The aim of this study was to assess the prevalence of malocclusion and its association with socio-demographic characteristics, caries experience, and level of oral hygiene in 12- to 14-year-old schoolchildren residing in two socio-economically different districts of Tanzania. A total of 1601 children (mean age 13 years, 60.5 per cent girls) attending 16 primary schools in Kinondoni and Temeke districts participated in a clinical examination and were interviewed in school settings. Chi-square and multiple logistic regression models were used to test for statistically significant differences between different groups. The results showed that 63.8 per cent (62.6 per cent in Kinondoni and 66.0 per cent in Temeke) of the subjects had at least one type of anomaly, with a midline shift (22.5 per cent), spacing of at least 2 mm (21.9 per cent), and an open bite (16.1 per cent) being the most frequently recorded. The majority (93.6 per cent) of the children showed a Class I molar relationship. Class II and Class III malocclusions were registered in 4.4 and 2.0 per cent, respectively. Multiple logistic regression analyses, controlling for socio-demographic factors, showed that the odds ratio for having an open bite was 1.8 if residing in a less socio-economically privileged district. Subjects with decayed, missing, and filled teeth (DNFT) (>0) were 1.7, 2.1, 2.4, and 1.7, respectively, more likely to be diagnosed with a malocclusion, a midline shift, Angle Class II and III, and an open bite. Schoolchildren with fair/poor oral hygiene were less likely than their counterparts with good oral hygiene to be diagnosed with a midline shift. Malocclusions were prevalent in the Tanzanian children investigated and were associated with environmental factors in terms of caries experience and residing in a less affluent district. Preventive programmes to combat the prevalence of malocclusion are recommended.

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The present light microscopic investigation was undertaken in order to study the initial phase of orthodontic root resorption in areas of pressure and, more specifically, to focus on the first cells that penetrate the root surface. Twenty-one upper first molars (rats) and 31 lower first molars (mice) were moved mesially by a fixed orthodontic appliance. The experimental periods were 1, 2, 3, 4, and 5 days in rats, and 1, 2, 3, 4, 5, 6, 7, and 8 days in mice. Tartrate-resistant acid phosphatase (TRAP) and Haematoxylin Eosin (H&E) stains were used. Root resorption related to a hyalinized zone showed a consistent pattern: Root resorption started in the circumference of the necrotic hyalinized tissue. In the central parts of the hyalinized zone frontal root resorption occurred 3-4 days later than in the periphery. Indications that the mechanisms for circumferential and central resorption differed was the reason for presenting only the periphery stage in this paper. The initial penetration of cells into precementum/cementum occurred at the peripheries or at a short distance from the peripheries of the hyalinized zone. These cells were TRAP-negative, indicating that they were not clasts or clast precursors. Before this happened TRAP-negative macrophage-like cells were observed at the borderline between the hyalinized tissue and vital periodontal membrane (PM). TRAP-positive cells were first observed in the bone marrow spaces. During the later stages mono- and multi-nucleated TRAP-positive cells were participating in active removal of the hyalinized tissue toward the root surface, and in resorption of cementum and dentine.

Remodelling of the periodontium after application of mechanical forces constitutes the basis of clinical orthodontics and various immunoregulatory molecules are involved in this process. The aim of this study was to investigate the expression of the cytokines interleukin-1alpha (IL-1alpha) and tumor necrosis factor-alpha (TNF-alpha) in dental tissues during the early phases of orthodontic tooth movement. Eightteen male Wistar rats were used. All maxillary right first molars were moved orthodontically, with a force of 0.5 N, for 3 h, 1 d, and 3 d. The contralateral sides served as untreated controls. Parasagittal sections of the maxillary molars and the surrounding tissues were subjected to immunohistochemical staining for IL-1alpha or TNF-alpha, and were evaluated with light microscopy. IL-1alpha and TNF-alpha were expressed in the bone and periodontal ligament (PDL) along the roots of the orthodontically moved molars and in the gingiva. Increased expression of both cytokines was observed in the aforementioned areas after 1 and 3 d of tooth movement. The pulp tissue exhibited only minor changes in cytokine expression during tooth movement. The results suggest that mechanical stress results in almost immediate inflammatory reactions in various dental tissues.

Previous research has indicated that orthodontically-induced root resorption is regularly associated with local trauma, most often with over-compression of the periodontal ligament (PDL). Recent research has revealed that the initial root resorption occurs in the periphery of the necrotic PDL, where mononucleated cells not stained by tartrate resistant acid phosphatase (TRAP), are the first cells to penetrate the root surface. The aim of the present transmission electron microscopic (TEM) investigation was to study in more detail the root surface during the initial penetration of cells into precementum and mineralized cementum. In 21 Wistar rats (age 40-45 days) the maxillary first molar was moved mesially by a closed coil spring for 6 and 12 hours, 1, 2, 3, 4, and 5 days. The results clearly indicate a role for mononucleated non-clast cells in the initial local removal of precementum and mineralized acellular cementum in the periphery not only near, but also at some distance from the compressed PDL. 1. Macrophage-like cells phagocytosed necrotic tissue in the middle of the PDL after 6 hours and near the root surface close to the hyalinized zone after 24 hours. 2. Fibroblast-like cells seemed to break down by phagocytic and collagenolytic activity the precementum near the hyalinized zone after 24 hours. 3. The surface layers of mineralized cementum were removed by mononucleated cells which occurred on the mineralized cementum after 3 days. 4. Multinucleated cells without ruffled border occurred in the PDL at some distance from the root surface after 24 hours. Multinucleated cells with a ruffled border towards the mineralized root surface were rare during the 5 days' period.