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Forces of Occlusion and Their Relation to Operative Dentistry*
FORCES OF OCCLUSION AND THEIR RELATION TO OPERATIVE DENTISTRY* By MARTIN DEWEY, D.D.S., New York City
F
deavor to speak o f the “ force of proximal contact” and the “ force o f occlusal sur faces.”
* R e a d b e fo r e the Section on O p era tiv e Dentistry, M a te ria M e d ic a and T h e ra p e u tics at the Sixty-N in th A n n u al Session o f the A m e rica n D en tal A ssocia tion , D etroit, M ich ., Oct. 25, 1927.
In speaking of occlusal surfaces, it must be remembered that we consider the cusp relation of the teeth of one arch as functioning with the teeth o f the op posing arch. In fact, all forces of oc clusion must be considered from a func tional standpoint and must be so studied in operative dentistry. F or example, in doing restorative work, inserting fillings and inlays, the object is not only to repair the tooth but to so repair the defect and shape the restoration that the tooth w ill be able to perform its proper function after being repaired, just as it did when it possessed its natural anatomic form. In fact, the close relation between foym and function must always be kept in mind in considering the forces o f oc clusion as related to operative dentistry. I do not think that it is necessary to go into a detailed description of tooth fo r m ; I shall simply call your attention to the relation existing between the cusp and contact point as regards function, and the effect o f this function on structure. N ot only does the shape o f the cusp have a definite bearing on the shape o f the contact surface, but also, we find, these two forces working together produce a typical jaw and face form as well as a definite temporomandibular articulation. These forces o f occlusion are so positive
O R C E S of occlusion have been de fined as those forces which cause teeth to assume and maintain a proper position in the line o f occlusion. T his definition might be changed to de fine “ forces of occlusion” as those forces which cause teeth to assume and main tain a proper relation to each other and a proper relation to the face and cranium. From the standpoint of oper ative dentistry, we can directly consider only those forces o f occlusion which have to do with maintaining teeth in their proper position, because teeth must necessarily have erupted before very much operative work can be instituted. T h e tw o most important forces of occlusion as related to operative den tistry are the force of proximal contact and the so-called “ force of the inclined plane.” By “ force of the inclined plane,” we mean the relation of the occlusal sur faces of teeth to the occlusal surfaces of the teeth o f the opposite arch. W e are trying to drop the words “ inclined plane” because, as D r. Prime called to the attention several years ago, occlusal surfaces o f the teeth and cusps do not possess inclined planes as defined in physics and mechanics, but present a series of curved surfaces. W e now en
Jour. A . D . A ., June, IQ28
1130
D ew ey — Forces of Occlusion and Their Relation to Operative Dentistry that we have formulated the follow ing anatomic laws, which hold true with all animals that have teeth, regardless of species, fam ily or order. T h e first law is : As the length of the cusp increases, the proximal contact de creases. T his law also works in the op posite direction; namely, as the proximal contact increases, the length o f the cusp decreases. T h e second law is : As the length o f the cusp increases, the depth of the glenoid fossa increases. T h e third law is : T h e greatest diameter o f the occlusal surfaces of the teeth is always at right angles to the greatest diameter of the condyle. As applied to the human individual, we find long cusped teeth have small proximal contacts, short cusped teeth have broader proximal con tacts. T h e temporomandibular articula tion varies in these individuals according to the laws that I have stated. It must also be remembered that a functional wear changes the length of the cusp and also changes the shape of the proximal contact surfaces in accord ance with the laws that I have stated. For example, young individuals may possess long cusped teeth and a small proximal contact point. W ith the long cusp, we find a deep glenoid fossa which is associated with a greater vertical man dibular movement in comparison to lateral movements. I f this individual uses the teeth properly and masticates as he should, there w ill be compensating changes taking place which w ill always keep the teeth in function, not only as regards the cusp and proximal contact but also as regards the supporting structures of the teeth. As function wears the cusp so as to make it shorter, it also wears the proximal contact to make it broader. As the cusps are worn down, the proximal contacts become wider, gradually ap proaching the occlusal margin. In other
1131
words, the wearing down o f the cusp, the occlusal surface and the proximal contact changes the shape o f the tooth so as to bring the proximal contact closer to the occlusal surface. T h e proximal contact moves occlusally as the result o f wear, changing a convex surface to a more flattened surface, and also, because the cusp becomes shorter, reducing the distance between the tip of the cusp and the cemento-enamel junction. As the cusp of the tooth becomes shorter, the occlusal surface necessarily becomes flat ter and the proximal contact becomes broader. T h e change in tooth form also produces a change in the temporoman dibular articulation whereby the glenoid fossa becomes shallower and the man dibular movements assume a greater lateral range than is found with the long cusped tooth. A compensating change also occurs in the supporting structures. T h e alveolar process and peridental membrane respond to these functional conditions and develop support for a par ticular form and definite function. N orm al cell metabolism has been named as one o f the forces o f occlusion. As related to operative dentistry, it must be considered as being responsible for the development o f the alveolar process and the peridental membrane in response to the function o f the teeth. H istologic examination reveals a great difference in the alveolar process in the mouth o f the same individual, who possessed teeth of different forms and functions on the two sides of the mouth. W e find function w ill also be greatly modified and the forces of occlusion deranged by mutila tion. Under mutilation, we consider extrac tion o f teeth as well as caries and im proper restorations. Caries which de stroys the proximal surfaces of the teeth makes it necessary for the proper restora
1132
T he Journal o f the American D en tal Association
tion to be supplied. T his restoration should not only consist of building a typical proximal contact such as would be found in the teeth at the time of eruption or which would be described as normal tooth form. I f the greatest de gree o f function is to be obtained, proximal contact and occlusal restoration must be made in accordance with the age of the patient. T hey must be so con structed as to give the proper mesiodistal diameter o f the teeth, and so shaped as to protect the gingiva, and must also be shaped according to the proximal con tacts of the normal teeth which have not been affected by caries. In mouths of individuals whose teeth show great occlusal wear, in which the cusps are short and the proximal con tacts have been worn flat, it w ould be a decided mistake to make a restoration with a small round proximal contact. T his mistake would also be more serious if an attempt were made to reproduce a cusp formation such as the individual possessed before functional wear had taken place. T his attempt to produce typical anatomic tooth forms in mouths of individuals whose teeth show great functional wear is a serious thing. Such a restoration not only interferes with occlusion, thereby throwing an added stress on the pericemental membrane and alveolar process, but likewise interferes with the proper mandibular movement and increases the strain on the temporo mandibular articulation. It is true that, in young individuals, the alveolar process and the temporomandibular articulation adjust themselves to tooth form and function. B ut even this development of the alveolar process in response to func tion occurs along histologic lines only when the individual shows normal cell metabolism or normal development. For example, in rachitic individuals, we find
normal tooth forms, but instead of func tion producing proper development as it w ould in a normal individual, we find that the functional use of the teeth in rachitic individuals not only produces malocclusion, but even produces jaw de formities. T h e development o f tissue from function occurs only, when cell metabolism is normal. In making extensive restorations in mouths in which the forces of occlusion have been greatly disturbed because of mutilation, it must be remembered that any restoration undertaken must be in accordance with the existing conditions, and the forces o f occlusion must not be put out o f balance. Certain operators become engrossed with a particular technic and attempt to make restorations along certain technical lines without any consideration of the forces of occlusion involved. In indi viduals whose teeth show considerable wear, we find men advocating an ex tensive opening of the bite in the attempt to restore the mouth o f a middle aged or old person to what it might have been in early life and before mutilation oc curred. These operators fail to realize that they are greatly changing the en vironment o f the individual and are throwing unusual function on the teeth and, in a few days or weeks, are bringing excessive stress to bear on the supporting tissues. It might be true that when these resto rations are mounted on an articulator and considered from a purely mechanical standpoint, they have an advantage from a masticating point o f view over what the individual possessed at the time the restoration was begun. T hey fail to realize that this excessive restoration in opening the bite is going to throw undue stress on the supporting tissues which is going to result in one o f two things:
D ew ey — Forces of Occlusion and Their Relation to Operative D entistry T h e supporting tissue is going to respond to that function and become strength ened, and change so as to take care of this added and increased stress; or will fail to respond and break down under the increased load. T his extensive resto ration w ill also produce a changed move ment in the mandible which makes it necessary for the temporomandibular articulation to adjust itself to this new restoration. It is true that the man dibular movement, the supporting tissue and the temporomandibular articulation in animals have all developed as a result of tooth form and function in accordance with a normal cell metabolism. In mak ing these extensive restorations in aged individuals, we have little assurance that normal cell metabolism is going to re spond as a result of this sudden change of form and function. T h e development o f the dental ap paratus and the growth o f the supporting structures extends over a period of many years and allows for a gradual adjust ment o f the supporting structures as these various changes o f tooth form occur. T h e individual develops his de ciduous teeth; they are replaced by per manent teeth, and the supporting tissue develops in accordance with the change of teeth. But it is a gradual change, which allows cell metabolism to adjust the various parts in accordance with changed function. In operative dentistry, when extensive restorations are made and the bite is open to a great degree, the change of form is so sudden that the supporting tissue breaks down under the excessive load and, instead o f cell meta bolism helping to develop new tissue, it becomes a factor in destroying what is present. W e realize that a great many mouths are, to a certain extent, ruined by mutilation, and the patient suiters from improper mastication. It must be
1133
remembered that the majority of those individuals have passed the “ crest o f the wave” and are on a decline. It is there fore very foolish, from a biologic stand point, to expect to be able to make an extensive restoration in these individuals and bring the mouth back to what it was at 20 years o f age, expecting the support ing tissue to respond. Realizing that something should be done to improve the mastication o f that individual, it must be done in such a way as not to be a detriment to what remain ing teeth there are. Care should be taken to make a restoration which will not make necessary an unusual ja w move ment or throw excessive stress on the supporting tissues. Restorations should be made in accordance with the forces of occlusion, remembering that any one force of occlusion thrown out o f balance w ill become a detriment and destroy all the rest that are acting properly. It is our opinion that in making restorations in accordance with the forces o f oc clusion, the age of the patient is a great factor and restorations should be made in accordance with tooth form and function as they existed at that time, rather than be made with the idea o f carrying out a particular technic. A mechanical piece of work, beautifully done, may become a great detriment because it does not allow the teeth to function according to the forces o f occlusion. 17 P ark A v en u e. DISCUSSION A b r a m H offm a n , B u ffa lo, N . Y .: T h e p ro p e r m aintenance o f tooth fo r m and rela tion in the w ork o f the op era tiv e dentist is o f utm ost im portance. It is to be regretted that such a m essage as D r. D e w e y has g iv en us com es only to a g rou p o f practition ers such as are g ath ered here— men w h om I k n o w to be th ou g h tfu l— men w h o think as they w ork. It is the g rea t rank and file o f op era tors not represen ted here w h o, in their restoration w ork , think on ly in term s o f the “ id ea l” in
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T he Journal o f the American D en tal Association
tooth fo r m o r sim ply in term s o f a “ fillin g .” W ith the introdu ction o f better ca v ity p rep a r it io n tw o o r three d eca d es ago, and then w ith the better con tou r w o rk resulting from in la y technic, there has resulted w h a t m ay alm ost be term ed a co m p le x in the m atter of tooth fo r m restoration. M u ch has been w r it ten in conn ection w ith the “ id e a l” re sto ra tion, and I w ish only to rem ind you that the three la w s m entioned by D r. D e w e y are fu n d am en tal and must be a part o f our d a ily w ork. W e m ust not lose sight o f the chan ges in fo r m that take p lace as the result o f w ear, age and the health o f the patient. T h e o c clusions that h ave been com p letely upset b e cause o f fa u lty restorations in both m orsal and a p p ro x im a l su rfaces are legion. T h e detrim ental results on o cclu sion o f such w ork are on ly too w e ll k now n to the orth odon tist— the p eriod on tist w ill rem in d you o f the ev il done the su pp ortin g tissues— to say nothing o f the ch an g es that take p lace in the g le n o id fo ss a in the case o f fa u lty prosthetic restora tions, p a rticu la rly in partial dentures. It should be rem em bered that the m utilation o f tooth fo r m and relation , fr o m w h a tev er cause, decreases the efficiency, and as the m utilation increases so, in p rop ortion , does the difficulty o r com p lex ity o f restoration, either through fillings or oth erw ise, increase. T h e restorations must be m ad e in a ccord an ce w ith the sum total o f con d ition s as w e find th em ; in other w ord s, the fo r c e s o f occlu sion must be o b se rv e d and be kept in harm ony w ith the g e n e ra l fu n ction o f the structures in v olv e d . D r. D e w e y ’ s w o r d o f caution re la tive to op e n in g the bite, e sp ecia lly in adult cases, sh ould be ca re fu lly con sid ered , fo r his statements are lo g ica l. T h is p ra ctice m ay be fo llo w e d in y o u n g in d iv id u a ls quite safely because o f the p ro lo n g e d and m ore active cell p ro life ra tio n and n atu re’s m ore re a d y a d a p ta tion to ch an ged en viron m en t and fu n ction , but, even then, the ch aracteristic m o rp h o lo g y o f the teeth and the fo r m an d fu n ction o f the tem p orom a n d ib u la r articu lation must be kept in m ind. O u r literature has been replete w ith description s and illustrations fo r r e p ro d u cin g
id ea l tooth form s in the v a riou s bran ch es o f p ra ctic e : the p oin t that should be stressed is the rep rod u ction o r d evelop m en t o f the in d i v id u a l norm al, fo r this o r that p articu la r case, so that the tooth o r teeth in question w ill fu n ction h a rm on iou sly w ith the dental org a n ism as a w h ole. A u stin F . Jam es, C h ica go, III.: T h e ideas b rou g h t out in D r. D e w e y ’s p a p er coin cide so p e rfe ctly w ith those o f the p eriod on tist in his efforts to p rev en t destruction o f, o r re store to a con d ition o f health, the su pportin g structures o f teeth that there is little to be discussed. H e has called attention to the w e a r o f cusps and contact points fr o m norm al fu n ction . I ag ree w ith his observation s and conclusion s, but the p eriod on tist sees m any cases o f p rom in en tly m arked teeth (those w ith lo n g cusps and deep su lci) w h ich show no w e a r in g d o w n fr o m the n orm al fu n ction o f m astica tin g fo o d , but do sh ow flat slanting su rfaces or facets on these cusps caused by constan t contact w ith each other. H ig h strung or n e rv ou s in d iv id u a ls som etim es fo r m the h abit o f ru b b in g these cusps t o g e t h e r ; others, o f g rittin g the t.eeth in sleep. U nd er these con d ition s, the cusps are n ot w orn shorter but sh arper, and act as w ed g es w h en m uscle pressure is exerted in closin g the ja w s , this p ro d u c in g a w e d g in g force, b rin g in g about in som e cases a low ered resistance o f the tissue cells an d in others a ctin g w ith sufficient d r iv in g fo r c e to cause irritation, congestion and absorption o f the a lv e o la r process, with the in ev itable form a tion o f pockets. I have a d v a n ce d this id ea fo r som e years and rea l ize that fe w h ave ag reed w ith m y interpreta tion o f the w e a r that I am attem pting to describe. But I h a v e m any m odels that, to m y m ind, illustrate the p oint that this w e a r is not the result o f norm al fu n ction . T o get back to the op era tiv e dentistry stan d p oin t: the p eriod on tist m ust h ave the coop eration o f the dental op era tor in the rep a ir o f m utilated teeth, and the restoration o f con tact points and occlu sion , as w ell as the replacem ent o f lost teeth by p ro p e rly constructed restora tions.
F
deavor to speak o f the “ force of proximal contact” and the “ force o f occlusal sur faces.”
* R e a d b e fo r e the Section on O p era tiv e Dentistry, M a te ria M e d ic a and T h e ra p e u tics at the Sixty-N in th A n n u al Session o f the A m e rica n D en tal A ssocia tion , D etroit, M ich ., Oct. 25, 1927.
In speaking of occlusal surfaces, it must be remembered that we consider the cusp relation of the teeth of one arch as functioning with the teeth o f the op posing arch. In fact, all forces of oc clusion must be considered from a func tional standpoint and must be so studied in operative dentistry. F or example, in doing restorative work, inserting fillings and inlays, the object is not only to repair the tooth but to so repair the defect and shape the restoration that the tooth w ill be able to perform its proper function after being repaired, just as it did when it possessed its natural anatomic form. In fact, the close relation between foym and function must always be kept in mind in considering the forces o f oc clusion as related to operative dentistry. I do not think that it is necessary to go into a detailed description of tooth fo r m ; I shall simply call your attention to the relation existing between the cusp and contact point as regards function, and the effect o f this function on structure. N ot only does the shape o f the cusp have a definite bearing on the shape o f the contact surface, but also, we find, these two forces working together produce a typical jaw and face form as well as a definite temporomandibular articulation. These forces o f occlusion are so positive
O R C E S of occlusion have been de fined as those forces which cause teeth to assume and maintain a proper position in the line o f occlusion. T his definition might be changed to de fine “ forces of occlusion” as those forces which cause teeth to assume and main tain a proper relation to each other and a proper relation to the face and cranium. From the standpoint of oper ative dentistry, we can directly consider only those forces o f occlusion which have to do with maintaining teeth in their proper position, because teeth must necessarily have erupted before very much operative work can be instituted. T h e tw o most important forces of occlusion as related to operative den tistry are the force of proximal contact and the so-called “ force of the inclined plane.” By “ force of the inclined plane,” we mean the relation of the occlusal sur faces of teeth to the occlusal surfaces of the teeth o f the opposite arch. W e are trying to drop the words “ inclined plane” because, as D r. Prime called to the attention several years ago, occlusal surfaces o f the teeth and cusps do not possess inclined planes as defined in physics and mechanics, but present a series of curved surfaces. W e now en
Jour. A . D . A ., June, IQ28
1130
D ew ey — Forces of Occlusion and Their Relation to Operative Dentistry that we have formulated the follow ing anatomic laws, which hold true with all animals that have teeth, regardless of species, fam ily or order. T h e first law is : As the length of the cusp increases, the proximal contact de creases. T his law also works in the op posite direction; namely, as the proximal contact increases, the length o f the cusp decreases. T h e second law is : As the length o f the cusp increases, the depth of the glenoid fossa increases. T h e third law is : T h e greatest diameter o f the occlusal surfaces of the teeth is always at right angles to the greatest diameter of the condyle. As applied to the human individual, we find long cusped teeth have small proximal contacts, short cusped teeth have broader proximal con tacts. T h e temporomandibular articula tion varies in these individuals according to the laws that I have stated. It must also be remembered that a functional wear changes the length of the cusp and also changes the shape of the proximal contact surfaces in accord ance with the laws that I have stated. For example, young individuals may possess long cusped teeth and a small proximal contact point. W ith the long cusp, we find a deep glenoid fossa which is associated with a greater vertical man dibular movement in comparison to lateral movements. I f this individual uses the teeth properly and masticates as he should, there w ill be compensating changes taking place which w ill always keep the teeth in function, not only as regards the cusp and proximal contact but also as regards the supporting structures of the teeth. As function wears the cusp so as to make it shorter, it also wears the proximal contact to make it broader. As the cusps are worn down, the proximal contacts become wider, gradually ap proaching the occlusal margin. In other
1131
words, the wearing down o f the cusp, the occlusal surface and the proximal contact changes the shape o f the tooth so as to bring the proximal contact closer to the occlusal surface. T h e proximal contact moves occlusally as the result o f wear, changing a convex surface to a more flattened surface, and also, because the cusp becomes shorter, reducing the distance between the tip of the cusp and the cemento-enamel junction. As the cusp of the tooth becomes shorter, the occlusal surface necessarily becomes flat ter and the proximal contact becomes broader. T h e change in tooth form also produces a change in the temporoman dibular articulation whereby the glenoid fossa becomes shallower and the man dibular movements assume a greater lateral range than is found with the long cusped tooth. A compensating change also occurs in the supporting structures. T h e alveolar process and peridental membrane respond to these functional conditions and develop support for a par ticular form and definite function. N orm al cell metabolism has been named as one o f the forces o f occlusion. As related to operative dentistry, it must be considered as being responsible for the development o f the alveolar process and the peridental membrane in response to the function o f the teeth. H istologic examination reveals a great difference in the alveolar process in the mouth o f the same individual, who possessed teeth of different forms and functions on the two sides of the mouth. W e find function w ill also be greatly modified and the forces of occlusion deranged by mutila tion. Under mutilation, we consider extrac tion o f teeth as well as caries and im proper restorations. Caries which de stroys the proximal surfaces of the teeth makes it necessary for the proper restora
1132
T he Journal o f the American D en tal Association
tion to be supplied. T his restoration should not only consist of building a typical proximal contact such as would be found in the teeth at the time of eruption or which would be described as normal tooth form. I f the greatest de gree o f function is to be obtained, proximal contact and occlusal restoration must be made in accordance with the age of the patient. T hey must be so con structed as to give the proper mesiodistal diameter o f the teeth, and so shaped as to protect the gingiva, and must also be shaped according to the proximal con tacts of the normal teeth which have not been affected by caries. In mouths of individuals whose teeth show great occlusal wear, in which the cusps are short and the proximal con tacts have been worn flat, it w ould be a decided mistake to make a restoration with a small round proximal contact. T his mistake would also be more serious if an attempt were made to reproduce a cusp formation such as the individual possessed before functional wear had taken place. T his attempt to produce typical anatomic tooth forms in mouths of individuals whose teeth show great functional wear is a serious thing. Such a restoration not only interferes with occlusion, thereby throwing an added stress on the pericemental membrane and alveolar process, but likewise interferes with the proper mandibular movement and increases the strain on the temporo mandibular articulation. It is true that, in young individuals, the alveolar process and the temporomandibular articulation adjust themselves to tooth form and function. B ut even this development of the alveolar process in response to func tion occurs along histologic lines only when the individual shows normal cell metabolism or normal development. For example, in rachitic individuals, we find
normal tooth forms, but instead of func tion producing proper development as it w ould in a normal individual, we find that the functional use of the teeth in rachitic individuals not only produces malocclusion, but even produces jaw de formities. T h e development o f tissue from function occurs only, when cell metabolism is normal. In making extensive restorations in mouths in which the forces of occlusion have been greatly disturbed because of mutilation, it must be remembered that any restoration undertaken must be in accordance with the existing conditions, and the forces o f occlusion must not be put out o f balance. Certain operators become engrossed with a particular technic and attempt to make restorations along certain technical lines without any consideration of the forces of occlusion involved. In indi viduals whose teeth show considerable wear, we find men advocating an ex tensive opening of the bite in the attempt to restore the mouth o f a middle aged or old person to what it might have been in early life and before mutilation oc curred. These operators fail to realize that they are greatly changing the en vironment o f the individual and are throwing unusual function on the teeth and, in a few days or weeks, are bringing excessive stress to bear on the supporting tissues. It might be true that when these resto rations are mounted on an articulator and considered from a purely mechanical standpoint, they have an advantage from a masticating point o f view over what the individual possessed at the time the restoration was begun. T hey fail to realize that this excessive restoration in opening the bite is going to throw undue stress on the supporting tissues which is going to result in one o f two things:
D ew ey — Forces of Occlusion and Their Relation to Operative D entistry T h e supporting tissue is going to respond to that function and become strength ened, and change so as to take care of this added and increased stress; or will fail to respond and break down under the increased load. T his extensive resto ration w ill also produce a changed move ment in the mandible which makes it necessary for the temporomandibular articulation to adjust itself to this new restoration. It is true that the man dibular movement, the supporting tissue and the temporomandibular articulation in animals have all developed as a result of tooth form and function in accordance with a normal cell metabolism. In mak ing these extensive restorations in aged individuals, we have little assurance that normal cell metabolism is going to re spond as a result of this sudden change of form and function. T h e development o f the dental ap paratus and the growth o f the supporting structures extends over a period of many years and allows for a gradual adjust ment o f the supporting structures as these various changes o f tooth form occur. T h e individual develops his de ciduous teeth; they are replaced by per manent teeth, and the supporting tissue develops in accordance with the change of teeth. But it is a gradual change, which allows cell metabolism to adjust the various parts in accordance with changed function. In operative dentistry, when extensive restorations are made and the bite is open to a great degree, the change of form is so sudden that the supporting tissue breaks down under the excessive load and, instead o f cell meta bolism helping to develop new tissue, it becomes a factor in destroying what is present. W e realize that a great many mouths are, to a certain extent, ruined by mutilation, and the patient suiters from improper mastication. It must be
1133
remembered that the majority of those individuals have passed the “ crest o f the wave” and are on a decline. It is there fore very foolish, from a biologic stand point, to expect to be able to make an extensive restoration in these individuals and bring the mouth back to what it was at 20 years o f age, expecting the support ing tissue to respond. Realizing that something should be done to improve the mastication o f that individual, it must be done in such a way as not to be a detriment to what remain ing teeth there are. Care should be taken to make a restoration which will not make necessary an unusual ja w move ment or throw excessive stress on the supporting tissues. Restorations should be made in accordance with the forces of occlusion, remembering that any one force of occlusion thrown out o f balance w ill become a detriment and destroy all the rest that are acting properly. It is our opinion that in making restorations in accordance with the forces o f oc clusion, the age of the patient is a great factor and restorations should be made in accordance with tooth form and function as they existed at that time, rather than be made with the idea o f carrying out a particular technic. A mechanical piece of work, beautifully done, may become a great detriment because it does not allow the teeth to function according to the forces o f occlusion. 17 P ark A v en u e. DISCUSSION A b r a m H offm a n , B u ffa lo, N . Y .: T h e p ro p e r m aintenance o f tooth fo r m and rela tion in the w ork o f the op era tiv e dentist is o f utm ost im portance. It is to be regretted that such a m essage as D r. D e w e y has g iv en us com es only to a g rou p o f practition ers such as are g ath ered here— men w h om I k n o w to be th ou g h tfu l— men w h o think as they w ork. It is the g rea t rank and file o f op era tors not represen ted here w h o, in their restoration w ork , think on ly in term s o f the “ id ea l” in
1134
T he Journal o f the American D en tal Association
tooth fo r m o r sim ply in term s o f a “ fillin g .” W ith the introdu ction o f better ca v ity p rep a r it io n tw o o r three d eca d es ago, and then w ith the better con tou r w o rk resulting from in la y technic, there has resulted w h a t m ay alm ost be term ed a co m p le x in the m atter of tooth fo r m restoration. M u ch has been w r it ten in conn ection w ith the “ id e a l” re sto ra tion, and I w ish only to rem ind you that the three la w s m entioned by D r. D e w e y are fu n d am en tal and must be a part o f our d a ily w ork. W e m ust not lose sight o f the chan ges in fo r m that take p lace as the result o f w ear, age and the health o f the patient. T h e o c clusions that h ave been com p letely upset b e cause o f fa u lty restorations in both m orsal and a p p ro x im a l su rfaces are legion. T h e detrim ental results on o cclu sion o f such w ork are on ly too w e ll k now n to the orth odon tist— the p eriod on tist w ill rem in d you o f the ev il done the su pp ortin g tissues— to say nothing o f the ch an g es that take p lace in the g le n o id fo ss a in the case o f fa u lty prosthetic restora tions, p a rticu la rly in partial dentures. It should be rem em bered that the m utilation o f tooth fo r m and relation , fr o m w h a tev er cause, decreases the efficiency, and as the m utilation increases so, in p rop ortion , does the difficulty o r com p lex ity o f restoration, either through fillings or oth erw ise, increase. T h e restorations must be m ad e in a ccord an ce w ith the sum total o f con d ition s as w e find th em ; in other w ord s, the fo r c e s o f occlu sion must be o b se rv e d and be kept in harm ony w ith the g e n e ra l fu n ction o f the structures in v olv e d . D r. D e w e y ’ s w o r d o f caution re la tive to op e n in g the bite, e sp ecia lly in adult cases, sh ould be ca re fu lly con sid ered , fo r his statements are lo g ica l. T h is p ra ctice m ay be fo llo w e d in y o u n g in d iv id u a ls quite safely because o f the p ro lo n g e d and m ore active cell p ro life ra tio n and n atu re’s m ore re a d y a d a p ta tion to ch an ged en viron m en t and fu n ction , but, even then, the ch aracteristic m o rp h o lo g y o f the teeth and the fo r m an d fu n ction o f the tem p orom a n d ib u la r articu lation must be kept in m ind. O u r literature has been replete w ith description s and illustrations fo r r e p ro d u cin g
id ea l tooth form s in the v a riou s bran ch es o f p ra ctic e : the p oin t that should be stressed is the rep rod u ction o r d evelop m en t o f the in d i v id u a l norm al, fo r this o r that p articu la r case, so that the tooth o r teeth in question w ill fu n ction h a rm on iou sly w ith the dental org a n ism as a w h ole. A u stin F . Jam es, C h ica go, III.: T h e ideas b rou g h t out in D r. D e w e y ’s p a p er coin cide so p e rfe ctly w ith those o f the p eriod on tist in his efforts to p rev en t destruction o f, o r re store to a con d ition o f health, the su pportin g structures o f teeth that there is little to be discussed. H e has called attention to the w e a r o f cusps and contact points fr o m norm al fu n ction . I ag ree w ith his observation s and conclusion s, but the p eriod on tist sees m any cases o f p rom in en tly m arked teeth (those w ith lo n g cusps and deep su lci) w h ich show no w e a r in g d o w n fr o m the n orm al fu n ction o f m astica tin g fo o d , but do sh ow flat slanting su rfaces or facets on these cusps caused by constan t contact w ith each other. H ig h strung or n e rv ou s in d iv id u a ls som etim es fo r m the h abit o f ru b b in g these cusps t o g e t h e r ; others, o f g rittin g the t.eeth in sleep. U nd er these con d ition s, the cusps are n ot w orn shorter but sh arper, and act as w ed g es w h en m uscle pressure is exerted in closin g the ja w s , this p ro d u c in g a w e d g in g force, b rin g in g about in som e cases a low ered resistance o f the tissue cells an d in others a ctin g w ith sufficient d r iv in g fo r c e to cause irritation, congestion and absorption o f the a lv e o la r process, with the in ev itable form a tion o f pockets. I have a d v a n ce d this id ea fo r som e years and rea l ize that fe w h ave ag reed w ith m y interpreta tion o f the w e a r that I am attem pting to describe. But I h a v e m any m odels that, to m y m ind, illustrate the p oint that this w e a r is not the result o f norm al fu n ction . T o get back to the op era tiv e dentistry stan d p oin t: the p eriod on tist m ust h ave the coop eration o f the dental op era tor in the rep a ir o f m utilated teeth, and the restoration o f con tact points and occlu sion , as w ell as the replacem ent o f lost teeth by p ro p e rly constructed restora tions.