31  What I actually do, and why

Thirty chapters of finding that the evidence is thinner than the label suggests raises an obvious question, and I would rather answer it than leave it hanging.

I brush twice a day. I brush last thing at night. I spit and I do not rinse. I have done all three since 2017, which is to say I did not stop when I found out what was behind them.

That is either hypocrisy or it is the point of the book, and this chapter argues it is the second.

The mistake this book could cause

Start with the failure mode, because it is real and I have watched it happen to other people’s work.

You establish that a recommendation rests on weaker evidence than its label claims. A reader concludes the recommendation is worthless. They stop doing it. Their teeth are worse. Nothing about the evidence changed; only their behavior did, and it changed in the wrong direction.

That inference is invalid, and the invalidity has a name. Evidence about the strength of a claim is not evidence about the truth of the claim. Finding that no search has turned up a test of whether brushing at bedtime beats brushing at nine o’clock tells you nothing about whether it does. It tells you that we do not know.

Under genuine uncertainty, you still have to do something this evening. The question is not “what has been proven” but “what should I do given what we know and do not know”, and those come apart constantly.

How I actually decide

Four questions, in this order. They are not sophisticated and that is deliberate: they are what is left when the evidence does not settle the matter.

1. What does it cost me? Brushing at bedtime rather than an hour earlier costs nothing. I was going to brush anyway; only the timing changed. When the cost is zero, even a small or uncertain benefit is worth having, because you cannot lose.

2. What happens if I am wrong? If bedtime brushing turns out not to matter, I have lost nothing. If it turns out to matter and I skipped it, I have lost something irreversible: enamel does not grow back and a filled tooth is filled forever. The asymmetry does most of the work in dentistry, where the errors run one way.

3. Is the mechanism coherent? Salivary flow falls during sleep, so fluoride left on the teeth persists longer and acid is buffered less. That is not proof, and Chapter 15 points out that three different recommendations lean on this one untested fact and thereby look better corroborated than they are. But a coherent mechanism plus weak evidence is a better position than weak evidence alone.

4. Would I regret this in twenty years? The honest form of the question. I would not regret two minutes a night. I would regret a mouthful of restorations.

Run those four over the book’s contents and the answers come out cleanly. Fluoride toothpaste: strong evidence, zero cost, obvious. Brushing at bedtime: no direct comparison found, zero cost, coherent mechanism, asymmetric downside. Do it. Charcoal toothpaste: no appraisal run here, real cost, abrasivity a concern, and many formulations carry no fluoride. Do not.

Where I changed my behavior

Writing this book did change some things, which is worth reporting because it would be suspicious if it had changed none.

I stopped having routine six-monthly check-ups. Chapter 28 found high-certainty evidence that for adults who attend regularly, risk-based intervals produce no measurable difference over four years in decay, gum bleeding or oral-health-related quality of life. The trial’s population was regular attenders, not a healthy-mouth subgroup, and its moderate-to-extensive caries outcome is rated moderate rather than high. I go when my dentist thinks I should, which is less often.

I stopped assuming a scale and polish was doing anything. Chapter 19 is the other high-certainty finding of little or no difference, for gingivitis, probing depths and quality of life over two to three years. My teeth feel cleaner afterwards, which the trials also measured, and I now understand that as the thing I am paying for.

Those two are the book’s high-certainty findings of no important difference. They are not the only high-certainty evidence in it: Chapter 8 reports high certainty that fluoride toothpaste at 1,000 to 1,250ppm reduces caries against no fluoride, from 55 trials. That one did not change my behavior because I was already doing it.

I switched from floss to interdental brushes. Chapter 17 found low-certainty evidence of a gingivitis advantage whose clinical importance is uncertain, which is why DBOH puts interdental brushes first and keeps the recommendation Conditional. I had been doing the traditional thing out of habit.

I stopped telling patients the two-minute rule was evidence-based. Chapter 18 found no studies relating brushing duration to caries, and found that DBOH’s graded summary tables do not carry a duration recommendation, while its chapter 8 advises at least two minutes as a way of making sure every surface is covered. That is also how I now describe it: a rule of thumb for coverage, which is what the guideline says it is.

Four changes, and every one of them was in the direction of doing less, not of abandoning prevention. That pattern is not accidental. Weak evidence for a free intervention is a reason to carry on. Strong evidence of no benefit for a procedure someone charges you for is a different matter entirely.

The one thing I would tell you to do

If everything in this book fell out of your head except one sentence, make it this: use fluoride toothpaste, twice a day, and spit rather than rinse.

The fluoride is the part with 55 randomized trials behind it (Chapter 8). The frequency is convention with observational support (Chapter 5). The spitting has one randomized trial of a bundle (Chapter 7). They are not equally well supported and I have spent the book saying so. But they cost nothing, they combine into a single routine of about two minutes, and the first of the three is as close to established fact as dentistry gets.

For caries specifically, much of the rest of the shelf is refinement around that. It is worth saying that caries is only one of the four disease domains the guideline covers: periodontal disease, oral cancer and tooth wear each have their own recommendations and their own evidence, and nothing in that sentence is a summary of them.

What I am not doing

I am not taking a position on whether your water should be fluoridated. Chapter 24 and Chapter 25 set out what the evidence shows and where it runs out, and the decision involves weighing a small uncertain benefit against a common cosmetic harm and an unresolved question. That is a values judgment and it is not mine to make for you.

I am not telling you to distrust your dentist. Almost everything in this book concerns the gap between how confident guidance sounds and how confident the evidence warrants. That gap is a drafting problem and a communication problem. It is not evidence that the profession is wrong about the big things, and on the big things, fluoride, sugar, tobacco, it is emphatically right.

And I am not claiming my four questions are a method. They are what one person does when the evidence stops. If you have better ones, use those.