What does information theory have to do with perio?

by Bill Landers
[email protected]

Everything! Without contextual information, data and measurements are meaningless. For instance: The weatherman says it’s twice as warm as yesterday. That’s a coincidence, not a fact. Obviously, it’s not twice as warm everywhere at the same time and it’s only twice as warm at a particular time and place if you arbitrarily decide to measure heat energy in Fahrenheit and it was exactly 40° yesterday and 80° today. Measure in degrees Celcius, and it’d be 7 times hotter than yesterday (4°C/ 27°C). Measure in degrees Kelvin, it’d be just 8% hotter (277°/300°).

Information theory reminds us of two things:

• All measurements are inherently arbitrary and purely statistical in nature1
• Measurements aren’t the same thing as the thing being measured

They’re surrogates for the thing, not the thing itself. So what’s that got to do with dentistry?

"Mr. Jones, that pocket on your molar is twice as deep as it was on your last visit."

Not really. It’s a coincidence of using a particular surrogate. It’s only true if the notches on a metal stick happen to be 1 mm apart. How much deeper would the pocket be in inches? Or microns? And what’s the point of arbitrarily putting notches 1 mm apart when experiments tell us that it is impossible to measure anything less than 2 mm because of confounding factors?2

Why are we still using imprecise surrogates for disease? Until the late 1800s, when germs were discovered, the symptomatic surrogates of inflammation, supperation, and tooth mobility were the only ways to diagnose pyorrhea.3 However, the object of diagnosis is to identify an illness, not its symptoms. Measuring pocket depths doesn’t diagnose periodontal disease because pockets aren’t the disease. They’re a sequella of a long-standing disease, not the disease itself.

Because of progress in microscopy, histopathology, and stereology, we now know that periodontal inflammation is caused by specific microbes that live in complex communities called biofilms that grow on the surfaces of teeth.4 They, in turn, provoke an immune response that eventually breaks down both connective tissue and bone.

Even though researchers have known about periodontal pathogens since the 1960s, it’s taken almost 50 years to develop clinical microbiological tests to reduce our historical dependence on clinical surrogates. Today, clinicians can choose from a wide variety of commercial microbiological tests, including cultures, DNA analysis, enzymatic tests, and phase contrast microscopy.

• DNA analysis – Every species of bacteria has unique segments of DNA that can be isolated and cloned as molecular primers. To check for pathogens, labs add the primers from about 11 periodontal pathogens to patient samples and clone the results thousands of times via polymerase chain reactions (PCR) to detectable levels. The results are tabulated in a report that summarizes both the types and approximate numbers of pathogens detected. DNA tests are available from OralDNA Labs (MyPerioPath, via saliva sample) and Hain Diagnostics (micro-IDent plus, via biofilm sample).

MyPerioPath
Equipment cost: Not applicable
Kit quantity/costs: 12/$199; ($16.58 each)
Processing: $99
Shipping: Prepaid; Federal Express
Results: 4-5 days
Source: OralDNA Labs
Phone: (877) 577-9055

Micro-IDent
Equipment cost: Not applicable
Kit quantity/costs: free
Processing: $89
Shipping: Prepaid; USPS
Results: 2-3 days
Source: Hain Diagnostic
Phone: (866) 756-4246

• BANA-zyme Enzyme Test – The BANA-zyme uses test strips to detect the three most common and pathogenic periodontal pathogens. They share a unique enzyme (a peptidase) not found in other bacteria. Biofilm is applied to a test strip that’s inserted into a small chairside processor. Over an automated five minute cycle, any peptidase in the sample hydrolyzes an embedded peptide (BANA). The by-product reacts with a diazo dye to produce a blue color. The depth of the color is proportional to the number of bacteria.

BANA enzyme
Equipment cost: $400
Kit quantity/costs: 20/$120; ($6 each)
Processing: Not applicable
Shipping: Not applicable
Results: Chairside
Source: OraTec
Phone: (800) 368-3529

• BioScan phase contrast microscopy – High numbers of Treponema species (spirochetes) and inflammatory WBCs are almost universally present in periodontal infections. Because of their unique shapes, both are easily seen without special preparation by placing whole biofilm samples on a slide and viewing with a phase contrast microscope. The chairside results are displayed on large video monitors for easy viewing and patient motivation.

BioScan
Equipment cost: Approximately $5,000
Kit quantity/costs: 25¢; glassware
Processing: Not applicable
Shipping: Not applicable
Results: Chairside
Source: OraTec
Phone: (800) 368-3529

• Anaerobic bacterial cultures – Most periodontal pathogens are either obligate or facultative anaerobes and notoriously difficult to culture. Two universities, University of Southern California in Los Angeles (OMTS) and Temple University in Philadelphia (OMTL), have laboratories dedicated to the culturing of anaerobic oral pathogens. Paper-point samples from patients are plated on species-specific media along with a panel of antibiotics. Growth reveals which pathogens are present and which antibiotics are most effective against them.

OMTS
Equipment cost: Not applicable
Kit quantity/costs: Free
Processing: $125
Shipping: Clinician pays
Results: 10 days
Source: OMTS
Phone: (800) 788-6687

OMTL
Equipment cost: Not applicable
Kit quantity/costs: Free
Processing: $115; ($160 with in vitro antibiotic)
Shipping: Clinician pays
Results: 10-12 days
Source: OMTL
Phone: (213) 740-3163

References

1. Sarle WS. Measurement theory: Frequently asked questions. Disseminations of the International Statistical Applications Institute, volume 1, edition 4, 1995,pp. 61-66.
2. DeRouen TA, Hujoel PP, Mancl LA. Concise Review: Statistical Issues in Periodontal Research. J DENT RES 1995 74: 1731.
3. Riggs IM (1882). Proceedings of the Southern Dental Association-Fourteenth Annual Session. Dental Cosmos 24 523-527.
4. Payne WA, Page RC, Ogilvie AL, Hall WB (May 1975). "Histopathologic features of the initial and early stages of experimental gingivitis in man." J. Periodont. Res. 10 (2): 51–64.

Bill Landers has been president of OraTec Corp. since 1992. He is also a leading expert on chairside and laboratory periodontal risk assessment technologies, and his essays on periodontal disease have been published in several dental hygiene journals. Mr. Landers is a popular speaker and has presented hundreds of continuing education seminars on the microbiology of periodontal diseases.