Irving M. Sheppard, Montefiore Hospital
DAD.,* and Stephen M. Sheppard** and Medical Center, New York, N. Y.
I-h e su b’Ject of occlusion for complete dentures is complicated by various theories and confusing terminoloXgy. lP4For example, centric occlusion, long considered a convenience position requiring correction to harmonize with centric relation, has more recently been applied to the latter. 5l G To further complicate the problem of denture occlusion, studies of this subject generally involve new, retentive, and stable bases.‘, * In view of the changes known to take place in the supporting tissues3 lo and the length of time dentures remain in use, the occlusal function of such new, ideal prostheses may not be representative of most denture wearers. The possibility that occlusal function may be a factor in the deterioration of supporting tissues indicates that a representative sampling of the function of denture wearers might provide useful information. Therefore, this article describes a study that was conducted to determine mandibular position during function utilizing primarily persons who had been wearing their dentures for an extended period of time. CONFUSION
In pursuing this study, it became evident that the terminology necessary for an occlusal reference position is indeed confusing. Centric occlusion, in addition to being used for two different positions, implies the precision of centricity of a geometric figure. Intercuspal position involves cusps, making this term less definitive in subjects with flat teeth, no teeth at all, or occlusion rims. “Habitual” position implies its use for good and/or poor habits. “Convenience centric” position implies that it is not correct and is being used as an improper substitute. Centric relation is generally an imposed, artificially obtained, maxillomandibular relationship inassociated with temporomandibular joint volving a retruded condyle position, This report IIealth, United
supported by Public Health
From the Dental Department and the Division of Diagnostic Radiology, tal and Medical Center, New York, N. Y. *Research Attending, Mont&ore Hospital and Medical Center, New **Research
Montefiore York, York,
dysfunction and discomfort.ll-l3 If it is considered to be a border position, centric relation is hardly “central,” nor is a retruded position “central.“1 Terminal hinge position is similarly questionable, inasmuch as it is obtained by rotation of the condyles, a motion not found during function of living human beings except in relatively rare instances of duress, disease, or injury.11-16 The term “functional occlusal” position seems more physiologic but requires opposing tooth contact. SWALLOWING
AS A REFERENCE
The multiplicity of terms, their basic errors of description, hazardous relationships with abnormality, lack of universal application (edentulous infants, adults), implications of a consistent precision and repeatability unusual for living human subjects,4* I17 I7 and general failure to adequately describe the basic maxillomandibular position or its function-all this causes us to question their usefulness. However, the position of the mandible during swallowing seems applicable. Swallowing is apparently a type of survival mechanism which persists in spite of mandibulectomies, removal of most of the tongue, and absence of condyles. Swallowing occurs during the day and night and involves occlusal contacts of considerably longer duration than those of mastication.1s-20 Cinefluorographic viewing of approximately 1,000 subjects gives the impression that the mandible braces itself against the maxillae during swallowing to counteract the posteriorly directed propulsive thrust of the bolus into the esophagus. The mobile mandible conceivably, and sometimes visibly, moves anteriorly with such thrusts. Where teeth or opposing tooth contacts are absent, the tongue is interposed between the maxillae and mandible, apparently for bracing purposes. While opposing edentulous ridges may contact or approach contact during mastication, they do not do so during swallowing.23 ATYPICAL
Atypical swallowing tends to occur without opposing tooth contact. The aberrant tongue movements and positions involved in atypical swallowing have long been associated with distortions of arch form familiar to orthodontists. That such muscular patterns may persist through adulthood to the denture stage is not generally recognized except perhaps by periodontists. The possible impact of such atypical muscular activity upon movable denture bases requires serious consideration. The patient who wears complete dentures and swallows atypically warrants inclusion in the definition of the basic maxillomandibular relationship even though he does not bring his opposing teeth into contact with each swallow. BRACING
USED AS A FUNCTIONAL
In view of the need for a descriptive functional term, free of geometric implications, as variable as other human functions, and applicable to any oral situation, the term “bracing” position was used in this study. The bracing position is synonymous with the swallowing position, the habitual position, and the intercuspal positions without their limitations. Condyles are not necessary for the bracing position, which can thus be used in subjects with fractured or misplaced condyles, agenesis of the condyles, and mandibulectomies.
.:. Plosthet. Nuvmbrr,
Fig. 1. Dcntnrw
METHODS The subject population consisted of 118 physically and mentally cooperative patients with complete dentures. A comprehensive examination procedure including cephalometric radiographs and cinefluorography was performed for each subject. The mean age of subjects was 60.5 years, the mean age of dentures was 6.4 years, and the mean experience with complete dentures was 12.4 years. Subjects with new dentures one month old or less constituted 10.2 per cent of the group. A majority of the subjects were women- -63.6 per cent. Two lead wires, 1 mm. wide and approximately 10 mm. long, were attached with methyl cyanoacrylate in the bicuspid-molar region of the maxillary and mandibular dentures so as to contact end to end when the mandible was in the bracing position (Fig. 1). The contact of the wires was confirmed or corrected clinically and cinefluoroscopically, by observing them during repeated swallows. Thee subjects were then cinefluorographed in a lateral view without confinement of the head during three functional mandibular sequences. The first sequence consisted of opening and closing mandibular movements under instructions to open and close. The second sequence involved the repeated swallowing of small sips of water. The third sequence involved the eating of an oatmeal cookie. Then, the processed 16 mm. films were viewed frame by frame. All closures were classified according to their anteroposterior positioning, namely, more than I mm. anterior to the bracing position, 1 mm. anterior, 0.5 mm. anterior, at the bracing position, and posterior to the latter. Anteroposterior and posteroantcrior sliding or gliding movements associated with mandibular closures were also recorded. In addition, the failure of the wires to contact upon swallowing was recorded with the swallowing sequence. The incidence of the various locations of closures and supplementary movements was thus obtained. In view of the various combinations found, the subjects were grouped into 14 classifications according to their utilization of various closures.
LOCATION OF MANDIBULAR CLOSURESBY PERCENTAGE OF TOTAL CLOSURES The location of mandibular closures by percentage of total closures is seen in Fig. 2 and Table I. Directed closures totalled 1,192, of which 83.4 per cent were in the bracing position, 15.6 per cent were anterior to the bracing position, and 1.O per cent were posterior to the bracing position. Anteroposterior and posteroanterior movements from the bracing position constituted 1.5 per cent. Closures during swallowing totalled 794, of which 49.4 per cent were in the bracing position, 47.5 per cent involved no contact of opposing teeth, 1.6 per cent were anterior to the bracing position, and 1.5 per cent were posterior to the bracing position. Anteroposterior and posteroanterior movements following closures during swallowing were 2.6 per cent. Masticatory closures occurred with 77.3 per cent in the bracing position, 15.1 per cent anterior to the bracing position, and 7.6 per cent posterior to the bracing position. Posteroanterior movements during mastication were 22.4 per cent. Most of the latter appeared characteristic of excursive movements as seen in the lateral view.
LOCATION OF MANDIBULAR
CLOSURES BY PERCENTAGE OF SUBJECTS
The location of mandibular closures by percentage of subjects is seen in Table II. Directed openings and closings. A substantial percentage of subjects closed exclusively in the bracing position with directed opening and closing (67.8 per cent). Of the remaining subjects, 17.8 per cent closed mostly in the bracing position, with some closures anterior to the bracing position. Some subjects, 11.9 per cent, closed mostly anterior to the bracing position, while a few subjects, 2.5 per cent, closed both in the bracing position and in positions posterior to it. Mandibular position during swallowing. With the swallowing of small sips of water, 33.1 per cent of subjects closed only in the bracing position, 25.4 per cent swallowed without occlusal contact at all, 20.3 per cent swallowed most times without occlusal contact, and 13.6 per cent swallowed most times with the mandible in the bracing position with some no-contact closures. Subjects who swallowed with the mandible both in the bracing position and in positions posterior to it constituted 1.7 per cent. Mandibular position during mastication. The largest group of subjects, 44.1 per cent, used mostly the bracing position for masticatory closures with some closures both anterior and posterior to the bracing position and with some anteroposterior and posteroanterior movements. In the next two largest groups, 16.1 per cent of the subjects used mostly the bracing position with some closures anterior to it, while another 16.1 per cent of the subjects used a combination of the bracing position and positions posterior to it with posteroanterior mandibular movements. Subjects who used only the bracing position in mastication constituted 11 per cent of the group. A smaller group of subjects, 5.9 per cent, used mostly the bracing position with substantial anteroposterior-posteroanterior movements. Another 4.2 per cent of subjects used mostly the bracing position with some closures posterior to the bracing position. A smaller group of 1.7 per cent of the subjects used mostly the bracing position but with a substantial number of closures posterior to it. The
J. lJrostbet. November.
AP PA I
1/‘2 B P APNC PA
Fig. 2. Location of directed swallowing and masticatory closures in percentages; numbers indicate the distance of mandibular closures anterior to the bracing position. (B) The bracing position. (F’) Mandibular closures posterior to the bracing position. (AP-PA) Anteroposteriorposteroanterior sliding mandibular movements. (NC) Mandibular closures with no tooth contact. The predominance of mandibular closures in the bracing position with directed closures is apparent, together with variations essentially anterior to this position. With swallowing, mandibular closures in the bracing position and no contact of teeth predominate. With mastication, mandibular closures in the bracing position also predominate with considerable indicative essentially of excursions. The anteroanteroposterior-posteroanterior movements posterior-posteroanterior movements with directed and swallowing closures were gliding movements rather than excursions.
of mandibular Opening
*B, The terior to the ments.
1 Per cent
56 58 72 994 12
A-l+ mm. A-l mm. A--O.5 mm. B I? No contact
Mastication Per cent
4.7 4.9 6.0 83.4 1.0 -
3 1 9 392 12 377
0.4 0.1 1.1 49.4 1.5 47.5
169 280 567 5,211 518 -
2.5 4.2 8.4 77.3 7.6 - -
A, positions anterior to the bracing AP-PA, anteroposterior-posteroanterior
P, positions posor gliding movc-
Opening and closing
B position only Majority of B + 0.5 mm., 1 mm., l+ mm. anterior Majority of 0.5 mm., 1 mm., l+ mm. anterior B position and P position Majority of B and some no contact No contact only Majority no contact B, 0.5 mm., 1 mm., l+ mm. anterior + no-contact Majority B + substantial P Majority of B + substantial AP-PA movements Majority B, 0.5 mm., 1 mm., 1+ mm., anterior, P, AP-PA movements Majority P, some B 8, Pa AP-PA movements Majority B, some P ‘B, The tcrior to the ments.
67.0 17.8 11.9 2.5
Mastication 11.0 16.1
1.7 13.6 25.4 20.3 5.9 1.7 5.9 44.1 .9 16.1 4.2
A, positions anterior to the bracing AP-PA, anteroposterior-posteroanterior
0.9 per cent closed some closures in the bracing position. remaining
P, positions posor gliding move-
DISCUSSION The aim of this study was to obtain representative information concerning the function of patients who wear dentures. The relatively large sample, the large number of mandibular closures, and the small percentage of subjects with new dentures would seem to make the findings more characteristic of the population of patients who wear dentures. The general similarity of the occlusal contacts to studies
of natural dcntitions using radio telemetry is surprising in view of the relativrl~ gross changes in the structures supporting the dentures, the progressive changes 111 maxillomandibular relations,” the migration of dentureqzl and the sliding. liftirw. and tilting of denture bases that takes place during function.” ‘l’hc findings indicate a lack of uniform constancy of mandibular closure durillo mastication, although 77.3 ljer cent of tllc contacts did occur in thcb bracing /I()sition. The general assumption that an excursivcx movement to centric t-rc~ciusion is uniformly characteristic of function \cas not bornfs out by thr: n1irrrbc.r f )I‘ antc~r‘r~I~osterior-postrro;Interior cscursions as smm frorri ihe I;itc.ral aspect. ‘l‘hc~ .Mulnpticrlj that cuspal confincriient (211 imposf: prrsistcnt \.crtical chewing strokes ,u~ti thui hircsponsibic for the prcdominancca of closurc~s in the bracing position st’ct11:, urllik(.l\ Previous studies”‘, 33 indicator that varying but conventionally shap~~l ztlasticaror\ cycles occurred regardless of cuspal ronfinement or the presencr or absc~lce (!I teeth. The general emphasis on consistently prccisc tooth and jaw relationshiljs SWILL understandable for subjects with substantial rtasidual ridges, t.cttcnti\ c”> stabk dentures, and muscular competency. Jlowevcr, thcrc seems little Iilwlihood that such precise relationships can be maintained for cld(>ntulous patients in th prcsen(‘f* of continuiq retrogressive changes in the basal seats. The cuspal confinetnrnt of such precision could. in time, create more movement of denture bases as the mandible attempted to reach the original position with changed ridges and ;I changed vertical dirnension of occlusion. The movement oi denture bases nlay bc an inlportant factor in the resorption of ridgcks. and the anThe initial ~mpllasis on terior rnigration of dentures might he seriously considcrcd. precise intercusping of opposin, (r teeth is iu contrast to concern for the provision if~r such changes. A previous studyaP employing well-fitting bases and wax occlusion rims: and illvolving 641 mandibular closures durirlg mastication with complete freedom 1.0 close in any position, yicldcd 3 per rent of closures posterior to (he bracing position. The present study of 6,745 masticatory strokes with characteristic variation> in cuspal conformation, retention, and stability yirtldcd 7.6 per cent of inandibular whether the postwiw closures posterior to the bracing position. I‘hus~ it is doubtful position should be considered a basic functional closurcb. It is concrivabic* that sonit‘ of these closures posteriol to the bracing positiont occurring during the maclstrolll of activity that takes place with moving denture bases, rv(>r(’ accidental. A major difference between our findings and those using telemctq is the ii-icidellce of lack of contact of teeth during swallo\vinp. One such study” found no tooth contact in 8 of 62 swallows with the lack of contact occurring mostly in OIU* of six dentulous subjects. iVe found a lack of tooth contact in 377 of 794 swallows. representing a rather gross difference bc:t\veen natllral trrth and dcuturcs. 110~ tooth contacts during the swallowin? of small sips ever , in our study we tabulated of water rather than during the mastication of food. Mastication apparently ITyuires strong bracing of the mandible for the propulsive thrust necessary for swallowing a semisolid bolus: and thus is likely to involve increased occlusal contact. ‘Therr* arc two other possible reasons for the greater incidence of swallowing without tooth contact in our study. First, an unconscious avoidance of ridge pressures may hc
present when a strong posterior propulsive thrust for swallowing is unnecessary. Sensory information pertaining to discomfort or pain resulting from movement of denture bases may act as a deterrent to the complete characteristic of normal swallowing.*” Second, the decrease in the vertical dimension of occlusion in many edentulous patients may deter occlusal contact from occurring readily during swallowing. This is because of the greater distance the mandible must travel to make such a contact. The significance of tooth contact in swallowing is considerable in its contribution to the stability of natural teeth.2”, zG I,ack of such contact which promotes stability of position in natural teeth may similarly affect complete dentures and possibly aggravate resorption of residual ridges through tongue and lip movement of denture bases. The influence of tongue pressures has been shown to be significantz7-“’ In view of the evidence that approximately 4-6 per cent of subjects in this study exhibited no contact of teeth during swallowing, the possible deleterious effects of such a pattern of deglutition warrant further investigation. SUMMARY
A study was conducted to determine mandibular position during selected functional movements. The subjects were largely made up of individuals who were accustomed to wearing their dentures. It appears from this study that the swallowing position was the mandibular closure most often used by representative denture patients. Some closures occurred anterior to this position and fewer posterior to it. The incidence of no-contact of teeth during swallowing appears particularly significant. In view of the evidence, the term “bracing position” seems to be more universally applicable and descriptive for the most important maxillomandibular relationship than other terms in current use. References 1.
Atwood, D. A.: A Critique of Research of the Posterior Limit of the Mandibular Position, J. PKOSTHET. DENT. 20: 21-36, 1968. ‘2. Ricketts, R. M.: Occlusion-the Medium of Dentistry, J. PKOSTHET. DENT. 21: 39-60, 1969. 3. Schweitzer, J. M.: Dental Occlusion: A Pragmatic Approach, Dent. Clin. North Am. 13: 701-724, 1969. 4. Ilickey, J. C.: Centric Relation--A Must for Complete Dentures, Dent. Clin. North. Am. Nov. 1964. 5. Walker, R. C.: A Comparison of Jaw Relation Recording Methods, J. PROSTHET. DEST. 12: 685-694, 1962. 6. Pameijer, J. II. N., Glickman, I., and Roeber, F.: Intraoral Telemetry. III. Tooth Contacts in Chewing, Swallowing and Bruxism, J. Periodont. Res. 40: 253-258, 1969. 7. Woelfel, J. B., Hickey, J. C., and Allison, M. L.: Effect of Posterior Tooth Form on Jaw and Denture Movement, J. PROSTHET. DENT. 12: 922-939, 1962. 8. Sheppard, I. M., and Sheppard, S. M.: Denture Occlusion, J. PROSTHET. DENT. 20: 307-318, 1968. 9. Tallgren, A.: The Reduction in Face IIeight of Edentulous and Partially Edentulous Subjrcts During Long Term Denture Wear, Acta Odont. Stand. 24: 195-239, 1966. 10. Atwood, D. A.: Postextraction Changes in the Adult Mandible as illustrated by Microradiographs of Midsagittal Sections and Serial Roentgenograms, J. PROSTHET. DENT. 13: 810-824, 1963.
Lucia, V. 0.: Modem Gnathological Concepts, St. Louis, 1961, The C. V. Mosby Conrparry, pp. 122-130. 12. Ricketts, R. M.: Variations of the Temporomandibular joint as Revealed by Cephal+ metric Laminography, Am. J. Orthod. 36: 877-897, 19.50. 13. Updegrave, W. J.: Roentgenographic Observations of Functioning Temporomandibulat Joints, J. Am. Dent. Assoc. 54: 488, 1957. 14. Schwartz, L.: Disorders of the Temporomandibular joint, Philadelphia. 1959; W’. B;. Saunders Company. 1.5. Sheppard, I. M.: The Relation of Occlusion and Temporornandibular Joint Morphology to Temporomandibular Joint Symptoms, J. PKOSTHET. DENI’. 6: 339-346, 1956. 16. Sheppard, I. M.: Range of Condylar Movement During Mandibular Opening. J. PROSTIIET. DEST. 15: 263-271, 1965. 17. Messerman, T.: A Concept of Jaw Function with a Related Clinical ,4pplication, j. PROSTIIET. DENT. 13: 130-142, 1963. 18. Graf, I-I., and Zander, H. A.: Tooth Contact Patterns in Mastication, .J. PKOS,~IIE.I.. DEST. 13: 1055-1066, 1963. 19. Schweitzer, J. M.: -Masticatory Function in Man, J. PROSTIIET. DENT. 12: 262-291. 1962. 20. Powell, R. S., and Gander, H. A.: The Frequency and Distribution of Tooth Contact During Sleep, J. Dent. Res. 44: 713-717: 1965. 2 1. Brigante, R. I!.: A Ccphalometric Study of the Settling and Migration of Demur+ J. PROSTHET. DEST. 15: 277-284, 1965. 22. Sheppard, I. M.: Denture Bases Dislodgement During Mastication, J. PROSTIIET. De.u~. 13: 462-468, 1963. 23. Sheppard, I. M.: The Bracing Position, Centric Occlusion, and Centric Relation, .IPROSTHET. DEST. 9: 1 I-20, 1959. 24. Kawamura, Y.: Oral Physiology and Clinical Dentistry, J. Dent. Educ. 29: 179-185, 1965. 25. O’Leary, T. J., Rudd, K. D., Nabers, C. L., and Stumpf, A. J.: The Effect of Mastication and Deglutition on Tooth Mobility, Periodontology 5: 26-28, 1967. 26. Sheppard, I. M.: The Tamping Effect, N. Y. State J. Dent. 29: 166-167, 1963. 27. Winders, R. V.: Forces Exerted on the Dentition in the Perioral and Lingual Musculature During Swallowing, Angle Orthod. 28: 226-235, 1958. 28. Kydd, W. I,.: Tongue and Lip Forces Exerted During Deglutition in Subjects With and Without an Anterior Open Bite, J. Dent. Res. 42: 858-866, 1963. 29. Kydd, W. L.: Maximum Forces Exerted on the Dentition by the Perioral and Lingual Musculature, J. Am. Dent. Assoc. 55: 646-651, 1957. 30. Neff, C. W., and Kydd, W. I,.: The Open Bite Physiology and Occlusion, Angle Orthod. 36: 351-357, 1966. U.: Need of Functional Analyses and Selective Grinding in 31. Algren, J., and Posselt, Orthodontics, Acta Odont. Stand. 21: 187-226, 1963. 32. Sheppard, I. M.: The Effect of Extreme Vertical Overlap on Masticatory Strokes, JPROSTHET. DENT. 15: 1035-1042, 1965. 33. Sheppard, I. M., and Sheppard, S. M.: The Mandibular Sideshift and Lateral Excursions, J. Oral Med. 22: 115-118, 1967. 111 E.210TH BROSX,XEW