- Email: [email protected]
The permeability of human dentine in vitro and in vivo
Archives of Oral Biology 45 (2000) 931 – 935 www.elsevier.com/locate/archoralbio
The permeability of human dentine in vitro and in vivo N. Vongsavan 1, R.W. Matthews 2, B. Matthews * Department of Physiology, School of Medical Sciences, Uni6ersity of Bristol, Uni6ersity Walk, Bristol BS8 1TD, UK Accepted 6 June 2000
Abstract Experiments in cats have shown that Evans blue dye diffuses at a greater rate into dentine in recently extracted teeth than in vivo. These experiments have now been repeated in man and similar results were obtained except that, after applications in vivo, visible concentrations of the dye were present in the dentine, and in a few cases, even in the pulp. It is concluded that, as in the cat, the diffusion in vivo was impaired by outward flow of fluid in the dentinal tubules but the mean velocity of flow in the human dentine was less than that in the cat. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Dentine permeability; Dentinal fluid; Evans blue
1. Introduction
2. Materials and methods
Both human (Anderson and Ronning, 1962) and cat (Vongsavan and Matthews, 1991) dentine were freely permeable to Evans blue dye when tested in recently extracted teeth. However, in the cat, the rate of diffusion of the dye through dentine was much lower when it was applied in vivo (Vongsavan and Matthews, 1991) and this difference was attributed to the presence of an outward flow of fluid through the exposed dentinal tubules in vivo which opposed inward diffusion (Vongsavan and Matthews, 1992a). The present experiments sought to compare the rates of diffusion of Evans blue through human dentine in vitro and in vivo.
The experiments were carried out on 12 first or second premolar teeth of six patients (age, 12 – 14 years) who were to have the teeth extracted under local anaesthetic as part of their orthodontic treatment. Patients were selected who were to have either both upper or both lower first premolars extracted. The tooth on one side was tested in vivo and the contralateral tooth in vitro. The experiments, which were carried out in the Division of Oral Medicine of the Bristol Dental Hospital, were approved by the Hospital Ethical Committee. Informed consent was obtained from each patient and their parents or guardians. At the appointment, at which the teeth were to be extracted, the tooth to be tested in vivo was anaesthetized with local anaesthetic. The anaesthetic (mepivacaine hydrochloride, 0.12 mol/l; Scandonest, 3%; Septodont, Dorking, UK) contained no vasoconstrictor. For an upper tooth, approx. 1 ml was infiltrated buccally and 0.5 ml palatally over the roots. For a lower tooth, 1 – 2 ml was injected to block the ipsilateral inferior alveolar nerve. Dentine was then exposed, as described below, at the tip of either just the buccal cusp or both buccal and palatal cusps of the tooth. An
* Corresponding author. Tel.: + 44-117-9287816; fax: +44117-9288923. E-mail address: [email protected] (B. Matthews). 1 Faculty of Dentistry, Mahidol University, Yothi Street, Bangkok 10400, Thailand. 2 Department of Oral and Dental Science, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK.
0003-9969/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 9 9 6 9 ( 0 0 ) 0 0 0 7 9 - 0
932
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
acrylic cap with a hole (2-mm diameter) over the tip of each cusp was then cemented over the tooth crown with calcium hydroxide (Life; Kerr Ltd., Peterborough, UK). The cap had been constructed before the appointment on a plaster model of the patient’s dentition. The space under the cap left by the removed enamel and dentine was filled with a drop of Evans blue (52 mmol/ l) solution, which was made up in sterile isotonic saline. The solution was passed through a 0.5-mm-pore filter immediately before use. After 15 min, the Evans blue was washed out and the tooth was extracted with forceps. The contralateral tooth was then also extracted under local anaesthetic. This tooth was prepared and exposed to Evans blue in the same way within 1 hr of the extraction. An axial, buccopalatal, longitudinal section, approx. 0.5-mm thick, was cut through the each cusp with a diamond disc under Ringer’s. The sections were dehydrated overnight in 100% ethyl alcohol, cleared in methyl salicylate and examined under a microscope (Wild, type M400) with variable darkground illumination. The maximum distance the dye penetrated into the dentine was measured. Dentine was exposed in one of two ways. In some cases, 2–3 mm of enamel and dentine were removed from the tip of a cusp with a diamond bur in an air-rotor handpiece under a constant stream of water. The exposed dentine surface was then etched with orthophosphoric acid (4.6 mol/l) for 30 s to remove the smear layer. In others cases, the dentine was exposed by fracturing. A groove was cut in the enamel 2–3 mm below the cusp tip with a diamond bur under a stream of water, then the cusp tip was fractured off with fine surgical shears under a drop of saline. In each pair of teeth from the same patient, the same procedures were used to expose the dentine for testing in vivo and in vitro.
3. Results In all of the teeth tested in vitro, Evans blue penetrated the exposed dentine, and in all but one it was visible in the underlying pulp horn (Fig. 1A). Much less dye was visible in the teeth that were tested in vivo, under two of the cusps there was none in either the dentine or the pulp apart from a very thin layer of stained, decalcified matrix at the etched dentine surface; in the other five, just a few of the tubules under the center of the area of exposed dentine were stained (Fig. 1B) and in two of these, there was faint staining of the pulp horn. The minimal penetration of the dye in the in vivo experiments contrasted markedly with the much heavier staining in the teeth that were tested in vitro. The results of the measurements of the maximum penetration distance of the dye, together with the thick-
ness of remaining dentine, are given in Table 1. There was no significant difference (P = 0.1 Student’s t-test) between the mean dye penetration in vitro (2.9 mm; S.D., 0.5) and in vivo (1.9 mm; S.D., 1.4) when measured in this way. The method of exposing the dentine had no obvious effect on the results.
4. Discussion The results obtained in vitro are similar to those of Anderson and Ronning (1962), bearing in mind that in the present experiments, the dye was applied for only 15 instead of 30 min. Anderson and Ronning applied Evans blue to fractured dentine, but in other preliminary experiments, we have confirmed that similar results are obtained with 30-min applications of the dye in recently extracted, human premolars independent of whether the dentine is exposed by fracturing or by drilling followed by etching with acid. The same was found in published work with cat dentine (Vongsavan and Matthews, 1991). The observation that less dye diffused into human dentine in vivo than in vitro corresponds with the results of similar experiments in cats (Vongsavan and Matthews, 1991) and it is likely that, as in the cat, the diffusion in vivo was impaired by outward flow of fluid in the dentinal tubules (Vongsavan and Matthews, 1992a). However, unlike the cat experiments, dye could be detected in the dentine in five of the seven human preparations, and in the pulp in two. Furthermore, there was no significant difference between the average maximum depth of penetration of the dye when it was applied in vivo instead of in vitro. It seems as if a small proportion of the tubules behaved in vivo in the same way as the majority did in vitro. These differences between the human and cat experiments in the penetration of the dye in vivo suggest that the mean velocity of flow through the tubules in the human dentine in vivo was less than that in the cat, and that in some of the human tubules there was little flow at all. A lower mean flow velocity in the tubules of human dentine compared with those of the cat could have been due to the resistance to flow through each tubule being greater, the hydraulic conductance of the odontoblast layer being lower, or the net filtration pressure between the pulp and dentine being lower in the human teeth. As the dentinal tubules tend to be larger in diameter in human than cat dentine (Forssell-Ahlberg et al., 1975; Garberoglio and Bra¨nnstro¨m, 1976; Vongsavan and Matthews, 1992a), it seems unlikely that the resistance to flow through the tubules was greater. Nothing is known of the hydraulic conductance of the odontoblast layer in either species under the conditions of these experiments. Species differences in either the pulpal tissue fluid pressure or the opposing osmotic effect of
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
constituents (e.g. protein) of the pulpal tissue fluid could have resulted in the net filtration pressure being lower in the human than that in the cat teeth, although the estimates that have been made indicate that they are similar, 1.5 kPa in the cat (Vongsavan and Matthews,
933
1992a) and 1.4 kPa in man (Ciucchi et al., 1995). Pulpal tissue fluid pressure has been estimated with the micropuncture technique in the cat and found to be of the order of 0.72 kPa (Tønder and Kvinnsland, 1983), whereas in man values in the range 1.4 – 3.3 kPa
Fig. 1. Photomicrographs of ground longitudinal sections through the crowns of two human premolar teeth. In each case, a solution of Evans blue had been applied for 15 min to dentine that had been exposed with a bur under the tip of a cusp then etched with acid. The sections were dehydrated and cleared in methyl salicylate. Original magnification, ×42. (A) Recently extracted tooth. The Evans blue penetrated through the exposed dentine to the pulp. No dye was visible in the pulp. (B) The dye was applied in vivo. The arrow indicates a small area in which a few tubules contained Evans blue. No dye was visible in other parts of the section. This section passed through the edge of the pulp and some dentine is superimposed on the outline of the pulp chamber.
934
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
Fig. 1. (Continued)
have been recorded with a closed cannulation technique (Beveridge and Brown, 1965; Andrews et al., 1972). Pulpal tissue fluid pressure may have been reduced in the present experiments as a result of pulpal vasoconstriction (Vongsavan and Matthews, 1992b) caused either by a high level of sympathetic vasoconstrictor tone in the stressed participants or by the mepivacaine. In cats, sympathetic stimulation can cause a reversal of the normal outward flow of dentinal fluid (Matthews and Vongsavan, 1994), which would facilitate inward diffusion of the dye. In other experiments in man, cavity
preparation under mepivacaine local anesthesia appeared to produce a fall in pulpal blood flow (S. Soo-Ampon et al., unpublished). Pulpal tissue fluid pressure may also have been affected by other factors (Matthews and Andrew, 1995). Although the method of application of the Evans blue was essentially the same in both the human and the cat experiments, except that it was applied for 15 instead of 30 min in the present experiments, the methods used to expose the dentine were not identical, the height of the cusp was gradually reduced with a bur in
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
935
Table 1 Remaining dentine thickness (RDT) and maximum penetration distance of Evans blue through exposed dentine in human teeth tested in vitro and in vivo Case number
1 2 3 4 5 6 7
Exposed by
Fracture Fracture Fracture Disc and Disc and Disc and Disc and Mean S.D.
etch etch etch etch
In vitro
In vitro
RDT (mm)
Penetration (mm)
RDT (mm)
Penetration (mm)
2.8 3.5 3.5 3.5 2.9 3.0 2.0 3.0 0.5
2.8 2.5 3.5 3.5 2.9 3.0 2.0 2.9 0.5
3.3 3.1 3.4 3.6 3.0 3.0 2.3 3.1 0.4
0 0 3.1 3.2 3.0 3.0 1.2 1.9 1.4
the human experiments whereas a disc was used to slice off the tip of the cusp in the cats. These techniques could have disrupted the odontoblasts by different amounts. Also, it was not possible to fracture off the tips of the cusps of the human teeth as accurately as in the cats, particularly in vivo. Thus, no definite conclusion can be drawn about the cause of the higher rate of diffusion of Evans blue into human than cat dentine in vivo. Further experiments are required to define more precisely the properties and location of the diffusional barriers in vivo and to obtain quantitative data on rates of diffusion. The results of the present experiments emphasize the need for care in predicting the effects of fluid flow through dentine in man from data obtained from experimental animals (see also Vongsavan et al., 2000; this issue).
Acknowledgements This work was supported by The Wellcome Trust.
References Anderson, D.J., Ronning, G.A., 1962. Dye diffusion in human dentine. Arch. Oral Biol. 7, 505–512. Andrews, S.A., Van Hassel, H.J., Brown, A.C., 1972. A method for determining the physiologic basis of pulp sensory response. A preliminary report. J. Hosp. Dental Practice 6, 49 – 53.
Beveridge, E.E., Brown, A.C., 1965. The measurement of human dental intrapulpal pressure and its response to clinical variables. Oral Surg. Oral Med. Oral Pathol. 19, 655 – 668. Ciucchi, B., Bouillaguet, S., Holz, J., Pashley, D., 1995. Dentinal fluid dynamics in human teeth, in vivo. J. Endodontics 21, 191 – 194. Forssell-Ahlberg, K., Bra¨nnstro¨m, M., Edwall, L., 1975. The diameter and number of dentinal tubules in rat, cat, dog and monkey. Acta Odontol. Scand. 33, 243 – 250. Garberoglio, R., Bra¨nnstro¨m, M., 1976. Scanning electron microscopic investigation of human dentinal tubules. Arch. Oral Biol. 21, 355 – 362. Matthews, B., Vongsavan, N., 1994. Interactions between neural and hydrodynamic mechanisms in dentine and pulp. Arch. Oral Biol. 39, 87S – 95S. Matthews, B., Andrew, D., 1995. Microvascular architecture and exchange in teeth. Microcirculation 2, 305 – 313. Tønder, K.J.H., Kvinnsland, I., 1983. Micropuncture measurements of interstitial fluid pressure in normal and inflamed dental pulp in cats. J. Endodontics 9, 105 – 109. Vongsavan, N., Matthews, B., 1991. The permeability of cat dentine in vivo and in vitro. Arch. Oral Biol. 36, 641 – 646. Vongsavan, N., Matthews, B., 1992a. Fluid flow through cat dentine in vivo. Arch. Oral Biol. 37, 175 – 185. Vongsavan, N., Matthews, B., 1992b. Changes in pulpal blood flow and in fluid flow through dentine produced by autonomic and sensory nerve stimulation in the cat. Proc. Finnish Dental Soc. 88 (Suppl. 1), 491 – 497. Vongsavan, K., Vongsavan, N., Matthews, B., 2000. The permeability of the dentine and other tissues that are exposed at the tip of a rat incisor. Arch. Oral Biol., 45, 927 – 930.
.
The permeability of human dentine in vitro and in vivo N. Vongsavan 1, R.W. Matthews 2, B. Matthews * Department of Physiology, School of Medical Sciences, Uni6ersity of Bristol, Uni6ersity Walk, Bristol BS8 1TD, UK Accepted 6 June 2000
Abstract Experiments in cats have shown that Evans blue dye diffuses at a greater rate into dentine in recently extracted teeth than in vivo. These experiments have now been repeated in man and similar results were obtained except that, after applications in vivo, visible concentrations of the dye were present in the dentine, and in a few cases, even in the pulp. It is concluded that, as in the cat, the diffusion in vivo was impaired by outward flow of fluid in the dentinal tubules but the mean velocity of flow in the human dentine was less than that in the cat. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Dentine permeability; Dentinal fluid; Evans blue
1. Introduction
2. Materials and methods
Both human (Anderson and Ronning, 1962) and cat (Vongsavan and Matthews, 1991) dentine were freely permeable to Evans blue dye when tested in recently extracted teeth. However, in the cat, the rate of diffusion of the dye through dentine was much lower when it was applied in vivo (Vongsavan and Matthews, 1991) and this difference was attributed to the presence of an outward flow of fluid through the exposed dentinal tubules in vivo which opposed inward diffusion (Vongsavan and Matthews, 1992a). The present experiments sought to compare the rates of diffusion of Evans blue through human dentine in vitro and in vivo.
The experiments were carried out on 12 first or second premolar teeth of six patients (age, 12 – 14 years) who were to have the teeth extracted under local anaesthetic as part of their orthodontic treatment. Patients were selected who were to have either both upper or both lower first premolars extracted. The tooth on one side was tested in vivo and the contralateral tooth in vitro. The experiments, which were carried out in the Division of Oral Medicine of the Bristol Dental Hospital, were approved by the Hospital Ethical Committee. Informed consent was obtained from each patient and their parents or guardians. At the appointment, at which the teeth were to be extracted, the tooth to be tested in vivo was anaesthetized with local anaesthetic. The anaesthetic (mepivacaine hydrochloride, 0.12 mol/l; Scandonest, 3%; Septodont, Dorking, UK) contained no vasoconstrictor. For an upper tooth, approx. 1 ml was infiltrated buccally and 0.5 ml palatally over the roots. For a lower tooth, 1 – 2 ml was injected to block the ipsilateral inferior alveolar nerve. Dentine was then exposed, as described below, at the tip of either just the buccal cusp or both buccal and palatal cusps of the tooth. An
* Corresponding author. Tel.: + 44-117-9287816; fax: +44117-9288923. E-mail address: [email protected] (B. Matthews). 1 Faculty of Dentistry, Mahidol University, Yothi Street, Bangkok 10400, Thailand. 2 Department of Oral and Dental Science, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK.
0003-9969/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 9 9 6 9 ( 0 0 ) 0 0 0 7 9 - 0
932
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
acrylic cap with a hole (2-mm diameter) over the tip of each cusp was then cemented over the tooth crown with calcium hydroxide (Life; Kerr Ltd., Peterborough, UK). The cap had been constructed before the appointment on a plaster model of the patient’s dentition. The space under the cap left by the removed enamel and dentine was filled with a drop of Evans blue (52 mmol/ l) solution, which was made up in sterile isotonic saline. The solution was passed through a 0.5-mm-pore filter immediately before use. After 15 min, the Evans blue was washed out and the tooth was extracted with forceps. The contralateral tooth was then also extracted under local anaesthetic. This tooth was prepared and exposed to Evans blue in the same way within 1 hr of the extraction. An axial, buccopalatal, longitudinal section, approx. 0.5-mm thick, was cut through the each cusp with a diamond disc under Ringer’s. The sections were dehydrated overnight in 100% ethyl alcohol, cleared in methyl salicylate and examined under a microscope (Wild, type M400) with variable darkground illumination. The maximum distance the dye penetrated into the dentine was measured. Dentine was exposed in one of two ways. In some cases, 2–3 mm of enamel and dentine were removed from the tip of a cusp with a diamond bur in an air-rotor handpiece under a constant stream of water. The exposed dentine surface was then etched with orthophosphoric acid (4.6 mol/l) for 30 s to remove the smear layer. In others cases, the dentine was exposed by fracturing. A groove was cut in the enamel 2–3 mm below the cusp tip with a diamond bur under a stream of water, then the cusp tip was fractured off with fine surgical shears under a drop of saline. In each pair of teeth from the same patient, the same procedures were used to expose the dentine for testing in vivo and in vitro.
3. Results In all of the teeth tested in vitro, Evans blue penetrated the exposed dentine, and in all but one it was visible in the underlying pulp horn (Fig. 1A). Much less dye was visible in the teeth that were tested in vivo, under two of the cusps there was none in either the dentine or the pulp apart from a very thin layer of stained, decalcified matrix at the etched dentine surface; in the other five, just a few of the tubules under the center of the area of exposed dentine were stained (Fig. 1B) and in two of these, there was faint staining of the pulp horn. The minimal penetration of the dye in the in vivo experiments contrasted markedly with the much heavier staining in the teeth that were tested in vitro. The results of the measurements of the maximum penetration distance of the dye, together with the thick-
ness of remaining dentine, are given in Table 1. There was no significant difference (P = 0.1 Student’s t-test) between the mean dye penetration in vitro (2.9 mm; S.D., 0.5) and in vivo (1.9 mm; S.D., 1.4) when measured in this way. The method of exposing the dentine had no obvious effect on the results.
4. Discussion The results obtained in vitro are similar to those of Anderson and Ronning (1962), bearing in mind that in the present experiments, the dye was applied for only 15 instead of 30 min. Anderson and Ronning applied Evans blue to fractured dentine, but in other preliminary experiments, we have confirmed that similar results are obtained with 30-min applications of the dye in recently extracted, human premolars independent of whether the dentine is exposed by fracturing or by drilling followed by etching with acid. The same was found in published work with cat dentine (Vongsavan and Matthews, 1991). The observation that less dye diffused into human dentine in vivo than in vitro corresponds with the results of similar experiments in cats (Vongsavan and Matthews, 1991) and it is likely that, as in the cat, the diffusion in vivo was impaired by outward flow of fluid in the dentinal tubules (Vongsavan and Matthews, 1992a). However, unlike the cat experiments, dye could be detected in the dentine in five of the seven human preparations, and in the pulp in two. Furthermore, there was no significant difference between the average maximum depth of penetration of the dye when it was applied in vivo instead of in vitro. It seems as if a small proportion of the tubules behaved in vivo in the same way as the majority did in vitro. These differences between the human and cat experiments in the penetration of the dye in vivo suggest that the mean velocity of flow through the tubules in the human dentine in vivo was less than that in the cat, and that in some of the human tubules there was little flow at all. A lower mean flow velocity in the tubules of human dentine compared with those of the cat could have been due to the resistance to flow through each tubule being greater, the hydraulic conductance of the odontoblast layer being lower, or the net filtration pressure between the pulp and dentine being lower in the human teeth. As the dentinal tubules tend to be larger in diameter in human than cat dentine (Forssell-Ahlberg et al., 1975; Garberoglio and Bra¨nnstro¨m, 1976; Vongsavan and Matthews, 1992a), it seems unlikely that the resistance to flow through the tubules was greater. Nothing is known of the hydraulic conductance of the odontoblast layer in either species under the conditions of these experiments. Species differences in either the pulpal tissue fluid pressure or the opposing osmotic effect of
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
constituents (e.g. protein) of the pulpal tissue fluid could have resulted in the net filtration pressure being lower in the human than that in the cat teeth, although the estimates that have been made indicate that they are similar, 1.5 kPa in the cat (Vongsavan and Matthews,
933
1992a) and 1.4 kPa in man (Ciucchi et al., 1995). Pulpal tissue fluid pressure has been estimated with the micropuncture technique in the cat and found to be of the order of 0.72 kPa (Tønder and Kvinnsland, 1983), whereas in man values in the range 1.4 – 3.3 kPa
Fig. 1. Photomicrographs of ground longitudinal sections through the crowns of two human premolar teeth. In each case, a solution of Evans blue had been applied for 15 min to dentine that had been exposed with a bur under the tip of a cusp then etched with acid. The sections were dehydrated and cleared in methyl salicylate. Original magnification, ×42. (A) Recently extracted tooth. The Evans blue penetrated through the exposed dentine to the pulp. No dye was visible in the pulp. (B) The dye was applied in vivo. The arrow indicates a small area in which a few tubules contained Evans blue. No dye was visible in other parts of the section. This section passed through the edge of the pulp and some dentine is superimposed on the outline of the pulp chamber.
934
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
Fig. 1. (Continued)
have been recorded with a closed cannulation technique (Beveridge and Brown, 1965; Andrews et al., 1972). Pulpal tissue fluid pressure may have been reduced in the present experiments as a result of pulpal vasoconstriction (Vongsavan and Matthews, 1992b) caused either by a high level of sympathetic vasoconstrictor tone in the stressed participants or by the mepivacaine. In cats, sympathetic stimulation can cause a reversal of the normal outward flow of dentinal fluid (Matthews and Vongsavan, 1994), which would facilitate inward diffusion of the dye. In other experiments in man, cavity
preparation under mepivacaine local anesthesia appeared to produce a fall in pulpal blood flow (S. Soo-Ampon et al., unpublished). Pulpal tissue fluid pressure may also have been affected by other factors (Matthews and Andrew, 1995). Although the method of application of the Evans blue was essentially the same in both the human and the cat experiments, except that it was applied for 15 instead of 30 min in the present experiments, the methods used to expose the dentine were not identical, the height of the cusp was gradually reduced with a bur in
N. Vongsa6an et al. / Archi6es of Oral Biology 45 (2000) 931–935
935
Table 1 Remaining dentine thickness (RDT) and maximum penetration distance of Evans blue through exposed dentine in human teeth tested in vitro and in vivo Case number
1 2 3 4 5 6 7
Exposed by
Fracture Fracture Fracture Disc and Disc and Disc and Disc and Mean S.D.
etch etch etch etch
In vitro
In vitro
RDT (mm)
Penetration (mm)
RDT (mm)
Penetration (mm)
2.8 3.5 3.5 3.5 2.9 3.0 2.0 3.0 0.5
2.8 2.5 3.5 3.5 2.9 3.0 2.0 2.9 0.5
3.3 3.1 3.4 3.6 3.0 3.0 2.3 3.1 0.4
0 0 3.1 3.2 3.0 3.0 1.2 1.9 1.4
the human experiments whereas a disc was used to slice off the tip of the cusp in the cats. These techniques could have disrupted the odontoblasts by different amounts. Also, it was not possible to fracture off the tips of the cusps of the human teeth as accurately as in the cats, particularly in vivo. Thus, no definite conclusion can be drawn about the cause of the higher rate of diffusion of Evans blue into human than cat dentine in vivo. Further experiments are required to define more precisely the properties and location of the diffusional barriers in vivo and to obtain quantitative data on rates of diffusion. The results of the present experiments emphasize the need for care in predicting the effects of fluid flow through dentine in man from data obtained from experimental animals (see also Vongsavan et al., 2000; this issue).
Acknowledgements This work was supported by The Wellcome Trust.
References Anderson, D.J., Ronning, G.A., 1962. Dye diffusion in human dentine. Arch. Oral Biol. 7, 505–512. Andrews, S.A., Van Hassel, H.J., Brown, A.C., 1972. A method for determining the physiologic basis of pulp sensory response. A preliminary report. J. Hosp. Dental Practice 6, 49 – 53.
Beveridge, E.E., Brown, A.C., 1965. The measurement of human dental intrapulpal pressure and its response to clinical variables. Oral Surg. Oral Med. Oral Pathol. 19, 655 – 668. Ciucchi, B., Bouillaguet, S., Holz, J., Pashley, D., 1995. Dentinal fluid dynamics in human teeth, in vivo. J. Endodontics 21, 191 – 194. Forssell-Ahlberg, K., Bra¨nnstro¨m, M., Edwall, L., 1975. The diameter and number of dentinal tubules in rat, cat, dog and monkey. Acta Odontol. Scand. 33, 243 – 250. Garberoglio, R., Bra¨nnstro¨m, M., 1976. Scanning electron microscopic investigation of human dentinal tubules. Arch. Oral Biol. 21, 355 – 362. Matthews, B., Vongsavan, N., 1994. Interactions between neural and hydrodynamic mechanisms in dentine and pulp. Arch. Oral Biol. 39, 87S – 95S. Matthews, B., Andrew, D., 1995. Microvascular architecture and exchange in teeth. Microcirculation 2, 305 – 313. Tønder, K.J.H., Kvinnsland, I., 1983. Micropuncture measurements of interstitial fluid pressure in normal and inflamed dental pulp in cats. J. Endodontics 9, 105 – 109. Vongsavan, N., Matthews, B., 1991. The permeability of cat dentine in vivo and in vitro. Arch. Oral Biol. 36, 641 – 646. Vongsavan, N., Matthews, B., 1992a. Fluid flow through cat dentine in vivo. Arch. Oral Biol. 37, 175 – 185. Vongsavan, N., Matthews, B., 1992b. Changes in pulpal blood flow and in fluid flow through dentine produced by autonomic and sensory nerve stimulation in the cat. Proc. Finnish Dental Soc. 88 (Suppl. 1), 491 – 497. Vongsavan, K., Vongsavan, N., Matthews, B., 2000. The permeability of the dentine and other tissues that are exposed at the tip of a rat incisor. Arch. Oral Biol., 45, 927 – 930.
.