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Year : 2020  |  Volume : 11  |  Issue : 2  |  Page : 31-32

The Influence of Miller’s Chemo-Parasitic Theory on 20th Century Clinical Dentistry and Dental Research

School of Dental Medicine, University of Connecticut, Farmington, CT, USA

Date of Submission15-Apr-2020
Date of Decision27-Apr-2020
Date of Acceptance27-Apr-2020
Date of Web Publication10-Jun-2020

Correspondence Address:
DDS, PhD, Professor Emeritus Edward F Rossomando
School of Dental Medicine, University of Connecticut, Farmington, CT 06030
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/denthyp.denthyp_39_20

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How to cite this article:
Rossomando EF. The Influence of Miller’s Chemo-Parasitic Theory on 20th Century Clinical Dentistry and Dental Research. Dent Hypotheses 2020;11:31-2

How to cite this URL:
Rossomando EF. The Influence of Miller’s Chemo-Parasitic Theory on 20th Century Clinical Dentistry and Dental Research. Dent Hypotheses [serial online] 2020 [cited 2023 Mar 21];11:31-2. Available from:

  Introduction to W.D. Miller Top

In 1959, when I started dental school, one first-year course was operative dentistry. Working on the occlusal surfaces of extracted teeth for several hours each week, we labored to perfect our class one outlines. Of course, in 1959 there were no air turbine high speed handpieces. We cut enamel using belt driven handpieces. The preparation for a class one had us removing all pits and fissures on the occlusal surface a technique introduced in 1891 G.V. Black that he called extension for prevention.[1] Since caries was a result of microbial action, the idea was to remove all areas on the tooth surface where bacteria resided or were likely to reside and replace this lost tooth structure with an amalgam restoration.

At the time, my classmates neither I nor any of my classmates knew who G.V. Black was nor did we stop to consider why, in 1959, we were following a technique that was 68 years old. Nor did we stop to ask about the experimental basis for the conclusion that bacteria caused dental caries. It was only later, as a third-year student, that I became aware of the work of W.D. Miller. (This insight only came about because at my dental school the student research society was named the Miller Research Society.) When I looked Miller up, I found that in the 1890s he published the results of his experiments that showed that dental microbes were causal for dental caries. In 1890 he published his chemo-parasitic theory of caries.[2]

  Verification of Miller’s theory Top

A good theory makes predictions that can be scientifically tested. In the case of the chemo parasitic theory the predication was clear: if microbes cause decay then the removal or reduction of microbial populations on the surface of the tooth would reduce or halt the decay process. In 1891, when Miller made this predication it was almost impossible to test it. But in the early 1950s germ free mice were developed and in 1954 Frank Orland and colleagues published the result of studies that showed that mice raised in germ free conditions did not develop dental caries.[3] By the 1970s, so persuasive was the evidence that caries was a microbial based disease, that a very serious effort was made by dental scientists to develop a vaccine against the bacteria responsible for the decay process.[4]

  Miller’s theory and the treatment of microbial-based dental diseases in 20th century clinical dentistry Top

As I think back, I am astounded to realize that the dental education I received in the early 1960s was based on a theory that was more than 70 years old. In fact, Miller’s work was so persuasive that his chemo-parasitic theory would dominate attempts at prevention, and well as guide approaches to diagnosis and treat dental decay. Because of the prevalence of caries, and the commitment of organized dentistry to control or eliminate the disease, a considerable effort was made by the dental research community to investigate the disease process.

Miller’s theory justified much more than extension for prevention. The theory supports the use of sealants and varnishes as well. Since microbes were shown to be causal for periodontal disease, procedures to removing and/or limiting access of microbes to the tooth procedures such as scaling, and root planning were introduced.

By the early 1900s, the chemo-parasitic theory dominated dental practice. In 1906 a Dr Alfred Fones, a dentist practicing in Bridgeport Connecticut, understanding the importance of controlling the microbial populations on teeth, coined the phrase dental hygienist and, in 1913, started the first school for hygienists in the US.[5]

During the 20th century, ideas about prevention, including restricting dietary sugar intake, flossing and brushing rest on the chemo-parasitic theory became the established paradigm for microbial based dental diseases. In fact, the toothbrush and toothpaste were introduced to reduce the number of microbes in the mouth.

Fluoride was added to tooth paste to make teeth more resistant to bacterial acids. This finding is predicted by Miller’s theory as the first step in the decay process is the dissolution of enamel by acids produced by bacterial metabolism. If tooth enamel could be made more acid resistant, dental decay would decline. This prediction was verified by observations by McCay and later by Dean that when teeth were formed in areas with fluoridated water, the incidence of caries was less.[6] Later studies would show that the in fluoridated water the hydroxyapatite crystalline structure was fluorapatite replaced by a fluoride containing structure.[7]By 1950 both the acid and microbial aspects of Miller’s chemo-parasitic theory had been validated and Miller’s theory remains relevant in 2020 more than 100 years after it was published but has had a significant role in influencing not only the practice of dentistry but in guiding the research agenda and major influence in the design of every dental school curriculum in the US and worldwide.

But what about the treatment of non-microbial dental diseases like malocclusion, clefting and enamel and dentin dysplasia? Does dentistry have a theory that guides the development of clinical treatments, research or education for these non-microbial dental diseases?

In the next editorial I will address this question.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

Editor’s note: A theory, or hypothesis, is formulated to explain an observation or phenomenon. Theories are important as they demonstrate an understanding and provide a framework for further research. There have been many important theories for example Harvey’s theory of circulation, Galileo’s heliocentric theory, Newton’s Theory of Gravity, Darwin’s Theory of Evolution and of course Einstein’s theory of relativity. All these theories not only explain a phenomenon but guide programs in research and educational curricula.

In dentistry a most important theory is W.D. Miller’s theory for dental caries. This theory was published in the late 1890 and in 2020, more than 130 years after publication, has had and continues to be, a major influence in many components of the dental enterprise including clinical dentistry, dental research and dental education.

But Miller’s theory applies only to those dental diseases of microbial origin. What of the dental diseases of non-microbial origin? At the present time dentistry does not have a unifying theory to guide clinical treatment, research and education. In the second editorial in this series I will discuss these non-microbial diseases and begin formulating a theory to explain the origins of these diseases.

  References Top

Orland F, Blayney Jr, Hreyniers JA, Trexler PC, Wagner M, Gordon HA, Luckey TD. Use of the germfree animal technic in the study of experimental dental caries. I. Basic observations on rats reared free of all microorganisms. J Dent Res 1954;33:147-74.  Back to cited text no. 3
Michalek SM1, Katz J, Childers NK. A vaccine against dental caries: an overview. BioDrugs 2001;15:501-8  Back to cited text no. 4
Hydroxy appetite and fluoride replacement. Materials (Basel) 2019;12:2683.Published online 2019 Aug 22. doi: 10.3390/ma12172683  Back to cited text no. 7

This article has been cited by
1 Twenty-first Century Dental Practice and the Treatment of Nonmicrobial Genetic-based Dental Diseases
EdwardF Rossomando
Dental Hypotheses. 2021; 12(3): 105
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