Plan a lesson on the theme of infectious diseases and human rights.
[7-5] Propose a new lifestyle for a new era of people living with the novel coronavirus in Cambodia.

Chapter 8

Eye and dental health
Learning objectives
You will be able to gain proper understanding and explain:- How we can see an object and why refractive errors occur, and explain how we can prevent eye
diseases.

References- The function of a tooth, the causes of dental caries, gingivitis, and periodontal disease, and explain
how we can prevent them.

1Center Hospital of the National Center for Global Health and Medicine, Antimicrobial Resistance Clinical Reference Center. Basics

2

Tokyo Food Hygiene Association. A guide to prevention of food poisoning as a threat to your family health. 2019. https://www.

This chapter explains the mechanisms of the eyes and the teeth, diseases related to them, and prevention

fukushihoken.metro.tokyo.lg.jp/shokuhin///pamphlet2/files/r1july_guide.pdf

of those diseases. Eyes and teeth, which are organs familiar to children in that they can easily observeof infectious diseases: What is an infectious disease? http://amr.ncgm.go.jp/general/1-1-1.html

3

Kitasato H, et al. Viruses and bacteria: Illustrated. Tokyo: Gijutsu Hyoronsha, 2020.

4

Hatanaka M and Shimada J, Ed. Microbiology. Tokyo: Bunkodo, 2004.

5

Yamazaki S, et al, Ed. Companion guide to infectious disease prevention. Tokyo: Japan Public Health Association, 2001.

make them realize the outcomes of health learning easily. Therefore, eye and dental health is one of the

6

World Health Organization. Vector-borne diseases. https://www.who.int/en/news-room/fact-sheets/detail/vector-borne-diseases

teaching and learning materials of school health familiar to all members of a class.

7

World Health Organization. Water sanitation hygiene. https://www.who.int/water_sanitation_health/diseases-risks/diseases/

them, provide them with opportunities to experience, for example, preventive measures in practice anddiarrhoea/en/
8

Byoki ga mieru: Vol. 6, Immunology, Collagen Diseases and Infectious Diseases (2nd ed). Medic Media, 2018.

9

WHO Western Pacific region. Update on the Dengue situation in the Western Pacific Region. Dengue Situation Update Number 610.
2020. https://www.who.int/docs/default-source/wpro---documents/emergency/surveillance/dengue/dengue-20201105.pdf?sfvrsn=
fc80101d_42

10 World Health Organization. Global Tuberculosis Report 2019: Executive Summary. https://www.who.int/tb/publications/global_
report/tb19_Exec_Sum_12Nov2019.pdf?ua=1
11 World Health Organization. Global Tuberculosis Report 2019: Annex2 Country Profile For 30High TB Burden Countries. https://www.who.int/tb/publications/global_report/tb19_Report_country_profiles_15October2019.pdf?ua=1
12 World Health Organization. Global Tuberculosis Report 2019: Annex 3 Regional and Global Profile. https://www.who.int/tb/
publications/global_report/tb19_Report_regional_global_15October2019.pdf?ua=1
13 World Health Organization. Tuberculosis: What is DOTS (Directly Observed Treatment, Short Course). http://origin.searo.who.int/
tb/topics/what_dots/en/
14 Cambodia Demographic and Health Survey 2014, 14. Child Health-Immunization of Children, P.152. National Institute of Statistics(Cambodia), Directorate General for Health (Cambodia) and The DHS Program (USA), 2015. https://dhsprogram.com/pubs/pdf/
FR312/FR312.pdf
15 World Health Organization. Foodborne trematode infection. 2020. https://www.who.int/news-room/fact-sheets/detail/foodbornetrematode-infections
16 World Health Organization. Emerging Infections Diseases. World Health Day 97.1. https://www.who.int/docstore/world-health-day/en/documents1997/whd01.pdf
17 Doshi P. The elusive definition of pandemic influenza. Bulletin of the World Health Organization 2011;89:532-538. doi: 10.2471/
BLT.11.086173. https://www.who.int/bulletin/volumes/89/7/11-086173/en/
18 WHO declares influenza A(H1N1) pandemic. https://www.youtube.com/watch?v=10Nfk0zcTAk
19 Coronavirus outbreak: WHO declares COVID-19 a global pandemic. https://www.youtube.com/watch?v=xKPWngYf2Wk

1. Eye health1) Importance of eye health
Eye and dental diseases signiﬁcantly affect our health not only during school age but also in adulthood.
Loss of sight in particular is a serious issue. Cambodia implemented the national strategic plan to prevent
loss of sight (2008–2015) with a focus on the National Program for Eye Health, and achieved the goalof making the rate of blindness 0.5% or lower.1 Nevertheless, an estimated 28,800 people still sufferfrom loss of sight or visual impairment. The leading cause of loss of sight and visual impairment iscataracts (approx. 19,000 people), but they can also be caused by leaving refractive errors that occur
during school age untreated. It is said that 80–90% of these causes are preventable or treatable.2
Meanwhile, about 20% of children have missed a class due to a toothache over the last 12 months,
indicating that dental health is an issue that should be given priority for school-age children.3 The school
age is a period in which milk teeth (deciduous teeth) are replaced by permanent teeth, and leaving dental
caries or periodontal disease untreated during this period can invite exacerbation later and result in lossof teeth in adulthood.
Therefore, it is very important to learn eye and dental health in school health classes during schoolage.

20 IFRC, UNICEF, WHO. Social Stigma associated with COVID-19: A guide to preventing and addressing social stigma. https://www.
who.int/docs/default-source/coronaviruse/covid19-stigma-guide.pdf
21 American Psychological Association. Combating bias and stigma related to COVID-19: How to stop the xenophobia that’s spreadingalong with the coronavirus. https://www.apa.org/topics/covid-19-bias

130

Chapter 8

Eye and dental health1312) How we can see an object

dermatitis, cases caused by a traumatic injury like perforation or the contusion of the eyeball, and casesof congenital cataracts. There are drug therapies and surgical treatments. Drug therapy can slow theThe ophthalmus is an intricate organ that allows us to clearly see things in the outside world and is often

progression of the disease but cannot remove the crystalline lens opacity. Recovery of sight requires

compared to a camera. The cornea and crystalline lens, which correspond to camera lenses, pass andsurgery in which the opaque crystalline lens is removed and replaced with an artificial lens.

refract light. The retina corresponds to camera film. An object in the outside world can be clearly seen
when the image refracted by the cornea and crystalline lens is focused on the retina surface (Figure 8.1).

(2) Glaucoma

The ciliary muscle surrounding the crystalline lens focuses an image on the retina by becoming tense or

Glaucoma is a disease in which increased intraocular pressure and the fragility of the optic nerve impair

loose according to the distance to the object that is seen. Whether an image can be focused on the retina

the optic nerve, resulting in visual impairment. Intraocular pressure is the pressure inside the eyeballsurface depends on the refractive power of the lens and the distance from the front surface of the lensand has the role of maintaining the shape of the eyeball. Symptoms of glaucoma are reduced vision andto the retina (the axial length of the eye).

visual field defects, but often, no symptoms are developed in the early stage. If the state of increased
intraocular pressure continues, it impairs the optic nerve and results in loss of sight. Although glaucoma
is mostly primary (cases in which there is no original disease or the cause is unknown), there are also

Column: Eye and ophthalmus

cases that occur secondary to other diseases. There are drug therapies and surgical treatments, one ofwhich is selected depending on the pathological condition (state of the disease).

The eye covers a region that is larger than the region of the ophthalmus. The eye refers to the entire
eye as a part of the face, including the eyelid, the inner corner of the eye, the outer corner of the eye,(3) Diabetic retinopathy

and the eyeball. Meanwhile, the ophthalmus, which is a term in medicine and physiology, refers to
the eyeball.

Diabetic retinopathy is a disease in which persistent hyperglycemia weakens vessel walls in the eye,causing angiopathic lesions of the retina. It is one of the three major complications of diabetes andoccurs several to ten-odd years after the person is affected by diabetes. There are often no symptoms in
the early stage, and retinopathy has already significantly advanced by the time symptoms are noticed.
Symptoms are misty vision (the whole vision is blurred), myodesopsia (a symptom in which a small

Retina (film)

flying object like an insect appears in the vision), reduced vision, and visual field defect, which eventually

Optic nerve

result in loss of sight. Depending on the symptom, surgery to coagulate retinal tissue using a laser, or
surgery on the vitreous body is performed. It is important to control blood glucose along with theCornea(first lens)Crystalline lens(second lens)Ciliary bodytreatment of diabetes.

Optic nerve head(4) Trachoma

These two are used to focus

Trachoma is conjunctivitis caused by repeated infection with Chlamydia trachomatis. In severe cases,
a lot of conjunctival vessels enter the cornea and make it opaque, resulting in loss of sight. It is common

Figure 8.1 How we can see an object (Structure of the eyeball)in preschool children. To treat the disease, new quinolone antibiotic eye drops or eye ointment are used,or a tetracycline or macrolide antibiotic is taken orally. Not sharing towels and bedding, as well as3) Eye diseases that can cause visual impairment

washing hands and faces frequently can help prevent home infection.
The real situation and magnitude of trachoma is still unknown. However, it is assumed that in

As diseases that can cause reduced vision or loss of sight, which are common in Cambodia, we can cite

Cambodia trachoma still remains a major public health problem, though no nationwide surveys have1

cataracts, glaucoma, diabetic retinopathy, trachoma, vitamin A deficiency, and refractive error.

ever been carried out. Cambodia is a member of the WHO Global Alliance for Elimination of Trachoma.

Described below are the outlines of these diseases.4

A rapid assessment of trachoma and its risk factors is planned in 3 provinces with objectives to determine(1) Cataracts
Cataract is a disease in which the crystalline lens becomes opaque. The opaque crystalline lens impairs

the occurrence of blinding trachoma, measure its magnitude, and the severity of the problem.2(5) Vitamin A deficiency

light transmission, resulting in visual impairment and eventually loss of sight. The leading cause of

Vitamin A is a nutrient that is related to the reception of photic stimulation as well as the differentiation

cataract is aging, but there are also cases associated with systemic disease such as diabetes and atopic

and functional maintenance of epithelial cells (see Chapter 5). Deficiency in vitamin A can cause night132

Chapter 8

Eye and dental health133blindness or make the conjunctiva and the cornea dry enough to cause visual impairment. Nightin Japan (Tokyo).6 The high prevalence of myopia in school children is a major issue of school healthblindness is a disease characterized by a significant reduction of vision in the dark, caused by impaired

and public hygiene in Asian countries.

rod cells that usually function in the dark (see Chapter 2). When the conjunctiva is dried, moving the

The causes of myopia are thought to be related to genetic factors and the environment. It has

eyeball may make wrinkles in the conjunctiva, or show dull, dirty white spots (Bitot spots) in the

been reported that seeing objects at a short distance for long hours during the growth period canpalpebral conjunctiva. If the symptoms progress further to dry the cornea, an ulcer is formed, and in

affect the prolongation of the axial length of the eye, indicating that the use of mobile games andsevere cases, a hole in the cornea may have been developed resulting in loss of sight. To treat the disease,

SNS could progress myopia; therefore, attention needs to be paid to lifestyles. Meanwhile, there isvitamin A is administered. Intake of a proper amount of vitamin A is also effective in prevention.

another survey of Chinese elementary school and junior high school children that reported that tasks(6) Refractive errors (hyperopia, myopia, and astigmatism)

performed at a short sight distance had no influence on myopia while a longer time of participationin outdoor activities was associated with a lower incidence of myopia in elementary school children.5

Uncorrected refractive error is major cause of visual impairment. An estimate of prevalence of visual

Moreover, it has been confirmed that increasing the time for outdoor activities at schools reduced

impairment due to refractive errors accounts for 52.8%. In children refractive errors affected

myopia. Increasing the time for outdoor activities is not only good for eye health but also expected1

to be effective in preventing lifestyle diseases including obesity, and therefore, it is a good effort in2

about 70% of refractive errors in children were myopia, indicating the importance of early detection

school health.7 However, in Southeast Asian countries including Cambodia, where sunlight is strong

and prevention of exacerbation of refractive errors, particularly myopia, during school age.

and temperatures are high, it is difficult to increase the time for outdoor activities and someapproximately 10% in urban areas and 1.5% in rural areas. Meanwhile, there is also a report stating that

Normal refraction refers to the condition of the ophthalmus in which parallel rays are correctly

consideration is needed.

focused on the retina when an object is seen in the non-accommodative state (state in which nothing isbeing done). The condition in which they are not correctly focused is called refractive error. There arethree types of refractive errors: hyperopia, myopia, and astigmatism (Figure 8.2).

a. Hyperopia

c. Astigmatism
Astigmatism is a condition in which parallel rays are not focused at a single point on the retina. This iscaused primarily by an unequal curvature, instead of a spherical surface, of the cornea. In astigmatism,

Hyperopia refers to the condition of the ophthalmus in which parallel rays are focused posterior to thehow objects are seen is different from, and more complicated than that in myopia and hyperopia. Objects

retina in the non-accommodative state, thus producing an unfocused, unclear image on the retina. The

look blurred regardless of the distance.

causes of this include a short axial length of the eye and weak refractive power of the cornea or the
crystalline lens. In hyperopia, it is difficult to clearly see both far and near objects, and particularly near
objects. Consultation with a specialist is required depending on the severity, but leaving it untreated maylead to reduced vision or cause amblyopia or esotropia.

Emmetropia

Focused on the retina

Myopia

Focused anterior to the retina

Hyperopia

Focused posterior to the retina

Astigmatism

Non focused on a single point(shifts up and down, and to
the left and right)

b. Myopia
Myopia refers to the condition of the ophthalmus in which parallel rays are focused anterior to the retina
in the non-accommodative state, thus producing an unfocused, unclear image on the retina. The causesof this include a long axial length of the eye and strong refractive power of the cornea or the crystalline
lens. In myopia, it is not possible to clearly see far objects but possible to clearly see near objects. School
children with myopia may find it difficult to see letters on the blackboard. In addition, as they have tonarrow their eyes, or knit their brows to see objects, they may experience headaches.
Column: Asians and myopia

The prevalence of myopia in schoolchildren has been reported to be higher in Asian countries thanin Europe and other regions (20–30%), with the rate of myopia being 45.7% for high school students
in Korea, 70.3% for those aged between 12 and 19 in Taiwan, 78.4%5 for those aged 15 in China(Guangzhou), and 76.5% for those aged between 6 and 11 and 94.9% for those between 12 and 14

134

Figure 8.2 Emmetropia and refractive errors
Chapter 8

Eye and dental health1354) Correction of refractive errors

In both types of contact lenses, attention needs to be paid to complications that may be caused byputting the lens on the surface of the cornea. Such complications include corneal infection, which is(1) Glasses

caused by damaging the cornea, conjunctivitis, which is caused by allergens attached to the contact

Glasses are used to correct refractive errors. There are the two types of lenses for glasses: a convex lenslens, and corneal epithelium disorder, which is caused by decreased oxygen supply to the surface layer

and a concave lens. The convex lens is used in a magnifying glass, and its shape is round in the centerof the cornea that is covered. To reduce these complications, it is important to properly manage and use

and tapered in thickness toward the periphery. Meanwhile, the concave lens is thin in the center andcontact lenses. First of all, pay attention to how many hours per day. Depending on the type of lens andthickens toward the periphery.

the condition of the wearer’s eye, generally 12 to 16 hours per day is seen as a guide. Second, contact

Since myopia is a condition in which rays converge anterior to the retina, glasses with concave

lenses should be kept clean, and contact lenses other than single-use lenses should be cleaned after use

lenses are used. The concave lenses converge rays posteriorly, thus adjusting the focal point to focus theand stored in a clean container. Also important is having an eye examination at an ophthalmologicalimage on the retina. In hyperopia, meanwhile, rays converge posterior to the retina, glasses with convex

clinic on a regular basis.

lenses are used. The convex lenses converge rays anterior to focus the image on the retina, making it
possible to see the object clearly (Figure 8.3).
Type

How rays travel

Column Fashionable contact lenses caused eye disorders!!

How the image is focused on the retina
Convex lensConvex lens(for hyperopia)

colored contact lenses to change the color of the iris as well as circle contact lenses to make thepupil look larger. As with contact lenses for visual correction, contact lenses for fashion may also
cause eye diseases if they are not properly used. Some people developed an eye disease by sleeping

Rays froma close distance

RetinaCrystalline

Converge rays

These days, some people use contact lenses not for visual correction but for fashion. They use

Concave lens

while wearing contact lenses, or borrowing/lending contact lenses from/to a friend. Avoid carelessuse, adhere to the same usage hours, and properly maintain the lenses. In addition, take care not topurchase inferior goods that use harmful substances to color the lenses. The abnormality of the eyeor an uncomfortable feeling that people experience while wearing colored contact lenses is a sign oftrouble in the eye.

Rays froma far distanceConcave lens(for myopia)
Diverge rays

Correction of myopia(rays are diverged by the concave lens before entering
the ophthalmus)

Figure 8.3 Mechanisms of visual correction by glasses(2) Contact lens

5) Protecting your eyes
Because myopia often occurs during school age, the prevention of myopia is discussed here. Preventing
the onset and progression of myopia can lead to the prevention of visual impairment in adulthood. The
progression of myopia due to “environmental factors” can be prevented by reviewing daily life.

(1) Posture

A contact lens, which is a medical device placed directly on the cornea, can be used for various eye

It is said that sitting in a bad posture during class, or watching television or reading books while lying

disorders, including myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia

can exacerbate myopia. Pay attention to posture during class. Sit straight up, and allow a fist-size space(poor focusing with reading material and other near vision tasks occurring typically in middle and oldbetween the desk and the belly. It is desirable that the height of the chair allow the bottoms of the feet toage). According to the material, it can be divided into hard contact lenses and soft contact lenses. The

reach the floor entirely. If that is not possible, adjust the height of the chair or use a stool (Figure 8.4).

hard contact lens is made of a hard material and generally used for a long period while receiving
maintenance such as cleaning. The soft contact lens is made of a material that softens with water and(2) Brightness

comes in different types: a single-use type, a type that is replaced every two weeks to one month, and aClassrooms and equivalent facilities require a brightness of 300 lux or more. Vertical TV and computer

type that is used for a long period of time. The soft contact lens is slightly less effective in correction

monitors should ideally give off 500–1000 lux (lux is a standard unit of measurement of light level

than the hard contact lens but has the advantages of giving the wearer a less uncomfortable feeling andintensity). In Japan, the “School environmental hygiene standards for environment of classrooms, etc.”

causing less slipping and dropping.

stipulate that when classrooms are used for learning, they are required to have a brightness of 300 lux or136

Chapter 8

Eye and dental health137

these, the functions of “eating” and “talking” that are acquired in infancy as the teeth and the mouth
develop are fulfilled by keeping those functions healthy throughout life. Therefore, keeping the teeth andDistance between the desk
and the bodythe mouth healthy will improve the person’s quality of life (QOL) throughout their life. Although QOL
Give a fist-size spacecan be interpreted variously depending on context, one popular understanding is that QOL represents theextent to which a person obtains satisfaction from life.
The number of teeth is 20 for milk teeth or deciduous teeth and 32 for permanent teeth. However,
eruption of the third molars (the wisdom teeth) varies among individuals. Without the third molars, theHumpback

number is 28. At around six months after birth, babies start teething with milk teeth and finish when they
are around two and a half to three years old. The order of teething varies among individuals. The firstpermanent tooth to grow is often a mandibular central incisor or a mandibular first molar. Teething of
permanent teeth is completed at 12 to 13 years old, with variations in the order of teething among
Feet do not reach the floor

individuals greater than those for milk teeth. Childhood is a period in which milk teeth are replaced by

Back: Straight
Bottoms of the feet: Entirely reachthe floor
Belly: Fist-size spacepermanent teeth (Figure 8.5).11 Because dental caries may affect how permanent teeth grow as well as
the tooth alignment, childhood is viewed as an important period also from the standpoint of developing
the characteristics, alignment, and occlusion of permanent teeth.
Individual teeth have shapes suitable for their roles concerning the function of eating. Incisors cut

Figure 8.4 Bad posture and good posture during classfoods. Canines play a role in tearing foods into pieces. Molars play a role in grinding foods to change
their shapes so that they can be easily swallowed. A tooth is comprised of the outside of very hard8

more for the entire classroom and a brightness of 500 lux or more for the blackboard surface.

enamel, the body of dentine, and the root surface of cementum (Figure 8.6).

During class, students repeatedly look at the blackboard, a book, and a notebook. Therefore, a large
difference between the brightness of the blackboard and that of the classroom causes eyestrain. In
addition, attention should be paid to any direct sunlight from the window or a light source that interferes

8-9 y.o. 7-8 y.o.

with the field of vision, as it can disturb visibility even if the intensity of illumination meets the standards.

(3) Rest eyes frequently
Staring at a close object for long hours will keep the ciliary muscle tense and likely exacerbate myopia.
Recently, there have been increasing opportunities to look at small screens of devices such as smartphones

17-18 y.o.
10-15 y.o.

12-14 y.o.

it is important to deliberately look away from the screen and look into the far distance to rest the eyes.

17-18 y.o.

followed in order to prevent eyestrain caused by continuing to stare computers or smartphone screens inparticular. The rule is to take at least a 20-second break to view something 20 feet (approx. 6 meters)
9away every 20 minutes.

2. Dental health
1) The roles and development of teeth
The functions of the teeth and the mouth are significantly related to vital functions including “eating,”“talking,” “creating expressions,” and “supporting movement and keeping a body in balance.”10 Among138

8 y.o. 7.5 y.o.

6-7 y.o.

and tablets. Small letters and screens make us particularly short-sighted and are likely to cause eyestrain;
The American Optometric Association (AOA) recommends that the 20-20-20 rule should be

Teeth newly added(accessional teeth)

10-11 y.o10.5 y.o10.5 y.o.
11.5 y.o.

Timing of teething of
permanent teeth

Timing of losing milk teeth

17-18 y.o.

11 y.o.

11-13 y.o

10 y.o.
9.5 y.o6-7 y.o.

7 y.o. 6 y.o.

10-12 y.o.
9-11 y.o.

9-10 y.o.
7-8 y.o. 6-7 y.o.

Nemes ofpermanet teeth
Third molar(wisdom tooth)Second molarFirst molar
Second premolarFirst premolar
CanineLateral incisor
Central incisor

Figure 8.5 Timing of losing milk teeth and timing of teething of permanent teeth11
Chapter 8

Eye and dental health139

caries.

Cementum Enamel Dentine(vii) Dental caries starts in enamel. Dental caries developed in enamel does not cause symptoms
such as toothache or a pain sensitive to cold water or sweet foods. If left untreated, dental caries
extends to dentine and the dental pulp (nerve). If dental caries extends to the dental pulp, a

Crown
Gum

Nerve

Tooth root

Periodontal membrane
Alveolar bonesevere pain develops. Leaving this condition untreated results in the death of the nerve, anddissipation of the pain. Further progression of dental caries causes the crown to collapse andleaves only the tooth root. Because conservative treatment is impossible for this condition of atooth, the tooth will be extracted.
Memo: Sucrose and sugar

ArterySucrose is the most common food sweetener. Industrial products mainly composed of sucrose areVeincollectively called sugar.

Figure 8.6 Structure of a tooth
PlaquePhosphorus2) Dental caries

Acid

EnamelDental caries is a disease in which enamel or dentine is destroyed by acid produced by the activity ofCalciumbacteria (mutans streptococci) and lactic acid bacteria in the mouth (see Chapter 4). Dental caries does
not heal on its own, nor does a tooth with caries return to the original health even if it is treated. The

DentineCambodia National Oral Health Survey, conducted in 2011, reported that the prevalence of dental caries
is 93% for children aged six, and 80% for those aged 12 and 13 and aged between 35 to 44, indicatingthat dental caries is a major health issue not only for children but also for adults in Cambodia.12(1) Mechanism of the development and progression of dental caries
Figure 8.7 Mechanism of the development of dental caries

Dental caries develops when the conditions of three factors, that is, bacteria, tooth quality/shape, andcarbohydrate (sucrose or sugar) are met, and time passes. Described below is the mechanism of thedevelopment of dental caries (Figure 8.7).
Infection with mutans streptococci (formal name: Streptococcus mutans) is established.

deciduous incisors as well as maxillary and mandibular deciduous molars are susceptible to dental(ii) Mutans streptococci in the oral cavity uses carbohydrate taken as food to produce sticky glucan

caries. Among permanent teeth, the maxillary molar region is the most susceptible to dental caries. The

from sucrose. The glucan attaches to the surface of the tooth and produces plaque (see Chapter

regions that are likely to cause dental caries are grooves in molars, gaps between the teeth, and boundaries

4) with other oral bacteria. Thus, the plaque is an aggregate of various bacteria.

between the tooth and the gum (Figure 8.8). In these regions, food particles tend to remain and the(i)(iii) Bacteria in the plaque further proliferate to produce acids using carbohydrates (sucrose) taken
as food.

cleaning effect of saliva is difficult to reach physically. Thus, the adhesion of plaque (see Chapter 4) islikely to occur.

(iv) When acidity in the plaque becomes pH ≤ 5.5, enamel on the tooth surface begins to decay

In addition, newly grown teeth are likely to develop dental caries. When a tooth comes in contact(decalcification; the dissolution of calcium and phosphoric acid from the enamel of the teeth).

with saliva, enamel absorbs calcium in the saliva to promote the crystallization of enamel, thus making(v) Acidity in the plaque returns to the original pH level thanks largely to the effect of saliva,

the tooth resistant to dental caries. But this is said to take two to four years in general. Given thatcausing remineralization (restoration by the activity of saliva).
(vi) Eating foods containing saccharides without a break leads to the disruption of the balance
between (iv) and (v), which makes decalcification greater than restoration, resulting in dental
140

There are teeth and regions that are likely to cause dental caries. Among milk teeth, maxillarypermanent teeth start to grow at six years old and complete growth by 12 or 13 years old, the school age
is a period in which the development of dental caries is rather common. This is also a reason why
establishing dental and oral health practice is necessary during school age.10
Chapter 8

Eye and dental health141

Gaps between teeth

Boundaries between teeth and gum4) Prevention of dental caries and periodontal disease10
The school age is a period in which milk teeth are replaced by permanent teeth and a lifestyle isestablished. It is therefore important to learn dental and oral health during school age. Establishingdental and oral health practice is a daily, common subject, in which it is easy to find challenges and see
the process of solving such challenges. For this reason, dental and oral health is a valuable teaching andGrooves in molars

learning matter that enables the direct observation of the body condition and its changes. Here, brushingteeth and diet are discussed as preventive measures against dental caries and periodontal disease.

Figure 8.8 Regions that are susceptible to dental caries(1) Toothbrushing
Toothbrushing is effective in removing plaque (an aggregate of living bacteria) that can cause dental

3) Gingivitis and periodontal diseasecaries and periodontal disease. Plaque is milk white, a color similar to that of a tooth, and rough when it
is tongued (see Chapter 4). Plaque tends to attach to gaps between the teeth, boundaries between thetooth and the gum, and the occlusal surface. Therefore, brush the teeth along the tooth alignment by

Periodontal disease is a general term for conditions where periodontal disease bacteria have caused

brushing one area at least 20 times and keeping the following three tips in mind: (i) properly place

inflammation of the periodontia around the tooth (e.g., the gum, periodontal membrane, alveolar bone,bristle ends of the toothbrush against the boundary between the tooth and the gum as well as gaps

and cementum). The condition in which inflammation is only caused in the gum is called gingivitis, andbetween the teeth, (ii) move it with light force that does not allow bristle ends of the toothbrush to

the condition in which inflammation extends to the alveolar bone and the periodontal membrane isbroaden, and (iii) wiggle the toothbrush within a range from approximately 5 to 10 mm, and brush one

called periodontitis. Having no subjective symptoms, gingivitis is often left untreated and progresses

by one (Figure 8.9). Brushing the teeth in a predefined order will enable uniform, complete brushing.

silently. By the time the disease is noticed, even the alveolar bone supporting the tooth has decayed due
to a toxin from periodontal disease bacteria and inflammation. This is called the resorption of the alveolarbone, and in this condition, the tooth is wobbly, chewing foods becomes difficult, and eventually the
tooth comes out.

Angle

How to move

Behind the front teeth

Place the toothbrush at an angleof 45 degrees against a gap
between the tooth and gum.

Wiggle the toothbrush.

Place the end of the toothbrushvertically.

Grooves in molars

Gaps between teeth

Properly place bristle ends
against grooves and brush them.

Place the tip of the toothbrush.

Inflammation of the gum is caused by plaque that attaches to the boundary between the tooth and thegum and then increases. Plaque is an aggregate of various types of bacteria, and periodontal disease
bacteria in particular, which like places where the amount of oxygen is small, enter the space between
the tooth and the gum (a periodontal pocket) and destroy periodontal tissues with a toxin and acid (seeChapter 4). While periodontal disease affects many adults, gingivitis starts during elementary and juniorhigh school age. Adolescent hormonal imbalance (particularly, changes in female hormone levels),stress, lifestyle habits such as smoking, and lifestyle diseases including diabetes are risk factors that can
exacerbate periodontal disease.

Bad example

Column: Causes and prevention of bad breath

Bad breath is a very common issue of oral hygiene. In most cases, causes are in the mouth; the two
major causes are coating of the tongue and periodontal disease. Bad breath is caused by systemic
diseases (metabolic diseases) such as diabetes, uremia, hepatic cirrhosis, liver cancer, andtrimethylaminuria.13 The best way of making sure you do not have bad breath is to keep your teeth,
tongue, and mouth clean. Preventive measures include twice-a-day gentle, careful brushing of the

Do not apply excessive force as
it can damage the gum.

teeth, the gum, and the tongue, removing food particles from the space between the teeth, notsmoking, and not taking in high-sugar drinks.14

142

Figure 8.9 How to use a toothbrush
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Eye and dental health143

Make it a rule to brush the teeth after eating breakfast, lunch, and dinner in order to prevent the acid state

10-15 cmof the oral cavity from lasting for a long time after meal ((iii), (iv), and (v) in the development andprogression of dental caries described above). Brush the teeth particularly carefully before going to bed
because, while sleeping, the amount of saliva secretion becomes small and the self-cleaning function
decreases.

1-2 cmColumn: A variety of toothpaste

What kind of toothpaste do you use? What standard do you apply to choose it?
Toothpaste contains various components. They include a polishing agent to remove stains(calcium carbonate, sodium bicarbonate), a refrigerant like mint, a forming agent to improve theCut floss to a length ofabout 40 cm (length froma fingertip to the elbow).

feeling of brushing, and fluoride to prevent dental caries (sodium fluoride, sodium monofluorophosphate).
It is only fluoride that has been shown to be effective in scientific studies. Although the foam ofWind floss around both
middle fingers (forefingers)
several turns lightly. Winda longer section aroundyour non-dominant hand.

Adjust floss to make thespace between both
middle fingers 10-15 cm
when floss in taut.

Hold floss with thumbs
and forefingers andhandle it while keeping aspace of 1-2 cm.

Figure 8.11 How to hold dental floss

toothpaste makes us feel the teeth have been cleaned, foaming agents are not effective in preventing
dental caries. The most important thing to prevent dental caries is to brush the teeth properly. It is
recommended that you should start brushing without toothpaste and finish brushing with toothpaste.
When you use toothpaste containing fluoride, it is also important to keep gargling to a minimum inorder to allow the component to spread over and coat the teeth.

Let’s experiment

Experiment for effective toothbrushing

Preparation: Plaque disclosing tablets, toothbrush, mirror, cotton swab, towel, clothespin, waterbottle (water for gargling), container to spit out water, etc.

(2) Dental floss

Experimental method (Figure 8.12)

It is difficult to remove plaque between the teeth with a toothbrush because bristle ends do not always(i)reach between teeth. Dental floss is made of thin bundled fiber (Figure 8.10). This allows it to pass(ii) Brush your teeth.

through a narrow gap between the teeth to scrape off plaque that cannot be completely removed with a(iii) Chew one plaque disclosing tablet firmly into small pieces. Apply them to your teeth with yourtoothbrush. Figure 8.11 shows the proper method for using dental floss.
Dental floss comes in two types: wax type and non-wax type. The wax type slides well and is easy

Put a towel around your neck and fix it with a clothespin.

tongue with the aid of a mirror, then spit them out.
(iv) Rinse out your mouth one or two times.

to insert into gaps between the teeth; it is thus recommended for novice users. The non-wax type can(v) Observe areas that have been stained red in the mirror.

scrape off plaque more efficiently because its fiber is not fixed with wax and thus can fit the surface of a(vi) Discuss regions that tend to remain uncleaned.

tooth when it sticks to it.

Figure 8.12 Staining experiment steps(3) Eating habits to maintain dental health (how and what to eat between meals)
Among carbohydrates, sucrose (sugar) can be a primary cause of dental caries because “it is used as amaterial to produce plaque” and “it is used as a material for acid production by bacteria.” At the same
Figure 8.10 Example of dental floss

144

time, sucrose is an important nutrient source. Therefore, the important thing is not just cutting the intake
of sucrose but taking it in a wise way. Specifically, it is important not to take foods containing it frequently
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Eye and dental health145

or irregularly (not to eat without a break) because the constant presence of sugar in the oral cavity creates
an environment in which acid is constantly produced and thus decalcification progresses (Figure 8.13).
In addition, eating sticky foods such as snack foods should be discouraged because carbohydrates
persistently remain in grooves in molars, which is a condition that is likely to cause dental caries.
Three meals a day

pH 7.06.5
6.0
pH
5.5~5.7 5.5
5.0
4.5
4.0
3.5
3

Remineralization Return to normal

Decalcification The teeth lose calcium

Frequent drinking and eating

pH 7.06.5
6.0
pH
5.5~5.7 5.5
5.0
4.5
4.0
3.5
3

Because saliva and/or toothbrushing clean
bacteria and acid, the period of normal pH
levels is lengthened.

Remineralization Return to normal

Decalcification The teeth lose calcium
The period of normal pH levels is limited.

Figure 8.13 Relationship between diet and oral cavity pH (Stephan curve)

References
1

Report of eye care activities in Cambodia 2011. http: //www.npehcambodia.com/filelibrary/Report_of_PBL_Activities_in_2011.pdf

2Sogbesab E, Yutho U. Cambodia’s National Eye Care Programme and VISION 2020: The Right to Sight. Community Eye Health13(36) : 57-59,2000. https: //www.ncbi.nlm.nih.gov/pmc/articles/PMC1705982/

Exercises for further thought and research[8-1] The prevalence of myopia among school children is said to be lower in Cambodia than in other3

Report.pdf
4Institute of Medical Information Science ed. Byoki ga mieru VOL12 Ophthalmology. Medic Media, 2019.

5

Lin Z, Vasudevan B, Jhanji V, Mao GY, Gao TY, et al., Near work, outdoor activity, and their association with refractive error.
Optometry and Vision Science. 91(4) : 376-382. 2014. https: //www.researchgate.net/publication/260874694_Near_Work_Outdoor_

Asian countries. Find reasons for that. Predict whether or not the number of children with myopia
will increase in the future by sharing views.
[8-2] Assume that you give an eye health class to elementary school students, consider the content andmethod, and give a mock class.

Activity_and_their_Association_with_Refractive_Error/link/5d0dabc092851cf44040e5b0/download
6

measures can be taken to increase time for outdoor activities for children.
[8-4] Investigate the habit of toothbrushing among elementary school students. Consider benefits andchallenges based on the section of “Toothbrushing.”[8-5] Consider an effective method for teaching toothbrushing taking into account ages at which teeth
are replaced by new growth.

Yotsukura E, Torii H, Inokuchi M, Tokumura M, Uchino M, et al., Current Prevalence of Myopia and Association of Myopia With
Environmental Factors Among Schoolchildren in Japan. JAMA Ophthalmology. 137(11) : 1233–1239. 2019.

7

Dolgin E. The Miopia Boom. Short-sightedness is reaching epidemic proportions. Some scientists think they have found a reason
why. Nature. 519: 276-278. 2015. https: //www.nature.com/news/polopoly_fs/1.17120!/menu/main/topColumns/topLeftColumn/[8-3] It is difficult to increase time for outdoor activities in Southeast Asian countries including
Cambodia, where the sunlight is strong and temperatures are high. Consider what kinds ofGlobal School Based Student Health Survey Cambodia 2013. https: //www.who.int/ncds/surveillance/gshs/Cambodia_2014_GSHS_

pdf/519276a.pdf
8

Ministry of Education, Culture, Sports, Science and Technology. School environmental hygiene standards: 2018. https: //www.mext.
go.jp/a_menu/kenko/hoken/__icsFiles/afieldfile/2018/05/28/1403737_02_1.pdf

9

American Optometric Association. 20/20/20 to Prevent Eye Strain. https: //www.aoa.org/AOA/Images/Patients/Eye%20
Conditions/20-20-20-rule.pdf

10 Ministry of Education, Culture, Sports, Science and Technology. School dental health reference material, Establishing dental andoral health practice at school to foster “zest for living,” Chapter 1 Introduction. https: //www.mext.go.jp/component/a_menu/
education/detail/__icsFiles/afieldfile/2011/06/23/1306939_03.pdf
11 Tsuchiya M. Children’s teeth: 2. Survey on children’s health and environment Eco & Child Miyagi Unit Center. http: //www.ec-muc.
med.tohoku.ac.%AD%90%E3%81%A9%E3%82%82%E3%81%AE%E6%AD%AF%E3%81%AB%E3%81%A4%E3%81%84%E
3%81%A6%E3%83%BB2%E3%80%91/
12 Chher T, Turton BJ, Hak S, Beltran E, Courtel F, et al. Dental Caries Experience in Cambodia: Findings from the 2011 Cambodia
National Oral Health Survey. Journal of International Oral Health 8(1): 1-7. 2016.
13 Ministry of Health, Labour and Welfare. e-healthnet: Causes and realities of bad breath. https: //www.e-healthnet.mhlw.go.jp/
information/teeth/h-07-001. html#:~:text=%E5%8F%A3%E8%87%AD%E3%81%AE%E5%A4%A7%E9%83%A8%E5%88%86%
EF%BC%8880,3) 2S%5D%E3%81%A7%E3%81%99%E3%80%82
14 National Health Service. Bad breath. https://www.nhs.uk/conditions/bad-breath/146

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Eye and dental health147