Swallowing and denture occlusion W. R. E. Laird, M.D.S.* Turner Dental School, Manchester, England
any investigators have suggested that most dentulous persons demonstrate contact of the opposing teeth when swallowing.‘-j ShanahanGl 7 suggested that during a swallowing sequence the mandible closes to a natural and reproducible position independent of the presence of teeth. Later work with a group of edentulous patients found this to be true with most people and indicated the value of this observation when evaluating and recording the vertical dimension of occlusion in the making complete dentures.*, y It might be expected, therefore, that occlusal contact during swallowing would occur in persons wearing complete dentures if the dentures have been designed to reproduce the oral physiologic pattern of the individual. The aim of the present study was to investigate such a hypothesis in patients wearing complete dentures constructed to a clinically acceptable vertical dimension of occlusion. In addition, the effect that reduction of the established vertical dimension of occlusion had on tooth contact during swallowing was to be determined.
MATERIALS AND METHODS The investigation was performed on 10 adult edentulous patients, three men and seven women, aged from 44 to 78 years, with a mean age of 60 years. They were volunteers who had been wearing complete dentures comfortably for a period of not less than 2 months and not more than 12 months. This permitted them to become accustomed to their dentures but limited the possibility of reduced vertical dimension of occlusion due to wear of the teeth. All subjects had dentures constructed either by the author or in clinics under the direct supervision of *Senior Lecturer in Prosthetic Dentistry. Based on a Thesis presented to the University degree of Master of Dental Surgery.
the author. The vertical dimension of occlusion for all patients was recorded by techniques other than swallowing.
Preparation of subjects Patients wearing dentures both at a clinically acceptable vertical dimension of occlusion to which they had become accustomed and at a reduced vertical dimension of occlusion were studied. This was achieved by duplicating their dentures. Fluid acrylic resin was poured into molds of reversible hydmcollbid duplicating material which had been prepared from their dentures. The mold plus resin was then placed in a pressure container, and polymerization was completed at room temperature at a pressure of 25 lb/in2 for 35 minutes. Two sets of duplicate dentures were made for each subject. These dentures were then mounted in the intercuspal position on an articulator. On one set, the occlusal surfaces and incisal edges of the teeth were reduced until a 3 mm space existed between the occlusal surfaces as measured by a machined spacing shim. In both upper and lower dentures, lead markers were placed inter-proximally between the premolar and incisor teeth for purposes of reference. Each subject was therefore provided with complete dentures at both the original and a reduced vertical dimension of occlusion.
Procedure The investigation was performed using videofiuorographic equipment,* with a moving radiographic image being transmitted directly to a television monitor and recorded simultaneously on videotape for later analysis. The technique already has been fully documented and described.8-‘0 Each patient was seated and the head positioned for a lateral jaw recording. A radiographic exposure was made with
of Glasgow for the
1978 The C. V. Moshv Co.
the teeth of the dentures in the intercuspal position to provide a baseline for comparative measurements. Patients were then provided with water and asked to sip a small amount and swallow it, during which time a radiographic exposure was made. They were not advised of the precise purpose of the investigation. Each patient performed three swallowing sequences with the dentures at the original vertical dimension of occlusion, followed by three sequences with dentures at the reduced vertical dimension of occlusion. An adhesive was used in all dentures to lessen the possibility of displacement.”
Analysis of recorded sequences The analysis of the swallowing sequences was made to detect (1) the presence or absence of denture occlusion during a swallowing sequence and (2) the effect on occlusion during swallowing resulting from reduced vertical dimension of occlusion of the dentures. Direct measurement from the videotape or television monitor was impossible. Swallowing sequences were therefore filmed from the television monitor on 35 mm fast panchromatic film using a camera with a motorized film transport system running at a speed of three frames per second. This’exposure rate was considered adequate, as it has been demonstrated previously that during a swallowing sequence the most elevated mandibular position is maintained for an average of 0.8 seconds. I2 From the photographic recordings, a frame analysis was made and prints from relevant frames were enlarged to a st’andard size. Measurements were made from the reference points and lines shown in Fig. 1, using a caliper gauge with a vernier scale calibrated to 0.1 mm. The line A joined the upper points of the upper lead markers and line B the lower points of the lower lead markers. The points were obtained by piercing the film negative with a sharp pin before printing, which gave a well-defined black spot on the resultant print. Length measurements during analysis were made from the uppermost border of the upper lead markers perpendicular to line B, i.e., in the incisor and premolar regions. The length measurements obtained during the swallowing sequences were compared to similar measurements obtained with the dentures in the intercuspal position. For this study it was considered that any measurement within +- 0.5 mm of the reference measurement at intercuspal position did not represent a real difference.“, ”
1. The reference lines are drawn from the black dots which indicate the position of the lead markers.
RESULTS The swallowing
For individual patients the swallowing sequences followed a general pattern. After the initial opening of the mouth to sip the water, the mandible moved vertically upward, assuming a new relationship to the maxillae. This position was usually maintained until the water was swallowed. True swallowing began with a backward and upward movement of the soft palate to contact the posterior pharyngeal wall, together with forward and upward movement of the hioid bone toward the lower border of the mandible. The termination of the sequences was evidenced by return of the soft palate and hyoid bone to their preswallowing position. Denture occlusion Estimation of denture occlusion during swallowing was made by comparing vertical measurements obtained during swallowing sequences with reference measurements obtained with the dentures in occlusion at the intercuspal position as described previously. The recorded values at the incisor and premolar regions at both the accustomed and reduced vertical dimensions are shown in Tables I and II. The incidence of denture occlusion in all patients at each vertical dimension is shown in Table III. This was recorded as positive only if it occurred both with incisor and premolar measurements. This table shows that denture occlusion during swallowing was demonstrated by eight patients at the accustomed vertical dimension but by only three
Table I. Measurements
in incisor Original
Subject No. 1 2 3 4 5 6 7 8 9 10
Intercuspal position 10.3 11.5 11.0 12.0 12.4 10.8 10.9 11.0 11.8 8.6
Reduced vertical dimension
11.5 11.5 11.0 12.0 14.5 10.8 13.5 11.2 12.0 8.7
12.0 11.6 10.8 11.8 14.0 11.9 13.0 10.9 12.3 8.6
10.1 11.6 10.8 11.7 14.0 14.7 13.2 10.7 11.5 8.4
Intercuspal position 8.4 10.1 8.9 10.5 11.2 8.9 11.6 8.0 9.7 6.3
*Distances (mm) from the upper lead pellet in the incisor region perpendicular sequences with dentures at the original and reduced vertical dimension.
Table II. Measurements
in premolar Original
Subject No. I 2 3 4 5 6 7 8 9 10
Intercuspal position 7.7 9.3 9.0 10.4 8.5 9.2 10.2 7.0 9.2 7.7
13.4 10.2 10.7 11.0 14.2 13.9 14.2 10.6 11.8 7.3
13.0 11.5 11.1 10.9 14.3 14.6 14.7 10.9 11.9 6.2
12.0 10.5 10.6 10.7 16.4 14.0 14.3 11.0 11.6 b.4
to line B at the intercuspal position and during swalluwing
Reduced vertical dimension
8.2 9.4 9.3 10.6 9.6 9.3 11.9 7.2 9.5 7.7
8.9 9.4 9.2 10.5 9.3 10.4 11.9 6.8 9.4 7.5
7.4 10.3 9.0 10.2 9.5 11.9 12.2 6.9 9.4 7.5
InteFcuspal position 7.6 9.0 6.4 8.9 8.0 6.9 9.9 5.2 8.1 6.0
*Distances (mm) from the upper lead pellet in the premolar region perpendicular sequences with dentures at the original and reduced vertical dimension,
patients at the reduced vertical dimension. In 30 swallowing sequences recorded at the accustomed vertical dimension, denture occlusion occurred in 19 of them. When the vertical dimension was reduced, occlusion was recorded only in seven of 30 sequences. These results were compared using a x’ (Chi-square) test. The difference between the number of subjects demonstrating denture occlusion at each vertical dimension was not significant (p > .05), but the difference between the total incidence of denture occlusion recorded at each vertical dimension was found to be significant (p < .Ol).
DV5CUSSION The incidence of denture occlusion recorded in swallowing sequences at the original vertical dimen-
11.3 8.9 7.8 9.2 9.4 11.4 11.6 7.0 9.6 6.7
10.4 10.5 8.0 9.2 9.0 11.7 12.3 7.3 9.9 6.1
10.0 8.9 8.0 9.2 10.5 11.0 12.0 7.3 9.4 6.2
to line B at the intercuspal position and during swallowing
sion of occlusion (63%) was greater than the incidence of occlusal tooth contact during swallowing (49%) recorded in a similar study on dentulous persons. I2 The difference recorded, however, was not statistically significant ($ > .20). It has been suggested that contact of the natural teeth during swallowing makes a significant contribution to the maintenance of tooth position.13 If this is also true for complete dentures, then any awareness by the subject of denture movement might be followed by tooth contact to maintain them in position. Such an action might explain the apparent greater incidence of tooth contact during swallowing in subjects wearing dentures. Noticeable movement of complete dentures during oral function has been reported previous-
Table III. Incidence during
swallowing* Original vertical dimension
Reduced vertical dimension
2 3 4 5 6 7
+ 0 +
0 0 +
+ 0 0
+ 0 +
+ 0 + 0
teeth. (a) = No contact of opposing
lY* I*-” It was observed, however, that if the patient had a favorable denture-bearing area with firm residual alveolar ridges, the denture movement was extremely small, being less than 1 mm.17 Although denture adhesive was used in the present study, it does not guarantee that dentures will remain in position. It is clear that any vertical displacment of the dentures during swallowing will interfere with the validity of results. For each relevant frame, therefore, measurements were made to assess vertical displacement of the denture from its basal seat. In the case of the upper denture, length measurements were made from the lead markers perpendicularly to a line on the print which passed through the junction of the compact bone of the anterior part of the hard palate with the floor of the nose and the point at which the contour of the hard palate intersected the posterior contour of the maxillae. For the lower denture, the corresponding line to which measurements were made from the lead markers was drawn at a tangent to the lower border of the mandible. These measurements were compared to similar ones recorded at the intercuspal position. Displacement of the upper denture occurred in only one of 60 swallowing sequences. There was a greater incidence of displacement of the lower denture, which took place primarily in one individual. The displacement did not affect the incidence of denture occlusion. The present results can be compared with those of Sheppard and Sheppard,‘” who demonstrated denture occlusion in 52.5% of swallowing sequences from patients with complete dentures. The difference between these results and the present study is not significant @ > .50). Those investigators, how-
ever, did consider the incidence of contact to be extremely low. They felt that this was because many’ of the dentures had insufficient vertica1 dimension of occlusion. It was also thought that some patients may have consciously avoided occlusal contact because of pain or discomfort under the dentures. These comments, however, are not applicabie to the present study, as the original vertical dimension of occlusion of the dentures was considered TC)be both sufficient and clinically correct and each patient had reported his or her dentures as being comfortable. In the present investigation, however, reduction of the vertical dimension of occlusion of the dentures was accompanied by a significant decrease in the incidence of denture occlusion during swallowing and would appear to support the opinioil expressed by Sheppard and Sheppard.‘”
CONCLUSIONS With dentures at a clinically acceptable vertical dimension of occlusion it is apparent, as with dentulous people, that the majority of denture wearers exhibit contact of the occlusal surfaces of posterior teeth when swallowing. In any individual, contact during swallowing is present on some occasions but not on others; this emphasizes the importance of considering several swallowing sequences when assessing contact. Reduction of the vertical dimension of occlusion, however, is associated with a significant decrease in the incidence of denture occlusion during swallowing. These findings suggest that if denture occlusion during swallowing is absent continuously, the vertical dimension of occlusion of the dentures may be insufficient. Furthermore, a reduction in tooth contacts during swallowing where occlusion had been demonstrated previously may be an early indication of the loss of vertical dimension of occlusion and the need for replacement dentures. REFERENCES 1. Rix, R. E.: Deglutition and the teeth. Denr Kec 66:105. 1946. 2. Rushmer, R. F., and Hendron, J. A.: The act of deglutition: a cinefluorographic study. J Appl Physiol 3:622, 1951. 3. Jankelson, B., Hoffman, G. M., and Hendron, J. A.: The physiology of the stomatognathic system. J Am Dent Assuc 46z37.5, 1953. 4. MQller, E.: The chewing apparatus. An electromyographic study of the action of the muscles of mastication and its correlation to facial morphology. Acta Physiol Stand 69:Suppl 280, 1966. 5. Ingervall, B., Bratt, C. M., Car&son, G. E., Helkimo, M.. and Lantz, B.: Position and movements of the mandihle and
9. 10. 11. 12. 13.
hyoid bone during swallowing. A cineradiographic study of swallowing with and without anesthesia of the temporomandibular joints. Acta Odontol Stand 29:549, 1971. Shanahan, T. E. J.: Physiologic jaw relations and occlusion of complete dentures. J PROSTHET DENT 5:319, 1955. Shanahan, T. E. J.: Physiologic vertical dimension and centric relation. J PROSTHET DENT 6:741, 1956. Laird, W. R. E.: Observations on some jaw relationships during swallowing as related to prosthetic dentistry. Thesis, University of Glasgow, 1973. Laird, W. R. E.: Vertical relationships of edentulous jaws during swallowing. J Dent 4:5, 1976. Davison, M., and Mason, W. N.: X-ray studies of movement. Glas Dent J 3:12, 1972. Sheppard, I. M., and Sheppard, S. M.: Denture occlusion. J PROSTHET DENT 20:307, 1968. Laird, W. R. E.: Intermaxillary relationships during deglutition. J Dent Res 53:127, 1974. O’Leary, J. T., Rudd, K. D., Nabers, C. L., and Stumpf, A. J.: The effect of mastication and deglutition on tooth mobility. Periodontics 5:26, 1967.
14. Ardran, G. A., Kemp, F. H., and Munz, F. R.: Observations on the behaviour of full lower dentures. An X-ray cinematographic study with special reference to the perspex tray impression method. Dent Pratt Dent Ret 7: 180, 1957. 15. Kaires, A. K.: A study of occlusal contacts in artificial dentures. J PROSTHET DENT 7:553, 1957. 16. Smith, D. E., Kydd, W. L., Wykhuis, W. A., and Phillips, L. A.: The mobility of artificial dentures during comminution. J PROSTHET DENT 13:839, 1963. 17. 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, 1962. 18. Sheppard, I. M., and Sheppard, S. M.: Denture occlusion. J PROSTHET DENT 26:468, 1971. Reprint requeststo: DR. W. R. E. LAIRD TURNER DENTAL SCHOOL BRIDGEFORD ST. MANCHESTER Ml5 6FH ENGLAND
ARTICLES TO APPEAR IN FUTURE ISSUES Restoration of endodontically Donald D.D.S.,
R. Brown, M.S.
treated posterior teeth with amalgam W. Barkmeier,
A mechanical and systems approach facilitating Austin
facial prosthesirr prods&ion
B. De Freece, Jr., D.D.S.
of an acrylic and metal band provisional
The upper anterior sectional denture P. M. H. Dummer,
Psychological Robert D.M.D.
and J. Gidden,
E. Gillis, Jr., D.M.D.,
in maxillofacial Wendell