from a site of initial injury”. The explanation for this phenomenon rests with the non-expansible character of the dental pulp. Authors such as Van Hassel (1 1) and Kin1 ( 1 2) have attributed this characteristic to the pulp’s rigid encasement within the dentine - even with the smallest rise in fluid content in the pulp, there is potentially a substantial rise in interstitial pressure (13). Another consideration, however, is the non- compressible nature of the ground substance due to its high degree of polymerisation; its gel-like property thus may also impart a low compliant environment to the pulp.

Kim (12) put forward a hypothetical mechanism for pulp necrosis. Since it has been found that pulp tissue pressure peripheral to the inflammatory site is within normal range (1 4), tissue pressure changes are a local phenomenon a t the site of inflammation. Kim (12) concluded that a totally necrotic pulp was the result of a gradual accumulation of local necroses; it is the highly hydrated gel-like state of the pulpal ground substance that has a direct bearing on this gradual spread, as inflammation produces a depolynierisation of the ground substance, which increases the permeability of the tissue and enhances the spread of inflammation.

References

1. Shuttleujorth C . A . Dental pulp matrix - collagens and glycoproteins. In Dynamic Aspects cf Dental Pulp - molecular 6iologx pharmacology and pathophysiology. 1st ed. (Eds. Inoki R . , Kudo T. and Olgart L.) 1990; pp239-257. Chapman and Hall, London.

2. Linde A . The extracellular matrix of the dental pulp and dentine. J. Dent Res 1985; 64 (Special Issue):523-9.

3. van Amerongen J.P, Lemmens I.G., Tonino G J M .

Concentration, extractability and characterisation of collagen in human dental pulp. Archs Oral Biol 1983; 28:339-45.

4. Skuttleu~orflz C.A., Ward]. L., Hirschma~n P!N.The presence of type 111 collagen in the developing tooth. Uiochem Biophys Acta 1978; 535:348-55.

5. Kiro M.Y.P, Lm W H . , Lin S.K., Tsai K.S., Halnz L J Collagen gene expresion in human dental pulp cell cultures. Archs Oral Biol 1992; 37:945-52.

6. Ten Cute A.R. Oral Histology: Development, Structirre and Function, Second ed. 1985; Mosby College Publishing, St. Louis.

7. Ruoslahti E. Structure and biology of proteoglycans. Ann Rev Cell Biol 1988; 4:229-55.

8. Weine ES. Endodonric Therapy, Fourth ed., 1989; Mosby College Publishing, St. Louis.

9. Harlamh S.C., Messer H.H. The identification of pro- teoglycan-associated niRNAs in dental pulp cells. In press with Archs Oral Biol 1996.

10. Kim S. Neurovascular interactions in the dental pulp in health and inflammation. J Endodon 1990; 16:48-53.

1 1. Van Hassel H J . Physiology of the human dental pulp. Oral Surg 1971; 32:126-34.

12. Kim S. Microcirculation in the dental pulp. In Experimental Endodontics. (Ed. Spangberg L.S.W.) 1990; pp52-76. CRC Press, Florida.

13. Sfenvik A . , Iversen]., Mjiir I. Tissue pressure and histology of normal and inflamed tooth pulps in Macaque monkeys. Archs Oral Biol 1972; 17:1501-11.

Tonder KJ . H. , Kvinnsland I. Micropuncture nieasure- ments of interstitial fluid pressure in normal and inflamed dental pulp in cats. J Endodon 1983; 9:105-9.

14.

The Cerebellum’s Sensitive Side American researchers claim to have overturned the century-

old belief that the area of the brain called the cerebellum co-ordinates muscle movements. They argue that the cere- bellum, tucked away at the back of the brain, processes sensory information.

Patients with cerebellar damage show no obvious sensory impairment, but their movements become awkward. But movement control needs sensory information, says Lawrence Parsons of the University ofTexas Health Science Centre in San Antonio.And most studies cannot tell which of the two tasks the cerebellum is doing.

Parsons and his colleagues used functional magnetic resonance imaging - a technique that detects changes in blood flow in the brain, and hence brain activity - as human volunteers performed a variety of tasks. A purely sensory task - detecting sandpaper rubbed across the subject’s hand - led to a mild

increase in blood flow in the cerebellum’s dentate nucleus, the region that funnels information to the rest of the brain.

In contrast, a simple motor task - picking up a small ball - produced no significant activation. However, when the subject was asked to pick up a ball in each hand and judge whether the two were identical, the dentate nucleus sprang into vigorous action (Science, vol. 272, p. 545).

This suggests that the cerebellum’s main role is in processing sensory information. But Farrel Robinson of the University of Washington in Seattle notes that the comparative task involved muscle niovements and high-level thought processes. H e argues that Parsons’ team has still not fully teased apart the tangle. “I t looks like the cerebellum may be dedicated to more that pure movement,” says Robinson. “But the question is, to what?”

By Bob Holmes New Scientist, May 11 1996

AUSTRALIAN ENDODONTIC NEWSLETTEKVOLUME 22 No. 3 DECEMBER 1YY6 27