One significant issue with this review article is the lack of criteria for selecting studies.
Some individuals discovered that the similarity in caries experience was more significant in MZ twins compared to DZ twins. This led the researchers to conclude that this resemblance was due to a genetic factor. Certain studies that were reviewed indicated a stronger environmental influence on caries experience, as there were no differences observed between MZ and DZ twins in these characteristics. However, there was limited focus on the direct measurement of dental caries traits and methodological issues in researching the relative contribution of gene-environment interactions. The heterogeneity in statistical methodology prevented the evaluation of results through meta-analysis. The statistical approaches used in twin studies to analyze dental caries included correlation coefficients, concordance/discordance rates, heritability estimates, and analysis of intra-pair covariances. If a specific trait showed a high correlation in MZ twins and a lower correlation in DZ twins, it could be inferred that there is a genetic contribution to the variation in that particular trait. The twin study model is based on the fact that identical (MZ) twins share all their genes, while fraternal (DZ) twins, like siblings, share an average of half their genes.
Only one study (Young & Bachrach, 1927) has enrolled children who had not received dental treatment, evaluating the importance of studying dental caries from sub-clinical disease to clinical disease and the transition from disease onset to disease progression. It is also important to assess the surfaces of teeth as they play a significant role in investigating the length of adequate longitudinal investigations. Additionally, when studying dental caries, it is crucial to consider important factors such as the modulation of genetic phenotype, exposure to fluoride, attendance at dental appointments, and the potential effects of treatment as modifiers that eliminate potential effects.
The age of the cohort has been defined. The majority of the reviewed studies, which might explain the contradictory reported results, had a wide range of age. If dental caries susceptibility is indeed inherited, it is likely to start affecting primary dentition in infancy and could extend to permanent dentition without intervention. Accordingly, tooth surfaces are more susceptible to re-mineralization and de- mechanisms during this time frame. Furthermore, variations in the severity or magnitude of lesions must be measured to determine the variations along the continuum from absolute dental health to the manifestation of rampant caries.
Some studies have used a limited number of teeth in their analysis, which makes it difficult to generalize the susceptibility or resistance of a particular person to dental caries overall. For example, Conry et al. (1993) and Boraas et al. (1988) found that the heritability estimates for dental caries can be altered by the small sample size originally used. In fact, the actual sample size was too small to derive definitive conclusions, especially for studies using twin samples for dental caries.
The serological assessment of zygosity was not performed in many reviewed studies. Because the basis of twin studies lies in the comparisons of DZ and MZ twins, a reliable method for the identification of zygosity is required for every twin. A visual criterion has been found to be accurate in ascertainment of twins, with a range of 90% to 95% (Cavalli-Sforza and Bohmer, 1971).
The precise description of caries traits is of paramount importance if the genetic contribution to a particular trait is clinically determined or if associations between genotype and phenotype are being performed. However, most studies assessing caries methods were performed under less than ideal conditions and sometimes the description of these methods was not provided at all. In addition, the majority of published twin studies on caries utilized simplistic methods, while more recent studies have employed sophisticated twin analysis methods. These studies could provide an overall measure of liability for a subject and were used to assess rates of decayed and surface-specific teeth in individuals ranging from 2 to 58 years old. However, it is important to note that there were no other comparable studies that used surface-specific rates as a measure of overall liability.
The author acknowledges that the findings suggest that the general population may have an extended susceptibility to dental caries. These findings also indicate that individuals in the general population who exhibit altered susceptibility to dental caries may have an increased development of caries, which is characterized by increased enamel porosity and decreased mineral content in syndromic phenotypes. Additionally, these findings suggest the possibility of linking specific allelic variations to the susceptibility of dental caries in the general population, which has been associated with increased colonization of cariogenic bacteria and defects in enamel that are regulated by complex immune genes.
Lastly, the author acknowledges that the multifactorial nature of dental caries has prevented direct correlations between inheritance and dental caries.