Appraisal of the cephalometric norms for the upper and lower lips of the South Indian ethnic population.

AIM: The guidelines for planning an improvement in the facial appearance till recently existed in the form of evaluation of linear and angular parameters and ratios related to the hard tissues in the various cephalometric analyses. The present study aimed at establishing Arnett et al.'s norms of the upper and lower lip for the local population and assessing the extent by which these differ from the original norms proposed by Arnett et al.
MATERIALS AND METHODS: Forty pretreatment lateral cephalograms (20 males and 20 females) with normal occlusion and well-balanced face were chosen for this study. Upper and lower lip lengths, thicknesses, and chin thickness were all measured according to soft tissue cephalometric analysis by Arnett et al.
RESULTS: The obtained data were statistically analyzed and compared with other studies.
CONCLUSION: Males had thicker and longer upper and lower lips when compared to females, but they were comparatively thinner than the results of Arnett et al. Females had more interlabial gap than males. The difference in soft tissue parameters in different ethnic groups shows the importance of defining what is optimal for a particular group.

Facial attractiveness influences personality development and social interactions. People mainly focus on another person's eyes and mouth during interpersonal interactions, with little time spent on other facial features. Soft tissues are the most important aspect in orthodontic treatment planning and cephalometrics plays an important role to quantify this.

With the knowledge of standard facial traits and the patient's soft tissue features, an individualized norm can be established for each patient to optimize facial attractiveness. Over the years, several lines and angles have been used to evaluate soft tissue facial esthetics. Most of these analyses had the disadvantage that the horizontal reference planes taken were either the Frankfort horizontal plane or the cranial base, the orientation of which could differ significantly from person to person. The vertical reference planes, which were related to the above horizontal planes, were obviously unreliable. Soft tissue mid-face landmarks were not given proper importance. To overcome these shortcomings, Arnett et al.[1] developed a new method of cephalometric analysis in the year 1999, which assessed the patient from their soft tissue measurements for altering the dento-alveolar as well as skeletal components. The analysis has the added advantage that it is based on natural head position (NHP). They specified a true vertical line (TVL) as the vertical reference plane to measure the soft tissue norms. Hence, this analysis has proved useful in planning strategies for both orthodontic and orthognathic surgery treatment. It is essential to establish the norms for local population based on Arnett et al.'s[1] cephalometric analysis as it may be inappropriate to apply directly the values of Arnett's analysis to local population because it is a known fact that facial features of different ethnic groups differ significantly.

Lip and chin form an important component of the oro-facial soft tissue profile. Soft tissue cephalometric analysis (STCA) analysis by Arnett et al.[1] is used in this study to establish the normal lip and chin parameters for the local population.

Materials and Methods

The present study was conducted on lateral cephalograms of 40 subjects (20 males and 20 females) of 18 years and above. The following criteria were used in the selection of the total sample:

Full permanent dentition regardless of the third molars

No history of previous orthodontic treatment

No history of facial trauma or craniofacial disorder, such as cleft palate

Class I occlusion with normal overjet and overbite

Acceptable facial profile

Bilateral Class I buccal segments “molar and canine”

Skeletal Class I relationship determined

Minor or no spacing or crowding.

All lateral head films were obtained with subjects in NHP with seated condyles and passive lips. After placing registration points on the cephalograms, the pretreatment radiographs were traced on acetate tracing sheets of 0.5 μm thickness using a sharp 4H pencil on a view box using transilluminated light in a dark room. When there was a lack of superimposition of the right and left structural outline, the average between the two was drawn by inspection and the cephalometric points were located in reference to the arbitrary line so obtained.

Cephalometric analysis

The TVL was positioned through subnasale and was perpendicular to the natural horizontal head position.[2]

Arnett et al.'s[1] soft tissue cephalometric analysis was used to diagnose the subjects for the following parameters [Figures 1 and 2]:

Figure 1

Soft tissue thickness at upper lip, lower lip, pogonion and menton are depicted

Figure 2

Upper lip length (ULL), lower lip length (LLL) and interlabial gap (ILG) are depicted

Upper lip thickness (mm)

Lower lip thickness (mm)

Pogonion–pogonion’ (mm)

Menton–menton’ (mm)

Upper lip length (mm)

Lower lip length (mm)

Interlabial gap (mm)

Results

The results were statistically analyzed for mean and standard deviation. The P values of <0.05 and <0.01 were considered statistically significant.

Means, standard deviation, and significance values were as follows:

The mean upper lip thickness for men was 14.01±1.3 and for women 12.09±1.8, with a P value of 0.05.

The mean lower lip thickness for women was 14.6±2.24 and for women was 13.24±1.43, with a P value of 0.01.

The upper lip length measured showed a mean of 23.4±3.42 for men and 20.02±2.89 for women, with a P value of 0.01.

The lower lip length was 49.83±5.2 for males and 41.27±7.08 for females, with a P value of 0.01.

The interlabial gap for women was 1.62±1.8 and for men was 0.24±1.1, with a P value of 0.01.

The chin thickness measured was established by the values of hard tissue pogonion to soft tissue pogonion, with mean values of 13.32±1.8 for men and 12.09±1.09 for women, with a P value of 0.001.

The value for the menton-menton’ was 8.64±2.15 for men and 7.18±2.30 for women, with a P value of 0.01.

Discussion

Soft tissues like lips and the chin are closely related to the dentition and being partially composed of the muscles therefore has a functional influence on the underlying dental structures. According to Subtelny,[3] the vermillion aspect of the lips tends to maintain a close postural relationship to their supporting structures. The most dramatic changes in the facial appearance seem to be correlated with cases exhibiting lip protrusions whether it is one or both the lips. With the lips forming a very important part of the face, modifications in this area can have a dramatic influence on the facial appearance. With lot of emphasis given on the cephalometric analysis, it is essential to know ethnically specific lip features of the group an orthodontist usually treats. In our study, we evaluated the lip features of the Komarapalayam population on the lateral cephalogram using STCA of Arnett et al.[1] In this study, upper and lower lip thickness, length, interlabial gap, and the chin thickness were measured.

In this study, the upper and lower lips and soft tissue chin were found to be thinner than that reported by Arnett et al.[1] and were nearly the same as that reported by Kalha et al.[4] This may be attributed to the ethnic factor or sample size. From the results, it can be seen that upper lip length, lower lip length, upper lip thickness, lower lip thickness, pogonion–pogonion’, and menton–menton’ were significantly greater in males than in females; this comes in agreement with the reports of Arnett et al.,[1] Kalha et al.,[4] Uysal et al.,[5] Lalitha and Kumar,[6] and Zainab.[7]

The interlabial gap was higher for female group as compared with the males. This is in accordance with the reports of Arnett et al.,[4] Kalha et al.,[4] and Lalitha and Kumar,[6] whereas Uysal et al.'s[5] finding is not in agreement with this. In this study, all the parameters are lower than those reported by Arnett et al.,[1] but in accordance with the reports of Kalha et al.[4] and Lalitha and Kumar,[6] as their studies were also based on almost similar ethnic group.

This study emphasizes the importance of the lips in treatment planning, especially where intrusion or retraction of incisors is planned. Soft tissue camouflage is the nature's way of treating malocclusion and this should be considered and respected when planning for orthodontic treatment. The sexual differences are due to the influence of the sex hormones on the facial contour, which become very evident by adolescence. The male bony structure is bolder and more prominent, with dominance of the forehead, nose, chin, and stronger contour of the mandible.[8] This comes with the general trend of males having greater measurements than females. This is because males have longer growth period than females[9-11]

Conclusion

Males have thicker soft tissue structures, especially lower lip thickness. Since the reduction in lip prominence (with the same amount of incisor retraction) is less in the individuals with thick lips than in those with average thickness of lips, the difference in male and female lip thickness will have to be considered while planning the amount of incisor retraction for improving esthetics. The difference in soft tissue parameters in different ethnic groups shows the importance of defining what is optimal for a particular group. In the Western population, straight profile with a prominent chin is considered normal and esthetic, whereas mild convexity in the Indian scenario is considered normal.