Dental caries prevalence and severity positively associate with AMY1 gene copy number

OBJECTIVE

To establish the possible relation between total caries (TC) and caries severity (CS) with the AMY1 gene copy number (AMY1GCN).

MATERIALS AND METHODS

This was an observational, cross-sectional, population-based, and association study with 303 participants. Each participant underwent a complete anamnesis and stomatological check-up, and peripheral blood was obtained to extract gDNA. TC and CS were determined as the number of caries at the dental exploration and the number of dental surfaces affected by caries, respectively, and AMY1GCN was determined by qPCR.

RESULTS

We found an elevated caries prevalence (92.7%); TC and CS were 8 ± 10 and 10 ± 13 (median ± IR). There were higher TC and CS in those participants with AMY1GCN above the mean value (0.02 and 0.01 p values, respectively). A positive correlation between TC and CS with AMY1GCN (0.11 and 0.125 r values, 0.03 and 0.01 p values, respectively) was found, in addition to an association between TC and CS with AMY1GCN (1.5 and 1.6 OR values, 0.48 and 0.26 p values, respectively).

CONCLUSION

TC and CS were positively related to the AMY1GCN.

CLINICAL RELEVANCE

Dental caries has a high prevalence and a multifactorial etiology and has been related to a genetic component. Indeed, the salivary enzyme alpha-amylase could play a significant role in caries susceptibility, considering that its codifying gene (AMY1) can show variation in its gene copy number. This can be considered an important factor for the development of caries at a genetic level.

Sweet Taste Receptor Gene and Caries Trajectory in the Life Course

This study aims to investigate whether the trajectory of dental caries in the life course is associated with rs307355 (TAS1R3) and rs35874116 (TAS1R2) and if there is an epistatic association between rs307355 (TAS1R3) and rs35874116 (TAS1R2). A representative sample of all 5,914 births from the 1982 Pelotas birth cohort was prospectively investigated, and the decayed, missing, and filled teeth (DMF-T) components were assessed at ages 15 (n = 888), 24 (n = 720), and 31 (n = 539) y. Group-based trajectory modeling was used to identify groups with similar trajectories of DMF-T components in the life course. Genetic material was collected, and rs307355 (TAS1R3) and rs35874116 (TAS1R2) were genotyped. Ethnicity was evaluated using ADMIXTURE. Generalized multifactor dimensionality reduction software was used to investigate epistatic interactions. Considering rs307355 (TAS1R3) in the additive effect, the genotype TT was associated with the high decayed trajectory group (odds ratio [OR] = 4.52; 95% confidence interval [CI], 1.15-17.74) and the high missing trajectory group (OR = 3.35; 95% CI, 1.09-10.26). In the dominant effect, the genotype CT/TT was associated with the high decayed trajectory group (OR = 1.64; 95% CI, 1.14-2.35). Allele T was associated with an increased odds of 64% (OR = 1.64; 95% CI, 1.20-2.25) for the decayed component and 41% (OR = 1.41; 95% CI, 1.04-1.92) for the missing component. No associations were observed between rs307355 (TAS1R3) and the filled component. rs35874116 (TAS1R2) was not associated with DMF-T components. Positive epistatic interactions were observed involving rs307355 (TAS1R3) and rs35874116 (TAS1R2) with the decayed component (OR = 1.72; 95% CI, 1.04-2.84). Thus, rs307355 (TAS1R3) genotypes and alleles seem positively associated with the trajectory of decayed and missing components in the life course. Epistatic interaction between rs307355 and rs35874116 may increase the decayed caries trajectory.

FCN1 polymorphisms are not the markers of dental caries susceptibility in Polish children: A case-control study

OBJECTIVE

To examine the association of four FCN1 SNPs: -542G>A (rs10120023), -144C>A (rs10117466), +6658C>T (rs148649884), and +7895A>G (rs150625869) with dental caries in Polish children.

SUBJECTS AND METHODS

The study group consisted of 261 15-year-old Polish teenagers: 82 children with "higher" caries experience (having Decayed Missing Filled Teeth, DMFT >5) and 179 children with "lower" caries experience (having DMFT ≤5). Moreover, in additional comparison, a group of 229 children with caries experience (DMFT ≥1) was compared to a caries-free (DMFT =0) group of 32 children. Extraction of genomic DNA was performed from buccal swabs, and genotyping was performed by Real-Time PCR.

RESULTS

FCN1 SNPs +6658C>T and +7895A>G appeared to be monomorphic in our sample. The genotype, allele, or haplotype distributions in FCN1 SNPs -542G>A and -144C>A in children with "higher" caries experience did not differ significantly from those in "lower" caries experience group. Similar results with no significant differences were demonstrated for subjects with DMFT ≥1 compared to subjects with DMFT =0.

CONCLUSION

FCN1 SNPs are not the markers of dental caries susceptibility in Polish children.

Precision Dentistry in Early Childhood: The Central Role of Genomics

Pediatric oral health is determined by the interaction of environmental factors and genetic influences. This is the case for early childhood caries, the most common disease of childhood. The complexity of exogenous-environmental factors interacting with innate biological predispositions results in a continuum of normal variation, as well as oral health and disease outcomes. Optimal oral health and care or precision dentistry warrants comprehensive understanding of these influences and tools enabling intervention on modifiable factors. This article reviews the current knowledge of the genomic basis of pediatric oral health and highlights known and postulated mechanistic pathways of action relevant to early childhood caries.

Caries: review of human genetics research

The NIH Consensus Development Program released a statement in 2001 (http://consensus.nih.gov/2001/2001DentalCaries115html.htm) and listed six major clinical caries research directions. One of these directions was the need for genetic studies to identify genes and genetic markers of diagnostic, prognostic and therapeutic value. This last decade has seen a steep increase in studies investigating the presence of genetic factors influencing individual susceptibility to caries. This review revisits recent caries human genetic studies and provides a perspective for future studies in order to fulfil their promise of revolutionizing our understanding of and the standard of care for the most prevalent bacteria-mediated non-contagious disease in the world.

Genetic association for caries susceptibility among cleft lip and/or palate individuals

AIM

To evaluate the association of the polymorphisms in the TGFB3 gene (rs2268626), and the BMP4 gene (rs17563) with dental caries in two different groups (noncleft group and oral cleft group) from a cleft center located at Rio de Janeiro, Brazil.

MATERIALS AND METHODS

A total of 486 unrelated children and adolescents with or without caries were evaluated using a cohort design. Data on oral health habits was obtained through a questionnaire and caries data was collected by clinical examination. Genotyping of the selected polymorphisms for TGFB3 and BMP4 were carried out by real-time PCR using the TaqMan assay method from a genomic DNA isolated from buccal epithelial cells of all children and adolescents.

RESULTS

No association was found between BMP4 polymorphism and caries among individuals from both groups. For TGFB3 polymorphism, significant differences were observed for allele and genotype frequencies between caries free and caries affected individuals in oral cleft group (p = 0.013 and 0.006 for allele and genotype frequencies respectively).

CONCLUSION

Our findings provide evidence suggesting that TGFB3 may be involved in caries susceptibility in oral cleft group.

CLINICAL SIGNIFICANCE

In the future, the possibility of identifying genes related to caries susceptibility can lead to counseling of the individual that carries gene alterations, with the aim of working on preventive measures for caries as well as bioengineering treatments.

Clustering tooth surfaces into biologically informative caries outcomes

Dental caries affects most adults worldwide; however, the risk factors for dental caries do not necessarily exert their effects uniformly across all tooth surfaces. Instead, the actions of some risk factors may be limited to a subset of teeth/surfaces. Therefore, we used hierarchical clustering on tooth surface-level caries data for 1,068 Appalachian adults (ages 18-75 yrs) to group surfaces based on co-occurrence of caries. Our cluster analysis yielded evidence of 5 distinct groups of tooth surfaces that differ with respect to caries: (C1) pit and fissure molar surfaces, (C2) mandibular anterior surfaces, (C3) posterior non-pit and fissure surfaces, (C4) maxillary anterior surfaces, and (C5) mid-dentition surfaces. These clusters were replicated in a national dataset (NHANES 1999-2000, N = 3,123). We created new caries outcomes defined as the number of carious tooth surfaces within each cluster. We show that some cluster-based caries outcomes are heritable (i.e., under genetic regulation; p < 0.05), whereas others are not. Likewise, we demonstrate the association between some cluster-based caries outcomes and potential risk factors such as age, sex, educational attainment, and toothbrushing habits. Together, these results suggest that the permanent dentition can be subdivided into groups of tooth surfaces that are useful for understanding the factors influencing cariogenesis.

ABBREVIATIONS

COHRA, Center for Oral Health in Appalachia, the principal study sample; C1-5, clusters 1-5, groups of similarly behaving tooth surfaces identified through hierarchical clustering; DMFS index, decayed, missing, or filled surfaces, a traditional caries measure representing the number of affected surfaces across the entire dentition; DMFS1-5, partial DMFS indices representing the number of affected surfaces within a hierarchical cluster; and NHANES, National Health and Nutrition Examination Survey, the secondary study sample.

Genetic and environmental factors associated with dental caries in children: the Iowa Fluoride Study

Dental caries remains the most common chronic childhood disease. Despite strong evidence of genetic components, there have been few studies of candidate genes and caries. In this analysis we tried to assess genetic and environmental factors contributing to childhood caries in the Iowa Fluoride Study. Environmental factors (age, sex, race, tooth-brushing frequencies and water fluoride level) and three dental caries scores (d(2)fs-total, d(2)fs-pit/fissure, and d(2)fs-smooth surface) were assessed in 575 unrelated children (mean age 5.2 years). Regression analyses were applied to assess environmental correlates. The Family-Based Association Test was used to test genetic associations for 23 single nucleotide polymorphism (SNP) markers in 7 caries candidate genes on 333 Caucasian parent-child trios. We evaluated the associations between caries status and the level of both single and multiple SNPs (haplotype) respectively. Permutation procedure was performed for correction of inflated type I errors due to multiple testing. Age, tooth-brushing frequency and water fluoride level were significantly correlated to at least one carious score. Caries on pit and fissure surfaces was substantially higher than on smooth surfaces (61 vs. 39%). SNPs in three genes (DSPP, KLK4 and AQP5) showed consistent associations with protection against caries. Of note, KLK4 and AQP5 were also highlighted by subsequent haplotype analysis. Our results support the concept that genes can modify the susceptibility of caries in children. Replication analysis in independent cohorts is highly needed in order to verify the validity of our findings.

[Genetics and caries]

Caries is a multi-factorial disease, primarily caused by acids. Acids are produced by bacteria which ferment sugar. The aetiology and progress of caries are influenced by life-style and environmental factors, as well as congenital components. Based on, among other things, research concerning twins, the literature suggests that there are hereditary components of caries and life-style and environmental components. With the unravelling of the human genome, it is more easy to study individual genes in relation to the caries process. Because of its multifactorial nature, one has to realise that there is only a beginning of understanding the caries processes at molecular level.

Dental features in patients with Turner syndrome

AIM

This was to investigate the dental characteristics (caries sensitivity and tooth crown size of permanent elements) in subjects affected by Turner Syndrome (TS).

PATIENTS AND METHODS

A group of 25 patients affected by TS, aged from 4 to 18 years, was selected and the data were compared to those of an age matched control healthy group. The caries index values in TS patients are higher in the permanent (6.4 vs. 3.9), mixed (0.5 vs. 0.75) and primary dentition (0 vs. 1). The mesio-distal diameter in TS patients was significantly reduced for every tooth measured (in particular for the lower first permanent molar).

RESULTS AND CONCLUSION

This investigation confirms that numeric aberration of the X chromosome most likely affects the quantitative and qualitative excretion of amelogenin so that teeth often present enamel defects (reduced crown size and enamel hypoplasia). High caries index values (DMFT) highlight the demand of early preventive measures mostly focused on special care patients.

Tuftelin, mutans streptococci, and dental caries susceptibility

The purpose of this study was to identify genetic factors that contribute to dental caries susceptibility, either alone or in combination with environmental factors. Dental examinations were performed and buccal swab samples collected from 3- to 5-year-old children with at least 4 surfaces of decay, or with no evidence of decay. SNP assays for each of 6 candidate genes were performed for all cases and controls. Chi-square analysis and regression analysis were used for the evaluation of individual gene effects, environmental effects, and gene-environment interactions. There were no significant associations between single candidate genes and caries susceptibility. Levels of S. mutans were positively and Lactobacilli were negatively associated with caries. Regression analysis revealed a significant interaction between tuftelin and S. mutans, with 26.8% of the variation in dmfs explained by the interaction. Future research will focus on the identification of these additional factors and the development of functional assays so that these interactions can be better understood.

A mouse caries model and evaluation of aqp5-/- knockout mice

Current techniques to alter gene expression in mice allow direct analysis of the net role of a host factor in caries development. Towards this goal we first established protocols to induce and score caries in NFS/N mice and determined caries susceptibility in mice with targeted deletion of the gene encoding aquaporin-5 (Aqp5-/-), a water channel involved in the production of saliva. In the NFS/N strain of mice total sulcal caries and severity scores were consistent between experiments, whereas smooth surface caries scores were lower, more variable but distributed fairly evenly among the buccal, lingual and sulcal surfaces. In Black Swiss/129SvJ mice (genetic background of Aqp5-/- mice) caries scores were 50-75% lower compared to NFS/N mice, suggesting strain variation in caries susceptibility under our experimental conditions. In Aqp5-/- mice, in which the volume of total salivary secretion is reduced by 60-65%, there was a significant increase in caries, primarily on the buccal and sulcal surfaces. Results indicate that caries susceptibility increases with a reduced salivary flow that is associated with decreased water content of saliva.

Identification of chromosomes associated with dental caries susceptibility using quantitative trait locus analysis in mice

Dental caries is a multifactorial, infectious disease with little known about the host genetic factors influencing susceptibility. This study aimed to identify the major candidate chromosomes for dental caries susceptibility and to detect the relevant regions within these. Quantitative trait locus (QTL) analysis was performed on genetic crosses of C3H/HeJ (caries-resistant) and C57BL/6J (caries-susceptible) mice inoculated with Streptococcus mutans serotype C. In a genomewide scan, three suggestive QTLs were detected on chromosomes 1, 2, and 7, one significant QTL was found on chromosome 2, and one highly significant QTL was detected on chromosome 8. The likelihood ratio statistic (LRS) was raised around the marker D1Mit21 in the middle region of chromosome 1, between D2Mit255 and D2Mit311 in the distal region of chromosome 2, and the region distal to D7Mit31 on chromosome 7. A significant QTL was located between the markers D2Mit237 and D2Mit101 on chromosome 2. The LRS was highly significantly raised between markers D8Mit208 and D8Mit280 on chromosome 8, and exceeded a highly significant level between markers D8Mit211 and D8Mit280. These results suggest that major gene(s) responsible for dental caries susceptibility or resistance are located in one or more of these regions.

The association of bacterial adhesion with dental caries

Saliva adhesion of bacteria is a key event in oral biofilm formation. Here, we used partial least-squares (PLS) analysis to correlate adhesion of cariogenic (Streptococcus mutans Ingbritt) and commensal (Actinomyces naeslundii LY7) model bacteria, and their agglutinin and acidic proline-rich protein ligands, respectively, with high and low caries experiences in 38 children reflecting today's skewed caries distribution. Adhesion of S. mutans was among the factors correlating strongest with high caries experience when PLS modeled together with traditional factors (e.g., sugar intake, lactobacilli counts). Saliva phenotypes with high agglutinin levels and Db-s (an acidic PRP variant) coincided with both high caries experience and S. mutans adhesion. A. naeslundii adhesion correlated with low caries experience. Non-Db phenotypes (i.e., acidic PRP-1 and PRP-2 variants) coincided with both low caries experience and S. mutans, but high A. naeslundii, adhesion. Thus, bacterial adhesion may modulate susceptibility and resistance to dental caries.

Inherited risks for susceptibility to dental caries

Dental caries incidence is affected by host factors that may be related to the structure of dental enamel, immunologic response to cariogenic bacteria, or the composition of saliva. Genetic variation of the host factors may contribute to increased risks for dental caries. This systematic review examined the literature to address the question, "Is the risk for dental decay related to patterns of genetic inheritance?" Numerous reports have described a potential genetic contribution to the risk for dental caries. Studies on twins have provided strong evidence for the role of inheritance. Establishing a basis for a genetic contribution to dental caries will provide a foundation for future studies utilizing the human genome sequence to improve understanding of the disease process. Inherited disorders of tooth development with altered enamel structure increase the incidence of dental caries. Specific genetic linkage has not been determined for all of the syndromes of altered tooth development. Consequently, genetic screens of large populations for genes or mutations associated with increased caries susceptibility have not been done. Altered immune response to the cariogenic bacteria may also increase the incidence of caries. Association between specific patterns of HLA genetic inheritance and dental caries risk is weak and does not provide a predictable basis for predicting future decay rates. The evidence supporting an inherited susceptibility to dental caries is limited. Genetic linkage approaches on well-characterized populations with clearly defined dental caries incidence will be required to further analyze the relationship between inheritance and dental caries.

Where will the genome lead us? Dentistry in the 21st century

BACKGROUND

Recent announcements of the deciphering and analysis of the human genome signal the inception of a new era of gene-based medicine. During the 21st century, patient treatment will be transformed and dentistry will be affected profoundly.

METHODS

The author explains the importance of the decoding of the genome and how--based on this now completely depicted molecular structure--genes build, maintain and control all the biological functions of humans and all other living organisms. The potential application of this knowledge to the practice of dentistry is addressed, as well as the ethical, legal and moral challenges to the profession engendered by this new technology.

CONCLUSION

During the next several decades, many of the current materials and methods will be abandoned in favor of emerging bioengineered technologies, genetically programmed for the prevention and treatment of oral disease as well as for the repair of damaged dental tissues.

PRACTICE IMPLICATIONS

The development and implementation of these innovative dental therapies will require intensive education of current practitioners. Considerable restructuring of dental school curricula will need to take place, and the emergence of a new dental specialty is anticipated.

Dental caries susceptibility in mice is closely linked to the H-2 region on chromosome 17

The generation of dental caries in humans is thought to be regulated by many intrinsic and social factors. In this study, we examined the effect of MHC on susceptibility to dental caries in mice. The mean carious score of BALB.K/Ola, a H-2 congenic strain in which the H-2 region derived from C3H/HeJ (H-2(k/k)) is introduced into BALB/cJ (H-2(d/d)), was markedly reduced as compared with that of its recipient strain (BALB/cJ). Mating experiments confirmed a strong genetic linkage between H-2 haplotype and caries susceptibility. These results demonstrate that one of the genetic factors of the susceptibility in the mouse is mapped within the H-2 region. This finding of a host genetic factor influencing the generation of dental caries will help in developing clinical preventive strategies.

Litter effects on caries in rats and implications for experimental design

The purpose of this study was to obtain quantitative estimates of litter effects on caries development in rats and to examine the implications for design of rat caries experiments. Twelve female Sprague-Dawley rats, aged 60 days, were bred with 4 male rats. Nine of the 12 dams had litters in close proximity. The litters were culled to 10 pups. One pup from each litter was placed with each of the other dams for nursing, leaving 2 pups from each litter with the birth dam. This design allowed the litter effect to be separated into a prenatal component, reflecting the shared genetic makeup and in utero environment of littermates, and a postnatal component reflecting a shared environment from shortly after birth to weaning. Pups were infected with Streptococcus sobrinus and fed Diet 2000 and 10% (w/v) sucrose water for 5 weeks. There was no significant evidence of a postnatal litter effect for smooth surface caries (p = 0.37) or sulcal caries (p = 0.43). The prenatal litter effect was significant for both smooth surface caries and sulcal caries (p<0. 01). When litter effects are present, the statistical power of caries studies is improved if animals from the same litter are divided evenly among experimental groups. In addition, if litter effects are present but not allowed for in data analysis, incorrect statistical inferences may be drawn. Based on our results and other reports of litter effects, we recommend planning for litter effects in the design and analysis of rat caries studies.

Genetic aspects of dental disorders

This paper reviews past and present applications of quantitative and molecular genetics to dental disorders. Examples are given relating to craniofacial development (including malocclusion), oral supporting tissues (including periodontal diseases) and dental hard tissues (including defects of enamel and dentine as well as dental caries). Future developments and applications to clinical dentistry are discussed. Early investigations confirmed genetic bases to dental caries, periodontal diseases and malocclusion, but research findings have had little impact on clinical practice. The complex multifactorial aetiologies of these conditions, together with methodological problems, have limited progress until recently. Present studies are clarifying previously unrecognized genetic and phenotypic heterogeneities and attempting to unravel the complex interactions between genes and environment by applying new statistical modelling approaches to twin and family data. Linkage studies using highly polymorphic DNA markers are providing a means of locating candidate genes, including quantitative trait loci (QTL). In future, as knowledge increases; it should be possible to implement preventive strategies for those genetically-predisposed individuals who are identified to be at risk.

Dermatoglyphic findings in dental caries: a preliminary report

The dermatoglyphs of caries-free students and the students with dental caries in 10 or more teeth were compared. The caries-free students had an increased frequency of ulnar loops on all fingers. In contrast, the students with dental caries had an increased frequency of whorls on all fingers.

[Value of dental treatment in interdisciplinary management of a child with epidermolysis bullosa dystrophica hereditaria (Hallopeau-Siemens)]

Severe dystrophic epidermolysis bullosa with oral involvement often leads to dental destruction and restricted food intake, resulting in malnutrition and maldevelopment. The patients become handicapped and have a poor prognosis. We report on a now 13-year-old Turkish child with normal secondary dentition who had severely damaged primary dentition. The teeth were treated surgically and then by continuous dental hygiene measures over the next 7 years. This care also resulted in an improvement in the nutritional state, associated anemia and the incidence of skin infections. Although cutaneous blistering and scarring has been progressive, with resulting mutilation of the fingers, the child is socially well adjusted in school and family. Its clinical course demonstrates that the fate of patients with severe dystrophic epidermolysis bullosa can be improved through multidisciplinary management.

Genetic influences in caries and periodontal diseases

Deciphering the relative roles of heredity and environmental factors ("nature vs. nurture") in the pathogenesis of dental caries and diseases of the periodontium has occupied clinical and basic researchers for decades. Success in the endeavor has come more easily in the case of caries; the complex interactions that occur between host-response mechanisms and putative microbiologic pathogens in periodontal disease have made elucidation of genetic factors in disease susceptibility more difficult. In addition, during the 30-year period between 1958 and 1987, only meager resources were targeted toward the "nature" side of the nature/nurture dipole in periodontology. In this article, we present a brief history of the development of genetic epistemology, then describe the three main research mechanisms by which questions about the hereditary component of diseases in humans can be addressed. A critical discussion of the evidence for a hereditary component in caries susceptibility is next presented, also from a historical perspective. The evolution of knowledge concerning possible genetic ("endogenous", "idiotypic") factors in the pathogenesis of inflammatory periodontal disease is initiated with an analysis of some foreign-language (primarily German) literature that is likely to be unfamiliar to the reader. We identify a turning point at about 1960, when the periodontal research community turned away from genetics in favor of microbiology research. During the past five years, investigators have re-initiated the search for the hereditary component in susceptibility to common adult periodontal disease; this small but growing body of literature is reviewed. Recent applications of in vitro methods for genetic analyses in periodontal research are presented, with an eye toward a future in which persons who are at risk--genetically predisposed--to periodontal disease may be identified and targeted for interventive strategies. Critical is the realization that genes and environment do not act independently of each other; the appearance or magnitude of heritability may differ with various environments.

Nature vs. nurture in dental caries

Why are some people more resistant to dental caries than others? Certainly diet plays a part, but are there hereditary factors that affect caries development? This report explores genetic components that appear related to caries resistance and susceptibility.

Genetic variation in experimental dental caries in four inbred strains of rats

The relative contribution of the host genetic effect on the susceptibility to dental caries was examined. Four inbred strains of male rats (BN/Sea, F344/Ms, PVG/cSea, and WKA/Sea) were inoculated with Streptococcus mutans and fed a cariogenic diet. The caries scores of the molar teeth were compared among these four strains, and the degree of genetic determination was estimated by analysis of variance. Statistically significant differences in caries scores were found among these strains (F344 > WKA > PVG/c > BN), and a high degree of genetic determination was obtained.

Host genes and dental caries

With the attention now being given to molecular genetic analysis of cariogenic microorganisms, the role of host genes in influencing susceptibility to caries should not be forgotten. Increasing knowledge in this field will lead to identification of individuals at particular risk of dental decay and will help in planning rational strategies for management and prevention.

Caries susceptibility in inbred mouse strains and inheritance patterns in F1 and backcross (N2) progeny from strains with high and low caries susceptibility

We studied dental caries susceptibility in various inbred mice strains infected with Streptococcus mutans and the inheritance pattern in the F1 and the N2 backcross animals. A high caries score was observed in four laboratory strains, BALB/cAJcl, C57BL/6NJcl, C57BL/10Slc and DBA/2NJcl. Three strains, C3H/HeNJcl, AKR/JSlc and CBA/JNCrj, showed less caries. Males of strain C57BL/10Slc (mean caries score = 112.2) and females of strain C3H/HeNJcl (mean caries score = 24.0) were chosen for examinations of the inheritance of the caries susceptibility. The mean caries score in (C57BL/10Slc x C3H/HeNJcl) F1 hybrids was 98.4, demonstrating that F1 progenies were susceptible. A number of N2 mice were obtained by mating the F1 male and the C3H/HeNJcl female. The caries scores of these N2 male mice had an extensive range, from 14 to 194. Assuming that a caries score over 74 (median of the scores between C57BL/10Slc and C3H/HeNJcl) belonged to the highly caries-susceptible group, N2 mice could be divided into groups with low or high caries susceptibility. Furthermore, the effect of nu/nu mutation on caries susceptibility in mice was also examined.