January, 2010

Assessment of Arnett Soft Tissue Cephalometric Norms in Indian Population

The present study aimed at establishing Arnett norms for the local population and assessing the extent by which these differ from the original norms proposed by Arnett et al.

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Dr.Ch.Lalitha and Dr. K.G. Gopa Kumar

Abstract

OBJECTIVES: The improvement of facial esthetics (along with attainment of functional occlusion) has been one of the desirable objectives of Orthodontic treatment for almost a century. But the treatment planning based on soft tissue measurements has received greater attention only during recent times. The guidelines for planning an improvement in the facial appearance till recently existed in the form of linear and angular parameters and ratios related to the hard tissues in the various cephalometric analyses. The present study aimed at establishing Arnett norms for the local population and assessing the extent by which these differ from the original norms proposed by Arnett et al.

METHODS: The present study sample size comprised of Sixty subjects (30 male and 30 female). Photographs, Dental Study casts and a Lateral cephalogram were taken. The Natural Head Position was recorded on the cephalograms following the method proposed by Dr. N. Sleeva Raju5 et al. The TVL was established on the subject’s face and then the Cephalograms were taken in a conventional manner. All reference points, landmarks and measurements were made according to the STCA. The data was subjected to statistical evaluation.

RESULTS: The results were statistically analyzed. Means and Standard deviations were computed and probability values were calculated to establish norms for Local population as well as to compare them with the findings of other studies.

INTERPRETATION AND CONCLUSION: The findings suggest that different set of cephalometric norms for different ethnic groups should be established. Because mildly proclined incisors, mild facial convexity and retruded lower faces are considered as normal in the Indian scenario, the Orthodontist and Oral surgeon should use local norms as reference for optimizing treatment planning to obtain optimum esthetic outcome.

Introduction

The modern society considers facial attractiveness as an important physical attribute. We unconsciously tend to associate desirable personal qualities (such as intelligence) and social ability with attractive faces. The relevance of facial esthetics in dentistry has gained great attention in recent times. Orthodontic practice also recognized the importance of facial harmony from Dr. Angle’s times. With the advent of cephalometric head films, various analyses were developed in an attempt to qualitate and quantitate esthetic facial profiles. However the primary correction aimed was of the dento-alveolar structures, under the tacit belief that the soft tissue improvement would necessarily follow that in the hard tissues. However, it was realized that this did not always happen. The response of the soft tissue movement to the hard tissue could be quite variable. This gave an impetus to the development of soft tissue analyses.

The rationale of the soft tissue analyses is as follows: Individual facial traits and their balance with one another should be identified before treatment. Orthodontic norms for facial traits can permit their measurement.
Further, 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. Some of them are: the Reidel plane, Steiner’s [1] plane, Zero meridian angle by Gonzales-Ulloa, Merrifield’s Z-angle, divine proportion (1.0 to1.618) as originally devised by Greeks and introduced into orthodontics by Ricketts [2], Ricketts’ E-line, Worm’s lip assessment, Holdaway [3] Hangle etc

But the disadvantages of the above analyses were:

1. 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.
2. The vertical reference planes, which were related to the above horizontal planes, were obviously unreliable.
3. Soft tissue mid-face landmarks were not given proper importance. Further, conventionally taken cephalograms do not show them clearly.

To overcome these shortcomings, Arnett [4] et al 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), thus enabling an assessment of a patient as he/she presents himself/herself to the society. Arnett [4] et al also used “mid face metallic markers” to locate soft tissue mid face landmarks. 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.

However, it may be inappropriate to apply directly the values of Arnett’s analysis to Indian population because it is a known fact that facial features of different ethnic groups differ significantly. Further, the esthetic concepts of different societies also differ widely. Therefore it is essential that norms are established for individual ethnic groups instead of relying on norms established for the Western population. Thus it was felt that there is a need to establish the norms for Local population based on Arnett [4] cephalometric analysis, which would be useful for the local (Andhra) population in particular and the Indian population in general.

Aims & Objectives

1. To establish cephalometric norms for male and female subjects of the Local (Guntur-Andhra) population based on Arnett [4] soft tissue analysis.
2. To compare the norms so established with the original norms published by Arnett, and also with the norms derived by other similar studies.
3. To derive the clinical implications of the study as applicable to orthodontic and Orthognathic surgery treatment planning.

Materials and Methods

The present study included a sample size of sixty subjects (30 male and 30 female), selected randomly from the local (Andhra) population, having acceptable facial profiles and the age ranging between 18-30 year. The records of each subject included Photographs, Dental study casts and a lateral cephalogram taken in Natural Head Position. The NHP was recorded based on the method proposed by Dr. N. Sleevaraju [5] et al. The method was chosen since it captures the true vertical, as related to the Natural Head Position of the person, on his/her face itself before the cephalogram is taken. Thereafter, there is no deviation from the routine procedure for obtaining the cephalogram.

The subject is made to assume the NHP. The shadow of a plumb line suspended on the right side of the subject is seen on the right side of the face from an illuminated light source. Two markings, one near the outer canthus of eye and the other near the angle of mandible, are made on the face over the shadow of the plumb line. The whole procedure is repeated few more times to ensure that the two markings repeatedly fall on the shadow of the plumb line. Thus the accuracy of the recording of NHP is ascertained. Metallic markers are fixed at the markings over the face. Then the cephalogram is taken in a conventional manner. The True Vertical Line (TVL) is established on the lateral cephalogram by connecting the shadows of two metallic markers. The vertical or horizontal position of soft tissue and hard tissue landmarks are assessed relative to the TVL. Cephalograms for all the subjects were obtained in this manner, after placing metallic markers to denote the midfacial structures.

All reference points were first identified, located and marked. A reference TVL was drawn through the Subnasale parallel to the TVL drawn on the cephalogram. When the bilateral structures cast double shadows on the film, the bilateral images were averaged. The landmarks were chosen and measurements were made according to the STCA. Structures to the right of the TVL were given a positive sign and those to the left of TVL were given a negative sign.

Setup Images.

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Results

The results were statistically analyzed to establish norms for the local population as well as to compare them with the findings of other studies. Statistical significance of the difference between the male and female samples of the present study as also in the comparison with norms from other studies was tested with the “t” test. A “P” value of ≤ 0.05 was considered statistically significant, “P” ≤0.01 as highly significant and “P” ≤ 0.001 as very highly significant. Means, Standard deviations and probability values for the 30 males and 30 females are shown in Table No. I. Normal values were calculated as mean ± 1 SD for reference in the treatment procedure.

The results are presented in the form of tables consisting of statistical comparison between:

1. The males and females in the present study.
2. The present study and the Arnett study (separately for male and female samples).
3. The present study and the Anmol .Kalha study (separately for male and female samples).

The comparisons are also graphically depicted.

Table 1. Statistical Comparison of males and females with respect to the Arnett analysis measurements.

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Table 2. Comparison of the present study (local population) with the Arnett study (Males).

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Table 3. Comparison of the present study (local population) with the Arnett study (Females).

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Table 4. Comparison of the present study (local population) with the Anmol .S.Kalha study (Males).

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Table 5. Comparison of the present study (local population) with the Anmol .S.Kalha study (Females).

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Graph 1. Comparison of the Mean and SD age of study subjects according to Gender.

Graph 2. Comparison of male and female samples with respect to some Dentoskeletal measurements.

Graph 3. Comparison of male and female samples with respect to soft tissue thickness measurements.

Graph 4. Comparison of male and female samples with respect to hard tissue measurements.

Discussion

The statistical results in the present study showed the following differences between the males and females:

Males have more upright maxillary and mandibular incisors, thicker soft tissue structures, increased facial length and lip length measurements, increased lower third of face, deep-set mid face structures and greater nasal
prominence than the females.

A comparison of the present study with the Arnett STCA showed:

1. Proclined maxillary and mandibular incisors with steeper occlusal plane in both males and females of the present study.
2. Lesser maxillary incisor exposure in both males and females than in the Arnett study.
3. Thicker lower lip, shorter and protrusive lips in both males and females of the present study.
4. Acute Nasolabial angle in the males of the present study.
5. Reduced lower face height in the present study sample.
6. Larger faces and thicker soft tissue structures in both males and females of the present study.
7. Increased nasal prominence in Arnett study.
8. Retrusive lower faces and recessive chins in both males and females of the present study.
9. Increased interlabial gap in both males and females of the present study.

A comparison of the present study with the study of Anmol S. Kalha et al showed:

1. Proclined maxillary incisors in males and steeper occlusal plane in females of the present study whereas proclined maxillary and mandibular incisors in the females of Anmol.S.Kalha study.
2. Thicker lower lip in both males and females of the present study.
3. Increased mandibular height in males of the present study.
4. More retruded mid face structures and larger faces in both males and females of Anmol .S. Kalha study.
5. Protrusive upper lip and increased soft tissue chin thickness in females of the present study.
6. Recessive chins in both males and females of the present study.

Clinical Implications

1. 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 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.
2. The difference in facial heights between men and women might be significant in treatment planning because these differences can be indications to increase or decrease facial height.
3. The difference in soft tissue parameters in different ethnic groups show 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.

Shortcomings of the Study

1. A major shortcoming of any such study to define norms is that it reflects the esthetic bias of the investigator/s in selecting the sample. It may not necessarily agree with the esthetic perception of the people at large. Even amongst the dental specialties, esthetic preferences are known to differ.
2. In common with any similar study, our study also suffered from the shortcoming of being a two dimensional study of the three dimensional face. With the merging of cone beam imaging and 3D photography, new levels of
   facial analysis are expected to be developed in near future.

Scope for Future Studies

1. Further studies could be carried out using much larger samples.
2. In judging the acceptable esthetics, a bigger panel of judges including other professionals and lay persons could be employed.

Conclusion

Arnett et al developed the STCA [4] for Orthodontic and Orthognathic surgery treatment planning as a follow up of their previously proposed clinical method of 3-dimensional blueprint for soft tissue analysis in the form of the facial keys. This analysis truly reflects the changed paradigm. Lateral cephalometric norms, however, may be specific to an ethnic group and cannot always be applied to other ethnic types. The findings in the present study suggest that different set of cephalometric norms for different ethnic groups should be established. These differences in the soft tissue norms in various populations depict the significance of defining what is normal or optimal for a particular group, and to establish separate norms for men and women. Because mildly proclined incisors, mild facial convexity and retruded lower faces are considered as normal in the Indian scenario, the Orthodontist and Oral surgeon should use local norms as reference for optimizing treatment planning to obtain optimum esthetic outcome.

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Contributed by:

Dr.Ch.Lalitha
Assistant Professor, Kamineni Institute of Dental Sciences, Narketpally, Nalgonda (Dt)-508254, Andhra Pradesh, India

Dr. K.G. Gopa Kumar
Senior Professor in Orthodontics, Trivandrum, India