J. Anat. (1977), 124, 1, pp. 157-164 With 1 figure Printed in Great Britain
157
The effect of adrenal glucocorticoid administration on eruption rates and tissue dimensions in rat mandibular incisors P. C. BALL The Dental School, University of Birmingham
(Accepted 21 June 1976) INTRODUCTION
The observation of Garren & Greep (1960) on the linear eruption rates of maxillary incisors in mature albino rats of the Holtzman strain indicated that doses of 1, 24, 5 and 10 mg of cortisone acetate a day caused a statistically significant increase in incisal eruption rate. This is surprising when it is remembered that the inhibition of cell division and growth which has been reported in many mesodermal structures as a result of increased levels of adrenal glucocorticoids has also been observed in dental tissues (Parmer, Katonah & Angrist, 1951; Glickman & Shklar, 1954). The object of the present investigation was to evaluate the changes which occur in the dental tissues of the rat incisor as a result of the administration of adrenal glucocorticoids, and to correlate these changes with the increased tooth eruption observed. METHODS AND MATERIALS
An experiment was first conducted to determine the dose of Depo-Medrone (an aqueous suspension of methylprednisolone acetate, 40 mg per ml) required to maintain a hyperglucocorticoid state in the adult rat. Of the five male and five female rats used in this initial investigation, two male and three female animals acted as untreated controls, while the other rats each received weekly subcutaneous injections of 0 1 ml Depo-Medrone for 5 weeks. Each rat was weighed at the start of the investigation and at weekly intervals. At the end of 5 weeks all ten animals were killed and their adrenal glands dissected out and weighed. Fifty three rats were used in the main investigation into possible dimensional changes occurring in the rat incisor as a result of adrenal glucocorticoid administration. These animals were all within the age range of 17 to 56 weeks at the start of the experiment. Twenty six of these rats were female and 27 male. After ear marking and weighing the rats were divided, within each litter, randomly into two groups. Twenty one animals formed the untreated control group, while 32 constituted the experimental group. The experimental animals were caged with their litter-mate controls and all animals received a similar soft diet and water. Within these two groups, ten control and ten experimental animals were selected for comparison of their mandibular incisal eruption rates. To effect this comparison measurements were taken throughout the experimental period to determine the movement relative to the gingival margin of fine scratch marks made in the enamel of these rats' mandibular incisors. Commencing on day 1 of the experimental period the hormone-treated, but not the control, group of rats received weekly injections of 01 ml Depo-Medrone. Throughout this time animals in each group were selected, as indicated in Table 1,
158
P. C. BALL
Table 1. Duration of experiments and numbers of animals used Days
Control group
Hormone group
7 14 21 28 35
2 2 2 2 3
4 5 6 4 3
and killed with Nembutal. Following decapitation their mandibles were dissected out and stored in formalin fixative. Sectioning technique for mandibular incisors Since the sections from these left mandibular incisors were to be used for a quantitative evaluation of dentine and pulp, decalcification had to be avoided. Ground sections were therefore prepared. The lower incisor is strongly curved, and a technique had to be devised so that a true transverse section of the tooth could be obtained in every case at a given position along the length of the tooth. The most suitable reference level along the lower incisor was considered to be the level just before the tooth had erupted sufficiently to lose any of its supporting bone (the alveolar reference level). This position was readily determined on a series of transverse ground sections as it presented as the last section in which the transversely cut incisor had a continuous ring of bone around it. The problem of obtaining true transverse sections was solved by carefully positioning the relevant part of the specimen on specially constructed plastic chucks. These plastic chucks were machined to fit into the Bovis ground section apparatus (Bovis, 1968) and had, on the face of the chuck that was presented to the diamond wheel, a deep groove. Reference marks on the side of the chuck in line with, and at right angles to, this groove enabled the operator to line the groove up exactly at right angles to the edge of the diamond wheel. The specimen was now fitted into the groove and after careful positioning fixed in place with cold cure methyl methacrylate. Several ground sections could now be cut and, after mounting in glycerine jelly, examined under the microscope. The one section cut at the alveolar reference level was selected from each of the series of ground sections and used in the quantitive evaluation of dentine and pulp (Fig. 1). Measuring technique for ground sections To obtain sufficiently accurate measurements the section was mounted on its slide on the stage of a carbon arc projector. The projector was positioned to give a magnification of the object, on a background illuminated screen of x 2200. At this magnification the image was sharp and distinct, enabling an outline tracing to be made of the total transverse section of the tooth. All tracings were made under constant conditions, and checks were carried out to ensure that a uniform magnification was used. Linear measurements of the section were considered unsatisfactory because of the difficulty in obtaining constant reference points. It was concluded that quantitive comparisons of tissues in different specimens would be best obtained from a study of the areas of the tracings representing the relevant tissues. By means of a planometer the areas of the tracing representing dentine and pulp
Glucocorticoids and tooth eruption
159
Tables 2 and 3. Mean body weights Control group Week
x
n
Hormone group
Week
S.E.
5 303 40 43-031 5 308-40 38-199 5 298-33 29-944 38 556 5 301-80 5 44-543 312-00 Mean control week 1 to mean control week 5: % difference - 2-79, insignificant (P > 0-02).
1 2 3 4 5
n
x
S.E.
1 5 300 40 23-635 2 5 254-00 24 971 3 5 234-70 23564 4 5 213-60 13-974 5 5 211-00 18 467 Mean hormone week 1 to mean hormone week 5: % difference - 34-96, significant (P < 0 02).
Table 4. Adrenal gland weights n
S.E.
x
Control group 0076 00077 5 Hormone group 0034 00000 5 Control to hormone group mean adrenal gland weight: % difference - 76-36, significant (P < 0-02).
Table 5. Mean weekly incisal eruption rates (mm per week) Control (n = 10) Week 1 2 3 4 5
x
S.E.
Hormone treated (n = 10) X
S.E.
0-225 5-19 5-32 0-231 4-81 0-160 0-210 4-61 0-217 4-38 in all weeks in rate Difference eruption significant (P < 0-02). 3-73 3-55 3-34 3-21 3-31
0-129 0-138 0-231 0-164 0-157
% difference 32-8 39-9 35-9 35-8 27-6
were measured separately. The total area of the transverse section of the incisor was also recorded. Method of analysis of results Experiment to determine the weekly dose of Depo-Medrone necessary to maintain a hypercorticoid state in the mature rat The weights of the five control and five hormone-treated rats were recorded in grams at weekly intervals throughout the 5 week experimental period. These weights were used to calculate, on a weekly basis, the mean and its standard error for the weights of the control and hormone-treated groups (Tables 2, 3). Comparisons between these means for week 1 and week 5 were carried out independently for control and hormone-treated groups. The weights of the paired adrenal glands from the ten rats were recorded in grams and a comparison between control and hormone group, in the mean weight of these glands, effected (Table 4).
160
P. C. BALL
Table 6. Transverse dimensions of incisors (mean in mm2 x 2200) Hormone &
Control d Total tooth Pulp Dentine
n
x
S.E.
n
x
S.E.
9 9 9
5497-5 340-2 4524-4
104-75 20-40 107-11
18 18 18
5289-4 705-0 3908-1
108-88 14-92 97 95
Hormone V
Control ,A
A
Total tooth Pulp Dentine
n
x
S.E.
n
x
S.E.
12 12 12
4964-6 305 8 4147-4
93-82 20-13 94-20
14 14 14
5179-9 778-1 3817-2
98-46 26-17
85-69
Area comparisons between males and females Control &, hormone d
% difference Total tooth Pulp
Dentine
3-86 6973 14-61
P
04-03 < 0-02 < 0-02
Control ?, hormone?
Total tooth Pulp Dentine
% difference 4-23 87-22 8-28
P
0-40-3 < 0-02 < 0-02
Comparisons between control and hormone-treated groups Incisal eruption rate The mean and its standard error were calculated for length of incisor erupted, in the control and hormone-treated groups, in each week of the experiment. The percentage difference in these means between the two groups was calculated and its significance tested (Table 5). Transverse dimensions of incisor Measurements of the tracings representing the areas of the incisor tissues in transverse section were recorded in square millimetres, at a magnification of x 2200. The mean and its standard error were calculated for areas of the transverse section of the whole 'incisor independently for male and female rats, in both the control and hormone-treated groups (Table 6). These means were used to calculate the percentage difference in transverse area of the incisor between: (i) male control and male hormone-treated groups, (ii) female control and female hormone-treated groups. Means and standard errors were then calculated for male and female rats in the control and hormone-treated groups for dentine and pulp and similar comparisons carried out between these means (Table 6). The significance of the percentage difference in the areas of pulp and dentine between the control and hormone-treated
Glucocorticoid and tooth eruption
161
Table 7. Transverse dimensions of dentine and pulp (control/hormone) (mean in mm2 x 2200 tabulated on a weekly basis) Dentine Control
Hormone
K
A ~~~
~
A,
Week
n
x
S.E.
n
x
S.E.
% difference
1 2 3 4 5
4 4 4 4 5
4192-25 4283 00 4605 25 4377-25 4131-40
169-16 193-58 179-80 215-70 243-86
6 7 8
4035-32 410714 4146-50 3452-94 3622 60
134-60 183-43 79 75 139-94 186-69
3-81 4-19
6 5
10-49* 23-63* 13-13*
Pulp Control
Hormone ~~~%
Week
n
x
1 2 3 4 5
4 4 4 4 5
351-50 297-75 300 25
S.E.
n
x
645-00 730-71 763-50 28-77 372-25 808-83 289-00 26-58 767 00 * Statistically significant (P < 0-02). 21-64
40 77 31-90
6 7 8 6 5
S.E.
difference
97 07 32-81 44-45 43-37 50-80
84-48* 84-32* 87-11 *
73.89* 90 53*
groups was tested independently for each week of the experimental period (Table 7). RESULTS
The subcutaneous injection of 0 1 ml Depo-Medrone per week to adult male and female rats of the Birmingham inbred strain caused a significant reduction in their body weight, and in the weight of their adrenal glands (Tables 2, 3, 4). This hormone also caused a significant increase in incisal eruption rate&(Table 5), together with a thinning of the dentine walls of these teeth (Table 6) and an increase in the size of their pulp chambers (Table 6). DISCUSSION
Rats receiving weekly injections of 01 ml Depo-Medrone in this experiment exhibited many of the features which have been described in hyperglucocorticoid animals. These included a fall in total body weight (Winter, Silber & Stoerk, 1950), exophthalmos (Alterman & Greenberg, 1953; Essex, 1955) and the disappearance of fat deposits (Winter, Silber & Stoerk, 1950). It therefore seems reasonable to conclude that the weekly subcutaneous injection of 01 ml Depo-Medrone to these animals in the present experiment produced a hypercorticoid state. The increase in incisal eruption rate observed in the hyperglucocorticoid rats in this present investigation confirms the findings of Garren (1955). Furthermore, the increased eruption rate in these hormone-treated animals was evident in the first week of the experimental period, indicating that the hormone had an immediate effect on eruption. Despite this marked increase in the length of tooth erupted, no alteration occurred in the transverse area of the incisors studied as a result of the hormone administration. This means that any alteration in the area of the tracing II
ANA I24
162
P. C. BALL
Fig. 1. Transverse ground section of rat mandibular incisor cut at the alveolar reference level. Note continuous ring of bone around tooth.
representing dentine could only result from an alteration in the thickness of the dentine walls of the tooth. Comparisons between control and hormone-treated groups in the mean area of dentine present in their incisors at the alveolar reference level indicate a significant reduction as a result of the Depo-Medrone administration (Table 6), whereas comparisons between the two groups in mean transverse area of pulp at the same reference level indicate a significant increase in the hypercorticoid animals (Table 6). A reduction in the rate of deposition of dentine in the rat molar as a result of cortisone administration was reported by Johannessen (1964). It is possible that, in this present study, a reduction in the rate of dentine deposition may have contributed to the thinning of the dentine walls seen in the incisors of these hormonetreated animals. It must be remembered, however, that, at the growing end of the rat incisor, dentine is first laid down in the form of. a thin-walled tube. Thickening of this wall results from continued deposition of dentine as the tooth erupts. At a particular point along the permanently erupting incisor the thickness of the dentine wall is therefore directly proportional to the rate of deposition of dentine and inversely proportional to the rate of eruption of the tooth. In this present investigation it was not possible to determine if thinning of the dentine walls at the one reference
Glucocorticoid and tooth eruption
163
level used was due to the increased eruption rate, to a possible reduction in the rate of deposition of dentine or to a combination of these factors. SUMMARY
A quantitative investigation was undertaken to evaluate the changes which occur in the dental tissues of the rat incisor following the systemic administration of adrenal glucocorticoid hormone. Of the 53 rats used in the 5 week experiment, 21 acted as untreated controls while the remaining 32 each received weekly subcutaneous injections of 01 ml Depo-Medrone. Throughout the experimental period the mandibular incisor eruption rates of a selection of both groups of rats were recorded. Transverse ground sections were prepared from the left mandibular incisor of each animal. Measurements taken on sections prepared at a standard reference level enabled comparisons to be made between control and hormone-treated animals in the dimensions of their incisor dentine and pulp. The results indicated that maintaining mature rats in a hyperglucocorticoid state caused a significant increase in incisal eruption rate, together with a thinning of the dentine walls and an increase in size of the pulp chambers of these teeth. REFERENCES
ATERMAN, K. &. GREENBERG, S. M. (1953). Experimental exophthalmos in rats produced by cortisone. Endocrinology 52, 510-517. Bovis, S. C. (1968). The preparation of piano-parallel sections of calcified tissue. British Dental Journal 125, 502-505. ESSEX, H. E. (1955). Exophthalmos in hypophysectomised and cortisone treated albino rats. American Journal ofPhysiology 181, 375-378. GARREN, L. D. (1955). The effects of endocrines on the eruption rate of the upper incisors of the rat. Journal of Dental Research 34, 687-688. GARREN, L. D. & GREEP, R. 0. (1960). Effect of adrenal cortical hormones on eruption rate of incisor teeth in the rat. Endocrinology 66, 625-628. GLICKMAN, I. & SHKLAR, G. (1954). The effect of systemic disturbances on the pulp of experimental animals. Oral Surgery 7, 550-558. JOHANNESSEN, L. B. (1964). The effects of cortisone on dentine apposition in rat molar teeth. Journal of Dental Research 43, 776-777. LEWIS, R. A., ROSENBERG, E. & WILKINS, L. (1950). The effects of 17 hydroxy-1 1 dehydrocorticosterone upon the adrenals of normal and hypophysectomised rats maintained with adrenocorticotropin. Endocrinology 47, 414-417. PARMER, L. G., KATONAH, F. &ANGRIST, A. A. (1951). ComparativeeffectsofA.C.T.H. cortisone, corticosterone, desoxycorticosterone, pregnenolone on growth and development of infant rats. Proceedings of the Society for Experimental Biology and Medicine 77, 215-218. WINTER, C. A., SILBER, I. & STOERK, H. C. (1950). Production of reversible hyperadrenocorticalism in rats by prolonged administration of cortisone. Endocrinology 47, 60-72.
II-2
157
The effect of adrenal glucocorticoid administration on eruption rates and tissue dimensions in rat mandibular incisors P. C. BALL The Dental School, University of Birmingham
(Accepted 21 June 1976) INTRODUCTION
The observation of Garren & Greep (1960) on the linear eruption rates of maxillary incisors in mature albino rats of the Holtzman strain indicated that doses of 1, 24, 5 and 10 mg of cortisone acetate a day caused a statistically significant increase in incisal eruption rate. This is surprising when it is remembered that the inhibition of cell division and growth which has been reported in many mesodermal structures as a result of increased levels of adrenal glucocorticoids has also been observed in dental tissues (Parmer, Katonah & Angrist, 1951; Glickman & Shklar, 1954). The object of the present investigation was to evaluate the changes which occur in the dental tissues of the rat incisor as a result of the administration of adrenal glucocorticoids, and to correlate these changes with the increased tooth eruption observed. METHODS AND MATERIALS
An experiment was first conducted to determine the dose of Depo-Medrone (an aqueous suspension of methylprednisolone acetate, 40 mg per ml) required to maintain a hyperglucocorticoid state in the adult rat. Of the five male and five female rats used in this initial investigation, two male and three female animals acted as untreated controls, while the other rats each received weekly subcutaneous injections of 0 1 ml Depo-Medrone for 5 weeks. Each rat was weighed at the start of the investigation and at weekly intervals. At the end of 5 weeks all ten animals were killed and their adrenal glands dissected out and weighed. Fifty three rats were used in the main investigation into possible dimensional changes occurring in the rat incisor as a result of adrenal glucocorticoid administration. These animals were all within the age range of 17 to 56 weeks at the start of the experiment. Twenty six of these rats were female and 27 male. After ear marking and weighing the rats were divided, within each litter, randomly into two groups. Twenty one animals formed the untreated control group, while 32 constituted the experimental group. The experimental animals were caged with their litter-mate controls and all animals received a similar soft diet and water. Within these two groups, ten control and ten experimental animals were selected for comparison of their mandibular incisal eruption rates. To effect this comparison measurements were taken throughout the experimental period to determine the movement relative to the gingival margin of fine scratch marks made in the enamel of these rats' mandibular incisors. Commencing on day 1 of the experimental period the hormone-treated, but not the control, group of rats received weekly injections of 01 ml Depo-Medrone. Throughout this time animals in each group were selected, as indicated in Table 1,
158
P. C. BALL
Table 1. Duration of experiments and numbers of animals used Days
Control group
Hormone group
7 14 21 28 35
2 2 2 2 3
4 5 6 4 3
and killed with Nembutal. Following decapitation their mandibles were dissected out and stored in formalin fixative. Sectioning technique for mandibular incisors Since the sections from these left mandibular incisors were to be used for a quantitative evaluation of dentine and pulp, decalcification had to be avoided. Ground sections were therefore prepared. The lower incisor is strongly curved, and a technique had to be devised so that a true transverse section of the tooth could be obtained in every case at a given position along the length of the tooth. The most suitable reference level along the lower incisor was considered to be the level just before the tooth had erupted sufficiently to lose any of its supporting bone (the alveolar reference level). This position was readily determined on a series of transverse ground sections as it presented as the last section in which the transversely cut incisor had a continuous ring of bone around it. The problem of obtaining true transverse sections was solved by carefully positioning the relevant part of the specimen on specially constructed plastic chucks. These plastic chucks were machined to fit into the Bovis ground section apparatus (Bovis, 1968) and had, on the face of the chuck that was presented to the diamond wheel, a deep groove. Reference marks on the side of the chuck in line with, and at right angles to, this groove enabled the operator to line the groove up exactly at right angles to the edge of the diamond wheel. The specimen was now fitted into the groove and after careful positioning fixed in place with cold cure methyl methacrylate. Several ground sections could now be cut and, after mounting in glycerine jelly, examined under the microscope. The one section cut at the alveolar reference level was selected from each of the series of ground sections and used in the quantitive evaluation of dentine and pulp (Fig. 1). Measuring technique for ground sections To obtain sufficiently accurate measurements the section was mounted on its slide on the stage of a carbon arc projector. The projector was positioned to give a magnification of the object, on a background illuminated screen of x 2200. At this magnification the image was sharp and distinct, enabling an outline tracing to be made of the total transverse section of the tooth. All tracings were made under constant conditions, and checks were carried out to ensure that a uniform magnification was used. Linear measurements of the section were considered unsatisfactory because of the difficulty in obtaining constant reference points. It was concluded that quantitive comparisons of tissues in different specimens would be best obtained from a study of the areas of the tracings representing the relevant tissues. By means of a planometer the areas of the tracing representing dentine and pulp
Glucocorticoids and tooth eruption
159
Tables 2 and 3. Mean body weights Control group Week
x
n
Hormone group
Week
S.E.
5 303 40 43-031 5 308-40 38-199 5 298-33 29-944 38 556 5 301-80 5 44-543 312-00 Mean control week 1 to mean control week 5: % difference - 2-79, insignificant (P > 0-02).
1 2 3 4 5
n
x
S.E.
1 5 300 40 23-635 2 5 254-00 24 971 3 5 234-70 23564 4 5 213-60 13-974 5 5 211-00 18 467 Mean hormone week 1 to mean hormone week 5: % difference - 34-96, significant (P < 0 02).
Table 4. Adrenal gland weights n
S.E.
x
Control group 0076 00077 5 Hormone group 0034 00000 5 Control to hormone group mean adrenal gland weight: % difference - 76-36, significant (P < 0-02).
Table 5. Mean weekly incisal eruption rates (mm per week) Control (n = 10) Week 1 2 3 4 5
x
S.E.
Hormone treated (n = 10) X
S.E.
0-225 5-19 5-32 0-231 4-81 0-160 0-210 4-61 0-217 4-38 in all weeks in rate Difference eruption significant (P < 0-02). 3-73 3-55 3-34 3-21 3-31
0-129 0-138 0-231 0-164 0-157
% difference 32-8 39-9 35-9 35-8 27-6
were measured separately. The total area of the transverse section of the incisor was also recorded. Method of analysis of results Experiment to determine the weekly dose of Depo-Medrone necessary to maintain a hypercorticoid state in the mature rat The weights of the five control and five hormone-treated rats were recorded in grams at weekly intervals throughout the 5 week experimental period. These weights were used to calculate, on a weekly basis, the mean and its standard error for the weights of the control and hormone-treated groups (Tables 2, 3). Comparisons between these means for week 1 and week 5 were carried out independently for control and hormone-treated groups. The weights of the paired adrenal glands from the ten rats were recorded in grams and a comparison between control and hormone group, in the mean weight of these glands, effected (Table 4).
160
P. C. BALL
Table 6. Transverse dimensions of incisors (mean in mm2 x 2200) Hormone &
Control d Total tooth Pulp Dentine
n
x
S.E.
n
x
S.E.
9 9 9
5497-5 340-2 4524-4
104-75 20-40 107-11
18 18 18
5289-4 705-0 3908-1
108-88 14-92 97 95
Hormone V
Control ,A
A
Total tooth Pulp Dentine
n
x
S.E.
n
x
S.E.
12 12 12
4964-6 305 8 4147-4
93-82 20-13 94-20
14 14 14
5179-9 778-1 3817-2
98-46 26-17
85-69
Area comparisons between males and females Control &, hormone d
% difference Total tooth Pulp
Dentine
3-86 6973 14-61
P
04-03 < 0-02 < 0-02
Control ?, hormone?
Total tooth Pulp Dentine
% difference 4-23 87-22 8-28
P
0-40-3 < 0-02 < 0-02
Comparisons between control and hormone-treated groups Incisal eruption rate The mean and its standard error were calculated for length of incisor erupted, in the control and hormone-treated groups, in each week of the experiment. The percentage difference in these means between the two groups was calculated and its significance tested (Table 5). Transverse dimensions of incisor Measurements of the tracings representing the areas of the incisor tissues in transverse section were recorded in square millimetres, at a magnification of x 2200. The mean and its standard error were calculated for areas of the transverse section of the whole 'incisor independently for male and female rats, in both the control and hormone-treated groups (Table 6). These means were used to calculate the percentage difference in transverse area of the incisor between: (i) male control and male hormone-treated groups, (ii) female control and female hormone-treated groups. Means and standard errors were then calculated for male and female rats in the control and hormone-treated groups for dentine and pulp and similar comparisons carried out between these means (Table 6). The significance of the percentage difference in the areas of pulp and dentine between the control and hormone-treated
Glucocorticoid and tooth eruption
161
Table 7. Transverse dimensions of dentine and pulp (control/hormone) (mean in mm2 x 2200 tabulated on a weekly basis) Dentine Control
Hormone
K
A ~~~
~
A,
Week
n
x
S.E.
n
x
S.E.
% difference
1 2 3 4 5
4 4 4 4 5
4192-25 4283 00 4605 25 4377-25 4131-40
169-16 193-58 179-80 215-70 243-86
6 7 8
4035-32 410714 4146-50 3452-94 3622 60
134-60 183-43 79 75 139-94 186-69
3-81 4-19
6 5
10-49* 23-63* 13-13*
Pulp Control
Hormone ~~~%
Week
n
x
1 2 3 4 5
4 4 4 4 5
351-50 297-75 300 25
S.E.
n
x
645-00 730-71 763-50 28-77 372-25 808-83 289-00 26-58 767 00 * Statistically significant (P < 0-02). 21-64
40 77 31-90
6 7 8 6 5
S.E.
difference
97 07 32-81 44-45 43-37 50-80
84-48* 84-32* 87-11 *
73.89* 90 53*
groups was tested independently for each week of the experimental period (Table 7). RESULTS
The subcutaneous injection of 0 1 ml Depo-Medrone per week to adult male and female rats of the Birmingham inbred strain caused a significant reduction in their body weight, and in the weight of their adrenal glands (Tables 2, 3, 4). This hormone also caused a significant increase in incisal eruption rate&(Table 5), together with a thinning of the dentine walls of these teeth (Table 6) and an increase in the size of their pulp chambers (Table 6). DISCUSSION
Rats receiving weekly injections of 01 ml Depo-Medrone in this experiment exhibited many of the features which have been described in hyperglucocorticoid animals. These included a fall in total body weight (Winter, Silber & Stoerk, 1950), exophthalmos (Alterman & Greenberg, 1953; Essex, 1955) and the disappearance of fat deposits (Winter, Silber & Stoerk, 1950). It therefore seems reasonable to conclude that the weekly subcutaneous injection of 01 ml Depo-Medrone to these animals in the present experiment produced a hypercorticoid state. The increase in incisal eruption rate observed in the hyperglucocorticoid rats in this present investigation confirms the findings of Garren (1955). Furthermore, the increased eruption rate in these hormone-treated animals was evident in the first week of the experimental period, indicating that the hormone had an immediate effect on eruption. Despite this marked increase in the length of tooth erupted, no alteration occurred in the transverse area of the incisors studied as a result of the hormone administration. This means that any alteration in the area of the tracing II
ANA I24
162
P. C. BALL
Fig. 1. Transverse ground section of rat mandibular incisor cut at the alveolar reference level. Note continuous ring of bone around tooth.
representing dentine could only result from an alteration in the thickness of the dentine walls of the tooth. Comparisons between control and hormone-treated groups in the mean area of dentine present in their incisors at the alveolar reference level indicate a significant reduction as a result of the Depo-Medrone administration (Table 6), whereas comparisons between the two groups in mean transverse area of pulp at the same reference level indicate a significant increase in the hypercorticoid animals (Table 6). A reduction in the rate of deposition of dentine in the rat molar as a result of cortisone administration was reported by Johannessen (1964). It is possible that, in this present study, a reduction in the rate of dentine deposition may have contributed to the thinning of the dentine walls seen in the incisors of these hormonetreated animals. It must be remembered, however, that, at the growing end of the rat incisor, dentine is first laid down in the form of. a thin-walled tube. Thickening of this wall results from continued deposition of dentine as the tooth erupts. At a particular point along the permanently erupting incisor the thickness of the dentine wall is therefore directly proportional to the rate of deposition of dentine and inversely proportional to the rate of eruption of the tooth. In this present investigation it was not possible to determine if thinning of the dentine walls at the one reference
Glucocorticoid and tooth eruption
163
level used was due to the increased eruption rate, to a possible reduction in the rate of deposition of dentine or to a combination of these factors. SUMMARY
A quantitative investigation was undertaken to evaluate the changes which occur in the dental tissues of the rat incisor following the systemic administration of adrenal glucocorticoid hormone. Of the 53 rats used in the 5 week experiment, 21 acted as untreated controls while the remaining 32 each received weekly subcutaneous injections of 01 ml Depo-Medrone. Throughout the experimental period the mandibular incisor eruption rates of a selection of both groups of rats were recorded. Transverse ground sections were prepared from the left mandibular incisor of each animal. Measurements taken on sections prepared at a standard reference level enabled comparisons to be made between control and hormone-treated animals in the dimensions of their incisor dentine and pulp. The results indicated that maintaining mature rats in a hyperglucocorticoid state caused a significant increase in incisal eruption rate, together with a thinning of the dentine walls and an increase in size of the pulp chambers of these teeth. REFERENCES
ATERMAN, K. &. GREENBERG, S. M. (1953). Experimental exophthalmos in rats produced by cortisone. Endocrinology 52, 510-517. Bovis, S. C. (1968). The preparation of piano-parallel sections of calcified tissue. British Dental Journal 125, 502-505. ESSEX, H. E. (1955). Exophthalmos in hypophysectomised and cortisone treated albino rats. American Journal ofPhysiology 181, 375-378. GARREN, L. D. (1955). The effects of endocrines on the eruption rate of the upper incisors of the rat. Journal of Dental Research 34, 687-688. GARREN, L. D. & GREEP, R. 0. (1960). Effect of adrenal cortical hormones on eruption rate of incisor teeth in the rat. Endocrinology 66, 625-628. GLICKMAN, I. & SHKLAR, G. (1954). The effect of systemic disturbances on the pulp of experimental animals. Oral Surgery 7, 550-558. JOHANNESSEN, L. B. (1964). The effects of cortisone on dentine apposition in rat molar teeth. Journal of Dental Research 43, 776-777. LEWIS, R. A., ROSENBERG, E. & WILKINS, L. (1950). The effects of 17 hydroxy-1 1 dehydrocorticosterone upon the adrenals of normal and hypophysectomised rats maintained with adrenocorticotropin. Endocrinology 47, 414-417. PARMER, L. G., KATONAH, F. &ANGRIST, A. A. (1951). ComparativeeffectsofA.C.T.H. cortisone, corticosterone, desoxycorticosterone, pregnenolone on growth and development of infant rats. Proceedings of the Society for Experimental Biology and Medicine 77, 215-218. WINTER, C. A., SILBER, I. & STOERK, H. C. (1950). Production of reversible hyperadrenocorticalism in rats by prolonged administration of cortisone. Endocrinology 47, 60-72.
II-2
