Bacterial cellulose nanocrystals may offset MPC’s damage to dental cement strength

Resin-modified glass ionomer cement (RMGIC) occupies a familiar place in restorative dentistry because it releases fluoride, bonds chemically to tooth structure, is biocompatible, and looks acceptably natural. Yet the material has long carried a well-known weakness: it is comparatively fragile, susceptible to fracture and marginal leakage, and its mechanical properties fall short of what permanent posterior fillings must endure. In permanent teeth, conventional glass ionomer cements are therefore generally restricted to small and mid-size Class II restorations, and in posterior regions they more often serve as a base or temporary material rather than a definitive filling.

The team, led by Maryam Saadat and Marzieh Moradian, incorporated bacterial cellulose nanocrystals (BCNCs) and 2-methacryloyloxyethyl phosphorylcholine (MPC) into RMGIC and measured how each additive, alone and in combination, affected flexural strength, diametral tensile strength, surface roughness, and microhardness.

The experimental design was straightforward. A total of 192 specimens were prepared in four groups of 48 each: unmodified RMGIC as a control, RMGIC with 1 wt% BCNC, RMGIC with 3 wt% MPC, and RMGIC containing both additives. The base material was Fuji II LC, a commercial resin-modified glass ionomer from GC Corporation, while the BCNC powder came from Nano Novin Polymer in Iran and the MPC from Sigma-Aldrich. Powders were weighed to an accuracy of 0.0001 g, hand-mixed, homogenized with a vibrator, sieved to prevent particle aggregation, and blended in an amalgamator for 20 seconds to ensure uniform distribution.

Each mechanical property was tested with a standardized protocol. Flexural strength specimens were rectangular bars of 2 by 2 by 25 millimeters, prepared according to ISO 9917.2 specifications and evaluated with a three-point bending test on a universal testing machine at a crosshead speed of 0.5 millimeters per minute. Diametral tensile strength was measured on disc-shaped specimens 7 millimeters in diameter and 2 millimeters high. Surface roughness was quantified with a profilometer at five positions on each specimen, and microhardness was assessed with a Vickers hardness tester using five indentations per specimen at a load of 300 grams-force for 15 seconds. All specimens were stored in distilled water for one week before testing, and statistical analysis was performed with SPSS version 25 using a significance threshold of 0.05.

The headline result concerns what did not change. Adding 1 wt% BCNC alone produced no statistically significant differences in any of the four measured properties compared with the control group, although the BCNC-modified cement did show the highest mean flexural strength of all groups at 20.17 megapascals, against 17.21 megapascals for the unmodified material. The authors interpret this as evidence that BCNC maintained the mechanical integrity of the cement, supporting its suitability as a reinforcing component. They attribute the effect to the nanocrystals’ high crystallinity and their capacity to form hydrogen bonds with both the hydroxyl groups of the glass particles and the carboxylic groups of the polyacrylic acid, creating an interconnected network of nanoscale fibers distributed within the matrix.

MPC told a very different story. The 3 wt% MPC group recorded the lowest flexural strength of all four groups at 7.96 megapascals, significantly lower than every other group, and its diametral tensile strength of 10.60 megapascals was also reduced relative to the control’s 14.47 megapascals. Surface roughness rose sharply in the MPC group, reaching 1.20 micrometers compared with 0.63 micrometers for the control, a statistically significant increase. Microhardness, however, remained statistically comparable to the control, suggesting that MPC’s influence was localized to surface morphology rather than bulk mechanical cohesion.

The authors offer a mechanistic explanation rooted in MPC’s chemistry. MPC is a zwitterionic polybetaine, prized in dental research for its antibacterial and protein-repellent characteristics, but it is also highly hydrophilic. The researchers suggest that this hydrophilicity promotes water uptake and disrupts cohesive bonding within the polymer matrix, potentially interfering with the ion-exchange reactions between polyacrylic acid and the fluoroaluminosilicate glass that give the cement its cross-linked strength. Consistent with this, previous studies have reported that MPC incorporation reduced elastic modulus and flexural strength in some composite specimens, and that higher MPC content increases water sorption in dental composites.

A striking observation during sample preparation reinforced this interpretation. A gelatinous, viscous substance formed on the surface of the MPC group’s specimens, and after immersion in distilled water the phenomenon persisted, with further MPC leaching observed. The authors attribute this to the weak bond between MPC and the glass ionomer matrix, to the hydrophilic nature of MPC and HEMA causing both to leach out by absorbing water, and to the possibility of a chemical reaction between these components resulting in incomplete setting of the cement.

The most intriguing finding emerged when the two additives were combined. Co-incorporating BCNC and MPC partially compensated for MPC’s negative effects: flexural strength, surface roughness, and microhardness all returned to values statistically similar to the control group. The researchers suggest that the reinforcing network formed by BCNC within the matrix helps stabilize the structure and limit the damage associated with MPC. However, the compensation was incomplete. The combined group’s diametral tensile strength of 9.99 megapascals remained significantly lower than the control’s, a reduction the authors link to the sensitivity of tensile testing to internal flaws and crack propagation, and to MPC’s enhanced water absorption and plasticizing effects still compromising internal matrix integrity even in the presence of BCNC reinforcement.

The authors are careful to frame these findings within the limits of an in-vitro design. Laboratory conditions cannot fully replicate the biological, chemical, and mechanical complexity of the oral environment, and variables such as thermal cycling, pH changes, salivary enzyme activity, and long-term aging may affect the performance of the modified materials. The study also tested only a single concentration of each additive, chosen on the basis of prior research, so varying those levels could produce different mechanical responses. Biological questions, including antibacterial efficacy, biofilm adhesion, and cytocompatibility, remain to be examined before MPC incorporation can be judged to deliver clinically beneficial antimicrobial effects without compromising mechanical strength. The authors propose that future work explore a wider range of additive concentrations and use scanning electron microscopy to analyze the microstructure of the modified cements. Within those limits, the study suggests that BCNC reinforcement can help preserve the mechanical stability of RMGIC while potentially enabling the addition of MPC, whose protein-repellent and antimicrobial promise has long attracted dental materials researchers.

Subject of Research: Effects of bacterial cellulose nanocrystals and 2-methacryloyloxyethyl phosphorylcholine on the mechanical properties of resin-modified glass ionomer cement

Article Title: Effect of bacterial cellulose nanocrystal and 2-methacryloyloxyethyl phosphorylcholine incorporation on the mechanical properties of resin-modified glass ionomer cement

Article References: Saadat, M., Moradian, M., Rouhbakhsh, H., Hashemi, M. A., & Khorshidi Asl, Z. (2026). Effect of bacterial cellulose nanocrystal and 2-methacryloyloxyethyl phosphorylcholine incorporation on the mechanical properties of resin-modified glass ionomer cement. Heliyon, 12(16), Article e45646. https://doi.org/10.1016/j.heliyon.2026.e45646

Image Credits: AI Generated

DOI: 10.1016/j.heliyon.2026.e45646

Keywords: resin-modified glass ionomer cement, bacterial cellulose nanocrystals, 2-methacryloyloxyethyl phosphorylcholine, dental materials, flexural strength, diametral tensile strength, surface roughness, microhardness, in-vitro study, nanomaterials, restorative dentistry, Heliyon