In vitro evaluation of experimental light activated gels for tooth bleaching.

Dental bleaching is an important part of aesthetic dentistry. Various strategies have been created to enhance the bleaching efficacy. As one such strategy, light-activated nanoparticles that enable localized generation of reactive oxygen species have been developed. Here, we evaluated the cellular response to experimental gels containing these materials in in vitro models. L-929 cells, 3T3 cells, and gingival fibroblasts were exposed to the gels at 50%, 10%, 2%, 0.4%, 0.08%, 0.016%, and 0.0032%. The gels contained TiO2/Ag nanoparticles, TiO2 nanoparticles, hydrogen peroxide (6% hydrogen peroxide), or no added component and were tested with and without exposure to light. Cells were exposed to gels for 24 h or for 30 min. The latter case mimics the clinical situation of a short bleaching gel exposure. Metabolic activity and cell viability were evaluated with MTT and neutral red assays, respectively. We found a dose-dependent reduction of formazan formation and neutral red staining with gels containing TiO2/Ag nanoparticles or TiO2 nanoparticles in the 24 h setting with and without illumination. The strongest reduction, which was not dose-dependent in the evaluated concentrations, was found for the gel containing hydrogen peroxide. Gels with TiO2 nanoparticles showed a similar response to gel without particles. TiO2/Ag gel showed a slightly higher impact. When the gels were removed by rinsing after 30 min of exposure without light illumination, gel containing TiO2/Ag nanoparticles showed a stronger reduction of formazan formation and neutral red staining than gel containing TiO2 particles. Exposure of cells for 30 min under illumination and consequent rinsing off the gels also showed that Ag-containing particles can have a higher impact on the metabolic activity and viability than particles from TiO2. Overall our results show that experimental bleaching gels containing TiO2/Ag or TiO2 nanoparticles are less cytotoxic than hydrogen peroxide-containing gel. When gels are removed, gel containing TiO2/Ag particles exhibit a stronger reduction of metabolic activity and viability than the gel containing TiO2.

Insight in the chemistry of laser-activated dental bleaching.

The use of optical radiation for the activation of bleaching products has not yet been completely elucidated. Laser light is suggested to enhance the oxidizing effect of hydrogen peroxide. Different methods of enhancing hydrogen peroxide based bleaching are possible. They can be classified into six groups: alkaline pH environment, thermal enhancement and photothermal effect, photooxidation effect and direct photobleaching, photolysis effect and photodissociation, Fenton reaction and photocatalysis, and photodynamic effect.

Laser teeth bleaching: evaluation of eventual side effects on enamel and the pulp and the efficiency in vitro and in vivo.

Light and heat increase the reactivity of hydrogen peroxide. There is no evidence that light activation (power bleaching with high-intensity light) results in a more effective bleaching with a longer lasting effect with high concentrated hydrogen peroxide bleaching gels. Laser light differs from conventional light as it requires a laser-target interaction. The interaction takes place in the first instance in the bleaching gel. The second interaction has to be induced in the tooth, more specifically in the dentine. There is evidence that interaction exists with the bleaching gel: photothermal, photocatalytical, and photochemical interactions are described. The reactivity of the gel is increased by adding photocatalyst of photosensitizers. Direct and effective photobleaching, that is, a direct interaction with the colour molecules in the dentine, however, is only possible with the argon (488 and 415 nm) and KTP laser (532 nm). A number of risks have been described such as heat generation. Nd:YAG and especially high power diode lasers present a risk with intrapulpal temperature elevation up to 22°C. Hypersensitivity is regularly encountered, being it of temporary occurrence except for a number of diode wavelengths and the Nd:YAG. The tooth surface remains intact after laser bleaching. At present, KTP laser is the most efficient dental bleaching wavelength.

The Decisive Role of Laser Doppler Flowmetry for Pulp Preservation in Discolored Traumatized Teeth.

Objective: It has been stated that blood pigments within discolored teeth may interfere with Laser Doppler Flowmetry (LDF) measurements. The aim of this study was to assess pulp vitality with LDF in a cohort of discolored traumatized teeth referred for endodontic treatment or where the referring dentist had doubts regarding maintained tooth vitality. Background: Discoloration of teeth is a common sequel of dental trauma. Still today, it is taken as an indicator for root canal treatment. Transient apical breakdown (TAB) is confused with apical periodontitis, although it is a sequel of dental trauma in young mature teeth and will result in revascularization and dissolution of the apical radiolucency. Methods: A total of 26 patients with 28 discolored teeth, belonging to a cohort of referred patients with traumatized teeth referred for root canal treatment and/or pulp vitality assessment were screened on color with photographs by three investigators, with traditional sensibility tests and with a Moor VMS II LDF meter. Results: The color of the intrinsically discolored teeth was grayish in 58% of teeth, blue 20%, pink/crimson 12%, and yellow 4%. Eighty-five percent were central maxillary incisors, 11% were mandibulary incisors. Thanks to LDF, 43% of the trauma cases in this small cohort with discoloration underwent root canal treatment instead of 70% with traditional sensibility tests as indicator. TAB was found in 11%. Conclusions: LDF was decisive in diagnosing vitality of discolored teeth and there was no negative impact of tooth discoloration on LDF measurements.

Laser-assisted cavity preparation and adhesion to erbium-lased tooth structure: part 2. present-day adhesion to erbium-lased tooth structure in permanent teeth.

With the introduction of the Er:YAG laser, it has become possible to remove enamel and dentin more effectively and efficiently than with other lasers. Thermal damage is reduced, especially in conjunction with water spray. Since FDA (Federal Drug Administration) approval of the Er:YAG laser in 1997--for caries removal, cavity preparation and conditioning of tooth substance - there have been many reports on the use of this technique in combination with composite resins. Moreover, cavity pretreatment with Er:YAG laser (laser etching) has been proposed as an alternative to acid etching of enamel and dentin. Reports evaluating the adhesion of glass-ionomer cements to Er:YAG-lased tooth substance are scarce. This article reviews the literature regarding adhesion and sealing efficacy using different (pre)treatment protocols in association with Er:YAG laser preparation. Recent research has shown that lasing of enamel and dentin may result in surface and subsurface alterations that have negative effects on both adhesion and seal. It is concluded that at present, it is advisable to respect the conventional pretreatment procedures as needed for the respective adhesive materials. Although the majority of present day reports show that microleakage and bond strength are negatively influenced by laser (pre)treatment (compared with conventional preparation), there is ongoing discussion of how adhesion is best achieved on Er:YAG-lased surfaces.

Laser induced explosive vapor and cavitation resulting in effective irrigation of the root canal. Part 2: evaluation of the efficacy.

BACKGROUND AND OBJECTIVES: Limited information exists regarding the efficacy of laser activated irrigation (LAI) on removal of root canal debris. This study compares the efficacy of LAI for removal of debris in root canals as compared to conventional irrigation (CI) and passive ultrasonic irrigation (PUI). MATERIALS AND METHODS: A splitted tooth model was constructed with straight roots prepared to a 0.06 taper and an apical diameter of ISO 40. A vertical groove was cut in the canal wall at 2-6 mm to the end of the canal in one halve of the root canal wall and filled with dentinal debris. In group 1 root canals were irrigated with 2.5% NaOCl by hand (20 seconds) with the needle 1 mm short from the apical stop, in group 2 NaOCl was ultrasonically activated (20 seconds) with an Irrisafe tip 1 mm short from the apical stop, and in group 3 NaOCl was activated with an Er,Cr:YSGG laser (Z2 Endolase tip -200 microm fiber, four times for 5 seconds, 75 mJ, 20 Hz, stationary at 5 mm from the apical stop). The remaining quantity of dentin debris in the groove was evaluated using a scoring system. RESULTS: LAI resulted in significantly less debris than PUI (P<0.005) and CI (P<0.0005). PUI also showed significantly less debris than CI (P<0.005). CONCLUSION: Under the conditions of this study LAI is statistically significantly more effective in removing artificially placed dentin debris in a root canal as PUI and CI.

Laser induced explosive vapor and cavitation resulting in effective irrigation of the root canal. Part 1: a visualization study.

BACKGROUND AND OBJECTIVES: Limited information exists regarding the induction of explosive vapor and cavitation bubbles in an endodontic rinsing solution. It is also not clear whether a fiber has to be moved in the irrigation solution or can be kept stationary. No information is available on safe power settings for the use of cavitation in the root canal. This study investigates the fluid movements and the mechanism of action caused by an Er,Cr:YSGG laser in a transparent root model. MATERIAL AND METHODS: Glass models with an artificial root canal (15 mm long, with a 0.06 taper and apical diameter of 400 microm) were used for visualization and registration with a high-speed imaging technique (resolution in the microsecond range) of the creation of explosive vapor bubbles with an Er,Cr:YSGG laser at pulse energies of 75, 125, and 250 mJ at 20 Hz using a 200 microm fiber (Z2 Endolase). Fluid movement was investigated by means of dyes and visualization of the explosive vapor bubbles, and as a function of pulse energy and distance of the fiber tip to the apex. RESULTS: The recordings in the glass model show the creation of expanding and imploding vapor bubbles with secondary cavitation effects. Dye is flushed out of the canal and replaced by surrounding fluid. It seems not necessary to move the fiber close to the apex. CONCLUSION: Imaging suggests that the working mechanism of an Er,Cr:YSGG laser in root canal treatment in an irrigation solution can be attributed to cavitation effects inducing high-speed fluid motion into and out the canal.

Laser-assisted cavity preparation and adhesion to erbium-lased tooth structure: part 1. Laser-assisted cavity preparation.

The use of the ruby laser (693.4 nm) was first described in 1960, and it was applied for hard tissue ablation in 1964. Different wavelengths [Nd:YAG (1.065 microm), CO2 (9.6 microm), Ho:YAG (2.12 microm)] were consequently explored. Due to massive thermal side effects, these wavelengths caused increased temperature in dental pulp, as well as microcracks and carbonization. The use of this laser for dental hard tissue preparation was eventually abandoned. At the end of the 1980s, excimer lasers (ultraviolet) and the erbium laser (infrared) were developed, with the advantages of improved temperature control and smaller penetration depths. With the development of smaller devices and improved knowledge of how to limit damage to the surrounding tissues, new ablation techniques were established in the 1990s. There is still contradiction in the current literature, however, in that different wavelengths are advocated for hard tissue removal, and heterogeneity in laser parameters and power densities remain. In this review, the effects of the wavelengths presently used for cavity preparation are evaluated. We conclude that erbium lasers (Er:YAG and Er,Cr:YSGG) are most efficient and, with the right parameters, the thermal side effects are small. There is a substantial need for "gold standards", although this is difficult to establish in practice owing to different laser parameters (including pulse repetition rate, amount of cooling, energy delivered per pulse, and types of pulses) and target specificity (tissue interaction with sound or decayed enamel or dentin, and the extent of (de)mineralization) which influence tissue interaction.

Scanning electron microscopic evaluation of enamel and dentin surfaces after Er:YAG laser preparation and laser conditioning.

OBJECTIVE: The aim of this study was to observe and evaluate the micro-morphology of enamel and dentin surfaces after Er:YAG laser preparation and conditioning. BACKGROUND DATA: Information regarding micro-morphologic changes of tooth substance as a result of a change of Er:YAG laser parameters for cavity preparation is limited. METHODS: Human enamel and dentin surfaces were irradiated with an Er:YAG laser with the following parameters : (1) energy output: 200 mJ, 250 mJ, 300 mJ, 350 mJ, and 400 mJ; (2) repetition rate: 5 Hz and 10 Hz; (3) pulse duration: 100 mus/VSP (very short pulse); (4) 5 and 10 passes over the surface at a distance of 7 mm, speed: 4 mm/s using a non-contact delivery tip; (5) water cooling: 5 mL/min. The hand piece was fixed in a power driven x-y moving table. Subsequently, half of the samples were laser-conditioned at 100 mJ, 10 Hz, 250 mus/SP (short pulse) for enamel, and 80 mJ, 10 Hz, SP for dentin at a distance of 10 mm. Surface morphology and surface alterations were evaluated using scanning electron microscopy (SEM). RESULTS AND CONCLUSION: SEM evaluation showed the characteristics of Er:YAG-lased enamel and dentin surfaces: irregular enamel surfaces with typical keyhole shaped prisms and rods, and protrusion of dentinal tubules with a cuff-like appearance. Laser conditioning rounded off the sharp edges on the enamel irregularities and dentin surface structures. First signs of vitrification were seen at 250 mJ for enamel samples and 300 mJ for dentin samples. Increase of the pulse repetition rate from 5 Hz to 10 Hz did not result in changes of surface morphology. Laser conditioning did not result in additional vitrification.

Microleakage of class V glass ionomer restorations after conventional and Er:YAG laser preparation.

OBJECTIVE: The aim of this study was to investigate the microleakage in class V cavities following Er:YAG laser or conventional preparation restored with two conventional glass ionomer cements (cGIC) and to evaluate the effect of conditioning on laser-prepared surfaces. BACKGROUND DATA: Information on this topic related to cGIC is scarce. METHODS: Sixty class V cavities were assigned to six groups: I and IV were Er:YAG-lased, II and V Er:YAG-lased and conditioned, and III and VI conventionally prepared and conditioned. Groups I, II, and III, were restored with Ketac Fil Plus Applicap; groups IV, V, and VI were restored with Fuji IX GP Capsule. Then, teeth were stored in distilled water (37 degrees C, 24 h), thermal cycled 1500 times (5-55 degrees C), placed in a 2% aqueous solution of methylene blue (37 degrees C, 24 h), embedded in acrylic resin, sectioned oro-facially, and analyzed for leakage. RESULTS: Statistically significant differences between occlusal and cervical regions were observed (p < 0.05). Group III showed significantly more microleakage at the occlusal margin compared to group II (p = 0.022). Group V showed significantly more microleakage at the gingival margin than group VI (p = 0.022). Leakage on the occlusal margins was significantly higher in group III than in group VI (p = 0.038). Scanning electron microscopy indicated that conditioning of laser-prepared dentin with Ketac conditioner partially closed the tubules' orifices, whereas the use of GC conditioner completely obliterated the tubules. CONCLUSION: The application of Ketac Fil Plus to laser-prepared enamel and dentin resulted in a better and more reproducible seal compared to conventionally prepared tooth surfaces. When using the more viscous Fuji IX application, Er:YAG lasing did not improve marginal adaptation.

Investigation of Coronal Leakage of Root Fillings after Smear Layer Removal with EDTA or Er,Cr:YSGG Laser through Capillary Flow Porometry.

No studies have been performed evaluating the marginal seal of root fillings after direct exposure of root canal (RC) walls to Er,Cr:YSGG laser irradiation. Therefore, 75 root filled teeth (5 × 15-cold lateral condensation) were analyzed for through-and-through leakage (TTL) using capillary flow porometry (CFP). The cleaning protocol determined the experimental groups: (1) irrigation with NaOCl 2.5% and EDTA 17% or standard protocol (SP), (2) SP + Er,Cr:YSGG lasing (dried RC), (3) NaOCl 2.5% + Er,Cr:YSGG lasing (dried RC), (4) SP + Er,Cr:YSGG lasing (wet RC), and (5) NaOCl 2.5% + Er,Cr:YSGG lasing (wet RC). Groups 6 to 10 consisted of the same filled teeth with resected apices. Resection was performed after the first CFP measurement. CFP was used to assess minimum, mean flow, and maximum pore diameters after 48 h. Statistics were performed using nonparametric tests (P > 0.05). Additional three roots per group were submitted to SEM of the RC walls. TTL was observed in all groups without statistically significant differences between the different groups for minimum, mean, and maximum pore diameter (P > 0.05). In this study, the use of EDTA and/or Er,Cr:YSGG laser did not reduce through-and-through leakage in nonresected and resected roots.

Investigation of coronal leakage of root fillings after smear-layer removal with EDTA or Nd:YAG lasing through capillary-flow porometry.

OBJECTIVE: This study investigates the effects of Nd:YAG laser irradiation combined with different irrigation protocols on the marginal seal of root fillings. BACKGROUND DATA: Limited information exists regarding the effects of morphologic changes to root canal (RC) walls after Nd:YAG laser irradiation after smear-layer removal with EDTA on the sealing ability of root fillings. METHODS: The 75 root-filled teeth (5 × 15 teeth) were analyzed for through-and-through leakage by using capillary flow porometry (CFP). The RC cleaning procedure determined the assignment to a group: (1) irrigation with NaOCl 2.5% and EDTA 17% or standard protocol (SP), (2) SP + Nd:YAG lasing (dried RC), (3) NaOCl 2.5% + Nd:YAG lasing (dried RC), (4) SP + Nd:YAG lasing (wet RC), or (5) NaOCl 2.5% + Nd:YAG lasing (wet RC). Groups 1r to 5r consisted of the same filled teeth with resected apices up to the most apical point of the preparation length. Resection was performed after the first CFP measurement. Roots were filled with cold lateral condensation. CFP was used to assess minimum, mean flow and maximum pore diameters after 48 h, and immediately after these measurements, including root resection. Statistics were performed by using nonparametric tests (p > 0.05). An additional three roots per group were submitted to SEM of the RC wall. RESULTS: Through-and-through leakage was observed in all groups. Statistically significant differences were observed in maximum pore diameter: 1r > 3r, and 1r > 5r; in mean flow pore diameter: 1r > 2r, 2r < 4r (p < 0.05). Typical Nd:YAG glazing effects were observed when the smear layer was present and exposed to the laser fiber (i.e., in the groups without use of EDTA) or when the fiber tip made direct contact with a smear-layer free RC wall. CONCLUSIONS: The reduction in through-and-through leakage is significantly higher with the Nd:YAG laser as smear-layer modifier than when smear layer is removed with an EDTA rinsing solution.

Longitudinal study on the influence of Nd:YAG laser irradiation on microleakage associated with two filling techniques.

OBJECTIVE: This study investigates the effects of Nd:YAG laser irradiation on apical and coronal seals, when used prior to two root canal filling techniques. BACKGROUND DATA: Limited information exists regarding the effects of morphologic changes to dentin walls following Nd:YAG laser irradiation on the sealing ability of root fillings. METHODS: Two hundred forty teeth were analyzed by observing coronal and apical leakage of Indian ink (DL), and 60 were analyzed for through-and-through leakage using the fluid transport model (FTM). The Nd:YAG laser parameters were 1.5 W, 100 mJ, and 15 Hz (four times for 5 s at 20 s intervals). Each group consisted of a lased and a nonlased subgroup: each subgroup had root fills done by either cold lateral condensation (CLC) or hybrid condensation (HC). Leakage was assessed after 48 h, and then at 1, 6, and 12 months. The DL group was divided into four groups of 15 teeth for each evaluation point. Through-and-through leakage (L in microliters/day) was measured for 48 h under a pressure of 1.2 atm using FTM, and recorded as L = 0 (L1), 0 < L 10 (L3). RESULTS: Apical and coronal dye leakage was observed in all groups. Significant differences (p < 0.05) in apical leakage were found between HC and HC + Nd after 1, 6, and 12 months, and between CLC and CLC + Nd at 6 and 12 months. No significant differences were found between laser-irradiated and non-laser-irradiated groups with FTM. CONCLUSION: Pulsed Nd:YAG laser irradiation following root canal preparation may reduce apical leakage in association with hybrid gutta-percha condensation.