The dynamic remodelling processes in the periodontal ligament (PDL) account for the reaction of PDL cells to different orthodontic force simulations. These occur mostly by degradation and synthesis of collagen types I, III, V, VI, XII and XIV. The purpose of this study was to quantify specific collagen types in the PDL from zones of tension and compression of experimental teeth. Such changes could then be correlated with the processes of orthodontic-stimulated tissue breakdown. Maxillary and mandibular premolars of three females and one male patient were orthodontically moved with a box loop for a total of 14 days, prior to tooth extraction. Teeth from the contralateral side of either the maxilla or the mandible served as the untreated controls. A total of seven experimental and seven control teeth were used in this investigation. PDL fibroblasts from the cervical third of the roots corresponding to the compression and tension zones of the experimental and control teeth, respectively, were scraped and cultured in vitro at 37 degrees C in a humidified incubator with 5 per cent CO2/95 per cent air. Collagen synthesis of types I, III, V and VI was quantified by using an ELISA. Application of orthodontic forces in the experimental teeth showed a significant increase (P < 0.05) of the synthesis of all collagen types in the compression as opposed to the tension zones. Collagen synthesis on the compression zone of experimental teeth was not significantly different in the mandible when compared with those of the maxilla. In addition, the proportional distribution of different types of collagen was also not significantly different in the PDL fibroblasts from either zone of experimental teeth of either the maxilla or the mandible. Collagen metabolism in response to orthodontic stimulation appears to be higher in the compression zones and lower in the tension zones. Contrary to what is traditionally assumed in the literature, such findings indicate that in addition to bone resorption, tissue remodelling is very active in zones of compression following the disappearance of the hyalinized areas. These findings constitute a model for future studies on collagen metabolism during orthodontic-stimulated tooth movement.
This paper confines itself to the description of the profile of a general dentist while outlining where the boundary between specialist and generalist may lie. The profile must reflect the need to recognize that oral health is part of general health. The epidemiological trends and disease variation of a country should inform the profile of the dentist. A particular tension between the provision of oral healthcare in publicly funded and private services may result in dentists practicing dentistry in different ways. However, the curriculum should equip the practitioner for either scenario. A dentist should work to standards appropriate to the needs of the individual and the population within the country’s legal and ethical framework. He/she should have communication skills appropriate to ascertain the patient’s beliefs and values. A dentist should work within the principles of equity and diversity and have the knowledge and clinical competence for independent general practice, including knowledge of health promotion and prevention. He/she should participate in life‐long learning, which should result in a reflective practitioner whose clinical skills reflect the current evidence base, scientific breakthroughs and needs of their patients. Within the 4–5 years of a dental degree it is not possible for a student to achieve proficiency in all areas of dentistry. He/she needs to have the ability to know their own limitations and to access appropriate specialist advice for their patients while taking responsibility for the oral healthcare they provide. The dentist has the role of leader of the oral health team and, in this capacity; he/she is responsible for diagnosis, treatment planning and the quality control of the oral treatment. The dental student on graduation must therefore understand the principles and techniques which enable the dentist to act in this role. He/she should have the abilities to communicate, delegate and collaborate both within the dental team and with other health professionals, to the benefit of the patient. The profile of a dentist should encompass the points raised but will also be based upon competency lists which are published by a variety of countries and organizations. It is important that these lists are dynamic so that they are able to change in light of new evidence and technologies.
Second-messenger systems have been implicated to transmit mechanical stimulation into cellular signals; however, there is no information on how mechanical stimulation is affected by such systemic factors as parathyroid hormone (PTH). Regulation of adenylyl cyclase and phosphatidylinositol pathways in rat dentoalveolar bone cells by mechanical strain and PTH was investigated. Two different cell populations were isolated after sequential enzyme digestions from dentoalveolar bone (group I and group II) to study potential differences in response. Mechanical strain was applied with 20 kPa of vacuum intermittently at 0.05 Hz for periods of 0.5, 1, 5, 10, and 30 minutes and 1, 3, and 7 days using the Flexercell system. Levels of cAMP, measured by RIA, and levels of inositol 1,4,5-triphosphate (IP3) and protein kinase C activity (PKC), measured by assay systems, increased with mechanical strain. When PTH was added to the cells, there was a significant increase in levels of all the intracellular signals, which appeared to potentiate the response to mechanical strain. IP3 levels (0.5 minute) peaked before those of PKC activity (5 minutes), which in turn peaked before those of cAMP (10 minutes). Group II cells showed higher levels of cAMP and IP3 than the group I cells. This suggests that the former may ultimately play the predominant roles in skeletal remodeling in response to strain. Immunolocalization of the cytoskeleton proteins vimentin and alpha-actinin, focal contact protein vinculin, and PKC showed a marked difference between strained and nonstrained cells. However, the addition of PTH did not cause any significant effect in cytoskeleton reorganization. Staining of PKC and vimentin, alpha-actinin, and vinculin suggests that PKC participates actively in the transduction of mechanical signals to the cell through focal adhesions and the cytoskeleton, although only PKC seemed to change with short time periods of strain. In conclusion, dentoalveolar osteoblasts responded to mechanical strain initially through increases in levels of IP3, PKC activity, and later cAMP, and this response was potentiated when PTH was applied together with mechanical strain.
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