牙本质无机物在牙本质粘接过程中的作用

目的探讨牙本质无机物在牙本质粘接过程中的作用。方法采用几种不同的牙本质处理方法，测试分析了牙本质与４ＭＥＴＡ／ＭＭＡＴＢＢ树脂之间的抗张粘接强度（ｔｅｎｓｉｌｅｂｏｎｄｉｎｇｓｔｒｅｎｇｔｈ，ＴＢＳ）。结果选用１０％柠檬酸和３％三氯化铁组成的酸盐体系预处理液（ａｃｉｄｓａｌｔｐｒｅｔｒｅａｔｉｎｇｓｏｌｕｔｉｏｎｓｙｓｔｅｍ，ＡＰＳＳ）去除牙本质污染层，再用次氯酸钠溶解牙本质胶原。暴露牙本质无机物时，牙本质的抗张粘接强度为５９３ＭＰａ，明显高于用蒸馏水冲洗的对照组（３７１ＭＰａ）（Ｐ＜００５）。结论说明牙本质无机物在牙本质粘接过程中确实具有一定的作用     

Contraction stress in dentin adhesives bonded to dentin

Adhesives cured under constrained conditions develop contraction stresses. We hypothesized that, with dentin as a bonding substrate, the stress would reach a maximum, followed by a continuous decline. Stress development was determined with a tensilometer for two total-etch systems and two systems with self-etching primers. The adhesives were placed in a thin layer between a glass plate and a flat dentin surface pretreated with phosphoric acid or self-etching primer. After an initial maximum shortly after light-curing, the stress decreased dramatically for the total-etch systems (70%) and, to a lesser extent, for the adhesives with self-etching primers (30%). The greater stress decrease for the total-etch systems was ascribed to water and/or solvents released into the adhesives from the fully opened dentinal tubules by the pulling/sucking action of the contraction stress. This happened less with the adhesives with self-etching primers, where the tubules remained mainly closed.     

Nanoleakage of dentin adhesive systems bonded to Carisolv-treated dentin

The hybrid layer created in caries-affected dentin has not been fully elucidated and may influence bond durability. This study investigated the nanoleakage patterns of caries-affected dentin after excavation with Carisolv or conventional instruments treated with one of three adhesive systems. Flat occlusal dentin surfaces, including carious lesions, were prepared from extracted human molars and finished with wet 600-grit silicon carbide paper. Carious dentin was removed with Carisolv or round steel burs in conjunction with Caries Detector. PermaQuik, Single Bond or One-Up Bond F was bonded to the excavated dentin surfaces and adjacent flat occlusal surfaces and it was covered with Silux Plus resin-based composite. After 24-hour storage in 37 degrees C water, the bonded interfaces were polished to remove flash, and the surrounding tooth surfaces were coated with nail varnish. Specimens were immersed in 50% (w/v) silver nitrate solution for 24 hours, exposed to photo developing solution for eight hours, then sectioned longitudinally through the bonded, excavated dentin or "normal" dentin surfaces. The sectioned surfaces were polished, carbon coated and observed in a Field Emission-SEM using back scattered electrons. Silver deposition occurred along the base of the hybrid layer for all specimens. However, Single Bond showed a greater density of silver deposition in the caries-affected dentin compared with normal dentin. PermaQuik had a thicker hybrid layer in caries-affected dentin than normal dentin. One-Up Bond F exhibited a thin hybrid layer in normal dentin, but the hybrid layer was often difficult to detect in caries-affected dentin.     

Bond strengths of single-bottle dentin adhesives to caries-affected dentin

There is concern that some acidic conditioners may not be strong enough to adequately etch sclerotic or caries-affected dentin. The hypothesis that was tested was that there were no significant differences in the bond strengths of single-bottle bonding systems to normal or caries-affected dentin, regardless of the strength of the phosphoric-acid conditioner. Extracted teeth with coronal caries extending into mid-dentin were prepared by grinding the occlusal surface flat. This left a central region of caries-affected dentin surrounded by normal dentin. The One-Step bonding system was used to bond dentin following etching with 10 or 32% phosphoric acid. The Single Bond system was used after etching dentin with 10 or 35% phosphoric acid. After 24 hours in water, serial vertical sections were made through the bonded teeth to create slabs 0.7 mm thick. Each tooth yielded four to five slabs, some of which included normal dentin, while others included caries-affected dentin. Each slab was trimmed into an hourglass configuration to limit the test area to normal or caries-affected dentin. The results obtained with One-Step following etching with 10% phosphoric acid showed lower (P < 0.05) tensile bond strengths to caries-affected dentin compared to normal dentin (36.9 +/- 8.0 MPa vs 47.7 +/- 6.5 MPa, respectively). This difference disappeared when using 32% phosphoric acid (49.7 +/- 6.1 MPa vs 45.0 +/- 7.2 MPa, respectively). Bonds made to caries-affected dentin with Single Bond were always lower than bonds to normal dentin regardless of the strength of the phosphoric acid. Scanning electron microscopy of polished cross sections sequentially challenged with acid and NaOCl revealed loss of the middle of the hybrid layers created by either bonding system in caries-affected dentin etched with 10% phosphoric acid. It is clear that 32-35% phosphoric acid is required to adequately etch caries-affected dentin in order to produce high bond strengths and well-infiltrated demineralized dentin.     

Nanotube-modified dentin adhesive—Physicochemical and dentin bonding characterizations

Objective

The aim of this study was to investigate the effect of aluminosilicate clay nanotubes (Halloysite, HNT) incorporated into the adhesive resin of a commercially available three-step etch and rinse bonding system (Adper Scotchbond Multi-Purpose/SBMP) on dentin bond strength, as well as the effect on several key physicochemical properties of the modified adhesive.

Methods

Experimental adhesives were prepared by adding five distinct HNT amounts (5–30 wt.%) into the adhesive resin (w/v) of the SBMP dentin bonding system. Bond strength to human dentin, microhardness, and degree of conversion (DC) of the modified adhesives were assessed.

Results

From the shear bond strength data, it was determined that HNT incorporation at a concentration of 30 wt.% resulted in the highest bond strength to dentin that was statistically significant (p = 0.025) when compared to the control. Even though a significant increase in microhardness (p < 0.001) was seen for the 30 wt.% HNT-incorporated group, a significantly lower DC (p < 0.001) was recorded when compared to the control.

Significance

It was concluded that HNT can be incorporated up to 20 wt.% without jeopardizing important physicochemical properties of the adhesive. The modification of the SBMP dentin bonding agent with 20 wt.% HNT appears to hold great potential toward contributing to a durable dentin bond; not only from the possibility of strengthening the bond interface, but also due to HNT intrinsic capability of encapsulating therapeutic agents such as matrix metalloproteinase (MMP) inhibitors.     

Demineralized dentin, hydroxylapatite and dentin chips as apical plugs

Abstract Demineralized dentin, hydroxylapatite, or dentin chips were condensed into the apical 2 mm of canals with perforated apexes in 36 anterior teeth of 8 adult cynomolgus monkeys. The coronal sections of the canals were then obturated with gutta percha and Grossman's sealer. Twelve additional canals with perforated apexes were obturated 2 mm short of their radiographic apexes and served as controls. The amount of hard tissue formation and the degree of inflammation were evaluated after 3 and after 6 months. No differences were noted between the various materials after 3 months. However, after 6 months the samples with apical plugs of hydroxylapatite had more hard tissue formation and less inflammation than the others.     

Eugenol diffusion through dentin related to dentin hydraulic conductance.

OBJECTIVES: The purpose of this study was (1) to find an easy way of evaluating the concentration of eugenol in cell culture fluids; (2) to confirm the relationship between the concentration and the cytotoxicity of eugenol in vitro; (3) to evaluate the cytotoxicity of four temporary eugenol-based filling materials: IRM, super EBA, Kalsogen and zinc oxide-eugenol cement; and (4) to establish a relationship between dentin permeability, eugenol diffusion and cytotoxicity. METHODS: (1) The concentration of eugenol was measured with a spectrofluorimeter; (2) the cell viability of L 929 cells cultivated for 24 h with eugenol-containing medium was evaluated by the MTT assay; (3) after measurement of hydraulic conductance, occlusal cavities in human teeth in vitro were filled with the restorative materials. The cytotoxicity was measured with undiluted test medium and with various dilutions in culture medium; (4) after Lp measurement, the eugenol concentration in the media in the pulp chamber that diffused from IRM and 10(3) mol/l eugenol solution was measured. RESULTS: (1) A proportional relationship (p = 0.001 and r = 1) was found between the concentration of eugenol; (2) eugenol started to be cytotoxic at 10(-5) mol/l and killed 95% of the cells at 10(-3) mol/l; (3) zinc oxide-eugenol cement was the most cytotoxic filling material when tested with the 1:100 dilution; (4) a significant relationship was found between Lp and cytotoxicity (p = 0.04) depending on the dilution of the test medium. A significant relationship was found between Lp and eugenol diffusion from a 10(-3) mol/l solution (p = 0.03) but not between Lp and eugenol diffusing from solid IRM (non significant). SIGNIFICANCE: Eugenol diffusion from zinc oxide-eugenol cement appears to depend more on the role of hydrolysis of eugenol from zinc oxide-eugenol cement than on dentin permeability.     

Porcelain to dentin bond strength with a dentin adhesive.

Adhesion of porcelain to dentin may be important in those cases with little remaining enamel. The purpose of this study was to determine the bond strength of porcelain to dentin using a dentin adhesive (All-Bond) and compare it to the enamel bond strength. Sixty human molar teeth had either a dentin or enamel bonding site prepared by flat grinding to a 600 grit. The teeth were divided into three groups of 20 each. Sixty porcelain cylinders were prepared, hydrofluoric acid etched on one end and silane treated. Twenty of the cylinders were bonded to enamel, 20 bonded to dentin with a dentin adhesive to be tested at 48 hours, and 20 bonded to dentin with a dentin adhesive to be tested after 24 hours of thermocycling (800 cycles at 6 degrees C to 60 degrees C). The specimens were tested in an Instron at a crosshead speed of 0.5 mm/minute. The following bond strengths were found: enamel (19.0 +/- 2.9 MPa), dentin at 48 hours (14.4 +/- 5.4 MPa), and dentin after thermocycling (10.1 +/- 3.8 MPa). When this data was subjected to statistical analysis (ANOVA), there was a significant difference between the groups. A Scheffe's test found that the dentin-porcelain bond at 48 hours was stronger than the thermocycled group, and that the enamel bond was significantly stronger than the two dentin bonds.     

Cytotoxicity test of dentin bonding agents using millipore filters as dentin substitutes in a dentin barrier test

Objectives

The purpose of this study was to find proper dentin substitute for standardized dentin barrier test and perform the cytotoxicity test of commercial bonding agents with the proper substitute.

Materials and methods

The three-dimensional cells attached to dentin disc or millipore filters as the dentin substitute were tested in a dentin barrier test by perfusion. MTT assay was performed as an evaluation method for the cell survival rate. The cytotoxicity test of serial phenol dilution by bovine dentin disc was done to determine a standard toxic material, and the test of this proper phenol by using various millipore combinations was performed to find the suitable dentin substitute. Also, the cytotoxicity test of bonding agents was performed by this standardized substitute. The cell viability was expressed as percentages of untreated group.

Results

Phenol concentration of 0.05 % was selected as the standard toxic material. The different combinations of millipore filters—two sheets of 0.45 μm, two sheets of 0.22 μm, and the combination of 0.65, 0.45, and 0.22 μm—showed similar cytotoxicity to natural dentin discs by 0.05 % phenol (p?>?0.05). The millipore combination of 0.65, 0.45, and 0.22 μm that had structural similarity to natural dentin discs was used as the substitute for cytotoxicity test of bonding agents. The toxic level of Adper Prompt L-Pop using the selected substitute was significantly the highest among four kinds of dentin bonding agents (p?<?0.05). Also, the dentin barrier test by the substitute showed constant results compared with the one by the natural dentin disc.

Conclusions

The millipore filter combination of 0.65, 0.45, and 0.22 μm could be used as the substitute for the cytotoxicity test of materials applied to dentin.

Clinical relevance

Dentin barrier test by standardized substitutes would be helpful for considering the potential toxicity of dentin bonding agents prior to clinical adaptations and reducing the variations of natural bovine dentin that has individually different characteristics.     

Unrestored dentin caries and deep dentin restorations in Swedish adolescents

The objectives of this longitudinal study were to assess: (a) the prevalence of unrestored dentin caries among 15-year-olds, (b) the proportion of these lesions that had progressed to deep dentin lesions (inner half of dentin) since the immediately preceding examination at the age of 14 and (c) the frequency of deep restorations (extending into the inner half of the dentin). The sample consisted of all 15-year-olds (n = 2,487) born in 1990 and included in the Public Dental Service in Malmo, Sweden. Bitewing radiographs taken during 2005-2007 and the immediately preceding radiographs were analysed and scored by two examiners. The main radiographic scores were: sound; radiolucency in the outer or inner half of dentin; restored surface. The results showed that 22% of the individuals had 1 or more dentin lesions left unrestored from the time of the examination at the age of 14 until the next recall examination at the age of 15. During the observation period (median time 1.2 years), 9% of the unrestored outer dentin lesions progressed to deep dentin lesions. The majority of these (93%) were in molars. One or more deep restorations were found in 22% of the 15-year-olds; the majority involved occlusal surfaces of first molars. In conclusion, unrestored dentin lesions were common in 15-year-olds. Progression to deep dentin lesions occurred in 9% of these lesions and was most common in first molars. Occlusal surfaces of first molars had the highest frequency of deep restorations.