Short-term extrusion of isolated teeth of adult monkey (Macaca fascicularis)

Extreme dentoalveolar compensation in the treatment of Class III malocclusion

The orthodontic treatment of an adult patient with a skeletal Class III malocclusion, increased anterior facial height, negative overjet, and bilateral posterior crossbite is presented. Treatment options included mandibular first premolar or third molar extractions with dentoalveolar compensation or combined surgical-orthodontic treatment. Mandibular third molar extraction with dentoalveolar compensation was the treatment choice. Biofunctional brackets, with accentuated lingual crown torque on the maxillary incisors and accentuated buccal crown torque on the mandibular incisors, were used. The anterior crossbite was corrected with intermaxillary elastics from the palatal aspect of the maxillary incisors to the labial aspect of the mandibular incisors. Class III elastics moved the maxillary teeth mesially and assisted in retruding the mandibular teeth. Patient compliance with the elastics was excellent, and satisfactory dentofacial esthetics were achieved. This treatment protocol has rigorous indications, and it is not a routine plan. The mechanotherapy and the pros and cons of this approach are discussed.

An RSPCA/FRAME Survey of the Use of Non-human Primates as Laboratory Animals in Great Britain, 1984–1988

A literature-based survey of the use of non-human primates as laboratory animals in Great Britain in 1984–1988 was carried out as a background to extending debate about the ethical and practical issues involved. The 289 publications considered were grouped in 15 subject areas and reviewed in terms of scientific purpose, methods employed, numbers and species of animals used, and their source, care and ultimate fate. In addition, the Association of the British Pharmaceutical Industry provided a comment on the use of non-human primates by pharmaceutical companies. Specific causes for concern were identified, and future prospects considered.

Some causes of failure of crowns, bridges and dentures

With increasing emphasis being placed on precision in the construction of prostheses the importance of the visco-elastic characteristics of tooth support should be understood. Since the tooth returns to its resting position quite slowly, especially when repeated or sustained forces have been applied, an impression prepared prior to fully recovery will convey erroneous relationships of the tooth with its neighbours to the working model and, eventually, to the prosthesis. Such an error has been identified in young human subjects when inter-dental wedges, gingival retraction cord, and rubber dam are placed. The preparation of conventional alginate impressions in special trays can displace abutment teeth to a clinically significant degree as was recorded for seven partially dentate patients. Simple precautions will circumvent these potential sources of error.

Biochemical changes in periodontal ligament ground substance associated with short-term intrusive loadings in adult monkeys (Macaca Fascicularis)

Proteoglycan-like fractions (PG) were isolated from the ligaments of teeth undergoing various degrees of intrusive loadings. The PG were characterized by their molecular-size profiles on Sepharose 4B, the presence of uronic acid in the separated fractions and by the electrophoretic detection of constituent glycosaminoglycans including heparan sulphate, hyaluronic acid, dermatan sulphate and chondroitin-4-sulphate. The high molecular-weight fraction, peak i (estimated minimum size, 2 X 10(6) daltons) of the normal-functioning (stressed) ligament was reduced approx. 70 per cent, compared with ligament undisturbed for 3 h. There was a decrease in peak-i size between 0.25 and 1 N loadings of approx. 72 per cent. The 4 N loadings produced a further decrease followed by an increase during a 3 h undisturbed recovery phase. Thus changes in the chemistry and properties of the ground-substance components of the periodontal ligament could partly explain changes in tooth mobility.

Changes in axial mobility of undisturbed teeth and following sustained intrusive forces in adult monkeys (Macaca fascicularis)

The axial mobility and changes in rest position were studied over 3-h periods. No loads were applied to 10 teeth. All displayed reduction in mobility; eight became extruded. Other teeth were displaced into their sockets to a sustained level by a screw for 3 h. Mobility decreased for those teeth which were intruded a distance equivalent to less than 800 mN force, but increased following greater intrusion. It is argued that vascular changes played no part; it is more likely that aggregation of proteoglycans occurred in the periodontal ground substance when there was little or no displacement of the tooth. Displacement would have generated tension in the collagen fibres of the periodontal ligament, leading to smaller proteoglycan molecules being formed and a consequent increase in mobility.