Dentistry questions & answers

Which criteria should one look at when purchasing an electric toothbrush?

From the medical perspective, the main outcome of using an electric toothbrush is if is capable to avoid, control or reduce two main dental diseases: periodontal and/or caries.
Such kind of trials are costly in time and resources, hence manufacturers and researchers use some surrogate outcomes as dental plaque reduction for caries/periodontal and gingivitis reduction for periodontal disease.
From the mode of action, powered toothbrushes can be classified as follow (source) :
  1. Side to side action, indicates a brush head action that moves laterally from side to side.
  2. Counter oscillation, indicates a brush action in which adjacent tufts of bristles (usually six to 10 in number) rotate in one direction and then the other, independently. Each tuft rotating in the opposite direction to that adjacent to it.
  3. Rotation oscillation, indicates a brush action in which the brush head rotates in one direction and then the other.
  4. Circular, indicates a brush action in which the brush head rotates in one direction.
  5. Ultrasonic, indicates a brush action where the bristles vibrate at ultrasonic frequencies (> 20 kHz).
  6. Ionic, indicates a brush that aims to impart an electrical charge to the tooth surface with the intent of disrupting the attachment of dental plaque.
  7. Unknown, indicates a brush action that the review authors have been unable to establish based on the trial report or confirm with the manufacturers.
The main result of a Cochrane Systematic review was:
An 11% reduction in plaque was shown at one to three months for the Quigley Hein (Turesky) index and a 21% reduction in plaque at longer than three months. The longer term result was based only on 14 trials, compared to 40 trials for the short-term analysis. With regard togingivitis a 6% reduction was seen at one to three months for the Löe Silness index, based on 44 trials, and a greater reduction of 11% in the long term (16 trials).
When looking at individual modes of action of powered brushes there are inconsistencies with regard to reductions of plaque and gingivitis. Rotation oscillation brushes showed statistically significant reductions in both plaque and gingivitis at both time points. All other brushes, apart from side to side, showed some statistically significant findings but not consistently across both outcomes and time points. It is difficult to explain this inconsistency that a particular toothbrush design could affect plaque or gingivitis at one time but not at another and so the findings of these analyses may warrant further research, particularly given the small number of trials for some modes of action.
So, currently, there is some evidence of effectiveness for rotation oscillation powered toothbrushes. You can see some examples of studied toothbrushes in the cited study.

Ways to reverse a cavity before it goes rotten?

There are many ways to prevent a early caries to get cavitated:
Anyway, if the lesion is black, most probably the carious lesion is inactive, hence no treatment is required.

What does fluoride toothpaste do to the dentin on the teeth?

This is usually seen in clinical settings: a child is left with an untreated enamel caries. Then the lesion progress and the lesion is cavitated. The dentin then start to react, ocludding the dentinal tubules. When the saliva (+ minerals) reach the dentin, the caries process start to slow down and the dentin change from dark brown to almost black. At the same time, the change in color represents a change in the surface composition, changing from a soft surface to a hard one.
This occurs with the minerals of the saliva. If you add fluoride, you will enhance this process. Hence, the fluoride of the toothpaste will slow down the caries process in the dentin.
About you side question: often. Keep in mind that any radicular surface clinically visible means exposed dentin. Google "radicular caries" images.
If you want to read the details, ten Cate has several (now classics) papers:
  • ten Cate JM. Remineralization of caries lesions extending into dentin. J Dent Res. 2001 May;80(5):1407-11.
  • Deng DM, van Loveren C, ten Cate JM. Caries-preventive agents induce remineralization of dentin in a biofilm model. Caries Res. 2005 May-Jun;39(3):216-23.
Bonus 1: nobody knows why the carious dentin is brown...
Bonus 2: a black spot in a teeth means a dentinal stopped carious lesion.

Getting rid of white spots on front teeth

Currently, there are three options to deal with white spots in frontal teeth after orthodontic treatment:
  1. remineralization,
  2. micro-abrasion, and
  3. resin infiltration.
There are several case report about micro-abrasion and resin infiltration, and some clinical trials about all, but a recent systematic review found the evidence of effectiveness was rated as low, that means that the results are inconsistent or there is a high risk of bias, i.e. the manufacturers of the products published the results.
The three options are different: Remineralization uses fluoride aiming to add something to the surfaces layer of the tooth. There are some clinical trials showing positive results ( and others showing no effect ( But the advantge of a non invasive therapy is that there is no loss of enamel surface, hence there is no irreversible alteration to the tooth surface.
Microabrasion on the other hand smooth irreversibly the surface of the eroded enamel with an acid.
Finally, infiltration, also irreversibly treatment, use an acid to remove a small layer of the eroded enamel and then add a resin layer. From the esthetic point of view this solve the issue immediately, but the lack of prospective studies add an interrogation mark to the long term results.
Hence, from all the three options, currently the remineralization is the only that is non-invasive.

Is dental floss really effective? According to studies, it is not

Recently I had to go through a lot of ultrasound teeth cleaning because my gums suffered inflammations in the past. I am doing the dental cleaning every 3 to 4 months and every time the dentist says that the gum is getting better and better because I am flossing thoroughly. Before the inflammation, I never flossed so this is kind of a novel procedure for me.
So I empirically assumed that flossing is really the thing that helps to heal, as also acknowledged by the dentist.
The thing is... there are actually no studies to prove this statement. I have looked for articles and I found for instance this and this and this. I understand from the articles that there is not sufficient proof to endorse the procedure. Despite this, the dentists still recommend flossing.


Is dental floss really effective? The evidence shows that we don't know. Here the main issue is the lack of good evidence.
How we find how effective is? Simple: we took a group of people with similar age, similar dental status, and divide randomly to one group who will use floss and other who don't. Then, we wait for one, two or five years and compare caries and periodontal disease.
This is the theory.
In practice, there is no experimental trials like this. All that we have are observational studiestracking the oral health of people who floss and people who don't. Hence, sometimes we see that people who floss have better oral health that people who dont and sometimes the contrary. For example, if we ask @jess, we will record the he floss AND he have periodontal issues.
The main issue with observational evidence is that, maybe, for some reason, the people who floss is essentially different from the people who don't. For example maybe the people who floss eat more vegetables and that is the reason why they have better oral health. Or, on the contrary, maybe the people who floss have more periodontal problems, and in such case we will find the opposite, that floss is correlated with periodontal disease.
Is hard to extract conclusions from observational evidence and that is the conclusion of most systematic reviews: we don't have evidence that indicate that floss is effective. But also we don't have evidence showing that floss is ineffective.
Hence, is wise to ask your dentist for your personal condition, taking in consideration all your particular characteristics and follow her/his advice.
TL;dr: The scientific research does not show that flossing is effective against tooth decay or gum disease. But it doesn’t show it’s not.
More info:

Are there any risks about switching to a non-fluoride toothpaste?

If all the rest is the same, your risk of caries would increase by 25% Source: Cochrane Syst Review.
Also, you will expend more money, since non fluoridated toothpastes are usually more expensive than regular fluoridated toothpaste. (list&prices NFT)
If you definitively has decided to not use fluoridated toothpaste, would be better to not to use any toothpaste at all (to keep your money) and reduce the consumption of sugar to less than 5% of your daily calories. WHO
There is no clinical evidence of any benefit about the use of non-fluoridated toothpaste and those toothpaste are usually used as negative controls, as seen in this research

Is it beneficial to keep using fluorised toothpaste after prolonged use?

As far as I understand, fluoride helps in hardening the enamel of our teeth by replacing the calcium element in hydroxyapatite to convert it in the stronger fluorapatite, like explained here. Wether that's worth other potential risks of using fluor is debatable, but let's keep that aside. I'm curious if it is still beneficial to keep using fluorised toothpaste if you already did so for like 10 years. I suppose all hydroxyapatite is long converted into fluorapatite already after so much brushing. Why would it still be recommendable to keep using it?


The main protective effect of fluoride is outside the tooth, not inside.
Small amounts of fluoride in solution around the tooth inhibit demineralization more effectively than incorporated fluoride and have a much greater caries-protective potential than a large proportion of fluorapatite in enamel mineral. Schweiz Monatsschr Zahnmed 122: 1030–1036 (2012)
For example, even an incredible amount of fluoride has limited protective effect. In a classic study, Ogaard compared the resistance of fluoroapatite (shark enamel) and hydroxyapatite (human enamel) against a high caries challenge in a human in vivo model. Two samples of shark enamel and human enamel were each placed in removable appliances in six children and carried for 1 month and a plaque retentive device was placed over each enamel sample. The results showed that the mean total mineral loss (delta Z) was 1680 vol% micron in human enamel and 965 vol% micron in shark enamel. The corresponding mean values for lesion depth were 90 micron and 36 micron, respectively. It was concluded that even shark enamel containing 30,000 ppm F has a limited resistance against caries attacks.
In a later review, the same author concludes that
The fluoride concentration in the apatitic structure of enamel does not have as significant an effect on reducing caries as a continuous presence of fluoride in the plaque liquid.
Hence, to receive the protective effect of the fluoride, we require to keep it near the tooth surface all time.

Does calculus also prevent caries?

Yes, the presence of calculus prevent the demineralization of the surface of the tooth. This is a common finding during routine scaling or calculus removal, where usually the underlying enamel is intact.
Also, there is a paper about this issue: Evidence for putting the calculus: caries inverse relationship to work who found
caries prevalence is highly significantly lower in calculus-prone than in calculus-free subjects
You can found the detailed explanation on the Fejerskov's Textbook of Dental Caries, and this graph summarize the principal ideal: if you have calculus means that the intraoral enviroment is saturated with minerals and with pH levels above 5.0, hence demineralization of enamel is very difficult if not not feasible at all.
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Is there any definitive prevention for tooth decay?

I understand (in a too simplified way) that the main cause of tooth decay is the mineral breakdown of the tooth enamel by the action of acids formed from food debris on the mouth.
If that's correct, wouldn't be a definitive solution for tooth decay coating the tooth with a fine layer of some anti-adherent/non-stick element like Polytetrafluoroethylene on a long-term regular basis?


Part of the answer is in your question:
acids formed from food debris on the mouth
the key here is debris. In the caries case, that means fermentable sugars. Hence, if you want to avoid caries, avoid the consumption of extrinsic (added) sugar.
Considering that this is almost impossible nowadays, the most effective and evidence-based preventive therapies for dental decay so far are
  1. fluoride for smooth surfaces of the teeth,
  2. sealants for pit and fissures surfaces of the teeth,
  3. and restrict the consumption of extrinsic sugar to less tha 5% of total calories per day

centric occlusion vs maximum intercuspation

I have found it very confusing that in the dental and orthodontic literature, it is often stated that "centric occlusion" (CO) and "maximum intercuspation" (MIC) are synonyms (for example), despite the fact that there is tons of research on the discrepancy between CO and MIC (for example). How can CO and MIC be considered synonyms, and yet also be different (and in fact, the difference between them is of interest to dentists?).
Further adding to my confusion, according to Wikipedia, MIC "used to be referred to as centric occlusion", but there isn't a reference to back up this specific claim.
Could someone 1) clarify appropriate terminology for me, and 2) provide a reference to support the correct terminology?


Centric occlusion is an articular position and maximum intercuspation is a dental position.
It suppose that, in a healthy person, both are the same, and that the problems with TMJ arises when there is a discrepancy.
Hence, for a rehabilitation of a total edentulous person, you should rehabilitate with MIC = CO.
Anyway, there is no evidence linking absence of CO in MIC with pathology.
References from the prosthodontics point of view and from orthodontics.

Which dental probiotics product is the most effective?

For caries there is not yet enough evidence of effectiveness. A recent systematic review of all available clinical trials concludes:
Probiotic therapy could be used for managing periodontal diseases. For caries, further studies should ascertain both efficacy and safety.

vigorous brushing a cause for dental issues or not?

A detrimental effect of toothbrushing can be influenced by
  1. use of an abrasive toothpaste
  2. use of hard bristles toothbrush
  3. use of excessive force during toothbrush
  4. excessive number of toothbrushing per day
  5. and any combination of the above
A recent review concludes:
The benefits of normal oral hygiene procedure exceed possible side effects by far, but excessive toothbrushing - especially of eroded teeth - might cause some harmful effects.
The usual reccomendation is to use regular fluoridated toothpaste with soft bristles toothbrush. To compensate the use of excessive force, the use of electric toothbrush could be reccomended (reference).

What happens if you use teeth-whitening strips too often?

Most whitening strips instruct the user to apply them only once every 6 months. What negative effects could occur if I used them once every 4 months instead?


There are no trials conducted in humans yet, but in vitro trials on bovine teeth has shown a decreased of the mechanical properties of the teeth.
The authors conclude:
Until the effect of whitening strips on mechanical properties of human dentin is fully elucidated, it remains prudent to advise patients to avoid excessive direct use of whitening strips on dentin.
Usually, a whitening strip is applied on the enamel surface, but part of the strip can contact the cervical area of the teeth, where dentin can be exposed. Hence is prudent to avoid excessive use of whitening strips.

How frequently should non-alcoholic mouthwashes be used?

You don't need at all to use any mouthwash. A healthy mouth is full of bacteria, almost all of them beneficial for our health, and
  1. There is no evidence so far of any long term preventive effect of any kind of mouthwash, only trials with transient effects (< one year) or 6 months in surrogate clinical endpoints as number of bacteria and gingivitis. The only one with some evidence are fluoridated-based mouthwashes, but you get the same effect if you don't spit after brushing with fluoridated toothpaste;
  2. If you still decide to use, the only risk is the staining and metallic taste from chlorhexidine-based mouthwashes. There is no evidence so far of risk of oral cancer associated with the use of essential oil–containing mouthrinses.
Instead, you may invest your money in cheese for your oral health.
Lastly, if you are interested in joining a study to increase our limited knowledge about mouthrinses for oral health, there are some trials recruiting.
So, in brief: daily use of fluoridated toothpaste without spitting after using it is enough if you already are eating enough fruits and vegetables and limiting the consumption of sugar.