A new optical detection method to assess the erosion inhibition by in vitro salivary pellicle layer

ObjectivesApplication of the recently developed optical method based on the monitoring of the specular reflection intensity to study the protective potential of the salivary pellicle layer against early enamel erosion.MethodsThe erosion progression was compared between two treatment groups: enamel samples coated by the 15 h-in vitro-formed salivary pellicle layer (group P, n = 90) and the non-coated enamel surfaces (control group C, n = 90). Different severity of the erosive impact was modelled by the enamel incubation in 1% citric acid (pH = 3.6) for 2, 4, 8, 10 or 15 min. Erosion quantification was performed by the optical method as well as by the microhardness and calcium release analyses.ResultsOptical assessment of the erosion progression showed erosion inhibition by the in vitro salivary pellicle in short term acidic treatments (≤4 min) which was also confirmed by microhardness measurements proving significantly less (p < 0.05) enamel softening in the group P at 2 and 4 min of erosion compared to the group C. SEM images demonstrated less etched enamel interfaces in the group P at short erosion durations as well.ConclusionsMonitoring of the specular reflection intensity can be successfully applied to quantify early erosion progression in comparative studies. In vitro salivary pellicle (2 h) provides erosion inhibition but only in short term acidic exposures.Clinical significanceThe proposed optical technique is a promising tool for the fast and non-invasive erosion quantification in clinical studies.     

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.     

Graded changes in enamel component volumes resulted from a short tooth bleaching procedure

AimTo test the hypothesis that changes in enamel component volumes (mineral, organic, and water volumes, and permeability) are graded from outer to inner enamel after a short bleaching procedure.Materials and methodsExtracted unerupted human third molars had half of their crowns bleached (single bleaching session, 3 × 15 min), and tooth shade changes in bleached parts were analyzed with a spectrophotometer. Ground sections were prepared, component volumes and permeability were quantified at histological points located at varying distances from the enamel surface (n = 10 points/location), representing conditions before and after bleaching.ResultsTooth shade changes were significant (p < 0.001; 95% CI = −1/−8; power = 99%), and most of the enamel layer was unaffected after bleaching, except at the outer layers. Multiple analysis of covariances revealed that most of the variance of the change in enamel composition after bleaching was explained by the combination of the set of types of component volume (in decreasing order of relevance: mineral loss, organic gain, water gain, and decrease in permeability) with the set of distances from the enamel surface (graded from the enamel surface inward) (canonical R² = 0.97; p < 0.0001; power > 99%).ConclusionsChanges in enamel composition after a short bleaching procedure followed a gradient within component volumes (mineral loss > organic gain > water gain > decrease in permeability) and decreased from the enamel surface inward.     

Sodium fluoride effect on erosion–abrasion under hyposalivatory simulating conditions

ObjectivesTo investigate the effect of fluoride (0, 275 and 1250 ppm F; NaF) in combination with normal and low salivary flow rates on enamel surface loss and fluoride uptake using an erosion–remineralization–abrasion cycling model.DesignEnamel specimens were randomly assigned to 6 experimental groups (n = 8). Specimens were individually placed in custom made devices, creating a sealed chamber on the enamel surface, connected to a peristaltic pump. Citric acid was injected into the chamber for 2 min followed by artificial saliva at 0.5 (normal flow) or 0.05 (low flow) ml/min, for 60 min. This cycle was repeated 4×/day, for 5 days. Toothbrushing with abrasive suspensions containing fluoride was performed for 2 min (15 s of actual brushing) 2×/day. Surface loss was measured by optical profilometry. KOH-soluble fluoride and enamel fluoride uptake were determined after the cycling phase. Data were analysed by two-way ANOVA.ResultsNo significant interactions between fluoride concentration and salivary flow were observed for any tested variable. Low caused more surface loss than normal flow rate (p < 0.01). At both flow rates, surface loss for 0 was higher than for 275, which did not differ from 1250 ppm F. KOH-soluble and structurally-bound enamel fluoride uptake were significantly different between fluoride concentrations with 1250 > 275 > 0 ppm F (p < 0.01).ConclusionsSodium fluoride reduced enamel erosion/abrasion, although no additional protection was provided by the higher concentration. Higher erosion progression was observed in low salivary flow rates. Fluoride was not able to compensate for the differences in surface loss between flow rates.     

The effect of magnesium hydroxide-containing dentifrice using an extrinsic and intrinsic erosion cycling model

ObjectiveTo evaluate, in vitro, the effect of Mg(OH)₂ dentifrice, and the influence of the number of experimental days, on the extrinsic (citric acid –CA) and intrinsic (hydrochloric acid –HCl) enamel erosion models.DesignHuman enamel slabs were selected according to surface hardness and randomly assigned to 3 groups (n = 9) as follows: non-fluoridated (negative control), NaF (1450 ppm F- positive control) and Mg(OH)₂ (2%) dentifrices. The slabs were daily submitted to a 2-h period of pellicle formation and, over a period of 5 days, submitted to cycles (3×/day) of erosive challenge (CA 0.05 M, pH = 3.75 or HCl 0.01 M, pH = 2 for 30 s), treatment (1 min −1:3 w/w of dentifrice/distilled water) and remineralization (artificial saliva/120 min). Enamel changes were determined by surface hardness loss (SHL) for each day and mechanical profilometry analysis. Data were analyzed by two-way ANOVA followed by Tukey’s test to % SHL and one-way ANOVA to profilometry (p < 0.05).ResultsThe number of experimental days influenced the erosion process for the two types of erosion models (p < 0.001). Mg(OH)₂-containing dentifrices were effective in reducing enamel extrinsic acid erosion as determined by % SHL (p < 0.001) when compared to the control group, being better than positive control (p < 0.001); however, the dentifrices were not effective for the intrinsic model (p = 0.295). With regards to surface wear, no statistically significant differences were found among the groups for CA (p = 0.225) and HCl (p = 0.526).ConclusionThe findings suggest that Mg(OH)₂ dentifrices might protect enamel against slight erosion, but protection was not effective for stronger acid erosion.     

In situ effect of chewing gum containing CPP–ACP on the mineral precipitation of eroded bovine enamel—A surface hardness analysis

ObjectivesStimulation of salivary flow is considered a preventive strategy for dental erosion. Alternatively, products containing calcium phosphate, such as a complex of casein phosphopeptide–amorphous calcium phosphate (CPP–ACP), have also been tested against dental erosion. Therefore, this in situ study analyzed the effect of chewing gum containing CPP–ACP on the mineral precipitation of initial bovine enamel erosion lesions.MethodsTwelve healthy adult subjects wore palatal appliances with two eroded bovine enamel samples. The erosion lesions were produced by immersion in 0.1% citric acid (pH 2.5) for 7 min. During three experimental crossover in situ phases (1 day each), the subjects chewed a type of gum, 3 times for 30 min, in each phase: with CPP–ACP (trident total), without CPP–ACP (trident), and no chewing gum (control). The Knoop surface microhardness was measured at baseline, after erosion in vitro and the mineral precipitation in situ. The differences in the degree of mineral precipitation were analyzed using repeated measures (RM-) ANOVA and post hoc Tukey's test (p < 0.05).ResultsSignificant differences were found among the remineralizing treatments (p < 0.0001). Chewing gum (19% of microhardness recovery) improved the mineral precipitation compared to control (10%) and the addition of CPP–ACP into the gum promoted the best mineral precipitation effect (30%).ConclusionsUnder this protocol, CPP–ACP chewing gum improved the mineral precipitation of eroded enamel.Clinical significanceSince the prevalence of dental erosion is steadily increasing, CPP–ACP chewing gum might be an important strategy to reduce the progression of initial erosion lesions.     

Vertical and horizontal polymerization shrinkage in composite restorations

ObjectivePolymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold.MethodsVertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured.ResultsThere was a significant correlation between vertical and horizontal polymerization shrinkage (r = 0.647, p = 0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r = −0.697, p = 0.025) and dentin (r = −0.752, p = 0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r = 0.829, p = 0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p > 0.05).SignificanceDuring the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.     

Contributions of stress corrosion and cyclic fatigue to subcritical crack growth in a dental glass-ceramic

ObjectiveThe objective of this study was to test the following hypotheses: (1) both cyclic degradation and stress-corrosion mechanisms result in subcritical crack growth (SCG) in a fluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent) and (2) there is an interactive effect of stress corrosion and cyclic fatigue to accelerate subcritical crack growth.MethodsRectangular beam specimens were fabricated using the lost-wax process. Two groups of specimens (N = 30/group) with polished (15 μm) or air-abraded surface were tested under rapid monotonic loading. Additional polished specimens were subjected to cyclic loading at two frequencies, 2 Hz (N = 44) and 10 Hz (N = 36), and at various stress amplitudes. All tests were performed using a fully articulated four-point flexure fixture in deionized water at 37 °C. The SCG parameters were determined using the ratio of inert strength Weibull modulus to lifetime Weibull modulus. A general log-linear model was fit to the fatigue lifetime data including time to failure, frequency, peak stress, and the product of frequency and logarithm of stress in ALTA PRO software.ResultsSCG parameters determined were n = 21.7 and A = 4.99 × 10⁻⁵ for 2 Hz, and n = 19.1 and A = 7.39 × 10⁻⁶ for 10 Hz. After fitting the general log-linear model to cyclic fatigue data, the coefficients of the frequency term (α₁), the stress term (α₂), and the interaction term (α₃) had estimates and 95% confidence intervals of α₁ = −3.16 (−15.1, 6.30), α₂ = −21.2 (−34.9, −9.73), and α₃ = 0.820 (−1.59, 4.02). Only α₂ was significantly different from zero.Significance(1) Cyclic fatigue does not have a significant effect on SCG in the fluorapatite glass-ceramic evaluated and (2) there was no interactive effect between cyclic degradation and stress corrosion for this material.     

Rinsing with antacid suspension reduces hydrochloric acid-induced erosion

ObjectiveMouthrinsing with antacids, following erosive episodes, have been suggested as a preventative strategy to minimize tooth surface loss due to their neutralizing effect. The purpose of this in situ study was to evaluate the effect of an antacid suspension containing sodium alginate, sodium bicarbonate and calcium carbonate in controlling simulated erosion of enamel of intrinsic origin.DesignThe experimental units were 48 slabs (3 × 3 × 2 mm) of bovine enamel, randomly divided among 12 volunteers who wore palatal appliances with two enamel slabs. One of them was exposed extra-orally twice a day to 25 mL of a hydrochloric acid (HCl) solution (0.01 M, pH 2) for 2 min. There were two independent phases, lasting 5 days each. In the first phase, according to a random scheme, half of the participants rinsed with 10 mL of antacid suspension (Gaviscon^®, Reckitt Benckiser Healthcare Ltd.), while the remainder was rinsed with deionized water, for 1 min. For the second phase, new slabs were inserted and participants switched to the treatment not received in the first stage. Therefore, the groups were as follows: (a) erosive challenge with HCl + antacid suspension; (b) erosive challenge with HCl + deionized water (DIW); (c) no erosive challenge + antacid suspension; (d) no erosive challenge + DIW. Specimens were assessed in terms of surface loss using optical profilometry and Knoop microhardness. The data were analyzed using repeated measures two-way analysis of variance and Tukey’s tests.ResultsCompared to DIW rinses, surface loss of enamel was significantly lower when using an antacid rinse following erosive challenges (p = 0.015). The Knoop microhardness of the enamel was significantly higher when the antacid rinse was used (p = 0.026).ConclusionsThe antacid suspension containing sodium alginate, sodium bicarbonate and calcium carbonate, rinsed after erosive challenges of intrinsic origin, reduced enamel surface loss.     

Effect of fluoride toothpaste with nano-sized trimetaphosphate on enamel demineralization: An in vitro study

ObjectiveThis study evaluated the effect of toothpastes containing 1100 ppm F associated or not with micrometric or nano-sized sodium trimetaphosphate (TMP) on enamel demineralization in vitro, using a pH cycling model.DesignBovine enamel blocks (4 mm × 4 mm, n = 96) were randomly allocated into eight groups (n = 12), according to the test toothpastes: Placebo (without fluoride or TMP); 1100 ppm F (1100F); 1100F plus micrometric TMP at concentrations of 1%, 3% or 6%; and 1100F plus nanosized TMP at 1%, 3% or 6%. Blocks were treated 2×/day with slurries of toothpastes and submitted to a pH cycling regimen for five days. Next, final surface hardness (SHf), integrated hardness loss (IHL), differential profile of integrated hardness loss (ΔIHL) and enamel fluoride (F) concentrations were determined. Data were analyzed by ANOVA and Student-Newman-Keuls’ test (p < 0.05).ResultsThe use of 1100F/3%TMPnano led to SHf 30% higher (p < 0.001) and IHL ∼ 80% lower (p < 0.001) when compared to 1100F. This toothpaste also resulted in ∼64% reduction of mineral loss (ΔIHL) when compared to 1100F. Moreover, the addition of nano-sized TMP promoted increases in enamel F uptake of 90%, 160% and 100%, respectively for the concentrations of 1%, 3% and 6%, when compared to 1100F (p < 0.001).ConclusionThe addition of nano-sized TMP at 3% to a conventional toothpaste significantly decreased enamel demineralization when compared to its counterparts without TMP or supplemented with micrometric TMP.     

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 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.     

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.     

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.     

Fabrication and characterization of remineralizing dental composites containing calcium type pre-reacted glass-ionomer (PRG-Ca) fillers

ObjectiveTo fabricate and characterize dental composites with calcium type pre-reacted glass-ionomer (PRG-Ca) fillers.MethodsPRG-Ca fillers were prepared by the reaction of calcium fluoroaluminosilicate glass with polyacrylic acid. Seven dental composites were produced from the same organic matrix (70/30 wt% Bis-GMA/TEGDMA), with partial replacement of barium borosilicate (BaBSi) fillers (60 wt%) by PRG-Ca fillers (wt%): E0 (0) – control, E1 (10), E2 (20), E3 (30), E4 (40), E5 (50) and E6 (60). Enamel remineralization was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), roughness (Ra), Knoop hardness (KHN), flexural strength (FS), flexural modulus (FM), water sorption (W_sp), water solubility (W_sl), and translucency (TP). Data were analyzed to one-way ANOVA and Tukey’s HSD test (α = 0.05).ResultsAll composites with PRG-Ca induced enamel remineralization. E0 and E1 presented similar and highest DC% than E2 = E3 = E4 = E5 = E6. Ra and KHN were not influenced by PRG-Ca fillers (p < 0.05). The higher the content of PRG-Ca, the lower FS, FM and TP (p < 0.05). W_sp increased linearly with the content of PRG-Ca fillers (p < 0.05). E6 presented the highest W_sl (p < 0.05), while the W_sl of the other composites were not different from each other (p > 0.05).SignificanceIncorporation of 10–40 wt.% of PRG-Ca fillers endowed remineralizing potential to dental composites without jeopardizing the overall behavior of their physicochemical properties. Dental composites with PRG-Ca fillers seems to be a good alternative for reinforcing the enamel against caries development.     

Frequency of intake and amount of fluoride in milk for remineralisation of artificial caries on enamel and dentine: Ex vivo/in situ study

ObjectivesThis study analysed the effect of frequency of intake and amount of fluoride in milk on the remineralisation of artificial enamel and dentine caries lesions ex vivo/in situ.Materials and methodsPre-demineralised bovine enamel and dentine slabs were randomly allocated into 5 groups and fixed in removable appliances used by subjects for 7 days in each phase. Each treatment comprised milk containing 2.5 ppm fluoride daily (T1), or every other day (T2), 5.0 ppm F daily (T3), or every other day (T4) or no treatment (T5).ResultsEnamel alterations were quantified by surface hardness recovery (%SHR) and transversal microradiography (TMR), and in dentine by TMR only. Data were analysed by ANOVA and Tukey’s test (p < 0.05). For enamel, the highest %SHR was found for T1 and T3 compared to control, without significant differences between them. All groups showed positive values of ΔΔZ − T1 (247.3 ± 198.5); T2 (110.9 ± 303.2); T3 (226.0 ± 299.2); T5 (5.0 ± 288.0), except T4 (−274.5 ± 407.3). For dentine, the only group that presented remineralisation was T2 (350.0 ± 657.5).ConclusionsFluoridated milk daily seems to have higher remineralising effect on enamel than its use every other day. Dentine, does not seem to benefit from daily use of fluoridated milk.     

Effects of different radiation doses on the microhardness,superficial morphology,and mineral components of human enamel

ObjectiveTo evaluate the effects of three different radiotherapy doses (20, 40, and 70 Gy) on the microhardness, superficial morphology, and mineral content (based on Ca and P values) of three different depths of human enamel (cervical, middle, and occlusal).DesignThirty-four third molars were cut, separated, and prepared. Microhardness samples (n = 30) were embedded in acrylic resin and then polished, and depths were delimited. Microhardness tests were performed on cervical, middle, and occlusal enamel pre- and post-radiotherapy with a load of 50 g for 30 s. For the scanning electron microscopy (SEM) analysis (n = 4) and energy dispersive X-ray spectroscopy (EDS) (n = 12), samples were fixed in a 3% glutaraldehyde solution, washed in 0.1 M cacodylate solution, and dehydrated in crescent concentrations of ethanol. Microhardness data were tested for significant differences using a two-way analysis of variance (ANOVA) and Tukey’s test (p < 0.05), while SEM and EDS were evaluated qualitatively.ResultsThe results showed a decrease in microhardness values only in the cervical enamel, regardless of the radiation dose used; no morphological or mineral change was observed.ConclusionRadiotherapy can affect the microhardness values of only cervical enamel without compromising the morphological or mineral (Ca and P) content at any depth.     

Experimental composites containing quaternary ammonium methacrylates reduce demineralization at enamel-restoration margins after cariogenic challenge

ObjectiveThis study evaluated the influence of experimental composites containing quaternary ammonium monomers (QAM) at different concentrations and alkyl chains on demineralization at enamel-composite margins after cariogenic challenge.MethodsStandardized 4 × 4 mm cavities were cut into 35 bovine enamel blocks, which were randomly divided into seven groups (n = 5) and restored with the following experimental composites and commercial materials: (G12.5) – 5% dimethylaminododecyl methacrylate (DMADDM) with a 12-carbon alkyl chain (G12.10) – 10% DMADDM, (G16.5) – 5% dimethylaminohexadecyl methacrylate (DMAHDM) with a 16-carbon alkyl chain (G16.10) – 10% DMAHDM, (CG) – control group (without QAM), (GZ250) – commercial composite (Filtek Z250^®), and (GIC) – glass ionomer cement (Maxxion R^®). After restorative procedures, initial microhardness was measured and experimental composites were subjected to Streptococcus mutans biofilm formation for 48 h. After cariogenic challenge, the samples were washed and microhardness was reassessed. A 3D non-contact profilometer was used to determine surface roughness and enamel demineralization was assessed by micro-CT. Microhardness results were analyzed by the Kruskal–Wallis and Mann-Whitney tests and micro-CT results were analyzed by Tukey’s HSD test (95% confidence interval).ResultsNone of the materials could prevent mineral loss at the enamel-restoration margins. The addition of 10% DMAHDM yielded the lowest, albeit statistically significant, mineral loss (p < 0.05). 3D non-contact profilometry showed enamel surface roughness modification after biofilm exposure. The CG had the highest roughness values. Micro-CT analysis revealed mineral loss, except for GIC.SignificanceThe addition of 10% QAM with a 16-carbon chain in experimental composites reduced mineral loss at the enamel-restoration margins after cariogenic challenge.     

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.     

Impact of hydrophilicity and length of spacer chains on the bonding of functional monomers

Objectives10-Methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) is currently considered as one of the most effective functional monomers for dental bonding, this in part thanks to its long and relatively hydrophobic spacer chain, adequately separating the polymerizable from the phosphate functionalities. This study compared functional monomers with different spacer chains’ length and hydrophilicity to 10-MDP on their dentin and enamel bonding performance.MethodsAtomic absorption spectroscopy (AAS) was used to characterize the chemical interaction. Micro-tensile bond strength (μTBS) and fractographic analyses were performed after 24 h and one year. Confocal micro-permeability and SEM nanoleakage assessments were also undertaken. The tested functional monomers were 2-MEP (2-carbon spacer), 10-MDP (10-carbon), 12-MDDP (12-carbon), MTEP (high hydrophilic polyether spacer chain) and CAP-P (intermediate hydrophilic ester spacer).ResultsAAS revealed clear differences (p < 0.05) in monomer-calcium salt formation in this order: 12-MDDP = 10-MDP > CAP-P > MTEP > 2-MEP. The highest initial dentin μTBS was obtained using 10-MDP or 12-MDDP. After 1-year aging, a significant drop (p < 0.05) in μTBS was observed for the adhesives with MTEP (enamel and dentin), 2-MEP (enamel) and CAP-P (enamel). MTEP presented the highest micro-permeability, while 2-MEP, CAP-P and MTEP showed increased nanoleakage after aging.SignificanceThese outcomes showed that more hydrophilic and shorter spacer chains may compromise the chemical interaction with calcium and the dentin/enamel bonding performance.