Center, New York, N. Y.
he definitive nature of the intercuspal position in functional maxillomandibular closures (centric occlusion) and its differentiation from centric relation in most instances with natural dentitions has been well documented.l-I3 This positional discrepancy has been credited with contributing to many ailments ranging from periodontal disease to the temporomandibular joint syndrome and medical problems.‘s-21 Deflective occlusal contacts from one position to the other have been demonstrated.18$ 22, 23 These deflective contacts have been corrected by equilibration and reconstruction of natural teeth, although considerable diversity of opinion exists as to the actual methods of achieving harmony between centric occlusion and centric relation.24-“* During the fabrication of complete dentures, the occlusion is under complete control of the dentist. Nevertheless, considerable difference of opinion exists concerning the location and methods of obtaining centric relation. 33-51The problem seems further complicated by factors such as movement of trial and finished denture bases, resilience of underlying tissues, and denture base deformation.51-61 The maelstrom of activity that constitutes oral function (the variation of mandibular movements from one masticatory stroke to another) and the variables previously mentioned question a repeated definitive closure in centric occlusion with the mandible in centric relation.6” Such precise closures seem possible with artificial cusped teeth. However, sliding of denture bases is common, and this could compensate for a closure in a position other than centric relation. Therefore, a study was conducted to determine where closures take place in an anteroposterior direction during actual function. This article reports the findings of this study. From the Dental
This investigation was supported in part by Research Grant DE02462 Institute for Dental Research, United States Public Health Service. *Research Associate. **Research
METHODS Fourteen edentulous subjects ranging Irma 46 IO 79 )-bares ot‘ age were studitxl. Only one subject had favorable maxillary and mandibular ridges. Master casts made for the subjects’ IWW dentures F+YW duplicated in plaster. on the ~lnrclicved casts to simulate Cold-curing acrylic resin bases WYYX~ma& finished denture bases. ‘l‘hr trimnlcti bases wert’ tried in 111~mouth and adjusted as guided by pressure indicator paste 11ntiI thry \verc (ornfortable. JY~x occIusion rims. with a total height slightly greatt’r tllan the measured vertical dimension of occlusion agreed upon by tl4.c) cxperienccd dtrntists. were attached to the bases. Trial closures \v-t’rv madtk, and any c’xc‘ess wax was rrmoved. The maxillary occlusion rim was lubricated, and the lower rim ~3s softened evenly with dq heat. Then, the subject was guided into a closure with the mandible in its most to slide his lower jaM posterior rc4ation to the masillac aik~ \vhich he was asI forward and from side to siclv. The occlusion rims wertb trimmed and smoothed to simulate the \,\idth of natural teeth, and then rewarmed. The mandibular mo\,cments were repeated. If the measured interridge distance decreased from the: predetermined rneasurc-
E F INSTRUCTED CLOSURES
ABCDEF MASTICATORY CLOSURES
Fig. 1. Location of different types of closures in per cent: A, closures more than 1 mm. anterior to the swallowing position; B, rlosures 1 mm. anterior to the swallowing position; C, closures 0.5 mm. anterior to the swallowing position: D, closures in the swallowing position; E, closures posterior to the swallowing position; and F, anteroposterior, posteroanterior, or combined anteroposterior-posteroanterior mandibular movements following closure.
Volume 20 Number 4
Fig. 2. Selected cinefluorographic frames from a masticatory sequence are shown (4 frames per second, 70 mm. film). Markers in the end-to-end position indicate the swallowing position: I, an instructed closure occurring in the swallowing position; 3, the mouth is open for reception of banana barely visible at left; 4, a closure approximately v4 second later; 6, another closure anterior to the swallowing position approximately % second later; 7, the mandible is open with the bolus between the jaws; 17, a later closure more than 1 mm. anterior to the swallowing position; 23, a masticator-y closure in the swallowing position; 25, a masticatory closure in the swallowing position; 36, a masticatory closure in the swallowing position after approximately three seconds of mastication; 39, a masticatory closure more than 1 mm. anterior to the swallowing position approximately 3/4 second following frame 36; and 57, a masticatory closure anterior to the swallowing position two seconds later than frame 39. Variously located closures occurred between frames 25 and 57, however only frames 36 and 39 are shown.
Instructed Swallow Hz0 Mastication Instructed Swallow Hz0 Mastication
Instructed Swallow Hz0 Mastication Instructed Swallow Hz0 Mastication
Swallow H,O Mastication
17 ii .J-1
Instructed Swallow H,O Ma4ticaticm
9 JO 31
Instructed Swallow H,O Mastication
1‘i h :i+
Instructed Swallow Hz0 Mastication
17 ‘4 56
1-k 2 28
Instructed Swallow Hz0 Mastication
7 6 13
Instructed Swallow II?0 Mastic3 tion
Instructed Swallow Hz0 Mastication Instructed Swallow Hz0 Mastication
movements Swall.-no contact
10 1 16
2 29 14 4
4 3 57
J. I’ros. Dent. October, 1968
I No. of clo.\urs~ j
20 ‘3 ‘0
of closures* 1 mm. ant.
Instnicted Swallow HD Mastication .
20 :; :itl
Instmcted Swallow IL0 Mastir;hon
‘98 9’2 641
*Ant., anterior; PA, posteroanterior; AP, anteroposterior.
wax. Thus, the subject was merits, the procedure was repeated with additional free to close in the most retruded position anterior to it: and he could move the mandible smoothly to any position. After repeated swallows of saliva and small sips of lcater, the swallowing position was marked and vertical wires were inserted end to end in the upper and lower rims on the left side. The corrcctncss of this swallowing position was verified clinically and cinefluorographically. The mandibles of some subjects could be manually retruded a short distance posterior to their marked swallowing positions. With the use of cinefluorographic equipment, instructed opening and closing mandibular movements were recorded in a lateral view. This was followed by the recording of movements that occurred during drinking small sips of water and eating a banana. The banana was easily managed by all the subjects. Denture adhesive was applied to those bases that evidenced gross movement in function; and the film sequence was repeated. The processed films were viewed frame by frame: and the location of the mandibular vertical marker in its relation to the maxillary marker during the described movements was recorded. Inasmuch as the markers were 1 mm. in diameter, closures with the mandibular marker a full width anterior to the maxillary marker were recorded as 1 mm. anterior to the swallowing position. Approximately half this distance was recorded as 0.5 mm. anterior; closing with the mandibular marker posterior to the maxillary one, which occurred seldom and only for very short distances, was classified as posterior to the swallowing position. OBSERVATIONS Of the 1,031 mandibular closures measured, 721 (70 per cent) occurred in the swallowing position, 133 (13 per cent) occurred approximately 0.5 mm. anterior, 12 per cent occurred 1 mm. anterior, 3 per cent occurred more than 1 mm. anterior, and 2 per cent occurred posterior to the swallowing position. Instructed closures. Of 298 instructed mandibular closures, 201 (67 per cent) occurred in the swallowing position, 36 (12 p er cent) occurred approximately 0.5
I+ mm. ant.
16 19 0 13 32
3 1 21 25
7 5 226
12 2 81
mm. anterior, 39 ( 13 per cent) occurred 1 mm. anterior, 19 (6 per cent) occurred more than 1 mm. anterior, and 3 ( 1 per cent) occurred posterior to the swallowing position. Posteroanterior mandibular movements followed 2 per cent, and anteroposterior movements followed 4 per cent of such instructed closures (Table I). Swallowing water. Of the 92 mandibular closures which occurred while swallowing water, approximately 91 per cent occurred in the swallowing position, 4 per cent occurred 0.5 mm. anterior, 3 per cent occurred 1 mm. anterior, and 1 per cent occurred posterior to the swallowing position. Posteroanterior mandibular movements followed 5 per cent of the swallowing closures, anteroposterior movements followed 2 per cent, while combined posteroanterior and anteroposterior movements occurred in 4 per cent. Two per cent of the swallows showed no evidence of contact of the opposing pins. One subject made no contact of the pins in most of the swallows. Mastication. Of 641 mandibular closures during mastication, 68 per cent occurred in the swallowing position, 15 per cent occurred 0.5 mm. anterior, 12 per cent occurred 1 mm. anterior, 2 per cent occurred more than 1 mm. anterior, and 3 per cent occurred posterior to the swallowing position. A total of 97 per cent of the closures during mastication occurred at the swallowing position or anterior to it. Posteroanterior movements of the mandible following closure occurred in 35 per cent of the records, anteroposterior movements occurred in 13 per cent, and combined posteroanterior-anteroposterior movements in 7 per cent. Swallowing during mastication, while not listed in Table I, occurred in the swallowing position. Incomplete masticatory closures were not listed. A few subjects had a high incidence of additional mandibular movements following closure as compared with the relatively rare occurrence in most (Figs. 1 and 2) . DISCUSSION
The method employed in this study has some bearing on the significance of the findings. The lateral view was put to use exclusively in recording mandibular movements which implies that the markers might have appeared in the swallowing posi-
tion, for example, when tlley rniqht IX clircctly lateral to it. H~MYXC~. this Jlortcomin,? was not consitlerc~cl serious irl \it’\\ of the small likelihood of a Ilure lateral lliOv(‘nient I\-itliout at1 aritrrior- cornponcrit ol rnfn.emt’nt. In addition. the antcl~ol)oslt.ric,1 rrationships \\ cr(’ considered of prime inttsrcst in thr% sti~tly &spite thch possibilit) of sonic latrral positioning a5 well. ‘l‘h(* 11s~’of ‘ii a~. occlusion rims in\-ol\,c5 possible err01 s tiur, to unc\‘cn softening of was. r&liencr, of the tissut‘s ~mdrr l~c~cording pressurcs5 and nio~crii~nt ol’ thrs bases during the registration of thr \ arious positions. However. the bases empl~yetl in the study fittf,d as will as the finished dentures and. csccpt for the absence of teeth and the UP of only one food, thrv simulated the l)rrlor-mancc of SLICI~ dcnturcs in actual f~nic.tiori. Considering the: corril)lcs acti\.ity that can be observt:ti during cinefluorograph) and cinefuoroscol~y of mastication, one is impressed by the frequency with which opposin,q &ntur?-s meet in the sam(’ an tc>r.oposterior location as seen in a lateral view. Despite denture base mo\.cment, resilience of soft tissues. tlcnture base deformation, and \.ariations in t&cntion and stability. thr relative- rept>atability of one position of closure seems remarkable. Yet. X2 per cent of the closure?; in mastication not onl) failed to appear at what was apparently centric occlusion but varied in distances from it, most of l\.hicll ~vere anterior. S\vallowing small sips of lvater: while yielding the hi,Thest degrr of repeatabilit>, of closure (91 per cent 1, showed sorer variations. mandibular most of which were’ anterior to the ~wallowi~~~ Ijosition. Instructed closures appeared less reliable (67 per c,rnt ! ‘I’ht: prevalence of posteroariteriol (35 per cent) and ariteroposterior ( 113 pt’r cent\ movements of the mancliblf* I‘ollowing closure may be related to denture base movement, particularly sliding. Some> subjects manifested considerably higher percentages of such movements. They ha\~ been observed prf~\~iously by Schweitzer.’ The movemrnts r~semhlc somewhat thus sliding movemcnt along occlusal surfaces of natuml t&l as shown by SchZrt~r and Stallard.?’ Kydd and Sanclcr,” and AhlgremF’ The disturbing effect of slidirug tooth contacts with natural teeth was demonstrated by Ramfjord.” However. such movrments oc~rrrred often with man\ subjects in the abscncc of occlusal interfcxretlcrs (Table 1) Previous studies indicate that this is a common occurrences with denture weart’rs.‘” The impact of such posteroanterior nlandibular movements coupled with the known sliding of denture bases may be of significance to the health of the underlying ridges. Some opening mandibular movrmrnls have been found to be anterior to closimg movementa.“~ ’ I- The posteroantcbrior occ~lusal movcmcnts following mandibular closure found in this study ~voulcl stxenl to Facilitate the star,t of such anterior opening movements. Short anteroposterior and, possibly, some short posteroanterior movements may have been components of the lateromedial and mediolateral movements of mastication. However, this does not seem likely for the longer movements. Inasmuch as the subjects could not be considered young patients with favorable ridges, the findings may be representative of denture patients. While the apex of a Gothic arch (needlepoint) tracing was not located in the subjects studied, if one assumes that the apex would be posterior to the swallowing position and, consequently, more compatible with definitions of centric relation, then the latter position was
seldom attained in function. Posseltl found the habitual path of mandibular closure followed a course anterior to the posterior path. Schweitzer4 found that the greatest proportion of masticatory cycles occurred anterior to the most retruded position. Kydd and Sande? and Graf and Zander’ found swallowing to be associated with the retruded position. Meyers*’ and Boucherc2 indicate that centric relation is controlled by a neuromuscular reflex which does not necessarily always function in the same position. The security of a definite starting position has long been sought in developing occlusion for edentulous patients. The accepted baseline of centric relation is somewhat vague in definition and has been shown to be anatomically and physiologically variable. The methods of attaining this position vary and tend to be mechanical and nonphysiologic. The emphasis has been on achieving a precise position which can be verified when repeated. The degree of this precision does not seem characteristic of living functioning tissues nor easily maintained considering the rapid rate of change known to take place in structures underlying complete dentures. If centric relation is a learned neuromuscular reflex as indicated by MoyerslO and, as such, requires reinforcement as shown by Brill, 63 then definite intercuspation of rigidly based denture teeth might seem less confusing to the musculature. However, instantaneous changes in denture position, due to resilience of underlying tissues, coupled with long-term changes and aggravated by sliding, tilting, dropping, and lifting of the denture bases seem to make routinely precise intercuspal and jaw relationships difficult to attain in function. SUMMARY Cinefluorographic studies of mandibular movements of edentulous subjects were related to the position of the mandible during swallowing. Most of the closing movements were found to occur in the swallowing position or slightly anterior to it. Posteroanterior and anteroposterior mandibular movements following closures made during mastication occurred with approximately one third of the records measured. Precise and complete reliability of closure in a definite place was not found during function. The authors appreciate the cooperation of Dr. Saul Rakoff.
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J. Pros.Dent. October,1968
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13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.
Denture occlusion 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55.
56. 57. 58. 59. 60. 61. 62.
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