Influence of using different toothpaste during bleaching with violet LED light (405 nm) on the colour and roughness of dental enamel: an in vitro study.

This in vitro study aimed to investigate potential changes in the color and roughness of dental enamel resulting from the use of different toothpaste formulations during bleaching with violet LED light (405 nm). Sixty specimens of bovine incisors, each measuring 6 × 6 × 3 mm, were segregated into six distinct experimental groups based on their respective treatments (n = 10): C + VL: Brushing with Colgate® Total 12 + bleaching with violet LED; LB + VL: Brushing with Colgate® Luminous White Brilliant + bleaching with violet LED; LI + VL: Brushing with Colgate® Luminous White Instant + violet LED bleaching; C: Brushing with Colgate® Total 12; LB: Brushing with Colgate® Luminous White Brilliant; LI: Brushing with Colgate® Luminous White Instant. The examined variables included alterations in color (∆L*, ∆a*, ∆b*, ∆Eab, and ∆E00), surface roughness (Ra), and scanning electron microscopy observations. No statistically significant distinctions emerged in total color variations (∆E00 and ∆E) among the groups under scrutiny. Notably, the groups that employed Colgate® Luminous White Instant displayed elevated roughness values, irrespective of their association with violet LED, as corroborated by scanning electron microscopy examinations. It can be concluded that whitening toothpastes associated to violet LED do not influence the color change of dental enamel in fifteen days of treatment. Toothpastes with a higher number of abrasive particles showed greater changes in enamel roughness, regardless of the use of violet LED.

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 different approaches of direct radiation on the surface structure and caries susceptibility of enamel.

It is not clear whether different radiation methods have different effects on enamel. The purpose of this study was to compare the effects of single and fractionated radiation on enamel and caries susceptibility and to provide an experimental basis for further study of radiation­related caries. Thirty-six caries-free human third molars were collected and randomly divided into three groups (n = 12). Group1 (control group) was not exposed to radiation. Group 2 received single radiation with a cumulative dose of 70 Gy. Group 3 underwent fractionated radiation, receiving 2 Gy/day for 5 days followed by a 2-day rest period, for a total of 7 weeks with a cumulative dose of 70 Gy. Changes in microhardness, roughness, surface morphology, bacterial adhesion and ability of acid resistance of each group were tested. Scanning electron microscope revealed that the enamel surface in both radiation groups exhibited unevenness and cracks. Compared with the control group, microhardness and acid resistance of enamel decreased, while roughness and bacterial adhesion increased in both the single radiation and fractionated radiation groups. Compared with the single radiation group, the enamel surface microhardness and acid resistance decreased in the fractionated radiation group, while roughness and bacterial adhesion increased. Both single radiation and fractionated radiation resulting in changes in the physical and biological properties of enamel, with these changes being more pronounced in the fractionated radiation group. Therefore, fractionated radiation is recommended as a more suitable method for constructing a radiation­related caries model in vitro.

[The effect of erbium laser pretreatment on bond strength between dentin and enamel and microleakage at the edge of CAD/CAM glass ionomer cement restorations for repairing tooth defects].

PURPOSE: To investigate the effects of erbium laser pretreatment on the bond strength of dentin and enamel,as well as microleakage at the edge of tooth defects repaired with computer-aided design (CAD) and computer-assisted manufacturing (CAM) glass-ceramic restorations for repairing dental defects. METHODS: A total of 62 fresh, nondecayed, nondiscoloration and noncracked wisdom teeth were collected from the Oral Surgery Clinic between January 2020 and January 2023. According to different pretreatment methods, they were randomly divided into two groups, erbium laser group and phosphoric acid group, with 31 teeth in each group. Each group was further divided into two subsets for bond strength testing (16 teeth) and microleakage testing (15 teeth).The shear bond strength between enamel and dentin of both groups was compared, as well as the degree and distribution of microleakage.Statistical analysis was performed with SPSS 17.0 software package. RESULTS: The shear bond strength between enamel and dentin of the erbium laser group was significantly higher than that of the phosphoric acid group (P＜0.05); the degree and distribution of microleakage at the lateral walls and gumline of the erbium laser group were significantly lower than those of the phosphoric acid group (P＜0.05). The scores of microleakage at the lateral walls of the erbium laser group mainly concentrated in grade 1 and 2, whereas those of the phosphoric acid group mainly concentrated in grade 2. There was significant difference in the distribution of lateral wall microleakage scores between the two groups (P＜0.05). The scores of microleakage at the gumline of the erbium laser group mainly concentrated in grade 1 and 2, whereas those of the phosphoric acid group mainly concentrated in grade 2 and 3. There was significant difference in the distribution of gumline microleakage scores between the two groups (P＜0.05). CONCLUSIONS: Erbium laser pretreatment can improve bonding strength between glass ionomer cement and dentin and enamel, reduce microleakage at the edge of CAD/CAM glass ionomer cement restorations, and enhance marginal fit.

The damage and remineralization strategies of dental hard tissues following radiotherapy.

OBJECTIVES: This study pursued two main purposes. The first aim was to expound on the microscopic factors of radiation-related caries (RRC). Further, it aimed to compare the remineralization effect of different remineralizing agents on demineralized teeth after radiotherapy. METHODS: The enamel and dentin samples of bovine teeth were irradiated with different doses of radiation. After analysis of scanning electron microscope (SEM), X-Ray diffraction (XRD), and energy dispersive spectrometer (EDS), the samples irradiated with 50 Gy radiation were selected and divided into the demineralization group, the double distilled water (DDW) group, the Sodium fluoride (NaF) group, the Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) group, the NaF + CPP-ACP group, and the Titanium tetrafluoride (TiF4) group. After demineralization, remineralizing agents treatment, and remineralization, the samples were evaluated using SEM, atomic force microscope (AFM), EDS, and transverse microradiography (TMR). RESULTS: A radiation dose of 30 Gy was sufficient to cause damage to the dentinal tubules, but 70 Gy radiation had little effect on the microstructure of enamel. Additionally, the NaF + CPP-ACP group and the TiF4 group significantly promoted deposit formation, decreased surface roughness, and reduced mineral loss and lesion depth of demineralized enamel and dentin samples after radiation. CONCLUSIONS: Radiation causes more significant damage to dentin compared to enamel. NaF + CPP-ACP and TiF4 had a promising ability to promote remineralization of irradiated dental hard tissues. ADVANCES IN KNOWLEDGE: This in vitro study contributes to determining a safer radiation dose range for teeth and identifying the most effective remineralization approach for RRC.

Impact of acid and laser etching of enamel on microleakage in different adhesive systems.

This study aimed to evaluate the microleakage of light-cured and self-cured adhesives on enamel surfaces selectively etched with Er, Cr: YSGG laser or 35% phosphoric acid. A total of 60 class V cavities were prepared 1 mm above the cemento-enamel junction (CEJ). The specimens were randomly divided into six groups. Group 1: Clearfil SE Bond with no conditioning, Group 2: Tokuyama Universal Bond with no conditioning, Group 3: Clearfil SE Bond conditioned with 35% phosphoric acid, Group 4: Tokuyama Universal Bond conditioned with 35% phosphoric acid, Group 5: Clearfil SE Bond conditioned with Er, Cr: YSGG laser and Group 6: Tokuyama Universal Bond conditioned with Er, Cr: YSGG laser. Microleakage was evaluated qualitatively (visually) and quantitatively (ImageJ). The data were analyzed using IBM SPSS V23 and submitted to Kruskal-Wallis and Wilcoxon tests. The significance level was set at p < 0.05. In all evaluation methods, the microleakage scores exhibit significant differences (p*<0.001). Group 1 and Group 3 exhibited similar and lower microleakage values than the Group 5. In the occlusal margin, the microleakage values were similar in Group 2, Group 4, and Group 6, whereas in the gingival margin Group 4 showed significantly lower leakage compared to Group 2. Regardless of the etching protocols and adhesive systems used, less microleakage was observed on the occlusal surface than on the gingival surface. Phosphoric acid etching provides better results than laser etching for enamel surface treatment on both occlusal and gingival surfaces.

Effect of shade and thickness on the microhardness of resin-based composite specimens at different points considering curing light beam's inhomogeneity.

BACKGROUND: Recent studies have reported the inhomogeneity in the light emitted by dental light-curing units (LCUs). It is essential to understand how this uneven light distribution affects the physical properties of resin-based composites (RBCs) at various points across their surfaces. This study aimed to evaluate the effect of LCU beam's inhomogeneity on the microhardness of RBCs with different shades and thicknesses. METHODS: Four body (A1B, A2B, A3B, and A4B), one dentin (A3D), and one enamel shade (A3E) of RBC (Filtek Z350 XT) were examined. The specimens were fabricated in four thicknesses (1, 2, 3, and 4 mm) and subjected to a 40-second light-curing. Vickers microhardness testing was performed at the center point, and 3 mm left and right from the center at the bottom surface of each sample. The LCU beam profile was characterized using a beam profiler, while irradiance after specimen passage was measured using a spectrometer. One-way analysis of variance (ANOVA) and Tukey's post-hoc tests were used to analyze the effects of shades and thicknesses on irradiance and microhardness, respectively. One-way repeated-measures ANOVA was used to compare the microhardness across different points. Pearson's correlation analysis examined the relationship between irradiance and microhardness. RESULTS: The beam profile of LCU revealed inhomogeneous light distribution. Light irradiance was decreased with both the increase in thickness and darker shade of the specimens (p < 0.05). Microhardness was found to decline with an increase in sample thickness (p < 0.05), and was consistently higher at the center point compared to the periphery, particularly in thicker (3 and 4 mm) and darker shades (A3B, A4B, and A3D). A positive correlation was found between the irradiance and microhardness across all evaluated points (p < 0.05). CONCLUSIONS: Inhomogeneous light emission from LCU significantly influences the microhardness of RBC samples, depending on the thicknesses and shades. The findings underline the importance of considering LCU beam inhomogeneity in clinical settings to ensure optimal polymerization of RBC.

Performance of two laser motion modes versus conventional orthodontic ceramic brackets debonding technique on enamel surface topography.

The risk of enamel deterioration that frequently coexists with debonding of orthodontic teeth brackets elevates the mandate for finding an optimum approach for debonding them without harmful effects. This in-vitro study is intended to compare the effects of two different laser modes (scanning and circular) and a conventional method on the enamel surface after debonding orthodontic brackets. 66 extracted premolars were assigned into 3 groups. After that, light-cure composite resin was used to attach the ceramic brackets to the teeth. Amongst the test groups, Group I: specimens that were debonded using conventional debonding using pliers; Group 2: specimens that were debonded using Er, Cr: YSGG laser applications using the circular motion method; and Group 3: specimens that were debonded using Er, Cr: YSGG laser applications using the scanning motion method. Adhesive Remnant Index (ARI) assessment, intra-pulpal temperature increase, enamel surface roughness after polishing, and assessment of the microstructure of enamel were carried out with scanning electron microscopy. The gathered information was examined statistically. The conventional debonding method had a significantly higher proportion of adhesive remnant index (ARI) scores of 2 and 3 in comparison to the circular (p < .004) and scanning laser groups (p < .001). There was no significant difference in ARI scores between the circular and scanning laser groups (p > .05). Moreover, the circular and scanning laser debonding methods resulted in a significantly higher proportion of Enamel Surface Roughness (ESR) scores of 0 and a lower proportion of ESR scores of 3 compared to the conventional technique group (p < .001). However, there was no significant difference in ESR scores between the circular and scanning laser methods (p = .945). Lastly, the average intra-pulpal temperature was significantly higher in the circular laser group (1.9 ± 0.5 ) compared to the scanning laser group (0.9 ± 0.2) with p < .001. Er, Cr: YSGG laser irradiation is a tool that shows promise for debonding ceramic brackets with minimal harm to the enamel surface. The scanning laser technique is more desirable due to the lower intra-pulpal temperature increase.

Effects of NaF versus SDF treatment on microhardness of artificial radiation caries at cervical and root areas.

This study aimed to compare the effect of silver diamine fluoride (SDF) and fluoride varnish (NaF) on the Vickers microhardness (VHN) of enamel and dentin after radiotherapy and pH-cycling. Human premolars were cut longitudinally, embedded and serially polished. The VHN of enamel/dentin and irradiated enamel/dentin were evaluated. The irradiated specimens were treated with either NaF or SDF, subjected to pH-cycling then VHN test for 4 days. Consequently, they were subjected to energy-dispersive X-ray (EDX) analysis. Radiation adversely affect enamel VHN (p<0.05), whereas dentin VHN was not affected (p>0.05). After pH-cycling, a significant decrease in dentin VHN was observed on day 2 for all groups, whereas enamel VHN was significantly decreased in the control group on day 4. SDF-treated enamel demonstrated higher VHN than that of NaF on day 3. Caries prevention effect of SDF and NaF were observed on enamel, where SDF was proved to be superior to NaF.

Comparison of Blue and Infrared Light Transmission Through Dental Tissues and Restorative Materials.

OBJECTIVES: The depth of cure using blue-light photocuring units (BL) is limited by tooth structure and qualities of the restorative material through which the activating wavelength must pass. Recent developments incorporate an infrared (IR) activated upconversion (UC) fluorescence of a lining agent filled with nanocrystals of NaYF4 and doped with YB+3 and Tm+3 that emit both blue and violet light locally at the interface of the liner and restorative resin. The purpose of this study was to evaluate the BL and 975 nm infrared (IR) light power transmission through dental tissues and restorative materials. METHODS AND MATERIALS: Power transmissions of the IR laser (975 nm) and a monowave blue-only light-curing unit (Bluephase 16i) through dental tissues (enamel, dentin, and enamel/dentin junction, or DEJ), eight (8) various dental resin composites, and eight (8) dental ceramics, each at four thicknesses (1, 2, 3 and 4 mm) were evaluated (n=5) using a thermopile sensor (PM10, Coherent Inc) connected to a laser power meter (Fieldmate, Coherent Inc). Power transmission values of each light source and restorative material were subjected to analysis of variance and Tukey test at a pre-set alpha of 0.05. RESULTS: A linear correlation (r=0.9884) between the supplied current and emitted IR power of the laser diode was found, showing no statistical power reduction with increased distances (collimated beam). For tooth tissues, the highest power transmissions for both light sources were observed using 1.0 mm enamel while the lowest values were found for 2.0 mm dentin and an association of 2.0 mm DEJ and 1.0 mm dentin. The only group where IR demonstrated significantly higher transmission when compared to BL was 1.0 mm enamel. For all resin composites and dental ceramics, increased thickness resulted in a reduction of IR power transmission (except for EverX Posterior fiber-reinforced composite and e.max HT ceramic). IR resulted in higher transmission through all resin composites, except for Tetric EvoCeram White. The highest BL transmission was observed for SDR Flow, at all thicknesses. Higher IR/BL ratios were observed for EverX Posterior, Herculite Ultra, and Lava Ultimate, while the lowest ratio was observed for Tetric EvoCeram White. Reduced translucency shades within the same material resulted in lower power ratio values, especially for BL transmission. Higher IR/BL ratios were observed for e.Max LT, VitaVM7 Base Dentin, and e.max CAD HT, while the lowest values were found for VitaVM7 Enamel and Paradigm C. CONCLUSION: IR power transmission through enamel was higher when compared to blue light, while no difference was observed for dentin. The power transmission of IR was higher than BL for resin composites, except for a high value and low chroma shade. Fiber-reinforced resin composite demonstrated the highest IR/BL power transmission ratio. A greater IR/BL ratio was observed for lower translucency ceramics when compared to high translucency.

Clinical and ex-vivo effect of LASERs on prevention of early-enamel caries: systematic review & meta-analyses.

To investigate the in vivo and in situ effect of different types of lasers in prevention of enamel demineralization in high caries risk cases (around orthodontic brackets, around restoration and in caries susceptible pits and fissures). PubMed was searched using the following keyword sequence; (Laser therapy OR laser irradiation OR laser application) AND (enamel caries prevention OR enamel demineralization OR enamel remineralization OR early enamel caries OR early-enamel caries OR enamel resistance OR enamel decalcification OR white spot lesions WSLs OR incipient lesion OR enamel decay OR enamel Dissolution OR enamel microhardness) AND (clinical trial OR Randomized clinical trial OR In situ study). The latest literature search was ended by "30 January 2023". PubMed was used as a primary data base for study selection. Scopus, EBSCO, and Google scholar are checked in our study after results of systematic search on PubMed. Only duplicates were found. Two meta-analyses were carried out. The first, clinical meta-analysis on incidence of white spot lesions (WSLs) following CO2 laser irradiation of enamel. The second meta-analysis on ex-vivo/in situ effect of CO2 laser on microhardness of enamel. In each meta-analysis three studies were included. Risk of bias was assessed. The search identified eight studies (four ex-vivo and four clinical trials). Regarding the clinical meta-analysis, the overall standardized mean difference was 0.21 [ 95% confidence interval (CI): 0.15-0.30, p < 0.00001]. This indicates that the incidence of new WSLs in patients who received low power CO2 laser treatment was highly significantly lower than placebo groups. The heterogeneity was considerable (I2 = 71%). In the second meta-analysis, the overall standardized mean difference was 49.55 [ 95% confidence interval (CI): 37.74, 61.37, p < 0.00001]. This indicates that microhardness of enamel receiving low power (0.4-5 W) CO2 laser irradiation is highly significantly lower than control untreated enamel. The heterogeneity was substantial (I2 = 48%). Within the limitations of this study, Low level laser therapy concept with CO2 laser seems to be effective in preventing enamel caries.Prospero registration number: CRD42023437379.

The effects of re-irradiation on the chemical and morphological properties of permanent teeth.

This study aimed to assess the in vitro effects of re-irradiation on enamel and dentin properties, simulating head and neck cancer radiotherapy retreatment. Forty-five human permanent molars were classified into five groups: non-irradiated; irradiated 60 Gy, and re-irradiated with doses of 30, 40, and 50 Gy. Raman spectroscopy, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) were employed for analysis. Raman spectroscopy assessed intensity, spectral area, and specific peaks comparatively. Statistical analysis involved Kolmogorov-Smirnov and One-Way ANOVA tests, with Tukey's post-test (significance level set at 5%). Significant changes in irradiated, non-irradiated, and re-irradiated enamel peaks were observed, including phosphate (438 nm), hydroxyapatite (582 nm), phosphate (960 nm), and carbonate (1070 nm) (p < 0.05). Re-irradiation affected the entire tooth (p > 0.05), leading to interprismatic region degradation, enamel prism destruction, and hydroxyapatite crystal damage. Dentin exhibited tubule obliteration, crack formation, and progressive collagen fiber fragmentation. EDX revealed increased oxygen percentage and decreased phosphorus and calcium post-reirradiation. It is concluded that chemical and morphological changes in irradiated permanent teeth were dose-dependent, exacerbated by re-irradiation, causing substantial damage in enamel and dentin.

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.

Efeito de doses terapêuticas de radioterapia sobre a morfologia, composição química e microdureza do esmalte e da dentina de dentes permanentes / Effect of therapeutic doses of radiotherapy on the morphology, chemical composition, and microhardness of enamel and dentin of permanent teeth

Introdução: Padrões atípicos de cárie dentária em pacientes submetidos a radioterapia para o tratamento do câncer de cabeça e pescoço podem estar associados aos efeitos da radiação sobre as glândulas salivares e tecidos dentários duros. Somados, podem contribuir para a cárie relacionada a radiação. Embora haja evidências sobre alterações sofridas pelos tecidos dentários duros após radioterapia, não há consenso na literatura sobre a gravidade destas alterações. Objetivo: avaliar a microestrutura, composição química e microdureza do esmalte e da dentina de dentes permanentes submetidos a doses terapêuticas de radioterapia in vitro. Material e métodos: estudo experimental, qualitativo, quantitativo e semiquantitativo. Foram obtidos fragmentos coronários de 24 terceiros molares. Constituiuse 2 grupos: NIR (controle): formado por fragmentos de dentes não irradiados e IVT (irradiado): formado por fragmentos de dentes irradiados in vitro (2 Gy/dia 5 vezes por semana, totalizando 70 Gy). Os fragmentos foram submetidos a análise da microdureza (n=24), Espectroscopia de Infravermelho com Transformada de Fourier (FTIR) (n=24), análise morfológica através de Microscopia Eletrônica de Varredura (MEV) (n=19) e análise de elementos químicos por Espectroscopia de Dispersão de Energia de Raio X (EDX) (n=19). As análises foram feitas antes e após a irradiação. Os dados foram testados para distribuição normal (teste de Shapiro-Wilk, α = 0,05) e igualdade de variâncias (teste de Levene, α = 0,05), seguido de testes estatísticos paramétricos. Para a comparação das variáveis quantitativas foi aplicado o teste T de Student. Um valor de p <0,05 (5%) foi considerado estatisticamente significativo. Resultados: em relação as propriedades mecânicas observamos redução significativa da microdureza do esmalte e dentina após irradiação (p<0,001). A análise da composição química por FTIR mostrou que no esmalte não houve alteração da razão matriz/mineral (M:M) no grupo irradiado (p<0,821), mas houve redução significativa do teor relativo de carbonato (RCC) após irradiação (p<0,039). Na dentina observamos redução significativa da razão matriz/mineral (M:M) e carbonato/mineral (C:M) no grupo irradiado (p<0,001), enquanto a razão amida I/amida III, não sofreu alteração significativa após irradiação (p<0,536). Na análise de EDX realizadas no esmalte, não observamos variação no conteúdo de cálcio e fósforo após radiação, mas a razão Ca/P mostrou-se significantemente mais elevada no grupo irradiado (p<0,001). Na dentina, não houve alteração do teor de cálcio e fósforo, assim como da razão Ca/P após irradiação (p<0,267). A análise morfológica através de MEV pós irradiação, mostrou que no esmalte a maioria das amostras apresentaram uma alteração das características microestruturais com a presença de microporosidades, perda de padrões regulares das áreas prismáticas e interprismáticas e presença de áreas amorfas. Na dentina observamos manutenção do padrão de dentina peritubular e intertubular, com a presença de túbulos dentinários desobliterados e com a rede de fibras colágenas mais evidente grupo irradiado. Conclusão: as doses terapêuticas de radioterapia provocaram redução da microdureza, alterações na microestrutura e composição química do esmalte e da dentina. Assim, inferimos que doses terapêuticas de radiação exercem um impacto negativo sobre as propriedades mecânicas, químicas e micro-morfológicas dos tecidos dentários duros aumentando a vulnerabilidade destes tecidos à cárie relacionada a radiação.

INTRODUCTION: Atypical patterns of dental caries in patients undergoing radiotherapy to treat head and neck cancer may be associated with the effects of radiation on salivary glands and dental hard tissues. Together, they can contribute to radiation-related caries. Although there is evidence of changes in hard dental tissues after radiotherapy, there is no agreement in the literature on the severity of these changes. PURPOSE: This study aims to evaluate the microstructure, chemical composition, and microhardness of enamel and dentin in permanent teeth subject to therapeutic doses of in vitro radiotherapy. MATERIAL AND METHODS: This is an experimental, qualitative, quantitative, and semi-quantitative study. Coronary fragments were obtained from 24 third molars. Two groups were created: NIR (control), including fragments of non-irradiated teeth, and IVT (irradiated), including fragments of in vitro irradiated teeth (2Gy/day five times a week, totaling 70Gy). The fragments underwent microhardness analysis (n =24), Fourier-transform Infrared Spectroscopy (FTIR) (n=24), morphological analysis by Scanning Electron Microscope (SEM) (n=19), and analysis of chemical elements by Energy-dispersive X-Ray Spectroscopy (EDX) (n=19). The analyses were performed before and after irradiation. Data were tested for normal distribution (ShapiroWilk test, α = 0.05) and equality of variances (Levene test, α = 0.05), followed by parametric statistical tests. The Student's T test was applied to compare the quantitative variables. A pvalue < 0.05 (5%) was considered statistically significant. RESULTS: Concerning the mechanical properties, we observed a significant reduction in enamel and dentin microhardness after irradiation (p<0.001). The analysis of the chemical composition by FTIR showed no change in the mineral/matrix ratio (M:M) in enamel in the irradiated group (p<0.821), but there was a significant reduction in the relative carbonate content (RCC) after irradiation (p<0.039). In dentin, we observed a significant reduction in the mineral/matrix ratio (M:M) and carbonate/mineral ratio (C:M) in the irradiated group (p<0.001). In contrast, the amide I/amide III ratio showed no significant change after irradiation (p<0.536). In the EDX analysis performed on enamel, we did not observe any calcium and phosphorus content variation after radiation. However, the Ca/P ratio was significantly higher in the irradiated group (p<0.001). In dentin, there was no change either in calcium and phosphorus contents or in the Ca/P ratio after irradiation (p<0.267). The morphological analysis through SEM after irradiation showed that there is a loss in the characteristics of the enamel surface of most fragments, with the presence of microporosities, loss of regular patterns of the prismatic and interprismatic areas, and the presence of amorphous areas. In dentin, we observed maintenance of the peritubular and intertubular dentin patterns, with the presence of unobliterated dentinal tubules and with the most evident network of collagen fibers in the irradiated group. CONCLUSION: Therapeutic doses of radiotherapy caused a reduction in microhardness and changes in the microstructure and chemical composition of enamel and dentin. Thus, we conclude that therapeutic doses of radiation have a negative impact on the mechanical, chemical, and micromorphological properties of hard dental tissues, increasing the vulnerability of these tissues to radiation-related caries

The effect of therapeutic radiation on dental enamel and dentin: A systematic review.

OBJECTIVES: The conventional radiotherapy protocol to treat head-and-neck cancer is usually followed by tooth-decay onset. Radiation impact on mineralized tooth structures is not well-understood. This systematic review aimed to collect the recorded effects of therapeutic radiation on tooth chemical, structural and mechanical properties, in relation with their means of investigation. DATA: Systematic search (January 01 2012 - September 30 2021) terms were "Radiotherapy", "Radiation effects", "Dental enamel", "Dentin", "Human" and "Radiotherapy" NOT "Laser". SOURCES: PubMed, DOSS and Embase databases were searched. STUDY SELECTION: Selected studies compared dental enamel, coronal and root dentin properties before and after in vitro or in vivo irradiation up to 80 Gy. RESULTS: The systematic search identified 353 different articles, with 28 satisfying inclusion criteria. Their reference lists provided two more. Twenty-two studies evaluated dental enamel evolution, nine assessed coronal dentin and eight concerned root dentin. Coronal and root dentin results indicate a major impact of the radiation on their organic matrix. Dental enamel's chemical properties are less modified. Enamel and root dentin's hardness are decreased by therapeutic radiation, but no consensus arises for coronal dentin. CONCLUSIONS: Our findings revealed some interesting information about enzymatic degradation mechanisms of dentin organic matrix and highlighted that dental hard-tissue characterization requires highly specific expertise in materials science. That scientific knowledge is necessary to design suitable protocols, adequately analyze the obtained data, and, thus, provide relevant conclusions. CLINICAL SIGNIFICANCE STATEMENT: Better knowledge and understanding of the mechanisms involved in the degradation of enamel and dentin would enable development of new preventive and therapeutic methods for improved medical care of patients undergoing radiotherapy.

Highly efficient optical fiber sensor for instantaneous measurement of elevated temperature in dental hard tissues irradiated with an Nd:YaG laser.

In this in vitro experiment, the effect of 1.064 µm pulsed laser on both enamel- and dentin-dental tissues has been investigated. A total of fifty-five dental hard tissue samples were exposed to Nd:YAG laser that possesses a pulse width of 9 ns and 850 mJ of total energy. An optical fiber sensor was put behind the samples to measure the temperature instantaneously. A novel, to the best of our knowledge, fiber sensor has been proposed and used to measure the heat generated in dental hard tissues instantaneously after the application of laser irradiation on the tissue surface. This optical sensor exhibits a fast response time of about 1 ms and high sensitivity with about 1.975 nm/°C. The findings of this study in decreasing the probability of pulpal necrosis structure while handling the tooth, whether for ablation, welding, or tooth resurfacing purposes, may establish standards for dentists and laser manufacturers (healthcare professionals) that should be followed.

Rehardening of Eroded Enamel with CPP-ACFP Paste and CO2 Laser Treatment.

BACKGROUND: Diet and lifestyle can destroy tooth structure due to the dissolution of enamel by acidic beverages. The present study evaluated the effect of CO2 laser irradiation and CPP-ACFP (casein phosphopeptide and amorphous calcium phosphate with fluoride) paste on the remineralization of enamel eroded by carbonated soft drinks. METHODS: In the present in vitro study, 46 human sound premolar teeth were sectioned mesiodistally to achieve 84 samples. Fourteen samples were assigned to the positive control group (G1), and the remaining samples were immersed in 500 mL of cola drink for 2 minutes, followed by rinsing with distilled water for 10 seconds. This procedure was carried out three times to create erosive lesions. Then, the 60 eroded samples were randomly assigned to five groups of G2 to G6 in terms of the treatment as follows: negative control (G2), CO2 laser irradiation (G3), CPP-ACFP paste (G4), CO2 laser irradiation followed by CPP-ACFP paste application (G5), and CPP-ACFP paste application followed by CO2 laser irradiation (G6). The mean surface microhardness of the enamel surface was evaluated and determined at three points for each sample. Data were analyzed with one-way ANOVA and Tukey HSD tests (α = 0.05). RESULTS: The highest and the lowest hardness values were recorded in the G1 (314 ± 12 kg/mm2) and G2 (213.7 ± 12 kg/mm2) groups, respectively. ANOVA revealed significant differences between the study groups (P < 0.001). Two-by-two comparisons showed significant differences between the G2 group and the other groups, indicating the efficacy of all the treatment modalities in tooth remineralization and rehardening procedures (P < 0.05). Only in group G6, the enamel microhardness was not significantly different from the G1 positive control group (P > 0.05). CONCLUSION: Considering the parameters used in the present study, CO2 laser irradiation or CPP-ACFP paste application alone increased eroded enamel's surface hardness; however, their sequential application was more effective in rehardening the eroded enamel's surface to near-normal levels.

Evaluation of bond strength of resin cement to Er:YAG laser-etched enamel and dentin after cementation of ceramic discs.

The purpose of this study was to investigate the shear bond strength (SBS) of ceramic discs luted to differently etched enamel and dentin surfaces. Occlusal surfaces of 64 carious-free human molars and vestibule surfaces of 64 first maxillary incisors were ground to get flat superficial dentin and flattened enamel respectively. After generating 4 groups according to the surface etching method (37% orthophosphoric acid, Er:YAG laser-contact handpiece/scanning handpiece (1 or 2 times of scanning)), ceramic discs were luted to the surfaces with adhesive resin cement (Variolink N, Vivadent Ets., Schaan/Liechtenstein). After etching and cementation, thermocycling of 5000 cycles (Sd Mechatronik Gmbh, Feldkirchen-Westerham, Germany) and SBS test (Servopulser EHFFD1; Shimadzu, Kyoto, Japan) were performed respectively. The surface morphologies of 2 specimens, etched enamel and dentin, prepared for each group were examined with SEM analysis. Failure modes were determined under a USB digital microscope. Data were analyzed with one-way analysis of variance (ANOVA) and Tukey HSD test (α = 0.05). SBS values in dentin surfaces showed statistically significant differences (p < 0.05) among tested groups. The highest SBS among dentin groups was determined in the group which had 2 times etching by Er:YAG laser (11.42 MPa) by a scanning handpiece. No statistical differences were observed in the other dentin or enamel groups. Laser etching seems to be a viable alternative to acid etching on both enamel and dentin surfaces while double etching of dentin with a scanning handpiece can improve the adhesion.

Dependence of Radiation-induced Signals on Geometry of Tooth Enamel Using a 1.15 GHz Electron Paramagnetic Resonance Spectrometer: Improvement of Dosimetric Accuracy.

ABSTRACT: We aim to improve the accuracy of electron paramagnetic resonance (EPR)-based in vivo tooth dosimetry using the relationship between tooth geometry and radiation-induced signals (RIS). A homebuilt EPR spectrometer at L-band frequency of 1.15 GHz originally designed for non-invasive and in vivo measurements of intact teeth was used to measure the RIS of extracted human teeth. Twenty human central incisors were scanned by microCT and irradiated by 220 kVp x-rays. The RISs of the samples were measured by the EPR spectrometer as well as simulated by using the finite element analysis of the electromagnetic field. A linear relationship between simulated RISs and tooth geometric dimensions, such as enamel area, enamel volume, and labial enamel volume, was confirmed. The dose sensitivity was quantified as a slope of the calibration curve (i.e., RIS vs. dose) for each tooth sample. The linear regression of these dose sensitivities was established for each of three tooth geometric dimensions. Based on these findings, a method for the geometry correction was developed by use of expected dose sensitivity of a certain tooth for one of the tooth geometric dimensions. Using upper incisors, the mean absolute deviation (MAD) without correction was 1.48 Gy from an estimated dose of 10 Gy; however, the MAD corrected by enamel area, volume, and labial volume was reduced to 1.04 Gy, 0.77 Gy, and 0.83 Gy, respectively. In general, the method corrected by enamel volume showed the best accuracy in this study. This homebuilt EPR spectrometer for the purpose of non-invasive and in vivo tooth dosimetry was successfully tested for achieving measurements in situ. We demonstrated that the developed correction method could reduce dosimetric uncertainties resulting from the variations in tooth geometric dimensions.

Effects of fractionation and ionizing radiation dose on the chemical composition and microhardness of enamel.

OBJECTIVE: To evaluate the chemical and mechanical properties of enamel submitted to different in vitro radiation protocols. DESIGN: Third molars were divided into seven groups (n = 8): non-irradiated (NI); a single dose of 30 Gy (SD30), 50 Gy (SD50), or 70 Gy (SD70) of radiation; or fractional radiation doses of up to 30 Gy (FD30), 50 Gy (FD50), or 70 Gy (FD70). Hemisections were analysed by Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS) and Knoop microhardness (KHN) test. One-way ANOVA followed by Bonferroni's post-hoc test compared the test groups with the NI. Two-way ANOVA was performed for the fractionation and radiation dose, followed by Bonferroni's test (α = 0.05). RESULTS: FTIR revealed differences for the amide I band between the NI and FD50 and NI and FD70 groups (p < 0.001). For the organic matrix/mineral ratio, the FD70 group presented a lower ratio compared to NI (p = 0.009). Excluding the NI group, there were differences between the FD30 and FD50 (p = 0.045) and the FD30 and FD70 groups (p < 0.001). For EDS, there were differences for Ca (p = 0.011) and Ca/P (p < 0.001), with the FD70 group presenting lower values compared to NI (p = 0.015; p < 0.001). For KHN, the FD70 group presented lower values than the NI (p = 0.002). Two-way ANOVA showed difference for the dose (p < 0.001), with the 70 Gy group presenting a lower KHN value within the fractionated groups. CONCLUSION: Fractional doses 70 Gy irradiation caused chemical and mechanical changes to enamel. Radiation applied in single or fractional doses produced different effects to enamel.