Commentary: What about the ethics?BMJ 1996; 313 doi: http://dx.doi.org/10.1136/bmj.313.7066.1183 (Published 09 November 1996) Cite this as: BMJ 1996;313:1183
- Gerald B Winter, EMERITUS professor of children's dentistrya
The substitution of xylitol for sucrose in the diet has been of considerable interest since the report of a two year study in Turku, Finland, which studied a young adult population and showed a significant reduction in dental caries.1 As total substitution of dietary sucrose by xylitol was deemed impossible in children, studies were subsequently limited to partial substitution in confectionery and chewing gum.2 3 These studies have demonstrated significant reductions in dental caries in schoolchildren when conducted over periods of two to three years. Xylitol is now accepted as non-cariogenic, and undoubtedly reduces the growth of Streptococcus mutans. It remains uncertain, however, to what extent this microbial effect on the oral flora is responsible for the cariostatic properties of xylitol seen in these clinical trials. It has also been observed that chewing xylitol gum increases salivary flow, thus aiding remineralisation of carious lesions and that this may be the main mechanism of its anticaries effect.4 The fact that xylitol has also been shown to suppress in vitro the growth of S pneumoniae in a manner similar to that for S mutans and that this led to the present clinical trial of xylitol chewing gum, which has shown a significant reduction in episodes of acute otitis media, is clearly fascinating. The failure to demonstrate a reduction in pneumococcal carriage rates between study and control groups leaves doubts as to the precise mode of action of xylitol, not too dissimilar to that met in dentistry.
The main point of this commentary, however, is to review the ethical decision to use chewing gum containing sucrose for the children in the control group. There are several reasons why an ethics committee based in the United Kingdom might have taken a different view from that reached in Finland.
Firstly, the use of chewing gum containing sucrose was not without risk to the dental health of children susceptible to caries in the control group. The previous study on xylitol that used a sucrose chewing gum in a control group was in older children (average age 10.2 years) and did not test the effect on the primary dentition which may be at greater risk.5 Admittedly this risk was small considering the very limited time of the experiment.
Secondly, the researchers seemed to be aware of the risk and therefore excluded children in whom caries was “noticed” when they took the first nasopharyngeal samples. They did not employ a dentally trained person to undertake this baseline examination, however, and may well have missed several children already suffering from the disease. This can be inferred from the observations of the dental nurse who, four months after the end of the trial, noted 44 children with dental decay. It is extremely unlikely that a fifth of the children developed new carious lesions in the six months in question, particularly when 21 children in the study group received xylitol chewing gum for the first two months. The precise nature of this examination by the dental nurse is not stated but probably did not include the use of dental radiographs. Without these further lesions may have been missed specifically on the proximal surfaces of the molar teeth, surfaces particularly at risk from sucrose in the diet.
Thirdly, children in the control group already suffering from caries would have been subjected to increased risk of new or extended carious lesions. Such a risk would be considered by many too great to justify the possible benefits likely to accrue from the clinical trial. Furthermore, it seems to take little account of the guidance that “parents and guardians of minors cannot give consent on their behalf to any procedures which are of no particular benefit to them and which may carry some risk of harm.”6