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Roentgencephalometric study of vertical dimension changes in immediate denture patients
ROENTGENCEPHALOMETRIC CHANGES IN IMMEDIATE
STUDY DENTURE
HERBERT
SWERDLOW, B.A., D.D.S., M.S.D.”
Bethesda,
Md.
T
HOMPSON~
OF VERTICAL PATIENTS
DIMENSION
CONCLUDED from a series of cephalometric studies that, “Without
exception, it has been shown that the mandible assumesits positional relationship to the head by the third month of life and thereafter does not change.” The constancy concept of physiologic rest position has gained widespread acceptance. It is utilized by many clinicians for the establishment of the vertical dimension of occlusion in restorative procedures, and for maintaining oral function. However, Swenson’s2viewpoint on the clinical application of prevailing concepts is also currently supported and merits consideration. He wrote, “It seemsthat any definite statements that have been made concerning a method of arriving at the correct vertical dimension have been easily disproved. Therefore, the only definite statement that should be made is that it is an indefinite procedure.” At the present time, the constancy concept of face height is being questioned in the light of evidence presented by Atwood3 and Tallgren4 in their cephalometric studies. PURPOSE OF THE STUDY
This investigation was designed primarily to determine alterations which may occur in the occlusal vertical dimension, the rest vertical dimension, and the freeway space (interocclusal distance) of adult patients in the transition from natural teeth to immediate dentures, and during the first 6 months of their use. A secondary aim of the project was to compare two clinically accepted methods of establishing the rest position of the mandible: the phonetic and swallowing methods. In this study, the term “immediate denture” denotes a complete artificial substitute constructed for insertion immediately following the removal of the last remaining natural teeth. The Broadbent-Bolton cephalometer was the instrument used for recording serial lateral cephalometric roentgenograms on each of 40 immediate denture patients during a continuous 6 month period. MATERIALS
AND METHODS
A total of 40 patients, including 30 women and 10 men with an age range of 17 to 66 years (mean age, 42 years), were utilized for this longitudinal cephalometric study. Condensed from a thesis completed at the University of Washington, School of Dentistry in partial fulfillment for the degree of Master of Science in Dentistry. Presented before the American Prosthodontic Society in Philadelphia, Pa. *Dental Department, Clinical Center, National Institutes of Health, Public Health Service, U. S. Department of Health, Education and Welfare. 835
636
SWERDLOW
J. Pros. July-Aug.,
Den. 1961
The first series of cephalometric roentgenograms was completed after clinical examination and the patient was accepted for treatment, but before the loss of occlusal stops. Prosthetic treatment for 17 patients consisted of complete upper and lower immediate dentures, while for 23 patients treatment was an immediate complete upper denture in combination with a removable partial lower denture. All of the partial dentures were of the bilateral distal extension type with most abutments covered with surveyed full crowns. The prosthetic appliances for all subjects in the study were fabricated by the same techniques. The final impressions for the immediate dentures were made by utilizing a custom acrylic resin tray with a zinc oxide and eugenol paste wash impression posterior to the remaining teeth ; compound or wax was used to complete the anterior section. A double impression technique was used for the lower partial dentures. A tissue rest impression of only the future tissue support area was made with a zinc oxide and eugenol paste in a custom acrylic resin tray. A second alginate impression was then made over the first with firm loading of the denture bearing tissue. The occlusal vertical dimension for all patients was recorded by wax occlusal rims. The adequacy of the occlusal vertical dimension was judged by the contact of the remaining natural teeth, and interocclusal distance of 3 to 4 mm., the facial expression, passive contact of the lips, phonetics, and esthetics. The teeth were set up in centric occlusion at the centric relation with bilateral balance, processed in methylmethacrylate resin, remounted to correct processing changes, and machine-paste milled. The delivery of the dentures and the post-insertion checks were performed within accepted prosthodontic standards. Two functional methods were employed in obtaining the roentgenographic registrations of rest position for this study. The phonetic and swallowing methods were selected because both use the patient’s own musculature to establish resting mandibular posture with ease after performing a common physiologic action. These methods did not require coaching or explanation, or the examiner’s subjective evaluation, to determine when the subject was “at rest.” DESCRIPTION
OF
THE
METHODS
EMPLOYED
Swallowing Method.-With the patient’s head adjusted in the cephalostat, a mouthful of water was drawn by means of a straw from a cup and held in the patient’s mouth. The subject was then asked to swallow and relax. The laryngeal structures and hyoid bone were observed to move upward, then return to their original position. A few seconds later the exposure was made. Phonetic Method.-The patient was asked to hum the letter “m” like the note of a song, allowing it to slowly fade away until the sound finally could no longer be heard. The lateral film was then exposed within a few seconds following cessation of the hum. At every sitting, the procedure was practiced before the exposure was made. The entire cephalometric procedure was explained to the patient as being one more step in the routine for immediate denture patients which would be helpful in their future denture service. The lateral roentgenographic registrations were made on 8 by 10 inch films
Volume
14
Number
4
VERTICAL
DIMENSION
CHANGES
637
in cassettes with intensifying screens. Each patient remained in the cephalostat until the series of five exposures was completed for each stage. STAGE I.--Pre-extraction (before the natural occlusal stop teeth were lost by extraction). (a) Two films were exposed with the natural teeth in centric occlusion. (b) Two films were exposed with the mandible in rest position, one determined by the phonetic method, and the other by swallowing. (c) One film was exposed with the mouth wide open. STAGE II.-Three weeks post-extraction (3 weeks after the insertion of the immediate dentures). (a) Four films were exposed in mandibular rest position, two with immediate dentures and two without dentures. (b) One film was exposed with the denture teeth in centric occlusion in the mouth. STAGE III.--Six months post-extraction (6 months after the immediate insertion of the dentures). (a) Four films were exposed in the mandibular rest position, two with the immediate dentures and two without dentures. (b) One film was exposed with the denture teeth in centric occlusion in the mouth. At each of the sittings for Stages I, II, and III, every pair of films made of mandibular rest position contained one exposure with the use of the water swallowing method, while the other exposure utilized the phonetic technique. The cephalometric films for Stage II were recorded after the patient had worn the immediate dentures for a period of 3 weeks. This period of 3 weeks post-extraction allowed the trauma from surgery to disappear and provided sufficient time for the patient to become relaxed and comfortable with the new dentures.
RADIATION
CONTROL
A total of 600 lateral roentgenograms were made during the entire study. The amount of radiation delivered to the patient’s head was measured with a Victoreen ionization chamber. A model phantom skull, filled and coated with wax to simulate human features, was used as a test object. The exposure time for each cephalometric roentgenogram was 0.5 seconds at 85 kilovolts, 20 milliamperes, 2.25 mm. filter with the anode-object distance of 60 inches. The radiation to the skin per exposure was found to be 0.04 r and to the center of the head 0.004 r. Richards,5 using the same measuring method (Victoreen chamber), found an average of 1.7 r dose to facial skin per intraoral film with the roentgen unit operating at 65 KVP, 10 Ma., 2.25 mm. filtration, 7 inch target distance. Thus, the radiation delivered to the patient’s facial skin during one intraoral exposure would be equivalent to the roentgen dosage from over 40 cephalometric films. The total radiation exposure to all the subjects in this study was less than the dosage delivered by a 15 film intraoral complete mouth roentgenographic examination. FILM
PLACEMENT
The distance from the median-sagittal plane of the head to the film was recorded for each subject at the first sitting. This midline to film distance was kept constant for each subsequent sitting throughout the study in order to control the magnification error.
J. Pros. Den. July-Aug., 1964
SWERDLOW
638
Menton Fig.
1.-A
REFERENCE
typical
master
template
tracing
illustrating
roentgenographic
landmarks.
POINTS
The reference points and landmarks used for measuring on the films are in accordance with those described by Krogman and Sassouni.g The two major osteologic landmarks considered were the nasion and the menton. Point Na, nasion, is the most anterior point of the naso-frontal suture seen from norma lateralis. The menton is located as the lowermost point on the symphyseal shadow as seen from norma lateralis (Me). Both measuring points are situated in the median-sagittal plane. In those subjects in whom double projections of the right and left sides of the mandible were seen, a mid-point was used.7 CEPHALOMETRIC
TRACINGS
In order to control the cumulative tracing errors, the measurements were made directly on the roentgenographic film. A master template of the centric occlusion film judged to be the clearest was traced on semi-transparent acetate paper. Structures of high contrast, such as the sella-turcica, inner and outer tables of the skull, pterygomaxillary fissure, anterior air sinuses, cortical plates of the
Volume 14 Nunlber 4
VERTICAL
\.
Fig.
2.-A
diagram
illustrating
\I
DIMENSION
occlusol
I
the linear positlon
639
CHANGES
Vertical
measurements roentgenograms.
(mm.)
made
on the
I
occlusal
and
rest
body and ramus of the mandible, the dense symphysis shadows, the external oblique line, inferior alveolar canal and teeth, were included, when possible, on the template tracing. A master template was traced for each patient (Fig. 1) . This tracing was superimposed on all of the films for that patient, so that the contours of the upper part of the face coincided, and with a sharp point the location of the nasion was punctured through the tracing into the film. For location of the point menton, the silhouette of the mandible and teeth were registered and the lowermost point on the symphyseal shadow of each fihn was pierced. The occlusal vertical dimension is the distance measured from nasion to menton when the maxillary and mandibular teeth (natural or artificial) were in contact. When the mandible assumed a resting position, the distance from nasion to menton on the rest position films determined the rest vertical dimension. The interocclusal distance or free-way space is the difference between rest vertical dimension and the occlusal vertical dimension. In each of the three stages of this investigation, the interocclusal distance constitutes the difference between the nasion-menton measurement on the films of the rest and occluding positions. All
640
J. Pros. lkw. July-Aug., 1964
SWERDLOW
122J
P= Phonetic S = Swallowing
a- 5Ze_WOY-
OJ
Fig.
3.-Facial
, Pre-extraction Natural Teeth
vertical
dimension
SPoce -----
0
II s’ -___
o _*e-
--
I 3 weeks Postextraction
means plotted at stages denture patients.
a
____-----
1 6 months Postextraction in a serial
study
cjf 40 immediate
linear measurements were made with the same millimeter ruler to the nearest 0.5 mm. (Fig. 2). Th linear measurements were subjected to statistical analysis in order to evaluate the significance of these recordings. The relationship of the variables at the different stages are demonstrated graphically (Fig. 3).
The phonetic method of establishing mandibular rest position resulted in consistently greater values as compared to the results of the swallowing procedure. The average difference is statistically significant. The occlusal vertical dimension showed an average increase from the pre-extraction stage to 3 weeks post-extraction, while a decrease was found at the 6 months post-extraction stage.
Extr ‘4”
VERTICAL
DIMENSION
641
CHANGES
The rest vertical dimension generally parallels the pattern of the occlusal vertical dimension. The average measurements of the interocclusal distance varied inversely to the pattern followed by the occlusal and rest vertical dimensions. In the final stages, the complete upper and lower denture group showed twice as much loss in the facial vertical dimensions as did the partial denture group. The occlusal vertical dimension, the rest vertical dimension, and the dimension of the interocclusal distance for each stage of the study are shown in Tables
TABLE
I.STAGE
I-PRE-EXTRACTION
occ. TYPE CASE
V.D. (MM.)
129.5 116 115.5 111.5 117.5 114 12.5 120 118 127 119 123 125 142 136 108 140 117.5 140 120 133 121 129.5 120 117 138 127 126 113 124 112 116.5 13.5 118 12.5 136 129 109 132 127 Legend: F-Immediate dimension. Rest V.D.-Rest
full denture. P-Removable partial vertical dimension. “P”-Phonetic
REST V.D. "P" (MM.)
FREEWAY SPACE (MM.)
REST V.D. 'Y (MM.)
FREEWAY SPACE (MM.)
133 117 118 113 119 116 127 121 119 134 120 126 131 144 138 114 142 126 143 121 139 126 134 126 118 140 130 128 117 128.5 116 126 137 119
3.5
132 117 117.5 112.5 119 115 126.5 123 121 130 119.5 126 128 143 138 111 141 121 142 123
2.5
139 126 130 126.5 119 140.5
i 0.5 6.5 2 2.5
128 132 115
ii 2
126 114 120
i 3.5
143 126
:
: 1.5 4
132 118 137 131
; 5 4
136 119 126.5 140 131 115 136 129
denture. method.
Oct. V.D.-Occlusal ‘3”-Swallowing
:.5 1.5 1.5 2 2 1 : : ! :, 2 8.5 3 1 Ei 4.5 6 1 3 i 4.5 4 9.5 2 1
1 1 1.5 :.5 3 i 0.5 3 3 ; 3 i.5 2 3
i 4 2 vertical method.
642
J. Pros.
SWERDLOW
July-Aug.,
Dm.
1964
I, II, III. The means of the entire study are illustrated graphically in Fig. 3, and listed in Table IV. The shading seen in hoth the phonetic and swallowing rest vertical dimensions are presented to aid in distinguishing the plotted means with dentures as opposed to without dentures at the various stages (Fig. 3).
Phonetic WYSUS Szvalloting Method.-The literature reviewed clearly demonstrates the elusiveness of determinations of the clinical rest position of the TABLE
II.STAGE
II-THREE WEEKS
POST-EXTRACTION
WITHDENTURES
PT.
AGE
SEX
TYPE CASE*
occ. V.D.t (MM.1
REST V.D.$ “P" (MM.)
FREEWAY SPACE (MM.)
136 119 119 116 121
4
119 130 126
: 4
135 119
:s
124 125.5 132 143 136 115 142 120 140 124 138 126 134.5 127.5 122 142 129
:.s
118.5 137
g.5
129 116.5 124 137 119
i3.S 4
126 144 133
: 1.5
118 138 130
; 1
WITHOUTDENTURES
REST V.D. ‘$9)
FREEWAY SPACE (MM.)
REST V.D. “P" (MM.1
REST V.D. %" (MM.)
135 119 117 114 119 115 127 125 118.5 129 123.5 124.5 130.5 143 137.5 110 144 122 139 125 138 126 132 124.5 122 141.5 128 136 119 128 116 122 137 119.5 126 140 134 119 138 131
3
136 120 119.5 113 119.5 118 128 122.5 122.5 133 119 126 134 145 135 113 142 120 139 121 136 127 134 125.5 119.5 143 128.5 13.5 115 127.5 115.5 125 134 123 123 144 132 114.5 136 129.5
130 119 119
denture. method.
Oct. V.D.-Occlusal “S”-Swallowing
,(MM.)
-. i
:i
3 4 5 6 7
37 48
; 10 ;1 13 14
2; i: 49 31 28 38 57 z:
2
17 18 ai
iI: 36 33 17 45
31 23 24
ii 67
5: 27
tt 40
;i 30 31 32 33 34 35 36 37 38 39 40
:7 44 36 22 46 ;: 34 36 60
Legend: P-Immediate dimension. Rest V.D.-Rest
Fir; F/P F/P F/P F/F F/P F/P F$F F/P F/F F/P F//F F/F F/F F/F F/P F/P F/F :;F’ F$ F/P F/,F F/F F/P F/F F/F F/P F/P g; F/P F/F F/F F/F
132 118 115.5
112.5 117.5 114 127 122 118 127.5 123 122 129 140 135 108 140 119 138 123 135 121 132 121.5 117.5 140 125.5 131 116 126 115 120 136 118 125 137 131.5 113 135 129
:.5 3.5 3.5
: : 2 1 2 .: 5 2.5 6 4.5 2 3.5
:
full denture. P-Removable partial vertical dimension. “P”-Phon&ic
1
1.5 1.5 1.5 1 Y 0.5 1.5 0.5 2.5 1.5 i.5 2 4 3 1 2 3 5 0 3 4.5 1.5
2.5 : 2 1 2 :.5 1 3 2.5 6 3 2
111
117 116 126 120.5 125 128 118 125 128 145 138 110 142 120 138 123 137 12.5 131 122.5 121 142 126.5 130 114 125 113 119 135 122 123 139 134 116 136 131 vertical method.
Volume Number
14 4
VERTICAL
DIMENSION
643
CHANGES
mandible. For convenience of classification, the majority of the clinical methods used for determining the facial vertical dimensions are either functional or by distraction techniques. The functional techniques include such patient actions as swallowing. During the act of swallowing, the mandible usually moves from rest position to occlusal contact and back to rest position. Another functional method is referred to as patient conditioning. This produces fatigue in the masticatory musculature through exercise, resulting in its relaxation and in the mandible assuming its TABLE
III.
STAGE III-SIX
MONTHS
WITH
POST-EXTRACTION
DENTURES
WITHOUTDENTURES
IPT.
AGE
SEX
TYPE CASE
occ. V.D. (MM.1
1 :: : 6 i 9 10 :a 13 14 f2 17 :; 20 21 :i 24 25 it 28 29 30 31 32
2;: 37 48 66 47
:: :: ii :: i; 36 33 17 4.5
ii 67 48
:t i: E 39
46 38 24
E
it
Legend: dimension.
z;t: F/F Ei:: F/P F/P F/P F/F
57
:i 3.5
it 40
F/F F/P F/P
60 42 49
F-Immediate Rest V.D.-Rest
FiF’ FiF F/F F/F F/P F/P
F/F FiF’ F/P F$F F/P :I; F/P F/F F/F F/P F/P F/P F/P F/P F/F F/F F/F
128 116.5 115.5 112.5 115.5 111 124 122 117 12.5 122 120 130 137 133 106 136 116 136 122 135 121 128 119.5 116 140 127 131 111.5 12.5 111 118 133 114.5 124 133.5 129 111 129.5 126
REST V.D. “P” (MM.)
FREEWAY SPACE (MM.:
REST V.D. “S” (MM.)
FREEWAY SP.4C13 (MM.:
134 117 116 116 117 114 129 123.5 124 131.5 123 124 135 142 136 109.5 138 118.5 140 23 136 125 132 121 116 142 130 133 113 130 11.5 123 137.5 118 12.5 140 132 115.5 136.5 128
6 0 5 0.5 3.5 1.5 3 5 1.5 7 6.5
132 117 116.5 113 117 112.5 127 123 121
4 0.5 1 0.5 1.5 1.5 3 1 4
128 122.5 123
ii.5 3
132 139.5 138 107 139 117.5 139 124 136 123 129 121 119 141 130.5 135.5 113 127 113 121 137 117 120 137
i.5 5 1 3 1.5 3 2 1 2
133 117.5 136 130
i.5 6.5 3
: .: :.5 2 2.5 4 1 1 : 1.5 ; 3 2 1.5 5 4 5 4.5 3.5 1 6.5 3 4.5 7 2
full denture. P-Removable partial vertical dimension. “P”-Phonetic
denture. method.
:.5 3 i.5 4.5 1.5 2 2 ;: 2.5 2 3.5
REST V.D. “P” (MM.1
REST V.D. l‘s” (MM.)
130 120 116.5 115 119 116 127 122 124 124 119 124.5 131 143 135 110 138 120 137 122 135 128 132 125.5 123 142.5 128.5 127 114 128 114.5 121.5 136 119 123 144 134 112 136 128
129 119.5 118 112 116 113 125.5 121 125 130 118.5 123 127 140 138.5 109 141 118 136 123 135 125 130 121.5 123 142 128.5 130 113.5 125 111 116 135.5 119.5 123 138 132 115 134 127
Oct. V.D.-Occlusal “S”-Swallowing
vertical method.
OF CASE
Patients
*F/F-Immediate IF/P-Immediate SP-Rest vertical IS-Rest vertical
STAGE (Average)
All
(23 Patients)
F/W
F/F* ( 17 Patients)
TYPE
-1
123.8
p-*-123.7
ti 8
4 $
full upper full upper dimension dimension
-
1
!
126.4
1 126.0
----J
DENTURES
125.8
I /
/ 127.3 ~___
( 126.5
WITH
--
PRE-EXTRACTION
STAGE
IV. AVERAGE
/
j
I
s:: 0
2
125.2
124.8
VERTICAL
over immediate full lower. over removable partial lower. by phonetic method. by swallowing method.
TABLE
1128.3~
1 127.8
I
3
DIMENSIONS
BY
TYPE OF
WITHOUT
/ 127.3
( 126.9
CASE,
/ 126.0
1 125.5
______
DENTURES
POST-EXTRACTION
II
j 126.7 ___~__127.4
WITH
WEEKS
STAGE
(MM.)
123.2 __~
123.5
2
2
ei
STAGE,
P
6
126.5
126.6
-____
125.7
126.9
s
125.7
P
/ 126.1
125.4
124.9
s
1 125.2
I
I
WITHOUT
/ 126.4
I I
/
DENTURES
POST-EXTRACTION
I I I
j 125.8
WITH
MONTHS
STAGE
PROCEDURE
126.4
-1-1
/-
AND
125.8
126.3
TOTAL
8
y&lml&
‘4”
VERTICAL
DIMENSION
CHANGES
645
natural rest position .8 The phonetic methods depend on the pronunciation of letters such as “M” and words such as “Mississippi” and “M-N-C” for the mandible to assume its true rest position.g-l” The “distractional” techniques employed attempt to locate the mandible in its resting state by distraction. These approaches have also been referred to as “no command” method” or the relaxation meth0d.l” Although this method does not require the patient to perform any preliminary action, it depends on the dentist’s judgment as to when the patient is in a state of appropriate physical and mental relaxation. Variations and combinations of the above procedures have been employed and reported with success .ls4 It has been reported that some of these methods of determining rest position showed no statistically significant differences,4,12 while other studies found the methods differed significantly.iO~tl The phonetic and swallowing methods were used in this study because these techniques require the patient to perform simple physiological actions. It was found that these methods were readily understood by the patients and were easily interpreted by the dentist. The two methods used for establishing rest positions were statistically compared. Although the differences between the means as seen in Table IV and Fig. 3 are of a small magnitude clinically, the difference of the means proved to be significant. Even though the measurements of the rest position differed from each other, the phonetic method gave consistently greater values at all stages. Thus, it is evident that the production of sounds, such as humming the letter “m,” will produce a greater interocclusal distance than a swallowing action. OCCLUSAL
VERTICAL
DIMENSION
The occlusal vertical dimension at the 3 weeks post-extraction period, with dentures, for all patients demonstrated a general increase from the original natural tooth pre-extraction stage. The mean at Stage I of 123.8 mm. increased to a mean of 125.2 mm. Testing the +1.4 mm. change of these means proved this difference to be statistically significant. Two types of prosthetic replacements were fabricated for the 40 patients. Immediate complete upper and lower dentures were constructed for 17 subjects, while immediate complete upper dentures with bilateral distal extension removable partial dentures were made for 23 subjects. The average vertical dimension readings in Stages I and II were consistently greater for subjects with full mouth extraction (F/F) than for those with partial dentures (Table IV). However, 6 months post-extraction (Stage III) the reverse was true, indicating that the more teeth lost in preparing the mouth for prosthesis the greater the ultimate loss in occlusal vertical dimension. In the last 6 months of the study (Stages II and III), the subjects with complete upper and lower (F/F) dentures demonstrated more than twice the loss (2-S mm. ) in the occlusal dimension than did the partial lower denture group (1.3 mm.). The final occlusal vertical dimension at the end of 6 months was slightly less than the original pre-extraction measurement, -0.6 mm. (Table IV). This sug-
646
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Den. 1961
gests the mechanism involved is not critically governed by the original dimension. The reduction may continue beyond the limits of this study, indicating the need to follow this type of investigation for longer time periods. After 6 months of denture use, the occlusal vertical dimension was decreased. The mean reduction of -2.0 mm. from Stage II (125.2 mm.) to Stage III (123.2 mm.) was statistically significant. Thirty subjects demonstrated a decrease in the occlusal vertical dimension, while 7 remained the same, and 3 showed an increase. Essentially, the same number of individuals show a reverse pattern in the earliar phase (Stages I and IT). A general reduction in the occlusal vertical dimension is expected after the extraction of teeth and the insertion of dentures. However, this marked decrease cannot be solely attributed to the forces placed upon the residual alveolar ridge through the denture. Part of it is due to the bone resorption which occurs after oral surgery. The settling and shifting of the denture bases into soft mucosal tissue may account for a small portion of this change. The settling of the denture is usually seen the first few weeks of denture wearing. Thus, some of the so-called settling could have occurred before Stage II. REST
VERTICAL
DIMENSION
The three weeks post-extraction, rest vertical dimension with dentures gave a mean of 128.3 mm. and 127.4 mm. for the phonetic and swallowing methods, respectively (Table IV). When these means are compared to the initial pre-extraction mean, a general increase is evident, similar to the change seen in the occlusal vertical dimension. An individual tally of the rest vertical dimension (phonetic method) with dentures revealed that in 26 subjects it increased, in 7 it remained the same, and in 7 it decreased. Essentially the same measurements were recorded by the swallowing method with an increase in 24 subjects, no change in 6 subjects, and a decrease in 10 subjects. Cephalometric records were made at the 3 weeks post-extraction stage withopt dentures. There was no change of the rest vertical dimension as determined by both the phonetic and the swallowing methods when compared with the corresponding pre-extraction measurements. The difference of the means for Stage I and Stage II without dentures was -0.4 mm. by the swallowing method and I~Q difference phonetically. Other investigators3a4,‘” have reported instability of the rest position and a pronounced decrease in rest face height after the removal of occlusal contacts. The reason suggested by Atwood3 is the destruction of the periodontal receptors by the extraction of teeth. It is thought that the periodontal receptors influence both the masticatory reflexes and postural reflex of the mandible. Therefore, the loss of periodontal nerve endings following tooth extraction results in hampering the orientation of the mandible to its normal rest position. The reduction of the rest vertical dimension (without dentures in the mouth) observed by the others was not found in this study. It should be emphasized that in the present investigation, the loss of occlusal stops by tooth extraction were immediately replaced and maintained by inserting the dentures. Thus, the sub-
Volume Number
14 4
VERTICAL
DIMENSION
CHANGES
647
jects did not experience a 2 to 3 month period of complete edentulousness. It would seem that the conditioned reflexes for mandibular position established with natural teeth (Stage I) are maintained for at least 3 weeks as demonstrated by the recordings of the rest position without dentures at Stage II (Fig. 3). Throughout the study, the measurements of rest vertical dimension with dentures were consistently larger (Fig. 3) than without dentures in the mouth. A change in the mandibular load and gravity appears to influence the rest position of the mandible. The presence of dentures, which provide occlusal contact as well as pressure to the exteroceptors in the mucosa of the denture supporting area, contribute to the regulating mechanism of mandibular posture. The exteroceptors of oral mucosa in complete or partially edentulous patients may compensate for the loss of periodontal receptors. Thus, the pressure sensory impulses initiated from the alveolar mucosa could influence maxillo-mandibular opening when tletermining the facial vertical dimensions during denture construction. This phenomenon may explain the discrepancy between the vertical dimension measurements with and without dentures. The rest vertical dimension from 3 weeks to 6 months post-extraction (Stage II to Stage III) underwent a decided reduction which was comparable to the pronounced decrease observed in the occlusal vertical dimension. The mean for the measurements of rest position with dentures decreased from 128.3 mm to 126.5 mm. in the phonetic technique, and from 127.4 mm. to 125.8 mm. with the swallowing method. At the same 6 months post-extraction sitting, the dentures were removed from the patient’s mouth and a record of the rest dimension was made. The rest vertical dimension means, with and without dentures, demonstrated no appreciable difference in either of the methods used. However, in comparing the change of rest dimension without dentures, a definite reduction between Stages II and III is evident. Attention is called to the fact that the rest vertical dimension at the last stage is very similar to the same measurement recorded at the onset of the study. JKTEROCCLUSAL
DISTANCE
The free-way space (interocclusal distance) also underwent some alterations (Fig. 3). At the pre-extraction stage, the mean interocclusal distance (phonetically) was 3.7 mm. and (swallowing) was 2.6 mm. This range of measurements of the interocclusal distance is in agreement with the average values reported for adults by other investigators.4y15-18 The mean measurements of the interocclusal distance decreased after the 3 week post-extraction stage to 3.2 mm. (phonetic) and 2.2 mm. (swallowing j. As the occlusal and rest vertical dimension increased from Stage I to Stage II, the interocclusal distance became smaller (Fig. 3). The fact that the rest position change in response to the changes in the occlusal vertical dimension is of major importance in order to maintain a functional interocclusal distance. Although the interocclusal distance may undergo transition, it seems to be capable of size variation, thus aiding the regulatory mechanism of the mandible in accommodating to a new situation. The inverse relationship of the interocclusal distance to the occlusal and rest
648
SWERDLOW
J. Pros. July-Aug.,
Deu. 1961
dimensions is seen again at the 6 month post-extraction stage. The interocclusal distance having increased to 3.3 mm. (phonetic) and 2.5 mm. (swallowing) has ahnost returned to the original pre-extraction recordings. The mean of the phonetically determined interocclusal distance indicates that the facial dimension may continue to change beyond the 6 months post-extraction stage. In clinical dentistry the average interocclusal distance of 2 to 4 mm. is accepted as being adequate. The broad measurement range of 1 to 9 mm. (see Tables I, II, III) would more accurately represent the general adult population. However, for any given patient the interocclusal distance should be specifically determined. Treating patients by average is not reliable and is fraught with error. Each individual patient should be evaluated objectively. The over-all pattern of the facial vertical dimension can be seen in Fig. 3. The occlusal vertical dimension and the rest position are directly related to each other. A change in one is reflected in the other. However, when dentures are removed from the mouth, the rest dimension does not seem to adapt quickly to the change in the occlusal vertical dimension. A change in occlusal vertical dimension seems to cause an adaptation in the neuromuscular mechanism, resulting in a similar change in the rest vertical dimension with dentures. It is conceivable that such adaptation is necessary in order to allow the regulatory mechanism to maintain continuously optimal function compatible with changing conditions. The role of the interocclusal distance during transition appears to conform by adjusting itself to the needs of the occlusal and rest position alterations. The value of the immediate denture for maintaining proper face height is supported in this study. Conventional methods require the patient to experience an edentulous healing period before denture construction. The data in this study suggest greater stability in facial vertical dimensions after the removal of occlusal contacts as compared to the reported variability in the conventional denture procedure without pre-extraction records.3,4s14 It is difficult to determine when the reduction in facial dimension stops or when equilibrium is established. The need for periodic recalling of all denture patients is imperative. At these visits, a change in the facial vertical dimension can be corrected either by refitting the denture base and/or re-establishing the occluding surfaces. The recall system could prevent the denture wearer from accommodating to an undesirable, destructive functional and esthetic relation which dominates the mandibular posture. SUMMARY
The primary purpose of this study was to determine any changes which may occur in the occlusal vertical dimension, the rest vertical dimension, and the interocclusal distance in adult patients in the transition from natural teeth to immediate complete and partial dentures, and during the initial 6 month period of use. The secondary aim was to compare the phonetic and swallowing methods for establishing the rest position of the mandible. Serial lateral cephalometric roentgenograms, using the Broadbent-Bolton cephalometer, were made for each of 40 immediate denture patients. The series of lateral head films were made at three
El% ‘4”
VERTICAL
DIMENSION
649
CHANGES
stages : Stage I-pre-extraction, Stage II-3 weeks post-extraction, and Stage III6 months post-extraction. The facial vertical dimensions were measured directly on the lateral head films between the nasion and the menton. CONCLUSIONS
1. The phonetic method of establishing mandibular rest position gave consistently greater values for the interocclusal distance in all three stages. When analyzed statistically, the functional swallowing method produced significantly different results from the phonetic method for determining the rest position of the mandible. 2. The occlusal vertical dimension increased significantly from Stage I to Stage II in spite of the guiding value of the natural teeth during the fabrication of the immediate dentures. 3. The occlusal vertical dimension decreased markedly in the 6 month period of wearing the dentures (Stage II to Stage III). At the end of the study, the occlusal vertical dimension was slightly smaller than before treatment was started. 4. The complete upper and lower denture group showed twice as much loss of occlusal vertical dimension than did the partial denture subjects. 5. The rest vertical dimension appears to parallel the alterations in the occlusal vertical dimension. 6. The interocclusal distance adjusts itself to accommodate the variations in facial vertical dimension. 7. A change in mandibular load and gravity may influence the rest position of the mandible. Comparison of means data showed that the rest vertical dimension with dentures was consistently greater than that without dentures. This suggests that the exteroceptors in the mucosa of the denture supporting area contribute to the regulating mechanism for mandibular posture. 8. The value of the immediate denture procedure is supported by this study. Greater stability is found in the facial vertical dimensions after the removal of occlusal contacts as compared to the reported variability in the usual denture procedure carried out without pre-extraction records. 9. The observations in this investigation indicate the need for periodic recalling of denture patients for appraising and re-establishing facial vertical dimension. The cooperation and assistance Graduate Division of the University acknowledged.
of Drs. A. W. Moore, W. of Washington, School
L. Kydd, and of Dentistry,
H. A. Young, are gratefully
REFERENCES
1. Thompson, J. R.: The Rest Position of the Mandible and Its Significance to Dental Science, J.A.D.A. 33:151, 1946. 2. Swenson, M. G.: Complete Dentures, St. Louis, 1940,. The C. V. Mosby Co., p. 311. 3. Atwood, D. A.: A Cephalometric Study of the Chnical Rest Position of the Mandible. Part I, J. PROS. DEN. 6:504, 1956; Part II. J. PROS. DEN. 7:544, 1957; Part III, J. PROS. DEN. 8:698, 1958. 4. Tallgren, A.: Changes in Adult Face Height Due to Ageing, Wear and Loss of Teeth and Prosthetic Treatment, Acta. Odont. Scandinav. 15:1-112, Suppl. 24, 1957. 5. Richards, A. G.: Roentgen-ray Doses in Dental Roentgenography, J.A.D.A. 56:351, 1958.
650 6.
SWERDLOW
Krogman!
W. M., and Sassouni, V. : A Syllabus in Roentgenographic Cephalometry, Philadelphia Center for Research in Child Growth, Philadelphia, Pa., 1957. 7. Thurow, R. C.: Cephalometric Methods in Research and Private Practice, Angle Orthodont. 21:104, 1951. 8. Boos. R. H.: Occlusion From Rest Position. T. PROS. DEN. 2:.575. 1952. 9. Gill&, R. R.: Establishing Vertical Dimension in Full Denture donstruction, J..‘i.D..A. 28 :4.x. 1941. 10. Anderson, R. M.: An Appraisal of Different Methods Used in Determining the Rest Position of the Mandible and the Resulting Free-way Space by Cephalometric Roentgenograms, Thesis, University of Washington, 1952. 11. Butori, E. F. : A Serial Cephalometric Study of the Rest Position of the Mandible of Individuals With Excellent Occlusions, Thesis, University of Washington, 1952. 12. Coulombe, J. A. R.: A Serial Cephalometric Study of the Rest Position of the Mandible on Edentulous Individuals, Thesis, University of Washington, 1952. 13. ThGrne, H.: The Rest Position of the Mandible and the Path of Closure From Rest to Occlusion Position. Methods of Cephalometric Determination, Acta. Odont. Scandinav. 11: 141, 1953. 14. Duncan, E. T., and Williams, S. T. : Evaluation of Rest Position as a Guide in Prosthetic Treatment, J. PROS DEN. 10:643, 1960. 15. Niswonger, M. E.: Obtaining the Vertical Relation in Edentulous Cases That Existed Prior to Extraction, J.A.D.A. 25:1842, 1938. 16. Thompson, J. R.: Concepts Regarding Function of the Stomatognathic System, J.A.D..;\. 48 ~626, 1954. 17. Sicher, H.: Oral Anatomy, ed. 3,. St. Louis, 1960, The C. V. Mosby Co. 18. Posselt, U.: Studies in the Mobility of the Human Mandible, Acta. Odont. Scandinav. 10:19, Suppl. 10, 1952. --
-
U.S. PUBLIC NATIOXAL BETHESDA
.--I
--
.-.
HEALTH INSTITUTES
14, MD.
SERVICE, DENTAL OF HEALTH
DEPARTMENT
STUDY DENTURE
HERBERT
SWERDLOW, B.A., D.D.S., M.S.D.”
Bethesda,
Md.
T
HOMPSON~
OF VERTICAL PATIENTS
DIMENSION
CONCLUDED from a series of cephalometric studies that, “Without
exception, it has been shown that the mandible assumesits positional relationship to the head by the third month of life and thereafter does not change.” The constancy concept of physiologic rest position has gained widespread acceptance. It is utilized by many clinicians for the establishment of the vertical dimension of occlusion in restorative procedures, and for maintaining oral function. However, Swenson’s2viewpoint on the clinical application of prevailing concepts is also currently supported and merits consideration. He wrote, “It seemsthat any definite statements that have been made concerning a method of arriving at the correct vertical dimension have been easily disproved. Therefore, the only definite statement that should be made is that it is an indefinite procedure.” At the present time, the constancy concept of face height is being questioned in the light of evidence presented by Atwood3 and Tallgren4 in their cephalometric studies. PURPOSE OF THE STUDY
This investigation was designed primarily to determine alterations which may occur in the occlusal vertical dimension, the rest vertical dimension, and the freeway space (interocclusal distance) of adult patients in the transition from natural teeth to immediate dentures, and during the first 6 months of their use. A secondary aim of the project was to compare two clinically accepted methods of establishing the rest position of the mandible: the phonetic and swallowing methods. In this study, the term “immediate denture” denotes a complete artificial substitute constructed for insertion immediately following the removal of the last remaining natural teeth. The Broadbent-Bolton cephalometer was the instrument used for recording serial lateral cephalometric roentgenograms on each of 40 immediate denture patients during a continuous 6 month period. MATERIALS
AND METHODS
A total of 40 patients, including 30 women and 10 men with an age range of 17 to 66 years (mean age, 42 years), were utilized for this longitudinal cephalometric study. Condensed from a thesis completed at the University of Washington, School of Dentistry in partial fulfillment for the degree of Master of Science in Dentistry. Presented before the American Prosthodontic Society in Philadelphia, Pa. *Dental Department, Clinical Center, National Institutes of Health, Public Health Service, U. S. Department of Health, Education and Welfare. 835
636
SWERDLOW
J. Pros. July-Aug.,
Den. 1961
The first series of cephalometric roentgenograms was completed after clinical examination and the patient was accepted for treatment, but before the loss of occlusal stops. Prosthetic treatment for 17 patients consisted of complete upper and lower immediate dentures, while for 23 patients treatment was an immediate complete upper denture in combination with a removable partial lower denture. All of the partial dentures were of the bilateral distal extension type with most abutments covered with surveyed full crowns. The prosthetic appliances for all subjects in the study were fabricated by the same techniques. The final impressions for the immediate dentures were made by utilizing a custom acrylic resin tray with a zinc oxide and eugenol paste wash impression posterior to the remaining teeth ; compound or wax was used to complete the anterior section. A double impression technique was used for the lower partial dentures. A tissue rest impression of only the future tissue support area was made with a zinc oxide and eugenol paste in a custom acrylic resin tray. A second alginate impression was then made over the first with firm loading of the denture bearing tissue. The occlusal vertical dimension for all patients was recorded by wax occlusal rims. The adequacy of the occlusal vertical dimension was judged by the contact of the remaining natural teeth, and interocclusal distance of 3 to 4 mm., the facial expression, passive contact of the lips, phonetics, and esthetics. The teeth were set up in centric occlusion at the centric relation with bilateral balance, processed in methylmethacrylate resin, remounted to correct processing changes, and machine-paste milled. The delivery of the dentures and the post-insertion checks were performed within accepted prosthodontic standards. Two functional methods were employed in obtaining the roentgenographic registrations of rest position for this study. The phonetic and swallowing methods were selected because both use the patient’s own musculature to establish resting mandibular posture with ease after performing a common physiologic action. These methods did not require coaching or explanation, or the examiner’s subjective evaluation, to determine when the subject was “at rest.” DESCRIPTION
OF
THE
METHODS
EMPLOYED
Swallowing Method.-With the patient’s head adjusted in the cephalostat, a mouthful of water was drawn by means of a straw from a cup and held in the patient’s mouth. The subject was then asked to swallow and relax. The laryngeal structures and hyoid bone were observed to move upward, then return to their original position. A few seconds later the exposure was made. Phonetic Method.-The patient was asked to hum the letter “m” like the note of a song, allowing it to slowly fade away until the sound finally could no longer be heard. The lateral film was then exposed within a few seconds following cessation of the hum. At every sitting, the procedure was practiced before the exposure was made. The entire cephalometric procedure was explained to the patient as being one more step in the routine for immediate denture patients which would be helpful in their future denture service. The lateral roentgenographic registrations were made on 8 by 10 inch films
Volume
14
Number
4
VERTICAL
DIMENSION
CHANGES
637
in cassettes with intensifying screens. Each patient remained in the cephalostat until the series of five exposures was completed for each stage. STAGE I.--Pre-extraction (before the natural occlusal stop teeth were lost by extraction). (a) Two films were exposed with the natural teeth in centric occlusion. (b) Two films were exposed with the mandible in rest position, one determined by the phonetic method, and the other by swallowing. (c) One film was exposed with the mouth wide open. STAGE II.-Three weeks post-extraction (3 weeks after the insertion of the immediate dentures). (a) Four films were exposed in mandibular rest position, two with immediate dentures and two without dentures. (b) One film was exposed with the denture teeth in centric occlusion in the mouth. STAGE III.--Six months post-extraction (6 months after the immediate insertion of the dentures). (a) Four films were exposed in the mandibular rest position, two with the immediate dentures and two without dentures. (b) One film was exposed with the denture teeth in centric occlusion in the mouth. At each of the sittings for Stages I, II, and III, every pair of films made of mandibular rest position contained one exposure with the use of the water swallowing method, while the other exposure utilized the phonetic technique. The cephalometric films for Stage II were recorded after the patient had worn the immediate dentures for a period of 3 weeks. This period of 3 weeks post-extraction allowed the trauma from surgery to disappear and provided sufficient time for the patient to become relaxed and comfortable with the new dentures.
RADIATION
CONTROL
A total of 600 lateral roentgenograms were made during the entire study. The amount of radiation delivered to the patient’s head was measured with a Victoreen ionization chamber. A model phantom skull, filled and coated with wax to simulate human features, was used as a test object. The exposure time for each cephalometric roentgenogram was 0.5 seconds at 85 kilovolts, 20 milliamperes, 2.25 mm. filter with the anode-object distance of 60 inches. The radiation to the skin per exposure was found to be 0.04 r and to the center of the head 0.004 r. Richards,5 using the same measuring method (Victoreen chamber), found an average of 1.7 r dose to facial skin per intraoral film with the roentgen unit operating at 65 KVP, 10 Ma., 2.25 mm. filtration, 7 inch target distance. Thus, the radiation delivered to the patient’s facial skin during one intraoral exposure would be equivalent to the roentgen dosage from over 40 cephalometric films. The total radiation exposure to all the subjects in this study was less than the dosage delivered by a 15 film intraoral complete mouth roentgenographic examination. FILM
PLACEMENT
The distance from the median-sagittal plane of the head to the film was recorded for each subject at the first sitting. This midline to film distance was kept constant for each subsequent sitting throughout the study in order to control the magnification error.
J. Pros. Den. July-Aug., 1964
SWERDLOW
638
Menton Fig.
1.-A
REFERENCE
typical
master
template
tracing
illustrating
roentgenographic
landmarks.
POINTS
The reference points and landmarks used for measuring on the films are in accordance with those described by Krogman and Sassouni.g The two major osteologic landmarks considered were the nasion and the menton. Point Na, nasion, is the most anterior point of the naso-frontal suture seen from norma lateralis. The menton is located as the lowermost point on the symphyseal shadow as seen from norma lateralis (Me). Both measuring points are situated in the median-sagittal plane. In those subjects in whom double projections of the right and left sides of the mandible were seen, a mid-point was used.7 CEPHALOMETRIC
TRACINGS
In order to control the cumulative tracing errors, the measurements were made directly on the roentgenographic film. A master template of the centric occlusion film judged to be the clearest was traced on semi-transparent acetate paper. Structures of high contrast, such as the sella-turcica, inner and outer tables of the skull, pterygomaxillary fissure, anterior air sinuses, cortical plates of the
Volume 14 Nunlber 4
VERTICAL
\.
Fig.
2.-A
diagram
illustrating
\I
DIMENSION
occlusol
I
the linear positlon
639
CHANGES
Vertical
measurements roentgenograms.
(mm.)
made
on the
I
occlusal
and
rest
body and ramus of the mandible, the dense symphysis shadows, the external oblique line, inferior alveolar canal and teeth, were included, when possible, on the template tracing. A master template was traced for each patient (Fig. 1) . This tracing was superimposed on all of the films for that patient, so that the contours of the upper part of the face coincided, and with a sharp point the location of the nasion was punctured through the tracing into the film. For location of the point menton, the silhouette of the mandible and teeth were registered and the lowermost point on the symphyseal shadow of each fihn was pierced. The occlusal vertical dimension is the distance measured from nasion to menton when the maxillary and mandibular teeth (natural or artificial) were in contact. When the mandible assumed a resting position, the distance from nasion to menton on the rest position films determined the rest vertical dimension. The interocclusal distance or free-way space is the difference between rest vertical dimension and the occlusal vertical dimension. In each of the three stages of this investigation, the interocclusal distance constitutes the difference between the nasion-menton measurement on the films of the rest and occluding positions. All
640
J. Pros. lkw. July-Aug., 1964
SWERDLOW
122J
P= Phonetic S = Swallowing
a- 5Ze_WOY-
OJ
Fig.
3.-Facial
, Pre-extraction Natural Teeth
vertical
dimension
SPoce -----
0
II s’ -___
o _*e-
--
I 3 weeks Postextraction
means plotted at stages denture patients.
a
____-----
1 6 months Postextraction in a serial
study
cjf 40 immediate
linear measurements were made with the same millimeter ruler to the nearest 0.5 mm. (Fig. 2). Th linear measurements were subjected to statistical analysis in order to evaluate the significance of these recordings. The relationship of the variables at the different stages are demonstrated graphically (Fig. 3).
The phonetic method of establishing mandibular rest position resulted in consistently greater values as compared to the results of the swallowing procedure. The average difference is statistically significant. The occlusal vertical dimension showed an average increase from the pre-extraction stage to 3 weeks post-extraction, while a decrease was found at the 6 months post-extraction stage.
Extr ‘4”
VERTICAL
DIMENSION
641
CHANGES
The rest vertical dimension generally parallels the pattern of the occlusal vertical dimension. The average measurements of the interocclusal distance varied inversely to the pattern followed by the occlusal and rest vertical dimensions. In the final stages, the complete upper and lower denture group showed twice as much loss in the facial vertical dimensions as did the partial denture group. The occlusal vertical dimension, the rest vertical dimension, and the dimension of the interocclusal distance for each stage of the study are shown in Tables
TABLE
I.STAGE
I-PRE-EXTRACTION
occ. TYPE CASE
V.D. (MM.)
129.5 116 115.5 111.5 117.5 114 12.5 120 118 127 119 123 125 142 136 108 140 117.5 140 120 133 121 129.5 120 117 138 127 126 113 124 112 116.5 13.5 118 12.5 136 129 109 132 127 Legend: F-Immediate dimension. Rest V.D.-Rest
full denture. P-Removable partial vertical dimension. “P”-Phonetic
REST V.D. "P" (MM.)
FREEWAY SPACE (MM.)
REST V.D. 'Y (MM.)
FREEWAY SPACE (MM.)
133 117 118 113 119 116 127 121 119 134 120 126 131 144 138 114 142 126 143 121 139 126 134 126 118 140 130 128 117 128.5 116 126 137 119
3.5
132 117 117.5 112.5 119 115 126.5 123 121 130 119.5 126 128 143 138 111 141 121 142 123
2.5
139 126 130 126.5 119 140.5
i 0.5 6.5 2 2.5
128 132 115
ii 2
126 114 120
i 3.5
143 126
:
: 1.5 4
132 118 137 131
; 5 4
136 119 126.5 140 131 115 136 129
denture. method.
Oct. V.D.-Occlusal ‘3”-Swallowing
:.5 1.5 1.5 2 2 1 : : ! :, 2 8.5 3 1 Ei 4.5 6 1 3 i 4.5 4 9.5 2 1
1 1 1.5 :.5 3 i 0.5 3 3 ; 3 i.5 2 3
i 4 2 vertical method.
642
J. Pros.
SWERDLOW
July-Aug.,
Dm.
1964
I, II, III. The means of the entire study are illustrated graphically in Fig. 3, and listed in Table IV. The shading seen in hoth the phonetic and swallowing rest vertical dimensions are presented to aid in distinguishing the plotted means with dentures as opposed to without dentures at the various stages (Fig. 3).
Phonetic WYSUS Szvalloting Method.-The literature reviewed clearly demonstrates the elusiveness of determinations of the clinical rest position of the TABLE
II.STAGE
II-THREE WEEKS
POST-EXTRACTION
WITHDENTURES
PT.
AGE
SEX
TYPE CASE*
occ. V.D.t (MM.1
REST V.D.$ “P" (MM.)
FREEWAY SPACE (MM.)
136 119 119 116 121
4
119 130 126
: 4
135 119
:s
124 125.5 132 143 136 115 142 120 140 124 138 126 134.5 127.5 122 142 129
:.s
118.5 137
g.5
129 116.5 124 137 119
i3.S 4
126 144 133
: 1.5
118 138 130
; 1
WITHOUTDENTURES
REST V.D. ‘$9)
FREEWAY SPACE (MM.)
REST V.D. “P" (MM.1
REST V.D. %" (MM.)
135 119 117 114 119 115 127 125 118.5 129 123.5 124.5 130.5 143 137.5 110 144 122 139 125 138 126 132 124.5 122 141.5 128 136 119 128 116 122 137 119.5 126 140 134 119 138 131
3
136 120 119.5 113 119.5 118 128 122.5 122.5 133 119 126 134 145 135 113 142 120 139 121 136 127 134 125.5 119.5 143 128.5 13.5 115 127.5 115.5 125 134 123 123 144 132 114.5 136 129.5
130 119 119
denture. method.
Oct. V.D.-Occlusal “S”-Swallowing
,(MM.)
-. i
:i
3 4 5 6 7
37 48
; 10 ;1 13 14
2; i: 49 31 28 38 57 z:
2
17 18 ai
iI: 36 33 17 45
31 23 24
ii 67
5: 27
tt 40
;i 30 31 32 33 34 35 36 37 38 39 40
:7 44 36 22 46 ;: 34 36 60
Legend: P-Immediate dimension. Rest V.D.-Rest
Fir; F/P F/P F/P F/F F/P F/P F$F F/P F/F F/P F//F F/F F/F F/F F/P F/P F/F :;F’ F$ F/P F/,F F/F F/P F/F F/F F/P F/P g; F/P F/F F/F F/F
132 118 115.5
112.5 117.5 114 127 122 118 127.5 123 122 129 140 135 108 140 119 138 123 135 121 132 121.5 117.5 140 125.5 131 116 126 115 120 136 118 125 137 131.5 113 135 129
:.5 3.5 3.5
: : 2 1 2 .: 5 2.5 6 4.5 2 3.5
:
full denture. P-Removable partial vertical dimension. “P”-Phon&ic
1
1.5 1.5 1.5 1 Y 0.5 1.5 0.5 2.5 1.5 i.5 2 4 3 1 2 3 5 0 3 4.5 1.5
2.5 : 2 1 2 :.5 1 3 2.5 6 3 2
111
117 116 126 120.5 125 128 118 125 128 145 138 110 142 120 138 123 137 12.5 131 122.5 121 142 126.5 130 114 125 113 119 135 122 123 139 134 116 136 131 vertical method.
Volume Number
14 4
VERTICAL
DIMENSION
643
CHANGES
mandible. For convenience of classification, the majority of the clinical methods used for determining the facial vertical dimensions are either functional or by distraction techniques. The functional techniques include such patient actions as swallowing. During the act of swallowing, the mandible usually moves from rest position to occlusal contact and back to rest position. Another functional method is referred to as patient conditioning. This produces fatigue in the masticatory musculature through exercise, resulting in its relaxation and in the mandible assuming its TABLE
III.
STAGE III-SIX
MONTHS
WITH
POST-EXTRACTION
DENTURES
WITHOUTDENTURES
IPT.
AGE
SEX
TYPE CASE
occ. V.D. (MM.1
1 :: : 6 i 9 10 :a 13 14 f2 17 :; 20 21 :i 24 25 it 28 29 30 31 32
2;: 37 48 66 47
:: :: ii :: i; 36 33 17 4.5
ii 67 48
:t i: E 39
46 38 24
E
it
Legend: dimension.
z;t: F/F Ei:: F/P F/P F/P F/F
57
:i 3.5
it 40
F/F F/P F/P
60 42 49
F-Immediate Rest V.D.-Rest
FiF’ FiF F/F F/F F/P F/P
F/F FiF’ F/P F$F F/P :I; F/P F/F F/F F/P F/P F/P F/P F/P F/F F/F F/F
128 116.5 115.5 112.5 115.5 111 124 122 117 12.5 122 120 130 137 133 106 136 116 136 122 135 121 128 119.5 116 140 127 131 111.5 12.5 111 118 133 114.5 124 133.5 129 111 129.5 126
REST V.D. “P” (MM.)
FREEWAY SPACE (MM.:
REST V.D. “S” (MM.)
FREEWAY SP.4C13 (MM.:
134 117 116 116 117 114 129 123.5 124 131.5 123 124 135 142 136 109.5 138 118.5 140 23 136 125 132 121 116 142 130 133 113 130 11.5 123 137.5 118 12.5 140 132 115.5 136.5 128
6 0 5 0.5 3.5 1.5 3 5 1.5 7 6.5
132 117 116.5 113 117 112.5 127 123 121
4 0.5 1 0.5 1.5 1.5 3 1 4
128 122.5 123
ii.5 3
132 139.5 138 107 139 117.5 139 124 136 123 129 121 119 141 130.5 135.5 113 127 113 121 137 117 120 137
i.5 5 1 3 1.5 3 2 1 2
133 117.5 136 130
i.5 6.5 3
: .: :.5 2 2.5 4 1 1 : 1.5 ; 3 2 1.5 5 4 5 4.5 3.5 1 6.5 3 4.5 7 2
full denture. P-Removable partial vertical dimension. “P”-Phonetic
denture. method.
:.5 3 i.5 4.5 1.5 2 2 ;: 2.5 2 3.5
REST V.D. “P” (MM.1
REST V.D. l‘s” (MM.)
130 120 116.5 115 119 116 127 122 124 124 119 124.5 131 143 135 110 138 120 137 122 135 128 132 125.5 123 142.5 128.5 127 114 128 114.5 121.5 136 119 123 144 134 112 136 128
129 119.5 118 112 116 113 125.5 121 125 130 118.5 123 127 140 138.5 109 141 118 136 123 135 125 130 121.5 123 142 128.5 130 113.5 125 111 116 135.5 119.5 123 138 132 115 134 127
Oct. V.D.-Occlusal “S”-Swallowing
vertical method.
OF CASE
Patients
*F/F-Immediate IF/P-Immediate SP-Rest vertical IS-Rest vertical
STAGE (Average)
All
(23 Patients)
F/W
F/F* ( 17 Patients)
TYPE
-1
123.8
p-*-123.7
ti 8
4 $
full upper full upper dimension dimension
-
1
!
126.4
1 126.0
----J
DENTURES
125.8
I /
/ 127.3 ~___
( 126.5
WITH
--
PRE-EXTRACTION
STAGE
IV. AVERAGE
/
j
I
s:: 0
2
125.2
124.8
VERTICAL
over immediate full lower. over removable partial lower. by phonetic method. by swallowing method.
TABLE
1128.3~
1 127.8
I
3
DIMENSIONS
BY
TYPE OF
WITHOUT
/ 127.3
( 126.9
CASE,
/ 126.0
1 125.5
______
DENTURES
POST-EXTRACTION
II
j 126.7 ___~__127.4
WITH
WEEKS
STAGE
(MM.)
123.2 __~
123.5
2
2
ei
STAGE,
P
6
126.5
126.6
-____
125.7
126.9
s
125.7
P
/ 126.1
125.4
124.9
s
1 125.2
I
I
WITHOUT
/ 126.4
I I
/
DENTURES
POST-EXTRACTION
I I I
j 125.8
WITH
MONTHS
STAGE
PROCEDURE
126.4
-1-1
/-
AND
125.8
126.3
TOTAL
8
y&lml&
‘4”
VERTICAL
DIMENSION
CHANGES
645
natural rest position .8 The phonetic methods depend on the pronunciation of letters such as “M” and words such as “Mississippi” and “M-N-C” for the mandible to assume its true rest position.g-l” The “distractional” techniques employed attempt to locate the mandible in its resting state by distraction. These approaches have also been referred to as “no command” method” or the relaxation meth0d.l” Although this method does not require the patient to perform any preliminary action, it depends on the dentist’s judgment as to when the patient is in a state of appropriate physical and mental relaxation. Variations and combinations of the above procedures have been employed and reported with success .ls4 It has been reported that some of these methods of determining rest position showed no statistically significant differences,4,12 while other studies found the methods differed significantly.iO~tl The phonetic and swallowing methods were used in this study because these techniques require the patient to perform simple physiological actions. It was found that these methods were readily understood by the patients and were easily interpreted by the dentist. The two methods used for establishing rest positions were statistically compared. Although the differences between the means as seen in Table IV and Fig. 3 are of a small magnitude clinically, the difference of the means proved to be significant. Even though the measurements of the rest position differed from each other, the phonetic method gave consistently greater values at all stages. Thus, it is evident that the production of sounds, such as humming the letter “m,” will produce a greater interocclusal distance than a swallowing action. OCCLUSAL
VERTICAL
DIMENSION
The occlusal vertical dimension at the 3 weeks post-extraction period, with dentures, for all patients demonstrated a general increase from the original natural tooth pre-extraction stage. The mean at Stage I of 123.8 mm. increased to a mean of 125.2 mm. Testing the +1.4 mm. change of these means proved this difference to be statistically significant. Two types of prosthetic replacements were fabricated for the 40 patients. Immediate complete upper and lower dentures were constructed for 17 subjects, while immediate complete upper dentures with bilateral distal extension removable partial dentures were made for 23 subjects. The average vertical dimension readings in Stages I and II were consistently greater for subjects with full mouth extraction (F/F) than for those with partial dentures (Table IV). However, 6 months post-extraction (Stage III) the reverse was true, indicating that the more teeth lost in preparing the mouth for prosthesis the greater the ultimate loss in occlusal vertical dimension. In the last 6 months of the study (Stages II and III), the subjects with complete upper and lower (F/F) dentures demonstrated more than twice the loss (2-S mm. ) in the occlusal dimension than did the partial lower denture group (1.3 mm.). The final occlusal vertical dimension at the end of 6 months was slightly less than the original pre-extraction measurement, -0.6 mm. (Table IV). This sug-
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gests the mechanism involved is not critically governed by the original dimension. The reduction may continue beyond the limits of this study, indicating the need to follow this type of investigation for longer time periods. After 6 months of denture use, the occlusal vertical dimension was decreased. The mean reduction of -2.0 mm. from Stage II (125.2 mm.) to Stage III (123.2 mm.) was statistically significant. Thirty subjects demonstrated a decrease in the occlusal vertical dimension, while 7 remained the same, and 3 showed an increase. Essentially, the same number of individuals show a reverse pattern in the earliar phase (Stages I and IT). A general reduction in the occlusal vertical dimension is expected after the extraction of teeth and the insertion of dentures. However, this marked decrease cannot be solely attributed to the forces placed upon the residual alveolar ridge through the denture. Part of it is due to the bone resorption which occurs after oral surgery. The settling and shifting of the denture bases into soft mucosal tissue may account for a small portion of this change. The settling of the denture is usually seen the first few weeks of denture wearing. Thus, some of the so-called settling could have occurred before Stage II. REST
VERTICAL
DIMENSION
The three weeks post-extraction, rest vertical dimension with dentures gave a mean of 128.3 mm. and 127.4 mm. for the phonetic and swallowing methods, respectively (Table IV). When these means are compared to the initial pre-extraction mean, a general increase is evident, similar to the change seen in the occlusal vertical dimension. An individual tally of the rest vertical dimension (phonetic method) with dentures revealed that in 26 subjects it increased, in 7 it remained the same, and in 7 it decreased. Essentially the same measurements were recorded by the swallowing method with an increase in 24 subjects, no change in 6 subjects, and a decrease in 10 subjects. Cephalometric records were made at the 3 weeks post-extraction stage withopt dentures. There was no change of the rest vertical dimension as determined by both the phonetic and the swallowing methods when compared with the corresponding pre-extraction measurements. The difference of the means for Stage I and Stage II without dentures was -0.4 mm. by the swallowing method and I~Q difference phonetically. Other investigators3a4,‘” have reported instability of the rest position and a pronounced decrease in rest face height after the removal of occlusal contacts. The reason suggested by Atwood3 is the destruction of the periodontal receptors by the extraction of teeth. It is thought that the periodontal receptors influence both the masticatory reflexes and postural reflex of the mandible. Therefore, the loss of periodontal nerve endings following tooth extraction results in hampering the orientation of the mandible to its normal rest position. The reduction of the rest vertical dimension (without dentures in the mouth) observed by the others was not found in this study. It should be emphasized that in the present investigation, the loss of occlusal stops by tooth extraction were immediately replaced and maintained by inserting the dentures. Thus, the sub-
Volume Number
14 4
VERTICAL
DIMENSION
CHANGES
647
jects did not experience a 2 to 3 month period of complete edentulousness. It would seem that the conditioned reflexes for mandibular position established with natural teeth (Stage I) are maintained for at least 3 weeks as demonstrated by the recordings of the rest position without dentures at Stage II (Fig. 3). Throughout the study, the measurements of rest vertical dimension with dentures were consistently larger (Fig. 3) than without dentures in the mouth. A change in the mandibular load and gravity appears to influence the rest position of the mandible. The presence of dentures, which provide occlusal contact as well as pressure to the exteroceptors in the mucosa of the denture supporting area, contribute to the regulating mechanism of mandibular posture. The exteroceptors of oral mucosa in complete or partially edentulous patients may compensate for the loss of periodontal receptors. Thus, the pressure sensory impulses initiated from the alveolar mucosa could influence maxillo-mandibular opening when tletermining the facial vertical dimensions during denture construction. This phenomenon may explain the discrepancy between the vertical dimension measurements with and without dentures. The rest vertical dimension from 3 weeks to 6 months post-extraction (Stage II to Stage III) underwent a decided reduction which was comparable to the pronounced decrease observed in the occlusal vertical dimension. The mean for the measurements of rest position with dentures decreased from 128.3 mm to 126.5 mm. in the phonetic technique, and from 127.4 mm. to 125.8 mm. with the swallowing method. At the same 6 months post-extraction sitting, the dentures were removed from the patient’s mouth and a record of the rest dimension was made. The rest vertical dimension means, with and without dentures, demonstrated no appreciable difference in either of the methods used. However, in comparing the change of rest dimension without dentures, a definite reduction between Stages II and III is evident. Attention is called to the fact that the rest vertical dimension at the last stage is very similar to the same measurement recorded at the onset of the study. JKTEROCCLUSAL
DISTANCE
The free-way space (interocclusal distance) also underwent some alterations (Fig. 3). At the pre-extraction stage, the mean interocclusal distance (phonetically) was 3.7 mm. and (swallowing) was 2.6 mm. This range of measurements of the interocclusal distance is in agreement with the average values reported for adults by other investigators.4y15-18 The mean measurements of the interocclusal distance decreased after the 3 week post-extraction stage to 3.2 mm. (phonetic) and 2.2 mm. (swallowing j. As the occlusal and rest vertical dimension increased from Stage I to Stage II, the interocclusal distance became smaller (Fig. 3). The fact that the rest position change in response to the changes in the occlusal vertical dimension is of major importance in order to maintain a functional interocclusal distance. Although the interocclusal distance may undergo transition, it seems to be capable of size variation, thus aiding the regulatory mechanism of the mandible in accommodating to a new situation. The inverse relationship of the interocclusal distance to the occlusal and rest
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dimensions is seen again at the 6 month post-extraction stage. The interocclusal distance having increased to 3.3 mm. (phonetic) and 2.5 mm. (swallowing) has ahnost returned to the original pre-extraction recordings. The mean of the phonetically determined interocclusal distance indicates that the facial dimension may continue to change beyond the 6 months post-extraction stage. In clinical dentistry the average interocclusal distance of 2 to 4 mm. is accepted as being adequate. The broad measurement range of 1 to 9 mm. (see Tables I, II, III) would more accurately represent the general adult population. However, for any given patient the interocclusal distance should be specifically determined. Treating patients by average is not reliable and is fraught with error. Each individual patient should be evaluated objectively. The over-all pattern of the facial vertical dimension can be seen in Fig. 3. The occlusal vertical dimension and the rest position are directly related to each other. A change in one is reflected in the other. However, when dentures are removed from the mouth, the rest dimension does not seem to adapt quickly to the change in the occlusal vertical dimension. A change in occlusal vertical dimension seems to cause an adaptation in the neuromuscular mechanism, resulting in a similar change in the rest vertical dimension with dentures. It is conceivable that such adaptation is necessary in order to allow the regulatory mechanism to maintain continuously optimal function compatible with changing conditions. The role of the interocclusal distance during transition appears to conform by adjusting itself to the needs of the occlusal and rest position alterations. The value of the immediate denture for maintaining proper face height is supported in this study. Conventional methods require the patient to experience an edentulous healing period before denture construction. The data in this study suggest greater stability in facial vertical dimensions after the removal of occlusal contacts as compared to the reported variability in the conventional denture procedure without pre-extraction records.3,4s14 It is difficult to determine when the reduction in facial dimension stops or when equilibrium is established. The need for periodic recalling of all denture patients is imperative. At these visits, a change in the facial vertical dimension can be corrected either by refitting the denture base and/or re-establishing the occluding surfaces. The recall system could prevent the denture wearer from accommodating to an undesirable, destructive functional and esthetic relation which dominates the mandibular posture. SUMMARY
The primary purpose of this study was to determine any changes which may occur in the occlusal vertical dimension, the rest vertical dimension, and the interocclusal distance in adult patients in the transition from natural teeth to immediate complete and partial dentures, and during the initial 6 month period of use. The secondary aim was to compare the phonetic and swallowing methods for establishing the rest position of the mandible. Serial lateral cephalometric roentgenograms, using the Broadbent-Bolton cephalometer, were made for each of 40 immediate denture patients. The series of lateral head films were made at three
El% ‘4”
VERTICAL
DIMENSION
649
CHANGES
stages : Stage I-pre-extraction, Stage II-3 weeks post-extraction, and Stage III6 months post-extraction. The facial vertical dimensions were measured directly on the lateral head films between the nasion and the menton. CONCLUSIONS
1. The phonetic method of establishing mandibular rest position gave consistently greater values for the interocclusal distance in all three stages. When analyzed statistically, the functional swallowing method produced significantly different results from the phonetic method for determining the rest position of the mandible. 2. The occlusal vertical dimension increased significantly from Stage I to Stage II in spite of the guiding value of the natural teeth during the fabrication of the immediate dentures. 3. The occlusal vertical dimension decreased markedly in the 6 month period of wearing the dentures (Stage II to Stage III). At the end of the study, the occlusal vertical dimension was slightly smaller than before treatment was started. 4. The complete upper and lower denture group showed twice as much loss of occlusal vertical dimension than did the partial denture subjects. 5. The rest vertical dimension appears to parallel the alterations in the occlusal vertical dimension. 6. The interocclusal distance adjusts itself to accommodate the variations in facial vertical dimension. 7. A change in mandibular load and gravity may influence the rest position of the mandible. Comparison of means data showed that the rest vertical dimension with dentures was consistently greater than that without dentures. This suggests that the exteroceptors in the mucosa of the denture supporting area contribute to the regulating mechanism for mandibular posture. 8. The value of the immediate denture procedure is supported by this study. Greater stability is found in the facial vertical dimensions after the removal of occlusal contacts as compared to the reported variability in the usual denture procedure carried out without pre-extraction records. 9. The observations in this investigation indicate the need for periodic recalling of denture patients for appraising and re-establishing facial vertical dimension. The cooperation and assistance Graduate Division of the University acknowledged.
of Drs. A. W. Moore, W. of Washington, School
L. Kydd, and of Dentistry,
H. A. Young, are gratefully
REFERENCES
1. Thompson, J. R.: The Rest Position of the Mandible and Its Significance to Dental Science, J.A.D.A. 33:151, 1946. 2. Swenson, M. G.: Complete Dentures, St. Louis, 1940,. The C. V. Mosby Co., p. 311. 3. Atwood, D. A.: A Cephalometric Study of the Chnical Rest Position of the Mandible. Part I, J. PROS. DEN. 6:504, 1956; Part II. J. PROS. DEN. 7:544, 1957; Part III, J. PROS. DEN. 8:698, 1958. 4. Tallgren, A.: Changes in Adult Face Height Due to Ageing, Wear and Loss of Teeth and Prosthetic Treatment, Acta. Odont. Scandinav. 15:1-112, Suppl. 24, 1957. 5. Richards, A. G.: Roentgen-ray Doses in Dental Roentgenography, J.A.D.A. 56:351, 1958.
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W. M., and Sassouni, V. : A Syllabus in Roentgenographic Cephalometry, Philadelphia Center for Research in Child Growth, Philadelphia, Pa., 1957. 7. Thurow, R. C.: Cephalometric Methods in Research and Private Practice, Angle Orthodont. 21:104, 1951. 8. Boos. R. H.: Occlusion From Rest Position. T. PROS. DEN. 2:.575. 1952. 9. Gill&, R. R.: Establishing Vertical Dimension in Full Denture donstruction, J..‘i.D..A. 28 :4.x. 1941. 10. Anderson, R. M.: An Appraisal of Different Methods Used in Determining the Rest Position of the Mandible and the Resulting Free-way Space by Cephalometric Roentgenograms, Thesis, University of Washington, 1952. 11. Butori, E. F. : A Serial Cephalometric Study of the Rest Position of the Mandible of Individuals With Excellent Occlusions, Thesis, University of Washington, 1952. 12. Coulombe, J. A. R.: A Serial Cephalometric Study of the Rest Position of the Mandible on Edentulous Individuals, Thesis, University of Washington, 1952. 13. ThGrne, H.: The Rest Position of the Mandible and the Path of Closure From Rest to Occlusion Position. Methods of Cephalometric Determination, Acta. Odont. Scandinav. 11: 141, 1953. 14. Duncan, E. T., and Williams, S. T. : Evaluation of Rest Position as a Guide in Prosthetic Treatment, J. PROS DEN. 10:643, 1960. 15. Niswonger, M. E.: Obtaining the Vertical Relation in Edentulous Cases That Existed Prior to Extraction, J.A.D.A. 25:1842, 1938. 16. Thompson, J. R.: Concepts Regarding Function of the Stomatognathic System, J.A.D..;\. 48 ~626, 1954. 17. Sicher, H.: Oral Anatomy, ed. 3,. St. Louis, 1960, The C. V. Mosby Co. 18. Posselt, U.: Studies in the Mobility of the Human Mandible, Acta. Odont. Scandinav. 10:19, Suppl. 10, 1952. --
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HEALTH INSTITUTES
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