Teeth and tooth decay
An important part of the previous phase of the study (6 years old) was examining the children’s teeth. We did this to not only see whether there was any tooth decay (holes in teeth), but also to see how the teeth were developing compared to the child’s age, by looking at what teeth had become wobbly or fallen out and how many permanent (adult) teeth had grown. We also looked for any developmental anomalies (marks) on the teeth that may have occurred before the teeth came into the mouth or soon after. In addition, we examined the health of the gums and collected biological samples (dental plaque) from along the gum line. We are also interested in finding out more about healthy mouths and how this affects other parts of the body and lifestyles.
We found the prevalence of tooth decay was similar to that of the broader population. Of the twins who had their teeth examined, there were 57% of twin pairs who had no signs of tooth decay. There were 23% who both had tooth decay. In 18% of twin pairs, only one twin had tooth decay. This is of particular interest as these twins have the same parents, were in the womb at the same time and are generally exposed to similar environmental influences such as maternal diet and lifestyle. Studying twins enables us to look at the potential strength of genetic influences (comparing fraternal and identical twins with and without tooth decay) and environmental influences, such as diet and tooth brushing. We already know there are many factors that can contribute to the risk for tooth decay. These are mostly environmental influences such as diet and tooth brushing. Frequent snacking, particularly of sugary foods, brushing less than twice a day can all have an adverse effect on oral health. What is not really understood is why two individuals who may have similar environmental influences result in one having tooth decay and not the other. In addition, there are a range of other influences that we don’t know a lot about, such as genetics and general health.
To try to better understand these influences, we collected and sent just over 940 dental plaque samples to our collaborators in the USA along with some fairly general information such as whether the twins were identical or fraternal, the children’s ages at the time of the sample collection, whether there was any tooth decay, how often the children cleaned their teeth and consumed sweetened foods or liquids.
From these samples we sought to establish whether there is an association between tooth decay and distinct plaque microbial communities in both MZ and DZ twins and how this might change with the severity of tooth decay. We were also interested in to what extent the microbiome patterns that are associated with tooth decay could be explained by genetic background (comparing DZ twin pairs and MZ twin pairs) or environmental influences (e.g. tooth brushing, diet, general health).
What we have found so far
Although dental plaque microbial communities are partly controlled by host genetic factors, the genetic contribution seems to be more related to a healthy state than a diseased one (e.g. tooth decay). Our data also shows that factors specific to individual twins have a strong influence on oral health. This could mean that it is important to focus on individuals to prevent tooth decay. We are all different and so are twins! However, further research is planned using these samples to learn more about the genetic and environmental influences on oral health and disease.
Dental anomalies on tooth enamel
Many parents asked about the white or yellow marks on their children’s teeth that did not disappear with tooth brushing. These dental anomalies have occurred when outer layer (enamel) of the tooth is developing, usually well before the tooth appears in the mouth. In some circumstances, affected teeth may be more sensitive or more susceptible to tooth decay. There are lots of theories about how this may have occurred (e.g. illnesses and infections of either the mother or infant during tooth development). We are also very interested in these anomalies and learning more about why they occur. By studying twins, and using the information we have already collected from before the children were born up to the present time, we are able to look more closely at possible influences.
From the dental examinations, we were able to discover that anomalies on the second primary molar (the very back baby tooth) were experienced by 68 children. Of these, there were 16 twin pairs where both children were affected and 36 pairs where only one was affected. More than half of all children had more than one tooth with these anomalies. Of the children with these marks, 48 were fraternal and 17 were identical. There were three children affected whose zygosity is unknown.