Osseointegration of fiber-reinforced composite implants: Histological and ultrastructural observations

ObjectivesThe aim of this study was to evaluate the bone tissue response to fiber-reinforced composite (FRC) in comparison with titanium (Ti) implants after 12 weeks of implantation in cancellous bone using histomorphometric and ultrastructural analysis.Materials and methodsThirty grit-blasted cylindrical FRC implants with BisGMA–TEGDMA polymer matrix were fabricated and divided into three groups: (1) 60 s light-cured FRC (FRC-L group), (2) 24 h polymerized FRC (FRC group), and (3) bioactive glass FRC (FRC–BAG group). Titanium implants were used as a control group. The surface analyses were performed with scanning electron microscopy and 3D SEM. The bone–implant contact (BIC) and bone area (BA) were determined using histomorphometry and SEM. Transmission electron microscopy (TEM) was performed on Focused Ion Beam prepared samples of the intact bone–implant interface.ResultsThe FRC, FRC–BAG and Ti implants were integrated into host bone. In contrast, FRC-L implants had a consistent fibrous capsule around the circumference of the entire implant separating the implant from direct bone contact. The highest values of BIC were obtained with FRC–BAG (58 ± 11%) and Ti implants (54 ± 13%), followed by FRC implants (48 ± 10%), but no significant differences in BIC or BA were observed (p = 0.07, p = 0.06, respectively). TEM images showed a direct contact between nanocrystalline hydroxyapatite of bone and both FRC and FRC–BAG surfaces.ConclusionFiber-reinforced composite implants are capable of establishing a close bone contact comparable with the osseointegration of titanium implants having similar surface roughness.     

In vitro stability of methylmethacrylic acid,TEGDMA and HEMA exposed to esterases

ObjectivesComonomers used in dental restorative materials, e.g. triethylenglycoledimethacrylate (TEGDMA), hydroxyethylmethacrylate (HEMA) and methylmethacylic acid (MMA) are methacrylic acid esters. Because of the chemical structure of these esters in earlier studies two different in vitro pathways were suggested. The present study was performed in order to analyze which of these chemical pathways is preferred in vitro: (a) saponification of TEGDMA, HEMA, and MMA leading to free methacrylic acid (MA) as an ionic intermediate or (b) enzymatically epoxidation of mother compounds leading to lipophilic intermediates.MethodsExperiments have been performed in an isolated system using MMA, TEGDMA or HEMA, respectively exposed to pig liver esterase (PLE) in phosphate buffer. The reaction of tested comonomers was terminated by the use of sodium hydroxide solution, sulfuric acid or saturated NaCl solution, respectively. The samples were analyzed by the use of headspace-gas chromatography–mass spectrometry.ResultsIn all samples a decomposition of comonomers by the use of PLE was observed. Due to the high rate constant k of MMA (e.g. k_MMA > 1.3 mg/(l s)) epoxidation of non-cleaved molecules of this substance can be excluded. Compared to MMA the decomposition of TEGDMA and HEMA is significantly slower (e.g. k_{(TEGDMA, PLE = 7 units/ml)} = 0.004 mg/(l s) and k_{(HEMA, PLE = 7 units/ml)} = 0.00013 mg/(l s)). Thus in case of a low liver enzyme concentration the epoxidation of non-cleaved molecules of TEGDMA and HEMA cannot be excluded.SignificanceIn the metabolic pathway of TEGDMA and HEMA the probability of an auxiliary chemical pathway was demonstrated. In case of MMA the formation of epoxidated metabolites can be excluded. In contrast to this the chemical pathway for TEGDMA and HEMA might lead to lipophilic intermediates which can be accumulated in fatty tissue.     

Release of monomers from different core build-up materials

ObjectiveThe aim of the present study was to evaluate and compare the elution of monomers from three different core build-up composite materials and correlate it with the degree of conversion.MethodsThree different core build-up composite materials (a chemically cured, a photo-cured, and a dual-cured) were tested. Ten samples (diameter: 4.5 mm and thickness: 2 mm) of each material were fabricated to evaluate the release of monomers. The photo-cured samples were polymerized for 40 s and the dual-cured samples for 20 s. The samples remained undisturbed for 10 min and then were stored in 1 ml of 75% ethanol at room temperature, and the storage medium was renewed after 24 h, 7 and 28 days. From the storage medium that was removed, samples were prepared and analyzed by LC–MS/MS. Additionally, four samples of each material were tested for the degree of conversion by using a FT-IR spectrometer.ResultsThe three composite materials differed significantly concerning the elution of monomers (BisGMA: p < 0.0001; TEGDMA: p < 0.0001; and Bisphenol A: p < 0.0001). A significantly higher amount of BisGMA and TEGDMA was released from the chemically cured composite compared to the other two materials. Between the photo-cured and the dual-cured material the latter eluted significantly higher amounts of BisGMA and TEGDMA. During the storage of the samples, the amounts of the eluted substances decreased. The degree of conversion of the chemically cured composite was significantly lower compared to the other two materials.SignificanceUsing the present parameters, the photo-cured material released less monomer and therefore they might be less dangerous with respect to toxicological effects.     

Effect of the addition of thiourethane oligomers on the sol⿿gel composition of BisGMA/TEGDMA polymer networks

ObjectivesThiourethane oligomers have been shown to increase the fracture toughness and reduce the polymerization stress of methacrylate-based materials. However, network formation has not been elucidated in these materials yet. The aim of this study was to evaluate how the addition of a thiourethane oligomer (TU) influences the sol/gel composition and network structure of methacrylate-based materials using dynamic mechanical analysis and extraction methods.Materials and methodsBisGMA/TEGDMA at systematically varied mass ratios (20/80 to 80/20 wt%) were mixed with pre-polymerized thiourethane oligomers at 0 (control) or 20 wt%, synthesized by combining pentaerythritol tetra-3-mercaptopropionate with dicyclohexylmethane 4,4⿲-Diisocyanate, at 1:2 isocyanate:thiol. 0.1 wt% of 2,2-Dimethoxy-2-phenylacetophenone was added as the photoinitiator and 0.3 wt% of 2,6-di-tert-butyl-4-methylphenol was added as a free radical inhibitor. Disk specimens (0.8 ÿ 10 mm in diameter, n = 3) were photoactivated at 270 mW/ (320⿿500 nm) for 1 min. The degree of conversion (DC) was measured in near-IR (˿6165 cm^⿿1). Specimens were immersed in two different solvents (water for 7 days or dicholoromethane for 48 h). Water sorption (WS) and solubility (SL) were obtained according to ISO 4049. The leachates for both solutions were analyzed with ¹H-NMR (400 MHz, CDCL₃). Bar specimens (1 ÿ 3 ÿ 25 mm, photocured and then post-processed at 180 °C for 8 h to DC > 95%) were subjected to dynamic mechanical analysis (⿿30 to 230 °C) to obtain glass transition temperature (Tg), tan delta curves and crosslinking density (ν). Data was analyzed with two-way ANOVA/Tukey⿿s test (95%).ResultsIn general, the presence of TU increased the overall conversion. The WS was similar for all groups, but the SL decreased by 2-fold with the addition of the TU oligomer for all compositions, except BisGMA/TEGDMA 80/20. The BisGMA concentration of the leachates increased with increasing BisGMA in the initial mixture, and with the presence of thiourethane. This compositional drift of the gel with the presence of TU was attributed to the preferential dissolution of TEGDMA into the TU network. Tg and ν decreased with the addition of TU, as expected. The addition of TU produced more homogeneous networks, as evidenced by narrower breadth of the tan delta curve.ConclusionThe addition of TU affected the composition of the sol/gel in crosslinked networks, which were more homogeneous and presented 2-fold less potentially toxic leachates than the methacrylate controls.Clinical significanceThe addition of TU may produce less cytotoxic materials based on the increased conversion and reduced amount of unreacted extractables from its network after water storage.     

Bis-GMA co-polymerizations: Influence on conversion,flexural properties,fracture toughness and susceptibility to ethanol degradation of experimental composites

ObjectivesThe aim of this study was to evaluate the influence of monomer content on fracture toughness (K_Ic) before and after ethanol solution storage, flexural properties and degree of conversion (DC) of bisphenol A glycidyl methacrylate (Bis-GMA) co-polymers.MethodsFive formulations were tested, containing Bis-GMA (B) combined with TEGDMA (T), UDMA (U) or Bis-EMA (E), as follows (in mol%): 30B:70T; 30B:35T:35U; 30B:70U; 30B:35T:35E; 30B:70E. Bimodal filler was introduced at 80 wt%. Single-edge notched beams for fracture toughness (FT, 25 mm × 5 mm × 2.5 mm, a/w = 0.5, n = 20) and 10 mm × 2 mm × 1 mm beams for flexural strength (FS) and modulus (FM) determination (10 mm × 2 mm × 1 mm, n = 10) were built and then stored in distilled water for 24 h at 37 °C. All FS/FM beams and half of the FT specimens were immediately submitted to three-point bending test. The remaining FT specimens were stored in a 75%ethanol/25%water (v/v) solution for 3 months prior to testing. DC was determined with FT-Raman spectroscopy in fragments of both FT and FS/FM specimens at 24 h. Data were submitted to one-way ANOVA/Tukey test (α = 5%).ResultsThe 30B:70T composite presented the highest K_Ic value (in MPa m^1/2) at 24 h (1.3 ± 0.4), statistically similar to 30B:35T:35U and 30B:70U, while 30B:70E presented the lowest value (0.5 ± 0.1). After ethanol storage, reductions in K_Ic ranged from 33 to 72%. The 30B:70E material presented the lowest reduction in FT and 30B:70U, the highest. DC was similar among groups (69–73%), except for 30B:70U (52 ± 4%, p < 0.001). 30B:70U and 30B:35T:35U presented the highest FS (125 ± 21 and 122 ± 14 MPa, respectively), statistically different from 30B:70T or 30B:70E (92 ± 20 and 94 ± 16 MPa, respectively). Composites containing UDMA or Bis-EMA associated with Bis-GMA presented similar FM, statistically lower than 30B:35T:35U.SignificanceComposites formulated with Bis-GMA:TEGDMA:UDMA presented the best compromise between conversion and mechanical properties.     

Influence of a Brazilian wild green propolis on the enamel mineral loss and Streptococcus mutans’ count in dental biofilm

ObjectiveThis study investigated the anti-demineralizing and antibacterial effects of a propolis ethanolic extract (EEP) against Streptococcus mutans dental biofilm.DesignBlocks of sound bovine enamel (n = 24) were fixed on polystyrene plates. S. mutans inoculum (ATCC 25175) and culture media were added (48 h–37 °C) to form biofilm. Blocks with biofilm received daily treatment (30 μL/1 min), for 5 days, as following: G1 (EEP 33.3%); G2 (chlorhexidine digluconate 0.12%); G3 (ethanol 80%); and G4 (Milli-Q water). G5 and G6 were blocks without biofilm that received only EEP and Milli-Q water, respectively. Final surface hardness was evaluated and the percentage of hardness loss (%HL) was calculated. The EEP extract pH and total solids were determined. S. mutans count was expressed by log₁₀ scale of Colony-Forming Units (CFU/mL). One way ANOVA was used to compare results which differed at a 95% significance level.ResultsG2 presented the lowest average %HL value (68.44% ± 12.98) (p = 0.010), while G4 presented the highest (90.49% ± 5.38%HL) (p = 0.007). G1 showed %HL (84.41% ± 2.77) similar to G3 (87.80% ± 6.89) (p = 0.477). Groups G5 and G6 presented %HL = 16.11% ± 7.92 and 20.55% ± 10.65; respectively (p = 0.952). G1 and G4 differed as regards to S. mutans count: 7.26 ± 0.08 and 8.29 ± 0.17 CFU/mL, respectively (p = 0.001). The lowest bacterial count was observed in chlorhexidine group (G2 = 6.79 ± 0.10 CFU/mL) (p = 0.043). There was no difference between S. mutans count of G3 and G4 (p = 0.435). The EEP showed pH 4.8 and total soluble solids content = 25.9 Brix.ConclusionThe EEP seems to be a potent antibacterial substance against S. mutans dental biofilm, but presented no inhibitory action on the de-remineralization of caries process.     

Experimental composites of polyacrilonitrile-electrospun nanofibers containing nanocrystal cellulose

ObjectiveTo test the effects of addition of polyacrilonitrile (PAN) nanofibers and nanocrystal cellulose (NCC)-containing PAN nanofibers on flexural properties of experimental dental composites.Methods11 wt% PAN in dimethylformamide (DMF) solution was electrospun at 17.2 kVA and 20 cm from the collector drum. NCC was added to the solution at 3 wt%. Fiber mats were produced in triplicates and tested as-spun. Strips (5 cm × 0.5 cm) were cut from the mat in an orientation parallel and perpendicular to the rotational direction of the collector drum. Tensile tests were performed and ultimate tensile strength (UTS), elastic modulus (E) and elongation at maximum stress (%) were calculated from stress/strain plots. Fiber mats were then infiltrated by resin monomers (50/50 BisGMA/TEGDMA wt%), stacked in a mold (2 × 15 × 25) and light-cured. Beams (2 × 2 × 25 mm) were cut from the slabs and tested in a universal testing machine. Data were analyzed by multiple t-test and one-way ANOVA (α = 0.05).ResultsAddition of 3% NCC resulted in higher tensile properties of the fibers. Fibers presented anisotropic behavior with higher UTS and E when tested in perpendicular orientation. The incorporation of 3% NCC–PAN nanofibers resulted in significant increase in work of fracture and flexural strength of experimental dental composite beams.SignificanceNCC was found to be a suitable nanoparticle to reinforce experimental dental composites by incorporation via nanofiber. This fundamental study warrants future investigation in the use of electrospun nanofibres as a way to reinforce dental composites.     

Effect of propionaldehyde or 2,3-butanedione additives on the mechanical properties of Bis-GMA analog-based composites

ObjectivesThe purpose of this study was to evaluate the effect of two additives, propionaldehyde/aldehyde or 2,3-butanedione/diketone, on mechanical properties of Bis-GMA-based composites containing TEGDMA, propoxylated Bis-GMA (CH₃Bis-GMA) or propoxylated fluorinated Bis-GMA (CF₃Bis-GMA).MethodsThree control composites, Bis-GMA/diluent monomer (25/75 mol%), and six test composites, Bis-GMA/diluent monomer/aldehyde or diketone (17/51/32 mol%) were prepared. All composites contained hybrid treated filler (barium aluminosilicate glass/pyrogenic silica; 60 wt%), and 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Degree of conversion (DC%), flexural strength (FS), modulus of elasticity (E), modulus of resilience (R) and diametral tensile strength (DTS) were determined. DC% (n = 3) was investigated by FT-IR. For FS and E, beam-shaped specimens (25 mm × 2 mm × 2 mm) were prepared (n = 6), stored for 7 days in 37 °C deionized water and tested on an Instron utilizing a three-point loading jig (0.5 mm/min). The R-values were obtained from the following equation: R = (FS)²/2E. For DTS, cylindrical specimens (4 mm × 8 mm) were prepared (n = 6), stored for 7 days in 37 °C deionized water and diametrically loaded on an Instron (0.5 mm/min). Data were analyzed by one-way ANOVA and Tukey's test (α = 0.05).ResultsIncorporation of additives led to an increase in DC%, FS and E for Bis-GMA/TEGDMA and Bis-GMA/CH₃Bis-GMA systems. R-values for all systems were unaffected by addition of additives. They had no significant effect on DC% or mechanical properties of Bis-GMA/CF₃Bis-GMA.SignificanceThe findings correlate with the ability of additives to improve degree of conversion of some composite systems thereby enhancing mechanical properties.     

Elemental ion release from four different fixed prosthodontic materials

ObjectiveElemental release is important because it plays a significant role in material biocompatibility. The aim of this study was to investigate the release of metal ions from four fixed prosthodontic materials.MethodsSpecimens were prepared using the conventional lost wax technique for gold and nickel–chromium (Ni–Cr) alloys, and by cutting blocks and bar for CAD–CAM ceramic and stainless-steel (St-St) alloy, respectively. All specimens were polished (600 grit SiC paper), and ultrasonically cleaned with ethanol for 5 min. After they were immersed in 0.9% sodium chloride (NaCl) and 1% lactic acid, and were kept at 37 °C for 7 days, the elemental release (μg/cm²) from each material was analyzed by using inductively coupled plasma mass spectroscopy. The rate (n = 5) was statistically analyzed by ANOVA/Tukey test (p < 0.05). Two immersion blank solutions were used as a negative control group.ResultsHigher elemental release (mean ± S.D.) of all elements from all materials was evident into the lactic acid solution except for Ag. In the gold alloy, there was significant difference (p < 0.05) between Zn and other released elements in the NaCl solution, and it also revealed significant difference between Pd or Ag and Cu which detection value was more than Zn (but no statistical difference) into lactic acid solution. The Ni was significantly more released from Ni–Cr alloy than the other elements into both NaCl and lactic acid solutions. The same was observed for Fe released from St-St alloy. There was more significant release of K than Al from CAD–CAM ceramic in only NaCl solution.SignificanceTransient exposure of tested materials to an acidic environment is likely to significantly increase the elemental release from them. The significant higher release of Ni from Ni–Cr alloy, and Zn, Cu from gold alloy was evident.     

Objective treatment outcome assessment of a completely customized lingual appliance: A retrospective study

ObjectiveTo assess the outcome quality of subjects treated with a completely customized lingual appliance (CCLA) in a postgraduate university program, using the ABO Objective Grading System (OGS), by testing the null-hypothesis of a significant proportion of post-treatment cases exceeding an adjusted ‘exam failure’ threshold value of OGS = 24.Materials and MethodsThis retrospective single-arm study included 66 consecutively debonded CCLA cases (m/f 19/47; mean age: 25.1 ± 9 years) treated at Hannover Medical School (MHH, Hannover, Germany). The discrepancy index (DI) was assessed on initial plaster casts. The OGS of the cast-radiograph evaluation was scored for both set-up and post-treatment casts, including the seven components of alignment/rotation, marginal ridges, buccolingual inclination, overjet, occlusal contacts, occlusal relationships and interproximal contacts, to parameterize differences between those.ResultsDI score distribution (≥ 20, < 20) was 25 (37.9%)/41 (62.1%) subjects. Mean initial DI was 17.3 ± 8.5. Mean set-up OGS was 10.4 ± 4.4 (min-max: 3–21), mean final OGS was 17.7 ± 5.9 (min-max: 7–33), and the difference 7.3 (post-treatment - set-up) was statistically significant (p < 0.0001; 95% CI [5.8, 8.7]). The null-hypothesis was rejected: A statistically significant proportion of the final casts (n = 58; 87.8%) scored below OGS = 24 by exact binomial test (P < 0.0001; 95% CI [77.5%, 94.6%]). The rate of a final OGS score < 24 was not significantly different (P = 0.98) between both DI (≥ 20, < 20) groups.ConclusionsThe outcome quality of the CCLA treatment in this postgraduate university setting was high and therefore sufficient for a vast majority of treated cases to pass the ABO-OGS clinical examination.     

Treatment outcome of the two-part semi-rigid oral appliance in obstructive sleep apnea

AimThe aim of this study was to assess the effectiveness of the two-part semi-rigid oral appliance, Silensor^® (Erkodent, Tuttlingen, Germany) which prevents the mandible from retracting during mouth opening.Materials and methodsTen patients with mild or moderate obstructive sleep apnea (2 males and 8 females; mean age = 62.5 ± 10.0 years) were recruited and lateral cephalometric radiographs were taken. The patients underwent polysomnography before and after 3 months of receiving treatment with the Silensor^®. The relationship between the improvement in the polysomnographic variables after the therapy and the cephalometric features was analyzed.ResultsA significant difference was observed in the apnea–hypopnea index after 3 months of Silensor^® therapy (1st (baseline), 17.1 ± 5.5; 2nd (therapy of Silensor^®), 11.0 ± 7.2, p = 0.011). Furthermore there was a significant positive correlation between the improvement in the degree of slow wave sleep (%) and the mandibular plane angle (R = 0.662, p = 0.037), as well as between the improvement in degree of slow wave sleep (%) and the lower face height (R = 0.845, p = 0.002). A significant negative correlation was observed between the improvement in degree of sleep efficiency (%) and the soft palate area (R = ?0.809, p = 0.005).ConclusionThese results suggested that keeping the nasopharyngeal airway space during mouth opening improves apnea–hypopnea index of some patients with mild or moderate obstructive sleep apnea and quality of sleep in obstructive sleep apnea patients with a long lower face height and a small soft palate.     

Inhibition of enamel mineral loss by fissure sealant: An in situ study

ObjectivesThis study evaluated the effect of fluoride and non-fluoride sealants on hardness decrease (HD) and marginal adaptation (MA) on enamel substrates after cariogenic challenge.MethodsOcclusal enamel blocks, from human third molars, were randomly divided into six groups (n = 12), according to occlusal fissures condition (S – sound; C – caries-like lesion; CF – caries-like lesion + topical fluoride) and sealants (F – FluroShield; H – Helioseal Clear Chroma). Lesion depths were 79.3 ± 33.9 and 61.3 ± 23.9 for C and CF groups, respectively. Sealants were placed on occlusal surface and stored at 100% humidity (37 °C; 24 h/d). HD was measured by cross-sectional microhardness analysis at the sealant margin distances: ?1 (under sealant), 0 (sealant margin), 1, 2 (outer sealant). Sealant MA was observed by polarized light microscopy and scored according to: 0 – failure (no sealant MA or total sealant loss); 1 – success (sealant MA present). MA and HD were analysed by ANOVA-R and mixed model analysis, respectively.ResultsFor HD (ΔS), F values (6900.5 ± 3686.6) were significantly lower than H values (8534.6 ± 5375.3) regardless of enamel substrates and sealant margin distances. Significant differences were observed among sealant margin distances: ?1 (5934.0 ± 3282.6) < 0 (8701.5 ± 6175.7) = 1 (8473.2 ± 4299.4) = 2 (7761.5 ± 4035.1), regardless of sealant and substrate. MA was similar for all groups (p ≥ 0.05).ConclusionMA was not affected by sealant type or substrate condition, whereas enamel HD was favourably impacted by fluoride in the sealant. In addition, sealants were more effective as a physical barrier than as its chemical potency in reducing enamel HD.Clinical significanceSealing with a fluoride material is a recommended procedure to prevent caries of occlusal permanent molars in high-caries-risk patients, even though those exhibiting white spot lesions, since the enamel hardness decrease when fluoride sealant was used in vitro.     

Middle mesial canals in mandibular first molars: A micro-CT study in different populations

ObjectiveTo describe the morphological aspects of middle mesial canals (MMC) in mandibular first molars using micro-CT.DesignMandibular first molars collected from the Brazilian (n = 136) and Turkish (n = 122) populations were scanned (voxel size: 9.9 μm) and mesial roots with MMC (n = 48) evaluated regarding several morphological aspects. The incidence of MMC in each population was statistically compared using Chi-square test (α = 0.05).ResultsOverall, the incidence of MMC was 18.6% (48 out of 258 molars) and was significantly higher in the Brazilian (n = 30; 22.1%) than in the Turkish (n = 18; 14.8%) population (p < 0.05). In both populations, confluent configuration of the MMC was the most frequent anatomy. Most of the specimens with MMC had 3 independent orifices (n = 26; 54.2%) and 3 apical foramina (n = 21; 43.8%). The mean minor diameter of the MMC orifice (0.16 mm) was 3 times less than the other orifices (∼0.50 mm). In mesial roots with independent configuration (n = 3; 6.3%), the mean volumes (mm³) of the MMC, mesiobuccal (MBC) and mesiolingual (MLC) canals were 0.20 ± 0.10, 0.75 ± 0.28, and 0.88 ± 0.19, respectively. In the specimens with canal confluence (n = 26; 54.2%), MMC merged to the MBC (n = 8; 16.7%), MLC (n = 4; 8.3%), or to both MBC and MLC (n = 14; 29.2%). Double mesial canal was observed in only 1 specimen. MMC with an independent foramen was observed mostly in Brazilian specimens.ConclusionsIncidence of MMC was higher in the Brazilian molars. Confluent configuration was the most prevalent anatomic variation, while independent and fin configurations, as well as, double MMC, were found only in a few specimens.     

Curing potential and color stability of different resin-based luting materials

PurposeTo determine the curing potential and color stability of resin-based luting materials for aesthetic restorations.Material and MethodsFour resin-based luting agents were tested: traditional dual-activated resin cement (RelyX ARC, ARC), amine-free dual-activated resin cement (RelyX Ultimate, ULT), light-activated resin cement (RelyX Veneer, VEN), and pre-heated restorative resin composite (Filtek Supreme, PHC). Degree of C = C conversion was determined by infrared spectroscopy (n = 3) with direct light exposure or with interposition of 1.5-mm-thick ceramic (e.max Press HT) between the luting material and light. The curing potential considered the ratio between these two scenarios. Color difference (n = 6) was determined by CIELAB (ΔE_ab) and CIEDE2000 (ΔE₀₀) methods, by spectrophotometer measurements made 24 h after photoactivation and 90 days after storage in water. Data was submitted to ANOVA and Tukey’s test (α = 0.05).ResultsThe luting agents affected both conversion and color stability. With ceramic, ARC produced the highest conversion among the tested groups (75 ± 1%) and the pre-heated composite (PHC) the lowest one (51 ± 3%), but the curing potential was similar for all materials. ULT produced lower ΔE_ab than ARC. PHC presented the lowest color difference when considered both CIELAB and CIE2000 methods (ΔE_ab 2.1 ± 0.4; ΔE₀₀ 1.6 ± 0.2).SignificanceAll luting strategies presented high curing potential. Amine-free dual-activated material was able to reduce color difference than that formulated with the amine component. Pre-heated composite produced the least color variation after storage.     

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.MethodsModel composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level.ResultsComposites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values.SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.     

Optimization of calcium concentration of saliva with phosphoryl oligosaccharides of calcium (POs-Ca) for enamel remineralization in vitro

ObjectivePhosphoryl oligosaccharides of calcium (POs-Ca) are highly soluble calcium source made from potato starch. The aim of this study was to investigate the optimal concentrations of POs-Ca for the remineralization of subsurface enamel lesions in vitro.DesignDemineralized bovine enamel slabs (n = 5) were remineralized in vitro for 24 h at 37 °C with artificial saliva (AS) containing 0–0.74% POs-Ca to adjust the Ca/P ratio to 0.4–3.0, then sectioned and analysed by transversal microradiography (TMR). The data were analysed by Scheffe's post hoc test. The Ca/P ratio with most remineralization was used to investigate the effect of calcium on enamel remineralization (n = 11). The demineralized slabs were treated with AS with calcium-chloride- (CaCl₂-) or POs-Ca with an identical calcium content, and sectioned for TMR and wide-angle X-ray diffraction (WAXRD) analyses to evaluate the local changes in hydroxyapatite (HAp) crystal content. The data were analysed using the Mann–Whitney U-test.ResultsThe highest mineral recovery rate resulted from addition of POs-Ca to adjust the Ca/P to 1.67. At this ratio, the mineral recovery rate for AS containing POs-Ca (24.2 ± 7.4%) was significantly higher than that for AS containing CaCl₂ (12.5 ± 11.3%) (mean ± SD, p < 0.05). The recovery rate of HAp crystallites for AS containing POs-Ca (35.7 ± 10.9%) was also significantly higher than that for AS containing CaCl₂ (23.1 ± 13.5%) (p < 0.05). The restored crystallites were oriented in the same directions as in sound enamel.ConclusionsPOs-Ca effectively enhances enamel remineralization with ordered HAp at a Ca/P ratio of 1.67.     

Retrospective analysis on the repair vs. replacement of composite restorations

ObjectiveOur retrospective study aimed to assess the impact of repairs on the longevity of anterior and posterior direct composite restorations and to compare longevity of repaired and replacement restorations.MethodsPatient records were retrospectively screened for anterior and/or posterior composite restorations with 2+ surfaces placed in permanent teeth between 2000 and 2015. During follow-up, repaired and replaced restorations were assessed and mean annual failure rates (mAFR) calculated. Outcome was considered in three levels: Success (no further intervention), survival 1 (first repair = survival, second repair = failure) and survival 2 (more than one repair = survival, all surfaces repaired = failure). Statistical analysis was performed using Kaplan–Meier statistics, log-rank tests, and multi-variate Cox-regression analyses with shared frailty (p < 0.05).Results8542 initial restorations placed in 3239 patients were included (4.7 ± 4.4 years follow-up, 2.5 ± 0.7 surfaces). Longevity of initial restorations was prolonged by repair(s) (after 10 years: success: 68.3%, mAFR: 3.7%; survival 1: 77.3%, mAFR: 2.5%; survival 2: 80.4%, mAFR: 2.2%; p < 0.001). 616 repaired restorations (4.9 ± 4.2 years follow-up, 3.5 ± 1.0 surfaces) and 264 replacement restorations (5.6 ± 4.1 years follow-up, 3.0 ± 0.8 surfaces) were analyzed. Success of repaired restorations amounted to 43.4% after 10 years (mAFR: 8.0%), further repair(s) prolonged survival (survival 1: 65.7%, mAFR: 4.1%; survival 2: 74.8%, mAFR: 2.9%; p < 0.001). Success of replacement restorations amounted to 48.6% after 10 years (mAFR: 7.0%), repair(s) prolonged survival (survival 1: 67.4%, mAFR: 3.9%, p = 0.044; survival 2: 74.1%, mAFR: 3.0%, p = 0.003).SignificanceRepairs are suitable to increase the survival of restorations; repaired restorations last as long as replacements.     

Evaluation of interface characterization and adhesion of glass ceramics to commercially pure titanium and gold alloy after thermal- and mechanical-loading

ObjectivesThis study evaluated the effect of thermal- and mechanical-cycling on the shear bond strength of three low-fusing glassy matrix dental ceramics to commercial pure titanium (cpTi) when compared to conventional feldspathic ceramic fused to gold alloy.MethodsMetallic frameworks (diameter: 5 mm, thickness: 4 mm) (N = 96, n = 12 per group) were cast in cpTi and gold alloy, airborne particle abraded with 150 μm aluminum oxide. Low-fusing glassy matrix ceramics and a conventional feldspathic ceramic were fired onto the alloys (thickness: 4 mm). Four experimental groups were formed; Gr1 (control group): Vita Omega 900–Au–Pd alloy; Gr2: Triceram–cpTi; Gr3: Super Porcelain Ti-22–cpTi and G4: Vita Titankeramik–cpTi. While half of the specimens from each ceramic–metal combination were randomly tested without aging (water storage at 37 °C for 24 h only), the other half were first thermocycled (6000 cycles, between 5 and 55 °C, dwell time: 13 s) and then mechanically loaded (20,000 cycles under 50 N load, immersion in distilled water at 37 °C). The ceramic–alloy interfaces were loaded under shear in a universal test machine (crosshead speed: 0.5 mm/min) until failure occurred. Failure types were noted and the interfaces of the representative fractured specimens from each group were examined with stereomicroscope and scanning electron microscope (SEM). In an additional study (N = 16, n = 2 per group), energy dispersive X-ray spectroscopy (EDS) analysis was performed from ceramic–alloy interfaces. Data were analyzed using ANOVA and Tukey's test.ResultsBoth ceramic–metal combinations (p < 0.001) and aging conditions (p < 0.001) significantly affected the mean bond strength values. Thermal- and mechanical-cycling decreased the bond strength (MPa) results significantly for Gr3 (33.4 ± 4.2) and Gr4 (32.1 ± 4.8) when compared to the non-aged groups (42.9 ± 8.9, 42.4 ± 5.2, respectively). Gr1 was not affected significantly from aging conditions (61.3 ± 8.4 for control, 60.7 ± 13.7 after aging) (p > 0.05). Stereomicroscope images showed exclusively adhesive failure types at the opaque ceramic–cpTi interfacial zone with no presence of ceramic on the substrate surface but with a visible dark titanium oxide layer in Groups 2–4 except Gr1 where remnants of bonder ceramic was visible. EDS analysis from the interfacial zone for cpTi–ceramic groups showed predominantly 34.5–85.1% O₂ followed by 1.1–36.7% Al and 0–36.3% Si except for Super Porcelain Ti-22 where a small quantity of Ba (1.4–8.3%), S (0.7%) and Sn (35.3%) was found. In the Au–Pd alloy–ceramic interface, 56.4–69.9% O₂ followed by 15.6–26.2% Si, 3.9–10.9% K, 2.8–6% Na, 4.4–9.6% Al and 0–0.04% Mg was observed.SignificanceAfter thermal-cycling for 6000 times and mechanical-cycling for 20,000 times, Triceram–cpTi combination presented the least decrease among other ceramic–alloy combinations when compared to the mean bond strength results with Au–Pd alloy–Vita Omega 900 combination.     

Influence of the application of a pre-sintered surface augmentation on zirconia and lithium disilicate bonding using an adhesive composite resin cement

ObjectiveThe purpose of this laboratory study is to evaluate the application of a pre-sintered surface augmentation to zirconia (Zir) and lithium disilicate (LDS) ceramics on the delamination strength of adhesive resin cement. The applied surface augmentation was the ruling of lines to the pre-sintered surface of the ceramics.MethodsNinety milled Zir and sixty pressed LDS specimens (3 mm × 0.5 mm × 25 mm) were created and divided into five groups (n = 30). Group 1: Zir no surface treatment (control Zir-NT); Group 2: Zir airborne particle abraded (Zir-APA) with 30 μm CoJet; Group 3: Zir pre-sintered surface augmentation (Zir-SA); Group 4: LDS etched (control LDS-etched) and; Group 5: LDS with pre-sintered surface augmentation and etching (LDS-SA). A resin adhesive cement (3 mm × 1 mm × 8 mm) was then applied and cured to the ceramic specimens. The delamination strength values of the resin cement from the ceramic were recorded. The delamination strength data were analysed statistically using one-way ANOVA and Turkey post hoc analysis.ResultsThe mean delamination strength and standard deviation, when comparing only the Zir-SA to the resin cement were statistically different (p < 0.001); Zir-SA 63.42 ± 11.85, Zir-NT 26.82 ± 12.07, and Zir-APA 48.11 ± 17.85 MPa. Comparison between LDS groups were not significantly different (p = 0.193); LDS-etched 33.49 ± 16.07 and LDS-SA 28.83 ± 10.15 MPa. The delaminated Weibull modulus was highest for surface augmentation Zir specimens (m = 13.56) but decreasing to less than half for Zir-APA (m = 6.27) and Zir-NT (m = 5.68). The Weibull values for the LDS-SA and LDS-etched specimens was 5.63 and 3.38 respectively.SignificanceIncorporating the pre-sintered surface augmentation to zirconia improved the delamination strength and reliability of Zir to the resin cement but not for LDS.     

Influence of chlorhexidine on the degree of conversion and E-modulus of experimental adhesive blends

ObjectivesThis study examined the effect of chlorhexidine (CHX) content on degree of conversion (DC) and E-modulus of experimental adhesive blends. The hypothesis tested was that increasing concentrations of CHX result in decreased DC and E-modulus in relation to adhesive hydrophilicity.MethodsExperimental adhesive blends with increasing hydrophilicity R2 (70% bisGMA, 28.75% TEGDMA); R3 (70% BisGMA, 28.75% HEMA); R4 (40% BisGMA, 30% TCDM, 28.75% TEGDMA); R5 (40% BisGMA, 30% BisMP, 28.75% HEMA) and different CHX concentrations (1 and 5%) were analyzed. 5% CHX could not be dissolved in R2. A differential scanning calorimeter was used to measure the DC of resin blends. Photopolymerized disks of the experimental comonomer mixtures (n = 10/gp) were used to measure the E-modulus of each specimen using a biaxial flexure test. Data were analyzed with two-way ANOVA (resin type and CHX concentration) and Tukey's post hoc test.ResultsThe addition of 1% CHX did not significantly alter the DC of R2 and R3. Significant decrease in R3 DC values was observed when 5% CHX was added. CHX significantly increased the DC of R4 and R5. 1% CHX reduced the E-modulus of all resins (p < 0.05) except for R2, in which the E-modulus was significantly increased (p < 0.05). 5% CHX significantly reduced the E-modulus of resins R3 to R5 (p < 0.05).SignificanceIn conclusion, increasing concentrations of CHX dissolved in resin blends had little adverse effect on DC but decreased the E-modulus 27–48% compared to controls. Solvation of CHX in ethanol prior to incorporation of CHX into R2 may permit higher CHX concentrations without lower polymer stiffness.