Influence of organic and inorganic particles on the properties of composite resins: a scoping review

Abstract

Background

The improvement of resin-based composites is closely linked to the evolution of their organic monomers and inorganic filler particles, which directly affect their mechanical, optical, and biological performance. Understanding how these components influence clinically relevant properties is essential to guide material development and clinical decision-making. This scoping review aimed to map and synthesize the available evidence on the influence of organic and inorganic particles on the physical, mechanical, optical, and biological properties of resin-based composites.

Methods

A scoping review was conducted following the PRISMA-ScR guidelines. Electronic searches were performed in PubMed, Embase, Web of Science, and Google Scholar. The literature search was initially conducted and subsequently updated in April 2026 to ensure the inclusion of the most recent evidence. In vitro studies evaluating commercially available resin-based composites intended for direct restorations were included. Data extraction focused on resin composition, organic monomers, inorganic filler characteristics, evaluated properties, and reported outcomes.

Results

A total of 13 in vitro studies met the eligibility criteria, indicating a limited evidence base. The findings suggest that both organic monomers and inorganic fillers influence composite performance. Monomers such as Bis-GMA, Bis-EMA, and UDMA tended to be associated with improved mechanical properties and higher microhardness, whereas more hydrophilic monomers were associated with increased water sorption and solubility. Inorganic filler characteristics—including type, size, morphology, and distribution—appeared to influence degree of conversion, light transmittance, surface roughness, and hydrolytic stability. Composites containing smaller, spherical fillers based on silica or zirconia generally showed more stable mechanical behavior and improved surface properties.

Conclusions

The interaction between organic and inorganic components appears to play an important role in the performance of resin-based composites. However, the limited number of studies, their methodological heterogeneity, and the exclusive reliance on in vitro evidence restrict the strength of the conclusions. Further well-designed, long-term clinical studies are required to validate these findings under real clinical conditions.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12903-026-08571-5.

Background

The structure of resin-based dental composites has undergone significant improvements since their introduction into dentistry. Until recently, the most relevant modifications have focused on changes in filler agents, whose particle size was deliberately reduced, resulting in materials with improved polishability and greater resistance to wear [1]. The use of resin composites is considered one of the major advances in restorative procedures, as they restore esthetics and function through less invasive preparations, with reduced removal of dental tissues and without the need to create mechanical retention for material adhesion [2].

The selection of an appropriate restorative material requires balancing various requirements. For enhanced restoration longevity, it is imperative to have improved mechanical properties, such as high strength, fracture toughness, surface hardness, optimized elastic modulus, low wear, water sorption and solubility, minimal polymerization shrinkage, low fatigue and degradation, and high radiopacity [3]. At the same time, good biocompatibility (both systemic and local) is essential, with no postoperative pain or hypersensitivity, preservation of tooth integrity by preventing fractures or cracks, and caries inhibition capabilities [4]. Additionally, aesthetic considerations, such as color matching and stability (translucency, shades), ideal polishability, long-term surface gloss, absence of marginal or surface discoloration, and long-term anatomical form are crucial [3, 5].

Different types of inorganic components, with particle sizes ranging from macro- to nanoscale, have been particularly necessary to enable the use of these materials in posterior teeth applications [1]. Current developments have also focused on the polymer matrix, mainly aiming to develop systems with reduced polymerization shrinkage and, perhaps more importantly, reduced shrinkage stress, as well as to render these materials self-adhesive to dental structures [6–8]. The proportion between organic and inorganic components also plays an important role in controlling the mechanical properties of composite resins, as reducing the amount of the organic matrix may decrease polymerization shrinkage, thereby lowering the stress generated at the adhesive interface during the photoactivation process and improving adhesion to the dental structure [9, 10].

In the current literature, several review studies have addressed the effects of filler particles on the clinical properties of composite resins [11–14]. Across these studies, it is well recognized that the performance of composite resins is largely governed by the interactions among their constituent particles, and that achieving a simultaneous balance among multiple properties remains a challenge in restorative dentistry. Therefore, the present review is relevant to dental practitioners, as it provides an updated and comprehensive overview of how composite composition directly influences the clinical performance of resin-based materials, supporting the selection of restorative materials with greater durability, esthetics, and predictability in direct restorations. Accordingly, this study aims to conduct a scoping review on the influence of organic and inorganic components on the mechanical, optical, and biological properties of composite resins.

Although previous reviews have addressed specific aspects of resin-based composites, such as filler characteristics or monomer composition, most studies have focused on isolated components or narrative summaries. In contrast, the present scoping review provides a structured and comprehensive mapping of the combined influence of organic and inorganic particles on multiple clinically relevant properties.

Additionally, this study incorporates a comparative qualitative synthesis across different outcome domains, enabling a broader understanding of how these components interact to influence composite performance. By systematically identifying methodological patterns and gaps in the literature, this review contributes to advancing both research design and material development in restorative dentistry.

Methodology

A scoping review was conducted following a multistep approach, which included: definition of the topic and the guiding research question; development of inclusion and exclusion criteria; identification of relevant publications in the selected databases; categorization and analysis of the studies; critical appraisal of the selected evidence; and presentation and synthesis of the results. Accordingly, the guiding research question was: What is known about the impact of organic and inorganic particles on the clinical properties of composite resins?

Registration and protocol

The methodology of the present study followed the PRISMA-ScR guidelines, given their recommended items for conducting systematic reviews with extensions to scoping reviews and meta-analyses [15]. Subsequently, after review and approval by all authors, the protocol was registered on the Open Science Framework (OSF; Center for Open Science, Charlottesville, United States of America) on April 13, 2025, under the protocol registration number https://doi.org/10.17605/OSF.IO/6QPZ9 [16]. The PRISMA-ScR checklist is provided as a supplementary file. The literature search was initially conducted and subsequently updated in April 2026 to ensure the inclusion of the most recent evidence.

Eligibility criteria

The research question was formulated based on the PCC acronym (Population, Concept, and Context): P (Population): Composite resins; C (Concept): Influence of inorganic and organic particles on clinical properties; C (Context): Current evidence on the influence of inorganic and organic particles on the performance of composite resins.

Accordingly, this review exclusively included in vitro laboratory studies that investigated composite resins with established clinical applications, whose formulations are available for use in direct dental restorations. To be eligible, these studies examined the clinical properties of inorganic and organic particles in composite resins intended for direct restorations.

Outcomes considered were related to the influence of these particles on clinical properties, including mechanical, optical, esthetic, biological, or handling characteristics of the composite resins. Additionally, the studies were required to clearly describe the methods used to assess these outcomes.

The exclusion criteria applied were as follows:

• Clinical studies, animal studies, ex vivo studies, narrative or integrative reviews, letters to the editor, book chapters, conference abstracts, clinical guidelines, panels, technique description articles, and opinion papers;

• Studies for which the full text was not available for comprehensive reading;

• Studies that did not assess any property applicable in a clinical context;

• Studies that did not address organic and inorganic particles with the commercial composite resins;

• Studies involving dental materials other than composite resins intended for direct restorations;

• Articles published before 2015, unless considered relevant to the topic;

• Studies that exclusively investigated experimental formulations, without commercial application or available only as prototypes.

The decision to exclude composite resins modified with experimental materials or formulations not yet available in the clinical setting was made to ensure greater methodological homogeneity and to preserve the practical relevance of the findings. The restriction to studies published predominantly from 2015 onwards was applied to ensure that the review reflects contemporary resin-based composite formulations and recent advances in material science, including developments in filler technology and monomer systems. Older studies were considered less representative of current commercially available materials and clinical practice. Finally, no restrictions were applied regarding the language or year of publication.

The exclusion of experimental or prototype composite formulations was intentionally applied to ensure clinical relevance and to focus on materials currently available for clinical use. This approach aimed to enhance the applicability of the findings to real-world dental practice.

Databases and search strategy

Electronic searches were conducted in the PubMed, Embase (1974–present), and Web of Science databases. An additional search was performed in Google Scholar as a source of gray literature. The search strategy applied in PubMed included indexed terms (MeSH) and their synonyms. Minor adjustments were made to adapt the strategy to the specific requirements of each database. In Google Scholar, the first 300 hits published since 2015 were considered [17] (Table 1).

Table 1.

Search strategy

Databases	Updated on April 15th, 2026	Studies found
Medline (Via Pubmed)	(“Composite resins” OR “Resin composite”) AND (“Fillers” OR “Inorganic filler” OR “Organic filler” OR “Filler particles” OR “monomer” OR “resin matrix” OR “polymer network” OR ‘UDMA’ OR “Bis-GMA”) AND (“Clinical properties” OR “Mechanical properties” OR “Physical properties” OR “Wear resistance” OR “Biological properties” OR “Optical properties” OR “Aesthetic properties”)	783
Web of Science	TS=(“composite resins” OR “resin composite”) AND TS=(“Fillers” OR “Inorganic filler” OR “Organic filler” OR “Filler particles” OR “monomer” OR “resin matrix” OR “polymer network” OR ‘UDMA’ OR “Bis-GMA”) AND TS=(“clinical properties” OR “mechanical properties” OR “physical properties” OR “wear resistance” OR “biological properties” OR “optical properties” OR “aesthetic properties”)	729
Embase	(‘composite resins’ OR ‘resin composite’) AND (‘Fillers’ OR ‘Inorganic filler’ OR ‘Organic filler’ OR ‘Filler particles’ OR ‘monomer’ OR ‘resin matrix’ OR ‘polymer network’ OR ‘UDMA’ OR ‘Bis-GMA’) AND (‘clinical properties’ OR ‘mechanical properties’ OR ‘physical properties’ OR ‘wear resistance’ OR ‘biological properties’ OR ‘optical properties’ OR ‘aesthetic properties’)	1.229
Google Scholar	(“Composite resins” OR “Resin composite”) AND (“Fillers” OR “Inorganic filler” OR “Organic filler” OR “Filler particles” OR “monomer” OR “resin matrix” OR “polymer network” OR ‘UDMA’ OR “Bis-GMA”) AND (“Clinical properties” OR “Mechanical properties” OR “Physical properties” OR “Wear resistance” OR “Biological properties” OR “Optical properties” OR “Aesthetic properties”)	300
Total		3.041

Additionally, the reference lists of the included studies and relevant systematic reviews were screened to identify additional eligible studies. The included studies were also checked for possible retractions due to error or fraud, ensuring the reliability and accuracy of the evidence base.

All references retrieved from the searches were imported into the online Rayyan software (Qatar Computing Research Institute, Doha, Qatar) [18] for duplicate removal, and all stages of the study selection process were conducted using the same platform.

Study selection

Two reviewers participated in the selection process to minimize potential selection bias. In the first phase, two review authors (C.J.C.P. and V.F.S.F.) independently and blindly screened titles and abstracts. Studies were coded as “included” if they met the inclusion criteria, “maybe” for potentially eligible or uncertain records, and “excluded” otherwise. To ensure consistency between reviewers, inter-rater reliability was assessed using Cohen’s kappa coefficient based on a random sample of twenty studies selected from the full dataset; the resulting kappa value was 0.901, indicating excellent agreement. Disagreements were resolved through discussion between the reviewers. When consensus could not be reached, a third reviewer (V.C.D.) was consulted to achieve a final decision through discussion.

In the second phase, the same two authors applied the eligibility criteria through full-text screening. Disagreements were resolved by discussion and, when necessary, consultation with the third reviewer (V.C.D.), with final decisions reached by consensus among the reviewers. The study selection process was documented in sufficient detail to complete the PRISMA flow diagram, in accordance with PRISMA 2021 reporting standards.

Data extraction

For the included studies, one author (C.J.C.P.) was responsible for data collection, while two additional reviewers (V.C.D. and V.F.S.F.) independently verified the extracted information. Data extraction was performed independently from the full-text articles using a customized data extraction spreadsheet. The following data were extracted from each included study: study characteristics (authors, year, country of publication, and study design); characteristics of the investigated item (sample size and age range) or (type of particles: organic or inorganic, particle size, and particle composition); evaluated properties, assessment methods, and reported effects.

In cases of disagreement between reviewers, the data were discussed until consensus was reached. When important data were missing or unclear, the corresponding authors were contacted by email to request additional or unpublished information. If no response was obtained, the unretrieved data were recorded in the table as missing or not reported.

Data synthesis

To improve transparency and reproducibility, a structured qualitative synthesis approach was used to generate the classification presented in Table 4. The scoring system (Ø–3) was developed to summarize the direction and magnitude of the effects reported in the included studies across different outcome domains.

Table 4.

Influence of inorganic and organic particles

Particles
Inorganic	DC	MP	T	R	S/S	M/N
Silanized silica	2	2	Ø	2	2	2
Zirconia	2	2	1	Ø	Ø	2
Barium glass	Ø	2	1	Ø	Ø	2
Borosilicate glass	Ø	2	1	Ø	Ø	2
Glass-ceramic	Ø	2	1	Ø	Ø	2
Ytterbium trifluoride	Ø	2	1	Ø	Ø	2
Oxides	Ø	Ø	1	Ø	Ø	Ø
Glass fibers	2	3	1	1	Ø	2
S-PRG	Ø	Ø	Ø	1	1	Ø
Isofiller/SphereTEC	Ø	2	Ø	Ø	Ø	2
Large particles/Irregular morphology	Ø	Ø	1	1	Ø	Ø
Organic/Monomers	DC	MP	T	R	S/S	M/N
Bis-GMA	Ø	2	Ø	Ø	Ø	2
Bis-EMA	2	2	Ø	Ø	Ø	2
UDMA	2	2	Ø	Ø	Ø	2
TEGDMA	2	Ø	Ø	Ø	1	Ø
PEGDMA/PEG-400 DMA	Ø	Ø	Ø	Ø	1	Ø
HEMA/GPDM/GDMA (hydrophilic)	Ø	1	Ø	1	1	1
TCD – Urethane acrylate	2	2	Ø	Ø	Ø	2
Pre-polymers	1	1	Ø	1	1	1
Photoinitiator systems	3*	2	Ø	Ø	Ø	2

Classification based on the direction, consistency, and magnitude of findings reported in the included studies: Ø = inconclusive or not reported; 1 = negative or negligible effect; 2 = positive effect; 3 = very positive effect consistently supported across multiple outcomes. *When alternative photoinitiators, more reactive than camphorquinone, are used

Abbreviations: DC Degree of conversion, MP Mechanical properties, T Translucency, R Roughness, S/S Sorption/solubility, microhardness/nanohardness

The direction of the effect was determined based on whether the reported outcomes indicated a beneficial, unfavorable, or inconclusive influence of the evaluated organic or inorganic components within each study. The magnitude of the effect was interpreted considering the consistency and extent of the reported findings across the assessed properties.

Accordingly, the classification was defined as follows: Ø indicated inconclusive findings or outcomes not reported; 1 represented a low or unfavorable effect, including small, inconsistent, or negative changes; 2 indicated a moderate positive effect, characterized by consistent improvement of limited magnitude; and 3 represented a strong positive effect, defined by substantial and consistently reported improvements across multiple outcomes within the same study.

The scoring framework was conceptually based on principles of qualitative evidence synthesis commonly applied in scoping reviews, aiming to identify patterns and trends rather than to quantify effect size or establish causality. No quantitative weighting or statistical aggregation was performed due to the heterogeneity of study designs, materials, and outcome measures.

To enhance consistency in the application of the scoring system, two reviewers underwent a calibration exercise prior to data extraction using a subset of five included studies. Inter-reviewer agreement was assessed using Cohen’s kappa coefficient, yielding a value of 0.899, indicating excellent agreement.

During the data extraction and classification process, disagreements between reviewers were initially resolved through discussion. When consensus could not be reached, a third reviewer was consulted to ensure a final decision, thereby minimizing subjective bias.

Critical appraisal of individual sources of evidence

A formal methodological quality or risk of bias assessment was not performed. In accordance with the Joanna Briggs Institute [19] and the PRISMA-ScR [15] scoping reviews aim to map the extent, range, and characteristics of available evidence, rather than to critically appraise study quality. Therefore, the omission of this step is consistent with the methodological framework adopted. Nevertheless, potential limitations and heterogeneity of the included studies are addressed narratively.

Results

Selection of sources of evidence

The initial search strategy yielded 3.041 records. After the removal of duplicate records, 1.999 articles were screened based on titles and abstracts (phase 1). Following the initial screening process, 38 articles advanced to phase 2 (full-text assessment). After the selection process, 13 articles were included in the review. Figure 1 presents the flow diagram summarizing the search and selection strategies.

Fig. 1.

PRISMA flowchart

During the full-text assessment stage, detailed reasons for exclusion were recorded and categorized to enhance transparency and reproducibility. The most common reasons for exclusion included: (i) evaluation of experimental or prototype materials without clinical availability; (ii) absence of outcomes related to clinically relevant properties; (iii) focus on materials other than resin-based composites for direct restorations; and (iv) insufficient methodological description. A summary of the exclusion reasons is provided in the PRISMA flow diagram and supplementary material.

The included studies were conducted across different geographic regions, including South America, Europe, and Asia. However, due to the limited number of studies, no formal bibliometric or geographic trend analysis was performed.

Individual results of the sources of evidence

The included studies evaluated different brands and types of composite resins, considering the characteristics of organic and inorganic particles, physicomechanical and optical properties, as well as polymerization effects and hydrolytic stability. The analyses included assessments of degree of conversion, microhardness, light transmission, flexural strength, and surface roughness, using methods such as mechanical testing, scanning electron microscopy (SEM), and spectroscopy (SEM–EDX). A detailed description of the individual characteristics of the included studies is provided in Tables 2 and 3.

Table 2.

Study characteristics

Author/Year	Country	Study design	Composite evaluated
Fronza et al. (2017) [20]	Brazil	In vitro	Five commercially available conventional and bulk-fill resin-based composites, including flowable and high-viscosity materials (Kerr, Dentsply, 3 M ESPE, Ivoclar Vivadent, GC)
Araújo-Neto et al. (2020) [21]	Brazil	In vitro	Commercial nanofilled, nanohybrid, hybrid, and bulk-fill resin-based composites, including one material with a powder–liquid system
Fidalgo-Pereira et al. (2022) [22]	Portugal	In vitro	Five commercially available high-viscosity and flowable resin-based composites (VOCO, Dentsply Sirona, Coltene)
Ruivo et al. (2019) [23]	Brazil	In vitro	Five commercially available resin-based composites (3 M Oral Care, Tokuyama Dental, Shofu, Kerr), including conventional, nanofilled, bioactive, and self-adhesive materials
Bilge; Ipek (2024) [24]	Tukey	In vitro	Three resin-based composites: EverX Posterior (GC, Japan), Filtek Bulk Fill (3 M ESPE, USA), and Filtek Z250 (3 M ESPE, USA)
González-Alenda et al. (2025) [25]	Spain	In vitro	Six universal resin-based composites: Essentia Universal, Filtek Universal, Gaenial A’Chord, Omnichroma, Tetric Prime, and Filtek Supreme Ultra
Balbinot et al. (2019) [26]	Brazil	In vitro	Multiple commercially available resin-based composites (e.g., Premise, Filtek Z250, Filtek Supreme Ultra, Opallis, Venus Diamond, Esthet-X HD, among others)
Iwasaki et al. (2022) [27]	Japan	In vitro	Seven flowable and bulk-fill resin-based composites (e.g., Beautifil Bulk Flowable, SDR, Gracefil BulkFlo, Clearfil Majesty ES Flow Low, Estelite Flow Quick, among others)
Sideridou; Karabela; Vouvoudi (2011) [28]	Greece	In vitro	Five commercially available resin-based composites (Tetric EvoCeram, Grandio, Protofill-nano, Filtek Supreme Body, Filtek Supreme Ultra)
Lu et al. (2006) [29]	USA	In vitro	Six commercially available resin-based composites (Estelite Σ, Filtek Supreme Ultra, Heliomolar, Renamel Microfill, Esthet X Improved, Tetric Ceram)
Rastelli et al. (2011) [30]	Brazil	In vitro	Four commercially available resin-based composites (Filtek Z250, Filtek Supreme Ultra, Filtek Supreme XT, TPH3)
Yan et al. (2019) [31]	China	In vitro	Two commercially available resin-based composites (Lava Ultimate and Tetric N-Ceram)
Kim et al. (2015) [32]	South Korea	In vitro	Six commercially available resin-based composites, including bulk-fill and conventional materials (Venus Bulk Fill, SDR, Charisma Flow, Tetric N-Ceram Bulk Fill, SonicFill, and Tetric N-Ceram)

Table 3.

Material composition and outcomes

Author (Year)	Organic matrix (monomers)	Inorganic fillers (type, size, morphology)	Properties evaluated	Main findings
Fronza et al. (2017) [20]	Methacrylate-based monomers including Bis-GMA, UDMA, Bis-EMA, TEGDMA, EBPDMA, PMMA, and proprietary resins	Aluminum borosilicate glass; boroalumino-fluorosilicate and strontium–aluminum fluorosilicate glass; zirconia/silica fillers; ytterbium trifluoride; barium glass; oxides; pre-polymerized fillers; E-glass fibers	Filler content; light transmittance; mechanical properties (biaxial flexural strength and flexural modulus)	Bulk-fill composites showed higher light transmittance than conventional composites, particularly SDR, with transmittance decreasing as thickness increased. Flexural strength remained stable across depths for bulk-fill materials, while conventional composites showed reduced strength at greater depths. Flexural modulus decreased with increasing depth for some bulk-fill materials. Filler morphology and composition varied among materials. Light attenuation did not compromise flexural strength of bulk-fill composites
Araújo-Neto et al. (2020) [21]	Methacrylate-based monomers including Bis-GMA, Bis-EMA, UDMA, TEGDMA, and PEGDMA	Silane-treated fillers including silica, zirconia, ceramic particles, barium and calcium–aluminum fluorosilicate glass, ytterbium trifluoride, mixed oxides, and proprietary filler technologies	Degree of conversion; polymerization rate; water sorption/solubility; filler characteristics; flexural strength; elastic modulus	Filler morphology and composition influenced physicomechanical performance. Dual curing improved degree of conversion, polymerization rate, flexural strength, and hydrolytic stability (e.g., Cention N). Self-cured and pre-polymerized filler systems showed inferior mechanical behavior. Monomer composition and photoinitiator systems significantly affected polymerization kinetics and water-related properties
Fidalgo-Pereira et al. (2022) [22]	Methacrylate-based monomers including Bis-GMA, Bis-EMA, UDMA, and TEGDMA; camphorquinone as the primary photoinitiator	Silanized silica nanoparticles; zirconia-based glass fillers; barium–aluminum borosilicate glass; ytterbium fluoride; amorphous silica; zinc oxide; iron and titanium oxides; pre-polymerized fillers; spherical filler technologies (SphereTEC™)	Filler characterization; optical transmittance; microhardness	Optical transmittance increased after polymerization, particularly with longer irradiation times, while higher filler content reduced light transmission. Composites with higher filler loadings (78–89 wt%) showed greater microhardness and elastic modulus. Flowable and low-filled materials exhibited lower mechanical performance and higher dependence on irradiation time
Ruivo et al. (2019) [23]	Methacrylate-based monomers including Bis-GMA, UDMA, TEGDMA, Bis-EMA, GPDM, HEMA, and GDMA, along with stabilizers, inhibitors, and photoinitiators	Silane-treated ceramic fillers; silica and zirconia; aluminum–fluoro–borosilicate glass; aluminum oxide; titanium dioxide; surface pre-reacted glass (S-PRG) fillers	Surface roughness; filler particle characterization (SEM)	All composites showed similar surface roughness after finishing and polishing. Simulated toothbrushing and water storage significantly increased roughness in all materials. Composites with larger, irregular fillers and higher hydrophilic monomer content exhibited greater roughness and susceptibility to degradation, while materials with smaller, spherical silica- and zirconia-based fillers maintained better surface smoothness. SEM analysis revealed filler exposure, crater formation, and surface morphological changes after aging
Bilge; Ipek (2024) [24]	R1: Bis-GMA, EGDMA; R2: Bis-GMA, Bis-EMA, UDMA; R3: UDMA, Bis-GMA, TEGDMA	R1: Glass fibers and hybrid fillers (silica fractions and barium glass fibers); R2: Zirconia/silica fillers and ytterbium trifluoride; R3: Zirconia/silica fillers	Degree of conversion (DC); Vickers microhardness (VHN); filler characterization (SEM-EDX)	Z250 showed the highest DC and VHN depending on the light-curing unit, while Filtek Bulk Fill presented lower values under certain conditions. Differences between light-curing units were observed for some materials. All composites achieved clinically acceptable DC. Polymerization outcomes were influenced by both light-curing unit and material characteristics, including translucency and filler properties
González-Alenda et al. (2025) [25]	Essentia Universal: UDMA, TCD, Bis-EMA, Bis-GMA; Filtek Universal: AUDMA, diurethane-DMA, 1,12-dodecane-DMA; Gaenial A’Chord: UDMA, TEGDMA, Bis-EMA; Omnichroma: Bis-GMA, TEGDMA; Tetric Prime: Bis-GMA, UDMA, Bis-EMA, D3MA; Filtek Supreme Ultra: Bis-GMA, UDMA, TEGDMA, Bis-EMA	Not clearly specified in detail across all materials; composites include proprietary filler systems typical of universal resin-based composites	Flexural strength; elastic modulus; hardness; water sorption; solubility; degree of conversion	Mechanical behavior varied according to material composition. Filtek Universal showed the highest flexural strength and elastic modulus. Thermocycling reduced most mechanical properties, although elastic modulus remained stable for Filtek Universal. Filtek Supreme Ultra exhibited the highest hardness, while Essentia Universal showed the lowest. Water sorption and solubility varied among materials. All composites showed similar degree of conversion, indicating that performance is influenced by multiple compositional factors
Balbinot et al. (2019) [26]	Predominantly methacrylate-based monomers, including Bis-GMA, UDMA, TEGDMA, Bis-EMA, and PEGDMA; some materials with modified urethane dimethacrylates (e.g., TCD-DI-HEA derivatives)	Silica nanoparticles; zirconia/silica; barium aluminoborosilicate glass; fluorinated barium aluminum glass; aluminum glass; silicon dioxide; nanosilica; barium fluoride-based fillers	Light transmittance; degree of conversion	Significant differences in light transmittance and degree of conversion were observed among composites and between enamel and dentin conditions. Filtek Supreme Ultra showed the highest transmittance in enamel, and Venus Diamond in dentin, while Esthet-X HD showed the lowest values. Opallis and Premise demonstrated higher degree of conversion, particularly after 24 h. No direct correlation was observed between light transmittance and degree of conversion, although a strong correlation existed between immediate and 24 h conversion values
Iwasaki et al. (2022) [27]	Methacrylate-based monomers including Bis-GMA, UDMA, Bis-EMA, TEGDMA, Bis-MPEPP, urethane acrylates, and modified UDMA derivatives	Fluoroboroaluminosilicate glass; barium-silica glass; strontium-silica glass; zirconia/silica; ytterbium trifluoride; silica-zirconia; silica-titania; silanated barium glass and silica	Depth of polymerization (bottom/top ratio); filler content; mechanical behavior (creep deformation)	Bulk-fill flowable composites showed higher bottom/top ratios compared to conventional flowable materials, indicating greater depth of polymerization. Filler content ranged from 61.2 to 69.5 wt% and was associated with improved mechanical properties, although no consistent linear relationship was observed across all materials. Greater creep deformation was observed on bottom surfaces
Sideridou; Karabela; Vouvoudi (2011) [28]	Methacrylate-based monomers including Bis-GMA, UDMA, TEGDMA, and Bis-EMA	Barium glass; ytterbium trifluoride; mixed oxides; pre-polymerized fillers; silica; zirconia/silica; barium–aluminoborosilicate; strontium aluminum borosilicate	Polymerization shrinkage; water sorption; solubility; flexural strength; elastic modulus	Grandio and Tetric EvoCeram showed lower polymerization shrinkage, while other composites exhibited higher values. Water sorption and solubility varied among materials, with Grandio presenting the lowest values. After 30 days, Grandio showed higher flexural strength and modulus compared to other materials. Overall, material performance varied according to composition, with some composites demonstrating more favorable physicomechanical behavior
Lu et al. (2006) [29] USA In vitro	Methacrylate-based monomers including Bis-GMA, Bis-EMA, UDMA, TEGDMA, multifunctional methacrylate esters, and urethane-modified dimethacrylates	Silica-zirconia; nanomeric and nanocluster fillers; silicon dioxide; ytterbium trifluoride; barium boron fluoroaluminosilicate glass; pyrogenic silica; pre-polymerized fillers	Polymerization shrinkage	Most materials showed similar polymerization shrinkage patterns, with approximately 99% of shrinkage occurring within the first 24 h. Estelite Σ and Filtek Supreme Ultra exhibited lower shrinkage values, whereas Renamel Microfill showed higher shrinkage
Rastelli et al. (2011) [30]	Methacrylate-based monomers including Bis-GMA, UDMA, Bis-EMA, TEGDMA, and other dimethacrylates	Zirconia/silica; nanoagglomerated silica; barium aluminoborosilicate glass	Degree of conversion; microhardness	Filtek Z250 showed higher degree of conversion and microhardness compared to other materials, whereas TPH3 exhibited lower mechanical performance. Nanofilled composites demonstrated mechanical properties comparable to hybrid composites, supporting their potential use in similar clinical indications, in addition to esthetic applications
Yan et al. (2019) [31] China In vitro	Methacrylate-based monomers including Bis-GMA, Bis-EMA, UDMA, and TEGDMA	Silica and zirconia/silica fillers; barium glass; mixed oxides; pre-polymerized fillers; ytterbium trifluoride	Flexural strength; flexural modulus; Vickers microhardness	Lava Ultimate exhibited higher flexural strength and microhardness compared to Tetric N-Ceram both before and after aging. Flexural modulus showed similar values between materials after water storage. Differences in mechanical behavior may be related to variations in filler composition and structure, particularly the presence of zirconia-based fillers
Kim et al. (2015) [32]	Methacrylate-based monomers including UDMA, Bis-GMA, TEGDMA, and EBADMA	Barium–aluminum–fluorosilicate glass; silica; strontium–aluminum–fluorosilicate glass; mixed oxides; pre-polymerized fillers; ytterbium trifluoride	Microhardness; translucency; bottom/top hardness ratio	Microhardness decreased with increasing specimen thickness across all materials. Bulk-fill composites exhibited bottom-to-top hardness ratios close to or above 80% at 4 mm thickness. Venus Bulk Fill showed higher translucency compared to other materials. A relationship between translucency and microhardness was observed for most composites, depending on thickness, although this trend was not consistent across all materials

Results synthesis

The included studies demonstrate that both organic and inorganic particles significantly influence the physicomechanical properties of resin composites. Materials containing larger inorganic particles, irregular morphology, or pre-polymerized fillers, such as Cention N and Beautifil II, showed a lower degree of conversion, higher water sorption and solubility, and increased surface roughness after simulated aging, indicating reduced resistance to abrasion and hydrolytic degradation. In contrast, resins with smaller, spherical particles based on silica or zirconia, such as Z100, Filtek Supreme Ultra, and Estelite Σ Quick, maintained better mechanical stability and surface smoothness. Monomer composition and photoinitiator systems affected the degree and kinetics of polymerization, while increased filler content and the presence of opaque particles reduced light transmittance and depth of cure.

Table 4 illustrates the effects of inorganic and organic particles on the evaluated outcomes, including degree of conversion, mechanical properties, translucency, surface roughness, sorption/solubility, and microhardness/nanohardness. The magnitude of the effect was classified into four levels: Ø (inconclusive or not reported); 1 (low or unfavorable effect, including small, inconsistent, or negative changes); 2 (moderate positive effect, indicating consistent improvement of limited magnitude); and 3 (strong positive effect, representing substantial and consistently reported improvements within the study).

The classification presented in Table 4 was based on a structured qualitative synthesis of the outcomes reported in each included study. For each outcome domain, the direction and magnitude of the reported effects were interpreted in relation to the specific organic or inorganic components evaluated within the same study. Given the heterogeneity of materials, formulations, and testing protocols, no quantitative weighting or causal inference was performed. Therefore, the classification reflects a descriptive mapping of trends rather than a comparative effectiveness assessment.

To enhance methodological rigor and reproducibility, the reviewers underwent a calibration exercise prior to data extraction, using five studies to standardize the interpretation of the scoring criteria. Inter-reviewer agreement was assessed using Cohen’s kappa coefficient, yielding a value of 0.899, which indicates excellent agreement.

It is important to note that classifications indicating strong positive effects (score 3) were based on the consistency of findings within individual studies and do not necessarily reflect a large body of evidence. Therefore, these ratings should be interpreted with caution.

Discussion

This scoping review aimed to evaluate the current evidence regarding the effects of organic and inorganic particles on the clinically relevant properties of resin-based composites. Previous literature reviews addressing similar topics have been published, and their findings are largely consistent with those observed in the present review [11–13]. Despite the availability of these reviews, a scoping review approach was deliberately chosen due to the heterogeneity of materials, formulations, outcome measures, and experimental protocols across in vitro studies, which precludes quantitative synthesis and justifies a comprehensive mapping of the existing evidence. An important contribution of this review lies in its structured synthesis approach, which integrates multiple outcome domains and highlights the interaction between organic and inorganic components, an aspect that has been insufficiently explored in previous reviews.

Although the final number of included studies was relatively limited, a scoping review approach remained appropriate due to the substantial heterogeneity observed across studies in terms of material formulations, experimental protocols, outcome measures, and evaluation methods. This variability precludes meaningful quantitative synthesis and supports the use of a scoping framework to systematically map the available evidence.

Moreover, the limited number of eligible studies highlights an important gap in the literature, reinforcing the relevance of this review in identifying areas that require further investigation rather than providing definitive conclusions.

It is important to emphasize that, consistent with the scoping review methodology, the present findings represent a descriptive mapping of the available evidence rather than an assessment of effectiveness or causal relationships. Therefore, the interpretations presented should be understood as indicative of trends and associations within the literature.

The composition of resin-based composites, based on the interaction between organic monomers and inorganic filler particles, appears to play an important role in their clinical performance. This interaction is associated with mechanical, optical, and chemical properties, influencing strength, hardness, surface roughness, translucency, and hydrolytic stability [33]. The findings of this review suggest that filler type, size, morphology, and content are associated with variability in composite performance reported in the literature, highlighting the relevance of optimizing the matrix–filler interface to potentially improve durability and clinical longevity [22].

Analysis of the included studies indicated that the organic matrix is associated with the physicomechanical behavior of resin-based composites. Monomers such as Bis-GMA, Bis-EMA, and UDMA were frequently associated with improved mechanical properties and higher microhardness values [20, 22]. Conversely, a higher content of hydrophilic monomers, as observed in materials such as Beautifil II (Shofu, Inc.) and Vertise Flow (Kerr Corporation), was associated with reduced mechanical resistance and increased susceptibility to degradation [23]. These findings are in agreement with previous reports suggesting that both the quality and proportion of organic components influence the mechanical performance of resin composites [22].

Water sorption and solubility are clinically relevant properties, as they may compromise both esthetic stability and flexural strength over time [34]. Monomers such as Bis-GMA and TEGDMA contain polar functional groups that increase hydrophilicity, thereby promoting higher water uptake and solubility [23]. In agreement with this mechanism, Filtek Supreme Ultra (3 M Oral Care, St. Paul, MN, USA) was associated with lower hydrolytic stability compared with materials formulated without Bis-GMA and TEGDMA, emphasizing the role of monomer composition in long-term material behavior [21].

Photopolymerization of resin composites begins with light activation, allowing photons to propagate through the material and activate the photoinitiator system. Photoinitiators generate free radicals that initiate chain reactions between carbon–carbon double bonds in monomers. When polymer network formation occurs in a heterogeneous manner, it may negatively influence the degree of conversion and the resulting mechanical properties [35]. In this context, Araújo-Neto et al. [21] reported higher maximum polymerization rates (Rp_max) in composites containing alternative photoinitiator systems more reactive than camphorquinone, such as bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO).

The degree of conversion reflects the efficiency of polymerization of the organic matrix and is related to the formation of a cross-linked polymer network, influencing hardness, strength, and overall stability [22]. In the present review, UDMA-containing materials were associated with favorable performance in terms of degree of conversion, particularly in Filtek Z250 (3 M ESPE, USA) [24]. However, despite also containing UDMA, Filtek Bulk Fill (3 M ESPE, USA) was associated with a lower degree of conversion, which may be related to its higher filler content, potentially affecting light transmission and polymerization efficiency [24].

Light transmittance has received increasing attention because it allows the placement of thicker increments, potentially reducing clinical chair time [36]. The evidence synthesized in this review suggests that both the proportion and morphology of inorganic fillers are associated with light transmittance [22]. Notably, despite its high filler content, EverX Posterior (GC Corporation, Tokyo, Japan) was reported to present higher light transmittance than the conventional control material, which may be related to the presence of glass fibers facilitating light propagation within the composite structure [20].

Vickers hardness testing is widely used to assess the resistance of a material surface to indentation [37]. Bilge and Ipek [24] reported that conventional resin composites with higher filler content were associated with greater microhardness than bulk-fill materials, regardless of the light-curing unit used. Furthermore, Fronza et al. [20] demonstrated that filler characteristics, including particle size and morphology, may influence light transmittance, indirectly affecting polymerization efficiency and the mechanical properties of resin composites.

Surface roughness is a critical parameter for predicting clinical failure, as increased roughness is associated with greater plaque accumulation and esthetic deterioration. This property is commonly evaluated using scanning electron microscopy (SEM) [38]. The studies included in this review indicated that variations in filler content, particle size, morphology, and composition are associated with differences in surface roughness outcomes. Lower roughness values were reported in zirconia-filled composites, which are recognized for their enhanced mechanical resistance and surface stability [23].

Although some materials were classified as having strong positive effects, these findings were often based on a limited number of studies. Therefore, caution is warranted when interpreting these results, as they may not represent consistent evidence across different experimental conditions.

A critical appraisal of the included studies revealed important methodological limitations. Most were inherent to the in vitro design, including small sample sizes, the use of different commercial brands with specific clinical indications, and substantial variability in experimental protocols, light-curing methods, and material formulations.

The relatively small number of included studies should be considered when interpreting the findings of this review. Although the search strategy was comprehensive, the strict eligibility criteria—particularly the focus on commercially available materials, clinically relevant outcomes, and the exclusion of experimental formulations—were intentionally applied to enhance the clinical applicability of the findings. However, this approach may have reduced the number of eligible studies and limited the breadth of the evidence base.

In addition, the possibility of publication and selection bias cannot be excluded. Studies with non-significant or unfavorable results may be underrepresented in the literature, and the exclusion of non-indexed or inaccessible studies may have further influenced the evidence mapping.

Consequently, the limited number of included studies reduces the confidence in the observed trends, and the findings should be interpreted as indicative rather than conclusive. This reinforces the exploratory nature of this scoping review and highlights the need for further research to strengthen the available evidence. The restriction to studies published from 2015 onwards may have excluded earlier evidence; however, this decision was made to focus on contemporary materials and formulations that better reflect current clinical practice.

These factors limit direct extrapolation to clinical conditions. Consequently, well-designed long-term clinical trials are required to further investigate the behavior of different combinations of organic monomers and inorganic fillers under oral conditions. Future studies should also explore novel polymer matrices with reduced water sorption and polymerization shrinkage stress, as well as inorganic fillers that may enhance light transmittance, microhardness, and surface smoothness.

Despite these limitations, this scoping review provides a comprehensive synthesis of the influence of organic and inorganic particles on the clinically relevant properties of resin-based composites. Strengths of this review include an extensive literature search across multiple databases, inclusion of gray literature, transparent and rigorous implementation of the scoping review methodology, clearly defined eligibility criteria, and a critical appraisal of the included studies. Together, these aspects provide a structured overview of the current evidence and support the relevance of this review for both researchers and clinicians.

Although the findings of this review are primarily derived from in vitro studies, they offer potentially relevant insights into the behavior of resin-based composites. However, caution is required when extrapolating these findings to clinical performance. In vitro conditions do not fully replicate the complexity of the oral environment, which involves dynamic factors such as saliva, temperature fluctuations, masticatory forces, biofilm activity, and patient-related variables.

In addition, commonly used laboratory aging protocols, such as water storage and thermocycling, only partially simulate intraoral degradation processes and may not accurately reflect long-term clinical behavior. As a result, the outcomes observed under controlled experimental conditions may differ from those observed in clinical practice.

Therefore, the clinical implications discussed in this review should be interpreted as indicative rather than predictive. These findings may support material selection and hypothesis generation but should not be considered definitive evidence of clinical performance. Further well-designed, long-term clinical studies are necessary to validate these observations under real-world conditions.

Conclusion

Based on the available evidence, the interaction between the organic and inorganic phases appears to play an important role in the clinical performance of resin-based composites, as it is associated with their physicomechanical and optical properties. Monomers such as Bis-GMA, Bis-EMA, and UDMA were frequently associated with improved mechanical behavior, with UDMA also showing favorable trends in terms of degree of conversion.

Additionally, the type, size, morphology, and distribution of inorganic filler particles were associated with variations in strength, surface roughness, and light transmittance. Composites containing smaller, spherical fillers tended to present higher microhardness and improved hydrolytic stability.

However, these findings should be interpreted as a descriptive synthesis of the available evidence rather than definitive conclusions regarding material performance. The limited number of studies, methodological heterogeneity, and exclusive reliance on in vitro data highlight the need for further well-designed clinical investigations. These findings should be interpreted with caution, particularly due to the exclusive reliance on in vitro data, which may not fully reflect clinical conditions.

Abbreviations

BAPO

Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide

BFS

Biaxial flexural strength

Bis-EMA

Ethoxylated bisphenol A dimethacrylate

Bis-GMA

Bisphenol A glycidyl methacrylate

CQ

Camphorquinone

DC

Degree of conversion

EDX

Energy-dispersive X-ray spectroscopy

EGDMA

Ethylene glycol dimethacrylate

FTIR

Fourier-transform infrared spectroscopy

GPDM

Glycerol phosphate dimethacrylate

HEMA

2-Hydroxyethyl methacrylate

LCU

Light-curing unit

MF

Flexural modulus

PMMA

Poly(methyl methacrylate)

PRISMA-ScR

Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews

Rpmax

Maximum rate of polymerization

SEM

Scanning electron microscopy

SEM–EDX

Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy

S-PRG

Surface pre-reacted glass-ionomer

TCD

Tricyclodecane dimethanol dimethacrylate

TEGDMA

Triethylene glycol dimethacrylate

TPO

Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide

UDMA

Urethane dimethacrylate

VHN

Vickers hardness number

Authors’ contributions

CJCP: Methodology, Research, Writing – Preparation, Writing - Review and Editing. VFS: Methodology, Research, Writing – Preparation, Writing - Review and Editing. AGS: Writing – Preparation, Writing - Review and Editing. RFCPM: Writing – Preparation, Writing - Review and Editing. TPM: Research; Writing – Preparation, Writing - Review and Editing. BLS: Research; Writing – Preparation, Writing - Review and Editing. VCD: Supervision, Methodology, Research, Writing – Preparation, Writing - Review and Editing.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

All data generated or analyzed during this study are included in this published article and its supplementary information files. The review protocol is publicly available in the Open Science Framework (OSF) repository at https://doi.org/10.17605/OSF.IO/6QPZ9.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.