脉冲Nd：YAG激光照射对牙本质通透性的影响

应用牙本质通透性测定装置，定量测定脉冲Ｎｄ：ＹＡＧ激光在不同参数条件下照射后对牙本质通透性的影响。结果表明：在４个不同的激光参数条件下，激光照射后牙本质通透性均较照射前呈显著性下降，其中以每秒１５个脉冲０．７５Ｗ的２．０ｍｉｎ组和每秒１５个脉冲１．００Ｗ的２．０ｍｉｎ组下降最为明显，与每秒１５个脉冲０．７５Ｗ的１．５ｍｉｎ组之间呈显著性差异（ＦＫＰＦＦ＜０．０５）。提示脉冲Ｎｄ：ＹＡＧ激光在一定参数条件下照射，可熔融和封闭牙本质小管，是治疗牙齿敏感症的有效手段之一     

Effects of CO2 laser irradiation on microstructure of dentin, dentin adhesion of resin composites and dental pulp

This study was designed to investigate the effects of CO2 laser irradiation on the dentin microstructure, dentin adhesion of resin composites and dental pulp. An artificial caries lesion was produced on the bovine dentin, immersing in 0.4 mol/l acetic acid. Three kinds of dentin (sound dentin, outer or inner caries dentin) surfaces were pretreated by the laser irradiation, acid etching or no-treatment. The tensile adhesion-test of these pretreated dentin surfaces was performed. The changes in these dentin surfaces by the various treatments including the laser irradiation and the resin-dentin interfaces were examined by the SEM. Furthermore, histopathological study using monkey teeth was conducted to examine the effect of the laser irradiation on the dental pulp. Histopathological changes in the pulp were found at 3 and 90 days after the operation. The findings were as follows: 1. The outer highly and inner partially decalcified layers produced in the bovine dentin were each approximately 200 microns in thickness. 2. The bond strength of the resin composites to the laser pretreated sound dentin was approximately 40 kgf/cm2. Those of the laser pretreated outer and inner decalcified dentins were about 60 kgf/cm2. 3. At the initial stage, the laser irradiation (output power 3W : irradiation period 0.5 second) exhibited a slight pulpal response, producing irritation dentin formation in the latter stage without any severe histopathological change.     

Measurement of vaporization cavity after CO2 laser irradiation on bovine dentin

Lasers are used for various clinical applications in dental practices, and many studies have examined the effects of lasers with different applications on enamel and dentin. The CO₂ laser was introduced into the dental clinic for the removal of caries and for cavity preparation of hard tissues, in anticipation of replacing air turban and micromotor devices. The aim of this study was to examine dentin structural changes by measuring 3-dimensional diameter, depth, and volume in bovine teeth irradiated with a CO₂ laser at 1, 3, or 5 W. According to our measurements, a vaporization depth of 400 μm was created by irradiation for a mere 100 ms in the case of 3 W irradiation and 500 μm in the case of 5 W irradiation. Further, at the same output power, the pulse mode transmitted energy to deeper layers of the tooth as compared with the continuous wave mode, indicating that the pulse mode has more penetrating power than the continuous wave mode. Moreover, the depth of cavity that after laser irradiated was > 500 μm at output power 5 W. Thus, irradiation at high output power and the influence of pulse mode on the pulp tissue cannot be disregarded. That is to say, it is important to consider irradiation output power, mode, direction, and distance when lasers are used for adjacent to pulp of tooth that primary incisors and deep cavities.     

The effects of the CO2 laser on human dentin and cementum

Polarizing microscopy, scanning electron microscopy and X-ray diffraction analysis have been used to study the effects of the radiations of a CO2 laser equipment on the dentine and cementum of sound human permanent teeth. The typical lesions induced in dentine and cementum differ only lightly because of the different composition of the tissues. They assume a crater-like aspect and show structural alterations, less and less severe when moving away from the beam focal center. The morphological analysis of the tissues, which loose their organic components through combustion, suggests that such lesions are the consequences of a very fast overheating followed by a fast cooling. X-ray diffraction analysis shows that the hydroxyapatite of the tissues submitted to the thermic stress does not undergo phase transformation, which means that the temperatures remain lower than 1200 degrees C.     

Increased resistance to artificial caries-like lesions in dentin treated with CO2 laser.

The crowns of 60 permanent human molars were sectioned transversally. The exposed dentin surface was divided into different parts: a first part was kept as control, a second part was immediately varnished, and a third part was irradiated with a CO2 laser using the same irradiation conditions as those applied for caries removal (10 impulses of the same energy; 0.2 s/impulse; energy density/impulse 280-715 J/cm2. After irradiation, a small portion of this area was varnished. The teeth were immersed for 4 weeks in a cariogenic gel (pH = 4.5) at 36 degrees C. Twenty teeth were studied by scanning electron microscopy, and longitudinal sections of the other teeth were prepared for microradiography and microdensitometry measurements. The lased dentin surface appeared smooth for energy densities lower than 425 J/cm2. Longitudinally fractured samples revealed a layer of dentin devoid of tubular structure (20-70 microns thick, depending on the energy density used), whereas below the sealed layer, the dentinal tubules retained their normal aspect. Although the sealed layer showed no demineralization when exposed to acid, demineralization of the underlying dentin occurred, but to a much lesser extent than in the unlased dentin.     

CO2 laser improves 45S5 bioglass interaction with dentin

Bioglass 45S5 is a bioactive glass that can create a layer of calcium-phosphate crystals on mineralized hard tissues. In this study, 45S5 bioglass was mixed with phosphoric acid and irradiated with CO(2) laser and examined as a possible aid in the treatment of dentin hypersensitivity. The dentinal surface modified by the aforementioned technique was chemically and micro-morphologically examined with a field emission scanning electron microscope (FE-SEM) equipped with an energy-dispersive x-ray spectroscope (EDS), and the crystalline structures of the examined dentinal surfaces were examined by x-ray diffraction (XRD). Moreover, the mechanical properties of the newly formed layer were examined by nanoindentation. The results showed that 45S5 bioglass could occlude the dentinal tubule orifices with calcium-phosphate crystals. The application of CO(2) laser potentially improved the mechanical organization of these crystals.     

Effects of CO2 laser irradiation on gingiva

A CO2 laser (Coherent Medical Model 400) was used to irradiate the gingival tissue of a cynomolgous monkey to determine laser effects on the epithelium and underlying connective tissue. A focal length of 400 mm and a 10-watt power setting at 0.2- and 0.5-second exposure was used. Biopsy results indicated that a 0.2-second duration of CO2 laser irradiation was inadequate to completely de-epithelialize the gingival tissue. A 0.5-second exposure exhibited complete epithelial destruction with little or no disturbance of the underlying connective tissue layer and viable connective tissue 1.0 mm below the impact site.     

Effects of ferric and aluminum oxalates on dentin permeability

The purpose of this study was to compare the efficacy of ferric oxalate, aluminum oxalate, or Tenure dentin conditioner, a marketed product containing aluminum oxalate, at reducing the permeability of human dentin in vitro. Topical treatment with these acidified agents or 2.5% nitric acid for 10, 30, or 60 seconds was compared. The results indicate that 10-second treatments of dentin with all agents increased dentin permeability. Extending the treatment to 30 seconds produced a decrease in dentin permeability for acidified aluminum and ferric oxalate with 60-second treatments being even more effective. Treatment with Tenure dentin conditioner for 60 seconds did not reduce dentin permeability as well as treatment with the other oxalate salts.     

Effects of two disinfection/sterilization methods for dentin specimens on dentin permeability

Clinical Oral Investigations - To investigate the effects of two disinfection/sterilization methods on the permeability of dentin specimens. Forty intact human third molars were freshly extracted...     

Effects of high-speed cutting on dentin permeability and bonding

The effects of high-speed cutting by use of a diamond bur with or without water coolant or sanding by 80-grit SiC paper on dentin permeability, before and after surface treatment, and dentin bonding of adhesive resins were compared. Three different bonding systems were used: Scotchbond DC, which requires no removal of smear layers, and two others, Clearfil Photobond and Superbond C&B, both of which remove smear layers (phosphoric acid gel or 10% citric acid containing 3% ferric chloride, respectively). Creation of smear layers by bur cutting or sanding reduced dentin permeability to levels that were only 1-3% of the maximum permeability values. Scotchbond DC gave low but consistent bond strengths (3.7-6.1 MPa) to dentin covered with smear layers. Clearfil PHotobond also produced consistent bond strengths (8.6-9.4 MPa). The increase in the permeability of dentin after phosphoric acid treatment was higher when the SiC paper was used (146%) than when the high-speed bur was used (87-90%). The smear layer and smear plugs produced by the diamond bur were more resistant to 10-3 treatment than were the SiC-created smear layers. The bond strengths of Superbond showed the highest bond strengths to the conditioned dentin when the high-speed cutting was used with water coolant (16.3 MPa), compared with the other two groups (12.2-12.5 MPa).     

Impact of combined CO2 laser irradiation and fluoride on enamel and dentin biofilm-induced mineral loss

Objectives

The caries-protective effects of CO₂ laser irradiation on dental enamel have been demonstrated using chemical demineralization models. We compared the effect of CO₂ laser irradiation, sodium fluoride, or both on biofilm-induced mineral loss (∆Z) and Streptococcus mutans adhesion to enamel and dentin in vitro.

Materials and methods

Ground, polished bovine enamel, and dentin samples were allocated to four groups (n = 12/group): no treatment (C); single 22,600-ppm fluoride (F) varnish (5 % NaF) application; single CO₂ laser treatment (L) with short pulses (5 μs/λ = 10.6 μm); and laser and subsequent fluoride treatment (LF). Samples were sterilized and submitted to an automated mono-species S. mutans biofilm model. Brain heart infusion plus 5 % sucrose medium was provided eight times daily, followed by rinses with artificial saliva. After 10 days, bacterial numbers in biofilms were enumerated as colony-forming units/ml (CFU/ml) (n = 7/group). ∆Z was assessed using transversal microradiography (n = 12/group). Univariate ANOVA with post hoc Tukey honestly-significant-difference test was used for statistical analysis.

Results

Bacterial numbers were significantly higher on dentin than enamel (p < 0.01/ANOVA). On dentin, LF yielded significantly lower CFUs than other groups (p = 0.03/Tukey), while no differences between groups were found for enamel. The lowest ∆Z in enamel was observed for L (mean/SD 2036/1353 vol%×μm), which was not only significantly lower than C (9642/2452 vol%×μm) and F (7713/1489 vol%×μm) (p < 0.05) but also not significantly different from LF (3135/2628 vol%×μm) (p > 0.05). In dentin, only LF (163/227) significantly reduced ∆Z (p < 0.05).

Conclusion/clinical relevance

CO₂ laser irradiation did not increase adhesion of S. mutans in vitro. Laser treatment alone protected enamel against biofilm-induced demineralization, while a combined laser-fluoride application was required to protect dentin.

     

Effects of CO2 laser on fluoride uptake in enamel

OBJECTIVES: The objective of this study was to investigate the effects of CO(2) laser on fluoride uptake in the loosely- and firmly-bound forms in enamel. METHODS: Five human molars were cut into halves before being treated with 2.0% NaF topical gel. Each half had three windows on the enamel surface, including one control and two experimental windows irradiated by two laser therapies. One half of each tooth was treated with 1 M KOH solution to remove the loosely-bound fluoride (calcium fluoride). A tooth section was obtained from each window and the relative fluorine concentration was analyzed with Secondary Ion Mass Spectrometry (SIMS). The morphology of the enamel surfaces in the windows was examined using an Environmental Scanning Electron Microscope (ESEM). RESULTS: Significant laser-induced increases in the uptake of fluoride were revealed in both loosely-bound and firmly-bound apatitic fluoride, with both laser treatments (all p<0.001). Calcium fluoride-like deposits on the enamel surfaces receiving the combined laser-fluoride treatment were revealed by ESEM. CONCLUSIONS: The finding of this study substantiated the laser effect in increasing the fluoride uptake into enamel.     

Effect of various pretreatments for dentin bonding on dentin permeability

Pretreatment of the dentinal surface with acidic solution is now considered to be necessary to obtain strong bonding between dentin and resin materials. Effects of various surface treatments for dentin bonding on dentinal smear removal have been reported by SEM observation. In this study, changes of dentin permeability after the surface treatments were measured using Pashley's technique. Forty-second treatments with either phosphoric acid gel, aqueous phosphoric acid, 10-3 solution or aqueous 10-20 Ca solution (10% citric acid containing 20% CaCl2) produced greater increases in dentin permeability compared with the treatments using either 10-20 Ca gel, Tenure Conditioner, Scotchprep or Gluma 2 for 40 seconds. Treatments with primers including adhesive monomers such as Scotchprep and Mirage Conditioner also increased the dentin permeability by removal of the smear layers and smear plugs. Application of a bonding agent (Clearfil Photobond) for 1 minute did not remove the smear plugs and the dentin permeability remained the same as before the treatment. The changes in dentin permeability were not predictable by SEM observation in some cases.     

Regional variation in permeability of young dentin.

Variation in the permeability of dentin in people 19 years and less in age was evaluated. The regions compared were the occlusal third versus the middle third versus the cervical third of approximal surfaces. Also compared were the mesial approximal surface versus the distal. The comparison was done by obtaining 1 mm-thick dentin discs from the area of dentin close to the dentinoenamel junction. It was seen that the cervical area was significantly more permeable than the occlusal area. The middle third, though not statistically significant, had mean values almost twice those in the occlusal third and almost half of the values in the cervical third. No difference was seen in permeability between the mesial and distal surfaces. The reasons for these regional variations and their clinical implications are presented.     

A comparison of the morphological changes after Nd-YAG and CO2 laser irradiation of dentin surfaces

The purpose of this study was to compare the morphological changes after Nd-YAG and CO2 laser irradiation on dentin surfaces with or without the smear layer. Eighty-one 3-mm-thick dentin specimens collected from the middle third of molar crowns were used. The dentin surfaces were ground to #320, #400, and #600 grit in series to create a smear layer. Half of the specimens were treated with 14% EDTA for 2 min to remove the smear layers. The lasers were applied on each specimen perpendicularly with 1-mm focus distance to the dentin surface for 4 s. The parameters for the Nd-YAG laser were 50 mJ, 100 mJ, and 150 mJ at 10 pps, 20 pps, and 30 pps, and for the CO2 laser were 2 W, 3 W, and 4 W at 5 ms x 20 pps, 10 ms x 10 pps, 20 ms x 20 pps, 50 ms x 2 pps, 100 ms x 2 pps, and 200 ms x 2 pps. The results showed that the Nd-YAG laser caused crater and melting of the dentin surface, especially in dentin specimens with smear layers. The CO2 laser produced extensive cracking lines on dentin surfaces with a smear layer, whereas surface erosion and crater formation were found on specimens without a smear layer. In conclusion, both the laser types and smear layer have a significant influence on the morphological changes of dentin surfaces irradiated by lasers.     

Effect of dentin conditioning on dentin permeability and micro-shear bond strength

The purpose of this study was to compare fluid flow rates across dentin surfaces treated with four conditioners. The effect of conditioning on the micro-shear bond strengths of glass ionomer cement (Fuji IX GP) and resin-based adhesives (Single Bond 2 or Clearfil SE Bond) were also investigated. Under a simulated pressure of 1.3 kPa, two dentin conditioners, phosphoric acid, and a self-etching primer were applied to the dentin surfaces. Dentinal fluid flows at baseline and after conditioning were recorded for 15 min each. The conditioned surfaces were examined using a scanning electron microscope. The micro-shear bond strengths of the glass ionomer cement and of the resin-based adhesives bonded to conditioned dentin surfaces were evaluated while simulated intrapulpal pressure was maintained at 0 or 1.3 kPa. Only the dentin surface etched with phosphoric acid showed a significant increase in permeability. Micro-shear bond strengths of Fuji IX GP were not affected by conditioning the dentin surfaces or by bonding at different intrapulpal pressures (0 or 1.3 kPa). The effects on bond strengths of resin-based adhesives depended on the system used. The simulated positive intrapulpal pressure during bonding significantly affected the adherence of Single Bond 2, whereas Clearfil SE Bond was unaffected.