Enzymes, dentinogenesis and dental caries: a literature review

Objectives

Search in PubMed with keywords “enzymes, dentinogenesis, and dental caries” revealed only 4 items, but when combined with “enzymes, osteogenesis, and osteoporosis” as high as 404 items resulted. Dental caries was associated with an order of magnitude fewer studies than the chronic bone disease, osteoporosis. This observation motivated this review.

Material and Methods

A comprehensive review of the available literature on role of enzymes in dentinogenesis and dental caries was undertaken using MEDLINE (PubMed) and Scopus. Keywords for the search were: enzymes and odontoblasts, enzymes and different forms of dentinogenesis as well as dental caries.

Results

Search revealed studies which described odontoblasts harbouring numerous enzymes (hydrolases, including metalloproteinases, transaminases and dehydrogenases) during primary dentinogenesis. Alkaline phosphatase activity sharply decreased when odontoblasts turned into quiescent odontoblasts. Tertiary dentinogenesis was characterized first by reactionary dentine formation when alkaline phosphatase was highly reactivated. Then later some of these odontoblasts may die out and be replaced by other progenitor cells of pulpal origin. This tertiary dentine was called reparative dentine. Pulpal progenitor/stem cells revealed alkaline phosphatase activity in areas encircling inflamed pulp sections. Soft carious dentine revealed high hydrolase, transaminase and dehyrogenase activities that may have originated from invading microbes, saliva or were endogenous. Proteolytic activity was especially demonstrable using histochemical and biochemical means. Specifically, matrix metalloproteases may have originated partly from activated proenzymes of host origin.

Conclusions

Though dental studies are scanty when compared to bone, the active role of large spectrum of enzymes in healthy and carious dentine was given support.

Review of 36,537 patient records for tooth health and longevity of dental restorations

To develop an automatic system for utilizing electronic dental records, a data mining system to extract the diagnostic and treatment codes from the records for an intermediate file and automatic drawing of Kaplan-Meier-type survival curves was first created. Then this intermediate file was analyzed with SAS software for the scientific determination of Kaplan-Meier survival of tooth/surface-specific healthy time and survival of restorations in each permanent tooth, health center, and age cohort and also combined. All patients born in 1985, 1990 or 1995 in 28 health centers in Finland were analyzed. Patients classified as caries-active were those who had caries in any first permanent molar under the age of 8 years, while resistant patients did not have caries in these teeth before 10 years. In the younger age cohorts, a shortening of survival of caries-free teeth was seen. The shortest caries-free survival was seen in mandibular and maxillary molars in the youngest age cohort. Occlusal surfaces of molars determined their caries onsets and proximal caries occurred equally in molars, incisors and premolars, whereas canines or mandibular incisors did not have caries in these age cohorts. Caries-prone subjects had the shortest survival in all their teeth. The median longevity of all restorations was 11.7 years, with great variation between health centers and teeth. Because of the great variation between individual teeth, the tooth-specific approach seems appropriate in both caries epidemiology and material sciences.

Use of statistical methods in dental research: comparison of four dental journals during a 10-year period

OBJECTIVE

To investigate development of the use of statistical methods in dental journals in 1996, 2001, and 2006 hypothesizing that methods are becoming more sophisticated.

MATERIAL AND METHODS

All original research articles in four dental journals in 1996, 2001, and 2006 were reviewed: Journal of Dental Research (JDR), Caries Research (CR), Community Dentistry and Oral Epidemiology (CDOE) and Acta Odontologica Scandinavica (AOS). Evaluation covered 928 articles reporting original research findings based on systematic collection and statistical analysis of research data. Aspects measured were: research design, statistical methodology, description of procedures, and presentation of results. Percentage frequencies of reported statistical procedures were compared between journals and between years.

RESULTS

The main findings of the study are: 1) that use of multivariate or specific methods did not increase from 1996 to 2006, 2) that traditional statistical significance testing is still widely used in dental journals and that use of confidence intervals increased in the period 1996 to 2006, 3) that statistical procedures are usually extensively described, and 4) that dental journals have different profiles in their statistical content.

CONCLUSIONS

The authors of articles in dental journals might apply these results when designing their dental research, i.e. to use statistical methods and to present results in line with the policy and presentation of the leading dental journals.

A practice-based study on the effect of a short sucrose/xylitol exposure on survival of primary teeth caries free

BACKGROUND

In a randomized double-blinded clinical trial, preschool children used sucrose or xylitol chewing gum regularly for 2 months to study the preventive effect of xylitol on acute otitis media (AOM). Salivary mutans streptococci (sm) levels of the children were measured before the exposure. Those with ≥10(5) sm CFU in 1 mL saliva were considered to have high sm levels (sm+); and those with <10(5) CFU low sm levels (sm-).

AIM

This practice-based study aims to evaluate long-term dental effects of the sucrose/xylitol exposure on primary teeth.

DESIGN

For analyses, individuals were divided into sub groups according to their study group in the original AOM trial and baseline sm levels. Outcome events owing to dental caries of their all primary teeth were followed from dental records up to 12 years. Survival of teeth caries free was determined by Kaplan-Meier method and analysed statistically by Wilcoxon testing.

RESULTS

Survival of primary teeth caries free of children with high sm levels in the sucrose group was significantly shorter compared with all other groups when followed until shedding.

CONCLUSIONS

Two months' regular exposure to sucrose was sufficient to induce dental caries in primary teeth of children with elevated sm levels at baseline.

Has dental caries prevalence some connection with caries index values in adults?

DMF index values have been used for 70 years and were originally meant to describe both dental status and treatment need in elementary school children. Since then its application to caries experience and severity determination has expanded. Today, WHO has standardized its use in oral health surveys in describing past and present caries experience in adults and the elderly as well. This expansion to all age cohorts creates some problems if the index is limited to dental caries, which can be easily avoided when individual values are not combined. This has been performed in some of the 7,187 DMF index publications included in PubMed. The high number of scientific articles using this index underlines its leading role in the present epidemiological caries research. On the other hand, WHO uses different determinations for clinical dental caries and missing teeth in ICD-10, the 10th revision of International Classification of Diseases, which does not include dental restorations. Combining the individual parameters of Oral Health Surveys and diseases of ICD-10, and analyzing the mean value of each parameter separately, will give a precise picture of dental health at different ages.

A practice-based study of the variation of diagnostics of dental caries in new and old patients of different ages

Data mining of digital dental records provides possibilities for analysing the variation between dentists when diagnosing caries. A total of 71,317 male and 82,302 female subjects visited the health centres in Vantaa and Kemi during the 'digital era' (1994-2005). As subjects were classified as 'new patients' at the first examination, all re-examinations of the same subjects thereafter by the same dentist produced 'old patients'. A mean number of decayed surfaces (DS) was counted as a function of the age of the subject during the follow-up. The significance of the difference between old and new patients was determined by the Mann-Whitney test for each age cohort at the cross sections, and for the whole follow-up. Caries was seen to affect new patients more than the old ones in both health centres after the age of 20 years. The mean DS values were the same, reaching about 1 for new and old patients at the age of 15 years. The mean DS had a peak for new patients in both health centres at the age of 25 years and another peak around 45-50 years in Kemi. With a few exceptions there was a significant difference between the DS values of new and old patients at most cross sections and for the whole follow-up time. Evidently dentists examine new patients more carefully than their old patients. After the age of 18 years patients may have changed their dentists because they have finished the free-of-charge treatment period.

Practice-based study of the cost-effectiveness of fissure sealants in Finland

OBJECTIVE

To retrospectively analyze the cost-effectiveness of sealant treatment in two health centers with different caries preventive strategies in Finland using a practice-based research protocol.

MATERIALS AND METHODS

The data of digital dental records were data-mined and analyzed retrospectively in the health center in Kemi where the preventive strategy was sealing selectively only high-caries risk patients, and in Vantaa where all patients were routinely sealed. Risk group determination in Kemi was based on the presence of Streptococcus mutans in dental plaque. Supervised use of xylitol was an additional caries preventive measure in Kemi. The subjects were divided into all-sealed and non-sealed groups in the beginning of the follow-up according to the sealant treatment status of their first permanent molars. The mean cumulative cost of restorations and sealing treatment was counted in children at 12 years of age.

RESULTS

Sealing of risk children in Kemi resulted in a total cost of 185euro per child whereas the respective cost of routinely sealed children in Vantaa was 235euro. The cost of restorations was 76euro in Kemi and 150euro in 5 years in Vantaa. Risk determination and the use of xylitol did not affect significantly the total treatment cost in Kemi.

CONCLUSION

The significant reduction in the cost of dental treatment can be achieved by leaving non-risk subjects unsealed and sealing only high-caries risk individuals.

Comparison of the effectiveness of fissure sealants in Finland, Sweden, and Greece

OBJECTIVE

To evaluate the effectiveness of sealant treatment in preventing dental restorations due to caries in a practice-based research network in Finland, Sweden, and Greece.

MATERIAL AND METHODS

Times of tooth emergence, sealing treatment, and dental caries were compiled from the dental charts of 4735 subjects born in 1970-72 in Finland and in 1980-82 in Finland, Sweden, and Greece. Survival time between tooth emergence and placement of first restoration was measured and estimated using survival analysis methodology.

RESULTS

At the end of follow-up (7-10+ years), 30-40% of sealed molars and 60-80% of non-sealed molars were restored. Early sealant placement compared to late sealing did not result in significantly higher survival of 1st molars. The strategy of sealing the 1st molars only in high caries risk subjects was as effective as sealing all the molars and premolars routinely without caries risk determination.

CONCLUSIONS

The sealing of all molar fissures proved to be no more effective than sealing risk fissures of subjects. Early sealing did not result in any better outcome than late sealing. The effectiveness of sealant treatment in preventing dental restorations is dependent on the caries risk of individuals and caries prevalence of the country.

Computed online determination of life-long mean index values for carious, extracted, and/or filled permanent teeth

OBJECTIVE

The purpose of this study was to develop and test a data-mining system for the online determination of mean DS, M, and FS or DMFS values per subject at different ages from electronic patient records at two health centers to see if there are north-south differences in oral health in Finland.

MATERIAL AND METHODS

The mean index values were determined at two health centers using the codes of dental charts and progress notes of electronic dental records during the digital era of more than 10 years in a total of 153,619 subjects of all ages. Extracted teeth, as well as sound, carious, and restored tooth surfaces, were recorded from the dental charts. Treatments were then additionally registered from progress notes of the records when performed.

RESULTS

The cumulative DS and FS values were similar in subjects under the age of 20 years at both health centers. In adults, caries was more abundant in northern Finland, where there was a higher number of restored surfaces (>40) registered, compared to only 30 in southern Finland at the age of 40 years. A high increase in the number of extractions began at age 45 in the north compared to age 70 in the south. These changes were clearly reflected in the DMFS index.

CONCLUSIONS

Online determination of health parameters is a feasible methodology. The results revealed that north-south regional differences in dental health still occur in adults in Finland, but not in subjects younger than 20 years of age.

A practice-based study of the sealant treatment effectiveness in Finns

OBJECTIVES

The effectiveness of fissure sealing in preventing dental caries in a subject-specific fashion was studied in order to forge a link between the controlled trials and knowledge creation in clinical practice.

METHODS

The subjects were divided retrospectively into three categories according to the sealant treatment status of their first permanent molars at the first examination after the eruption and the survival of first molars in each group were estimated using the Kaplan-Meier method.

RESULTS

Sealing of all first molars in caries-prone subjects was an effective caries preventive method. The highest survival of first molars was observed in the unsealed subjects in the health center focusing on sealing risk-subjects only. The first molars of partly sealed subjects had the lowest probability of survival in both health centers.

CONCLUSION

Sealing all four permanent first molars rather than some of them in high caries risk subjects and leaving unsealed the first molars of caries resistant subjects enable to decrease unnecessary sealant treatment by focusing it especially to those benefiting it.

A seven-year survival analysis of caries onset in primary second molars and permanent first molars in different caries risk groups determined at age two years

OBJECTIVE

To investigate in a group of children (n=183) the effect of possible risk factors registered at the age of 2 years on caries development in 7 years of follow-up, and to study associations between risk groups.

MATERIAL AND METHODS

Consumption of candies, use of a nursing bottle at night, use of fluorides, toothbrushing, pacifier sucking, and prolonged breastfeeding (>or=12 months) were recorded at the age of 2 years. The timing of caries onset in different groups was compared by applying a survival analysis method--the survival curves produced separately for selected teeth in different risk groups.

RESULTS

The survival curves of caries onset for both primary and permanent molars were consistently lower for children who consumed candies more than once a week, did not brush their teeth daily, were given a nursing bottle at night or a pacifier at age 2 years. The multivariate survival analysis confirmed that consumption of candies and lack of daily toothbrushing were the factors that had the major impact on caries onset in both primary and permanent molars. Prolonged pacifier sucking (>or=2 years) was related only with short duration of breastfeeding. Children with prolonged use of a nursing bottle at night also consumed candies more than once a week, did not brush their teeth regularly, and did not use fluoride tablets.

CONCLUSIONS

Consumption of candies and inadequate oral hygiene at age 2 years are important long-term risk factors for caries development in both primary and permanent molars.

Matrix metalloproteinase-8 (MMP-8) is the major collagenase in human dentin

OBJECTIVE

Previously an unidentified collagenolytic metalloprotease together with gelatinase (matrix metalloproteinase-2, MMP-2), and enamelysin (MMP-20) have been detected in human dentin. The aim of the study was to characterize dentinal collagenolytic enzymes. Furthermore, we hypothesized that the dentinal MMPs are protected by the mineral phase, and studied the stability of dentinal MMPs.

DESIGN

To characterize dentinal collagenolytic enzymes, we used Western blotting with specific antibodies against MMP collagenases (MMP-1, -8, and -13) and cathepsin K. MMP-8 immunofluorometric assay (IFMA) was also used for MMP-8 detection, and functional collagenase activity was examined with type I collagen degradation assay. The stability of dentinal MMPs was examined by autoclaving dentin blocks before protein extraction and subsequent examination of protein levels and the activities of dentin collagenase and gelatinases.

RESULTS

MMP-8 (collagenase-2) was detected in dentin both with Western blot and IFMA, and dentinal samples also cleaved the intact type I collagen into characteristic 3/4(alphaA)-cleavage products in vitro. No other collagenases or cathepsin K were detected. In autoclaved samples no MMP-8 was found, but gelatinase activity was observed in protein fractions of mineralized dentin.

CONCLUSIONS

MMP-8 represents the major collagenase in human dentin. Unlike MMP-8, dentinal gelatinases can be detected after autoclave treatment of dentin, indicating their high resistance to external sample treatment procedures.

Analysis of gene and protein expression in healthy and carious tooth pulp with cDNA microarray and two-dimensional gel electrophoresis

Complementary DNA (cDNA) microarray and two-dimensional (2-D) gel electrophoresis, combined with mass spectrometry, enable simultaneous analysis of expression patterns of thousands of genes, but their use in pulp biology has been limited. Here we compared gene and protein expression of pulp tissues from sound and carious human teeth using cDNA microarray and 2-D gel electrophoresis to evaluate their usefulness in pulp biology research and to identify the genes with changes in carious teeth. The cDNA microarray revealed several differentially expressed genes and genes with a high expression in both tissues. These genes have various functions, e.g. effects on vascular and nerve structures, inflammation, and cell differentiation. Variability between cDNA hybridizations indicates that the overall gene expression pattern may vary significantly between individual teeth. The 2-D gel electrophoresis revealed no change between healthy and diseased tissue. The identification of 96 proteins in the pulp tissue revealed none of the gene products with corresponding high/different mRNA expression in cDNA microarray. Interestingly, we detected also a hypothetical protein (putative nucleoside diphosphate kinase), and present therefore the first evidence for the existence of this protein. Even though the methods reveal potentially important gene expression, they may currently have only limited value in in vivo pulp biology research.

Effects of protein deficiency induced by raw soy with and without sucrose on dentine formation and dentinal caries in young rats

OBJECTIVES

The effects of protein deficiency and sucrose on formation and mineralization of dentine and dental caries in the molars of young rats were investigated.

MATERIALS AND METHODS

Two groups of weaning Wistar rats received raw soy flour to induce protein deficiency with sucrose or starch as the carbohydrate source; the other two groups received skim milk powder as the protein source with sucrose or starch as the carbohydrate source. At the onset, tetracycline was injected to mark the dentine formed at that moment. After 6 weeks, lower molars were sectioned sagittally, and the areas of dentine formation and dentinal caries developed during the experiment were quantified separately in the first and second molars. Dental caries was also classified according to Schiff's reaction. Calcium (Ca), phosphorus (P) and total mineral elements were analyzed using an electron probe microanalyzer.

RESULTS

Rats in both protein-deficient groups and normal protein sucrose group had significantly larger areas of dentine formed compared with rats fed with normal protein starch diet. Ca, P and total mineral elements in dentine were significantly reduced by normal protein sucrose diet. P content was significantly reduced in dentine of rats in protein-deficient sucrose group. Rats in normal protein sucrose group had significantly more and larger dentinal caries lesions than in any other group.

CONCLUSION

This study suggests that protein deficiency induced by soy prevents the progression of dental caries even in highly cariogenic environment.

Matrix metalloproteinase-13 (MMP-13, collagenase-3) is highly expressed in human tooth pulp

Matrix metalloproteinases (MMPs) and their specific tissue inhibitors (TIMPs) participate into extracellular matrix degradation in physiological and pathological conditions. We hypothesized that MMP expression in pulp tissue changes in response to caries attack and investigated the gene expression profiles of MMPs and TIMPs in pulp tissue of sound and carious teeth with cDNA microarray. cDNA microarray demonstrated an extremely high MMP-13 (collagenase-3) mRNA expression in pooled pulp samples of sound and carious teeth, with less pronounced expression of MMP-16 (MT3-MMP) and TIMP-1. Real-time quantitative polymerase chain reaction of individual pulp samples revealed a wide range of the MMP-13 expression level between pulp samples with possible downregulation of MMP-13 expression during caries progression. Western blot and immunohistochemical staining confirmed the presence of MMP-13 with no observable differences between sound and carious teeth pulp tissues. The results reveal that MMP-13 is expressed and synthesized in pulp tissue, an interesting feature considering the very limited expression of MMP-13 in normal adult tissues. Further studies with a larger sample size are needed to clarify the changes in MMP-13 expression during caries progression.

Tooth by tooth survival analysis of dental health in girls with epilepsy

AIM

The aim of this study was to analyse, tooth by tooth, the timing of caries attacks leading to dental restoration in girls with epilepsy.

STUDY DESIGN

The series comprised 60 girls with epilepsy, 8-18 years old, treated in the Departments of Paediatrics or Neurology of the Oulu University Hospital. A group of healthy age matched girls served as control.

METHODS

A tooth by tooth survival analysis of the time between tooth eruption and caries attacks to a stage leading to the restorations of the permanent teeth was conducted retrospectively using data from the dental health records with annual examinations.

RESULTS

The rate of dental restorations placed due to caries was constantly higher in the girls with epilepsy than in their controls.

STATISTICS

The difference was significant between the first molars (p=<0.03), second molars (p=<0.02) and central incisors (p=<0.02) in the maxilla.

CONCLUSION

The present observation supports the hypothesis that factors related to epilepsy, the antiepileptic medication in particular, might increase the risk of caries.

Expression profile of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs in mature human odontoblasts and pulp tissue

Previous studies have demonstrated that (at least) matrix metalloproteinase (MMP)-2, -8, -9, -14 and -20 are expressed by human odontoblasts. Here, we analysed the expression of 19 MMPs and their specific tissue inhibitors (TIMP)-1, -2 and -3) -1, -2 and -3 in mature human odontoblasts and pulp tissue. Since MMP-20 is almost exclusively expressed by the dentin-pulp complex cells, we further analysed the effect of transforming growth factor (TGF)-beta1 and bone morphogenetic protein (BMPs)-2 on its expression. Matrix metalloproteinase-9 served as a positive control for growth factor responsiveness. It was found that MMP-1, -2, -9, -10, -11, -13, -14, -15, -16, -17, -19, -20 and -23, in addition to TIMP-1, -2 and -3 were expressed by both odontoblasts and pulp tissue. Neither MMP-3 nor MMP-12 were expressed in odontoblasts or pulp tissue, and MMP-7, -8, -24 and -25 were expressed only in the odontoblasts; MMP-2, -10, -11, -14 and -20 were expressed more abundantly by odontoblasts, whereas pulp tissue expressed more MMP-13 and MMP-17. Transforming growth factor-beta1 (1 ng ml(-1)) and BMP-2 (100 ng ml(-1)) did not markedly affect MMP-20 mRNA expression. In contrast, TGF-beta1 alone and with BMP-2 significantly upregulated MMP-9 mRNA by 2.4-fold and by 2.6-fold, respectively, in odontoblasts, while in pulp tissue no effects could be detected. The wide-scale expression of MMPs and TIMPs by mature human odontoblasts and pulp tissue suggests that they may participate in dentin matrix organization prior to mineralization, and that growth factors may further control dentin matrix modeling by differentially regulating individual MMPs.

Dental age and dental health determined longitudinally from patient records in three towns in Finland

The aims of this study were to test the suitability of normal dental records in determining the eruption times of teeth and to compare the retrospective longitudinal DMF values with the statistical cross-sectional means. Patient records for two cohorts (1970 and 1980) were collected from three Finnish towns. The study population comprised 1910 children. The eruption times of the permanent teeth, DMFT and DMFS curves (excluding F due to fractures and M due to orthodontic reasons) were investigated for the year of examination in different study locations. The cross-sectional DMF values were compared to longitudinally calculated data. Tooth eruption was earlier in girls than in boys. However, girls did not have significantly higher DMF values than boys. In all towns, dental health was significantly better in the 1980 cohort than in the 1970 cohort. Comparison of the cross-sectional DMF values in the municipal health center statistics showed that the mean statistics gave considerably higher values than the measured values did after 15 years of age. The inconsistency between measured longitudinal DMF values and the cross-sectional statistical DMF values indicates the importance of creating computer programs for analyzing data longitudinally from normal dental records.

Tooth-by-tooth survival analysis of the first caries attack in different age cohorts and health centers in Finland

The aims of this study were to test the hypothesis that existing patient records serve as a source of data for survival analysis of dental health and to develop a system for routinely conducted survival analysis of dental health from tooth eruption to first caries attack. Patient records for three cohorts were collected from four towns in Finland: Oulu, Turku, Kuopio, and Kemi. The study population comprised 2103 children born and living in these towns. The Kaplan-Meier curves for dental caries were drawn separately for each tooth and for the maxilla and mandible (for each age cohort). Placements of the first restoration of all teeth in each age cohort were investigated. The 1960 cohort had an extremely high post-eruptive morbidity in all teeth. The 1970 cohort had relatively high immediate post-eruptive morbidity in both molars, but much lower than that of the 1960 cohort. The filling increment rates for second molars were lower than those of the first molars in the 1970 cohort. Characteristic of the 1980 cohort was a rapid increase in the caries increment of the premolars and second molars 4 years after eruption. The results indicate a big difference in tooth-by-tooth dental health in Finland. A huge decline in caries attack was seen from the 1960 cohort to the 1980 cohort, but a deterioration of dental health in premolars and second molars is clearly seen in the 1980 cohort in the 1990s.

The localization of matrix metalloproteinase-20 (MMP-20, enamelysin) in mature human teeth

MMP-20 (enamelysin), the matrix metalloproteinase family member discovered in the enamel organ, has also been detected in odontoblasts during dentin formation. We studied the presence and localization of MMP-20 in mature human teeth in health and disease. In immunohistochemistry, MMP-20-positive staining was observed most intensively in the radicular odontoblastic layer and also in dilated dentinal tubuli of caries lesions. By Western blotting, MMP-20 was detected in odontoblasts and pulp tissue of both sound and carious teeth, in dentinal fluid and dentin of sound teeth, but not in soft carious dentin. We conclude that MMP-20 produced during primary dentinogenesis is incorporated into dentin and may be released during caries progression. The main cellular source of MMP-20 in the dentin-pulp complex is the odontoblasts, which secrete MMP-20 into the dentinal fluid.

Caries occurrence in a fluoridated and a nonfluoridated town in Finland: a retrospective study using longitudinal data from public dental records

The tap water of Kuopio, Finland, was fluoridated from 1959 to 1992. In the first decade of fluoridation, children in Kuopio had lower DMF values than children in Jyväskylä, a nearby low-fluoride town, but later differences between the towns have been small and inconsistent. The present study aimed to gain further insight into caries occurrence in Kuopio and Jyväskylä using longitudinal tooth-specific data from public health records on cohorts born in 1970/71 and 1980/81 (total n = 1,503). Survival analyses were used to summarize the tooth-specific times elapsed between eruption and the first filling (used as a proxy for dental caries). Generally, the first filling was placed sooner after eruption in the 1970/71 cohort than in the 1980/81 cohort. The curves for the two towns were virtually identical except for the first molars of the 1970/71 cohort, for which the percentage of filled first molars was consistently lower in Jyväskylä than in Kuopio. This study indicates that, among children and adolescents whose permanent teeth erupted in the mid-1970s or thereafter, even a longitudinal approach did not reveal a lower caries occurrence in the fluoridated than in the low-fluoride reference community. The main reason for the modest effect of water fluoridation in Finnish circumstances is probably the widespread use of other measures for caries prevention. The children have been exposed to such intense efforts to increase tooth resistance that the effect of water fluoridation does not show up any more. The results must not be extrapolated to countries with less intensive preventive dental care.

The effect of a high-sucrose diet on dentin formation and dental caries in hyperinsulinemic rats

A high-sucrose diet decreases dentin formation and its minerals, but the mechanisms behind the effect are largely unknown. We studied the combined and separate effects of sucrose and insulin on dentin formation and mineral metabolism in growing rats. At weaning, animals were randomized into 4 groups: control/sucrose diets both with and without external insulin (1 U/x 100 g body weight daily). After 4 weeks, we measured areas of dentin formation, numbers and areas of dentinal caries lesions, and serum and urine glucose, insulin, Ca, Na, K, and P. Exogenous insulin increased serum and urine insulin levels and decreased serum glucose level, but did not affect dentin formation or dentinal caries lesion formation or progression. A high-sucrose diet decreased dentin formation independently of insulin. The differences in serum and urine minerals between the groups were minor. The findings confirm that sucrose-diet-induced reduction in dentinogenesis is independent of insulin and loss of minerals in urine.

Regulation and interactions of MT1-MMP and MMP-20 in human odontoblasts and pulp tissue in vitro

MT1-MMP is a cell-membrane-bound metalloenzyme that activates other proMMPs such as proMMP-2 and -13. We studied MT1-MMP expression in mature human odontoblasts and pulp tissue, the regulation of MT1-MMP expression by growth factors TGF-beta1 and BMP-2, and the activation of odontoblast-derived MMP-20 by MT1-MMP. MT1-MMP mRNA is expressed by native and cultured mature human odontoblasts and pulp tissue. Western blot analysis of human odontoblasts and pulp tissue detects 65- and 51-kDa pro- and active forms of MT1-MMP, and smaller truncated MT1-MMP forms. BMP-2 down-regulates MT1-MMP expression in odontoblasts and pulp tissue, while TGF-beta1, alone or with BMP-2, decreases MT1-MMP mRNA levels only slightly. We also demonstrate that MT1-MMP is capable of converting proMMP-20 into a form corresponding to the active MMP-20. In conclusion, this study demonstrates the expression and differential regulation of MT1-MMP in human dentin-pulp complex cells, and the activation of MMP-20 by MT1-MMP.

The effects of high levels of glucose and insulin on type I collagen synthesis in mature human odontoblasts and pulp tissue in vitro

High levels of dietary sucrose affect the metabolism of the pulp-dentin complex and enhance the caries process in dentin. The high-sucrose diet reduces dentin formation in young rats (Tjäderhane et al., 1994; Hietala and Larmas, 1995; Tjäderhane, 1996) and in pups of rat dams fed high-sucrose diet during lactation (Pekkala et al., 2000a). However, the mechanisms behind the effects are unknown. A direct effect of elevated blood glucose or an indirect effect via insulin has been suggested. We investigated the effects of high glucose and insulin on type I collagen synthesis in human odontoblasts and pulp tissue in vitro, using an organ culture method for functional post-mitotic odontoblasts. Odontoblasts and pulp tissue were cultured separately for 10 days in DMEM with 15% FBS containing additional glucose (G) (4.45 g/L) or insulin (I) (0.6 microgram/mL) or both together (GI). We evaluated type I collagen synthesis with RIA, measuring the level of N-terminal propeptide of type I collagen (PINP) secreted into the culture media. PINP secretion decreased in odontoblasts and pulp tissue in G and GI groups when compared with the control and insulin samples (p = 0.001 in both groups in the pulp samples). Insulin alone did not affect PINP secretion distinctly. The results indicate that high levels of glucose, but not insulin, directly down-regulate the type I collagen synthesis in young, differentiated human odontoblasts and pulp tissue. Insulin does not affect the inhibitory effect of high sucrose. These in vitro findings indicate that the high-sucrose diet may alter odontoblast function independently of insulin.

Human odontoblast culture method: the expression of collagen and matrix metalloproteinases (MMPs)

Studies on mature human odontoblasts have suffered for the lack of in vitro models. We recently introduced a human odontoblast and pulp tissue organ culture method, in which the odontoblasts are cultured in the pulp chamber after removal of the pulp tissue, and the pulp tissue can be cultured separately (Tjäderhane et al., 1998a). With this method, we have studied the effects of growth factors on the expression of collagen and extracellular matrix (ECM)-degrading enzymes, matrix metalloproteinases (MMPs), in mature human odontoblasts. TGF-beta 1 was selected because of its ability to regulate the response of the dentin-pulp complex to external irritation. The effect of TGF-beta 1 (10 ng/mL) on pro alpha 1(I) collagen mRNA was analyzed by quantitative PCR, and type I procollagen propeptide (PINP) was analyzed from conditioned culture media with RIA. Odontoblast media were also assayed for respective type III procollagen propeptide (PIIINP). TGF-beta had a negligible effect on collagen mRNA expression or protein synthesis, indicating that TGF-beta alone does not markedly induce dentin matrix formation per se in the human dentin-pulp complex (Palosaari et al., 2001). However, TGF-beta 1 seems to regulate MMP expression in mature human odontoblasts differentially. A strong down-regulation of MMP-8 (Palosaari et al., 2000), a modest down-regulation of MMP-20 (Tjäderhane et al., 2000), and considerable up-regulation of MMP-9, with no apparent effect on MMP-2 expression (Tjäderhane et al., 1998b), indicate that growth factors may affect the matrix synthesis by controlling the expression and activity of MMPs instead of collagen synthesis. The altered expression of MMPs may result in altered ECM formation, which in turn may contribute to the formation of atubular reparative dentin.

Odontoblast function seen as the response of dentinal tissue to dental caries

Microbes are responsible for the initiation and maintaining of carious processes. They have an efficient machinery for dissolving crystalline hydroxyapatite. When initiating carious processes, microbial acid formation determines the rate of the process in enamel. When the process reaches dentin, the micro-environment changes. Dential fluid in dentin tubules is the liquid where dissolving products of apatites are destroyed. Inorganic composition of dentinal fluid, however, is not altered much during the carious process, indicating that a functional secretory domain is working to pump the dissolved calcium and phosphate ions out of the fluid. Activation of odontoblast alkaline phosphatase and dentin latent collagenases is the known cellular event during the carious process in dentin. Because the caries lesion is by definition undermining, this suggests that, in this degradation process, the extracellular compartment, crystalline hydroxyapatite is dissolved by microbial acids, and a mixture of proteinases degrades the organic matrix. The degradation products of collagen and other matrix components in dentinal fluid must be transported either through the caries lesion in the enamel to saliva or through the odontoblast to the pulp (active transport). This facilitates further processing of the degradation products intracellularly during the passage through the cell.

The effects of MMP inhibitors on human salivary MMP activity and caries progression in rats

Previous studies suggest that salivary and pulp-derived host enzymes, matrix metalloproteinases (MMPs), may be involved in dentin caries pathogenesis. To study the inhibition of acid-activated human salivary MMPs by non-antimicrobial chemically modified tetracyclines (CMTs), we used a functional activity assay with 125I-labeled gelatin as a substrate. To address the role of MMPs in the progression of fissure caries in vivo, we administered the MMP inhibitors CMT-3 and zoledronate to young rats per os for 7 weeks, 5 days a week. Caries lesions were visualized by Schiff reagent in sagittally sectioned mandibular molars. Marked reduction in gelatinolytic activity of human salivary MMPs was observed with CMT-3. CMT-3 and zoledronate, both alone and in combination, also reduced dentin caries progression in the rats. These results suggest that MMPs have an important role in dentin caries pathogenesis, and that MMP inhibitors may prove to be useful in the prevention of caries progression.

High-sucrose diet reduces defensive reactions of the pulpo-dentinal complex to dentinal caries in young rats

The significance of systemic dietary effects on the response of the pulpo-dentinal complex to dentinal caries was examined. Weanling rats were divided into high sucrose or control diet groups both with and without cariogenic bacterial inoculation. At the onset, tetracycline was injected to mark the dentin formation during the experiment. After 5-6 week, mandibular molars were sectioned sagittally. The areas of dentin formed during the experiment and those of dentinal caries were quantified separately in the first and second molars. In the control diet groups the area of dentin was significantly greater under carious fissures, whereas in the high sucrose diet groups the area of dentin formed did not differ between intact and carious fissures. The high sucrose diet resulted in a significantly smaller area of dentin formation than did the control diet. The high sucrose diet with cariogenic bacterial inoculation resulted in the greatest area of dentinal caries. With the control diet a positive response against dentinal caries occurs, but the high dietary sucrose content impairs the defensive reactions of pulpo-dentinal complex against dentinal caries. These findings add further evidence of the importance of the local endogenous factors of caries progression.

Baseline expression and effect of TGF-β1 on Type I and III collagen mRNA and protein synthesis in human odontoblasts and pulp cellsIn Vitro

Since growth factors have been suggested to regulate dentin collagen formation in response to external irritation, we investigated the effect of TGF-β1 on proα1(I) collagen mRNA expression in cultured mature human odontoblasts and pulpal fibroblasts, as well as cultured human pulp tissue, using quantitative PCR. Cultured gingival fibroblasts (GF) and osteoblasts (OB) served as controls. Also, type I collagen synthesis in cultured odontoblasts and pulp tissue, as well as type III collagen synthesis in odontoblasts, were studied by measuring respective procollagen (PINP and PIIINP) secretion into culture media with radioimmunoassay (RIA). Odontoblasts expressed significantly higher basic level of type I collagen mRNA than pulp tissue or pulp fibroblasts in culture, but markedly lower level than GF and OB cells. TGF-β1 (10 ng/ml) had negligible effects on type I collagen mRNA expression or PINP synthesis in cultured odontoblasts and pulp tissue, and PIIINP synthesis in the odontoblasts. In PF cells, the effect of TGF-β1 depended on culturing conditions; a 6-fold increase in mRNA expression was observed using serum-free medium but no effect was seen in the cells cultured with 10% FBS. In contrast, GF cells serving as controls were not markedly affected by the culture conditions, with 2-3-fold increase in mRNA expression by TGF-β1. These experiments demonstrate that mature human odontoblasts are capable of synthesizing type III collagen protein, and that TGF-β1 has negligible effect on mature human odontoblast and pulp tissue collagen expression.

Baseline expression and effect of TGF-beta 1 on type I and III collagen mRNA and protein synthesis in human odontoblasts and pulp cells in vitro

Since growth factors have been suggested to regulate dentin collagen formation in response to external irritation, we investigated the effect of TGF-beta 1 on pro alpha 1 (I) collagen mRNA expression in cultured mature human odontoblasts and pulpal fibroblasts, as well as cultured human pulp tissue, using quantitative PCR. Cultured gingival fibroblasts (GF) and osteoblasts (OB) served as controls. Also, type I collagen synthesis in cultured odontoblasts and pulp tissue, as well as type III collagen synthesis in odontoblasts, were studied by measuring respective procollagen (PINP and PIIINP) secretion into culture media with radio-immunoassay (RIA). Odontoblasts expressed significantly higher basic level of type I collagen mRNA than pulp tissue or pulp fibroblasts in culture, but markedly lower level than GF and OB cells. TGF-beta 1 (10 ng/ml) had negligible effects on type I collagen mRNA expression or PINP synthesis in cultured odontoblasts and pulp tissue, and PIIINP synthesis in the odontoblasts. In PF cells, the effect of TGF-beta 1 depended on culturing conditions; a 6-fold increase in mRNA expression was observed using serum-free medium but no effect was seen in the cells cultured with 10% FBS. In contrast, GF cells serving as controls were not markedly affected by the culture conditions, with 2-3-fold increase in mRNA expression by TGF-beta 1. These experiments demonstrate that mature human odontoblasts are capable of synthesizing type III collagen protein, and that TGF-beta 1 has negligible effect on mature human odontoblast and pulp tissue collagen expression.

Effects of a high sucrose diet and intragastric sucrose feeding on the dentinogenesis, dental caries, and mineral excretion of the young rat

Previous studies show that a high sucrose diet reduces the rate of primary dentinogenesis and increases dental caries, although their cause-effect relationship is still obscure. The purpose of this study was to explore whether the effect of sucrose load on the dentinogenesis and dental caries of young rat molars is mediated by systemic (intragastric) or by systemic and local (dietary) factors. At weaning (19 days), animals were randomized into the control, intragastric sucrose, and dietary sucrose groups for 4 weeks. The areas of dentin appositions and dentinal caries lesions were measured planimetrically. Caries was also determined with Shiffs staining and the width of predentin by histology. Urinary Ca, K, and Na levels were measured by flame photometry, urinary P levels using an UV method, and serum insulin levels using radioimmunoassay. Systemic and local sucrose load reduced dentin appositions and intragastric sucrose increased urinary Ca excretion. No differences in the width of predentin were noticed. Only dietary sucrose enhanced the occurrence and progression of caries. The present findings show that sucrose load reduces dentinogenesis by impairing the synthesis of dentin matrix, but also point out the crucial importance of the local sucrose challenge in the initiation of dental caries.

The reducing effects of a calcium-deficient diet and high sucrose diet on dentin apposition of rat molars

A high sucrose diet reduces dentin apposition of growing rats. The mechanisms of reduction are unclear, but disturbances in calcium balance or in mineralization of predentin may explain them. In this experiment, 29 Sprague-Dawley rats, 21 days old, were weaned and randomized into calcium-deficient, high-sucrose or standard-diet groups for 3 weeks. They were given food and water ad libitum. During the experiment, animals were individually housed in metabolic cages where urine samples were collected. At ages of 21 and 40 days mineralizing dentin was marked using I.P. injections of oxytetracycline hydrochloride. At 42 days of age, the animals were anesthetized and their blood was collected by cardiac puncture. Right hemimandibles were sectioned sagittally and left hemimandibles were fixed, decalcified, and cut into histological sections. Dentin appositions were measured planimetrically, predentin width, from histological sections. Ca, K, and Na levels of serum and urine were measured flame photimetrically and P levels were measured by the UV method. Statistical analyses were done using one-way analysis of variation (ANOVA) Tuckey's HSD t test. In the calcium-deficient group, hypocalcemia, reduced dentin apposition, and increased predentin width were noticed when compared with the control group (P<0.05). Also, the increase in predentin width, caused by calcium deficiency, was significant compared with sucrose-fed animals (P<0.05). Sucrose diet reduced dentinogenesis, increased Ca excretion to urine, but also reduced urinary levels of P, K, and Na, and the differences were significant for the controls (P<0.05). In conclusion, despite the same kind of reduced dentinogenesis in calcium-deficient and high-sucrose groups, calcium imbalance or reduced mineralization of predentin does not explain reduced dentinogenesis in sucrose-fed animals.

The effect of sucrose diet of rat dams on the dentine apposition and dental caries of their pups

The purpose was to examine whether a sucrose diet in rat dams reduces dentine apposition and enhances dental caries in their pups. Sprague-Dawley rat pups were randomized into four groups on the day of birth. During the lactation period three dams received a standard rodent diet and three a diet containing 41% sucrose. At the age of 3 weeks the pups were weaned and given an intraperitoneal injection of oxytetracycline hydrochloride. During the experimental period, half of the pups of control dams received a sucrose diet (Cnt-Suc pups) and half of the pups of sucrose dams received a standard diet (Suc-Cnt pups). The pups in the other halves received the same diet as given to their dams during lactation (Cnt-Cnt and Suc-Suc pups). Urine samples were collected from dams and pups during the test periods. After 4 weeks the pups were killed, their blood was collected and their jaws sectioned sagittally. Dentine apposition was determined planimetrically and dental caries using Schiffs staining. Ca, K and Na of serum and urine were measured flame photometrically and P using an ultraviolet method. The lactational sucrose diet was associated with decreased P and Na excretion in the dams, and also with reduced dentine apposition in their pups. Reduced dentine apposition and induced Ca excretion with decreased P, K and Na excretions were observed in Suc-Suc pups and Cnt-Suc pups during the experiment period. Fewer intact teeth with more enamel and dentinal caries lesions occurred in sucrose-exposed groups (Suc-Cnt, Cnt-Suc and Suc-Suc pups). It was concluded that the sucrose diet given to dams during lactation changed the function of the pulp dentine complex of their pups leading to reduced dentinogenesis, but also predisposed to a reduction of dentinogenesis in pups during the experimental period and enhanced the occurrence of dental caries.

The expression of MMP-8 in human odontoblasts and dental pulp cells is down-regulated by TGF-beta1

Recent findings show that matrix metalloproteinase-8 (MMP-8) is expressed, in addition to neutrophils, by human chondrocytes, cultured fibroblasts, and endothelial cells. We investigated the expression of MMP-8 in other human mesenchyme-derived cells, odontoblasts, and pulp tissue. Odontoblasts and pulp tissue were collected from extracted human teeth for MMP-8 mRNA analysis with reverse-transcription/polymerase chain-reaction (RT-PCR) and Southern blot. The expression, localization, and secretion of MMP-8 protein were studied with Western blot, immunohistochemistry, and immunofluorometric assay. The effect of TGF-beta1 (10 ng/mL) on the expression, secretion, and concentration of secreted MMP-8 was studied by odontoblast and pulp tissue culture methods (Tjäderhane et al., 1998a). RT-PCR demonstrated MMP-8 mRNA expression in native and cultured odontoblasts and pulp tissue and cultured pulp fibroblasts, with a 522-bp transcript comparable with that of bone marrow cells. The specificity of PCR was confirmed with Southern blot. Western blot with MMP-8-specific antibody detected 65- and 50-kDa proteins in native samples, representing latent and active forms of mesenchymal-type MMP-8, and in the conditioned odontoblast culture media, 50-kDa protein was observed. TGF-beta down-regulated the MMP-8 mRNA and concentration of secreted protein in both cultures. Immunohistochemical staining detected MMP-8 in odontoblasts. These findings indicate that mesenchyme-derived cells of the dentin-pulp complex express, synthesize, and activate MMP-8, which may, in concert with odontoblast-derived gelatinases, participate in organization of dentin organic matrix prior to mineralization.

An electron probe x-ray microanalytical study of dentine minerals in sucrose-fed or glucocorticoid-medicated rats

A high sucrose diet and glucocorticoid medication reduced dentine formation in molars of growing rats. This study was undertaken to determine whether the treatment schedules could have produced commensurate reductions in dentine minerals, and the particular concentrations of calcium (Ca) and phosphorus (P). Forty Spraque-Dawley rats were weaned at the age of 3 weeks. Tetracycline was injected i.p. to produce a fluorescent line which demarcated the preweaning from the postweaning dentine. The animals were then divided into two groups. Control rats were fed a commercial rat chow, test animals were fed a 43% sucrose diet. Half the animals in each group were also subjected to surgical implantation (s.c.) of cortisone pellets which released 0.42 mg into the circulation over a 24-hour period. At the end of the 6 week trials rats were killed and the mandibles were defleshed and prepared for electron probe microanalyzer. Each animal served as its own control, as the content of Ca, P, and total minerals were analyzed in the pre- and postweaning regions of dentine. During the preweaning there were no differences between the groups in any minerals. There was a slight reduction of minerals during the postweaning compared with the preweaning. During the postweaning, the sucrose diet significantly reduced the amount of Ca, P, and total minerals compared with the preweaning. During the postweaning, the sucrose diet reduced Ca compared with glucocorticoid medication and total minerals compared with other groups. On the contrary glucocorticoid medication seemed to compensate the reduction of minerals induced by the sucrose diet.

Effects of continuous glucocorticoid infusion on the progression of dentinal caries in growing rats

This study was undertaken to test the effects of a low dose of continuous glucocorticoid infusion on the rate of progression of dentinal caries in molars of young rats. Forty-seven rats were inoculated in the mouth with Streptococcus sobrinus and fed ad libitum a cariogenic diet and 10% sweetened water. After 10 days of caries initiation ten animals were killed to serve as a reference group. In the rest of the animals the cortisone or placebo pellet was implanted subcutaneously in the back of the neck. The daily release of cortisone was 0.42 mg per rat. Sweetened water was changed to pure water, and the diet was the same cariogenic diet. After 6 weeks of medication the areas of dentinal caries were quantified planimetrically. Schiff's staining was used to classify caries. Although cortisone medication slightly increased the number of carious lesions, statistical significance was not reached. However, compared with the placebo group, the rats receiving cortisone medication showed significantly increased dentinal caries progression and severity of lesions. This study suggests that glucocorticoids with a cariogenic diet reduce the intrinsic modulation or response of the odontoblasts to caries attack.

A high sucrose diet decreases the mechanical strength of bones in growing rats

High sucrose diets alter mineral metabolism in humans and animals. We examined the effect of a high sucrose diet on bone growth, composition and mechanical strength in growing rats. Weanling Wistar rats received a high sucrose (43 g/100 g) diet (9 males, 11 females). In the control diet (8 males, 8 females), sucrose was replaced with potato starch, providing an equal energy value. At the onset of the experiment, bones were marked by tetracycline. After 5 wk, the tibias and femurs were weighed, and maximum breaking strengths were determined. Tibias were cut at the tibia-fibular junction; the widths of the bone at the start of the experiment, the periosteal bone formation during the experiment, the widths of the medullary cavity and the final bone width were determined from tetracycline lines. Bone ash weight, Ca and P contents were determined. The breaking strengths of both bones were significantly lower in the sucrose-fed groups of both sexes. In females, the weight of both bones and the final width of the tibias were significantly lower in the sucrose-fed group. The Ca concentration in both bones and the P concentration in tibias were significantly lower in the sucrose-fed group. It was concluded that the metabolic interference induced by sucrose was the reason for the differences. The alterations were more pronounced in females, but independent of body weight.

Comparison of dentin apposition and dentinal caries progression in the mandibular and maxillary molars of the rat

To show that the rate and the rate of reduction of dentin apposition are about the same in mandibular and maxillary molars, 23 Sprague-Dawley rat pups were randomized into 2 groups on the day of birth. During lactation half of their dams received a standard rodent diet; the other half, a diet containing 41% sucrose. At the age of 3 weeks the pups were weaned, weighed, given an intraperitoneal injection of oxytetracycline hydrochloride, and inoculated with oral Streptococcus sobrinus. During the experiment the pups received the same diet as their dams during lactation. After 5 weeks the pups were decapitated, their jaws sectioned sagittally, the first and second molars photographed, and the areas of dentin apposition and dentinal caries measured planimetrically. The area of dentin formation was about the same in maxilla and mandible in the first molars, but slightly smaller in the mandibular second molars of the control group. The sucrose diet reduced dentin apposition significantly in both jaws, although the areas were significantly smaller in the mandibles than in the maxillae. Caries did not affect the rate of dentin apposition. The areas of caries lesions were smaller in the maxillary molars of both diet groups. The results show that the hypothesis of equal rate of dentin apposition in mandible and maxilla was not valid because the reduction, caused by sucrose, was more prominent in mandibular molars for unknown reasons. The reduction of dentin apposition was reflected as acceleration of caries progression among the diet groups and the jaws. It was concluded that the response of the pulpodentinal complex to sucrose and dentinal caries during the primary dentinogenesis cannot be seen as a formation of reactionary or reparative dentin, as with adult rats.