Department of Orthodontic Abstracts and Reviews

Edited by

DRS. EGON NEUSTADT AND JOSEPH D. EBY, NEW YOBK CITY

All communications concerning further information about abstracted material and the accept- ance of articles or books for consideration in this department should be addressed to Dr. Egon

Neustadt, 133 East Fifty-Eighth Street, New York City.

New Thoughts on Tooth Biology. Review of ‘ ‘ Zahnfleisch-Entzuendung und Zahnlockerung ” by Dr. B. Gottlieb and Dr. B. Orban, 1933, Berlin, Berlin- ische Verlagsanstalt.

BIOLOGY. AUTIVE TOOTH ERTJPTION

The most interesting chapter of this interesting book is the one dealing with the biology of the suspensory apparatus of the tooth. Here we find first a discussion of tooth eruption. The development of the root is considered as a driving force in eruption. However, the alveolar bone also takes a part in the occlusal movement of erupt,ing teeth. Its actions are influenced by secretions of the thyroid, the parathyroids, and the hypophysis, which accel- erate or retard eruption. When a tooth makes occlusal contact with its antagonist, it may be said to be completely erupted, as far as its active erup- tion is concerned.

PASSIVE TOOTH ERUPTION

There is, however, another phase of tooth eruption which is concerned with the attachment of the gingiva to the tooth. First of all, it is important to r1ot.e that t,he gingiva is not merely hugging the tooth closely (as was the old conception), but that it is organically connected with it. This connection is called the gingival attachment, and it is brought about by a hornification of its epithelial layers which cohere very firmly to the enamel. The invasion of bacteria into the periodontal tissues is thereby prevented.

Under absolutely normal conditions, the gingival pocket has practically no depth (Figs. l-4). In other words, t’here is no gingival pocket at all, and the retention of food particles and bacteria is not possible. The place of the gingival attachment on the tooth crown varies, From its highest point on the tooth crown, where the attachment lies right after the tooth makes its first appearance in the mouth, it very gradually recedes toward the cementum (Fig. 1). When the person is between twenty and thirty years of age, t,he gingival attachment is near the enamel cementum junction of the tooth (Figs. 2 and 3). In the old person, it is on the cementum itself (Fig. 4).

717

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Jn this way, the free portion of the tooth, which is called tlw clinical crovvn. becomes continuolwly l~nper. .Zt first, the clinical (:I’OWII is shorter tha.11 tire anatomic. crown (ohil(1, Fig. 1) ; at some time tluring life (from twent,y to thirty years) they are the same size (Fig. 3) : at a later ape, the clinical crown is longer than the anat,omic crown, and it includes a portion of the root, which is denuded from the gingiva. However, the uurmal wearing down of the occlusal surface of the crown counteracts this tendency. The greatest amount of wearing down occurs not during mastication but, outside of mastication, especially at night when the t,eeth are tightly clinched together. ( This viewpoint can hardly be accepted. Alany people who show decided wear on their occlusal surfaces

tlo not- grit. their teeth at, all. Ra.ces which live on hard foods that re(1rtir.e vigorous chewing show more attrition than races that live on soft foods. I)uriup mastication. while t,herr is. a.t a given moment. food between some teeth. thr cusps of other teeth strike and wear against. each other.)

Tinder idea.1 condit,ions, the receding of the gingival attachment holds eym pace with the attrition, and the clinical crown remains the same size. This is important in a functional respect because in mastication the clinical crown repre-

Orthodo,ntic Abstracts and Reviews ‘719

sents one part of a lever, while the other part is represented by the clinical root. The shorter the clinical crown and the longer the clinical root, the more favorable are the conditions. (Th e relationship of clinical crown to clinical root also has a bearing on orthodontic treatment. Teeth with longer clinical crowns and shorter clinical roots [adults] are more liable to tipping.)

Furthermore, the eruptive force of the tooth is also counterbalanced by the force of occlusal contact which presses the tooth back into its alveolus, some- times with resorpt,ion of bone at the apex. If this occlusal pressure were not present, the tooth would continue to erupt and would lock the bite. Attrition on one side and occlusal pressure on the other side prevent excessive eruption of each individual tooth. For this reason, it is essential that the incisors meet in edge-to-edge bite, so that their level may not. exceed that, of the back teeth. (This argument would be valid only if attriti’on were confined to the centric position of the jaws. But the functional position for the incisors is the pro- trusive bite where they are subject to attrition like the rest of the teeth. Fur- thermore, with molars, premolars, and canines in normal occlusion, the incisors cannot be in edge-to-edge bite without spaces being present in the mandibular arch. From an anatomic, as well as orthodontic and periodontic standpoint, the edge-to-edge bite cannot be considered as having a place in normal occlusion.)

ROOl’ DEPOSITION AND ROOT RESORPTIOX

The most important life phenomenon of the tooth root is the continuous deposition of new cementum layers around its circumference. An nncalcified layer is formed first which, later on, takes up calcareous matter. This con- tinuity of deposition makes the cemontum very much different from the bone which under normal conditions undergoes resorption as well as deposition. The difference in the reaction between bone and cementum has a significance in orthodontic tooth movement which would be impossible if cementum and bone would both react in the same manner, namely? by resorption. The con- tinuous deposition of new cementum is a safeguard for the root of the tooth. Absorption of cementum is always due to forces which are excessivelyT strong and of long duration, and it is always a sign of a pathologic condition.

(‘ementum hypertrophy is occasioned by inflammatory react,ions (pulp gangrene) or by excessive functional demands on the tooth. lf we compare the width of the periodont~al membrane on teet,h which are in function with those which have not antagonists, me find that, the functioning tooth has a wider periodontal space.

PATHOLOGY

In the following chapters, pathologic conditions of the periodontal tissues are discussed. Among the subdivisions, we find gingivitis due to lack of mouth hygiene, faulty dental restorations, and deposits on the tooth surface. The deposit,s are always considered to be soft in the beginning, and easily removable with the toothbrush; later on, they become hard through the in- corporation of calcium salts, The distinct,ion between salivary and serumal deposits is discarded.

Another type of pathologic condition is characterized by a diffusca atropl~~ of the alveolar bone. In such instances, ik drifting of the tooth lakes placcl. because of the formatiou of granulation tissue \vIiich is replacing 11112 bouil. ‘I’hc: cause is seen in a sq’stemic condit,ioll. {It is tlificult to uiitltlrstantl that the systemic tlist,urbancc would bring about an atrophy of the alst?ola.r hon(, without producing sympt,oms in the other bones of the body. Ill orclf~r 1st explain the drifting of teeth in t,his wa,,v, it, is nrwssary lirst 10 I.IIL~ 1,111 21 Ii loci> 1 interferences with thr rqnilibrium of the forces of occlnsioll. P'urthc~r*-

more, the presence of a granlllation tissnr would have to be vrrifit~tl b,~, I hct

I’o~tlt~~erlo~rarrl.)

‘I’RBUMATIC O~‘(‘I,IJSION

Histologic examination of teeth under exvrssive ooclusal strrss shows

distinct signs of damage to the tissues at the place of pressure: the damalj,tA h leads from slight rcsorptions to severe injuries and necrosis of the perioctoitta I

tissues. How much in,juq- occurs is dependent II~OII the rrsistan(*c of tllc> tooth and its periodontal st,ruct,ures.

THERAP I’

The daily intake of vitamins A and C! is recommended during the forma- tive period. In later years, only vitamin A is beneficial because an incrrasetl rate of calcification is not, desirable in the adult.

The use of a hard-bristle toothbrush is advised, with the bristles held at an angle to teeth and gingivae, in order to insure the best cleaning action and

to avoid irritation of the gingivae.

As mentioned before, an edge-to-edge bite of the incisors is regn.rdetl as norrnal occlusion. Therefore, in all cases of overbites the wearing of a bite plate at night. is suggested. (Such a procedure should depend upon t,lrr oc~clu- siou of the other teeth. In distoclusions and in rnutilat,ed cases, a. bite plate

would merely tip the mandibular incisors forward and produce spaces bet,wetrrt them. Tn protrusions of the maxillary incisors, the bite plat,e would not briny t~llem in contact with the mandibular incisors. It is, therefore, questionable how much a bite pla,te wit,hout other orthodontic treatment can accomplish.

It must. also be kept in mind, tha.t, the bite plate which prevents mola,rs, pre- molars, and canines from occluding, throws a tremendous force upon the front teeth which cannot, but be felt by l-heir periodontal tissues.j

TII further consequence 1 of t,he viewpoint that, thca most seww bit.itlg ;ru(l grinding OCC’II~S at night. rubber bite blocks are constructrtl for patierlts who show excessi\-r wear on tltr teeth. This is done especially in inst,ances n~hrrf~

extensive gold or amalgam rc>storat,ions and porcelain *jacket far-owns must. btl safepuardfvl. (Wf, cl0 not share ihe vifw that the occlnsal pressnrr is greater

during periods of’ r& tbari i i is tlurin g niasticat,ion ; a porcelain crown which llreds such rnbbcr pl~ot~cction at night will probably break in the course of a hearty meal.)

In the treatment of deep pyorrhea pockets, gingivectomy is used quite extensively, and the pockets are thereby eliminated as much as possible. Therapeutic reattachment of the gingivae is regarded as unattainable and, therefore, is not even attempted. Dunlop’s paraffin wax and oxygen method is also used (~vhich is interesting to note, because it is being abandoned in this country) .

In cases of excessive overbite and shifting of teeth, from diffuse bone atrophy (?), orthodontic methaods are employed for their correction. The appliance most used is a high labial arch wire with hooks in the canine region. The incisors are banded, and spurs, open occlusally, are put on the bands. Silk ligatures or rubber bands are placed under the spurs and attached to the hooks on the high labial wire to move the incisors upward and backward. (The silk ligatures or rubber bands are liable to exert a very quick acting force and one that is difficult to control; their substitution by a thin gauge ‘wire seems advisable.)

Finally, several types of appliances are demonstrated which may be used for the fixation of loose teeth.

In this book, the authors have combined many ideas previously expressed in longer or shorter articles. The chapter on biology must be considered as one of the most important contributions that has ever been made to the science of dentistry. It replaces the old conception of the tooth as a rather inert struct,ure with the view of a highly animated organ which reacts to all occur- rences around it, which lives, changes, grows, becomes old and sick, just like the person that bears it The illustrations are photomicrographs of SLIC~I per- fection that they can, at the present time, hardly be surpassed in clearness and vividness. In t,his respect, the authors’ own rich collection has been aided by contributions of R. Kronfeld, A. &I. Schwarz, W. Meyer, and others. The set-up of the volume is exemplary. The only ma.jor fault that an American dentist, may find with the book is that it is not writ,ten in F:nglislr.

E. N