Adhesives doi: 10.3390/adhesives2030016

Authors: Cléa Wagner Tatiana Roman Hamdi Jmal Jihed Zghal Berangere Cournault Nadia Bahlouli Naji Kharouf Olivier Etienne

This in vitro study evaluated the shear bond strength (SBS), morphology, and chemistry of CAD/CAM (computer-aided design/computer-aided manufacturing) ceramics and composites bonded to Er:YAG-irradiated dentin using universal adhesive strategies. A total of 102 human dentin discs were randomly allocated to etched control (E), laser-irradiated (I; 10 Hz, 150 mJ, 5 s), or irradiated-and-etched (IE) conditions. Ninety specimens were bonded to a Cerasmart composite (CSM) or leucite-reinforced ceramic (LRF), while 12 were used for scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). EDX showed marked mineral depletion after etching, with the Ca/P ratio decreasing from 1.58 in control dentin to 1.28 in E and IE specimens. LRF showed higher SBS than CSM (14.12 ± 5.14 vs. 10.94 ± 3.76 MPa); E-LRF had the highest SBS (15.48 ± 3.75 MPa) and I-CSM the lowest (9.57 ± 4.05 MPa), with Tukey significance only seen between these groups (p = 0.009). A two-way ANOVA showed a significant material effect on SBS (p = 0.002), whereas dentin pretreatment (p = 0.185) and material × pretreatment interaction (p = 0.719) were not significant. In conclusion, although Er:YAG irradiation modified dentin morphology and surface chemistry, dentin pretreatment had no statistically significant effect on SBS. Phosphoric acid etching nonetheless remained the most consistent conditioning approach in descriptive terms, as irradiated-and-etched dentin achieved SBS values comparable to etched-only dentin, whereas irradiation alone yielded the lowest descriptive values. This observation should be confirmed by studies incorporating thermocycling, long-term storage, and fatigue loading.

Adhesives doi: 10.3390/adhesives2030015

Authors: Sergio Luis Parra-Angarita Juan Federico Herrera-Ruiz Guillermo H. Gaviria Angélique Léonard

Mechanical properties such as viscoelastic, rheological, and textural properties, particularly adhesiveness and cohesiveness, play a significant role in the optimization of handling, processing and drying of dewatered sludge. However, there is no currently standardized methodology for quantifying these properties, leading researchers to adopt various techniques based on economic feasibility, equipment availability, and research objectives. This review systematically compiles and analyzes the most relevant experimental methodologies for evaluating the mechanical properties of dewatered sewage sludge (DSS). This work presents a general overview of the composition and structure of DSS, followed by a comprehensive bibliometric analysis that revealed literature gaps (particularly in adhesiveness evaluation) and identified regulatory frameworks that incremented interest in researching DSS’ properties in the broader push for sustainability. Consequently, a discussion of the experimental set-ups, data treatment and visualization, advantages and disadvantages, and mathematical models with their physical significance is presented for the different techniques identified. The methods analyzed include oscillatory rheology, penetrometry (cylinder and cone), uniaxial compression tests (TPA), shear testing (e.g., Jenike shear test, Atterberg limit test, direct box shear test, triaxial shear test, unconfined shear test, and vane shear test), tomography and slump tests. By comparing these techniques, this study provides insights into the most appropriate approaches for sludge characterization, emphasizing the need for a unified framework to standardize the evaluation of viscoelastic and textural properties in DSS.

Adhesives doi: 10.3390/adhesives2030014

Authors: Amelie Haring Bart Vande Vannet

This in vitro study compared the bond strength performance and adhesive remnant characteristics of two metallic orthodontic pre-coated bracket systems: APC™ Plus and APC™ Flash Free. Forty extracted human premolars were randomly allocated to two groups (n = 20). Following enamel etching with 37% phosphoric acid, brackets were bonded according to the manufacturers’ recommendations. Bond strength testing was performed using a custom-made apparatus in which failure was induced through a progressively increasing load. Because the experimental setup generated a combined loading configuration involving shear, tensile, and bending components, the measured values should be interpreted as comparative bond strength measurements rather than absolute shear bond strength values. Adhesive Remnant Index (ARI) scores were recorded after debonding to evaluate failure patterns. Median bond strength values were 17.75 MPa (IQR: 13.53–21.98) for APC™ Plus and 14.28 MPa (IQR: 9.81–18.74) for APC™ Flash Free. No statistically significant difference was found between groups (Mann–Whitney U test, p = 0.102). In contrast, ARI score distributions differed significantly (Fisher’s exact test, p = 0.001). APC™ Plus brackets predominantly exhibited ARI scores of 2–3, whereas APC™ Flash Free brackets mainly demonstrated ARI scores of 1–2, indicating less adhesive remaining on the enamel surface after debonding. Three enamel fractures were observed in the APC™ Plus group, while none occurred in the APC™ Flash Free group; however, no statistically significant association between bracket type and enamel fracture was identified. Within the limitations of this in vitro study, both bracket systems demonstrated comparable bond strength performance under the experimental conditions investigated. APC™ Flash Free brackets were associated with reduced adhesive remnants on enamel, which may facilitate post-debonding cleanup. Further studies using standardized testing methods and prospective clinical investigations are required to confirm these findings and determine their clinical relevance.

Adhesives doi: 10.3390/adhesives2030013

Authors: Nicolas Nassar Karim Corbani Roland Kmeid Carlos Enrique Cuevas-Suárez Abigailt Flores-Ledesma Rim Bourgi

Background: Clear aligners fabricated via computer-aided design and manufacturing are increasingly used in orthodontics and may also serve as carriers for peroxide-based bleaching agents. However, exposure to bleaching agents may affect the physical and surface properties of aligner polymers, which could influence their clinical performance. Objective: This systematic review aims to evaluate the available evidence on the use of clear aligners as carriers for tooth bleaching agents, with a focus on bleaching efficacy and reported effects on aligner materials based on the identified literature. Methods: A systematic search was conducted in PubMed, Web of Science, Scopus, Scielo, and Embase for studies published up to January 2026. Eligible clinical and in vitro studies investigated bleaching procedures using clear aligners or conventional trays and reported color change outcomes and/or changes in material properties such as hardness, surface integrity, or mechanical performance. Risk of bias was assessed using the Cochrane Risk of Bias tools and standardized criteria for in vitro and clinical studies. Results: Six studies (three clinical and three in vitro) met the inclusion criteria. Clinical evidence indicated that bleaching delivered through clear aligners achieved similar whitening outcomes to conventional tray-based systems. In vitro studies reported changes in surface hardness and mechanical properties of polymer-based aligner materials after peroxide exposure; however, no major structural degradation was observed. Clinical studies were generally at high risk of bias, while in vitro studies showed low to moderate risk. Conclusions: Within the limitations of this systematic review, clear aligners may represent a potential carrier for tooth bleaching agents with outcomes comparable to conventional trays. However, the available evidence is limited and heterogeneous. Well-designed randomized controlled trials are needed to confirm clinical effectiveness and long-term material safety.

Adhesives doi: 10.3390/adhesives2020012

Authors: Yukinori Maruo Kumiko Yoshihara Masao Irie Noriyuki Nagaoka Naoki Kodama Yuki Tanaka Miho Kuwahara Kentaro Akiyama

Polyetheretherketone (PEEK) is a high-performance thermoplastic polymer with low surface energy, chemical inertness, and a highly crystalline structure, which limit durable adhesion to resin-based materials and require improved bonding strategies. This in vitro study evaluated the effect of incorporating multifunctional methacrylate (TMPTMA) and acrylate monomers (A-TMPT and A-DPH) into an experimental primer on the 24 h shear bond strength (SBS) of resin cement to PEEK (n = 6 per group). Experimental primers were prepared by adding varying amounts (100–500 µL) of each multifunctional monomer to a UDMA/MMA-based primer, and SBS was measured after cementation with a dual-cure resin cement. TMPTMA-containing primers produced median SBS values of approximately 10–12 MPa, while acrylate-based primers showed slightly higher values, particularly at higher concentrations, reaching up to ~15.8 MPa; however, no statistically significant improvement over the control group was observed (p > 0.05). Failure modes were predominantly mixed across all conditions. These findings indicate that multifunctional monomers, despite their potential to enhance cross-link density and wetting, do not substantially overcome the intrinsic adhesion-resistant nature of polished PEEK. The results underscore that monomer modification alone is insufficient and that effective adhesion to PEEK likely requires integrated strategies combining chemical activation with mechanical surface conditioning.

Adhesives doi: 10.3390/adhesives2020011

Authors: Reiko Kohsaka Saho Komatsu Keigo Nakamura Akiko Haruyama Aya Miyashita-Kobayashi Kuniko Kohda Miho Komachiya Hirokazu Abo Atsushi Kameyama

This study investigated the influence of solvent evaporation on the ultimate tensile strength (UTS) and water-related weight changes in contemporary universal dental adhesives. Two two-step universal adhesives (OptiBond eXTRa Universal and G2-BOND Universal) and two one-step universal adhesives (OptiBond Universal and BeautiBond Xtreme) were evaluated. Adhesives were used either under normal storage conditions or after active solvent evaporation by removal of the bottle caps and storage at 37 °C for 2 weeks. Hourglass-shaped specimens were prepared, light-cured, and stored in water at 37 °C for 1 h or 7 days prior to UTS testing (n = 10). Specimen weights were measured before and after water storage. For OptiBond eXTRa Universal, no significant difference in UTS was observed between the original and desiccated groups after 7 days of water storage (p > 0.05). In contrast, G2-Bond Universal exhibited significantly higher UTS values in the desiccated group compared with the original group (p < 0.05). In the original group, the one-step universal adhesives failed to polymerize under the original (non-evaporated) conditions, whereas adequate polymerization was achieved following active solvent evaporation. Weight changes after water storage varied depending on the adhesive composition. These results suggest that residual solvent may influence the polymerization behavior, mechanical performance, and water-related properties of universal dental adhesives, emphasizing the importance of adequate solvent evaporation before light curing.

Adhesives doi: 10.3390/adhesives2020010

Authors: Florian Cavodeau Sophie Bistac Maurice Brogly

The present work focuses on a characterization method using optical microscopy to follow the swelling of expanded adhesive formulations. The original aspect of the method consists of incorporating a heating plate into the optical microscope in order to apply a curing process to the adhesive and to directly observe its expansion between two glass plates with a defined gap. Different heating rates and curing temperatures were applied to observe the influence on the expansion process, characterized by the time needed to fill the gap between the glass plates, the homogeneity and quality of the contact on the upper plate and the stability of the adhesion. Bisphenol A diglycidyl ether/dicyandiamide adhesive formulations were particularly considered in this study. Adhesives were also analyzed by DSC to clearly define the curing process in function of the heating rate and curing temperature. The expansion process presented in this work implies the use of a physical expansion agent to validate the analytical method. Their expansion was also studied under an optical microscope to define a blowing profile matching the curing process of the epoxy-amine adhesive. Results showed that the synchronization between the expansion and the curing of the adhesive could be followed and analyzed qualitatively by the proposed method and could be applied to various expanded formulations.

Adhesives doi: 10.3390/adhesives2020009

Authors: Margherita Ceravolo Filipe Castro Antonio González-Mosquera Alicia López-Solache Patrícia Manarte-Monteiro Lígia Pereira da Silva

The management of deep subgingival carious lesions presents significant challenges for achieving durable adhesive restorations due to limited access, moisture control, and proximity to periodontal tissues. Two main approaches are currently adopted to manage these cases: Deep Margin Elevation (DME) and Surgical Crown Lengthening (SCL). This systematic review (PROSPERO registration CRD420250654262) aimed to compare the performance and survival of restorations placed following DME versus SCL in teeth with deep subgingival margins. A comprehensive literature search was conducted in PubMed, B-ON, and the Cochrane Library for studies published between 2014 and 2025. Following PRISMA guidelines, six studies were included. Methodological quality and risk of bias were assessed using ROBINS-I, RoB 2, and the CARE guidelines. The available evidence indicates that both DME and SCL provide satisfactory periodontal stability, high restoration survival rates, and a low incidence of recurrent caries. DME emerged as a minimally invasive strategy that facilitates adhesive procedures by relocating deep margins to more accessible positions, potentially improving marginal integrity while preserving tooth structure and gingival architecture, particularly in patients with a thick gingival biotype. The choice between DME and SCL should be individualized. Further long-term clinical studies are required to clarify their impact on adhesive interface durability in subgingival environments.

Adhesives doi: 10.3390/adhesives2020008

Authors: Chiharu Kawamoto Ryotaro Yago Jiayuan Zhang Asiful Islam Rin Miyake Yu Toida Pipop Saikaew Atsushi Tomokiyo

Tooth bleaching improves dental esthetics but may cause color mismatch with existing resin composite restorations and complicate restorative treatment planning because tooth color may change during the post-bleaching stabilization period, sometimes requiring delayed restoration placement or replacement of existing restorations. Universal shade resin composite (UC) has been introduced to simplify shade selection; however, its ability to adapt to dynamic tooth color changes associated with bleaching has not been sufficiently documented. A 61-year-old male patient underwent tooth bleaching for esthetic improvement. One year later, secondary caries was detected on tooth #22 and restored using a UC. The restoration was placed prior to additional bleaching procedures. Clinical follow-up indicated that the UC restoration appeared to maintain shade adaptation after bleaching. Furthermore, at the two-year follow-up, generalized tooth discoloration was observed; however, the restoration remained harmonized with the surrounding tooth structure. Subsequent additional bleaching resulted in further lightening of the tooth structure while shade harmony with the restoration was preserved. Favorable shade adaptation was maintained throughout the three-year follow-up. This case suggests that a UC restoration placed before bleaching appeared to maintain shade compatibility over long-term follow-up, despite bleaching-induced color improvement and subsequent intrinsic and extrinsic discoloration.

Adhesives doi: 10.3390/adhesives2020007

Authors: Grzegorz Maciaszek Damian Nabel Julia Maciaszek

In the present study, the influence of the parameters of the bonding process, namely the applied pressure during curing, as well as the duration and temperature of curing, on the tensile strength of the bonded joints was investigated. Pull-off tests were conducted in accordance with the ASTM C633 standard. The samples were bonded using a single-component thermosetting adhesive, HTK Ultra Bond 100. On the basis of the results obtained, it was concluded that the tensile strength of the bonded joint, and thus its overall quality, is strongly influenced by the curing parameters of the thermosetting adhesive. The most effective bonding conditions were identified.

Adhesives doi: 10.3390/adhesives2010006

Authors: Francisco Javier Simón Portillo Óscar Cuadrado Sempere Eduardo André de Sousa Marques Miguel Sánchez Lozano Lucas Filipe Martins da Silva

Highly deformable adhesive materials are increasingly employed in engineering applications where flexibility, energy dissipation and damage tolerance are required. The mechanical characterisation of these materials, however, presents significant challenges due to their pronounced non-linear behaviour, large deformations, and, in many cases, time-dependent effects. This paper provides a critical review of experimental, constitutive and numerical approaches used for the characterisation of highly deformable adhesive materials, considered here as bulk materials independently of a specific joint configuration. The review covers mechanical testing methods under large strains, hyperelastic and visco-hyperelastic constitutive models, and the application of fracture mechanics concepts and numerical techniques as exploratory tools for material analysis and comparison. Particular attention is given to the capabilities and limitations of the different approaches, their domains of applicability and the assumptions involved in their use. By highlighting current practices, open challenges and recent developments, this work aims to support the selection of appropriate characterisation methodologies and modelling strategies for highly deformable adhesive materials.

Adhesives doi: 10.3390/adhesives2010005

Authors: Florian Rothenhäusler Holger Ruckdaeschel

Reactive structural adhesives—epoxies, polyurethanes, and acrylics—are essential in high-performance applications, yet their development remains complex due to multiscale adhesion mechanisms, combinatorial formulation spaces, and stringent performance requirements. Traditional trial-and-error approaches are time- and resource-intensive. Machine learning (ML) provides a powerful framework to accelerate adhesive design by capturing nonlinear relationships between formulation, processing, and performance, while enabling predictive modeling, optimization, and experiment prioritization. This review presents a process-oriented guide for ML-assisted adhesive development, covering component selection, feature engineering, initial dataset design, model choice, and iterative workflows integrating classical design-of-experiments, active learning, and Bayesian optimization. Emphasis is placed on interpreting ML outputs through the lens of polymer chemistry, reaction kinetics, and fracture mechanics to extract mechanistic insights and guide rational formulation design. Key challenges—including small, noisy datasets, multi-component interactions, and multi-objective trade-offs—are discussed, along with emerging directions such as collaborative databases, automated knowledge extraction, and hybrid ML–chemistry approaches to further enhance structural adhesive development. The review underscores the potential of integrating ML into adhesive R&D to reduce experimental burden, improve formulation efficiency, and enable data-driven exploration of complex chemistries.

Adhesives doi: 10.3390/adhesives2010004

Authors: Aoto Seki Tetsuto Terabayashi Kazumasa Shimamoto Chiaki Sato Yu Sekiguchi

A detailed understanding of interface degradation in humid environments is essential for improving the reliability of adhesive bonding technologies. Water absorption within the adhesive layer significantly affects joint strength, a factor considered to be long-term degradation. However, even if water does not approach the interface from the inside due to absorption, it can reach the interface from the outside through the crack tip and instantaneously affect the fracture behavior of the interface, highlighting the need to investigate short-term degradation mechanisms. In this study, the effect of water at the aluminum/epoxy resin interface on crack propagation was quantitatively evaluated by measuring the mode I energy release rate through double cantilever beam (DCB) tests. By changing the surface condition of the adherend, interfacial and cohesive failures were achieved, and DCB tests were conducted in air and underwater conditions to compare the effect of water on the fracture energy. Results showed that the interfacial fracture energy decreased by more than 50% when the crack propagated in water, but no significant reduction was observed in the cohesive fracture energy. The decrease in interfacial fracture energy in the presence of water indicates the immediate disruption of chemical bonding.

Adhesives doi: 10.3390/adhesives2010003

Authors: Sumit Suryakant Kolte Siddhi Sunil Atharva Harinath Shastri Vinayak Vijayan Lihua Lou

Biopolymer adhesives are moving toward frontline use in medicine and manufacturing as the limitations in some petrochemical systems, including cytotoxicity, challenges in wet adhesion for specific families of synthetic resins and formaldehyde emissions associated with amino-formaldehyde materials are becoming increasingly difficult to accept. This review integrates mechanisms, material classes and quantitative performance across biopolymer-based adhesives. We focus on architectures that combine permanent covalent anchoring with reversible, energy-dissipating bonds and on how functional group density, crosslink density, microstructure and additives act as design knobs for wet performance, durability and degradation. Across biomedical applications, chitosan, alginate, gelatin and related hydrogels achieve wet lap-shear strengths on the order of tens of kilopascals, cut liver-bleeding times by roughly half, provide strong antibacterial activity and close diabetic wounds by about 92 percent by day 14. Thermoresponsive alginate–gelatin sealants exceed clinically relevant burst pressures and microneedle patches withstand more than 120 mmHg while sealing arteries in under a minute. In industrial settings, dialdehyde-based starch resins deliver 0.83 to 1.05 MPa dry shear and maintain strength after water immersion while meeting stringent emission classes, and silane-modified nanocellulose in urea–formaldehyde markedly reduces free formaldehyde without sacrificing the internal bond. We conclude by identifying priorities for standardized wet testing, and lifetime matching of strength and degradation that can support large-scale clinical and industrial translation.

Adhesives doi: 10.3390/adhesives2010002

Authors: Prosper Mensah Rafael Rodolfo de Melo Alexandre Santos Pimenta James Amponsah Gladys Tuo Fernando Rusch Edgley Alves de Oliveira Paula Humphrey Danso Juliana de Moura Márcia Ellen Chagas dos Santos Couto Giorgio Mendes Ribeiro Francisco Leonardo Gomes de Menezes

The fiberboard industry remains heavily reliant on synthetic, formaldehyde-based adhesives, which, despite their cost-effectiveness and strong bonding performance, present significant environmental and human health concerns due to volatile organic compound (VOC) emissions. In response to growing sustainability imperatives and regulatory pressures, the development of non-toxic, renewable, and high-performance bio-based adhesives has emerged as a critical research frontier. This review, conducted through both narrative and systematic approaches, synthesizes current advances in green adhesive technologies with emphasis on lignin, tannin, starch, protein, and hybrid formulations, alongside innovative synthetic alternatives designed to eliminate formaldehyde. The Evidence for Policy and Practice Information and Coordinating Centre (EPPI) framework was applied to ensure a rigorous, transparent, and reproducible methodology, encompassing the identification of research questions, systematic searching, keywording, mapping, data extraction, and in-depth analysis. Results reveal that while bio-based adhesives are increasingly capable of approaching or matching the mechanical strength and durability of urea–formaldehyde adhesives, challenges persist in terms of water resistance, scalability, cost, and process compatibility. Hybrid systems and novel crosslinking strategies demonstrate particular promise in overcoming these limitations, paving the way toward industrial viability. The review also identifies critical research gaps, including the need for standardized testing protocols, techno-economic analysis, and life cycle assessment to ensure the sustainable implementation of these solutions. By integrating environmental, economic, and technological perspectives, this work highlights the transformative potential of green adhesives in transitioning the fiberboard sector toward a low-toxicity, carbon-conscious future. It provides a roadmap for research, policy, and industrial innovation.

Adhesives doi: 10.3390/adhesives2010001

Authors: José Miguel Martín-Martínez

This Editorial provides a personal view on the evolution of adhesives technology and research over the years [...]

Adhesives doi: 10.3390/adhesives1040015

Authors: Satoshi Migita Masaki Sato

Metallic biomaterials play essential roles in modern medical devices, but their long-term performance depends critically on protein adsorption and subsequent cellular responses at material interfaces. This review examines the molecular mechanisms governing these interactions and discusses surface modification strategies for controlling biocompatibility. The physicochemical properties of oxide layers formed on metal surfaces—including Lewis acid-base chemistry, surface charge, surface free energy, and permittivity—collectively determine protein adsorption behavior. Titanium surfaces promote stable protein adsorption through strong coordination bonds with carboxylate groups, while stainless steel surfaces show complex formation with proteins that can lead to metal ion release. Surface modification strategies can be systematically categorized based on two key parameters: effective ligand density (σ_eff) and effective mechanical response (E_eff). Direct control approaches include protein immobilization, self-assembled monolayers, and ionic modifications. The most promising strategies involve coupled control of both parameters through hierarchical surface architectures and three-dimensional modifications. Despite advances in understanding molecular-level interactions, substantial challenges remain in bridging the gap between surface chemistry and tissue-level biological performance. Future developments must address three-dimensional interfacial interactions and develop systems-level approaches integrating multiple scales of biological organization to enable rational design of next-generation metallic biomaterials.

Adhesives doi: 10.3390/adhesives1040014

Authors: Abdul Wasay Khan Kaixin Xu Nikolas Manousides Claudio Balzani

Short fibre-reinforced adhesives (SFRAs) are increasingly used in wind turbine blades to enhance stiffness and fatigue resistance, yet their heterogeneous microstructure poses significant challenges for predictive modelling. This study presents a fully automated digital workflow that integrates micro-computed tomography (µCT), image processing, and finite element modelling (FEM) to investigate the mechanical response of SFRAs. Our aim is also to establish a computational foundation for data-driven modelling and future AI surrogates of adhesive joints in wind turbine blades. High-resolution µCT scans were denoised and segmented using a hybrid non-local means and Gaussian filtering pipeline combined with Otsu thresholding and convex hull separation, enabling robust fibre identification and orientation analysis. Two complementary modelling strategies were employed: (i) 2D slice-based FEM models to rapidly assess microstructural effects on stress localisation and (ii) 3D voxel-based FEM models to capture the full anisotropic fibre network. Linear elastic simulations were conducted under inhomogeneous uniaxial extension and torsional loading, revealing interfacial stress hotspots at fibre tips and narrow ligaments. Fibre clustering and alignment strongly influenced stress partitioning between fibres and the matrix, while isotropic regions exhibited diffuse, matrix-dominated load transfer. The results demonstrate that image-based FEM provides a powerful route for structure–property modelling of SFRAs and establish a scalable foundation for digital twin development, reliability assessment, and integration with physics-informed surrogate modelling frameworks.

Adhesives doi: 10.3390/adhesives1040013

Authors: Dimitrios Moutousidis Konstantina Karidi Eleftheria Athanassiadou Katiana Filippi Nikos Giannakis Apostolos Koutinas Eleni Stylianou

Bio-based phenolic resins were developed with phenol substitution levels of 20% and 40% with crude extracts obtained from spent coffee grounds. The experimental resins were characterized in terms of their physical, chemical and bonding properties and exhibited the typical property levels of Phenol-Formaldehyde-type resins. Plywood panels were produced bonded with the novel experimental resins, exhibiting satisfactory performance, comparable to the reference panels in terms of both shear strength and wood failure, based on the requirements of the European standards. The results demonstrate the potential of using biomass-derived compounds as substitutes for petrochemical phenol in the production of wood adhesives, thereby increasing the bio-based content of the wood panel composites produced with them and improving their sustainability.

Adhesives doi: 10.3390/adhesives1040012

Authors: Matias Fioretti Maria Fernanda Torres Federico Becerra Mauricio Filippa Yiancarlo Kolodziej Dario Diaz Martin Masuelli

Chañar brea gum exhibits properties that make it a promising material for paper adhesion. As the concentration of chañar brea gum (CBG) in solution increases, the following key changes are observed in its properties, which are relevant to its use as an adhesive. The surface tension (σ) decreases with increasing gum concentration. Viscosity (η) increases dramatically with increasing chañar brea gum concentration. While higher viscosity is often desirable for many adhesives, excessive viscosity, as may be observed at very high concentrations, can hamper application. However, adequate viscosity is crucial to ensure initial bond strength, as it allows for the formation of a uniform layer and prevents excessive penetration into porous substrates. A concentration of 10% wt. by weight offers this balance. Surface adsorption (Γ2(1)) increases linearly with gum concentration, indicating that higher interfacial adsorption is crucial for the formation of an effective adhesive layer. The contact angle (θ) increases slightly with concentration; although a lower contact angle typically indicates better wetting, the increase is marginal (from 88° ± 4 for water to 99° ± 4 for 30% wt.), so wetting is still acceptable. Chañar brea gum exhibits good surface adsorption capacity and reduced surface tension, which favors interaction with the paper surface. The adhesive strength of chañar brea gum (CBG) clearly depends on its concentration, increasing from 6.36 ± 0.22 MPa (at 5% wt.) to a significant maximum of 50.24 ± 1.19 MPa at a concentration of 10% wt. The decrease in adhesive strength at concentrations above 10% wt. by weight is an important aspect to consider in order to optimize its performance as a paper adhesive. Therefore, intermediate concentrations, such as 10% wt., offer the most favorable balance of properties for achieving good adhesive performance.

Adhesives doi: 10.3390/adhesives1030011

Authors: Vasileios Koutsos

The interfacial adhesion of fibres with the polymer matrix plays a major role in the mechanical properties of fibre-reinforced polymers (FRPs) [...]

Adhesives doi: 10.3390/adhesives1030010

Authors: Athanasios Karageorgiou Maria Fostiropoulou Maria Antoniadou Eftychia Pappa

Deep margin elevation (DME) is a widely adopted technique for managing subgingival cervical proximal margins by repositioning them to a supragingival location. This approach enhances access, visibility, and control in these anatomically challenging areas. This narrative review aimed to evaluate current evidence on the indications, materials, clinical protocols, and outcomes of DME. A structured search was conducted in PubMed, the Cochrane Library and Scopus up to February 2025, using keywords such as “deep margin elevation”, “proximal box elevation” and “subgingival margin.” Clinical studies, in vitro investigations, relevant reviews and reports in English were included. A total of 59 articles were selected based on eligibility criteria. The hypothesis was that DME can serve as a reliable alternative to surgical crown lengthening in appropriate cases. A variety of materials have been investigated for use as the intermediate layer, with composite resins of varying viscosities and filler compositions being preferred due to their favorable long-term mechanical properties. DME may reduce the need for surgical intervention while maintaining periodontal health; however further randomized clinical trials are needed to clarify the material selection, establish long-term outcomes, and standardize clinical protocols. Understanding the indications, limitations, and protocol of DME is critical for achieving biologically sound and predictably functional restorations.

Adhesives doi: 10.3390/adhesives1030009

Authors: Valentin L. Popov

Adhesion plays a crucial role across a wide range of natural systems and technological applications. High adhesion is typically observed in contacts involving highly deformable materials, which are generally viscoelastic in nature. Although some of the key concepts explored in this work—such as the application of energy-based criteria to viscoelastic adhesive contacts—have been addressed in earlier studies, including the seminal work by Greenwood and Johnson, these approaches relied on considerably more complex analytical methods. In this paper, we build on those foundational insights and present a significantly simplified and more accessible formulation by employing the Method of Dimensionality Reduction (MDR). We propose that the processes of adhesive crack propagation and viscoelastic material relaxation occur on well-separated timescales, which allows the use of a Griffith-like energy balance criterion even in viscoelastic systems. This MDR-based energetic approach not only provides conceptual clarity but also enables the straightforward analytical treatment of a wide range of practical problems, including arbitrary loading scenarios. The theory naturally explains the different effective works of adhesion during attachment and detachment and offers a unified, first-principles framework for analyzing and designing soft adhesive systems.

Adhesives doi: 10.3390/adhesives1020008

Authors: Rani D’haese Valentin Vervack Inas Hamid Stefan Vandeweghe

Purpose: The aim of this in vitro study was to investigate the adhesive bond strength of glass fiber posts when cemented with universal resin cement in two different adhesion modes: adhesive and self-adhesive. Methods: A total of 20 extracted single-root teeth were endodontically treated, decoronated and prepared to receive glass fiber posts (GFPs) with a diameter of 1.6 mm (RelyX fiber post 3D). Specimens were randomly divided into two groups: (G1) GFPs were cemented using RelyX Universal cement in self-adhesive mode, and (G2) GFPs were cemented using Scotch Bond Universal Plus and RelyX Universal cement (adhesive mode). Afterwards, the specimens were sliced at three root levels: coronal, middle and apical. Bond strength was measured using a push-out test. Data were analyzed with a two-way analysis of variance (ANOVA) test and independent sample T-test. Results: Bond strength was significantly influenced by the adhesive strategy (p < 0.025) and the position of the root third (p < 0.007). Microscopic analysis of failure mode revealed a higher prevalence of adhesive failures (cement–dentine). Conclusions: Glass fiber posts cemented with universal resin cement applied in adhesive mode showed significantly higher push-out bond strength than when applied in self-adhesive mode. In both study groups, the apical root regions exhibited the highest retention values, followed by the middle and coronal regions.

Adhesives doi: 10.3390/adhesives1020007

Authors: Emmanuel Georgiou Dirk Drees Michel De Bilde Lais Lopes Angelos Koutsomichalis

Tapes are widely utilized across various industries, offering versatile solutions for bonding, sealing, and packaging applications. Their ease of use, strength, and adaptability make them essential in manufacturing, construction, and consumer markets. However, the effectiveness of tapes depends heavily on their adhesive performance, which is influenced by factors such as the adhesive layer composition, material compatibility, environmental conditions, and contact parameters. Quantifying adhesive performance through standardized testing is critical to ensuring reliability, optimizing functionality, and meeting industry-specific requirements. Traditional methods, such as peel and shear tests, are commonly used to evaluate the adhesive and shear strength of tapes. However, these methods typically operate at macro-load scales and often use complex sample geometries and significant material quantities. Recently, precision indentation–retraction testing has emerged as a promising technique for accurately quantifying the adhesion and cohesion forces of viscoelastic fluids. This study adapts this method to evaluate and compare the adhesive strength of various commercially available adhesive tapes. The adhesion force and separation energy of five commercial tapes, namely paper masking tape, high-temperature tape, insulation tape, duct tape, box wrapping tape, and double-sided tape, were measured using a Falex Tackiness Adhesion Analyser (TAA) tester, under controlled conditions (approach speed: 0.01 mm/s, retraction speed: 0.1 mm/s, and load: 50 mN). The results indicated that the adhesion force and separation energy varied significantly among the tapes, whereas a different pattern in the indentation–retraction curves was obtained for these tapes. In addition, the significance of difference among the adhesive properties of the tapes was assessed with the use of analysis of variance (ANOVA). This innovative approach not only enhances the precision of adhesive strength measurements but also provides valuable insights into adhesive layer properties, offering a novel tool for research, development, and quality control in tape production.

Adhesives doi: 10.3390/adhesives1020006

Authors: Dimokritos Papalexopoulos Ashot Torchyan Eleftheria Pani Theodora-Kalliopi Samartzi

The classical approach for the preparation of an endodontically treated molar with a post and core involves widening the anatomically complex system of canals, which may be narrow or curved with variable angulation. The aforementioned along with the fact that restorative dentistry stands against the wastage of tooth tissue make endocrowns an appealing alternative. Bindl and Mörmann first described an all-ceramic crown anchored to the internal portion of the pulp chamber and on the cavity margins, thus obtaining macromechanical retention provided by the axial opposing pulpal walls and microretention attained with the use of adhesive cementation. The purpose of this report is to describe the protocol for the treatment plan selection, preparation, impression, and adhesive cementation of an endocrown with a follow-up of 5 years. A 56-year-old male patient presented to the Postgraduate Clinic of Prosthodontics seeking rehabilitation for tooth No. #36. A clinical examination revealed multiple immediate composite resin restorations with unacceptable morphology and adaptation to the remaining tooth as well as a lack of a contact point but, rather, a large, concave contact area facilitating food entrapment. Since the tooth was endodontically treated, the proposed treatment plan included the fabrication of an all-ceramic endocrown. The steps of preparation, attribution of the correct shape, impression, and adhesive luting under rubber dam isolation are thoroughly described. The final functional and aesthetic result, patient’s satisfaction, and the 5-year follow-up render restorations such as endocrowns, which draw their retention from adhesive luting, a viable alternative to conventional approaches.

Adhesives doi: 10.3390/adhesives1010005

Authors: Vasileios Koutsos

Natural adhesives such as tree resins, gums, and tars have been used since prehistoric times (going back to at least 200,000 years [...]

Adhesives doi: 10.3390/adhesives1010004

Authors: Mattia Frascio Stefano Morchio Francesco Musiari Khalid Muhammad Usman Federico Dittamo Matilde Minuto Massimiliano Avalle

Additive manufacturing enables new design solutions across various engineering fields. This work presents a method to enhance the sustainability of adhesive joints by designing joints that can be disassembled and repaired multiple times. The approach involves the use of a Multi-Material Additive Manufacturing process to produce substrates with integrated circuits and electrical resistance, printed using a conductive filament. This resistance can be used to heat the thermoplastic adhesive layer up to 110 °C, allowing for reversibility in the assembly process and enabling joint re-use and repair without constraints on the component’s materials and thicknesses. The joints tested after successive assembly/disassembly operations reach maximum strength during the first iteration, which decreases by around 50% after five repair iterations. The focus of the work is on the feasibility of this process, but it is expected that performance can be improved after process optimization. This result could be highly valuable for enabling component in-service healing and the design for demanufacturing and remanufacturing.

Adhesives doi: 10.3390/adhesives1010003

Authors: Roberta Janaína Soares Mendes Regina Maria Puppin-Rontani Aline Rogéria Freire de Castilho

This study investigated the impact of natural compound enrichment, specifically quercetin and trans, trans-farnesol (tt-farnesol), on the physicochemical properties of a universal adhesive system. A preliminary DPPH assay was conducted to determine the optimal concentrations of quercetin (0.24 mg/mL) and tt-farnesol (1.43 mg/mL) based on their radical scavenging abilities. These compounds were then incorporated into the adhesive system. Specimens (n = 5; 7 mm × 1 mm) of the adhesive system, both with and without the added compounds, were prepared and tested for water sorption, solubility, Knoop hardness, and softening percentage. Water sorption and solubility were measured after immersion in deionized water for 7 days, and Knoop hardness was measured before and after immersion in 75% ethanol. Softening percentage was calculated based on changes in hardness. Data on water sorption, solubility, and percentage of softening were submitted to the Student’s t-test (α = 5%) while Knoop hardness values were submitted to the Mann–Whitney test (α = 5%). Both quercetin and tt-farnesol exhibited important antioxidant activity (85.5% and 82%, respectively). Water sorption was similar for both groups (p > 0.05) but the experimental adhesive had a significantly higher solubility, lower hardness, and higher softening. The incorporation of quercetin and tt-farnesol into a universal adhesive system detrimentally affects its essential physicochemical properties, compromising its performance.

Adhesives doi: 10.3390/adhesives1010002

Authors: Huaping Yao Jimei Niu Ruihua Zhang Ping Huang

Water-based lubricants have become increasingly prevalent across various fields due to their accessibility, cooling properties, and environmentally friendly characteristics. This study investigated the non-Newtonian properties of polyoxyethylene oxide (PEO) aqueous solutions. The rheological behaviors of 1%, 2%, and 3% PEO aqueous solutions were assessed using a flat plate rheometer. Shear strain responses were comprehensively analyzed, resulting in the derivation of the corresponding power law functions. The total loads of 1%, 2%, and 3% PEO aqueous solutions can be obtained by the numerical integration of Reynolds equations. Results indicate that at high shear strain rates, load-carrying capacity increased; however, the rate of increase gradually diminished as the shear strain rate rose. In practical applications, shear stress is subject to fluctuations; negative viscosity occurs resulting in reduced hydrodynamic pressure and potential lubrication failure. Full viscosity and incremental viscosity are introduced, with the latter being identified as a crucial factor that provides a more direct characterization of the relationship between shear stress and shear strain rate. This factor significantly influences the load-bearing capacity of the lubrication film in non-Newtonian fluids.

Adhesives doi: 10.3390/adhesives1010001

Authors: Philipp Moritz Lienhard Wegewitz Wolfgang Maus-Friedrichs

Cyanoacrylates, known for their rapid polymerization and strong bonding capabilities, are widely used in industrial and medical applications. This study investigates the impacts of different process atmospheres with varying water and oxygen contents—air, argon, and argon/silane—on the curing and adhesion mechanisms of cyanoacrylate adhesives on oxidized copper substrates. Raman spectroscopy indicated that the curing process in argon and argon/silane atmospheres was slower compared to ambient air, likely due to the reduced moisture content of the atmosphere. However, the degree of curing and the inter- and intramolecular interactions within the adhesive volume showed no significant differences across atmospheres. X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) revealed that strong ionic interactions between cyanoacrylate and the copper surface oxide were absent in the low-moisture argon atmosphere. The introduction of silane resulted in the formation of silicon oxides and other silane-derived compounds, which probably contributed to the formation of these ionic interactions, similar to those observed in air. This study highlights the critical influence of the surrounding atmosphere on the adhesive properties of cyanoacrylates, with implications for optimizing bonding processes in various environments.