Original article
Influence of removable complete denture adjustment on brain activity
2021 年 21 巻 2 号 p. 17-22
詳細
2021 年 21 巻 2 号 p. 17-22
Purpose: This study used electroencephalogram to examine how eliminating pain through complete denture treatment can affect cerebral function. Materials and Methods: Twenty-four individuals with full maxillary and mandibular dentures (11 males and 13 females; average age, 76) were enrolled. All were diagnosed by two prosthodontists as needing denture treatment. Twelve subjects who had complained of pain from dentures (study group) were compared to 12 without prior pain (control). Occlusal force and electroencephalogram were measured before and after treatment. Changes in brain functional activity were estimated by electroencephalogram, from which Dα was calculated using Diagnosis Method of Neuronal Dysfunction analysis. The Wilcoxon rank-sum test (α = 0.05) was used to compare Dα and occlusal force before and after treatment. Results: A significant increase in occlusal force was noted after treatment in all subjects in the study group (p < 0.01) and 11 in the control group (p < 0.01). Dα increased significantly for all study group subjects after treatment (p < 0.01). Conclusion: It was found that eliminating pain through denture treatment improves brain functional activity. Eliminating pain through denture treatment not only restored mastication but also relieved stress.
Clinical prosthodontics to manage diseases and disorders related to occlusion and mastication involves an integrated approach that encompasses treatment and prevention with edentulous. Thus, prosthodontics is linked directly to health, longevity, and quality of life (QOL). And it contributes to improving the health and wellbeing of the people who are treated. As people become increasingly health-conscious, there has been a growing interest in preventing dementia and immobility. However, not much is known about how the use of dentures and denture treatment may affect these conditions. Informing and enlightening people on the importance of prosthodontics based on scientific evidence constitutes not only an important goal for the field of dental medicine, but also is crucial for prosthodontics to make a greater contribution to society.
According to Onozuka et al. [1], mice with their molars removed exhibit decreased acetylcholine levels in the hippocampal CA1 region, resulting in a low hippocampal pyramidal cell count. This suggests that losing occlusal support can adversely affect brain functional activity. Losing several teeth attenuates trigeminal stimulation that controls periodontal and masticatory sensations, and inhibits higher brain functions, such as learning and memory. Poor denture function (decreased occlusal vertical dimension and altered mandibular position) reduces masticatory muscle function and disrupts the α-γ coupling mechanism, which could cause brain function activity to deteriorate [2]. Therefore, treatment that removes pain caused by dentures not only alleviates psychological stress that is a suspected risk factor for Alzheimer's dementia but also improves denture function and thus heightens the trigeminal sensation, which potentially activates brain function.
On the other hand, Hara et al. [3] noted that, while the electrical potentials registered on the scalp of a healthy individual were distributed evenly, losing neuron function in the cerebellar cortex could distort the scalp potential distribution, as seen in patients with Alzheimer's dementia. Based on this observation, they developed the Diagnosis Method of Neuronal Dysfunction (DIMENSION), an analytical tool that quantitatively estimates synaptic/neuronal dysfunction in the brain based on α waves. Musha, et al. [4] reported that the Dα and Dσ values derived from DIMENSION analysis are useful to distinguish patients with Alzheimer's dementia from healthy individuals. Dα and Dσ values are correlated strongly with cerebral blood flow, as measured by single-photon emission computed tomography (SPECT) as well as with mini mental state examination (MMSE) scores.
Morokuma [5] carried out DIMENSION analysis of electroencephalographic data to obtain Dα values to evaluate brain function activity. This was, in fact, the first such attempt in the field of dentistry. They compared before and after denture treatment in a single group of fully edentulous patients who had undergone occlusal adjustment, mucosal adjustment, relief, and relining.
However, a before-and-after comparison in a single group of individuals who had undergone denture treatment does not provide clues on whether or not the changes observed were due to denture treatment or to other factors (conversation with the attending physician or hospital stay). Although a controlled trial is useful to verify treatment effects, defining appropriate study and control groups can be quite challenging in a clinical environment. Despite such difficulties, the present study recruited two groups of individuals, who were almost identical, except in the presence or absence of pain, to evaluate how denture treatment affects brain function. The present study is the first in the field of dentistry to analyze Dσ.
Patients with removable complete dentures who visited the Department of Removable Prosthodontics, Tsurumi University Dental Hospital were included in the present study. The selection condition of patients is shown Table 1.
Table 1 Selection condition of patients of the study participants
| Category | Condition of patients |
|---|---|
| 1 | Patients who were diagnosed by, and received denture treatment from, one of the two dentists (prosthodontists) clinical experience working at Department of Removable Prosthodontics Tsurumi University School of Dental Medicine. |
| 2 | Patient diagnosed by the attending physician as needing denture treatment. |
| 3 | Patients who received all treatment for dentures in the treatment room of the Prosthodontics Tsurumi University Dental Hospital. |
| 4 | Patients whose treatment consisted only of occlusal adjustment and relief. |
| 5 | Patients whose denture treatment took 30 to 60 min to be fully complete. |
Twenty-four individuals with removable complete dentures (11 males and 13 females aged 63 to 87 years, average age being 76) who met all five of the conditions shown in Table 1 were included in the present study. The controlled trial was carried out by assigning 12 patients with complete dentures, who had visited the hospital with a chief complaint of pain from dentures, to the study group, and a control group of 12 patients who had not complained of any denture discomfort but who were diagnosed by their attending physicians as needing denture treatment. The study group consisted of six males and six females aged 63 to 87 years, average age 75. The control group consisted of five males and seven females aged 69 to 85 years, average age 77. Both groups happened to have the same number of subjects, with similar age and gender distribution, though not by design. Treatment successfully eliminated denture pain in all subjects in the study group. No subject had any history of brain disorder, such as cerebral infarction, nor had they been diagnosed with dementia, such as Alzheimer's. Informed consent was obtained from every subject prior to performing measurements according to a procedure approved by the ethics review committee of Tsurumi University School of Dental Medicine (approval number: 305, accepted on August 31, 2005).
Evaluation of the denture functionThe measuring system for occlusal force with pressure sensitive sheet (Dental Prescale Occluzer FPD-705 and Dental Prescale 50H, no wax, GC, Tokyo, Japan) was used for objective measurement of the occlusal force before and after denture treatment. Measurements were performed as follows: The Frankfurt plane of the patient's head was first aligned so that it was parallel to the floor surface. The operator pulled the patient's lips away from their teeth and had the patient bite down to determine whether the patient could bite with ease. The patient was subsequently asked to bite in central occlusion for 3 s to measure the maximum occlusal force [6].
Evaluation of brain function activityElectroencephalography (EEG) was recorded in patients with complete dentures for 3 min before and after denture treatment. Dα and Dσ were calculated using DIMENSION analysis to evaluate changes in brain functional activity. EEG was recorded by a dentist trained in electroencephalography in a semi-anechoic room located inside the jaw function examination laboratory in the treatment area of the Department of Removable Prosthodontics at Tsurumi University School of Dental Medicine.
EEG measurement was made with ESA-Pro system (Brain Functions Laboratory, Inc., Kawasaki, Japan) and a helmet with pasteless electrodes. The analysis was performed at a sampling frequency of 200 Hz using high-pass filter (HPF, 1.6 Hz, 12 dB/oct), low-pass filter (LPF, 60 Hz, 12 dB/oct), and HUM (50 Hz, 2D) digital filters. Pasteless electrodes were arranged in the helmet according to the international 10-20 system. The 21-channel scalp EEG was performed with the reference electrodes placed on both earlobes. During the measurement, subjects were seated comfortably at rest with their eyes closed. After making sure that activity detected from all electrodes were stable, EEG was recorded for three minutes. The EEG data recorded were transferred to the electroencephalogram analysis center of Brain Functions Laboratory, Inc., where DIMENSION analysis was estimated Dα and Dσ.
Measurement procedure and statistical processingDenture function and brain function activity were evaluated before and after denture treatment (Fig. 1). The Wilcoxon rank-sum test ( α = 0.05) was used to compare the changes in denture function (occlusal force) and brain function activity (Dα and Dσ).
Fig. 1 Flow chart of measurements
Complete denture function and the degree of brain functional activation were measured before and after denture treatment.
Figure 2 shows the average occlusal force in the study and control groups, before and after denture treatment. A significant increase in the maximum occlusal force ( p < 0.05) was observed in the study group after denture treatment, where all 12 subjects exhibited increased maximum occlusal force. Similarly, a significant increase in the maximum occlusal force ( p < 0.05) was observed in the control group after treatment, where 11 subjects exhibited an increase. However, no significant differences in the maximum occlusal force were observed between; i) the study group and the control group before treatment, ii) the study group and the control group after treatment, iii) the study group after treatment and the control group before treatment, and iv) the control group before treatment and the study group after treatment ( p > 0.05).
Comparison of occlusal force before and after denture treatment in the study and control groups
A significant increase in occlusal force was noted after denture treatment in all subjects in the study group and in 11 subjects in the control group (p < 0.05).
Evaluation of brain function activityDα and Dσ in the study and control groups before and after denture treatment are shown in Figs. 3 and 4, respectively. A significant increase in Dα ( p < 0.05) was observed in the study group after denture treatment, in which all 12 subjects exhibited increased Dα. Two patients in the study group had Dα in the normal range (Dα > 0.952) before denture treatment, and the number increased to seven after treatment. On the other hand, no significant increase in Dα ( p > 0.05) was observed in the control group after denture treatment, where eight subjects exhibited increased Dα. In the control group six patients had Dα in the normal range (Dα > 0.952) before denture treatment, and the number remained the same after treatment.
A significant decrease in Dσ ( p < 0.05) was observed in the study group, involving 10 of 12 subjects. Six of 12 subjects in the control group exhibited decreased Dσ, without reaching significance ( p > 0.05).
Fig. 3 Comparison of Dα before and after denture treatment in the study and control groups
A significant increase in Dα was observed in all subjects in the study group after denture treatment ( p < 0.05). In the control group a slight increase in Dα was observed in eight subjects after treatment ( p > 0.05).
Fig. 4 Comparison of Dσ before and after denture treatment in the study and control groups
A significant decrease in Dσ ( p < 0.05) was observed in the study group, involving 10 of 12 subjects with decreased Dσ. Six of 12 subjects exhibited decreased Dσ without significance ( p > 0.05).
The present study was conducted on study and control groups that both were similar in the following respects; i) they were diagnosed and treated by the same dentists, ii) they required denture treatment and were treated in the same place, and iii) they received the same treatment for the same period. In clinical trials, targeting patients visiting medical institutions, and defining appropriate study and control groups that meet the specified conditions can be quite challenging. In the present study, patients who met the specified conditions were recruited by two prosthodontists at Tsurumi University School of Dental Medicine over a period of approximately three years. Subjects were examined to identify whether eliminating pain through denture treatment could activate brain function.
A significant increase in occlusal force was observed in both the study and control groups following denture treatment. Because both groups comprised patients diagnosed by their attending physicians as needing denture treatment, denture treatment is believed to have increased occlusal contact area, as well as enhanced retention and stability of dentures. However, occlusal force increased more in the study group after denture treatment than in the control group ( p > 0.05). This was probably due to the alleviation of pain that had been the chief complaint in the study group.
EEG data were recorded, and brain function activity was evaluated using the DIMENSION analysis. DIMENSION analysis does not involve any exposure to radiation and is less invasive than other techniques, such as SPECT or position emission tomography (PET), which are used to diagnosis several types of dementia, including Alzheimer's. Furthermore, evaluating brain function activity using EEG can detect changes in brain function activity much more efficiently than other physiological measures because EEG captures the action potential of the synapses and neurons of the cerebral cortex that regulates brain activity.
In general, when neuronal activity in the cerebral cortex is uniform, potentials are distributed evenly from high to low in the scalp. However, diseases such as Alzheimer's dementia depress neuronal activity in certain parts of the cerebral cortex, distorting potential distribution in the scalp. In DIMENSION analysis, an ideal potential distribution of α waves, which indicates stable neuronal activity, is defined as Dα = 1 and Dσ = 0. Dα decreases and Dσ increases as brain functional activity deteriorates. Musha et al. [4], defined Dα > 0.952 as the normal range of Dα, which can be used as a reference point to distinguish patients. The present study counted the number of subjects whose Dα and Dσ were in the normal range to evaluate brain functional activity.
A significant increase in Dα ( p < 0.05) was observed in the study group, with the number of patients in the normal range increasing from two to seven following denture treatment. On the other hand, no significant increase in Dα ( p > 0.05) was observed in the control group, with the number of patients in the normal range at six before and after treatment. In addition, while a significant decrease in Dσ was noted in the study group ( p < 0.05), no significant decrease was observed in the control group ( p > 0.05).
Shalat [7], who participated in a joint epidemiological research project sponsored by the World Health Organization (WHO) and the National Institute on Aging (NIA), reported that losing teeth is a risk factor for Alzheimer's dementia. Other risk factors for Alzheimer's dementia include genetic predisposition, environmental factors, head trauma, depression, and psychological stress [8,9,10,11,12,13,14]. Loss of many teeth attenuates trigeminal sensory information and inhibits higher brain functions, such as learning and memory [15,16].
Taste and texture of food are perceived during mastication. Its specific control mechanism is directly innervated by the trigeminal system [2]. The trigeminal nerve, which is the largest of the occlusal nerves, consisting of motor and sensory roots, occupies one third of the primary somatosensory cortex, as depicted by Penfield’s homunculus [17]. Masticatory stimuli travel from the masticatory muscles to the trigeminal nerve and thence to the hypothalamus. The hypothalamus regulates learning, memory, emotion, and sleep, which suggests that improving mastication through denture treatment can have a great impact on brain functional activity. Pain caused by dentures can produce abnormalities not only in information transmitted from the sensory root but also in kinetic information transmitted from the motor root, including disruption of the α-γ coupling mechanism, both of which can undermine brain functional activity. Treatment of patients who complain of pain from dentures and decreased brain functional activity improves denture function in a short time and also restores the appropriate mechanism to carry sensory information to the trigeminal nerve, which is believed to activate brain function.
Brain functional activity can be activated by various stimuli. Via DIMENSION analysis, Wada et al. [18], demonstrated that rehabilitation through clinical art and robot therapy activates brain function not only in patients with Alzheimer's dementia but also in their care assistants with no signs of Alzheimer's. Denture treatment in edentulous patients who showed no signs of Alzheimer's dementia and who complained of pain from dentures was just as effective as clinical art and robot therapy.
The present study demonstrated that, in fully edentulous patients who have many risk factors for dementia, pain from dentures can potentially deteriorate brain functional activity, whereas eliminating pain through denture treatment can enhance brain functional activity. This finding suggests that eliminating pain through denture treatment restores mastication function and is strongly associated with preventing dementia, improved health, and better QOL.
Conflict of Interest
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. There are no conflicts of interest in this paper.
