Abstract
Purpose: This study aimed to evaluate masticatory performance in cases where one molar was missing.
Methods: Participants were 156 adults with one molar missing from their natural teeth, who were divided into group A (without prosthetic treatment) and group B (with prosthetic treatment). The non-missing side was designated as A1 or B1, and the missing side was designated as A2 or B2. The amount of glucose eluted (AG) when the participants chewed a gummy jelly was measured and used as a parameter for masticatory performance. AG was compared between the non-missing side (A1, B1) and missing side (A2, B2), and between the first molar missing group and second molar missing group.
Results: AG was significantly greater on the dentate side (P < 0.001) and was significantly less in the A2 group when the first molar was missing (P = 0.002). The rate of decrease of AG was 11.1%, 14.3%, and 8.4% in groups A+B, A, and B, respectively.
Conclusion: Masticatory performance appears to decrease even with only one missing molar. Although improvement is achieved by prosthetic treatment, performance remains inferior to that on the dentate side.
Introduction
To evaluate masticatory function, attempts have been made to examine masticatory movements, muscular activity, and masticatory performance, as well as occlusal force. Among these, occlusal force and masticatory performance are widely used in clinical research because they can be easily measured [1,2,3,4,5,6,7,8]. Occlusal force is affected by aging [9,10], whereas it has become clear that masticatory performance is less affected by aging [8,9]. Therefore, masticatory performance is considered to be the more important of these parameters for evaluating masticatory function.
Numerous methods have been proposed for measuring masticatory performance, including the sieving method. In addition, measurement of the amount of glucose eluted during chewing of gummy jelly is relatively simple and easy to perform, and has a significant correlation with masticatory performance determined by the sieving method [11]. Accordingly, analysis of masticatory performance by measurement of glucose eluted has become widely used in young adults, elderly adults, and denture wearers.
Masticatory performance is significantly associated with occlusal support. It decreases as the number of occlusal supports decrease with tooth loss, but has been reported to improve with dental prosthetic treatment [4,12,13,14,15]. It is necessary to exclude the effect of occlusal support when examining the effect of age on masticatory performance; therefore, studies focusing on the effect of occlusal support have been carried out. A previous study [7] reported that there was no correlation between masticatory performance and age in participants who had at least 26 remaining teeth and were classified as Eichner A. In addition, no significant difference in masticatory performance was found between young, middle-aged, and elderly people who had complete natural dentition [8]. These findings indicate that masticatory performance is maintained without any effect of aging.
In contrast, it has been reported that masticatory performance is significantly reduced when one molar tooth is lost, even with all occlusal supports [4]. However, the degree of reduction in masticatory performance by the loss of one molar and of recovery by prosthetic treatment, have yet to be clarified.
The aim of this study was to clarify masticatory performance in participants with only one molar (excluding the third molar) missing from the natural dentition, by analyzing the amount of glucose eluted on each of the missing and non-missing sides when chewing gummy jelly.
The null hypothesis was that the loss of one molar does not reduce masticatory performance. If masticatory performance is significantly reduced by the loss of one molar tooth, it is clinically significant because it can indicate the need for dental prosthetic treatment even when only one molar tooth is missing.
Materials and Methods
Ethics statement
This study was conducted in accordance with the Declaration of Helsinki. The experiment was conducted with the approval of the ethics committee of The Nippon Dental University School of Life Dentistry (No. NDU-T2020-31). Informed consent was obtained prior to participation after an explanation of the purpose of the study.
Participants
A total of 156 adults (age range, 36-85 years; mean age, 65.6 years) who had only one molar missing from their natural teeth, excluding the third molar, participated in this study. The participants were recruited from people who participated in a dietary education fair sponsored by Kita-ku, Tokyo, and staff and students of The Nippon Dental University. Inclusion criteria were 1) no clinical abnormalities in the masticatory system; 2) only one molar missing from the natural dentition, excluding the third molar; and 3) adequate cognitive function. Exclusion criteria were 1) previous orthodontic treatment and 2) signs and symptoms of temporomandibular disorders or maxillofacial pain.
The sample size was calculated using a software program (G*Power 3.1.9.3, Heinrich Heine University Düsseldorf, Dusseldorf, Germany), with an α of 0.05, a β of 0.8 and an effect size of 0.5, requiring 34 participants.
Test food
Gummy jelly containing 5% glucose (Glucolumn, GC, Tokyo, Japan) was used as the test food.
Experimental design
The participants were divided into group A (without prosthetic treatment on the missing side) and group B (with prosthetic treatment on the missing side). The non-missing side of the participants was designated as A1 or B1, and the missing side was designated as A2 or B2. The participants were also classified into the first molar missing and second molar missing groups (Table 1).
Participants were asked to chew the test food on one side for 20 s and then were asked to hold 10 mL of water in their mouth and to spit into a cup with a filter. Then, the glucose concentration of the filtrate was measured using a glucose measuring device (GS-2; GC) and used as the amount of glucose eluted. The value was used as a parameter for masticatory performance (Fig. 1).
Table 1
Distribution of participants
|
Group A |
Group B |
| Missing |
U6 |
L6 |
U7 |
L7 |
U6 |
L6 |
U7 |
L7 |
| Number |
7 |
10 |
25 |
31 |
30 |
38 |
8 |
7 |
U6, upper jaw first molar; L6, lower jaw first molar; U7, upper jaw second molar; L7, lower jaw second molar
Statistical analysis
All data were analyzed using statistical software (SPSS for Windows 27.0, IBM Corp., Armonk, NY, USA). After confirming the normality of the data with the Shapiro-Wilk test, the amount of glucose eluted was compared between the dentate side (combined A1+B1 groups) and the missing side (combined A2+B2 groups), between the A1 and A2 groups, and between the B1 and B2 groups. Next, the amount of glucose eluted was compared between the A1 and B1 groups and between the A2 and B2 groups. In addition, the amount of glucose eluted on the missing side was compared between the first molar missing and second molar missing groups. A paired t-test was used to compare the non-missing side and the missing side, and an independent t-test was used to compare groups A and B, the first molar missing, and second molar missing groups. Due to the small sample size, post hoc power analysis was performed for comparisons between the first molar missing and second molar missing groups. In all analyses, P values less than 0.05 were considered statistically significant.
Results
In comparisons between the combined A1+B1 and A2+B2 groups, between the A1 and A2 groups, and between the B1 and B2 groups, more glucose was eluted on the non-missing side than on the missing side, and there was a significant difference between the two sides for each of these comparisons (P < 0.001) (Table 2).
Comparing the A1 and B1 groups, the amount of glucose eluted was similar and there was no significant difference between these groups (P = 0.397). Comparing the A2 and B2 groups, significantly more glucose was eluted in the B2 group than in the A2 group (P = 0.008) (Table 2).
Regarding the amount of glucose eluted according to the type of missing tooth, no difference was found in the B2 group (P = 0.350). In the A2 group, significantly less glucose was eluted when the first molar was missing than when the second molar was missing (P = 0.002) (Table 3). Power analysis for the missing tooth revealed power of 0.850, which confirmed the validity of the sample size.
The rate of decrease in the amount of glucose eluted on the missing side compared to the non-missing side was 11.1%, 14.3%, and 8.4% in groups A+B, A, and B, respectively. There was no difference in the amount of glucose eluted in terms of tooth type in group B (with prosthetic treatment), but in group A (without prosthetic treatment) the rate of decrease was 12.2% in the second molar missing group and 21.1% in the first molar missing group (Table 4).
Table 2
Mean and standard deviation of masticatory performance in each group
| Group |
A1+B1 |
A2+B2 |
A1 |
A2 |
B1 |
B2 |
A1 |
B1 |
A2 |
B2 |
| Number (n) |
156 |
156 |
73 |
73 |
83 |
83 |
73 |
83 |
73 |
83 |
| Mean (mg/dL) |
212.2 |
188.6 |
213.9 |
183.3 |
210.7 |
193 |
213.9 |
210.7 |
183.3 |
193 |
| SD (mg/dL) |
23.6 |
23.1 |
23.8 |
22.5 |
23.5 |
22.8 |
23.8 |
23.5 |
22.5 |
22.8 |
| P value |
<0.001 |
<0.001 |
<0.001 |
0.397 |
0.008 |
A, without prosthetic treatment; B, with prosthetic treatment; A1, B1, dentate side; A2, B2, missing side; SD, standard
Table 3
Mean and standard deviation of masticatory performance by type of missing tooth
| Group |
A1 |
A2 |
B1 |
B2 |
| Missing tooth |
6 |
7 |
6 |
7 |
6 |
7 |
6 |
7 |
| Number (n) |
17 |
56 |
17 |
56 |
68 |
15 |
68 |
15 |
| Mean (mg/dL) |
214.2 |
213.9 |
168.8 |
187.8 |
210.3 |
212.7 |
192.0 |
198.1 |
| SD (mg/dL) |
23.2 |
24.1 |
17.5 |
22.1 |
23.4 |
25.2 |
22.6 |
22.9 |
| P value |
0.962 |
0.002 |
0.722 |
0.350 |
A, without prosthetic treatment; B, with prosthetic treatment; A1, B1, dentate side; A2, B2, missing side; 6, first molar; 7, second molar; SD, standard deviation
Table 4
Mean and standard deviation of rate of reduction in masticatory performance
| Group |
A+B |
A |
B |
| Missing tooth |
6 or 7 |
6 |
7 |
6 or 7 |
6 |
7 |
6 or 7 |
6 |
7 |
| Number (n) |
156 |
85 |
71 |
73 |
17 |
56 |
83 |
68 |
15 |
| Mean (%) |
11.1 |
11.1 |
11.1 |
14.3 |
21.1 |
12.2 |
8.4 |
8.7 |
6.9 |
| SD (%) |
5.1 |
5.9 |
3.8 |
4.9 |
3.8 |
3.2 |
3.2 |
3.3 |
2.5 |
A, without prosthetic treatment; B, with prosthetic treatment; 6, first molar; 7, second molar, SD, standard deviation
Discussion
A previous investigation of masticatory performance during free chewing in adults with missing molars [12] found significantly reduced masticatory performance in those with missing molars on both sides, but not in those with unilateral molar loss because these individuals chewed on the non-missing side with high masticatory performance. In a study that investigated masticatory performance before and after implant treatment in adults with unilateral molar loss [5], a clear difference was observed between before and after treatment during unilateral chewing, but no clear difference was observed during free chewing. These findings [5,12] suggest that when people with unilateral molar loss are allowed to masticate freely, they chew more on the non-missing side and are therefore less susceptible to the loss. Therefore, the effects of unilateral molar loss should be investigated by evaluating unilateral chewing rather than free chewing. Accordingly, in the present study, unilateral chewing was used as the recording condition instead of free chewing.
Occlusal force on the missing and non-missing sides in adults with a fixed prosthesis or an implant prosthesis was found to be significantly larger on the non-missing side than on the missing side [2,3]. Regarding masticatory performance, it has been reported that performance improved when prosthetic treatment was applied to unilateral molar loss [5,16]; however, no comparison has been made between the missing and non-missing sides.
The present study investigated masticatory performance of the missing and non-missing sides of participants in group B with prosthetic treatment on the missing side, and found significantly higher masticatory performance on the non-missing side than on the missing side. This result indicates that masticatory performance does not recover to the level of natural dentition even after dental prosthetic treatment. However, masticatory performance on the missing side of group A, who had no dental prosthetic treatment, was significantly lower than that on the missing side of group B. Furthermore, the reduction in masticatory performance of the missing side relative to the non-missing side was smaller in group B (8.4%) than in group A (14.3%). It is thought that these findings indicate the efficacy of prosthetic treatment for tooth loss, as well as its necessity.
The comparison of masticatory performance according to type of missing tooth revealed that masticatory performance on the missing side was significantly worse when the first molar was missing compared with the second molar missing. This finding might be related to the ‘main occluding area’ for crushing and fragmenting food, which is considered to be that of the first molar [17]. In the case of normal occlusion, the main occluding area has been reported as the first molar in all cases [17]. Another study found that when the first molar was lost, the main occluding area moved to another tooth, but when dental prosthetic treatment was performed, the main area returned to the site of the first molar [1]. Based on these reports and the results of the present study, it appears that loss of the first molar leads to loss of the site for crushing and fragmenting food, which results in a significant reduction in masticatory performance.
In the present study, masticatory performance was evaluated in participants with one missing molar by measuring the amount of glucose eluted while chewing gummy jelly on the missing and non-missing sides. Masticatory performance decreased significantly even with one missing molar, and although there was significant improvement after prosthetic treatment, masticatory performance was significantly inferior to that on the non-missing side.
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