at Subnasale, Labrale superius, and Labrale inferius in each skeletal Class. Conclusion: Facial soft tissue thickness varies considerably among different population group, sex and sagittal relationship of jaws.


INTRODUCTION
Since the Angle era, the aim and objectives of orthodontic treatment is to achieve a harmonious skeletal, dental and soft tissue relationship. However, in recent years there has been a change in treatment goals. A harmonious and balanced face (having normal soft tissue proportion and adaptation) with optimal functional occlusion are the primary and secondary goals of contemporary orthodontic and orthognathic treatment respectively. Considering this new "Soft Tissue Paradigm", an increased emphasis is given on soft tissue evaluation during diagnosis and treatment planning of patients requiring orthodontic treatment and/or orthognathic surgeries. 1 Over the years, various studies have been carried out to evaluate facial soft tissue and establish soft tissue norms for individual population. [2][3][4][5][6] Most of these studies have found racial/ethnic variations and sexual dimorphism for facial soft tissue thickness. Also, a difference in facial soft tissue thickness among different sagittal skeletal malocclusion has been observed in previous studies. [7][8][9][10][11][12] Hence, availability of a population specific measurement data for facial soft tissue thickness can be very useful.
However, based on our electronic literature search using key words "facial soft tissue thickness", "skeletal malocclusion" and "Nepalese population" we could not find any published study evaluating facial soft tissue thickness and its variation. Hence, the present study was undertaken to obtain facial soft tissue thickness of Nepalese adult male and female subjects seeking orthodontic treatment at a tertiary level hospital in Central Nepal, study sexual dimorphism and evaluate variation in facial soft tissue thickness among different sagittal skeletal malocclusion. • Cephalograms of patients having any known genetic/craniofacial abnormalities, growth related disorders, with history of facial trauma and or who had undergone orthodontic treatment/craniofacial surgery • Cephalograms of patients with positional errors as reflected by ear rod markers.

MATERIALS AND METHOD
• Cephalograms in which landmarks could not be identified because of artifacts, motion, resolution disparity or lack of contrast.
All the cephalograms acquired were taken from the same digital cephalometer (PlanmecaPromax, PlanmecaOy, Helsinki, Finland) and had the calibration ruler for determination of magnification. X-ray images were printed on 8''X10'' radiographic film using compatible printer (Drypro Sigma 2, Konica Minolta, Tokyo, Japan) and manual tracing was done using standard protocols. Calibration of the actual size of each image in millimeters was done based on measurement of the known distance (10 mm) between the two fixed points of the ruler on the cephalogram. Using a millimeter ruler the facial soft tissues thickness were measured to the nearest 0.5 mm at 11 points: Glabella, Nasion, Rhinion, Subnasale, Labrale superius, Stomion, Labrale inferius, Labiomentale, Pogonion, Gnathion and Menton ( Figure  1). After adding magnification factor to the obtained linear measurements final values were recorded and were entered into an Excel spreadsheet. To avoid intraobserver bias all the assessments (tracing as well as measurement) were done by a same investigator (RKM).
Also, only five cephalograms were analyzed daily to minimize errors due to the human fatigue. To evaluate the errors due to landmark identification, tracing and measurement 15 cephalograms were randomly selected. After three weeks gap, all the landmarks were replotted. Manual tracing and measurements were repeated on these cephalograms.
All the statistical analyses were carried out using the Statistical Package for Social Sciences version 16.0 (SPSS Inc,Chicago, IL). Intraclass correlation coefficient (ICC) was done to determine intra-observer reliability and reproducibility for repeated measurements. Normality of data distribution was checked using Shapiro-Wilk test. Mean, standard deviation and standard error mean values were calculated for facial soft tissue thickness at eleven different points measured in the study. One-way Analysis of variances [one-way ANOVA] was used for analyzing difference in mean facial soft tissue thickness among three sagittal skeletal groupsat each point.When a significant difference was observed, Least significant difference (LSD) post hoc testwas used to find out individual difference.In addition to these tests, Student's RESULT ICC values were more than 0.9 for repeated cephalometric measurements. This is suggestive of a very high intra-observer reliability and reproducibility as ICC value of > 0.75 is indicative of a good agreement.  t-test was used to find out difference in mean facial soft tissue thickness between the male and female subjects in each sagittal skeletal groupat each point. The level of significance was noted at three levels (*p < 0.05); (**p < 0.01); (***p < 0.001).