774

Journal of the Royal Society of Medicine Volume 85 December 1992

with keratoconus. They attributed this frequent association to an event during embryogenesis affecting at the same time the corneal stroma and mitral valve both of which form during the sixth to seventh week of fetal life. Although the exact aetiology of either mitral valve prolapse or keratoconus is still unknown, this embryogenetic theory of Sharif and associates is attractive and plausible. It has also been proposed as the explanation for the frequent association with mitral valve prolapse of secundum atrial septal defect, straight back and pectus excavatum, because the development of atrioventricular valves and septum secundum as well as the thoracic vertebrae and sternum proceeds simultaneously between days 42 and 49 of embyronic life"2.

1992 JRSM, p 457) Drs Heaton and Mountford conclude that 'bitten nails are not a feature of IBS, but rather of youth'. They state that they are not aware of any other scientific studies on nail-biting; in fact at least two studies were carried out on American naval personnel during the Second World War. In one study' out of a sample of 6946 recruits 21% were found to be nail biters. In line with the findings of Drs Heaton and Mountford the frequency of nailbiting declined with age. Another study2 examined the characteristics of 100 nail biters in the navy, and the author describes 73 ofthem as being of an unduly irritable disposition. The conclusion from this study was that nail-biters were less useful in military combat than their non-biting peers. But there was no mention of their bowel habits.

T 0 CHENG

M PHELAN

Professor of Medicine Division of Cardiology The George Washington University Medical Centre 2150 Pennsylvania Ave, NW, Washington DC 20037, USA

References 1 Barlow JB, Cheng TO. Mitral valve billowing and prolapse. In: Cheng TO, ed. The international textbook of cardiology. New York: Pergamon Press, 1986:497-524 2 Cheng TO. Mitral valve prolapse. Dis Month 1987; 33:481-534

The laser in dentistry I have read with interest the odontology report - let there be light (August 1992 JRSM, p 505). May I add my comments on medical dental use of lasers. Lasers are used to treat or rid the host of unwanted tissue. In essence iatrogenic thermal lesion is inflicted on focused tissue. It is fundamental that tissue enzyme systems orchestrate the defense and health of the body. These enzyme systems are heat labile and are easily destroyed by laser, cautery and as in days of old when boiling oils were applied to wounds. Thus with the damage or destruction of the aforementioned essential systems we are then left to wonder why infection, delayed healing and separation of eschar and subsequent haemorrhage occur. Perhaps we would be more judicious in our use of this modality. T A ARMAO 1-78th St (Cor Shore Road) Brooklyn, NY 11209, USA

Medical education and substance abuse Dr Fenton invokes the 'many commonalities' among the 'misuse' of illegal drugs and that of alcohol, but cites the 'extent of criminal involvement' as a difference (August 1992 JRSM, p 435). However ifwe take his earlier message about the role of 'the cost and availability' of alcohol to heart, by increasing the former and reducing the latter, surely at least we can quite quickly remove this difference? M J CHAPMAN Toxicologiste Conseil BP 19 F-69881 JONAGE Cedex, France

Nail biters in the navy In their article 'Nail-biting in the population and its relationship to irritable bowel syndrome' (August

Institute of Psychiatry De Crespigny Park London SE5 8AZ

References 1 Pennington LA. The Incidence of nail-biting among adults. Am J Psychiatry 1945;102:241-4 2 Hill JM. Nail-biting. Am J Psychiatry 1946;103:185-7

Age changes in teeth Further to the correspondence to the Journal (August 1992 JRSM, p 507) on the article by Dr Whittaker on age changes in the teeth, the matter of continuous, passive tooth eruption in the human adult is of more than academic interest. Chronic inflammatory periodontal diseases are the most widespread of all human diseases. The destructive stage, chronic periodontitis, results in loss of attachment of tooth to jaw, and of the supporting alveolar bone itself. The periodontal literature, while it frequently notes that a portion ofthe tooth root surface may be bare, implying attachment loss, singularly fails to appreciate that in older patients this may simply reflect that functional tooth wear is accompanied by continuing tooth eruption. Our measurements' and Dr Whittaker's2 make it clear that the alveolar bone is not lost in such groups with naturally functioning masticatory systems, but that the bone crest is maintained through life at the same distance from that fixed vertical growth reference line in the mandible, the upper border of the inferior alveolar canal. Even in modern dentitions, functioning with less natural foodstuffs, face height increases, with tooth eruption continuing, and with a concurrent partial exposure of the root surface. This has nothing to do with disease, and is nevertheless often wrongly interpreted as such3, with possibly quite unnecessary treatment a risk. HUBERT N NEWMAN

Institute of Dental Surgery

(British Postgraduate Medical Federation) University of London, Eastman Dental Hospital 256 Gray's Inn Road London WC1X 8LD

References 1 Newman HN, Levers BGH. Tooth eruption and function in an early Anglo-Saxon population. J R Soc Med 1979; 72:341-50 2 Whittaker D. Quantitative studies on age changes in the teeth and surrounding structures in archaeological material: a review. J R Soc Med 1992;85:97-101 3 Gilbert GH, Heft MW. Periodontal status of older Floridians attending senior activity centers. J Clin Periodont 1992;19:249-55

Age changes in teeth.

774 Journal of the Royal Society of Medicine Volume 85 December 1992 with keratoconus. They attributed this frequent association to an event during...
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