Original research

Varied sensory-motor adaptation to new dentures among full denture wearers and non wearers

Alberto Enrique Nuño Licona,*^,§ Mónica Núñez,* Fernando Ángeles Medina,* Araceli Galicia Arias,* Nicolás Pacheco Guerrero*

* Physiology Laboratory, Research Division, Graduate School, National School of Dentistry, National University of Mexico (UNAM).

^§ National Rehabilitation Institute (Instituto Nacional de Rehabilitacion), Research Division, Physiology Laboratory.

Correspondence

ABSTRACT

Teeth loss elicits significant changes in the sensory-motor activity of patients thus afflicted. These changes can in turn be affected upon placement of a full denture (FD). Overall changes can alter mastication processes, to the point of affecting the patient's general state of health, as would be the case when impinging on proper feeding. This shows the importance of studying masticatory muscles response to the placement of a full denture. It is as well opportune to compare patients who have previously worn dentures with new denture wearers, since it must be borne in mind they could present different functional states. To this end, electromyographic records (EMR) were conducted in masseter muscles of 29 patients before (1^st session) at 8 and 30 days (2^nd and 3^rd session) of FD placement. Two groups were tailored: Group 1 (G1) (n = 15, 12 ♀, 5 ♂, average age 67.2 years) those who had previously worn a full denture, and group 2 (G2), (n =12, 8 ♀, 4 ♂, average age 66.5 years) comprising individuals who had never before worn a full denture. Results indicated there was functional difference among muscles of patients having previously worn FD when compared to muscles of patients who had never worn a FD. Lesser EMG amplitude was found in G1 when compared to G2 in the first session as well as lesser ability to generate masticatory cycles. In the long run, this could also bear upon masticatory ability decrease and patients quality of life. It is necessary to continue this type of studies to substantiate recorded results of the present study, as well as to implement measures geared at contributing to improved FD adaptation.

Key words: Full denture, masseter electromyography, sensory motor integration.

INTRODUCTION

Edentulous patients experiment important changes which affect sensory-motor activity of the stomatognathic system.¹ Loss of posterior teeth can by itself elicit unbalance of muscle activity patterns. Prolonged use of full dentures (FD), sometimes for many years, has been associated to a marked activity of masseter muscles. This in turn can be related to muscle efforts generated by the progressive decrease of denture retention.² In some cases, adaptation of a new FD can be difficult both in new wearers as in patients having already worn dentures. This could be due to a different muscle response and is seldom taken into account in clinical practice. With respect to muscle activity, 30 days after initiating use of a FD, an increase in electromyographic (EMG) interference pattern (IP) recording amplitude has been reported.³ Nevertheless there are also reports⁴ pointing out that FD wearers present a lesser amplitude of integrated EMG activity than that recorded in subjects with natural dentition.

It is possible that different reports of recorded EMG response could be due to the fact of disregarding whether patients had previously worn full dentures or not. With respect to this latter point, it has been demonstrated there is presence of biochemical changes in rats masseter muscles, induced, at initial stages, by occlusal alterations created experimentally.⁵ On the other hand, it has been suggested^6,7 that inherent instability in full denture wearers when combined with parafunctional habits, can precipitate a vicious circle which alters function, and elicits muscle pain as well as alterations in other tissues.

All the aforementioned factors affecting motor and sensory activity of the stomatognatic system could as well bear influence in the response to placement of a full denture. For these reasons, the aim of the present study was to study, with the help of electromyographic (EMG) records, the recording of the Interference Pattern (IP) as well as the recording of its integration (I), and the activity of masseter muscles in edentulous patients, before and up to three months after placing a FD. The present study also aimed at achieving a comparison between two different groups of subjects: those who had previously used a FD and those who were first time users, so as to elicit whether there could be a different functional state.

MATERIALS AND METHODS

EMG records of masseter muscles IP and I activity in 29 patients who attended the Prosthetic Service of the Graduate School, National School of Dentistry, National University of Mexico (UNAM) requesting placement of a FD. EMG recordings were performed before placing a FD (1^st session), and at 8 and 30 days (2^nd and 3^rd sessions). Patients were divided into two groups: Group 1 (G1) (n = 15, 12♀5♂, average age 67.2 years) patients were previous users of a FD, and group 2 (G2) (n = 12; 8♀, 4♂, average age 66.5 years) corresponding to patients never having previously worn a full denture.

Recording was bi-polar. To this effect 5 mm diameter surface electrodes were used (Grass E5G) and placed upon the skin covering muscle belly at approximately 1 cm in front of the ear and 1 cm above the lower angle of mandibular ramus. Electrodes were connected to the pre-amplifiers terminals (Grass 7P3B) connected to the amplifiers (Grass 7DAG) of channels 1 and 3 for IP activity and to channels 2 and 4 for I activity in a 4 channel Grass polygraph (model RPS7C8B). Recorded activity was the following: 30 second maximum voluntary contraction, and later (two minutes later) chewing a sweet (standard colloid sweet) until its deglutition (60 seconds later).

FD were manufactured at one-week intervals. All of them were made following the same technique and using the same materials.

In order to analyze EMG recording amplitude as well as number of masticatory cycles, average values were obtained from each one of the recording sessions. In-Stat 3 statistical program was used to analyze differences in their variables.

RESULTS

Table I shows values of EMG recording amplitudes in microvolts (µv), in interference patterns as well as in integrated recordings obtained from masseter muscles in G1 patients before initiating design and placement of a FD. The recordings were also obtained when using the old prosthesis and when not using it. No statistical significant differences were found between these two situations. Tables II and III show EMG values obtained in respectively 2^nd and 3^rd recording sessions, for G1 when wearing the new FD.

When performing statistical analysis, it was observed there was a significant decrease in integrated EMG for G 1 of average values of 2^nd session when compared to 1^st. Statistical significant boundary was found to appear between 3^rd session when compared to 1^st (Figure 1).

Tables IV, V and VI present EMG recording values in IP as well as those obtained from the respective recording sessions in G2 patients. In the G2 group, no statistically significant differences were established when comparing average values in all recording sessions.

When comparing EMG recording values obtained in all sessions among study groups it was found that values obtained in the first PI recording session were significantly lower in G1 as compared to G2 (Figure 2).

The third recording session revealed the fact that I values obtained for G1 were also significantly lower than those of G2 (Figure 3).

Figure 4 shows average values obtained when recording masticatory cycles present in a 10 second span during the process of chewing a gummy candy, performed by all patients in all recording sessions. A, C and E bars correspond to G1 1^st, 2^nd and 3^rd sessions, respectively. B, D and F bars correspond to 1^st, 2^nd and 3^rd sessions of Group 2. In the first recording session, a statistically significant difference was found between both groups (p < 0.01 Tukey-Kramer test); G2 exhibited the greater number of cycles. A significant decrease in cycle numbers was observed in the second session (p < 0.01). The 3^rd session showed recovery. Figure 5 shows integrated EMG scope average values in these masticatory cycles for each session. Masticatory cycle numbers exhibited similar behavior.

DISCUSSION

Results show there is a functional difference in muscles of patients having previously worn FD with respect to muscles of non wearers. Lesser IP amplitude recorded in G1 first session when compared to G2 indicates lesser motor unit activity in masseter muscles of G1 patients. This could elicit lesser ability to generate masticatory cycles in this group. The response in following sessions was to decrease IP amplitude even more. This was found to be in agreement with other reports.⁴ G2 did not show differences in this respect. This would indicate there were no changes with respect to motor units in this group. There are reports indicating an increase in IP of masticatory muscles in patients who wear a FD for the first time.^3,8 Nevertheless, none of the papers mention whether patients had previously worn FD.

Besides significant differences found among groups, IP recording for the first session, as well as I activity in the third session were lesser for G1, which tends to indicate lesser electrical activity in this group. This would imply the fact that prolonged use of devices in the oral cavity elicits changes in muscular activity. This would then be the cause of the difference found in this study between G1 and G2 from the first recording session. We could therefore suggest that ability to generate muscle electrical activity is decreased in former FD wearers. This could even bear repercussion in the lesser number of masticatory cycles generated within a masticatory period, decreasing thus their effectiveness.

It has been demonstrated⁹ that FD wearers experience chewing problems which significantly impair their quality of life. This is especially true in senior citizens. It therefore would be advisable to conduct this type of EMG studies in a larger number of patients wearing dentures for the first time. These studies could also be routinely conducted to verify results presented in this paper and also, if pertinent, implement measures to help FD better adaptation. This could be the application of an exercise regime which could improve patients' functional muscle condition.

CONCLUSIONS

Loss of teeth entails changes in the EMG activity of masseter muscles. Use of a FD seems to elicit, in the long run, decrease of electrical activity in the aforementioned muscles. This has been related to the presence of smaller motor units as well as the decrease in number of masticatory cycles per time unit. The aforementioned facts could also influence, in the long run, the decrease in patients' masticatory capacity and quality of life.

Routine EMG studies of masticatory muscles will give rise to an objective assessment of these events and the possible preventive and therapeutic measures which could be adopted.

REFERENCES

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Mailing address:
Alberto Enrique Nuño Licona
Laboratorio de Fisiología, División de Investigación,
Unidad de Estudios de Postgrado,
Facultad de Odontología,
Ciudad Universitaria (UNAM),
México, D.F.
Tel: 00 52 55 56 22 5561
E-mail: an.el.20@gmail.com