Cytotoxicity of contemporary resin-based dental materials in contact with dentin

Cytotoxic effects on human dental pulp stem Cells after exposure to adhesive bonding agents

Studies regarding cytotoxic effects attributed to the use of adhesive bonding agents on pulp tissue are not conclusive. To point out whether these materials are safe for clinical use, in vivo exposure of dental pulp to adhesive bonding agents was simulated using an experimental setup in which Human Dental Pulp Stem Cells (hDPSC) are exposed to the action of two kinds of adhesives: self-etching adhesives and two-step bonding agents through a dentine barrier. Cytotoxic effects on these cells were evaluated by MTT assay protocol and fluorescence microscopy, and their results were contrasted to those obtained through Raman spectra taken on single hDPSCs. Overall, no significant cytotoxic effects were observed by combining all the techniques, and cell viability close to 90% was achieved for a dentine barrier of at least 1 mm thick. Moreover, Raman spectroscopy was able to detect structural DNA damage in some dental pulp cells when exposed to two-step bonding agents, suggesting that this technique could be considered a complementary tool with the potential to evaluate cell toxicity beyond cell viability.

Effect of Rapid High-Intensity Light-Curing on Increasing Transdentinal Temperature and Cell Viability: An In Vitro Study

BACKGROUND

This study investigated effects of rapid high-intensity light-curing (3 s) on increasing transdentinal temperature and cell viability.

METHODS

A total of 40 dentin discs (0.5 mm) obtained from human molars were prepared, included in artificial pulp chambers (4.5 × 5 mm), and subjected to four light-curing protocols (n = 5), with a Valo Grand light curing unit: (i) 10 s protocol with a moderate intensity of 1000 mW/cm2 (Valo-10 s); (ii) 3 s protocol with a high intensity of 3200 mW/cm2 (Valo-3 s); (iii) adhesive system + Filtek Bulk-Fill Flow bulk-fill composite resin in 10 s (FBF-10 s); (iv) adhesive system + Tetric PowerFlow bulk-fill composite resin in 3 s (TPF-3 s). Transdentinal temperature changes were recorded with a type K thermocouple. Cell viability was assessed using the MTT assay. Data were analyzed using one-way ANOVA and Tukey tests for comparison between experimental groups (p < 0.05).

RESULTS

The 3 s high-intensity light-curing protocol generated a higher temperature than the 10 s moderate-intensity standard (p < 0.001). The Valo-10 s and Valo-3 s groups demonstrated greater cell viability than the FBF-10s and TPF-3 s groups and statistical differences were observed between the Valo-3 s and FBF-10 s groups (p = 0.023) and Valo-3 s and TPF-3 s (p = 0.025), with a potential cytotoxic effect for the FBF-10 s and TPF-3 s groups.

CONCLUSIONS

The 3 s rapid high-intensity light-curing protocol of bulk-fill composite resins caused a temperature increase greater than 10 s and showed cell viability similar to and comparable to the standard protocol.

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.

Desquamated Epithelial Cells of Unstimulated Human Whole Saliva Express Both EGF Transcript and Protein

Objective

The aim of this study was to investigate if desquamated oral epithelial cells (DOECs) express the epidermal growth factor (EGF) and if these cells thereby may contribute to salivary EGF contents.

Background

DOECs have recently been shown to harbor the antimicrobial peptide LL-37, proposing that they may also store other biologically important salivary peptides/proteins. The EGF peptide is a growth factor which plays a critical role to maintain epithelial integrity and promote epithelial healing. The EGF is produced by salivary glands, but it is not known whether DOECs contain the EGF and thereby contribute to salivary EGF levels.

Materials and Methods

DOECs were isolated from unstimulated whole saliva collected from four healthy volunteers. EGF protein expression was determined in cell lysates by dot blot and ELISA. Cellular distribution of cytokeratin, the proliferation marker Ki67, and EGF immunoreactivity were assessed by immunocytochemistry. EGF gene expression was investigated by qPCR. Expression of EGF transcript and protein in DOECs was compared to that in the human cultured keratinocyte cell line (HaCaT) cells.

Results

EGF protein expression was detected in DOEC cell lysates by both dot blot and ELISA. Strong cytoplasmic EGF immunoreactivity was observed in DOECs, although some cells showed only a weak immunoreactive signal for EGF. Moreover, DOECs, besides containing EGF protein, also expressed transcript for EGF. Interestingly, ELISA analysis revealed that EGF protein contents were higher in DOECs than in HaCaT cells. ELISA analysis also disclosed that EGF concentration was about 10 times higher in whole saliva compared to DOECs. EGF transcript expression was about 50% lower in HaCaT cells stimulated with high (10%) compared to low (0.1%) concentration of fetal bovine serum, representing growth-stimulated and growth-restricted conditions, respectively, implying that growth-stimulus exerts negative feedback on EGF gene activity in HaCaT cells.

Conclusion

Here, we show for the first time that DOECs express the EGF, arguing that these cells contribute to salivary EGF contents and hence may play a role in gingival epithelial repair and wound healing.

Characterization of Contemporary Conventional, Bulk-fill, and Self-adhesive Resin Composite Materials

OBJECTIVE

To evaluate the physical and biological properties of different types of flowable resin composites and their bonding ability to dentin, comparing the performance of self-adhesive and bulk-fill materials with a conventional control.

METHODS AND MATERIALS

Four flowable resin composites were tested: two self-adhesive (Y-flow [SA_YF]; and Dyad Flow [SA_DF]); one bulk-fill (Filtek Bulk Fill Flow [BF]); and one conventional composite (Opallis Flow [OF]). The microshear bond strength (μSBS) to dentin (bovine samples) was investigated at 24 hours and 6 months of storage. The materials were also characterized by degree of conversion, cross-link density, water contact angle, color stability, and cell viability (ISO 10993-5/2009) analyses. Data were analyzed using Analysis of Variance and Tukey tests (α=0.05).

RESULTS

The μSBS values were higher for control specimens at 24 hours, whereas the resin-dentin bonds were similarly distributed among the groups after aging. Adhesive failure was the most frequent pattern observed at both time intervals. SA_YF was the only material that increased the bond strength over time. Degree of conversion increased in the following order: SA_YF (28.6±1.4%) < BF (49.7±0.8%) < OF (60.0±2.0%) = SA_DF (63.6±2.3%). Cross-link density was similar among all materials. The self-adhesive composites were more hydrophilic than the other types, with BF showing the lowest water contact angle and the greatest color alteration. All resin composites had a biocompatible behavior.

CONCLUSION

Chemical composition appeared to be an influential factor affecting the physicomechanical and biological behavior of the materials tested.

Modeling Liquids and Resin-Based Dental Composite Materials-A Scoping Review

Several lubricant materials can be used to model resin-based composites (RBCs) during restorative procedures. Clinically, instruments or brushes are wet with bonding agents (BAs) or modeling liquids (MLs) for sculpturing purposes. However, a knowledge gap exists on their effects on the mechanical properties of RBCs, requiring greater insight. Five databases were searched, including 295 in vitro studies on the use of lubricant materials for modeling RBCs during restorative procedures. Only articles in the English language were included, with no limits on the publication date. The last piece of research was dated 24 March 2022. In total, 16 studies were included in the review process, together with a paper retrieved after screening references. A total of 17 BAs and 7 MLs were investigated. Tensile (n = 5), flexural strength (n = 2), water sorption (n = 2), color stability (n = 8) and translucency (n = 3), micro-hardness (n = 4), roughness (n = 3), degree of conversion (n = 3), and monomer elution (n = 2) tests were carried out. In general, a maximum of 24 h of artificial storage was performed (n = 13), while four papers tested the specimens immediately. The present review identifies the possibilities and limitations of modeling lubricants used during restorative procedures on the mechanical, surface, and optical properties of RBCs. Clinicians should be aware that sculpturing RBCs with modeling resins might influence the composite surface properties in a way that is material-dependent.

Nanomaterials in Dentistry: Current Applications and Future Scope

Nanotechnology utilizes the mechanics to control the size and morphology of the particles in the required nano range for accomplishing the intended purposes. There was a time when it was predominantly applied only to the fields of matter physics or chemical engineering, but with time, biological scientists recognized its vast benefits and explored the advantages in their respective fields. This extension of nanotechnology in the field of dentistry is termed ‘Nanodentistry.’ It is revolutionizing every aspect of dentistry. It consists of therapeutic and diagnostic tools and supportive aids to maintain oral hygiene with the help of nanomaterials. Research in nanodentistry is evolving holistically but slowly with the advanced finding of symbiotic use of novel polymers, natural polymers, metals, minerals, and drugs. These materials, in association with nanotechnology, further assist in exploring the usage of nano dental adducts in prosthodontic, regeneration, orthodontic, etc. Moreover, drug release cargo abilities of the nano dental adduct provide an extra edge to dentistry over their conventional counterparts. Nano dentistry has expanded to every single branch of dentistry. In the present review, we will present a holistic view of the recent advances in the field of nanodentistry. The later part of the review compiled the ethical and regulatory challenges in the commercialization of the nanodentistry. This review tracks the advancement in nano dentistry in different but important domains of dentistry.