Thesis (Dr. P.H.)--University of Michigan. / Includes abstract (1 leaf). Photocopy of typescript. Ann Arbor, Mich. : University Microfilms International, 1980. -- 21 cm. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 75-83).

published_or_final_version / Dentistry / Master / Master of Orthodontics

<p>The Aim of this study was to determine wheteher there are changes in the interdental arch widths and arch lengths of the madibular and maxillary arches during no-extraction and extraction orthodontic treatment. The records of 78 patients treated by one orthodontist were used for this study. Statistical data analysis included descriptive statistics of the data, analysis of the matrices, Wilcoxon Signed Rank tests and Kruskal-Wallis tests of the changes which occured during treatment. The study concluded that extraction treatment does not necessarily lead to the narrowing of the dental arches in the canine region.</p>

<p>&quot / Although facial aesthetics has always been a part of orthodontic diagnosis and treatment planning, the criteria for facial evaluation have been somewhat arbitrary. They are often based on parameters from the field of art or from evaluating faces chosen by orthodontists or other professionals. The aims and objectives of the study were to determine the soft-tissue profile preference of a group of lay persons and professionals / to compare the preferences of the male and female assessors (lay persons group) with regard to the preferred profiles for the maleand female patient respectively / to test similarities and differences in the professional's perceptions of the various profiles. This qualitative study was undertaken at the orthodontic clinic at UWC using post-treatment soft tissue profile photographs of patients who had attended the orthodontic clinic...&quot / </p>

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It has been well recorded that, until fairly recent times in this country, dentitions disintegrated at a relatively young age. In way of explanation it has generally been assumed that the complete lack of oral hygiene that existed resulted in a rapidly advancing periodontitis. The almost universal finding of exposed root surfaces at a young age did much to confirm the hypothesis that the attachment loss observed was inflammatory in origin. Furthermore, from the 17<SUP>th</SUP> century onwards the prevalence of dental caries escalated rapidly as the carbohydrate level of diets in this country rose due the importation of sugars from abroad. The existence of these two dental diseases seemed to explain adequately the observed early loss of dentitions. However, in studying historic skeletal material close inspection often reveals that despite the severe attachment loss the alveolar bone appear to be reasonably healthy with only minimally damaged septal areas. A further observation in almost all historic skeletal material is that of severe occlusal attrition of dietary origin. Many of the earlier workers in the field of dental paleopathology believed that the root exposure they observed was not due to inflammatory alveolar bone loss but was secondary to occlusal attrition and was in fact explained by the teeth continuing to erupt to compensate for the lost tooth height. This thesis investigates the relationship between occlusal attrition, compensatory eruption and the prevalence of periodontitus. It attempts to determine the reasons for the early disintegration of dentitions and investigates material covering a period of some three thousand years. The findings suggest that the prevalence of periodontal disease has changed little over this period and was therefore unlikely to have been responsible for the early loss of dentitions. Evidence is provided to show that compensatory eruption of the human dentition does occur in response to occlusal wear of dietary origin and that this supereruption is past a static alveolar crest, thus exposing root surface. The conclusion is drawn that the early loss of dentitions in this country prior to the 17<SUP>th</SUP> century was more likely to be due to complications associated with compensatory tooth eruption secondary to severe attrition of dietary origin. But after this period the escalating prevalence of dental caries became the major factor in tooth loss. Softer diets reduced the incidence of supereruption of the teeth. From the results of this study recommendations are made regarding epidemiological studies on both clinical and skeletal material and the point is stressed of the importance of recording the presence or absence of occlusal attrition if linear measurements of attachment loss are used to record periodontal status.

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Crowns have been used since the 5th century AD to improve both the form and function of teeth in the mouth. A great proportion of the total expenditure on dental care is spent on the provision and replacement of crowns and bridges and the number is increasing every year. A full coverage crown is a restoration placed over a single prepared tooth or it acts as an abutment in a bridge for the restoration of a missing tooth or teeth. Crowns are considered successful only when they meet both the aesthetic and functional requirements of the patient. For these to be met, certain principles for the preparation of the abutment tooth must be adhered to / such principles include features that are incorporated in the tooth preparation that enable it to withstand the forces of dislodgement that the tooth is exposed to both at rest and function. These features are described as the retention and resistance form of the preparation and the important aspect of these is taper. The taper of a tooth preparation is inversely proportional to the retention provided by the preparation. Volumes have been written on the difficulties encountered in making crowns with an adequate taper. Training, experience and operating conditions are among the many determinants of taper obtained by clinicians. Taper values of 2&ordm / to 5&ordm / were recommended initially for successful crown restorations but over time it was realized that these values were difficult to achieve under clinical conditions without creating undercuts in the preparation. Besides it was shown that even higher taper values might provide adequate retention for crowns. In addition, extra-retentive features such as axial grooves and boxes have been shown to improve retention of crowns. Many of the new luting cements also have adhesive properties that contribute to better retention of crowns and bridges. Various studies have established the prevalent taper obtained by dental students, general practice dentists, residents and prosthodontists while some of these studies have compared the prevalent taper among the different categories of clinicians. None of the studies so far reported has shown the prevalent taper in this environment / all without exception have investigated conditions in Europe, North America and Asia. Aim: This study therefore investigated the prevalent taper obtained routinely under clinical conditions by dental students, general dental practitioners and prosthodontists in two African countries and compared them with the recommended range of 10&ordm / to 22&ordm / . <br /> <br /> Method: 432 dies of teeth prepared by students, general practice dentists, resident and practicing prosthodontists were collected and analysed for taper using the double silicone technique. This involved making silicone replicas of the dies, sectioning these at various points and using photographs of the sections to measure their taper. Comparisons of the tapers obtained were carried out between the students, general practitioners and prosthodontists as well as between taper obtained on the different tooth types. Results: Taper ranging from 2&ordm / to 100&ordm / was obtained on the various tooth types. A mean mesio-distal (MD) and bucco-lingual (BL) taper of 22.5&ordm / (SD 11.2) and 26.2&ordm / (SD 11.1) respectively and a mean overall taper of 24.3&ordm / (SD 9.2) were obtained. Prosthodontists obtained the lowest taper (MD = 20.5&ordm / (SD 10.6)), BL = 24. 5&ordm / (SD 10.1) and a mean overall taper of 22.5&ordm / (SD 8.4). Students were second with a mean MD taper of 23.8&ordm / (SD 10.1), BL taper of 26.1&ordm / (SD 10.9) and a mean overall taper of 25.0&ordm / (SD 8.4). The general practice dentists obtained a mean MD and BL taper of 24.5&ordm / (SD 12.4) and 29.1&ordm / (SD 12.1) respectively and a mean overall taper of 26.8&ordm / (SD 10.6). The lowest taper was seen on premolars while the highest was on molars. Conclusion and recommendation: Most of the preparations analysed had a taper outside the recommended range of 10&ordm / to 22&ordm / . However, these tapers were similar to those found in other studies. Routinely incorporating extra-retentive features into crown preparation designs will improve success of crown restorations and adhesive cements should be used whenever conditions that allow for adequate retention are not met. The importance of taper should be emphasized more in dental schools and tooth preparation support systems should be used for teaching wherever possible. The need for regular refresher courses for practicing dentists and prosthodontists cannot be over-emphasized.