Adhesive/Dentin interface: the weak link in the composite restoration

Acid resistance and bond strength of calcium-containing adhesive on ename

INTRODUCTION AND AIMS

Marginal sealing by enamel bonding is important to enhance the durability of the restoration and prevent secondary caries after operative procedure. This study aimed to evaluate the enamel acid resistance and bond strength of an experimental calcium-containing adhesive system.

METHODS

All materials were provided by Kuraray Noritake Dental, Inc. (Tokyo, Japan). A calcium-containing primer (CaP) was formulated by blending 10% CaCl2 into Clearfil SE Bond2 primer. The original primer (SEP) served as a control. Clearfil SE Bond2 Bond and Clearfil Protect Bond (PBB) were used as bonding agents. Human molar enamel was used for acid-resistance evaluation. After the adhesive was applied, a resin composite was built and light-cured. The samples were then subjected to an acid-base challenge and observed under scanning electron microscopy after 1 day and 3 months of storage. Mechanical strength was evaluated using microshear bond strength (μSBS) testing on bovine incisor enamel, with tests conducted 1 day after bonding (TC0) and after 5000 thermal cycles (TC5000). Statistical analysis was performed using two-way ANOVA and t tests (α = 0.05).

RESULTS

Acid-base resistant zones (ABRZs) formed in all groups, with thicker ABRZ formation in the CaP groups than in the SEP groups. A slope formation at the bottom of the outer lesion was noted in the PBB group. No morphological differences were found between the immediate and 3-month storage groups. The thermal cycling mode did not significantly affect the μSBS between the CaP and SEP groups.

CONCLUSION

The experimental calcium-containing adhesive system formed a thicker ABRZ on enamel without affecting the μSBS.

CLINICAL RELEVANCE

The study suggests that the experimental adhesive system enhances enamel acid resistance, forming a thicker ABRZ while maintaining bond strength, offering improved long-term protection against caries for clinical use.

Synergistic effects of bacteria, enzymes, and cyclic mechanical stresses on the bond strength of composite restorations

Predicting how tooth and dental material bonds perform in the mouth requires a deep understanding of degrading factors. Yet, this understanding is incomplete, leading to significant uncertainties in designing and evaluating new dental adhesives. The durability of dental bonding interfaces in the oral microenvironment is compromised by bacterial acids, salivary enzymes, and masticatory fatigue. These factors degrade the bond between dental resins and tooth surfaces, making the strength of these bonds difficult to predict. Traditionally studied separately, a combined kinetic analysis of these interactions could enhance our understanding and improvement of dental adhesive durability. To address this issue, we developed and validated an original model to evaluate the bond strength of dental restorations using realistic environments that consider the different mechanical, chemical, and biological degradative challenges working simultaneously: bacteria, salivary esterases, and cyclic loading. We herein describe a comprehensive investigation on dissociating the factors that degrade the bond strength of dental restorations. Our results showed that cariogenic bacteria are the number one factor contributing to the degradation of the bonded interface, followed by cyclic loading and salivary esterases. When tested in combinatorial mode, negative and positive synergies towards the degradation of the interface were observed. Masticatory loads (i.e., cycling loading) enhanced the lactic acid bacterial production and the area occupied by the biofilm at the bonding interface, resulting in more damage at the interface and a reduction of 73 % in bond strength compared to no-degraded samples. Salivary enzymes also produced bond degradation caused by changes in the chemical composition of the resin/adhesive. However, the degradation rates are slowed compared to the bacteria and cyclic loading. These results demonstrate that our synergetic model could guide the design of new dental adhesives for biological applications without laborious trial-and-error experimentation.

Scale dependent nanomechanical properties of dentin adhesive and adhesive-collagen composite

The complex micrometer construct at the interface that joins the composite material to the tooth surface in restorative dentistry is composed of the composite formed by infiltrating adhesive into demineralized dentin (collagen matrix). The overall performance of composite restorations is therefore directly linked to the properties of the polymerized adhesive and adhesive-collagen composite. Nanoindentation and nanoDMA tests are performed on model methacrylate based adhesive and collagen-adhesive composite to study their mechanical properties. The adhesive collagen composite is prepared by the infiltration of dentin adhesive into a completely demineralized bovine dentin. The obtained experimental results show that both the neat adhesive and the collagen-adhesive composite are heterogeneous materials at the spatial scales of property interrogation. It is also found that the reduced elastic modulus generally decreases with increasing indentation contact depth reaching an asymptote for both neat adhesive and collagen-adhesive composite. This reduced modulus behavior can be attributed to the increase in the indentation interaction volume. In addition, the measured frequency dependent storage and loss moduli indicate that both the neat adhesive and collagen adhesive composites are viscoelastic materials which are likely to exhibit creep deformation and rate-dependent behavior in physiological function.

Natural Antibacterial Compounds with Potential for Incorporation into Dental Adhesives: A Systematic Review

Dental adhesives are essential in modern restorative dentistry and are constantly evolving. However, challenges like secondary caries from bacterial infiltration at the adhesive-tooth interface persist. While synthetic antibacterial agents in adhesives show promise, safety concerns have shifted interest toward natural options that are biocompatible, sustainable, and effective. Therefore, this study evaluated whether natural antibacterial compounds in dental adhesives can provide effective antimicrobial activity without compromising their integrity. This systematic review followed PRISMA 2020 statement guidelines. Four databases were screened, PubMed, Scopus, EMBASE, and Web of Science, without language or publication date restrictions until July 2024. The selection criteria were in vitro studies in which natural antimicrobial substances were incorporated into dental adhesives and the resulting composites were tested for their antibacterial and physicochemical properties. A quality assessment was conducted on the selected studies. Most of the studies reviewed reported significant antibacterial activity while retaining the adhesive's integrity, generally achieved with lower concentrations of the natural agents. Higher concentrations increase the antimicrobial effectiveness but negatively impact the adhesive's properties. This review highlights the promising role of natural antibacterial compounds in enhancing the functionality of dental adhesives while also pointing to the need for continued research to address current challenges.

Synthesis and challenges of fluorinated divinyl urethane monomers as a strategy for masking hydrolytic sensitive methacrylate groups in resin composites

OBJECTIVE

The biodegradation of methacrylate (MA)-based dental restoratives has been suggested to contribute to a loss of adhesion and subsequent detachment, or secondary caries, both major causes of restoration failure. Previous studies have demonstrated that intermolecular interactions between resin monomers may affect the hydrolytic-susceptibility of composites. Altering the intermolecular interactions by shielding or masking the hydrolytically-susceptible ester groups found in MA monomers could be an effective strategy to mitigate the biodegradation of resin composites. The objective of this work was to assess whether shielding/masking MAs using fluorinated groups could improve the biostability of experimental composites.

METHODS

Eight fluorinated monomers (FM) were synthesized, characterized (1H NMR), and formulated into experimental resin composites (FC, 65 wt%, microfill). FCs were assessed for interactions with water (water contact angle, water sorption, gel fraction), mechanical properties (both compressive and flexural strength and modulus), cytocompatibility, resistance to biodegradation using simulated human salivary esterase (SHSE) and compared to a control composite (CC) without FM.

RESULTS

Integration of FMs was found to generally decrease both the physical and mechanical properties under all incubation conditions when compared to the CC. Additionally, all FCs had a negative influence on composite biodegradation following immersion in SHSE when compared to the CC.

SIGNIFICANCE

Shielding/masking MA-esters inherently inserts molecular spaces between the polymer chains within the resin network, and shielding is likely not possible while also maintaining the necessary cohesive forces that regulate the physical and mechanical properties of resin composites. Novel dental resin development should seek to remove/replace vulnerable ester-containing MAs rather that adopting a shielding/masking approach.

Evaluation of adhesive properties and enzymatic activity at the hybrid layer of a simplified adhesive loaded with 0.2 % Cu and 5 % ZnO nanoparticles: A Randomized Clinical Trial and ex vivo analysis

OBJECTIVE

The aim of this study was to evaluate the effect of an adhesive loaded with 0.2 % copper (Cu) and 5 % zinc oxide (ZnO) nanoparticles (Nps) on its adhesive properties and enzymatic activity at the hybrid layer ex vivo in a randomized clinical model.

METHODS

Fifteen patients participated in this study, and a total of 30 third molars were used. Occlusal cavities (4 × 4 × 2 mm) were made in each tooth, and randomly divided into 2 groups: (i) Experimental group: commercial adhesive loaded with 0.2wt % CuNps and 5wt % ZnONps; and (ii) Control Group: non-loaded commercial adhesive. Teeth were restored with resin composite. Thirty days later, extractions were performed. Extracted teeth were longitudinally sectioned. Nps in powder were characterized by field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray (EDX) analysis. Microtensile bond strength (μTBS), degree of conversion (DC), and nanoleakeage (NL) tests were executed. In situ zymography (Zym) was performed to evaluate the gelatinolytic activity at the hybrid layer. Student's t-test (α = 0.05) was applied for all tests.

RESULTS

μTBS and DC did not show significant differences (p > 0.05) between both groups. However, NL and gelatinolytic activity at the hybrid layer showed significant values (p < 0.05) for experimental group in comparison with control group.

CONCLUSION

The addition of 0.2 % CuNps and 5 % ZnONps to a universal adhesive decreases NL and gelatinolytic activity at the hybrid layer, without jeopardizing its adhesive properties.

SIGNIFICANCE

This randomized clinical trial with ex vivo analysis demonstrate that a commercial adhesive modified with 0.2wt % Cu and 5wt % ZnO Nps that does not affect its adhesive properties, reducing gelatinolytic activity and nanoleakage at the hybrid layer, which should contribute to an improvement of long term bonding-dentine clinical performance.

Influence of diode laser irradiation on microtensile bond strength of etch-and-rinse adhesive to dentin using two different etchants: An in vitro study

Aim

The aim of this study was to evaluate the influence of 970 nm diode laser (DL) irradiation on the microtensile bond strength (µTBS) of etch-and-rinse adhesive (ERA) to dentin using phosphoric acid (PA) or alpha-hydroxy glycolic acid (GA) as etchants.

Materials and Methods

A total of 32 human third molars were selected and assigned randomly among two different groups and four subgroups based on etching protocols and DL irradiation: PA, PA-DL, GA, and GA-DL. After tooth preparation and subsequent incremental composite build-up, the samples were stored in distilled water for 24 h at 37°C. µTBS values were obtained using the universal testing machine. The failure modes observed in dentin were categorized as adhesive, cohesive within dentin/resin, or mixed.

Statistical Analysis

The data were analyzed using one-way analysis of variance, followed by Tukey's post hoc test (P ≤ 0.001).

Results

GA showed better or similar bond strength values to PA. Furthermore, irradiation of DL increased the µTBS to dentin when both PA or GA are used as etchants.

Conclusion

GA can be used as an alternative etchant to PA. DL irradiation stands as a promising approach for elevating the performance of ERA adhesive systems to dentin.

Marginal integrity in minimally invasive molar resin composite restorations: Impact of polymerization shrinkage

OBJECTIVES

This study utilized non-linear finite element (FE) models to explore polymerization shrinkage and its impact on marginal integrity in molars following both selective caries removal (SCR) and conventional treatment. Specifically, we performed 2D in silico simulations to study residual stresses post-resin polymerization shrinkage and their influence on the marginal integrity of various restoration types.

METHODS

Initially, FE models were developed based on a cohesive zone framework to simulate crack propagation along the bonded interfaces between restoration and tooth structure in SCR-treated molars with class I and class II restorations. The modeled resin composite restorations first underwent polymerization shrinkage and were then subjected to various occlusal loading conditions. Stress magnitudes and distributions were identified to evaluate the margin integrity and predict the mechanism and location of interfacial failure.

RESULTS AND DISCUSSION

The FE models computed polymerization shrinkage stresses of less than 1 MPa, exerting a minor influence on the composite/tooth interface. Occlusal loading, however, significantly impacted the load-bearing capacity of the composite/tooth (c/t) interface, potentially jeopardizing the restoration integrity. Especially under bi-axial occlusal loading, interfacial debonding occurred in the vertical cavity walls of the class I restorations, increasing the risk of failure. Notably, SCR-treated teeth exhibited better margin integrity than restored teeth after complete caries removal (NCR). These findings provide valuable insights into the mechanical behavior of SCR-treated teeth under different loading conditions and highlight the importance of considering the load scenarios that may lead to failure at the c/t interface. By investigating the factors influencing crack initiation and delamination, this novel research contributes to the optimization of restorative treatments and aids in the design of more resilient dental restorations.

Awareness of possible complications associated with direct composite restorations: A multinational survey among dentists from 13 countries with meta-analysis

OBJECTIVES

Resin-based composites (RBCs) evolved into favoured materials for teeth restorations, marking a significant change in dental practice. Despite many advantages, RBCs exhibit various limitations in their physical and chemical properties. Therefore, we assessed the dentists' awareness of possible complications after direct composite restorations and their opinions about this material.

METHODS

The online questionnaire was created in English in May 2023. A 16-item survey was dedicated to general dentists and specialists. The first section included four questions related to demographic characteristics. The second section comprised twelve questions and focused on awareness of potential side effects of composite restorations, the most crucial advantages and disadvantages of composite resins, and the frequency of experienced clinical complications after the application of composite materials.

RESULTS

A total of 1830 dentists from 13 countries took part in the survey. Dentists most often declared awareness of low adhesion to the dentine (77.5 %) and, most rarely, solubility in oral fluids (42.6 %). Aesthetics was identified as the main advantage of composite fillings (79 %), followed by the possibility of repair (59 %) and adhesion to enamel (57 %). Polymerisation shrinkage was a major disadvantage for most countries (70 % overall). Analysing the declared potential clinical complications for all countries, statistically significant findings were obtained for marginal discolouration (OR=2.982, 95 % CI: 1.321-6.730, p-value=0.009) and borderline significance for secondary caries (OR=1.814, 95 % CI: 0.964-3.415, p-value=0.065).

CONCLUSIONS

Dentists value aesthetics and repairability but are aware of shrinkage and experience discolouration. The issue of toxicity and solubility seems to be the least known to dentists.

CLINICAL SIGNIFICANCE

Dentists should use RBCs with critical caution due to possible side effects. Despite the undoubted aesthetics of direct composite restorations, it is necessary to remember potential clinical complications such as marginal discolouration or secondary caries.

Comparisons of ammonia- and water-based silver-containing solutions on dentin bonding and enzymatic activity: 1-yr evaluation

OBJECTIVE

To evaluate the effects of an ammonia-based and a water-based silver-containing solutions on bonding performance and matrix-metalloproteinases (MMPs) activity of a universal adhesive to dentin after 1 year of artificial aging.

METHODS

Mid-coronal dentin surfaces of 60 sound human molars were exposed and the following groups were formed according to the surface pre-treatment and etching mode of the universal adhesive (Zipbond Universal, SDI) (n = 10): G1) Zipbond in the self-etch mode (ZSE); G2) Riva Star (SDI) applied before ZSE; G3) Riva Star Aqua (SDI) applied before ZSE; G4) Zipbond in the etch-and-rinse mode (ZER); G5) Riva Star applied before ZER; G6) Riva Star Aqua applied before ZER. The specimens were sectioned and subjected to microtensile bond strength (µTBS) test at baseline (T0) and after 12 months (T12) of artificial storage. Scanning electron microscope (SEM) and energy dispersive spectroscopy analysis (EDS) were also conducted. Three additional molars per group were processed for the in situ zymography analysis at T0 and T12. Data were statistically analyzed (p < 0.05).

RESULTS

Dentin pre-treatments and aging decreased bonding values, regardless of the etching mode (p < 0.05). No differences in µTBS were observed between the two silver-containing solutions, both at T0 and T12. Riva Star Aqua and etching significantly increased the MMPs activity, independent of the storage period (p < 0.05).

SIGNIFICANCE

Dentin surface pre-treatment with silver-containing solutions negatively affects the bonding performances of resin composite restorations placed with a universal adhesive. However, the ammonia-based product Riva Star might show better stability in the long term, due to lower activation of MMPs.

Dentin remineralization using a stimuli-responsive engineered small molecule GSK3 antagonists-functionalized adhesive

OBJECTIVES

Tideglusib has shown great performance in terms of dentin regenerative properties. This study aims to evaluate bonding ability, of demineralized dentin infiltrated with polymeric nanoparticles (NPs) doped with tideglusib (TG) (TG-NPs).

METHODS

Dentin conditioned surfaces were infiltrated with NPs and TG-NPs. Bonded interfaces were created and stored for 24 h and then submitted to mechanical, chemical and thermal challenging. The resin-dentin interface was evaluated through a doubled dye fluorescent technique and a calcium chelator fluorophore under a confocal laser scanning microscopy, and by field emission scanning electron microscopy.

RESULTS

Dentin surfaces treated with TG-NPs and load cycled produced higher bond strength than the rest of the groups. Immersion of dentin specimens treated with undoped-NPs in collagenase solution attained the lowest microtensile bond strength (MTBS) values. Both porosity and nanoleakage decreased when dentin was infiltrated with TG-NPs, that revealed strong signals of xylenol orange stain at both hybrid layer and dentinal tubules. The presence of NPs, in general, inducted the presence of mineralized interfaces after mechanical loading and thermocycling.

CONCLUSIONS

Nanoparticles doped with tideglusib promoted the highest dentin bonding efficacy among groups, as they facilitated the maximum bond strength values with creation of mineral deposits at the hybrid layer and dentinal walls. Tideglusib enabled scarce porosity, nanoleakage and advanced sealing among dentin groups.

SIGNIFICANCE

Doping hydrophilic polymeric NPs with tideglusib, infiltrated in etched dentin represents a reproducible technique to create reparative dentin at the resin-dentin interface, by inducing therapeutic bioactivity.

Polyvinylpyrrolidone as a primer for resin-dentin bonding

OBJECTIVE

This study aimed to investigate the effects of polyvinylpyrrolidone (PVP)-containing primer (PCP) on dentin bonding.

METHODS

PVP and anhydrous ethanol were used to prepare the PCPs, which were prepared at concentrations of 0.5%, 1%, and 2% (w/v). These PCPs were subsequently applied to the dentin surface, denoted as E1, E2, and E3, respectively. In the control group, no primer was applied. Following the treatment, the dentin surfaces were subjected to analysis using Fourier-transform infrared spectroscopy (FTIR), and the micro-tensile bond strength (MTBS) was evaluated. The failure mode, nanoleakage, and bonding longitudinal section were observed utilizing scanning electron microscopy (SEM). Additionally, the effect of PCPs on matrix metalloproteinases (MMPs) activity was analyzed through an in situ zymography test. Data were subjected to statistical analysis using ANOVA tests (α = 0.05).

RESULTS

Significant alterations in the infrared resonances associated with collagen cross-linking within the collagen matrix were observed across all PCP groups. The application of PCP demonstrated a noteworthy enhancement in micro-tensile bond strength (MTBS) compared to group C (p < 0.05). Notably, group C exhibited the lowest MTBS (41 ± 7.7 MPa), whereas group E2 demonstrated the highest MTBS (66 ± 11.9 MPa). Even after undergoing aging, the MTBS of the PCP groups remained superior to that of group C (p < 0.05). The resin tag length in the PCP groups was found to be greater than that of group C, and the occurrence of nanoleakage was comparatively lower in the PCP groups, both before and after aging. Additionally, PCP exhibited a dose-dependent inhibition of matrix metalloproteinases (MMPs) activity, which was statistically significant (p < 0.05).

CONCLUSIONS

The utilization of PCP Primer exhibits notable enhancements in bond strength, mitigates nano-leakage, and suppresses enzyme activity within the hybrid layer.

Internal Adaptation of Composite Fillings Made Using Universal Adhesives-A Micro-Computed Tomography Analysis

This study aimed to evaluate internal tooth-filling interfaces of composite fillings made using universal adhesives using micro-computed tomography (µCT). Sixty class V cavities were randomly assigned into six groups: Peak Universal etch and rinse (PER), Peak Universal self-etch (PSE), Adhese Universal etch and rinse (AER), and Adhese Universal self-etch (ASE). Two further adhesives considered gold standards were used as control groups: OptiBond FL (OER) for the etch and rinse technique and Clearfil SE for the self-etch technique (CSE). All teeth were subjected to thermomechanical loading and four-year water storage. Next, they were analyzed using µCT to investigate the internal tooth-filling interfaces. The proportions between the gap volume (GV) at the tooth-filling interface and the volume of applied composite filling (FV), between the gap and cavity volumes (CV), and between the gap volumes at the tooth-filling interface of the external (EGV) and internal (IGV) parts were calculated. Adhese Universal achieved the significantly lowest gap-to-filling- and gap-to-cavity-volume ratios for both types of etching techniques comparing to those of the Peak Universal and control groups. Significant differences between the gaps in external and internal parts of the tooth-filling interface were only noted in the control groups. Internal gap formation and development at the tooth-filling interface depend on the material as well as the type of its application.

Dentine biomodification by sulphonamides pre-treatment: bond strength, proteolytic inhibition, and antimicrobial activity

We evaluated the effects of dentine biomodification after pre-treatment with two sulphonamide carbonic anhydrase inhibitors (CAIs) of the N-[4-sulphamoylphenethylcarbamoyl]benzenesulphonamide type, investigating matrix metalloproteases activity, resin-dentine micro tensile bond strength, dentine surface wettability, and antimicrobial activities. Ninety-five sound-extracted human molars were selected for the study. Inhibitory effects were evaluated by gelatinase and collagenase activity tests and collagen degradation FT-IR spectroscopic analysis. Pre-treatment with the two CAIs kept the micro tensile values after 12 months of storage (32.23 ± 5.95) and cariogenic challenge (34.13 ± 2.71) similar to the initial, pre-treatment values (33.56 ± 4.34). A decreased Streptococcus mutans biofilm formation on dentine surfaces and antibacterial activity against planktonic bacteria were observed after CAI treatment. Dentine pre-treatment with sulphonamide CAIs maintained adhesion strength stability, allowed better dentine wettability, maintained matrix collagen, and showed anti-S. mutans activity.

Interfacial fracture toughness of different surface treatments on zirconia-reinforced lithium silicate glass-ceramics

This study investigated the influence of different surface treatments on unfiring or firing zirconia-reinforced lithium silicate (ZLS) glass-ceramics. Celtra Duo and IPS e.max CAD blocks were cut and process following manufacturer protocols. The specimen surface was treated with seven different protocols. Two ceramic blocks with the same surface treatment were bonded with luting agent and prepared for mini-interfacial fracture toughness tests (mini-iFT). The specimens were tested after 1-week storage. The data was statistically analyzed using two-way ANOVA and Dunnett's T3 comparison (α=0.05). The highest mini-iFT of both Celtra Duo unfired and fired was shown in the HF+S group, which was not significantly different from HF+S+UA. For IPS e.max CAD, the mini-iFT was higher in the groups treated with hydrofluoric acid. Additional adhesive after silane application did not significantly improve bonding effectiveness. Therefore, surface treatment with hydrofluoric acid and silane is recommended for both unfiring and firing ZLS glass ceramics.

Study of Water Sorption in Methacryl-Based Polyhedral Oligomeric Silsesquioxane (POSS) Dental Composites Using Molecular Dynamics Simulations

Methacrylate-based polyhedral oligomeric silsesquioxane (POSS) is one of the new composites used as a dental resin. Both monofunctional methacryl isobutyl POSS (MIPOSS) and multifunctional methacryl POSS (MAPOSS) are reported to be possible resins that possess the desired properties for using them as dental resins. Our group's previous comparative study on these two resins showed that the MAPOSS composite has superior mechanical properties compared with the MIPOSS composite. In this article, molecular dynamic simulations (MD simulations) are performed to study the water sorption in these two composites. Water sorption in dental composites can have several effects on the material properties, performance, and longevity of dental restorations. Water sorption in MAPOSS and MIPOSS composites is analyzed by studying the hydrogen bonding, cluster analysis, density projection calculations, and diffusion coefficient calculation of water molecules within the resin matrix. MD simulations results are further used to understand the interaction of water molecules with the resin matrix comprehensively, which governs the composite's mechanical properties. The water sorption study showed that the MAPOSS composite has less water sorption capacity than the MIPOSS composite. The practical significance of this study is to find properties that affect dental restoration and longevity, which can help in the design of better materials for dental applications.

Impact of Shelf-Life Simulation on a Self-Adhesive Composite: Polymerization Kinetics, Chemical and Color Stability

PURPOSE

To determine the polymerization kinetics and color stability of a self-adhesive and conventional resin composite after accelerated shelf-life simulation.

MATERIALS AND METHODS

Two composites were tested - universal Filtek Z250 (3M Oral Care) and self-adhesive Constic (DMG). They were stored for 2 months in an incubator to simulate an Arrhenius aging model (60°C) and tested at 5 different time points. Polymerization kinetics (n = 3) were studied using an attenuated total reflectance technique (ATR), through continuous FTIR spectral acquisition (20 min). Spectra were obtained before, during and after 20 s of light curing. With the spectral data, qualitative analysis was performed yielding chemical stability, and quantitative data including extrapolated degree of conversion (DCmax) and polymerization rate (Rpmax) were assessed. To evaluate color stability (n = 3), a spectrophotometer was used to record CIELAB color parameters. Inferential statistics, including repeated measures two-way ANOVA were carried out at a significance level of 5%.

RESULTS

The composites did not appear to undergo significant chemical changes after 2 months of accelerated aging. There was a significant impact of aging on the mean DCmax (p < 0.001). Similarly, a reduction in Rpmax, measured for both composites, was also noted (ANOVA; Z = 203.7; p < 0.001). The two-way ANOVA confirmed that the composite had no influence on the color stability (F = 0.94; p = 0.34), while aging did (p = 0.013).

CONCLUSION

Minimal changes in absorbance levels were noted for both composites, without overly affecting their chemical composition. The presence of an acidic monomer did not seem to potentiate the degradation of the self-adhesive composite. This composite even showed greater color stability after aging.

Crosslinking Improve Demineralized Dentin Performance and Synergistically Promote Biomimetic Mineralization by CaP_PILP

OBJECTIVE

to explore the effects of optimal crosslinking (chemical treatment) on demineralized dentin matrix and the possible synergism with calcium phosphate polymer-induced liquid precursor (CaP-PILP) bionic remineralization (physical treatment), and offer benefit to the clinic of resin-dentin bonding and dentin hypersensitivity.

METHODS

demineralized dentin was treated with glutaraldehyde (GA), carbodiimide (EDC), and procyanidin (PA) for crosslinking, followed by CaP-PILP biomimetic remineralization. The morphology, surface mechanical and physio-chemical properties, and enzymatic resistance were evaluated regardless of the modification.

RESULTS

the collagen fibers appeared morphologically complete with higher surface microhardness and characteristic peaks of amide I-III bands were visible after GA, PA, and EDC crosslinking. Collagen collapse and dissolution were seen in untreated demineralized dentin with enzyme attack, while the collagen fiber structure remained intact in GA- and PA-treated specimens. The lamellar mineral phase was visible at 2 days and the dentin tubules were almost completely enclosed at 4-6 days after PA crosslinking and mineralization. However, demineralized collagen fibers and open tubules were still visible between the dentinal tubules on day 8 in the control group.

CONCLUSION

the structure integrity, enzyme resistance, and mechanical properties of the collagen fiber network could be significantly preserved by GA and PA crosslinking than EDC and no treatment. While, strongest synergistic effects were observed in PA on bionic remineralization by CaP-PILP, and further significantly improve the quality and shorten the duration of mineralization. These findings would be beneficial for dental clinical practice of resin-dentin bonding and dentin hypersensitivity.

Degradation and Failure Phenomena at the Dentin Bonding Interface

Damage in the bonding interface is a significant factor that leads to premature failure of dental bonded restorations. The imperfectly bonded dentin-adhesive interface is susceptible to hydrolytic degradation and bacterial and enzyme attack, severely jeopardizing restorations' longevity. Developing caries around previously made restorations, also called "recurrent or secondary caries," is a significant health problem. The replacement of restorations is the most prevailing treatment in dental clinics, leading to the so-called "tooth death spiral". In other words, every time a restoration is replaced, more tooth tissue is removed, increasing the size of the restorations until the tooth is eventually lost. This process leads to high financial costs and detriment to patients' quality of life. Since the complexity of the oral cavity makes prevention a challenging task, novel strategies in Dental Materials and Operative fields are required. This article briefly overviews the physiological dentin substrate, features of dentin bonding, challenges and clinical relevance. We discussed the anatomy of the dental bonding interface, aspects of the degradation at the resin-dentin interface, extrinsic and intrinsic factors affecting dental bonding longevity, perspectives on resin and collagen degradation and how these subjects are connected. In this narrative review, we also outlined the recent progress in overcoming dental bonding challenges through bioinspiration, nanotechnology and advanced techniques to reduce degradation and improve dental bonding longevity.

Novel bioactive dental restorations to inhibit secondary caries in enamel and dentin under oral biofilms

OBJECTIVE

To provide the first review on cutting-edge research on the development of new bioactive restorations to inhibit secondary caries in enamel and dentin under biofilms. State-of-the-art bioactive and therapeutic materials design, structure-property relationships, performance and efficacies in oral biofilm models.

DATA, SOURCES AND STUDY SELECTION

Researches on development and assessment new secondary caries inhibition restorations via in vitro and in vivo biofilm-based secondary caries models were included. The search of articles was carried out in Web of Science, PubMed, Medline and Scopus.

CONCLUSIONS

Based on the found articles, novel bioactive materials are divided into different categories according to their remineralization and antibacterial biofunctions. In vitro and in vivo biofilm-based secondary caries models are effective way of evaluating the materials efficacies. However, new intelligent and pH-responsive materials were still urgent need. And the materials evaluation should be performed via more clinical relevant biofilm-based secondary caries models.

CLINICAL SIGNIFICANCE

Secondary caries is a primary reason for dental restoration failures. Biofilms produce acids, causing demineralization and secondary caries. To inhibit dental caries and improve the health and quality of life for millions of people, it is necessary to summarize the present state of technologies and new advances in dental biomaterials for preventing secondary caries and protecting tooth structures against oral biofilm attacks. In addition, suggestions for future studies are provided.

Novel antibacterial and apatite forming restorative composite resin incorporated with hydrated calcium silicate

Background

White Portland cement is a calcium silicate material. It exhibits antibacterial properties and is biocompatible. In addition, calcium silicate-based materials are known to release calcium ions and form apatite. The purpose of this study was to develop a novel bioactive restorative resin composite with antibacterial and apatite forming properties to prevent tooth caries at the interface of teeth and restorative materials, by incorporation of hydrated calcium silicate (hCS) derived from white Portland cement.

Methods

To prepare the experimental composite resins, a 30 wt% light-curable resin matrix and 70 wt% filler, which was mixed with hCS and silanized glass powder were prepared in following concentrations: 0, 17.5, 35.0, and 52.5 wt% hCS filler. The depth of cure, flexural strength, water sorption, solubility, and antibacterial effect were tested. After immersion in artificial saliva solution for 15, 30, 60, and 90 days, ion concentration by ICP-MS and apatite formation using SEM-EDS, Raman spectroscopy and XRD from experimental specimens were analyzed.

Results

All experimental groups showed clinically acceptable depths of cure and flexural strength for the use as the restorative composite resin. Water sorption, solubility, released Ca and Si ions increased with the addition of hCS to the experimental composite resin. Experimental groups containing hCS showed greater antibacterial effects compared with the 0 wt% hCS filler group (p < 0.05). The 52.5 wt% hCS filler group produced precipitates mainly composed of Ca and P detected as hydroxyapatite after immersion in artificial saliva solution for 30, 60, and 90 days.

Conclusions

This results show that composite resins containing hCS filler is effective in antibacterial effects. hCS has also apatite formation ability for reducing gap size of microleakage by accumulating hydroxyapatite precipitates at the restoration-tooth interface. Therefore, novel composite resin containing hCS is promising bioactive resin because of its clinically acceptable physiochemical properties, antibacterial properties, and self-sealing potential for prevention of microleakage for longer usage of restorations.

Release and MMP-9 Inhibition Assessment of Dental Adhesive Modified with EGCG-Encapsulated Halloysite Nanotubes

Degradation of the collagen fibrils at the dentin-resin interface by the enzymatic activity of matrix metalloproteinases (MMPs) has been known to permit some dental restoration complications, such as microleakage, secondary caries, and, ultimately, restoration failures. This study aimed to evaluate a modified adhesive by adding an MMP inhibitor from green tea extract with and without nanotube encapsulation to sustain the drug release. Epigallocatechin-3-gallate (EGCG) and Halloysite nanotubes (HNTs) were prepared to produce three variant combinations of modified adhesive (EGCG, EGCG-encapsulated HNT, and EGCG-free HNT). The drug loading efficiency and EGCG release over time were evaluated using UV-vis spectrometry. MMP-mediated β-casein (BCN) cleavage rate assays were used to determine the ability of the EGCG in eluates of the adhesive to inhibit MMP-9 activities. For up to 8 weeks, HNT encapsulation reduced release to a statistically significant level. MMP-mediated β-casein cleavage rate assays showed a significant decrease for the EGCG groups compared to the non-EGCG adhesive groups. Furthermore, the use of HNT for EGCG encapsulation to modify a dental adhesive helped slow down the rate of EGCG release without impacting its MMP inhibitory capabilities, which may help to maintain the dentin-resin interface's integrity over the long term after dental restoration placement.

Shear Bond Strength and Color Stability of Novel Antibacterial Nanofilled Dental Adhesive Resins

Experimental adhesives containing co-doped metaloxide nanoparticles were demonstrated to display strong and long-term antibacterial properties against Streptococcus mutans biofilms. The present study represents an effort to characterize the shear-bond strength (SBS) and color stability (CS) of these novel biomaterials. Experimental adhesives were obtained by dispersing nitrogen and fluorine co-doped titanium dioxide nanoparticles (NF_TiO2, 10%, 20% or 30%, v/v%) into OptiBond Solo Plus (OPTB). Dentin surfaces were wet-polished (600-Grit). Specimens (n = 5/group) of Tetric EvoCeram were fabricated and bonded using either OPTB or experimental (OPTB + NF_TiO2) adhesives. Specimens were stored in water (37 °C) for twenty-four hours (T1), three months (T2), and six months (T3). At T1, T2, or T3, specimens were removed from water storage and were tested for SBS. Disc-shaped specimens (n = 10/group; d = 6.0 mm, t = 0.5 mm) of adhesives investigated were fabricated and subjected to thermocycling (10,000 cycles, 5−55 °C, 15 s dwell time). Specimens’ colors were determined with a VITA Easyshade® V spectrophotometer (after every 1000 cycles). SBS data was analyzed using two-way ANOVA and post-hoc Tukey tests, while CS data was analyzed using one-way ANOVA and post-hoc Tukey tests (α = 0.05). Mean values of SBS ranged from 16.39 ± 4.20 MPa (OPTB + 30%NF_TiO2) to 19.11 ± 1.11 MPa (OPTB), from 12.99 ± 2.53 MPa (OPTB + 30% NF_TiO2) to 14.87 ± 2.02 (OPTB) and from 11.37 ± 1.89 (OPTB + 20% NF_TiO2) to 14.19 ± 2.24 (OPTB) after twenty-four hours, three months, and six months of water storage, respectively. Experimental materials had SBS values that were comparable (p > 0.05) to those from OPTB independently of nanoparticle concentration or time-point considered. Experimental materials with higher NF_TiO2 concentrations had less intense color variations and were more color stable than OPTB even after 10,000 thermocycles. In combination, the results reported have demonstrated that experimental adhesives can establish strong and durable bonds to human dentin while displaying colors that are more stable, thereby suggesting that the antibacterial nanotechnology investigated can withstand the harsh conditions within the oral cavity without compromising the esthetic component of dental restorations.

Development of Proanthocyanidin-Loaded Mesoporous Silica Nanoparticles for Improving Dental Adhesion

Dentin biomodification is a promising approach to enhance dental tissue biomechanics and biostability for restorative and reparative therapies. One of the most active dentin tissue biomodifiers is proanthocyanidin (PAC)-rich natural extracts, which are used in the dental bonding procedure in combination with resin-based adhesives (RBAs). This study aimed to investigate the use of mesoporous silica nanoparticles (MSNs) for the sustained delivery of PACs for dentin biomodification as a novel drug-delivery system for dental applications. The effects of the incorporation of MSN functionalized with 3-aminopropyltriethoxysilane (APTES) and loaded with PAC into an experimental RBA were assessed by characterizing the material mechanical properties. In addition, the immediate and long-term bonding performance of an experimental resin-based primer (RBP) containing MSN-APTES loaded with PAC was also evaluated. For that, different formulations of RBA and RBP were prepared containing 20% w/v MSN-APTES loaded with PAC before or after functionalization (MSN-PAC-APTES and MSN-APTES-PAC, respectively). The incorporation of MSN-APTES-PAC did not negatively impact the degree of conversion or the overall mechanical properties of the RBA. However, adding MSN-PAC-APTES resulted in inferior mechanical properties of the experimental RBA. In the adhesion studies, APTES-functionalized MSN was successfully added to an experimental RBP for drug-delivery purposes without compromising the bond strength to the dentin or the failure mode. Interestingly, the sequence of surface functionalization with APTES resulted in differences in the bonding performance, with better long-term results for RBP containing MSN loaded with PAC after functionalization.

The antimicrobial, physical, and chemical properties of a riboflavin-loaded dental resin intended for antimicrobial photodynamic therapy

BACKGROUND

Dental caries remain a significant global health challenge. Unfortunately, current dental materials lack sufficient antimicrobial power to address the pathogenic species involved in this disease. In this study the potential to load a dental resin blend (RB) with riboflavin (B2) for use in an antimicrobial photodynamic therapy (aPDT) approach was investigated.

METHODS

B2 was added to our experimental RB (0.1 - 10 wt%). Upon investigating the degree of conversion and specimen integrity of the RB as a function of B2 concentration, it was determined that loading should be restricted to 0.1, 1.0, and 1.5 wt%. Subsequent investigation included water sorption (WS) and solubility (SL), as well as shear bond strength (SBS) and flexural strength (FS) of the specimens after 24 h and 28-day water storage. Lastly, the antimicrobial response of Streptococcus mutans (S. mutans) biofilm following 6 h growth and 60 s of blue LED light (1.3 J/cm²) in an aPDT-based approach was measured.

RESULTS AND CONCLUSIONS

Adding up to 1.5 wt% B2 had minimal impact on the FS or SBS of the RB. However, aging for 28-days notably increased the FS by as much as 50% for the 1.5 wt% B2-loaded RB. In addition, adding 1.5 wt% B2 resulted in a significant reduction in WS/SL of the RB. Lastly, while adding B2 did not change the antimicrobial response, this was an initial study under these conditions and future investigation will seek to optimize light parameters to produce a more agonistic response. Overall, a riboflavin-loaded dental resin shows significant promise for utilization in restorative dentistry with aPDT.

Fast Construction of Biomimetic Organic-Inorganic Interface by Crosslinking of Calcium Phosphate Oligomers: A Strategy for Instant Regeneration of Hard Tissue

The organic-inorganic structure in biological hard tissues ensures their marvelous characteristics but these hybrids are easily destroyed by the demineralization of inorganic components, e.g., the damage of dentin. Current clinical materials for hard tissue regeneration commonly act as "fillers" and their therapeutic effect is limited by the failures of biological-linked organic-inorganic interface reconstruction. Herein, a fast in situ crosslinking of calcium phosphate oligomers (CPOs) on collagen matrixes for efficient organic-inorganic interface re-construction, which can result in a biomimetic hybrid, is demonstrated. By using damaged dentin as an example, the inorganic ionic crosslinking can instantly infiltrate into the dentin matrix to rebuild a dense and continuous calcium phosphate-collagen hybrid within only 5 min, where the structurally integrated organic-inorganic interface is identical to natural dentin. As a result, the damaged dentin can be fully recovered to a healthy one, which is superior to any current dentin treatments. The fast construction of biomimetic hybrid by inorganic ionic crosslinking provides a promising strategy for hard tissue repair and follows great potentials of CPOs as advanced biomedical materials in future.

Engineering peptide-polymer hybrids for targeted repair and protection of cervical lesions

By 2060, nearly 100 million people in the U.S. will be over age 65 years. One-third of these older adults will have root caries, and nearly 80% will have dental erosion. These conditions can cause pain and loss of tooth structure that interfere with eating, speaking, sleeping, and quality of life. Current treatments for root caries and dental erosion have produced unreliable results. For example, the glass-ionomer-cement or composite-resin restorations used to treat these lesions have annual failure rates of 44% and 17%, respectively. These limitations and the pressing need to treat these conditions in the aging population are driving a focus on microinvasive strategies, such as sealants and varnishes. Sealants can inhibit caries on coronal surfaces, but they are ineffective for root caries. For healthy, functionally independent elders, chlorhexidine varnish applied every 3 months inhibits root caries, but this bitter-tasting varnish stains the teeth. Fluoride gel inhibits root caries, but requires prescriptions and daily use, which may not be feasible for some older patients. Silver diamine fluoride can both arrest and inhibit root caries but stains the treated tooth surface black. The limitations of current approaches and high prevalence of root caries and dental erosion in the aging population create an urgent need for microinvasive therapies that can: (a) remineralize damaged dentin; (b) inhibit bacterial activity; and (c) provide durable protection for the root surface. Since cavitated and non-cavitated root lesions are difficult to distinguish, optimal approaches will treat both. This review will explore the multi-factorial elements that contribute to root surface lesions and discuss a multi-pronged strategy to both repair and protect root surfaces. The strategy integrates engineered peptides, novel polymer chemistry, multi-scale structure/property characterization and predictive modeling to develop a durable, microinvasive treatment for root surface lesions.

Long-term Evaluation of Bonding Performance of Universal Adhesives based on Different Dentinal Moisture Levels

PURPOSE

To evaluate the microtensile bond strength (μTBS) and silver nitrate uptake (SNU) of three universal adhesives used in etch-and-rinse (ER) and self-etch (SE) modes on dry, wet, and oversaturated dentin surfaces after 24 h and 1 year of water storage. The morphology of the hybrid layer (MHL) and the degree of conversion (DC) were also evaluated.

MATERIALS AND METHODS

Human molars were divided into 36 groups according to combinations of the following variables: (i) universal adhesives (Ambar Universal APS [AMB], Prime&Bond Active [PBA], Scotchbond Universal Adhesive [SBU]), (ii) adhesive strategies (ER or SE), (iii) moisture level (dry, wet, or oversaturated dentin surface), and (iv) storage time (24 h or 1 year). After restoration, the specimens were sectioned into resin-dentin sticks and tested for μTBS and SNU according to storage time. For MHL, the specimens were sectioned and evaluated after 24 h using SEM. DC was evaluated using FTIR. ANOVA and Tukey's test were used for statistical analyses (5%).

RESULTS

When 24-h vs 1-year data were compared, there was a significant decrease in μTBS and an increase in SNU values for the majority of experimental groups (p < 0.0001). On dry (ER) and oversaturated (ER and SE) dentin, AMB showed higher μTBS than did PBA (p < 0.00001). No significant decrease in μTBS was observed when universal adhesives were applied in the SE mode to dry dentin (p > 0.05). Regarding SNU, at all moisture levels, AMB showed lower SNU values than SBU (p < 0.001). Regarding MHL, SBU showed several imperfections when applied to oversaturated dentin in comparison with AMB and PBA. Regarding DC, when dentin was kept dry or was oversaturated, AMB showed a higher DC than PBA (p < 0.0001).

CONCLUSION

The behavior of the different universal adhesives evaluated did not vary when applied to wet or dry dentin. However, the results with oversaturated dentin were dependent on the universal adhesive. Independent of the moisture level and the universal adhesive evaluated, significant degradation of the bonding properties occurred after 1 year of water storage, with the exception of universal adhesives applied to dry dentin in the SE strategy.

Etch-mineralizing treatment to improve dentin bonding

OBJECTIVES

This study aimed to investigate the effect of etch-mineralizing solution as a dentin treatment agent on dentin bonding.

METHODS

This study designed four kinds of etch-mineralizing solutions (EMs) by adding sodium fluoride in 35% phosphoric acid aqueous solution with four different concentrations (5, 10, 20, and 30 mg/ml), and named F1, F2, F3 and F4, respectively. 35% phosphoric acid gel treatment was the control group. SEM, EDS, FTIR and microhardness tests were performed on the treated dentin. Shear bond strength was measured before and after aging. Nanoleakage was also evaluated. Fracture mode was researched after SBS testing. The antibacterial properties of treated dentin were also investigated through live/dead staining of biofilms.

RESULTS

The smear layer was removed and mineralization substances were observed on the dentin surface and tubule, and no obvious collagen fibers were observed compared with the control group. FTIR spectrums showed that the ratios of phosphate/collagen on EMs treated dentin surfaces were significantly increased (P<0.05). F2 group had the highest bonding strength (32.14±7.33 MPa) and microhardness (66.08±10.58), while the control group had the lowest bonding strength (21.81±4.03 MPa) and microhardness (42.34±7.08) (p<0.05), and excellent bonding strength caused the more cohesive fracture. Experimental groups showed less nanoleakage than group C (P<0.05). Moreover, experimental groups had better antiaging performance and antibacterial properties than the control group (p<0.05).

CONCLUSION

EMs treatment not only improved dentin bonding and antibacterial ability, but also remineralized dentin with autologous mineral elements.

CLINICAL SIGNIFICANCE

The treatment provides a novel therapeutic strategy for obtaining ideal dentin bonding strength and prolonging the longevity of the restoration.

Comparative Assessment of Different Pre-Treatment Bonding Strategies to Improve the Adhesion of Self-Adhesive Composites to Dentin

The aim of this study is to compare the adhesive interface formed in dentin, using self-adhesive composites applied with different bonding strategies, by testing the microtensile bond strength (μTBS) and ultramorphology through the use of light microscopy. Permanent, sound human molars were randomly allocated to six experimental groups. The groups included a negative control group, where only etching was performed via EtchOnly; a positive control group where an adhesive was applied, OptiBondFL (OBFL); and an experimental group where a primer was applied using a co-curing strategy together with a composite (Primer_CoCuring). The samples were sectioned into microspecimens for μTBS (n = 8) and into 1-mm thick slabs for light microscopy using Masson’s trichrome staining protocol (n = 3). The statistical analysis included a two-way ANOVA for μTBS data and Tukey’s HSD was used as a post-hoc test (significance level of 5%; SPSS v. 26.0). The results of the μTBS revealed that the self-adhesive composite (F = 6.0, p < 0.018) and the bonding strategy (F = 444.1, p < 0.001) significantly affected the bond strength to dentin. However, their interactions were not significant (F = 1.2, p = 0.29). Etching dentin with no additional treatment revealed the lowest μTBS (VF_EtchOnly = 2.4 ± 0.8 MPa; CC_EtchOnly = 2.0 ± 0.4 MPa), which was significantly different from using a primer (VF_CoCu = 8.8 ± 0.8 MPa; CC_CoCu = 6.3 ± 1.0 MPa) or using the full adhesive (VF_OptiBondFL = 22.4 ± 0.3 MPa; CC_OptibondFL = 21.2 ± 0.4 MPa). Microscopy images revealed that the experimental Primer_CoCuring was the only group with no collagen fibers exposed to the dentin−composite interface. Overall, the use of a primer, within the limitations of this study, increased the bonding of the self-adhesive composite and provided sufficient infiltration of the collagen based on light-microscopic imaging.

Effects of the Combined Application of Trimethylated Chitosan and Carbodiimide on the Biostability and Antibacterial Activity of Dentin Collagen Matrix

The structural integrity of a dentin matrix that has been demineralized by the clinical use of etchants or calcium-depleting endodontic irrigants, such as endodontic ethylenediaminetetraacetic acid (EDTA), is often deteriorated due to the collagenolytic activities of reactivated endogenous enzymes as well as the infiltration of extrinsic bacteria. Therefore, the biomodification of dentin collagen with improved stability and antibacterial activity holds great promise in conservative dentistry. The purpose of this study was to evaluate the effects of the combined application of trimethylated chitosan (TMC) and 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) on the biostability and antibacterial activity of the demineralized dentin collagen matrix. The morphological changes in the collagen matrix were observed by scanning electron microscopy (SEM), the amount of TMC adsorbed on the collagen surface was detected by X-ray photoelectron spectroscopy, and the elastic modulus was measured by a three-point bending device. Dry weight loss and amino acid release were detected to evaluate its anti-collagenase degradation performance. The antibacterial performance was detected by confocal microscopy. The TMC-treated group had less collagen space and a more compact collagen arrangement, while the untreated group had a looser collagen arrangement. The combined application of TMC and EDC can increase the elastic modulus, reduce the loss of elastic modulus, and result in good antibacterial performance. The current study proved that a dentin collagen matrix biomodified by TMC and EDC showed improved biodegradation resistance and antibacterial activities.

Collagen-depletion strategies in dentin as alternatives to the hybrid layer concept and their effect on bond strength: a systematic review

Strategies aiming to improve the longevity of resin-dentin adhesive interface developed so far have only been able to retard the problem. Different approaches are thus needed. The objective of this review was to determine whether the use of collagen-depletion strategies after acid-etching procedures may improve the bond strength of resin-based materials to dentin. A systematic review was planned following 2021 PRISMA statement guidelines, with a search strategy performed in five electronic databases: PubMed/Medline, Scopus, EMBASE, SciELO and IADR Abstract Archive (last search: 17/01/2022). Inclusion criteria encompassed studies which evaluated a collagen-depletion strategy in acid-etched human dentin and tensile/shear bond strength tests. Risk of bias assessment was carried out by two reviewers, working independently on an adapted five-domain risk of bias (RoB) checklist for laboratory studies. Results were synthesized qualitatively, as a meta-analysis was not possible due to limited number of studies and their RoB. A total of eight studies were eligible for inclusion in the systematic review after inclusion/exclusion criteria application. Out of these, two evaluated the effect of using NaOCl followed by an antioxidant, and the remaining six evaluated different enzymatic treatments (bromelain, chondroitinase ABC, papain, and trypsin). None of the studies reported a decrease of bond strength when a collagen-depletion strategy was used, in comparison to traditional hybrid layers (control). All enzymatic treatment studies which respected the inclusion criteria improved the bond strength to dentin. Some specific collagen-depletion strategies seem to play a favorable role in improving immediate bond strengths to dentin. Further research with sound methodology is required to consolidate these findings, since limitations in RoB and a low number of studies were found. The assessment of further proteolytic agents and long-term outcomes is also required.

Deterioration of anterior resin composite restorations in moderate to severe tooth wear patients: 3-year results

OBJECTIVES

Deterioration in anterior resin composite restorations placed in tooth wear patients was investigated after 36 months.

MATERIALS AND METHODS

Data collected prospectively for 47 participants of the Radboud Tooth Wear Project were used (41 ± 8 years, 90% male, n = 270 restorations). Restorations were individually evaluated using intraoral photographs and 3D scans to rate modified FDI scores and to record the presence of degradation features. Four groups with distinct combinations of composites and techniques were assessed, and multivariable logistic regression models were used to analyze the data (p < 0.05).

RESULTS

For all groups together, early degradation signs were present at 1 month: irregularities (41.5%) and ditching (7.4%) were observed at the surface and adhesive interfaces. The frequency of irregularities decreased in the 36-month evaluation (37%), but ditching (12.2%) and fractures (10.7%) were more common. The most frequent deterioration (based on photographs) was observed for staining (44%) and loss of luster (31%). In 3D scans, the most frequent were for wear (25%), marginal adaptation (24%), and the presence of irregularities (19%). Canines had 5.5 times more chances of deterioration by ditching than incisors (p < 0.001). The differences between composites and restorative techniques were minor.

CONCLUSIONS

A continuous degradation process of restorations placed in tooth wear patients was observed in anterior teeth restored with different composites, with a progression of the deterioration over 36 months.

CLINICAL RELEVANCE

When placing anterior resin composite restorations in tooth wear patients, it could be important to establish realistic expectations and the need for checkup appointments.

An in vitro micro-CT assessment of bioactive restorative materials interfacial adaptation to dentin

BACKGROUND

The background of this study was to improve the longevity of a restoration and optimal adaptation of restorative material to the prepared cavity walls is crucial. The study aimed to evaluate the interfacial adaptation of Activa, Micron, and Predicta bulk bioactive restorative materials to coronal dentin using micro-computed tomography (CT) analysis.

MATERIALS AND METHODS

In this in vitro micro-CT assessment study, Class II mesio- and disto-occlusal cavities were prepared on 60 extracted human mandibular molar teeth. After etching and bonding procedures, all the mesial cavities (n = 60) were restored with Tetric N-Ceram and the disto-occlusal cavities with Activa or Micron or Predicta bioactive (n = 20 each) restoratives. Interfacial gap percentages were evaluated under micro-CT before (baseline) and after thermo-mechanical load cycling (TMC). Acquired data were analyzed statistically using one-way analysis of variance, Paired t-test, and Tukey's multiple post hoc procedures, at P < 0.05 level of significance.

RESULTS

The interfacial gap percentages were lowest for Predicta bioactive and highest for the Micron group (P < 0.05). The number of gaps increased significantly after TMC in all the groups (P < 0.05). The adaptation of tested materials was inferior to axial wall and pulpal floor, whereas considerably better adaptation was observed on buccal and lingual walls.

CONCLUSION

Predicta bioactive followed by Activa bioactive has shown superior interfacial adaptation, whereas Micron bioactive demonstrated maximum microgaps compared to nanohybrid composite. Artificial aging with TMC has a negative influence on the internal adaptation of all tested materials.

Effect of Intraoral Humidity on Dentin Bond Strength of Two Universal Adhesives: An In Vitro Preliminary Study

This study investigated the effect of intraoral humidity on microtensile bond strength (μTBS) to dentin of two universal adhesives applied in self-etch (SE) mode. Forty extracted human molars were selected for this study. Dentin specimens were allocated into four groups, standardized and then bonded with two commercial multimode adhesives, according to two humidity conditions (50% relative humidity (RH) and 90% RH). Following composite resin build-up and 24 h of water storage, the μTBS of the bonded interface was analyzed. The 50% RH was higher for Scotchbond Universal (SBU) than Prime&Bond Universal (PBU), while for 90% RH, SBU had significantly lower values than PBU. With PBU, the mean bond strength was not significantly different between both humidity settings tested (p > 0.05), while for SBU, the mean bond strength was significantly different between both conditions tested (p < 0.05); μTBS was significantly higher for 50% RH than for the other group. Within the limitation of this in vitro study, it can be concluded that: 1) the bonding performance of adhesives systems depends on the humidity settings; 2) increased RH exerts a detrimental effect on the bond strength of 2-hydroxyethyl methacrylate (HEMA)-containing adhesive tested. However, this phenomenon was not observed for HEMA-free adhesive tested; 3) further research in this area is needed to investigate different adhesive systems, temperatures and humidity settings.

Marginal Adaptation of Flowable vs Sonically Activated or Preheated Resin Composites in Cervical Lesions

PURPOSE

To investigate marginal integrity of restorations applied with preheated and non-preheated composite, flowable composite, sonically activated composite, and a new thermo-viscous bulk-fill composite using near-infrared technology for preheating, in class V cavities of human molars.

MATERIALS AND METHODS

Standardized cavities were prepared on the buccal surfaces of 60 human mandibular molars and restored with one of the following resin composite materials after application of an etch-and-rinse adhesive (OptiBond FL, Kerr): non-preheated or preheated conventional composite (Filtek Supreme XTE, 3M Oral Care), preheated thermo-viscous composite (VisCalor bulk, Voco), soncially activated composite (SonicFill 3, Kerr), or flowable composite (Filtek Supreme XTE Flowable, 3M Oral Care) applied in bulk or as a lining material using the snow-plow technique. After light curing and polishing, the percentage of continuous margins (PCM) of the restorations in enamel and dentin was assessed using SEM both before and after thermomechanical loading (TML). TML was carried out with 3000 thermal cycles (5°C-50°C) and a simultaneous mechanical stress application with 1.2 million load-cycles (1.7 Hz, 49 N) in a computer-controlled masticator. Non-parametric statistical analysis was performed using Wilcoxon, Kruskal-Wallis, and Mann-Whitney U-tests (α = 0.05).

RESULTS

All groups revealed a significant decline in marginal integrity after TML in both enamel and dentin. Although the flowable group in enamel and the snow-plow group in dentin showed the highest PCM before TML, the differences between the groups were compensated after TML.

CONCLUSION

All of the tested composites and application methods showed similar marginal integrities after thermomechanical loading and can be recommended for clinical implementation.

Development and Assessment of Bioactive Coatings for the Prevention of Recurrent Caries Around Resin Composite Restorations

OBJECTIVE

To develop hydrophilic resin-based surface coatings containing bioactive agents (proanthocyanidins from Vitis vinifera and calcium silicate) and assess their protective role at the dentin and enamel margins of cervical restorations against demineralization under simulated conditions of high and low caries activity.

METHODS

Suboptimal resin composite restorations were placed on cervical cavity preparations on buccal and lingual surfaces of thirty-two molars after a contamination protocol. Groups were divided according to the resin-based coatings (n=8): resin without bioactive (C), resin containing 2% enriched Vitis Vinifera (VVE), and resin coat containing 10% calcium silicate (CaSi). The control group did not receive a resin (NC). To simulate a hydrolyticenzymatic degradation, specimens were subjected to 2-month storage followed by incubation in esterase at 37°C for 8 days. Afterwards, recurrent caries was induced using a pH-proteolytic model on half of the specimens to simulate high caries activity, and the other half remained in simulated body fluid (SBF). Measurements of cross-section microhardness (KHN) and infiltration with rhodamine-B assessed the micropermeability (MP), the extent of demineralization (ED), and the demineralization area (DA). Data were analyzed using analysis of variance (ANOVA) and post-hoc tests (α=0.05).

RESULTS

VVE and CaSi presented higher cross-sectional KHN values for enamel and dentin (p<0.001). The bioactive coatings resulted in lower MP, ED, and DA compared to NC (p<0.005) in enamel and dentin. CaSi coating preserved the enamel from demineralization (p=0.160).

CONCLUSION

The application of bioactive coatings represents a potential strategy to protect the enamel-dentin margins of resin restorations.

A multi-functional dentine bonding system combining a phosphate monomer with eugenyl methacrylate

OBJECTIVE

The tooth-resin composite interface is frequently associated with failure because of microbial contamination, hydrolytic and collagenolytic degradation. Thus, designing a dentine bonding system (DBS) with an intrinsically antimicrobial polymerisable monomer is of significance especially if it can be used with self-etching primers enabling resistance to degradation of the interface.

METHODS

Experimental adhesives were developed incorporating eugenyl methacrylate (EgMA) at concentrations of 0,10 or 20 wt%, designated as EgMA0, EgMA10 and EgMA20, respectively, for use as a two-step self-etch DBS with the functional monomer bis[2-(methacryloyloxy) ethyl] phosphate (BMEP) in the primer. The curing, thermal and wettability properties of the adhesives were determined, and hybrid layer formation was characterised by confocal laser scanning microscopy, microtensile bond strengths (µTBS) and nanoleakage by back-scattered SEM. In situ zymography was used to assess MMP inhibitory activity of the BMEP-EgMA DBS.

RESULTS

EgMA in the adhesives lowered the polymerisation exotherm and resulted in higher Tg, without negatively affecting degree of conversion. Water sorption and solubility were significantly lower with higher concentrations of EgMA in the adhesive. The formation of a distinct hybrid layer was evident from confocal images with the different adhesives, whilst EgMA20 yielded the highest µTBS post water storage challenges and lowest nanoleakage after 6 months. The experimental DBS exhibited minimal to no MMP activity at 3 months.

SIGNIFICANCE

The hydrophobic nature of EgMA and high cross-link density exerts considerable benefits in lowering water uptake and polymerisation exotherm. The application of EgMA, adhesives in conjunction with BMEP in a multi-functional self-etching DBS can resist MMP activity, hence, enhance longevity of the dentine-resin composite interface.

Enhancing the Stability of the Resin-Dentin Bonding Interface with Ag+- and Zn2+-Exchanged Zeolite A

Enhancing the stability of the resin-dentin bonding interface via simultaneously improving the antibacterial, mechanical, and adhesive properties of a dental adhesive is the key to prolonging the longevity of dental restoration for caries treatment. Herein, we present the stabilization effect of Ag⁺- and Zn²⁺-exchanged zeolite A (denoted as Ag-A and Zn-A, respectively) on the resin-dentin bonding interface. Ag-A and Zn-A zeolites exhibited sustained ion release capability, outstanding biocompatibility to L929 cells (<2 mg/mL), and excellent antibacterial ability to Streptococcus mutans (minimum inhibitory concentration: 100 μg/mL for Ag-A and 200 μg/mL for Zn-A). One-step self-etching adhesives modified by Ag-A, Zn-A, or Ag-/Zn-A (1/1 in weight) zeolites with an ultralow loading of 0.2 wt % exhibited favorable antibacterial activity with the inhibition of biofilm formation by 70.33, 56.47, and 62.54%, respectively. Compared to the control group, Zn-A- and Ag-/Zn-A-modified adhesives significantly increased the wettability properties of the adhesive and the long-term resin-dentin bond strength (by ∼25%) after 5000 thermocycles of aging. The current data demonstrated that the introduction of 0.2 wt % Zn-A or Ag-/Zn-A into the adhesive remarkably enhanced the stability of the resin-dentin bonding interface. Our findings provide a new strategy to modify the dental adhesive for further optimizing the longevity of dental restorations for caries.

Potential of Fluoride-Containing Zinc Oxide and Copper Oxide Nanocomposites on Dentin Bonding Ability

Despite recent advances in bonding restorations, which are the basis of restorative dentistry, secondary caries are still able to form. Previously, a novel fluoride-containing zinc and copper (ZCF) nanocomposite was introduced to prevent the formation of caries due to its antibacterial activity. In this study, we studied the impact of ZCF nanoparticles on the adhesive strength of bonding restorations through micro-tensile bond strength (µTBS) testing. The impact of antibacterial and matrix metalloproteinase (MMP) inhibitors on the nanoparticles was also examined. The nanocomposites were prepared using a simple one-step homogeneous co-precipitation method at a low temperature. A self-etch adhesive was applied to 10 extracted caries-free human molars with (test group) and without (control group) the ZCF nanoparticles. This was followed by composite resin build-up and µTBS testing, MMP activity assays, and evaluation of the antibacterial effects. The results showed no significant differences in the µTBS between the ZCF and the control groups. However, the ZCF exhibited a significant inhibitory effect against MMP-2, MMP-8, and MMP-9, in addition to an antibacterial effect on Streptococcus mutans. Therefore, the present study demonstrated that the addition of ZCF nanoparticles to adhesive systems can result in MMP inhibition and antibacterial action while maintaining the mechanical properties of the bonding restorations.

Improving Properties of an Experimental Universal Adhesive by Adding a Multifunctional Dendrimer (G-IEMA): Bond Strength and Nanoleakage Evaluation

A vast number of adhesive formulations exist currently. However, available adhesives still have several drawbacks such as increased hydrophilicity, polymerization deficiency, potential cytotoxicity and limited monomer interdiffusion within dentin. To improve material properties, a Bisphenol A-free adhesive containing a novel dendrimer G(2)-isocyanatoethyl methacrylate (G-IEMA) in replacement of Bis-GMA was made and tested. Sound human molars were sectioned to expose mid-coronal dentin, which was bonded using four adhesives—Futurabond, Scotchbond Universal and experimentals EM1 and EM2. The experimental adhesive EM2 contained G-IEMA, while EM1 had Bis-GMA. Groups were further allocated to two different adhesive strategies: etch-and-rinse (20 s etching) or self-etch. Immediate (24 h) microtensile bond strength to dentin (n = 5) was tested using a universal testing machine (1 mm/min, 5 kN; Shimadzu AGS-X Autograph, Tokyo, Japan), while the ultrastructure of the interface (n = 2) was assessed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Nanoleakage expression was evaluated using silver nitrate penetration and posterior SEM-EDS analysis (n = 3). Linear mixed models/Generalized models were used for inferential statistics (5% significance level). Bond strength results did not depend on the adhesive choice, although differences were found between strategies (p < 0.001). Regarding nanoleakage, when applied in an etch-and-rinse mode, experimental adhesives scored lower nanoleakage means than Futurabond and Scotchbond Universal. The novel adhesive shows interesting interfacial properties, with favorable nanoleakage results and a bond strength to dentin that matches current commercial adhesives.

Dentin collagen denaturation status assessed by collagen hybridizing peptide and its effect on bio-stabilization of proanthocyanidins

OBJECTIVE

To assess dentin collagen denaturation from phosphoric acid and enzyme treatments using collagen hybridizing peptide (CHP) and to investigate the effect of collagen denaturation on bio-stabilization promoted by proanthocyanidins (PA).

METHODS

Human molars were sectioned into 7-µm-thick dentin films, demineralized, and assigned to six groups: control with/without PA modification, H₃PO₄-treated collagen with/without PA modification, enzyme-treated collagen with/without PA modification. PA modification involved immersing collagen films in 0.65% PA for 30 s. H₃PO₄ and enzyme treatments were used to experimentally induce collagen denaturation, which was quantitated by fluorescence intensity (FI) from the fluorescently-conjugated-CHP (F-CHP) staining (n = 4). FTIR was used to characterize collagen structures. All groups were subject to collagenase digestion to test the bio-stabilization effect of PA on denatured collagen using weight loss analysis and hydroxyproline assay (n = 6). Data were analyzed using two-factor ANOVA and Games-Howell post hoc tests (α = 0.05).

RESULTS

FTIR showed collagen secondary structural changes after denaturation treatments and confirmed the incorporation and cross-linking of PA in control and treated collagen. F-CHP staining indicated high-degree, medium-degree, and low-degree collagen denaturation from H₃PO₄-treatment (FI = 83.22), enzyme-treatment (FI = 36.54), and control (FI = 6.01) respectively. PA modification significantly reduced the weight loss and hydroxyproline release of all groups after digestion (p < 0.0001), with the results correlated with FI values at r = 0.96-0.98.

SIGNIFICANCE

A molecular method CHP is introduced as a sensitive technique to quantitate dentin collagen denaturation for the first time. PA modification is shown to effectively stabilize denatured collagen against collagenase digestion, with the stabilization effect negatively associated with the collagen denaturation degree.

Effect of Active Bonding Application after Selective Dentin Etching on the Immediate and Long-Term Bond Strength of Two Universal Adhesives to Dentin

The objective was to evaluate the influence of active bonding applications (ABA) for different time intervals after selective dentin etching (SDE) for 3 s on the microtensile bond strength (μTBS) to dentin of two universal adhesive systems (UAs): one containing 2-hydroxyethyl methacrylate (HEMA) (Scotchbond Universal, SBU), and one that was HEMA-free (Prime&Bond Universal, PBU). Dentin bovine specimens were divided into four groups: self-etch as control (SE), SDE + ABA for 15 s (SDE15), SDE + ABA for 20 s (SDE20), and SDE + ABA for 25 s (SDE25). The μTBS test was performed after a water storage of 24 h and 6 months. Scanning electron microscopy (SEM) was used in order to examine the resin−dentin interface. For the PBU, the µTBS was significantly influenced only by the aging factor (p < 0.026). A statistically significant decrease in the µTBS after 6 months of aging was observed only for the SDE15 group. For SBU, µTBS was significantly influenced by the protocol application and the aging time (p ≤ 0.041). The groups SDE15, SDE20, and SDE25 achieved statistically significant higher values (after 24 h and 6 months). No considerable variances were noticed in the homogeneity and continuity of the hybrid layer (HL) among the groups. In conclusion, SDE and ABA improved the µTBS only of a HEMA-containing universal adhesive.

Examination of caries-affected dentin and composite-resin interface after different caries removal methods: A scanning electron microscope study

To evaluate the caries-affected dentin and composite-resin interface with scanning electron microscopy (SEM) after different caries removal methods in human molars. Twelve with extensive approximal caries lesions that did not reach the pulp and five caries-free molars (control group [CG]) were used. Carious teeth were divided into four experimental groups: Atraumatic Restorative Treatment (ART), Rotary Instrument (RI), Photo-Ablation, and Papain-Based Enzymatic Gel (Brix 3000®, Brix, Brazil). Class II slot cavities were prepared with RI in the CG. Then all caries removed teeth and control groups were restored (All-Bond Universal, BISCO, USA; Clearfil MajestyES-2, Kuraray, Japan). Specimens were prepared for SEM examinations. Hybrid layer (HL) thicknesses were measured using ImageJ programme. Gap measurements were performed with micro-CT. Data were analyzed with ANOVA and posthoc Dunnett's t-tests (p < .05). The highest HL thickness was found in Photo-Ablation Group, and a statistically significant difference was observed among the control and experimental groups (p < .05). The lowest HL thickness was measured in the Enzymatic Gel Group. In terms of internal gap formation, CG showed statistically significant differences compared to the other groups (p < .05). The highest internal gap was observed in RI Group, while the lowest gap was observed in CG. According to SEM, a uniform HL and resin tags were seen in the CG. Smear layer, irregular HL, and gap formation were observed in ART Group. In RI Group, nonuniform HL formation and resin tags were observed. In Photo-Ablation Group, a uniform HL without smear layer and internal gap was observed. In the Enzymatic Gel Group, both opened dentinal tubules, and melting-like formations were observed on the dentin surface. Especially melting-like formations were observed in peritubular dentin. It can be concluded that all caries removal methods except rotary instrumentation were conservative methods, which preserve more healthy dental tissues.

Bonding performance and ultramorphology of the resin-dentine interface of contemporary universal adhesives

OBJECTIVES

This study aimed at evaluating the microtensile bond strength (μTBS) and the resin-dentine ultramorphology (24 h and 10 months ageing) of contemporary universal adhesives applied in self-etch (SE) or etch-and-rinse (ER) mode.

MATERIALS AND METHODS

Sixty-four sound human molars were collected and randomly allocated in 4 main experimental groups (n = 16) according to the adhesive system employed and subsequently divided into two subgroups depending on their application mode SE or ER (n = 8): ZipBond X (ZBX-SE; ZBX-ER), Prime and Bond Active (PBA-SE; PBA-ER), Clearfil Universal Bond Quick (CBQ-SE; CBQ-ER) or Scotchbond Universal (SCH-SE; SCH-ER). The specimens were cut into sticks with a cross-sectional area of approximately 0.9 mm² and subjected to μTBS testing at 24 h or after 10 months of ageing in artificial saliva (AS). Five representative fractured specimens from each group were analysed using field-emission scanning electron microscopy (FE-SEM). Resin-dentine slabs (Ø 0.9mm²) from each experimental group were immersed in Rhodamine B and subsequently analysed using confocal microscopy analysis (CLSM). The μTBS results were analysed using a two-way ANOVA and Newman-Keuls multiple-comparison test (α = 0.05).

RESULTS

ZBX, PBA and SCH exhibited greater μTBS values than CQB at 24 h in both SE and ER modes (p < 0.05). CQB showed a significant decrease in μTBS values after ageing both when used in SE and ER mode (p < 0.05). ZBX-ER exhibited no significant differences in the μTBS test after ageing (p > 0.05), while a significant drop in μTBS was seen in SCH-ER and APB-ER after 10-month ageing (p < 0.05). Clear signs of degradation were evident in the resin-dentine interface created with CQB regardless of the application mode or the ageing time. In APB-ER and SCH-ER groups, such signs of degradation were evident after ageing in AS. ZBX showed slight dye infiltration both when used in ER and SE mode.

CONCLUSIONS

The long-term bonding performance of modern universal adhesives is usually influenced by the adhesive strategy employed; self-etching application should be prioritised during dentine bonding. Moreover, the use of shortened bonding protocols may compromise the quality of the resin-dentine interface and the bonding performance of most modern universal adhesives.

CLINICAL RELEVANCE

The use of etch-and-rinse bonding procedures, as well as "shortened" application protocols should be eluded when using modern universal adhesives in dentine. However, new generation universal adhesives based on innovative chemical formulations may probably allow clinicians to achieve long-term bonding performance with such simplified system also when employed in ER mode.

Zn-containing Adhesives Facilitate Collagen Protection and Remineralization at the Resin-Dentin Interface: A Narrative Review

This is a narrative review of the literature assessing the potential effectiveness of doping dentin polymeric adhesives with zinc compounds in order to improve bonding efficacy, remineralization and protection against degradation. A literature search was conducted using electronic databases, such as PubMed, MEDLINE, DIMDI and Web of Science. Through our search, we found literature demonstrating that Zn-doped dentin adhesives promote protection and remineralization of the resin-dentin interfaces. The increased bioactivity has also facilitated dentinal tubules' occlusion by crystals' precipitation contributing to improved sealing efficacy of restorations. Loading dentin adhesives with zinc gives rise to an increase of both crystallinity of mineral and crosslinking of collagen. The main role of zinc, in dentin adhesives, is to inhibit collagen proteolysis. We concluded that zinc exerts a protective effect through binding at the collagen-sensitive cleavage sites of matrix-metalloproteinases (MMPs), contributing to dentin matrix stabilization. Zinc may not only act as a MMPs inhibitor, but also influence signaling pathways and stimulate metabolic effects in dentin mineralization and remineralization processes. Zn-doped adhesives increase the longevity of dentin bonding through MMPs inhibition. Zn poses a remineralization strategy in demineralized dentin.

Biomimetic Growth of Metal-Organic Frameworks for the Stabilization of the Dentin Matrix and Control of Collagenolysis

The dentin matrix is a collagenous scaffold structurally involved in anchoring resin-based materials to the tooth. Time-dependent degradation of this scaffold at the resin-dentin interface remains a core problem in adhesive dentistry, limiting the service life of dental fillings. This study explored the use of emergent materials termed metal-organic frameworks (MOFs)─formed by the self-assembly of metal ions and organic building blocks─to safeguard the collagen integrity in the functional dentin matrix. We demonstrate that collagen fibrils (from demineralized human dentin) can induce the biomimetic growth of MOF crystals as protective coatings to strengthen and stabilize the fibrils. Zeolitic imidazolate framework-8 (ZIF-8), a zinc-based microporous MOF, was used to fabricate the MOF composites via a "one-pot" reaction in water. The ZIF-modified dentin matrix presented superior mechanical strength and resistance to proteolysis, which can positively affect the longevity of collagen as an anchoring substrate. This work identifies a potential biomedical application of biomimetically synthesized MOFs in repairing dental tissues critical to restorative therapies.

An In-Vitro Evaluation of Microleakage in Resin-Based Restorative Materials at Different Time Intervals

A vital feature of conservative dentistry is the adhesion of the restorative material to the tooth structure for restoration of the tooth substance lost due to dental decay, trauma, or dental imperfections. In a perfect world, a restorative material should generate a lasting adhesion by bonding the restoration with tooth tissues. The ingress of micro-organisms, oral fluids, molecules, and ions through microscopic spaces due to faulty adhesion between restoration and tooth structure is known as microleakage. This study is focuses on the evaluation of adhesive failures between the restorative materials. In the past, studies have focused more on the bonding potential of a restorative material with the tooth surface. Therefore, there is need to carry out a study that compares the microleakage between resin-based restorative materials in a sandwich manner with and without the intermediate bonding layer after immersion in 2% methylene blue dye at different time intervals. The restorative materials used were composite Ceram X Mono plus (DENTSPLY) and Z350 (3M ESPE), Vitremer resin modified glass ionomer cement (RMGIC) (3M ESPE), smart dentine replacement SDR (3M ESPE), Bond NT (DENTSPLY), and Universal Bond (3M ESPE). A light emitting diode (LED) was used to cure the specimens. Artificial saliva was used as a storage medium for the specimens. Thermocycling of specimens was carried out at 500 cycles/30 s and 1000 cycles/30 s. The world health organization (WHO) grading tool for microleakage was used to analyze fluid ingress in the specimens through disclosing by 2% methylene blue dye. The statistical analysis was carried out with one-way analysis of variance (ANOVA) and Tukey post hoc test, keeping the level of significance at p ≤ 0.05. In Grade 0 = 85 samples, Grade 1 = 10 samples, Grade 2 = 7 samples, Grade 3 = 16 samples, and in Grade 4 = 2 samples were identified. This study describes that no microleakage was observed in SDR and resin composite groups as compared to Vitremer and resin composite groups.