Xiaomei Yao

Dentin surface treatment using a non-thermal argon plasma brush for interfacial bonding improvement in composite restoration

The objective of this study was to investigate the treatment effects of non-thermal atmospheric gas plasmas on dentin surfaces used for composite restoration. Extracted unerupted human third molars were prepared by removing the crowns and etching the exposed dentin surfaces with 35% phosphoric acid gel. The dentin surfaces were treated using a non-thermal atmospheric argon plasma brush for various periods of time. The molecular changes of the dentin surfaces were analyzed using Fourier transform infrared spectrophotometry/attenuated total reflectance (FTIR/ATR), and an increase in the amount of carbonyl groups was detected on plasma-treated dentin surfaces. Adper Single Bond Plus adhesive and Filtek Z250 dental composite were applied as directed. To evaluate the dentin/composite interfacial bonding, the teeth thus prepared were sectioned into micro-bars and analyzed using tensile testing. Student-Newman-Keuls tests showed that the bonding strength of the composite restoration to peripheral dentin was significantly increased (by 64%) after 30 s of plasma treatment. However, the bonding strength to plasma-treated inner dentin did not show any improvement. It was found that plasma treatment of the peripheral dentin surface for up to 100 s resulted in an increase in the interfacial bonding strength, while prolonged plasma treatment of dentin surfaces (e.g. 5 min) resulted in a decrease in the interfacial bonding strength.

Morphological and chemical characterization of bonding hydrophobic adhesive to dentin using ethanol wet bonding technique

OBJECTIVE BisGMA, a widely used component in dentin adhesive has very good mechanical properties after curing, but is relatively hydrophobic and thus, does not adequately infiltrate the water wet demineralized dentin collagen. Developing techniques that would lead to optimum infiltration of the hydrophobic component into the demineralized dentin matrix is very important. The purpose of this study was to evaluate interfacial morphological and chemical characteristics of the resultant adhesive-dentin interface when the ethanol wet bonding technique is used with hydrophobic adhesives. MATERIALS AND METHODS The occlusal one-third of the crown was removed from six unerupted human third molars; a uniform smear layer was created with 600 grit SiC. The dentin surface was etched with 35% phosphoric acid for 15s before applying BisGMA/HEMA model adhesive using either water wet or ethanol wet bonding technique. Five-micro-thick sections of adhesive/dentin interface specimens were cut and stained with Goldners trichrome for light microscopy. Companion slabs were analyzed with SEM and micro-Raman spectroscopy. RESULTS The presence of ethanol in the demineralized dentin increased adhesive collagen encapsulation as indicated by trichrome staining. The SEM results confirmed that the ethanol wet bonding improved the quality of the interface. Micro-Raman spectral analysis of the dentin/adhesive interface indicated there was a gradual decrease in penetration of BisGMA component for specimens using water wet bonding, while relatively homogeneous distribution of the hydrophobic BisGMA component was noted in the interface with ethanol wet bonding. SIGNIFICANCE Wet bonding with ethanol instead of water permits better BisGMA infiltration improving the quality of interface. We speculate that the higher infiltration of hydrophobic BisGMA and better collagen encapsulation observed from the specimens using ethanol wet bonding would lead to more durable bonds because of improved resistance to hydrolytic attack.

Grape seed proanthocyanidins increase collagen biodegradation resistance in the dentin/adhesive interface when included in an adhesive

OBJECTIVES Contemporary methods of dentin bonding could create hybrid layers (HLs) containing voids and exposed, demineralised collagen fibres. Proanthocyanidins (PA) have been shown to cross-link and strengthen demineralised dentin collagen, but their effects on collagen degradation within the HL have not been widely studied. The purpose of this study was to compare the morphological differences of HLs created by BisGMA/HEMA model adhesives with and without the addition of grape seed extract PA under conditions of enzymatic collagen degradation. METHODS Model adhesives formulated with and without 5% PA were bonded to the acid etched dentin. 5-μm-thick sections cut from the bonded specimens were stained with Goldners trichrome. The specimens were then exposed to 0.1% collagenase solution for 0, 1, or 6 days. Following collagenase treatment, the specimens were analysed with SEM/TEM. RESULTS Staining did not reveal a difference in the HLs created with the two adhesives. SEM showed the presence of intact collagen fibrils in all collagenase treatment conditions for specimens bonded with adhesive containing PA. These integral collagen fibrils were not observed in the specimens bonded with adhesive without PA after the same collagenase treatment. TEM confirmed that the specimens containing PA still showed normal collagen fibril organisation and dimensions after treatment with collagenase solution. In contrast, disorganised collagen fibrils in the interfacial zone lacked the typical cross-banding of normal collagen after collagenase treatment for specimens without PA. CONCLUSIONS The presence of grape seed extract PA in dental adhesives may inhibit the biodegradation of unprotected collagen fibrils within the HL.

Chemical Profile of the Dentin Substrate in Non-Carious Cervical Lesions

OBJECTIVE The molecular structural nature of the dentin substrate in non-carious cervical lesions (NCCLs) is poorly understood. This investigation characterized the chemical structure including inhomogeneities, composition, mineral crystallinity, collagen organization of normal dentin and affected dentin substrates within NCCLs using Raman microspectroscopic mapping/imaging. MATERIALS AND METHODS Three extracted human pre-molars affected with NCCLs were selected and cavities matching the natural lesion with respect to size and location were prepared on the lingual/palatal surface of each tooth to serve as controls. The specimens were sectioned to expose the gingival and occlusal margins of the NCCLs and the control cavities. Micro-Raman spectra and imaging were acquired at 1.5 microm spatial resolution at positions perpendicular to the lesion surfaces. RESULTS The Raman spectra and imaging comparisons showed the distinct compositional and structural alterations in mineral and matrix components of NCCL affected dentin. A heterogeneous hyper-mineralized layer, with characteristic features such as high phosphate/low carbonate content, high degree of crystallinity and partially denatured collagen were revealed in affected dentin substrate of NCCLs. SIGNIFICANCE Generating Raman images based on different strategies from the same data set provides a powerful means to study the structural alterations within heterogeneous dental tissues. Direct overlay of the images indicated that the changes in chemical structure and composition are synchronized. Further studies are required to understand the role that these alterations play in response to acid etching and bonding to these clinically relevant substrates.

Enhancement in dentin collagen's biological stability after proanthocyanidins treatment in clinically relevant time periods.

OBJECTIVE To investigate whether proanthocyanidins (PA) is capable of improving dentin collagens biological stability through cross-linking within time periods that are clinically relevant. MATERIALS AND METHODS Demineralized dentin collagen slabs were treated with 3.75 wt% PA solution for 10s, 1 min, 30 min, 60 min, 120 min, 360 min, and 720 min, respectively. The resultant cross-linked collagen samples were subject to digestion with 0.1% collagenase at 37°C for 2h, 6h, 12h, 24h, 36 h, and 48 h. The percentage of weight loss after digestion was calculated to evaluate PA-treated collagens resistance toward enzymatic degradation. Fourier-transformed infrared (FTIR) spectroscopy was used to probe evidences of PA-collagen interactions after various periods of PA treatment. RESULTS The collagenase digestion assay suggests that PA treatment as short as 10s can enhance collagens resistance toward enzymatic challenge. The FTIR spectroscopy further verifies that PA is indeed incorporated into collagen regardless of treatment time, possibly via a mechanism involving the chemical interactions between PA and collagen. SIGNIFICANCE This study confirmed that PA can effectively cross-link collagen and improve its biological stability in time periods as short as 10s. The use of PA as a priming agent is therefore clinically feasible and is a promising approach to improving the durability of current dentin bonding systems.

Morphological/Chemical Imaging of Demineralized Dentin Layer in Its Natural, Wet State

OBJECTIVE Measuring the structure, composition or suitability for bonding of the acid-etched dentin substrate, especially in its hydrated state, has been a formidable problem. The purpose of this study was to determine the morphological and structural profiles of the dentin demineralized layer measured in its natural wet state using environmental scanning electron microscopy (ESEM) and micro-Raman imaging. MATERIALS AND METHODS The occlusal 1/3 of the crown was removed from nine extracted, unerupted human third molars. Dentin surfaces were abraded with 600-grit SiC sandpaper under water to create smear layers. The prepared dentin surfaces were randomly selected for treatment with the self-etching agent (Adper Prompt L-Pop) or the total-etching agent 35% H(3)PO(4) gel (with/without agitation). Micro-Raman spectra and imaging were acquired at 1-1.5microm spatial resolution at positions perpendicular to the treated surfaces; since this technique is non-destructive, the same specimens were also imaged with ESEM. Specimens were kept wet throughout spectral acquisition and ESEM observations. RESULTS ESEM could be used to reveal demineralized layers in acid-etched dentin, but the resolution was low and no collagen fibrils were disclosed. The detailed chemical maps/profiles of demineralized dentin layers under wet conditions could be obtained using Raman imaging. It was shown that the mineral existed in the superficial layer of all etched dentin covered with smear layers. The mineral was much easier to be removed underneath the superficial layer. The depth, degree, and profile of dentin demineralization were dependent on the types of acids (self-etching vs. total etching) and application procedures (with vs. without agitation). SIGNIFICANCE Most current adhesives are applied using wet bonding techniques in which the dentin is kept fully hydrated throughout the bonding. Our ability to fully characterize the hydrated, etched dentin substrates is very important for understanding bonding under in vivo conditions.

Effect of a non-thermal, atmospheric-pressure, plasma brush on conversion of model self-etch adhesive formulations compared to conventional photo-polymerization

OBJECTIVE To determine the effectiveness and efficiency of non-thermal, atmospheric plasmas for inducing polymerization of model dental self-etch adhesives. METHODS The monomer mixtures used were bis-[2-(methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA), with mass ratios of 70/30, 50/50 and 30/70. Water was added to the above formulations: 10-30wt%. These monomer/water mixtures were treated steadily for 40s under a non-thermal atmospheric plasma brush working at temperatures from 32 to 35°C. For comparison, photo-initiators were added to the above formulations for photo-polymerization studies, which were light-cured for 40s. The degree of conversion (DC) of both the plasma- and light-cured samples was measured using FTIR spectroscopy with an attenuated total reflectance attachment. RESULTS The non-thermal plasma brush was effective in inducing polymerization of the model self-etch adhesives. The presence of water did not negatively affect the DC of plasma-cured samples. Indeed, DC values slightly increased, with increasing water content in adhesives: from 58.3% to 68.7% when the water content increased from 10% to 30% in the adhesives with a 50/50 (2MP/HEMA) mass ratio. Conversion values of the plasma-cured groups were higher than those of light-cured samples with the same mass ratio and water content. Spectral differences between the plasma- and light-cured groups indicate subtle structural distinctions in the resultant polymer networks. SIGNIFICANCE This research if the first to demonstrate that the non-thermal plasma brush induces polymerization of model adhesives under clinical settings by direct/indirect energy transfer. This device shows promise for polymerization of dental composite restorations having enhanced properties and performance.

Characterization of Interfacial Chemistry of Adhesive/Dentin Bond Using FTIR Chemical Imaging With Univariate and Multivariate Data Processing

Fourier transform infrared (FTIR) chemical imaging can be used to investigate molecular chemical features of the adhesive/dentin interfaces. However, the information is not straightforward and is not easily extracted. The objective of this study was to use multivariate analysis methods, principal component analysis, and fuzzy c-means clustering and to analyze spectral data in comparison with univariate analysis. The spectral imaging data collected from both the adhesive/healthy dentin and adhesive/caries-affected dentin specimens were used and compared. The univariate statistical methods such as mapping of intensities of specific functional group do not always accurately identify functional group locations and concentrations because of more or less band overlapping in adhesive and dentin. Apart from the ease with which information can be extracted, multivariate methods highlight subtle and often important changes in the spectra that are difficult to observe using univariate methods. The results showed that the multivariate methods gave more satisfactory, interpretable results than univariate methods and were conclusive in showing that they can discriminate and classify differences between healthy dentin and caries-affected dentin within the interfacial regions. It is demonstrated that the multivariate FTIR imaging approaches can be used in the rapid characterization of heterogeneous, complex structure.

Application of multivariate spectral analyses in micro-Raman imaging to unveil structural/chemical features of the adhesive/dentin interface.

This study presents the application of multivariate analyses to analyze micro-Raman spectral imaging data in reference to the adhesive/dentin interface as well as comparison with univariate analysis. The univariate statistical methods, such as mapping of specific functional group peak intensities, do not always detect functional group positions and quantities due to peak overlapping. A comprehensive chemical analysis of the adhesive/dentin interface, along with the multivariate statistical methods, principal component analysis, and fuzzy c-means clustering, is studied. Compared to univariate analysis, multivariate methods present the entire hyperspectral information from the specimen in a concise and uncorrelated way. Apart from the ease with which information can be extracted and presented, multivariate methods also highlight minute and often important variations in the spectra that are difficult to observe using univariate methods. The results show for the first time the clear chemical and structural classifications in the adhesive/dentin interface at successively greater resolutions.

Degradation of dentin-bonded interfaces treated with collagen cross-linking agents in a cariogenic oral environment: An in situ study

OBJECTIVES To evaluate the effect of treatment using collagen cross-linking agents as primer on resin-dentin bond interfaces subjected to cariogenic oral environment (COE). METHODS Each of forty human teeth had two cavities (4×4×1.5mm) prepared within enamel margins. These cavities were acid-etched and treated by the primers containing one of the following treatment agents (6.5% proanthocyanidins, 0.1% riboflavin-UVA activated light, 5% glutaraldehyde or distilled water as a control group). After that the cavities were bonded and restored with resin composite. One restoration for each tooth was tested immediately (IM) and another was included in an intra-oral palatal device that was placed in each mouth of ten adult volunteers for 14 days in COE. After 14 days, the teeth were removed and each restoration was sectioned to obtain a slice for Knoop microhardness (KHN) and resin-dentin bonded sticks for microtensile bond strength (μTBS) and nanoleakage (NL) evaluation. Data were evaluated by two-way ANOVA and Tukeys tests (α=0.05). RESULTS After 14days in a COE, the KHN was reduced for all groups, except for the glutaraldehyde group; however, the proanthocyanidins group retained the highest KHN in IM and after COE (p<0.05). The μTBS was not reduced after COE for the proanthocyanidins and glutaraldehyde groups, however only the proanthocyanidins treatment did not increase the NL after COE (p>0.05). CONCLUSION The in situ study model seems to be a suitable short-term methodology to investigate the degradation of the bonding interfaces under a more realistic condition. Under COE, the proanthocyanidins and glutaraldehyde treatments produced stable interfaces that are worth further clinical investigation.