Sir, I refer to the paper by Dr Lucy Wray, The diabetic patient and dental treatment: an update (BDJ 2011: 211: 209–215).

Whilst a paper on what is an increasingly prevalent disorder with oral implications is to be welcomed, it is unfortunate that the author has used the words 'sugar' and 'glucose' interchangeably throughout, implying that they refer to the same compound. Some of your readers must have found this very confusing.

Glucose is a monosaccharide and is indeed 'a sugar'. Poor hormonal control of its concentration in blood is the underlying cause of diabetes mellitus. However, the compound generally referred to as sugar is in fact a disaccharide consisting of a glucose molecule linked to a fructose molecule. Although a dietary constituent, it does not occur in blood, being degraded to glucose and fructose in the alimentary canal before absorption. Dietary sucrose, however, is especially cariogenic because it can be metabolised by oral bacteria not only to acidic end products, but the glucose and fructose moieties can also be polymerised to form glucans and fructans which contribute to the matrix of dental plaque with the associated adverse effects on the gingivae and dentition.

It is unfortunate that the lay press still all too frequently refers to blood glucose as 'blood sugar'. This terminology probably came into use decades ago when the disorder was poorly understood and clinicians tasted the urine of diabetic patients to differentiate between diabetes mellitus and diabetes insipidus! That from the diabetes mellitus patient tasted sweet or honey like, thereby giving it its name.

The paper also implies that ketones are acidic and are the products which cause ketoacidosis. What actually happens is that when cells are deprived of glucose because of lack of insulin (some tissues require insulin for glucose uptake), fat is degraded to form a group of compounds known as 'ketone bodies'. Two of these, acetoacetate and β-hydroxybutyrate, are indeed acidic, but only the first is a ketone. The third one, acetone, is the ketone which gives the breath its characteristic smell, but it is not acidic.

Lastly, haemoglobin is not 'attached' to the erythrocytes (red blood cells), but is contained within them. Erythrocyte membranes are glucose permeable which is why the % haemoglobin A1c reflects the long term blood glucose concentration.

I hope these comments will be helpful and lead to a better understanding of this disorder.

Dr Wray responds: Josie Beeley is of course perfectly correct in saying that 'blood sugar' and 'blood glucose' are different entities.

However, the words 'blood glucose' and 'blood sugar' are routinely used interchangeably both by diabetics themselves and those treating them. Dentists treating such patients will no doubt come across both terms when speaking with their patients. The purpose of the article was to try to address an important topic in a straightforward and practical manner. However, I am sure Josie Beeley's comments are helpful to those who may wish to understand the underlying physiology and biochemistry further.