The main villain is sugar. Dried fruit and fruit in syrup have a high amount of sugar. It is important to conduct a proper oral hygiene after consumption of such food.

Yes! All carbohydrates are potentially cariogenic although frequency is indeed more important than quantity. Many oral bacteria possess a transport system involving phosphoenolpyruvate. This system transports maltose and other disaccharides including sucrose into bacterial cells. Maltose is a major product of amylase in the oral cavity. The more often starch is ingested, the more often is maltose taken up and metabolized to lactate by oral bacteria, especially oral streptococci. Sucrose is also metabolized extracellularly by bacteria such as S mutans which possess a glycan transferase. The introduction to the attached paper by Pikis et al. gives a nice overview of the disaccharide transport system and also discusses the metabolism of disaccharides derived from sucrose.

In principle, any sugar has cariogenic potential, but whether a particular food is significantly cariogenic depends on it sugar content and frequency with which it is eaten. A large recent study [Vargas et al.: J Am Dent Ass 2014;145:1254-61] suggests that 100% fruit juice is not a risk factor for early childhood caries and this seems to agree with most of the literature. One study suggests that excecssive fruit intake is a risk factor [Arora and Evans: J Investig Clin Dent. 2012;3:17-22] which supports the importance of intake frequency. However, the odds ratio (1.5) was quite low even for high intake, so overall fruit  is probably not very cariogenic at usual levels of consumption. Fruits and fruit juices might be more important as risk factors for erosive tooth wear.

Fruits and fruit juices might be more important as risk factors for erosive tooth wear, because of the acid content?

Yes of course, but the consumption frequency, the amount of sugar content and the consistency of the fruit are much important factors.

I completely agree with explanation given by Robert Peter.

This is an interesting question and it has to be carefully analyzed. Indeed, fruits have a cariogenic potencial, once they have frutose. Nevertheless, it is important to take into account the importance of eating fruits, their consumption should be encouraged. The only proven health risk of nutritive

sweeteners at typical consumption levels is dental caries (also known as tooth decay). However, when compared to other nutritive sugars, fructose is among the least cariogenic.

I am going to give an example. I study erosive tooth wear, and I it is well known that acidic fruits such as lemon, orange, etc are potencial risk factors for erosion. Nevertheless, I will not advise my patients not to consume this fruits unless they present a tooth erosion. With regard to the association of fruits and dental caries, I am quite sure that I would never tell a patient not to eat fruits due to its possible cariogenic potential. If you think about the population eating habits, there are so many other risk factors other than fruits, that I would dare to say that eating fruits instead of other food stuff/ fastfoods is "protection factor".

Of course is the consumption of fruit carcinogenic. Already the Egyptians knew that Dates cause the teeth to rot, 3000 years ago.

For caries to occur, the pH of dental biofilm (Plaque) should become acidic  Fruits convert the pH of whole mouth  /saliva to acidic levels  which causes more erosions as Martin mentioned, than caries.

Most fruits contain high concentrations of citric acid as well as sugars. Citric acid has a pH of 2.2 and is a very strong chelator preferentially stripping calcium out of tooth structure. Citric acid is also a strong salivary stimulant causing increased stimulated flow rates. Normally stimulated saliva is rich in buffers  and the combination of increased flow rate and increased buffering capacity neutralises both plaque and mouth acids and physically helps flush out the mouth. Where salivary function is normal and oral hygiene good, normal fruit consumption should not cause problems as teeth have time to re-mineralise. However, erosion may result whenever there is excessive fruit consumption or drinking of beverages containing citric acid.  In patients with salivary gland hypo-function (SGH) saliva function is compromised. In SGH patients, citric acid may not cause any increase in stimulated saliva flow rates to buffer and neutralise mouth acids. SGH patients who ingest excessive  amounts of fruit  or fruit juice containing citric acid will cause progressive acidification of the mouth. All these effects are exacerbated in patients with SGH, poor oral hygiene and poor ability to chew hard foods, leading to increased decay rates and GIC washout as often found in the frail and elderly 

Very well explained. Thank you Alan for such a nice description.

We have been taught the an apple a day can keep the doctor away but not the dentist. It seems consumption of fruits ( apple) lead to lower the ph and can lead to demineralization.

 I do agree with explanation given by Alan Deutsch 

In addition to Deutsch´ explanation . Because of the complex nature of the interactions between dietary constituents and the teeth in the development of dental caries it is inappropriate to try to arrive at an absolute determination of whether or not consumption of a food will always give rise to the formation of cavities (Edgar WM. Prediction of the cariogenicity of various foods. Int Dent J. 1985 Sep;35(3):190-4.)

There is no evidence that sugars naturally incorporated in the cellular structure of foods (intrinsic sugars) or lactose in milk or milk products (milk sugars) have adverse effects on health. (Sheiham A. Dietary effects on dental diseases. Public Health Nutr. 2001 Apr;4(2B):569-91.)

It has been proven that fruits are cariogenic. There are many studies who have shown that fruits are cariogenic

Yes some fruits are cariogenic but if one rinse properly after eating fruit then the acidity is cleansed and there is no risk of carcinogenicity.

     All the fruits do not have the same amount of citric acid. Hence, they cannot be taken as a single entity. Citric fruits consumption like lemon, sour oranges etc needs to be regularised. Brushing immediately after fruit consumption should be avoided. 

  I do agree with explanation given by Alan Deutsch and José Francisco Gómez-Clavel.