Dentin dysplasia type I: A scanning electron microscopic analysis of the primary dentition Michael Melnick, D.D.S., Ph.D.,* L. Stefan Levin, D.D.S., M.S.D.,** and John Brady, D.D.S., M.S.P.H., *** Los Angeles, Calif., Baltimore, Md., and Washington, D. C.

SCHOOL OF DENTISTRY, UNIvERSlTY OF SOUTHERN CALIFORNIA; DEPARTMENT OF ~TOLARYNGOLOGY, THE JOHNS HOPKINS UNIVERSITY; UNITED STATES ARMY INSTITUTE FOR DENTAL RESEARCH, WALTER REED

ARMY MEDICAL CENTER

Dentin dysplasia type I (DD-I) is a rare autosomal dominant disorder which affects both the deciduous and permanent dentitions. The affected deciduous and permanent teeth have short conical roots with sharp, apical constrictions and frequently periapical radiolucencies in the absence of caries. Apical to a thin layer of normal coronal dentin are large, calcified, dentin masses which nearly obliterate the pulp chamber and canals. Presented here are light microscopic and scanning electron microscopic observations of deciduous teeth from three unrelated persons with the disorder. In general, the deciduous teeth had (1) normal enamel, (2) a thin layer of normal dentin adjacent to the dentinoenamel junction, (3) a crescent-shaped pulpal remnant below the normal dentin, (4) dysplastic dentin masses (ranging from atubular to a few small tubules) between which are spaces presumed to previously have contained smaller remnants of the original mesenchymal dental papilla, and (5) root dentin, which is dysplastic throughout. The SEWdefined phenotype, however, was noticeably variable among all three persons. Based on the current concepts of tooth morphogenesis, it is most likely that the abnormal root morphology of DD-I teeth is secondary to the abnormal differentiation and/or function of the ectomesenchymally derived odontoblasts.

D entin dysplasia type I (DD-I) is a rare autosomal dominant disorder which affects both the deciduous and permanent dentitions. Clinically, the deciduous and the permanent teeth are of normal size, shape, and consis- tency, although affected teeth may be slightly amber in color. The teeth are frequently malaligned. Radio- graphically, affected teeth have short, conical roots with sharp, apical constrictions and frequently periapi- cal radiolucencies in the absence of caries. Pre-eruptive pulpal obliteration results in a crescent-shaped pulp chamber remnant parallel to the cementoenamel junc- tion in the permanent dentition and often total pulp chamber obliteration in the deciduous dentition. The pulp canals of the root are completely obliterated in both dentitions. On light microscopy, much of the co-

This study was supported in part by Program Project Grant DE-02848 (M. M.), by Training Grant in Craniofacial Biology DE-07006 (M. M.), and by Research Career Development Award K04 DEOOO21 (L. S. L.) from the NIDR, National Institutes of Health. *Graduate Program in Craniofaciaf Biology and Section of Biochem- istry and Nutrition, Department of Basic Sciences.

ronal dentin is normal, although there are occasional areas of atubular dentin, particularly in deciduous teeth. Apical to this normal dentin are found the pulpal remnants. Further apically are large masses of calcified tubular dentin, atypical “osteodentin,” and true denti- cles. Several reviews of the clinical, radiographic, and histologic findings of DD-I have been published.1-3

The results of scanning electron microscopy (SEM) of permanent teeth have been reported.‘. 3 Sauk and associates4 made observations on fractured and metal- lurgically polished, EDTA-etched teeth from an af- fected 19-year-old white man with a positive family history. In the fractured specimens the root canals were obliterated and the defective dentin was fused into a contiguous mass with the root dentin. They described the dentinal tubules of the individual dentinal globules or “cascades” as being normal except for orientation. Polished and etched specimens displayed a similar morphology. Higher magnifications revealed a horizon- tal anastomosis between the various cascading masses which resembled the Haversian system of bone; hence,

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336 Melnick, Lerfn, and B&J Oral Surg. October, 1980

DENTIN DYSPLASIA TYPE I

Fig. 1. Case 1. Radiographically the teeth have short conical roots with sharp apical constrictions and nearly total pulpal obliterations. Note that the crescent-shaped pulpal remnant is more apical in location in the permanent than in the deciduous dentition.

Fig. 2. Mother of the patient in Case 1, The radiographic characteristics of the permanent dentition are similar to those of the proband in Fig. 1.

a justification for the term osteodenfin. Wesley and as- sociates ,5 using a similar SEM technique, confirmed the findings of Sauk and associates4 in permanent teeth from a 17-year-old boy, also with a positive family history. Wesley and associates5 noted that there was only “a narrow band of dentin adjacent to the dentino- enamel junction ” that was morpholocially normal. The remainder of the dentin was characterized by whorls in which the tubules took atypical directions.

The objective of this investigation was to delineate the SEM findings in affected deciduous teeth and to correlate them with light microscopic findings in the same specimens.

Case 1

o-;a

\ ‘0. *t 0

0. Examined female, normal .Examined male, GD-I

Cl. Exammed male. normal cl 2 Two normal males

by history Exammed female, DO-I

Proband

Fig. 3. Case 1. Pedigree of the proband’s family

MATERIALS AND METHODS

Deciduous teeth from three unrelated persons with DD-I were obtained from Dr. Roger E. Sanger (Uni- versity of Colorado) and Dr. Norbert J. Burzynski (University of Louisville, KY.). The teeth were fixed and preserved in 10 percent formalin, washed with dis- tilled water, and fractured buccolingually with a chisel along their entire lengths. In order to provide the greatest surface detail possible, the teeth were not sec- tioned with a disc, nor were the sectioned surfaces polished. All specimens were washed again in distiIled water, deproteinized in several changes of 2 percent sodium hypochlorite, dehydrated in a graded ethanol series, fixed to specimen stubs, and sputter-coated in a vacuum evaporator (Hummer V) with a thin layer of gold palladium. The specimens were examined in an AMR SEM operating at 30 kv. and equipped with a Polaroid photographic unit.

After SEM examination was completed, the same specimens were removed from the stubs, decalcified in sodium citrate and formic acid, and imbedded in paraffin. Sections 7 pm thick were cut, stained with hematoxylin and eosin, and viewed with a stan- dard light microscope.

CASEREPORTS Case 1

The proband was an 8%-year-old white boy who had the typical features of DD-I on radiography (Fig. 1). Of particular note was that the crescent-shaped radiolucent areas in the pulp

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Fig. 4. SEM of fractured primary molar from Case 1. a, Note the normal enamel and thin layer of dentin below the DEJ as well as the dysplastic dentin below the normal dentin. (x25.) b, Note that the dysplastic dentin extends to the junction with root cementurn. (~58.) The arrow designates CEJ. c, Higher magnification of dysplastic dentin masses reveals atubular clusters of smaller mineralized globules. (X2,160.)

chambers were more apically placed in the permanent teeth to those in Case 1. The dysplastic dentin masses had a slightly than in the deciduous teeth. On examination, the proband’s different appearance, resembling that of gnarled wood or mother (Fig. 2) and his maternal grandmother were also knots (Fig. 6, b). Higher magnification of these “knots” found to be affected. The proband’s father and 11-year-old revealed a regular array of small tubules parallel to one an- sister were not affected; nor were other family members by other and traveling in a circular path (Fig. 6, c). Light mi- history (Fig. 3). croscopic findings did not differ from those seen in Case 1.

Eight deciduous teeth (canines and molars) were removed surgically from the proband to facilitate preventive orthodon- tic therapy. On SEM examination, the outer enamel surface, the enamel surface on fracture planes, and a thin layer of the dentin below the dentinoenamel junction were normal (Fig. 4, a). Apical to the normal dentin were multiple, irregularly shaped, calcified masses with irregularly placed and shaped spaces separating them. This dysplastic dentin extended to the junction with root cementum (Fig. 4,6). For the most part, on higher magnification the dysplastic dentin masses were seen to consist of atubular clusters of smaller mineralized globules (Fig. 4, c). The pulp canals were completely obliterated with this material. Light microscopy supported the impressions gained with SEM (Fig. 5).

SEM findings in the teeth of Case 3 (Fig. 7, u) were similar to those in Cases 1 and 2. The thin layer of regular dentin just

below the dentinoenamel junction was normal (Fig. 7, 6). The abnormal dentin, however, differed from that of the other two cases in that the calcified masses were generally less chaotic, with many more tubules in a regular pattern (Fig. 7. c). Nevertheless, the light microscopic findings were the same as those for Cases 1 and 2.

DISCUSSION

Cases 2 and 3

Both probands were the only confirmed affected members in their families. Unfortunately, other family members re- fused examination. Clinical and radiographic findings in these two white female patients were identical to those seen in Case 1. Four deciduous molars from Case 2 and three deciduous molars from Case 3 were available for SEM examination. These teeth had been surgically removed for various thera- peutic reasons.

SEM findings in the teeth of Case 2 (Fig. 6, a) were similar

The results of our SEM investigation of deciduous teeth with DD-I are similar to those found in permanent teeth by Sauk and associates4 and Wesley and associ- ates.” These observations include: (1) normal enamel, (2) a thin layer of normal dentin adjacent to the den- tinoenamel junction, (3) a crescent-shaped pulpal rem- nant below the normal dentin, (4) dysplastic dentin masses between which are spaces presumed to previ- ously have contained smaller remnants of the original mesenchymal dental papilla, and (5) root dentin, which is dysplastic throughout. There was, however, at least one important difference. Dentin tubules in teeth from all three of our probands appear to be fewer in number

338 M&tick, Levin, and Body

October, 1980

Fig. 5. Light microscopy of the decalcified molar pictured in Fig. 4. a, Low-magnification (X 10) view of the tooth showing the initial layer of normal dentin, the space occupied in vivo by the pulpal remnant, and the more apically placed masses of dysplastic dentin. b, Higher magnification (x60) of the same tooth (area in box) showing the normal tubular dentin (top) and the mostly atubular dentin masses (bottom) with spaces once occupied by pulpal tissue remnants.

Fig. 6. SEM of fractured primary molar from Case 2. a, Note the normal enamel and thin layer of dentin adjacent to the DEJ as well as the more apically located dysplastic dentin masses. (~22.) Box outlines area in b. b, Dysplastic dentin masses resembled gnarled wood or knots. (X 11 I .) Box outlines area in c. c, Higher magnifica- tion revealed these “knots” to have a regular array of small tubules parallel to one another. (X 1,109.)

and generally smaller in diameter than normal dentin lae at the level of the developing crown, inducing ec- tubules. topic dentin formation. ” They went on to suggest that

The pathogenesis of DD-I continues to be an enigma. “it appears that dentinal dysplasia is a defect in the Based upon SEM observations, Sauk and associates4 epithelial component in which the invagination of the proposed that “displacement of inner cells of the de- root sheath, first, occurs too soon and, then, in a se- veloping dental organ proliferate into the dentinal papil- quence of futile attempts to correct itself, results in a

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Fig. 7. SEM of fractured primary molar from Case 3. a, Features similar to those in Figs. 4 and 6. (~54.) b, Higher magnification (X 1,469) of normal dentin. c, Higher magnification ( x 1,368) of typical dysplastic dentin masses from the teeth of Case 3.

stunted root form with an unusual whorl-like pattern of dentin obliterating the pulp chambers. ” Bixler,3 how- ever, disagreed with this interpretation: “This expla- nation does not seem to consider the probable role of dentin as an inductive force in cementum formation. Since a primary dentin defect has already been demon- strated in DD type I, at this stage it seems unnecessary to postulate a primary defect in the root sheath epithe- lium. ” Wesley and associate9 echoed this objection to the hypothesis of Sauk and associates4 and as an alter- native suggested “an error in the continual induction of odontoblasts after the interaction with the ameloblastic layer. ’ ’

We agree with the objections of Bixler3 and Wesley and associates,j based on what is known about tooth development. The developmental responsibility for tooth size and shape, including roots, rests with the ectomesenchyme of the dental papilla.6-g It is more likely, then, that the abnormal root morphology of DD-I teeth is secondary to the abnormal differentiation and/or function of the ectomesenchymally derived odontoblasts. That crown morphology is normal is probably related to the fact that the initial odontoblast differentiation and function are normal.

The authors wish to thank Ms. Gwen Airkens and Ms. Peggy Meek for preparing the manuscript and Dr. Todd Beckerman for assistance in preparing the tissue for light

REFERENCES

1. Logan, J., Becks, H., Silverman, S., and Pindborg, 3. J.: Dentin- al Dysplasia, ORAL SURG. 15: 317-333, 1962.

2. Shields, E. D., Bixler, D., and El-Kafrawy, A, M.: A Proposed Classification for Heritable Human Dentine Defects With a De- scription for a New Entity, Arch. Oral. Biol. 18: 543-553, 1973.

3. Bixler, D.: Heritable Disorders Affecting Dentin, in Stewart, R. E., and Prescott, G. H., editors: Oral Facial Genetics, St. Louis, 1976, The C. V. Mosby Company, pp. 237-239.

4. Sauk, J. J., Lyon, H. W., Trowbridge, H. 0.) and Witkop, C. I.: An Electron Optic Analysis and Explanation for the Etiology of Dentinal Dysplasia. OAL SURG. 33: 763-771, 1972.

5. Wesley, R. K., Wysocki, G. P., Mintz, S. M., and Jackson, J.: Dentin Dysplasia Type I, ORAL SURG. 41: 516-524, 1976.

6. Kollar, E. J., and Baird, G. R.: The Influence of the Dental Papilla on the Development of Tooth Shape in Embryonic Mouse Tooth Germs, J. Embryol. Exp. Morphol. 21: 131-148, 1969.

7. Kollar, E. J., and Baird, G. R.: Tissue Interactions in Embryonic Mouse Tooth Germs. I. Reorganization of the Dental Epithelium During Tooth Germ Reconstruction, J. Embryoi. Exp. Morphol. 24: 159-161, 1970.

8. Kollar E. J.: Histogenetic Aspects of Dermal-Epidermai Interac- tions, in Slavkin, H. C., and Bavetta, L. A., editors: Devel- opmental Aspects of Oral Biology, New York, 1972, Academic Press, Inc., p. 125.

9. Kollar, E. J.: Epithelial-Mesenchymal Interactions in the Control of Tooth Shape and Size, in Melnick, M., Shields, E. D., and Burzynski, N. J., editors: Craniofacial Genetics: Principles and Practice, Littleton, Mass., 1980, PSG Publishing, Inc.

Reprinr requesfs to: Dr. Michael Melnick Laboratory for Developmental Biology Andrus Gerontology Center-325 University of Southern California University Park

microscopy. Los Angeles, Calif. 90007