Dental histology and embryology

Dental histology and embryology

686 Orthodontic Abstracts and Reviews Vincent's infection is caused by a fusiform bacillus and a spirochete. Each seems to produce the same sort of ...

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Orthodontic Abstracts and Reviews

Vincent's infection is caused by a fusiform bacillus and a spirochete. Each seems to produce the same sort of infection, which responds to the same treatment. "These germs cause persistent ulcers on the tonsils and the gums, and when associated with pus forming germs cause a most serious pyorrhea with even loosening of the teeth, bleeding from the gums, very fetid breath, and may cause a general infection of the body. The immediate treatment consists of abolishing all toothbrushes and cleaning with gauze and cotton, swashing around the teeth with full strength peroxide of hydrogen solution, or swabbing with it, and then the use of strong solutions of sodium perborate several times d a i l y . " The tongue is most generally indicative of the conditions of the gastrointestinal tract, and it also has a characteristic appearance in scarlet fever, typhoid fever, Addison's disease, etc. " T h e physician who does not look at the tongue is derelict in his d u t y . " Exuberant post nasal adenoid tissue is frequent among young children. It may cause deformities of the face and nose, and interfere with the development of the jaws; therefore it should be removed. Furthermore, attention is directed to the probable presence of osteomyelitis, cancer, sarcoma, and actinomycosis. The author does not approve the use of bristle toothbrushes because they may wound the sensitive mucous membrane and start a canker sore or some other inflammation. A bristle toothbrush once used will develop germs on culture, even if it is washed with ordinary water. " T h e best method of sterilization is by formaldehyde vapor, but all cheap brushes soon soften and lose their bristles constantly in the mouth and between the teeth. When any infection is present in the mouth, a rubber toothbrush or some gauze or cotton substitute should be used." The list of clinical conditions serves as a reminder to the physician and the dentist that mouth infections may seriously affect general health.

Alexander Sved.

Dental Histology and Embryology by Theodore B. Beust, M.D., D.D.S., August, 1934, Philadelphia, W. B. Saunders Company. Dr. Beust attempts in this volume to correlate the morphologic data of histology with the biologic phenomena occurring in the teeth and their associated structures. His object is to present to the reader the scientific foundation for the theories which are being advanced by modern dietitians and investigators of dental caries. This view of explaining the physiologic happenings by means of the anatomic description is carefully carried out in the chapters dealing with enamel, dentin, and cementum. The structural characteristics of these tissues are deseribed in a simple and instructive manner. The differentiation between primary and secondary dentin is considered as unjustified, as "dentin deposition is a continuous process, active throughout the life of the pulp regardless Of whether the tooth is erupted or n o t . " In a similar manner, cement deposition is also continuous throughout life. Teeth of adults exhibit heavier

Orth,adontic Abstracts and Reviews


teposits of cementum than those of children. The claim that tlypercemeutosis s due to excessive stress and malocclusion is not accepted by the author. DENTIN

The chapter on the biology of the dental tissues reads like a page from history book. Decay is the aggressor, and it sends its troops into the dentin, ~fter destroying the first line of defense, the enamel. The dentin, which in ;he newly erupted tooth consists of uniformly translucent tubules, permeable ;o dies, becomes in part opaque, sclerosed, and impermeable. This takes place :hrough the irritation from caries, abrasions, erosions, or exposure to trauma. k certain amount of opacity of dentin is, however, a normal growth phenomenon, and its formation is accelerated only through the irritations. This )paque dentin is by no means dead. Sclerosis retards the progress of caries ;o the point of completely stopping it (healed caries). Calcification of the outer parts of the pulp is only one stage in the process )f tooth maturation. It is intended to keep pace with the progress of tooth ~brasion. In this process of maturation, the number of odontoblasts and lymph conducting tubules gradually decreases while the opaque and transparent tubules increase. This provides for a greater resistance to chemicals, to wear, and to trauma. ENAMEL

Analogous reactions appear in the enamel after eruption, though enamel metabolism is not comparable to that occurring iu organic tissues. The fact that stains brought into the pulp cavities can diffuse into the enamel justifies the view that a physiologic infiltration of lymph may take place. Susceptibility to dietary deficiencies may be explained in this way as well as the appearance of zones of higher resistance found in the enamel of teeth with slowly progressing caries. These zones of resistance are comparable to the.• translucent zones in the dentin. PERIDENTAL MEMBRANE

The peridental membrane which suspends the tooth in its alveolus is able to withstand enormous stresses. Through deposition of bone on one side, and of cementum on the other side, its thickness decreases with age. But it also varies with function and increases if the function to which the tooth is sub~ jected increases. (The author's belief that the osteoblasts and eementoblasts in the peridental membrane are derived from the fibroblasts may be questioned. The fibroblasts are already highly specialized cells, and they, as well as the highly specialized osteoblasts and cementoblasts, are probably derived from an undifferentiated mother cell, the embryonic mesenchyme cell, which is present everywhere that connective tissue is found.) JAW


Like the other dental tissues, the jaw bone also is "acutely sensitive to alterations in the functions imposed on i t . " I f one part of the jaw is kept


Orthodontic Abstracts and Reviews

in disuse, a thinning of the bone trabeculae occurs accompanied by a widening of the marrow spaces. The manner in which bone (bundle bone) is deposited on the distal walls of the alveoli and sometimes on the buccal or lingual walls indicates that a physiologic movement of the teeth occurs in a forward direction and sometimes in a buccal o r lingual direction. EMBRYOLOGY

The chapter on embryology deals with the growth of the face, the mouth, and the jaws. It also includes the postnatal development of the teeth. The formation of the teeth is described with great clearness, first by means of analogies in the formation of plaeoid scales, and the tooth bearing cord of the shark with its continuous replacement of damaged teeth. After a discussion of the manner in which the tissues participate in the development, the formation of the human tooth is taken up. The older theories regarding tooth development and also the most modern thoughts on these subjects are recorded. The volume is illustrated with fine photomicrographs, all of which are original with the author. There is also a number of instructive diagrams, very cleverly used in the author's endeavor to simplify explanations, theories, and descriptions which in the field of histology sometimes tend to become ponderous and complicated. In certain parts, the author might have gone even further on this road to simplification. Another valuable feature of the book is the attempt to correlate the " c u t and d r i e d " microscopic sections with biological happenings and clinical findings. A good example of this endeavor is found in the chapter on the relationship between histologic tooth structure and cavity wall reparation. Such an attitude is conducive toward tearing down the wall that often has limited histologic interest to a small and highly specialized class. It will help the average dentist toward a better understanding of his work, and will help to remove the spell of fear which invariably appears on his face when histology is mentioned. E.N.