Xylitol's five carbon atoms vs. Sugar
The Chemical profile of Xylitol
Excerpt from Professor Kauko K. Makinen
Xylitol is a natural sugar alcohol of the pentitol type, i.e. the xylitol molecule contains five carbon atoms and five hydroxyl groups (Fig. 1). Therefore, xylitol can be called a pentitol. Xylitol belongs to the polyalcohols (polyols) which are not, strictly speaking, "sugars" which traditionally include certain nutritive carbohydrate sweeteners (sucrose, corn sugar, corn syrup, invert sugar, D-fructose, D-glucose, etc.; in some reports the term "sugars" is collectively used to refer to mono- and disaccharides). However, the legitimacy for including polyols in the sugar field results from biochemical relationships; polyols are formed from, and can be converted to, sugars (i.e. aldoses and ketoses). Some chemical encyclopedias define sugars as crystalline, sweet carbohydrates. The sugar alcohols thus fall in this category.
To fully understand the dental effects of xylitol, it is important to refer to the structural differences between various dietary polyols (3). Sorbitol is another sugar alcohol, a hexitol type of polyol, owing to its 6-carbon structure. Because of this, sorbitol can support the growth of cariogenic mutans streptococci and other oral bacteria which are not normally able to utilize xylitol for growth. Because of evolutionary expediency, cariogenic organisms prefer 6-carbon ("hexose-based") structures, such as D-glocose, as an energy source. Therefore, it is important to akcnowledge the inevitable biochemical differences between xylitol (a pentitol and pentose-derived) and sorbitol (a hexitol and hexose-derived), and to understand the nomenclature-related definitions described above.
In spite of the existence of some differences between the various sugar alcohols, xylitol and most other polyols also display dentally interesting common properties: they can form certain type of complexes with calcium and certain other polyvalent cations. Such Ca-xylitol complexes can be present, for example, in the oral cavity and in the intestines. In the former, such complexes may contribute to the remineralization of demineralized enamel and dentine caries lesions observed in subjects who habitually consume xylitol. In the intestines, those complexes can facilitate the absorption of calcium through the gut wall; this effect has been suggested to play a role in the xylitol-associated prevention of osteoporosis in experimental animals (4). From the dental point of view, the role of xylitol (and certain other polyols) as stabilizers of the salivary calcium and phosphate ions may be important. It is possible that xylitol stabilizes the calcium phosphate system present in saliva in the same manner some salivary peptides (such as statherin) do (5).
