Case report

A novel vibratory stimulation-based splint for chronic and untreatable

masticatory myofascial pain: A case-series

Emilio Satoshi Hara DDSa,d, Andrea Lusvarghi Witzel DDS, MDS, PhDb,Carlos Eduardo Pitta de Luca DDS, MDSb, Rafael Yague Ballester DDS, PhDc,

Marcelo Costa Bolzan DDS, PhDd,*a Oral Rehabilitation and Regenerative Medicine, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Japan

b Department of Clinical Stomatology, School of Dentistry, University of Sao Paulo, Brazilc Department of Dental Materials, School of Dentistry, University of Sao Paulo, Brazil

d Fundacao para o Desenvolvimento Cientifico e Tecnologico da Odontologia attached to the School of Dentistry, University of Sao Paulo, Brazil

Received 5 October 2011; received in revised form 25 July 2012; accepted 6 August 2012

Available online 3 November 2012

Abstract

Aim: This clinical report aimed to introduce a novel vibratory stimulation-based occlusal splint (VibS) for management of chronic and untreatable

masticatory myofascial pain (MMFP).

Methods: This study was conducted on four chronic MMFP patients (mean age: 27.5 � 5.56 years, females) who were diagnosed according to the

research diagnostic criteria for temporomandibular disorders (RDC/TMD), and who were using stabilization splints for more than 6 months and

still complained of pain above 40 mm in a 100-mm VAS scale. The included subjects utilized the active VibS and subsequently the inactive VibS

during 30 days in each trial, separated by a wash-out period of at least 8 months. VAS pain levels were the only measured dependent variable, and

were recorded before and after the use of active VibS and inactive VibS.

Results: At baseline, mean VAS pain levels before using the active or inactive splint were 54.5 � 19.8 mm and 44.0 � 13.6 mm, respectively.

After using the active VibS, mean pain level decreased by 77% (VASpos-pre = �42.0 � 30.3 mm). On the other hand, after using the inactive VibS,

severe pain aggravation of 67% in magnitude was observed (VASpos-pre = +29.5 � 21.5 mm).

Conclusion: This case-series study demonstrated a good tendency of this novel VibS in chronic MMFP alleviation after a 4-week management

period compared to a control inactive VibS.

# 2012 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.

Keywords: Chronic myofascial pain; Occlusal splint; Vibratory stimulation; Feedback device

www.elsevier.com/locate/jpor

Available online at www.sciencedirect.com

Journal of Prosthodontic Research 57 (2013) 62–66

1. Introduction

Morbidity of chronic masticatory myofascial pain (MMFP)

has been reported to cause significant psychological impair-

ment and decrease in individuals’ perceived quality of life [1,2].

Its etiology has been accepted to be multi-factorial, involving

both peripheral and central sensitization mechanisms [3,4].

Additionally, chronic and untreatable MMFP has been reported

to be aggravated and perpetuated by cognitive and emotional

* Corresponding author at: Avenida Prof. Lineu Prestes, 2227, Cidade

Universitaria, Sao Paulo, Postal Code 05508-000, Brazil.

Tel.: +55 11 5531 1422; fax: +55 11 5531 1619.

E-mail address: marcelo_bolzan@uol.com.br (M.C. Bolzan).

1883-1958/$ – see front matter # 2012 Japan Prosthodontic Society. Published b

http://dx.doi.org/10.1016/j.jpor.2012.08.005

disturbances such as stress, depression, anxiety, and/or

somatization, as well as clenching habit [3,5–8].

Management of chronic MMFP still remains as a great

challenge in clinical practice. Although several studies show

satisfactory efficacy of occlusal stabilization splints in MMFP

alleviation, MMFP may persist in a particular number of

subjects even with continuous use of the splint [2,9]. Better

symptom improvement is sometimes achieved with concomi-

tant prescription of systemic drugs, e.g., tricyclic anti-

depressants, benzodiazepines, muscle relaxants, and anti-

inflammatory drugs. However, patients are reluctant to take

such medicines, or do not tolerate the various adverse side

effects.

Alternative approaches reported in the literature are

biofeedback devices, such as transcutaneous electrical nerve

y Elsevier Ireland. All rights reserved.

Table 1

Pain levels (raw data, 100 mm VAS scale).

Patients Gender Age Active splint Wash-out period Inactive splint

Before After Pain variation (months) Before After Pain variation

1 F 33 46 13 �33 20 63 91 28

2 F 30 84 0 �84 22 31 91 60

3 F 27 47 35 �12 8 39 50 11

4 F 20 41 2 �39 12 43 62 19

Mean 27.5 54.5 12.5 �42 15.5 44 73.5 29.5

SD 4.8 19.8 16.0 30.3 6.6 13.6 20.8 21.5

E.S. Hara et al. / Journal of Prosthodontic Research 57 (2013) 62–66 63

stimulation (TENS) [10,11]. However, there is still lack of

evidence supporting its efficacy [12]. Another option of

biofeedback device could be based on vibratory stimulation.

Previous studies have demonstrated that vibratory stimuli could

reduce experimental pain as well as clinical painful conditions

(e.g., chronic musculoskeletal pain or delayed muscle soreness)

by raising the muscular pain threshold [13–17]. Ludenberg

reported that approximately 70% of the analyzed patients

presented an average in chronic pain reduction of more than

50% during vibratory stimulation [15]. In the orofacial region,

vibration applied superficially in the skin or at a moderate

pressure level has also been reported to significantly decrease

painful temporomandibular joint disorders (TMDs) and chronic

orofacial pain [15,18].

Vibratory stimulation-based devices, however, have been

scarcely explored in the management of chronic MMFP. One

previous case report introduced a full-arch acrylic splint

containing occlusal sensors connected to an extra-oral vibratory

apparatus at the lip region, with a significant decrease in the

number and duration of the sensor activations after 4 weeks,

which implied a reduction in nocturnal muscle hyperactivity

[19]. Despite the promising results, no further studies were

carried out to evaluate its efficacy on masticatory muscle pain

relief or suppression of bruxism events. One reason could be the

lip hypersensitiveness to the intensity of the vibratory stimuli,

which could have disturbed the subject’s sleep quality.

In this study, we introduce a novel vibratory stimulation-

based occlusal splint (VibS), which has the vibratory apparatus

positioned intra-orally, embedded in the occlusal splint. We

report a case series of four patients with chronic MMFP that

presented symptom relief after a four-week treatment with the

VibS compared to inactive/control VibS.

2. Outline of the cases

This case series included four myofascial pain patients (all

females, mean age of 27.5 � 5.56 years), diagnosed according

to the RDC–TMD criteria [20], who were using SS for more

than 6 months and still complained of chronic MMFP above

40 mm in a 100 mm visual analogue scale (VAS), as shown in

Table 1. They presented none of the following conditions: acute

intra-capsular inflammation, secondary pain caused by other

factors such as dental or periodontal diseases, any drug intake

that could alter peripheral or central pain threshold or sleep

quality (e.g., analgesics, anti-depressants, anti-convulsants) up

to 2 months prior to the study’s onset, missing more than four

posterior teeth on one quadrant or edentulous subjects, systemic

diseases such as rheumatoid arthritis and fibromyalgia, or

unwillingness to participate or inability to attend all scheduled

follow-up returns for any reasons.

This study was carried out from August, 2007 to October,

2009 at the Orofacial Pain and Temporomandibular Disorder

Clinic of the Fundacao para o Desenvolvimento Cientifico e

Tecnologico da Odontologia attached to the Faculty of

Dentistry of University of Sao Paulo. Subjects were provided

with the study guidelines and were asked to sign the informed

consent previously approved by the Ethics Committee of the

Faculty of Dentistry of University of Sao Paulo (FR-195462,

185/2007).

The included 4 patients initially utilized the active VibS and

subsequently the inactive (control) VibS during 30 consecutive

days in each trial only at night, e.g., during sleep time (Fig. 1).

The wash-out period between the two trials was at least 8

months.

2.1. Vibratory stimulation-based occlusal splint (VibS)

The present VibS prototype consisted of two layers of

vacuum-pressed silicone (Whiteness1, FGM) completely and

hermetically covering a vibratory apparatus placed in the

buccal shelf region, near the molars and the masseter muscle

insertion (Fig. 2). The vibratory apparatus consisted of two

silver-oxide micro-batteries (1.55 V, 60 mAh, SR927W, Max-

ell) in series supplying a coin-type micro-vibrator (10 mm in

diameter, 3 mm thick, 9000 rpm, Lufa, Hong Kong) which

were connected to a two-metallic-foil-layered pressure sensor

(approximately 1.5 mm thick) positioned on the occlusal

surface of the molars. On the contra-lateral side, a small

silicone strip of the same thickness was placed on the occlusal

area of the molars in order to promote a balanced occlusion

(Fig. 2).

The threshold level that activated the vibrator was

approximately 40N. However, due to small inter-individual

variations in the occlusal forces, slight changes in the threshold

level were necessary in order that high-intensity occlusal forces

could trigger the VibS, whereas light-occlusal forces, such as

tooth tapping during swallow, would not trigger the VibS.

As a control group, the same VibSs were utilized, however,

with the batteries completely discharged by intentional

application of prolonged pressure onto the occlusal sensor.

Fig. 1. Study design. All patients initially used the VibS and thereafter the control splint for 30 days in each trial. VAS values were taken at T0–T3.

Fig. 2. Prototype of the vibratory stimulation-based occlusal splint. (1) Occlusal sensor composed of two metalic-foil layers. (2) Coin-type micro-vibrator. (3) Coin-

type micro-batteries. (4) Silicone strip on the contra-lateral side.

E.S. Hara et al. / Journal of Prosthodontic Research 57 (2013) 62–6664

All VibS were tested and kept immersed in water overnight

before being delivered to the patients in order to confirm that

the two silicone layers were tightly and hermetically closed, so

to avoid any harm to the patients, such as fluids going into or out

from the VibS or any component of the apparatus being

swallowed. Additionally, all patients were informed to

immediately stop the usage of the VibS if they noticed any

change in the splint’s color or functioning.

2.2. Outcome variables

The measured variable was patients’ reported pain levels in a

100 mm visual analogue scale (VAS) administered before and

after the use of each (active or inactive) VibS splint (Fig. 1, at

T0–T3). Patients’ sleep quality, hours of sleep, and comfort

with using the VibS were recorded in the patients’ charts based

on the professional–patient conversations. Patients were

followed up weekly or biweekly.

3. Discussion

In this study, we introduced a new concept of occlusal

splints compared to all previous hard or soft splints, which

were inactive, i.e., they only elevated the occlusal vertical

dimension (OVD) and protected teeth from attrition and

excessive occlusal forces due to clenching and bruxism. This

present VibS prototype, aside from the teeth-protective

attribute, generates a light vibration in response to abnormal

tooth clenching. We observed that pain complaint levels

decreased eventually to less than 15 mm in the VAS scale in

three out of the four patients, after using the active VibS (Table

1). Mean pain level decreased by 77% (VASpos–pre =

–42.0 � 30.3 mm).

On the other hand, when the patients used the inactive VibS,

all of them reported increased pain levels at an average of

29.5 � 21.5 mm (Table 1). Two of them complained of pain

levels above 90 mm and declared it was impossible to continue

using the inactive VibS.

Fig. 3 shows the overall fluctuation of pain levels before and

after using the active or inactive VibS. It is notable that the

active VibS could decrease pain complaint levels, whereas the

inactive VibS increased them. One possible reason for such an

increase in VAS levels could be the fact that soft splints may

increase muscle activity [21] due to their elasticity, which is

hypothesized to return the same applied force to masticatory

muscles.

Regarding the mechanisms involved in the effect of

vibration-induced decrease in MMFP, one hypothesis could

be that vibratory stimuli could evoke jaw opening reflexes, and

thereby, decrease the intensity and/or frequency of masticatory

muscle activity and, eventually, decrease pain levels. This

hypothesis is based on a similar jaw opening reflex observed

when a solid material is unexpectedly found between the upper

and lower teeth during mastication [22]. In this present

investigation, we were unfortunately unable to investigate

whether the light vibratory stimulation could actually have any

evoke potential or produce any alteration in the activity of

masticatory muscles.

Previous studies have also demonstrated that vibratory

stimulus could reduce chronic musculoskeletal pain or delayed

muscle soreness by raising the muscular pain threshold [13–

16], with higher efficacy than TENS and aspirin administration

[15,23]. Several researchers reported that vibration is particu-

larly capable of exciting afferents from both Pacinian

Corpuscles and large-diameter afferents from low-threshold

rapidly adapting receptors of the skin, periodontium, muscle

spindles and tendon organs [14,16]. Also, according to the Gate

Control Theory [24], such large diameter sensory fibers can

interact with impulse transmission in pain pathways at the

spinal level, thereby modulating painful sensation [14,16,25].

Fig. 3. Pain levels (mean) before and after using the active and inactive VibS.

Notable decrease in VAS scores after utilization of the VibS.

E.S. Hara et al. / Journal of Prosthodontic Research 57 (2013) 62–66 65

In this study, application of vibration stimulus was

extremely short-termed (only for a few seconds per night)

and was not directly forced onto specific sites of muscles or

teeth as described in previous literature [14–16,23,26]. The

micro-vibrator was placed in the buccal shelf of the molar

region in order to allow a soft stimulation of periodontal

ligament mechanoreceptors and muscle spindles. Therefore,

the mechanisms of pain alleviation may involve not only the

abovementioned low-threshold receptors, but also other

receptors in mucosa, periodontal ligaments, or the tempor-

omandibular joint.

The effect of light vibration in decreasing MMFP complaint

could also be because of patient’s better sleep quality. Three

patients reported better sleep quality with using the active VibS

due to an absence of pain-related awakenings during the night,

which had been very frequent before the trial even with the use

of the SS. On the other hand, one subject reported difficulty in

falling asleep during the first night using the active splint.

However, this complaint did not repeat in the following nights.

Therefore, we assumed that some patients may need a one-night

conditioning to adapt to vibratory stimuli, and that vibration

could reduce nocturnal masticatory muscle activity and pain-

related awakenings, and consequently the patient could have a

better sleep.

This case series presented several weak points. First, despite

the good tendency of the obtained results, it is difficult to draw

conclusive findings concerning the actual effectiveness of the

VibS in reducing MMFP due to the small number of gathered

subjects. Second, pain variation was assessed by VAS alone,

without other objective parameters such as muscle tenderness

or pain to palpation. Third, the patient’s sleep quality, hours of

sleep, and comfort with using the VibS were only recorded on

the patient’s chart based on the professional–patient conversa-

tions, rather than self-administered VAS-questionnaire assess-

ments. Fourth, all patients used the active VibS in the first trial

and then the inactive VibS, due to lack of an on/off switch to

control vibration activity. In order to preserve the splint’s shape

(height, thickness, comfort, etc.), we intentionally delivered the

active VibS in the first trial to all patients. Subsequently, the

batteries were completely discharged in order to obtain the

inactive splint for the second trial. Fifth, the threshold level to

activate the vibratory apparatus was not systematically

controlled. This present VibS prototype was mainly developed

to test the concept of an intra-orally delivered vibratory

stimulation in the alleviation of MMFP complaint. Research is

ongoing to develop a more sophisticated and personalized

system that enables adjustment of the intensity of the vibratory

stimuli to each patient.

4. Conclusion

In this case series, we introduced a novel VibS as a low-cost,

simple and safe device with a good tendency for management of

chronic MMFP. Future studies should evaluate the efficacy of

the VibS in a larger subject sample as well as in different

population samples, such as fibromyalgia patients. Addition-

ally, a more structured protocol should be applied to avoid bias

due to sample non-randomization, as well as to assess changes

in masticatory muscle activity.

Conflict of interest

The authors declare no conflict of interest.

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