Use of NIR light and upconversion phosphors in light-curable polymers.
Dent Mater. 2012 Jan 25;
Authors: Stepuk A, Mohn D, Grass RN, Zehnder M, Krämer KW, Pellé F, Ferrier A, Stark WJ
Abstract
OBJECTIVE: Light-curable polymers are commonly used in restorative surgery, prosthodontics and surgical procedures. Despite the fact of wide application, there are clinical problems due to limitations of blue light penetration: application is restricted to defects exposed to the light source, layered filling of defect is required. METHODS: Combining photo-activation and up conversion allows efficient polymer hardening by deep penetrating near-infrared (NIR) light. The prerequisite 450nm blue light to polymerize dental resins could be achieved by filler particles, which absorb the incident NIR irradiation and convert it into visible light. RESULTS: The on spot generated blue light results in uniform polymer hardening. Composite samples of 5mm thickness were cured two times faster than pure polymer cured by blue light (30 and 60s, respectively). Overall degree of monomer conversion resulted in higher values of more than 40%. The enhanced transmission of NIR light was confirmed by optical analysis of dentin and enamel. The NIR transmittance surge in the 800-1200nm window could improve sealing of complex and deep caries lesions. SIGNIFICANCE: We demonstrate faster curing and an improved degree of polymerization by using upconversion filler particles as multiple light emission centers. This study represents an alternative approach in curing dental resins by NIR source.
PMID: 22284385 [PubMed - as supplied by publisher]
Effects of resinous monomers on the odontogenic differentiation and mineralization potential of highly proliferative and clonogenic cultured apical papilla stem cells.
Dent Mater. 2012 Jan 23;
Authors: Bakopoulou A, Leyhausen G, Volk J, Koidis P, Geurtsen W
Abstract
OBJECTIVE: The aim of this study was to investigate the effects of resinous monomers on the odontogenic differentiation and mineralization potential of apical papilla stem cells (SCAP). METHODS: Cultures were established from developing third molars of healthy donors aged 14-18 years-old and were extensively characterized for proliferation rate, colony forming unit efficiency and expression of stem cell markers (STRO-1, CD146, CD34, CD45, CD105, CD117-c-Kit, CD24, CD90, Nanog, Oct3/4), in order to select those with enhanced stem cell and odontogenic differentiation properties. SCAP enriched cultures were then induced for odontogenic differentiation in the continuous presence of low concentrations (0.05-0.5mM) of the monomers 2-hydroxy-ethyl-methacrylate-HEMA and triethylene-glycol-dimethacrylate-TEGDMA for 3 weeks (long-term exposure). Additionally, the effects of a single exposure (72h) to higher concentrations of HEMA (2mM) and TEGDMA (1mM) were evaluated. RESULTS: The results showed that both types of monomer-exposure significantly delayed the odontogenic differentiation and mineralization processes of SCAP cells. A down-regulation followed by recovery in the expression of differentiation markers, including dentin sialophosphoprotein-DSPP, bone sialoprotein-BSP, osteocalcin-OCN and alkaline phosphatase-ALP was recorded. This was accompanied by reduction of the mineralized matrix produced by monomer-treated-compared to non-treated contol cultures. Furthermore, a concentration-dependence was observed for both monomers during long-term exposure, whereas the effects of HEMA were evident at much lower concentrations compared to TEGDMA. SIGNIFICANCE: These findings suggest that resinous monomers can delay the odontogenic differentiation of SCAP cells, potentially disturbing the physiological repair and/or developmental processes of human permanent teeth.
PMID: 22277349 [PubMed - as supplied by publisher]
Marginal and internal fit of pressed lithium disilicate partial crowns in vitro: A three-dimensional analysis of accuracy and reproducibility.
Dent Mater. 2012 Jan 20;
Authors: Schaefer O, Watts DC, Sigusch BW, Kuepper H, Guentsch A
Abstract
OBJECTIVES: The objective of this in vitro study was to visualize and to quantify the marginal and internal fit of heat-pressed ceramic restorations by a novel three-dimensional procedure. Accuracy and reproducibility of the employed measuring method were determined. METHODS: An acrylic model of a lower left first molar was prepared to receive a partial crown and duplicated by single step dual viscosity impressions. Corresponding working casts were formed from Type IV die stone and indirect restorations were fabricated from heat-pressable lithium disilicate ceramics (IPS e.max Press, Ivoclar Vivadent AG, Schaan, Liechtenstein). The acrylic tooth model and the ceramic partial crowns were digitized by a structure light scanner with a measurement-uncertainty of 4μm and subjected to computer-aided quality inspection. Visual discrepancies in marginal and internal fit were displayed with colors. For quantitative analysis, mean quadratic deviations (RMS) were computed and analyzed by Student’s t-test (n=5, α=0.05). RESULTS: Mean RMS-values for accuracy (reproducibility) ranged from 34 (14)μm for internal areas to 78 (23)μm for marginal surfaces. Differences in accuracy (p=0.003) and reproducibility (p<0.001) were statistically significant. In general, areas with sharp internal line angles such as occlusal ridges and the preparation finish line exhibited oversized dimensions, whereas areas with rounded and soft internal line angles were undersized. SIGNIFICANCE: The viability of a computer-aided and three-dimensional approach for assessing marginal and internal fit of indirect restorations was demonstrated. Thereby, the obtained results track complex form changes as they occur during laboratory processing.
PMID: 22265824 [PubMed - as supplied by publisher]
Nickel release from orthodontic retention wires-The action of mechanical loading and pH.
Dent Mater. 2012 Jan 17;
Authors: Milheiro A, Kleverlaan C, Muris J, Feilzer A, Pallav P
Abstract
Nickel (Ni) is a potent sensitizer and may induce innate and adaptive immune responses. Ni is an important component of orthodontic appliances (8-50wt%). Due to chemical and mechanical factors in the oral environment, Ni is released from these appliances. Retention wires are in situ for a long period of time. OBJECTIVES: To quantitatively evaluate the influence of mechanical loading and pH on the nickel release from orthodontic retention wires. METHODS: Five different types of multi-stranded wires (Original Wildcat, Noninium, Lingual retainer, Dentaflex 3-s, Dentaflex 6-s), were submersed for 24h in either 10ml of distilled water or lactic acid, both submitted to cyclic loading in a 3-point bending test (0×, 1000×, 10,000×). The solutions were analyzed by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), and the data was statistically analyzed (ANOVA, p<0.05). RESULTS: Mechanical loading has a strong effect on the Ni release from orthodontic retention wires, especially in distilled water. Acidity has more impact on Ni release when compared to mechanical loading. Manganese-steel “Ni-free” wires released quantifiable amounts of Ni due to trace elements of Ni within the wire. SIGNIFICANCE: All investigated wires release considerable amounts of Ni to which exposure may have biological implications.
PMID: 22260951 [PubMed - as supplied by publisher]
Tissue engineering: From research to dental clinics.
Dent Mater. 2012 Jan 10;
Authors: Rosa V, Della Bona A, Cavalcanti BN, Nör JE
Abstract
Tissue engineering is an interdisciplinary field that combines the principles of engineering, material and biological sciences toward the development of therapeutic strategies and biological substitutes that restore, maintain, replace or improve biological functions. The association of biomaterials, stem cells, growth and differentiation factors has yielded the development of new treatment opportunities in most of the biomedical areas, including Dentistry. The objective of this paper is to present the principles underlying tissue engineering and the current scenario, the challenges and the perspectives of this area in Dentistry. SIGNIFICANCE: The growth of tissue engineering as a research field has provided a novel set of therapeutic strategies for biomedical applications. Indeed, tissue engineering may lead to new strategies for the clinical management of patients with dental and craniofacial needs in the future.
PMID: 22240278 [PubMed - as supplied by publisher]
OBJECTIVES: The study was aimed at investigating the cytotoxicity of different composites as a function of composite shade and the light curing unit (LCU) employed. METHODS: Non-polymerized and polymerized samples of the composites Grandio(®) (VOCO, Cuxhaven), Solitaire(®) (Heraeus Kulzer, Hanau) and Filtek Z 250(®) (3M/Espe, Seefeld) in two markedly differing shades (A2, C2) were prepared. Polymerization was performed with two LCUs: Heliolux II (Ivoclar/Vivadent, Ellwangen) and Swiss Master Light (EMS, Nyon, Switzerland). To obtain composite extracts, the samples were immersed in cell culture medium (DMEM – Dulbecco’s Modified Eagle Medium), which was replaced daily up to the 7th day of the experiment, and then on the 14th, 21st and 28th day. After incubation of human gingival fibroblasts (HGF) with the extracts obtained, cytotoxicity was determined using the MTT test. RESULTS: With the non-polymerized samples, essentially no influence of the composite shades investigated on HGF viability was detected, with the exception of the Solitaire material, where a higher cytotoxicity of the shade C2 in the non-polymerized state was found at the end of the observation period. After polymerization of the different composites, the cytotoxic reaction observed for the extracts of shade C2 was stronger than that observed for A2. After polymerization with the Heliolux II (HLX) LCU, the extracts of composites Grandio and Solitaire C2 were significantly more toxic than those of the A2 shade (p<0.01). Polymerization with the Swiss Master Light (SML) reduces this cytotoxic effect. The extracts of the Grandio composite showed the least cytotoxic effect throughout the observation period, irrespective of the LCU used. For the extracts of the Z250 specimens, the cytotoxicity observed was generally higher. SIGNIFICANCE: The results show that the shade of the composite has an influence on its cytotoxicity and that this cytotoxicity is also influenced by the light curing unit used. It was observed that composites of the darker shade (C2) had a higher cytotoxicity, which varied with the LCU employed.
PMID: 22240279 [PubMed - as supplied by publisher]
A clinical evaluation of all-ceramic bridges placed in patients attending UK general dental practices: Three-year results.
Dent Mater. 2012 Jan 11;
Authors: Crisp RJ, Cowan AJ, Lamb J, Thompson O, Tulloch N, Burke FJ
Abstract
OBJECTIVES: To report the results at year three of an evaluation of fixed-fixed all-ceramic bridges, constructed in a yttria oxide stabilized tetragonal zirconium oxide polycrystal (Y-TZP) substructure, placed in adult patients in UK general dental practices and luted using a self-adhesive resin-based cement. METHODS: Ethical approval was obtained. Four UK general dental practitioners were asked to recruit patients in accordance with the trial protocol. After obtaining informed written consent, appropriate vitality and radiographic assessments were completed and the pre-operative status of the gingival tissues noted. The teeth were prepared and bridges constructed in accordance with the manufacturer’s instructions. Each bridge was reviewed annually within 3months of the anniversary of its placement by a calibrated examiner, together with the clinician who had placed the restoration. The examiners evaluated the integrity of the restoration, its anatomic form, marginal adaptation, surface quality, sensitivity, the condition of the adjacent gingivae, and the presence or absence of secondary caries. RESULTS: A total of 34 bridges were examined at the three-year review. All Y-TZP frameworks were intact and no bridge retainers had debonded. Two veneering ceramic chips, in total, were detected over the three-year period of observation: the patients in whom this had occurred were unconcerned. A further abutment tooth had been successfully endodontically treated, through an occlusal access cavity, in addition to the two already reported at year one. SIGNIFICANCE: At year three, the 34 Lava Y-TZP fixed-fixed bridges, placed in patients attending UK general dental practices, were found to be performing satisfactorily.
PMID: 22244732 [PubMed - as supplied by publisher]
Leucite-reinforced glass ceramic inlays luted with self-adhesive resin cement: A 2-year in vivo study.
Dent Mater. 2012 Jan 9;
Authors: Taschner M, Krämer N, Lohbauer U, Pelka M, Breschi L, Petschelt A, Frankenberger R
Abstract
OBJECTIVES: Aim of the present prospective controlled clinical study was to compare the clinical performances of two different cementation procedures to lute IPS Empress inlays and onlays. METHODS: Eighty-three IPS Empress restorations (70 class-II inlays, 13 onlays/47 premolars, 36 molars) were placed in 30 patients (19 females/11 males, mean age=39 years). Two cementation procedures were tested: group 1: forty-three restorations were luted with a self-adhesive resin cement (RelyX Unicem, RX, 3M ESPE); group 2: forty restorations were luted with an etch-and-rinse multistep adhesive (Syntac Classic, Ivoclar-Vivadent) and Variolink II low (SV, Ivoclar-Vivadent). All restorations were evaluated after 2 weeks (baseline=1st recall=R1, n=83), 6 months (R2, n=83), 1 year (R3, n=82), and 2 years (R4, n=82) by two independent blinded calibrated examiners using modified USPHS criteria. RESULTS: From R1 to R4, one failure occurred in the SV group (at R2) due to marginal enamel chipping. After 2 years of clinical service (R4), better marginal and tooth integrity (p<0.05) was found in group 2 (SV) compared to the use of the self-adhesive cement (RX, group 1), while no differences were found for all remaining investigated criteria (p>0.05). The absence of enamel in proximal boxes (10% with no enamel and 51% of the restorations with less than 0.5mm enamel width at the bottom of the proximal box) did not affect marginal performance (p>0.05). SIGNIFICANCE: The self-adhesive resin cement RelyX Unicem showed clinical outcomes similar to a conventional multi-step cementation procedure after 2 years of clinical service for most of the tested criteria.
PMID: 22236770 [PubMed - as supplied by publisher]
OBJECTIVES: The aim of the study was to analyze the dissolving depth of adhesive resin monomers into pre-polymerized fiber-reinforced composites (FRC) with either a semi-interpenetrating polymer network (semi-IPN) or a cross-linked polymer (CLP) matrix. METHODS: Five unidirectional FRCs were tested, including one semi-IPN FRC (everStick(®) C&B, StickTech, (ES)) and four CLP-FRCs (GrandTec(®), VOCO, (GT); Dentapreg(®), ADM, (DP); TenderFiber(®), Micerium, (TF); Splint-It(®), Pentron Clinical Technologies, (SI)). The FRCs were light-polymerized following manufacturers’ instructions: the oxygen inhibition layers were removed and the adhesive resin (Optibond-FL(®), KerrHawe) was labeled with a fluorescent dye (Rhodamine-B-isothiocyanate), which was then applied to the FRCs (5min) and light-polymerized (40s). Specimens were then prepared for confocal laser scanning microscopy. Three FRC strands per group were sectioned orthogonally to the direction of fibers, thus forming nine slices in each group. Four images were taken from each slice and the depths of adhesive penetration were measured in four sites per image (n=144 measurements per group). SIGNIFICANCE: Dissolving depths were 17.28 (3.04)μm (ES), 12.58 (2.94)μm (SI), 7.57 (1.91)μm (TF), 3.27 (0.73)μm (DP) and 2.55 (0.63)μm (GT). Samples were normally distributed. Differences between groups were analyzed by ANOVA (PostHoc Scheffé) showing four subgroups (p=0.05). The infiltration layers detected were either continuous/homogenous (ES, TF, DP GT) or discontinuous/insular (SI). CONCLUSION: The adhesive resin monomers were able to diffuse significantly deeper into pre-polymerized semi-IPN specimens than into CLP materials. Semi-IPN specimens showed a homogenous and comparatively deeper layer of infiltration. The diffusion capabilities of secondary-IPN formation might increase the opportunity to establish a good bond between pre-polymerized FRC and new resin.
PMID: 22230106 [PubMed - as supplied by publisher]
Resin composite blocks via high-pressure high-temperature polymerization.
Dent Mater. 2012 Jan 7;
Authors: Nguyen JF, Migonney V, Ruse ND, Sadoun M
Abstract
OBJECTIVES: The aim of this study was to thermo-polymerize under high pressure four commercially available dental resin composites to obtain and characterize composite blocks suitable for CAD/CAM procedures. METHODS: Gradia (GC, Japan), Vita VM LC (Vita Zahnfabrik, Germany), Grandio (VOCO, Germany), and EsthetX (Dentsply, Germany), were selected for this study. Paradigm (3M ESPE, USA), a CAD/CAM composite block, was included for comparison. Composite blocks were obtained through polymerization at high-temperature high-pressure (HT/HP). Samples for mechanical/physical characterizations were cut from Paradigm and HT/HP composite blocks while control samples were obtained by photo-polymerizing (PP) the materials in molds. Flexural strength (σ(f)), fracture toughness (K(IC)), hardness, and density (ρ) were determined and compared by pairwise t-tests (α=0.05). Fractured surfaces were characterized under a scanning electron microscope. RESULTS: The results have shown that HT/HP polymerization resulted in a significant (p<0.05) increase in σ(f), hardness, and ρ for all composites investigated. Even if K(IC) of all materials was increased by HT/HP polymerization, significant increases were detected only for Gradia and EsthetX. The Weibull modulus of HT/HP polymerized composites was higher than that of PP counterparts. HT/HP materials had higher σ(f), Weibull modulus, and K(IC) compared to Paradigm. The most significant SEM observation of fractured K(IC) specimens from all the materials tested was the presence of fewer and smaller voids in HT/HP polymerized composites. SIGNIFICANCE: The results of this study suggest that HT/HP polymerization could be used to obtain dental resin composite blocks with superior mechanical properties, suitable for CAD/CAM processing.
PMID: 22230107 [PubMed - as supplied by publisher]
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