Differential termination times of enamel formation on human deciduous anterior-tooth surfaces revealed by tetracycline labelling

Differential termination times of enamel formation on human deciduous anterior-tooth surfaces revealed by tetracycline labelling

Arc/u orcrl Biol. Vol. 30, No. 5. pp. 409-414, Printed in Great Britain. All nghts reserved 1985 Copyright Q 0003-9969/U $3.00 + 0.00 1985 Pergamon...

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Arc/u orcrl Biol. Vol. 30, No. 5. pp. 409-414, Printed in Great Britain. All nghts reserved

1985 Copyright

Q

0003-9969/U $3.00 + 0.00 1985 Pergamon Press Ltd

DIFFEtRENTIAL TERMINATION TIMES OF ENAMEL FORMATION ON HUMAN DECIDUOUS ANTERIOR-TOOTH SlJRFACES REVEALED BY TETRACYCLINE LABELLING T. Ooii and Y. OGURA-FUTAKI Department of Anatomy, National Defense Medical College, 2 Namiki 3 Chome, Tokorozawa, Saitama, 359 Japan Summary-The positional relationships between the cervical-enamel margin and the intersecting point of a fluorescent (tetracyline) line in dentine, with the outer dentine surface or the dentine+namel junction, were investigated by ultraviolet microscopy of the human deciduous anterior teeth. The results suggest that enamel formation (1) ended earlier on the mesial than on the distal surface in 18 instances and, nearly simultaneously Ion both of these surfaces in four, (2) ended earlier on the distal than on the labial surface in all 28 specimens and (3) ended earlier on the labial than on the lingual surface in 14 instances and nearly simultaneously on both of these surfaces in eight instances.

INTRODUCTION

faces. When the linear cervical line did not undulate, the mid-point of cervical line in approximal view was used. Thus the machine enabled us to prepare a mesio-distal section as well as a labio-lingual section from one tooth. Ground sections of about 80 pm thickness were examined with an Olympus BHF342 ultraviolet microscope, using transmitted ultraviolet light with an excitation filter BG12 and barrier filter 0515. Out of 409 teeth, 249 teeth (58 per cent) contained tetracycline lines. Ground sections were photographed, using Kodak Tri-Xpan film, and detailed observations were made on enlarged photomicrographs. The margin of the enamel on the section was designated as point A, and the intersecting point of a given fluorescent line with the outer dentine surface or dentine-enamel junction was designated as point B. In the majority of 249 labelled teeth, point B was either incisal or apical to point A on both of the two sides examined. They were excluded from further consideration, even if the distance between points A and B differed on the two sides because it has not been determined whether dentine formation proceeds equally on opposing tooth surfaces. As only specimens in which positional relationships between points A and B differed between two opposing sides were useful for the present investigation, the ultimate observations were much smaller in number.

The formation of the roots of human teeth is thought to begin after the crown is completed (Diamond and Applebaum, 1942; Diab and Stallard, 1965). However, considering a tooth three-dimensionally, this statement is not valid because perikymata, namely manifestations of the incremental lines of enamel on the outer enamel surface, in the enamel of the cervical region of the crown, are interrupted by the curve drawn by cervical margin of enamel; therefore, crown formation can be continuing on one side of a tooth, while root formation has started on another side. This aspect of the tooth development has not been thoroughly studied in deciduous teeth, because their incremental lines of enamel are so indistinct. However, the availability of human deciduous anterior teeth, labelled with tetracycline, makes it possible to study their incremental lines of dentine. Consequently, we have been able to study positional relationships between the cervical margin of enamel and the intersecting point of a given tetracycline line in dentine with the outer dentine surface.

MATERIA.LS AND METHODS Four hundred and nine extracted human deciduous incisor and canine teeth were sectioned, using a Bronwill sectioning machine; sections were finally ground on a whetstone lubricated with water. Prior to sectioning, two cut planes were marked with Indian ink. To begin with, the iabio-lingual section was prepared through the plane connecting the centre of the incisal edge and the two points where enamel extended most cervically on both the labial and lingual surfaces. The labio-lingual sectioned surfaces exhibited tetracycline lines. The two halves were then placed together and sectioned in mesio-distal direction. The mesio-distal section was cut through the following three points: the centre of the incisor edge and the two points where the cervical line of enamel was indented most incisally on the approximal sur-

RESULTS Labial us Iingual tooth surface

Twenty-three specimens were suitable for analysis and the results are presented in Table 1. Positional relationships between points A and B were classified into three types. Type I denotes the group in which point A was incisal to point B on the labial, and apical on the lingual surface (Fig. 1). This mutual positional relationship reveals that the enamel formation terminated earlier on the labial than on the lingual surface 409

T. Ooil and Y. OGURA-FUTAKI

410

Table 1. Number of instances of each type, divided into each tooth species: A, B and C denote the central, lateral incisor and canine, respectively Type I II III

A

A

_B

B

C

c

Total

1 0 100331 0 0

0

0

8

4

0

0

0

I

14 8 1

of a tooth. Instances in which points A and B coincided on one side (Fig. 2) were also included in this type. Type I was the most frequent; 12 of the 14 instances were canines. In type II, points A and B coincided on both the labial and lingual surfaces (Fig. 3). In these instances, enamel formation finished nearly simultaneously on both sides. Eight specimens showed this relationship. Type III showed the reverse relationship to type I: point A was apical to point B on the labial, and incisal on the lingual surface. In these instances, enamel formation ended earlier on the lingual than on the labial surface. Only one specimen belonged to type III. Mesial

us distal tooth surface

Twenty-two specimens were suitable for analysis and the results are indicated in Table 2. Type I denotes the group in which point A was incisal to point B on the mesial and apical on the distal surface (Fig. 4). In some instances, points A and B coincided with each other on one side. In type I, enamel formation ended earlier on the mesial than on the distal surface; this type was the most frequent, being present in 18 out of the 22 specimens. In type II, points A and B coincided on both the mesial and distal surfaces: in these, enamel formation ended nearly simultaneously on both sides. Only four specimens showed this relationship. There were no specimens belonging to type III, in which point A was incisal to point B on the distal and apical on the mesial side.

Table

Labial

2. Number of instances divided into each tooth

of each type, species

Type

_A

A

_B

B

_C

C

Total

I II III

3 2 000022 0 0

4

3

3

3

0

0

0

0

18 4 0

us distal tooth surface

Twenty-eight specimens allowed us to study the mutual positional relationship of two points between the labial and the distal tooth surfaces. Theoretically there are three types, but actually point B was incisal to point A on the labial, and apical to point A on the distal surface in all useful specimens (Fig. 5 and Table 3). Namely, enamel formation was completed earlier on the distal than on the labial surface in all 28 specimens examined.

Table

Type

3

A

A

B

B

C

c

Total

1

5

5

4

10

3

29

DISCUSSION

Yoshioka (1970) counted on each of four tooth surfaces the number of perikymata located cervically to those perikymata that were distinctly continuous on all four tooth surfaces, and pointed out that enamel formation ends in the sequence of the mesial, distal, labial and lingual tooth surface in the permanent incisors. In the permanent canine, the enamel formation ends earlier on the lingual than on the labial surface. Therefore, our findings in respect of deciduous teeth agree with the observed order of tooth surfaces in permanent incisors. Fewer incisors were suitable for our investigation than canines (Table 1); this difference may be related to the straight course of the cervical line of enamel margin in deciduous incisors. The order of the tooth surfaces also agrees with the results obtained in embryological studies of serial sections of human fetuses (Ooi and Yoshioka, 1974). Oo& (1981) indicated that the epithelial portion of incisor tooth germs at the bell stage contains less amount of stellate reticulum on the approximal surfaces than on the labial and lingual surfaces; he noted further that the stellate reticulum disappears in an orderly sequence of the mesial, distal, labial and finally lingual surface. A figure 14 of Schour and Massler (1940), in which the enamel margin and the intersecting point of the given incremental line of dentine with the dentine surface coincide on both labial and lingual side, is commonly cited in textbooks. Enamel formation is assumed to terminate simultaneously on the opposing sides. A figure 903 of Ebner (1902), showing dentine lamellae, enamel formation is shown to end earlier on the labial than on the lingual side and thus accords more closely with our findings. The conclusion we draw from our findings is that, expressed three-dimensionally, the root formation begins on one tooth surface, while the crown (enamel) is still being formed on the other tooth surfaces. Acknowledgements--We express sincere acknowledgement to Dr L. Moss-Salentijn, Department of Anatomy, Columbia University, and Professor A. E. W. Miles, Royal College of Surgeons of England, for assistance with the English of our manuscript. And we are much obliged to Dr Sumihisa Gohdo, for collection of materials and to Miss Masako Oo& for secretarial assistance.

REFERENCES

Diab M. A. and Stallard R. E. (1965) A study of the relationship between epithelial root sheath and root development. Periodontics 3, 1614. Diamond M. and Applebaum E. (1942) The epithelial sheath: Histogenesis and function. J. dent. Res. 21, 403-411. Ebner V. (1902) Hand&h der Gewehelehre des Menschen (Edited by Kiilliker A.) Vol. 3, p. 76. Wilhelm Engelmann, Leipzig.

Termination

times of enamel

Oo& T. (1981) Differential development and extension of hard tissue on the tooth surfaces. In: Human Tooth and Dental Arch Development, pp. 54-60. Ishiyaku, Tokyo. Oo& T. and Yoshioka M. (1974) Le developpement du germe dentaire differentiel des faces dentaires. Acfa anat. 87, 467-478.

Plates

formation

411

Schour I. and Massler M. (1940) Studies in tooth development: the growth pattern of human teeth. Part II. J. Am. dent. Ass. 27, 191&1931. Yoshioka M. (1970) Difference in time of crown completion among dental surfaces. Okajima Folia anat. Jap. 47, 213-228.

1 and 2 overleaf.

412

T. OoE and Y. OGURA-FUTAKI

All photographs

were taken under ultraviolet microscopy. In Figs 1-3, the labial surfaces lingual on the right. Plate

are left and the

1.

Fig. 1. Labio-lingual ground section of an upper canine. A fluorescent line on the labial side intersects with the dentine surface (point B), apically to the enamel margin (point A). The same fluorescent line on the lingual side terminates at the dentine-enamel border (point B), incisally to point A. Fig. 2. Labio-lingual ground section of another upper canine. On the labial side the point of intersection (B) is apical to the enamel margin (A), whereas on the lingual side points A and B coincide. Fig. 3. Labio-lingual

ground

section of a third upper canine. sides.

The two points A and B coincide

on both

Plate 2. Fig. 4. Mesio-distal ground section of an upper lateral incisor. Mesial is to the right and distal to the left. Mutual relation of the two points A and B differs between on the two opposing sides. Fig. 5. Labial

(left, a) and distal (right,

b) halves

of ground

sections

taken

from an upper

canine.

Termination times of enamel formation

Plate 1.

413

414

T. Ooil and Y. OGURA-FUTAKI

Plate 2.