Toshimoto Yamada

Comparison between Er:YAG Laser and Conventional Technique for Root Caries Treatment in vitro

Effective ablation of dental hard tissues by means of the erbium-doped:yttrium-aluminum garnet (Er:YAG) laser has been reported recently, and its application to caries removal and cavity preparation has been expected. However, few studies have investigated the capability of the Er:YAG laser to treat caries. In the present study, the effectiveness of caries removal by using an Er:YAG laser in vitro was compared with that of conventional mechanical treatment. Thirty-one extracted human teeth with root caries were used. Half of the caries in each tooth was treated with the Er:YAG laser, and the other was removed with a conventional bur or was left untreated as a control. Laser treatment was performed by means of a combination of contact and non-contact irradiation modes with cooling water spray, with a new fiber delivery and contact probe system. Conventional bur treatment was conducted by means of a low-speed micromotor. Measurements of the time required for caries removal, histopathological observations of decalcified serial sections, scanning electron microscope (SEM) observations, and hardness measurements of the treated cavity-floor dentin were performed for each treatment. Due to the careful irradiation technique, a longer treatment time was required for the complete removal of carious dentin by the Er:YAG laser. However, the Er:YAG laser ablated carious dentin effectively with minimal thermal damage to the surrounding intact dentin, and removed infected and softened carious dentin to the same degree as the bur treatment. In addition, a lower degree of vibration was noted with the Er:YAG laser treatment. The SEM examination revealed characteristic micro-irregularities of the lased dentin surface. Our results show that the Er:YAG laser system is promising as a new technical modality for caries treatment.

Shear and tensile bond testing for resin cement evaluation

OBJECTIVES The aim of this study was to compare the tensile and shear bond strengths of one experimental and four commercially available resin cements following the ISO document TR 110405 for bond measurement. METHODS Tensile and shear bond tests were performed using bovine enamel and dentin as the tooth substrate with each of the resin cements. Resin composite rods were cemented to the prepared tooth surfaces. The bond strengths were obtained 24 h after cementation, and mode of failure was classified after fracture of the bonds, both visually and by SEM observation. RESULTS Significant differences existed between the two bond test methods for all materials with enamel and three of the five cements when bonded to dentin. The shear test results were always the higher of the two test methods. Mode of fracture varied little for the visual classification, but the morphology from SEM observations showed considerable differences. SIGNIFICANCE Although there are deficiencies in the current test methods these may be outweighed by substrate variables. A test model should be designed to determine which stresses, tensile or shear, are the greatest for different types of restorations. With this information, the type of test selected could provide appropriate information before clinical trials are commenced.

SEM and elemental analysis of composite resins

Twenty-four chemically cured, 21 light-cured anterior, three light-cured anterior/posterior, and 18 light-cured posterior composite resins were examined using scanning electron microscopy, and the elemental composition of their filler particles was analyzed with an energy dispersive electron probe microanalyzer. According to the results obtained, the composite resins were divided into five groups (traditional, microfilled type, submicrofilled type, hybrid type, and semihybrid), with two additional hypothetical categories (microfilled and hybrid). Characteristics of each type were described with clinical indications for selective guidance of respective composite resins for clinical use.

The extent of the odontoblast process in normal and carious human dentin.

When observed by SEM, after being treated with the HCl-collagenase method, the odontoblast processes extended throughout the whole thickness of dentin in intact teeth and the whole thickness of normal and the inner carious dentin in carious teeth. Small holes and depressions were found on the processes in the transparent layer.

Adhesion of resin-modified glass ionomer cements using resin bonding systems

OBJECTIVES To compare the in vitro shear bond strength of two commercially available resin-modified glass ionomer cements (RmGIC) to bovine dentine, with and without the use of adhesive bonding systems. METHODS Ninety-six flat bovine dentine surfaces were divided into eight groups for bonding procedures. Fuji II LC and Vitremer were bonded to dentine that had been treated with and without Clearfil Photo Bond, Clearfil Liner Bond, or Clearfil Liner Bond II. The control group consisted of specimens that were treated as recommended by the manufacturer of each resin-modified glass ionomer cement. The bonded assemblies were stored in tap water for 24 h at 37 degrees C, and shear bond strengths measured using a universal-testing machine at a crosshead speed of 1 mm/min. RESULTS For the control group, shear bond strength of Fuji II LC was significantly greater than Vitremer (P < 0.005). However, when any of the resin bonding systems was applied, no statistical difference between Fuji II LC and Vitremer was determined (P > 0.05). The Clearfil PhotoBond and Liner Bond groups showed similar bond strengths (P > 0.05), but were significantly less than Liner Bond II (P < 0.001). CONCLUSIONS A recent bonding system combined with the RmGICs exhibited the greatest shear bond strength to dentine, irrespective of chemical differences that may exist between the two RmGICs.

Microhardness of in vitro caries inhibition zone adjacent to conventional and resin-modified glass ionomer cements

OBJECTIVE This study was conducted to correlate Knoop and triangular hardness numbers by measuring the microhardness of in vitro caries-inhibited and -demineralized dentin adjacent to a conventional and two resin-modified glass ionomer cements. METHODS Box-shaped cavities were prepared on bovine root dentin and restored with either Fuji II, Fuji II LC, or Vitremer. The teeth were then decalcified in an acid buffered solution of 50 mmol l-1 acetic acid adjusted to pH = 4.5 for 3 days. Knoop and triangular microhardness indentations were performed perpendicular to the surface and parallel to the cavity wall, in the demineralized lesion and inhibition zone. Calcium and phosphorous contents of the outer lesions and inhibition zones were compared using energy-dispersive X-ray spectrometry (EDS). The correlation between Knoop and triangular hardness was analyzed by correlation coefficient. The statistical significance of hardness data was analyzed by one-way ANOVA and Fishers PLSD test (p < 0.05). RESULTS Triangular hardness (HT) correlated well with Knoop hardness number (KHN) (r2 = 0.81, p < 0.05). The microhardness of the inhibition zone created by Fuji II was of 59.2 +/- 3.8 HT and was statistically significantly higher than the zone produced by Fuji II LC and Vitremer. Fuji II LC and Vitremer produced inhibition zones with similar microhardness [48.3 +/- 3.5 HT and 44.0 +/- 7.6 HT, respectively (p > 0.05)]. Calcium and Phosphorous were present in the inhibition zone, but did not exist in the demineralized lesion. SIGNIFICANCE Knoop and triangular hardness numbers correlated significantly (p < 0.05), and the latter seems to be a promising alternative method for measuring very narrow surfaces. Despite the fact that all glass ionomer materials used in this study were effective in producing an acid-resistant layer, microhardness and intensity of these layers were material dependent.

Remineralization of etched dentin

To simulate a clinical cavity wall with the inner layer of carious dentin preserved, an artificially demineralized layer was made on the axial wall class V cavities of monkeys by a quick decalcifying solution. The cavities were then restored with a chemically adhesive composite resin after etching with a 40% phosphoric acid jelly etchant. Comparison of the Knoop hardness, the calcium concentration, and the scanning electron microscope observation of the dentin at the axial wall revealed that the dentin, demineralized by etching, was completely remineralized after 4 months.

Effect of Moisture Contamination on High-Copper Amalgam

Moisture contamination caused delayed excessive expansion and deterioration of the physical properties only with the non-high-copper lathe-cut alloy amalgam containing zinc, but not with the new high-copper amalgam and the non-high-copper spherical alloy amalgam containing zinc. It affected the compressive strength and creep but not the hardness. The setting dimensional change of all amalgams containing zinc was slightly affected by it.

Er:YAG laser: the promising procedure for caries treatment

The effectiveness of the Er:YAG laser for caries removal was evaluated in vitro and in vivo. As the in vitro study, thirty-two extracted human teeth with cervical root caries were used. An axially divided half of each caries lesion was treated with the Er:YAG laser, and the other was removed with round steel burs mounted on a micromotor or was left untreated as a control. Laser irradiation was performed in contact and non-contact mode at 145 mJ/pulse (51.3 J/cm2/pulse) and 10 pps under water spray. Conventional micromotor treatment was performed at 10,000 rpm using some different size of round steel burs. Measurement of time required for caries removal, histological observation of decalcified serial sections, SEM observation and hardness measurement of the cavity floor dentin were conducted with both laser and conventional treatments. In addition to the above in vitro study, the usefulness of root caries treatment with the Er:YAG laser was assessed in vivo as a clinical trial. The results indicated that removal of carious dentin using the Er:YAG laser was completed effectively to the same extent as the conventional treatment and thermal damage of the lased cavity was minimum. The Er:YAG laser treatment diminished unpleasant sound and vibration, when compared with the conventional rotary technique. We conclude that the Er:YAG laser possesses the promising characteristics for caries removal.

Application of Er:YAG laser to treat root caries lesion

The effect of the Er:YAG laser on caries removal was studied. Extracted human teeth with cervical root caries were used. Each root caries lesion was divided into two areas axially. A divided half was treated with the Er:YAG laser, and the other was removed with round steel burs mounted on an electric engine or was nontreated as a control. Laser irradiation was performed at 160 mJ/pulse (56.5 J/cm2/pulse) and 10 pps under water spray using a fiber delivery system with a contact probe. The time required for caries removal was measured with each treatment. SEM observation and hardness measurement of cavity floor dentin, and observation of the decalcified serial sections of the specimens were compared. The results indicated that the removal of carious dentin using Er:YAG laser could be performed to the same degree as the electric engine treatment. In addition, the Er:YAG laser treatment diminished unpleasant sound and vibration. However, it was noticed that careful laser irradiation was necessary for the removal of infected dentin layer without overreduction of intact dentin layer. The time required for the laser treatment was longer than that for the electric engine treatment under the conditions of the present experiment.