Structure, chemical composition and mechanical properties of coronal cementum in human deciduous molars

ObjectivesIt was hypothesized that the coronal cementum containing collagen forms a weak junction with enamel unlike the well integrated DEJ and CDJ.MethodsThe hypothesis was investigated in two parts: (1) evaluate the structure, chemical composition and mechanical properties of coronal cementum and its junction with enamel using scanning electron microscopy, micro-X-ray computed tomography, and atomic force microscopy. The chemical composition and mechanical properties were determined by evaluating the spatial variations of inorganic (PO₄^3? ν₁ mode at 960 cm^?1) and organic (C–H deformation at 1452 cm^?1; C–H stretch at 2940 cm^?1) contents using Raman microspectroscopy and elastic modulus and hardness values using nanoindentation. (2) Estimate the strength and evaluate the microstructure of coronal cementum interface with enamel using SEM and MicroXCT?.Results and conclusionsCoronal cementum is heterogeneous because it is a combination of laminar acellular afibrillar cementum and acellular extrinsic fiber cementum with relatively higher organic content. It integrates micromechanically via a scallop-like weak interface with enamel unlike the biomechanically efficient DEJ and CDJ and is continuous with primary root cementum. A single tooth could exhibit all three types of cementum enamel junctions; an overlap, butt and a gap depending on the sectioning plane. The elastic modulus of coronal cementum (11.0 ± 5.8 GPa) is significantly lower (p < 0.05; Student's t-test with 95% confidence interval) than primary cementum (15.8 ± 5.3 GPa).     

Efficacy of a mouthrinse based on hydroxyapatite to reduce initial bacterial colonisation in situ

ObjectiveThe present in situ - investigation aimed to specify the impact of pure hydroxyapatite microclusters on initial bioadhesion and bacterial colonization at the tooth surface.DesignPellicle formation was carried out in situ on bovine enamel slabs (9 subjects). After 1 min of pellicle formation rinses with 8 ml of hydroxyapatite (HA) microclusters (5%) in bidestilled water or chlorhexidine 0.2% were performed. As negative control no rinse was adopted. In situ biofilm formation was promoted by the intraoral slab exposure for 8 h overnight. Afterwards initial bacterial adhesion was quantified by DAPI staining and bacterial viability was determined in vivo/in vitro by live/dead-staining (BacLight). SEM analysis evaluated the efficacy of the mouthrinse to accumulate hydroxyapatite microclusters at the specimens’ surface and spit-out samples of the testsolution were investigated by TEM.ResultsCompared to the control (2.36 × 10⁶ ± 2.01 × 10⁶ bacteria/cm²), significantly reduced amounts of adherent bacteria were detected on specimens rinsed with chlorhexidine 0.2% (8.73 × 10⁴ ± 1.37 × 10⁵ bacteria/cm²) and likewise after rinses with the hydroxyapatite testsolution (2.08 × 10⁵ ± 2.85 × 10⁵ bacteria/cm², p < 0.001). No demonstrable effect of HA-particles on Streptococcus mutans viability could be shown. SEM analysis confirmed the temporary adsorption of hydroxyapatite microclusters at the tooth surface. Adhesive interactions of HA-particles with oral bacteria were shown by TEM.ConclusionHydroxyapatite microclusters reduced initial bacterial adhesion to enamel in situ considerably and could therefore sensibly supplement current approaches in dental prophylaxis.     

Effect of composition, viscosity and thickness of the opaquer on the adhesion of resin composite to titanium

ObjectivesThe objectives of this study were to determine the bond strength of powder-liquid and paste opaquers with different chemical compositions and viscosity to a metal substructure when they were applied in two thicknesses and to evaluate the failure modes after the bond strength test.MethodsTitanium plates (51 mm × 25 mm × 1 mm) (n_plates = 25, N = 80, n = 10 per group) were conditioned with chairside silica coating (CoJet-Sand, 30 μm silica coated Al₂O₃) from a distance of approximately 10 mm at a pressure of 2.8 bar for 15 s/cm² and silanized. Four types of opaquers, namely one powder-liquid (Sinfony, 3 M ESPE), and three paste opaquers [(Cimara, Voco), (Monopaque, Ivoclar Vivadent), (Cavex Experimental, Cavex)] were applied either in 0.25 or 0.50 mm thicknesses using standard polyethylene molds and photo-polymerized. Resin composite (Quadrant Posterior Dense, Cavex) was applied incrementally and photo-polymerized. The specimens were thermocycled (5–55 °C, 6000 cycles) prior to shear bond strength test (1 mm/min). Failure types were analyzed using an optical microscope and scores were given according to the modified Adhesive Remnant Index (ARI) (Score 0 = no opaquer on the surface, Score 1 = <1/2 covered with opaquer, Score 2 = >1/2 covered with opaquer, Score 3 = completely covered with opaquer).ResultsWhile thickness did not significantly affect the bond strength results (p = 0.523), type of opaquers had a significant influence on the results (p < 0.01) (Univariate ANOVA, Tukey's test). Interaction terms between thickness and opaquer type were significant (p < 0.01). Debonded specimens during thermocycling were considered as 0 MPa. At both 0.25 and 0.5 mm thicknesses, powder-liquid based opaquer (Sinfony) showed significantly higher results (8.4 ± 5.6 and 8.4 ± 4.9 MPa, respectively) than those of other opaquers (1.4 ± 1 to 4.3 ± 3.8 MPa) (p < 0.05). Only when Cimara was applied in 0.25 mm (6.9 ± 4.2 MPa), there were no significant differences with Sinfony (p > 0.05). The lowest results in both thicknesses were obtained from Monopaque (4 ± 3.8 to 1.6 ± 1 MPa, respectively) and Cavex (1.4 ± 1 to 4.2 ± 2.9 MPa, respectively) paste opaquers. In all opaquers, the incidence of Score 0 (30) was more frequent followed by Score 1 (27) and Score 2 (20).SignificanceThe use of powder-liquid opaquer in order to mask the metal in repair actions provided higher bond strength than those of the paste opaquers in both thin and thick applications. In all opaquers, the incidence of adhesive failure between the opaquer and the metal was more common implying inadequate adhesion.     

Effects of biglycan on physico-chemical properties of ligament-mineralized tissue attachment sites

Matrix proteoglycans define matrix structure, mineralization, and resulting biomechanics of tissues and their attachment sites.ObjectiveWe therefore investigated physical and (bio)chemical differences in enamel and periodontal tissues/attachment sites from mice that lack a specific nanoscale small leucine-rich proteoglycan (SLRPs) named biglycan (BGN).DesignExperimental groups consisted of N = 4, biglycan knockout (BGNKO) and N = 5 wildtype (WT) 8-week-old, male C3H mice. Morphology, histochemical and mechanical analyses were performed through micro X-ray computed tomography (Micro XCT?), immunohistochemistry, and microindentation. Unless mentioned otherwise, all differences between BGNKO and WT were demonstrated to be statistically significant through Student's t-tests with a 95% confidence interval (P ≤ 0.05).ResultsHistomorphometry performed by using Micro XCT? images indicated significantly higher BGNKO-enamel (0.46 ± 0.03 mm³) and BGNKO-root (1.81 ± 0.10 mm³) volumes compared to WT-enamel (0.37 ± 0.02 mm³) and WT-root (1.65 ± 0.07 mm³). BGNKO tooth size was relatively larger than WT mice, with no significant difference between skull sizes. Immunohistochemistry indicated BGN expression in the periodontal ligament (PDL), alveolar bone (AB), at the bone–PDL and cementum–PDL attachment sites in WT mice. Deeper AB resorption pits within interdental region of BGNKO specimens compared to WT resulting in significant differences in PDL-space of BGNKO (93 ± 13 μm) and WT (74 ± 11 μm) were observed. Microhardness of BGNKO-enamel (2.46 ± 0.60 GPa) and BGNKO-AB (0.52 ± 0.10 GPa) was significantly lower than WT-enamel (2.67 ± 0.60 GPa) and WT-AB (0.54 ± 0.10 GPa).ConclusionResults indicate that BGNKO-mice exhibit significant differences in tissue properties compared to WT-mice.     

Effects of regular and highly fluoridated toothpastes in combination with saliva substitutes on artificial enamel caries lesions differing in mineral content

ObjectiveFor patients with hyposalivation fluorides are supportive to prevent caries lesions. Remineralization of subsurface lesions might be improved by toothpastes containing 5000 μg F^?/g compared with those having 1400 μg F^?/g. This could be influenced by the degree of baseline mineralization. Therefore, this in vitro study evaluated the effects of fluoride toothpastes differing in fluoride concentration in combination with de- and remineralizing saliva substitutes using two lesion types.DesignSpecimens with shallow (SL; ΔZ (SD): 1915 (543) vol% × μm) or deep lesions (DL; 5804 (427) vol% × μm) were either stored in mineral water [saturation with respect to octacalcium phosphate (S_OCP): 0.5], demineralizing experimental (Exp, S_OCP: 0.3), demineralizing commercial (Glandosane, S_OCP: 0.3), or remineralizing saliva substitute (modified Saliva natura; S_OCP: 1.9) for five weeks (37 °C). Either one of three brushing procedures was performed additionally three times daily: no brushing, Elmex anticaries toothpaste (E; 1400 μg F^?/g), Duraphat toothpaste (D; 5000 μg F^?/g). Mineral parameters before and after storage were evaluated using microradiographs.ResultsStorage in Exp as well as Glandosane induced a significant demineralization (p < 0.05; relatively more pronounced in SL than DL). Additional brushing in particular with D reduced these effects. Storage alone in modified Saliva natura remineralized specimens (p < 0.05).ConclusionsUnder the in vitro conditions chosen shallow lesions seem to be more susceptible for demineralization compared with deeper ones when stored in an undersaturated (with respect to OCP) saliva substitute. The highly fluoridated toothpaste seemed to be more beneficial than a regular one.     

Effect of biomimetic mineralization on enamel and dentin: A Raman and EDX analysis

ObjectiveTo investigate the effect of an experimental biomimetic mineralization kit (BIMIN) on the chemical composition and crystallinity of caries-free enamel and dentin samples in vitro.MethodsEnamel and dentin samples from 20 human teeth (10 for enamel; 10 for dentin) were divided into a control group without treatment and test samples with BIMIN treatment. Quantitative analysis of tissue penetration of fluoride, phosphate, and calcium was performed using energy-dispersive X-ray spectroscopy (EDX). Mineralization depth was measured by Raman spectroscopy probing the symmetric valence vibration near 960 cm⁻¹ as a marker for crystallinity. EDX data was statistically analyzed using a paired t-test and Raman data was analyzed using the Student’s t-test.ResultsEDX analysis demonstrated a penetration depth of fluoride of 4.10 ± 3.32 μm in enamel and 4.31 ± 2.67 μm in dentin. Calcium infiltrated into enamel 2.65 ± 0.64 μm and into dentin 5.58 ± 1.63 μm, while the penetration depths for phosphate were 4.83 ± 2.81 μm for enamel and 6.75 ± 3.25 μm for dentin. Further, up to 25 μm of a newly mineralized enamel-like layer was observed on the surface of the samples. Raman concentration curves demonstrated an increased degree of mineralization up to 5–10 μm into the dentin and enamel samples.SignificanceBiomimetic mineralization of enamel and dentin samples resulted in an increase of mineralization and a penetration of fluoride into enamel and dentin.     

“Metabolism of Odontoblast-like cells submitted to transdentinal irradiation with blue and red LED”

ObjectivesThe present study evaluated the trans-dentinal effect of light emitting diodes (LEDs) irradiation on the metabolism of odontoblast-like cells.MethodsSeventy-two dentin discs (0.2 mm thick) were obtained from human molar teeth. MDPC-23 cells (20,000 cells/disc) were seeded on the pulpal side of the discs using DMEM, supplemented with 10% fetal bovine serum (FBS). After 12 h, the culture medium was replaced with DMEM containing 0.5% FBS. After additional 12 h, blue (455 ± 10 nm) or red (630 ± 10 nm) LEDs were used at irradiances of 80 and 40 mW/cm², respectively, to irradiate the occlusal side of the discs. The energy doses were fixed at 2 or 4 J/cm². Cell viability, alkaline phosphatase activity (ALP), total protein production and collagen synthesis were evaluated 72 h after irradiation. Data were submitted to Kruskal-Wallis and Mann-Whitney tests (α=0.05).ResultsRed light promoted proliferative effects at the energy dose of 4 J/cm²_. Conversely, cell cultures irradiated with 2 J/cm² emitted by the blue light showed reduced viability. ALP production was stimulated by red light in comparison with blue light at 4 J/cm². Total protein production was reduced after exposure to blue light at 4 J/cm², while no effect was observed on collagen production.ConclusionsIrradiation with red LED at 4 J/cm² bio-stimulated the viability of odontoblast-like cells, whilst blue light had unfavorable effects on the cellular metabolism.     

Remineralization effectiveness of the PAMAM dendrimer with different terminal groups on artificial initial enamel caries in vitro

ObjectiveDisruption of the demineralization–remineralization balance could trigger the development of dental caries, making it challenging for enamel to “self-heal”. Thus, extrinsic assistance is needed to restore enamel lesions and stop undermining progression. The aim of this study was to investigate enamel remineralization in a simulated oral environment via poly (amino amine) (PAMAM) dendrimers quantitatively.MethodsBovine enamel specimens were shaken in demineralization solution (pH 4.5, 37 °C, 50 rpm/min) for 72 h to create initial enamel carious lesions. The subsurface-demineralized specimens were then divided into four groups: enamel treated with PAMAM-NH₂, enamel treated with PAMAM−COOH, enamel treated with PAMAM−OH, and enamel treated with deionized water. The treated specimens underwent subsequent 12-day pH cycling. Enamel blocks were analyzed by transverse microradiography (TMR), surface microhardness testing and scanning electron microscopy (SEM) before and after demineralization and pH cycling.ResultsGroups treated with PAMAM dendrimers showed lower lesion depth and less mineral loss, attained more vertical-section surface microhardness recovery, and adsorbed more mineral deposits (p < 0.05). The enamel lesion remineralization values of PAMAM-NH₂, PAMAM-COOH, and PAMAM-OH groups were 76.42 ± 3.32%, 60.07 ± 5.92% and 54.52 ± 7.81%, respectively.SignificanceIn conclusion, PAMAM with different terminal groups could induce enamel remineralization, among which PAMAM-NH₂ showed the most prominent competence, followed by PAMAM-COOH and PAMAM-OH, in that order.     

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.     

Bond strength durability of a resin composite on a reinforced ceramic using various repair systems

ObjectivesThis study compared the durability of repair bond strength of a resin composite to a reinforced ceramic after three repair systems.MethodsAlumina-reinforced feldspathic ceramic blocks (Vitadur-α^®) (N = 30) were randomly divided into three groups according to the repair method: PR-Porcelain Repair Kit (Bisco) [etching with 9.5% hydrofluoric acid + silanization + adhesive]; CJ-CoJet Repair Kit (3M ESPE) [(chairside silica coating with 30 μm SiO₂ + silanization (ESPE^®-Sil) + adhesive (Visio?-Bond)]; CL-Clearfil Repair Kit [diamond surface roughening, etching with 40% H₃PO₄ + Clearfil Porcelain Bond Activator + Clearfil SE Bond)]. Resin composite was photo-polymerized on each conditioned ceramic block. Non-trimmed beam specimens were produced for the microtensile bond strength (μTBS) tests. In order to study the hydrolytic durability of the repair methods, the beam specimens obtained from each block were randomly assigned to two conditions. Half of the specimens were tested either immediately after beam production (Dry) or after long-term water storage (37 °C, 150 days) followed by thermocyling (12,000 cycles, 5–55 °C) in a universal testing machine (1 mm/min). Failure types were analyzed under an optical microscope and SEM.ResultsμTBS results were significantly affected by the repair method (p = 0.0001) and the aging conditions (p = 0.0001) (two-way ANOVA, Tukey's test). In dry testing conditions, PR method showed significantly higher (p < 0.001) repair bond strength (19.8 ± 3.8 MPa) than those of CJ and CL (12.4 ± 4.7 and 9.9 ± 2.9, respectively). After long-term water storage and thermocycling, CJ revealed significantly higher results (14.5 ± 3.1 MPa) than those of PR (12.1 ± 2.6 MPa) (p < 0.01) and CL (4.2 ± 2.1 MPa) (p < 0.001). In all groups when tested in dry conditions, cohesive failure in the composite accompanied with adhesive failure at the interface (mixed failures), was frequently observed (76%, 80%, 65% for PR, CJ and CL, respectively). After aging conditions, while the specimens treated with PR and CJ presented primarily mixed failure types (52% and 87%, respectively), CL group presented mainly complete adhesive failures at the interface (70%).SignificanceHydrolytic stability of the repair method based on silica coating and silanization was superior to the other repair strategies for the ceramic tested.     

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.     

FTIR characterization of the setting reaction of biodentine™

Objective

To provide insight of the setting reactions of Biodentine?, a hydraulic calcium silicate cement, based upon observations using Fourier Transform Infra-Red (FTIR) spectroscopy.

Effect of iron on enamel demineralization and remineralization in vitro

ObjectiveTo evaluate the effect of ferrous sulphate on enamel demineralization and remineralization, using pH-cycling models.DesignFifty blocks were selected by their initial surface hardness and subjected to a pH-cycling demineralization process. Artificially demineralized lesions were produced in 60 blocks; out of these blocks, the surface hardness of 50 blocks and the cross-sectional hardness of 10 blocks were determined. The 50 blocks were then subjected to a remineralization pH-cycling process. Treatments were carried out using ferrous sulphate solutions of different concentrations (0.333, 0.840, 18.0, and 70.0 μg Fe/mL) and a control group (deionized water). The final surface hardness (SH₂) was determined, and the integrated subsurface hardness (ΔKHN) was calculated. The enamel blocks were analysed for fluoride, calcium, phosphorus, and iron. The obtained data were distributed heterogeneously and were analysed using the Kruskal–Wallis test (p < 0.05).ResultsIn demineralization pH cycling, the group treated with the 18.0 μg Fe/mL solution had higher secondary surface hardness and lower integrated subsurface hardness (ΔKHN) than the other groups. In remineralization pH cycling, the control group showed the lowest value of ΔKHN. A decline in Ca and P concentration was observed when the Fe concentration increased (p < 0.05). There was no significant difference in the F concentration (p > 0.05) and an increase in Fe concentration (p < 0.05) in the enamel was observed when the Fe concentration increased in both the demineralization and remineralization experiments.ConclusionThe results suggest that iron reduces demineralization but does not allow remineralization to occur.     

Electrocatalytic oxidation of nitrite on a carbon paste electrode modified with Co(II) porphyrin adsorbed on SiO2/SnO2/Phosphate prepared by the sol–gel method

This paper describes the immobilization of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphyrin ion on SiO₂/SnO₂/Phosphate obtained by the sol–gel processing method. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co(II) ion. The porphyrin metallation process was followed using UV–Vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. A carbon paste electrode modified with material containing metallated porphyrin was used to study the electro-catalytic oxidation of nitrite ions by means of cyclic voltammetry, chronoamperometry and RDE voltammetry. The modified electrode was very stable and exhibited the electro-catalytic oxidation of nitrite ions at 0.72 V vs. SCE by a two electron mechanism producing nitrate ions at pH 5.4. The kinetic parameters of the electrode reaction process were calculated; (1 ? α)n_a was 0.479, D was (5.3 ± 0.11) × 10^?5 cm s^?1, and k⁰ could be determined as (5.4 ± 0.14) × 10^?3 cm s^?1.     

Opalescence of bleached teeth

ObjectivesTo evaluate the influence of tooth bleaching on the opalescence properties of enamel.MethodsColor of 38 specimens was determined by colorimetric analysis before and after bleaching in the reflectance and transmittance modes. The results were described as CIELab color coordinates. The Opalescent Parameter (OP) was calculated as the difference in yellow–blue color coordinate (CIE Δb*) and red–green color coordinate (CIE Δa*) between the reflected and transmitted colors.ResultsMean OP value of the specimens was 18.9 (±1.6) before bleaching and 16.1 (±1.0) after bleaching.ConclusionsBleaching decreases the OP of the specimens (p > 0.001). OP decrease was correlated with differences in b* color coordinate in the transmittance mode.     

Long term effect of low intensity pulsed ultrasound on a human tooth slice organ culture

ObjectiveInvestigate the effect of therapeutic Low Intensity Pulsed Ultrasound (LIPUS) on human dentine–pulp complex in an in vitro model.Design92 premolars were extracted from 23 adolescent orthodontic patients. The premolars were sectioned transversely into 600 μm thick slices. The slices were divided into two main groups according to how often the LIPUS was applied (single or daily application), and then subdivided into five subgroups each (5, 10, 15 and 20 min and one control group). The tooth slices were cultured at (37 °C/5% CO₂) in a humidified incubator where medium was changed every 48 h. LIPUS was applied using a 3.9 cm² transducer that produces an incident intensity of 30 mW/cm². After five days, tissue was harvested for histomorphometrical analysis and real time PCR to investigate expression of genes of interest (Collagen I, DMP1, DSPP, TGF-β1, RANKL and OPG).ResultsHistomorphometric analyses revealed that odontoblast cell count was higher in the single application groups (5, 10 and 15 min, respectively) than in the control and other treatment groups. Predentin thickness was higher in the single application group (10, 5 and 15 min) respectively than in the daily application group and the control groups, however they were not significantly different from each other. Real time PCR demonstrated no statistically significant difference between the groups in the expression of Collagen I, DMP1, TGF-β1, DSPP, RANKL and OPG.ConclusionReproducible responses from cultured dentine–pulp complex were observed in groups with single application of LIPUS for 5, 10 and 15 min.     

Electrochemical behaviour of LixNi1−xO in molten Li2CO3+Na2CO3 eutectic

To elucidate the mechanism of Li incorporation into NiO in molten carbonates, the open-circuit potential of the cell: O₂+CO₂ (g) ∣ Ni or Co oxide (s) ∣ Li₂CO₃+Na₂CO₃ (1) ∣ Au (s) ∣ O₂+CO₂ (g) was examined for porous Li_xNi_1?xO (0≤x≤0.5), LiCoO₂ and Co₃O₄ electrodes. These studies and X-ray diffraction examination of the samples before and after submersion in carbonate melt indicated that LiNiO₂ is formed in small amounts as an ultimate product of the reaction. Consequent extraction of Li⁺ ions from LiNiO₂ formed this way occurs due to polarisation of the electrode by the electro-reduction of oxygen dissolved in molten carbonates and results in turn in partial decomposition of LiNiO₂.     

In vitro enamel erosion and abrasion-inhibiting effect of different fluoride varnishes

ObjectiveTo investigate the erosion and abrasion inhibiting effect of CPP-ACP/NaF and xylitol/NaF varnishes.MethodsBovine enamel samples (n = 40) were exposed to the following treatments (n = 10): NaF varnish (Duraphat^®, positive control); CPP-ACP/NaF varnish (MI varnishTM); xylitol/NaF (Profluorid^®) or distilled and deionized water (MilliQ^®, negative control). The samples were submitted for 3 days to 4 cycles/day of erosion (5 min in Sprite Zero) and 2 cycles of abrasion/day after the first and last erosive challenge, with a toothbrush machine and slurries of a placebo toothpaste for 15 s (50 strokes/s). Among the cycles and after the last daily cycle, the specimens remained in artificial saliva. The change in the enamel surface was evaluated by using 3D non-contact optical profilometry with surface roughness (Ra and Sa values) and tooth structure loss (TSL) measurements. Scanning electron microscopy (SEM) assessed the enamel topographic characteristics. Differences in the Ra, Sa and TSL among treatments were tested using one-way ANOVA followed by the Tukey test.ResultsAll varnishes promoted better results for Ra and Sa values than the negative control (p = 0.0001), without difference among them (p > 0.05). However, CPP-ACP/NaF varnish stimulated fewer TSL (7.09 ± 0.70 μm) compared to NaF varnish (10.33 ± 1.36 μm, p = 0.002), xylitol/NaF varnish (9.96 ± 0.41 μm, p = 0.007) and the negative control (18.38 ± 3.32 μm, p = 0.0001).ConclusionA single-application of fluoride topical varnishes was effective in reducing enamel wear. The CPP-ACP/NaF varnish had the best effect against enamel loss from an erosion-abrasion challenge.     

Effect of thermal expansion mismatch on the Y-TZP/veneer interfacial adhesion determined by strain energy release rate

PurposesThe aim of this study was to assess the effect of differences in the thermal expansion behaviour of veneering ceramics on the adhesion to Y-TZP, using a fracture mechanics approach.MethodsSeven veneering ceramics (VM7, VM9, VM13, Lava Ceram, Zirox, Triceram, Allux) and one Y-TZP ceramic were investigated. Thermal expansion coefficients and glass transition temperatures were determined to calculate residual stresses (σ_R, MPa) between core and veneer. Subsequently, the veneering ceramics were fired onto rectangular shaped zirconia specimens, ground flat and notched on the veneering porcelain side. Then specimens were loaded in a four-point bending test and load-displacement curves were recorded. The critical load to induce stable crack extension at the adhesion interface was evaluated to calculate the strain energy release rate (G, J/m²) for each system.ResultsResidual stresses ranged from ?48.3 ± 1.5 MPa (VM7) to 36.1 ± 4.8 MPa (VM13) with significant differences between all groups (p < 0.05). The strain energy release rate of the Y-TZP/veneer specimens ranged from 8.2 ± 1.7 J/m² (Lava Ceram) to 17.1 ± 2.8 J/m² (VM9). Values for G could not be obtained with the VM7, Allux and VM13 specimens, due to spontaneous debonding or unstable crack growth. Except for Triceram and Zirox specimens, strain energy release rate was significantly different between all groups (p < 0.05).ConclusionThermal residual stresses and strain energy release rates were correlated. Slight compressive stresses in the region of ?20 MPa were beneficial for the Y-TZP/veneer interfacial adhesion. Stresses higher or lower than this value exhibited decreased adhesion.     

Pilot study to assess the potential of oral myofunctional therapy for improving respiration during sleep

PurposeThe present study was designed to assess the potential of oral myofunctional therapy (OMFT) for improving respiration parameters, Apnea-Hypopnea Index (AHI), and saturation of peripheral oxygen (SpO₂) during sleep.MethodsThe Epworth Sleepiness Scale (ESS) was administered to 92 students in class time at the Nihon University School of Dentistry at Matsudo. The results showed that 15 students had a high ESS. Of the 15 students who had learnt about their excessive sleepiness, six students expressed their intention to receive treatment for their sleep condition. They volunteered as subjects for the study. The Lip Trainer Patakara^® was used for labial closure force (LCF) training for 2 months. LCF, AHI and SPO₂ during sleep were measured before training and after 2 months training. The paired t-test was applied for statistical analyses.ResultLCFs before and 2 months after training were 8.8 ± 1.6 and 12.9 ± 0.6 N, respectively. LCF significantly increased after training compared to that before training. SpO₂ before training and after training were 90.0 ± 2.9% and 96.8 ± 0.8%, respectively. SpO₂ after training was significantly increased compared to that before training. AHI before and after training were 15.1 ± 3.4 and 9.2 ± 1.5 events/h, respectively. AHI after training was significantly decreased compared to that before training.ConclusionFrom this study, the following conclusions were made: (1) OMFT significantly increases LCF; and (2) the AHI and SpO₂ during sleep are significantly improved after OMFT.