Minimally-invasive dentistry via dual-function novel bioactive low-shrinkage-stress flowable nanocomposites

The mechanical, wear, antibacterial properties and biocompatibility of injectable restorative materials under wet challenge

OBJECTIVES

To evaluate the mechanical, wear, antibacterial properties, and biocompatibility of injectable composite materials.

METHODS

Two injectable composite resins (GU and BI), one flowable composite resin (FS), and one flowable compomer (DF), in A2 shade, were tested. Mechanical properties were tested via three-point bending test immediately after preparation and after 1-day, 7-day, 14-day, and 30-day water storage. Under water-PMMA slurry immersion, specimens were subjected to a 3-body wear test (10,000 cycles) against stainless steel balls, while the roughness, wear depth, and volume loss were recorded. After 1-day and 3-day MC3T3-E1 cell culture, cell viability was evaluated with CCK-8 test kits, while the cell morphology was observed under CLSM and SEM. Antibacterial properties on S. mutans were assessed via CFU counting, CLSM, and SEM observation. SPSS 26.0 was used for statistical analysis (α = 0.05).

RESULTS

The mechanical properties were material-dependent and sensitive to water storage. Flexural strength ranked GU > FS > BI > DF at all testing levels. Three nanocomposites had better wear properties than DF. No significant difference on 1-day cell viability was found, but DF showed significantly lower cell proliferation than nanocomposites on 3-day assessment. GU and FS had more favourable cell adhesion and morphology. CFU counting revealed no significant difference, while FS presented a slightly thicker biofilm and BI showed relatively lower bacteria density.

CONCLUSIONS

Injectable nanocomposites outperformed the compomer regarding mechanical properties, wear resistance, and biocompatibility. The tested materials presented comparable antibacterial behaviours. Flowable resin-based composites' performances are affected by multiple factors, and their compositions can be attributed.

CLINICAL SIGNIFICANCE

A profound understanding of the mechanical, wear, and biological properties of the restorative material is imperative for the clinical success of dental restorations. The current study demonstrated superior properties of highly filled injectable composite resins, which imply their wider indications and better long-term clinical performances.

A narrative review of minimally invasive techniques in restorative dentistry

This narrative review aimed to provide a comprehensive overview of minimal invasive dentistry (MID) by synthesizing relevant articles obtained from various sources, including electronic databases such as PubMed, SCOPUS, EMBASE, the COCHRANE library, and Science Direct, as well as through manual searches of cross-references and textbooks. The search employed MeSH terms and keywords related to MID, such as "minimally invasive dentistry," "atraumatic restorative treatment (ART)," "MID," and "minimum intervention dentistry." The inclusion criterion was English-language articles published between the years 2000 and June 2023 that aligned with the study objectives. After a thorough assessment of the included articles, 34 high-quality articles were selected for this review. The selected articles elucidate the characteristics of MID, the application of the ART, and the principles of minimum intervention in dentistry. Animal-based studies and narrative reviews on MID were excluded from the analysis. This narrative review serves as a valuable resource for dental professionals, researchers, and educators interested in staying abreast of the latest developments and evidence in the field of MID.

Do nanofillers provide better physicomechanical properties to resin-based pit and fissure sealants? A systematic review

The purpose of this study was to systematically review the impact of nanofillers on the physicomechanical properties of resin-based pit and fissure sealants (RBS). This review included in vitro studies with full-length English-language articles reporting on the physicomechanical properties of nanofilled RBS until February 2023. PubMed, Web of Sciences, Scopus, and LILACS databases were accessed for literature searches. The review was formulated based on the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines and used the Consolidated Standards of Reporting Trials (CONSORT) guidelines and risk of bias Cochrane tool for quality assessment. The search resulted in 539 papers, of which 22 were eligible to be included in the review. Inorganic, polymeric, core-shell, and composite nanomaterials were used to reinforce the studied RBS. The inherent nature of the nanomaterial used, its morphology, concentration, and volume used were the primary parameters that determined the nanomaterial's success as a filler in RBS. These parameters also influenced their interaction with the resin matrix, which influenced the final physicomechanical properties of RBS. The use of nanofillers that were non-agglomerated and well dispersed in the resin matrix enhanced the physicomechanical properties of RBS.

Inorganic Compounds as Remineralizing Fillers in Dental Restorative Materials: Narrative Review

Secondary caries is one of the leading causes of resin-based dental restoration failure. It is initiated at the interface of an existing restoration and the restored tooth surface. It is mainly caused by an imbalance between two processes of mineral loss (demineralization) and mineral gain (remineralization). A plethora of evidence has explored incorporating several bioactive compounds into resin-based materials to prevent bacterial biofilm attachment and the onset of the disease. In this review, the most recent advances in the design of remineralizing compounds and their functionalization to different resin-based materials' formulations were overviewed. Inorganic compounds, such as nano-sized amorphous calcium phosphate (NACP), calcium fluoride (CaF₂), bioactive glass (BAG), hydroxyapatite (HA), fluorapatite (FA), and boron nitride (BN), displayed promising results concerning remineralization, and direct and indirect impact on biofilm growth. The effects of these compounds varied based on these compounds' structure, the incorporated amount or percentage, and the intended clinical application. The remineralizing effects were presented as direct effects, such as an increase in the mineral content of the dental tissue, or indirect effects, such as an increase in the pH around the material. In some of the reported investigations, inorganic remineralizing compounds were combined with other bioactive agents, such as quaternary ammonium compounds (QACs), to maximize the remineralization outcomes and the antibacterial action against the cariogenic biofilms. The reviewed literature was mainly based on laboratory studies, highlighting the need to shift more toward testing the performance of these remineralizing compounds in clinical settings.

Low-Shrinkage Resin Matrices in Restorative Dentistry-Narrative Review

Dimethacrylate-based resin composites restorations have become widely-used intraoral materials in daily dental practice. The increasing use of composites has greatly enhanced modern preventive and conservative dentistry. They have many superior features, especially esthetic properties, bondability, and elimination of mercury and galvanic currents. However, polymeric materials are highly susceptible to polymerization shrinkage and stresses that lead to microleakage, biofilm formation, secondary caries, and restoration loss. Several techniques have been investigated to minimize the side effects of these shrinkage stresses. The primary approach is through fabrications and modification of the resin matrices. Therefore, this review article focuses on the methods for testing the shrinkage, as well as formulations of resinous matrices available to reduce polymerization shrinkage and its associated stress. Furthermore, this article reviews recent cutting-edge developments on bioactive low-shrinkage-stress nanocomposites to effectively inhibit the growth and activities of cariogenic pathogens and enhance the remineralization process.