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

The genetic determinants of oral diseases in Africa: The gaps should be filled

Oral diseases are a major health concern and are among the most prevalent diseases globally. This problem is becoming more prominent in the rapidly growing populations of Africa. It is well documented that Africa exhibits the most diverse genetic make-up in the world. However, little work has been conducted to understand the genetic basis of oral diseases in Africans. Oral health is often neglected and receives low prioritisation from funders and governments. The genetic determinants of highly prevalent oral diseases such as dental caries and periodontal disease, and regionally prevalent conditions such as oral cancer and NOMA, are largely under-researched areas despite numerous articles alluding to a high burden of these diseases in African populations. Therefore, this review aims to shed light on the significant gaps in research on the genetic and genomic aspects of oral diseases in African populations and highlights the urgent need for evidence-based dentistry, in tandem with the development of the dentist/scientist workforce.

Deficiency of Mineralization-Regulating Transcription Factor Trps1 Compromises Quality of Dental Tissues and Increases Susceptibility to Dental Caries

Dental caries is the most common chronic disease in children and adults worldwide. The complex etiology of dental caries includes environmental factors as well as host genetics, which together contribute to inter-individual variation in susceptibility. The goal of this study was to provide insights into the molecular pathology underlying increased predisposition to dental caries in trichorhinophalangeal syndrome (TRPS). This rare inherited skeletal dysplasia is caused by mutations in the TRPS1 gene coding for the TRPS1 transcription factor. Considering Trps1 expression in odontoblasts, where Trps1 supports expression of multiple mineralization-related genes, we focused on determining the consequences of odontoblast-specific Trps1 deficiency on the quality of dental tissues. We generated a conditional Trps1Col1a1 knockout mouse, in which Trps1 is deleted in differentiated odontoblasts using 2.3kbCol1a1-CreERT2 driver. Mandibular first molars of 4wk old male and female mice were analyzed by micro-computed tomography (μCT) and histology. Mechanical properties of dentin and enamel were analyzed by Vickers microhardness test. The susceptibility to acid demineralization was compared between WT and Trps1Col1a1cKO molars using an ex vivo artificial caries procedure. μCT analyses demonstrated that odontoblast-specific deletion of Trps1 results in decreased dentin volume in male and female mice, while no significant differences were detected in dentin mineral density. However, histology revealed a wider predentin layer and the presence of globular dentin, which are indicative of disturbed mineralization. The secondary effect on enamel was also detected, with both dentin and enamel of Trps1Col1a1cKO mice being more susceptible to demineralization than WT tissues. The quality of dental tissues was particularly impaired in molar pits, which are sites highly susceptible to dental caries in human teeth. Interestingly, Trps1Col1a1cKO males demonstrated a stronger phenotype than females, which calls for attention to genetically-driven sex differences in predisposition to dental caries. In conclusion, the analyses of Trps1Col1a1cKO mice suggest that compromised quality of dental tissues contributes to the high prevalence of dental caries in TRPS patients. Furthermore, our results suggest that TRPS patients will benefit particularly from improved dental caries prevention strategies tailored for individuals genetically predisposed due to developmental defects in tooth mineralization.

In Vivo Colonization with Candidate Oral Probiotics Attenuates Colonization and Virulence of Streptococcus mutans

A collection of 113 Streptococcus strains from supragingival dental plaque of caries-free individuals were recently tested in vitro for direct antagonism of the dental caries pathogen Streptococcus mutans, and for their capacity for arginine catabolism via the arginine deiminase system (ADS). To advance their evaluation as potential probiotics, twelve strains of commensal oral streptococci with various antagonistic and ADS potentials were assessed in a mouse model for oral (i.e., oral mucosal pellicles and saliva) and dental colonization under four diets (healthy or high-sucrose, with or without prebiotic arginine). Colonization by autochthonous bacteria was also monitored. One strain failed to colonize, whereas oral colonization by the other eleven strains varied by 3 log units. Dental colonization was high for five strains regardless of diet, six strains increased colonization with at least one high-sucrose diet, and added dietary arginine decreased dental colonization of two strains. Streptococcus sp. A12 (high in vitro ADS activity and antagonism) and two engineered mutants lacking the ADS (ΔarcADS) or pyruvate oxidase-mediated H₂O₂ production (ΔspxB) were tested for competition against S. mutans UA159. A12 wild type and ΔarcADS colonized only transiently, whereas ΔspxB persisted, but without altering oral or dental colonization by S. mutans In testing four additional candidates, S. sanguinis BCC23 markedly attenuated S. mutans' oral and dental colonization, enhanced colonization of autochthonous bacteria, and decreased severity of smooth surface caries under highly cariogenic conditions. Results demonstrate the utility of the mouse model to evaluate potential probiotics, revealing little correlation between in vitro antagonism and competitiveness against S. mutans in vivo IMPORTANCE Our results demonstrate in vivo testing of potential oral probiotics can be accomplished and can yield information to facilitate the ultimate design and optimization of novel anti-caries probiotics. We show human oral commensals associated with dental health are an important source of potential probiotics that may be used to colonize patients under dietary conditions of highly varying cariogenicity. Assessment of competitiveness against dental caries pathogen Streptococcus mutans and impact on caries identified strains or genetic elements for further study. Results also uncovered strains that enhanced oral and dental colonization by autochthonous bacteria when challenged with S. mutans, suggesting cooperative interactions for future elucidation. Distinguishing a rare strain that effectively compete with S. mutans under conditions that promote caries further validates our systematic approach to more critically evaluate probiotics for use in humans.

Pyrosequencing of Plaque Microflora In Twin Children with Discordant Caries Phenotypes

Despite recent successes in the control of dental caries, the mechanism of caries development remains unclear. To investigate the causes of dental decay, especially in early childhood caries, the supragingival microflora composition of 20 twins with discordant caries phenotypes were analyzed using high-throughput pyrosequencing. In addition, the parents completed a lifestyle questionnaire. A total of 228,789 sequencing reads revealed 10 phyla, 84 genera, and 155 species of microflora, the relative abundances of these strains varied dramatically among the children, Comparative analysis between groups revealed that Veillonella, Corynebacterium and Actinomyces were presumed to be caries-related genera, Fusobacterium, Kingella and Leptotrichia were presumed to be healthy-related genus, yet this six genera were not statistically significant (P>0.05). Moreover, a cluster analysis revealed that the microbial composition of samples in the same group was often dissimilar but that the microbial composition observed in twins was usually similar. Although the genetic and environmental factors that strongly influence the microbial composition of dental caries remains unknown, we speculate that genetic factors primarily influence the individual's susceptibility to dental caries and that environmental factors primarily regulate the microbial composition of the dental plaque and the progression to caries. By using improved twins models and increased sample sizes, our study can be extended to analyze the specific genetic and environmental factors that affect the development of caries.

The Mystery of Handprints: Assesment and Correlation of Dermatoglyphics with Early Childhood Caries A Case-Control Study

BACKGROUND

It has been acknowledged that genetics play a significant role in determination of dermatoglyphic patterns. Since caries is a multifactorial disease with the influence of genetic pattern, this study was undertaken to assess dermatoglyphic patterns and correlate them with early childhood caries.

AIM

The aim of the study was to determine the association and correlation of dermatoglyphic patterns with early childhood caries.

MATERIALS AND METHODS

The study sample consisted of 100 children aged between 3 and 6 years, divided into two groups of 50 children each. The deft score was evaluated to select the experimental group and control group. Finger and palm prints were recorded using the ink method described by Cummins and Midlo. The handprints obtained were checked for their clarity with a magnifying glass (×2) and coded. The presence of core and the triradii of the dermatoglyphic pattern were checked thoroughly to include the handprint in the study. A total of 1000 digital prints and 200 palmar prints were obtained.

RESULTS

The presence of whorls in the index finger of the right hand predicts significantly lower risk of caries in children (male and female; combined). Presence of whorls in the ring finger of the right hand predicts significantly lower risk of caries in female children. Statistically no correlation between atd angle and early childhood caries was obtained from the present data.

CONCLUSION

The results obtained from the present study creates a notion on the validity of the results of the previous studies and point them to be chance findings. Due to increasing acceptability of dermatoglyphics as a diagnostic tool for congenital diseases, further large scale extensive research should be undertaken to evaluate the role of the same in children with Early Childhood Caries (ECC).

Association of DLX3 gene polymorphism and dental caries susceptibility in Japanese children

OBJECTIVE

In this study, we investigated whether single nucleotide polymorphisms (SNPs) in DLX3 are associated with dental caries susceptibility in Japanese children.

DESIGN

Genomic DNA of 201 Japanese children was extracted from buccal epithelial cells. The subjects were divided into two groups: 'low level' group with <10,000 colony forming units (CFU) of Streptococcus mutans/mL saliva (level 0) and 'high level' group with ≥ 10,000 CFU/mL (more than level 1). Each group was further divided according to decayed, missing, filled teeth (dmft) into low caries experience (dmft ≤2) and high caries experience (dmft ≥ 3). Seven SNPs in DLX3 were genotyped using TaqMan1® SNP Genotyping Assay.

RESULTS

Statistical significant association was observed between DLX3 (rs2278163) and caries experience in 'high level Mutans streptococci' group.

CONCLUSION

These findings suggest that rs2278163 SNP of DLX3 might be associated with dental caries susceptibility in Japanese children. T and C alleles of rs2278163 SNP may potentially be involved in caries susceptibility and caries protection respectively.

Association of sweet taste receptor gene polymorphisms with dental caries experience in school children

Sweet taste is a powerful factor influencing food acceptance. The peripheral taste response to sugar is mediated by the TAS1R2/TAS1R3 taste receptors. The aim of the study was to determine the relationship between TAS1R2 (rs35874116 or rs9701796) and/or TAS1R3 (rs307355) single nucleotide polymorphisms with dental caries experience in schoolchildren. A total of 184 schoolchildren aged between 7 and 12 years (101 girls, 83 boys) were included in the study. Genomic DNA was extracted from saliva samples and the genotypes were identified by qPCR. The genotype frequencies were as follows: 6.6% for homozygous wild type, 41.8% for heterozygous and 51.6% for homozygous polymorphic genotype carriers of TAS1R2 gene rs35874116; 27.8% for heterozygous and 72.2% for homozygous polymorphic genotype carriers of TAS1R2 gene rs9701796, and 83.1% for homozygous wild type and 16.9% for heterozygous genotype carriers of TAS1R3 gene rs307355 polymorphism. A significant association was observed between total caries experience (dft + DMFT - decayed filled primary teeth + decayed, missing and filled permanent teeth) and TAS1R2 rs35874116 (p = 0.008) and TAS1R3 rs307355 (p = 0.04) gene polymorphisms but not for TAS1R2 gene rs9701796 polymorphism. TAS1R3 gene rs307355 polymorphism has been found to be an independent risk factor for dental caries experience by logistic regression analysis and to have increased the risk of caries. Moderate caries experience (4-7 caries) was found to be associated with TAS1R3 rs307355 heterozygous genotype, whereas high-risk caries experience (>8 caries) was found to be associated with TAS1R2 rs35874116 homozygous polymorphic genotype.

Weaker dental enamel explains dental decay

Dental caries continues to be the most prevalent bacteria-mediated non-contagious disease of humankind. Dental professionals assert the disease can be explained by poor oral hygiene and a diet rich in sugars but this does not account for caries free individuals exposed to the same risk factors. In order to test the hypothesis that amount of amelogenin during enamel development can influence caries susceptibility, we generated multiple strains of mice with varying levels of available amelogenin during dental development. Mechanical tests showed that dental enamel developed with less amelogenin is "weaker" while the dental enamel of animals over-expressing amelogenin appears to be more resistant to acid dissolution.

Enamel formation genes associated with dental erosive wear

Dental erosive wear is a multifactorial condition that is greatly affected by environmental factors. So far, no study has investigated how dental erosive wear is influenced by variations in enamel formation genes. The aim of the present study was to investigate polymorphisms in genes involved in enamel formation and their influence on enamel susceptibility to dental erosion. DNA samples were collected from 795 Norwegian adolescents aged 16-18 years. Five single-nucleotide polymorphism markers were genotyped in selected candidate genes (ameloblastin, amelogenin, enamelin, tuftelin 1 and tuftelin interacting protein 11), reported to influence enamel formation. Allele and genotype frequencies were compared within two patient groups with dental erosions; all participants with dental erosion and only those with severe dental erosion (erosion extending into dentine). Overrepresentation of the G allele of the enamelin marker was seen in the erosion group compared to the unaffected group (p = 0.047). When erosion severity was considered, statistical significant difference in allele frequency was observed for amelogenin, with the C allele suggesting a protective role (p = 0.02). A suggestive overrepresentation of the TT genotype of the amelogenin marker was also seen in cases with severe erosion (p = 0.049) when compared to cases with no dentine erosion. Amelogenin was also associated with severe erosion in the recessive model; the TT genotype was significantly more frequent in the affected group than in the unaffected group (p = 0.01). The present study suggests that polymorphisms in enamel formation genes are statistically associated with an individual's susceptibility to dental erosive wear.

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.

Role of TRAV locus in low caries experience

Caries is the most common chronic, multifactorial disease in the world today; and little is still known about the genetic factors influencing susceptibility. Our previous genome-wide linkage scan has identified five loci related to caries susceptibility: 5q13.3, 13q31.1, 14q11.2, 14q 24.3, and Xq27. In the present study, we fine mapped the 14q11.2 locus to identify genetic contributors to caries susceptibility. Four hundred seventy-seven subjects from 72 pedigrees with similar cultural and behavioral habits and limited access to dental care living in the Philippines were studied. An additional 387 DNA samples from unrelated individuals were used to determine allele frequencies. For replication purposes, a total of 1,446 independent subjects from four different populations were analyzed based on their caries experience (low versus high). Forty-eight markers in 14q11.2 were genotyped using TaqMan chemistry. Transmission disequilibrium test was used to detect over transmission of alleles in the Filipino families, and Chi-square, Fisher's exact and logistic regression were used to test for association between low caries experience and variant alleles in the replication data sets. We finally assessed the mRNA expression of TRAV4 in the saliva of 143 study subjects. In the Filipino families, statistically significant associations were found between low caries experience and markers in TRAV4. We were able to replicate these results in the populations studied that were characteristically from underserved areas. Direct sequencing of 22 subjects carrying the associated alleles detects one missense mutation (Y30R) that is predicted to be probably damaging. Finally, we observed higher expression in children and teenagers with low caries experience, correlating with specific alleles in TRAV4. Our results suggest that TRAV4 may have a role in protecting against caries.

Genetics and caries: prospects

Caries remains the most prevalent non-contagious infectious disease in humans. It is clear that the current approaches to decrease the prevalence of caries in human populations, including water fluoridation and school-based programs, are not enough to protect everyone. The scientific community has suggested the need for innovative work in a number of areas in cariology, encompassing disease etiology, epidemiology, definition, prevention, and treatment. We have pioneered the work on genetic studies to identify genes and genetic markers of diagnostic, prognostic, and therapeutic value. This paper summarizes a presentation that elaborated on these initial findings.

Fine-mapping of 5q12.1-13.3 unveils new genetic contributors to caries

Caries is a multifactorial disease and little is still known about the host genetic factors influencing susceptibility. Our previous genome-wide linkage scan has identified the interval 5q12.1-5q13.3 as linked to low caries susceptibility in Filipino families. Here we fine-mapped this region in order to identify genetic contributors to caries susceptibility. Four hundred and seventy-seven subjects from 72 pedigrees with similar cultural and behavioral habits and limited access to dental care living in the Philippines were studied. DMFT scores and genotype data of 75 single-nucleotide polymorphisms were evaluated in the Filipino families with the Family-Based Association Test. For replication purposes, a total 1,467 independent subjects from five different populations were analyzed in a case-control format. In the Filipino cohort, statistically significant and borderline associations were found between low caries experience and four genes spanning 13 million base pairs (PART1, ZSWIM6, CCNB1, and BTF3). We were able to replicate these results in some of the populations studied. We detected PART1 and BTF3 expression in whole saliva, and the expression of BTF3 was associated with caries experience. Our results suggest BTF3 may have a functional role in protecting against caries.

Analysis of polymorphisms in the lactotransferrin gene promoter and dental caries

Regarding host aspects, there has been strong evidence for a genetic component in the etiology of caries. The salivary protein lactotransferrin (LTF) exhibits antibacterial activity, but there is no study investigating the association of polymorphisms in the promoter region of LTF gene with caries. The objective of this study was firstly to search the promoter region of the human LTF gene for variations and, if existent, to investigate the association of the identified polymorphisms with dental caries in 12-year-old students. From 687 unrelated, 12-year-old, both sex students, 50 individuals were selected and divided into two groups of extreme phenotypes according to caries experience: 25 students without (DMFT = 0) and 25 with caries experience (DMFT ≥ 4). The selection of individuals with extreme phenotypes augments the chances to find gene variations which could be associated with such phenotypes. LTF gene-putative promoter region (+39 to −1143) of the selected 50 individuals was analyzed by high-resolution melting technique. Fifteen students, 8 without (DMFT = 0) and 7 with caries experience (mean DMFT = 6.28), presented deviations of the pattern curve suggestive of gene variations and were sequenced. However, no polymorphisms were identified in the putative promoter region of the LTF gene.

Taste genes associated with dental caries

Dental caries is influenced by a complex interplay of genetic and environmental factors, including dietary habits. Previous reports have characterized the influence of genetic variation on taste preferences and dietary habits. We therefore hypothesized that genetic variation in taste pathway genes (TAS2R38, TAS1R2, GNAT3) may be associated with dental caries risk and/or protection. Families were recruited by the Center for Oral Health Research in Appalachia (COHRA) for collection of biological samples, demographic data, and clinical assessment of oral health, including caries scores. Multiple single-nucleotide polymorphism (SNP) assays for each gene were performed and analyzed by transmission disequilibrium test (TDT) analysis (FBAT software) for three dentition groups: primary, mixed, and permanent. Statistically significant associations were seen in TAS2R38 and TAS1R2 for caries risk and/or protection.

Analysis of the association between lactotransferrin (LTF) gene polymorphism and dental caries

OBJECTIVE

The present study evaluated the association between lactotransferrin (LTF) gene polymorphism (exon 2, A/G, Lys/Arg) and dental caries.

MATERIAL AND METHODS

A convenience sample of 110 individuals, 12 years old, was divided into: group 1, 48 individuals without caries experience (DMFT=0), and group 2, 62 subjects with caries experience (DMFT>or=1). DNA was obtained from a mouthwash with 3% glucose solution, followed by a scrapping of the oral mucosa. After DNA purification, polymerase chain reaction (PCR), single strand conformation polymorphism (SSCP) was performed to access the study polymorphism. The LTF A/G (Lys/Arg) polymorphism had been previously reported as located in exon 1.

RESULTS

Allele 1 of the study polymorphism was associated with low DMFT index and showed a protective effect against caries experience (OR=0.16, IC=0.03-0.76, p=0.01).

CONCLUSIONS

Lactotransferrin A/G (exon 2, Lys/Arg) polymorphism was associated with susceptibility to dental caries in 12-year-old students.

Genome-wide scan finds suggestive caries loci

Here we report the first genome-wide scan performed for caries. Evidence from twin studies suggests a genetic component to caries. We aimed to identify genetic factors contributing to caries in a population similarly influenced by confounding factors, such as diet, oral hygiene habits, fluoride exposure, and access to dental care. Forty-six families with similar cultural and behavioral habits, and living in the Philippines, were studied, and genome-wide genotype data and DMFT (Decayed, Missing due to caries, Filled Teeth) scores were evaluated. Suggestive loci logarithmic odds (LOD) scores above 2.0 or non-parametric p-values below 0.0009) were found for low caries susceptibility (5q13.3, 14q11.2, and Xq27.1) and high caries susceptibility (13q31.1 and 14q24.3). Genes that may be related to saliva flow and diet preferences are proposed as possible candidates. A protective locus for caries in the X chromosome may explain the gender differences seen in caries frequency.

Possible association of amelogenin to high caries experience in a Guatemalan-Mayan population

There is evidence for a genetic component in caries susceptibility, but the disease is greatly influenced by environmental factors, which are extremely difficult to control in humans. For the present study, we used DNA samples collected from 110 unrelated, non-cleft individuals older than 12 years of age from Tiquisate, Guatemala: a population with similar cultural, dietary and hygiene habits, similar access to the dentist and fluoride exposure. Forty-four individuals were designated 'very low caries experience' (DMFT < or = 2), and 66 were designated 'higher caries experience' (DMFT > or = 3). Single-nucleotide polymorphism markers were genotyped in selected candidate genes (ameloblastin, amelogenin, enamelin, tuftelin-1, and tuftelin interacting protein 11) that influence enamel formation. Having at least one copy of the rare amelogenin marker allele was associated with increased age-adjusted caries experience. This association was stronger in individuals with higher DMFT (DMFT > or = 20; p = 0.0000001). Our results suggest that variation in amelogenin may contribute to caries susceptibility in the population studied. The approach of comparing individuals with extremely distinct caries experiences could be valuable for decreasing the potential influence of environmental factors on genetic studies of caries.

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.

Heritability estimates for dental caries and sucrose sweetness preference

OBJECTIVE

The aim of this study was to determine heritability estimates for dental caries traits and sucrose sweetness preference.

DESIGN

Participants included 115 pairs of twins 4-7-years-old. Caries exams followed NIDCR criteria where the severity of the lesion was also determined. Twins ranked their preference for five concentrations of sucrose/grape juice solutions (0.15-1.17M) with a Face Scale. Variables submitted to analysis: (1) surface-based caries prevalence rate (SBCPR); (2) lesion severity index (LSI); (3) sucrose sweetness preference score (SSPS). Heritability analyses were performed with the SOLAR software package.

RESULTS

Heritability estimates adjusted for age and gender were: SBCPR-h(2)=64.6 (p<.00001), LSI-h(2)=61.7 (p<.00001) and SSPS-h(2)=55.2 (p<.00001). Treating SPSS as a covariate in the SBCPR and LSI models did not alter heritability estimates.

CONCLUSIONS

These results suggest that variation in dental caries traits and sucrose sweetness preference have a significant genetic contribution that is mediated independently.

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.