Prefrontal hemodynamic activity evoked by occlusal discomfort
近赤外分光法による噛みあわせ違和感の検出
Yumie Ono1, Goh Kobayashi2, Yu Ishikawa1, Kohei Sakurai1, Motohiro Munakata2 , Tomoaki Shibuya2 ,Atsushi Shimada2, Hideo Miyachi3, Hiroyuki Wake2, Katsushi Tamaki2
1 Graduate School of Science and Engineering, Meiji University
2 Dept. of Prosthodontic dentistry for function of TMJ and Occlusion, Kanagawa Dental University
3 Dept. of Special Denture and Occlusion & Liaison, Kanagawa Dental University Hospital, 4 Dept. of Psychiatry, Kitasato University School of Medicine

Aim of study

Exp. 1: Occlusal discomfort induces prefrontal activity• We used functional near-infrared spectroscopy (fNIRS) tomeasure prefrontal brain activity accompanying the physicalsensation of oral discomfort.

• The HbO responses of selected channels in the frontopolar and dorsolateralprefrontal cortices increased in participants who reported increased severity ofocclusal discomfort during grinding metal strips, while they decreased in those
who reported no change or decreased occlusal discomfort (Fig. 4a).

• We investigated prefrontal activity in the simulated occlusal
discomfort in healthy volunteers and in the dental outpatients withocclusal discomfort syndrome (ODS: 咬合違和感症候群[1]), who
has vague complaints in the intraoral area such as occlusal
discomfort without any identifiable organic cause.

• Most of the prefrontal channels showed significant correlation between AUC
and subjective severity of occlusal discomfort (Fig. 4cd). GLM analysis of∆HbO signals demonstrated that participants who reported severe or moderate
discomfort showed common neural activity in Brodmann area 9/10 (Fig. 4e:n=13, p<0.05, uncorrected).

Experiment 1: healthy volunteer study [2]
(a)

(d)

(c)

AUC

Ch17Participants: 25 young adults with normal stomatognathic function(14 males, 11 females, 28.9±1.6 years)∆VAS

Simulated occlusal discomfort:• Grinding the teeth with tasteless and odorless
metal strip (96 𝜇m) at their first molar of thehabitual chewing side (Fig. 1).

fNIRS data acquisition:• A block design with alternating 30s of grinding
and 40s of rest for 5 times.
• A 22-channel fNIRS probes were positioned
over the prefrontal cortices (Fig. 2).
• Participants performed the grinding task withand without metal strips. To cancel out themotion artifact, the differential Oxy/deoxy
hemoglobin responses (∆HbO/∆HHb) wereused for the further analysis.

p<0.01(e)Figure 1. Simulation ofocclusal discomfort using
active grinding paradigm

(b)

∆HbO

∆HHb
Severe (∆VAS>20; n=3)
Moderate (20>∆VAS>8; n=10)
Mild to none or improved comfort (∆VAS<8; n=12)

Figure 2. a whole-headtype fNIRS measurement(Hitachi Med. ETG-7100)∆HbO/∆HHb= HbO/HHb (grinding w/ strips) – HbO/HHb (grinding w/o strips)

Subjective evaluation of perceived occlusal discomfort:• All participants evaluated the subjective severity of discomfort using
a visual analog scale (VAS). The VAS varied from 0 (a state with nodiscomfort at all) to 100 (a state of intolerable discomfort).
Correlation between fNIRS signals and discomfort strength:• Correlation between the cumulative ∆HbO signals (area under thecurve (AUC) during grinding period) and the ∆VAS (difference ofVAS: between with and without strips) was calculated to determine
the prefrontal area that responds to the change in the perceived
strength of occlusal discomfort.
Regional brain activity related to occlusal discomfort:• Regional brain activities corresponding to the ∆HbO signals wereidentified using statistical parametric mapping (NIRS-SPM[3]) with ageneralized linear model (GLM).

Figure 4. Comparison of the time-course of mean hemodynamic responses in participants withdifferent severities of perceived discomfort (a, b) and results of channel-based correlation analysis
between ∆HbO AUC responses and reported severities of perceived discomfort (∆VAS: c,d) andGLM analysis (e). Only ∆HbO responses were shown in (a) for better visibility.

Exp. 2: ODS patients show unique HHb pattern• ODS patients showed task-dependent increase of HHb signals, which wasquite different from those of control patients without ODS (Fig. 5ab).
• This is due to neither motion artifact nor skin blood flow response, because
fNIRS signals recorded with small inter-probe interval did not show such timecourses (Fig. 5cd). All four prefrontal channels showed similar tendency.
(a)

(b)

(c)

(d)

Experiment 2: ODS patients study
Participants: 6 ODS patients (1 male, 5 females,
49.5±7.5 years) and 8 age- and sexmatched dental patients without ODS

p<0.05Figure 5.
Comparison ofgrinding-related fNIRS
signals in dental
patients with (a,c) andwithout ODS (b,d).
Despite the typicalactivation pattern foundin control patients, ODS
patients shows uniquepattern of HHb increase.
Skin blood flow wascomparable between
groups (c,d).

time (s) →fNIRS probes

fNIRS data acquisition:
Astem Hb13
• A block design with 10s of holding the metal strip in
the mouth,15s of gentle grinding, and 30s of rest.
• A 4-channel wireless fNIRS probes were positioned
over the prefrontal cortices (Fig. 3). Skin andFigure 3.
cortical blood flow were simultaneously recorded
Wireless fNIRS
with optical probes with two different inter-probe
measurement in aclinical settingintervals (4mm and 30mm).
(ASTEM Hb13)• The thickness of metal strips was gradually
increased from 0𝜇m to the threshold thickness in which participants
perceived occlusal discomfort (12-72𝜇m, no statistical difference inthe threshold thickness between patient groups).

Discussion and Summary• Prefrontal hemodynamic responses could be a possible marker to detect thesubjective sense of occlusal discomfort in healthy volunteers.
• ODS patients showed specific HHb increase after they put metal strip into
their mouth, even before they perform grinding (duration of “Hold” in Fig. 5b),which may reflect the excessive attention to the intraoral sensation. Studywith larger number of ODS patients are necessary.

References
1. 玉置勝司ら，咬合違和感症候群，日補綴会誌，5: 369-386, 2013.
2. Y. Ono et al., Prefrontal Hemodynamic Changes Associated with Subjective Sense of
Occlusal Discomfort, BioMed Research International, Article ID 395705, 2014.
3. J.C. Ye et al., “NIRS-SPM: statistical parametric mapping for near-infrared spectroscopy,”
NeuroImage, 44(2): 428–447, 2009.

Contact: Yumie Ono (yumie@meiiji.ac.jp)