Biomedical subjects
Publications and source records attributed to J S Rees.
This article describes the treatment of a large maxillary cyst by root canal treatment and decompression using a hollow drain made from surgical suction tubing. The rationale behind the use of this technique is reviewed and its advantages highlighted.
Composite restorative materials were introduced to the dental profession in the early 1960s and quickly became the principal anterior restorative material. Following improvements in composite technology, these materials were also developed as aesthetic posterior materials but were initially hampered by problems of poor wear resistance. In this, the first of two articles on the uses of composite replacement materials, the development of composite resins are discussed and the problems of using direct-placement composite to restore posterior teeth are examined in detail. The second article will review the use of the composite inlay technique.
A characteristic feature of the sperm P1 protamines of eutherian mammals is the constant presence of six to nine cysteine residues per molecule. During spermiogenesis these residues become oxidized to form a three-dimensional network of disulfide bridges between, and within, protamine molecules in the sperm chromatin. This covalent cross linking strongly stabilizes eutherian sperm nuclei. In contrast, protamines sequenced from teleost fish, birds, monotremes, and marsupials all lack cysteine residues and their sperm nuclei, without the stabilizing cross links, are easily decondensed in vitro. We have now found that one genus of tiny, shrewlike dasyurid marsupials, the Planigales, possess P1 protamines containing five to six cysteine residues. These residues appear to have evolved since the divergence of Planigales from other members of the family Dasyuridae, such as the marsupial mouse, Sminthopsis crassicaudata. We believe this constitutes a case of convergent evolution in a subfamily of dasyurid marsupials toward the cysteine-rich eutherian form of sperm protamine P1.
The finite element method was used to model an in vitro tooth loading system. The dentine was modelled as a linear elastic and isotropic material, while the enamel was modelled as an anisotropic material to take account of the biological variation in prism angulation. The elastic modulus values of enamel and dentine used in this analysis were altered in order to replicate the movement of the in vitro system. It was found that a dentine modulus of 15 GPa and an enamel modulus of 80 GPa in the principal prism direction gave the best replication of cuspal movement.
The purpose of this investigation was to determine a static elastic modulus of dentine using a three point beam test and a dynamic modulus in the frequency range of 0.1 Hz and 10 Hz across a temperature range of 27-37 degrees C. At body temperature, the mean static modulus was 8.6 GPa, (standard deviation 0.86 GPa). The dynamic test produced a range of modulus values. At 0.1 Hz the modulus ranged from 14.3 to 15.2 GPa; for 1.0 Hz the range was 14.6-15.5 GPa and for 10 Hz the range was 14.9-15.8 GPa. The results are of value in the design and analysis of restorative materials.
The present paper deals with the problem of stresses generated during the setting process of polymer tooth fillings. A finite element procedure capable of accurately predicting the stresses along an interface between two different materials is presented. Adaptation of the finite element mesh is carried out based on a simple error estimator. The procedure is tested against benchmark problems and then applied to polymer tooth fillings. The results of the study are relevant in understanding and improving the behaviour of dental restorations.
The present study used the finite element method to model the stresses generated by a composite luting cement around a class I composite restoration and a ceramic inlay. In many cases maximum tensile stresses of greater than 20 MPa were found, and failure of the restoration-dentine and restoration-glass ionomer interfaces was predicted.
Over the last two decades there have been many changes in the basic concepts of periodontology, which have had profound effects on clinical practice. The aim of this series is to highlight the main areas of change to assist the busy GDP in staying up-to-date. Part 1 discussed current concepts in the histopathology of periodontal disease and part 2 looked at the problems of diagnosis. Part 3 will now examine the central role of plaque control in periodontics.
The requirements for luting agents for ceramic and polymeric inlays and onlays are reviewed and discussed. The current overriding consideration seems to be the chemical adhesion of the restoration to tooth substance and this is challenged as being an overambitious goal. The systems in use are principally the dual cure resin based cements and these have some disadvantages such as restricted and slow cure, chemical degradation and, most importantly, shrinkage on setting. This shrinkage, when the material is used in conjunction with a dentine bonding agent, is almost certain to guarantee the rupture of any bond formed. It is suggested that the objectives of the luting agent should be rethought with reference back to the well established principles of cast metal restorations.
Over the last two decades there have been many changes in the basic concepts of periodontology, which have had profound effects on clinical practice. The aim of this series is to highlight the main areas of change and to assist the busy general practitioner in staying up-to-date. The first article deals with the current understanding of the histopathogenesis of gingivitis and periodontitis.
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In recent years a new technique in periodontal surgery, known as guided tissue regeneration, has been developed in Scandinavia and the USA. After raising a flap and debriding the root surface, an inert membrane is placed between the flap and the underlying tissues. This allows the periodontal ligament to regain some of the connective tissue attachment lost during the disease process, something which has been unobtainable until now. The purpose of this paper is to review the area of periodontal reattachment and to introduce the new technique of guided tissue regeneration.
In the context of composite systems, the need for complete adhesion to cavity walls was discussed in the first paper. It would prevent the formation of interfacial gaps with the consequences of microleakage and bacterial infection.
The second article of this series reviewed the ways in which adhesion to tooth may be achieved. If such adhesion is a real possibility then it must be demonstrated convincingly to the world at large, both to substantiate claims and to promote marketing. This article reviews the ways in which adhesion can be demonstrated and discusses the many pitfalls which bedevil such studies.
The previous article reviewed the problems of demonstrating adhesion, either to a flat surface or within the confines of a cavity. In the context of the intracoronal cavity, microleakage experiments may demonstrate the net effects of bonding agents, cavity preparation and material properties.
The majority of methods used for the determination of volumetric polymerization shrinkage rely on mercury as the immersion medium. With current concern for industrial hygiene, the water-filled dilatometer may have advantages. The purpose of this study was to adapt this method for external-energy-cured materials. Six materials were investigated: Aurafill, Silar, Concise, Heliomolar, P-30, and Occlusin. Measurements were taken over one hour, and results ranged from 0.9 to 2.24 volume percent.
This series of articles reviews the current status, clinical techniques and developments in tooth coloured restorative materials and adhesive systems.