Archs orot Biol. Vol. 18, pp. 1255-1260, 1973. Pergamon Press. Printed in Great Britain.

NEUROHISTOLOGY OF HUMAN DENTAL PULP POLYPS

J. C. SOUTHAM* and J. J. HODSON

Department of Oral Pathology, University of Sheffield, Sheffield, England

Summary-Examination of human non-epitheliated and epitheliated pulp polyps, using paraffin sections stained with Holmes’ silver stain, showed nerve fibres present in the connective tissue of the pedicle region, in the granulation tissue of the polyp, and in the epithelium. A similar innervation was present in some of the epitheliated polyps to that described in the oral mucosa. Pulp nerves never innervate epithelium under normal circumstances, so that the innervation of epithelium covering a pulp polyp is a unique example of innervation of a newly formed mature tissue after foetal life.

INTRODUCTION

PULP polyps are usually regarded as being relatively insensitive to external stimuli, the conventional explanation for this being that they contain few, if any, nerves or nerve endings (TIECKE, 1965). RADDEN (1939) gives the only description of the clinical ex- amination of pulp polyps as regards neurological sensation and he reports that “if there is no epithelial covering the polyp has no sensation or only protopathic sensation; with an epithelial covering it may possess both protopathic and epicritic sensation”. Histological examinations of the innervation of pulp polyps are reported in only three papers. RADDEN (1939) examined 18 polyps and describes bundles con- taining 6-8 nerve fibres extending from the pulp tissue to the external surface and breaking up into smaller branches among the capillaries. He also describes in epitheliated polyps fine nerve filaments running among the epithelial cells. DIXON and PEACH (1965) examined 5 polyps by electron microscopy and reported a few small bundles of unmyelinated nerve fibres in the connective tissue probably concerned with the autonomic innervation of the vascular elements. No myelinated or intra-epithelial fibres were seen. MARTINELLI and TOLEDO (1970) examined 14 polyps and found them all to be richly innervated with myelinated and unmyelinated fibres and nerve fibres were present in the epithelium in most cases.

Although some of the variations in these descriptions may be due to the different methods of investigation (e.g. paraffin or frozen sections, light or electron microscopy), the number of polyps examined in each investigation was relatively small. This paper describes a neurohistological investigation of a large series of pulp polyps, and dis- cusses the general biological significance of the innervation of pulp polyps.

MATERIALS AND METHODS

Paraffin-embedded serial sections, 5 pm thick, of 132 human dental pulp polyps have been prepared for examining the process of epithelialization and growth of pigmented melanocytes in the epithelium. Care was taken to exclude the possibility of any of the polyps being continuous with the adjacent

* Present address: Department of Dental Surgery, University of Edinburgh, Edinburgh, Scotland.

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1256 J. C. SOUTHAM AND J. J. HODS~N

gingival mucosa. Five of the polyps were examined in situ in the tooth after decalcification. The re- mainder were carefully dissected from the tooth, usually after fixation, and any polyp was discarded which was not intact and in which a clear derivation from the pulp was not obvious. At least one section from 125 of these polyps was stained with Holmes silver stain for nerves and examined for the presence and distribution of nerve fibres. A few of the polyps had been processed by the DOPA reaction for melanin and sections of these specimens were also stained with Holmes silver stain. A number of polyps were divided in two and one-half was impregnated with gold chloride for study of the epithelial Langerhans cells. Some nerve fibres were also stained by this method. Of the 125 polyps, 73 were epitheliated (43 from deciduous teeth and 30 from permanent teeth) and 52 were non- epitheliated (10 from deciduous teeth and 42 from permanent teeth). Serial sections stained with haematoxylin and eosin were also available for study.

Silver impregnation techniques for the demonstration of nerve fibres are notoriously capricious, and although this is partly due to errors in preparation of solutions and in the technique, the faults may also be due to fixation artifacts. Paraffin sections can only be used to determine the presence or absence of the coarser nerve fibres and it is not possible to show the finest fibres and nerve endings. Thin sections usually show nerve fibres as short segments because the fibres run through the tissue in many directions. Our results therefore must not be regarded as showing the full extent of innervation of the polyps.

RESULTS

Nerves were present in sections of 40 of the 52 non-epitheliated polyps examined. In the 73 epitheliated polyps, nerves were seen in the connective tissue in 47 polyps, with nerves also present in the epithelium in 18 of these polyps (9 deciduous and 9 permanent teeth).

Bundles of nerve fibres were frequently seen in the connective tissue of the pedicle regions of the polyps, where they were growing out of the pulp chambers and were continuous with more normal pulp tissue. These bundles were often associated with blood vessels (Fig. 1) and were part of, or an extension of, the normal neuro-vascular structure of the pulp. These nerve bundles however soon divided into smaller nerve bundles and fibres which generally permeated the granulation tissue of the polyp as tortuous fibres which in any one section were relatively infrequently seen (Fig. 2). In one of the non-epitheliated polyps, thesefibres were extremely numerous with a very complex pattern and resembled a traumatic neuroma. The non-epitheliated polyps were covered by a fibrinous meshwork containing inflammatory cells and nerve fibres were seen extending to the surface of the granulation tissue beneath the fibrin (Fig. 3).

Nerve fibres were seen in the epithelium in 18 of the 73 polyps which were epi- theliated. These fine intra-epithelialfibres had a tortuous course and extended into the upper layers of the epithelium (Fig. 4). No specialised nerve endings were seen. In one polyp, there was a fairly extensive plexus of nerve fibres lying just beneath the epithe- lium with branches extending across the basement membrane into the epithelium (Fig. 5). Schwann cell nuclei were occasionally present alongside the nerve fibres sometimes just before they crossed the basement membrane into the epithelium (Fig. 6). The epithelium of all the epitheliated polyps which were impregnated with gold chloride contained Langerhans cells but there appeared to be no relation between these cells and the free nerve endings.

DISCUSSION

In wound healing, the granulation tissue is innervated by autonomic nerves in relation to the vessels. In wounds of the skin and oral mucosa, healing is also associated

NEUROHISTOLOGY OF HUMAN DENTAL PULP POLYPS 1257

with re-innervation from the proximal ends of sensory fibres which previously supplied the dermis and epidermis, or mucosa and submucosa. In a pulp, however, apart from the autonomic innervation of the granulation tissue from similar fibres in the pulp, innervation cannot strictly be compared with healing wounds elsewhere.The sensory nerves in the pulp form a network of unmyelinated fibres in the plexus of Raschkow with a few fibres crossing the cell-free zone to form a plexus on the surface of the predentine, a few fibres also extending into the dentine. A pulp polyp develops as a hyperplastic mass of granulation tissue growing out of the pulp chamber which may then be epitheliated by a spontaneous grafting of desquamated epithelial cells from either the saliva or adjacent gingiva or mucosa. Occasionally a pulp polyp may spon- taneously graft with the adjacent gingiva, with the gingival epithelium growing directly over the surface of the polyp. An attempt was made to exclude such polyps from the present study. The nerves in the pulp under normal circumstances never in- nervate epithelium and so the innervation of the epithelium covering a pulp polyp cannot be described as re-innervation but is a unique example of the innervation of a newly formed mature tissue after foetal life.

It is interesting to compare the innervation of the pulp-polyp epithelium as described in this paper with the innervation of oral mucosa and skin. A subepithelial network of fine nerve fibres is present in oral mucosa (DIXON, 1963) and skin, from which rela- tively straight intra-epithelial fibres are derived (DIXON, 1961). Intra-epithelial fibres in the skin are mainly present in thick skin especially where there is a thick layer of keratin, the fibres extending to the level of the granular layer (WINKELMANN, 1960). However, ALLENBY (1970), considers that there is a direct relationship between the presence and number of intra-epithelial fibres, and the mitotic and metabolic activity that is taking place in the epidermis.The rich epithelial innervation in the foetus and the dermatoses, and after Sellotape stripping of the surface layers, is evidence of this. No information is available as to the mechanism of the inter-relationship between intra-epidermal nerves and the epidermal growth rate.

A subepithelial nerve plexus was present in one polyp (Fig. 5). Intra-epithelial fibres were seen in only 18 of the 73 epitheliated polyps examined and their number varied greatly in different polyps. The fibres were usually rather tortuous and not as straight as described in normal oral mucosa. Mitotic activity was a feature of the epithelium covering the polyps but this did not appear to be associated with a plentiful innervation as suggested by the proliferation of nerve fibres in mitotically active skin. Innervation of pulp polyps is likely to be related in some way to the length of time that a polyp has been present, as the growth of granulation tissue and epithelialization are likely to be more rapid than nerve growth. A comparison of the frequency with which nerves were present in epitheliated and non-epitheliated polyps did not suggest that an epithelial covering with an associated diminution in the intensity of inflammation favours the growth of nerves.

FEARNHEAD (1967) gives evidence for a continuous dynamic activity present at the tips of the pulp nerves. The nerves in a normal pulp are confined by the walls of the dentine and so proliferate within these walls to form the plexus of Raschkow; odd fibres also extend across the cell-free zone to enter the dentinal tubules. If this concept

1258 J. C. SOUTHAM AND J. J. HOD o

is correct, the growth of nerves into a pulp polyp would be expected following a breach in the dentine wall. Regional variations in the pattern of epidermal innervation are determined by the character of the epithelium and not by the nerve source (FITZ- GERALD, 1968). The findings of an essentially similar innervation in epitheliated pulp polyps and in the oral mucosa can therefore be seen as a natural development.

Pain is the only sensation which can be elicited in the normal pulp. VON FREY (cited by WEDDEL, PALMER and PALLIE, 1955) at the end of the last century described four primary modalities of sensation, i.e. touch, cold, pain and warmth, and he considered that different types of nerve fibres and endings were responsible for these four types of sensation. The finding that pulp nerves can apparently be responsible for other sen- sations besides pain (RADDEN, 1939) lends support to the now generally accepted theory that the responses evoked when different stimuli are applied depends on the manner in which the unencapsulated nerve endings are stimulated and not upon the particular endings. It is popularly believed that increased innervation is associated with increased sensory acuity, but, in psoriasis which is associated with increased intra- epithelial innervation, sensory acuity is not detectably improved (FITZGERALD, 1968). Therefore the number of nerve fibres in pulp polyps cannot be presumed to be directly related to the sensory acuity found on clinical examination.

R&m+-L’examen de polypes pulpaires Cpithelialises ou non, apres inclusion % la paraffine et coloration argentique selon Holmes, montre la presence de fibres nerveuses dans le tissu conjonctif de la region pediculaire, dans le tissu de granulation du polype et l’tpithblium. Une innervation de m&me type que celle de la muqueuse buccale, est visible dans certains des polypes Bpithelialises. Les nerfs pulpaires n innervent pas l’tpithelium, dans des conditions normales, de telle sorte que l’innervation de l’epitht- hum du poIype pulpaire est un exemple unique d’innervation dun tissu adulte neoforme.

Zusammenfassung-Die Untersuchung nichtepithelisierter und epithelisierter Puipa- polypen an mit Holmes’ Silberfiirbung behandelten Paraffinschnitten ergab Nervenfasern im Bindegewebe der Basisregion, im Granulationsgewebe des Polypen und im Epithel. Eine Bhnliche Innervation war in einigen von der Mundschleimhaut herstammenden epithelisierten Polypen vorhanden. Pulpanerven innervieren unter nonnalen Umstlnden keinesfalls Epithel; deshalb ist die Innervation des Epithels, das einen Pulpapolypen bedeckt, ein Ausnahmebeispiel fur die Innervation neu entwickelten ausgereiften Gewebes auBerhalb der Fetalzeit.

REFERENCES

ALLENBY, C. F. 1970. Nerves of the skin. In: An Introduction to the Biology of the Skirz (edited by CHAMPION. R. H.. GILLMAN. T.. ROOK. A. J. and SIMS. R. T.). DV. 124138. Blackwell. Oxford.

DIXON, A. D. 1961. Sensory nerve terminations in the oral ‘muco&.‘krchs oral Biol. 5, 105-l 14. DIXON, A. D. 1963. Nerve plexuses in the oral mucosa. Archs oral Biol. 8, 4355447. DIXON, A. D. and PEACH, R. 1965. Fine structure of epithelial and connective tissue elements in human

dental polyps. Arch; oral Biol. 10, 71-81. FEARNIIEAD. R. W. 1967. Innervation of dental tissues. In: Structural and Chemical Organisation of

teeth (edited by MILES, A. E. W.), Vol. 1, pp. 247-281. Academic Press, New York. FITZGERALD, M. J. T. 1968. The innervation of the epidermis. In: The Skin Senses (edited by

KENSHALO, D. R.), p. 67. Thomas, Springfield. MARTINELLI, C. and TOLEDO, 0. A. 1970. The innervation of human pulp polyps. BUN. Tokyo dent.

CON. 11, 11-18. RADDEN, H. G. 1939. Some observations on the epithelialisation and innervation of pulp polypi.

Proc. Congr. Aust. dent. Ass. 203-219.

NEUROHISTOLOGY OF HUMAN DENTAL PULP POLYPS 1259

TIECKE, R. W. 1965. Oral Pathology, p. 244. McGraw-Hill, New York. WEDDEL, G., PALMER, E. and PALLIE, W. 1955. Nerve endings in mammalian skin. Biol. Rev. 30,

159-195. WINKELMANN, R. K. 1960. Nerve Endings in Normal andPathologic Skin, p. 127. Thomas, Springfield.

PLATE 1 OVERLEAF

1260 J. C. SOUTHAM AND J. J. HODSON

PLATE 1

FIG. 1. Nerve bundle running alongside a vessel in the pedicle region of a polyp. Holmes silver stain. x 334

FIG. 2. Group of fairly straight nerve fibres in the highly inflamed granulation tissue of the polyp. Holmes silver stain. x 430

FIG. 3. Nerve fibres extending close to the surface of the granulation tissue of the polyp. Holmes silver stain. x 430

FIG. 4. Tortuous intra-epithslial nerve fibre extending between the prickle cells. DOPA and Holmes silver stain. x 330

FIG. 5. Subepithelial plexus of nerve fibres lying just below the basement membrane. DOPA and Holmes silver stain. x 530

FIG. 6. Two nerve fibres in the connective tissue of the polyp extending across the basement membrane into the epithelium with Schwann cell nuclei present in the con-

nective tissue. Holmes silver stain. x 1070

NEUROHISTOLOGY OF HUMAN DENTAL PULP POLYPS

PLATE 1