'"LLI

BY JOHN O.B. FEATHERSTONE, MSC, PHO

D::~ With an in-depth understanding of the caries process, dental hygienists can lead the fight

IIIIIiIIIIIIIII to reduce or eliminate caries.

UT

he dental hygienist should be at the forefront ofcaries prevention and intervention in the dentaloffice and in the community. Understanding the

caries process is essential to perform this role. Dentalhygienists should be major players in driving a cross dis-

ciplinary approach to caries risk assessment and cariesmanagement with the goal of significantly reducing theprevelance of dental decay in our population.Comprehensive knowledge and the application of this

knowledge to practice are necessary for this result.Caries is a transmissible bacterial infection. Caries

progress or reversal is determined by the balance betweenpathological and protective factors. Pathological factorsinclude acid-producing bacteria, fermentable carbohy-drates, and reduced salivary function. Protective factorsinclude salivary components, fluoride together with calci-um and phosphate to remineralize the lesion, and anti-bacterial therapy. The hygienist can provide education,

participate in caries risk assessment, and provide therapyand follow-up for successful control of caries.

Dental caries is a transmissible bacterial infection, yetwe do not deal with the infection in our management of

dental decay. Co~ventional oral hygiene is simply notenough iR many instances. Remineralization is our naturalrepair mechanism for carious lesions, provided they are

not cavitated. Fluoride therapy enhances this repairprocess. However, if the bacterial challenge is too high,our efforts at repair are overcome and caries progresses to

a cavity. This simple concept is the caries balance.During the 1960s and 1970s, the fluoridation of water

supplies in the United States reduced dental caries preva-lence considerably.' In the 1970S .and 1980s, the almostuniversal use of fluoride-containing dentifrices brought

14 Dimensions OF DENTAL HYGIENE wIMN.dimensionsofdentalhygiene:com

further reductions in decay.> During this same period,the acceptance of fluoride and remineralization in the

dental office, together with fluoride topicals and sealantapplications, made a major impact. However, we all knowthat millions of hours are spent annually in the UnitedStates placing restorations to "fix" caries.

, Many people continue to get caries and some childrenand adults have a continual caries problem in spite ofour preventive efforts.3.4 In these high risk individuals,

we need to deal with the bacterial infection if the pre-ventive measures are to be effective. We need a para-

digm shift in our approach.

BACTERIAL INFECTIONThe primary requirement for dental decay is the presenceof acid-producing (acidogenic) bacteria. The bacteria needa substrate of fermentable carbohydrates to feed on to pro-duce the acids that dissolve our tooth mineral.5,6 Certainspecies of bacteria have gone in and out of favor as the cul-

prit over recent decades. It is now well established thatmultiple species are involved. We have all heard ofSteptococcus mutans and, during the 1980s, this was pro-

posed as the only causative agent by several sources.6Efforts were considerable in studying this species and itsmany strains, in finding a vaccine, genetically altering thespecies, and trying to find ways to eliminate it}

The key point, however, is that multiple species areinvolved, especially the mutans streptococci group and the

lactobacillus species.5os The mutans streptococci groupincludes several species of which S. mutans and S. sobrinusare the two most common that appear in human plaque. S.sobrinus does not occur as commonly as S. mutans butwhen it does, it is associated with high caries individuals.

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Several lactobacillus species are associ-ated with dental caries-both coronal and

root caries. It was previously thought thatlactobacilli colonized when cavities had

already formed but several clinical studieshave shown that lactobacilli are strongly

associated with caries progression beforethe observation of cavities.s.B Further, in

patients with cavities, the lactobacilli arepresent in the remainder of the mouthafter restorations are completed and con-tinue to thrive and produce acids to cause

future caries. These acidogenic bacteria

only occupy about 1% or less of the totalflora in the plaque. That such a small frac-

tion of the bacteria present can cause such

major problems is amazing.The bottom line is that multiple species

of acidogenic bacteria cause dental cariesand the predominant groups identified sofar are the mutans streptococci and the lac-tobacilli. Actinomyces species and some

yeasts have also recently been suggested.From a practical therapeutic perspective,this means we need to use a broad spectrum

antibacterial to reduce or eliminate theseacidogenic bacteria in order to control cariesin patients with a high bacterial loading.

Studies in the 1970S showed that specificstrains of S. mutans are transmitted frommother to child.7.1O.1l This conclusion wasconfirmed in the 1980s by DNA technolo-

gyp> It has taken 20 years for us to accept

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THE CARIES BALANCE

this conclusion and to start thinking aboutthe source of the pathogenic (cariogenic, ie,

caries-causing) bacteria that colonize themouth. Studies have now established that

early colonization, even before the teetherupt, can occur in infants by transmissionfrom the mother or caregiver. Transmissionfrom child-to-child and adult-to-adult has

also been reported for S. mutans.

Presumably the same is also the case for lac-tobacilli. Children who are colonized earlyhave more decay later.'3'14 From a preven-

tive perspective, we should target mothersand caregivers with high caries risk and con-trol their bacteria, and, in the case of preg-nant mothers, even before a child is born.

rather than total amount of carbohydrate

ingested. Every time we ingest one or moreof these carbohydrates, the acidogenic bac-teria produce acids, such as lactic, acetic,formic, or propionic acids, that within min-utes lower the pH in the plaque and dis-

solve some tooth mineral. So snacking

throughout the day and night producesmultiple acid attacks. Substitution of the

fermentable carbohydrates by noncario-genic sweeteners, such as aspartame, sor-bitol, or xylitol, can playa big part in reduc-

ing the acid challenge to the teeth.

Chewing gum enhances salivary function,helps neutralize any acids present, and pro-motes remineralization.

FERMENTABLECARBOHYDRATES

SALIVARY DYSFUNCTIONThe saliva is a very complex fluid that con-

tains calcium and phosphate necessary for

remineralization, proteins that keep calci-um in solution, proteins and lipids that form

the protective pellicle on the tooth surface,

antibacterial pro;teins and immunoglobu-lins, and components that buffer and neu-

tralize the acids produced by the bacteria.'sWhen salivary function is reduced or elimi-nated by disease or radiation therapy, all of

these protective functions are reduced orlost and rampant caries can result.'6

In some patients, the reduction in sali-

vary function is the primary determinantof caries progression for them. The protec-

The acidogenic bacteria described abovecan metabolize carbohydrates consumed byhumans. They derive energy from them,

just as we do, but the byproduct of theirmetabolism is organic acid. Common fer-mentable carbohydrates are glucose,

sucrose, fructose, and cooked starch.Sucrose is particularly bad because themutans streptococci can produce extracel-lular polysaccharides from sucrose that

sticks the plaque together and also providesa food source for the bacteria between the

times when eating provides that source.

Frequency of ingestion is the key factor

www.dimensionsofdentalhygiene.com Dimensions OF DENTAL HYGIENE 15

THE CARIES PROCESS1 proposed the caries balance concept as asimple way to look at the caries process and

see whether it was progressing or revers-ing.S"9 The most important components areillustrated in Figure 2 (see page 18). The

pathological factors are: 1) acidogenicbacteria, 2) frequency of ingestion of fer-

mentable carbohydrates, and 3) salivary dys-function. The three most important protec-tive factors are: 1) salivary components and

flow, 2) fluoride, calcium, phosphate, andremineralization, and 3) antibacterial thera-

py. Additional therapies, such as sealants, canbe added to the protective factors.

So what are the practical implicationsof this concept? The balance can be usedto assess the risk of an individual develop-ing caries in the future, to determine whythe individual has caries now, or to drive a

preventive or interventive program forthe individual or even community.'8,20 Thebalance between demineralization and

remineralization is the key to progressionor reversal of caries at any time. We canintervene to tip the balance.

Additional fluoride therapy will usuallyenhance remineralization, whereas in thecase of high bacterial challenge, we need

to apply aggressive antibacterial therapy toreduce the acidogenic bacterial loading inthe mouth. Placing a restoration does not

reduce the overall bacterial loading in themouth.2l It certainly removes the bacteriafrom that specific cavity, but does little tohelp reduce the future bacterial challenge.

Chlorhexidine mouthrinse can be used

to help with this. In the United States, wehave 0.12% chlorhexidine gluconate.22Studies suggest that daily mouthrinsing for

2 weeks substantially reduces the loadingof mutans streptococci but they recolonize

within a few weeks. Therefore, repeatedtreatments are necessary to control the bac-terial infection. A useful regiment is torinse daily for 1 week every month. This

regimen enhances compliance and reducesthe bacterial loading over several months.

CONCLUSIONDental caries progression or reversal is

18 Dimensions OF DENTAL HYGIENE WWVi

determined by the balance betweenpathological and protective factors.Fluoride inhibits demineralization and

enhances remineralization. Saliva is veryimportant as a protective factor and sali-

vary dysfunction is a common pathologi-cal factor. If the bacterial challenge ishigh, then protective factors may not besufficient to overco"me the demineraliza-tion process. Antibacterial therapy andintervention in the transmission of bacte-

ria must become part of the standard ofcare in caries control and part of the tool

chest of the dental hygienist. The dental

hygienist should be responsible for edu-cating patients, for delivering caries risk

assessment, for providing preventivecare, and being the front line person inthe paradigm shift to reduce or eliminatedental caries. .

john D.B. Featherstone, MSc, PhD, is pro-

fessor and chair of the Department ofPreventive and Restorative Dental

Sdences at the University of California,San Frandsco.

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11. Berkowitz RJ, Jordan HV. (1975) Similarity of

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JB. Distinct bacteriocin groups correlate with dif-

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