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Endogenous tooth movement
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1. Johnstone, M . The human cardiovascular response to fluothane anaesthesia. Brit. J. Anaesth. 28:392 Sept. 1956. 2. Chang, J.; Macartney, H. H., and Graves, H. B. Clinical experience with fluothane. J. Canad. Anaesth. Soc. 4:187 July 1957. 3. MacKay, I. M. Clinical evaluation of fluothane with special reference to a controlled vaporizer. J. Canad. Anaesth. Soc. 4:235 July 1957. 4. Sadove, M. S., and others. Ethyl vinyl ether in
/
dental anesthesia: preliminary report. J.A.D.A. 51:536 Nov. 1955. 5. Stephen, C. R., and others. Evaluation of fluothane for clinical anaesthesia. J. Canad. Anaesth. Soc. 4:246 July 1957. 6. Severinghaus, J. W., and Cullen, S. C. Depression of myocardium and body oxygen consumption with fluo thane, Anesthesiology 19:165 March-April 1958. 7. Burnap, T. K.; Galla, S. J., and Vandam, L. D. Anesthetic, circulatory and respiratory effects of fluo thane. Anesthesiology 19:307 May-June 1958.
Endogenous tooth movement
Ira Franklin Ross* D.D.S., New York
The three types of endogenous tooth movement are (1) the continuous erup tion of teeth, (2) migration due to in herent weakness of the attachment appa ratus, and (3) the adaptive movements of the teeth. Adaptive tooth movement is controlled by: (I ) the contact relation ships between adjacent and opposing teeth, and (2) the interaction of the com ponents of the masticatory musculature. Knowledge of the various patterns of tooth movement is important to the prac tice of all phases of dentistry. Tooth movement is important to all phases of dentistry. In the past, its study has been associated primarily with the practice of orthodontics. Recently, how ever, increased knowledge of the various nuances of tooth repositioning has en abled each branch of dentistry to ap preciate its relationship to the problem. For example, the placement of a restora tion in a single tooth can induce move ment either of that tooth or of opposing teeth if the restoration is not in harmony with its environment. Further, a partial
denture may create a change in tooth position as a result of torque from a clasp, from excessive pressure against con tiguous teeth or as a result of ridge resorp tion under the saddle areas.1 The extrac tion of a tooth will create space into which neighboring teeth can migrate un less prevented by some obstructive force such as steep intercuspation. All these situations can lead to periodontal de struction in the region and additional mobility of teeth. Two types of tooth movement have been observed; one is the result of forces produced by. an external mechanism or appliance which is introduced into the oral cavity. This may be called exogenous tooth movement. The force may be a short sudden one, as with a blow, or may be a series of longer intermittent ones as observed when an orthodontic appliance is used or when a habit such as threadbiting or pencil-biting is practiced. Only those habits which include the introduc tion of an extraoral object into the mouth may be considered as capable of pro ducing exogenous movement.2 The second type of tooth movement is the result of forces produced by mecha nisms from within the oral cavity. This is
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endogenous tooth movement. Examples are the continuous eruption of teeth, mi gration due to an inherent weakness in the attachm ent apparatus of the tooth as seen in periodontosis, and the adaptive movements resulting from interocclusal contacts and muscular activity. No direct external moving force has been applied to these teeth. Movement following the reshaping of teeth by grinding or the re moval of granulomatous tissue from a periodontal pocket is endogenous in character because here the change in tooth position is primarily the result of a change in the contact relationships of the teeth or in the surrounding periodontal structures. The instruments used, namely the grinding stone and the curet, do not in themselves exert force, as would be the case in exogenous tooth movement, but they do aid in changing the functional environment of the tooth. The condition of the teeth, the periodontium, and the surrounding oral mucosa which results from all constitutional, physiologic and pathologic factors may be called the functional environment. The many varieties of endogenous movements may be grouped into three distinct patterns. The first is the response to a systemic regulatory mechanism. The second is the result of the failure of a weakened attachm ent apparatus to sup port the tooth properly in its alveolus. The third type is an adaptive one, acti vated and controlled by contact relation ships between adjacent and opposing teeth, by the interaction of the various components of the masticatory muscula ture, and by the effect of the movement pattern of the mandible as governed by the temporomandibular joint, the muscu lature and the teeth.
lyst, possibly endocrine in nature, stimu lates the developing tooth to move occlusally until contact with its antagonist is made. Despite strong opposition this same force may continue throughout the life of the tooth, moving it occlusally as its morsal surfaces are worn. If the antagonist is lost, thereby removing the inhibiting ef fect, the eruptive force again may elevate the tooth until the opposing gingiva pre vents further movement (Fig. 1). Fre quently, however, the unopposed tooth will cease moving before the opposite gin giva is reached, indicating that possibly the eruptive force is no longer operable. Moreover, the cessation of continuous eruption after apparent removal of the obvious deterrent may also be the result of ankylosis of the tooth in its socket, bulbous root formation, a powerful biting
TO O TH ERUPTION
The first type of endogenous movement, that governed by a systemic regulatory mechanism, is seen in the phenomenon of tooth eruption. Here an unknown cata
Fig. I • S tre n g th o f e ru p tiv e fo rc e of a d u lt d e n tition. A b o v e : U n o p p o s e d m a n d ib u la r th ird m olar w h ich is ex tru d e d fa r b e y o n d o c clu sa l level o f a d ja c e n t teeth. Below: U n o p p o s e d m axillary first m o lar has ex tru d e d d e sp ite re stra in in g effe ct o f c o n ta c t with a d ja c e n t teeth
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habit such as pipestem biting or tongue thrusting, or a combination of tongue and cheek pressures. As the eruptive move ment continues throughout life, the alveolar structures may grow with the tooth or the movement may be a simple extrusion without alveolar growth. MIGRATION BECAUSE OF W EA K N E SS OF PERIODONTIUM
The next type of endogenous movement is the extremely rare wandering of teeth observed in patients with precocious ad vanced alveolar atrophy or periodon tosis.3'5 Glickman6 states that this may result from “degeneration of the perio dontal fibers, inadequacy in the con tinuous deposition of cementum or loss of alveolar bone.” The teeth which most frequently exhibit this type of migration are the maxillary and m andibular central and lateral incisors, although on occasion posterior teeth, particularly the maxillary and m andibular first molars, may be similarly affected. Once the primary periodontal defect has occurred, sec ondary factors such as occlusal trauma, habits, and exuberant granulomatous tissue in a periodontal pocket may cause further migration. It is important to dif ferentiate between this type of movement resulting from an intrinsic lack of tissue integrity modified by secondary factors, and types of movement showing similar clinical migration where the initiating factor is an abnormal habit or food im paction mechanism leading to periodontal destruction.2
to its environment. This may be a re versible reaction. If the tooth moves away sufficiently from the force which origi nally induced the movement, or if the forces themselves are reduced, the tooth may again become firm in its socket. I’his would indicate a regaining of adaptation. If the tooth cannot move out of the orbit of these traum atic forces, mobility will increase as a result of the increased perio dontal destruction. Several examples of adaptive tooth movement have been noted; namely, the limited buccolingual rocking of a tooth in its alveolus during both masticatory and nonmasticatory m andibular move ment, the mesial drifting of teeth result ing from the anterior component of
ADAPTIVE T O O TH M OVEM ENT
Adaptive tooth movement occurs as a result of physiologic accommodation to the forces of interocclusal contact and muscular activity. When these forces ex ceed physiologic limits, destruction of the supporting tissues occurs. From this point on, the tooth will exhibit perceptible mo bility, and will have lost its adaptability
Fig. 2 • V a rio u s a sp e cts o f m esial m o v e m e n t of teeth. A b o v e : M e s ia l in c lin a tio n o f m a n d ib u la r m olars .can b e seen. T h e ir ro o t s p a c in g an d c u r v a tu re s u g g e s t a s tro n g b ra c in g effe ct w hich p re v e n ts excessive tooth m ovem en t. Below : M e sia l in clin a tio n o f b o th m axillary a n d m a n d ib u la r teeth is seen. A n g le s a t which teeth m eet in ce n tric o c c lu sio n are ex trem ely im p o rta n t in p ro d u c in g s u b s e g u e n t m o v e m e n t o f teeth
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stresses exceeds that which can be toler ated by the periodontium and if gingival inflammation is present, damage may occur which implies loss of adaptation of the tooth to its environment.1,7,8 Destruc tive changes on the pressure sides of the alveoli of experimental animals have been described as necrosis of the periodontal ligament fibers, thrombosis of the vessels in the ligament, and osteoclasis of the walls of the alveoli. The tension sides showed widening of the periodontal mem brane, thrombosis and bone formation.9 12 Stahl13 recently described similar changes in a hum an periodontium where the oc clusal force was directed against the crown of a molar tooth adjacent to the space of a previously extracted tooth. This force was directed primarily in the mesial direction and produced tipping which resulted in a definite pressure area on the mesial aspect and a definite tension zone on the distal aspect of the traum a tized tooth. However, when intermittent Fig. 3 • A b o v e : M e s ia l m o v e m e n t o f b oth m a n tooth rocking occurs in a buccolingual d ib u la r m ola rs can be seen a fte r loss o f m a n d ib u la r first m olar. M a x illa r y first m o la r has direction as a result of mastication, swal extruded, d e m o n stra tin g fo rc e o f co n tin u o u s e r u p lowing or tensional clenching, and where tion. Below: A d a p t iv e tooth m o v e m e n t o f m a n d ib u la r teeth is n o te d a fte r loss o f m a n d ib u la r alveolar support is insufficient, the de first m olar. S e c o n d m o la r has m o v e d m esially and structive changes previously described b ic u s p id s ha ve a lso sh ifte d th e ir p o sitio n s. L atter will not have an opportunity to progress c h a n g e is in d ic a t e d b y op e n c o n t a c t betw een c u s p id a n d first b ic u s p id a n d b y axial in clin a tio n into the healing phase, and increased o f se c o n d b ic u s p id bone loss may occur. Inasmuch as exces sive tooth rocking resulting from tensional clenching and grinding is observed so force, the malpositioning of teeth due to frequently, it is postulated that the re blocking or moving occlusal interferences, sultant lack of periodontal healing com and the reactive positioning of malposed bined with the bone loss associated with gingival inflammation is responsible for teeth. the bone loss in many persons with chronic periodontal disease. FU NCTIO N A L ROCKING Functional buccolingual rocking and de pression of a tooth in its alveolus as a re sult of interocclusal contact is an adaptive physiologic activity. It is usually clinically imperceptible and is thought to be a pro tective mechanism, preventing the frac ture of the tooth by the distribution of the effects of occlusal stress throughout the periodontium. If the effect of occlusal
M ESIAL AND DISTAL M OVEM ENTS
Mesial drifting of teeth due to the an terior component of force is the next type of endogenous tooth movement which re sults from the interplay between inter occlusal contacts and masticatory muscu lature (Fig. 2, 3 ).14 Although mesial drifting is observed with the great ma-
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Fig. 5 • A d a p t iv e tooth m o v e m e n t is n oted in b o th m a n d ib le a n d m axilla. Loss o f m axillary se c o n d b ic u s p id a n d m a n d ib u la r first m o la r has p ro d u c e d d ista l m o v e m e n t o f m axillary first b i c u s p id a n d m esial m o v e m e n t o f m axillary first m o la r a n d m a n d ib u la r se c o n d a n d third m olars. This d e m o n stra te s th a t m o v e m e n t is a re a c tio n to sp e cific fo rc e s a n d d o e s n ot alw ays o c c u r in m esial d ire c tio n
posing teeth apart and produce open con tacts and posterior displacement of teeth (Fig. 4, below). Frequently, elimination Fig. 4 • A b o v e : A d a p t iv e s p a c in g a n d d riftin g of the steep inclines by cuspal reshaping o f teeth is seen a fte r d e v e lo p m e n ta l m a lp o sit io n in g o f b ic u s p id s a n d loss o f m a n d ib u la r first will permit the teeth once again to ap m olar. Below: In sufficien t s p a c e in arch has p re proximate one another. Therefore, sove n te d the m a n d ib u la r se c o n d b ic u s p id from e r u p tin g into its p ro p e r p ositio n . R e su lta n t in te r called mesial drifting is not the result of a m axillary cu sp a l re la tio n s h ave p re v e n te d m esial systemic regulatory mechanism, but is m o v e m e n t o f m axillary m olars. This in te rfe re n ce rather the result of intercuspal and mus has cre a te d the o p e n c o n ta c t b etw e en m axillary se c o n d b ic u s p id a n d first m olar cular pressures. In addition, the anterior movement is not universally present, but rather is seen only with an intact arch jority of teeth, certain factors may be or arch segment (Fig. 5). present which do not permit this to occur in all instances. When contact is broken M A LPOSITION ING OF T EE TH after the loss of a tooth, this force is no longer operable. A single unopposed tooth Malpositioning is another type of adap will not migrate mesially but will move tive tooth movement to be considered occlusally or remain more or less constant (Fig. 6, above left and below left; Fig. 7, in its position. W ith the loss of a m an above left and below le ft). A tooth may dibular first molar, the adjacent m an be out of normal alignment as a result of dibular first and second bicuspids fre either a developmental or an acquired quently will move distally (Fig. 4, above). defect. Malpositioned tooth buds and an Similarly, a maxillary second molar fre uncoordinated eruptive pattern between quently will move distally after the ex maxillary and mandibular teeth are two traction of the adjacent third molar. An possible mechanisms of developmental other example of distal movement is seen malpositioning.15 where steep plunger cusps, the result of Developmental deviations of tooth bud excessive tensional clenching, wedge op position may result in :
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1. Spacing between two or more teeth. 2. Labial, buccal, lingual, mesial, dis tal, infraclusal or supraclusal positioning of one or more teeth. 3. Rotational deviation of a tooth. A faulty eruptive pattern may pro duce : 1. Cross-bite between maxillary and m andibular teeth. 2. Lingual version of a mandibular posterior tooth where the buccal cusps are lingual to the lingual cusps of its antagonist. 3. Supraclusion of one tooth and infraclusion of its opposing member. 4. Labial, lingual, mesial, or distal positioning of a mandibular or maxillary tooth due to crowding, resulting either from premature loss or prolonged reten tion of a deciduous tooth affecting the ultimate position of its permanent counterpart. It also may result from in sufficient room in the mandible or
maxilla to accommodate the entire denti tion.15 Malpositioned teeth may show con siderable mobility after occlusal contact is established, primarily as a result of rocking during the various m andibular excursive movements. Tooth movement is also seen associated with malpositioning after an acquired disability such as the extraction of a tooth with resultant shift ing of the adjacent and opposing teeth or by the adoption of any habit producing excessive occlusal wear. Tensional clench ing and bruxism may cause spacing as a result of the wedging action of steeply worn cuspal inclines and ridges. A malpositioned tooth may be con sidered as successfully adapted to its func tional environment if it becomes firmly anchored in a healthy periodontium, even though it is malaligned. However, if mo bility and concomitant signs of periodon tal breakdown continue, it must be recog
Fig. 6 • W o m a n , a g e d 40. D e v e lo p m e n ta l m a lp o s it io n in g a n d s u b s e q u e n t re a c tiv e p o s it io n in g o f righ t a n d left m axillary a n d m a n d ib u la r c u s p id s afte r c o m p le te p e rio d o n ta l th e ra p y . In a d d itio n , a re d u ctio n in d e g re e o f o v e rb it e is noted . N o o r t h o d o n t ic a id s w ere used to p ro d u c e to o th m o v e m e n t
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F ig. 7 • M a n , a g e d 28. D e v e lo p m e n ta l m a lp o s itio n in g a n d s u b se q u e n t re a c tiv e p o s it io n in g o f righ t m a xillary lateral in c is o r a fte r c o m p le te p e r io d o n t a l th e ra p y . N o o r t h o d o n t ic a id s w ere used to p r o d u c e to o th m o v e m e n t
nized that adaptation is lacking and a Therefore, the forces which prevent the desired repositioning of the affected pathologic condition exists.7 tooth must be recognized and eliminated in order to permit the ultimate favorable REACTIVE PO SITIO N IN G solution. A typical example of such an The final type of adaptive tooth move interfering mechanism is seen when in ment is reactive positioning (Fig. 6, above creased sensitivity of a partially adjusted right and below right; Fig. 7, above right tooth may cause the patient to avoid the and below right).15' 16 This refers to the affected side, thereby inducing unilateral inherent tendency of malposed teeth to function.1 The teeth on the unused side assume a new position in the dental arch have been observed to extrude, thereby with the elimination of the forces which preventing harmonious bilateral function originally induced the malalignment. The during the various m andibular move new position is usually more favorable ments. Only after the involved surfaces than the one which existed prior to have been adequately desensitized and re therapy. However, it has been observed shaped will the ultimate favorable posi recently that an intermediate position tion of the teeth be reached. may be reached prior to the final reposi The process whereby reactive position tioning. This intermediate position may ing occurs involves continuous tooth produce an interceptive contact during eruption, integrated action between the any of the m andibular movements and tongue, cheeks and other elements of the thus may create an unstable occlusion. masticatory musculature, and favorable
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interocclusal contact relationships as gov erned by the movement patterns of the mandible. Therapy required to induce re active positioning includes all necessary procedures to eliminate the cause and ef fect of the disease process, as would be necessary for any patient with periodontal disease not possessing malposed teeth. However, additional emphasis must be placed on the phase of occlusal reshaping so that the tooth movement may be anticipated, observed and directed. Several treatment considerations are vital to successful reactive positioning:1“ 1. Occlusal trauma as either a primary or secondary factor usually contributes to acquired tooth malpositioning. Pocket formation with its concomitant exuberant granulomatous tissue formation also may be important in promoting pathologic tooth migration. From the clinical view point, however, it would seem that pocket formation by itself produces tooth mal alignment much less frequently than does the combination of occlusal trauma and pocket formation. 2. Sufficient mesiodistal space must exist to receive the malposed tooth. 3. The blocking forces must be re duced or eliminated in order to allow for movement. 4. Sufficient tooth structure must re main after the reshaping of the blocking force. 5. Routine periodontal therapy plus occlusal equilibration must be utilized in order to realize maximum results. 6. Varying degrees of reactive posi tioning are possible rather than only an all-or-none response to the removal of the disruptive force. 7. Occlusal adjustments must be re peated as the malposed teeth move into new positions to achieve the most favor able results. 8. Reactive positioning may be antici pated either in the presence or absence of mobility of a malposed tooth. However,
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although repositioning is easily induced in an extremely mobile tooth, its post positioning prognosis is less favorable un less it can be adequately stabilized after treatment. SUM M ARY
1. Knowledge of the various patterns of tooth movement is important to the practice of all phases of dentistry. 2. Endogenous tooth movement refers to all types of tooth movement which are primarily the result of intrinsic local or systemic regulatory mechanisms. 3. Exogenous tooth movement implies that the movement follows the applica tion of force by an extrinsic object or appliance. 4. Endogenous tooth movement may result from either physiologic or patho logic forces. 5. There are three primary patterns of endogenous tooth movement: the re sponse to a systemic regulatory mecha nism (tooth eruption) ; the result of failure of a weakened attachment appa ratus to support a tooth properly in its alveolus (migration as seen in periodon tosis) ; and the result of adaptation of a tooth to its functional environment. Adaptive tooth movement is controlled by the contact relationships between ad jacent and opposing teeth, by the inter action of the various components of the masticatory musculature, and by the ef fect of the movement pattern of the man dible as governed by the temporoman dibular joint, the musculature and the teeth. 6. Four examples of adaptive move ment are observed; namely, functional rocking during masticatory and nonmasticatory mandibular movements, mesial drifting resulting from the anterior com ponent of force, malpositioning of teeth due to developmental or acquired fac tors, and the reactive positioning of mal posed teeth. /
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^Assistant professor, department of periodontia and oral medicine; assistant clinical professor, department of oral pathology, New York University C ollege Den tistry. 1. Miller, S. C. Textbook of periodontia, ed. 3. Philadelphia, Blakiston Co., 1950, p. 72-75. 2. Sorrin, S. Habit, an etiologic factor of periodontal disease. D. Digest 41:290 Sept. 1935. 3. Glickman, I. Periodontosis, a critical evaluation. J.A.D.A. 44:706 June 1952. 4. Miller, S. C. Precocious advanced alveolar atrophy. J. Periodont. I9:i46 Oct. 1948. 5. Ross, I. F.; Kupperman, H. S., and Miller, S. C. Endocrine and laboratory studies on precocious a d vanced alveolar atrophy; a prelimiarny report. J.A.D.A. 51:585 Nov. 1955. 6. Glickman, Irving. Clinical periodontology. Phila delphia, W . B. Saunders Co.. 1953, p. 305-311. 7. Cohen, D. W. Personal communication, March 1958. 8. Wentz. F. M.; Jarabak, J., and Orban, B. Experi mental occlusal trauma imitating cuspal interferences. J. Periodont. 29:117 A pril 1958.
df
9. Bhaskar, S. N., and Orban, B. Experimental occlusat trauma. J. Periodont. 26:270 Oct. 1955. 10. Glickman, I., and Weiss, L. A . Role of trauma from occlusion in initiation of periodontal pocket for mation in experimental animals. J. Periodont. 26:14 Jan. 1955. 11. Stahl, S. S.; Müler, S. C., and Goldsmith, E. D. Effects of vertical occlusal trauma on periodontium of protein deprived young adult rats. J. Periodont. 28:87 A pril 1957. 12. Waerhaug, J. Pathogenesis of pocket formation in traumatic occlusion. J. Periodont. 26:107 A p ril 1955. 13. Stahl S. S. Personal communication, December 1957. 14. Hemley, Samuel. Orthodontic therapy and prac tice. New York, Grune & Stratton, 1953, p. 259-270. 15. Ross, I. F. Reactive tooth positioning. Oral Surg., Oral Med. & Oral Path. 10:725 July 1957. 16. Ross, I. F. Considerations governing choice of treatment of periodontal diseases. J. Periodont. 29:37 Jan. 1958.
Compressive properties of hard tooth tissues and some restorative materials
John W. Stanford * M .S .; K eith V. W eigel;* George C. Paffenbarger,* D.D.S., and W. T. Sweeney ,f A.B., Washington, D. C.
Improved methods of preparing and test ing specimens of hard tooth tissue to de termine their modulus of elasticity, pro portional limit and strength have yielded more precise data than were hitherto available. The compressive properties of enamel appear to depend on the orientation of the specimens in the tooth. Enamel is stiffer than dentin. The com pressive properties of deciduous enamel and dentin are similar to those of enamel and dentin from permanent teeth. The stiffness of enamel is. higher than that of the restorative materials tested, with the exception of the medium and hard inlay casting gold alloys.
A knowledge of the compressive proper ties of hard tooth tissues may be of assist ance in designing cavity preparations, in evaluating dental filling materials, in demonstrating possible physical changes in teeth with age, in pulp disease and death and in different environments of development. A review of previous de terminations of compressive properties of hard tooth tissues was presented in 1958.1 At about the time of that report data were published by Craig and Peyton2 on the elastic and mechanical properties of human dentin giving values of 2.4 X 10® to 2.7 X 10® psi for modulus of elasticity, 24,200 psi for proportional limit and 43,100 psi for compressive strength. These
1. Johnstone, M . The human cardiovascular response to fluothane anaesthesia. Brit. J. Anaesth. 28:392 Sept. 1956. 2. Chang, J.; Macartney, H. H., and Graves, H. B. Clinical experience with fluothane. J. Canad. Anaesth. Soc. 4:187 July 1957. 3. MacKay, I. M. Clinical evaluation of fluothane with special reference to a controlled vaporizer. J. Canad. Anaesth. Soc. 4:235 July 1957. 4. Sadove, M. S., and others. Ethyl vinyl ether in
/
dental anesthesia: preliminary report. J.A.D.A. 51:536 Nov. 1955. 5. Stephen, C. R., and others. Evaluation of fluothane for clinical anaesthesia. J. Canad. Anaesth. Soc. 4:246 July 1957. 6. Severinghaus, J. W., and Cullen, S. C. Depression of myocardium and body oxygen consumption with fluo thane, Anesthesiology 19:165 March-April 1958. 7. Burnap, T. K.; Galla, S. J., and Vandam, L. D. Anesthetic, circulatory and respiratory effects of fluo thane. Anesthesiology 19:307 May-June 1958.
Endogenous tooth movement
Ira Franklin Ross* D.D.S., New York
The three types of endogenous tooth movement are (1) the continuous erup tion of teeth, (2) migration due to in herent weakness of the attachment appa ratus, and (3) the adaptive movements of the teeth. Adaptive tooth movement is controlled by: (I ) the contact relation ships between adjacent and opposing teeth, and (2) the interaction of the com ponents of the masticatory musculature. Knowledge of the various patterns of tooth movement is important to the prac tice of all phases of dentistry. Tooth movement is important to all phases of dentistry. In the past, its study has been associated primarily with the practice of orthodontics. Recently, how ever, increased knowledge of the various nuances of tooth repositioning has en abled each branch of dentistry to ap preciate its relationship to the problem. For example, the placement of a restora tion in a single tooth can induce move ment either of that tooth or of opposing teeth if the restoration is not in harmony with its environment. Further, a partial
denture may create a change in tooth position as a result of torque from a clasp, from excessive pressure against con tiguous teeth or as a result of ridge resorp tion under the saddle areas.1 The extrac tion of a tooth will create space into which neighboring teeth can migrate un less prevented by some obstructive force such as steep intercuspation. All these situations can lead to periodontal de struction in the region and additional mobility of teeth. Two types of tooth movement have been observed; one is the result of forces produced by. an external mechanism or appliance which is introduced into the oral cavity. This may be called exogenous tooth movement. The force may be a short sudden one, as with a blow, or may be a series of longer intermittent ones as observed when an orthodontic appliance is used or when a habit such as threadbiting or pencil-biting is practiced. Only those habits which include the introduc tion of an extraoral object into the mouth may be considered as capable of pro ducing exogenous movement.2 The second type of tooth movement is the result of forces produced by mecha nisms from within the oral cavity. This is
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endogenous tooth movement. Examples are the continuous eruption of teeth, mi gration due to an inherent weakness in the attachm ent apparatus of the tooth as seen in periodontosis, and the adaptive movements resulting from interocclusal contacts and muscular activity. No direct external moving force has been applied to these teeth. Movement following the reshaping of teeth by grinding or the re moval of granulomatous tissue from a periodontal pocket is endogenous in character because here the change in tooth position is primarily the result of a change in the contact relationships of the teeth or in the surrounding periodontal structures. The instruments used, namely the grinding stone and the curet, do not in themselves exert force, as would be the case in exogenous tooth movement, but they do aid in changing the functional environment of the tooth. The condition of the teeth, the periodontium, and the surrounding oral mucosa which results from all constitutional, physiologic and pathologic factors may be called the functional environment. The many varieties of endogenous movements may be grouped into three distinct patterns. The first is the response to a systemic regulatory mechanism. The second is the result of the failure of a weakened attachm ent apparatus to sup port the tooth properly in its alveolus. The third type is an adaptive one, acti vated and controlled by contact relation ships between adjacent and opposing teeth, by the interaction of the various components of the masticatory muscula ture, and by the effect of the movement pattern of the mandible as governed by the temporomandibular joint, the muscu lature and the teeth.
lyst, possibly endocrine in nature, stimu lates the developing tooth to move occlusally until contact with its antagonist is made. Despite strong opposition this same force may continue throughout the life of the tooth, moving it occlusally as its morsal surfaces are worn. If the antagonist is lost, thereby removing the inhibiting ef fect, the eruptive force again may elevate the tooth until the opposing gingiva pre vents further movement (Fig. 1). Fre quently, however, the unopposed tooth will cease moving before the opposite gin giva is reached, indicating that possibly the eruptive force is no longer operable. Moreover, the cessation of continuous eruption after apparent removal of the obvious deterrent may also be the result of ankylosis of the tooth in its socket, bulbous root formation, a powerful biting
TO O TH ERUPTION
The first type of endogenous movement, that governed by a systemic regulatory mechanism, is seen in the phenomenon of tooth eruption. Here an unknown cata
Fig. I • S tre n g th o f e ru p tiv e fo rc e of a d u lt d e n tition. A b o v e : U n o p p o s e d m a n d ib u la r th ird m olar w h ich is ex tru d e d fa r b e y o n d o c clu sa l level o f a d ja c e n t teeth. Below: U n o p p o s e d m axillary first m o lar has ex tru d e d d e sp ite re stra in in g effe ct o f c o n ta c t with a d ja c e n t teeth
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habit such as pipestem biting or tongue thrusting, or a combination of tongue and cheek pressures. As the eruptive move ment continues throughout life, the alveolar structures may grow with the tooth or the movement may be a simple extrusion without alveolar growth. MIGRATION BECAUSE OF W EA K N E SS OF PERIODONTIUM
The next type of endogenous movement is the extremely rare wandering of teeth observed in patients with precocious ad vanced alveolar atrophy or periodon tosis.3'5 Glickman6 states that this may result from “degeneration of the perio dontal fibers, inadequacy in the con tinuous deposition of cementum or loss of alveolar bone.” The teeth which most frequently exhibit this type of migration are the maxillary and m andibular central and lateral incisors, although on occasion posterior teeth, particularly the maxillary and m andibular first molars, may be similarly affected. Once the primary periodontal defect has occurred, sec ondary factors such as occlusal trauma, habits, and exuberant granulomatous tissue in a periodontal pocket may cause further migration. It is important to dif ferentiate between this type of movement resulting from an intrinsic lack of tissue integrity modified by secondary factors, and types of movement showing similar clinical migration where the initiating factor is an abnormal habit or food im paction mechanism leading to periodontal destruction.2
to its environment. This may be a re versible reaction. If the tooth moves away sufficiently from the force which origi nally induced the movement, or if the forces themselves are reduced, the tooth may again become firm in its socket. I’his would indicate a regaining of adaptation. If the tooth cannot move out of the orbit of these traum atic forces, mobility will increase as a result of the increased perio dontal destruction. Several examples of adaptive tooth movement have been noted; namely, the limited buccolingual rocking of a tooth in its alveolus during both masticatory and nonmasticatory m andibular move ment, the mesial drifting of teeth result ing from the anterior component of
ADAPTIVE T O O TH M OVEM ENT
Adaptive tooth movement occurs as a result of physiologic accommodation to the forces of interocclusal contact and muscular activity. When these forces ex ceed physiologic limits, destruction of the supporting tissues occurs. From this point on, the tooth will exhibit perceptible mo bility, and will have lost its adaptability
Fig. 2 • V a rio u s a sp e cts o f m esial m o v e m e n t of teeth. A b o v e : M e s ia l in c lin a tio n o f m a n d ib u la r m olars .can b e seen. T h e ir ro o t s p a c in g an d c u r v a tu re s u g g e s t a s tro n g b ra c in g effe ct w hich p re v e n ts excessive tooth m ovem en t. Below : M e sia l in clin a tio n o f b o th m axillary a n d m a n d ib u la r teeth is seen. A n g le s a t which teeth m eet in ce n tric o c c lu sio n are ex trem ely im p o rta n t in p ro d u c in g s u b s e g u e n t m o v e m e n t o f teeth
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stresses exceeds that which can be toler ated by the periodontium and if gingival inflammation is present, damage may occur which implies loss of adaptation of the tooth to its environment.1,7,8 Destruc tive changes on the pressure sides of the alveoli of experimental animals have been described as necrosis of the periodontal ligament fibers, thrombosis of the vessels in the ligament, and osteoclasis of the walls of the alveoli. The tension sides showed widening of the periodontal mem brane, thrombosis and bone formation.9 12 Stahl13 recently described similar changes in a hum an periodontium where the oc clusal force was directed against the crown of a molar tooth adjacent to the space of a previously extracted tooth. This force was directed primarily in the mesial direction and produced tipping which resulted in a definite pressure area on the mesial aspect and a definite tension zone on the distal aspect of the traum a tized tooth. However, when intermittent Fig. 3 • A b o v e : M e s ia l m o v e m e n t o f b oth m a n tooth rocking occurs in a buccolingual d ib u la r m ola rs can be seen a fte r loss o f m a n d ib u la r first m olar. M a x illa r y first m o la r has direction as a result of mastication, swal extruded, d e m o n stra tin g fo rc e o f co n tin u o u s e r u p lowing or tensional clenching, and where tion. Below: A d a p t iv e tooth m o v e m e n t o f m a n d ib u la r teeth is n o te d a fte r loss o f m a n d ib u la r alveolar support is insufficient, the de first m olar. S e c o n d m o la r has m o v e d m esially and structive changes previously described b ic u s p id s ha ve a lso sh ifte d th e ir p o sitio n s. L atter will not have an opportunity to progress c h a n g e is in d ic a t e d b y op e n c o n t a c t betw een c u s p id a n d first b ic u s p id a n d b y axial in clin a tio n into the healing phase, and increased o f se c o n d b ic u s p id bone loss may occur. Inasmuch as exces sive tooth rocking resulting from tensional clenching and grinding is observed so force, the malpositioning of teeth due to frequently, it is postulated that the re blocking or moving occlusal interferences, sultant lack of periodontal healing com and the reactive positioning of malposed bined with the bone loss associated with gingival inflammation is responsible for teeth. the bone loss in many persons with chronic periodontal disease. FU NCTIO N A L ROCKING Functional buccolingual rocking and de pression of a tooth in its alveolus as a re sult of interocclusal contact is an adaptive physiologic activity. It is usually clinically imperceptible and is thought to be a pro tective mechanism, preventing the frac ture of the tooth by the distribution of the effects of occlusal stress throughout the periodontium. If the effect of occlusal
M ESIAL AND DISTAL M OVEM ENTS
Mesial drifting of teeth due to the an terior component of force is the next type of endogenous tooth movement which re sults from the interplay between inter occlusal contacts and masticatory muscu lature (Fig. 2, 3 ).14 Although mesial drifting is observed with the great ma-
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Fig. 5 • A d a p t iv e tooth m o v e m e n t is n oted in b o th m a n d ib le a n d m axilla. Loss o f m axillary se c o n d b ic u s p id a n d m a n d ib u la r first m o la r has p ro d u c e d d ista l m o v e m e n t o f m axillary first b i c u s p id a n d m esial m o v e m e n t o f m axillary first m o la r a n d m a n d ib u la r se c o n d a n d third m olars. This d e m o n stra te s th a t m o v e m e n t is a re a c tio n to sp e cific fo rc e s a n d d o e s n ot alw ays o c c u r in m esial d ire c tio n
posing teeth apart and produce open con tacts and posterior displacement of teeth (Fig. 4, below). Frequently, elimination Fig. 4 • A b o v e : A d a p t iv e s p a c in g a n d d riftin g of the steep inclines by cuspal reshaping o f teeth is seen a fte r d e v e lo p m e n ta l m a lp o sit io n in g o f b ic u s p id s a n d loss o f m a n d ib u la r first will permit the teeth once again to ap m olar. Below: In sufficien t s p a c e in arch has p re proximate one another. Therefore, sove n te d the m a n d ib u la r se c o n d b ic u s p id from e r u p tin g into its p ro p e r p ositio n . R e su lta n t in te r called mesial drifting is not the result of a m axillary cu sp a l re la tio n s h ave p re v e n te d m esial systemic regulatory mechanism, but is m o v e m e n t o f m axillary m olars. This in te rfe re n ce rather the result of intercuspal and mus has cre a te d the o p e n c o n ta c t b etw e en m axillary se c o n d b ic u s p id a n d first m olar cular pressures. In addition, the anterior movement is not universally present, but rather is seen only with an intact arch jority of teeth, certain factors may be or arch segment (Fig. 5). present which do not permit this to occur in all instances. When contact is broken M A LPOSITION ING OF T EE TH after the loss of a tooth, this force is no longer operable. A single unopposed tooth Malpositioning is another type of adap will not migrate mesially but will move tive tooth movement to be considered occlusally or remain more or less constant (Fig. 6, above left and below left; Fig. 7, in its position. W ith the loss of a m an above left and below le ft). A tooth may dibular first molar, the adjacent m an be out of normal alignment as a result of dibular first and second bicuspids fre either a developmental or an acquired quently will move distally (Fig. 4, above). defect. Malpositioned tooth buds and an Similarly, a maxillary second molar fre uncoordinated eruptive pattern between quently will move distally after the ex maxillary and mandibular teeth are two traction of the adjacent third molar. An possible mechanisms of developmental other example of distal movement is seen malpositioning.15 where steep plunger cusps, the result of Developmental deviations of tooth bud excessive tensional clenching, wedge op position may result in :
R O SS . . . V O L U M E 60, JU N E I960 • 63/743
1. Spacing between two or more teeth. 2. Labial, buccal, lingual, mesial, dis tal, infraclusal or supraclusal positioning of one or more teeth. 3. Rotational deviation of a tooth. A faulty eruptive pattern may pro duce : 1. Cross-bite between maxillary and m andibular teeth. 2. Lingual version of a mandibular posterior tooth where the buccal cusps are lingual to the lingual cusps of its antagonist. 3. Supraclusion of one tooth and infraclusion of its opposing member. 4. Labial, lingual, mesial, or distal positioning of a mandibular or maxillary tooth due to crowding, resulting either from premature loss or prolonged reten tion of a deciduous tooth affecting the ultimate position of its permanent counterpart. It also may result from in sufficient room in the mandible or
maxilla to accommodate the entire denti tion.15 Malpositioned teeth may show con siderable mobility after occlusal contact is established, primarily as a result of rocking during the various m andibular excursive movements. Tooth movement is also seen associated with malpositioning after an acquired disability such as the extraction of a tooth with resultant shift ing of the adjacent and opposing teeth or by the adoption of any habit producing excessive occlusal wear. Tensional clench ing and bruxism may cause spacing as a result of the wedging action of steeply worn cuspal inclines and ridges. A malpositioned tooth may be con sidered as successfully adapted to its func tional environment if it becomes firmly anchored in a healthy periodontium, even though it is malaligned. However, if mo bility and concomitant signs of periodon tal breakdown continue, it must be recog
Fig. 6 • W o m a n , a g e d 40. D e v e lo p m e n ta l m a lp o s it io n in g a n d s u b s e q u e n t re a c tiv e p o s it io n in g o f righ t a n d left m axillary a n d m a n d ib u la r c u s p id s afte r c o m p le te p e rio d o n ta l th e ra p y . In a d d itio n , a re d u ctio n in d e g re e o f o v e rb it e is noted . N o o r t h o d o n t ic a id s w ere used to p ro d u c e to o th m o v e m e n t
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F ig. 7 • M a n , a g e d 28. D e v e lo p m e n ta l m a lp o s itio n in g a n d s u b se q u e n t re a c tiv e p o s it io n in g o f righ t m a xillary lateral in c is o r a fte r c o m p le te p e r io d o n t a l th e ra p y . N o o r t h o d o n t ic a id s w ere used to p r o d u c e to o th m o v e m e n t
nized that adaptation is lacking and a Therefore, the forces which prevent the desired repositioning of the affected pathologic condition exists.7 tooth must be recognized and eliminated in order to permit the ultimate favorable REACTIVE PO SITIO N IN G solution. A typical example of such an The final type of adaptive tooth move interfering mechanism is seen when in ment is reactive positioning (Fig. 6, above creased sensitivity of a partially adjusted right and below right; Fig. 7, above right tooth may cause the patient to avoid the and below right).15' 16 This refers to the affected side, thereby inducing unilateral inherent tendency of malposed teeth to function.1 The teeth on the unused side assume a new position in the dental arch have been observed to extrude, thereby with the elimination of the forces which preventing harmonious bilateral function originally induced the malalignment. The during the various m andibular move new position is usually more favorable ments. Only after the involved surfaces than the one which existed prior to have been adequately desensitized and re therapy. However, it has been observed shaped will the ultimate favorable posi recently that an intermediate position tion of the teeth be reached. may be reached prior to the final reposi The process whereby reactive position tioning. This intermediate position may ing occurs involves continuous tooth produce an interceptive contact during eruption, integrated action between the any of the m andibular movements and tongue, cheeks and other elements of the thus may create an unstable occlusion. masticatory musculature, and favorable
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interocclusal contact relationships as gov erned by the movement patterns of the mandible. Therapy required to induce re active positioning includes all necessary procedures to eliminate the cause and ef fect of the disease process, as would be necessary for any patient with periodontal disease not possessing malposed teeth. However, additional emphasis must be placed on the phase of occlusal reshaping so that the tooth movement may be anticipated, observed and directed. Several treatment considerations are vital to successful reactive positioning:1“ 1. Occlusal trauma as either a primary or secondary factor usually contributes to acquired tooth malpositioning. Pocket formation with its concomitant exuberant granulomatous tissue formation also may be important in promoting pathologic tooth migration. From the clinical view point, however, it would seem that pocket formation by itself produces tooth mal alignment much less frequently than does the combination of occlusal trauma and pocket formation. 2. Sufficient mesiodistal space must exist to receive the malposed tooth. 3. The blocking forces must be re duced or eliminated in order to allow for movement. 4. Sufficient tooth structure must re main after the reshaping of the blocking force. 5. Routine periodontal therapy plus occlusal equilibration must be utilized in order to realize maximum results. 6. Varying degrees of reactive posi tioning are possible rather than only an all-or-none response to the removal of the disruptive force. 7. Occlusal adjustments must be re peated as the malposed teeth move into new positions to achieve the most favor able results. 8. Reactive positioning may be antici pated either in the presence or absence of mobility of a malposed tooth. However,
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although repositioning is easily induced in an extremely mobile tooth, its post positioning prognosis is less favorable un less it can be adequately stabilized after treatment. SUM M ARY
1. Knowledge of the various patterns of tooth movement is important to the practice of all phases of dentistry. 2. Endogenous tooth movement refers to all types of tooth movement which are primarily the result of intrinsic local or systemic regulatory mechanisms. 3. Exogenous tooth movement implies that the movement follows the applica tion of force by an extrinsic object or appliance. 4. Endogenous tooth movement may result from either physiologic or patho logic forces. 5. There are three primary patterns of endogenous tooth movement: the re sponse to a systemic regulatory mecha nism (tooth eruption) ; the result of failure of a weakened attachment appa ratus to support a tooth properly in its alveolus (migration as seen in periodon tosis) ; and the result of adaptation of a tooth to its functional environment. Adaptive tooth movement is controlled by the contact relationships between ad jacent and opposing teeth, by the inter action of the various components of the masticatory musculature, and by the ef fect of the movement pattern of the man dible as governed by the temporoman dibular joint, the musculature and the teeth. 6. Four examples of adaptive move ment are observed; namely, functional rocking during masticatory and nonmasticatory mandibular movements, mesial drifting resulting from the anterior com ponent of force, malpositioning of teeth due to developmental or acquired fac tors, and the reactive positioning of mal posed teeth. /
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^Assistant professor, department of periodontia and oral medicine; assistant clinical professor, department of oral pathology, New York University C ollege Den tistry. 1. Miller, S. C. Textbook of periodontia, ed. 3. Philadelphia, Blakiston Co., 1950, p. 72-75. 2. Sorrin, S. Habit, an etiologic factor of periodontal disease. D. Digest 41:290 Sept. 1935. 3. Glickman, I. Periodontosis, a critical evaluation. J.A.D.A. 44:706 June 1952. 4. Miller, S. C. Precocious advanced alveolar atrophy. J. Periodont. I9:i46 Oct. 1948. 5. Ross, I. F.; Kupperman, H. S., and Miller, S. C. Endocrine and laboratory studies on precocious a d vanced alveolar atrophy; a prelimiarny report. J.A.D.A. 51:585 Nov. 1955. 6. Glickman, Irving. Clinical periodontology. Phila delphia, W . B. Saunders Co.. 1953, p. 305-311. 7. Cohen, D. W. Personal communication, March 1958. 8. Wentz. F. M.; Jarabak, J., and Orban, B. Experi mental occlusal trauma imitating cuspal interferences. J. Periodont. 29:117 A pril 1958.
df
9. Bhaskar, S. N., and Orban, B. Experimental occlusat trauma. J. Periodont. 26:270 Oct. 1955. 10. Glickman, I., and Weiss, L. A . Role of trauma from occlusion in initiation of periodontal pocket for mation in experimental animals. J. Periodont. 26:14 Jan. 1955. 11. Stahl, S. S.; Müler, S. C., and Goldsmith, E. D. Effects of vertical occlusal trauma on periodontium of protein deprived young adult rats. J. Periodont. 28:87 A pril 1957. 12. Waerhaug, J. Pathogenesis of pocket formation in traumatic occlusion. J. Periodont. 26:107 A p ril 1955. 13. Stahl S. S. Personal communication, December 1957. 14. Hemley, Samuel. Orthodontic therapy and prac tice. New York, Grune & Stratton, 1953, p. 259-270. 15. Ross, I. F. Reactive tooth positioning. Oral Surg., Oral Med. & Oral Path. 10:725 July 1957. 16. Ross, I. F. Considerations governing choice of treatment of periodontal diseases. J. Periodont. 29:37 Jan. 1958.
Compressive properties of hard tooth tissues and some restorative materials
John W. Stanford * M .S .; K eith V. W eigel;* George C. Paffenbarger,* D.D.S., and W. T. Sweeney ,f A.B., Washington, D. C.
Improved methods of preparing and test ing specimens of hard tooth tissue to de termine their modulus of elasticity, pro portional limit and strength have yielded more precise data than were hitherto available. The compressive properties of enamel appear to depend on the orientation of the specimens in the tooth. Enamel is stiffer than dentin. The com pressive properties of deciduous enamel and dentin are similar to those of enamel and dentin from permanent teeth. The stiffness of enamel is. higher than that of the restorative materials tested, with the exception of the medium and hard inlay casting gold alloys.
A knowledge of the compressive proper ties of hard tooth tissues may be of assist ance in designing cavity preparations, in evaluating dental filling materials, in demonstrating possible physical changes in teeth with age, in pulp disease and death and in different environments of development. A review of previous de terminations of compressive properties of hard tooth tissues was presented in 1958.1 At about the time of that report data were published by Craig and Peyton2 on the elastic and mechanical properties of human dentin giving values of 2.4 X 10® to 2.7 X 10® psi for modulus of elasticity, 24,200 psi for proportional limit and 43,100 psi for compressive strength. These