The effect of lasers on dental hard tissues

Effect of Dentin and Zirconia Surface Treatments with Laser Irradiation Versus Sandblasting on the Bonding Ability of Zirconia

Objective: This study aimed to investigate the effects of laser irradiation applied to zirconia and tooth surfaces on shear bond strength (SBS) compared with acid etching and sandblasting. Background: The effect of laser irradiation on the bond strength between zirconia and adhesives is a controversial issue for dentin surface treatments. In addition, the effects of different combinations of surface treatments to increase adhesion on both the zirconia and dentin surfaces remain unclear. Materials and methods: A total of 90 tooth samples were assigned into groups according to various pretreatments: control group was left untreated, acid etching, and Erbium, Chromium:Yttrium Scandium Gallium Garnet (Er,Cr:YSGG) laser irradiation group (15 Hz, 2 W). In addition, the zirconia specimens were separated into three groups (n = 10) according to the different surface treatments performed: sandblasting (120 μm Al2O3), Er,Cr:YSGG laser (15 Hz, 2 W), and as untreated surface. The zirconia samples were cemented to the dentin surface using dual-cure resin cement and subjected to an SBS test at a speed of 0.5 mm/min under a universal testing machine until fractures occurred in the bonding surface. Results: The highest SBS values were observed in Group tooth acid (TA)-zirconia Er,Cr:YSGG laser (ZL), followed by Group tooth Er,Cr:YSGG laser (TL)-zirconia sandblasting (ZS) and Group TA-zirconia control (ZC). The lowest SBS values were found in Group TA-ZS. Significant intergroup difference was noted between Group TA-ZL, Group tooth control (TC)-ZC, Group TL-ZS, and Group TC-ZC. However, no significant difference was noted between Group TA-ZL, Group TL-ZS, and Group TA-ZC. Conclusions: Acid etching and laser treatments applied to the dentin and zirconia surfaces were found to be effective techniques for improving the zirconia-dentin bond, respectively. Clinical Trial Registration number: 33216249-604.01.02-E.24308.

Er:YAG Laser Physical Etching and Ultra-High-Molecular-Weight Cross-Linked Sodium Polyacrylate Chemical Etching for a Reliable Dentin Dry Bonding

Dentin bond interface stability is the key issue of dental adhesion in present clinical dentistry. The concept of selective extrafibrillar demineralization has opened a new way to maintain intrafibrillar minerals to prevent interface degradation. Here, using ultra-high-molecular-weight sodium polyacrylate [Carbopol (Carbo) > 40 kDa] as a calcium chelator, we challenge this concept and propose a protocol for reliable dentin dry bonding. The results of high-resolution transmission electron microscopy revealed periodic bands of 67 nm dentin collagen fibrils after Carbo etching, and the hydroxyproline concentration increasing with prolonged chelating time denied the concept of extrafibrillar demineralization. The results that wet and dry bonding with Carbo-based demineralization produced a weaker bond strength than the traditional phosphoric acid wet adhesion suggested that the Carbo-based demineralization is an unreliable adhesion strategy. A novel protocol of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion revealed that a micro-/nano-level rough, rigid, and non-collagen exposed dentin surface was produced, the micro-tensile bond strength was maintained after aging under dry and wet bonding modes, and in situ zymography and nanoleakage within the hybrid layers presented lower signals after aging. Cell culture in vitro and a rabbit deep dentin adhesion model in vivo proved that this protocol is safe and biocompatible. Taken together, the concept of extrafibrillar demineralization is limited and insufficient to use in the clinic. The strategy of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion produces a bonding effect with reliability, durability, and safety.

Assessment of chemical, ultrasonic, diode laser, and Er:YAG laser application on debonding of ceramic brackets

Background

Risk of enamel damage that often accompanies ceramic brackets debonding raises the demand of finding an optimal method for debonding of them without adverse effects. Different techniques were proposed in an attempt to facilitate their debonding. Comparison of these techniques is crucial. The aim of this study was to evaluate and compare different techniques for debonding of ceramic brackets in terms of shear bond strength and adhesive remnant index.

Materials and methods

A total of 100 extracted premolars were randomly allocated into 5 groups. Ceramic brackets were then bonded to teeth using light cure composite resin. Among test groups; group I: served as control, group II: chemical aided debonding via peppermint oil, group III: ultrasonic aided debonding, group IV: diode laser aided debonding, and group V: Er:YAG laser aided debonding. Brackets were shear tested using universal testing machine followed by ARI assessment and evaluation of enamel microstructure was performed using scanning electron microscopy.

Results

A significantly lower shear bond strength was found in ultrasonic, diode, and Er:YAG laser groups. However, no significant difference was found in the chemical group. A significantly higher adhesive remnant index was found solely in Er:YAG laser group with minimal enamel microstructure alterations.

Conclusions

Er:YAG laser is a promising tool in debonding ceramic brackets. Ultrasonic and diode laser significantly reduced shear bond strength. Yet, adhesive remnant index in both groups revealed no difference. Chemical aided debonding had little effect and hence, it cannot be recommended without further development.

Establishment of Pulp Damage Repair Models in Miniature Pigs Using Diode Lasers

Objective: To establish a controlled pulp damage repair model in miniature pigs by using a diode laser. Background: Laser is a novel kind of controllable energy, and it is widely used in dentistry. Methods: The premolars of four 24- to 28-month-old miniature pigs were divided into three laser groups, according to the output powers of a diode laser, and the nonirradiated first molars acted as controls. The teeth in laser groups were irradiated under three parameters (output powers 1.5, 2.5, 4 W, continuous wave, frequency 50 Hz for 60 sec). The dental and gingival morphology was observed at 0, 7, 14, and 21 days after laser irradiation. The animals were sacrificed for qualitative and quantitative pulp histopathological analysis. Results: The three laser groups present no seriously irreversible dental and gingival damage. In the 1.5-W group, dental pulp exhibited angiectasis and hyperemia with no inflammation, and did not significantly differ with the control groups at 21 days (p > 0.05). In the 2.5-W group, pulpal inflammation was highest at 7 days and then decreased significantly at 21 days, and the tissue repair appeared at 14 days (p < 0.05). In the 4-W group, pulpal inflammation was significantly highest at 7 days, with an increase in the degree of tissue repair (p < 0.05). Conclusions: The output power of 1.5 W developed a reversible pulpitis model; the output powers of 2.5 and 4 W within 7 days led to the development of irreversible pulpitis models, which proceeded as chronic pulpitis with obvious tissue repair.

Laser Analgesia Associated with Restorative Dental Care: A Systematic Review of the Rationale, Techniques, and Energy Dose Considerations

It is a common experience amongst laser dentists and patients that mid-IR wavelength application in cavity preparation may be achieved without causing any associated pain. The erbium family of lasers (Er,Cr:YSGG 2780 nm and Er:YAG 2940 nm) are frequently used without employing injectable local anesthesia as an adjunct: the phenomenon arising from the application of these devices is known as laser analgesia. This review seeks to apply a systematic approach to the examination of appropriate published studies but also to highlight the need for much more structured clinical investigations that consolidate photonic dose and methodology. A search of published data using PRISMA criteria was carried out to examine clinical trials into laser analgesia in conjunction with restorative dentistry, applying inclusion and exclusion criteria. From this, 10 published articles were selected for analysis. Suitability assessment was carried out, using a modified Cochrane risk of bias methodology. In 8/10 of the included studies, laser-induced analgesia is claimed to be better and effective, while in 2/10 of the studies, no difference was exhibited compared to the control group. Statistical analysis of three split mouth studies concluded that only one of these investigations reviewed demonstrated a significant analgesic effect for laser treatment while the other two did not support this observation. From this data, it is inconclusive to assess the predictability of laser analgesia in cavity preparation. A possible rationale and laser operating parametry has been discussed. Successful implementation of this treatment modality remains technique sensitive and subject to further investigation.

Use of Laser Systems in Orthodontics

Laser systems have been used in the practice of dentistry for >35 years. Laser systems have so many advantages, such as increase patient cooperation, reduce the duration of treatment time, and help the orthodontists to enhance the design of a patient's smile to improve treatment efficacy, and the success of orthodontic treatments can also be improved by diminishing the orthodontic pain and the discomfort of the patients. Laser systems also have some disadvantages, such as cost, large space requirements for some types, and high-risk potential for physician and patient if not used at the appropriate wavelength and power density, that is why before incorporating lasers into clinical practice, the physician must fully understand the basic science, safety protocol, and risks associated with them. Lasers have many applications in orthodontics, including accelerating tooth movement, bonding and debonding processes, pain reduction, bone regeneration, etching procedures, increase mini-implant stability, soft tissue procedures (gingivectomy, frenectomy, operculectomy, papilla flattening, uncovering temporary anchorage devices, ablation of aphthous ulcerations, and exposure of impacted teeth), fiberotomy, scanning systems, and welding procedures. In reviewing the literature on the use of laser in orthodontics, many studies have been conducted. The purpose of the present study was to give information about the use of laser in the field of orthodontics, the effects of laser during the postoperative period, and its advantages and disadvantages and to provide general information about the requirements to be considered during the use of laser.

Effect of Er:YAG and Er,Cr:YSGG Lasers on Ceramic Bracket Debonding from Composite Blocks

Objectives:

This study aimed to assess the effect of erbium-doped yttrium aluminum garnet (Er:YAG) and erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) lasers on the shear bond strength (SBS) of ceramic brackets debonding from the surface of composite blocks.

Materials and Methods:

Thirty-six composite blocks were fabricated using Filtek Z250 light-cure composite. Block surfaces were etched with 37% phosphoric acid for 30 seconds and then rinsed with water for 20 seconds and dried. Maxillary right central incisor ceramic orthodontic brackets were bonded to the surfaces of composite blocks using Transbond XT adhesive and were cured for 40 seconds. Twelve samples were irradiated with Er:YAG laser, while 12 samples were irradiated with Er,Cr:YSGG laser, and the brackets were then debonded using a universal testing machine. Twelve samples served as controls (debonding using the universal testing machine without using a laser). The adhesive remnant index (ARI) score and bracket or composite cracks were evaluated under a stereomicroscope. One-way analysis of variance (ANOVA) was used for the comparison of the three groups. Kruskal-Wallis test was used to compare the ARI scores.

Results:

The mean SBS was 17.01±5.22 MPa with Er:YAG laser, 18.03±6.46 MPa with Er,Cr:YSGG laser, and 16.61±6.73 MPa in the control group; the difference of the three groups was not significant (P=0.835). The difference in the ARI scores and enamel and composite cracks was not significant either (P>0.05).

Conclusion:

This study did not show any reduction in the bond strength of ceramic bracket to composite blocks after Er:YAG and Er,Cr:YSGG laser irradiation.

Comparison of Different Energy Levels of Er:YAG Laser Regarding Intrapulpal Temperature Change During Safe Ceramic Bracket Removal

OBJECTIVE

This study was done to compare the intrapulpal temperature change generated by different energy levels of Er:YAG laser used during debonding of ceramic brackets and find the most suitable level for clinical use.

MATERIAL AND METHODS

Eighty polycrystalline alumina brackets were bonded on bovine incisor teeth, which were randomly divided into 4 groups of 20. One group was assigned as control. In the study groups, after laser exposure with 2, 4, or 6 Watt energy levels, brackets were debonded using an Instron Universal Testing machine. Adhesive remnant index (ARI) scores were recorded to evaluate the site of debonding. To assess intrapulpal thermal increase, 60 human premolar teeth that were prepared in the same way, at the same energy levels, by a thermocouple were used.

RESULTS

When the debonding forces, intrapulpal temperature increases, and ARI of the groups were examined, statistically significant difference was observed between the groups. Mean temperature increases of 0.67°C ± 0.12°C, 1.25°C ± 0.16°C, and 2.36°C ± 0.23°C were recorded for the 2, 4, and 6 Watt laser groups. The mean shear bond strength was 21.35 ± 3.43 megapascals (MPa) for the control group, whereas they were 8.79 ± 2.47, 3.28 ± 0.73, and 2.46 ± 0.54 MPa for the 2, 4, and 6 Watt laser groups, respectively.

CONCLUSIONS

Four watts is the most efficient and safe energy level to be used, utilizing Er:YAG laser with water cooling spray for 6 sec by scanning method during debonding of polycrystalline alumina brackets without any carbonization effects and detrimental temperature changes at debond sites.

Efficiency of Er:YAG laser in debonding of porcelain laminate veneers by contact and non-contact laser application modes (in vitro study)

OBJECTIVE

To determine the efficiency of debonding porcelain laminate veneers (PLV) by using several laser parameters and two different application modes of Er:YAG laser [contact (CM) and non-contact (NCM)], by verification of the consumed PLV debonding time and the changes in dental pulp temperature.

MATERIALS AND METHODS

Forty extracted non-carious human maxillary premolars were prepared for receiving PLV. Sixteen of them were divided into two groups, each of them comprised eight samples based on the application mode; group A with NCM, and group B with CM. Veneers of both groups were debonded by the same laser parameters (360 mJ, 15 Hz) during loading of a 15 N force on specially fabricated veneer cervical margins. The primary results showed that the NCM was more efficient, thus, additional groups (C, D, and E) of the same mode and number of samples were tested with different laser parameters of energy and frequency; group C (400 mJ, 10 Hz), group D (270 mJ, 15 Hz), group E (300 mJ, 10 Hz). The failure mode was determined and classified for the debonded samples of all groups.

RESULTS

All veneers were debonded and samples of the NCM group had considerably lower debonding time (12.6 seconds) than the CM samples (96.3 seconds), however, higher changes of temperature in NCM (4.2°C) than in CM were observed (2.9°C). The failure mode of samples was either type 1 or 3.

CONCLUSION

Er:YAG laser is an effective tool in debonding PLVs. The NCM application mode was more efficient in reducing debonding time than CM application mode but with a higher change in pulp temperature.

CLINICAL SIGNIFICANCE

Investigating the efficacy of Er:YAG laser as a non-invasive particle technique for debonding of failed or malpositioned of porcelain laminated veneers.

Bond strength of etch-and-rinse and self-etch adhesive systems to enamel and dentin irradiated with a novel CO2 9.3 μm short-pulsed laser for dental restorative procedures

The objective of this study was to evaluate the influence of CO₂ 9.3 μm short-pulsed laser irradiation on the shear bond strength of composite resin to enamel and dentin. Two hundred enamel and 210 dentin samples were irradiated with a 9.3 µm carbon dioxide laser (Solea, Convergent Dental, Inc., Natick, MA) with energies which either enhanced caries resistance or were effective for ablation. OptiBond Solo Plus [OptiBondTE] (Kerr Corporation, Orange, CA) and Peak Universal Bond light-cured adhesive [PeakTE] (Ultradent Products, South Jordan, UT) were used. In addition, Scotchbond Universal [ScotchbondSE] (3M ESPE, St. Paul, MN) and Peak SE self-etching primer with Peak Universal Bond light-cured adhesive [PeakSE] (Ultradent Products) were tested. Clearfil APX (Kuraray, New York, NY) was bonded to the samples. After 24 h, a single plane shear bond test was performed. Using the caries preventive setting on enamel resulted in increased shear bond strength for all bonding agents except for self-etch PeakSE. The highest overall bond strength was seen with PeakTE (41.29 ± 6.04 MPa). Etch-and-rinse systems achieved higher bond strength values to ablated enamel than the self-etch systems did. PeakTE showed the highest shear bond strength with 35.22 ± 4.40 MPa. OptiBondTE reached 93.8% of its control value. The self-etch system PeakSE presented significantly lower bond strength. The shear bond strength to dentin ranged between 19.15 ± 3.49 MPa for OptiBondTE and 43.94 ± 6.47 MPa for PeakSE. Etch-and-rinse systems had consistently higher bond strength to CO₂ 9.3 µm laser-ablated enamel. Using the maximum recommended energy for dentin ablation, the self-etch system PeakSE reached the highest bond strength (43.9 ± 6.5 MPa).

Intrapulpal Temperature Increase During Er:YAG Laser-Aided Debonding of Ceramic Brackets

OBJECTIVE

The purpose of this study was to evaluate the temperature changes in the pulp chamber while using a newly introduced application of Er:YAG laser to debond ceramic brackets in a study model with a pulpal circulation with and without thermocycled samples.

BACKGROUND DATA

An esthetic alternative to stainless steel brackets, ceramic brackets have been proposed. However, because of their low fracture resistance and high bond strengths, ceramic brackets can cause a problem when they are being removed using conventional techniques.

MATERIALS AND METHODS

Experimental Groups A and B were established for samples with or without thermocycling. The same 20 maxillary central incisor and 20 premolar teeth were used in both groups. Pulpal blood microcirculation was simulated using an apparatus described in a previous study. Monocrystalline brackets were bonded by using Transbond XT. In Group A, brackets were debonded using the Er:YAG laser (600 mJ, 2 Hz, long pulse, and no air or water spray) after being stored in distilled water for 24 h. In Group B, brackets were debonded using the same laser system as that used in Group A after being stored in distilled water for 24 h and then thermocycled for a total of 5000 cycles between 5°C and 55°C. The laser irradiation duration and intrapulpal temperature changes were measured.

RESULTS

In Group B, the intrapulpal temperature increase of the central incisors was significantly higher than that of the premolar teeth. In the central incisor and premolar teeth groups, there were no statistically significant difference between Groups A and B (p > 0.05). A positive correlation was found between laser irradiation duration and temperature increase (p < 0.01).

CONCLUSIONS

The use of Er:YAG laser is an effective method for debonding the monocrystalline ceramic brackets. This method can be used safely under the consideration of intrapulpal temperature changes.

Effect of Er:Yag laser on dentin demineralization around restorations

The aim of this study was to evaluate the effect of cavity preparation with Er:YAG laser on dentin adjacent to restorations submitted to cariogenic challenge in situ, by subsuperficial microhardness analysis. Bovine incisors were sectioned, flattened, and polished, resulting in 40 dentin slabs. The slabs were randomly assigned to four groups (n = 10), according to the cavity preparation method: I-high-speed handpiece (control); II-Er:YAG laser (160 mJ; 3 Hz); III-Er:YAG laser (260 mJ; 3 Hz); IV-Er:YAG laser (300 mJ; 3Hz). Cavities were restored with composite resin, and the specimens were fixed in intra-oral appliances, which were worn by 10 volunteers for 14 days for simulating cariogenic challenge in situ. During the experimental period, 20% sucrose solution was dripped over each specimen 6 times a day. Samples were removed, sectioned, and examined for subsuperficial Knoop microhardness at 100, 200, and 300 μm from the restoration and at 30 μm from dentin surface. Split-plot analysis of variance showed no significant difference among the cavity preparation techniques (p = 0.1129), among distances (p = 0.9030), as well as no difference in the interaction between the main factors (p = 0.7338). It was concluded that the cavity preparation with Er:YAG laser did not influence on dentin microhardness submitted to cariogenic challenge in situ.

Debonding of ceramic brackets by Er:YAG laser

Purpose:

The objective of the present study is to evaluate the effects of Er:YAG laser debonding of ceramic brackets on the bond strength and the amount of adhesive resin remnant.

Materials and Methods:

Twenty human mandibular incisors were randomly divided into two groups of 10 and polycrystalline ceramic brackets (Transcend series 6000, 3M Unitek, Monrovia, CA, USA) were bonded on enamel surfaces. Group 1 was the control group in which no laser application was performed prior to the shear bond strength (SBS) testing. In Group 2, Er:YAG was applied in 3W power for 6 seconds using the scanning method. The brackets were tested for SBS with an Instron universal testing machine and results were expressed in megapascals (MPa). The amount of adhesive remnant was evaluated with Adhesive Remnant Index (ARI). One-way analysis of variance and Tukey’s post-hoc tests were used for statistical analysis.

Results:

Mean ± standard deviation of SBS values in the control group was 13.42 ±1.23 MPa and 8.47 ±0.71 MPa in the Er:YAG group and this difference was statistically significant (p<0.05). The evaluation of ARI scores demonstrated more adhesive was left on the enamel surface with Er:YAG group.

Conclusion:

3W power Er:YAG laser application with the scanning method to polycrystalline ceramic brackets demonstrated lower bond strengths and higher ARI scores during the debonding procedure.

Femtosecond laser for cavity preparation in enamel and dentin: ablation efficiency related factors

To study the effects of laser fluence (laser energy density), scanning line spacing and ablation depth on the efficiency of a femtosecond laser for three-dimensional ablation of enamel and dentin. A diode-pumped, thin-disk femtosecond laser (wavelength 1025 nm, pulse width 400 fs) was used for the ablation of enamel and dentin. The laser spot was guided in a series of overlapping parallel lines on enamel and dentin surfaces to form a three-dimensional cavity. The depth and volume of the ablated cavity was then measured under a 3D measurement microscope to determine the ablation efficiency. Different values of fluence, scanning line spacing and ablation depth were used to assess the effects of each variable on ablation efficiency. Ablation efficiencies for enamel and dentin were maximized at different laser fluences and number of scanning lines and decreased with increases in laser fluence or with increases in scanning line spacing beyond spot diameter or with increases in ablation depth. Laser fluence, scanning line spacing and ablation depth all significantly affected femtosecond laser ablation efficiency. Use of a reasonable control for each of these parameters will improve future clinical application.

Laser-Aided Ceramic Bracket Debonding: A Comprehensive Review

Different techniques have been introduced for the removal of ceramic brackets. Since the early 1990s, lasers have been used experimentally for debonding ceramic brackets. The goal of this study is to give a comprehensive literature review on laser-aided ceramic bracket debonding. PubMed and Google Scholar databases were used to identify dental articles with the following combination of key words: Ceramic brackets, Debonding, and Laser. Sixteen English articles from 2004 to 2015 were selected. The selected studies were categorized according to the variables investigated including the intrapulpal temperature, shear bond strength, debonding time, enamel damage and bracket failure. Most articles reported decreased shear bond strength and debonding time following laser irradiation without any critical and irritating increase in pulpal temperature. There were no reports of bracket failure or enamel damage. Laser irradiation is an efficient way to reduce shear bond strength of ceramic bracket and debonding time. This technique is a safe way for removing ceramic bracket with minimal impact on intrapulpal temperature and enamel surface and it reduces ceramic bracket failure.

The use of lasers for direct pulp capping

Direct pulp capping helps extend the life of a diseased tooth by maintaining tooth vitality. Nowadays, lasers are more frequently used during direct pulp capping in the clinic, but their use has not been previously reviewed. This review presents the basic properties of currently available lasers, scientific evidence on the effects of laser application on direct pulp capping, and future directions for this technology. An extensive literature search was conducted in various databases for articles published up to January 2015. Original in vitro, in vivo, and clinical studies, reviews, and book chapters published in English were included. Various laser systems have been increasingly and successfully applied in direct pulp capping. Lasers offer excellent characteristics in terms of hemostasis and decontamination for field preparation during direct pulp capping treatment; however, the sealing of exposed pulp with one of the dental materials, such as calcium hydroxide, mineral trioxide aggregates, and bonded composite resins, is still required after laser treatment. Clinicians should consider the characteristics of each wavelength, the emission mode, irradiation exposure time, power, type of laser tip, and the distance between the laser tip and the surface being irradiated.

Pulpal thermal changes following Er-YAG laser debonding of ceramic brackets

Lasers are effective in debonding ceramic brackets. Unfortunately, while reducing the adhesive bond strength, lasers are also reported to increase pulpal temperature. The aim of this study was to evaluate the shear bond strengths and temperature increase levels after debonding ceramic brackets using an Er-YAG laser with or without water-cooling. Sixty polycrystalline upper premolar ceramic brackets were placed on the labial surface of sixty human premolar teeth which were randomly divided into three groups of twenty. A laser pulse at 5 W for 9 seconds was delivered to each bracket in both study groups either with water-cooling (water group) or without water-cooling (waterless group) using an Er-YAG laser. Debonding was performed 45 seconds after laser exposure and shear bond strengths were measured. Data comparison revealed a statistically significant difference between the groups. Mean temperature increases of 2.41°C and 4.59°C were recorded for the water and waterless laser groups, respectively. The shear bond strength value for the control group was 22.76 MPa and 10.46 and 6.36 MPa for the water and waterless laser groups, respectively. The application of Er-YAG laser with water-cooling was an efficient and safe method of debonding ceramic brackets.

Effect of Er:YAG laser on debonding strength of laminate veneers

Objective:

The purpose of this study was to evaluate the debonding strength of laminate veneers after using erbium-doped: yttrium aluminium garnet (Er:YAG) laser.

Materials and Methods:

A total of 60 bovine mandibular incisor teeth were divided into two groups (n = 30). Cylindrical specimens (0.7 mm × 5 mm) were fabricated from Empress II ceramic. Then, they were cemented to incisors using dual-cured resin cement (Variolink II). In the first group, no laser application was performed. The Er:YAG laser was applied on each laminate veneer at the test group for 9 s by using the scanning method. Shear force to remove the laminate veneers were applied with universal testing machine at a crosshead speed of 1 mm/min.

Results:

Results of this study exhibited significant differences between the control (27.28 ± 2.24 MPa) and test group (3.44 ± 0.69 MPa) (P < 0.05).

Conclusion:

This study shows that application of Er:YAG laser decreased the bond strength of laminate veneers.

Importance of laser-induced breakdown spectroscopy for hard tissues (bone, teeth) and other calcified tissue materials

Laser-induced breakdown spectroscopy (LIBS) as a sensitive optical technique capable of fast multielemental analysis proved to be a versatile tool in different applications. It became visible in the analytical atomic spectroscopy scene in the late 1980s and since then, its applications having been developed continuously in different field of science and technology including biomedical science. Here, we review the use and importance of LIBS for trace element determination in different calcified tissue materials. In this article, we have also reported a comprehensive review of the recent progress of biomedical applications of LIBS.

Photodynamic therapy versus ultrasonic irrigation: interaction with endodontic microbial biofilm, an ex vivo study

INTRODUCTION

Photodynamic therapy was introduced as an adjuvant to conventional chemo-mechanical debridement during endodontic treatment to overcome the persistence of biofilms. The aim of this study was to evaluate the ability of photodynamic therapy (PDT) to disrupt an experimental microbial biofilm inside the root canal in a clinically applicable working time.

MATERIALS AND METHODS

Thirty extracted teeth were prepared and then divided in three groups. All samples were infected with an artificially formed biofilm made of Enterococcus faecalis, Streptococcus salivarius, Porphyromonas gingivalis and Prevotella intermedia bacteria. First group was treated with Aseptim Plus® photo-activated (LED) disinfection system, second group by a 650 nm Diode Laser and Toluidine blue as photosensitizer, and the third group, as control group, by ultrasonic irrigation (PUI) using EDTA 17% and NaOCl 2.6% solutions. The working time for all three groups was fixed at 3 min. Presence or absence of biofilm was assessed by aerobic and anaerobic cultures.

RESULTS

There was no statistically significant difference between results obtained from groups treated by Aseptim Plus® and Diode Laser (P<0.6267). In cultures of both groups there was a maximal bacterial growth. The group that was treated by ultrasonic irrigation and NaOCl and EDTA solutions had the best results (P<0.0001): there was a statistically significant reduction of bacterial load and destruction of microbial biofilm.

CONCLUSION

Under the condition of this study, Photodynamic therapy could not disrupt endodontic artificial microbial biofilm and could not inhibit bacterial growth in a clinically favorable working time.

Antimicrobial effect of photodynamic therapy using high-power blue light-emitting diode and red-dye agent on Porphyromonas gingivalis

BACKGROUND AND OBJECTIVE

Antimicrobial photodynamic therapy (a-PDT) using a combination of red-colored laser/light-emitting diode (LED) and blue dye has been employed for periodontal therapy and the antimicrobial effect seems promising. Blue light, which has favorable wavelength properties, would be more effective as a light source for a-PDT because blue light itself possesses an antimicrobial effect. This study aimed to investigate the effect of a-PDT using a novel combination of high-power blue LED and red-dye agent on Porphyromonas gingivalis in vitro.

MATERIAL AND METHODS

Porphyromonas gingivalis ATCC 33277 suspension was irradiated with blue LED (BL) (425-470 nm) or red LED (RL) (625-635 nm) at 30-90 J/cm(2) , or was mixed with erythrosine (ER), phloxine B (PB) or rose bengal (RB) with or without BL irradiation (30 J/cm(2) ). RL (30 J/cm(2) ) in combination with toluidine blue was employed as positive control. All the suspensions of P. gingivalis were serially diluted, plated and incubated anaerobically, and the numbers of colony-forming units (CFUs) were counted on day 7.

RESULTS

BL irradiation at 60 and 90 J/cm(2) demonstrated a significant reduction in the numbers of CFUs. ER, PB and RB solutions at 160 μg/mL showed almost no or only a minimal reduction in the numbers of CFUs. BL at 30 J/cm(2) combined with ER, PB or RB at 160 μg/mL resulted in a log reduction of 0.9, 1.0 and 7.1, respectively, in the numbers of CFUs; 30 J/cm(2) BL with RB at 1.6, 16 and 160 μg/mL demonstrated a log reduction of 6.3, 8.0 and 5.5, respectively; and a log reduction of 5.2 was obtained after 30 J/cm(2) RL with 16 μg/mL TB.

CONCLUSION

Within the limits of this study, BL was found to have an antimicrobial/growth-inhibiting effect on P. gingivalis, and a-PDT using a combination of BL and RB shows promise as a new technical modality for bacterial elimination in periodontal therapy.

Effect of Er,Cr:YSGG laser on human dentin fluid flow

The aim of the current investigation was to assess the rate and magnitude of dentin fluid flow of dentinal surfaces irradiated with Er,Cr:YSGG laser. Twenty extracted third molars were sectioned, mounted, and irradiated with Er,Cr:YSGG laser at 3.5 and 4.5 W power settings. Specimens were connected to an automated fluid flow measurement apparatus (Flodec). The rate, magnitude, and direction of dentin fluid flow were recorded at baseline and after irradiation. Nonparametric Wilcoxon signed ranks repeated measure t test revealed a statistically significant reduction in fluid flow for all the power settings. The 4.5-W power output reduced the flow significantly more than the 3.5 W. The samples showed a baseline outward flow followed by inward flow due to irradiation then followed by decreased outward flow. It was concluded that Er,Cr:YSGG laser irradiation at 3.5 and 4.5 W significantly reduced dentinal fluid flow rate. The reduction was directly proportional to power output.

Influence of sodium hypochlorite on Er:YAG laser-irradiated dentin and its effect on the quality of adaptation of the composite restoration margins

OBJECTIVE

The aims of this in vitro study were to evaluate: (1) the influence of 5% NaOCl application on Er:YAG-irradiated dentin; and (2) its effect on the quality of adaptation of the composite restoration margins.

BACKGROUND DATA

Previous research has shown that Er:YAG dentin irradiation produces a thermally affected tissue layer that results in lower bond strength than that of nonirradiated dentin. The removal of this thermally-affected layer may enhance the quality of dentin bonding.

MATERIALS AND METHODS

Forty-nine caries-free extracted human molars were transversely sectioned in order to totally expose the dentin. Four standardized cavities were created on the dentinal surface of each molar. First, two cavities were irradiated with Er:YAG laser (2.94 nm): 150 mJ, 10 Hz, variable square pulse (VSP) mode (100 μsec), beam diameter=0.9 mm, speed of irradiation=1 mm/sec, 20% air and 20% water. Then, one of irradiated cavities and one of nonirradiated cavities were treated for 30 sec with 5% NaOCl solution. Finally, they went through a standard bonding treatment for composite restoration, etching, bonding, and composite filling. We obtained four groups of cavities: (1) one control group of nonirradiated cavities not pretreated with NaOCl; (2) one group of nonirradiated cavities, pretreated with NaOCl; (3) one group of irradiated cavities, not pretreated with NaOCl; and (4) one group of irradiated cavities, pretreated with NaOCl. All samples were subjected to thermocycling. Every cavity was immersed into a 0.5% solution of methylene blue. The percentage of dye penetration (microleakage) in the composite-dentin interface was evaluated. Six molars were analyzed by scanning electron microscope.

RESULTS

Dye infiltration depth was significantly reduced in irradiated cavities treated with 5% NaOCl solution.

CONCLUSIONS

The application of a 5% NaOCl solution on Er:YAG irradiated cavities can significantly improve the marginal quality of composite bonding.

Shear strength of composite bonded to Er:YAG laser-prepared enamel: an in vitro comparative study

The primary objective of this study is to investigate the adhesion properties between four current generations of bonding systems and enamel surface conditioned by Er:YAG laser, using an energy density comparable to the ablation threshold of enamel. By including an energy density comparable to published adhesion studies, the secondary objective is to compare the adhesion effects of these selected laser conditioning parameters on enamel with other similar published studies.

MATERIAL AND METHODS

Buccal sides of randomly selected human molars (N=117) were prepared and divided into nine experimental groups depending on the generations of bonding system represented by the corresponding number (G4, G5, G6, G7) and the additional laser conditioning on the enamel surface represented by laser etch (LE) and laser etch with a higher pulse energy, followed by acid etch (AE), if required. The bonding resin systems and their specific requirements were applied after the enamel surfaces were laser conditioned following a specific set of laser parameters. Composite posts of 1.6 mm in diameter and approximately 6 mm in length were then restored on each of the sample surfaces. After 48 h, the composite assemblies were tested to failure under compression using a knife edge loading head at a cross head speed of 1 mm/min until the composite cylinders were separated from the surface. The data collected were then analyzed using one-way analysis of variance and SAS software program (9.1, TS1M3).

RESULTS

No significant difference was found among these groups: AE+G4/LEAE+G4, G6/LE+G6, and G7/LE+G7. Significant differences were found in the remaining groups: AE+G5/LEAE+G5, AE+G5/LEAE-H+G5, and LEAE+G5/LEAE-H+G5. The bond strength results were compared among similar published data and possible influences from different laser parameters, bonding systems, and their combined impact on the enamel surface and its adhesion properties were analyzed.

CONCLUSION

Under our specific settings, additional laser conditioning after phosphoric acid etch is beneficial to one generation of bonding resin (G5). There is no significant change or detrimental effect to the other three groups (G4, G6, and G7) of bonding resins with respect to their final bond strength. The published reports of lower bond strength after additional laser conditioning may be related to thermal damage or unfavorable alteration to the enamel surface by excessive laser energy and the chemistry of bonding systems studied. These factors will affect the overall wettability and the subsequent adhesion properties of the enamel surface.

The effect of Nd:YAG and Er,Cr:YSGG lasers on the microhardness of human dentin

The current investigation determined the microhardness of dentin tissue irradiated with erbium, chromium-doped yttrium scandium gallium garnet (Er,Cr:YSGG) and neodymium-doped yttrium-aluminum garnet (Nd:YAG) lasers. Thirty non-carious human molars were used in this study. Dentin disks were prepared by horizontal sectioning of one third of the occlusal surface. Halves of dentin specimens were irradiated with 3.5- and 4.5-W Er,Cr:YSGG lasers and with a 2-W Nd:YAG laser. The remaining halves served as controls. The microhardness measurements were recorded with a Vickers surface microhardness tester. The results were statistically evaluated by paired t test and one-way ANOVA (p = 0.05). Laser irradiation has significantly reduced the microhardness of dentin within each group compared to its control. Moreover, statistically significant differences were observed among the different groups (p < 0.05). The 3.5-W Er,Cr:YSGG laser produced the greatest reduction in microhardness of dentin followed by 4.5 W and Nd:YAG laser. The differences between all the groups were statistically significant. It was concluded that both laser devices used in this study have resulted in significant thermal damage and subsequent reduction in dentin microhardness values.

Comparison of shear bond strengths of ceramic brackets after different time lags between lasing and debonding

Laser use is effective in the debonding of ceramic brackets. However, a standardization of the laser debonding techniques used has not yet been implemented. The purpose of this study was to evaluate the effect of the time lag elapsed between lasing and shearing on debonding of ceramic brackets. One hundred polycrystalline ceramic brackets were placed on human premolar teeth, which were randomly divided into five groups of 20. One group was assigned as the control. The Er-YAG laser was applied on each bracket in four experimental groups at 5 W for 6 s with the scanning method. Debonding was performed 1 s, 18 s, 30 s, or 60 s after laser exposure. Shear bond strengths and adhesive remnant index scores were measured. Statistically significant difference was observed between the control and experimental groups when the data for the shear bond strengths was considered (p < 0.05). Adhesive remnant index scores of the groups were not statistically different (p > 0.05). Debonding ceramic brackets after 18 s when lased 6 s using an Er-YAG laser with the scanning method is safe and also suitable for clinical use since three brackets can be debonded at a time in succession.

Platelet Derived Growth Factor Secretion and Bone Healing After Er:YAG Laser Bone Irradiation

Er:YAG laser irradiation has been reported to enhance wound healing. However, no studies have evaluated the synthesis of growth factors after laser irradiation. The present study investigated the effects of laser irradiation on the amount of secretion of platelet derived growth factor (PDGF) in the wound, clarifying the effects of the Er:YAG laser on the bone healing. Osteotomies were prepared in the tibiae of 28 rats using an Er:YAG laser (test group). Maximum power of 8 watts, energy per pulse of 700 mJ, and frequency up to 50 Hz were used. The laser was used with external water irrigation, a spot size of 2 mm, energy per pulse of 500 to 1000 mJ/pulse, and energy density of 32 J/cm2. Twenty eight additional rats served as a control group and their osteotomies were prepared with a drill 1.3 mm in diameter at 1000 rpm, with simultaneous saline irrigation. Two rats from the tested group and 2 from the control group were sacrificed on each day following surgery (1–14 days), and the tissue specimens were prepared for histologic evaluation. Immunohistochemical staining with anti-PDGF was performed after histologic examination. The difference between the PDGF staining intensities of the 2 treatment groups was analyzed using a multivariate logistic regression test. A significant rise in PDGF staining occurred in both groups 2–3 days following surgery. However, while high PDGF counts remained for the 2-week experimental period in the laser group, PDGF levels in the control group returned to baseline levels 8 days post surgery. The 2 groups (laser and control) were found to be different throughout the experiment, and the rat type was found to be a significant predictor (P  =  .000011). The present study demonstrated that Er:YAG laser irradiation seems to stimulate the secretion of PDGF in osteotomy sites in a rat model. It is possible that the high levels of PDGF are part of the mechanism that Er:YAG irradiation enhances and improves the healing of osteotomy sites.

Tensile bond strength of sealants following Er:YAG laser etching compared to acid etching in permanent teeth

The aim of this in vitro study was to assess the effect of Er:YAG laser surface treatment on the tensile bond strength of a sealant in permanent teeth. A total of 30 sound third molars were selected and embedded in cold-cure acrylic resin. The enamel surfaces were flattened by a grinding. The teeth were randomly divided into three groups and pretreated as follows: (1) 37% phosphoric acid; (2) Er:YAG laser (1.5 ml/min water spray, 100 mJ energy output, 10 Hz frequency, focal distance 17 mm); (3) Er:YAG laser + 37% phosphoric acid. The treated surfaces were isolated by double adhesive Sellotape and after insertion of a split Teflon matrix at an isolated site, sealant was applied. The specimens were thermocycled and stored at 37°C in distilled water for 72 h, then subjected to a tensile bond strength test (50 kgf at 0.5 mm/min). The mean tensile bond strengths (± SD, in megapascals) were: 18.51 ± 5.68 in group 1, 8.06 ± 2.69 in group 2, and 17.33 ± 5.04 in group 3. Data were submitted to analysis of variance and the Tukey test. No significant difference were found between groups 1 (37% phosphoric acid) and group 3 (Er:YAG laser + 37% phosphoric acid) but treatment with the Er:YAG laser alone (group 2) resulted in significantly lower tensile bond strength than seen in the other groups. In this setting, the Er:YAG laser prepared the enamel surface for sealing but did not eliminate the need for acid etching before sealant application.

Micromorphology of resin-dentin interfaces using one-bottle etch&rinse and self-etching adhesive systems on laser-treated dentin surfaces: a confocal laser scanning microscope analysis

BACKGROUND AND OBJECTIVES

This study evaluated the hybrid layer (HL) morphology created by three adhesive systems (AS) on dentin surfaces treated with Er:YAG laser using two irradiation parameters.

STUDY DESIGN

Occlusal flat dentin surfaces of 36 human third molars were assigned into nine groups (n = 4) according to the following ASs: one bottle etch&rinse Single Bond Plus (3M ESPE), two-step Clearfil Protect Bond (Kuraray), and all-in-one S(3) Bond (Kuraray) self-etching, which were labeled with rhodamine B or fluorescein isothiocyanate-dextran and were applied to dentin surfaces that were irradiated with Er:YAG laser at either 120 (38.7 J/cm(2)) or 200 mJ/pulse (64.5 J/cm(2)), or were applied to untreated dentin surfaces (control group). The ASs were light-activated following MI and the bonded surfaces were restored with resin composite Z250 (3M ESPE). After 24 hours of storage in vegetable oil, the restored teeth were vertically, serially sectioned into 1-mm thick slabs, which had the adhesive interfaces analyzed with confocal laser microscope (CLSM-LSM 510 Meta). CLSM images were recorded in the fluorescent mode from three different regions along each bonded interface.

RESULTS

Non-uniform HL was created on laser-irradiated dentin surfaces regardless of laser irradiation protocol for all AS, while regular and uniform HL was observed in the control groups. "Stretch mark"-like red lines were found within the HL as a result of resin infiltration into dentin microfissures, which were predominantly observed in 200 mJ/pulse groups regardless of AS. Poor resin infiltration into peritubular dentin was observed in most regions of adhesive interfaces created by all ASs on laser-irradiated dentin, resulting in thin resin tags with neither funnel-shaped morphology nor lateral resin projections.

CONCLUSION

Laser irradiation of dentin surfaces at 120 or 200 mJ/pulse resulted in morphological changes in HL and resin tags for all ASs evaluated in the study.

Atomic analysis and hardness measurement of the cavity prepared by laser

The purpose of this study was to compare the compositional changes and microhardness of the cavity floor prepared by erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation with those of the conventional bur-prepared cavity. A total of 16 extracted human molar teeth (with no carious lesions or repairs) were selected for this study. On the buccal and lingual (palatal) surfaces of each tooth, cavities (diameter 3 mm, depth 2 mm) were prepared with an Er,Cr:YSGG laser system (Waterlase MD(TM), USA) and high-speed turbine. The cavities were cross-sectioned and subjected to atomic analysis by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX) and Vickers hardness test. Statistical analyses were performed with t-tests. Surface characteristics of the prepared cavities were also investigated by SEM. No significant differences were found between the calcium/phosphorus (Ca/P) ratio and Vickers hardness of laser- and bur-prepared cavities. The SEM observation revealed that the lased cavity surface was irregular, and there was also an absence of smear layer; the orifices of dentinal tubules were exposed. Microhardness measurement of the cavity floor confirmed that the Er,Cr:YSGG laser produced a clean-cut surface of the cavity.

Effect of Er,Cr: YSGG Laser on the Microtensile Bond Strength of Two Different Adhesives to the Sound and Caries-affected Dentin

The microtensile bond strength of a three-step etch-and-rinse and a two-step self-etch adhesive is not negatively affected by Er,Cr:YSGG laser irradiation in sound and caries-affected dentin.

Effect of different laser devices on the composition and microhardness of dentin

This study determined the compositional changes and microhardness of the cavity floor prepared by Er,Cr:YSGG and Er:YAG lasers and compared the results with the conventional method of bur preparation. Fifteen non-carious human molars were used in this study. On the buccal and lingual surfaces of each tooth, two cavities (mesio-distal 3 mm, inciso-gingival 3 mm, depth 2 mm) were prepared with two different laser devices (Er,Cr:YSGG laser; Waterlase MD and Er:YAG laser; KaVo Key Laser 3) and a high-speed turbine. The teeth were embedded into polyester resin and cross-sectioned. The microhardness measurements from the floor of each half cavity were recorded with the Vickers surface hardness tester. The remaining halves of the cavities were subjected to SEM-EDS atomic analysis. The results were statistically evaluated by one-way ANOVA and Kruskal Wallis tests (p = 0.05). No significant differences were observed among the microhardness values, quantities of Ca (Ca weight %), P (P weight %) and Ca/P ratio of the lased and conventionally prepared cavities (p > 0.05). The cavity preparation techniques and differences in laser devices did not significantly alter the composition and microhardness of dentin tissue. Both laser devices used in this study were observed to lead to minimal thermal damage in the dentin tissue and minimal thermally-induced changes in dentinal compositions.

SEM evaluation of the hybrid layer after cavity preparation with Er:YAG laser

This study compared the thickness of the hybrid layer formed using Scotchbond Multi-Purpose Plus, Single Bond 2, Prime & Bond 2.1 and Xeno III on a dentin surface prepared with a diamond bur in a high speed handpiece or prepared with an Er:YAG laser used with two parameters of pulse energy (200 and 400 mJ) and two parameters of frequency (4 and 6 Hz). Flat dentin surfaces obtained from 20 human third molars were treated with the two methods and were then prepared with the dentin adhesive systems according to the manufacturers' instructions. After a layer of composite was applied, the specimens were sectioned, flattened, polished and prepared for Scanning Electronic Microscopy observation. Five different measurements of the hybrid layer thickness were obtained along the bonded surface in each specimen. The results were statistically analyzed using Analysis of Variance and Student-Newman-Keuls tests (p < or = 0.05). When analyzing the hybrid layer thickness and comparing the cavity preparation method, four groups were formed: Group I (diamond bur) > Group II (Laser 200 mJ/4 Hz) = Group III (Laser 200 mJ/6 Hz) > Group IV (Laser 400 mJ/4 Hz) > Group V (Laser 400 mJ/6 Hz). When comparing the dentin adhesive systems, there were no statistically significant differences. These results showed that the four tested dentin adhesive systems produced a 2.90 +/- 1.71 microm hybrid layer in dentin prepared with a diamond bur. This hybrid layer was regular and routinely found. In the laser groups, the dentin adhesive systems produced hybrid layers ranging from 0.41 +/- 1.00 microm to 2.06 +/- 2.49 microm, which were very irregular and not routinely found. It was also concluded that the Er:YAG laser, with the parameters used in this experiment, has a negative influence on the formation of a hybrid layer and cavity preparation methods influence formation of the hybrid layer.