🦷 Plaque Biofilm pH (Stephan Curve) Simulator

Resting Plaque pH — The Neutral Starting Point

Between meals, plaque fluid sits close to neutral pH.

• 6.7–7.2: Resting plaque pH (mouth at rest)
• 0.3–0.4: Unstimulated saliva flow (mL per minute)
• 10⁸/mg: Plaque bacteria density (biofilm dry weight)
• 5.5: Critical pH threshold (enamel dissolves below)

A biofilm in equilibrium

Resting plaque balances acid production with salivary buffering.

Saliva as the baseline buffer

Bicarbonate and phosphate hold plaque fluid near neutral.

Why the baseline matters

Every Stephan curve drop starts and ends near this resting value.

Sugar Intake Triggers Rapid Acid Production

Fermentable sugars feed bacteria that produce acid within minutes.

• <2 min: Acid onset delay (after sugar contact)
• Lactic acid: Dominant acid (from Streptococcus mutans)
• ~1 pH/min: Max drop rate (high-sugar exposure)
• Sucrose, glucose: Fastest triggers (readily fermentable sugars)

Glycolysis in the biofilm

Cariogenic bacteria ferment sugar into organic acids almost immediately.

Sugar type changes the curve

More fermentable sugar produces a steeper, deeper pH drop.

Frequency over quantity

Frequent small exposures matter more than one large one.

The pH Nadir — Plaque Acidity Peaks

Plaque pH plunges sharply below the critical threshold.

• 4.5–5.0: Typical nadir pH (high-sugar snack)
• 5–20 min: Time to nadir (after exposure)
• Sugar frequency: Nadir depth driver (not just total amount)
• Immediate: Recovery onset (once nadir is reached)

Curve shape defined by Stephan

Robert Stephan first plotted this rapid-drop, slow-recovery pattern in 1943.

Depth depends on the person

Buffering capacity and bacterial load shift the nadir up or down.

The turning point

Past the nadir, dilution and buffering start pulling pH back up.

Critical Zone — Enamel Demineralization Window

Below pH 5.5, enamel loses more mineral than it gains.

• pH 5.5: Demineralization threshold (hydroxyapatite dissolves)
• 20–40 min: Typical critical duration (per sugar exposure)
• >40 min/day: Daily critical minutes (raises caries risk)
• Calcium, phosphate: Ions lost from enamel (dissolved into plaque fluid)

Below the critical pH

Hydroxyapatite crystals dissolve faster than they reform.

Cumulative exposure adds up

Repeated critical windows across a day compound enamel loss.

A reversible window

Short critical periods can still be offset by later remineralization.

Recovery — Saliva Restores Baseline pH

Salivary buffering gradually lifts plaque pH back to normal.

• 30–60 min: Full recovery time (back to baseline pH)
• Bicarbonate, phosphate: Key buffering agents (delivered by saliva)
• Fluoride-assisted: Remineralization boost (reverses early lesions)
• Each bite resets curve: Snacking risk (exposures compound risk)

Buffering restores balance

Saliva neutralizes acid and clears sugars from the biofilm.

Remineralization follows

Calcium and phosphate redeposit into weakened enamel.

Why timing between snacks matters

Spacing exposures lets each Stephan curve fully recover.