Biodegradation of Dental Resin-Based Composite—A Potential Factor Affecting the Bonding Effect: A Narrative Review

[Effects of cell area on single odontoblast polarization and differentiation via microarray technology]

OBJECTIVES

This study aimed to explore the impact of cell spreading area on odontoblast polarization and differentiation using micropatterned surfaces ge-nerated by photolithography.

METHODS

Micropatterned surfaces with differential adhesive properties were prepared using polyethylene glycol diacrylate (PEGDA)-ba-sed photolithography. Human dental pulp stem cells (hD-PSCs) were isolated into single cells and cultured on micropatterned surfaces with areas of 1 800, 2 700, and 3 600 μm2. Immunofluorescence staining was used to observe cell morphology and analyze the relocating of the golgi apparatus and nucleus. Alkaline phosphatase staining was preformed to examine odontogenic differentiation.

RESULTS

The hDPSCs were successfully isolated and cultured on micropatterned surfaces mimicking the morphology of polarized odontoblasts. Phalloidin staining confirmed that the isolated hDPSCs successfully recapitulated the morphology of predesigned micropatterns. Immunofluorescence staining showed that the polarization and differentiation levels of the hDPSCs with a 3600 μm2 area were significantly higher than those with 1 800 and 2 700 μm2 areas (P<0.05).

CONCLUSIONS

The polarization and differentiation of single hDPSCs increased with the cell areas on micropatterned surfaces.

The Effect of Chemical Surface Modification on the Repair Bond Strength of Resin Composite: An In Vitro Study

This in vitro study investigates the impact of the chemical modification of resin composite surfaces on repair bond strength of micro-hybrid resin composite material. First, 7 mm circular × 3 mm thick resin composite disks were prepared using teflon molds. Then, 50 specimens out of 100 were allocated for stimulated aging using a thermo-cycling (10,000 cycles) device. Both the 24 h and 1-year-aged composite discs were embedded in epoxy resin using a 2.5 cm wide × 1.5 cm thick circular mold. The surfaces were treated with Clearfil S3 bond alone or with the additional application of silane or porcelain primer. The other two groups were bonded with CRB bond with or without a porcelain primer. Using a teflon mold, a 2 mm circular and 3 mm high repair composite cylinder was built on the treated surfaces. The specimens were then stressed to de-bond by applying shear force to measure repair bond strength, and they were observed under the microscope to determine the failure pattern. The data were analyzed using SPSS26.0. Univariate analysis showed a significant effect (p = 0.013) of the bonding protocol on the repair bond strength; however, the effect of aging was insignificant (p = 0.170). The S3 bond with additional silane and the CRB bond showed the significantly higher repair bond strength of the 1-year-aged micro-hybrid composite. However, in case of 24 h aged specimens, the repair bond strength was statistically insignificant among the tested groups (p = 0.340). Chemical surface modification with silane has the potential to improve the repair bond strength of micro-hybrid resin composite materials.

Towards the Standardization of Artificial Aging Protocols for Dental Composites: Evaluation of Proposed Methods

In restorative dentistry, there are no standardized in vitro accelerated aging methods to evaluate the long-term stability of dental composites. Current research aimed at extending the clinical success of restorations emphasizes the need for post-aging evaluation. This study represents the final stage of assessing three selected aging protocols that utilize a 0.1 M sodium hydroxide solution as the primary agent to accelerate degradation processes. Twelve resin-based composites, categorized into five types, were evaluated for flexural strength (FS), diametral tensile strength (DTS), hardness (HV), and fracture toughness (FT) both before and after aging. The proposed aging methods significantly degraded the mechanical properties of most materials, highlighting the effectiveness of 0.1 M NaOH as a medium for hydrolytic stability testing. Materials with a high filler content (approximately 80 wt.%) were notably prone to degradation, underscoring the importance of optimizing the filler and coupling agent. The findings suggest that incorporating thermocycling into aging protocols may enhance the development and evaluation of innovative dental composites. This work contributes to establishing a foundation for standardized aging protocols, supporting the accurate assessment of composites in vitro.

Sub-Nanoscale Caffeic Acid-Functionalized TiO2 Composite: Enhancing Mechanical Properties and Odontogenic Differentiation Capacity of Resin-Based Dental Restoration

Resin-based materials (RBMs) are widely applied in dentistry because they withstand the recurrent multi-dimensional force striking and the hydrolysis of teeth. Sub-nanoscale materials can enhance the mechanical strength and bioactivity of RBMs, but the effects are still limited and the mechanisms to enhance bioactivity remain unclear. Here, a TiO2-based sub-nanocomposite modified with caffeic acid (CA) to enhance mechanical robustness, structural stability, and bioactivity of RBMs is reported. This sub-nanocomposite can promote the proliferation, adhesion, and odontogenic differentiation of human dental pulp stem cells (hDPSCs) through specifically up-regulating the expression of genes related to cell-matrix adhesion, integrin-mediated signaling pathways, and collagen fibril organization. These effects lead to a better capacity for up-regulating odontogenic differentiation of RBMs.

The unseen perils of oral-care products generated micro/nanoplastics on human health

The extensive use of plastics in modern dentistry, including oral care products and dental materials, has raised significant concerns due to the increasing evidence of potential harm to human health and the environment caused by the unintentional release of microplastics (MPs) and nanoplastics (NPs). Particles from sources like toothpaste, toothbrushes, orthodontic implants, and denture materials are generated through mechanical friction, pH changes, and thermal fluctuations. These processes cause surface stress, weaken material integrity, and induce wear, posing health risks such as exposure to harmful monomers and additives, while contributing to environmental contamination. MPs/NPs released during dental procedures can be ingested, leading to immune suppression, tissue fibrosis, and systemic toxicities. The gut epithelium absorbs some particles, while others are excreted, entering ecosystems, accumulating through the food chain, and causing ecological damage. Although analytical techniques have advanced in detecting MPs/NPs in oral care products, more robust methods are needed to understand their release mechanisms. This review explores the prevalence of MPs/NPs in dentistry, the mechanisms by which MPs/NPs are released into the oral environment, and their implications for human and ecological health. It underscores the urgency of public awareness and sustainable dental practices to mitigate these risks and promote environmental well-being.

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.

Constructing the Enamel-Like Dentin Adhesion Interface to Achieve Durable Resin-Dentin Adhesion

Enamel adhesion is acknowledged as durable; however, achieving long-lasting dentin adhesion remains a formidable challenge due to degradation of exposed collagen matrix after acid-etching of dentin. The idea of developing an enamel-like adhesion interface holds great promise in achieving enduring dentin adhesion. In this study, we constructed an enamel-like adhesion interface using a rapid remineralization strategy comprising an acidic primer and a rapid remineralization medium. Specifically, the acidic primer of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and epigallocatechin-3-gallate (EGCG) nanocomplex (MDP@EGCG primer) was utilized to partially demineralize dentin within 30 s, and the MDP@EGCG nanocomplex showed a strong interaction with exposed collagen, enhancing collagen remineralization properties. Then, the rapid remineralization medium containing polyaspartate (Pasp) stabilized amorphous calcium and phosphorus nanoclusters (rapid Pasp-CaP) was applied to modified dentin collagen for 1 min, which caused rapid collagen remineralization within a clinically acceptable time frame. This strategy successfully generated an inorganic rough and porous adhesive interface resembling etched enamel, fundamentally addressed issues of collagen exposure, and achieved durable dentin adhesion in vitro and in vivo while also ensuring user-friendliness. It exhibited potential in prolonging the lifespan of adhesive restorations in clinical settings. In addition, it holds significant promise in the fields of caries and dentin sensitivity treatment and collagen-based tissue engineering scaffolds.

Effect of finishing and polishing systems on surface roughness and color stability of aesthetic restorations exposed to staining solution

The color and the surface roughness of aesthetic restorations are related to the clinical sucess and longevity of these treatments. Aim: This study evaluated the influence of finishing and polishing systems, and storage media on the surface roughness and color stability of aesthetic restorative composites. Materials and Method: Cylindrical specimens (n=10) were prepared and treated according to: 1. Type of composite resin (nanofilled- Filtek Z350XT, suprananofilled- Estelite Omega, nanohybrid- Empress Direct); 2. Type of finishing and polishing systems (no polishing, aluminum oxide discs or abrasive rubber polishers); and 3. Type of immersion medium (water or coffee, 3 h/day/30 days). Surface roughness (Ra - μm) and color stability (L, ΔEab, and ΔE00) were evaluated at baseline (after polishing) and final time (after immersion). Data were subjected to Kruskal-Wallis, Mann-Whitney, Wilcoxon, and Student-Newman-Keuls tests (α=0.05). Results: Nanohybrid (p<0.001) and suprananofilled composite resins (p=0.004) showed an increase in Ra after polishing, regardless the finishing and polishing system. After immersion in coffee, the nanofilled composite had the highest roughness values (p=0.032). L values increased for all resins after polishing (p<0.05). Suprananofilled composites had the greatest color stability with the lowest values of ΔEab and ΔE00. Conclusions: Finishing and polishing systems had an impact on the surface roughness and color stability of all aesthetic resins, and their effectiveness depended on the type of composite resin.

Water absorption in artificial composites: Curse or blessing?

OBJECTIVES

This study evaluated the impact of mutable water uptake on the durability of mechanical properties and the long-term reliability of artificial composites.

METHODS

Three resin-based CAD/CAM restorative materials (CRMs) were investigated in three-point bending tests to calculate flexural strength (FS), modulus of elasticity (ME), modulus of resilience (MR), modulus of toughness (MT), and elastic recovery (ER). All specimens (n = 180) were stored under the same conditions and tested in four subsets (n = 15 per material) that were respectively withdrawn after repeated thermocycling (5000 cycles; 5-55 °C, H2O) and repetitive drying (7 d; 37 °C, air). For every specimen, weight differences were determined per storage condition. Likewise, loss tangent data were separately recorded via dynamic mechanical analysis to reliably assess damping characteristics.

RESULTS

Repeated thermocycling always induced weight increase and a concurrent significant loss in all mechanical properties except for MT and ER of a polymethylmethacrylate-based CRM. Drying consistently provoked weight loss and raised mechanical properties to initial values. Weight increase, however, enhanced loss tangent values and accordingly distinct damping characteristics, whereas weight decrease markedly lowered damping properties.

SIGNIFICANCE

Water uptake repeatedly induced a decrease in common mechanical properties but concurrently increased damping behavior. Invertible equilibrium processes were found with no evidence for permanent material degradation.

Computational analysis of 3D printing: Selecting the better among newly released materials

Resin-based three-dimensional (3D) printing finds extensive application in the field of dentistry. Although studies of cytotoxicity, mechanical and physical properties have been conducted for newly released 3D printing resins such as Crowntec (Saremco), Temporary Crown Resin (Formlabs) and Crown & Bridge (Nextdent), the resistance of these materials to esterases in saliva has not been demonstrated at the molecular level. Therefore, in this study, the binding affinities and stability of these new 3D printing resins to the catalytic sites of esterases were investigated using molecular docking and molecular mechanics with Poisson-Bolzmann and surface area solvation (MM/PBSA) methods after active pocket screening. Toxicity predictions of the materials were also performed using ProTox-II and Toxtree servers. The materials were analyzed for mutagenicity, cytotoxicity, and carcinogenicity, and LD50 values were predicted from their molecular structures. The results indicated that out of the three novel 3D printing materials, Nexdent exhibited reduced binding affinity to esterases, indicating enhanced resistance to enzymatic degradation and possessing a superior toxicity profile.

Equivalence study of the resin-dentine interface of internal tunnel restorations when using an enamel infiltrant resin with ethanol-wet dentine bonding

This preregistered ex vivo investigation examined the dentinal hybrid layer formation of a resinous infiltrant (Icon), with reference to both thickness (HLT) and homogeneity when combined with modified tunnel preparation (occlusal cavity only) and internal/external caries infiltration. The adhesives Syntac and Scotchbond MP were used as controls (Groups 1 and 3) or in combination with Icon (Groups 2 and 4). A split-tooth design using healthy third molars from 20 donors resulted in 20 prepared dentine cavities per experimental group. The cavity surfaces (n = 80) were etched (37% H3PO4), rinsed, and air-dried. Rewetting with ethanol was followed by application of the respective primers. After labeling with fluorescent dyes, either Syntac Adhesive/Heliobond or Scotchbond MP Adhesive was used alone or supplemented with Icon. HLT, as evaluated by scanning electron microscopy, did not significantly differ (P > 0.05), and confocal laser scanning microscopy revealed homogeneously mixed/polymerized resin-dentine interdiffusion zones in all groups. Icon can be successfully integrated into an ethanol-wet dentine bonding strategy, and will result in compact and homogeneous hybrid layers of comparable thickness considered equivalent to the non-Icon controls, thus allowing for preservation of the tooth's marginal ridge and interdental space in the case of internal/external infiltration of proximal caries.

Biodegradation of Urethane Dimethacrylate-based materials (CAD/CAM resin-ceramic composites) and its effect on the adhesion and proliferation of Streptococcus mutans

OBJECTIVE

To investigate whether urethane dimethacrylate (UDMA) -based dental restorative materials biodegrade in the presence of Streptococcus mutans (S. mutans) and whether the monomers affect the adhesion and proliferation of S. mutans in turn.

METHODS

Cholesterol esterase and pseudocholinesterase-like activities in S. mutans were detected using p-nitrophenyl substrate. Two UDMA-based CAD/CAM resin-ceramic composites, Lava Ultimate (LU) and Vita Enamic (VE), and a light-cured UDMA resin block were co-cultured with S. mutans for 14 days. Their surfaces were characterized by scanning electron microscopy and laser microscopy, and the byproducts of biodegradation were examined by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). Then, the antimicrobial components (silver nanoparticles with quaternary ammonium salts) were added to the UDMA resin block to detect whether the biodegradation was restrained. Finally, the effect of UDMA on biofilm formation and virulence expression of S. mutans was assessed.

RESULTS

Following a 14-day immersion, the LU and UDMA resin blocks' surface roughness increased. The LU and VE groups had no UDMA or its byproducts discovered, according to the UPLC-MS/MS data, whereas the light-cured UDMA block group had UDMA, urethane methacrylate (UMA), and urethane detected. The addition of antimicrobial agents showed a significant reduction in the release of UDMA. Biofilm staining experiments showed that UDMA promoted the growth of S. mutans biofilm and quantitative real-time polymerase chain reaction results indicated that 50 μg/mL UDMA significantly increase the expression of gtfB, comC, comD, comE, and gbpB genes within the biofilm.

CONCLUSIONS

UDMA in the light-cured resin can be biodegraded to produce UMA and urethane under the influence of S. mutans. The formation of early biofilm can be promoted and the expression of cariogenic genes can be up-regulated by UDMA.

CLINICAL SIGNIFICANCE

This study focuses for the first time on whether UDMA-based materials can undergo biodegradation and verifies from a genetic perspective that UDMA can promote the formation of S. mutans biofilms, providing a reference for the rational use of UDMA-based materials in clinical practice.

Considerations about Cytotoxicity of Resin-Based Composite Dental Materials: A Systematic Review

The dental material industry is rapidly developing resin-based composites (RBCs), which find widespread use in a variety of clinical settings. As such, their biocompatibility has gained increasing interest. This literature review presents a summary of research into the cytotoxicity of methacrylate-based composites published from 2017 to 2023. Subject to analysis were 14 in vitro studies on human and murine cell lines. Cytotoxicity in the included studies was measured via MTT assay, LDH assay, and WST-1 assay. The QUIN Risk of Bias Tool was performed to validate the included studies. Included studies (based entirely on the results of in vitro studies) provide evidence of dose- and time-dependent cytotoxicity of dental resin-based composites. Oxidative stress and the depletion of cellular glutathione (GSH) were suggested as reasons for cytotoxicity. Induction of apoptosis by RBCs was indicated. While composites remain the golden standard of dental restorative materials, their potential cytotoxicity cannot be ignored due to direct long-term exposure. Further in vitro investigations and clinical trials are required to understand the molecular mechanism of cytotoxicity and produce novel materials with improved safety profiles.

The germicidal effect, biosafety and mechanical properties of antibacterial resin composite in cavity filling

In recent years, dental resin materials have become increasingly popular for cavity filling. However, these materials can shrink during polymerization, leading to microleakages that enable bacteria to erode tooth tissue and cause secondary caries. As a result, there is great clinical demand for the development of antibacterial resins. The principle of antibacterial resin includes contact killing and filler-release killing of bacteria. For contact killing, quaternary ammonium salts (QACs) and antibacterial peptides (AMPs) can be added. For filler-release killing, chlorhexidine (CHX) and nanoparticles are used. These antibacterial agents are effective against gram-positive bacteria, gram-negative bacteria, fungi, and more. Among them, QACs has a lasting antibacterial effect, and silver nanoparticles even have a certain ability to kill viruses. Biocompatibility-wise, QACs, AMPs, and CHX have low cytotoxicity to cells when added into the resin. However, nanoparticles with smaller particle sizes have higher cytotoxicity. In terms of mechanical properties, QACs, AMPs, and CHX do not negatively affect the resin. However, the addition of magnesium oxide can have a negative impact. This paper reviews the types and antibacterial principles of commonly used antibacterial resins in recent years, evaluates their antibacterial effect, biological safety, and mechanical properties, and provides references for selecting clinical filling materials.

Evaluation of Physical-Chemical Properties of Contemporary CAD/CAM Materials with Chromatic Transition "Multicolor"

The use of materials for computer-aided design/computer-aided manufacturing (CAD/CAM) has been rapidly increasing in daily practice. However, one of the main issues regarding modern CAD/CAM materials is their aging in the oral environment, which may lead to significant changes in their overall properties. The aim of this study was to compare the flexural strength, water sorption, cross-link density (softening ratio%), surface roughness, and SEM analysis of three modern CAD/CAM "multicolor" composites. Grandio (Grandio disc multicolor-VOCO GmbH, Cuxhaven, Germany), Shofu (Shofu Block HC-Shofu Inc., Kyoto, Japan), and Vita (Vita Enamic multiColor-Vita Zahnfabrik, Bad Sackingen, Germany) were tested in this study. They were prepared in stick-shaped specimens and submitted to different tests after several aging protocols, such as thermocycling and mechanical cycle loading challenge. Further disc-shaped specimens were also created and tested for water sorption, cross-link density, surface roughness, and SEM ultramorphology, before and after storage in an ethanol-based solution. For flexural strength and ultimate tensile strength, Grandio showed the greatest values both at baseline and after aging (p < 0.05). Grandio and Vita Enamic presented the highest modulus of elasticity and the lowest water sorption (p < 0.05). A significant reduction (p < 0.05) in microhardness after ethanol storage (softening ratio%) was observed especially in Shofu. Grandio had the lowest roughness parameters compared to the other tested CAD/CAM materials, while ethanol storage significantly increased the Ra and RSm values in Shofu (p < 0.05). Despite the comparable modulus of elasticity of Vita and Grandio, this latter showed greater flexural strength and ultimate tensile strength both at baseline and after aging. Hence, Grandio and Vita Enamic may be employed for the anterior teeth and for those restorations requiring load-bearing capacity. Conversely, aging seems to affect several properties of Shofu, so its use for permanent restorations should be well-pondered based on the clinical situation.

MODERN TRENDS AND PERSPECTIVES OF THE DEVELOPMENT OF ADHESIVE DENTISTRY. INNOVATIVE TECHNIQUES FOR THE APPLICATION OF ADHESIVE SYSTEMS

OBJECTIVE

The aim: To study the latest approaches to optimizing the composition and application protocols of modern adhesive systems, which are used during the restoration of defects in hard dental tissues with restorative materials.

PATIENTS AND METHODS

Materials and methods: Thirty articles published between January 1, 2020 and February 1, 2023 in the scientific databases PubMed, Scopus, and Google Scholar were selected. The selected scientific works contained the results of laboratory studies, systematic reviews, meta-analyses of the physical and mechanical characteristics of adhesive systems with a modified composition or application protocols different from the instructions of the manufacturing companies.

CONCLUSION

Conclusions: The most promising directions for improving adhesive systems are modifications of the composition and protocols of their use with the aim of deactivating matrix metalloproteinases, improving the structure of the hybrid layer due to the creation of a three-dimensional mesh of collagen fibres with optimal properties, the introduction of antimicrobial agents to slow down the growth of bacterial colonies along the line of the adhesive joint. The available research results of modified adhesive systems are often contradictory, which determines the need to develop standardized test methods to obtain more reliable indicators of their physical, mechanical and biological properties. In some cases, the consequences of non-compliance with the recommendations of the manufacturing companies are a significant deterioration of the characteristics of the hybrid layer, adhesive strength, marginal fit, which, in turn, explains the need for further search for an optimized composition and techniques for applying bonding agents to improve the prognosis of restorative treatment.

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.

Effect of Pre-Heating on the Monomer Elution and Porosity of Conventional and Bulk-Fill Resin-Based Dental Composites

The pre-heating of dental resin-based composites (RBCs) improves adaptability to cavity walls, reducing microleakages. However, the rapid cooling of the pre-heated RBC may change the polymerization kinetics, and thus the final network configuration of the RBC. It is well known that unreacted monomers remaining in the set RBC can leach into the oral cavity. However, it is still not clear how the pre-heating and cooling of RBCs alter monomer elution (ME). Thus, the purpose was to determine the ME from room-temperature and pre-heated RBCs, in addition to determining the closed porosity (CP) volume. Bulk-filled RBCs and layered conventional RBC samples were prepared. The pre-polymerization temperature was set at 24 °C and 55/65 °C. The ME from RBC samples was assessed with high-performance liquid chromatography using standard monomers. CP was measured with micro-computed tomography. ME decreased significantly from bulk fills and increased from layered samples as a result of pre-heating. Pre-heating was unfavorable in terms of CP in most RBCs. Based on the effect size analysis, ME and CP were greatly influenced by both material composition, pre-polymerization temperature, and their interaction. While the pre-heating of high-viscosity bulk-fill RBCs is advantageous from a clinical aspect regarding biocompatibility, it increases CP, which is undesirable from a mechanical point of view.