Changes in heated and in laser-irradiated human tooth enamel and their probable effects on solubility

EFFECT OF LASER IRRADIATION ASSOCIATED WITH FLUORIDE IN DECREASING EROSIVE TOOTH WEAR: A SYSTEMATIC REVIEW WITH A NETWORK META-ANALYSIS

OBJECTIVE

The present systematic review with a network meta-analysis (NMA) aimed to evaluate the effect of high-power lasers, associated or not with fluoride compounds, to control and prevent Erosive Tooth Wear (ETW).

METHODS

The review was registered in the PROSPERO (CRD42021242547) and followed the PICO question: P (population): enamel and dentin substrate; I (Intervention): high-power laser irradiation, associated or not with fluoride compounds; C (Control): no-treatment; and O (Outcomes): prevention/control of ETW. The electronic databases PubMed, Scopus, and EMBASE were searched. Two independent reviewers evaluated in vitro and in situ studies. The risk of bias was assessed using the RoBDEMAT tool. The estimated treatment effect derived from direct and indirect comparisons were analyzed and the difference between these effects was calculated based on the data of enamel and dentin surface loss (in μm).

RESULTS

A total of 179 studies were retrieved and after the exclusion of duplicates, 103 studies had their titles and abstracts evaluated. Thirty-nine studies had their full text analyzed for data extraction (Cohen Kappa = 0.88). For sound enamel, the laser irradiation (L), fluoride application (F) and, the association of treatments (L + F) promoted higher protection than No-Treatment (NT). For eroded enamel, L + F and F did not differ, but both treatments reduced surface loss compared to NT and L. For sound and eroded dentin, treatments with laser increased surface loss.

CONCLUSIONS

Although a high-power laser has some potential to prevent erosive tooth wear, this effect is not better than that of standard fluoride. The use of laser in the management of dentin erosive wear can be harmful.

Effect of Er:YAG Laser Irradiation on Preventing Enamel Caries: A Systematic Review and Meta-Analysis

Caries is a global health problem, and its prevention has become a main goal of modern dentistry. Laser irradiation is believed to have potential in preventing dental caries. The purpose of this systematic review and meta-analysis was to evaluate whether Er:YAG laser irradiation has the potential to prevent enamel caries. Based on inclusion and exclusion criteria, PubMed, Web of Science, and EMBASE databases were searched; 2 reviewers independently used these search strategies to review titles and abstracts, with no language or date restrictions, up to June 2023. For the quantitative analysis, continuous variables were analysed by standard mean difference (SMD) with a 95% confidence interval (CI). The statistical analyses were conducted using Review Manager and Cochrane Collaboration (2020). A total of 51 potentially eligible studies were identified, of which 16 in vitro studies were eventually included in the quantitative meta-analysis. Three studies showed a low risk of bias, and 13 studies a medium risk of bias. In general, there was no significant difference between the calcium ions released under acidic conditions after laser irradiation. The final results indicated that after Er:YAG laser irradiation, enamel could maintain higher surface microhardness in acidic environments, as well as smaller lesion depth and less mineral loss, revealing its potential in preventing enamel caries. However, the effect of laser irradiation on the release of calcium ions in acidic solutions and the surface microhardness of demineralised enamel was not significant. Therefore, more in vitro and clinical trials are needed in to evaluate whether Er:YAG laser irradiation can effectively prevent enamel caries in clinical settings.

CO2 laser irradiation combined with fluoridated dentifrice improved its protective effect on caries lesion progression regardless of the acidulated phosphate fluoride gel application: An in situ study

OBJECTIVE

This in situ study aimed to investigate the efficacy of CO2 laser at a 10.6-µm wavelength combined with 1.23% acidulated phosphate fluoride (APF) and fluoridated dentifrice with 1100 µg F/g (FD) to control enamel caries progression.

MATERIALS AND METHODS

Sixteen volunteers wore palatal appliances containing eight demineralized enamel specimens for four 14-day phases under sucrose exposure. These specimens were submitted to CO2 laser irradiation and APF alone or combined with FD. Treatment groups were non-fluoridated dentifrice-NFD, NFD + CO2 laser, NFD + APF, NFD + CO2 laser + APF, FD, FD + CO2 laser, FD + APF, and FD + CO2 laser + APF. Mineral loss, calcium fluoride (CaF2), fluorapatite (FAp), and fluoride in the biofilm were analyzed by analysis of variance followed by the Student-Newman-Keuls test, p < 0.05.

RESULTS

The highest mineral loss inhibition was noted when FD and CO2 laser irradiation were combined, which did not significantly differ from the FD + CO2 laser + APF group. The CaF2, FAp, and F in the biofilm were more pronounced when the FD and APF were combined. The CO2 laser irradiation promoted a slightly higher concentration of CaF2 in the enamel and F in the biofilm.

CONCLUSION

Although APF promotes the high formation of CaF2 and FAp, the combined use of FD with CO2 laser overcomes the APF effect in inhibiting the progression of artificial caries-like lesions in situ.

CLINICAL SIGNIFICANCE

Under the in situ design of this study, remineralization of white spot lesions was achieved through CO2 laser irradiation and daily use of fluoridated dentifrice. Future clinical trials are encouraged to substantiate this finding.

Do erbium lasers promote changes in the tooth enamel during debonding of ceramic laminate veneers? A systematic review

The longevity of ceramic laminate veneers can be influenced by several factors, which can result in the need for a removal process. Laser removal has emerged as a good alternative to facilitate the procedure, and its repercussions on tooth enamel have been investigated. We aimed to evaluate the efficacy of erbium lasers for debonding ceramic laminate veneers without damaging the tooth enamel. This systematic review based on the PICOS model adhered to the PRISMA statement. The PubMed/MEDLINE, Web of Science, Embase, and Scopus databases were systematically searched until December 1, 2022, and 2902 studies were retrieved. After screening, four in vitro studies that analyzed the dental morphology using scanning electron microscopy, optical analysis, stereomicroscopy, or x-ray dispersion spectroscopy were included. The risk of bias was assessed using the Cochrane Collaboration tool. Our findings suggest that erbium lasers are useful for ceramic laminate veneer removal without damaging the tooth enamel. However, the removal is influenced by the type and thickness of ceramic and type of cement used. It could be concluded that the application of Erbium laser did not promote superficial changes in the dental enamel. This effect was observed in all analysis performed.

Comparison of micromorphological changes in enamel using SEM analysis after conventional and erbium, chromium:yttrium, scandium, gallium, and garnet hard-tissue laser fissurotomy: An in vitro study

Background

Well articulated by John Knowles - "Everything has to evolve or else it perishes." With the paradigm shift of emphasis toward the prevention of dental caries, it has been proven that laser irradiation protects against both caries initiation and caries progression.

Aim

The aim of the study was to evaluate and compare the micromorphology of caries-free extracted premolars using a Scanning electron microscope (SEM) after fissurotomy by conventional fissurotomy bur and erbium, chromium: yttrium, scandium, gallium, and garnet (ER, CR: YSGG) hard-tissue laser.

Methodology

Sixty caries-free premolars extracted atraumatically for orthodontic treatment were included in the study. The samples were divided into two groups randomly (Group 1: fissurotomy by bur, n = 30, and Group 2: fissurotomy by hard-tissue laser, n = 30). Each sample was further divided into halves from the occlusal surface wherein one-half of the occlusal surface received fissurotomy procedure and the other half was control. Samples were analyzed by scanning electron microscopy (SEM) for micromorphological changes.

Results

Profile image of control samples revealed the disorganization of enamel surface at the junction of fissures forming a heterogeneous tissue and agglomeration of enamel with deep pit and fissure. On the contrary, the image of experimented samples (with laser fissurotomy) showed smooth enamel surface and homogeneous enamel subsurface with wider pit and fissure owing to self-cleansing ability.

Conclusion

On the grounds of the present study results, it could be concluded that the intervention of ER, CR: YSGG hard-tissue laser possesses self-cleansable pit and fissures for caries prevention and has the potential to irradicate the smear layer entirely for superior attachment of remineralizing agents.

Raman Analyses of Laser Irradiation-Induced Microstructural Variations in Synthetic Hydroxyapatite and Human Teeth

The microstructural and molecular-scale variations induced by laser irradiation treatment on human teeth enamel in comparison with synthetic hydroxyapatite (HAp) were examined through Raman microprobe spectroscopy as a function of irradiation power. The results demonstrated that laser irradiation could modify stoichiometry, microstructure, and the population of crystallographic defects, as well as the hardness of the materials. These modifications showed strong dependences on both laser power and initial nonstoichiometric structure (defective content of HPO₄), because of the occurrence of distinct reactions and structural reconstruction. The reported observations can redirect future trends in tooth whitening by laser treatment and the production of HAp coatings because of the important role of stoichiometric defects.

Effect of sodium fluoride plus tricalcium phosphate with and without CO2 laser on remineralization of white spot lesions

Objectives

The aim of this in vitro study was to evaluate the effect of NaF plus TCP with and without CO₂ laser irradiation on management of demineralized enamel using microhardness test and digital microscopy.

Methods

Eighty intact extracted human premolar teeth were randomly divided into 4 groups (20/each). Each group was subjected to a demineralizing solution to create white spot lesion. Group 1 was treated with 3M Vanish™. Group 2 was irradiated with CO₂ laser. Group 3 was subjected to CO₂ laser followed by 3M Vanish™. Group 4 was treated by 3M Vanish™ then CO₂ laser. The teeth were immersed in artificial saliva. Surface microhardness was measured for each tooth before demineralization at base line (M1 as a control), after demineralization (M2) and after management (M3). Comparison of microhardness values between groups was performed using one way ANOVA test with significant level (0.05) followed by multiple comparisons post-hoc Tukey test between groups. Enamel surface was photographed by digital microscope.

Results

All intervention methods used in the current study significantly increased microhardness values of demineralized enamel (P < 0.001). Little improvement of enamel appearance was observed in all groups meanwhile using CO₂ laser on demineralized enamel directly led to signs of white and black dots affecting the appearance of enamel surface.

Significance

The most effective intervention regarding microhardness was group 2 followed by group 3, group 4 and group 1. Coating the enamel surface with 3M Vanish™ before CO₂ laser irradiation acted as a protective layer from the undesirable effects of laser on the teeth with increasing enamel microhardness values more than using Vanish alone. So the promising intervention method regarding both microhardness and appearance was group 4.

Electron Paramagnetic Resonance Characterization of Sodium- and Carbonate-Containing Hydroxyapatite Cement

Ionizing radiation-induced paramagnetic defects in calcified tissues like tooth enamel are indicators of irradiation dose. Hydroxyapatite (HA), the principal constituent in these materials, incorporates a variety of anions (CO₃^2-, F^-, Cl^-, and SiO₄^4-) and cations (Mn²⁺, Li⁺, Cu²⁺, Fe³⁺, Mg²⁺, and Na⁺) that directly or indirectly contribute to the formation of stable paramagnetic centers upon irradiation. Here, we used an underexploited synthesis method based on the ambient temperature setting reaction of a self-hardening calcium phosphate cement (CPC) to create carbonate-containing hydroxyapatite (CHA) and investigate its paramagnetic properties following γ-irradiation. Powder X-ray diffraction and IR spectroscopic characterization of the hardened CHA samples indicate the formation of pure B-type CHA cement. CHA samples exposed to γ-radiation doses ranging from 1 Gy to 150 kGy exhibited an electron paramagnetic resonance (EPR) signal from an orthorhombic CO₂^•- free radical. At γ-radiation doses from 30 to 150 kGy, a second signal emerged that is assigned to the CO₃^•- free radical. We observed that the formation of this second species is dose-dependent, which provided a means to extend the useful dynamic range of irradiated CHA to doses >30 kGy. These results indicate that CHA synthesized via a CPC cement is a promising substrate for EPR-based dosimetry. Further studies on the CHA cement are underway to determine the suitability of these materials for a range of biological and industrial dosimetry applications.

Caries inhibition of simulated active caries lesions with CO2 laser irradiation and fluoride

It has been well established that CO₂ laser irradiation can be used to transform the mineral phase of dental enamel to make it more resistant to acid dissolution. The purpose of this study was to investigate if carbon dioxide laser irradiation and topical fluoride can be used to treat incipient caries lesions to inhibit further progression, i.e. treat active lesion surfaces as opposed to sound surfaces prior to subjecting them to an acid challenge. Simulated active caries lesions were produced on twenty eight bovine enamel samples using a pH cycling model and those surfaces were irradiated by a 9.4 μm CO₂ laser and treated with topical fluoride. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, optical coherence tomography (OCT), and SWIR reflectance surface dehydration rate measurements at 1950 nm after exposure to a further acid challenge. There was a significant reduction (P < 0.05) of further lesion progression for lesion windows treated with CO₂ laser irradiation followed by the application of an acidulated phosphate fluoride gel compared to the untreated lesion windows on each sample. Treatment by laser irradiation alone was not effective. The degree of lesion inhibition was not as high as has been previously observed for laser irradiated sound enamel surfaces exposed to an acid challenge.

Effect of Er:YAG Laser Irradiation and Acidulated Phosphate Fluoride Therapy on Re-Mineralization of White Spot Lesions

Statement of the Problem:

Studies on the efficacy of erbium laser for enhancement of enamel resistance to acid attacks and its effects on fluoride uptake by the enamel are limited.

Purpose:

This study sought to assess and compare the effects of erbium-doped yttrium aluminum garnet (Er:YAG) laser irradiation and application of acidulated phosphate fluoride (APF) gel (alone and in combination) on remineralization of artificial white spot lesions (WSLs).

Materials and Method:

This in vitro, experimental study evaluated 90 buccal and lingual slabs of extracted human premolars. The specimens underwent pH cycling to induce WSLs. They were then randomly divided into 6 groups of caries-free positive control (c+), negative control with WSLs (ws), 1.23% APF gel applied on the enamel (F), Er:YAG laser irradiation (80 mJ, 10 Hz, and 8 J/cm²) of enamel (L), APF gel application followed by laser irradiation (FL), and laser irradiation followed by fluoride gel application (LF). The fluoride ion content of specimens was measured before and after the intervention using a potentiometer. Data were analyzed by ANOVA (p< 0.05).

Results:

APF gel application before/after laser irradiation maximally increased the fluoride uptake by the enamel (p= 0.000). Application of APF gel in group F and laser irradiation in group L increased fluoride uptake by the enamel, compared with groups 1 and 2 (p= 0.000). Laser- treated (L) and APF-treated (F) groups had no significant difference in this respect (p= 0.945). Maximum fluoride concentration was noted in combined laser and fluoride groups (FL=332.07ppm and LF=341.27ppm) with no significant difference between the two (p= 1.000).

Conclusion:

Er:YAG laser irradiation changes the chemical composition of enamel and probably promote its remineralization, especially when combined with APF gel application, which highlights its cariostatic potential.

Assessment of the preventive effects of Nd:YAG laser associated with fluoride on enamel caries using optical coherence tomography and FTIR spectroscopy

Objective

This in vitro study characterized and monitored, by Optical Coherence Tomography (OCT) and Fourier Transformed Infrared Spectroscopy (FTIR), the effects of the association of acidulated phosphate fluoride gel (APF-gel) and Nd:YAG (neodymiun:yttrium-aluminum-garnet) laser, as sequencial treatments, in the prevention of incipient enamel caries lesions.

Methods

120 human enamel samples were randomized into 3 groups (n = 40): APF-gel (1.23% F^-, 4 min.); Laser+APF (Nd:YAG laser irradiation—0.6W, 84.9J/cm², 10Hz, followed by APF-gel); and APF+Laser (APF-gel followed by laser irradiation). The samples were subjected to a 15-day pH-cycling, evaluated by OCT (quantification of optical attenuation coefficient–OAC) and FTIR (analysis of carbonate and phosphate content) before treatments, after treatments, and on the 5^th, 10^th and 15^th days of pH-cycling. The statistical analysis was performed (α = 5%).

Results

The Optical Attenuation Coefficient (OAC) assessed by OCT increases with the progression of demineralization, and the Laser+APF presented the highest values of OAC in 10^th and 15^th days of pH-cycling. Nd:YAG decreased the carbonate content after treatment regardless of the application order of the APF-gel, while APF-gel did not interfere in the composition of enamel. The carbonate content was also changed in the first 5 days of the pH-cycling in all groups.

Conclusion

Nd:YAG laser irradiation before or after the application of APF-gel did not influence the appearance of incipient caries lesions, showing no synergistic effect. Regardless of the application order of the APF-gel, laser irradiation reduces the carbonate content of the enamel, which also changes during the demineralization process. However, irradiation before the application of APF-gel increased the speed of progression of the lesions, which positively impacts public health as it can prevent caries disease, even in high risk individuals. OCT and FTIR are suitable for assessing this effect.

Effect of Er,Cr:YSGG Laser on the Prevention of Primary and Permanent Teeth Enamel Demineralization: SEM and EDS Evaluation

Objective: To evaluate in vitro the effect of the erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser on resistance of primary and permanent human enamel to demineralization using water cooling and fluoride coapplication as variable parameters. Methods: Enamel specimens were prepared from extracted primary and permanent teeth (n = 225 each). The specimens were separated into 15 subgroups (n = 15/group) based on laser application at three different power settings (0.25, 0.50, and 0.75 W), laser application with and without water cooling, and application of acidulated phosphate fluoride (APF) gel before laser treatment. Morphological changes were assessed with scanning electron microscopy (SEM), and the specimens' chemical contents were determined with energy-dispersive X-ray spectroscopy. Results: In both the primary and permanent teeth, the highest Ca and P content was observed in the noncooled 0.75 W laser group (p < 0.05), irrespective of APF pretreatment (p > 0.05). The Ca and P content for the noncooled APF +0.75 W laser group was lower than that for the APF group and the noncooled 0.75 W laser group. For both dentitions, the F mass content for the APF+laser groups was significantly higher than laser-only groups (p < 0.05). Under SEM, both the primary and permanent enamel exhibited cracks, craters, and surface roughness without water cooling, consistent with increased power output. Conclusions: Er,Cr:YSGG laser application at 0.75 W without water cooling increased enamel resistance to demineralization. Compared with topical APF application, Er,Cr:YSGG laser application barely improved enamel resistance against demineralization, and coapplication did not result in a synergistic effect.

Shear bond strength of acid and laser conditioned enamel and dentine to composite resin restorations: An in vitro study

Objective

To compare the shear bond strength of enamel or dentin conditioned with either Er,Cr:YSGG (erbium, chromium: yttrium–scandium–gallium–garnet) laser or phosphoric acid to composite resin restoration.

Material and methods

Forty posterior human extracted teeth were used. After mesiodistal sectioning of the teeth crowns, the samples were randomly divided into two groups—in the first group (E), bonding was performed on the enamel after roughening and in the second group (D), the enamel was removed and bonding was performed on the dentin. These groups were further randomly divided into two subgroups according to the type of etching (n = 20 each). In the acid‐etched groups (EA and DA), the surfaces were etched with 37% phosphoric acid. In the laser‐conditioned groups (EL and DL), the surfaces were conditioned with Er,Cr:YSGG laser. Total‐etch adhesive system was used to bond all the 80 specimens resin composite. The composite was vertically light‐cured, and the specimens were subjected to a shear bond strength test. Modes of bond failure were determined with a stereomicroscope.

Results

The highest shear bond strength was observed for the DA group (16.25 ± 1.10 MPa, p < 0.0001), whereas the lowest was observed for the DL group (8.56 ± 0.67 MPa). The adhesive failure mode was the most frequently observed in all groups.

Conclusions

The shear bond strength of composite resin bonded to enamel and dentin etched with phosphoric acid was higher than when conditioned with Er,Cr:YSGG laser. Thus, laser conditioning is not recommended.

Thermal, morphological, and spectral changes after Er, Cr:YSGG laser irradiation at low fluences on primary teeth for caries prevention

The aim of this study was to determine the temperature increase in the pulp chamber and possible thermal effects on molecular structure of primary teeth during the irradiation with Er,Cr:YSGG laser. Primary central incisors were divided into three groups (n = 20). Labial surfaces in each group were irradiated by Er,Cr:YSGG laser within different power and frequencies as following groups: I: 0.25 W, 20 Hz, II: 0.50 W, 20 Hz, III: 0.75 W, 20 Hz. A thermocouple was placed inside the pulp chamber so that the temperature increments were recorded during the enamel irradiation. Morphological changes of enamel surfaces were experimentally evaluated by SEM. Fourier-transform infrared spectroscopy and RAMAN analyses were carried out to determine the differentiations in the molecular structure. The experimental results obtained were analyzed statistically by means of one-way analysis of variance. Statistically significant differences were detected between groups (p < .05). Group III exhibited the highest values for the temperature parameters. Besides, the conical craters, cracks, and formation of ablation areas were observed for all the groups. Also, it was obtained that the hydroxyapatite lost the hydroxyl ions due to the thermal effect of the laser. Temperature rise throughout the Er,Cr:YSGG laser irradiation for prevention of primary enamel demineralization presented a positive correlation with the laser output power level. The formations of adverse morphological and spectral changes were detected on the surface of teeth after the laser application. On this basis, the Er,Cr:YSGG laser applications should be treated with much more caution considering enamel surface and pulpal tissues in primary teeth.

Lasers to prevent dental caries: a systematic review

OBJECTIVE

To assess the effectiveness of lasers (at sub-ablative parameters) in reducing caries incidence compared with traditional prophylactic interventions (TPIs) when used alone or together with other TPIs such as pits and fissures sealant or fluoride gels or varnishes.

DESIGN

A systematic review. Data sources include Medline (via PubMed), Embase, Web of Science and the Cochrane Library (December 2019).

ELIGIBILITY CRITERIA

Only randomised trials (RCTs) and controlled clinical trials (CCTs) dealing with prophylactic lasers use (vs TPI or untreated teeth) were considered as eligible. We excluded in vitro and ex vivo studies.

DATA EXTRACTION

Eligible studies were selected and data extracted independently by two reviewers. Risk of bias was assessed adopting the Cochrane Risk of Bias tool. Data on caries incidence, sealant retention, fluoride uptake, adverse events, treatment duration, patients' discomfort and cost-effectiveness ratio was extracted.

DATA ANALYSIS

Extracted data were presented narratively due to the heterogeneity of included studies.

RESULTS

Seven RCTs and two CCTs, all with an evident risk of bias, met inclusion criteria, pooling together 269 individuals and 1628 teeth. CO₂, neodymium-doped yttrium aluminium garnet, erbium-doped yttrium aluminum garnet (Er:YAG), erbium, chromium: yttrium scandium gallium garnet (Er,Cr:YSGG) and Argon lasers were used. In the permanent dentition, lasers only when used in combination with TPIs were effective in reducing caries when compared with untreated teeth (risk ratio (RR)=0.44 (0.20-0.97); Er:YAG laser) or with TPIs used alone (RR=0.39 (0.22-0.71); CO₂ laser). Moreover, Argon laser significantly improved the fluoride uptake into the enamel surfaces (ANalysis Of VAriance (ANOVA) tests: 95%, p<0.0001). Likewise, sealant retention improved when acid etching was performed on previously irradiated enamel fissures by CO₂ laser (RR=0.63 (0.38-1.04)) or Er:YAG laser (RR=0.54 (95% CI: 0.34 to 0.87)). In addition, laser resulted safe and well tolerated by patients.

CONCLUSION

Despite some positive indications, an inadequate level of evidence was found in the included studies concerning the lasers' effectiveness in preventing caries. Further studies with a higher methodological quality level are required.

Model-driven spatial evaluation of nutrient recovery from livestock leachate for struvite production

Nutrient pollution is one of the major worldwide water quality problems, resulting in environmental and public health issues. Agricultural activities are the main source of nutrient release emissions, and the livestock industry has been proven to be directly related to the presence of high concentrations of phosphorus in the soil, which potentially can reach waterbodies by runoff. To mitigate the phosphorus pollution of aquatic systems, the implementation of nutrient recovery processes allows the capture of phosphorus, preventing its release into the environment. Particularly, the use of struvite precipitation produces a phosphorus-based mineral that is easy to transport, enabling redistribution of phosphorus to deficient locations. However, livestock leachate presents some characteristics that hinder struvite precipitation, preventing extrapolation of the results obtained from wastewater studies to cattle waste. Consideration of these elements is essential to determine the optimal operating conditions for struvite formation, and for predicting the amount of struvite recovered. In this work, a detailed thermodynamic model for precipitates formation from cattle waste is used to develop surrogate models to predict the formation of struvite and calcium precipitates from cattle waste. The variability in the organic waste composition, and how it affects the production of struvite, is captured through a probability framework based on the Monte Carlo method embedded in the model. Consistent with the developed surrogate models, the potential of struvite production to reduce the phosphorus releases from the cattle industry to watersheds in the United States has been assessed. Also, the more vulnerable locations to nutrient pollution were determined using the techno-ecological synergy sustainability metric (TES) by evaluating the spatial distribution and balance of phosphorus from agricultural activities. Although only struvite formation from cattle operations is considered, reductions between 22% and 36% of the total phosphorus releases from the agricultural sector, including manure releases and fertilizer application, can be achieved.

Morphological, optical, and elemental analysis of dental enamel after debonding laminate veneer with Er,Cr:YSGG laser: A pilot study

Laminate veneer removal is becoming a routine procedure at the dental clinic and the use of laser can facilitate its removal. This work aimed to evaluate the morphological, elemental, and optical changes in the remaining enamel after veneer removal using Er,Cr:YSGG laser. Forty-four enamel slabs were prepared and randomly distributed into nine experimental groups, for bonding using lithium disilicate laminates with three different luting agents (Variolink Veneer, RelyX U200, and RelyX Veneer). Then each agent was debonded using Er,Cr:YSGG laser (2.78 μm) using two different protocols:3.5 W, 48.14 J/cm² , 20 Hz non-contact and 3.0 W, 48.14 J/cm² , 20 Hz non-contact. The morphological, optical, and elemental analysis of enamel was performed before cementation and after laser debonding, using scanning electron microscopy (SEM), optical coherence tomography (OCT), and energy-dispersive X-ray spectroscopy (EDS). The level of statistical significance adopted was 5%. The EDS analysis of enamel after debonding revealed a significant increase in silane and carbon, as well as a decrease in calcium and phosphate contents. Analysis showed the presence of residual cement in most experimental groups but the morphological analysis showed alteration of the enamel's prisms only in the groups that used RelyX Veneer and Variolink Veneer cements. There was no evidence of deleterious morphological changes resulting from irradiation. However, an increase in the optical attenuation coefficient by the OCT was observed due to the presence of the remaining cement. It can be concluded that the Er,Cr:YSGG laser, in the mean powers used, is efficient for veneer removal without causing deleterious effects for the enamel.

Use of mechanistic information to derive chemical-specific adjustment factors - Refinement of risk assessment

When extrapolating data from animal toxicological studies a default factor (dUF) of 100 is applied to derive a heath based guidance value. The UF takes into account the interspecies differences (ID) and the intraspecies variability (IV). When re-evaluating the safety of phosphates used as food additives nephrocalcinosis was identified as the critical endpoint. The underlying mechanism for nephrocalcinosis was attributed to the precipitation of calcium phosphate in the kidney, depending on its solubility, irrespective of the species and the population. Based on the mechanism, the volume of primary urine, for which the glomerular filtration rate (GFR) was used as a proxy, was considered to be the only parameter relevant for ID and IV. Median value of GFR in rats was 4.0 ml/min/kg bw. In humans it was 1.6 ml/min/kg bw in healthy adults and 0.9 in elderly. These values were calculated from the distribution of the GFR data from 8 studies in rats (n = 191), 16 studies in adults (n = 1540) and 5 studies in elderly (n = 2608). Multiplying the distribution of the ratio rat/healthy humans (ID) with the distribution of the ratio healthy humans/elderly human (IV) resulted in a phosphate specific factor of 4.5 (3.3-6.7) (median; 25th - 75th percentile).

The effect of CO2 9.3 μm short-pulsed laser irradiation in enamel erosion reduction with and without fluoride applications-a randomized, controlled in vitro study

The aim of this in vitro study was to evaluate the protective effect of short-pulsed CO₂ 9.3 μm laser irradiation against erosion in human enamel without and combined with TiF₄ and AmF/NaF/SnCl₂ applications, respectively, as well as compared to the protective effect of these fluoride treatments alone. After polishing, ninety enamel samples (3 × 3mm) were used for 9 different treatment groups: 4% TiF₄ gel (pH 1.5, 24,533 ppm F^-); AmF/NaF/SnCl₂ rinse (pH 4.5; 500 ppm F^-, 800 ppm Sn²); CO₂ laser (average power 0.58 W); CO₂ laser (0.58 W) + TiF₄; CO₂ laser (0.58 W) + AmF/NaF/SnCl₂; CO₂ laser (0.69 W); CO₂ laser (0.69 W) + TiF₄; CO₂ laser (0.69 W) + AmF/NaF/SnCl₂; negative control (deionized water). TiF₄ gel was brushed on only once before the first erosive cycling, while samples treated with AmF/NaF/SnCl₂ were daily immersed in 5 ml of the solution before cycling. Laser treatment occurred with a CO₂ laser (wavelength 9.3 μm, pulse repetition rate 100 Hz, pulse duration 14.6 μs/18 μs, average power 0.58 W/0.69 W, fluence 1.9 J/cm²/2.2 J/cm², beam diameter 0.63 mm, irradiation time 10 s, air cooling). TiF₄ was applied only once, while AmF/NaF/SnCl₂ was applied once daily before the erosive challenge. Surface loss (in μm) was measured with optical profilometry immediately after treatment, and after 5 and 10 days of erosive cycling (0.5% citric acid, pH 2.3, 6 × 2 min/day). Additionally, scanning electron microscopy investigations were performed. All application measures resulted in loss of surface height immediately after treatment. After 5 days, significantly reduced surface loss was observed after applying laser irradiation (both power settings) followed by applications of TiF₄ or AmF/NaF/SnCl₂ solution (p < 0.05; 2-way ANOVA and Tukey test) compared to fluoride application alone. After 10 days, compared to after 5 days, a reduced tissue loss was observed in all groups treated with AmF/NaF/SnCl₂ solution. This tissue gain occurred with the AmF/NaF/SnCl₂ application alone and was significantly higher when the application was combined with the laser use (p < 0.05). Short-pulsed CO₂ 9.3 μm laser irradiation followed by additional application of AmF/NaF/SnCl₂ solution significantly reduces the progression of dental enamel erosion in vitro.

In vitro CO2 9.3-μm short-pulsed laser caries prevention-effects of a newly developed laser irradiation pattern

Caries prevention with different lasers has been investigated in laboratory studies and clinical pilot trials. Objective of this in vitro study was to assess whether 9.3-μm microsecond short-pulsed CO₂ laser irradiation enhances enamel caries resistance without melting, with and without additional fluoride application. Seven groups of enamel, totaling 105 human enamel samples, were irradiated with 2 different carbon dioxide lasers with 2 different energy application systems (original versus spread beam; 9.3 μm wavelength, pulse repetition rate 43 Hz vs 100 Hz, fluence ranges from 1.4 to 3.9 J/cm², pulse duration 3 μs to 18 μs). The laboratory pH-cycling was performed with or without additional fluoride, followed by cross-sectional microhardness testing. To assess caries inhibition, the mean relative mineral loss delta Z (∆Z) was determined. To evaluate for melting, scanning electron microscopy (SEM) examinations were performed. For the non-laser control groups with additional fluoride use, the relative mineral loss (ΔZ, vol% × μm) ranged between 512 ± 292 and 809 ± 297 (mean ± SD). ΔZ for the laser-irradiated samples with fluoride use ranged between 186 ± 214 and 374 ± 191, averaging a 58% ± 6% mineral loss reduction (ANOVA, P < 0.01 to P < 0.0001). For the non-laser-treated controls without additional fluoride, the mineral loss increased (ΔZ 914 ± 422 to 1224 ± 736). In contrast, the ΔZ for the laser-treated groups without additional fluoride ranged between 463 ± 190 and 594 ± 272 (P < 0.01 to P < 0.001) indicative of 50% ± 2% average reduction in mineral loss. Enhanced caries resistance was achieved by all applied fluences. Using the spread beam resulted in enhanced resistance without enamel melting as seen by SEM. CO₂ 9.3-μm short-pulsed laser irradiation with both laser beam configurations resulted in highly significant reduction in enamel mineral loss. Modifying the beam to a more homogenous profile will allow enamel caries resistance even without apparent enamel melting.

Laser-Aided Enamel Conditioning: A Comparison of Microleakage Under Brackets Following Different Aging Procedures

Objective:

To evaluate microleakage under the orthodontic adhesives applied following two version of erbium:yttrium aluminum garnet (Er:YAG) laser-aided enamel conditioning after thermal and thermomechanical simulators.

Materials and Methods:

A comparative analytical study based on metal braces bonded on the enamel of extracted teeth ( n = 160) etched with acid, Er:YAG laser and Er:YAG laser with an X-Runner handpiece, and self-etch adhesives. An arch wire was ligatured to samples which were embedded in acrylic blocks by two with periodontal ligaments. The specimens were subdivided into two groups: those aged with thermal cycling and thermomechanical aging procedures. The samples were immersed in basic fuchsin solution (0.5%) for 24 h. Buccolingual sections were performed on the mesial and distal wings of the braces. The color penetration at the gingival and occlusal margins of the adhesive-bracket and enamel-adhesive was evaluated under a stereomicroscope. The median and mean values of microleakage in both groups were evaluated with Kruskal–Wallis and Mann–Whitney U tests ( P < .05).

Results:

The highest microleakage was recorded in the gingival part of the samples aged with the thermomechanical aging procedure ( P = .001). The amount of microleakage generally increased in the samples subjected to thermomechanical loading, but the only significant difference was recorded in the gingival part in each four different conditioning methods.

Conclusion:

Microleakage of the phosphoric acid-etched groups was recorded with lower values for both aging methods. Thermomechanical aging should be included to microleakage studies due to increased microleakage on gingival side for all etching groups.

The Impact of CO2 Laser Treatment and Acidulated Phosphate Fluoride on Enamel Demineralization and Biofilm Formation

Introduction: This study evaluated the impact of CO₂ laser treatment and acidulated phosphate fluoride (APF) on enamel demineralization and biofilm formation, using in vitro and in situ designs. Methods: Demineralized enamel slabs were distributed among 8 groups: placebo, placebo + continuous CO₂ laser, placebo + repeated CO₂ laser, placebo + ultrapulsed CO₂ laser, 1.23% APF, APF + continuous CO₂ laser, APF + repeated CO₂ laser and APF + ultrapulsed CO₂ laser. In the in vitro study, 15 enamel slabs from each group were subjected to a pH-cycling regimen for 14 days. In the cross over in situ design, 11 volunteers wore palatal appliances with demineralized enamel slabs for 2 periods of 14 days each. Drops of sucrose solution were dripped onto enamel slabs 8×/day. Biofilms formed on slabs were collected and the colony-forming units (CFU) of Streptococcus mutans and Lactobacillus were determined. Results: For both in vitro and in situ studies, there was no significant difference between treatments (P>0.05). However, all treatments increased microhardness of demineralized enamel (P<0.05). After a further in situ cariogenic challenge, with the exception of the placebo, all treatments maintained microhardness values (P<0.05). Microbiological analysis showed no difference in Streptococcus mutans (P>0.05) or Lactobacillus (P>0.05) counts between groups. Conclusion: The results suggest that APF gel combined with the CO₂ laser, regardless of the pulse emission mode used, was effective in controlling enamel demineralization, but none of the tested treatments was able to prevent bacterial colonization.

Effects of Er:YAG Laser Treatment on the Mineral Content and Morphology of Primary Tooth Enamel

Objective: The aim of this study was to evaluate the mineral content and morphology of primary tooth enamel prepared using an Er:YAG laser at different power settings. Materials and methods: The buccal surfaces of 45 noncarious primary molars were assessed in this study. The surfaces were cleaned and the teeth were randomly divided into nine groups (n = 5 each) to evaluate the effects of Er:YAG laser treatment at different energy levels: 200 mJ, 2 Hz; 200 mJ, 3 Hz; 200 mJ, 10 Hz; 250 mJ, 2 Hz; 250 mJ, 3 Hz; 250 mJ, 10 Hz; 300 mJ, 2 Hz; 300 mJ, 3 Hz; and 300 mJ, 10 Hz. The mean percentage weight (wt%) of calcium (Ca), phosphorous (P), fluoride (F), magnesium (Mg), potassium (K), and sodium (Na) in the primary tooth enamel was calculated for each group using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy before and after laser application. The enamel morphology was also evaluated using SEM. The obtained data were statistically analyzed by one-way analysis of variance and Tukey's honest significant difference test. Results: The mean wt% of Ca, P, and F in the enamel exhibited a significant change after laser treatment (p < 0.05); the wt% of Mg, K, and Na remained unchanged (p > 0.05). There was no association between the power setting of the laser and changes in the wt% of minerals in the enamel (p > 0.05). SEM showed that enamel irradiated at different energy levels exhibited a characteristic lava flow appearance, and more surface irregularities were observed with the 250-mJ setting than with the 200-mJ setting. Conclusions: Our findings suggest that the mineral content and morphology of the enamel of primary teeth are affected by Er:YAG laser irradiation.

Altered adhesion of dental sealant to tooth enamel microscopically modified by Er:YAG laser irradiation: An in vitro study

Background and Aims

Er:YAG laser has become optional for enamel and dentin preparation for a decade. However, it is unclear if Er:YAG laser is acceptable for enamel conditioning prior to an application of a pit-and-fissure sealant. This in vitro study thus aimed to investigate shear bond strength of a sealant to enamel etched with Er:YAG laser, as well as to demonstrate an alteration of enamel surface after the laser was applied.

Materials and Methods

One hundred and twenty extracted human premolars were divided into 4 groups (N = 30 per group) in which the enamel surfaces were treated with 1) 37% phosphoric acid, 2) Er:YAG laser 80 mJ/pulse, 2 Hz, 3) Er:YAG laser 120 mJ/pulse, 10 Hz, and 4) Er:YAG laser 140 mJ/pulse, 2 Hz. Prior to sealant application. Shear bond strength was determined by using a universal testing machine. Statistical analysis was performed using One-way ANOVA. Modification of enamel surface after laser ablation was also investigated using scanning electron microscope.

Results

Phosphoric acid-etched enamel yielded the highest shear bond strength when bonded with a sealant. Ablation of enamel with Er:YAG laser did not significantly improve sealant bonding since it demonstrated lower shear bond strength, compared to acid-etched enamel. Despite the presence of cracks after Er:YAG laser application, dissolution of enamel substances was limited.

Conclusion

Our study has shown a reduced shear bond strength of dental sealant to an Er:YAG laser-irradiated enamel, compared with phosphoric acid-etched enamel.

Effect of Erbium Laser on Microtensile Bond Strength of Fissure Sealant in Primary Teeth: An in vitro Study

Background:

Laser etching has several advantages as compared with conventional acid etching. However, results of earlier studies on conditioning surfaces with erbium, chromium:yttrium–scandium–gallium–garnet (Er, Cr:YSGG) before application of the fissure sealant have been inconclusive.

Aim:

The study aimed to evaluate the microtensile strength of resin-based fissure sealant bonded to primary enamel conditioned by Er, Cr:YSGG laser with varying power outputs.

Materials and Methods:

Fifty sound primary first molars were randomized into the following five groups based on pretreatment choice: Group 1: 3.5 W laser etching + acid etching; Group 2: 2.5 W laser etching + acid etching; Group 3: 3.5 W laser etching with no acid; Group 4: 2.5 W laser etching with no acid and Group 5: acid etching with no laser. Acid etch was performed with 35% orthophosphoric acid for 30 s. Laser etching was performed with Er, Cr:YSGG (2780 nm) laser using G6 tips and 600 μm diameter, 2.5 W or 3.5 W power outputs, pulse duration of 140 μs and a repetition rate of 20 Hz. Sealant was applied on the buccal surface followed by an incremental buildup with composite resin. Microtensile bond strength was assessed and compared among the five groups using one- and two-way ANOVA.

Results:

There was no statistical difference in the mean bond strength between groups except in Group 4 (9.66 MPa) (Group 1: 15.57 MPa; Group 2: 14.18 MPa; Group 3: 14.78 MPa; Group 5: 14.63 MPa).

Conclusion:

Pretreatment with 3.5 W Er, Cr:YSGG laser alone results in microtensile bond strengths similar to that produced by acid etching, indicating that enamel etching using 3.5 W Er, Cr:YSGG laser would result in the long-term success of pit and fissure sealants in primary teeth.

Effect of fluoride application during radiotherapy on enamel demineralization

OBJECTIVE

Radiation-related caries are one the most undesired reactions manifested during or after head and neck radiotherapy. Fluoride application is an important strategy to reduce demineralization and enhance remineralizaton. To evaluate the effect of the topical application of fluoride during irradiation on dental enamel demineralization.

MATERIAL AND METHODS

Thirty molars were randomly divided into three groups: Non-irradiated (NI), Irradiated (I), Irradiated with fluoride (IF). Each group was subdivided according to the presence or absence of pH-cycling (n=5). In the irradiated groups, the teeth received 70 Gy. The enamel's chemical composition was measured using Fourier Transform Infrared Spectrometry (organic matrix/mineral ratio - M/M and relative carbonate content - RCC). Vickers microhardness (VHN) and elastic modulus (E) were evaluated at three depths (surface, middle and deep enamel). Scanning electron microscopy (SEM) was used to assess the enamel's morphology.

RESULTS

The FTIR analysis (M/M and RCC) showed significant differences for irradiation, pH-cycling and the interaction between factors (p<0.001). Without pH-cycling, IF had the lowest organic matrix/mineral ratio and relative carbonate content. With pH-cycling, the organic matrix/mineral ratio increased and the relative carbonate content decreased, except for IF. VHN was influenced only by pH-cycling (p<0.001), which generated higher VHN values. ANOVA detected significant differences in E for irradiation (p<0.001), pH-cycling (p<0.001) and for the interaction between irradiation and pH-cycling (p<0.001). Increased E was found for group I without pH-cycling. With pH-cycling, groups I and IF were similar, and showed higher values than NI. The SEM images showed no morphological changes without pH-cycling. With pH-cycling, fluoride helped to maintain the outer enamel's morphology.

CONCLUSIONS

Fluoride reduced mineral loss and maintained the outer morphology of irradiated and cycled enamel. However, it was not as effective in preserving the mechanical properties of enamel. Radiotherapy altered the enamel's elastic modulus and its chemical composition.

Influence of Ultrapulsed CO2 Laser, before Application of Different Types of Fluoride, on the Increase of Microhardness of Enamel In Vitro

Objective

To evaluate the influence of ultrapulsed CO₂ laser in combination with commercial fluoride products in order to verify the increase of microhardness of artificial enamel caries lesions.

Materials and Methods

Bovine enamel specimens were prepared, and artificial enamel caries lesions were created. Teeth were randomly divided into 5 groups (n=10): treated with laser (L), laser + neutral fluoride gel 2% (LNF), laser + acidulated phosphate fluoride gel 1.23% (LAFG), laser + acidulated fluoride mousse 1.23% (LAFM), and laser + fluoride varnish 5% (LFV). Microhardness was evaluated at baseline, after caries induction, after CO₂ laser irradiation + fluoride treatment in the 1st week, and after fluoride treatment at 3rd and 5th week.

Results

There was a decrease in microhardness in all groups after artificial enamel caries lesion formation; no increase in microhardness was found in the first and third weeks in all groups (p > 0.05). In the fifth week, an increase in microhardness occurred in all groups (p < 0.05).

Conclusion

Although CO2 laser irradiation in combination with different commercial fluoride products was capable of increasing microhardness on enamel caries lesions in bovine tooth enamel it is necessary to confirm these results by testing the isolated effect of fluoride on enamel surface microhardness. Also, although microhardness was higher in the fluoride varnish group than in the other groups in the fifth week it is not possible to discard the best effect of fluoride varnish treatment on absence of artifacts that may occur with the other fluoride treatments.

Clinical Relevance

In order to prove that CO2 laser may contribute to an increase in microhardness when applied to enamel lesions in combination with different commercial fluoride products it is necessary to conduct additional studies. Also, higher microhardness of fluoride varnish group should be carefully considered.

Evaluation of a clinical preventive treatment using Er,Cr:YSGG (2780 nm) laser on the susceptibility of enamel to erosive challenge

The purpose of this in vitro study was to evaluate the effect of a clinical preventive treatment using Er,Cr:YSGG laser irradiation on bovine enamel susceptibility after erosive challenge. Twelve sound bovine incisors were used and twenty-four enamel specimens were prepared in total. Two experimental groups (n = 12) were assigned as follows: Group 1 was the control group and in Group 2, the enamel specimens were irradiated with an Er,Cr:YSGG (2780 nm) laser system for 20 s, with average output power of 0.25 W, pulse repetition rate at 20 Hz without water or air flow and the pulse duration was fixed at 140 μsec. The tip diameter was 600 μm, the tip to tissue distance was 1 mm, the speed of handpiece movement was 2 mm/s, the power density was 88.34 W/cm², and the fluence was 31.25 J/cm². The specimens were submitted to erosive challenge using a common soft drink. Surface microhardness changes, surface roughness changes, and surface loss were evaluated after erosive challenge. The data were statistically analyzed using one-way ANOVA and Tukey's post-hoc test at a level of significance a = 0.05. Er,Cr:YSGG laser-treated enamel exhibited significantly less decrease in surface microhardness and significant less surface loss compared to control enamel after the erosive challenge (p < 0.05). The experimental groups did not show significant differences in surface roughness increase after the erosive challenge (p > 0.05). Er,Cr:YSGG laser treatment may be promising for the limitation of enamel erosive tooth wear induced by excessive consumption of soft drinks. Clinical studies are needed to clarify whether this protective effect is clinically significant.

Relationship between Er,Cr:YSGG laser power and surface roughness of lased radicular dentin

Background: This study sought to assess the effect of Er,Cr:YSGG laser power on the surface roughness of lased radicular dentin using atomic force microscopy (AFM).

Methods: Fifteen human radicular dentin samples were randomly divided into five groups: one control (G1, intact) and four experimental groups treated with 0.25W (G2), 0.5W (G3), 0.75W (G4) and 1W (G5) powers of Er,Cr:YSGG laser (2.78µm) at a repetition rate of 20 Hz, with a 600-µm-diameter sapphire tip. After irradiation, surface topography was analyzed by AFM using a Si probe in tapping mode. Quantitative information concerning the arithmetic average roughness (Ra) and quadratic mean roughness (Rq) was obtained from three 5×5µm areas of each sample. The data were analyzed using one-way ANOVA (P<0.05).

Results: The Ra and Rq values increased in G2 and G5 and decreased in G3 and G4 groups compared to the control group. The maximum Ra and Rq values were noted in G5, which were significantly higher than the corresponding values in G3 (P<0.05).

Conclusion: No direct correlation was found between Er,Cr:YSGG laser power and surface roughness of lased radicular dentin. Laser therapy with a mean power of 0.5W and 1W caused the lowest and highest surface roughness, respectively.

Non-contact profilometry of eroded and abraded enamel irradiated with an Er:YAG laser

Literature has reported positive results regarding the use of lasers in the control of erosive lesions; however, evaluating whether they are effective in the control of the progression of erosive/abrasive lesions is important.

The Rate of Demineralization in the Teeth Prepared by Bur and Er:YAG Laser

Introduction: The present in vitro study evaluated the recurrence rate of caries following cavity preparations with bur (conventional technique) and irradiation by Erbium:Yttrium- Aluminum-Garnet (Er:YAG) laser through micro hardness test. Methods: A total of 72 human extracted molars were randomly divided into 3 groups and class 5 cavities were prepared on them with 3 different methods: G1) conventional bur, G2) Er:YAG laser irradiation alone and G3) laser irradiation + laser treatment. The specimens were immersed in the artificial caries solution with pH of 2.0 and 5.0 (12 days) and then immersed in re-mineralizing solution with pH of 7.0 (25 days). The specimens were longitudinally sectioned and their Vickers micro hardness was determined. Data were statistically analyzed by means of three-way analysis of variance (ANOVA) and Tukey multiple comparisons tests. Results: The micro hardness of the samples was affected by substrate type (enamel and dentin) and low values were achieved in dentin (P<0.001). Moreover, no significant difference was observed between preparation methods by bar and laser irradiation alone (P ≤0.499). Although laser irradiation + laser treatment decreased micro hardness of enamel compared to other methods. In dentin samples, different methods of preparation showed no significant effect on micro hardness (P ≤0.874). Conclusion: Due to the similar values of micro hardness following G1 and G2, it seems that Er:YAG laser alone is as much effective as the conventional bur to prevent recurrence caries. However, because of the high prices of laser instruments, bur preparations can be done commonly.

Variation on Molecular Structure, Crystallinity, and Optical Properties of Dentin Due to Nd:YAG Laser and Fluoride Aimed at Tooth Erosion Prevention

This in vitro study evaluated the compositional, crystalline, and morphological effects promoted by Nd:YAG laser on root dentin, and verified the effects of laser and topical acidulated phosphate fluoride application (APF-gel) on dentin erosion. 180 bovine dentin slabs were randomized into 4 groups (n = 45): G1–untreated, G2–APF-gel (1.23% F⁻, 4 min), G3–Nd:YAG (1064 nm, 84.9 J/cm², 10 Hz), and G4–APF-gel application followed by Nd:YAG laser irradiation. The compositional, crystalline, and morphological effects promoted by treatments were investigated on five samples of each experimental group. The other samples were submitted to a 5-day, 10-day, or 15-day erosive and abrasive demineralization and remineralization cycling in order to create erosion lesions. The area and depth of lesions, as well as the optical attenuation coefficient, were assessed, and all data were statistically analysed (p < 0.05). Nd:YAG laser promoted the reduction of carbonate, the formation of tetracalcium phosphate, as well as the melting and recrystallization of the dentin surface. Laser significantly decreased the area and depth of erosion lesions and altered the optical attenuation coefficient when compared to untreated and APF-gel groups, but the association of APF-gel and laser did not promote an additional effect. Nd:YAG laser irradiation can be a promissory treatment to prevent dentin erosion and the abrasion process.

Sub-ablative Er,Cr:YSGG laser irradiation under all-ceramic restorations: effects on demineralization and shear bond strength

This study evaluated the caries resistant effects of sub-ablative Er,Cr:YSGG laser irradiation alone and combined with fluoride in comparison with fluoride application alone on enamel prepared for veneer restorations. And also, evaluated these treatments' effects on the shear bond strength of all-ceramic veneer restorations. One hundred and thirty-five human maxillary central teeth were assigned to groups of 1a-control, 1b-laser treated, 1c-fluoride treated, 1d-laser + fluoride treated for shear bond testing and to groups of 2a-positive control(non-demineralised), 2b-laser treated, 2c-fluoride treated, 2d-laser + fluoride treated, 2e-negative control (demineralised) for microhardness testing (n = 15, N = 135). Demineralisation solutions of microhardness measurements were used for the ICP-OES elemental analysis. The parameters for laser irradiation were as follows: power output, 0.25 W; total energy density, 62.5 J/cm² and energy density per pulse, 4.48 J/cm² with an irradiation time of 20 s and with no water cooling. Five percent NaF varnish was used as fluoride preparate. ANOVA and Tukey HSD tests were performed (α = 5%). Surface treatments showed no significant effects on shear bond strength values (p = 0.579). However, significant differences were found in microhardness measurements and in elemental analysis of Ca and P amounts (p < 0.01). Surface-treated groups showed significantly high VNH values and significantly low ICP-OES values when compared with non-treated (-control) group while there were no significance among surface-treated groups regarding VHN and ICP-OES values. Sub-ablative Er,Cr:YSGG treatment alone or combined with fluoride is as an effective method as at least fluoride alone for preventing the prepared enamel to demineralization with no negative effect on shear bond strength.

Influence of multi-wavelength laser irradiation of enamel and dentin surfaces at 0.355, 2.94, and 9.4 μm on surface morphology, permeability, and acid resistance

OBJECTIVE

Ultraviolet (UV) and infrared (IR) lasers can be used to specifically target protein, water, and mineral, respectively, in dental hard tissues to produce varying changes in surface morphology, permeability, reflectivity, and acid resistance. The purpose of this study was to explore the influence of laser irradiation and topical fluoride application on the surface morphology, permeability, reflectivity, and acid resistance of enamel and dentin to shed light on the mechanism of interaction and develop more effective treatments.

METHODS

Twelve bovine enamel surfaces and twelve bovine dentin surfaces were irradiated with various combinations of lasers operating at 0.355 (Freq.-tripled Nd:YAG (UV) laser), 2.94 (Er:YAG laser), and 9.4 μm (CO₂ laser), and surfaces were exposed to an acidulated phosphate fluoride gel and an acid challenge. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, polarized light microscopy, near-IR reflectance, fluorescence, polarization sensitive-optical coherence tomography (PS-OCT), and surface dehydration rate measurements.

RESULTS

Different laser treatments dramatically influenced the surface morphology and permeability of both enamel and dentin. CO₂ laser irradiation melted tooth surfaces. Er:YAG and UV lasers, while not melting tooth surfaces, showed markedly different surface roughness. Er:YAG irradiation led to significantly rougher enamel and dentin surfaces and led to higher permeability. There were significant differences in acid resistance among the various treatment groups.

CONCLUSION

Surface dehydration measurements showed significant changes in permeability after laser treatments, application of fluoride and after exposure to demineralization. CO₂ laser irradiation was most effective in inhibiting demineralization on enamel while topical fluoride was most effective for dentin surfaces. Lasers Surg. Med. 49:913-927, 2017. © 2017 Wiley Periodicals, Inc.

A New Laser-Processing Strategy for Improving Enamel Erosion Resistance

In the present study, a new automatic laser-processing strategy allowing standardized irradiation of natural tooth areas was investigated. The objective was to find a combination of laser parameters that could cause over a 600°C temperature increase at the enamel surface while not damaging enamel, avoiding temperature change above 5.5°C in the pulp and increasing enamel erosion resistance. Seventy-seven bovine enamel samples were randomly divided into 6 laser groups and 1 negative control (C/no treatment/ n = 11). A scanning strategy (7 × 3 mm) was used for the CO₂ laser treatment (λ = 10.6 µm, 0.1-18 J/cm²) with different pulse durations-namely, 20 µs (G20), 30 µs (G30), 55 µs (G55), and 490 µs (G490), as well as 2 modified pulse distances (G33d, G40d). Measurements of temperature change were performed at the surface (thermal camera/50 Hz), at the underside (thermocouples), and at the pulp chamber using a thermobath and human molars ( n = 10). In addition, histology and X-ray diffraction (XRD/ n = 10) were performed. Erosion was tested using an erosive cycling over 6 d, including immersion in citric acid (2 min/0.05 M/pH = 2.3) 6 times daily. Surface loss was measured using a profilometer and statistical analysis with a 2-way repeated-measures analysis of variance (α = 0.05). Only G20 fulfilled the temperature requirements at the surface (619 ± 21.8°C), at the underside (5.3 ± 1.4°C), and at the pulp (2.0 ± 1.0°C), and it caused no mineral phase change and significant reduction of enamel surface loss (-13.2 ± 4.0 µm) compared to C (-37.0 ± 10.1 µm, P < 0.05). A laser-scanning strategy (20 µs/2 kHz/1.25 J/cm², 3.4 mm/s) has been established that fulfilled the criteria for biological safety and significantly increased enamel erosion resistance (64%) in vitro.

Nd:YAG laser irradiation associated with fluoridated gels containing photo absorbers in the prevention of enamel erosion

This study evaluated the combined effect of Nd:YAG laser irradiation and fluoridated gels containing photo absorbers against enamel erosion. Enamel specimens from bovine teeth were polished, eroded (10 min, with 1% citric acid, pH = 2.6), and randomly allocated into the experimental groups (n = 8), according to the different surface treatments: fluoridated gels (F: 9047 ppm F and F + Sn: 9047 ppm F and 3000 ppm Sn), with or without photo absorbers (E: erythrosine and MB: methylene blue), and associated or not with Nd:YAG laser irradiation (in contact; 0.5 W; 50 mJ; ~41.66 J/cm²; 10 Hz; 40 s; pulse duration of 120 μs). A placebo gel (PLA) associated or not with laser was used as control. All gels had pH = 4.5 and were applied for 2 min. Laser irradiation was performed during gel application. The specimens were then submitted to a 5-day erosion-remineralization cycling model using 0.3% citric acid (pH = 2.6), 4×/day. Enamel surface loss (SL) was analyzed by optical profilometry in the end of the cycling (in μm). Data were analyzed by ANOVA and Tukey tests (α = 0.05). Means (SD) of SL for the groups were the following (different superscript letters imply significant difference among groups): PLA (21.02 ± 1.28)^a, PLA + laser (19.20 ± 0.96)^ab, laser (17.47 ± 1.50)^b, F + Sn + E + laser (13.69 ± 0.62)^c, F + E + laser (13.52 ± 1.16)^c, F (13.10 ± 1.08)^c, F + laser (11.94 ± 1.44)^cd, F + Sn + MB + laser (11.90 ± 4.02)^cd, F + MB + laser (11.42 ± 1.42)^cd, F + Sn (11.12 ± 1.20)^cd, and F + Sn + laser (10.35 ± 0.89)^d. In conclusion, all fluoridated gels and the Nd:YAG laser irradiation reduced erosion development, but the combination of treatments did not promote further protection. The addition of photo absorbers to the fluoridated gels did not influence the anti-erosive effect of the combination of laser plus fluoridated gels.

Influence of Multi-Wavelength Laser Irradiation of Enamel and Dentin Surfaces on Surface Morphology and Permeability

UV and IR lasers can be used to specifically target protein, water, and the mineral phase of dental hard tissues to produce varying changes in surface morphology. In this study, we irradiated enamel and dentin surfaces with various combinations of lasers operating at 0.355, 2.94, and 9.4 μm, exposed those surfaces to topical fluoride, and subsequently evaluated the influence of these changes on surface morphology and permeability. Digital microscopy and surface dehydration rate measurements were used to monitor changes in the samples overtime. The surface morphology and permeability (dehydration rate) varied markedly with the different laser treatments on enamel. On dentin, fluoride was most effective in reducing the permeability.

Synergistic effect of fluoride and laser irradiation for the inhibition of the demineralization of dental enamel

Both laser irradiation and fluoride treatment alone are known to provide increased resistance to acid dissolution. CO₂ lasers tuned to a wavelength of 9.3 μm can be used to efficiently convert the carbonated hydroxyapatite of enamel to a much more acid resistant purer phase hydroxyapatite (HAP). Further studies have shown that fluoride application to HAP yields fluoroapatite (FAP) which is even more resistant against acid dissolution. Previous studies show that CO₂ lasers and fluoride treatments interact synergistically to provide significantly higher protection than either method alone, but the mechanism of interaction has not been elucidated. We recently observed the formation of microcracks or a "crazed" zone in the irradiated region that is resistant to demineralization using high-resolution microscopy. The microcracks are formed due to the slight contraction of enamel due to transformation of carbonated hydroxyapatite to the more acid resistant pure phase hydroxyapatite (HAP) that has a smaller lattice. In this study, we test the hypothesis that these small cracks will provide greater adhesion for topical fluoride for greater protection against acid demineralization.

Effect of Nd:YAG and CO2 Laser Irradiation on Prevention of Enamel Demineralization in Orthodontics: In Vitro Study

OBJECTIVE

The aim of this study was to investigate Nd:YAG and CO₂ laser effects in the prevention of demineralization in deeper layers of enamel via successive acid challenge cycles.

BACKGROUND DATA

Lasers are promising in the prevention of enamel demineralization around the orthodontic brackets; however, there are very few studies that evaluate if the effects of treatment could be extended after successive acid challenge cycles due to permanent enamel structural alterations.

MATERIALS AND METHODS

Human enamel samples were divided into five groups (n = 12): G1-application of 1.23% acidulated fluoride phosphate gel (AFP, control); G2-Nd:YAG laser irradiation (0.6 W, 84.9 J/cm², 10 Hz, 110 μs, contact mode); G3-Nd:YAG laser irradiation associated with AFP; G4-CO₂ laser irradiation (0.5 W, 28.6 J/cm², 50 Hz, 5 μs, and 10 mm focal distance); and G5-CO₂ laser irradiation associated with AFP. The samples were submitted to successive acid challenge cycles. Quantitative light-induced fluorescence and scanning electron microscopy were used to assess enamel demineralization. The data were statistically compared (α = 5%).

RESULTS

G1: 50.87 ± 4.57; G2: 47.72 ± 2.87; G3: 50.96 ± 4.01; G4: 28.21 ± 2.19; and G5: 30.13 ± 6.38. The CO₂ laser groups had significantly lower mineral losses than those observed in all other groups after successive acid challenge cycles.

CONCLUSIONS

Only the CO₂ laser (10.6 μm) irradiation prevents enamel demineralization around the orthodontic brackets even after exposure to successive acid challenges. The CO₂ laser at 10.6 μm showed a deeper effect in enamel regarding caries prevention.

Influence of a pulsed CO2 laser operating at 9.4 μm on the surface morphology, reflectivity, and acid resistance of dental enamel below the threshold for melting

Below the threshold for laser ablation, the mineral phase of enamel is converted into a purer phase hydroxyapatite with increased acid resistance. Studies suggest the possibility of achieving the conversion without visible surface alteration. In this study, changes in the surface morphology, reflectivity, and acid resistance were monitored with varying irradiation intensity. Bovine enamel specimens were irradiated using a CO 2 laser operating at 9.4 ?? ? m with a Gaussian spatial beam profile—1.6 to 3.1 mm in diameter. After laser treatment, samples were subjected to demineralization to simulate the acidic intraoral conditions of dental decay. The resulting demineralization and erosion were assessed using polarization-sensitive optical coherence tomography, three-dimensional digital microscopy, and polarized light microscopy. Distinct changes in the surface morphology and the degree of inhibition were found within the laser-treated area in accordance with the laser intensity profile. Subtle visual changes were noted below the melting point for enamel that appear to correspond to thresholds for denaturation of the organic phase and thermal decomposition of the mineral phase. There was significant protection from laser irradiation in areas in which the reflectivity was not increased significantly, suggesting that aesthetically sensitive areas of the tooth can be treated for caries prevention.

A comparative evaluation of retention of pit and fissure sealants placed with conventional acid etching and Er,Cr:YSGG laser etching: A randomised controlled trial

Aim: The aim of this study was to compare the retention rates of sealant placed either with conventional acid etching or Er,Cr:YSGG laser pretreatment of enamel surface. Materials and methods: This is a prospective, single blind randomised controlled clinical trial enrolling 200 permanent first molars in 50 patients, aged 6-12 years for sealant placement. Study followed split mouth design where each side of the arch was randomly allocated to the two treatment group. Group A(Acid etch group): 37 % phosphoric acid (Scotchbond, 3M ESPE, Seefeld, Germany) was applied for 15 seconds, rinsed with water for 20 seconds and then air-dried using air spray. Group L(Laser etch group): Fissures were prepared with an Er,Cr:YSGG laser system (Waterlase, BIOLASE Technology, San Clemente, CA, USA) emitting photons at a wavelength of 2.78 µm. Laser irradiation at 1.5 W (60% air and 40% water), in a noncontact mode, with a repetition rate of 20 Hz for 10seconds was used. Pit and fissure sealant (3M ESPE, Clinpro) was applied and cured for 20 seconds. One blinded, calibrated examiner, who was unaware of which preparation method has been used and who was not involved in the treatment procedures, evaluated the sealant at baseline and at 3, 6, 9 and 12 month follow-up visits. Results: It was observed that overall retention rate in group A was slightly higher as compared to group L at all time periods, however, the difference was statistically non-significant (p-value>0.05).

CONCLUSION

Er,Cr:YSGG laser etching is comparable to acid etching in terms of retention and patient acceptability.

An In Vitro Comparison of the Bond Strength of Composite to Superficial and Deep Dentin, Treated With Er:YAG Laser Irradiation or Acid-Etching

Introduction: The aim of this study was to compare the micro-shear bond strength of composite resin on superficial and deep dentin after conditioning with phosphoric acid and Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser. Methods: Thirty human molars were selected, roots were removed and crowns were bisected to provide a total of 60 half-crowns. Specimens were ground to expose superficial and deep dentin. Samples were assigned to six groups: (1) AS (acid etching of superficial dentin); (2) AD (acid etching of deep dentin); (3) LS (Er:YAG laser irradiation on superficial dentin); (4) LD (Er:YAG laser irradiation on deep dentin); (5) LAS (Er:YAG laser irradiation on superficial dentin followed by acid etching); (6) LAD (Er:YAG laser irradiation on deep dentin followed by acid etching) The adhesive protocol was performed. Samples were thermocycled and micro-shear bond strength was tested to failure. The data were submitted to statistical analysis with one-way analysis of variance (ANOVA) and Tukey post hoc test. Results: The AS group, demonstrated the greatest amount of micro-shear bond strength. Statistical analysis showed a decrease in bond strength in laser-treated groups which was more significant for deep dentin. Conclusion: Preparation of dentin with laser did not improve bonding to superficial and deep dentin.

Caries inhibition with a CO2 9.3 μm laser: An in vitro study

BACKGROUND AND OBJECTIVES

The caries preventive effects of different laser wavelengths have been studied in the laboratory as well as in pilot clinical trials. The objective of this in vitro study was to evaluate whether irradiation with a new 9.3 μm microsecond short-pulsed CO2 -laser could enhance enamel caries resistance with and without additional fluoride applications.

STUDY DESIGN/MATERIALS AND METHODS

One hundred and one human tooth enamel samples were divided into seven groups. Each group was treated with different laser parameters (CO2 -laser, wavelength 9.3 μm, 43 Hz pulse-repetition rate, pulse duration between 3 µs at 1.5 mJ/pulse to 7 µs at 2.9 mJ/pulse). A laboratory pH-cycling model followed by cross-sectional microhardness testing determined the mean relative mineral loss delta Z (ΔZ) for each group to assess caries inhibition in tooth enamel by the CO2 9.3 µm short-pulsed laser irradiation. The pH-cycling was performed with or without additional fluoride.

RESULTS

The non-laser control groups with additional fluoride had a relative mineral loss (ΔZ, vol% × µm) that ranged between 646 ± 215 and 773 ± 223 (mean ± SD). The laser irradiated and fluoride treated samples had a mean ΔZ ranging between 209 ± 133 and 403 ± 245 for an average 55% ± 9% reduction in mineral loss (ANOVA test, P < 0.0001). Increased mean mineral loss (ΔZ between 1166 ± 571 and 1339 ± 347) was found for the non-laser treated controls without additional fluoride. In contrast, the laser treated groups without additional fluoride showed a ΔZ between 470 ± 240 and 669 ± 209 (ANOVA test, P < 0.0001) representing an average 53% ± 11% reduction in mineral loss. Scanning electron microscopical assessment revealed that 3 µs pulses did not markedly change the enamel surface, while 7 µs pulses caused some enamel ablation.

CONCLUSION

The CO2 9.3 µm short-pulsed laser energy renders enamel caries resistant with and without additional fluoride use. The observed enhanced acid resistance occurred with the laser irradiation parameters used without obvious melting of the enamel surface as well as after irradiation with energies causing cutting of the enamel. Lasers Surg. Med. 48:546-554, 2016. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Structural and Morphological Changes in Human Dentin after Ablative and Subablative Er:YAG Laser Irradiation

INTRODUCTION

This study investigated the influence of Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser on microhardness, chemical composition and subsurface morphology of dentin cavity walls.

METHODS

Forty sound human premolars were selected and randomly assigned into four groups. Class V cavities were prepared either with an Er:YAG laser (groups 1 and 2; 15 Hz, 250 mJ for enamel, 10 Hz, 200 mJ for dentin) or with a high speed handpiece (groups 3 and 4). The specimens in groups 1 and 3 served as the control, whereas those in groups 2 and 4 were exposed to subablative laser irradiation following cavity preparation (10 Hz, 50 mJ). After bisecting the specimens, one half was subjected to microhardness assessment and the other half was evaluated by SEM-EDS analysis.

RESULTS

Microhardness was significantly greater in the specimens prepared by both ablative and subablative laser irradiation (group 2) than that of the bur-prepared cavities (groups 3 and 4) (P < 0.05). The quantity of calcium ion was significantly greater in cavities prepared by the Er:YAG laser (groups 1 and 2) compared to that of the bur cavities (groups 3 and 4) (P < 0.05). Subablative irradiation improved microhardness and weight percentage of calcium ion in both laser and bur cavities, but the difference was not significant compared to that of the relevant control group (P > 0.05).

CONCLUSION

Cavity preparation with an Er:YAG laser could be considered as an alternative to the conventional method of drilling, as it enhances the mechanical and compositional properties of lased dentin, especially when combined by subablative irradiation.

Impact of CO2 laser and stannous fluoride on primary tooth erosion

This study evaluated in vitro the effect of input power of CO2 laser, either associated or not to stannous fluoride (SnF2) gel, for the control of intrinsic erosion in primary teeth. One hundred four enamel slabs (3 × 3 × 2 mm) from human primary molars were flattened and polished. Adhesive tapes were placed on their surface leaving a window of 3 × 1 mm. Slabs were then cycled four times in 0.01 M hydrochloric acid (pH 2, 2 min) and in artificial saliva (2 h) for creation of erosive lesions. Specimens were randomly assigned into eight groups (n = 13) according to fluoride application [absent (control) or 0.4% stannous fluoride gel (SnF2)] and input power of CO2 laser [unlased (control), 0.5, 1.0 or 1.5 W]. The CO2 laser irradiation was performed in an ultra-pulse mode (100 μs of pulse duration), 4-mm working distance, for 10 s. Specimens were then submitted to further erosive episodes for 5 days and evaluated for enamel relative permeability. Fluoride did not show any protective effect for any of the laser-treated groups or control (p = 0.185). However, a significant effect was detected for input power of CO2 laser (p = 0.037). Tukey's test showed that there was a significant statistically difference between specimens irradiated with 0.5 and 1.5 W (p = 0.028). The input power of 0.5 W showed lower permeability. Variation of input power CO2 laser can influence enamel permeability, at the power of 1.5 W which promoted greater permeability.

Evaluation of enamel surface modification using PS-OCT after laser treatment to increase resistance to demineralization

At laser intensities below ablation, carbonated hydroxyapatite in enamel is converted into a purer phase hydroxyapatite with increased acid resistance. Previous studies suggested the possibility of achieving the conversion without surface modification. This study attempts to evaluate the thresholds for the modification without additional changes in physical and optical properties of the enamel. Bovine specimens were irradiated using an RF-excited CO₂ laser operating at 9.4-µm with a pulse duration of 26-µs, pulse repetition rates of 100-1000 Hz, with a Gaussian spatial beam profile - 1.4 mm in diameter. After laser treatment, the samples were subjected to acid demineralization for 48 hours to simulate acidic intraoral conditions of a caries attack. The resulting demineralization and erosion were assessed using polarization sensitive OCT (PS-OCT) and 3D digital microscopy. The images from digital microscopy demonstrated a clear delineation between laser protected zones without visual changes and zones with higher levels of demineralization and erosion. Distinct changes in the surface morphology were found within the laser treated area in accordance with the Gaussian spatial beam profile. There was significant protection from the laser in areas that were not visually altered.