Edentulous
position
Liu Hongchen, Postgraduate
of the temporomandibular
MD, PhD,a Zhou Jilin,
Medical
College
and General
joint
DDS,b and Liu Ning, MScMC
Hospital
of Chinese
PLA,
Beijing,
China
Two bilateral &huller’s position radiographs were made of 10 edentulous patients with complete dentures. In one radiograph, the complete dentures were in place in centric occlusion. For the other radiograph, the complete dentures were removed and the maxillary and mandibular residual ridges approximated as closely as possible. This position is referred to as the edentulous position of the temporomandibular joint (TMJ). Findings indicate that in the edentulous position the average size of the upper and posterior TMJ spaces and the distance from the center of the condyle to the center of the glenoid fossa on the Y axis of the TMJ are smaller than measurements in the intercuspal position. The size of the anterior space and the distance between the two centers on the X axis are larger in the edentulous position. Because vertical dimension is reduced in the edentulous position, the mentum is in a superior and protrusive position. The study indicates that when the maxillary and mandibular residual ridges are approximate there is a pathologic position of the TMJ and the mandible caused by the loss of all teeth. The study shows that the condyle has the potential to move backward and upward excessively. As a result of the study, the concept of the edentulous position of TMJ is introduced. This concept is important in determining the proper position of the condyle in the glenoid fossa and the correct vertical and horizontal jaw relationship of an edentulous patient when complete dentures are made. (J PROSTHET DENT 1992;67:401-4.)
T he relationship between the
condyle and the glenoid fossaof the temporomandibular joint (TM& has usually been studied with natural teeth in place. This relationship has rarely been studied in edentulous patients especially when the residual ridges are approximated. The purpose of this study is to identify the spatial relationship within the TMJ in edentulous patients when (1) a complete denture is occluded at the correct vertical and horizontal position and (2) the maxillary and mandibular residual ridges are approximated as closely as possible. This study evaluates (1) the positional change of the condyle in the glenoid fossa;(2) changesin the upper, anterior, and posterior joint spaces;and (3) the relationship between the maxillary and mandibular residual ridges. MATERIAL
AND
METHODS
Ten edentulouspatients, six womenand four men, 57 to 79years of age,were studied. Their teeth were absentfrom 5 to 33 years (average 10.1 years), and complete dentures had beenusedfor 3 months to 33 years (average9.5 years). In five patients, the residual ridges were markedly absorbed. Schuller’s positional radiographs were made of each paaAssociate Professor, Department of Stomatology. bProfessor, Department of Stomatology. CPostgraduate student, Department of Stomatology. 10/1133878
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Line
Line
A
C
Line
Fig. 1. Location of anterior, upper, and posterior joint spaces.
tient in the two positions, occlusalvertical and overclosed. Schuller’s position adjuststhe head to place the midsagittal plane parallel to, and the interpupillary line perpendicular to, the plane of the film. The beamis placed at a 25” caudal angleto enter the upper parietal region and exit in the TMJ areaadjacent to the film. The overclosedposition wasreferred to asthe edentulousposition of the TMJ. With the jaws maintained in this position, the relationship of the central points of the residualridgeswere noted horizontally
401
HONGCHEN,
Center
of
Glenoid
Fosso
/Posterior
X Axis
JILIN,
AND
NING
perpendicular to the reference line at the point where the reference line intersected the height of the fossa represented the Y axis. The point of intersection of the X and Yaxes indicated the center of the glenoid fossa (Fig. 2). The distance from the center of the condyle to the center of the glenoid fossa on the X axis and the Y axis was measured and recorded. RESULTS
I
Y Axis
Fig. 2. Location of centers of condyle and glenoid fossa.
and the vertical dimension recorded between a point on the chin and the junction of the philtrum and the columella. A piece of acetate paper was placed over the completed radiograph and a tracing of the condyle and the glenoid fossa was made. All locations and measurements were recorded. For measurement of the joint space between the condyle and the glenoid fossa the method suggested by Zhang Zhenkangl was used (Fig. 1). A reference line was drawn parallel with the Frankfort horizontal plane and tangent to the most superior aspect of the glenoid fossa. Through the highest point of the glenoid fossa, line A was drawn perpendicular to the reference line. Line B was drawn at a 45degree angle to the reference line across the thinnest part of the anterior joint space. Line C was also drawn at 45degrees to the reference line passing through line A and line B . Line C also passes through the posterior joint space. The length of lines A, B, and C between the condyle and the glenoid fossa represented the width of the upper anterior and posterior joint spaces. The center of the condyle and the center of the fossa were located as suggested by Brewka,2 Willis,3 and Hatjigiorgis4 (Fig. 2). Line 1 was made parallel to the reference line and tangent to the highest point of the condyle. Line 2 was drawn perpendicular to line 1 and tangent to the most anterior aspect of the condyle. Line 3 was drawn parallel to line 2 and tangent to the most posterior aspect of the condyle. Line 4 was drawn parallel to line 1 and at a distance to line 1 equal to that between line 2 and line 3. The four lines formed a square. The intersection point of the two diagonals of this square represented the center of the condyle. Line E -F was drawn parallel to the reference line and tangent to the crest of the articular eminence. The line representing the X axis was then drawn midway between and parallel to line E-F and the reference line. The line
402
Analysis of the data obtained in the study showed no statistical difference (at the 5% level) between the values of the left and right TMJs in all measurements (Tables I and II). When the values of both sides were combined, those in the intercuspal position and the edentulous position were compared. The average values of upper and posterior joint spaces and the distance from the center of the condyle to the center of the glenoid fossa on the Y axis were statistically narrower in the edentulous position than those in the intercuspal position. The average values of the anterior space and the distance between the two centers on the X axis were found to be larger in the edentulous position than those in the intercuspal position. The statistical t-test of these two independent values showed no statistical difference at the 5% level of significance (Table III). In the intercuspal position, the vertical dimension was 6.75 * 0.55 cm (x f SD) and, in the edentulous position, it was 5.50 f 0.34 cm (x f SD). At rest position in 17 patients, the relationship of the residual ridges did not show protrusion of the mandible. In the edentulous position, three of 17 residual ridges could be approximated tightly without protrusion of the mandible and the other 14 patients showed protrusion of 3.36 + 1.86 mm (x + SD). In seven patients, the maxillary and mandibular residual ridges could be approximated tightly and, in another seven patients, a space of 4.6 t 1.52 mm (x + SD) was noted between the maxillary and mandibular residual ridges. DISCUSSION After the loss of all teeth in one or both dental arches, the intercuspal position and the retruded contact position disappear. When the maxillary and mandibular residual ridges approach, the position of the condyle in the glenoid fossa may change. Because this changed condylar position may be a pathologic one, it is referred to as the edentulous position of the TMJ. In this position, the upper and posterior joint spaces are obviously reduced. The distance on the Y axis between the center of the glenoid fossa and the center of the condyle is shortened, indicating that the condyle may move upward and backward after the loss of natural occlusal stops. The anterior joint space and the distance between the center of the glenoid fossa and the center of the condyle on the X axis does not increase significantly, indicating that
MARCH
1992
VOLUME
67
NUMBER
3
EDENTULOUS
POSITION
OF THE
TMJ
I. Comparison between right and left average measurements edentulous patients
Table
Right
Left x
Anterior space Upper space Posterior space X axis Y axis
1.73 2.47 1.18
(mm) of the TMJ in the edentulous position of 10
SD
x
SD
t
0.713
1.51 2.58 1.50 -2.39 -4.65
0.137 0.820 0.499 1.245 1.163
0.848 1.173 1.328 0.314
0.618
-2.23
0.207 1.385
-4.13
1.480
0.110
P
>0.05 >0.05 >0.05 >0.05 >0.05
Table II. Comparisonbetween right and left average measurements(mm) of the TMJ in the intercuspal position of 10 edentulouspatients Right
Left x
Anterior space Upper space Posterior space X axis Y axis
SD
1.38
0.838 0.836
3.05
2.18
0.793 1.131 1.052
-2.02
-5.29
s
SD
1.47 3.18 2.45
0.603 1.104
-1.95 -5.39
0.842
1.011 1.216
t 0.341
0.279 1.096 0.217 0.808
P
>0.05 >0.05 >0.05 >0.05 >0.05
Table III. Comparison of the average measurementsof the TMJ between the intercuspal position (IP) and the edentulous position (EP) of 10 Edentulous Patients (mm) EP TI
Anterior space Upper space Posterior space X Axis Y Axis
IP SD
JOURNAL
OF
PROSTHETIC
SD
t
P
1.62
0.715
1.43
0.712
1.896
>0.05
2.63
0.709 0.406
3.12 2.32
0.955 0.895
3.795 5.866
position
Liu Hongchen, Postgraduate
of the temporomandibular
MD, PhD,a Zhou Jilin,
Medical
College
and General
joint
DDS,b and Liu Ning, MScMC
Hospital
of Chinese
PLA,
Beijing,
China
Two bilateral &huller’s position radiographs were made of 10 edentulous patients with complete dentures. In one radiograph, the complete dentures were in place in centric occlusion. For the other radiograph, the complete dentures were removed and the maxillary and mandibular residual ridges approximated as closely as possible. This position is referred to as the edentulous position of the temporomandibular joint (TMJ). Findings indicate that in the edentulous position the average size of the upper and posterior TMJ spaces and the distance from the center of the condyle to the center of the glenoid fossa on the Y axis of the TMJ are smaller than measurements in the intercuspal position. The size of the anterior space and the distance between the two centers on the X axis are larger in the edentulous position. Because vertical dimension is reduced in the edentulous position, the mentum is in a superior and protrusive position. The study indicates that when the maxillary and mandibular residual ridges are approximate there is a pathologic position of the TMJ and the mandible caused by the loss of all teeth. The study shows that the condyle has the potential to move backward and upward excessively. As a result of the study, the concept of the edentulous position of TMJ is introduced. This concept is important in determining the proper position of the condyle in the glenoid fossa and the correct vertical and horizontal jaw relationship of an edentulous patient when complete dentures are made. (J PROSTHET DENT 1992;67:401-4.)
T he relationship between the
condyle and the glenoid fossaof the temporomandibular joint (TM& has usually been studied with natural teeth in place. This relationship has rarely been studied in edentulous patients especially when the residual ridges are approximated. The purpose of this study is to identify the spatial relationship within the TMJ in edentulous patients when (1) a complete denture is occluded at the correct vertical and horizontal position and (2) the maxillary and mandibular residual ridges are approximated as closely as possible. This study evaluates (1) the positional change of the condyle in the glenoid fossa;(2) changesin the upper, anterior, and posterior joint spaces;and (3) the relationship between the maxillary and mandibular residual ridges. MATERIAL
AND
METHODS
Ten edentulouspatients, six womenand four men, 57 to 79years of age,were studied. Their teeth were absentfrom 5 to 33 years (average 10.1 years), and complete dentures had beenusedfor 3 months to 33 years (average9.5 years). In five patients, the residual ridges were markedly absorbed. Schuller’s positional radiographs were made of each paaAssociate Professor, Department of Stomatology. bProfessor, Department of Stomatology. CPostgraduate student, Department of Stomatology. 10/1133878
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Line
Line
A
C
Line
Fig. 1. Location of anterior, upper, and posterior joint spaces.
tient in the two positions, occlusalvertical and overclosed. Schuller’s position adjuststhe head to place the midsagittal plane parallel to, and the interpupillary line perpendicular to, the plane of the film. The beamis placed at a 25” caudal angleto enter the upper parietal region and exit in the TMJ areaadjacent to the film. The overclosedposition wasreferred to asthe edentulousposition of the TMJ. With the jaws maintained in this position, the relationship of the central points of the residualridgeswere noted horizontally
401
HONGCHEN,
Center
of
Glenoid
Fosso
/Posterior
X Axis
JILIN,
AND
NING
perpendicular to the reference line at the point where the reference line intersected the height of the fossa represented the Y axis. The point of intersection of the X and Yaxes indicated the center of the glenoid fossa (Fig. 2). The distance from the center of the condyle to the center of the glenoid fossa on the X axis and the Y axis was measured and recorded. RESULTS
I
Y Axis
Fig. 2. Location of centers of condyle and glenoid fossa.
and the vertical dimension recorded between a point on the chin and the junction of the philtrum and the columella. A piece of acetate paper was placed over the completed radiograph and a tracing of the condyle and the glenoid fossa was made. All locations and measurements were recorded. For measurement of the joint space between the condyle and the glenoid fossa the method suggested by Zhang Zhenkangl was used (Fig. 1). A reference line was drawn parallel with the Frankfort horizontal plane and tangent to the most superior aspect of the glenoid fossa. Through the highest point of the glenoid fossa, line A was drawn perpendicular to the reference line. Line B was drawn at a 45degree angle to the reference line across the thinnest part of the anterior joint space. Line C was also drawn at 45degrees to the reference line passing through line A and line B . Line C also passes through the posterior joint space. The length of lines A, B, and C between the condyle and the glenoid fossa represented the width of the upper anterior and posterior joint spaces. The center of the condyle and the center of the fossa were located as suggested by Brewka,2 Willis,3 and Hatjigiorgis4 (Fig. 2). Line 1 was made parallel to the reference line and tangent to the highest point of the condyle. Line 2 was drawn perpendicular to line 1 and tangent to the most anterior aspect of the condyle. Line 3 was drawn parallel to line 2 and tangent to the most posterior aspect of the condyle. Line 4 was drawn parallel to line 1 and at a distance to line 1 equal to that between line 2 and line 3. The four lines formed a square. The intersection point of the two diagonals of this square represented the center of the condyle. Line E -F was drawn parallel to the reference line and tangent to the crest of the articular eminence. The line representing the X axis was then drawn midway between and parallel to line E-F and the reference line. The line
402
Analysis of the data obtained in the study showed no statistical difference (at the 5% level) between the values of the left and right TMJs in all measurements (Tables I and II). When the values of both sides were combined, those in the intercuspal position and the edentulous position were compared. The average values of upper and posterior joint spaces and the distance from the center of the condyle to the center of the glenoid fossa on the Y axis were statistically narrower in the edentulous position than those in the intercuspal position. The average values of the anterior space and the distance between the two centers on the X axis were found to be larger in the edentulous position than those in the intercuspal position. The statistical t-test of these two independent values showed no statistical difference at the 5% level of significance (Table III). In the intercuspal position, the vertical dimension was 6.75 * 0.55 cm (x f SD) and, in the edentulous position, it was 5.50 f 0.34 cm (x f SD). At rest position in 17 patients, the relationship of the residual ridges did not show protrusion of the mandible. In the edentulous position, three of 17 residual ridges could be approximated tightly without protrusion of the mandible and the other 14 patients showed protrusion of 3.36 + 1.86 mm (x + SD). In seven patients, the maxillary and mandibular residual ridges could be approximated tightly and, in another seven patients, a space of 4.6 t 1.52 mm (x + SD) was noted between the maxillary and mandibular residual ridges. DISCUSSION After the loss of all teeth in one or both dental arches, the intercuspal position and the retruded contact position disappear. When the maxillary and mandibular residual ridges approach, the position of the condyle in the glenoid fossa may change. Because this changed condylar position may be a pathologic one, it is referred to as the edentulous position of the TMJ. In this position, the upper and posterior joint spaces are obviously reduced. The distance on the Y axis between the center of the glenoid fossa and the center of the condyle is shortened, indicating that the condyle may move upward and backward after the loss of natural occlusal stops. The anterior joint space and the distance between the center of the glenoid fossa and the center of the condyle on the X axis does not increase significantly, indicating that
MARCH
1992
VOLUME
67
NUMBER
3
EDENTULOUS
POSITION
OF THE
TMJ
I. Comparison between right and left average measurements edentulous patients
Table
Right
Left x
Anterior space Upper space Posterior space X axis Y axis
1.73 2.47 1.18
(mm) of the TMJ in the edentulous position of 10
SD
x
SD
t
0.713
1.51 2.58 1.50 -2.39 -4.65
0.137 0.820 0.499 1.245 1.163
0.848 1.173 1.328 0.314
0.618
-2.23
0.207 1.385
-4.13
1.480
0.110
P
>0.05 >0.05 >0.05 >0.05 >0.05
Table II. Comparisonbetween right and left average measurements(mm) of the TMJ in the intercuspal position of 10 edentulouspatients Right
Left x
Anterior space Upper space Posterior space X axis Y axis
SD
1.38
0.838 0.836
3.05
2.18
0.793 1.131 1.052
-2.02
-5.29
s
SD
1.47 3.18 2.45
0.603 1.104
-1.95 -5.39
0.842
1.011 1.216
t 0.341
0.279 1.096 0.217 0.808
P
>0.05 >0.05 >0.05 >0.05 >0.05
Table III. Comparison of the average measurementsof the TMJ between the intercuspal position (IP) and the edentulous position (EP) of 10 Edentulous Patients (mm) EP TI
Anterior space Upper space Posterior space X Axis Y Axis
IP SD
JOURNAL
OF
PROSTHETIC
SD
t
P
1.62
0.715
1.43
0.712
1.896
>0.05
2.63
0.709 0.406
3.12 2.32
0.955 0.895
3.795 5.866
