Radiotherapy in the head and neck region influences the chemical and mechanical properties of intraradicular dentin.

OBJECTIVES: To investigate the chemical and mechanical properties of intraradicular dentin submitted to radiotherapy. MATERIALS AND METHODS: Sixteen mandibular incisors were divided into two groups (n = 8): non-irradiated and irradiated. The irradiated teeth were obtained from head and neck radiotherapy patients, with a total dose ranging from 70.2 to 72 Gy divided into 1.8 Gy daily. After sample preparation, intraradicular dentin slices of each root third were evaluated by Raman spectroscopy, energy dispersive spectroscopy and Knoop microhardness test. Data were analyzed by Two-way ANOVA and Tukey's test (α = 0.05). RESULTS: In Raman spectroscopy, carbonate and amide III showed a significant difference for irradiation and third (carbonate p = 0.021 and p < 0.001; amide III p < 0.001 and p = 0.001, respectively). For amide I, there was a significant difference for third (p < 0.001). For carbonate/mineral ratio, there was a significant difference for irradiation (p = 0.0016) and third (p < 0.001), with the irradiated middle third showing the lowest values. For amide I/amide III ratio, there was a significant difference for irradiation (p = 0.005) in the cervical third. In energy dispersive spectroscopy, carbon (p = 0.004; p = 0.020), phosphorus (p < 0.001; p = 0.009) and calcium (p = 0.008; p = 0.007) showed differences for irradiation and third, with the irradiated groups presenting lower values in cervical and middle thirds. For calcium/phosphorus ratio, there was a significant difference for irradiation (p < 0.001) in cervical and middle thirds. Regarding microhardness, there was a significant difference for irradiation (p < 0.001), with all irradiated groups showing lower microhardness values. CONCLUSIONS: The radiotherapy altered the chemical and mechanical properties of intraradicular dentin, mainly in the cervical and middle root thirds.

Does radiotherapy treatment alter the pulp condition in patients with head and neck cancer? A systematic review.

The main purpose of this study was to answer the question: "Can radiotherapy cause changes in the dental pulp condition of patients treated with irradiation in the head and neck region?" Clinical observational studies in adults with head and neck cancer undergoing treatment with ionizing radiation, longitudinal or cross-sectional follow-up to measure oxygen saturation (SpO2), and/or pulp sensitivity test to cold stimulation, were considered eligible. A systematic literature search was performed in six different databases, including the gray literature, and in article references. Two independent evaluators selected the studies, extracted the data, recorded the data on electronic spreadsheets, and then evaluated the methodological quality using the Checklist for Quasi-Experimental Studies tool devised by JBI. The data were assessed qualitatively using the Synthesis Without Metanalysis (SWiM) guidelines. After removing the duplicate articles, carefully analyzing the titles and abstracts, and reading the papers in full, seven studies were included. Four of the studies evaluated applied the cold sensitivity test, two associated pulse oximetry and cold sensitivity, and only one used just pulse oximetry. Evaluation using the cold sensitivity test and pulse oximetry in the initial periods before radiotherapy showed a decrease in the sensitive response and in SpO2 levels during a maximum period of 1 year. However, analyses thereafter indicated a normal response in both tests from 5 to 6 years after the end of radiotherapy treatment. Radiotherapy causes changes in pulp behavior patterns in the short term; however, recovery and return to average values occurs after long periods.

Oral care and the use of fluoride in the prevention of radiation-related caries: A scoping review.

OBJECTIVE: This scoping review aimed to map the literature on oral hygiene protocols and fluoride use in patients undergoing radiotherapy. STUDY DESIGN: A comprehensive search was performed in 10 databases, including part of the "gray literature." Clinical trials and observational studies that used radiotherapy in the head and neck region and evaluated the occurrence of radiation-related caries (RRC) were included. RESULTS: Twenty-one studies were included in the review. The studies generally presented different methods of oral care and fluoride use. Several studies have shown promising results for oral care instructions in preventing RRC. The main strategies found in the articles were oral hygiene instructions, professional teeth cleaning, recommendations for the use of fluoride toothpaste, and monthly follow-ups. Fluoride gel was the most commonly used fluoride product (72%). Its main recommendation for use was at least 5 min at night daily. Most of these studies (60%) used custom-made trays. Other fluoride methods were fluoride varnish, mouthrinses, and high-fluoride-containing toothpaste. CONCLUSION: Oral care, such as hygiene instructions with regular dental follow-up and daily fluoride, seem to be promising strategies for preventing RRC. Periodically monitoring these patients is one of the most important strategies.

Does irradiation of the tooth structure interfere with oxygen saturation measured by pulse oximetry?-An ex vivo laboratorial study.

The effect of tooth structure subjected to ionising radiation on oxygen saturation levels (SpO2 ) measured by pulse oximetry was investigated. Fifty-four extracted human third molars were sectioned mesiodistally. Pulse oximeter diodes were placed in prefabricated silicone moulds, secured on a vise with tooth surfaces placed between the diodes and the participant's finger, and SpO2 levels were measured. After that, the tooth surfaces were subjected to ionising radiation in fractionated doses of up to 70 Gy, and SpO2 was measured according to the protocol described. The Kolmogorov-Smirnov test was used for the analysis of normality of the quantitative variables, and Student's t-test compared mean SpO2 levels before and after irradiation. Mean SpO2 after irradiation was 94.6 ± 0.9%, without a statistically significant difference from SpO2 before irradiation, which was 94.7 ± 0.6%. Irradiation of the tooth structure did not interfere with SpO2 levels measured by pulse oximetry.

Does radiotherapy treatment alter the pulp condition in patients with head and neck cancer? A systematic review

Abstract The main purpose of this study was to answer the question: "Can radiotherapy cause changes in the dental pulp condition of patients treated with irradiation in the head and neck region?" Clinical observational studies in adults with head and neck cancer undergoing treatment with ionizing radiation, longitudinal or cross-sectional follow-up to measure oxygen saturation (SpO2), and/or pulp sensitivity test to cold stimulation, were considered eligible. A systematic literature search was performed in six different databases, including the gray literature, and in article references. Two independent evaluators selected the studies, extracted the data, recorded the data on electronic spreadsheets, and then evaluated the methodological quality using the Checklist for Quasi-Experimental Studies tool devised by JBI. The data were assessed qualitatively using the Synthesis Without Metanalysis (SWiM) guidelines. After removing the duplicate articles, carefully analyzing the titles and abstracts, and reading the papers in full, seven studies were included. Four of the studies evaluated applied the cold sensitivity test, two associated pulse oximetry and cold sensitivity, and only one used just pulse oximetry. Evaluation using the cold sensitivity test and pulse oximetry in the initial periods before radiotherapy showed a decrease in the sensitive response and in SpO2 levels during a maximum period of 1 year. However, analyses thereafter indicated a normal response in both tests from 5 to 6 years after the end of radiotherapy treatment. Radiotherapy causes changes in pulp behavior patterns in the short term; however, recovery and return to average values occurs after long periods.

In vitro evaluation of the antibacterial and cytotoxic activities of the Euclea natalensis crude extract and fractions against oral infection agents.

OBJECTIVE: This study aimed (i) to evaluate the antibacterial and cytotoxic activities of the crude extract and fractions obtained from Euclea natalensis A.D.C. roots against bacteria that cause periodontal disease and caries and (ii) to identify the isolated compounds. DESIGN: The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of the extract and fractions were determined by the microplate dilution assay. The cytotoxicity of the extract and fractions was evaluated by using the XTT colorimetric assay and normal human fibroblast cells (GM07492A, lung fibroblasts). The compounds present in the most promising fraction were determined by qualitative analysis through liquid chromatography coupled to mass spectrometry (HPLC-MS-ESI). RESULTS: The MIC results ranged from 25 to > 400 µg/mL for the extract and from 1.56 to > 400 µg/mL for the fractions. To evaluate cytotoxicity, the tested concentrations of the extract and fractions ranged from 19.5 to 2500 µg/mL; IC50 values between 625 and 1250 µg/mL were obtained. Analysis of the main bioactive fraction by HPLC-MS-ESI identified phenolic acids, coumarins, naphthoquinones, lignans, and fatty acids. CONCLUSIONS: The E. natalensis root extract and fractions displayed good antibacterial activity against periodontal pathogenic and cariogenic bacteria. The antibacterial activity may be due to compounds present in the extract and fractions, which also showed low cytotoxicity to normal human cells. These data are relevant and encourage further research into this plant species, which may contribute to the discovery of new herbal medicines that will help to mitigate the problems caused by oral pathogenic bacteria.

Effect of an enamel matrix derivative (Emdogain) on the microhardness and chemical composition of human root dentin: an in vitro study.

The advantage of using an Enamel matrix derivative EMD Emdogain as an intracanal medication could be a manner to strength the tooth structure, improving the physical and chemical properties of dentin. We tested, in vitro, the effect of Emdogain on the surface microhardness and chemical composition of root dentin. Ten human teeth were used to produce dentin specimens originated from the canal walls (n = 30) that remained in contact to Emdogain gel for 90 days. Baseline and 90-days after Emdogain treatment measurements were performed using Fourier Transform Infrared Spectroscopy (ATR/FTIR), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) and Knoop indenters. The use of EMD (Emdogain) for 90 days in contact with human root canal dentin specimens did not alter the microhardness and morphology of dentin. The elemental structure of dentin was altered because there was a reduction in carbonate content.

Chemical analysis of irradiated root dentin and its interaction with resin cements.

OBJECTIVES: To investigate the chemical changes in root dentin submitted to ionizing radiation and how it affects the interaction with resin cements. MATERIALS AND METHODS: Forty human premolars were randomly divided into two groups (n = 20): non-irradiated and irradiated. They were randomly subdivided according to the type of resin cement (n = 10): conventional (RelyX ARC, 3 M ESPE) or self-adhesive (RelyX U200, 3 M ESPE). After cementation of the fiberglass posts, the roots were sectioned to be analyzed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and confocal laser scanning microscopy (CLSM). The data obtained from FTIR and Raman were analyzed using two-way ANOVA followed Tukey's test (α = 0.05). For CLSM, a descriptive analysis was performed. RESULTS: In the FTIR, there was a significant difference between the non-irradiated and irradiated groups for phosphate (p = 0.011), carbonate (p < 0.001), amide III (p = 0.038), and carbonate/mineral ratio (p < 0.001). Regarding the root third, there was a difference for amide I (p = 0.002), mineral/matrix ratio (p = 0.001), and amide I/CH2 (p = 0.026) between the cervical and the others. Raman spectroscopy revealed no difference between groups for 961/1458 cm-1 in the diffusion zone. CLSM showed a different interaction pattern for the two cements with the irradiated dentin from the cervical third. CONCLUSIONS: Ionizing radiation altered the chemical composition of root dentin, especially in the cervical third. The resin cements showed less interaction with the irradiated root dentin. CLINICAL RELEVANCE: As radiotherapy alters the chemical composition of root dentin, the interaction of resin cement with dentin can compromise the success of rehabilitation with fiberglass posts.

Effect of ionizing radiation and cariogenic biofilm challenge on root-dentin caries.

OBJECTIVES: To evaluate the effect of ionizing radiation and cariogenic biofilm challenge using two continuous flow models, normal and reduced salivary flow, on the development of initial root-dentin caries lesions. MATERIALS AND METHODS: Microcosm biofilms were grown under two salivary flow rates (0.06 and 0.03 mL min-1) and exposed to 5% sucrose (3 × daily, 0.25 mL min-1, 6 min) dripped over non-irradiated and irradiated root-dentin blocks for up to 7 days. The vibration modes of root dentin, matrix/mineral (M/M), and carbonate/mineral (C/M) ratios were evaluated by FTIR. The mineral density was assessed by micro-CT. RESULTS: With normal salivary flow, FTIR revealed an increase in the organic matrix (amide III) and a decrease in the mineral phase (ν4, ν2 PO43-, AII + ν2 CO32-, C/M) in caries lesions. Irradiated dentin exhibited a reduction in the mineral phase (ν1, ν3 PO43-, ν2 CO32-, C/M). Differences in mineral densities were not significant. With reduced salivary flow, FTIR also revealed increased organic matrix (amide III) for irradiated caries lesions and decrease in mineral phase (v4, v2 PO43-, v2 CO32-, and C/M) in caries lesions. ν1, ν3 PO43- precipitated on the surface of irradiated dentin and a lower mineral density was observed. CONCLUSIONS: Initial caries lesions differed between non-irradiated and irradiated dentin and between normal and reduced salivary flow rates. Significant mineral loss with exposure of the organic matrix and low mineral density were observed for irradiated dentin with a reduced salivary flow rate. CLINICAL RELEVANCE: Ionizing radiation associated with a reduced salivary flow rate enhanced the progression of root-dentin caries.

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.

Head and neck cancer therapy-related oral manifestation management in the COVID-19 pandemic: a critical review.

With the onset of the new coronavirus disease (COVID-19) pandemic, the dental treatment of patients at risk of infection has become quite challenging. In view of this, patients with head and neck cancer may present with oral complications due to anticancer therapy, making dental assistance necessary. Thus, the objective of the study was to review the literature and critically discuss important concerns about the treatment of patients with head and neck cancer during the COVID-19 pandemic. Because dental professionals are in close contact with the main viral transmission routes, this study presents recommendations for management and protection during clinical dental care. The main characteristics and transmission routes of COVID-19 are also discussed. Dental professionals should control pain and the side effects of antineoplastic treatment and use preventive measures for infection control. During this pandemic, patients with head and neck cancer should not undergo elective procedures, even if they do not have symptoms or a history of COVID-19; therefore, in asymptomatic or painless cases, only preventive actions are recommended. In symptomatic or painful cases, precautions for safe interventional treatments must be implemented by following the hygiene measures recommended by health agencies and using personal protective equipment. During health crises, new protocols emerge for cancer treatment, and professionals must act with greater attention toward biosafety and updated knowledge. It is important to offer adequate individualized treatment based on the recommendations of preventative and interventional treatments so that patients can face this difficult period with optimized quality of life.

Head and neck cancer therapy-related oral manifestation management in the COVID-19 pandemic: a critical review

Abstract With the onset of the new coronavirus disease (COVID-19) pandemic, the dental treatment of patients at risk of infection has become quite challenging. In view of this, patients with head and neck cancer may present with oral complications due to anticancer therapy, making dental assistance necessary. Thus, the objective of the study was to review the literature and critically discuss important concerns about the treatment of patients with head and neck cancer during the COVID-19 pandemic. Because dental professionals are in close contact with the main viral transmission routes, this study presents recommendations for management and protection during clinical dental care. The main characteristics and transmission routes of COVID-19 are also discussed. Dental professionals should control pain and the side effects of antineoplastic treatment and use preventive measures for infection control. During this pandemic, patients with head and neck cancer should not undergo elective procedures, even if they do not have symptoms or a history of COVID-19; therefore, in asymptomatic or painless cases, only preventive actions are recommended. In symptomatic or painful cases, precautions for safe interventional treatments must be implemented by following the hygiene measures recommended by health agencies and using personal protective equipment. During health crises, new protocols emerge for cancer treatment, and professionals must act with greater attention toward biosafety and updated knowledge. It is important to offer adequate individualized treatment based on the recommendations of preventative and interventional treatments so that patients can face this difficult period with optimized quality of life.

Chemical analysis of in vivo-irradiated dentine of head and neck cancer patients by ATR-FTIR and Raman spectroscopy.

OBJECTIVES: To evaluate the effect of in vivo radiotherapy on the chemical properties of human dentine by Fourier-transform infrared spectroscopy (FTIR) and Raman analysis. MATERIALS AND METHODS: Chemical composition was evaluated comparing control and irradiated group (n = 8). Irradiated teeth were obtained from radiotherapy patients subjected to fractionated X-ray radiation of 1.8 Gy daily totaling 72 Gy. The teeth were sectioned according to the type of dentine (crown or root dentine), obtaining 3-mm dentine cervical slices. The analyzed parameters by FTIR and Raman spectroscopies were mineral/matrix ratio (M:M), carbonate/mineral ratio (C:M), amide I/amide III ratio, and amide I/CH2 ratio. Raman also calculated the phosphate and carbonate crystallinity. RESULTS: FTIR revealed that M:M had a decrease in both factors (p = 0.008; p = 0.043, respectively) and root dentine showed a lower C:M in the irradiated group (p = 0.003). Raman revealed a higher phosphate crystallinity and a lower carbonate crystallinity in crown dentine of irradiated group (p = 0.021; p = 0.039). For amide I/amide III, the irradiated showed a lower ratio when compared to the control group (FTIR p = 0.002; Raman p = 0.017). For amide I/CH2, the root dentine showed a higher ratio than the crown dentine in both methods (p < 0.001). CONCLUSIONS: Radiotherapy altered the chemical composition of human dentine. The exchange of phosphate-carbonate ions in the hydroxyapatite and higher concentration of organic components was found after radiotherapy. CLINICAL RELEVANCE: The increased risk of radiation-related caries in patients undergoing head and neck radiotherapy is due not only to salivary, dietary, and microbiological changes but also to changes in tooth chemical composition.

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.

Impact of Implant Number on Mandibular Implant-Supported Profile Prostheses: A Systematic Review.

PURPOSE: To assess studies on edentulous patients rehabilitated using mandibular implant-supported profile prostheses and analyze the impact of different numbers of implants used on the implant survival rate, peri-implant bone loss, and prosthesis survival rate. MATERIALS AND METHODS: This systematic review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) statement and was registered on PROSPERO. The PubMed/MEDLINE database was searched for articles published before July 18, 2016. The study attempted to answer the following PICO question: In edentulous patients, do full-arch fixed prostheses supported by three implants have a satisfactory implant survival rate, marginal bone loss, and prosthesis survival rate compared with those supported by different numbers of implants? Evidence levels of each study were evaluated using the Oxford Centre for Evidence-Based Medicine (OCEBM); methodologic quality was evaluated using the Methodological Index for Nonrandomized Studies (MINORS) scale and Cochrane Risk of Bias Tool. Descriptive statistics were performed when applicable. Implant survival curves were constructed using the Kaplan-Meier method, and marginal bone loss was analyzed using the Kruskal-Wallis, Dunn's, and Mann-Whitney tests. RESULTS: This analysis included 21 published studies of 4,712 implants and 1,245 mandibular implant-supported profile prostheses in 1,245 patients. The patients were grouped by the number of implants used: group 1 (three implants) had an implant survival rate of 90%; group 2 (four implants) had a rate of 95%; and group 3 (five implants) had the lowest rate, 74%. Groups 1 and 3 had the lowest first-year bone losses (median: 0.73 and 0.70 mm, respectively), and were significantly different from group 2 (median: 1.31 mm; P < .001). CONCLUSION: Despite the limitations in the studies with low levels of evidence and the methodology of MeSH term research, it was concluded that the implant survival rate and first-year bone loss of full-arch fixed prostheses supported by three implants were satisfactory. However, the prosthesis survival rate was inferior to that of other groups, which suggests a longer follow-up of these rehabilitations.

Influence of radiotherapy on the dentin properties and bond strength.

OBJECTIVES: The objective of this study was to evaluate the biomechanical properties of dentin and the microtensile bond strength (µTBS) performed before or after radiotherapy (RT). MATERIAL AND METHODS: Dentin chemical composition (infrared spectroscopy-FTIR), SEM images, and mechanical properties (Vickers microhardness-VHN and elastic modulus-E) were evaluated comparing no irradiated and irradiate dentin (n = 5). RT was defined by application of 72 Gy (1.8 Gy daily, 5 days per week, during 8 weeks) with sample immersed in distilled water. µTBS evaluated three groups (n = 10): NI-no irradiated; IB-irradiation before restoration; and IA-irradiation after restoration. Resin-dentin sticks (1.0 mm2) were obtained and submitted to µTBS. Analysis of the bonding interface was made by confocal microscopy. RESULTS: After RT, percentage ratio of FTIR analysis showed increased absorption for all bands. SEM image showed a disorganized dentin structure. Two-way ANOVA showed increased VHN (p = 0.005) and decreased E (p < 0.001). For µTBS, one-way ANOVA and Duncan test showed significant differences among groups (p = 0.018). IB group presented the lowest bond strength values. CONCLUSIONS: RT alters the absorption bands and SEM images showed a disorganization of the dentin structure. Mechanical properties were changed with increased VHN and decreased E. µTBS was affected by the radiotherapy and restoration period (before or after). CLINICAL RELEVANCE: RT causes changes that contribute to increased risk of tooth decay. Restorative treatments can be performed using adhesive procedures, but it is preferable to be performed before of the irradiation protocol, to guarantee better adhesive properties to restoration.

Influence of Screw Surface Treatment on Retention of Implant-Supported Fixed Partial Dentures.

The aim of this study was to assess the effect of a diamond-like carbon (DLC) coating on the removal torque of prefabricated implant screws after cyclic loading. Four groups with two crowns supported by two implants (n = 5) were obtained according to splinted and nonsplinted prosthesis, using titanium or DLC screws (splinted crowns with titanium screw [STi], splinted crowns with DLC screw [SC], nonsplinted crowns and titanium screw [NSTi], and nonsplinted crowns and DLC screw [NSC]). The prosthetic screws were tightened at 32 Ncm and retightened, and the specimens were submitted to 106 mechanical cycles (4 Hz/98 N). After cyclic loading, loosening torque was evaluated, and the final measurements were performed. Data were analyzed by two-way analysis of variance and Tukey's test (α = .005). There was statistically significance in the interaction of screw × splinting (P = .003). For the group that used titanium screws, NSTi showed smaller removal torque compared with STi. It was concluded that the use of the DLC coating screws in nonsplinted prosthesis maintain the torque after cyclic loading.

Influence of Resin Cements on Color Stability of Different Ceramic Systems.

The purpose of this study was to evaluate color stability of two dental ceramics cemented with two resin cements, assessing the color difference (ΔE00) by the measurement of L*, a*, b*, c* and h* of transmittance. The combination of two ceramic system (feldspathic and lithium disilicate) and two resin cements - color A3 (RelyX ARC and Variolink II) resulted in 4 groups (n=5). Ten disks-shaped specimens were fabricated for each ceramic system (10x1.5 mm), etched with hydrofluoric acid (10%) and silanized prior to cementation. The color analysis was performed 24 h after cementation of the samples and after 6 months of storage in relative humidity by means of spectrophotometry. The ΔE00 values were analyzed statistically by two-way ANOVA followed by the Tukey test (p<0.05). One-way ANOVA were calculated for the means of individual color coordinates (L*, a*, b*, c* and h*). Two-way ANOVA showed that only the ceramic factor was significant (p=0.003), but there was no difference for the cement factor (p=0.275) nor for the ceramic/cement interaction (p=0.161). The feldspathic ceramic showed the highest values of ΔE00. Variations in L*, a*, b*, c* and h* were more significant for feldspathic ceramic. In conclusion, storage alters similarly the optical properties of the resin cements and feldspathic porcelain was more susceptible to cement color change after aging.

Influence of Resin Cements on Color Stability of Different Ceramic Systems

Abstract The purpose of this study was to evaluate color stability of two dental ceramics cemented with two resin cements, assessing the color difference (ΔE00) by the measurement of L*, a*, b*, c* and h* of transmittance. The combination of two ceramic system (feldspathic and lithium disilicate) and two resin cements - color A3 (RelyX ARC and Variolink II) resulted in 4 groups (n=5). Ten disks-shaped specimens were fabricated for each ceramic system (10x1.5 mm), etched with hydrofluoric acid (10%) and silanized prior to cementation. The color analysis was performed 24 h after cementation of the samples and after 6 months of storage in relative humidity by means of spectrophotometry. The ΔE00 values were analyzed statistically by two-way ANOVA followed by the Tukey test (p<0.05). One-way ANOVA were calculated for the means of individual color coordinates (L*, a*, b*, c* and h*). Two-way ANOVA showed that only the ceramic factor was significant (p=0.003), but there was no difference for the cement factor (p=0.275) nor for the ceramic/cement interaction (p=0.161). The feldspathic ceramic showed the highest values of ΔE00. Variations in L*, a*, b*, c* and h* were more significant for feldspathic ceramic. In conclusion, storage alters similarly the optical properties of the resin cements and feldspathic porcelain was more susceptible to cement color change after aging.

Resumo O objetivo deste estudo foi avaliar a estabilidade da cor de dois sistemas cerâmicos em função de dois cimentos resinosos, avaliando a diferença de cor (ΔE00) pela mensuração de L*, a*, b*, c* e h* de transmitância. Formou-se 4 grupos (n=5) de acordo com as duas cerâmicas (reforçada com dissilicato de lítio e feldspática) e dois cimentos resinosos - cor A3 (RelyX ARC e Variolink II). Dez discos foram confeccionados para cada sistema cerâmico (10 x 1,5 mm), tratados com ácido fluorídrico (10%) e silanizados antes da cimentação. A análise de cor foi feita 24 h após a cimentação das amostras e após 6 meses de armazenamento em umidade relativa por meio de espectrofotometria. ANOVA a dois fatores foi utilizada para análise dos dados de ΔE00 seguido pelo teste de Tukey (p<0,05). ANOVA a um fator foi realizada para avaliação das coordenadas individuais de cor (L*, a*, b*, c* e h*). Apenas o fator cerâmica foi significativo (p=0,003),mas não houve diferença para o fator imento (p=0,275) nem para a interação entre cerâmica e cimento (p=0,161). A cerâmica feldspática apresentou os maiores valores de ΔE00. Variações de L*, a*, b*, c* e h* foram mais significativas para cerâmica feldspática. Concluiu-se que o armazenamento alterou as propriedades ópticas dos cimentos resinosos de forma semelhante e a porcelana feldspática foi mais susceptível à mudança de cor do cimento após o envelhecimento.

Degree of conversion and bond strength of resin-cements to feldspathic ceramic using different curing modes.

OBJECTIVE: The aim of this study was to assess the performance of resin cements when different curing modes are used, by evaluating the degree of conversion and bond strength to a ceramic substrate. MATERIAL AND METHODS: Three resin cements were evaluated, two dual-cured (Variolink II and RelyX ARC) and one light-cured (Variolink Veneer). The dual-cured resin cements were tested by using the dual activation mode (base and catalyst) and light-activation mode (base paste only). For degree of conversion (DC) (n=5), a 1.0 mm thick feldspathic ceramic disc was placed over the resin cement specimens and the set was light activated with a QTH unit. After 24 h storage, the DC was measured with Fourier transform infrared spectroscopy (FTIR). For microshear bond strength testing, five feldspathic ceramic discs were submitted to surface treatment, and three cylindrical resin cement specimens were bonded to each ceramic surface according to the experimental groups. After 24 h, microshear bond testing was performed at 0.5 mm/min crosshead speed until the failure. Data were submitted to one-way ANOVA followed by Tukey test (p<0.05). Scanning electron microscopy (SEM) was used for classifying the failure modes. RESULTS: Higher DC and bond strength values were shown by the resin cements cured by using the dual activation mode. The Variolink II group presented higher DC and bond strength values when using light-activation only when compared with the Variolink Veneer group. CONCLUSION: The base paste of dual-cured resin cements in light-activation mode can be used for bonding translucent ceramic restorations of up to or less than 1.0 mm thick.