Journal of Dentistry, 4, 5-l 0
Vertical relationships of edentulous jaws during swallowing* W. R. E. Laird,
BDS, MDS, HDD, FDS
Turner Dental School, Manchester ABSTRACT Twenty edentulous subjects were X-rayed while sipping water. Measurements were made to determine the constancy of the vertical jaw position during swallowing and to relate it to the clinical rest position. The findings indicate that swallowing may be a useful clinical technique in establishing vertical jaw relationships in the construction of complete dentures.
INTRODUCTION THE observation that ‘more dentures fail from wrong jaw relationships than from any other causes’ (Berry, 1960) illustrates the importance of recording correctly the relationship of the mandible to the maxilla in the design and construction of complete dentures. Jaw relationships exist in the vertical plane (sagittally and coronally) and in the horizontal plane (anteroposteriorly and laterally), and the above observation has been enlarged upon by other workers (Young, 1949; Morrison, 1959; Fenn et al., 1961; Swerdlow, 1965), who have asserted that one of the commonest causes of failure of complete dentures is their construction to an incorrect vertical jaw relationship. Furthermore, it has been stated (Downs, 1963) that the establishment of the correct vertical distance between the mandible and the maxilla is one of the most perplexing problems in complete denture design. As a result, the techniques involved in the determination of vertical jaw relationships are *Presented at the Annual Conference of the British Society for the Study of Prosthetic Dentistry in April 1974.
many. It would appear logical, however, that if the dentures are to be satisfactory in function, then a greater degree of success might be expected if these relationships were recorded with reference to natural movements of the jaws. One such movement which finds favour amongst clinicians is swallowing. It has been suggested that during a swallowing sequence, the mandible moves vertically upwards from its rest jaw relationship to assume a new temporary relationship to the maxilla, which in dentulous subjects is thought to be at the position of occlusion of the teeth (Gillis, 1941; Rushmer and Hendron, 1951; Posselt, 1968). After completion of swallowing, the mandible returns to the position of rest jaw relationship (Niswonger, 1934; Tallgren, 1957; Fenn et al., 1961). Shanahan (1955) has indicated that the elevated position of the mandible attained during swallowing is an habitual vertical closing terminal, and, accordingly, that the function of swallowing may be used to establish a natural vertical dimension of occlusion in the design and construction of complete dentures. These observations have stimulated the present study which was undertaken for the following reasons : 1. To establish whether or not a constant and reproducible vertical closing terminal of the mandible existed in the edentulous subject during swallowing. This will be referred to as the ‘swallowing level’. 2. To examine the relationship between the swallowing level and the vertical position of the mandible at the rest jaw relationship which existed prior to commencement of the swallowing sequence.
Journal of Dentistry, Vol. ~/NO. 1
Fig.
I.-A general view of the X-ray, television and recording equipment, with a subject in position prior to radiography. A, X-ray tube; B, image intensifier; C, television camera; D, television monitors; F. video-recorder.
MATERIALS Apparatus
AND METHODS
Selection
The investigation was performed using fluorographic techniques, the subject being positioned between an X-ray source and a fluorescent screen. The apparatus* (Fig. I) employed an electronic image intensifier which increased the brightness of the fluorescent screen, resulting in a reduced radiation dosage and permitting a longer recording time. The image produced was photographed by a television camera embodied in the apparatus andsimultaneously transcribed on to videotape. Viewing could, therefore, be performed either during the investigation or at a later date. Satisfactory images were obtained with radiation levels of 5-10 mR/s to the skin surface nearest the X-ray tube, which indicated that in approximately 20 seconds of exposure a subject would receive a radiation dose similar to that required for a dental periapical film. The total filming time including trial exposures did not normally exceed 45 seconds, and the radiation dose was, therefore, well within safety limits (Smith and Heighway, 1969). *Siemens Germany.
(Medical
Division),
Erlangen,
West
of subjects
The investigation was performed on a group of 20 edentulous adult subjects. No upper age limit was fixed and subjects were included in the investigation provided that they had been edentulous for at least 12 months. Subjects with skeletal or developmental anomalies (e.g. cleft palate) were excluded.
Procedure Each subject was seated and so positioned that the median plane of the head was at right angles to the central beam of the X-ray tube. This allowed a lateral jaw recording. As repetition of recordings was not required for comparative measurements, and as it is preferable to have the head position in natural balance for lateral projections of functional movements (Bjiirk, 1954; Cleall, 1965), no cephalostat was used. Lateral movement of the head was controlled by placing the lateral surface of the face against the flat surface of the housing of the imageintensifying apparatus. Before commencing each recording, a trial exposure was performed to assess the position of the head and the clarity of the image. As image density was influenced by morphological features of the subject, the
7
Laird : Jaw Relationships during Swallowing
exposure factors required individual modification, the most common being 75 kV and 1.8 mA. All the subjects were informed that they would be provided with water and would be asked to sip a small amount and swallow it. They were not advised of the precise purpose of the investigation. Swallowing was by command and six sequences were recorded for each subject. Before commencing sequences, subjects were asked to allow their mandible to relax, i.e. assume the clinical situation of rest jaw relationship. Each sequence was viewed directly on the television monitor and simultaneously recorded on videotape for later analysis.
ANALYSIS
7 Fig. 2.-The reference lines from which measurements were made. NL, Nasal line; X, junction of anterior part of the hard palate and floor of the nose; pm, pterygomaxillare; ML, mandibular line.
OF RECORDINGS
Direct measurement from either the television screen or the videotape was impossible, and therefore each sequence was filmed from the television monitor on 35-mm fast Panchromatic film using a cameia* with a motorized film transport system running at a speed of 3 frames per second. This rate of exposure was considered adequate, as previous work using an intra-oral transmitting system (Laird, 1974) had shown that in dentulous subjects the most elevated position of the mandible during swallowing was maintained for an average of 0.8 seconds. From the photographic recordings a frame analysis was performed. In order to obtain more detailed measurements, prints were made from relevant frames to a standard enlargement. Reference lines from which measurements could be made (Fig. 2) were based on a system suggested by BjSrk and Palling (1955) and were designated as follows : NL, The nasal line, which passed through the junction of the compact bone of the anterior part of the hard palate and the floor of the nose (point X) and the pterygomaxillare (pm). ML, The mandibular line, which was at a tangent to the lower border of the mandible. The points from which these lines were constructed were obtained by piercing the film *Nikon F., Nippon Kogaku, Tokyo, Japan.
negative with a pin before printing. This resulted in the appearance on the print of a well-defined black spot. The points were then joined by lines O-1 mm thick. From these reference lines length measurements were made from point X perpendicularly to the mandibular line, which gave an indication of jaw separation in the region of the extracted premolar/molar teeth. All the measurements were made using the blade of a calliper gauge with a vernier scale calibrated to 0.1 mm.
Accuracy of measurements the frame analysis of the swallowing were made as sequences, measurements described from relevant photographic frames. The reliability of reference points and lines, however, constituted a possible source of error in the results. In order to investigate this, 30 identical exposures were made of a subject with his teeth in occlusion. Prints were then made to the standard enlargement. Reference points and lines were located on these prints and length measurements made as previously described. The values of the readings ranged from 32.3 mm to 33.3 mm, with a mean of 32.72 mm and standard deviation of fO.26, thus indicating tight groupings of readings about the mean with a small range of
In
8
Journal of Dentistry, Vol. ~/NO. 1
dispersion. According to statistical convention, 95 per cent of such readings in a normal distribution lie within f2 standard deviations of the mean. At this level, therefore, there is only a 5 per cent chance that any reading would be greater than -&to*5mm from the mean. Thus, in the analysis of the results any single measurement which lay within f0.5 mm of the mean value for a series of readings was not considered to represent a true difference from that mean value.
The swallowing
level
The recorded measurements of vertical jaw separation during each swallowing sequence for the premolar/molar regions of each subject, together with the mean values and standard deviations, are presented in Table I. The mean values for the swallowing levels were used as references to which the other values in the sequence were compared. A reproducible swallowing level was only considered present if at least three of the readings for jaw separation fell within 50.5 mm of the mean value. The results indicated that a reproducible swallowing level was present in 16 subjects and absent in 4 subjects. The relationship between the swallowing level and the relaxed position of the mandible was determined by comparing the mean value for the vertical jaw separation throughout the swallowing sequences for each subject with the corresponding value for the relaxed position of the mandible at the commencement of the sequences. This has been presented as a scatter diagram (Fig. 3), the value for the mean swallowing level being plotted against the value for the relaxed position for each subject. If the recorded value for the swallowing level fell within f0.5 mm of the value for the relaxed position, then it was considered indistinguishable from the relaxed position and fell within the double lines on the diagram. In only 5 cases did the mean swallowing level and the E relaxed position correspond. The majority of .f points were outside the range of the relaxed g position and indicated that the vertical jaw .E CD separation during swallowing was less than at r” the relaxed position in 11 subjects and greater a in 4 subjects. d
Laird
: Jaw
Relationships
9
during Swallowing
DISCUSSION Little has been reported in the literature regarding vertical jaw separation in edentulous subjects during swallowing. The present results, however, appear to indicate that a reproducible swallowing level may be present in the majority of subjects over a limited period of time. If a null hypothesis of a reproducible level is assumed and the present results compared to it using a x2 test, the difference is not statistically significant (P~0.2) and the hypothesis of a reproducible swallowing level cannot be rejected. This, however, does not imply that each subject will demonstrate permanently a constant andreproducible swallowing level. Investigation into such a hypothesis would require an extensive longitudinal study. Rather, it indicates that such reproducibility may be present over a limited range of time. The relaxed position to which the swallowing level was compared is a clinical situation which is thought to correspond to the rest jaw relationship. It cannot be stated with any certainty, however, whether or not the mandible and its associated musculature are at a true rest jaw relationship, determination of which would require recordings of the electrical activity of the muscles controlling the mandibular position. Nevertheless, the relaxed jaw relationship in the present study corresponded to the rest jaw relationship obtained by the clinician. The number of edentulous subjects (11) who demonstrated a vertical jaw separation during swallowing of less than that at the relaxed position was compared with results from a similar study on dentulous subjects, of whom 20 from 28 demonstrated occlusal tooth contact during swallowing (Laird, 1973). (Occlusal tooth contact will also occur at a vertical jaw separation of less than that at the rest position.) The difference between the results from each group of subjects when subjected to a x2 test was not statistically significant (P>O*2). It would appear, therefore, that there may be some association between dentulous and edentulous subjects with regard to the swallowing level relative to the relaxed position.
oc__~ ........_.... i.
j. 40
Relaxedporxion
(mm)
Fig. 3.-Comparison between the mean vertical jaw separation at the swallowing level with that at the relaxed position. The double lines are constructed at f0.5 mm of the value for the relaxed position.
From these observations, it follows that the recording of the swallowing level may well be useful in helping to establish a natural vertical dimension of occlusion in the design of complete dentures.
CONCLUSIONS From the results and discussions regarding jaw relationships in the sample of subjects selected for this study, the following conclusions were drawn : 1. The majority of edentulous subjects demonstrated a constant and reproducible vertical jaw separation during swallowing which was termed the ‘swallowing level’. 2. In most cases the swallowing level was less than or equal to the vertical jaw separation at the relaxed position of the jaws. 3. The action of swallowing may be a useful method in recording and evaluating the vertical dimension of occlusion in the design and construction of complete dentures. REFERENCES
BERRY D. C. (1960) The constancy of the rest position of the mandible. Dent. Pratt. Dent. Rec. 10,129-132.
10
BJ~RK A. (1954) Cephalometric
X-ray investigations in dentistry. Znt. Dent. J. 4, 718-744. BJ~RK A. and PALLING M. (1955) Adolescent age changes in sagittal jaw relation, alveolar prognathy and incisal inclination. Acta Odontol. &and. 12,201-232. C&ALL J. F. (1965) Deglutition: a study of form and function. Am. J. Orthod. 51, 566594. DOWNS B. H. (1963) In discussion of paper by BREWER A. A. Prosthodontic research at the School of Aerospace Medicine. J. Prosthet. Dent. 13, 70. FENN H. R. B., LIDDEL~WK. P. and GIM~~N 3. P. (1961) Clinical Dental Prosthetics, 2nd ed. London, Staples Press. GILLIS R. R. (1941) Establishing vertical dimension in full denture construction. J. Am. Dent. Assoc. 28,430-436. LAIRD W. R. E. (1973) Observations on some jaw relationships during swallowing as related to prosthetic dentistry. MDS Thesis, University of Glasgow. LAIRD W. R. E. (1974) Intermaxillary relationships during deglutition. J. Dent. Res. 53, 127131.
Journal of Dentistry, Vol. ~/NO.
1
MORRISONM. L. (1959) Phonetics as a method of determining vertical dimension and centric relation. J. Am. Dent. Assoc. 59, 690-695. NISWONGERM. E. (1934) The rest position of the mandible and the centric relation. J. Am. Dent. Assoc. 21, 1572-1582. POSSELTU. (1968) Physiology of Occlusion and Rehabilitation, 2nd ed. Oxford, Blackwell. RUSHMERR. F. and HENDRONJ. A. (1951) The act of deglutition: a cinefluorographic study. J. Appl. Physiol. 3, 622-630. SHANAHANT. E. J. (1955) Physiologic jaw relations and occlusion of complete dentures. J. Prosth. Dent. 5, 319-324. SMITH N. J. D. and HEIGHWAY W. P. (1969) Patient dose in dental cinefluorography. Oral Surg. 27, 349-357. SWERDLOWH. (1965) Vertical dimension literature review. J. Prosth. Dent. 15, 241-247. TALLGRENA. (1957) Changes in adult face height due to ageing, wear and loss of teeth, and prosthetic treatment. Acta Odontol. &and. 15, Suppl. 24. YOUNGH. A. (1949) Diagnosis of problems in complete denture prosthesis. J. Am. Dent. Assoc. 39, 185-200.
Vertical relationships of edentulous jaws during swallowing* W. R. E. Laird,
BDS, MDS, HDD, FDS
Turner Dental School, Manchester ABSTRACT Twenty edentulous subjects were X-rayed while sipping water. Measurements were made to determine the constancy of the vertical jaw position during swallowing and to relate it to the clinical rest position. The findings indicate that swallowing may be a useful clinical technique in establishing vertical jaw relationships in the construction of complete dentures.
INTRODUCTION THE observation that ‘more dentures fail from wrong jaw relationships than from any other causes’ (Berry, 1960) illustrates the importance of recording correctly the relationship of the mandible to the maxilla in the design and construction of complete dentures. Jaw relationships exist in the vertical plane (sagittally and coronally) and in the horizontal plane (anteroposteriorly and laterally), and the above observation has been enlarged upon by other workers (Young, 1949; Morrison, 1959; Fenn et al., 1961; Swerdlow, 1965), who have asserted that one of the commonest causes of failure of complete dentures is their construction to an incorrect vertical jaw relationship. Furthermore, it has been stated (Downs, 1963) that the establishment of the correct vertical distance between the mandible and the maxilla is one of the most perplexing problems in complete denture design. As a result, the techniques involved in the determination of vertical jaw relationships are *Presented at the Annual Conference of the British Society for the Study of Prosthetic Dentistry in April 1974.
many. It would appear logical, however, that if the dentures are to be satisfactory in function, then a greater degree of success might be expected if these relationships were recorded with reference to natural movements of the jaws. One such movement which finds favour amongst clinicians is swallowing. It has been suggested that during a swallowing sequence, the mandible moves vertically upwards from its rest jaw relationship to assume a new temporary relationship to the maxilla, which in dentulous subjects is thought to be at the position of occlusion of the teeth (Gillis, 1941; Rushmer and Hendron, 1951; Posselt, 1968). After completion of swallowing, the mandible returns to the position of rest jaw relationship (Niswonger, 1934; Tallgren, 1957; Fenn et al., 1961). Shanahan (1955) has indicated that the elevated position of the mandible attained during swallowing is an habitual vertical closing terminal, and, accordingly, that the function of swallowing may be used to establish a natural vertical dimension of occlusion in the design and construction of complete dentures. These observations have stimulated the present study which was undertaken for the following reasons : 1. To establish whether or not a constant and reproducible vertical closing terminal of the mandible existed in the edentulous subject during swallowing. This will be referred to as the ‘swallowing level’. 2. To examine the relationship between the swallowing level and the vertical position of the mandible at the rest jaw relationship which existed prior to commencement of the swallowing sequence.
Journal of Dentistry, Vol. ~/NO. 1
Fig.
I.-A general view of the X-ray, television and recording equipment, with a subject in position prior to radiography. A, X-ray tube; B, image intensifier; C, television camera; D, television monitors; F. video-recorder.
MATERIALS Apparatus
AND METHODS
Selection
The investigation was performed using fluorographic techniques, the subject being positioned between an X-ray source and a fluorescent screen. The apparatus* (Fig. I) employed an electronic image intensifier which increased the brightness of the fluorescent screen, resulting in a reduced radiation dosage and permitting a longer recording time. The image produced was photographed by a television camera embodied in the apparatus andsimultaneously transcribed on to videotape. Viewing could, therefore, be performed either during the investigation or at a later date. Satisfactory images were obtained with radiation levels of 5-10 mR/s to the skin surface nearest the X-ray tube, which indicated that in approximately 20 seconds of exposure a subject would receive a radiation dose similar to that required for a dental periapical film. The total filming time including trial exposures did not normally exceed 45 seconds, and the radiation dose was, therefore, well within safety limits (Smith and Heighway, 1969). *Siemens Germany.
(Medical
Division),
Erlangen,
West
of subjects
The investigation was performed on a group of 20 edentulous adult subjects. No upper age limit was fixed and subjects were included in the investigation provided that they had been edentulous for at least 12 months. Subjects with skeletal or developmental anomalies (e.g. cleft palate) were excluded.
Procedure Each subject was seated and so positioned that the median plane of the head was at right angles to the central beam of the X-ray tube. This allowed a lateral jaw recording. As repetition of recordings was not required for comparative measurements, and as it is preferable to have the head position in natural balance for lateral projections of functional movements (Bjiirk, 1954; Cleall, 1965), no cephalostat was used. Lateral movement of the head was controlled by placing the lateral surface of the face against the flat surface of the housing of the imageintensifying apparatus. Before commencing each recording, a trial exposure was performed to assess the position of the head and the clarity of the image. As image density was influenced by morphological features of the subject, the
7
Laird : Jaw Relationships during Swallowing
exposure factors required individual modification, the most common being 75 kV and 1.8 mA. All the subjects were informed that they would be provided with water and would be asked to sip a small amount and swallow it. They were not advised of the precise purpose of the investigation. Swallowing was by command and six sequences were recorded for each subject. Before commencing sequences, subjects were asked to allow their mandible to relax, i.e. assume the clinical situation of rest jaw relationship. Each sequence was viewed directly on the television monitor and simultaneously recorded on videotape for later analysis.
ANALYSIS
7 Fig. 2.-The reference lines from which measurements were made. NL, Nasal line; X, junction of anterior part of the hard palate and floor of the nose; pm, pterygomaxillare; ML, mandibular line.
OF RECORDINGS
Direct measurement from either the television screen or the videotape was impossible, and therefore each sequence was filmed from the television monitor on 35-mm fast Panchromatic film using a cameia* with a motorized film transport system running at a speed of 3 frames per second. This rate of exposure was considered adequate, as previous work using an intra-oral transmitting system (Laird, 1974) had shown that in dentulous subjects the most elevated position of the mandible during swallowing was maintained for an average of 0.8 seconds. From the photographic recordings a frame analysis was performed. In order to obtain more detailed measurements, prints were made from relevant frames to a standard enlargement. Reference lines from which measurements could be made (Fig. 2) were based on a system suggested by BjSrk and Palling (1955) and were designated as follows : NL, The nasal line, which passed through the junction of the compact bone of the anterior part of the hard palate and the floor of the nose (point X) and the pterygomaxillare (pm). ML, The mandibular line, which was at a tangent to the lower border of the mandible. The points from which these lines were constructed were obtained by piercing the film *Nikon F., Nippon Kogaku, Tokyo, Japan.
negative with a pin before printing. This resulted in the appearance on the print of a well-defined black spot. The points were then joined by lines O-1 mm thick. From these reference lines length measurements were made from point X perpendicularly to the mandibular line, which gave an indication of jaw separation in the region of the extracted premolar/molar teeth. All the measurements were made using the blade of a calliper gauge with a vernier scale calibrated to 0.1 mm.
Accuracy of measurements the frame analysis of the swallowing were made as sequences, measurements described from relevant photographic frames. The reliability of reference points and lines, however, constituted a possible source of error in the results. In order to investigate this, 30 identical exposures were made of a subject with his teeth in occlusion. Prints were then made to the standard enlargement. Reference points and lines were located on these prints and length measurements made as previously described. The values of the readings ranged from 32.3 mm to 33.3 mm, with a mean of 32.72 mm and standard deviation of fO.26, thus indicating tight groupings of readings about the mean with a small range of
In
8
Journal of Dentistry, Vol. ~/NO. 1
dispersion. According to statistical convention, 95 per cent of such readings in a normal distribution lie within f2 standard deviations of the mean. At this level, therefore, there is only a 5 per cent chance that any reading would be greater than -&to*5mm from the mean. Thus, in the analysis of the results any single measurement which lay within f0.5 mm of the mean value for a series of readings was not considered to represent a true difference from that mean value.
The swallowing
level
The recorded measurements of vertical jaw separation during each swallowing sequence for the premolar/molar regions of each subject, together with the mean values and standard deviations, are presented in Table I. The mean values for the swallowing levels were used as references to which the other values in the sequence were compared. A reproducible swallowing level was only considered present if at least three of the readings for jaw separation fell within 50.5 mm of the mean value. The results indicated that a reproducible swallowing level was present in 16 subjects and absent in 4 subjects. The relationship between the swallowing level and the relaxed position of the mandible was determined by comparing the mean value for the vertical jaw separation throughout the swallowing sequences for each subject with the corresponding value for the relaxed position of the mandible at the commencement of the sequences. This has been presented as a scatter diagram (Fig. 3), the value for the mean swallowing level being plotted against the value for the relaxed position for each subject. If the recorded value for the swallowing level fell within f0.5 mm of the value for the relaxed position, then it was considered indistinguishable from the relaxed position and fell within the double lines on the diagram. In only 5 cases did the mean swallowing level and the E relaxed position correspond. The majority of .f points were outside the range of the relaxed g position and indicated that the vertical jaw .E CD separation during swallowing was less than at r” the relaxed position in 11 subjects and greater a in 4 subjects. d
Laird
: Jaw
Relationships
9
during Swallowing
DISCUSSION Little has been reported in the literature regarding vertical jaw separation in edentulous subjects during swallowing. The present results, however, appear to indicate that a reproducible swallowing level may be present in the majority of subjects over a limited period of time. If a null hypothesis of a reproducible level is assumed and the present results compared to it using a x2 test, the difference is not statistically significant (P~0.2) and the hypothesis of a reproducible swallowing level cannot be rejected. This, however, does not imply that each subject will demonstrate permanently a constant andreproducible swallowing level. Investigation into such a hypothesis would require an extensive longitudinal study. Rather, it indicates that such reproducibility may be present over a limited range of time. The relaxed position to which the swallowing level was compared is a clinical situation which is thought to correspond to the rest jaw relationship. It cannot be stated with any certainty, however, whether or not the mandible and its associated musculature are at a true rest jaw relationship, determination of which would require recordings of the electrical activity of the muscles controlling the mandibular position. Nevertheless, the relaxed jaw relationship in the present study corresponded to the rest jaw relationship obtained by the clinician. The number of edentulous subjects (11) who demonstrated a vertical jaw separation during swallowing of less than that at the relaxed position was compared with results from a similar study on dentulous subjects, of whom 20 from 28 demonstrated occlusal tooth contact during swallowing (Laird, 1973). (Occlusal tooth contact will also occur at a vertical jaw separation of less than that at the rest position.) The difference between the results from each group of subjects when subjected to a x2 test was not statistically significant (P>O*2). It would appear, therefore, that there may be some association between dentulous and edentulous subjects with regard to the swallowing level relative to the relaxed position.
oc__~ ........_.... i.
j. 40
Relaxedporxion
(mm)
Fig. 3.-Comparison between the mean vertical jaw separation at the swallowing level with that at the relaxed position. The double lines are constructed at f0.5 mm of the value for the relaxed position.
From these observations, it follows that the recording of the swallowing level may well be useful in helping to establish a natural vertical dimension of occlusion in the design of complete dentures.
CONCLUSIONS From the results and discussions regarding jaw relationships in the sample of subjects selected for this study, the following conclusions were drawn : 1. The majority of edentulous subjects demonstrated a constant and reproducible vertical jaw separation during swallowing which was termed the ‘swallowing level’. 2. In most cases the swallowing level was less than or equal to the vertical jaw separation at the relaxed position of the jaws. 3. The action of swallowing may be a useful method in recording and evaluating the vertical dimension of occlusion in the design and construction of complete dentures. REFERENCES
BERRY D. C. (1960) The constancy of the rest position of the mandible. Dent. Pratt. Dent. Rec. 10,129-132.
10
BJ~RK A. (1954) Cephalometric
X-ray investigations in dentistry. Znt. Dent. J. 4, 718-744. BJ~RK A. and PALLING M. (1955) Adolescent age changes in sagittal jaw relation, alveolar prognathy and incisal inclination. Acta Odontol. &and. 12,201-232. C&ALL J. F. (1965) Deglutition: a study of form and function. Am. J. Orthod. 51, 566594. DOWNS B. H. (1963) In discussion of paper by BREWER A. A. Prosthodontic research at the School of Aerospace Medicine. J. Prosthet. Dent. 13, 70. FENN H. R. B., LIDDEL~WK. P. and GIM~~N 3. P. (1961) Clinical Dental Prosthetics, 2nd ed. London, Staples Press. GILLIS R. R. (1941) Establishing vertical dimension in full denture construction. J. Am. Dent. Assoc. 28,430-436. LAIRD W. R. E. (1973) Observations on some jaw relationships during swallowing as related to prosthetic dentistry. MDS Thesis, University of Glasgow. LAIRD W. R. E. (1974) Intermaxillary relationships during deglutition. J. Dent. Res. 53, 127131.
Journal of Dentistry, Vol. ~/NO.
1
MORRISONM. L. (1959) Phonetics as a method of determining vertical dimension and centric relation. J. Am. Dent. Assoc. 59, 690-695. NISWONGERM. E. (1934) The rest position of the mandible and the centric relation. J. Am. Dent. Assoc. 21, 1572-1582. POSSELTU. (1968) Physiology of Occlusion and Rehabilitation, 2nd ed. Oxford, Blackwell. RUSHMERR. F. and HENDRONJ. A. (1951) The act of deglutition: a cinefluorographic study. J. Appl. Physiol. 3, 622-630. SHANAHANT. E. J. (1955) Physiologic jaw relations and occlusion of complete dentures. J. Prosth. Dent. 5, 319-324. SMITH N. J. D. and HEIGHWAY W. P. (1969) Patient dose in dental cinefluorography. Oral Surg. 27, 349-357. SWERDLOWH. (1965) Vertical dimension literature review. J. Prosth. Dent. 15, 241-247. TALLGRENA. (1957) Changes in adult face height due to ageing, wear and loss of teeth, and prosthetic treatment. Acta Odontol. &and. 15, Suppl. 24. YOUNGH. A. (1949) Diagnosis of problems in complete denture prosthesis. J. Am. Dent. Assoc. 39, 185-200.
