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Almost half of dental restorations have failed in less than 10 years, and approximately 60% of practice time has been consumed to replace these dental restorations. As such, contemporary dentin adhesives should be modified to treat secondary caries and prevent the degradation of adhesive–dentin interfaces. To achieve this goal, we developed a versatile therapeutic adhesive in the present study by incorporating quercetin, which is a naturally derived plant extract, into a commercial adhesive at three concentrations (100, 500 and 1000 µg/mL). An unmodified adhesive served as a control. The antibacterial ability on Streptococcus mutans biofilm, conversion degree, microtensile bond strength, failure modes, in situ zymography, nanoleakage expression and cytotoxicity of quercetin-doped adhesive were comprehensively evaluated. Results showed that the quercetin-doped adhesive (500 µg/mL) preserved its bonding properties against collagenase ageing and inhibited the growth of S. mutans biofilm. Efficient bonding interface sealing ability, matrix metalloproteinase inhibition and acceptable biocompatibility were also achieved. Thus, a simple, safe and workable strategy was successfully developed to produce therapeutic adhesives for the extension of the service life of adhesive restorations.

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In dental clinic, unsatisfactory management of the dentin surface after dentin exposure often leads to the occurrence of dentin hypersensitivity and caries. Current approaches can occlude the tubules on the dentin surface to relieve dentin hypersensitivity; however, the blocked tubules are generally weak in combating daily tooth erosion and abrasion. Moreover, cariogenic bacteria, such as Streptococcus mutans, produce biofilm on the dentin surface, causing caries and compromising the tubules' sealing efficacy. To overcome this problem, the present study focused on establishing a versatile biomaterial, epigallocatechin-3-gallate-encapsulated nanohydroxyapatite/mesoporous silica nanoparticle (EGCG@nHAp@MSN), for therapeutic management of the dentin surface. The effectiveness of the biomaterial on dentinal tubule occlusion, including resistances against acid and abrasion, was evaluated by field-emission scanning electron microscopy (FESEM) and dentin permeability measurement. The inhibitory capability of the biomaterial on S. mutans biofilm formation was investigated by confocal laser scanning microscopy (CLSM), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony forming units (CFU) counts, and FESEM. Results demonstrated for the first time that the use of EGCG@nHAp@MSN on the dentin surface was capable of effectively occluding dentinal tubules, reducing dentin permeability, and achieving favorable acid- and abrasion-resistant stability. Furthermore, EGCG@nHAp@MSN held the capability to continuously release EGCG, Ca, and P, and significantly inhibit the formation and growth of S. mutans biofilm on the dentin surface. Thus, the development of EGCG@nHAp@MSN bridges the gap between multifunctional concept and dental clinical practice and is promising in providing dentists a therapeutic strategy for the management of the dentin surface to counter dentin hypersensitivity and caries.

The aim of this study was to investigate the effect of silane pretreatment on the universal adhesive bonding between lithium disilicate glass ceramic and composite resin. IPS e.max ceramic blocks etched with hydrofluoric acid were randomly assigned to one of eight groups treated with one of four universal adhesives (two silane-free adhesives and two silane-containing adhesives), each with or without silane pretreatment. Bonded specimens were stored in water for 24 h. The shear bond strength (SBS) of the ceramic-resin interface was measured to evaluate bond strength, and the debonded interface after the SBS test was analysed using field-emission scanning electron microscopy to determine failure mode. Light microscopy was performed to analyse microleakage and marginal sealing ability. Silane pretreatment significantly and positively influenced SBS and marginal sealing ability. For all the universal adhesive groups, SBS increased and the percentage of microleakage decreased after the pretreatment. Without the pretreatment, SBS and the percentage of microleakage were not significantly different between the silane-containing universal adhesive groups and the silane-free groups. Cohesive failure was the main fracture pattern. The results suggest that additional silane pretreatment can effectively improve the bonding strength and marginal sealing of adhesives to lithium disilicate glass ceramics. The bonding performance of silane-containing universal adhesives without pretreatment is similar to that of silane-free adhesives.

Self-assembled nanolayering structures have been reported in resin-dentin interfaces created by adhesives that contain 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP). These structures have been hypothesized to contribute to bond durability. The objective of the present study was to determine the extent of nanolayering in resin-dentin interfaces after application of commercialized 10-MDP-containing self-etch and universal adhesives to human dentin. Seven commercialized adhesives were examined: Adhese Universal (Ivoclar-Vivadent), All-Bond Universal (Bisco, Inc.), Clearfil SE Bond 2, Clearfil S3 Bond Plus, Clearfil Universal Bond (all from Kuraray Noritake Dental Inc.), G-Premio Bond (GC Corp.), and Scotchbond Universal (3M ESPE). Each adhesive was applied in the self-etch mode on midcoronal dentin according to the respective manufacturer's instructions. Bonded specimens (n = 6) were covered with flowable resin composite, processed for transmission electron microscopy, and examined at 30 random sites without staining. Thin-film glancing angle X-ray diffraction (XRD) was used to detect the characteristic peaks exhibited by nanolayering (n = 4). The control consisted of 15%wt, 10%wt, and 5%wt 10-MDP (DM Healthcare Products, Inc.) dissolved in a mixed solvent (ethanol and water weight ratio 9:8, with photoinitiators). Experimental primers were applied to dentin for 20 s, covered with hydrophobic resin layer, and examined in the same manner. Profuse nanolayering with highly ordered periodicity (~3.7 nm wide) was observed adjacent to partially dissolved apatite crystallites in dentin treated with the 15% 10-MDP primer. Three peaks in the 2θ range of 2.40° (3.68 nm), 4.78° (1.85 nm), and 7.18° (1.23 nm) were identified from thin-film XRD. Reduction in the extent of nanolayering was observed in the 10% and 5% 10-MDP experimental primer-dentin interface along with lower intensity XRD peaks. Nanolayering and characteristic XRD peaks were rarely observed in specimens prepared from the commercialized adhesives. The sparsity of nanolayering in resin-dentin interfaces created by commercialized adhesives challenges its clinical effectiveness as a mechanism for improving bond longevity in dentin bonding.

Anisotropic structure is key for exploring the biomimetic functions of anisotropic hydrogels. However, the anisotropic hydrogel study should not be limited to its architecture design but must include the understanding and improvement of the internal interaction among their components. Herein, a noncovalent mediated assembly strategy is proposed to simultaneously improve the chitin chain mobility and enhance the interfacial interaction, for achieving anisotropic chitin/2D material (molybdenum disulfide and brushite as example) hydrogels via mechanical deformation. Tannic acid (TA) is used to i) introduce the dynamic noncovalent crosslinking structure among the chitin chains for affording considerable molecular mobility to allow chitin chains alignment under mechanical deformation; ii) enhance chitin–2D interfacial interaction for benefiting 2D materials orientation under the chitin chains driving. The design concept achieves multiple noncovalent assembly crosslinks (chitin–chitin, chitin–TA, and chitin–TA–2D) and biomimetic anisotropic nanofibrous morphology, leading to the superior mechanical performance. The anisotropic chitin–TA/brushite hydrogel effectively accelerates bone regeneration by promoting cell osteogenic differentiation and directional migration, showing potential in tissue engineering. It is anticipated that the noncovalent mediated assembly concept could be used to fabricate other polymer based composite anisotropic hydrogels for diverse applications.

Currently available drug delivery systems for oral diseases suffer from short retention time and poor local concentrations at the target site. A biodegradable stimulus-responsive hydrogel was synthesized in the present study to evaluate its application as an environmentally sensitive carrier for on-demand intraoral drug delivery. The hydrogel was synthesized from diacrylate-containing polyethylene glycol–based scaffolds and a cysteine-terminated peptide crosslinker (CGPQG↓IWGQC) via a Michael-type addition reaction. Because CGPQG↓IWGQC can be cleaved by matrix metalloproteinase 8 (MMP-8), minocycline hydrochloride, bovine serum albumin, or an antibacterial peptide (KSL) was incorporated into the scaffolds to evaluate the MMP-8-responsive release behavior of the on-demand drug delivery system. Hydrogel characterization and gelation kinetics were examined with gel time, Fourier-transform infrared spectroscopy, scanning electron microscopy, and measurements of rheologic parameters. Degradation behavior and MMP-8-responsive drug release were performed by high-performance liquid chromatography and protein-specific assay. Biocompatibility evaluation indicated that the hydrogels were noncytotoxic. Antibacterial testing demonstrated that the released drugs were able to maintain bioactivity. Taken together, these results suggest that the MMP-8-sensitive hydrogel is a promising candidate for on-demand intraoral localized drug delivery. Because MMP-8 is one of the most important biomarkers for periodontitis, the MMP-8-responsive hydrogel has potential to be used for in situ adaptive degradation in response to chronic periodontitis and peri-implantitis. This notion has to be tested in animal models of periodontal disease.