22.2 Epidemiology, Caries Indices & Public Health
Key Takeaways
- Prevalence is the proportion with disease at a point (or period); incidence is new cases over time in a population at risk—do not interchange them in exam stems.
- DMFT/DMFS index permanent teeth/surfaces that are Decayed, Missing due to caries, or Filled; dmft/dmfs is the primary-dentition analogue.
- Public health dentistry prioritizes population measures (water fluoridation, school programs, sealant programs, equity) alongside individual clinical care.
- Risk and burden concentrate unevenly: socioeconomic status, access barriers, special needs, and behavioral factors create disparities Canadian practitioners must recognize.
- Surveillance uses standardized indices and sampling so programs can target prevention where disease concentrates—not only where patients already attend private clinics.
22.2 Epidemiology, Caries Indices & Public Health
Quick Answer: Prevalence = who has disease now (or in a period); incidence = new cases over time. DMFT/dmft counts teeth that are decayed, missing due to caries, or filled—the classic caries burden index. Public health dentistry uses these measures to plan fluoridation, sealant programs, school screening, and equity-focused prevention beyond the operatory.
AFK stems may ask you to interpret a table of DMFT scores, choose the correct epidemiologic term, or pick a population-level intervention. This section builds that vocabulary and links it to Canadian-style public health thinking.
Core Epidemiologic Vocabulary
| Term | Definition | Dental example |
|---|---|---|
| Population | Group about which you want to draw conclusions | All 12-year-olds in a province |
| Sample | Subset actually measured | Schoolchildren examined in selected schools |
| Prevalence | Proportion of a population with a condition at a specified time (point) or during a period | 40% of surveyed adults have untreated coronal caries |
| Incidence | Number of new cases occurring in a population at risk during a time interval | 0.8 new carious surfaces per child-year |
| Rate | Events relative to population and time | Incidence rate of oral cancer per 100,000 person-years |
| Risk | Probability of an event in a defined time | Probability a high-risk child develops new caries in 12 months |
| Odds | Probability of event / probability of non-event | Used in case–control logistic models |
| Epidemic / outbreak | Excess cases vs expectation | Cluster of herpetic whitlow in a clinic (infection control link) |
| Endemic | Constant presence in a population | Caries is endemic in most communities at some level |
| Pandemic | Worldwide epidemic | COVID-era impacts on access (context, not dental-specific) |
Prevalence vs incidence—exam traps
| Feature | Prevalence | Incidence |
|---|---|---|
| Counts | Existing cases | New cases |
| Time | Snapshot (or period stock of disease) | Flow over interval |
| Raised by | Longer disease duration, better survival with disease, higher incidence | Higher rate of new disease |
| Lowered by | Cure, death, out-migration of cases, prevention of new cases over time | Prevention of new disease |
| Clinical analogy | How many patients in your city have periodontitis today? | How many new periodontitis cases appear this year among previously healthy adults? |
Relation (concept): prevalence ≈ incidence × average duration (for steady-state stable conditions)—chronic diseases can have high prevalence even when incidence is moderate.
Descriptive vs analytic epidemiology
| Mode | Question answered | Methods |
|---|---|---|
| Descriptive | Who, what, where, when? | Surveys, surveillance, DMFT maps by age/region |
| Analytic | Why? What associations? | Cohort, case–control, trials (Section 22.3) |
Measuring Caries: Indices
DMFT and DMFS (permanent dentition)
| Component | Meaning | Rules of thumb |
|---|---|---|
| D (Decayed) | Untreated carious teeth (or surfaces in DMFS) | Count teeth meeting diagnostic threshold used in the survey |
| M (Missing) | Teeth missing due to caries (not ortho extractions, not trauma-only, not congenitally missing—survey rules specify) | Context matters; know the concept “missing because of caries” |
| F (Filled) | Teeth restored because of caries | Crowns/fillings from caries counted per protocol |
| DMFT | Sum of D + M + F teeth per person (usually 28 teeth max; third molars often excluded in surveys) | Population mean DMFT is a common headline statistic |
| DMFS | Surface-level analogue (more sensitive to small changes) | Used in clinical trials and detailed surveys |
Interpretation:
- High D relative to F → untreated disease / access problem.
- High F with low D → disease experienced but treated.
- High M → historical severe disease or extraction-heavy care patterns.
- DMFT = 0 (“caries-free” by index) does not mean zero risk forever.
dmft and dmfs (primary dentition)
| Index | Use |
|---|---|
| dmft | Decayed, missing (due to caries), filled primary teeth |
| dmfs | Surface-level primary index |
| ECC metrics | Special definitions for children under 6 (any dmfs in under-6; severe ECC patterns)—link to pediatric chapter |
Case: A 5-year-old with decayed primary molars and filled incisors contributes to dmft, not adult DMFT.
Other dental indices (recognition level)
| Index / measure | What it captures |
|---|---|
| ICDAS | Clinical caries severity codes from sound to extensive cavitation |
| ICDAS/ICCMS | Links detection to management decisions |
| Plaque index / oral hygiene indices | Biofilm load for perio/caries risk teaching |
| Gingival index / bleeding on probing % | Gingival inflammation burden |
| CPITN / basic periodontal examination concepts | Periodontal treatment need screening (perio chapters detail staging/grading) |
| Dean’s fluorosis index | Population fluorosis severity scoring |
| OHIP / quality-of-life scales | Subjective oral health impact |
Worked DMFT mini-example
Adult examined (third molars excluded):
- 2 decayed teeth
- 1 tooth extracted due to caries
- 4 filled teeth
- Remaining teeth sound
DMFT = 2 + 1 + 4 = 7.
If those 2 decayed teeth involve 3 surfaces total, filled surfaces and missing tooth surfaces follow survey rules for DMFS—you do not need to invent a full scoring sheet on AFK, but you must know tooth vs surface granularity.
Public Health Dentistry Principles
Levels of prevention (classic framework)
| Level | Goal | Dental examples |
|---|---|---|
| Primary | Prevent disease before it occurs | Water fluoridation, toothpaste F, sealants on sound fissures, diet education, tobacco cessation counseling |
| Secondary | Detect early and intervene to halt progression | Screening exams, bitewings when indicated, varnish on white spots, early restorations/SDF arrest |
| Tertiary | Reduce impact of established disease, restore function | Crowns, dentures, implants, perio surgery, rehab after cancer surgery |
AFK often rewards primary prevention answers when the stem is population-level (fluoridation, school sealant programs).
Population strategies vs high-risk strategies
| Strategy | Idea | Strengths | Limits |
|---|---|---|---|
| Population (universal) | Shift risk for everyone (e.g., water F) | Equity, no targeting error, passive | Political acceptance; doesn’t eliminate all disease |
| High-risk (targeted) | Intense resources to those at greatest risk | Efficient use of clinical time | Screening imperfect; misses some cases; may widen access gaps if only clinic-based |
| Combined | Universal foundation + targeted intensification | Best practice conceptually | Needs data systems and workforce |
Major public health levers in oral health
| Lever | Notes for AFK |
|---|---|
| Community water fluoridation | Cost-effective population primary prevention (~0.7 ppm Canada teaching) |
| School-based sealant programs | Target permanent molars soon after eruption; reduce disparities |
| Fluoride varnish programs | Preschool/medical–dental integration for ECC |
| Tobacco and sugar policy | Upstream determinants; counseling still chairside duty |
| Access & insurance equity | Disease concentrates where care is least available |
| Infection control standards | Protects patients and workforce (next chapter cluster) |
| Surveillance | National/provincial surveys of DMFT, edentulism, access barriers |
Social determinants and disparities
Caries and periodontitis are not randomly distributed:
| Factor | Direction of association (typical) |
|---|---|
| Low income / food insecurity | Higher untreated caries, extractions |
| Lower education / health literacy | Delayed care, poorer prevention uptake |
| Indigenous and remote communities | Documented access and outcome gaps in Canadian discourse—know that disparity exists and needs culturally safe, system-level responses |
| Disability / special healthcare needs | Higher disease, more GA reliance, access barriers |
| Immigrant/newcomer transitions | Variable prior care systems; AFK candidates themselves often navigate this |
| Ageing / long-term care | Root caries, dry mouth, dependency for hygiene |
Ethical link: public health data justify advocacy and equitable practice—not stereotyping individual patients.
Screening and Survey Concepts (Bridge to Biostats)
Public programs use screening (e.g., school visual exams) that must balance:
- Sensitivity vs specificity (detailed in 22.3)
- Referral capacity (screening without treatment pathways wastes trust)
- Acceptability and consent
Lead-time and length-time bias concepts appear when early detection looks better than it is—more fully in study-design bias teaching (22.3).
Using Indices in Clinical Communication
Even outside pure public health roles, indices help:
- Baseline burden: “Your DMFT is high because of past disease; today we focus on stopping new D.”
- Outcomes: reduction in new DMFS increments after prevention program.
- Quality improvement: clinic rates of sealant placement in eligible molars.
- Research literacy: reading papers that report mean DMFT ± SD.
Common AFK traps
- Calling a snapshot survey “incidence”
- Including ortho extractions as M in DMFT without cause rules
- Using DMFT for primary teeth instead of dmft
- Claiming fluoridation is tertiary prevention
- Assuming mean DMFT = 0 means prevention programs are unnecessary forever
- Confusing toothpaste ppm with water ppm
Rapid review list
- Prevalence = existing cases; incidence = new cases
- DMFT = D + M + F permanent teeth (caries-related M/F)
- dmft = primary dentition analogue
- DMFS/dmfs = surface sensitivity
- Primary prevention: fluoridation, sealants on sound teeth, hygiene/diet population programs
- High D vs high F tells different access/treatment stories
- Disparities track social determinants—public health responds at system level
- Combine universal and high-risk strategies
Section 22.3 turns measurement into evidence appraisal: study designs, diagnostic test metrics, levels of evidence, and bias—so you can answer “which study best supports this claim?” on the AFK.
In a provincial survey, 25% of 12-year-olds examined on a single day have at least one untreated carious permanent tooth. This 25% figure is best described as:
An adult has 3 decayed permanent teeth, 2 teeth missing due to caries, and 5 filled teeth (third molars excluded). The DMFT score is:
Which intervention is the clearest example of primary prevention at the population level?
The dmft index is used to measure caries experience in: