Long-term mechanical properties of EDTA-demineralized dentin matrix.

PURPOSE: To determine the long-term ultimate tensile strength (UTS) and modulus of elasticity (E) of EDTA-demineralized human dentin after storage in PBS (phosphate buffered saline) for up to 48 months. MATERIALS AND METHODS: Dentin beams measuring 0.7 x 0.7 x 8.0 mm were prepared from the crowns of extracted human third molars. The ends of the beams were covered with resin composite and demineralized for 6 days in 0.5 mol/L EDTA (pH = 7.0). Demineralized control specimens were subjected to tensile testing at 0.5 mm/min after 24 hours of immersion in PBS solution. Experimental specimens were stored in PBS at room temperature (25 degrees C) and tested after 18 and 48 months. The maximum load at failure and the load/displacement curves were used to calculate the UTS as a function of the cross-sectional area and E, respectively. The results were analyzed by ANOVA and Student Neuman Keuls tests. TEM micrographs were obtained from the control specimens and from those that were stored and tested after 48 months. RESULTS: No significant changes in either UTS or E were observed in the specimens after long-term storage. The 48-month values were not statistically significantly different from the values obtained at 24 hours (p > 0.05). TEM images revealed a normal, intact structure of the collagen fibrils with no signs of degradation or denaturation. CONCLUSION: Long-term storage of EDTA-demineralized human dentin in PBS solution did not cause any significant reduction of its mechanical properties. The structure of the collagen fibrils as observed by TEM appeared normal and did not seem affected by long-term storage.

In vitro study on the dimensional changes of human dentine after demineralization.

Dentine rods measuring approximately 0.7 x 0.7 x 5.0 mm were prepared from dentine of extracted human third molars stored in saline containing 0.5% sodium azide at 4 degrees C until used. Forty specimens were demineralized in 10% citric acid plus 3% ferric chloride (w/w) solution for 8 h, then assigned to four groups (A, B, C and D) of 10 specimens each. Groups A and B were used to investigate volumetric changes after air-drying and further immersion in either water, an aqueous solution of 50% 2-hydroxymethylmethacrylate (HEMA) or 100% HEMA, followed by air-drying. Groups C and D were used to investigate the ability of 100% HEMA or 100% ethylene glycol to prevent shrinkage of demineralized dentine during exposure to air. Demineralization caused a small, non-significant (1.9%) reduction in dentine volume. Air-drying further reduced the volume by 65.6%. When demineralized, shrunken specimens were immersed in water for 24 h, they recovered their original demineralized volume. Immersion in 100% HEMA did not re-expand demineralized shrunken dentine. Specimens immersed in 50% HEMA yielded a 50% volume shrinkage when exposed to air for 24 h. Both 100% HEMA and 100% ethylene glycol were effective in preventing shrinkage of demineralized dentine. The technique used provided useful information about maximal dimensional changes that may occur at a microscopic level during adhesive dental restorative procedures.

Dimensional changes of demineralized human dentine during preparation for scanning electron microscopy.

Dentine rods measuring approx. 0.7 x 0.7 x 5.0mm were prepared from the crowns of extracted human third molars. The specimens were demineralized in 0.5 M EDTA (pH 7.0) for 3 days and their volume measured with a digital micrometer under a dissecting microscope. The specimens were randomly assigned to experimental groups and were chemically dehydrated in acetone. Next they were dried using either hexamethyldisilazane, Peldri II, or critical-point drying techniques. The dimensions of the specimens were measured again after each step and the changes in volume were expressed as a percentage of the original demineralized volume. The effects of fixing the specimens in 10% buffered formalin before dehydration with acetone were also investigated for every drying procedure. Dehydration in acetone caused a small but significant reduction in the volume of demineralized formalin-fixed specimens but unfixed specimens did not change significantly. In general, all three drying procedures caused some shrinkage in demineralized dentine specimens. Unfixed specimens exhibited a volumetric shrinkage of approx. 15-20% after drying with any of the methods. Fixed specimens shrank more than unfixed specimens after drying (25-35%). Regardless of the drying technique, the specimens shrank a further 10-20% when measured in the vacuum chamber of the scanning electron microscope. Among the three drying techniques employed, hexamethyldisilazane seems to be a very useful alternative to critical-point drying for the preparation of dentine specimens for scanning electron microscopy.

Bonding mechanism of VariGlass to dentin.

PURPOSE: This study investigated the hypothesis that the new resin-reinforced, light-cured ionomer cement (GIC) can develop mechanical retention by forming a hybrid layer in acid-etched dentin. MATERIALS AND METHODS: Dentin discs were obtained from extracted human third molars and sanded with 320 SiC abrasive paper. One third of the surface was acid etched with 10% maleic acid for 15 seconds, washed and gently air-dried for 5 seconds. ProBond primer from the VariGlass (VG) GIC kit was applied onto the acid-etched surface (A) and another third of the unetched surface (B) for 30 seconds. One third of the surface was not treated (C). VG GIC was then applied onto the ++entire surface of the disc. After 24 hours the discs were fractured along their diameters. One half of the fractured disc was highly polished at the interface and treated with 6N HCl for 30 seconds while the other half of the fractured specimen was left untreated. Both halves were viewed by SEM. In another part of the study, a micro-tensile bond strength (MTBS) test was carried out to compare the acid-etched group vs. the nonetched group. RESULTS: SEM pictures revealed a well defined demineralized, resin-infiltrated zone approximately 3 micrometers in thickness for group (A) for both fractured and polished surface. Dentin surfaces that only received primer (B) showed an irregular zone 0.5 micrometers thick. Such a resin-infiltrated layer was resistant to HCl treatment. A gap was observed between the GIC and dentin in group (C). Polished interfaces appeared to be highly infiltrated. However, fractured interfaces revealed considerable porosity within the demineralized-infiltrated zone. MTBS results were (X +/- SD, MPa): 28.9 +/- 5.8 for the etched group and 24.5 +/- 4.9 for the nonetched group. This difference was statistically significant.