Santiago González-López

Decalcifying effect of 15% EDTA, 15% citric acid, 5% phosphoric acid and 2.5% sodium hypochlorite on root canal dentine

AIM To evaluate and compare ex vivo the decalcifying effect of 15% EDTA, 15% citric acid, 5% phosphoric acid and 2.5% sodium hypochlorite on root canal dentine. METHODOLOGY Two 2-mm-thick slices were cut from the coronal third of the root of 10 human incisors. Each slice was sectioned into two equal parts. Specimens were assigned to one of four groups (n = 10) for immersion in 20 mL of either 15% EDTA, or 15% citric acid, 5% phosphoric acid or 2.5% NaOCl, for three time periods (5, 10 and 15 min). The concentration of Ca(2+) extracted from the dentine was measured by atomic absorption spectrophometry. The amount of calcium extracted was analysed using the Kruskal-Wallis test for global comparisons and the Mann-Whitney U-test for pairwise comparisons. RESULTS In the three time periods, 15% EDTA and 15% citric acid extracted the largest amount of calcium, with no significant differences between them. The 2.5% NaOCl solution extracted insignificant amounts of calcium, whereas 15% EDTA extracted 86.72% of the calcium in the first 5 min, and 15% citric acid and 5% phosphoric acid had a similar pattern of calcium removal (77.03% and 67.08% in first 5 min, respectively). CONCLUSIONS Solutions of 15% EDTA, 15% citric acid and 5% phosphoric acid decalcify root dentine, with most calcium extracted during the first 5 min of action. The efficacy of 15% citric acid and 15% EDTA solutions was significantly greater than that of 5% phosphoric acid solution at each time period (5, 10 and 15 min).

Wettability and bonding of self-etching dental adhesives. Influence of the smear layer.

OBJECTIVES To evaluate dentin wettability and bonding of self-etching and total-etch adhesives on smear layer-covered and smear layer-free dentin. METHODS Three self-etching adhesives (Clearfil SE Bond, AdheSE and Xeno III) and one total-etch adhesive (SingleBond) were evaluated. The substrates were mid coronal smear layer-covered and smear layer-free dentin. Dentin wettability by resins was studied from contact angle measurement using sessile drop method and Axisymmetric Drop Shape Analysis (ADSA). Shear-bond strength was evaluated using a push-out technique (ad hoc design). Data were analysed with two-way ANOVA and Tukeys test. RESULTS Similar values of dentin wettability were obtained for all adhesives tested regardless the presence of smear layer. Even though, Xeno III and AdheSE exhibited slightly lower wettability (higher contact angles values) on smear layer-free dentin. Likewise, the presence of smear layer did not affect the shear-bond strength. Total-etch adhesive obtained higher shear-bond strength than self-etching adhesives, which obtained similar values. SIGNIFICANCE Wettability is similar between self-etching and total-etch adhesives. The smear layer affects slightly the wettability of self-etching adhesives. Shear-bond strength is not sensitive to the smear layer presence. Total-etch adhesion is stronger than self-etching adhesion. There is no clear relationship between wettability and bond strength.

Effects of phosphoric acid on bovine enamel bleached with carbamide peroxide

The aim of this study was to measure the demineralization capacity of 37% phosphoric acid on bovine enamel at different time-points after bleaching with 30% carbamide peroxide. Five, 4 x 4-mm sections were obtained from the enamel of 10 bovine incisors. After applying 30% carbamide peroxide (Vivastyle) for 90 min, specimens were stored in artificial saliva for 0, 24, 72 h, or 7 d and then immersed in 37% phosphoric solution. At 15, 30, 60, 90, and 120 s, 5-ml aliquots were extracted. A control group of specimens was not bleached. Ca(2+) concentrations were measured by atomic absorption spectrophotometry. A larger amount of Ca(2+) was extracted from enamel by phosphoric acid after the application of 30% carbamide peroxide. Twenty-four hours after bleaching, significantly more Ca(2+) was extracted from bleached than from control specimens at all time-points, and this greater susceptibility to the action of the acid persisted for at least 1 wk after bleaching.

Interfacial morphology and bond strength of self-etching adhesives to primary dentin with or without acid etching

The aim of the study was to determine the interfacial morphology and bond strength of three current self-etching adhesives (SEAs) to primary dentin and to evaluate the effect of introducing an additional step of phosphoric acid etching. Three human primary molars were assigned to each adhesive group for testing microtensile bond strength (microTBS) and three for studying interface morphology. Groups were: group 1, Excite, a total-etch adhesive (control); group 2, Adhese (ASE); group 3, Adper-Prompt-L-Pop (APLP), and group 4: Xeno III (XE) SEAs; groups 5-7 received application of 37% phosphoric acid for 15 s before applying ASE, APLP, and XE, respectively. A class I cavity was performed in each molar to study the interface morphology. Two halves of each tooth were used for examination either by optical microscopy, using Massons trichromic dye technique, or by scanning electron microscopy. For microTBS determination, composite/dentin bars (1 mm(2) section) were obtained from each tooth, and tested in tension until debonding. The microTBS was significantly lower in the APLP than in the rest of the groups. The performance of SEAs on primary dentin depends on the product. Inclusion of dentin pre-etching step did not significantly modify microTBS results. All SAEs achieved greater decalcification depth on etched versus nonetched dentin.

Regional bond strength to lateral walls in class I and II ceramic inlays luted with four resin cements and glass-ionomer luting agent.

PURPOSE To investigate regional shear bond strength to lateral walls of ceramic inlays in occlusal and occlusoproximal cavities using etch-and-rinse and self-adhesive resin cements and a glass-ionomer luting agent. MATERIALS AND METHODS IPS e.max Press ceramic inlays were made in 50 Class I and 50 Class II standardized cavities in intact extracted human molars and divided into 5 luting agent subgroups (n = 10): Variolink II (VL); Multilink Sprint (MLS); Multilink Automix (MLA); RelyX Unicem (RLX), and Ketac Cem Aplicap (KC). Inlays were pre-etched with IPS Ceramic etching gel for 60s. After 48 h, two disks of ca 1.0 mm thickness, one of superficial and the other of deep dentin, were push-out tested in a universal testing machine at a crosshead speed of 1.0 mm/min. The mode of failure was determined under a stereomicroscope at 20X. Data were analyzed with one way ANOVA, and Scheffés test was used for post-hoc comparisons (α = 0.05). RESULTS There were no significant differences in shear bond strength between Class I and Class II cavities for the dual-curing system in light-curing mode (VL=MLS=RLX), except that RLX demonstrated greater bond strength to deep dentin in Class II cavities. Bond strength values were significantly higher on deep than on superficial dentin. KC showed the worst result. Failures were mixed (adhesive/cohesive) for the resin luting cements and solely adhesive (cement/ceramic) for the glass-ionomer luting agent. CONCLUSION Dual-curing etch-and-rinse or self-etching self-adhesive resin luting cements achieved greater bond strength when light curing was applied, with no differences between Class I and Class II cavities but higher values for deep vs superficial dentin. The weakest adhesion was obtained with glass-ionomer luting agent in both cavity types.

Synthesis, biocompatibility and mechanical properties of ZrO2-Al2O3 ceramics composites

This study evaluated cell viability, microhardness and flexural strength of two ceramic composites systems (ZA and AZ), pure alumina and zirconia. There were prepared homogeneous mixtures of 78wt%Al2O3+20wt%3Y-TZP+2wt%Al2O3w (AZ) and 80wt%3YTZP+18wt%Al2O3+2wt%Al2O3w (ZA), as well as 3Y-TZP (Z), pure Al2O3 (A) and commercial monolithic 3Y-TZP (Zc). Also mouse fibroblast cells 3T3-L1 and a MTT test was carried out at 24, 48 and 72 h. The surfaces were observed with SEM and the microhardness and three-point flexural strength values were estimated. The absolute microhardness values were: A>AZ>Z>Zc>ZA. Flexural strength of Zc, Z, and ZA were around double than AZ and A. All groups showed high biocompatibility trough cell viability values at 24, 48 and 72 h. Factors like grain shape, grain size and homogeneous or heterogeneous grain distributions may play an important role in physical, mechanical and biological properties of the ceramic composites.

Demineralization effects of phosphoric acid on surface and subsurface bovine enamel bleached with in-office hydrogen peroxide.

PURPOSE To measure the demineralization capacity of 37% phosphoric acid on surface and subsurface bovine enamel after bleaching with hydrogen peroxide (H2O2). MATERIALS AND METHODS Three equally-sized sections with 16 mm2 of exposed enamel surface were obtained from the enamel of 10 bovine incisors. One specimen sample from each crown was assigned to one of three groups (n = 10): group I, no bleaching agent; group II, bleached with 38% H202 for 20 min; or group III, 30% H202 for 60 min. After 24 h, the thickness of specimens was measured and they were immersed in 37% phosphoric acid solution, of which 5-ml aliquots were collected at 30 s and 60 s. Specimens were then ground to a depth of 25 μm and again immersed in 37% phosphoric acid solution. This procedure was repeated for enamel depths of 50 and 100 μm. Ca2+ concentrations in the phosphoric acid aliquots were measured by atomic absorption spectroscopy. RESULTS No significant differences were found in the total amounts of extracted Ca2+ between bleached and unbleached specimens (F = 0.142; p = 0.869). The amount of Ca2+ extracted was similar among the four depth levels in the unbleached and in the 30% H202 bleached specimens. A significantly larger amount of Ca2+ was obtained at 25 μm depth (subsurface) from specimens treated with 38% H202. CONCLUSIONS Pre-bleaching with 38% H202 significantly increased the decalcifying effect of phosphoric acid on subsurface enamel at a depth of 25 μm compared to 100 μm, whereas pre-bleaching with 30% H202 did not modify this effect at any level.

Restoration of posterior teeth using occlusal matrix technique

This article describes a technique for duplicating occlusal surface anatomy using the Biteperf device. Duplication requires an intact occlusal enamel surface and is only indicated when caries lesions are hidden. The occlusal matrix technique allows for preservation of all anatomic details. When the last layer of composite has been placed, the occlusal matrix is forced into the uncured composite to replicate the original occlusal surface, instead of performing manual curing and shaping as in the standard approach. It is technically possible to achieve this effect with any material that is able to copy anatomic details. The main benefits of the occlusal matrix technique, more precisely the Biteperf, are the technical ease of use due to its simplicity and its high accuracy in reconstructing occlusal morphology.

Effects of chronic lead exposure on bone mineral properties in femurs of growing rats

Lead exposure has been associated with several defective skeletal growth processes and bone mineral alterations. The aim of the present study is to make a more detailed description of the toxic effects of lead intoxication on bone intrinsic material properties as mineral composition, morphology and microstructural characteristics. For this purpose, Wistar rats were exposed (n=12) to 1000ppm lead acetate in drinking water for 90days while control group (n=8) were treated with sodium acetate. Femurs were examined using inductively coupled plasma optical emission spectrometry (ICP-OES), Attenuated Total Reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), and micro-Computed Tomography (μCT). Results showed that femur from the lead-exposed rats had higher carbonate content in bone mineral and (Ca2++Mg2++ Na+)/P ratio values, although no variations were observed in crystal maturity and crystallite size. From morphological analyses, lead exposure rats showed a decreased in trabecular bone surface and distribution while trabecular thickness and cortical area increased. These overall effects indicate a similar mechanism of bone maturation normally associated to age-related processes. These responses are correlated with the adverse actions induced by lead on the processes regulating bone turnover mechanism. This information may explain the osteoporosis diseases associated to lead intoxication as well as the risk of fracture observed in populations exposed to this toxicant.

Selective removal of mineral and organic components of bovine enamel by phosphoric acid.

PURPOSE To follow the chemical composition of bovine enamel during phosphoric acid-induced demineralization. MATERIALS AND METHODS Enamel samples were ground into a fine powder, selecting the 150- and 200-µm fractions in order to obtain a more homogeneous study material. They were immersed in diluted phosphoric acid (0.1%) for increasing durations ranging from 1 to 1440 min. The chemical composition of the solution and enamel powder was determined after each sequential treatment by means of atomic absorption (AA) and Fourier transform infrared (FTIR) spectroscopy. RESULTS AA data revealed that the amount of calcium mobilized to the solution by the acid treatment was higher at shorter exposure times. However, FTIR data showed that the degree of mineralization of the enamel remained constant during the treatment, indicating that the mineral and organic components were lost at the same rate. Interestingly, poorly crystalline phosphate and carbonate-rich mineral components were preferentially removed and were presumably the main source of calcium released by the acid exposure. FTIR results also demonstrated that organic components rich in hydrophobic groups were preferentially removed during acid treatment. CONCLUSION Etching with phosphoric acid produces a nonhomogeneous demineralization of bovine enamel, with the selective removal of poorly crystalline mineral and hydrophobic organic components.