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Marcomini N, Albaricci MCDC, Costa JLDSG, Besegato JF, Godoy EF, Dantas AAR, Kuga MC. Effects of alpha-tocopherol antioxidant on fracture strength and adhesion of endodontically treated teeth restored after dental bleaching. Eur J Oral Sci 2024; 132:e12965. [PMID: 38115770 DOI: 10.1111/eos.12965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 11/14/2023] [Indexed: 12/21/2023]
Abstract
This study evaluated the effect of different concentrations of alpha-tocopherol in gel form on fracture strength, hybrid layer formation, and microtensile bond strength of endodontically treated teeth bleached with 40% hydrogen peroxide (H2 O2 ). Sixty bovine incisors were randomized into one of six groups (n = 10 incisors per group) defined by the interventions carried out after endodontic treatment. In the control group, no additional intervention was carried out, while all teeth in the five intervention groups were bleached with 40% H2 O2 and subsequently treated with alpha-tocopherol at concentrations of 15% (15AT), 20% (20AT), or 25% (25AT), with 10% sodium ascorbate (10SA), or with nothing (40HP). Fracture strength was evaluated in a mechanical testing machine, hybrid layer formation was assessed using scanning electron microscopy, and bond strength was determined using microtensile bond-strength testing. Data were analyzed using Kruskal-Wallis and Dunn's tests. No statistically significant difference regarding fracture strength was observed among groups. Hybrid layer formation was greater in the 15AT group than in groups 40HP and 10SA. Teeth in groups 15AT, 20AT, and 25AT demonstrated higher bond strength than teeth in groups 40HP and 10SA. Alpha-tocopherol, preferably at 15%, effectively reverses the deleterious effects, of bleaching, on hybrid layer formation and bond strength to dentin.
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Affiliation(s)
- Natália Marcomini
- Department of Restorative Dentistry, School of Dentistry, Araraquara, São Paulo State University - UNESP, Araraquara, São Paulo, Brazil
| | - Maria Carolina da Costa Albaricci
- Department of Restorative Dentistry, School of Dentistry, Araraquara, São Paulo State University - UNESP, Araraquara, São Paulo, Brazil
| | - Joatan Lucas de Sousa Gomes Costa
- Department of Restorative Dentistry, School of Dentistry, Araraquara, São Paulo State University - UNESP, Araraquara, São Paulo, Brazil
- Department of Restorative Dentistry, School of Dentistry, Federal University of Minas Gerais - UFMG, Belo Horizonte, Minas Gerais, Brazil
| | - João Felipe Besegato
- School of Dentistry, Federal University of Mato Grosso do Sul - UFMS, Campo Grande, Mato Grosso do Sul, Brazil
| | | | - Andréa Abi Rached Dantas
- Department of Restorative Dentistry, School of Dentistry, Araraquara, São Paulo State University - UNESP, Araraquara, São Paulo, Brazil
| | - Milton Carlos Kuga
- Department of Restorative Dentistry, School of Dentistry, Araraquara, São Paulo State University - UNESP, Araraquara, São Paulo, Brazil
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Fitzgerald JM, Souza GD, Tam L. Effect of Tooth Bleach on Dentin Fatigue Resistance in Situ. Oper Dent 2023; 48:638-647. [PMID: 37881145 DOI: 10.2341/22-093-c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/10/2023] [Indexed: 10/27/2023]
Abstract
BACKGROUND Negative effects of bleaching on dentin have previously been reported in vitro. OBJECTIVE The purpose of this study was to determine the effect of carbamide peroxide bleaching on dentin fatigue resistance using a clinically relevant in situ model. METHODS AND MATERIALS Following research ethics board approval, 60 human teeth requiring extraction were collected. Sterilized human dentin specimens were cut (1.2x1.2x10 mm) and secured into customized bleaching trays to be used by study participants. Participants were randomly assigned to either bleach (10% carbamide peroxide, n=23) or control (gel without bleach, n=26) treatment groups. Treatment was applied to the bleaching trays and worn overnight by participants for 14 days. After treatment completion, dentin specimens were removed from the bleaching trays and subjected to fatigue testing (10 N, 3 mm/s, 2x105 cycles) while submerged in artificial saliva. Kaplan-Meier survival analysis was conducted to compare the number of cycles to failure during fatigue testing in both groups. A log rank test was run to determine if there were differences in the survival distribution between the two groups (α<0.05). RESULTS The median number of cycles to failure was 352 ± 202 and 760 ± 644 for the bleach and control groups, respectively. The survival distributions for the two groups were significantly different (p=0.020). Dentin fatigue resistance was significantly lower in the bleach group compared to the control. CONCLUSIONS Direct bleaching of human dentin using an at-home tray bleaching protocol in situ reduced dentin fatigue resistance. This has implications for tooth fracture risk and longevity.
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Affiliation(s)
- J M Fitzgerald
- *Jacob M Fitzgerald, DDS, MSc, University of Toronto Faculty of Dentistry, Toronto, Ontario, Canada
| | - G De Souza
- Grace De Souza DDS, MSc, PhD, FADM, University of Louisville, Louisville, KY, USA
| | - L Tam
- Laura Tam, DDS, MSc, University of Toronto, Toronto, Ontario, Canada
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Ubaldini ALM, Pascotto RC, Sato F, Soares VO, Zanotto ED, Baesso ML. Effects of Bioactive Agents on Dentin Mineralization Kinetics After Dentin Bleaching. Oper Dent 2020; 45:286-296. [DOI: 10.2341/18-272-l] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
SUMMARY
Objectives:
This study evaluated effects of Bioglass 45S5 (BG) and Biosilicate (BS) remineralization on the chemical composition and bond strength of control dentin (CD) and bleached dentin (BD) surfaces.
Methods and Materials:
Dentin bleaching treatment was performed using the walking bleaching technique with 0.01 g of sodium perborate and 0.5 mL of 3% hydrogen peroxide for 14 days. Remineralization treatment was carried out by rubbing a remineralization solution (0.015 g of BG or BS diluted in 1.35 mL of distilled water) on the etched dentin surface for 30 seconds. Micro-Raman spectroscopy (MRS) was used to quantitatively analyze the mineral matrix ratios of CD and BD (n=5) after remineralization treatment with BG and BS over 15 days of incubation in artificial saliva. The CD and BD discs (n=10) with and without remineralization treatment with BG and BS were restored using a two-step etch-and-rinse adhesive system (Optibond S, Kerr) and five layers of 1-mm-thick composite resin (Filtek Z250, 3M ESPE). The restored dentin discs were sectioned into nine bonded beams with cross-sectional areas of approximately 0.9 mm2 and tested for microtensile bond strength (μTBS). The dentin surface of one fractured beam per tooth was submitted to MRS to characterize the physicochemical composition (n=10) at the interface. The data were analyzed using one-way analysis of variance and the Tukey-Kramer post hoc test (p<0.005).
Results:
MRS bioactive analyses revealed that both BG and BS promoted increased mineral matrix ratios in the CD and BD. Significantly higher μTBS values were found after CD treatment with BG (CD: 57 MPa±11; CD-BG: 78 MPa±15) and when BG and BS were applied to the BD (BD: 42 MPa±5; BD-BG: 71 MPa±14; BD-BS: 64 MPa±11) (p<0.005). The MRS analysis of the fractured dentin beam showed that the remineralization treatment significantly increased the dentin relative mineral concentration and promoted the appearance of new interface peaks, indicating a chemical interaction (p<0.005).
Conclusion:
Remineralization of BD is an effective therapy to restore damage caused by dentin bleaching and acid conditioning. This approach not only increases dentin mineral compounds but also improves dentin's ability to interact chemically with the adhesive system.
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Affiliation(s)
- ALM Ubaldini
- Adriana Lemos Mori Ubaldini, DDS, PhD, Department of Dentistry, State University of Maringá, Maringá, PR, Brazil
| | - RC Pascotto
- Renata Corrêa Pascotto, DDS, PhD, Department of Dentistry, State University of Maringá, Maringá, PR, Brazil
| | - F Sato
- Francielle Sato, PhD, Department of Physics, State University of Maringá, Maringá, PR, Brazil
| | - VO Soares
- Viviane Oliveira Soares, PhD, Department of Science, State University of Maringá, Goioerê, PR, Brazil
| | - ED Zanotto
- Edgar Dutra Zanotto, PhD, Department of Materials Engineering, Federal University of São Carlos, São Carlos, SP, Brazil
| | - ML Baesso
- Mauro Luciano Baesso, PhD, Department of Physics, State University of Maringá, Maringá, PR, Brazil
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Barbosa JG, Benetti F, de Oliveira Gallinari M, Carminatti M, da Silva ABD, Lopes INI, Briso ALF, Cintra LTA. Bleaching gel mixed with MI Paste Plus reduces penetration of H 2O 2 and damage to pulp tissue and maintains bleaching effectiveness. Clin Oral Investig 2019; 24:1299-1309. [PMID: 31302769 DOI: 10.1007/s00784-019-03009-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 07/03/2019] [Indexed: 02/07/2023]
Abstract
OBJECTIVES MI Paste Plus remineralizer (Rem) strengthens dental structures after bleaching. We investigated the effect of Rem on the penetration of hydrogen peroxide (H2O2), bleaching effectiveness, and pulp inflammation after bleaching. MATERIALS AND METHODS Bovine disks were grouped as follows (n = 10): control (untreated), bleached (Ble; 35% H2O2, 30 min), Ble-Rem (H2O2 followed by Rem, 30 min), Rem-Ble (Rem followed by H2O2), Rem-Ble-Rem (Rem before and after H2O2), and Ble+Rem (mixture of Rem with H2O2, 1:1, 30 min). The penetration of H2O2 was quantified and bleaching efficacy was analyzed. Upper rat molars (n = 10) received the same treatments at random. The rats were euthanized after two days and 30 days, and their jaws were removed for histological analysis. Statistical tests were performed (P < 0.05). RESULTS The bleached groups, except Ble+Rem (P > 0.05), showed significant H2O2 penetration compared with control (P < 0.05). Color alteration analysis showed that ΔL and ΔE were significantly higher in the bleached groups than those in control (P < 0.05); the Δb of the bleached groups differed from that of control at 24 h (P < 0.05). At two days, necrosis or inflammation was observed in the bleached groups compared with control (P < 0.05), except Ble+Rem, which was similar to control (P > 0.05). At 30 days, tertiary dentin formation was significant in the bleached groups (P < 0.05), except Ble+Rem (P > 0.05). CONCLUSION The mixture of MI Paste Plus and bleaching gel reduces H2O2 penetration and pulp damage and maintains bleaching effectiveness. CLINICAL RELEVANCE Because bleaching can damage dental tissues, we studied a new bleaching protocol that reduces damage to the pulp tissue while maintaining bleaching efficiency: a single application of 30 min of MI Paste Plus mixed with 35% H2O2 bleaching gel (1:1).
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Affiliation(s)
- Jéssica Galbiati Barbosa
- Department of Endodontics, São Paulo State University (Unesp), School of Dentistry, Araçatuba, SP, Brazil
| | - Francine Benetti
- Department of Endodontics, São Paulo State University (Unesp), School of Dentistry, Araçatuba, SP, Brazil
- Restorative Dentistry, School of Dentistry, UFMG - Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | | | - Marina Carminatti
- Department of Endodontics, São Paulo State University (Unesp), School of Dentistry, Araçatuba, SP, Brazil
| | - Anna Beatriz Dias da Silva
- Department of Endodontics, São Paulo State University (Unesp), School of Dentistry, Araçatuba, SP, Brazil
| | | | - André Luiz Fraga Briso
- Department of Restorative Dentistry, São Paulo State University (Unesp), School of Dentistry, Araçatuba, SP, Brazil
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Jiang T, Guo YR, Feng XW, Sa Y, Yang X, Wang M, Li P, Wang YN. Hydrogen Peroxide Might Bleach Natural Dentin by Oxidizing Phosphoprotein. J Dent Res 2018; 97:1339-1345. [PMID: 29939809 DOI: 10.1177/0022034518784260] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Recent studies suggested that bleaching agents may whiten teeth by oxidizing the fluorescent materials, which are the proteins located in the organic-inorganic interface. Therefore, we postulated that fluorescence of dentin came from dentin phosphoprotein (DPP) and that bleaching agents might bleach dentin by oxidizing DPP. Fifty-six specimens were randomly divided into 4 groups and exposed to distilled water, hydrogen peroxide (HP), ethylenediamine tetraacetic acid disodium salt (EDTA), and acetic acid for 24 h. After measuring the organic and inorganic components, fluorescence, and color characteristics of dentin before and after exposure, we found that when DPP was removed from dentin by EDTA, fluorescent intensity declined proportionally with the reduction in Raman relative intensity, and dentin was whitened considerably, with an Δ E value 6 times higher than that of the distilled water group. On the contrary, due to the incapability of acetic acid to dissolve DPP during decalcification, fluorescent intensity values and tooth color remained nearly unchanged after exposure to acetic acid. Dentin exposed to neutral HP showed no obvious morphologic and organic/inorganic component changes except for the destruction of DPP. Similarly, dramatically decreased fluorescent intensity and lightened color were found in the HP group. Moreover, DPP solution of the HP group exhibited decreased ultraviolet absorbance, especially between 250 and 300 nm, which arose from aromatic amino acids. The results indicated that DPP was responsible for the fluorescent properties of dentin and that HP might bleach dentin by the oxidization of aromatic amino acids in DPP. These findings are of great significance in promoting our further understanding of the mechanism of tooth bleaching and the fluorescent property of normal dentin.
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Affiliation(s)
- T Jiang
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
- 2 Department of Prosthodontics, Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Y R Guo
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - X W Feng
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Y Sa
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
- 2 Department of Prosthodontics, Hospital of Stomatology, Wuhan University, Wuhan, China
| | - X Yang
- 3 Department of Oral Biology, School of Dental Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - M Wang
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - P Li
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Y N Wang
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China
- 3 Department of Oral Biology, School of Dental Medicine, University of Pittsburgh, Pittsburgh, PA, USA
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Guo YR, Yang X, Feng XW, Sa Y, Wang M, Li P, Jiang T. New Insights into Effects of Aromatic Amino Acids on Hydroxyapatite. J Dent Res 2017; 97:402-408. [PMID: 29130776 DOI: 10.1177/0022034517741274] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Biomimetics inspired by superstructures and extraordinary properties of teeth have resulted in tooth repair and the generation of novel materials. However, little attention has been paid to tooth color, whose origin remains unknown. Based on recent studies, fluorophores-mainly aromatic amino acids (AAAs) in proteins-might be responsible for tooth color. We synthesized carbonated hydroxyapatite (HA; the mineral phase of teeth) in the presence of different amino acids (AAs; the basic units of protein matrix of teeth) as a simplified model of teeth to explore the color source at the AA level. After measuring the fluorescence and color characteristics of HA-AAs before and after bleaching treatment, we found that only HA, synthesized in the presence of AAAs, exhibited remarkable fluorescence and color property. Furthermore, linearly increased fluorescence intensity and deeper color were observed with an increase in AAA content in HA-AAAs. Similarly, significantly decreased absorbance of HA-AAAs between 250 and 300 nm in ultraviolet spectra, declined fluorescence intensity, and decolored performance of HA-AAAs were observed after bleaching treatment. The results showed that AAAs contributed to the fluorescence and color properties of HA and that hydrogen peroxide might whiten HA-AAAs by oxidizing the benzene ring in AAAs. These findings are of great significance in promoting the synthesis of advanced tooth-colored materials and furthering our understanding of the possible mechanisms of hydrogen peroxide. Moreover, our study shed light on the importance of AAAs and might provide new ideas for investigations of biomineralization and biomimetics.
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Affiliation(s)
- Y R Guo
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - X Yang
- 2 Department of Oral Biology, School of Dental Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - X W Feng
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - Y Sa
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China.,3 Department of Prosthodontics, Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - M Wang
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - P Li
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - T Jiang
- 1 The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China.,3 Department of Prosthodontics, Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
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Effect of tooth whitening strips on fatigue resistance and flexural strength of bovine dentin in vitro. PLoS One 2017; 12:e0173480. [PMID: 28278191 PMCID: PMC5344512 DOI: 10.1371/journal.pone.0173480] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Accepted: 02/21/2017] [Indexed: 11/23/2022] Open
Abstract
Objective To determine the effects of whitening strips on bovine dentin fatigue resistance and flexural strength in vitro. Materials and methods A total of eighty bovine dentin specimens (2x2x17mm) were treated with either: control glycerine gel on plastic film wrap or whitening strips containing 9.5% hydrogen peroxide. Treatment was applied for 30 minutes, twice a day, for 1- or 4-weeks. After the last treatment, ten specimens per group were randomly selected to undergo fatigue testing (106 cycles, 3Hz, 20N) while the other ten were subjected to flexural strength testing after ten days of storage in artificial saliva. Kaplan-Meier method with a log rank test, Wilcoxon test and Cox regression were used to assess fatigue test results (p<0.05). One-way ANOVA and Tukey’s tests were used to compare the flexural strength results (p<0.05). Results There were significant differences in survival during the fatigue test among the groups (p<0.001). Treatment (control or bleach) was a significant factor for specimen survival (p<0.001, Exp(B) = 33.45). There were significant differences in mean flexural strength (p<0.001). No significant difference was found between “1-wk control” and “4-wk control”. The mean flexural strength and fatigue resistance of the “4-wk bleach” were significantly lower than all the other groups. Conclusions The use of whitening strips reduced the fatigue resistance and flexural strength of bovine dentin in vitro. Until the effect of whitening strips on mechanical properties of human dentin is fully elucidated, it remains prudent to advise patients to avoid excessive direct use of whitening strips on dentin.
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Evaluating the effect of antioxidant agents on shear bond strength of tooth-colored restorative materials after bleaching: A systematic review. J Mech Behav Biomed Mater 2017; 71:156-164. [PMID: 28327437 DOI: 10.1016/j.jmbbm.2017.03.010] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 03/06/2017] [Accepted: 03/09/2017] [Indexed: 11/21/2022]
Abstract
PURPOSE The main objective of the present study was to make a systematic review of how antioxidant agents affect shear bond strength of tooth-colored restorative materials after bleaching. DATA SOURCES Electronic search was used to extract the related articles on the targeted key words such as "antioxidant", "dental bleaching" and "shear bond strength" (SBS) from MeSH, PubMed, Medline, and Cochrane electronic data bases. These articles were all published before 2016. STUDY SELECTION Inclusion criteria were restricted to English journal articles concerning humans, clinical trials, cohorts and case-control studies. Therefore, systematic reviews, case reports, letters to editors, editorials and congress abstracts were excluded from the analysis. CONCLUSIONS Most studies conducted on the issue have produced experimental data which are rather controversial, and there is no general agreement about the reported outcomes. As an illustration, most studies have not considered the relationship between the type of antioxidant materials and the shear bond strength. In point of fact, some researchers (e.g Kimyai et al.) have concluded that antioxidants like gel and solution leave similar effects on SBS. Alternatively, certain studies (e.g., Kunt et al.) have produced inconclusive data regarding the impact of one week postponement of the restorative process on SBS after the bleaching process. The results of the studies evaluating the role of various adhesive systems used after bleaching have demonstrated that regardless of the type of adhesive system used, applying antioxidants before restorative procedures can adversely affect the bleaching agents utilized for SBS. It has also been suggested that the type of the adhesive system used might be correlated with the magnitude of SBS. The results obtained from the systematic review of the articles under investigation reflected that the use of antioxidant agents, regardless of their type, form, concentration and duration of application, can improve SBS after bleaching.
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Fracture toughness of chairside CAD/CAM materials - Alternative loading approach for compact tension test. Dent Mater 2016; 32:847-52. [PMID: 27133875 DOI: 10.1016/j.dental.2016.03.003] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 04/12/2015] [Accepted: 03/10/2016] [Indexed: 11/22/2022]
Abstract
OBJECTIVE This in-vitro study determined plane-strain fracture toughness (KIC) of five different chairside CAD/CAM materials used for crown fabrication, following alternative innovative loading approach of compact tension test specimens. METHODS Rectangular-shaped specimens were cut from CAD/CAM blocks (n=10): Vita Mark II (Vident) (VMII); Lava-Ultimate (3M/ESPE) (LU); Vita Enamic (Vident) (VE); IPS e.max CAD (Ivoclar Vivadent); crystallized and un-crystallized (E-max and E-max-U, respectively); and Celtra Duo (Dentsply) fired and unfired (CD and CD-U, respectively). Specimens were notched with thin diamond disk prior to testing. Instead of applying tensile loading through drilled holes, a specially-made wedge-shaped steel loading-bar was used to apply compressive load at the notch area in Instron universal testing machine. The bar engaged the top ¼ of the notch before compressive load was applied at a cross-head speed of 0.5mm/min. Fracture load was recorded and KIC calculated. Data was statistically-analyzed with one-way ANOVA at 95% confidence level and Tukey's tests. RESULTS Means and SDs of KIC in MPam(1/2) for VMII, LU, VE, E-max, E-max-U, CD and CD-U were: 0.73 (0.13), 0.85 (0.21), 1.02 (0.19), 1.88 (0.62), 0.81 (0.25), 2.65 (0.32) and 1.01 (0.15), respectively. ANOVA revealed significant difference among the groups (p<0.001). CD and E-max had significantly highest mean KIC values. SIGNIFICANCE Mean KIC values of the tested materials varied considerably, however, none of them reached mean KIC of dentin (3.08MPam(1/2)) previously reported. For E-max and CD, specimens firing significantly increased mean KIC. The modified test arrangement was found to be easy to follow and simplified specimen preparation process.
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Resin Bonding of Self-Etch Adhesives to Bovine Dentin Bleached from Pulp Chamber. BIOMED RESEARCH INTERNATIONAL 2016; 2016:1313586. [PMID: 27747220 PMCID: PMC5056244 DOI: 10.1155/2016/1313586] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 08/30/2016] [Indexed: 11/21/2022]
Abstract
This study evaluated the microtensile bond strength (μTBS) of 1-step self-etch adhesives (1-SEAs) and 2-step self-etch adhesives (2-SEAs) to pulp chamber dentin immediately after bleaching with 2 types of common bleaching techniques. Pulp chamber dentin of bovine teeth was bleached using 30% hydrogen peroxide (H2O2) solution with quartz-tungsten-halogen light-curing unit (Group 1) and 3.5% H2O2-containing titanium dioxide (TiO2) (Pyrenees®) activated with 405-nm violet diode laser for 15 min (Group 2). Unbleached specimens were placed in distilled water for 15 min and used as controls. After treatment, dentin was bonded with resin composite using 1-SEA or 2-SEA and stored in water at 37°C for 24 h. Each specimen was sectioned and trimmed to an hourglass-shape and μTBS was measured. Fractured specimens were examined under a scanning electron microscope to determine fracture modes. All specimens in Group 1 failed before proper bonding tests. In Group 2, the μTBS of 2-SEA was significantly greater (with no failed specimens) than 1-SEA (where 21 out of 36 failed). These results indicate that 2-SEA is a better adhesive system than 1-SEA on bleached dentin. Our results also demonstrated that application of H2O2 significantly decreases bond strength of resin to dentin; however, in the case of nonvital tooth bleaching, Pyrenees® is a better alternative to the conventional 30% H2O2 bleaching.
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11
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Carvalho AO, Ayres APA, de Almeida LCAG, Briso ALF, Rueggeberg FA, Giannini M. Effect of peroxide bleaching on the biaxial flexural strength and modulus of bovine dentin. Eur J Dent 2015; 9:246-250. [PMID: 26038658 PMCID: PMC4439854 DOI: 10.4103/1305-7456.156845] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Objective: This study evaluated the effects of carbamide peroxide and hydrogen peroxide on the biaxial flexural strength and flexural modulus of bovine dentin. Materials and Methods: Thirty coronal dentin disks (0.5 mm thick × 6.0 mm diameter) were prepared from bovine teeth. The disks were randomly divided into three groups (n=10): A control group (unbleached), a group bleached with 10% carbamide peroxide (8 h at 37°C), and a group bleached with 38% hydrogen peroxide (three 10 min applications at 37°C). The specimens were tested in a biaxial flexural apparatus held in a universal testing machine at 1.27 mm/min until failure occurred, and the biaxial mechanical properties were calculated. For each test parameter, the data were statistically analyzed by Fisher's PLSD test (predetermined α = 0.05). Results: The group bleached with 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group. Hydrogen peroxide treatment resulted in a significantly lower flexural modulus compared with the control group and with carbamide peroxide bleaching. Conclusion: Exposure of dentin to hydrogen peroxide significantly reduced both the flexural strength and the flexural modulus compared with the no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.
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Affiliation(s)
- Adriana Oliveira Carvalho
- Department of Restorative Dentistry, Operative Dentistry Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil
| | - Ana Paula Almeida Ayres
- Department of Restorative Dentistry, Operative Dentistry Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil
| | | | - André Luiz Fraga Briso
- Department of Restorative Dentistry, Operative Dentistry Division, Araçatuba Dental School, São Paulo State University, Araçatuba, SP, Brazil
| | - Frederick Allen Rueggeberg
- Department of Oral Rehabilitation, Dental Materials Section, College of Dental Medicine, Georgia Regents University, Augusta, GA, USA
| | - Marcelo Giannini
- Department of Restorative Dentistry, Operative Dentistry Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil
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Tam LE, Cho W, Wang BY, De Souza G. Effect of Bleaching Treatment on Fatigue Resistance and Flexural Strength of Bovine Dentin. J ESTHET RESTOR DENT 2015; 27:374-82. [DOI: 10.1111/jerd.12157] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Laura E. Tam
- Restorative Dentistry; Department of Clinical Sciences; Faculty of Dentistry; University of Toronto; Toronto Canada
| | - Woohyun Cho
- Restorative Dentistry; Department of Clinical Sciences; Faculty of Dentistry; University of Toronto; Toronto Canada
| | - Bridget Y. Wang
- Restorative Dentistry; Department of Clinical Sciences; Faculty of Dentistry; University of Toronto; Toronto Canada
| | - Grace De Souza
- Restorative Dentistry; Department of Clinical Sciences; Faculty of Dentistry; University of Toronto; Toronto Canada
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Lima AF, Ribeiro APD, Soares DGS, Sacono NT, Hebling J, de Souza Costa CA. Toxic effects of daily applications of 10% carbamide peroxide on odontoblast-like MDPC-23 cells. Acta Odontol Scand 2013; 71:1319-25. [PMID: 23351219 DOI: 10.3109/00016357.2012.762992] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND bleaching has been widely studied, mainly due to the possible undesirable effects that can be caused by this esthetic procedure. The cytotoxicity of the bleaching agents and its components to pulp cells has been demonstrated in several researches. The aim of this study was to evaluate the toxic effects of successive applications of 10% carbamide peroxide (CP) gel on odontoblast-like cells. MATERIALS AND METHODS Enamel-dentin discs obtained from bovine incisors were adapted to artificial pulp chambers (APCs). The groups were formed as follows: G1: Without treatment (control group); G2: 10% carbamide peroxide, CP (five applications/one per day); G3: 10% CP (one unique application); and G4: 35% hydrogen peroxide, HP (three applications of 15 min each). After treatment, cell metabolism (MTT), alkaline phosphatase (ALP) activity and plasma membrane damage (flow cytometry) were analyzed. RESULTS Reductions in cell metabolism and alkaline phosphatase activity along with severe damage of the cytoplasmic membrane were noted in G2. In G3, no damage was observed, compared to the control group. Intermediary values of toxicity were obtained after 35% HP application. CONCLUSION It can be concluded that one application of 10% CP did not cause toxic effects in odontoblast-like cells, but the successive application of this product promoted severe cytotoxic effects. The daily application of the bleaching agents, such as used in the at-home bleaching technique, can increase the damages caused by this treatment to the dental pulp cells.
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Affiliation(s)
- Adriano Fonseca Lima
- Department of Restorative Dentistry, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
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Dudek M, Roubickova A, Comba L, Housova D, Bradna P. Effect of Postoperative Peroxide Bleaching on the Stability of Composite to Enamel and Dentin Bonds. Oper Dent 2013; 38:394-407. [DOI: 10.2341/11-429-l] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
SUMMARY
This study investigated the effect of peroxide bleaching gel on the durability of the adhesive bond between composite material, enamel, and dentin created with the etch-and-rinse adhesive Gluma Comfort Bond (GLU) and with the self-etch adhesives Clearfil SE Bond (CLE), Adper Prompt (ADP), and iBond (IBO). The adhesives were applied to flattened enamel and dentin of extracted human molars and built up with a microhybrid composite (Charisma). After 25 eight-hour cycles of bleaching with a 20% carbamide peroxide bleaching gel (Opalescence PF 20), the shear bond strength was measured and compared with one-day and two-month control specimens stored in water. The data were analyzed using nonparametric Mann-Whitney and Kruskal-Wallis statistics (p<0.05). Detailed fractographic analysis was performed using scanning electron microscopy. The bleaching gel significantly decreased the bond strength on both enamel and dentin for the simplified single-step self-etch adhesives ADP and IBO and markedly affected a fracture pattern of ADP specimens at the periphery of their bonded area. The results of our study indicate that the durability of adhesive restorations can be detrimentally influenced by carbamide peroxide bleaching and that different adhesives show varying sensitivity levels to the bleaching gel.
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Affiliation(s)
- M Dudek
- Michal Dudek, MD, Institute of Clinical and Experimental Dental Medicine, First Faculty of Medicine of the Charles University in Prague, General University Hospital, Prague, Czech Republic
| | - A Roubickova
- Adela Roubickova, MD, Institute of Clinical and Experimental Dental Medicine, First Faculty of Medicine of the Charles University in Prague, General University Hospital, Prague, Czech Republic
| | - L Comba
- Lukas Comba, MD, Institute of Clinical and Experimental Dental Medicine, First Faculty of Medicine of the Charles University in Prague, General University Hospital, Prague, Czech Republic
| | - D Housova
- Devana Housova, MD, PhD, Institute of Clinical and Experimental Dental Medicine, First Faculty of Medicine of the Charles University in Prague, General University Hospital, Prague, Czech Republic
| | - P Bradna
- Pavel Bradna, PhD, Institute of Clinical and Experimental Dental Medicine, First Faculty of Medicine of the Charles University in Prague, General University Hospital, Prague, Czech Republic
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Khoroushi M, Saneie T. Post-bleaching application of an antioxidant on dentin bond strength of three dental adhesives. Dent Res J (Isfahan) 2012; 9:46-53. [PMID: 22363363 PMCID: PMC3283978 DOI: 10.4103/1735-3327.92943] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Background: Antioxidizing agents have recently been suggested to compensate decreased bond strength of resin materials to bleached tooth tissues. This study compared the shear bond strength (SBS) of three different adhesives on bleached dentin immediately after bleaching, bleached/delayed for 1 week, and bleached/applied antioxidizing agent. Materials and Methods: The dentinal surfaces of 132 intact extracted molars were prepared and divided into 12 groups. The following adhesives were investigated: Optibond FL (OFL) (three-step etch-and-rinse), Optibond Solo Plus (two-step etch-and-rinse), and Optibond all-in-one (OA) (one-step self-etch) (Kerr, Orange, USA). Unbleached dentin groups (groups 1-3) were prepared as negative controls (NC). The remainder surfaces (groups 4-12) were bleached with 20% Opalescent PF (Ultradent, USA). Specimens were bonded immediately after bleaching (groups 4-6), after 1 week (groups 7-9), or after using 10% sodium ascorbate (SA) gel (groups 10-12). Subsequent to bonding of composite resin, the samples were tested for SBS and analyzed using Kruskal-Wallis and Mann-Whitney tests (α=0.05). Results: Regarding control groups, OA showed the highest SBS among the studied adhesives (P<0.05). The SBS decreased for the adhesives after bleaching except for OFL. No statistically significant difference in SBS were noted when the SA and delayed bonding groups were compared with their similar NC groups (P>0.05) except the of delay bonding with OA. Conclusions: The findings suggest that bond strength of resin to bleached dentin may be affected with the adhesive system. Reduced SBS to bleached dentin can be amended by the use of SA as an antioxidizing agent. However, the amount of reversed bond strength subsequent to applying antioxidant might be related to the kind of dental adhesive.
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Affiliation(s)
- Maryam Khoroushi
- Department of Operative Dentistry and Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
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Tam LE, Bahrami P, Oguienko O, Limeback H. Effect of 10% and 15% carbamide peroxide on fracture toughness of human dentin in situ. Oper Dent 2012; 38:142-50. [PMID: 22934528 DOI: 10.2341/12-127-c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
PURPOSE Although damage to the structural integrity of the tooth is not usually considered a significant problem associated with tooth bleaching, there have been some reported negative effects of bleaching on dental hard tissues in vitro. More studies are needed to determine whether the observed in vitro effects have practical clinical implications regarding tooth structural durability. OBJECTIVES This in situ study evaluated the effect of 10% and 15% carbamide peroxide (CP) dental bleach, applied using conventional whitening trays by participants at home, on the fracture toughness of dentin. METHODS Ninety-one adult volunteers were recruited (n ≈ 30/group). Compact fracture toughness specimens (approximately 4.5 × 4.6 × 1.7 mm) were prepared from the coronal dentin of recently extracted human molars and gamma-radiated. One specimen was fitted into a prepared slot, adjacent to a maxillary premolar, within a custom-made bleaching tray that was made for each adult participant. The participants were instructed to wear the tray containing the dentin specimen with placebo, 10% CP, or 15% CP treatment gel overnight for 14 nights and to store it in artificial saliva when not in use. Pre-bleach and post-bleach tooth color and tooth sensitivity were also evaluated using ranked shade tab values and visual analogue scales (VASs), respectively. Within 24-48 hours after the last bleach session, the dentin specimens were tested for fracture toughness using tensile loading at 10 mm/min. Analysis of variance, Kruskal-Wallis, χ (2) , Tukey's, and Mann-Whitney U tests were used for statistical analysis. The level of significance was set at p<0.05 for all tests, except for the Mann-Whitney U tests, which used a Bonferroni correction for post hoc analyses of the nonparametric data (p<0.017). Results : The placebo, 10% CP, and 15% CP groups contained 30, 31, and 30 participants, respectively. Mean fracture toughness (+ standard deviation) for the placebo, 10% CP, and 15% CP groups were 2.3 ± 0.9, 2.2 ± 0.7, and 2.0 ± 0.5 MPa*m(1/2) respectively. There were no significant differences in mean fracture toughness results among the groups (p=0.241). The tooth sensitivity VAS scores indicated a significantly greater incidence (p=0.000) and degree of tooth sensitivity (p=0.049 for VAS change and p=0.003 for max VAS) in the bleach groups than in the placebo group. The color change results showed generally greater color change in the bleach groups than in the placebo group (p=0.008 for shade guide determination and p=0.000 for colorimeter determination). CONCLUSIONS There were no significant differences in in situ dentin fracture toughness results among the groups. The results of this study provide some reassurance that dentin is not overtly weakened by the bleaching protocol used in this study. However, the lack of a statistically significant difference cannot be used to state that there is no effect of bleach on dentin fracture toughness.
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Affiliation(s)
- L E Tam
- University of Toronto, Toronto, Canada.
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Khoroushi M, Mazaheri H, Manoochehri AE. Effect of CPP-ACP Application on Flexural Strength of Bleached Enamel and Dentin Complex. Oper Dent 2011; 36:372-9. [DOI: 10.2341/10-280-l] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Clinical Relevance
In the absence of saliva, flexural strength of the bovine enamel-dentin complex decreases after in vitro simulation of both at-home and in-office bleaching procedures. Application of Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) subsequent to both bleaching regimens could compensate for this decrease.
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Khoroushi M, Feiz A, Khodamoradi R. Fracture resistance of endodontically-treated teeth: effect of combination bleaching and an antioxidant. Oper Dent 2010; 35:530-7. [PMID: 20945744 DOI: 10.2341/10-047-l] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
UNLABELLED This in vitro study assessed the fracture resistance of endodontically-treated teeth undergoing combination bleaching with 38% and 9.5% hydrogen peroxide gels as in-office and at-home bleaching techniques, respectively. In addition, the effect of an antioxidizing agent, sodium ascorbate, was investigated. METHODS AND MATERIALS Sixty maxillary premolars were endodontically-treated, received a glass ionomer barrier as a mechanical seal and were embedded in acrylic resin up to the cemento-enamel junction. The specimens were divided into four groups (n = 15) as follows: G I: no bleaching, access cavity restored with resin composite (negative control); G II: bleached for three weeks daily using 9.5% hydrogen peroxide for two hours and three sessions of in-office bleaching using 38% hydrogen peroxide every seven days, then restored (positive control); G III: bleached similar to G II and restored after one week; G IV: bleached similar to G II, along with the use of an antioxidizing agent for 24 hours, then restored. In each in-office and at-home bleaching session, the whitening gels were applied to the buccal surface of the tooth and placed inside the pulp chamber (inside/outside bleaching technique). Finally, the specimens underwent fracture resistance testing; the data were analyzed using ANOVA and Scheffé's test (alpha = 0.05). RESULTS Significant differences were observed among the study groups (p < 0.05). Groups I and II demonstrated the highest and lowest fracture resistance, respectively. The samples that were not bleached (Group I) and the 10% sodium ascorbate gel group (Group IV) demonstrated significantly higher fracture resistance than the positive control group (p < 0.05). No significant differences were found between Groups III and II (p > 0.05). CONCLUSION Within the limitations of the current study, it can be concluded that the fracture resistance of endodontically-treated teeth decreases after combination bleaching. The use of sodium ascorbate can reverse decreased fracture resistance.
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Affiliation(s)
- Maryam Khoroushi
- Department of Operative Dentistry & Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran.
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WOO JOHNATHANM, HO STEPHANIE, TAM LAURAE. The Effect of Bleaching Time on Dentin Fracture Toughness in Vitro. J ESTHET RESTOR DENT 2010; 22:179-84. [DOI: 10.1111/j.1708-8240.2010.00333.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Soderholm KJ. Review of the fracture toughness approach. Dent Mater 2010; 26:e63-77. [DOI: 10.1016/j.dental.2009.11.151] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Accepted: 11/20/2009] [Indexed: 10/20/2022]
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Abstract
The chemical reactions that take place at the amalgam surface when exposed to bleaching agents are not well-understood. It is known, however, that mercury ions are released from dental amalgam when bleached. We hypothesized that increasing concentrations of hydrogen peroxide are more effective than water at increasing mercury ion release from dental amalgam. We prepared dental amalgam discs (n = 65) by packing amalgam into cylindrical plastic molds and divided them into 13 equal groups of 5 discs each. The discs in each group were individually immersed in either 0%, 3.6%, 6%, or 30% (w/v) hydrogen peroxide at exposure periods of 1, 8, 48, and 168 hrs. Samples were taken for mercury ion release determination by inductively coupled plasma mass spectrometry. There were significant increases in mercury release between control and all other hydrogen peroxide concentrations at all exposure times (p < 0.05).
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Affiliation(s)
- S K Al-Salehi
- School of Dentistry, The University of Manchester, Manchester, UK.
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Pobbe PDODS, Viapiana R, Souza-Gabriel AE, Marchesan MA, Sousa-Neto MD, Silva-Sousa YTC, Silva RG. Coronal resistance to fracture of endodontically treated teeth submitted to light-activated bleaching. J Dent 2008; 36:935-9. [PMID: 18771836 DOI: 10.1016/j.jdent.2008.07.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 07/18/2008] [Accepted: 07/21/2008] [Indexed: 11/27/2022] Open
Abstract
OBJECTIVES The aim of this study was to assess the fracture resistance of endodontically treated teeth submitted to bleaching with 38% hydrogen peroxide activated by light-emitting diode (LED)-laser system. METHODS Fifty maxillary incisors were endodontically treated, received a zinc phosphate barrier and were embedded in acrylic resin until cemento-enamel junction. The specimens were distributed into five groups (n=10) according to the number of bleaching sessions: GI, no treatment (control); GII, one session; GIII, two sessions; GIV, three sessions and GV, four sessions. The whitening gel was applied to the buccal surface of the tooth and inside the pulp chamber for three times in each session, followed by LED-laser activation. Specimens were submitted to the fracture resistance test (kN) and data were submitted to the Tukey-Kramer multiple comparisons test. RESULTS No significant difference (p>0.05) was found between GI (0.71+/-0.30) and GII (0.65+/-0.13), which presented the highest strength values to fracture. Groups III (0.35+/-0.17), IV (0.23+/-0.13) and V (0.38+/-0.15) showed lower resistance to fracture (p<0.01) when compared to GI and GII. CONCLUSIONS The fracture resistance of endodontically treated teeth decreased after two sessions of bleaching with 38% hydrogen peroxide activated by LED-laser system.
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