The limited durability of resin-dentin bonds severely compromises the longevity of composite resin restorations. Resin-dentin bond degradation might occur via degradation of water-rich and resin sparse collagen matrices by host-derived matrix metalloproteinases (MMPs). This review article provides overview of current knowledge of the role of MMPs in dentin matrix degradation and four experimental strategies for extending the longevity of resin-dentin bonds. They include: (1) the use of broad-spectrum inhibitors of MMPs, (2) the use of cross-linking agents for silencing the activities of MMPs, (3) ethanol wet-bonding with hydrophobic resin, (4) biomimetic remineralization of water-filled collagen matrix. A combination of these strategies will be able to overcome the limitations in resin-dentin adhesion.

The purpose of this study is to observe and compare the remineralization tendencies of artificial enamel caries lesion by remineralization solutions of different degree of saturations at pH 5.5, using a polarizing microscope and computer programs (Photoshop, Image pro plus, Scion Image, Excel).

For this study, 48 sound permanent teeth with no signs of demineralization, cracks, or dental restorations were used. The specimens were immersed in lactic acid demineralization solution for 2 days in order to produce artificial dental caries that consist of surface and subsurface lesions. Each of 9 or 10 specimens was immersed in pH 5.5 lactic acid buffering remineralization solution of four different degrees of saturation (0.507, 0.394, 0.301, and 0.251) for 12 days. After the demineralization and remineralization, images were taken by a polarizing microscope (×100). The results were obtained by observing images of the specimens, and using computer programs, the density of caries lesions were estimated.

While the group with the lowest degree of saturation (0.251) showed total remineralization feature from the surface to the subsurface of the lesion, the group with the highest degree of saturation (0.507) showed demineralization mainly on the surface of the lesion at the constant organic acid concentration 0.01 M and pH 5.5.

The aim of this vitro-study is to evaluate the effects of fluoride on remineralization of artificial dentine caries. 10 sound permanent premolars, which were extracted for orthodontic reason within 1 week, were used for this study. Artificial dentine caries was created by using a partially saturated buffer solution for 2 days with grounded thin specimens and fractured whole-body specimens. Remineralization solutions with three different fluoride concentration (1 ppm, 2 ppm and 4 ppm) were used on demineralized-specimens for 7 days. Polarizing microscope and scanning electron microscope were used for the evaluation of the mineral distribution profile and morphology of crystallites of hydroxyapatite.

The results were as follows :

When treated with the fluoride solutions, the demineralized dentine specimens showed remineralization of the upper part and demineralization of the lower part of the lesion body simultaneously.

The purpose of this study is to investigate the response of human pulp cell on Portland cement mixed with β-glycerophosphate. To investigate the effect of β-glycerophosphate and/or dexamethasone on human pulp cell, ALP activity on various concentration of β-glycerophosphate and dexamethasone was measured and mineral nodule of human pulp cell was stained with Alizarin red S. MTS assay and ALP activity of human pulp cell on Portland cement mixed with various concentration of β-glycerophosphate (10 mM, 100mM, 1M) was measured and the specimens were examined under SEM.

Addition of β-glycerophosphate or dexamethasone alone had no effect however, the addition of 5 mM β-glycerophosphate and 100 nM dexamethasone had the largest increasement in ALP activity. There was no toxicity in all samples and the data showed that Portland cement mixed with 10 mM β-glycerophosphate had more increase in ALP activity compared with control.

In conclusion, Portland cement mixed with β-glycerophosphate has no toxicity and promotes differentiation and mineralization of pulp cell compared with additive-free Portland cement. This implicated that application of Portland cement mixed with β-glycerophosphate might form more reparative dentin and in turn it would bring direct pulp capping to success.

The purpose of this study is to observe and compare the dynamic change of artificially demineralized enamel by remineralization solutions of different degrees of saturation at pH 4.3.

In this study, 30 enamel specimens were demineralized artificially by lactic acid buffered solution. Each of 10 specimens was immersed in pH 4.3 remineralization solution of three different degrees of saturation (0.22, 0.30, 0.35) for 10 days. After demineralization and remineralization, images were taken by a polarizing microscope (× 100). The density of lesion were determined from images taken after demineralization and remineralization.

During remineralization process, mineral deposition and mineral loss occurred at the same time. After remineralization, total mineral amount and width of surface lesion increased in all groups. The higher degree of saturation was, the more mineral deposition occurred in surface lesion and the amount of mineral deposition was not much in subsurface lesion. Total demineralized depth increased in all groups.

There are considerable in vitro and in vivo evidences for remineralization and demineralization occurring simultaneously in incipient enamel caries. In order to "heal"the incipient dental caries, many experiments have been carried out to determine the optimal conditions for remineralization. It was shown that remineralization is affected by different pH, lactic acid concentrations, chemical composition of the enamel, fluoride concentrations, etc.

Eighty specimens from sound permanent teeth without demineralization or cracks, 0.15 mm in thickness, were immersed in lactic acid buffered demineralization solutions for 3 days. Dental caries with a surface zone and subsurface lesion were artificially produced. Groups of 10 specimens were immersed for 10 or 12 days in lactic acid buffered remineralization solutions consisting of pH 4.3 or pH 6.0, and 100, 50, 25, or 10 mM lactic acid. After demineralization and remineralization, images were taken by polarizing microscopy (x100) and micro-computed tomography. The results were obtained by observing images of the specimens and the density of the caries lesions was determined.

As the lactic acid concentration of the remineralization solutions with pH 4.3 was higher, the surface zone of the carious enamel increased and an isotropic zone of the subsurface lesion was found. However, the total decalcification depth increased at the same time.

In the lactic acid buffer solutions with the lower pH and higher lactic acid concentration, there were dynamic changes at the deep area of the dental carious lesion.

The purpose of this study is to observe and compare the remineralization tendencies of artificially demineralized enamel by remineralization solutions of different degree of saturations at pH 5.5, using a polarizing microscope and computer programs (Photoshop, Image pro plus, Scion Image, Excel).

For this study, 36 sound permanent teeth with no signs of demineralization, cracks, or dental restorations were used. The specimens were immersed in lactic acid demineralization solution for 3 days in order to produce dental caries artificially that consist of surface and subsurface lesions. Each of 9 or 10 specimens was immersed in pH 5.5 lactic acid buffered remineralization solution of three different degrees of saturation (0.25, 0.30, 0.35) for 12 days. After the demineralization and remineralization, images were taken by a polarizing microscope (× 100). The results were obtained by observing images of the specimens, and using computer programs, the density of caries lesions were determined.

In conclusion, in the group with the lowest degree of saturation, remineralization occurred thoroughly from the surface to the subsurface lesion, whereas in the groups with greater degree of saturation showed no significant change in the subsurface lesion, although there was corresponding increase in the remineralization width on the surface zones.

Since it was reported that incipient enamel caries can be recovered, previous studies have quantitatively evaluated that enamel artificial caries have been remineralized with fluoride, showing simultaneously the increase of width of surface layer and the decrease of width of the body of legion. There is, however, little report which showed that remineralization could occur without fluoride. In addition, the observations on the change of hydroxyapatite crystals also have been scarcely seen.

In this study, enamel caries in intact premolars or molars was induced by using lactic acidulated buffering solutions over 2 days. Then decalcified specimens were remineralized by seven groups of solutions using different degree of saturation (0.212, 0.239, 0.301, 0.355) and different pH (5.0, 5.5, 6.0) over 10 days. A qualitative comparison to changes of hydroxyapatite crystals after fracturing teeth was made under SEM (scanning electron microscopy) and AFM (atomic force microscopy).

The results were as follows:

1. The size of hydroxyapatite crystals in demineralized area was smaller than the normal ones. While the space among crystals was expanded, it was observed that crystals are arranged irregularly.

2. In remineralized enamel area, the enlarged crystals with various shape were observed when the crystals were fused and new small crystals in intercrystalline spaces were deposited.

3. Group 3 and 4 with higher degree of saturation at same pH showed the formation of large clusters by aggregation of small crystals from the surface layer to the lesion body than group 1 and 2 with relatively low degree of saturation at same pH did. Especially group 4 showed complete remineralization to the body of lesions. Group 5 and 6 with lower pH at similar degree of saturation showed remineralization to the body of lesions while group 7 didn't show it. Unlike in Group 3 and 4, Group 5 and 6 showed that each particle was densely distributed with clear appearance rather than crystals form clusters together.

Protein microarray or protein chips is potentially powerful tools for analysis of protein-protein interactions. APin cDNA was previously identified and cloned from a rat odontoblast cDNA library. The purpose of this study was to investigate the APin-protein interactions during ameloblast differentiation. Protein microarray was carried with recombinant APin protein and MEF2, Aurora kinase A, BMPR-IB and EF-hand calcium binding protein were selected among 74 interacting proteins. Immortalized ameloblast cells (ALCs) were transfected with pCMV-APin construct and U6-APin siRNA construct. After transfection, the expression of the mRNAs for four proteins selected by protein micoarrays were assessed by RT-PCR.

The results were as follows:

1. APin expression was increased and decreased markedly after its over-expression and inactivation, respectively.

2. Over-expression of the APin in the ALCs markedly down-regulated the expression of MEF2 and Aurora kinase A, whereas their expression remained unchanged by its inactivation.

3. Expression of BMPR-IB and EF-hand calcium binding protein were markedly increased by the overexpression of the APin in the ALCs, whereas expression of BMPR-IB remained unchanged and expression of EF-hand calcium binding protein was markedly decreased by its inactivation.

These results suggest that APin plays an important role in ameloblast differentiation and mineralization by regulating the expression of MEF2, Aurora kinase A, BMPR-IB and EF-hand calcium binding protein.

Dental caries is the most common disease in the oral cavity. However, the mechanism and treatment of dental caries is not completely understood since many complex factors are involved. Especially the effect of pH on remineralization of early stage of dental caries is still controversial.

In this study, dental caries in dentin was induced by using lactic acidulated buffering solutions and the loss of inorganic substance was measured. Also decalcified specimens were remineralized by three groups of solution with different pH (group of pH 4.3, 5.0, and 5.5). Then, the amount and the area of inorganic substance precipitation was quantitatively analyzed with microradiograph. Also a qualitative comparison of the normal phase, the demineralized phase, and the remineralized phase of hydroxyapatite crystal was made under SEM.

The results were as follows;

In microradiograghic analysis, as the pH increased, the amount of remineralization in decalcified dentin tended to increase significantly. As the pH decreaced, deeper decalcification, however, occurred along with remineralization. The group of pH 5.5 had a tendency to be remineralized without demineralization (p < 0.05).

In according to the results of this experiment, the decalcifying and remineralizing process of dentine is neither simple nor independent, but a dynamic process in which decalcification and remineralization occur simultaneously. The remineralization process occurred from the hydroxyapatite crystal surface.

The purpose of this study is to compare and to evaluate the effect of pH and lactic acid concentration on the progression of artificial root caries lesion using polarizing microscope, and to evaluate the morphological changes of hydroxyapatite crystals of the demineralized area and to investigate the process of demineralization using scanning electron microscope.

Artificial root caries lesion was created by dividing specimens into 3 pH groups (pH 4.3, 5.0, 5.5), and each pH group was divided into 3 lactic acid concentration groups (25 mM, 50 mM, 100 mM). Each group was immersed in acid buffer solution for 5 days and examined. The results were as follows:

1. Under polarized microscope, the depth of lesion was more effected by the lactic acid concentration rather than the pH.

2. Under scanning electron microscope, dissolution of hydroxyapatite crystals were increased as the lactic acid concentration increased and the pH decreased.

3. Demineralized hydroxyapatite crystals showed peripheral dissolution and decreased size and number within cluster of hydroxyapatite crystals and widening of intercluster and intercrystal spaces as the pH decreased and the lactic acid concentration increased.

4. Under scanning electron microscope evaluation of the surface zone, clusters of hydroxyapatite crystals were dissolved, and dissolution and reattachment of crystals on the surface of collagen fibrils were observed as the lactic acid concentration increased.

5. Under scanning electron microscope, demineralization of dentin occurred not only independently but also with remineralization simultaneously.

In conclusion, the study showed that pH and lactic acid concentration influenced the rate of progression of the lesion in artificial root caries. Demineralization process was progressed from the surface of the cluster of hydroxyapatite crystals and the morphology of hydroxyapatite crystals changed from round or elliptical shape into irregular shape as time elapsed.

This study was aimed to elucidate the biological function of OD314 (Apin protein), which is related toameloblast differentiation and amelogenesis. Apin protein, calcifying epithelial odontogenic (pindborg) tumors (CEOTs)-associated amyloid, were isolated from CEOTs, and has similar nucleotide sequences to OD314. We examined expression of the OD314 mRNA using in-situ hybridization during tooth development in mice. Expression of OD314 and several enamel matrix proteins were examined in the cultured ameloblast cell line up to 28 days by reverse transcription-polymerase chain reaction (RT-PCR) amplification. After inactivation and over-expression of the OD314 gene in ameloblast cell lines using U6 vector-driven RNA interference and CMV-OD314 construct, RT-PCR were performed to evaluate the effect of the OD314 during amelogenesis.

The results were as follows:

1. In in-situ hybridization, OD314 mRNAs were more strongly expressed in ameloblast than odontoblast.

2. When ameloblast cells were cultured in the differentiation and mineralization medium for 28 days, the tuftelin mRNA expression was maintained from the beginning to day 14, and then gradually decreased to day 28. The expressions of amelogenin and enamelin were gradually decreased according to the ameloblast differentiation.

3. Inactivation of OD314 by U6-OD314 siRNA construct down-regulated the expression of OD314, MMP-20, and tuftelin, whereas over-expression of OD314 by CMV-OD314 construct up-regulated the expression of OD314 and MMP-20 without change in tuftelin.

These results suggest that OD314 is considered as an ameloblast-enriched gene and may play the important roles in ameloblast differentiation and mineralization.

The purpose of this study is to compare and to evaluate the effects of the degree of saturation on the progression of artificial root caries lesion.

A total of 8 human premolars without any defects and cracks selected and the cementum were removed and the teeth were cleaned with ultrasonic device and pumice without fluoride.

Each tooth was sectioned into 6 pieces and they were ground with #800 sandpaper until they had a thickness of 200µm. Specimens were applied with nail vanish except for the 2-3 mm window area after application of bonding agent. Under the constant pH, the specimens were divided into 6 groups (degree of saturation; 0.1415, 0.1503, 0.1597, 0.1676, 0.1771, 0.1977). Each group was immersed in acid buffer solution for 1, 2, 3, 5 days under controlled temperature (25℃) and imbibed in water and examined using the polarizing microscope.

The results were as follows

1. Although the degree of saturation of demineralization solution decreased, the depth of penetration in the dentin was constant.

2. Erosion was observed on the surface of all the teeth in the group I, II. In the group III, IV, V, surfaces were not changed. The teeth in the group VI showed the more mineralized surface but not the shape of the dentinal tubules distinctively.

3. In all groups, the lesion progressed rapidly at the first day of the experiment, but increased gradually as time elapsed.

Odontoblasts are responsible for the formation and maintenance of dentin. They are known to synthesize unique gene products including dentin sialophosphoprotein (DSPP). Another unique genes of the cells remain unclear.

OD314 was isolated from the odontoblasts/pulp cells of rats and partially characterized as an odontoblast-enriched gene (Dey et al., 2001). This study aimed to elucidate the biological function of OD314, relating to odontoblast differentiation and dentinogenesis. After determining the open reading frame (ORF) of OD314 by transient transfection analysis using green fluorescent protein (GFP) expression vector, mRNA in-situ hybridization, immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) and western analysis were performed.

The results were as follows:

1. In in-situ hybridization, OD314 mRNAs were expressed in odontoblasts of developing coronal and root pulp.

2. OD314 was a novel protein encoding 154 amino acids, and the protein was mainly expressed in cytoplasm by transient transfection analysis.

3. Mineralized nodules were associated with multilayer cell nodules in the culture of human dental pulp cells and first detected from day 21 using alizarin-red S staining.

4. In RT-PCR analysis, OD314, osteocalcin (OC) and DSPP strongly expressed throughout 28 days of culture. Whereas, osteonectin (ON) mRNA expression stayed low up to day 14, and then gradually decreased from day 21.

5. Western blots showed an approximately 17 kDa band. OD314 protein was expressed from the start of culture and then increased greatly from day 21.

In conclusion, OD314 is considered as an odontoblast-enriched gene and may play important roles in odontoblast differentiation and dentin mineralization.

Dental caries is a chronic disease that causes the destruction of tooth structure by the interaction of plaque bacteria, food debris, and saliva.

There has been attempts to induce remineralization by supersaturating the intra-oral environment around the surface enamel, where there is incipient caries.

In this study, supersaturated remineralized solution "R" was applied to specimens with incipient enamel caries, and the quantitative ananlysis of remineralization was evaluated using microradiography. Thirty subjects volunteered to participate in this study. Removable appliances were constructed for the subjects, and the enamel specimen with incipient caries were embedded in the appliances. The subjects wore the intra-oral appliance for 15 days except while eating and sleeping.

The removable appliance were soaked in supersaturated solution "R", saline, or Senstime® to expose the specimen to those solutions three times a day, 5 minutes each time. After 15 days, microradiography was retaken to compare and evaluate remineralization.

The results were as the following:

1. The ratio of remineralized area to demineralized area was significantly higher in the supersaturated solution "R" and Senstime® than in the saline. (p<0.05)

2. Remineralization in the supersaturated buffer solution "R" occurred in the significantly deeper parts of the tooth, compared to the Senstime® group containing high concentration of fluoride.(p<0.05)

As in the above results, the remineralization effect of remineralized buffer solution "R" on incipient enamel caries has been proven. For clinical utilization, further studies on soft tissue reaction and the effect on dentin and cementum are necessary.

In conclusion compared to commercially available fluoride solution, remineralization solution "R" showed better remineralization effect on early enamel caries lesion, so it is considered as effecient solution for clinical application.