Chapter 2: Saliva — The Unsung Hero

In which we discover that the clear fluid you've been swallowing your whole life is actually a supersaturated mineral repair solution with built-in buffering, antimicrobial peptides, and a sophisticated protein system for managing crystal growth

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Let me tell you about the most underappreciated fluid in your body.

You produce about a liter of it every day.¹ You barely notice it unless something goes wrong. You probably think of it primarily as "spit"—something that helps you swallow food, something that you try not to let escape when you're talking, something that occasionally pools embarrassingly on your pillow at night.

But saliva is extraordinary. And if you understood what it's actually doing every moment of every day, you would treat your salivary glands with the reverence they deserve.

The Composition of Saliva

Let's start with what's actually in this fluid. Saliva is approximately 99% water,² which might make you think it's not particularly special. The magic is in the other 1%.

Component	Typical Concentration	What It Does
Calcium (Ca²⁺)	1-2 mM	Remineralization substrate
Phosphate (PO₄³⁻)	3-6 mM	Remineralization substrate
Bicarbonate (HCO₃⁻)	5-25 mM (stimulated)	Acid neutralization, pH buffering
Sodium (Na⁺)	2-21 mM	Electrolyte balance
Chloride (Cl⁻)	10-40 mM	Activates salivary amylase
Potassium (K⁺)	10-36 mM	Electrolyte balance
Fluoride (F⁻)	0.01-0.05 ppm	Enhances remineralization
Mucins	Variable	Lubrication, protection
Amylase	0.1-0.5 mg/mL	Starts starch digestion
Lysozyme	10-20 μg/mL	Antimicrobial (breaks bacterial cell walls)
Lactoferrin	1-10 μg/mL	Antimicrobial (sequesters iron)
Histatins	10-30 μg/mL	Antifungal, wound healing
Secretory IgA	15-30 mg/dL	Immune protection
Statherin	10-100 μg/mL	Controls mineral precipitation
Proline-rich proteins	Variable	Pellicle formation, mineral management

Look at that list. Really look at it.

You have calcium and phosphate—the raw materials for rebuilding enamel. You have bicarbonate—nature's acid neutralizer. You have antimicrobial proteins that defend against infection. You have immune components. You have specialized proteins that manage how and where minerals precipitate.

This isn't just water with some stuff dissolved in it. This is a carefully formulated repair and protection fluid that evolution spent hundreds of millions of years optimizing.

The Supersaturation Secret

Remember from the last chapter that enamel health depends on the saturation state of surrounding fluids? Here's the remarkable thing about saliva:

Healthy saliva is supersaturated with respect to hydroxyapatite.

At neutral pH, typical saliva contains more dissolved calcium and phosphate than the equilibrium with hydroxyapatite would predict. This means saliva is constantly "trying" to deposit minerals onto any available surface. The thermodynamic drive is toward remineralization, all the time.

This is not an accident. Your body deliberately maintains saliva in this supersaturated state precisely because it protects your teeth. Every moment that saliva is in contact with enamel at reasonable pH, it's pushing minerals back into the crystal structure.

Think about what this means: you have a built-in repair system that operates automatically, continuously, without any conscious effort on your part. While you're sleeping, while you're working, while you're doing anything at all—saliva is bathing your teeth in a mineral-rich solution that promotes remineralization.

The system fails only when something disrupts it: acid that drops the pH below critical levels, conditions that reduce saliva flow, or behaviors that don't give the repair process enough time to work.

The Buffering System

Saliva doesn't just provide minerals. It also fights to maintain the pH that makes remineralization possible.

The primary buffering system in saliva is the bicarbonate buffer, which operates through these equilibria:

H⁺ + HCO₃⁻ ⇌ H₂CO₃ ⇌ CO₂ + H₂O

When acid enters your mouth, the hydrogen ions react with bicarbonate. This produces carbonic acid, which quickly breaks down into carbon dioxide and water. The carbon dioxide escapes (you might notice a slight fizzy sensation when saliva encounters strong acid), effectively removing acid from the system.

The beauty of this buffer is that it's self-replenishing. Your salivary glands continuously secrete bicarbonate, especially when saliva flow is stimulated by eating or chewing. The more you chew, the more buffer you produce, the faster you neutralize acid.

This is why chewing—almost anything—after a meal helps protect your teeth. Sugar-free gum is ideal (especially if it contains xylitol, which we'll discuss later), but even chewing food thoroughly produces the same buffering benefit. You're not just mechanically cleaning; you're activating your chemical defense system.

Unstimulated saliva (the small amount you produce between meals) has lower bicarbonate content and lower buffering capacity. This is part of why overnight—when saliva flow drops dramatically—your mouth becomes more vulnerable. The attack phase continues (bacteria keep producing acid), but the defense is diminished.

Statherin and the Precipitation Problem

Here's a puzzle that must have troubled evolution for some time: if saliva is supersaturated with calcium and phosphate, why doesn't mineral just precipitate everywhere? Why doesn't your whole mouth gradually coat itself in calcium phosphite scale, like the inside of a hard-water kettle?

The answer involves some elegant protein chemistry.

Statherin is a small protein (only 43 amino acids)³ that plays a crucial role in managing mineral behavior in saliva. It contains a cluster of negatively charged amino acids at one end that bind powerfully to calcium ions and to hydroxyapatite surfaces.

In bulk saliva, statherin binds to calcium ions and prevents them from spontaneously precipitating with phosphate. It keeps the supersaturated solution stable, in what chemists call a metastable state—supersaturated but not actively crystallizing.

But when statherin encounters a tooth surface, something different happens. It binds to the enamel, becoming part of a thin protein layer called the acquired pellicle. And from this position, it seems to actually promote controlled mineral deposition into the underlying enamel.

In other words, statherin prevents random mineralization in bulk saliva while facilitating targeted remineralization at tooth surfaces. It's a precision guidance system for mineral delivery.

The proline-rich proteins (PRPs) work similarly. They inhibit calcium phosphate precipitation in solution, but when adsorbed onto enamel surfaces, they help template the orderly growth of new hydroxyapatite crystals.

This is sophisticated stuff. Your body isn't just dumping minerals into your mouth and hoping for the best. It's running a carefully controlled delivery system that prevents unwanted precipitation while optimizing repair at exactly the right locations.

When Saliva Fails: Xerostomia

Understanding how much saliva does for you makes it easier to understand what happens when you don't have enough.

Xerostomia—dry mouth—is one of the most damaging conditions for oral health. It can result from:

• Medications: Hundreds of common drugs reduce saliva production as a side effect.⁴ Antidepressants, antihistamines, blood pressure medications, diuretics, and many others all can cause dry mouth.

• Medical conditions: Sjögren's syndrome⁵ (an autoimmune condition that attacks salivary glands), diabetes, and various other conditions can impair saliva production.

• Radiation therapy: Cancer treatment targeting the head and neck can permanently damage salivary glands.

• Aging: Saliva production tends to decrease with age, though severe xerostomia usually involves additional factors.

• Dehydration: Even mild chronic dehydration can reduce saliva volume and alter its composition.

• Mouth breathing: Sleeping with your mouth open dramatically increases evaporation and reduces the protective effect of saliva.

Without adequate saliva, every protective mechanism we've discussed is compromised:

• Less mineral is available for remineralization
• Acid clearance is slower
• Buffering capacity is reduced
• Antimicrobial protection diminishes
• Food debris isn't washed away effectively

People with xerostomia can develop rampant cavities in months—decay spreading faster than would seem possible under normal conditions. I've watched it happen, and it's devastating. Teeth that survived decades of normal use crumble when the protective fluid disappears.

If you experience chronic dry mouth, this isn't a minor inconvenience to ignore. It's a dental emergency in slow motion. Talk to your doctor about whether medication adjustments are possible. Use saliva substitutes. Stay aggressively hydrated. Consider prescription products that stimulate saliva production. And be meticulous about every other protective strategy in this book, because you need them more than most.

Stimulating Saliva: Practical Strategies

Even without medical xerostomia, most people could benefit from more saliva flow, especially after meals when remineralization matters most.

Chewing gum is the most practical approach. The mechanical act of chewing stimulates saliva production dramatically—increasing flow rate from around 0.3 mL/min to 2-3 mL/min or more.⁶ Choose sugar-free varieties to avoid feeding acid-producing bacteria.

Xylitol-sweetened gum is particularly valuable. Xylitol is a sugar alcohol that S. mutans cannot metabolize effectively.⁷ The bacteria take it up, attempt to ferment it, waste energy, and produce no acid. Meanwhile, the xylitol triggers saliva flow just as effectively as real sugar would. It's a double benefit.

Sour flavors also stimulate saliva powerfully—think of how your mouth waters when you taste something tart. The irony is that sour usually means acidic, so while a lemon drop would stimulate saliva, it would also deliver an acid challenge. Sugar-free sour candies can provide the stimulation without the sugar problem, but you're still dealing with the acid.

Adequate hydration matters more than people realize. Saliva is 99% water; if you're not drinking enough, your body will prioritize other uses of water over saliva production. There's no magic number for water intake, but if your urine is consistently dark or you feel thirsty often, you're probably not drinking enough.

Humidity in your sleeping environment helps if you tend to breathe through your mouth at night. Dry air accelerates evaporation of the limited saliva you produce during sleep.

The Nighttime Vulnerability

I've already mentioned this, but it deserves emphasis: nighttime is when your teeth are most vulnerable.

During sleep:

• Saliva production drops by 80-90%⁸
• Bicarbonate concentration decreases
• Swallowing frequency drops, so what saliva is produced pools rather than circulating
• Any bacteria present continue metabolizing available nutrients and producing acid

This is why what you do—or don't do—before bed matters so much. The last thing your teeth are exposed to before sleep will sit with them for hours, with minimal saliva to dilute, buffer, or rinse it away.

Eating or drinking anything acidic or sugary late at night is particularly damaging. You're introducing a challenge at the exact moment when your defenses are about to shut down for the night.

Conversely, what you put on your teeth right before bed has extended contact time. This is why fluoride toothpaste is most effective when used before sleep—the fluoride has hours to integrate into enamel surfaces without being washed away by drinking or eating.

The old advice about brushing before bed isn't arbitrary tradition. It's based on understanding this rhythm of protection and vulnerability.

What Saliva Teaches Us

The existence of saliva—this elaborate, precisely formulated, supersaturated mineral solution with built-in buffering and protein-guided delivery—tells us something profound about how evolution solved the problem of maintaining teeth.

Evolution didn't design teeth to be perfectly acid-resistant. It didn't make enamel out of diamond or ceramic or some impervious material. Instead, it built a repair system. It accepted that damage would happen and created a mechanism for continuous healing.

This is important because it changes how we should think about oral health. We're not trying to prevent all damage—that's impossible. We're trying to ensure that repair exceeds damage over time. We're managing a dynamic equilibrium, not defending a static fortress.

The strategies that work with this system are different from the ones you might choose if you thought you were defending a fortress. Fortress thinking leads to antiseptics and barriers and scorched-earth approaches. Equilibrium thinking leads to supporting natural repair processes, maintaining optimal pH, ensuring adequate mineral supply, and giving the system time to do what it does.

Your teeth want to heal. Saliva is the evidence. The question is whether you'll let them.

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Now let's meet the residents of your mouth—the hundreds of bacterial species that live there, and why understanding their ecology is more important than trying to kill them all.

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1. Humphrey, S. P., & Williamson, R. T. (2001). A review of saliva: normal composition, flow, and function. Journal of Prosthetic Dentistry, 85(2), 162-169. Adults produce approximately 0.5-1.5 liters of saliva per day. ↩

2. Saliva — Wikipedia. Saliva is approximately 99% water, with the remaining 1% consisting of electrolytes, mucus, antibacterial compounds, and enzymes. ↩

3. Raj, P. A., Johnsson, M., Levine, M. J., & Nancollas, G. H. (1992). Salivary statherin: dependence on sequence, charge, hydrogen bonding potency, and helical conformation for adsorption to hydroxyapatite and inhibition of mineralization. Journal of Biological Chemistry, 267(9), 5968-5976. ↩

4. Xerostomia — Wikipedia. Over 400 medications list dry mouth as a potential side effect. ↩

5. Sjögren's syndrome — Wikipedia. An autoimmune disease characterized by dry eyes and dry mouth due to lymphocytic infiltration of the lacrimal and salivary glands. ↩

6. Dawes, C. (1987). Physiological factors affecting salivary flow rate, oral sugar clearance, and the sensation of dry mouth in man. Journal of Dental Research, 66(Spec Iss), 648-653. Stimulated saliva flow can increase 10-fold compared to resting flow. ↩

7. Mäkinen, K. K. (2010). Sugar alcohols, caries incidence, and remineralization of caries lesions: a literature review. International Journal of Dentistry, 2010, 981072. Xylitol inhibits the growth of S. mutans by disrupting its energy production processes. ↩

8. Dawes, C. (1972). Circadian rhythms in human salivary flow rate and composition. Journal of Physiology, 220(3), 529-545. Salivary flow rate drops to near zero during sleep. ↩