- Email: [email protected]
Degradation of dental polymers
152
J. Dent.
1987;
15: No. 4
Smith D. C. (1975) In: Silverstone L. M. and Dogan I. L. (eds), Proceedings of an International Symposium on the Acid Etch Technique. St Paul, MN, North Central Publishing Co., pp. 163.
Smith D. C. (1982) A milestone in dentistry. Oper. Dent. 7, 14-25.
Wilson A. D., Prosser H. J. and Powis D. M. (1983) Mechanism of adhesion of polyelectrolyte cements to hydroxyapatite. J. Dent. Res. 62, 590-592.
Correspondence should be addressed to: Mr Y. E. Y. Aboush, Department of Conservative Dentistry, Bristol Dental Hospital and School, Lower Maudlin Streeet, Bristol BSl 2LY, UK.
Book Reviews Degradation of Dental Polymers. J-F. Roulet. Pp. 228. 1987. Basle, Karger. Hardback, f 77.70. I This important publication is rather misleadingly titled, for it is concerned solely with the degradation of composite resins and glass-ionomer cements and does not deal with any of the other polymer systems used in dentistry. The book opens with an invaluable and comprehensive account of the ‘state of the art’ in composite resin technology. Polymer structures, resin systems, polymerization mechanisms and filler types are considered in detail. The second chapter deals with modern concepts of the wear mechanisms at work in composite resins, with coverage of abrasive and adhesive wear, the degradation of fillers and the loosening of the structure of composite materials through fatigue and chemical attack on the highly stressed resin/filler interface. The various methods of wear testing in vitro are compared and the relevance of their results discussed at length. Studies of wear in vivo are similarly compared, contrasting their methods, accuracy and duration. The author reports in detail on his three recent studies. First, he describes a computer-based system for the measurement of wear in vivo by the mapping of the occlusal surface of replicas at loo-pm intervals which is capable of detecting changes of less than 1 ym. This revealed greatly increased wear in regions of occlusal contact. Second, fatigue testing with thermal cycling revealed that some composites showed catastrophic failure due to crazing of their surface. Third, he reports on a 2-3-year study of the changes in composite resin specimens attached to the underside of sanitary pontics and thus protected from tooth brushing and occlusal load. There was considerable deterioration due to chemical and biological attack from the oral environment, and the weakness appeared to be the interface between filler or prepolymerized blocks and the resin matrix. This book, copiously illustrated and with extensive bibliographies, will be of great value to all those concerned with the study of modern restorative materials
and is a timely reminder of the disappointing resistance of composites to fatigue-related wear generated by occlusal forces. A. R. Ogden Sweetness: ILSI Human Nutrition Reviews. Edited by John Dobbing. Pp. xvii +282. 1987. Springer-Verlag. Hardback, f42.00.
London,
This book is based on a symposium organized by three nutrition societies and including as contributors nutritionists, chemists, neurophysiologists, psychologists and social scientists. It opens with a cross-section of present views on what types of molecule are perceived as sweet and how the sensation of sweetness is coded by sensory receptors and modified by psychological factors. The behavioural scientists consider changing attitudes to sugar and sweetness, seeing the development of a critical attitude as part of a guilt response to pleasurable sensations. The psychophysicists review the evidence that sweetness is an inborn taste and preference. An interesting sidelight here is the theory that sweet taste perception causes release of endogenous opioids and affects pain sensation. The relation between sweetness and food preference is considered by the nutritionists, together with the question of what determines satiety. Sweet foods are often eaten in an otherwise satiate state. No particular patterns of sweetness perception have been found in patients with obesity, bulimia or anorexia. There is no good evidence that sugar intake itself can be related to antisocial behaviour, although, in a different context, sugars have been used as a kind of currency in attempts to condition behaviour. Finally, two food chemists consider the adjustment of sweet flavours in relation to public demand. This is a book which dentists might profitably dip into: the coverage is wide and the scientific standard high but it remains readable and interesting. If we are to condemn the intake of simple sugars because of their role in dental disease, it is important that we should be wellinformed about these other aspects of the physiology and psychology of sweetness. D. B. Ferguson
J. Dent.
1987;
15: No. 4
Smith D. C. (1975) In: Silverstone L. M. and Dogan I. L. (eds), Proceedings of an International Symposium on the Acid Etch Technique. St Paul, MN, North Central Publishing Co., pp. 163.
Smith D. C. (1982) A milestone in dentistry. Oper. Dent. 7, 14-25.
Wilson A. D., Prosser H. J. and Powis D. M. (1983) Mechanism of adhesion of polyelectrolyte cements to hydroxyapatite. J. Dent. Res. 62, 590-592.
Correspondence should be addressed to: Mr Y. E. Y. Aboush, Department of Conservative Dentistry, Bristol Dental Hospital and School, Lower Maudlin Streeet, Bristol BSl 2LY, UK.
Book Reviews Degradation of Dental Polymers. J-F. Roulet. Pp. 228. 1987. Basle, Karger. Hardback, f 77.70. I This important publication is rather misleadingly titled, for it is concerned solely with the degradation of composite resins and glass-ionomer cements and does not deal with any of the other polymer systems used in dentistry. The book opens with an invaluable and comprehensive account of the ‘state of the art’ in composite resin technology. Polymer structures, resin systems, polymerization mechanisms and filler types are considered in detail. The second chapter deals with modern concepts of the wear mechanisms at work in composite resins, with coverage of abrasive and adhesive wear, the degradation of fillers and the loosening of the structure of composite materials through fatigue and chemical attack on the highly stressed resin/filler interface. The various methods of wear testing in vitro are compared and the relevance of their results discussed at length. Studies of wear in vivo are similarly compared, contrasting their methods, accuracy and duration. The author reports in detail on his three recent studies. First, he describes a computer-based system for the measurement of wear in vivo by the mapping of the occlusal surface of replicas at loo-pm intervals which is capable of detecting changes of less than 1 ym. This revealed greatly increased wear in regions of occlusal contact. Second, fatigue testing with thermal cycling revealed that some composites showed catastrophic failure due to crazing of their surface. Third, he reports on a 2-3-year study of the changes in composite resin specimens attached to the underside of sanitary pontics and thus protected from tooth brushing and occlusal load. There was considerable deterioration due to chemical and biological attack from the oral environment, and the weakness appeared to be the interface between filler or prepolymerized blocks and the resin matrix. This book, copiously illustrated and with extensive bibliographies, will be of great value to all those concerned with the study of modern restorative materials
and is a timely reminder of the disappointing resistance of composites to fatigue-related wear generated by occlusal forces. A. R. Ogden Sweetness: ILSI Human Nutrition Reviews. Edited by John Dobbing. Pp. xvii +282. 1987. Springer-Verlag. Hardback, f42.00.
London,
This book is based on a symposium organized by three nutrition societies and including as contributors nutritionists, chemists, neurophysiologists, psychologists and social scientists. It opens with a cross-section of present views on what types of molecule are perceived as sweet and how the sensation of sweetness is coded by sensory receptors and modified by psychological factors. The behavioural scientists consider changing attitudes to sugar and sweetness, seeing the development of a critical attitude as part of a guilt response to pleasurable sensations. The psychophysicists review the evidence that sweetness is an inborn taste and preference. An interesting sidelight here is the theory that sweet taste perception causes release of endogenous opioids and affects pain sensation. The relation between sweetness and food preference is considered by the nutritionists, together with the question of what determines satiety. Sweet foods are often eaten in an otherwise satiate state. No particular patterns of sweetness perception have been found in patients with obesity, bulimia or anorexia. There is no good evidence that sugar intake itself can be related to antisocial behaviour, although, in a different context, sugars have been used as a kind of currency in attempts to condition behaviour. Finally, two food chemists consider the adjustment of sweet flavours in relation to public demand. This is a book which dentists might profitably dip into: the coverage is wide and the scientific standard high but it remains readable and interesting. If we are to condemn the intake of simple sugars because of their role in dental disease, it is important that we should be wellinformed about these other aspects of the physiology and psychology of sweetness. D. B. Ferguson