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Further Studies of Skulls in Relation to Periodontal Disease
FURTHER STUDIES OF SKULLS IN RELATION TO PERIODONTAL DISEASE By ISAD O R HIRSCHFELD, D .D .S., New York City
(R e a d b e fo re the Section on O rth odon tia and P eriod on tia o f the A m erican Dental A ssociation, L o u isv ille , K y ., Septem ber 22, 1 9 2 5 )
N a previous paper,1 I stressed the benefits which a periodontologist may derive from a study of a large collection of skulls such as is to be found in the American Museum of Nat ural History. This source of informa tion should play an important part in the future development of periodontology. In the presentation of a study of skulls in relation to periodontal health in a single paper, one is compelled to limit his use of material and observa tions within rather severe bounds. The subject matter, at this time, therefore, will be confined largely to a discussion of occlusal wear in relation to perio dontal health and disease, and only those observations at the Museum will be in cluded which have a direct bearing on this topic.
I
O CCLU SAL C O N TO U R
The relationship of occlusal contour to periodontal health and disease is probably the most fascinating phase in a consideration of the biophysics of periodontology. The romance of the cusps is worthy of eloquence. The 1. H irsch fe ld , D ecem ber, 1923.
Isa d o r:
Jour. A . D . A ., July, 1926
J.
D en t.
Res.,
rounded contour of these, of the ridges, and of the lesser occlusal prominences, as well as their respective strategic loca tions and positions, are physical assets in the maintenance of normal function and health. Throughout the continu ous modifications in the character of the occlusal contour brought about by wear, corresponding changes take place, not alone in the form and size of the pulp chamber but even in the periodon tium, which withstands the stress occa sioned by occlusal pounding. In the early years of childhood, when the jaws are small and tender, and the masticating muscles comparatively weak, the crowns of the deciduous teeth tend to taper occlusally, i. e., the buccolingual diameter of the molars at the points of the cusps is short as compared with that of the alveolar rim, which forms its fulcrum during mastication. The tendency of the crown to be coneshaped, with the centric or working cusps practically opposite the center of the diameter of the alveolar rim, re sults in physical advantages which are easily discernible. Normally, such me chanical construction minimizes the strain on the tender periodontium and requires less dynamic exertion on the
958
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of Skulls in Relation to Periodontal Disease
959
part of the small masticating muscles. I n addition, it is conducive to greater penetration into, and easier maceration of, the food masticated. T h e great spread of the roots is no doubt an additional advantage. Let :IS consider the permanent teeth. (Fig. 1.) A t the time of their eruption, their buccolingual diameter at the cuspal points is shortest and the occlusal prominences are a series of normally
cially, is an advantage in view of the fact that, at this time, the roots are only partly developed, and the pericementum is very thick and yielding, and the alveolar process thin and likely to give on undue pressure. Fitting in with this mechanical scheme of minimum strain is the comparatively weak musculature which furnishes the dynamic force. 'Thus, once more, there is a coordinated arrangement conducive to economic functioning.
Fig. I .-Diagrammatic cross-section of a lower molar, outlining progressive changes in occlusal wear: A, normal convexity of cusp (not worn) ; B (left), small facet making its appearance a t the beginning of occlusal wear; B (right), concavity which may appear on the lingual cusp a t the same stage j C, almost complete disappearance of the buccal cusp with a slight exposure of the dentin, the lingual cusp being only partly worn away; D, buccal cusp completely missing and the concavity now formed in the dentin having its greatest depth opposite the point of the original cusp, as shown by line G ; E, concavity in the dentin of the lingual cusp, the enamel in the center of the occlusal surface being still in evidencej F, disappearance of enamel in center of occlusal surface and fusion of concavities in the dentin.
Fig. 2 . 4 c c l u s a l wear resulting in exposure of dentin opposite the original cuspal points. T h e buccolingual diameter of the incisal surface is greater in the central than in the incisors. This occurs often, but not always.
rounded convexities. These mechanical features suggest a maximum functioning efficiency and a minimum strain on the periodontium. T h e latter, espe-
As each succeeding change in the character of the occlusal contour gradually takes place, through wear, there is a readjustment of the component parts of the masticating apparatus. T h e entire picture changes kaleidoscopically. T h e convexities of the principal and minor cusps and of the various ridges become constantly widening facets, which may eventually merge into each other, forming larger facets or planes. According to laws of physics, the crushing power of occluding planes is less
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than that of convexities; therefore, at first, these concavities become larger since normal functioning now requires and larger through continued abrasion, a greater dynamic force and rigidity of until the entire occlusal surface is one the parts, we find, accordingly, greater large concavity of greater or less depth, muscular development, thinner perio with the buccolingual diameter, prob dontal membrane, and thicker alveolar ably, at its maximum. The eccentric process associated with the occlusal border of the occlusal surface, extending far beyond the confines of the alveolar facets. rim, now produces tremendous leverage during mastication. (Fig. 3.) In some instances, extrusion of the tooth out of the alveolus, due to excessive wear, fur-
Fig. 3.— Denture in which wear in the first molars is greater than in the other teeth. The wear in the centric cusps is also usually greater than that in the eccentric.
F ig . 4-.— A b o v e : H orizon ta l w ear. HW in dicates w ear to the extent o f obliteration o f the m a rgin al ridges and g rooves, also o f the occlusal embrasure. A n exam ination o f skulls leads one to believe that this, by itself, m ay not affect the a lv eola r septum, I shows app ro x im a l w ear. C on trary to the b e lie f ex pressed by som e, neither this n o r the reduction o f the m esiodistal diam eter, resulting fr o m advanced occlusal wear ( A) , w ill alone tend to cause f o o d im paction between the posterior teeth, because the anteroposterior V-shaped relationship between the occlu sal planes o f the m a x illa ry and m andibular arches during m astication tends to cro w d all the posterior teeth in a m esial direction. T h is holds them tigh tly together. B e lo w : M esiodistal occlusal p lan in g. T h is tends to p rod u ce f o o d im pac tion.
Later, along with further changes in occlusal character, a still greater strain is developed. The planes resulting from the gradual wearing away of the cusps are themselves worn down further till the dentin underneath is exposed. As this tissue is softer than the enamel, it yields much more readily to the abra ther accentuates this leverage. From a sive action of coarse substances and purely mechanical point of view, the wears away faster, thus producing con combination of this extreme leverage cavities where before there were sharp plus the maximum muscular develop convexities. (Fig. 2.) Though small ment obtaining at this time should by
Hirschféld— Studies of Skulls in Relation to Periodontal Disease
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itself prove destructive to the periodon tium, but it is interesting to note that it does not— the defensive biologic ele-
not by the opposing teeth themselves, but through mechanical abrasion by foods and other substances. In skulls,
F ig . 5.— Denture sh ow in g m arked con cav i ties in the exposed dentin o f the first and second m o la rs; obliteration o f m argin al ridges and grooves, also o f occlu sal em brasures, and m arked in terproxim a l wear.
F ig. 7.— D enture show n in Figures 5 and 6, h a vin g apparently healthy a lv eola r sep tums in spite o f changes described in F igure 6. In the m esiodistal p la n in g type, loss o f the m argin al ridges and g roov es w o u ld be lik ely to result in f o o d im paction and inter dental destruction. N o n p a th o lo g ic r oot den udation is here caused b y tooth extrusion due to extrem e occlusal w ear. T h e eventual ex posure o f the b ifu rca tion to the m outh flora m ay result in in fection at this point.
ment plays its part—according to the evidence arrayed in the skulls at the Museum, as pointed out elsewhere in this paper. The above described concavities in the dentin are, in most cases, produced,
F ig . 6.— Side v ie w o f denture in F igu re 5, sh ow in g n orm al a lv e o la r septums, and ex trusion o f the first m o la r resulting fr o m extrem e occlusal w e a r ; also the b ifu rca tio n in same tooth denuded o f a lv e o la r co v e rin g .
it is possible to view from all angles the occlusal contact between opposing
F ig . 8.— R a d iog ra p h ic show n in F igu res 5-7.
v iew
of
denture
teeth during the excursion of the man dible from one extreme end to the
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other, and it is often found that the depth of these concavities cannot be reached by any part of the opposing
present merely facets or planes. Since the surfaces of the concavities are highly polished and hard instead of etched and soft, it is evident that me chanical abrasion rather than chemical erosion brought them about. OCCLUSAL W E A R
Generally speaking, the type, extent and rapidity of occlusal wear may be modified by the following fac tors: 1. The original form of the tooth. 2. Its position and location in the arch. 3. Its mesiodistal or buccolinF ig . 9.— M an d ible w ith occlusal w ear sim ilar to that in F igu res 5 and 6, o n ly to a greater
degree,
reaching
o rig in a l contact p oin t.
d ow n
beyon d
the
C ontrary to the b e lie f
o f som e writers, this does not necessarily result in
fo o d
im paction
septal process.
and
destruction
of
the
T h is m andible is a concrete
dem onstration o f line
A in F igu re 4 .
teeth in any position of the mandible. Furthermore, in mouths in which mas tication takes place habitually on one
F ig . 10.— Side v iew o f m andible show n in F igu re 9.
F ig . 11.-— R ad iog ra p h ic v ie w o f denture sh ow n in F igu res 9 and 10. N ote the partial extrusion o f the roots o f the first m ola r, w h ich n o w appear shorter than those o f the ad jacen t teeth. T h e a lv eola r septums are all intact except the one m esially to the first m ola r, w h ich has been affected by f o o d im p action , o w in g to the breakin g d ow n o f the occlu sal w a ll o f a m esial cavity in that tooth. W hen a ro o t surface is exposed in terp rox im a lly , it is v ery susceptible to caries, not alon e through occlusal f o o d im paction but also th rou gh an unhygienic con d ition . The so fter r o o t su rface is m ore easily affected by the latter than is the denser enam el su rface o f the crow n . T h e in terproxim a l caries here show n was p rob a b ly n ot caused by f o o d im paction.
side only, deep concavities may be gual relationship to the opposing teeth, formed on that side; while, on the 4. The character of the food mastiother, the exposed dentinal surfaces may cated and of other substances chewed
Hirschfeld-Studies
of Skulls in Relation to Periodontal Disease
habitually, vocationally or f o r other utilitarian purposes. 5. T h e amount of chewing done-either because of quantity of food consumed or the thoroughness with which i t is masticated. 6. T h e concentration of mastication at one area. 7. Faulty nutrition or metabolism, affecting the rapidity o f occlusal wear. T Y P E S O F OCCLUSAL WEAR
1. Mesiodistal Planing. (Fig. 4.) Ry this, I refer to the characteristic
Fig. 12.-Extreme direction.
963
the marginal ridges and grooves does not necessarily result in food impaction; therefore, it is apt to be less injurious than the one previously mentioned. (Figs. 5-1 1.) I n fact, it seems that, with the wearing away of the cusps, these ridges and grooves are no longer required f o r their original function. I t is also interesting to note on many of the skulls, that, in this type of wear, loss of the occlusal embrasure does not in itself seem to affect, necessarily, the interdental alveolar septum
oblique wear with the occlusal inclines in the normal
wear of the mesial and distal inclines of the occlusal surface into oblique, more or less straight, facets. I n this type, the loss of the marginal ridges and grooves usually tends to produce food impaction in spite of the apparently close contacts. I n office practice, I have often eliminated food impaction here by forming new marginal grooves with a stone and by reducing the circumference of the facets. Failure to reproduce marginal ridges and grooves in mesioclusal or distoclusal restorations in a mouth of this type invites food impaction. 2. Horizontal Wear (Mesiodistally). I n this type, the obliteration of
in jaws otherwise not affected pathologically. 3. Oblique Wear. (Fig. 12.) T h e wearing away of the occlusal surfaces of the posterior teeth with a buccolingual incline, facing bucally in the lower and lingually in the upper, may be considered the normal in advanced occlusal wear because of its frequent occurrence. I t is caused, evidently, by the normal buccolingual relationship between the opposing teeth and by the normal limitation of the range of lateral oscillation of the mandible. T h i s type of wear may be explained as follows: Normally, the palatal cusps of the upper teeth and the buccal cusps of
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the lower (referred to in this paper as lating radius of the mandible, receive centric cusps), because of the relation much less and slower wear than the of each to the occlusal fossa of the centric cusps, and so they may still be opposing teeth, are the working cusps of their respective teeth and thus tend to get greater wear than the other cusps (referred to as eccentric cusps). On the other hand, the eccentric cusps, be ing partly outside the limit of the oscil-
F ig . 14.— T h e first perm anent m ola r in this illustration is an exam ple o f leverage p rod u ced by occlusal w ear as described in F igu re 13.
F ig . 13.— D iagram m a tic d ra w in g sh ow in g bu ccolin g u a l v ie w o f the lo w e r first m olar. O r ig in a lly , the height o f the cusps is at W, that o f the buccal cusp bein g inside the al v e o la r rim ( D) , w h ile that o f the lin g u a l cusp is ap p roxim ately d irectly above the lin gu a l a lv e o la r bord er ( OF-D ) . M ark ed occlu sal w ear ( OW ) m ay be accom panied by a partial extrusion o f the tooth out o f the alveolus ( RD ) . E ither this o r the r o o t m ay have been denuded o f a lv eola r plate to the same extent at this stage o f occlusal w ear th rou g h atroph y o r otherwise. T h e result accru in g fr o m these changes is a m arked leverage prod u ced by the n ew high p oin t ( P ) o f the lin g u a l cusp standing fa r beyon d the n ew fu lcru m ( SF) , w h ich is n o w inside the o rig in a l fu lcru m (OF). Leverage m ay fu r ther be accentuated in this case through the decrease in length o f the part o f the r o o t rem aining im bedded in the alveolus. T h is leverage m ay easily be reduced to a m inim um by g r in d in g o ff the vertical section ( F ) and the darker triangular section im m ediately be neath it in the diagram . T h is brings the height o f the cusp to its o rig in a l relative p o sition, ap p roxim ately opposite the alv eolar bord er at OF.
in evidence after the centric have en tirely disappeared, with their centric sides either vertical or oblique. Where
F ig . IS.— L in gu a l v ie w o f m andible in F igu re 14, sh ow in g no evidence o f a lv eola r absorption, notw ithstanding leverage.
this type of wear becomes far advanced, the highest point of the eccentric cusp is carried considerably outside the alveo
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lar rim or fulcrum on that side. I t is obvious that this final arrangement must result in severe leverage especially in the lower first molar during mastication of hard food. Yet a conscientious
Fig. 16.-Skull of Australian aboriginal, showing extreme labial incline of the anterior teeth. This should result in great leverage.
examination of the alveolar border on the lingual side of this tooth, in skulls, discloses the fact that, unless there are
Fig. 18.-View of skull showing upper left temporary cuspid retained in an adult. This tooth has extruded out of the alveolar socket because of the greater size of the permanent teeth and because of its own marked occlusal wear. T h e change thus produced in the proportion between the power arm and the weight arm, should result in leverage, yet no alveolar destruction is evident.
Fig. 19.-Radiogt.aphic shomt: in Figure 18.
Fig. 17.-Anterior view of skull in Figure 16, showing that, in spite of the leverage, the alveolar border is intact.
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virw of
cuspid
evidences of alveolar destruction about other parts of the dental apparatus, the bone here is apt to be intact on both the crest and the pericemental side of the
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The Journal of the American Dental Association
alveolar plate. This would seem to indi cate that leverage, unless very extreme, will not cause periodontoclasia except when an underlying, probably systemic, causative factor coexists. Apropos of this statement, illustrations are shown, among others, of several distinctlydifFer-
ever possible, in disease, as one would traumatic occlusion. The oblique buccolingual wear tends to assume a re verse direction where the lower posterior teeth stand bucally to the uppers, i. e., the incline faces lingually in the lower and bucally in the upper. (Fig. 22.) In this case, what I called the eccentric cusps in the normal arrangement are now the centric, and are accordingly
Fig. 21.— Skull showing characteristic long necks of the deciduous anterior teeth, which invite leverage; yet no alveoloclasia is evi dent. F ig . 20.— Skull o f P eruvian ch ild between 8 and 9 years o f age. T h e central crow ns are v ery la rg e in p ro p o rtio n to the roots as show n in the radiogram s, yet there seems to be no evidence o f a lv eola r destruction due to leverage.
worn down first. This, of course, is normal in relation to the reverse ana tomic conditions, though abnormal, generally speaking. When the oppos ing teeth are more nearly in cusp to cusp occlusion, or the mandible takes on a greater radius of lateral oscillation, extreme occlusal wear tends to become horizontal buccolingually.
ent types of marked leverage, which, nevertheless, betray no evidence of alveoloclasia. (Figs. 13-21.) This is not intended to belittle the important role that traumatic leverage plays as a poten O CCLUSAL W E A R IN R E L A T IO N TO tial etiologic factor in periodontoclasia. T R A U M A T IC OCCLUSION In fact, it might be advantageous to reduce such leverage as a preventive step It is a well known fact that the during health, and to correct it, when mouth with a perfect occlusal arrange
Hirschfeld-Studies
of Skulls in Relation to Periodontal Disease
ment is extremely rare. An inharmonious occlusal relationship, to a greater or less extent, is found in practically every mouth during the earlier years. However, with use, the high spots may wear themselves down into a harmonious arrangement without having established permanent symptoms of periodontoclasia. Other instances of such beneficial occlusal wear are : ( I ) the correction of the inharmonious occlusion caused by a mesiodistal drifting due
967
terior teeth wear down more rapidly than the anteriors, the latter take on an occlusal strain even in centric position. Traumatic occlusion may similarly be visited on the anterior teeth either through mesiodistal drifting of the posteriors caused by the extraction of individual teeth, or through the absence of many or all of the posteriors. Traumatic occlusion thus produced on the anterior teeth is often more pronounced when an individual incisor tooth stands
Fig. 22.-Skull in which the lower posterior teeth stand buccally to the uppers. This results in a reversal of the buccallingual direction of the occlusal wear.
to the nonreplacement of an extracted restorations of occlusal tooth and (2) . . surfaces with gold, especially of softer alloys, eventually conforming to the normal occlusion. Although occlusal wear may abort or prevent the effects of an existing traumatic occlusion, it may, on the other hand, bring about traumatic occlusion. T h e posterior teeth are so built and occlude with their opponents in such a way that they limit the degree of approximation between the mandible and maxilla. T h e anterior~may assist in this respect, but to a comparatively secondary degree. When, through excessive use, the pos-
in torsion and is the only one to strike in bite-to-bite fashion. T h e same may be said of the lower incisors, abruptly stopped by a horizontal trough worn out on the palatal side of the uppers. OCCLUSAL WEAR I N RELATION T O NONINFECTIOUS ROO?' EXPOSURE
Among the various deviations from the normal in the mouth is the noninf ectious root exposure, a condition often improperly diagnosed as of pathologic origin. This subject has been discussed in a previous paper, but it bears repetition. Although extra-oral agencies, such as tooth brushing, etc., may often
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cause such a condition, it happens occa sionally that the partial extrusion of a tooth out of the alveolar socket is alone responsible. This extrusion may result from a congenital lack of occlusion, or the absence of an opposing tooth, or from excessive occlusal wear. An out standing instance of root exposure due to excessive occlusal wear is that of the palatal root of the upper first molar. This tooth is several years older thanany
Fig. 23.— Exposure o f the palatal root of the upper first molar, caused by extrusion of the tooth out of its alveolar socket, because o f extreme occlusal wear. The alveolar process in this skull is apparently in perfect condition.
other tooth in the posterior part of the mouth and must necessarily become worn down proportionately. In addi tion, it is practically the center of the masticating area of the dental arch. Because its palatal cusp has received greater and longer wear generally than that of any other tooth, this molar must of necessity drop down to its opponent. This in itself might result in a certain amount of cervical denudation. But the extreme incline or flare of the pala tal root so often present in this tooth
tends to carry with it the gingiva and the thin alveolar plate, with the result that both are soon absorbed physiologi cally by the pressure brought against them, by food and the tongue, during mastication. The cervical part of the root is thus exposed. (Fig. 23.) The condition of the lower central incisor also may be referred to as an
Fig. 2+.— Mandible showing greater oc clusal wear on the central than on the lateral incisors. This is occasionally the result o f a certain type o f anatomic relationship between the central incisors and their opponents.
outstanding example of improper diag nosis in this regard. Under certain conditions, this tooth, wearing off faster than the other anterior teeth, is there fore being constantly “fed” up to its opponent in proportion to the amount of wear— like the lead in an “Eversharp” pencil. As a result, the neck is soon exposed to view, and eventually the root surface. A differential diag nosis of the nonpathologic root exposure
H irsch feld— Studies of Sku lls in Relation to Periodontal D isease
of this tooth may be easily made by means of the following facts: 1. The labiolingual diameter of the occlusal surface which now displaces the incisal margin on the central is greater than that of the lateral; in fact, this surface may even have become square, while that of the lateral still remains oblong. (Figs. 2 and 24.) 2. The root of the central may appear much shorter radiographically than that of the lateral. 3. Aside from these, no abnormal or pathologic symptoms may be present. In a generally healthy individual, the above described central may continue extruding until a great part of the crown is worn off without showing any evidence of actual periodontal disease. However, should this process of extru sion be accompanied by a systemic con dition, which, to my mind, usually underlies periodontoclasia, this tooth is apt to be among the first affected path ologically, for the following reasons: The central incisor has the smallest root in the mandible, and, when normal, it has, accordingly, a short narrow in cisal edge which, through its contiguity with the edges of the other anterior teeth, takes on a minimum of perio dontal strain during function. When this tooth is partly extruded on account of marked incisal wear, the following physical changes tend to increase the periodontal strain: 1. The presence of a broad occlusal surface instead of a thin incisal edge. 2. Shortening of the portion of the root remaining imbedded in the socket on account of the incisal wear, the leverage of that tooth being increased proportionately. 3. The par tial extrusion out of the alveolar socket, resulting in a lessened contact surface
969
between the root and the process. This results in an increased pressure in versely proportionate to the decreased alveolar and pericemental support. SUMMARY
1. Mesiodistal planing of the oc clusal surfaces by masticating wear tends to food impaction especially if the marginal ridges and grooves have been obliterated. 2. In horizontal occlusal wear, ob literation of these protective anatomic features does not seem to produce interproximal food impaction, the alveolar septums, apparently, remaining un affected. 3. This is also true regarding the obliteration of the occlusal embrasure. 4. The last two statements, how ever, should not be misconstrued as minimizing the importance of replacing these anatomic features in the rounding out of contour in proximal restorations. 5. Oblique occlusal wear invites leverage which may become an impor tant local etiologic factor in periodonto clasia and has to be reckoned with in treatment. 6. A close examination of the skulls discloses the fact that leverage, unless very extreme, will not by itself produce periodontoclasia. This fact is proved rep'eatedly in many instances of leverage produced by different causes as shown in the accompanying photographs. 7. Occlusal wear may be a means of obliterating traumatic occlusion in some instances and of producing it in others, directly or indirectly. 8. Excessive occlusal wear may re sult in extrusion of the tooth out of the
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alveolar process until part of the root surface is exposed to view, creating the optical illusion of a gingival recession. I wish to take this op p ortu n ity to express my
appreciation
of
the p riv ileg es
extended
by the officers o f the A m erican M useu m o f N atural H istory and to thank them f o r their kin d cooperation. I also wish to ack n o w le d g e the able assist ance o f D r . Samuel M . G e tzo ff o f N e w Y o r k in m a k in g the rad iogram s o f the d ry speci mens. 730 F ifth A venue.
y o u n g e r men com e into the p ro fe ssio n , w ith their better prelim inary training, there is hope o f ap p ro a ch in g this subject w ith greater and m ore scientific understanding.
W ith in the last
f e w years, it is bein g approached fr o m the en g in e e rin g standpoint, as in D rs. A n d erson and M c M illa n ’ s study o f bone and the p ositions o f the teeth, and in D r . M . M . H ou se’s studies in In fa ct, the sub
ject is bein g approached fr o m so m any stand points that the o ld time practition er realizes he is b e in g surrounded and ov erw h elm ed
w ith
m any things that he kn ow s little about.
It is
m y op in io n that w e have been d o in g to o m uch g r in d in g o f cusps w ith stones f o r r e lie f o f w e d g in g fo rce s, and in the fu tu re w e must m ake greater use o f orth o d o n tic appliances as a means o f p reven tin g traum a and as a means W hen one o r m ore teeth have
been lost in the arch and the adjacen t teeth have begun to tip into the space, w e should use the o rth od on tic appliances to replace them and f o l l o w this p rocedure by p ro p e rly restor in g the lost tooth o r teeth. of
D r.
In the sixth item
H ir sc h fe ld ’ s sum m ary
he
says that
levera ge, unless very extrem e, w ill not o f it s e lf cause periodontoclasia. T h is is true in the skulls o f
by the use o f p rop er massage and stim ulation w ith the toothbrush.
Arthur H. Merritt, New York City. It has been m y p riv ileg e to be associated with- D r. H irsch feld in this m ost interesting, n ot to say fascin ating, study o f the skulls in the A m er ican
M useum
of
N atural
H istory.
T hese
mute witnesses o f the past, w h o liv ed their lives under con d ition s quite unlike those o f the present, shed a flo o d o f lig h t on som e o f and w ith w h ich w e o f this generation are. fa ce
Austin F. James, Chicago, III. : A s the
o f correction .
It has been m y observation that in the p eople o f toda y w e m ay b u ild up tissue cell resistance
the problem s w h ich civiliza tion has brough t
D ISCU SSIO N
the m echanics o f ^occlusion.
in the m outh o f otherw ise healthy individuals.
p rim itive races a m o n g w h om
h eavy m astication was used fr o m
ch ild h o o d ,
because the heavy usage did b u ild up tissue cell resistance and strengthen the su pp ortin g structures. But in m odern existence, w here w e eat so fte r fo o d s , there is n ot the b u ild in g up of resistance in su pp ortin g struc tures and w e do fin d a lv e o la r destruction
to fa ce .
Great credit is due to D r . H irsch
fe ld f o r his m ost ca r e fu l and painstaking ob servations.
H e has gone back to those records,
n ot written b y the errin g hand o f m an, but by N ature herself— records w h ich are open o n ly to those w h o have eyes to see and ears to hear— and w ith vestigator,
the spirit o f
fr e e ly
investigations.
true
in
gives us the fr u it o f
the
his
It is o n ly thus that progress
Is m ade, and fortu n a te indeed is that p ro fe s sion w h ich numbers a m on g its m embers those w h o are w illin g to m ake such sacrifices.
P er
haps the m ost impressive observations noted in this study, has been the trem endous strain im posed on the teeth o f these barbarians as m anifested in occlu sal w ear, o fte n to the ex tent o f com p lete oblitera tion o f cusps, and, in some instance, exposure and death o f the p u lp , w ith ou t any breakin g d o w n o f alv eolar sup p ort.
A n d in ad d ition
to
this strain,
the
m ouths, in m any instances, must have been filth y in the extrem e, w ith tartar abundant, and every elem ent m akin g f o r g in g iv a l irri tation was present.
Y et the teeth remained
firm in their sockets, w ith n o evidence o f dis ease in their osseous support. T h is w o u ld seem to indicate that that p henom enon w hich has com e to be kn ow n as traum atic occlu sion, and to w h ich is assigned such an im portant role in the e tio lo g y o f p eriod on toclasia, is in reality an occlu sion w h ich does n ot traum atize under n orm al conditions. D r . H irsch fe ld ’s observation on this p oin t is that it “ tends to indicate that levera ge, unless v ery extrem e, w ill not cause p eriod on toclasia except where an u n derly in g systemic causative fa c to r c o exists.” T h e question w h ich natu rally sug
Hirschfeld— Studies of Skulls in Relation to Periodontal Disease
971
gests itse lf in this conn ection is: W h a t was
w h ich a ll the others flo w as a natural co n
there in those prehistoric races that m ade f o r
sequence, is relative disuse.
p eriod on tal health that is la ck in g in the civ i
ja w s and teeth as did those races o f the past
lized races o f the present?
has resulted in p o o r ly nourished tissues, un
they had, w ith clusion.
fe w
In the first place,
exceptions, n orm a l o c
T h e ir teeth w ere w e ll fo r m e d and
so related to each other, and to those o f the
F ailu re to use ou r
d evelop ed ja w s, irregu lar teeth and a greater susceptibility to disease.
T h is , plus heredity
and chan ged environm ent, w ill explain w h y
op p osin g ja w , that they did the m axim u m o f
w e cannot be com pared, fr o m a dental stand
w o r k w ith a m inim um o f strain.
T h e y were
p oin t, w ith those liv in g in the past, and w h y
also not subject to dental caries.
T h is m eant
we cannot hope to e n jo y their relative im
that they retained their teeth th rou gh ou t life ,
m unity to dental disease.
so that the strain im posed on them was borne
Dr. Hirschfeld ( closing) : I f it w ere not
by th irty -tw o teeth, a ll in n orm al occlu sion ,
f o r the practical experience o f the “ o ld time
in stead -of, as is so o fte n the case in the present, by a sm aller num ber, w ith the a ccom p an yin g
p ractition er”
changes in occlu sal relations and added strain,
o cca sion a lly in their new theories and ideas.
w hich alw ays fo llo w s tooth loss.
referred to by D r. James, the
y o u n ge r men w o u ld p rob a b ly g o
fa r afield
G iven these
N o doubt we have to make great allow ances
condition s o f n o rm a l occlu sion and fu l l co m
f o r the difference between the aboriginies and
plem ent o f
that
civilize d m an both in respect to period ontal developm ent and the fa ct that the m asticating
v ig orou s use was translated into w e ll-n o u r -
apparatus in m ost m ouths today is disarranged
fibrous
teeth, plus a diet o f
fo o d s ,
it
natu rally
hard and
f o llo w e d
ished and w e ll-d e v e lo p e d ja w s, w h ich
were
w ith traum atizing results, th rou g h extractions.
A n d when w e re
T h e n , again , w e o f today have to contend
flect on h o w different this record o f the past
w ith dental restorations w h ich do not fit in
h ig h ly resistant to disease.
is as written by the hand o f N ature on these
w ith
skeletal remains o f ou r barbaric ancestors, and
tection o f the p eriod ontium .
com pare it w ith the con d ition s p re v a ilin g in
M e rritt is g iv in g m e too m uch credit f o r m y efforts in m y w o r k at the museum. The m aterial there is rich in in form a tion and is availa ble to anyone w h o is genuinely inter ested.
the present, w e have the answer to ou r inquiry. T h e condition s are n ot com p arab le.
Perhaps
the fa c to r that is m ost
in
im portant
this
changed con d ition o f the present, and ou t o f
nature’ s scheme
of
fu n ctio n
and p r o
I fe a r that D r.
(R e a d b e fo re the Section on O rth odon tia and P eriod on tia o f the A m erican Dental A ssociation, L o u isv ille , K y ., Septem ber 22, 1 9 2 5 )
N a previous paper,1 I stressed the benefits which a periodontologist may derive from a study of a large collection of skulls such as is to be found in the American Museum of Nat ural History. This source of informa tion should play an important part in the future development of periodontology. In the presentation of a study of skulls in relation to periodontal health in a single paper, one is compelled to limit his use of material and observa tions within rather severe bounds. The subject matter, at this time, therefore, will be confined largely to a discussion of occlusal wear in relation to perio dontal health and disease, and only those observations at the Museum will be in cluded which have a direct bearing on this topic.
I
O CCLU SAL C O N TO U R
The relationship of occlusal contour to periodontal health and disease is probably the most fascinating phase in a consideration of the biophysics of periodontology. The romance of the cusps is worthy of eloquence. The 1. H irsch fe ld , D ecem ber, 1923.
Isa d o r:
Jour. A . D . A ., July, 1926
J.
D en t.
Res.,
rounded contour of these, of the ridges, and of the lesser occlusal prominences, as well as their respective strategic loca tions and positions, are physical assets in the maintenance of normal function and health. Throughout the continu ous modifications in the character of the occlusal contour brought about by wear, corresponding changes take place, not alone in the form and size of the pulp chamber but even in the periodon tium, which withstands the stress occa sioned by occlusal pounding. In the early years of childhood, when the jaws are small and tender, and the masticating muscles comparatively weak, the crowns of the deciduous teeth tend to taper occlusally, i. e., the buccolingual diameter of the molars at the points of the cusps is short as compared with that of the alveolar rim, which forms its fulcrum during mastication. The tendency of the crown to be coneshaped, with the centric or working cusps practically opposite the center of the diameter of the alveolar rim, re sults in physical advantages which are easily discernible. Normally, such me chanical construction minimizes the strain on the tender periodontium and requires less dynamic exertion on the
958
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of Skulls in Relation to Periodontal Disease
959
part of the small masticating muscles. I n addition, it is conducive to greater penetration into, and easier maceration of, the food masticated. T h e great spread of the roots is no doubt an additional advantage. Let :IS consider the permanent teeth. (Fig. 1.) A t the time of their eruption, their buccolingual diameter at the cuspal points is shortest and the occlusal prominences are a series of normally
cially, is an advantage in view of the fact that, at this time, the roots are only partly developed, and the pericementum is very thick and yielding, and the alveolar process thin and likely to give on undue pressure. Fitting in with this mechanical scheme of minimum strain is the comparatively weak musculature which furnishes the dynamic force. 'Thus, once more, there is a coordinated arrangement conducive to economic functioning.
Fig. I .-Diagrammatic cross-section of a lower molar, outlining progressive changes in occlusal wear: A, normal convexity of cusp (not worn) ; B (left), small facet making its appearance a t the beginning of occlusal wear; B (right), concavity which may appear on the lingual cusp a t the same stage j C, almost complete disappearance of the buccal cusp with a slight exposure of the dentin, the lingual cusp being only partly worn away; D, buccal cusp completely missing and the concavity now formed in the dentin having its greatest depth opposite the point of the original cusp, as shown by line G ; E, concavity in the dentin of the lingual cusp, the enamel in the center of the occlusal surface being still in evidencej F, disappearance of enamel in center of occlusal surface and fusion of concavities in the dentin.
Fig. 2 . 4 c c l u s a l wear resulting in exposure of dentin opposite the original cuspal points. T h e buccolingual diameter of the incisal surface is greater in the central than in the incisors. This occurs often, but not always.
rounded convexities. These mechanical features suggest a maximum functioning efficiency and a minimum strain on the periodontium. T h e latter, espe-
As each succeeding change in the character of the occlusal contour gradually takes place, through wear, there is a readjustment of the component parts of the masticating apparatus. T h e entire picture changes kaleidoscopically. T h e convexities of the principal and minor cusps and of the various ridges become constantly widening facets, which may eventually merge into each other, forming larger facets or planes. According to laws of physics, the crushing power of occluding planes is less
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than that of convexities; therefore, at first, these concavities become larger since normal functioning now requires and larger through continued abrasion, a greater dynamic force and rigidity of until the entire occlusal surface is one the parts, we find, accordingly, greater large concavity of greater or less depth, muscular development, thinner perio with the buccolingual diameter, prob dontal membrane, and thicker alveolar ably, at its maximum. The eccentric process associated with the occlusal border of the occlusal surface, extending far beyond the confines of the alveolar facets. rim, now produces tremendous leverage during mastication. (Fig. 3.) In some instances, extrusion of the tooth out of the alveolus, due to excessive wear, fur-
Fig. 3.— Denture in which wear in the first molars is greater than in the other teeth. The wear in the centric cusps is also usually greater than that in the eccentric.
F ig . 4-.— A b o v e : H orizon ta l w ear. HW in dicates w ear to the extent o f obliteration o f the m a rgin al ridges and g rooves, also o f the occlusal embrasure. A n exam ination o f skulls leads one to believe that this, by itself, m ay not affect the a lv eola r septum, I shows app ro x im a l w ear. C on trary to the b e lie f ex pressed by som e, neither this n o r the reduction o f the m esiodistal diam eter, resulting fr o m advanced occlusal wear ( A) , w ill alone tend to cause f o o d im paction between the posterior teeth, because the anteroposterior V-shaped relationship between the occlu sal planes o f the m a x illa ry and m andibular arches during m astication tends to cro w d all the posterior teeth in a m esial direction. T h is holds them tigh tly together. B e lo w : M esiodistal occlusal p lan in g. T h is tends to p rod u ce f o o d im pac tion.
Later, along with further changes in occlusal character, a still greater strain is developed. The planes resulting from the gradual wearing away of the cusps are themselves worn down further till the dentin underneath is exposed. As this tissue is softer than the enamel, it yields much more readily to the abra ther accentuates this leverage. From a sive action of coarse substances and purely mechanical point of view, the wears away faster, thus producing con combination of this extreme leverage cavities where before there were sharp plus the maximum muscular develop convexities. (Fig. 2.) Though small ment obtaining at this time should by
Hirschféld— Studies of Skulls in Relation to Periodontal Disease
961
itself prove destructive to the periodon tium, but it is interesting to note that it does not— the defensive biologic ele-
not by the opposing teeth themselves, but through mechanical abrasion by foods and other substances. In skulls,
F ig . 5.— Denture sh ow in g m arked con cav i ties in the exposed dentin o f the first and second m o la rs; obliteration o f m argin al ridges and grooves, also o f occlu sal em brasures, and m arked in terproxim a l wear.
F ig. 7.— D enture show n in Figures 5 and 6, h a vin g apparently healthy a lv eola r sep tums in spite o f changes described in F igure 6. In the m esiodistal p la n in g type, loss o f the m argin al ridges and g roov es w o u ld be lik ely to result in f o o d im paction and inter dental destruction. N o n p a th o lo g ic r oot den udation is here caused b y tooth extrusion due to extrem e occlusal w ear. T h e eventual ex posure o f the b ifu rca tion to the m outh flora m ay result in in fection at this point.
ment plays its part—according to the evidence arrayed in the skulls at the Museum, as pointed out elsewhere in this paper. The above described concavities in the dentin are, in most cases, produced,
F ig . 6.— Side v ie w o f denture in F igu re 5, sh ow in g n orm al a lv e o la r septums, and ex trusion o f the first m o la r resulting fr o m extrem e occlusal w e a r ; also the b ifu rca tio n in same tooth denuded o f a lv e o la r co v e rin g .
it is possible to view from all angles the occlusal contact between opposing
F ig . 8.— R a d iog ra p h ic show n in F igu res 5-7.
v iew
of
denture
teeth during the excursion of the man dible from one extreme end to the
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The Journal of the American Dental Association
other, and it is often found that the depth of these concavities cannot be reached by any part of the opposing
present merely facets or planes. Since the surfaces of the concavities are highly polished and hard instead of etched and soft, it is evident that me chanical abrasion rather than chemical erosion brought them about. OCCLUSAL W E A R
Generally speaking, the type, extent and rapidity of occlusal wear may be modified by the following fac tors: 1. The original form of the tooth. 2. Its position and location in the arch. 3. Its mesiodistal or buccolinF ig . 9.— M an d ible w ith occlusal w ear sim ilar to that in F igu res 5 and 6, o n ly to a greater
degree,
reaching
o rig in a l contact p oin t.
d ow n
beyon d
the
C ontrary to the b e lie f
o f som e writers, this does not necessarily result in
fo o d
im paction
septal process.
and
destruction
of
the
T h is m andible is a concrete
dem onstration o f line
A in F igu re 4 .
teeth in any position of the mandible. Furthermore, in mouths in which mas tication takes place habitually on one
F ig . 10.— Side v iew o f m andible show n in F igu re 9.
F ig . 11.-— R ad iog ra p h ic v ie w o f denture sh ow n in F igu res 9 and 10. N ote the partial extrusion o f the roots o f the first m ola r, w h ich n o w appear shorter than those o f the ad jacen t teeth. T h e a lv eola r septums are all intact except the one m esially to the first m ola r, w h ich has been affected by f o o d im p action , o w in g to the breakin g d ow n o f the occlu sal w a ll o f a m esial cavity in that tooth. W hen a ro o t surface is exposed in terp rox im a lly , it is v ery susceptible to caries, not alon e through occlusal f o o d im paction but also th rou gh an unhygienic con d ition . The so fter r o o t su rface is m ore easily affected by the latter than is the denser enam el su rface o f the crow n . T h e in terproxim a l caries here show n was p rob a b ly n ot caused by f o o d im paction.
side only, deep concavities may be gual relationship to the opposing teeth, formed on that side; while, on the 4. The character of the food mastiother, the exposed dentinal surfaces may cated and of other substances chewed
Hirschfeld-Studies
of Skulls in Relation to Periodontal Disease
habitually, vocationally or f o r other utilitarian purposes. 5. T h e amount of chewing done-either because of quantity of food consumed or the thoroughness with which i t is masticated. 6. T h e concentration of mastication at one area. 7. Faulty nutrition or metabolism, affecting the rapidity o f occlusal wear. T Y P E S O F OCCLUSAL WEAR
1. Mesiodistal Planing. (Fig. 4.) Ry this, I refer to the characteristic
Fig. 12.-Extreme direction.
963
the marginal ridges and grooves does not necessarily result in food impaction; therefore, it is apt to be less injurious than the one previously mentioned. (Figs. 5-1 1.) I n fact, it seems that, with the wearing away of the cusps, these ridges and grooves are no longer required f o r their original function. I t is also interesting to note on many of the skulls, that, in this type of wear, loss of the occlusal embrasure does not in itself seem to affect, necessarily, the interdental alveolar septum
oblique wear with the occlusal inclines in the normal
wear of the mesial and distal inclines of the occlusal surface into oblique, more or less straight, facets. I n this type, the loss of the marginal ridges and grooves usually tends to produce food impaction in spite of the apparently close contacts. I n office practice, I have often eliminated food impaction here by forming new marginal grooves with a stone and by reducing the circumference of the facets. Failure to reproduce marginal ridges and grooves in mesioclusal or distoclusal restorations in a mouth of this type invites food impaction. 2. Horizontal Wear (Mesiodistally). I n this type, the obliteration of
in jaws otherwise not affected pathologically. 3. Oblique Wear. (Fig. 12.) T h e wearing away of the occlusal surfaces of the posterior teeth with a buccolingual incline, facing bucally in the lower and lingually in the upper, may be considered the normal in advanced occlusal wear because of its frequent occurrence. I t is caused, evidently, by the normal buccolingual relationship between the opposing teeth and by the normal limitation of the range of lateral oscillation of the mandible. T h i s type of wear may be explained as follows: Normally, the palatal cusps of the upper teeth and the buccal cusps of
964
The Journal of the American Dental Association
the lower (referred to in this paper as lating radius of the mandible, receive centric cusps), because of the relation much less and slower wear than the of each to the occlusal fossa of the centric cusps, and so they may still be opposing teeth, are the working cusps of their respective teeth and thus tend to get greater wear than the other cusps (referred to as eccentric cusps). On the other hand, the eccentric cusps, be ing partly outside the limit of the oscil-
F ig . 14.— T h e first perm anent m ola r in this illustration is an exam ple o f leverage p rod u ced by occlusal w ear as described in F igu re 13.
F ig . 13.— D iagram m a tic d ra w in g sh ow in g bu ccolin g u a l v ie w o f the lo w e r first m olar. O r ig in a lly , the height o f the cusps is at W, that o f the buccal cusp bein g inside the al v e o la r rim ( D) , w h ile that o f the lin g u a l cusp is ap p roxim ately d irectly above the lin gu a l a lv e o la r bord er ( OF-D ) . M ark ed occlu sal w ear ( OW ) m ay be accom panied by a partial extrusion o f the tooth out o f the alveolus ( RD ) . E ither this o r the r o o t m ay have been denuded o f a lv eola r plate to the same extent at this stage o f occlusal w ear th rou g h atroph y o r otherwise. T h e result accru in g fr o m these changes is a m arked leverage prod u ced by the n ew high p oin t ( P ) o f the lin g u a l cusp standing fa r beyon d the n ew fu lcru m ( SF) , w h ich is n o w inside the o rig in a l fu lcru m (OF). Leverage m ay fu r ther be accentuated in this case through the decrease in length o f the part o f the r o o t rem aining im bedded in the alveolus. T h is leverage m ay easily be reduced to a m inim um by g r in d in g o ff the vertical section ( F ) and the darker triangular section im m ediately be neath it in the diagram . T h is brings the height o f the cusp to its o rig in a l relative p o sition, ap p roxim ately opposite the alv eolar bord er at OF.
in evidence after the centric have en tirely disappeared, with their centric sides either vertical or oblique. Where
F ig . IS.— L in gu a l v ie w o f m andible in F igu re 14, sh ow in g no evidence o f a lv eola r absorption, notw ithstanding leverage.
this type of wear becomes far advanced, the highest point of the eccentric cusp is carried considerably outside the alveo
Hirschfeld-Studies
of Skulls i n Relation to Periodontal Disease
lar rim or fulcrum on that side. I t is obvious that this final arrangement must result in severe leverage especially in the lower first molar during mastication of hard food. Yet a conscientious
Fig. 16.-Skull of Australian aboriginal, showing extreme labial incline of the anterior teeth. This should result in great leverage.
examination of the alveolar border on the lingual side of this tooth, in skulls, discloses the fact that, unless there are
Fig. 18.-View of skull showing upper left temporary cuspid retained in an adult. This tooth has extruded out of the alveolar socket because of the greater size of the permanent teeth and because of its own marked occlusal wear. T h e change thus produced in the proportion between the power arm and the weight arm, should result in leverage, yet no alveolar destruction is evident.
Fig. 19.-Radiogt.aphic shomt: in Figure 18.
Fig. 17.-Anterior view of skull in Figure 16, showing that, in spite of the leverage, the alveolar border is intact.
965
virw of
cuspid
evidences of alveolar destruction about other parts of the dental apparatus, the bone here is apt to be intact on both the crest and the pericemental side of the
966
The Journal of the American Dental Association
alveolar plate. This would seem to indi cate that leverage, unless very extreme, will not cause periodontoclasia except when an underlying, probably systemic, causative factor coexists. Apropos of this statement, illustrations are shown, among others, of several distinctlydifFer-
ever possible, in disease, as one would traumatic occlusion. The oblique buccolingual wear tends to assume a re verse direction where the lower posterior teeth stand bucally to the uppers, i. e., the incline faces lingually in the lower and bucally in the upper. (Fig. 22.) In this case, what I called the eccentric cusps in the normal arrangement are now the centric, and are accordingly
Fig. 21.— Skull showing characteristic long necks of the deciduous anterior teeth, which invite leverage; yet no alveoloclasia is evi dent. F ig . 20.— Skull o f P eruvian ch ild between 8 and 9 years o f age. T h e central crow ns are v ery la rg e in p ro p o rtio n to the roots as show n in the radiogram s, yet there seems to be no evidence o f a lv eola r destruction due to leverage.
worn down first. This, of course, is normal in relation to the reverse ana tomic conditions, though abnormal, generally speaking. When the oppos ing teeth are more nearly in cusp to cusp occlusion, or the mandible takes on a greater radius of lateral oscillation, extreme occlusal wear tends to become horizontal buccolingually.
ent types of marked leverage, which, nevertheless, betray no evidence of alveoloclasia. (Figs. 13-21.) This is not intended to belittle the important role that traumatic leverage plays as a poten O CCLUSAL W E A R IN R E L A T IO N TO tial etiologic factor in periodontoclasia. T R A U M A T IC OCCLUSION In fact, it might be advantageous to reduce such leverage as a preventive step It is a well known fact that the during health, and to correct it, when mouth with a perfect occlusal arrange
Hirschfeld-Studies
of Skulls in Relation to Periodontal Disease
ment is extremely rare. An inharmonious occlusal relationship, to a greater or less extent, is found in practically every mouth during the earlier years. However, with use, the high spots may wear themselves down into a harmonious arrangement without having established permanent symptoms of periodontoclasia. Other instances of such beneficial occlusal wear are : ( I ) the correction of the inharmonious occlusion caused by a mesiodistal drifting due
967
terior teeth wear down more rapidly than the anteriors, the latter take on an occlusal strain even in centric position. Traumatic occlusion may similarly be visited on the anterior teeth either through mesiodistal drifting of the posteriors caused by the extraction of individual teeth, or through the absence of many or all of the posteriors. Traumatic occlusion thus produced on the anterior teeth is often more pronounced when an individual incisor tooth stands
Fig. 22.-Skull in which the lower posterior teeth stand buccally to the uppers. This results in a reversal of the buccallingual direction of the occlusal wear.
to the nonreplacement of an extracted restorations of occlusal tooth and (2) . . surfaces with gold, especially of softer alloys, eventually conforming to the normal occlusion. Although occlusal wear may abort or prevent the effects of an existing traumatic occlusion, it may, on the other hand, bring about traumatic occlusion. T h e posterior teeth are so built and occlude with their opponents in such a way that they limit the degree of approximation between the mandible and maxilla. T h e anterior~may assist in this respect, but to a comparatively secondary degree. When, through excessive use, the pos-
in torsion and is the only one to strike in bite-to-bite fashion. T h e same may be said of the lower incisors, abruptly stopped by a horizontal trough worn out on the palatal side of the uppers. OCCLUSAL WEAR I N RELATION T O NONINFECTIOUS ROO?' EXPOSURE
Among the various deviations from the normal in the mouth is the noninf ectious root exposure, a condition often improperly diagnosed as of pathologic origin. This subject has been discussed in a previous paper, but it bears repetition. Although extra-oral agencies, such as tooth brushing, etc., may often
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The Journal o f the Am erican D ental Association
cause such a condition, it happens occa sionally that the partial extrusion of a tooth out of the alveolar socket is alone responsible. This extrusion may result from a congenital lack of occlusion, or the absence of an opposing tooth, or from excessive occlusal wear. An out standing instance of root exposure due to excessive occlusal wear is that of the palatal root of the upper first molar. This tooth is several years older thanany
Fig. 23.— Exposure o f the palatal root of the upper first molar, caused by extrusion of the tooth out of its alveolar socket, because o f extreme occlusal wear. The alveolar process in this skull is apparently in perfect condition.
other tooth in the posterior part of the mouth and must necessarily become worn down proportionately. In addi tion, it is practically the center of the masticating area of the dental arch. Because its palatal cusp has received greater and longer wear generally than that of any other tooth, this molar must of necessity drop down to its opponent. This in itself might result in a certain amount of cervical denudation. But the extreme incline or flare of the pala tal root so often present in this tooth
tends to carry with it the gingiva and the thin alveolar plate, with the result that both are soon absorbed physiologi cally by the pressure brought against them, by food and the tongue, during mastication. The cervical part of the root is thus exposed. (Fig. 23.) The condition of the lower central incisor also may be referred to as an
Fig. 2+.— Mandible showing greater oc clusal wear on the central than on the lateral incisors. This is occasionally the result o f a certain type o f anatomic relationship between the central incisors and their opponents.
outstanding example of improper diag nosis in this regard. Under certain conditions, this tooth, wearing off faster than the other anterior teeth, is there fore being constantly “fed” up to its opponent in proportion to the amount of wear— like the lead in an “Eversharp” pencil. As a result, the neck is soon exposed to view, and eventually the root surface. A differential diag nosis of the nonpathologic root exposure
H irsch feld— Studies of Sku lls in Relation to Periodontal D isease
of this tooth may be easily made by means of the following facts: 1. The labiolingual diameter of the occlusal surface which now displaces the incisal margin on the central is greater than that of the lateral; in fact, this surface may even have become square, while that of the lateral still remains oblong. (Figs. 2 and 24.) 2. The root of the central may appear much shorter radiographically than that of the lateral. 3. Aside from these, no abnormal or pathologic symptoms may be present. In a generally healthy individual, the above described central may continue extruding until a great part of the crown is worn off without showing any evidence of actual periodontal disease. However, should this process of extru sion be accompanied by a systemic con dition, which, to my mind, usually underlies periodontoclasia, this tooth is apt to be among the first affected path ologically, for the following reasons: The central incisor has the smallest root in the mandible, and, when normal, it has, accordingly, a short narrow in cisal edge which, through its contiguity with the edges of the other anterior teeth, takes on a minimum of perio dontal strain during function. When this tooth is partly extruded on account of marked incisal wear, the following physical changes tend to increase the periodontal strain: 1. The presence of a broad occlusal surface instead of a thin incisal edge. 2. Shortening of the portion of the root remaining imbedded in the socket on account of the incisal wear, the leverage of that tooth being increased proportionately. 3. The par tial extrusion out of the alveolar socket, resulting in a lessened contact surface
969
between the root and the process. This results in an increased pressure in versely proportionate to the decreased alveolar and pericemental support. SUMMARY
1. Mesiodistal planing of the oc clusal surfaces by masticating wear tends to food impaction especially if the marginal ridges and grooves have been obliterated. 2. In horizontal occlusal wear, ob literation of these protective anatomic features does not seem to produce interproximal food impaction, the alveolar septums, apparently, remaining un affected. 3. This is also true regarding the obliteration of the occlusal embrasure. 4. The last two statements, how ever, should not be misconstrued as minimizing the importance of replacing these anatomic features in the rounding out of contour in proximal restorations. 5. Oblique occlusal wear invites leverage which may become an impor tant local etiologic factor in periodonto clasia and has to be reckoned with in treatment. 6. A close examination of the skulls discloses the fact that leverage, unless very extreme, will not by itself produce periodontoclasia. This fact is proved rep'eatedly in many instances of leverage produced by different causes as shown in the accompanying photographs. 7. Occlusal wear may be a means of obliterating traumatic occlusion in some instances and of producing it in others, directly or indirectly. 8. Excessive occlusal wear may re sult in extrusion of the tooth out of the
970
The Journal of the American Dental Association
alveolar process until part of the root surface is exposed to view, creating the optical illusion of a gingival recession. I wish to take this op p ortu n ity to express my
appreciation
of
the p riv ileg es
extended
by the officers o f the A m erican M useu m o f N atural H istory and to thank them f o r their kin d cooperation. I also wish to ack n o w le d g e the able assist ance o f D r . Samuel M . G e tzo ff o f N e w Y o r k in m a k in g the rad iogram s o f the d ry speci mens. 730 F ifth A venue.
y o u n g e r men com e into the p ro fe ssio n , w ith their better prelim inary training, there is hope o f ap p ro a ch in g this subject w ith greater and m ore scientific understanding.
W ith in the last
f e w years, it is bein g approached fr o m the en g in e e rin g standpoint, as in D rs. A n d erson and M c M illa n ’ s study o f bone and the p ositions o f the teeth, and in D r . M . M . H ou se’s studies in In fa ct, the sub
ject is bein g approached fr o m so m any stand points that the o ld time practition er realizes he is b e in g surrounded and ov erw h elm ed
w ith
m any things that he kn ow s little about.
It is
m y op in io n that w e have been d o in g to o m uch g r in d in g o f cusps w ith stones f o r r e lie f o f w e d g in g fo rce s, and in the fu tu re w e must m ake greater use o f orth o d o n tic appliances as a means o f p reven tin g traum a and as a means W hen one o r m ore teeth have
been lost in the arch and the adjacen t teeth have begun to tip into the space, w e should use the o rth od on tic appliances to replace them and f o l l o w this p rocedure by p ro p e rly restor in g the lost tooth o r teeth. of
D r.
In the sixth item
H ir sc h fe ld ’ s sum m ary
he
says that
levera ge, unless very extrem e, w ill not o f it s e lf cause periodontoclasia. T h is is true in the skulls o f
by the use o f p rop er massage and stim ulation w ith the toothbrush.
Arthur H. Merritt, New York City. It has been m y p riv ileg e to be associated with- D r. H irsch feld in this m ost interesting, n ot to say fascin ating, study o f the skulls in the A m er ican
M useum
of
N atural
H istory.
T hese
mute witnesses o f the past, w h o liv ed their lives under con d ition s quite unlike those o f the present, shed a flo o d o f lig h t on som e o f and w ith w h ich w e o f this generation are. fa ce
Austin F. James, Chicago, III. : A s the
o f correction .
It has been m y observation that in the p eople o f toda y w e m ay b u ild up tissue cell resistance
the problem s w h ich civiliza tion has brough t
D ISCU SSIO N
the m echanics o f ^occlusion.
in the m outh o f otherw ise healthy individuals.
p rim itive races a m o n g w h om
h eavy m astication was used fr o m
ch ild h o o d ,
because the heavy usage did b u ild up tissue cell resistance and strengthen the su pp ortin g structures. But in m odern existence, w here w e eat so fte r fo o d s , there is n ot the b u ild in g up of resistance in su pp ortin g struc tures and w e do fin d a lv e o la r destruction
to fa ce .
Great credit is due to D r . H irsch
fe ld f o r his m ost ca r e fu l and painstaking ob servations.
H e has gone back to those records,
n ot written b y the errin g hand o f m an, but by N ature herself— records w h ich are open o n ly to those w h o have eyes to see and ears to hear— and w ith vestigator,
the spirit o f
fr e e ly
investigations.
true
in
gives us the fr u it o f
the
his
It is o n ly thus that progress
Is m ade, and fortu n a te indeed is that p ro fe s sion w h ich numbers a m on g its m embers those w h o are w illin g to m ake such sacrifices.
P er
haps the m ost impressive observations noted in this study, has been the trem endous strain im posed on the teeth o f these barbarians as m anifested in occlu sal w ear, o fte n to the ex tent o f com p lete oblitera tion o f cusps, and, in some instance, exposure and death o f the p u lp , w ith ou t any breakin g d o w n o f alv eolar sup p ort.
A n d in ad d ition
to
this strain,
the
m ouths, in m any instances, must have been filth y in the extrem e, w ith tartar abundant, and every elem ent m akin g f o r g in g iv a l irri tation was present.
Y et the teeth remained
firm in their sockets, w ith n o evidence o f dis ease in their osseous support. T h is w o u ld seem to indicate that that p henom enon w hich has com e to be kn ow n as traum atic occlu sion, and to w h ich is assigned such an im portant role in the e tio lo g y o f p eriod on toclasia, is in reality an occlu sion w h ich does n ot traum atize under n orm al conditions. D r . H irsch fe ld ’s observation on this p oin t is that it “ tends to indicate that levera ge, unless v ery extrem e, w ill not cause p eriod on toclasia except where an u n derly in g systemic causative fa c to r c o exists.” T h e question w h ich natu rally sug
Hirschfeld— Studies of Skulls in Relation to Periodontal Disease
971
gests itse lf in this conn ection is: W h a t was
w h ich a ll the others flo w as a natural co n
there in those prehistoric races that m ade f o r
sequence, is relative disuse.
p eriod on tal health that is la ck in g in the civ i
ja w s and teeth as did those races o f the past
lized races o f the present?
has resulted in p o o r ly nourished tissues, un
they had, w ith clusion.
fe w
In the first place,
exceptions, n orm a l o c
T h e ir teeth w ere w e ll fo r m e d and
so related to each other, and to those o f the
F ailu re to use ou r
d evelop ed ja w s, irregu lar teeth and a greater susceptibility to disease.
T h is , plus heredity
and chan ged environm ent, w ill explain w h y
op p osin g ja w , that they did the m axim u m o f
w e cannot be com pared, fr o m a dental stand
w o r k w ith a m inim um o f strain.
T h e y were
p oin t, w ith those liv in g in the past, and w h y
also not subject to dental caries.
T h is m eant
we cannot hope to e n jo y their relative im
that they retained their teeth th rou gh ou t life ,
m unity to dental disease.
so that the strain im posed on them was borne
Dr. Hirschfeld ( closing) : I f it w ere not
by th irty -tw o teeth, a ll in n orm al occlu sion ,
f o r the practical experience o f the “ o ld time
in stead -of, as is so o fte n the case in the present, by a sm aller num ber, w ith the a ccom p an yin g
p ractition er”
changes in occlu sal relations and added strain,
o cca sion a lly in their new theories and ideas.
w hich alw ays fo llo w s tooth loss.
referred to by D r. James, the
y o u n ge r men w o u ld p rob a b ly g o
fa r afield
G iven these
N o doubt we have to make great allow ances
condition s o f n o rm a l occlu sion and fu l l co m
f o r the difference between the aboriginies and
plem ent o f
that
civilize d m an both in respect to period ontal developm ent and the fa ct that the m asticating
v ig orou s use was translated into w e ll-n o u r -
apparatus in m ost m ouths today is disarranged
fibrous
teeth, plus a diet o f
fo o d s ,
it
natu rally
hard and
f o llo w e d
ished and w e ll-d e v e lo p e d ja w s, w h ich
were
w ith traum atizing results, th rou g h extractions.
A n d when w e re
T h e n , again , w e o f today have to contend
flect on h o w different this record o f the past
w ith dental restorations w h ich do not fit in
h ig h ly resistant to disease.
is as written by the hand o f N ature on these
w ith
skeletal remains o f ou r barbaric ancestors, and
tection o f the p eriod ontium .
com pare it w ith the con d ition s p re v a ilin g in
M e rritt is g iv in g m e too m uch credit f o r m y efforts in m y w o r k at the museum. The m aterial there is rich in in form a tion and is availa ble to anyone w h o is genuinely inter ested.
the present, w e have the answer to ou r inquiry. T h e condition s are n ot com p arab le.
Perhaps
the fa c to r that is m ost
in
im portant
this
changed con d ition o f the present, and ou t o f
nature’ s scheme
of
fu n ctio n
and p r o
I fe a r that D r.