Face Scales and Facial Expression Analysis to Assess Clinical Pain Intensity

Face Scales and Facial Expression Analysis
to Assess Clinical Pain Intensity

Yoriko Matsuoka, Kakuhiro Fukai

Abstract ：Healthcare providers are hard to know patients' pain intensity directly because of subjective
experience of patients themselves. While patients are usually apt to hesitate to express their pain
just as they feel in front of health professionals because of their reserve or fear to diagnose severe
disease. For that, healthcare providers may underestimate patients' pain intensity. This paper
aims to discuss how much grasp and assess patients' clinical pain for healthcare providers, fromthe viewpoint of Face Scales and Facial Expression Analysis. Face Scales are available forpatients themselves to express their pain intensity towards healthcare providers, even if it is noteasy to convey verbally. Facial Expression Analysis is applicable for health professionals in clinicalsituations as to subtle facial expressions, avoiding misinterpretation and overlooking through thetraining of Facial Action Coding System (FACS) developed by Ekman and Friesen (1978). Applying both merits of Face Scales and Facial Expression Analysis would be helpful to understandpatients, pain intensity.
Key words : pain intensity, Face Scales, Facial Expression Analysis, FACS
impaction. Besides them, there is a transient

1. Introduction
Pain, one of the defense reactions of a humanpain after setting of prosthetic appliance.

body, is important to diagnose one's disease andSince pain is a subjective experience known

to prognose one's treatments. Various sorts of

only to patients themselves, it is difficult for

pain in dentistry are such as pulpitis, gingivitis,

healthcare providers to grasp its intensity of

tooth mobilization, hypersensitivity, and foodpatients directly. In many cases, healthcare
providers know it from medical interview. Eachindividual has various range of pain threshold.

【著者連絡先】〒341-0003 埼玉県三郷市彦成3-86
深井歯科医院・深井保健科学研究所
松岡順子
TEL&FAX： 048-957-3315
E-mail ： yorikom@wg8.so-net.ne.jp

Even if health providers judge that theirpatients' pain intensity is not so severe, while
the patient may be intolerable pain1）. Pain intensity is identified as significant predictors forpain medication2）. Moreover, patients usually― 34 ―

ヘルスサイエンス・ヘルスケア

Volume 8，No.1（2008）

tend to hesitate to express themselves just as

While in dental researches, Williams JMG., etthey feel in front of health professionals because

al. (1985) assessed anxiety of children (mean ageof their reserve or fear to diagnose severe dis-11.5 years) before dental treatments with a Pic-ease. For that, healthcare providers tend to mis-ture Analogue Scale, face version of Visual Ana-take to interpret patients' pain intensity. Thatlogue Scale (VAS). It comprises 7 drawings of ais, there are two opposite points from each side:

face graded from distressed to happy32）. If it ispatients should encode their expressions ofdifficult to grade with Visual Analogue Scaleemotional messages as they feel ; and healthwhich is widely used to assess pain, one canprofessionals should decode their patients' mes-

easilysages they have expressed.

Buchanan H., et al. (2002) developed Facial

answersomequestions

with

FS.

This paper will discuss from the viewpoint of

Image Scale (FIS) for young children to assess

Face Scales and Facial Expression Analysis

the state of dental anxiety. It is consisted of 5

how much health professionals grasp and assess

faces ranging from very happy to very unhap-patients' clinical pain.

py, which makes young children easier to recognize and easier to score in a clinical situation17）. FIS was also a suitable measure for2. Face Scales and clinical assessment
for patients' pain

young children as well as their parents and den-Face Scales (FS) are a spectrum of facial

tists18）. It is possible to assess them objectively

expressions assigned to numeric values to rep-even if it is practiced by the infants, their par-resent their rank order within a series from theents, and healthcare providers. The data given

least distressful to the most distressful. Mainly

by both patients and healthcare providers canthey have been separately developed for pedi-beatric patients to assess pain intensity, to show

Buchanan H. (2005) developed a Smiley Faces

such as anxiety, distress, or QOL.

Program (SFP), an interactive computerized

For the applied medical researches after
1980s (Table 1), Face Scales were used withcompared

with

each

other.

Moreover,version of the Facial Image Scale for dental
anxiety19）.

hand-drawn illustrations for those who are

For others, in dental researches regarding

unable to fill out in questionnaires because ofpain intensity the following cases were report-

language difficulties or pain of rheumatoid

ed: temporomandibular disorder pain (1988);

arthritis

3,4）. From 1984, in mainly Pediatrics,

pain and its side effects as a result of orthodon-

Face Scales have been used to assess anxiety

tic therapy with fixed appliances (1999); painl5-28）. Clinical pain intensi-

and discomfort after periodontal scaling andty is a significant problem for the elderly. Herrroot planing (1999)33-35）. From the research ofKA., et al. (1998) evaluated and demonstrated

Ando et al. (2003), modified face scale of Lorish

the validity and reliability of the Faces PainCD., et al. (1986) was used to assess QOL of 70

Scale developed by Bieri et al., using them forand 80-year-old elderly from the viewpoint ofand pain intensity level29）

the elderly aged from 65 and older . Especially,

masticatory function, and it showed its correla-it has been applied to the fields for elderly

tion36）. Then, Face Scales are used widely for

adults who are cognitively impaired or unaccus-

post-operative pain of dental surgery as to29-31）

tomed to answer the questionnaires.

impacted mandibular third molars (2004); initial― 35 ―

Face Scales and Facial Expression Analysis to Assess Clinical Pain Intensity

Table 1

Face scales on medical and dental research papers (1982-2007)― 36 ―

ヘルスサイエンス・ヘルスケア

Volume 8，No.1（2008）

injection pressure for local dental anesthesia

tle facial expressions showing real intention(2005); and to assess patients' mood for the use

appear and disappear immediately in 1/5 of aof denture37-39）. After the middle of 1980s, typesecond or less. Motion of muscles surroundingof Face Scales have been diversified, and relia-

eyes, particularly eyebrows, shows key points

bility and validity of Face Scales have been

to know this subtle feeling 41,46）. The application

examined in view of the number of faces andof FACS is useful to become more sensitive forthe methods of face illustration such as hand-

subtle facial expressions and to avoid missing

drawn pictures, computerized images, or pho-small motion or misinterpreting as signals other8,27）

tographs

than pain44）.

.

In medical researches, Prkachin KM., et al.
3. Applied Facial Expression Analysis

intensely examined to decode patients' pain,

to assess clinical pain intensity

using 4 facial movements associated with pain

Facial Expression Analysis is a study tobased on FACS: brow lowering, tightening ofunderstand the mechanism of expressing one's

the orbital muscles, nose-wrinkling or lip rais-

feeling in facial displays (encoding), and inter-

ing, and eyelid closure44,47）. The 30 min. of train-

preting the meaning of its message (decoding).

ing would be required to learn 4 facial move-

From the first systematic research of facial

ments of FACS. The ratings of untrained

expressions studied by Charles Darwin (1872),

observers significantly underestimate patients'

40)

many researches have been practiced . What is

self-reports by 50-80%44）. The research indicates

important for the system describing facialthat FACS training is more effective to read

expressions objectively is to analyze the specificsubtle facial expressions induced by low levels

facial expression. Facial Action Coding Systemof pain, and more sensitive to variations in facial(FACS) developed by Ekman and Friesen (1978)

expressions which still signal a state of emo-is one of the approaches anatomically based ontions other than pain, in order to avoid misinter-the system for measuring all facial movements

pretation or overlooking.

of a single facial muscle or a group of muscles

Gilbert CA., et al. (1999) developed Child

40-43）. The basic elements ofFacial Coding System (CFCS), combined system

FACS relie on 44 Action Units (AUs). It alsowith the elements both Neonatal Facial Coding

allows for coding of the intensity of each facial

System (NFCS) of Grunau RVE (1987) andaction reliably graded on a 5-point scale for

Facial Action Coding System (FACS) of Ekman

intensity.

and Friesen (1978). It is a system coded for thewhich move as a unit

Researches applying FACS have demonstrat-

13 facial pain actions such as to open lips, toed that useful information of pain can belower brows, etc, to assess post-operative pain

obtained through the observation of facialin infants aged 13-74 months. It is reported that44-45）. Observers can also distinguishwithin an hour after a minor surgery, children

facial expressions of pain from the ones of otheraged 1-6 consistently display the following facial

expressions
emotions

45）. Important message from facial

actionpattern:browlowering,

deepened

expressions tends to be overlooked, since mostnasolabial furrow, cheek raising, open mouthof all, facial expressions with emotion appear inhorizontally and vertically 48）.

very short time, a few seconds. Especially, sub― 37 ―In dentistry, LeResche L., et al. (1992) ana-

Face Scales and Facial Expression Analysis to Assess Clinical Pain Intensity

lyzed chronic pain over of temporomandibular

times; to limit the generalizability of the find-disorder over 6 months continuously, usingings of the studies. They are liable to be

FACS. Facial pain expressions became more

impractical in the clinical practice44,53）. There-

frequent in chronic cases compared with recent

fore, Cohn JF., et al. (1999) developed automatedonset cases

49）. Patients with chronic pain may

method of facial display analysis based on man-tend to face with more daily stress because ofual FACS coding. Average agreement with

anxiety for the period of treatment, distress tomanual FACS coding is 92% or higher for thepain, mastication disorder, trismus, and so on.

actionunits

around

the

brow,

eyes,

and

53）

These factors would be related with encoding

mouthfacial expression of chronic pain. Moreover, Hsu

al. applied to FACS with 4 limited facial actions

K-T., et al. (2007) applied FACS, limited to 6

with clinical and experimental pain: brow lower-

Action Units as to pain, to evaluate orofacialing, tightening of the orbital muscles, nose-wrin-

pain in cognitively impaired older adults aged

kling / lip raising and eyelid closure44,47,54）.

. In clinical settings, Prkachin KM., etover 65. This study suggests that the facial

The elderly people tend to be weak withexpressions which are significantly correlated

encoding of facial expressions. Facial structural

with orofacial pain, is upper-face expressions:change such as wrinkling makes hard to decodebrow lowering, lid tightening, and cheek rais-

facial expressions compared of those of theing 50）.

youth. Various emotions will be appeared on
the face, that is, not alone. Complex emotions

4. Limitations of using Face Scales and Facialsuch as anxiety, surprise, sadness, or anger will

Expression Analysis as a Clinical Research

be mixed on the face and immediately disap-

Face scales beginning withsmiling

pear. Even if it is the same emotion, expression

faces show significantly higher pain intensity

will be different according to their grade andrating than those with

one's experience. Some will hide it with smilingfaces

13,51）

no painno painneutral. Some patients recognize that thethough they really feel severe pain46）.

faces of the Facial Pain Scales represent sadness rather than pain. Therefore, researchers

5. Conclusion

recommend for clinicians to select at least two

To know patients' pain intensity from theirdifferent scales to use in daily practice, forfacial expressions is taken in daily practice as

instance, Faces Pain Scale and Visual Analogue

supplementary elements for patients' verbal

Scale52）.

description. Although Visual Analogue Scale isOn the other hand, though FACS can exactly

widely used to assess clinical pain, Face Scales

assess the change of facial expressions, at least

make especially young children and elderly peo-

100 hours will be required for health care

ple easier to score their delicate pain intensity

providers to master FACS with 44 action units

which is hard to convey verbally. On the other(AUs).

ishand, subtle facial expressions appear and dis-required for analyzing the facial expression byappear immediately. Facial Expression Analysis

slow motion of video recording. These problems

is applicable for health professionals to become

tend to encourage the use of small subjects andmore sensitive for a moment change of facial

behavior samples; to prolong study completion

expressions through FACS training. It would be

Also

enormoustime

consuming― 38 ―

ヘルスサイエンス・ヘルスケア Volume 8，No.1（2008）

effective to notice patients' pain intensity froma moment change of subtle facial expressions
under treatment or in the case of patients' persevering. Facial Expression Analysis has been
applied from infants to elderly people on the
researched reports. Applying both merits ofFace Scales and Facial Expression Analysis
would be helpful to understand patients' pain
intensity.
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