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Masticatory Function after jaw Resection and Rehabilitation with Dental Implants
Ihara, Goto Asian J Oral Maxillofac Surg 2003;15:19-30. CLINICAL OBSERVATIONS
Masticatory Function after Jaw Resection and Rehabilitation with Dental Implants Koichiro Ihara,1 Masaaki Goto2 Department of Oral and Maxillofacial Surgery, Saga Medical School, Saga, Japan 2 Department of Oral and Maxillofacial Surgery, Saga Medical School, Saga, Japan 1
Abstract Objective: To assess masticatory function after jaw resection and prosthodontic treatment using implants and to evaluate the effectiveness of such treatment. Patients and Methods: Masticatory function was investigated in 21 patients who underwent jaw resection and 23 non-resection patients rehabilitated with dental implants. Twenty-eight volunteers with natural dentition acted as control subjects. Masticatory function was assessed by 4 tests and the 3 groups were compared. Results: No significant differences in all tests were found between the control group and the non-resection patients. There were significant differences in masseter muscle action potential amplitudes between patients who underwent jaw resection and the other groups. No specificity was seen in the factor score distribution in the principal component analysis. Conclusion: Masticatory function can be restored to almost normal levels by appropriate reconstruction of soft tissues combined with prosthodontic treatment with dental implants, even for patients undergoing jaw resection. Key Words: Dental implants, Jaw, Mastication, Principal component analysis
Introduction Jaw reconstruction is performed for morphological and functional recovery for patients who have undergone jaw resection due to oral and maxillofacial disease. In addition, prosthodontic treatment is administered to restore masticatory function. However, an adequate level of rehabilitation is not easily accomplished for patients undergoing jaw reconstruction.1,2
patients undergoing rehabilitation of occlusal function using implants subsequent to jaw resection The aim of this study was to quantitatively assess masticatory function in patients having prosthodontic treatment using implants following jaw resection, and to evaluate the effectiveness of such treatment in the restoration of masticatory function after jaw resection.
Haraldson et al reported that masticatory function in patients with missing teeth could be restored to the same level as that in healthy persons by the use of osseo-integrated implants.3-7 It has also been reported recently that osseo-integrated implants could restore masticatory function in patients undergoing jaw resection.8,9 However, few reports have quantitatively assessed the restoration of masticatory function in
Patients and Methods
Correspondence: Koichiro Ihara, Department of Oral and Maxillofacial Surgery, Saga Medical School, 5-1-1 Nabeshima, Saga, 849-8501, Japan. Tel: (81 952) 34 2397, Fax: (81 952) 34 2044 E-mail: [email protected]
The total number of implants placed was 208, of which 12 failed before evaluation of masticatory function, 13 survived but were not functional, and
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Forty four patients (27 men and 17 women) underwent prosthodontic treatment using implants at the Department of Oral and Maxillofacial Surgery at the Saga Medical School Hospital in Japan between 1989 and 1998. Twenty healthy volunteers acted as control subjects. Patients and controls had an age range from 10 to 80 years.
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Masticatory Function after Jaw Resection and Rehabilitation
the remaining 183 implants were successful. Implant success was judged according to the following criteria proposed by Naert et al,10 that the implants were immobile, functional at the time of evaluation and did not cause pain or show infection or peri-implant radiolucency. The follow-up period at the time of evaluation of masticatory function ranged from 1.3 to 9.9 years, with a mean follow-up period of 5.1 years. Patients were divided into 3 groups: • group A comprised 21 patients (15 men, 6 women) with jaw resection and implants • group B consisted of 23 patients (12 men and 11 women) with ordinary dental implants without jaw resection • group C consisted of 28 healthy volunteers (13 men and 15 women) who had normal oral and maxillofacial function (Table 1). The subjects in the control group ranged in age from their teenage years to their 30s (Figure 1).
Resection patients (group A) Non-resection patients (group B) Normal subjects with natural dentition (group C)
Male
Female
Total
15 12 13
6 11 15
21 23 28
Table 1. Sex distribution of each group in this study.
Group A Group B
Number of patients
Group C
15
10
5
0
10
20
30
40
50
Age (years)
Figure 1. Age distribution of all patients.
20
60
70
Of the 21 patients in group A, 10 had malignant tumours, 8 had benign tumours, 2 had cysts, and 1 had osteomyelitis (Table 2). Five patients in this group who had partial maxillectomy (patients 1 to 5) had dental implants placed in the remaining bone, and a removable denture was made that had an obturator supported by dental implants (RDI). Thirteen patients with marginal mandibulectomy (patients 6 to 18) had a fixed denture supported by dental implants (FDI) inserted in the resected region. For 8 of these patients (patients 9 and 12 to 18), iliac bone was grafted to the resected region. Three patients with segmental mandibulectomy (patients 19 to 21) had dental implants placed in the remaining mandibular bone and an FDI was made, while maintaining mandibular continuity with a reconstruction plate. Seven of the 10 patients with malignant tumour had radiotherapy, with an exposure dose ranging from 15 Gy to 60 Gy. Most patients had 30 Gy prior to tumour resection. In group B, prior to implantation, severe resorption of alveolar bone with missing teeth was diagnosed in 12 patients, post-trauma in 8, malignant tumour of the floor of the mouth in 2, and lichen planus in 1 (Figure 2). No radiotherapy was performed for the 2 patients with malignant tumour in this group. Dental implants were placed after maxillary sinus augmentation in 2 patients. Ordinary implants with FDI or RDI were placed in the remaining patients.
25
20
Osseo-integrated implants (Brånemark System, Nobel Biocare Inc., Gothenburg, Sweden) were placed in an attempt to restore masticatory function for the 44 patients in groups A and B. Following conventional surgical procedures, fixtures were placed and abutments connected.11
80
The following masticatory function tests were performed at 3 months or more after delivery of the denture supported with dental implants: • mandibular movement test • masticatory test using low-adhesive, colourdeveloping chewing gum • electromyography of the masseter muscle • molar occlusal force test. Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto Patient
Conditions of resected jaw Residual teeth
Implant prosthesis
Type of prosthesis on opposing jaw
Subjectively preferred chewing side
Diagnosis
Number of implants (useless implants)
1
5 (0)
0
RDI
FD
R
Malignant tumour
2
3 (0)
0
RDI
FDI
R
Malignant tumour
3
1 (0)
0
RDI
FDI + ND
R
Malignant tumour
4
2 (0)
0
RDI
FD
R
Benign tumour
5
3 (0)
0
RDI
RPD
R
Malignant tumour
6
4 (0)
1 1-7
FDI
ND
R
Malignant tumour
7
2 (0)
76 2-7
FDI
ND
R
Benign tumour
8
4 (0)
7-4 4-7
RDI
ND
/
Malignant tumour
9
1 (0)
75- --7
FDI
ND
R
Odontogenic cyst
10*
4 (0)
875- -8
FDI
ND
R
Malignant tumour
11
4 (0)
7-3 567
FDI
ND
R
Benign tumour
12
3 (0)
5- -7
FDI
ND
R
Benign tumour
13
3 (0)
7- -3
FDI
ND
R
Osteomyelitis
14
4 (1)
76 3-7
FDI
ND
R
Benign tumour
15
4 (1)
7-1
FDI
ND
R
Benign tumour
16
3 (0)
8-4
FDI
ND
R
Malignant tumour
17
3 (0)
3-7
FDI FDI
N.D.
R
Benign tumour
18
3 (0)
2-6
FDI
RPD
R
Odontogenic cyst
19*
2 (0)
0
FDI
RPD
R
Malignant tumour
20
9 (2)
0
FDI
RPD + ND
R
Benign tumour
21*
5 (2)
0
FDI
RPD
R
Malignant tumour
Implants Natural teeth Resected site Grafted bone
Abbreviations: FDI = fixed denture supported with dental implant; RDI = removable denture supported with denal implant; FD = full denture; RPD = removal partial denture; ND = natural dentition; R = resected side; N = non-resected side. * Tongue resection. Table 2. Characteristics of resection patients (group A).
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
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Masticatory Function after Jaw Resection and Rehabilitation
points each on the front and back with a chromatometer, and the mean value was calculated (Figure 3b).
Group A
12
Group B
For EMG of the masseter muscle, the upper end of the surface electrode was applied to a point midway between the lateral angle of the eye and the mandibular angle to obtain measurements using the Bio-EMG (Figure 3a). The mean value for the difference in action potential amplitudes at rest and with maximum clenching force was calculated.
10
Number of patients
8
6
4
2
0
ur
mo
lign
tu ant
Ma
Ben
ur
mo
tu ign
t
Cys
on ma nus rpti rau pla eso teeth T en r h e c i L er ng Sev missi and tis
yeli
om
e Ost
Figure 2. Diagnosis for patients with resection and nonresection.
In group A, the patients were interviewed to determine whether the subjectively preferred chewing side was on the resection side or non-resection side. The mandibular movement test was conducted using a BioPAK mandibular movement analyser (BioResearch Associates, Milwaukee, USA), which consisted of a Bio-electrognathography (EGN) and a Bio-electromyograph (EMG). With the Bio-EGN, jaw movements can be recorded in 3 dimensions by tracking the location of a magnet delivered to the mandibular incisal point with a magnetic sensor (Figure 3a). Mandibular movements were measured in the maximum mouth opening movement test, which was repeated 10 times, and the mean values for the maximum lateral shift of the incisal point and the maximum mouth opening distance were obtained. The masticatory test was performed in accordance with the method of Matsui et al12 using low-adhesive, colour-developing chewing gum (Meiji Chewing Gum Co., Ltd., Nagoya, Japan), with a weight ratio of gum A to gum B of 4:1 and a total weight of 3 g. The chromatic value (a*) of the gum was measured using a chromatometer (Color Reader CR-13, Minolta, Tokyo, Japan). The patients were instructed to chew the gum 50 times in each of 3 repeated measurements, the chromatic values of the gum were measured at 5 22
Occlusal force was measured using a dental occlusal force meter GM-10 (Nagano Keiki Seisakusho, Osaka, Japan) [Figure 3c]. The subject was instructed to firmly clench the sensor of the occlusal force meter with the first molar or second premolar. The test was repeated 3 times, and the mean value was calculated as the maximum occlusal force. The mean values of the measurement results obtained in the 4 tests were also computed for group B and group C subjects. The mean values were compared against those obtained in group A patients, including those who had undergone partial maxillectomy, marginal mandibulectomy, or segmental mandibulectomy. Statistical analysis was performed using Statistica software (Stat Soft Inc., Tulsa, USA) for principal component analysis and calculation of the correlation coefficients for the 5 test items, and the relationships between pairs of the test items were assessed. Principal component analysis is generally done to identify relationships between variables after classifying them into a smaller number of factors by grouping highly correlated variables.13 The purpose of conducting a principal component analysis in this study was to identify, from among the examination items, the important factors for the evaluation of masticatory function, and to closely examine similarities between pairs of the examination items. Based on the results obtained, the examination items extracted as the first and the second principal components were determined as the most important and the second most important factors related to masticatory function, respectively, and an attempt was also made to interpret each relationship. All factor scores in groups A, B, and C were plotted with the first component on the X-axis and the second Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto
a
component on the Y-axis for distribution of factor scores. The graph shows the masticatory function in individual patients as a scatter diagram based on the factors (the first and second principal components) identified by principal component analysis. Significant differences between the 3 groups in the values for each test item were identified by analysis of variance, the least significant difference (LSD) test, and the t-test.
Results Maximum Lateral Shift of the Incisal Point The mean maximum lateral shift of the incisal point was approximately 8 mm in both group B and group C, with no significant differences between these groups. The lateral shift of the incisal point in the partial maxillectomy subgroup of group A patients tended to be greater than that in groups B or C. In contrast, in both the marginal mandibulectomy and segmental mandibulectomy subgroups, the lateral shift tended to be smaller than that in groups B or C (Figure 4). However, no statistically significant b
c
Figure 3. (a) Measurement of mandibular movement by Bio-electrognathography and surface action potential amplitude of masseter muscle by Bio-electromyograph; (b) measurement of chromatic value of low-adhesive color-developing chewing gum using a chromatometer; (c) measuring device for occlusal force and disposable cap.
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Masticatory Function after Jaw Resection and Rehabilitation
16 Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup
Maximum lateral shift of incisal point (mm)
14
Mean value for group B patients 12
Mean value for group C patients * Tongue resection
10 8 6
* *
4 2 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
* 19
20
21
Patients
Figure 4. Results for maximum lateral shift of the incisal point in patients undergoing resection.
differences were noted between groups A, B, and C (Tables 3 and 4). Maximum Mouth Opening Distance No specific trends were noted with regard to the maximum mouth opening distance for group A according to the resected region or range. In almost 50% of patients in group A, the maximum mouth opening distance was larger than that of subjects of groups B or C, and no significant differences were observed between groups B or C (Figure 5, Tables 3 and 4). Masticatory Test Using Low-adhesive, Colour-developing Chewing Gum Two of the 5 patients in the partial maxillectomy subgroup in group A showed a lower value than that of group B. In the mandibulectomy subgroup, masticatory efficiency was found to be lower than in Group B in 1 patient who underwent marginal Test
F value
p Value
Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential amplitude of electromyography between sides Difference in occlusal force between sides
0.911 0.853 1.891 4.741
0.407 0.430 0.159 0.012*
0.499
0.609
Table 3. Results of analysis of variance between all groups. *p < 0.05.
24
mandibulectomy with tongue resection and in 2 patients who underwent segmental mandibulectomy. In most patients in Group A, masticatory efficiency was equal or superior to that in group B (Figure 6). No statistically significant differences were observed between the groups (Tables 3 and 4). Differences in Action Potential Amplitude on the Masseter Muscle Between the Left and Right Sides To evaluate the differences in action potentials on the masseter muscle between the resection and non-resection sides in group A, the differences in action potential amplitude between both sides were calculated and compared with those in groups B and C. In group A, the mean difference in action potential amplitude between the sides was larger than in groups A-B Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential * amplitude of electromyography between sides Difference in occlusal force between sides
A-C
B-C
*
Table 4. Results of t-test between the 3 groups. *p < 0.05.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto
Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup
60
Maximum mouth opening (mm)
Mean value for group B patients Mean value for group C patients * Tongue resection
50
40 *
*
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
* 19
20
21
Patients
Figure 5. Results for maximum mouth opening in patients undergoing resection.
B or C (Figure 7), irrespective of the resected region or range, indicating a greater difference between sides in group A than in groups B or C (Tables 3 and 4).
the differences in occlusal force between the sides were calculated and compared with those in groups B and C. Among patients in group A, occlusal force tended to be reduced in the partial maxillectomy or segmental mandibulectomy subgroups. However, in the marginal mandibulectomy subgroup, differences in occlusal force between the left and right sides were
Differences Between Sides in Molar Occlusal Force To evaluate differences in occlusal force between the resection and the non-resection sides in group A, 80
Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup Mean value for group B patients Mean value for group C patients * Tongue resection
70
Chromatic value (a*)
60 50 40 30
* 20
* *
10 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Patients
Figure 6. Results for chromatic values of low-adhesive colour-developing chewing gum system in patients undergoing resection.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
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Masticatory Function after Jaw Resection and Rehabilitation
Difference in mean action potential amplitude (μV)
300 Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup Mean value for group B patients Mean value for group C patients * Tongue resection
250
200
150
100
50 *
* 0
1
2
3
4
5
6
7
8
9
10 11 12 Patients
13
14
15
16
17
18
* 19
20
21
Figure 7. Difference in mean action potential amplitude of surface electromyograms on the masseter muscle between the left and right sides in patients undergoing resection.
larger than those in groups B or C in 6 patients, that is, in almost 50% of the patients (Figure 8). Nonetheless, no statistically significant differences were noted (Tables 3 and 4).
side was the non-resection side for all patients (Table 2). Statistical Analysis Correlation coefficients were determined for the 5 test items (maximum lateral shift of the incisal point, maximum mouth opening distance, masticatory test using chewing gum, differences in action potential
Subjectively Preferred Chewing Side Interviews with the patients undergoing resection showed that the subjectively preferred chewing 40 Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup Mean value for group B patients Mean value for group C patients * Tongue resection
Difference in occlusal force (kgf)
35 30 25 20 15 10
*
5 0
*
*
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Patients
Figure 8. Difference in maximum occlusal force of the molar region between the left and right sides in patients undergoing resection.
26
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto Maximum lateral shift Maximum Chromatic Difference in mean action Diffference in of incisal point mouth opening value potential amplitude of electro- occlusal force myography between sides between sides Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential amplitude of electromyography between sides Difference in occlusal force between sides
0.84*
-0.33 -0.09
0.84* -0.33 -0.10
-0.09 0.02
0.19
-0.12
-0.21
0.24
-0.10 0.02 0.19
-0.12 -0.21 0.24 0.12
0.12
Table 5. Correlation coefficients between the 5 tests.
amplitude between sides, and differences in molar occlusal force between sides) and a principal component analysis was performed. With regard to correlation coefficients, a high correlation of 0.84 was observed between the maximum lateral shift of the incisal point and the maximum mouth opening distance (Table 5). In the principal component analysis, the eigenvalue of the first component was 2.04 and a factor loading of 0.50 or higher was found in the maximum lateral shift of the incisal point and the maximum mouth opening distance. For the second component, the eigenvalue was 1.21 and a factor loading of 0.50 or higher was found in the masticatory test using chewing gum, differences in action potential amplitude between the sides, and differences in molar occlusal force between sides (Table 6).
Test
First Second component component
Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential amplitude of electromyography between sides Difference in occlusal force between sides
-0.94* -0.96* 0.22 -0.09
-0.15 0.02 0.71* 0.70*
0.18
0.59*
Eigenvalue
2.04
1.21
Table 6. Eigenvalue and factor loading by principal component analysis for the 5 tests of masticatory function. * Factor loading greater than 0.50 by varimax method.
As to the distribution of factor scores in all subjects, including those in groups A and B, nearly all the scores (except for patients 19 and 35) converged within a specified range in groups A, B, and C. No remarkable differences in the distribution pattern were seen in these groups (Figure 9).
3.5 a a
2.5
c
bc ba a
Second component
1.5
c a
b
0
-1.5
-2.5
a
ab
b a a ca b bc c ab c ca c c a cbc b c a b b c bc c c c aca a c ccc c c b b bcc c b a a b b b b b
0.5
-0.5
a
Patient 19
b Patient 35
-5
-4
-3
-2
-1
0
1
First component
Figure 9. Distribution of factor scores for all groups.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
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Masticatory Function after Jaw Resection and Rehabilitation Group A Group A Group B Group C
0.011* 0.007†
Group B
Group C
0.011*
0.007 0.929
†
0.929
Table 7. Results of least significant difference test in difference in mean action potential amplitude of electromyography between sides. *p < 5%; † p < 1%.
In order to evaluate the differences in the mean values of each test item in the 3 groups, analysis of variance was done. Significant differences were recognised in action potential amplitude on the masseter muscle between the left and right sides — an F-value was 4.741 with a level of significance of 0.012 (Table 3). The LSD test was performed to identify the patients who exhibited significant differences. The levels of significance in thusidentified subjects were as follows: 5% between groups A and B, and 1% between groups A and C (Table 7). The t-test also revealed significant differences in action potential amplitude between the sides between groups A and B and between groups A and C, with a level of significance of 5% (Table 4).
Discussion To determine whether patients who have undergone mandibular resection or reconstruction can chew properly wearing an implant-supported prosthesis, masticatory function in such patients should be evaluated by comparison with healthy control subjects. Masticatory function in patients with conventional tooth defects has been reported multilaterally and objectively, for example by Haraldson et al.3-7 However, in only a few studies has multilateral assessment of reconstructive surgery been conducted in patients undergoing jaw resection.14-16 Methods for evaluating masticatory function may be divided into subjective evaluation, in which patients are questioned regarding chewable foods, and quantitative evaluation, in which test equipment or samples are employed. Subjective evaluation is easily performed because no special tools or samples are required — the results however may not agree with those obtained by quantitative evaluation, as subjective evaluation is influenced by the patient’s eating habits, favourite foods, and personality.17 28
Quantitative evaluation of masticatory function is essential for an accurate determination of the effectiveness of prosthodontic treatment. A variety of methods have been developed for measuring masticatory efficiency, and methods for recording and evaluating mandibular movement,18,19 muscular dynamics,20 and occlusal force7,21 recently became available thanks to advances in medical electronics. In this study, evaluation of masticatory function was conducted in 72 subjects using principal component analysis to examine the mutual relationships of the 5 tests. Since both the maximum lateral shift of the incisal point and the maximum mouth opening distance were identified as the first component, mandibular movement was considered to be the most important factor in the function of mastication. The masticatory test using chewing gum, EMG of the masseter muscle, and the occlusal force test were identified as the second component. These were taken to be the factors that comprehensively describe the condition of the hard and soft tissues (tongue, masticatory muscles, teeth, and jaw) related to masticatory efficiency. However, the eigenvalue of the second component was approximately 60% that of the first component. This finding suggests that mandibular movement is more strongly correlated to masticatory function. In the distribution of factor scores for all subjects (Figure 9), markedly different distribution patterns were observed in 1 patient who had undergone segmental mandibulectomy for malignant tumour (patient 19) and another patient receiving prosthodontic treatment using implants for lichen planus (patient 35). The different distribution patterns seen in these patients may have been due to the extremely small occlusal contact area in patient 19, and marked pain due to erosion of the buccal mucosa or tongue secondary to lichen planus in patient 35. In all other patients, factor scores were distributed in a specified range, regardless of which of the 3 groups they were classified into. Based on these findings, we consider that the use of dental implants permits masticatory function in patients undergoing jaw resection to be restored to a level comparable to that of non-resection jaw patients or normal subjects. Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto
In patients undergoing jaw resection, the mouth opening distance was reduced in 9 patients compared to that of healthy controls or non-resection jaw patients. However, mouth opening was restored to 30 mm or more in 7 patients by mouth-opening exercises after surgery for the underlying disease. Accordingly, no significant differences were noted between the 3 groups. Given that mandibular movement is the most important factor in masticatory function, as revealed in principal component analysis, positive postoperative mouth-opening practice is essential. In the tests of masticatory efficiency using lowadhesive, colour-developing chewing gum, patients undergoing resection showed lower values than nonresection patients, including 2 patients who had undergone partial maxillectomy and 3 patients who had undergone mandibulectomy plus tongue resection. In the former patients, the prostheses were not satisfactorily stabilised for mastication because only 1 or 2 implants were placed. In the latter patients, the chewing gum could not be moved to the occlusal table of the denture due to limitations in tongue movement. Thus, denture stability and tongue mobility must be importantly related to the function of mastication. EMG of the masseter muscle showed that there were significant differences between patients undergoing resection and non-resection patients or normal subjects with regard to the differences in action potential amplitude between the left and right sides. This finding suggests that irreversible changes may have taken place in the masticatory system probably induced by surgery. However, masticatory function may be less seriously affected by a difference in the action potentials between the 2 sides of the masticatory muscle, this being a second principal component as compared to mandibular movement (a first principal component). With regard to differences in occlusal force, no significant differences were found between the 3 groups by the t-test or analysis of variance. However, in 50% of the patients with marginal mandibulectomy, the differences tended to be larger. In patients with larger differences in occlusal force, the differentials were presumably related to a number of findings. First of all, the occlusal force on the resected side, where Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
the prosthesis was placed with implants, was lower than that in the non-resection side. Secondly, the subjectively preferred chewing side was the nonresection side. And lastly, significant differences were seen in occlusal action potential amplitude between the 2 sides. It was expected that the non-resection side would be the subjectively preferred chewing side and this was true for marginal mandibulectomy patients without tongue resection, even though masticatory function was fully restored by prosthodontic treatment using dental implants. This is presumably because the subjectively preferred chewing side before the placement of implants tended not to change, since the implants were placed with a considerable passage of time after surgery. However, such preferences may not continue indefinitely, and satisfactory chewing on the resected side should be achievable with practice. No statistically significant differences were detected in any of the test items between the normal function control and non-resection groups, in agreement with the findings of Haraldson et al.3-7 If jaw resection is not required, masticatory function can be fully restored by prosthetic rehabilitation using dental implants, which results in a satisfactory function of mastication comparable to that of normal subjects. On the other hand, for patients undergoing resection, significant differences were recognised only in action potential amplitude in the masseter muscle between the left and right sides. However, we maintain that masticatory function in patients undergoing resection was successfully restored to a level comparable to that of non-resection patients or healthy controls based on the following findings: • tests of action potential amplitude of the masseter muscle were identified as the second component in the principal component analysis • no significant differences existed between resection and non-resection patients or healthy controls in other test items • no specificity was seen in the distribution of factor scores in resection patients. After resection, jaw reconstruction is possible using bone grafts or biocompatible materials, and 29
Masticatory Function after Jaw Resection and Rehabilitation
missing teeth may be compensated for by prosthetic rehabilitation with dental implants. That being the case, functional reconstruction of the oral or maxillofacial soft tissues such as the tongue or masticatory muscles is called for. Masticatory function can be restored to a level comparable to that of healthy controls once the functional reconstruction of all these tissues has been achieved.
References 1. Marunick MT, Mathes BE, Klein BB. Masticatory function in hemimandibulectomy patients. J Oral Rehabil 1992:19:289-295. 2. Wedel A, Yontchev E, Carlsson GE, Ow R. Masticatory function in patients with congenital and acquired maxillofacial defects. J Prosthet Dent 1994:72:303-308. 3. Haraldson T, Ingervall B. Muscle function during chewing and swallowing in patients with osseointegrated oral implant bridges, an electromyographic study. Acta Odontol Scand 1979:37: 207-216. 4. Haraldson T, Carlsson GE, Ingervall B. Functional state, bite force and postural muscle activity in patients with osseointegrated oral implant bridges. Acta Odontol Scand 1979:37:195-206. 5. Haraldson T, Carlsson GE. Chewing efficiency in patients with osseointegrated oral implant bridges. Swed Dent J 1979:3:183-191. 6. Haraldson T. Comparisons of chewing patterns in patients with bridges supported on osseointegrated implants and subjects with natural dentitions. Acta Odontol Scand 1983:41:203-208. 7. Haraldson T, Karlsson U, Carlsson G. Bite force and oral function in complete denture wearers. J Oral Rehabil 1979:6:41-48. 8. Ihara K, Goto M, Miyahara A, Toyota J, Katsuki T. Multicenter experience with maxillary prostheses supported by Brånemark Implants. A clinical report. Int J Oral Maxillofac Implants 1998: 13:531-538. 9. Matsui Y, Neukam FW, Schmelzeisen R, Ohno K. Masticatory function of postoperative tumor patients rehabilitated with osseointegrated implants. J Oral Maxillofac Surg 1996:54:441-447. 10. Naert I, Qulrynen MV, Steenberghe D. A six year prosthodontic study of 509 consecutively inserted
30
implants for the treatment of partial edentulism. J Prosthet Dent 1992:67:236-241. 11. Brånemark PI, Zarb GA, Albrektsson T. Tissueintegrated prostheses. Chicago: Quintessence Publishing Co Inc; 1985:211-225. 12. Matsui Y, Neukam FW, Wichmann M, Ohno K. Application of a low-adhesive color developing chewing gum system to patients with osseointegrated implant-supported prostheses. Int J Oral Maxillofac Implants 1995:10:583-588. 13. Stevens J. Applied multivariate statistics for the social sciences. Hillsclale: Erlbaum; 1986:125. 14. Stern RM, Perren R, Raveh J. Life table analysis and clinical evaluation of oral implants supporting prostheses after resection of malignant tumors. Int J Oral Maxillofac Implants 1999:14:673-680. 15. Schliephake H, Neukam WF, Schmelzeisen R, Wichmann M. Long-term results of endosteal implants used for restoration of oral function after oncologic surgery. Int J Oral Maxillofac Surg 1999:28:260-265. 16. Schmelzeisen R, Neukam FW, Shirota T, Specht B, Wichmann M. Postoperative function after implant insertion in vascularized bone grafts in maxilla and mandible. Plast Reconstr Surg 1996: 97:719-725. 17. Boretti G, Bickel M, Geering AH. A review of masticatory ability and efficiency. J Prosthet Dent 1995:74:400-403. 18. Book K, Karlsson S, Jemt T. Functional adaptation to full-arch fixed prosthesis supported by osseointegrated implants in the edentulous mandible. Clin Oral Impl Res 1992:3:17-21. 19. Jemt T, Lindquist L. Changes in chewing patterns of patients with complete denture after placement of osseointegrated implants in the mandible. J Prosthet Dent 1985:53:578-583. 20. Hosman H, Naeije M. Reproducibility of the normalized electromyographic recordings of the masseter muscle by using the EMG recording during maximal clenching as a standard. J Oral Rehabil 1979:6:49-54. 21. Gibbs CH, Mahan PE, Lundeen HC, Brehnan K, Walsh EK, Sinkewiz SL, Ginsberg SB. Occlusal forces during chewing-influences of biting strength and food consistency. J Prosthet Dent 1981:46:561-567.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Masticatory Function after Jaw Resection and Rehabilitation with Dental Implants Koichiro Ihara,1 Masaaki Goto2 Department of Oral and Maxillofacial Surgery, Saga Medical School, Saga, Japan 2 Department of Oral and Maxillofacial Surgery, Saga Medical School, Saga, Japan 1
Abstract Objective: To assess masticatory function after jaw resection and prosthodontic treatment using implants and to evaluate the effectiveness of such treatment. Patients and Methods: Masticatory function was investigated in 21 patients who underwent jaw resection and 23 non-resection patients rehabilitated with dental implants. Twenty-eight volunteers with natural dentition acted as control subjects. Masticatory function was assessed by 4 tests and the 3 groups were compared. Results: No significant differences in all tests were found between the control group and the non-resection patients. There were significant differences in masseter muscle action potential amplitudes between patients who underwent jaw resection and the other groups. No specificity was seen in the factor score distribution in the principal component analysis. Conclusion: Masticatory function can be restored to almost normal levels by appropriate reconstruction of soft tissues combined with prosthodontic treatment with dental implants, even for patients undergoing jaw resection. Key Words: Dental implants, Jaw, Mastication, Principal component analysis
Introduction Jaw reconstruction is performed for morphological and functional recovery for patients who have undergone jaw resection due to oral and maxillofacial disease. In addition, prosthodontic treatment is administered to restore masticatory function. However, an adequate level of rehabilitation is not easily accomplished for patients undergoing jaw reconstruction.1,2
patients undergoing rehabilitation of occlusal function using implants subsequent to jaw resection The aim of this study was to quantitatively assess masticatory function in patients having prosthodontic treatment using implants following jaw resection, and to evaluate the effectiveness of such treatment in the restoration of masticatory function after jaw resection.
Haraldson et al reported that masticatory function in patients with missing teeth could be restored to the same level as that in healthy persons by the use of osseo-integrated implants.3-7 It has also been reported recently that osseo-integrated implants could restore masticatory function in patients undergoing jaw resection.8,9 However, few reports have quantitatively assessed the restoration of masticatory function in
Patients and Methods
Correspondence: Koichiro Ihara, Department of Oral and Maxillofacial Surgery, Saga Medical School, 5-1-1 Nabeshima, Saga, 849-8501, Japan. Tel: (81 952) 34 2397, Fax: (81 952) 34 2044 E-mail: [email protected]
The total number of implants placed was 208, of which 12 failed before evaluation of masticatory function, 13 survived but were not functional, and
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Forty four patients (27 men and 17 women) underwent prosthodontic treatment using implants at the Department of Oral and Maxillofacial Surgery at the Saga Medical School Hospital in Japan between 1989 and 1998. Twenty healthy volunteers acted as control subjects. Patients and controls had an age range from 10 to 80 years.
19
Masticatory Function after Jaw Resection and Rehabilitation
the remaining 183 implants were successful. Implant success was judged according to the following criteria proposed by Naert et al,10 that the implants were immobile, functional at the time of evaluation and did not cause pain or show infection or peri-implant radiolucency. The follow-up period at the time of evaluation of masticatory function ranged from 1.3 to 9.9 years, with a mean follow-up period of 5.1 years. Patients were divided into 3 groups: • group A comprised 21 patients (15 men, 6 women) with jaw resection and implants • group B consisted of 23 patients (12 men and 11 women) with ordinary dental implants without jaw resection • group C consisted of 28 healthy volunteers (13 men and 15 women) who had normal oral and maxillofacial function (Table 1). The subjects in the control group ranged in age from their teenage years to their 30s (Figure 1).
Resection patients (group A) Non-resection patients (group B) Normal subjects with natural dentition (group C)
Male
Female
Total
15 12 13
6 11 15
21 23 28
Table 1. Sex distribution of each group in this study.
Group A Group B
Number of patients
Group C
15
10
5
0
10
20
30
40
50
Age (years)
Figure 1. Age distribution of all patients.
20
60
70
Of the 21 patients in group A, 10 had malignant tumours, 8 had benign tumours, 2 had cysts, and 1 had osteomyelitis (Table 2). Five patients in this group who had partial maxillectomy (patients 1 to 5) had dental implants placed in the remaining bone, and a removable denture was made that had an obturator supported by dental implants (RDI). Thirteen patients with marginal mandibulectomy (patients 6 to 18) had a fixed denture supported by dental implants (FDI) inserted in the resected region. For 8 of these patients (patients 9 and 12 to 18), iliac bone was grafted to the resected region. Three patients with segmental mandibulectomy (patients 19 to 21) had dental implants placed in the remaining mandibular bone and an FDI was made, while maintaining mandibular continuity with a reconstruction plate. Seven of the 10 patients with malignant tumour had radiotherapy, with an exposure dose ranging from 15 Gy to 60 Gy. Most patients had 30 Gy prior to tumour resection. In group B, prior to implantation, severe resorption of alveolar bone with missing teeth was diagnosed in 12 patients, post-trauma in 8, malignant tumour of the floor of the mouth in 2, and lichen planus in 1 (Figure 2). No radiotherapy was performed for the 2 patients with malignant tumour in this group. Dental implants were placed after maxillary sinus augmentation in 2 patients. Ordinary implants with FDI or RDI were placed in the remaining patients.
25
20
Osseo-integrated implants (Brånemark System, Nobel Biocare Inc., Gothenburg, Sweden) were placed in an attempt to restore masticatory function for the 44 patients in groups A and B. Following conventional surgical procedures, fixtures were placed and abutments connected.11
80
The following masticatory function tests were performed at 3 months or more after delivery of the denture supported with dental implants: • mandibular movement test • masticatory test using low-adhesive, colourdeveloping chewing gum • electromyography of the masseter muscle • molar occlusal force test. Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto Patient
Conditions of resected jaw Residual teeth
Implant prosthesis
Type of prosthesis on opposing jaw
Subjectively preferred chewing side
Diagnosis
Number of implants (useless implants)
1
5 (0)
0
RDI
FD
R
Malignant tumour
2
3 (0)
0
RDI
FDI
R
Malignant tumour
3
1 (0)
0
RDI
FDI + ND
R
Malignant tumour
4
2 (0)
0
RDI
FD
R
Benign tumour
5
3 (0)
0
RDI
RPD
R
Malignant tumour
6
4 (0)
1 1-7
FDI
ND
R
Malignant tumour
7
2 (0)
76 2-7
FDI
ND
R
Benign tumour
8
4 (0)
7-4 4-7
RDI
ND
/
Malignant tumour
9
1 (0)
75- --7
FDI
ND
R
Odontogenic cyst
10*
4 (0)
875- -8
FDI
ND
R
Malignant tumour
11
4 (0)
7-3 567
FDI
ND
R
Benign tumour
12
3 (0)
5- -7
FDI
ND
R
Benign tumour
13
3 (0)
7- -3
FDI
ND
R
Osteomyelitis
14
4 (1)
76 3-7
FDI
ND
R
Benign tumour
15
4 (1)
7-1
FDI
ND
R
Benign tumour
16
3 (0)
8-4
FDI
ND
R
Malignant tumour
17
3 (0)
3-7
FDI FDI
N.D.
R
Benign tumour
18
3 (0)
2-6
FDI
RPD
R
Odontogenic cyst
19*
2 (0)
0
FDI
RPD
R
Malignant tumour
20
9 (2)
0
FDI
RPD + ND
R
Benign tumour
21*
5 (2)
0
FDI
RPD
R
Malignant tumour
Implants Natural teeth Resected site Grafted bone
Abbreviations: FDI = fixed denture supported with dental implant; RDI = removable denture supported with denal implant; FD = full denture; RPD = removal partial denture; ND = natural dentition; R = resected side; N = non-resected side. * Tongue resection. Table 2. Characteristics of resection patients (group A).
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
21
Masticatory Function after Jaw Resection and Rehabilitation
points each on the front and back with a chromatometer, and the mean value was calculated (Figure 3b).
Group A
12
Group B
For EMG of the masseter muscle, the upper end of the surface electrode was applied to a point midway between the lateral angle of the eye and the mandibular angle to obtain measurements using the Bio-EMG (Figure 3a). The mean value for the difference in action potential amplitudes at rest and with maximum clenching force was calculated.
10
Number of patients
8
6
4
2
0
ur
mo
lign
tu ant
Ma
Ben
ur
mo
tu ign
t
Cys
on ma nus rpti rau pla eso teeth T en r h e c i L er ng Sev missi and tis
yeli
om
e Ost
Figure 2. Diagnosis for patients with resection and nonresection.
In group A, the patients were interviewed to determine whether the subjectively preferred chewing side was on the resection side or non-resection side. The mandibular movement test was conducted using a BioPAK mandibular movement analyser (BioResearch Associates, Milwaukee, USA), which consisted of a Bio-electrognathography (EGN) and a Bio-electromyograph (EMG). With the Bio-EGN, jaw movements can be recorded in 3 dimensions by tracking the location of a magnet delivered to the mandibular incisal point with a magnetic sensor (Figure 3a). Mandibular movements were measured in the maximum mouth opening movement test, which was repeated 10 times, and the mean values for the maximum lateral shift of the incisal point and the maximum mouth opening distance were obtained. The masticatory test was performed in accordance with the method of Matsui et al12 using low-adhesive, colour-developing chewing gum (Meiji Chewing Gum Co., Ltd., Nagoya, Japan), with a weight ratio of gum A to gum B of 4:1 and a total weight of 3 g. The chromatic value (a*) of the gum was measured using a chromatometer (Color Reader CR-13, Minolta, Tokyo, Japan). The patients were instructed to chew the gum 50 times in each of 3 repeated measurements, the chromatic values of the gum were measured at 5 22
Occlusal force was measured using a dental occlusal force meter GM-10 (Nagano Keiki Seisakusho, Osaka, Japan) [Figure 3c]. The subject was instructed to firmly clench the sensor of the occlusal force meter with the first molar or second premolar. The test was repeated 3 times, and the mean value was calculated as the maximum occlusal force. The mean values of the measurement results obtained in the 4 tests were also computed for group B and group C subjects. The mean values were compared against those obtained in group A patients, including those who had undergone partial maxillectomy, marginal mandibulectomy, or segmental mandibulectomy. Statistical analysis was performed using Statistica software (Stat Soft Inc., Tulsa, USA) for principal component analysis and calculation of the correlation coefficients for the 5 test items, and the relationships between pairs of the test items were assessed. Principal component analysis is generally done to identify relationships between variables after classifying them into a smaller number of factors by grouping highly correlated variables.13 The purpose of conducting a principal component analysis in this study was to identify, from among the examination items, the important factors for the evaluation of masticatory function, and to closely examine similarities between pairs of the examination items. Based on the results obtained, the examination items extracted as the first and the second principal components were determined as the most important and the second most important factors related to masticatory function, respectively, and an attempt was also made to interpret each relationship. All factor scores in groups A, B, and C were plotted with the first component on the X-axis and the second Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto
a
component on the Y-axis for distribution of factor scores. The graph shows the masticatory function in individual patients as a scatter diagram based on the factors (the first and second principal components) identified by principal component analysis. Significant differences between the 3 groups in the values for each test item were identified by analysis of variance, the least significant difference (LSD) test, and the t-test.
Results Maximum Lateral Shift of the Incisal Point The mean maximum lateral shift of the incisal point was approximately 8 mm in both group B and group C, with no significant differences between these groups. The lateral shift of the incisal point in the partial maxillectomy subgroup of group A patients tended to be greater than that in groups B or C. In contrast, in both the marginal mandibulectomy and segmental mandibulectomy subgroups, the lateral shift tended to be smaller than that in groups B or C (Figure 4). However, no statistically significant b
c
Figure 3. (a) Measurement of mandibular movement by Bio-electrognathography and surface action potential amplitude of masseter muscle by Bio-electromyograph; (b) measurement of chromatic value of low-adhesive color-developing chewing gum using a chromatometer; (c) measuring device for occlusal force and disposable cap.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
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Masticatory Function after Jaw Resection and Rehabilitation
16 Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup
Maximum lateral shift of incisal point (mm)
14
Mean value for group B patients 12
Mean value for group C patients * Tongue resection
10 8 6
* *
4 2 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
* 19
20
21
Patients
Figure 4. Results for maximum lateral shift of the incisal point in patients undergoing resection.
differences were noted between groups A, B, and C (Tables 3 and 4). Maximum Mouth Opening Distance No specific trends were noted with regard to the maximum mouth opening distance for group A according to the resected region or range. In almost 50% of patients in group A, the maximum mouth opening distance was larger than that of subjects of groups B or C, and no significant differences were observed between groups B or C (Figure 5, Tables 3 and 4). Masticatory Test Using Low-adhesive, Colour-developing Chewing Gum Two of the 5 patients in the partial maxillectomy subgroup in group A showed a lower value than that of group B. In the mandibulectomy subgroup, masticatory efficiency was found to be lower than in Group B in 1 patient who underwent marginal Test
F value
p Value
Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential amplitude of electromyography between sides Difference in occlusal force between sides
0.911 0.853 1.891 4.741
0.407 0.430 0.159 0.012*
0.499
0.609
Table 3. Results of analysis of variance between all groups. *p < 0.05.
24
mandibulectomy with tongue resection and in 2 patients who underwent segmental mandibulectomy. In most patients in Group A, masticatory efficiency was equal or superior to that in group B (Figure 6). No statistically significant differences were observed between the groups (Tables 3 and 4). Differences in Action Potential Amplitude on the Masseter Muscle Between the Left and Right Sides To evaluate the differences in action potentials on the masseter muscle between the resection and non-resection sides in group A, the differences in action potential amplitude between both sides were calculated and compared with those in groups B and C. In group A, the mean difference in action potential amplitude between the sides was larger than in groups A-B Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential * amplitude of electromyography between sides Difference in occlusal force between sides
A-C
B-C
*
Table 4. Results of t-test between the 3 groups. *p < 0.05.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto
Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup
60
Maximum mouth opening (mm)
Mean value for group B patients Mean value for group C patients * Tongue resection
50
40 *
*
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
* 19
20
21
Patients
Figure 5. Results for maximum mouth opening in patients undergoing resection.
B or C (Figure 7), irrespective of the resected region or range, indicating a greater difference between sides in group A than in groups B or C (Tables 3 and 4).
the differences in occlusal force between the sides were calculated and compared with those in groups B and C. Among patients in group A, occlusal force tended to be reduced in the partial maxillectomy or segmental mandibulectomy subgroups. However, in the marginal mandibulectomy subgroup, differences in occlusal force between the left and right sides were
Differences Between Sides in Molar Occlusal Force To evaluate differences in occlusal force between the resection and the non-resection sides in group A, 80
Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup Mean value for group B patients Mean value for group C patients * Tongue resection
70
Chromatic value (a*)
60 50 40 30
* 20
* *
10 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Patients
Figure 6. Results for chromatic values of low-adhesive colour-developing chewing gum system in patients undergoing resection.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
25
Masticatory Function after Jaw Resection and Rehabilitation
Difference in mean action potential amplitude (μV)
300 Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup Mean value for group B patients Mean value for group C patients * Tongue resection
250
200
150
100
50 *
* 0
1
2
3
4
5
6
7
8
9
10 11 12 Patients
13
14
15
16
17
18
* 19
20
21
Figure 7. Difference in mean action potential amplitude of surface electromyograms on the masseter muscle between the left and right sides in patients undergoing resection.
larger than those in groups B or C in 6 patients, that is, in almost 50% of the patients (Figure 8). Nonetheless, no statistically significant differences were noted (Tables 3 and 4).
side was the non-resection side for all patients (Table 2). Statistical Analysis Correlation coefficients were determined for the 5 test items (maximum lateral shift of the incisal point, maximum mouth opening distance, masticatory test using chewing gum, differences in action potential
Subjectively Preferred Chewing Side Interviews with the patients undergoing resection showed that the subjectively preferred chewing 40 Partial maxillectomy subgroup Marginal mandibulectomy subgroup Segmental mandibulectomy subgroup Mean value for group B patients Mean value for group C patients * Tongue resection
Difference in occlusal force (kgf)
35 30 25 20 15 10
*
5 0
*
*
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Patients
Figure 8. Difference in maximum occlusal force of the molar region between the left and right sides in patients undergoing resection.
26
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto Maximum lateral shift Maximum Chromatic Difference in mean action Diffference in of incisal point mouth opening value potential amplitude of electro- occlusal force myography between sides between sides Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential amplitude of electromyography between sides Difference in occlusal force between sides
0.84*
-0.33 -0.09
0.84* -0.33 -0.10
-0.09 0.02
0.19
-0.12
-0.21
0.24
-0.10 0.02 0.19
-0.12 -0.21 0.24 0.12
0.12
Table 5. Correlation coefficients between the 5 tests.
amplitude between sides, and differences in molar occlusal force between sides) and a principal component analysis was performed. With regard to correlation coefficients, a high correlation of 0.84 was observed between the maximum lateral shift of the incisal point and the maximum mouth opening distance (Table 5). In the principal component analysis, the eigenvalue of the first component was 2.04 and a factor loading of 0.50 or higher was found in the maximum lateral shift of the incisal point and the maximum mouth opening distance. For the second component, the eigenvalue was 1.21 and a factor loading of 0.50 or higher was found in the masticatory test using chewing gum, differences in action potential amplitude between the sides, and differences in molar occlusal force between sides (Table 6).
Test
First Second component component
Maximum lateral shift of incisal point Maximum mouth opening Chromatic value Difference in mean action potential amplitude of electromyography between sides Difference in occlusal force between sides
-0.94* -0.96* 0.22 -0.09
-0.15 0.02 0.71* 0.70*
0.18
0.59*
Eigenvalue
2.04
1.21
Table 6. Eigenvalue and factor loading by principal component analysis for the 5 tests of masticatory function. * Factor loading greater than 0.50 by varimax method.
As to the distribution of factor scores in all subjects, including those in groups A and B, nearly all the scores (except for patients 19 and 35) converged within a specified range in groups A, B, and C. No remarkable differences in the distribution pattern were seen in these groups (Figure 9).
3.5 a a
2.5
c
bc ba a
Second component
1.5
c a
b
0
-1.5
-2.5
a
ab
b a a ca b bc c ab c ca c c a cbc b c a b b c bc c c c aca a c ccc c c b b bcc c b a a b b b b b
0.5
-0.5
a
Patient 19
b Patient 35
-5
-4
-3
-2
-1
0
1
First component
Figure 9. Distribution of factor scores for all groups.
Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
27
Masticatory Function after Jaw Resection and Rehabilitation Group A Group A Group B Group C
0.011* 0.007†
Group B
Group C
0.011*
0.007 0.929
†
0.929
Table 7. Results of least significant difference test in difference in mean action potential amplitude of electromyography between sides. *p < 5%; † p < 1%.
In order to evaluate the differences in the mean values of each test item in the 3 groups, analysis of variance was done. Significant differences were recognised in action potential amplitude on the masseter muscle between the left and right sides — an F-value was 4.741 with a level of significance of 0.012 (Table 3). The LSD test was performed to identify the patients who exhibited significant differences. The levels of significance in thusidentified subjects were as follows: 5% between groups A and B, and 1% between groups A and C (Table 7). The t-test also revealed significant differences in action potential amplitude between the sides between groups A and B and between groups A and C, with a level of significance of 5% (Table 4).
Discussion To determine whether patients who have undergone mandibular resection or reconstruction can chew properly wearing an implant-supported prosthesis, masticatory function in such patients should be evaluated by comparison with healthy control subjects. Masticatory function in patients with conventional tooth defects has been reported multilaterally and objectively, for example by Haraldson et al.3-7 However, in only a few studies has multilateral assessment of reconstructive surgery been conducted in patients undergoing jaw resection.14-16 Methods for evaluating masticatory function may be divided into subjective evaluation, in which patients are questioned regarding chewable foods, and quantitative evaluation, in which test equipment or samples are employed. Subjective evaluation is easily performed because no special tools or samples are required — the results however may not agree with those obtained by quantitative evaluation, as subjective evaluation is influenced by the patient’s eating habits, favourite foods, and personality.17 28
Quantitative evaluation of masticatory function is essential for an accurate determination of the effectiveness of prosthodontic treatment. A variety of methods have been developed for measuring masticatory efficiency, and methods for recording and evaluating mandibular movement,18,19 muscular dynamics,20 and occlusal force7,21 recently became available thanks to advances in medical electronics. In this study, evaluation of masticatory function was conducted in 72 subjects using principal component analysis to examine the mutual relationships of the 5 tests. Since both the maximum lateral shift of the incisal point and the maximum mouth opening distance were identified as the first component, mandibular movement was considered to be the most important factor in the function of mastication. The masticatory test using chewing gum, EMG of the masseter muscle, and the occlusal force test were identified as the second component. These were taken to be the factors that comprehensively describe the condition of the hard and soft tissues (tongue, masticatory muscles, teeth, and jaw) related to masticatory efficiency. However, the eigenvalue of the second component was approximately 60% that of the first component. This finding suggests that mandibular movement is more strongly correlated to masticatory function. In the distribution of factor scores for all subjects (Figure 9), markedly different distribution patterns were observed in 1 patient who had undergone segmental mandibulectomy for malignant tumour (patient 19) and another patient receiving prosthodontic treatment using implants for lichen planus (patient 35). The different distribution patterns seen in these patients may have been due to the extremely small occlusal contact area in patient 19, and marked pain due to erosion of the buccal mucosa or tongue secondary to lichen planus in patient 35. In all other patients, factor scores were distributed in a specified range, regardless of which of the 3 groups they were classified into. Based on these findings, we consider that the use of dental implants permits masticatory function in patients undergoing jaw resection to be restored to a level comparable to that of non-resection jaw patients or normal subjects. Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
Ihara, Goto
In patients undergoing jaw resection, the mouth opening distance was reduced in 9 patients compared to that of healthy controls or non-resection jaw patients. However, mouth opening was restored to 30 mm or more in 7 patients by mouth-opening exercises after surgery for the underlying disease. Accordingly, no significant differences were noted between the 3 groups. Given that mandibular movement is the most important factor in masticatory function, as revealed in principal component analysis, positive postoperative mouth-opening practice is essential. In the tests of masticatory efficiency using lowadhesive, colour-developing chewing gum, patients undergoing resection showed lower values than nonresection patients, including 2 patients who had undergone partial maxillectomy and 3 patients who had undergone mandibulectomy plus tongue resection. In the former patients, the prostheses were not satisfactorily stabilised for mastication because only 1 or 2 implants were placed. In the latter patients, the chewing gum could not be moved to the occlusal table of the denture due to limitations in tongue movement. Thus, denture stability and tongue mobility must be importantly related to the function of mastication. EMG of the masseter muscle showed that there were significant differences between patients undergoing resection and non-resection patients or normal subjects with regard to the differences in action potential amplitude between the left and right sides. This finding suggests that irreversible changes may have taken place in the masticatory system probably induced by surgery. However, masticatory function may be less seriously affected by a difference in the action potentials between the 2 sides of the masticatory muscle, this being a second principal component as compared to mandibular movement (a first principal component). With regard to differences in occlusal force, no significant differences were found between the 3 groups by the t-test or analysis of variance. However, in 50% of the patients with marginal mandibulectomy, the differences tended to be larger. In patients with larger differences in occlusal force, the differentials were presumably related to a number of findings. First of all, the occlusal force on the resected side, where Asian J Oral Maxillofac Surg Vol 15, No 1, 2003
the prosthesis was placed with implants, was lower than that in the non-resection side. Secondly, the subjectively preferred chewing side was the nonresection side. And lastly, significant differences were seen in occlusal action potential amplitude between the 2 sides. It was expected that the non-resection side would be the subjectively preferred chewing side and this was true for marginal mandibulectomy patients without tongue resection, even though masticatory function was fully restored by prosthodontic treatment using dental implants. This is presumably because the subjectively preferred chewing side before the placement of implants tended not to change, since the implants were placed with a considerable passage of time after surgery. However, such preferences may not continue indefinitely, and satisfactory chewing on the resected side should be achievable with practice. No statistically significant differences were detected in any of the test items between the normal function control and non-resection groups, in agreement with the findings of Haraldson et al.3-7 If jaw resection is not required, masticatory function can be fully restored by prosthetic rehabilitation using dental implants, which results in a satisfactory function of mastication comparable to that of normal subjects. On the other hand, for patients undergoing resection, significant differences were recognised only in action potential amplitude in the masseter muscle between the left and right sides. However, we maintain that masticatory function in patients undergoing resection was successfully restored to a level comparable to that of non-resection patients or healthy controls based on the following findings: • tests of action potential amplitude of the masseter muscle were identified as the second component in the principal component analysis • no significant differences existed between resection and non-resection patients or healthy controls in other test items • no specificity was seen in the distribution of factor scores in resection patients. After resection, jaw reconstruction is possible using bone grafts or biocompatible materials, and 29
Masticatory Function after Jaw Resection and Rehabilitation
missing teeth may be compensated for by prosthetic rehabilitation with dental implants. That being the case, functional reconstruction of the oral or maxillofacial soft tissues such as the tongue or masticatory muscles is called for. Masticatory function can be restored to a level comparable to that of healthy controls once the functional reconstruction of all these tissues has been achieved.
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Asian J Oral Maxillofac Surg Vol 15, No 1, 2003