All PhD Theses

E.A. Al Yami

Orthodontics: treatment need and treatment outcome.


A scientific essay in Medical Sciences

DOCTORAL THESIS defended in public on 23rd of September 1997


Chapter 1 elucidates the background of the study and gives a review of the literature in the field of orthodontic treatment need and treatment outcome. The Index of Orthodontic Treatment Need (IOTN) and the Peer Assessment Rating (PAR) index which were utilized in this study were explained thoroughly.

Chapter 2 evaluates whether dental aesthetics as measured by the Aesthetic Component (AC) of the IOTN correlates with facial aesthetics. Facial attractiveness of 69 males and 75 females was scored on facial photographs at two different ages (1.1 to 13 years and 14 to 16 years). Scoring of the AC of the IOTN was undertaken on the dental casts. Increments between the observations at the two ages were calculated. To assess the association between scores of dental and facial aesthetics, correlation coefficients were calculated. There was a highly significant influence of orthodontic treatment on facial and dental aesthetic scores in the group which was not treated orthodontically at the first observation and was treated orthodontically at the second observation. No correlation, however, was found between the increments in the facial aesthetic score and the increments in dental aesthetic score. The results indicate that facial aesthetics and dental aesthetics are influenced by different factors. It was concluded that both dental and facial aesthetics should be evaluated when judging dento-facial aesthetics.

Chapter 3 assesses the effect of normal growth and development on the PAR index between 12 and 22 years of age. The sample consisted of 49 non-orthodontic subjects (24 male and 25 females) from the Nijmegen Growth Study. The mean age at the first observation was 12.2 ± 0.7 years and at the second observation 22.1 ± 0.6 years. The influence of the Angle classification and malocclusion severity on changes over time in the PAR score were evaluated. The mean changes in the PAR scores over time between cases which had more than 30% improvement to those which had less than 30% improvement were calculated. No significant differences between the mean PAR score at 12 years of age (12.20 ± 0.91) and at 22 years of age (12.45 ± 1.28) were found, but there where relevant differences in individual cases. The changes were irrespective of the Angle classification or the malocclusion severity. Changes over time in the weighted PAR score were mainly correlated to changes in the anterior crossbite and the overjet. This correlation may be influenced, however, by the applied weighting factor for those occlusal traits.

Chapter 4 describes the evaluation of dental casts of 920 patients (400 male and 520 females) with the IOTN index at the pretreatment (TP) and 5 years postretention stages (T5). The mean age at TP was 12.2 ñ 3.0 years and at T5 21.6 + 3.1 years. At TP and T5 the Aesthetic Component (AC) and the Dental Health Component (DHC were assessed. The difference between TP and T5 was compared for males and females and tested by the t-test. The changes in AC, DHC and treatment need categories were described at TP and at T5. Based on the combined AC and DHC treatment need categories 83% of the patients was falling in the "Definite need" prior to treatment and 10% of the patients was categorised as "Definite need" at 5 years postretention. No significant differences were found between males and females for the change in AC and DHC between TP and T5. The results indicated that the policy used in the department for patient selection is giving priority to the patients with a high treatment need. The results also provide a general impression of treatment outcome utilising the IOTN by analysing the change in the treatment need categories.

Chapter 5 evaluates the overall quality of orthodontic treatment. Standard orthodontic study models of 1870 patients (799 male and 1071 females) were evaluated at the pretreatment and post-treatment stage using the PAR index. The mean age at the pretreatment stage was 13 ± 4.1 years and at the post-treatment stage 16 ± 3.9 years. Mean and standard deviation (weighted) PAR score were calculated at the pretreatment stage and at the end of active treatment. The percentage reduction in the weighted PAR score was calculated to assess the improvement. The percentage of perfect scores (score = 0) of the different components of the PAR index was calculated. The analysis of variance was applied to compare the quality of treatment for the variables treatment period and gender. The results show that the mean weighted PAR score was 27.6 ± 10, and 7.7 ± 6.1, for the pretreatment and post-treatment dental casts respectively. The mean percentage improvement was 68.9%. The mean treatment duration was 3.0 ± 1.4 years. 42.6% of the sample was greatly improved, 49.1% was improved and 8.3% was not improved or became worse. The improvement of the PAR score at the post-treatment stage was explainable to some extent by the treatment period: the more recent was the period the better was the quality.

In chapter 6 dental casts of 2368 patients were evaluated for the long term treatment outcome using the PAR index. The PAR index was applied at the pretreatment stage, directly post-treatment, postretention, 2 years post-retention, 5 years postretention and then every 5 years until 20 years post-retention. The mean absolute change as well as the percentual change per year (relapse) related to the postretention stage was calculated. ANOVA was applied to compare the mean change in the PAR between cases with and without a fixed retainer at the postretention stage and up to 10 years post-retention. The results indicate that 64% of the achieved orthodontic treatment result was maintained 20 years post-treatment. In the first two years after retention 19.2% per year of the orthodontic treatment relapse as measured with the PAR index takes place. Cases which finished the retention period earlier than 15 (female) or 16 (male) years of age showed more relapse. All occlusal traits relapsed gradually over time but remained stable at later stages with the exception of the lower anterior contact point displacement which showed a fast and continuous increase, even exceeding the initial score. It should be more commonly considered to maintain retainers if some growth is still expected. Also, all patients should be informed prior to treatment about treatment limitations in order to better meet their expectations.

In chapter 7 dental casts of 2368 patients were evaluated using the PAR index at pretreatment, post-treatment, postretention, 2 years postretention and 5 years postretention. One-way ANOVA was used to compare the treatment duration, the mean PAR, and the absolute and percentual change in the PAR for the different Angle Classes at all stages. The Scheffe test was used for multiple comparison. The lowest PAR at the post-treatment stage was found for Class II/2 patients (6.2 + 4.7), maintaining the lowest PAR until 5 years postretention. Class III malocclusions have the highest PAR at the pretreatment stage and at all other post-treatment stages. There were no significant differences in the amount of relapse between different Angle Classes at all post-treatment stages.

Chapter 8 discusses the results from the previous chapters and gives suggestions for future research.