Influence of human tooth cryopreservation on dentin bond strength.

OBJECTIVES: The goal of this study was to evaluate the effects of cryopreservation of teeth on dentin bond strength as a function of remaining dentin thickness. METHODS: Flat occlusal surfaces of human dentin were prepared in 54 freshly extracted teeth and 54 thawed, cryopreserved teeth. In each group, 18 bonds were performed in superficial dentin, 18 in mid-coronal, and 18 in deep dentin. A resin composite cylinder, 3 mm in diameter and in height, was bonded orthogonally to the surface. After storage in distilled water at room temperature for 1 wk, the bonded cylinders underwent shear testing at a crosshead speed of 0.5 mm min-1. The mean remaining dentin thickness was calculated after longitudinally sectioning the debonded samples through the center of the bonded area. Non-parametric statistical analyses were used to correlate the shear bond strength with the remaining dentin thickness among the storage modes and within the different dentin regions. RESULTS: The lowest shear bond strength values were found in the deep dentin of both fresh and cryopreserved dentin, while the values in deep and mid-coronal dentin were not significantly different in fresh and cryopreserved dentin. In the superficial and mid-coronal dentin of cryopreserved samples, the shear bond strength values were identical. There was a significant difference between the shear bond strength values in the superficial dentin of fresh teeth compared to the values for cryopreserved teeth. SIGNIFICANCE: According to the experimental conditions, tooth cryopreservation shows some promise as a substitute for freshly extracted teeth, provided that the experiments are performed in midcoronal and deep dentin.

Evaluation of temporary restorations' microleakage by means of electrochemical impedance measurements.

The aim of this study was to quantify the changes in the watertightness of three temporary filling materials over 1 wk with a new electrochemical technique: the impedance a measurement technique. Forty sound extracted human maxillary teeth were selected and prepared for the measurements. They were divided into three groups in addition to positive and negative controls. The resistance, and therefore the watertightness, of the intact crown and the resistance after preparation of an endodontic access cavity were registered. After a randomization procedure, 12 teeth were obturated with Cavit G, 12 teeth with Fermit-N, and 12 teeth with Intermediate Restorative Material (IRM). The changes in the resistance were measured first just after obturation (time 0), then after days 1, 2, 3, 4, and 7. The results showed that the IRM group was significantly more watertight than the Fermit-N group (p < 0.05) and much more than the Cavit G group (p < 0.005).

Microleakage of Cavit, CavitW, CavitG and IRM by impedance spectroscopy.

The aim of this study was to quantify the sealing ability of four temporary filling materials over 9 days using a new electrochemical technique. Fifty-two extracted human maxillary bicuspids were selected and prepared for the measurements. They were divided into four groups of 12 teeth each, in addition to two positive and two negative controls. After preparation of the endodontic access cavity the sealing ability was registered. After a randomization procedure one group was obturated with IRM, another group with Cavit, a third group with CavitW and the last group with CavitG. The sealability was measured just after obturation (time 0) and after days 1, 2, 3, 4, 7 and 9. The results showed that the IRM group was significantly more watertight than the different Cavit formulations. Throughout the experiment no significant difference was noticed between the Cavit and CavitW groups (P > 0.05). The CavitG group was significantly less watertight throughout the measurements (P < 0.05).

Scanning electron microscopic evaluation of ultrasonic debridement comparing sodium hypochlorite and Bardac-22.

This study compared in vitro the debridement ability of a 3% sodium hypochlorite with a new quaternary ammonium derivative, a 0.5% Bardac-22 solution, in the apical third of freshly extracted teeth with straight root canals. Root canals were instrumented sequentially from size 10 to size 35 using alternatively hand and ultrasonic files. When the hand file was loose in the canal, the ultrasonic instrument of the same size was operated at working length for 30 s, delivering 15 ml of the selected solution. Both solutions were able to flush out pulpal debris from the canal space. At the apical end of the preparation, sodium hypochlorite left a thicker smear layer than Bardac-22 did. The quaternary ammonium derivative easily dissolved the inorganic portion of the smear layer, but did not dissolve proteins as well as sodium hypochlorite.

Effect of the tooth microstructure on the shear bond strength of a dental composite.

Plane human enamel and dentin surfaces were used for microstructural investigation and shear bond testing. The dental tissue microstructure was characterized through the surface topology, the concentration in mineral elements (determined by electron microprobe analysis), and the Vickers microhardness for the same dental tissue. The etched prismatic enamel presents a surface roughness of about 200% of the apparent area, while the intertubular surface fraction of the dentin is, on the average, equal to 75%. The calcium concentration lies between 23.2 and 37.8% of the enamel total mineral content, and 18.5 and 28.2% of the dentin. The microhardness varies from 205 to 378 Hv for the enamel and from 37 to 98 Hv for the dentin. Also, the shear bond strength to a chemosetting adhesive/composite system varies from 10.4 to 23.9 MPa for the enamel and from 0.0 to 5.0 MPa for the dentin. It is shown that the shear bond strength is strongly correlated to the microhardness through a simple linear equation valid for both enamel and dentin surfaces. In turn, the microhardness is correlated to the calcium concentration through two distinct linear relations. These correlations lead to the intrinsic dependence of the shear bond strength on the calcium concentration of the dental tissue, providing that corrections are applied to the bond strength data in order to take into consideration the effective solid area of the adherend and the polymerization retraction stress. Consequently, it is proposed that the adhesion mechanisms for the both enamel and the dentin are controlled, to a major extent, by the mineral content and the surface topology of the tooth.

Influence of calcium concentration on the dentin wettability by an adhesive.

Plane dentin surfaces were abraded perpendicular to the radicular axis of sound human molars. They were cleaned to reveal the tubules, and the morphological features of each surface were studied microscopically. For a first series of teeth, the Vickers microhardness of the dentin surfaces was measured and the calcium and phosphorus composition was determined by electron microprobe analysis. For a second series, the microhardness and wettability of the surface by the Scotchbond adhesive were compared. Positive correlations were found between the following parameters: degree of minerality, dentin compactness, hardness, and spreading capability of the adhesive.