Effect of Air-Abrasion on Shear Bond Strength of Resin Composite to Dentin: A Study in Vitro

The purpose of this study was to evaluate in vitro the efficacy of alumina, sodium bicarbonate and erythritol-based tooth air-abrasion on shear bond strength (SBS) of resin composite to dentin. Methods and Results: In order to assess the strength of the adhesive bond of the resin composite to tooth dentin, 50 tooth samples were prepared in accordance with the Ultradent Shear Bond Test method. All samples were divided into 5 groups. In Group 1 (n=10) and Group 2 (n=10), for air-abrasion of dentin surface 2 powders based on aluminum oxide with a particle size of 50μm and 27μm, respectively, were used (RONDOflex plus 360, KaVo, Biberach, Germany). In Group 3 (n=10) and Group 4 (n=10), other abrasive powders based on sodium bicarbonate (40μm) and erythritol (14μm), respectively, were used for a similar purpose (Air-Flow Classic comfort, Air-Flow Plus, EMS, Nyon, Switzerland). The control group (n=10) consisted of the remaining tooth samples in which the dentin surface, after preparation with a carbide bur, was not subjected to an air-abrasion.The one-day adhesive strength of bonded interfaces was evaluated on an UltraTester device (Ultradent Products Inc., USA) after resin bonding without aging simulation. The speed of movement of the test clamp with the installed sample was set to 1 mm/min. The maximal value of bonding failure was fixed in pounds (lb). The dentin surface ultrastructure was studied on 10 additional tooth samples, which were prepared for SEM analysis. It was found that the treatment of dentin surface with air-abrasive powders based on alumina (50 μm and 27 μm) and sodium bicarbonate (40 μm) did not improve the strength of the adhesive bond of resin composite to dentin. The strength of adhesion of the resin composite to dentin decreased significantly after air-abrasion of the tooth surface with erythritol-based powder.

Effect of experimental moringa and propolis toothpastes on surface microhardness of simulated hypersensitive dentin

Objective Objective was to investigate the effect of NovaMin toothpaste and two experimental toothpastes on surface microhardness of hypersensitive dentin. Methods Eighty specimens were prepared and divided randomly into eight groups (n = 10/group) according to the tested toothpastes (NovaMin, moringa and propolis toothpastes) and the acidic challenge (with or without 6% citric acid challenge). Enamel surfaces were removed, and the dentin surfaces were exposed on which the three tested toothpastes were brushed twice a day for 1 week using an electric toothbrush, then a 4-d citric acid cycling model with pH 5 was performed. The prepared specimens were stored in artificial saliva until the microhardness test was performed. Statistical analysis was done using One-way ANOVA followed by Tukey post hoc test. Results NovaMin-containing toothpaste showed an increased dentin surface microhardness following a week of twice daily brushing compared to other groups. However, NovaMin-containing toothpaste showed the highest microhardness values following pH cycling with citric acid of pH 5 compared to other tested groups. Conclusions NovaMin-containing toothpaste showed a partial recovery of dentin microhardness at pH 5 during the acidic challenge. Moreover, propolis- and moringa-containing toothpastes had an insignificant effect on dentin surface microhardness with and without citric acid challenge.

Effect of Cavity Cleanser With Long-Term Antibacterial and Anti-Proteolytic Activities on Resin–Dentin Bond Stability

ObjectiveSecondary caries caused by oral microbiome dysbiosis and hybrid layer degradation are two important contributors to the poor resin–dentin bond durability. Cavity cleansers with long-term antimicrobial and anti-proteolytic activities are in demand for eliminating bacteria-induced secondary caries and preventing hybrid layers from degradation. The objectives of the present study were to examine the long-term antimicrobial effect and anti-proteolytic potential of poly(amidoamine) dendrimers with amino terminal groups (PAMAM-NH2) cavity cleanser.MethodsAdsorption tests by attenuated total reflectance–infrared (ATR-IR) spectroscopy and confocal laser scanning microscopy (CLSM) were first performed to evaluate whether the PAMAM-NH2 cavity cleanser had binding capacity to dentin surface to fulfill its relatively long-term antimicrobial and anti-proteolytic effects. For antibacterial testing, Streptococcus mutans, Actinomyces naeslundii, and Enterococcus faecalis were grown on dentin surfaces, prior to the application of cavity cleanser. Colony-forming unit (CFU) counts and live/dead bacterial staining were performed to assess antibacterial effects. Gelatinolytic activity within the hybrid layers was directly detected by in situ zymography. Adhesive permeability of bonded interface and microtensile bond strength were employed to assess whether the PAMAM-NH2 cavity cleanser adversely affected resin–dentin bonding. Finally, the cytotoxicity of PAMAM-NH2 was evaluated by the Cell Counting Kit-8 (CCK-8) assay.ResultsAdsorption tests demonstrated that the binding capacity of PAMAM-NH2 on dentin surface was much stronger than that of 2% chlorhexidine (CHX) because its binding was strong enough to resist phosphate-buffered saline (PBS) washing. Antibacterial testing indicated that PAMAM-NH2 significantly inhibited bacteria grown on the dentin discs as compared with the control group (p < 0.05), which was comparable with the antibacterial activity of 2% CHX (p > 0.05). Hybrid layers conditioned with PAMAM-NH2 showed significant decrease in gelatin activity as compared with the control group. Furthermore, PAMAM-NH2 pretreatment did not adversely affect resin–dentin bonding because it did not decrease adhesive permeability and microtensile strength. CCK-8 assay showed that PAMAM-NH2 had low cytotoxicity on human dental pulp cells (HDPCs) and L929.ConclusionsPAMAM-NH2 cavity cleanser developed in this study could provide simultaneous long-term antimicrobial and anti-proteolytic activities for eliminating secondary caries that result from a dysbiosis in the oral microbiome and for preventing hybrid layers from degradation due to its good binding capacity to dentin collagen matrix, which are crucial for the maintenance of resin–dentin bond durability.

Dentin surface and hybrid layer morphological analysis after use of a copaiba oil- based dentin biomodifier

This study evaluated dentin surface and hybrid layer’s morphology, using copaíba (CO) emulsion as dentin biomodifier before traditional and self-etching adhesive, by environmental scanning electron microscopy (ESEM). Ninety-six third sound molars were divided into 16 groups, according to the dentin substrate, tested substances, and the adhesive system used. The conditioned dentin surface treated with clorexidina (CHX) 2% showed phosphate salts on two dentin substrates as well as the sound conditioned or not surface treated with calcium hydroxide solution (CHS), where the mineral precipitate deposition obstructs the tubules lumen. A significant difference (p <0.0001) in dentin surface morphology was observed at the CHS group on conditioned and not conditioned sound dentin. The CO emulsion produced a regular and homogenous hybrid layer with many resin tags on both dentin surfaces, irrespective of the adhesive system used, with better performance than CHS and CHX 2% (p =0.0007) on caries-affected dentin at the self-etching group. CO emulsion showed no morphological changes on sound and caries-affected dentin and presented a regular hybrid layer, regardless of the adhesive system used. Keywords: Copaiba oleoresin; Emulsions; Dentin-bonding agents; Phytotherapy.

The effect of commercial herbal toothpastes on dental wear: a comparative evaluation by Optical coherence tomography

The purpose of this study was to compare the tooth wear in function of the use of different commercial herbal toothpastes through the analysis of Optical Coherence Tomography (OCT). Twenty bovine teeth were obtained and distributed in 4 groups (n = 5) according to the dentifrice used: G1: Captive Nature (Chamomile, Xylitol, Juá and Salvia); G2: Suavetex Content (Turmeric); G3: Colgate Triple Action (positive control); G4: distilled water (negative control). The samples were painted in the half of the fragment with nail polish so that only half of the fragment was brushed. The simulated brushing (20,000 cycles) was performed with linear movements, under static axial load of 200g and speed of 4.5 cycles per second. After this step, an analysis was performed through OCT and and the images obtained were evaluated to identify possible changes in the specimen surface. According to the qualitative analysis of the OCT images, enamel wear was not observed, since all measurements were null. Regarding the evaluation of dentin, surface wear was observed in all groups except G4, but G3 had the highest number of samples with surface wear around 21.32%. All dentifrices had abrasive wear on the dentin surface to a greater or lesser extent, but there was no wear on the enamel surface.

Mechanical Stimulation-Induced Calcium Signaling by Piezo1 Channel Activation in Human Odontoblast Reduces Dentin Mineralization

Odontoblasts play critical roles in dentin formation and sensory transduction following stimuli on the dentin surface. Exogenous stimuli to the dentin surface elicit dentinal sensitivity through the movement of fluids in dentinal tubules, resulting in cellular deformation. Recently, Piezo1 channels have been implicated in mechanosensitive processes, as well as Ca2+ signals in odontoblasts. However, in human odontoblasts, the cellular responses induced by mechanical stimulation, Piezo1 channel expression, and its pharmacological properties remain unclear. In the present study, we examined functional expression of the Piezo1 channel by recording direct mechanical stimulation-induced Ca2+ signaling in dentin matrix protein 1 (DMP-1)-, nestin-, and dentin sialophosphoprotein (DSPP)-immunopositive human odontoblasts. Mechanical stimulation of human odontoblasts transiently increased intracellular free calcium concentration ([Ca2+]i). Application of repeated mechanical stimulation to human odontoblasts resulted in repeated transient [Ca2+]i increases, but did not show any desensitizing effects on [Ca2+]i increases. We also observed a transient [Ca2+]i increase in the neighboring odontoblasts to the stimulated cells during mechanical stimulation, showing a decrease in [Ca2+]i with an increasing distance from the mechanically stimulated cells. Application of Yoda1 transiently increased [Ca2+]i. This increase was inhibited by application of Gd3+ and Dooku1, respectively. Mechanical stimulation-induced [Ca2+]i increase was also inhibited by application of Gd3+ or Dooku1. When Piezo1 channels in human odontoblasts were knocked down by gene silencing with short hairpin RNA (shRNA), mechanical stimulation-induced [Ca2+]i responses were almost completely abolished. Piezo1 channel knockdown attenuated the number of Piezo1-immunopositive cells in the immunofluorescence analysis, while no effects were observed in Piezo2-immunopositive cells. Alizarin red staining distinctly showed that pharmacological activation of Piezo1 channels by Yoda1 significantly suppressed mineralization, and shRNA-mediated knockdown of Piezo1 also significantly enhanced mineralization. These results suggest that mechanical stimulation predominantly activates intracellular Ca2+ signaling via Piezo1 channel opening, rather than Piezo2 channels, and the Ca2+ signal establishes intercellular odontoblast-odontoblast communication. In addition, Piezo1 channel activation participates in the reduction of dentinogenesis. Thus, the intracellular Ca2+ signaling pathway mediated by Piezo1 channels could contribute to cellular function in human odontoblasts in two ways: (1) generating dentinal sensitivity and (2) suppressing physiological/reactional dentinogenesis, following cellular deformation induced by hydrodynamic forces inside dentinal tubules.

Influence of Dentin Priming with Tannin-Rich Plant Extracts on the Longevity of Bonded Composite Restorations

Objective. This in vitro study evaluated the influence of bioactive plant extracts as dentin biomodifying agents to improve the longevity of bonded restorations. For that, plant extracts were applied to the dentin surface prior to the adhesive system. Materials and Methods. Bovine incisors were ground flat to obtain 2 mm thick slices in which conical preparations were made (N = 10). Tannin-containing plant extracts were applied to dentin before the application of the restorative system, as follows: control group (untreated, CTL), chlorhexidine 0.12% (CHX), mastruz (Dysphania ambrosioides, MTZ), cat’s claw (Uncaria tomentosa, CTC), guarana (Paullinia cupana, GUA), galla chinensis (Rhus chinensis, GCH), and tannic acid (extracted from Acacia decurrens, TNA). The push-out bond strength test was conducted (0.5 mm/min). Dentin biomodification was assessed by the modulus of elasticity and mass change in bovine tooth sections (0.5 × 1.7 × 7.0 mm). The dentin staining after extract treatments of dentin slices was compared. The dentin surface wettability was also evaluated by means of the contact angles of the adhesive system with the dentin surface and compared with the untreated control group. Data were subjected to ANOVA/Tukey’s test (α = 0.05). Results. The bond strength of the restoratives to dentin was not significantly improved by the plant extracts, irrespective of the evaluation time ( p > 0.05 ). Except for TNA, the elastic modulus of demineralized dentin significantly reduced after treatment with the plant extracts ( p < 0.05 ). The dentin staining correlated with the tannin content of the extracts. The contact angle was significantly reduced when treated with CTC, GCH, and TNA. Conclusions. The tannin-containing extracts had a questionable effect on the longevity of bonded restorations. The dentin modulus was negatively affected by the extract treatments. Although some of the extracts changed the contact angle, which seems to improve the adhesive monomer permeation, the tannin-rich plant extract application prior to adhesive application was proven to be clinically unfeasible due to dentin staining.

Integration of Dental Implants in Conjunction with EDTA-Conditioned Dentin Grafts: An Experimental Study

This study was undertaken to investigate the integration of titanium micro-implants installed in conjunction with previously dentin-grafted areas and to study the morphological appearance, mineral content, and healing pattern of xenogenic EDTA-conditioned dentin blocks and granules grafted to cavities in the tibial bone of rabbits. Demineralized and non-demineralized dentin blocks and granules from human premolars were implanted into cavities prepared on the lateral aspects of the tibias of rabbits. After a healing period of six months, micro-implants were installed at each surgical site. Histological examinations were carried out after 24 weeks. Characterization of the EDTA-conditioned dentin blocks was performed by means of light microscopy, dental X-rays, scanning electron microscopy, and energy dispersive X-ray analysis (EDX). No implants were found to be integrated in direct contact with the dentin particles or blocks. On the EDTA-conditioned dentin surface, the organic marker elements C and N dominated, as revealed by EDX. The hydroxyapatite constituents Ca and P were almost absent on the dentin surface. No statistically significant difference was observed between the EDTA-conditioned and non-demineralized dentin, as revealed by BIC and BA. The bone-inductive capacity of the dentin material seemed limited, although demineralization by means of EDTA indicated higher BIC and BA values in conjunction with the installed implants in the area. A 12 h EDTA treatment did not fully decalcify the grafts, as revealed by X-ray analysis.