Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin-resin interface.

OBJECTIVES: As the bond strength of composite resin to Er,Cr:YSGG laser-irradiated dentin has not yet been evaluated, the objectives of this study were to investigate the tensile bond strength and to analyze the resin-dentin interface among bur-cut/acid-etched, Er,Cr:YSGG laser-ablated/acid-etched and Er,Cr:YSGG laser-ablated human dentin. METHODS: Crown dentin disks prepared from extracted human third permanent molars were used for the observation of surface morphological changes by scanning electron microscope (SEM). The laser energy parameters were 3.5 W and 20 Hz with water spray (air pressure level, 80%; water pressure level, maximum level). Another group of crown dentin disks were prepared for composite resin restoration and observation of resin-dentin bond interface after demineralization in 6N hydrochloric acid (HCl) for 1 min and deproteinization in 1% sodium hypochlorite solution (NaOCl) for 10 min. The tensile bond strengths of the three groups were measured by a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture types at the dentin-resin interface were analyzed using the digital stereoscopic microscope and fractured surfaces of the debonded specimens were examined by SEM. RESULTS: All three groups showed that the treated surfaces were free of dentin debris and smear layer. The peritubular dentin protruded from the surrounding intertubular dentin after laser irradiation. The dentin-resin interface treated with Er,Cr:YSGG laser irradiation and acid etching demonstrated numerous resin tags converging into a bulge and then diverging again. The length of resin tags was greater than 100 microm. The tensile bond strengths of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were 5.37+/-1.51, 5.17+/-1.41 and 3.29+/-0.86 MPa, respectively. No statistical significance was found between the bur-cut/acid-etched and laser-ablated/acid-etched groups. The predominant fracture modes of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were Type 1 (50%), Type 2 (70%) and Type 1 (70%), respectively. SIGNIFICANCE: Er,Cr:YSGG laser irradiation affects adversely adhesion of resin to dentin but acid etching following laser irradiation could increase the tensile bond strength as high as that of bur-cut/acid-etched human dentin.

Tensile bond strength of Er, Cr: YSGG laser-irradiated human dentin to composite inlays with two resin cements.

The purpose of this study was to investigate the tensile bond strength of composite inlays to human dentin with two different cavity preparation tools (bur versus Er, Cr: YSGG laser) and with two different bonding procedures (total-etch: Variolink II versus self-etch: Maxcem). The specimens were divided into four groups: bur-cut/Variolink II, bur-cut/Maxcem, laser-ablated/Variolink II, and laser-ablated/Maxcem. The following characteristics were then investigated: morphological change, dentin-resin cement interface, surface roughness, and tensile bond strength. Results demonstrated that the tensile bond strengths of the four groups were 19.11 +/- 5.88 MPa, 8.54 +/- 2.38 MPa, 13.72 +/- 3.43 MPa, and 12.11 +/- 3.71 MPa, respectively. We concluded that Variolink II provided higher tensile bond strength to composite inlays than Maxcem. On the other hand, the bond strength of Variolink II with dentin cavity prepared by Er, Cr: YSGG laser was statistically lower than that prepared by bur.

The role of organic tissue on the punch shear strength of human dentin.

OBJECTIVES: The tendency to fracture of human teeth has been attributed to numerous reasons, including pulpless tooth dehydration, tooth structure degeneration, and excessive spreader loading. To date, however, no consistent data has been gathered to ascertain the effect of organic tissue on the biomechanical properties of human dentin. This study explored the influences of organic tissue removal on the morphological changes and punch shear strength by means of low vacuum wet scanning electron microscope (Wet-SEM) and punch shear apparatus. METHODS: The crown dentin slices with a thickness of 0.45-0.50 mm were prepared from extracted human molars. These specimens were immersed in 5% NaOCl for 1, 3, and 6 h to remove the organic tissue. The dynamic morphological changes of these dentin slices after immersion were observed using Wet-SEM. In addition, the punch shear strength and stiffness of specimens were measured. RESULTS: The removal of organic tissue by 5% sodium hypochlorite treatment caused many cracks on the specimen surfaces. Intertubular and peritubular dentin were also affected, causing an abnormal configuration of dentinal tubule orifices. The 5% sodium hypochlorite treatment for 1, 3, and 6 h significantly reduced the punch shear strength of dentin. As the immersion time increased, the values of punch shear strength also diminished. CONCLUSIONS: The organic tissue loss of human dentin would affect the structure of intertubular and peritubular dentin and cause many cracks on the dentin surface. The punch shear strength of human dentin also reduced after removal of organic tissue.

Bond strengths of orthodontic bracket after acid-etched, Er:YAG laser-irradiated and combined treatment on enamel surface.

Laser ablation has been proposed as an alternative method to acid etching: however, previous studies have obtained contrasting results. The purpose of this study was to compare the bond strengths after acid etching, laser ablation, acid etching followed by laser ablation, and laser ablation followed by acid etching. Forty specimens were randomly assigned to one of the four groups. Two more specimens in each group did not undergo bond test and were prepared for observation with scanning electron microscope (SEM) after the four kinds of surface treatment. After the bond test, all specimens were inspected under the digital stereomicroscope and SEM to record the bond failure mode. Student's t-test results showed that the mean bond strength (13.0 +/- 2.4 N) of the laser group was not significantly different from that of the acid-etched group (11.8 +/- 1.8 N) (P > .05). However, this strength was significantly higher than that of the acid-etched then laser-ablated group (10.4 +/- 1.4 N) or that of the laser-ablated then acid-etched group (9.1 +/- 1.8 N). The failure modes occurred predominantly at the bracket-resin interface. Er:YAG laser ablation consumed less time compared with the acid-etching technique. Therefore, Er:YAG laser ablation can be an alternative tool to conventional acid etching.

Blindness and basal ganglia hypoxia as a complication of Le Fort I osteotomy attributable to hypoplasia of the internal carotid artery: a case report.

Le Fort I osteotomy is used as a surgical procedure for correction of maxillofacial deformities. The common complications of this procedure are hemorrhage and infection, with incidence of 6% to 9%. Blindness associated with Le Fort I osteotomy was reported in 8 patients. An 18-year-old female complained of loss of sight in the left eye after recovery from hypotensive general anesthesia. The visual field of the left eye was dark and only perceived some movement. She presented with motor dysfunction and regressive behavior 2 weeks later as a result of hypoxia of bilateral basal ganglia. Two months later, her visual acuity recovered gradually and regressive behavior improved. Carotid angiography showed congenital hypoplasia of the left internal carotid artery. We suspected that hypoplasia could cause hypoxia of the central nervous system.

Bactericidal effects of diode laser on Streptococcus mutans after irradiation through different thickness of dentin.

BACKGROUND AND OBJECTIVES: A reliable method to eradicate the bacteria of residual carious dentin has not yet been developed. The aim of this study was to evaluate the antibacterial effect of a diode laser on Streptococcus mutans through different thickness (500, 1,000, and 2,000 microm) of human dentin. The thermal effect of laser irradiation was also investigated. STUDY DESIGN/MATERIALS AND METHODS: Dentin specimens were inoculated with 2 microl of S. mutans on one side and irradiated by a diode laser on the other side with a power output ranging from 0.5 to 7 W. The laser tip was swept with the whole irradiation area of 7 mm x 3 mm at a speed of about 10 mm/second with a total irradiation time of 30 seconds. Cooling with distilled water (30 ml/minute) was applied simultaneously during laser irradiation. After laser irradiation, the bacteria was removed from the dentin surfaces and cultured for 48 hours at 37 degrees C anaerobically to assess the colony forming units (CFU) per ml. The morphology of the lased bacteria and the temperature rise during laser irradiation were observed by scanning electron microscope (SEM) and measured by thermocouple, respectively. RESULTS: The results revealed that 7 W of laser power could kill 97.7% of CFU through 500 microm thickness of dentin. However, the bactericidal efficiency was significantly reduced as the dentin thickness was increased. The morphological changes of lased bacteria ranged from less affected such as loss of their wall bands and existence of minicells to more severely degenerated, such as disintegration and fusion of cells with pores on the cell wall. Only the dentin specimens with a thickness of 500 microm exhibited a temperature rise greater than 5.5 degrees C after receiving 5 or 7 W of laser irradiation. CONCLUSIONS: A diode laser can eliminate the Streptococcus mutans of the residual carious dentin without inducing high pulpal temperature rise when the remaining dentin thickness is greater than 1 mm.