Electromyographic assessment of jaw muscles in edentulous patients with implant-supported prostheses Shereen M Kabeel*

Electromyographic assessment of jaw muscles in edentulous patients with
implant-supported prostheses
Shereen M Kabeel*, Dina M Kholief**
Abstract;This study aimed to evaluate the effect of implant-supported oral rehabilitation in the mandible on the electromyographic (EMG) activity during chewing in completely edentulous individuals. Material & methods; Twelve completely edentulous patients were selected for this study, being six females and six males, aged 55 to 65 years old. The patients divided into three groups according to the treatment protocol; (GI) All the completely edentulous patients having conventional maxillary and mandibular complete denture, (GII) six patients had two mandibular implants supported overdenture at the canine region and (GIII) six patients had one mandibular implants supported overdenture at the symphesial area. All patients were submitted to EMG evaluation of the masseter, and the temporalis muscles, after three months of placement of the conventional prosthesis and after three months of both implant-supported systems by using different textures soft and hard foods.. The recordings data were analyzed using One Way ANOVA followed by post hoc analysis using LSD test. p < 0.05 was considered statistically significant. Results; The highest EMG activity of the masseter and temporalis muscles was recorded by chewing of soft and hard foods in GI, while the reduction of muscular activity after implant supported oral rehabilitation was seen. No significant differences in the analyzed EMG parameters were found between the patients in GII and GIII. Conclusion; Mandibular implant-supported prostheses in edentulous individuals revealed a decrease in EMG amplitude for the masseter and temporalis muscles during chewing, which may indicate adaptation to new conditions of stability provided by support of the complete denture in the mandibular arch.

Key words: Mastication, Implant-supported prosthesis, Electromyography.

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*Lecturer of Removable Prosthodontics, Faculty of Dental Medicine for girls, Al-Azhar University.

**Assistant Professor of Removable Prosthodontics, Faculty of Dental Medicine for girls, Al-Azhar University.

Introduction
The aging process causes physiological changes that affect the whole organism. Specifically in relation to the stomatognathic system, in addition to tooth loss, there is reduced masticatory force, alveolar bone decomposition, changes in oral mucosa, and reduction in the number of functional motor units, leading to decreased muscular activity1.

For many years, traditional complete denture designs have been modified to gain additional support and stability from a few retained and suitably prepared natural teeth. Mericske-Stern et al.2 attested to the effectiveness of such tooth-supported complete dentures or overdentures as alternative to complete dentures. Nowadays, overdenture treatment with the use of implants has become popular for edentulous elderly patients who are maladaptive to complete dentures3.

Implant-supported prosthesis may be considered a viable and efficient technique for the rehabilitation of partial or full edentulism, and this was confirmed by long-term studies4, 5. A well-planned and performed implant technique provides safe treatments that can significantly improve the neuromuscular function of the masticatory system, and therefore, the quality of life6, 7.

Electromyography (EMG) is a safe, effective and reliable system, widely used to measure the muscular performance of the stomatognathic system in both static and dynamic activities8. It forms the only tool to assess the muscle activity of the stomatognathic system since its first concerted use in dentistry by Robert moyers in 1949. Over years clinicians and researchers have tried EMG activity to detect the chewing abilities in denture wearers9.

Observation of the effect of tooth loss in elderly individuals shows that the presence of natural teeth allows a better masticatory performance compared to the use of removable complete dentures with regards to masticatory efficiency, masticatory time, selection of more consistent foods and EMG activity10. Within this context, edentulous adults and elderly individuals wearing removable complete dentures exhibit reduced muscular activity at the working side, which is poorly adapted to the food texture, as well as decreased EMG activity, especially of the masseter muscle, when compared to dentate individuals11. The stability of complete dentures also influences the masticatory performance of individuals, as damages to this aspect would result in less regularity and uniformity of mastication cycles12. Moreover, use of prostheses damages the sensitivity, oral stereognosis and taste and may also influence the feeding, swallowing and nutritional status of elderly individuals13.

The type of dental treatment performed in adults and elderly individuals also influences the masticatory efficiency, which is greater in individuals rehabilitated with tooth supported and implant-supported dentures compared to removable complete dentures. It should be highlighted that individuals wearing tooth-supported dentures exhibit greater EMG activity of the anterior temporalis muscle during masticatication, both in the amplitude and value of integrated activity, compared to individuals wearing removable complete and implant-supported dentures in the mandibular arch14. Thus, the use of implant-supported prostheses leads to improved masticatory function characterized by an increase in EMG activity and reduced masticatory cycle time15, although neuromuscular coordination is lower compared to individuals with natural teeth16.

The objective of this study was to evaluate the muscular activity involved in processes of mastication on foods of different textures in edentulous individuals using electromyography to compare their performance before and after placement of implant-supported prostheses in the mandibular arch.

Material and methods
Patient selection;
Twelve completely edentulous individuals were selected for this study of both genders (six females and six males), aged 55-65 years old. All subjects were free from systemic diseases as confirmed by history taking and laboratory examinations. All patients were with no evident signs and symptoms of stomatognathic system disorder. The patients had been wearing dentures for about five years and had no abnormal habits such as clenching, bruxism and tongue thrust, they did not taking drugs that affect muscle activity, and had adequate mandibular bone structure for placement of implants. Each patient received a written consent explaining the study description, the advantages and possible risks if present. Patients underwent implant insertion and electromyography recording of masseter and temporalis muscles, in addition to Cone beam computed tomography (CBCT) was made for each patient for accurate determination of height and width of bone and size of the proposed implant at specific site or sites.

Patient grouping;
All the selected twelve completely edentulous patients received conventional maxillary and mandibular complete denture (Group I), which are in turn divided into
Two equal groups according to the gender, number and position of implant supported overdentures
Group II: Six patients had received two-screw type, root form mandibular implants supported overdenture at the canine region and a complete maxillary removable conventional denture.

Group III: Six patients had received one screw type, root form mandibular implant supported overdenture at the symphesial area and a complete maxillary removable conventional denture.

Prosthetic procedures for group I:
– Construction of maxillary and mandibular conventional heat cured acrylic resin complete dentures was done by usual manner. Final adjustments were made, the dentures checked for retention and occlusion and the patients were satisfied and free of any discomfort with the dentures and asked to wear the denture for three months. Thereafter, EMG recordings were made.

Surgical procedures for group II and III;- All patients’ mandibular dentures were transformed into two or one implant supported mandibular overdenture with ball and socket attachments.

– The surgical procedures of implant insertion were done by two-stage technique to minimize the risk of infection. A mucoperiosteal flap was reflected exposing the mandibular interforaminal region for optimal implant placement. Two implants (Dentium Superline, Dentium Co. Ltd., Korea) were screwed in position. The length of the implants was 10 mm and the diameter was3.6 mm.

– All patients received screw shaped, root form implant to permit primary fixation between implant and the bone during initial healing period in addition to increasing area of contact between implant surface and surrounding bone, in addition to that, it has been established that the survival of the root form titanium implants is very high in the anterior mandible and that the incidence of surgical complications is very low. Thus, the implants in-group II were inserted at the canine regions, while in-group III, the symphesial region was selected17.

– The preplanned implants number, type, position, length and width were inserted. The patients were not allowed wearing their dentures for two weeks after surgery then the denture was relieved at the implant area to be seated properly in the patient moth. Healing period of three months was allowed to assure complete implant bone ossiointegration.

– Second stage surgery was carried out after three months, attachment installation (Dentium Superline, Dentium Co. Ltd., Korea) and pick up technique was doneby auto-polymerized acrylic resin.

-The finished mandibular implant supported over dentures were inserted into patient’s mouth and checked for retention and occlusion, final adjustments were made and the patients were instructed to care and use his/her maxillary complete denture and implant supported mandibular prosthesis for three months (Fig 1 a & b). Thereafter, EMG recordings were made17.

2800350175260

Fig.1 (a) patient has two implants with ball and (b) patient has single implant with ball and socket
socket attachment at the canine region . attachment at symphesial area .

Electromyographic activity measurements;
– EMG recording were made after three months for edentulous patients wearing conventional complete denture, then after three months from wearing the two implants supported mandibular over dentures as well as from wearing the single implant supported mandibular over denture opposed to maxillary conventional complete denture.

– EMG recording were made by computer electromyography based data acquisition system (Nemus II) and were expressed as root mean square (RMS).

– The surface EMG recordings provided a safe, easy, and noninvasive method that allowed objective quantification of the energy of the muscle. Standard amounts and sizes of banana and carrot were used to reduce patient variability. These test foods were examples of soft and hard food, respectively. During all recordings, the patients were seated with their head unsupported and were asked to maintain a naturally erect position.
– Before electrode placement, the skin was cleaned with ethanol to reduce impedance then electro-conductive gel was applied on the electrodes before they contacted the skin then fixed by adhesive tapes. This followed by asking the patients for chewing on his denture or implant supported over denture teeth at upright position. Thus creating a region of facial muscle contraction, which produce impulses. These impulses were printed by laser printer18.

Statistical Analysis
Data were collected, revised, coded and entered to the Statistical Package for Social Science (IBM SPSS) version 23. The quantitative data were presented as mean, standard deviations and ranges when their distribution found parametric. The comparison between more than two groups regarding quantitative data with parametric distribution were done by using One-Way ANOVA followed by post hoc analysis using LSD test. The confidence interval was set to 95% and the margin of error accepted was set to 5%. So, the p-value was considered significant at the level of < 0.05.

Results
A 100% survival and success rate was reported for all implant rehabilitations. All patients finished the study without any dropout. All patients in the three groups reported an adequate masticatory efficiency and were satisfied with their prostheses. None of the patients reported any dysfunction or dissatisfaction for the treatment.

Results referring to the bioelectric activity of masseter muscle during chewing of soft & hard foods. Exhibits postprosthetic reduction in EMG activity of the masseter muscles in-groups II and III, comparing to group I with statistically significant differences (p<0.043, p<0.042) respectively at 3 months for chewing of soft & hard foods (Table 1, Fig 2 ).

Results referring to the bioelectric activity of temporalis muscle during chewing of soft & hard foods. Exhibits postprosthetic reduction in EMG activity of the temporalis muscles in-groups II and III, comparing to group I with statistically significant differences (p<0.042, p<0.028) respectively at 3 months for chewing of soft & hard foods (Table 1, Fig 2).

Concerning the activity of masseter muscle during chewing of soft &hard food, there was reduction in EMG activity after treatment, though there is no statistically significant difference between groups II and III (p<0.442, p<0.896) among the recorded values (Table 1, Fig 2).

Observing the activity of temporalis muscle during chewing of soft &hard food, there was reduction in EMG activity after treatment, though there is no statistically significant difference between groups II and III (p<0.302, p<0.801) among the recorded values (Table 1, Fig 2).

Table1. Comparison between different numbers of mandibular implants supported overdenture regarding EMG activity of the masseter and temporalis muscles.

Groups
Muscles Two implant denyureSingle implant denture Conventional denture One Way ANOVA test Post hoc analysis
F P-value P1 P2 P3
Masseter muscle Soft food 201.17 ± 107.73 231.92 ± 45.87 290.11 ± 40.58 3.587 0.043 0.442 0.034 0.012
Hard food 256.24 ± 75.03 261.2 ± 83.55 335.58 ± 45.28 3.638 0.042 0.896 0.015 0.032
Temporalis muscle Soft food 123.13 ± 54.73 145.9 ± 33.17 170.58 ± 9.21 3.637 0.042 0.302 0.021 0.047
Hard food 183.55 ± 51.61 188.17 ± 16.17 229.55 ± 35.2 4.16 0.028 0.801 0.042 0.006
P-value > 0.05: Non significant; P-value < 0.05: Significant; P-value < 0.01: Highly significant
P1: Two implants Vs Single implant
P2: Two implant Vs conventional denture
P3: Single implant Vs conventional denture

Fig (2) Bar chart showing Comparison between different number of mandibular implants supported overdenture regarding EMG activity of the masseter and temporalis muscles.

Discussion
Among the study limitations there is the use of a convenience sample: the patients were not randomly selected, and their prosthetic rehabilitations were chosen independently from the present investigations. Only well-satisfied patients were asked to undergo the EMG investigation. Therefore, the extrapolation of the present results to a wider population should be done with caution 19-21.

In the present study, EMG analysis was used to detect and record the activity of the muscle fibers, and to obtain additional information for the diagnosis, management of patients who need oral rehabilitation with implants supported prostheses and wearing it for three months as a necessary interval for anyone to show satisfactory chewing ability after the restoration was inserted. It should also be mentioned that the present subjects chewed a standardized bolus that allows focusing on specific parameters22, 23.

EMG has been used to assess the masticatory function of mandibular implant supported and implant retained overdentures. The electrical output of a muscle, measured by electromyography is proportional to the energy consumed to produce contractions. The masseter and temporalis muscles on both sides were evaluated because they are the largest and strongest of the masticatory muscles, the most superficial and are accessible to surface EMG examination18.
The results of this study, showed significant increased EMG activity of the masseter and temporalis muscles during food chewing in subjects with conventional complete dentures (group I) than the same patients with implant-supported systems (group II and group III), the muscle activity in patients wearing one implant supported prostheses does not differ from the other group of patients wearing two implant supported over dentures. This may be explained by complete removable denture wearers have been demonstrated to perform less regular and uniform chewing cycles because of the poor adaptation to food consistency and of the limited stability of the device, thus increasing the number of cycles, amplitude and duration of mastication 24,25. Also, other explanation for these muscular behaviors could be associated with functional adjustments induced by the implant-supported rehabilitation, modulated by the dynamic aging process26.

The presence of numerically lower values for the masseter and temporalis muscles after implant-supported oral rehabilitation seems to be associated to physiological adjustments expected during the aging process, since studies conducted on dentate individuals found reduction in EMG amplitude with age27, 28. This population, however, was not investigated in the present study.

The reduction of muscular activity after implant supported oral rehabilitation observed in this study is different from the findings of other investigations that reported increased masticatory activity after implant placement29, 30. However, Chen, et al.28 investigated edentulous patients and observed lower amplitude results for the masseter muscle in the group treated with implant supported dentures, in agreement with the findings of the present study. Conversely, Haraldson, et al.31, Haraldson and Inger-Vall32 verified that electromyographic activity related to the masticatory muscles and the superior orbicularis oris muscle in adult women wearing implant-supported prostheses was similar to those with natural teeth at the same age range. This contradictory results may be attributed to that, muscle fiber recruitment in individuals rehabilitated via invasive surgical techniques can increase the myoelectric activity to perform the same masticatory patterns of a normal system33.

Further studies are necessary to observe the behavior patterns of the masticatory muscles in individuals submitted to treatment with implant supported prostheses, as well as the time of use, adaptation and stability of the prosthesis. Prosthetic rehabilitation is commonly used in dentistry34; therefore, research on the topic is of paramount importance to achieve the correct muscle behavior pattern for the proposed treatment.

Conclusion
Mandibular implant-supported prostheses in elderly individuals revealed a decrease in EMG amplitude for the masseter and temporalis muscles during swallowing of soft & hard foods, which may indicate adaptation to new conditions of stability provided more support of the complete denture in the mandibular arch.

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