Water sorption of flowable composites

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	TUScholarShare (Temple University)
Authors	Faleh Alajmi
Analysis	Full AI Review Included

Technical Analysis and Documentation: Water Sorption of Flowable Composites

This document analyzes the research concerning the degradation and biological interaction of dental flowable composites, pivoting the findings toward the superior material properties and custom manufacturing capabilities offered by 6CCVD’s MPCVD diamond products.

Executive Summary

Critical Material Failure: The study confirms that polymer-based dental composites exhibit significant water sorption (W_sp up to 103 µg/mm³) and solubility (W_sl up to 77.2 µg/mm³), leading to hydrolytic degradation, filler-matrix debonding, and elution of unreacted monomers.
Environmental Sensitivity: Mass gain due to water sorption is exacerbated in acidic environments (pH 4.0), accelerating material breakdown and reducing the longevity of restorative materials.
Inertness Requirement: The negative control (Titanium disc) demonstrated zero mass gain, sorption, and solubility, establishing a benchmark for chemically inert materials required for long-term physiological stability.
6CCVD Diamond Solution: MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) offer zero water sorption and solubility, providing unparalleled chemical inertness and mechanical stability compared to conventional dental polymers or ceramics.
Superior Mechanical Properties: Diamond’s extreme hardness and wear resistance directly mitigate the decrease in surface hardness and wear resistance reported for flowable composites.
Customization for Biomedical Research: 6CCVD specializes in providing custom diamond wafers and plates (up to 125mm PCD) with ultra-low surface roughness (Ra < 1nm for SCD), ideal for advanced biomedical applications requiring minimal surface defects for reduced bacterial adhesion.

Technical Specifications

The following data points were extracted from the experimental methodology and results, focusing on material performance and testing parameters.

Parameter	Value	Unit	Context
Specimen Geometry (Diameter)	15	mm	Standardized disc size (ISO 4049)
Specimen Geometry (Thickness)	1	mm	Standardized disc size (ISO 4049)
Curing Light Intensity	1200	mW/cm²	LED Curing Unit
Mass Measurement Repeatability	0.1	mg	Electronic balance precision
Standard Immersion Duration	30	days	Used for W_sp and W_sl calculation
Maximum Immersion Duration	180	days	Total observation period for mass gain
Storage Temperature	37	°C	Physiological simulation
Highest Water Sorption (W_sp)	103 ± 8.5	µg/mm³	Virtuoso composite (pH 7.0, 30 days)
Lowest Water Sorption (W_sp)	30.1 ± 3.8	µg/mm³	SureFill composite (pH 7.0, 30 days)
Control Material Performance	Zero	Mass Gain/W_sp/W_sl	Titanium disc (Inert benchmark)
Biofilm Incubation Temperature	37	°C	For S. mutans and S. sanguis growth

Key Methodologies

The water sorption and solubility tests were conducted in strict adherence to the ISO 4049:07-2009 standard for Polymer Based Restorative Materials.

Specimen Fabrication: Three disc-shaped specimens (15 mm diameter, 1 mm thickness) of each flowable composite were prepared in a Teflon mold and cured using a light-emitting diode (LED) unit at 1200 mW/cm².
Initial Conditioning (M₁): Discs were stored in a desiccator over anhydrous silica gel (first 3 days at room temperature, then 37 °C) and weighed daily until a constant mass (M₁) was achieved (up to 35 days).
Volume Determination (V): Specimen volume was calculated using V = π(d/2)²h, based on caliper measurements of diameter (d) and thickness (h).
Immersion and Mass Gain (M₂): Specimens were immersed in buffer solutions at pH 4.0, 5.5, and 7.0. Mass (M₂) was recorded after 30 days of immersion for standardized W_sp/W_sl calculations.
Reconditioning (M₃): Specimens were reconditioned in a desiccator to constant mass (M₃) to determine the mass of leachable components.
Sorption and Solubility Calculation:
- Water Sorption (W_sp) was calculated as (M₂-M₃)/V in µg/mm³.
- Water Solubility (W_sl) was calculated as (M₁-M₃)/V in µg/mm³.
Biofilm Assessment: Equal mass specimens were incubated with S. mutans or S. sanguis at 37 °C for 6 hours. Biofilm formation was quantified using crystal violet staining and spectrophotometric analysis at 500 nm.

6CCVD Solutions & Capabilities

The research highlights the inherent limitations of polymer-based materials in long-term, high-wear, aqueous, and acidic environments. 6CCVD’s MPCVD diamond materials provide the ultimate solution for applications demanding chemical inertness, zero sorption, and extreme mechanical durability, far exceeding the performance of the tested composites and the titanium control.

Applicable Materials for Advanced Biomedical Applications

For researchers and engineers developing next-generation biomedical or dental components that require absolute stability and wear resistance, 6CCVD recommends the following diamond materials:

Material Grade	Key Advantage	Application Relevance
Optical Grade SCD	Highest purity, ultra-low roughness (Ra < 1nm).	Sensor windows, micro-tools, surfaces requiring minimal bacterial adhesion.
High-Quality PCD	Large area capability (up to 125mm), superior thermal management.	Wear components, large-scale implant surfaces, high-durability substrates.
Boron-Doped Diamond (BDD)	Electrochemical stability, conductive, inert.	Advanced sensing, electrochemical analysis in physiological buffers (e.g., pH monitoring, redox reactions).

Customization Potential for Research Replication and Extension

The study utilized specific disc geometries (15 mm diameter x 1 mm thickness) and a titanium control (6.5 mm diameter x 1 mm thick). 6CCVD is uniquely positioned to supply diamond materials tailored precisely to these demanding specifications:

Custom Dimensions: We routinely manufacture SCD and PCD plates/wafers up to 125mm in diameter, easily accommodating the 15 mm discs required for ISO 4049 testing.
Precision Thickness Control: We offer SCD and PCD layers from 0.1 µm up to 500 µm, and robust substrates up to 10 mm thick, allowing researchers to precisely control the volume (V) parameter critical for W_sp and W_sl calculations.
Ultra-Smooth Surfaces: To investigate the lack of correlation between water sorption and biofilm formation, researchers need highly controlled surface topography. 6CCVD provides polishing services achieving Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, minimizing surface defects that act as incubation chambers for microbes like S. sanguis.
Custom Metalization: While the paper did not require metalization, 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu for creating custom electrodes or bonding layers on diamond substrates, essential for integrated sensor development in physiological environments.

Engineering Support

The observed material failures (hydrolytic degradation, filler leaching, reduced mechanical properties) are directly addressed by the intrinsic properties of CVD diamond. 6CCVD’s in-house PhD team specializes in material selection and optimization for similar Biomedical and High-Wear projects. We can assist researchers in designing experiments to quantify the zero-sorption, zero-solubility, and enhanced wear performance of diamond relative to conventional restorative materials.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

ABSTRACT Objectives: Flowable composites are characterized by lower filler loading and a greater proportion of diluent monomers in their formulation. These composites were traditionally created by retaining the same small particle size of the conventional hybrid composites, but reducing the filler content and allowing the increased resin to reduce the viscosity of the mixture However, their various mechanical properties such as flexural strength and wear resistance have been reported to be generally inferior compared to those of the conventional composites. Dental restorative materials are in continuous contact with fluids and saliva in the patient’s mouth. Consequently, the water sorption and solubility of these materials are of considerable importance. Resin based materials demonstrate water sorption in the oral cavity, which is the amount of water absorbed by the material on the surface and into the body while the restoration is in service. The water intrusion in the dental material can lead in a deterioration of the physical/mechanical properties, decreasing the life of resin composites. Water uptake can promote breakdown causing a filler-matrix debonding. Water sorption affects the physical and mechanical properties of resin composite such as dimensional change, decrease in surface hardness and wear resistance, filler leaching, change in color stability, reduction in elastic modulus, and an increase in creep and a reduction in ultimate strength, fracture strength, fracture toughness, and flexural strength. In addition, penetration of water into the composite may cause release of unreacted monomers (solubility) which may stimulate the growth of bacteria and promote allergic reactions. The effect of water sorption on conventional composites has been extensively studied and reviewed in the dental literature. However , there are no published studies on the water sorption of flowable composites. Water sorption increases as the amount of resin matrix increases and filler content decreases, since the filler particles do not absorb water. Thus, it is of utmost importance to study the water sorption of flowable composite. Hence the aim of this study was to evaluate and compare water sorption and solubility values of different light-activated flowable composite materials in solutions with varying pH values. And, since water filled porosities in the flowable composites may form small incubation chambers, a second related objective was to compare and correlate water sorption values of the various flowables to their ability to form Streptococcus mutans and Streptococcus sanguis single species biofilms in/on their surfaces. Methods: In this study, water sorption and solubility tests were performed according to the ISO standards (International Organization for Standardization specification 4049:07-2009- Dentistry- Polymer Based Restorative Materials [available at http://www.iso.org/iso/home/store.htm]). Three disc-shaped specimens of each flowable composite were made in a jig consisting of a Teflon mold (15 mm in diameter by 1 mm in thickness) compressed between 2 glass slabs with mylar strips used as separating sheets. The flowable resin was inserted in the Teflon mold in a single increment. All specimens were cured with a light-emitting diode curing unit. According to the ISO standard, discs were weighted every day for 35 days using the same balance, with a repeatability of 0.1 mg, until a constant mass (M1) was obtained. Once a constant M1 was obtained, the volume (V) was then calculated in cubic millimeters as follow: V =π(d/2)2h, where π=3.14; d is the mean diameter of the specimen; and h is the mean thickness of the specimen. After M1 was achieved, each flowable composite resin group of 3 discs was placed into buffers of pH = 4.0,5.5 and 7.0. After 24 hrs, specimens were wiped free of excess buffer with absorbent paper and weighed. This cycle was repeated at one week , one month, and six months. When a constant mass was achieved it was designated M2. Mass gain (Mg) was defined as follows: (M2 -M1). Per cent mass gain (%Mg) was defined as follows: (M2-M1/M1). Finally, the specimens were reconditioned to constant mass, once again following the above-mentioned procedure. This constant mass was recorded as M3. Water sorption (Wsp) was calculated in micrograms per cubic millimeter for each of the specimens by using the following equation provided by ISO 4049 standard: Wsp=(M2-M3)/V, where M2 is the mass of the specimens in micrograms after immersion in buffer for 30 days; M3 is the reconditioned mass of the specimen, in micrograms; and V is the volume of the specimen in cubic millimeters. Water solubility (Wsl) was calculated in micrograms per cubic millimeter for each of the specimens, using the following equation, provided by ISO 4049 standard: Wsl=(M1-M3)/V, where M1 is the conditioned mass of the specimen in micrograms before immersion in buffer; M3 is the reconditioned mass of each specimen in micrograms, and V is the volume of the specimen in cubic millimeters. For biofilm experiments, flowable discs were prepared as described above. Each disc was then sectioned into three equal portions using high speed and low speed handpieces , a diamond bur, and sandpaper discs, such that the three samples of each flowable had the same mass to within 0.3 mg. The samples were sterilized by dipping in 1.2% sodium hypochlorite (Chlorox), followed by rinsing with sterile distilled water, and then conditioning to a constant mass as described above, inside a desiccator that was wiped with 1.2 % Chlorox. Biofilm experiments were conducted as follows: three equal mass specimens of each flowable composite were placed in a series of wells of a sterile culture disc. Then sterile BHI broth (2 ml) was added to each well. One well served as control and no growing bacteria were added to it. To the other specimens was added 40 μl log phase S. mutans or S. sanguis cells. The culture dishes were then placed on a rotator at 37C for six hrs. Biofilm formation was measured by staining attached cells with crystal violet, destaining with 30% acetic acid, and measuring the satin spectrophotometically. Results: The pH of the solution influenced the % mass gain, as all samples gained more mass at pH 4.0 as compared to pH 5.5 and 7.0. The flowable resin SureFill showed the least % mass gain at each pH. However, there was no statistical difference in % mass gain based on pH of storage buffer for any of the flowable composites (P=.05) . Time had a significant influence on the % mass gain for the first week for all samples, with minor gains thereafter, and became steady after 1 month. Surefill showed the least water sorption when stored in buffer for 30 days, however it was not significant compared to the other flowables (P= 0.05). Filtek showed the least water solubility, but is not significant compared to the other flowables (P=0.05). The highest significant values (P&lt; 0.05) for water sorption and solubility were observed for Virtuoso. Two trials indicated that strains of S. mutans and S. sanguis form biofilm readily on the surface of the composites, with S. sanguis having a higher predilection to form biofilm on all composites (Figure 6). However, no correlation was found between water sorption and solubility values of the flowable composites and biofilm formation. Conclusions: Within the limitations of this study the following is concluded: Time and storage conditions are important to the % mass gain due to water, with all flowable composites showing more mass gain at low PH. Due to its hydrophilic nature, as well as to the filler characteristics, the flowable composite Virtuoso exhibited significantly higher values of water sorption and water solubility than the other flowable composites that were tested. All flowable composites formed S. sanguis and S. mutans single species biofilm on their surfaces, with S. sanguis forming higher concentrations of biofilm on all samples. There was no clear correlation to water sorption and biofilm formation characteristics of the composites.

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Original Source

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