All PhD Theses

R.H.J. Peerlings

Orthodontie en dento-faciale esthetiek

25-05-1992

A scientific essay in Medical Sciences

DOCTORAL THESIS defended in public on 25th of May 1992

SUMMARY

In chapter 1 a general introduction concerning the importance of appearance in modern society is given. Many people attach value to an attractive appearance. As a consequence of this cosmetic dentistry has got more and more attention. For many patients an improvement of their appearance is one of the main reasons to undergo orthodontic treatment. However not much is known about the influence of orthodontic treatment on facial appearance. In this thesis the relationship between orthodontic treatment and dento-facial appearance is studied.

In chapter 2 the existing knowledge about the relationship between anatomical and facial features, and dento-facial appearance is discussed. Furthermore attention is given to the applied methodology and to problems encountered in studies concerning this topic. Photographs seem to be appropriate to get valid ratings of facial appearance. In several studies panels were used to evaluate dento-facial appearance. The results suggest that individuals, although no objective standard is available, hold a common standard of attractiveness, which they use to evaluate the physical appearance of others. On the basis of the acquired knowledge the aim of the study is formulated.

In chapter 3 a pilot study is described. One of the objectives of this study is to investigate whether individuals can use dento-facial esthetics as a criterion when judging facial appearance of children. Also the influence of dental features, and outdated fashion and hair-dress on the ratings of facial appearance is studied. It was concluded that inter-observer agreement is good. No influence could be determined of outdated fashion and hair-dress on the ratings. Facial expression on the other hand seems to influence the ratings obtained for dentofacial esthetics.

In chapter 4 some information is given about scales in general, their qualities and different levels of measurement. With the aid of scales, opinions of people regarding heterogenious matters can be measured. In this chapter, more detailed information is given on several scaling techniques, suitable for the development of a scale for rating dento-facial esthetics. Ratio estimation, a technique developed in psycho-physical research and later on succesfully applied in social sciences, is chosen as technique for the development of the scales which will be used in this thesis. With this technique it is possible to get repeated measurements during the construction of the scale without sensitivity for memory effects The level of measurement is log-interval This means that after logarithmic transformation of the data statistics on an interval level can be applied. Finally one has to remark that this technique leads to a scale with metric qualities.

In chapter 5 the development of four scales, for boys and girls, aged 11.0 to 13.0 and 14.0 to 16.0 years is described. Photographs from children at this age with a standard three quarter view of the smiling face were available. These photographs are rated for facial esthetics by three panels consisting of orthodontists, parents and children by means of ratio estimation. Intra- as well as inter-observer agreement is satisfactory. Reliability of the composed score, and agreement between the different panels is good For all observers together a mean score per photograph is calculated For the construction of the scales, from each group five photographs with their respective scores are selected.They represent the whole range, from unattractive to beautiful, and are evenly distributed. Next reliability and discrimination of the scales is tested. Both meet the requirements.

In chapter 6 the design of the study is given. A jury of six judges will rate dento-facial esthetics of two groups of children with the developed scales. For this purpose photographs of these children were available at two different ages. The experimental group consists of children before and after orthodontic treatment, 11 0 to 13 0 and 14.0 to 16 0 years old respectively The reference group consists of orthodontically treated children after treatment, and some years later, also 11 0 to 13.0 and 14 0 to 16.0 years old respectively. From all children dental casts and head films are available These will be measured to study the relationship between dento-facial esthetics on one hand, and malocclusion and cephalometric features on the other hand. Firstly the procedure followed for the selection of the jury is described. Next the material to be rated and the composition of the two groups is discussed.

In chapter 7 a description is given of the malocclusion features of the two groups at both ages, boys and girls separately Arch length discrepancy, overjet, overbite, diastema, ectostemic cuspids and missing front teeth are measured. For the measurement of all these features intra- as well as mterobserver agreement is good The data show that in the experimental group the degree of malocclusion decreases importantly. In the reference group on the other hand, the values are at both ages more or less the same.

In chapter 8 the cephalometric features of the children of both groups are presented. Angle ANB, angle Mp/SN, angle +1/NA, T-angle according to Schwartz, and the distances sn'-me' and Pg-NB are measured. Firstly the projection error is quantified. This error appeared to be neglectable. Intra- and inter-observer agreement are good for the measurement of the different angles, distances and their increments, with exception of the T-angle according to Schwartz and angle Mp/SN. The most important differences between the reference and experimental group are found for angle ANB and the lower facial height. For the other features the differences between the groups are neglectible.

In chapter 9 the measurement of dento-facial esthetics of children from both groups is described, and the results are presented. Reliability of the measurements is good. A significant and positive effect of orthodontic treatment on dento-facial esthetics for girls is found. For boys the effect is also positive, but not significant. Malocclusion features with regard to regularity of the teeth, and cephalometric features expressing lower facial height and the convexity of the face, are significantly related to the ratings for dento-facial esthetics of the children of both groups aged 11.0 to 13.0 years. Irregularity of the teeth, a convex profile and a high value for lower facial height result in less positive ratings for dento-facial esthetics. When examining the relationship between correction of the various features by means of orthodontic treatment, and the ratings for dento-facial esthetics of the children from both groups aged 14.0 to 16.0 years, only the correction of overjet for boys seems to be of any importance. A positive correlation is found between the degree of overjet correction and the ratings for dento-facial esthetics.

In chapter 10 the results of the thesis are discussed and some suggestions are given for research in the future.