A Study on the Photopolymerization Kinetics of Selected Dental Resins Using Fourier Infrared Spectroscopy (FTIR)

At a Glance

Metadata	Details
Publication Date	2022-08-25
Journal	Materials
Authors	Mirosław Kwaśny, Jakub Polkowski, Aneta Bombalska
Institutions	Military University of Technology in Warsaw
Citations	10
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Materials for Advanced Spectroscopic Research

Executive Summary

This document analyzes the research on photopolymerization kinetics in dental resins, highlighting the critical role of high-performance diamond materials in advanced spectroscopic analysis, specifically Attenuated Total Reflection (ATR) FTIR.

Core Value Proposition: The study successfully performed a comparative analysis of the Degree of Conversion (DC) kinetics for eleven dental resins under varying irradiation conditions (power density, exposure time, thickness).
Methodology Reliance on Diamond: Real-time and long-term kinetic measurements (up to 7 days) were enabled by the use of a diamond crystal window in the ATR-FTIR setup, leveraging diamond’s chemical inertness and optical properties.
Key Kinetic Finding: Polymerization occurs in three stages: a rapid initial phase (70-75% DC achieved within 5 s post-irradiation), a moderate phase (15-20% DC increase over 15-20 min), and a very slow residual phase (5-10% DC increase over 5 days).
Technical Advancement: A highly reliable DC calculation method was validated, focusing solely on the monomer absorption band at 1638 cm^-1, thereby eliminating systematic errors associated with traditional, unstable reference bands (e.g., 1608 cm^-1).
Optimal Parameters: Optimal clinical conditions were identified as 400 or 1000 mW/cm² power density, 10 s exposure time, and a maximum layer thickness of 2 mm.
6CCVD Relevance: Replication and extension of this high-precision spectroscopic work require ultra-high purity, custom-polished Single Crystal Diamond (SCD) or Polycrystalline Diamond (PCD) windows, a core offering of 6CCVD.

Technical Specifications

The following hard data points were extracted from the research paper detailing the experimental parameters and results:

Parameter	Value	Unit	Context
Maximum DC Range (General)	45-60	%	Achieved by the majority of final materials
Maximum DC Range (Estelite)	82-83	%	Highest observed DC value
Initial Rapid DC Achievement	70-75	%	Achieved 5 s after irradiation completion
Residual Polymerization Duration	5	days	Time until DC changes practically cease
Optimal Irradiance (P)	400 or 1000	mW/cm²	Optimal for most tested materials
Optimal Exposure Time (t)	10	s	Standard dental practice
Maximum Layer Thickness (d)	2	mm	For negligible thickness effect on DC
Monomer Absorption Band	1638	cm^-1	C=C stretching vibration (Vinyl Group)
ATR IR Penetration Depth	Several	µm	Depth of measurement in reflection mode
FTIR Spectral Range	1200-1800	cm^-1	Range used for absorbance measurements
FTIR Resolution	4	cm^-1	Spectral measurement setting

Key Methodologies

The study employed precise spectroscopic techniques and controlled irradiation parameters to analyze polymerization kinetics:

Dual Measurement Modes: DC was measured using FTIR in both Transmission mode (samples between KBr crystals, 0.2 mm thickness) and Reflection mode (ATR).
Diamond ATR Interface: The ATR reflection adapter utilized a diamond crystal window to interface with the resin sample. This setup allowed for direct measurement of the polymerization kinetics at the resin surface, crucial for simulating real dental conditions.
Irradiation Control: A blue light LED source was used, offering precise control over power density (400, 1000, and 1600 mW/cm²) and exposure time (10, 20, and 40 s).
Kinetic Monitoring: DC was tracked over extended periods, from 0 s immediately after irradiation up to 7 days, revealing the slow, long-term residual polymerization process.
Reliable DC Calculation: The DC was calculated based on the decrease in the vinyl group C=C stretching vibration at 1638 cm^-1, utilizing a kinetic method that avoids the systematic errors inherent in using traditional, unstable reference bands (e.g., 1608 cm^-1).

6CCVD Solutions & Capabilities

The high-precision FTIR-ATR methodology described in this research relies fundamentally on the unique properties of diamond—specifically its broad optical transparency, extreme hardness, and chemical inertness—to withstand contact with reactive methacrylate monomers over long measurement periods.

6CCVD is uniquely positioned to supply the advanced diamond materials necessary to replicate, scale, and extend this type of high-fidelity spectroscopic research.

Applicable Materials

Research Requirement	6CCVD Material Recommendation	Rationale
High-Purity ATR Window	Optical Grade Single Crystal Diamond (SCD)	SCD offers the highest purity and lowest defect density, ensuring maximum IR transmission and minimal scattering. This is critical for the low absorbance measurements (0.02-0.07) observed in ATR mode, maximizing the signal-to-noise ratio.
Robust, Large-Area Windows	High-Quality Polycrystalline Diamond (PCD)	For custom ATR modules or larger experimental setups, 6CCVD provides PCD plates up to 125 mm, offering exceptional mechanical strength and thermal stability.
Advanced Sensing/Electrodes	Boron-Doped Diamond (BDD)	For future studies integrating electrochemical analysis or high-power density thermal management alongside FTIR, BDD offers a conductive, chemically stable platform.

Customization Potential

The precision of the ATR measurement depends entirely on the quality and geometry of the diamond crystal. 6CCVD offers full customization to meet the exacting standards of spectroscopic research:

Custom Dimensions: We supply diamond plates and wafers in custom sizes, including inch-size PCD wafers and SCD plates, necessary for integration into specialized FTIR modules.
Ultra-Polishing: 6CCVD guarantees surface roughness (Ra) of < 1 nm for SCD and < 5 nm for inch-size PCD. This ultra-smooth finish is essential for ensuring perfect, consistent optical contact between the resin sample and the ATR crystal throughout multi-day kinetic tests.
Thickness Control: We provide SCD and PCD materials with precise thickness control, ranging from 0.1 µm up to 500 µm for windows, and substrates up to 10 mm.
Metalization Services: If the ATR crystal requires specific mounting or integrated thermal control, 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu).

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing diamond properties for demanding optical and sensing applications. We offer consultation services to assist researchers in selecting the ideal diamond grade, thickness, and surface finish required for similar photopolymerization kinetics or advanced dental material projects.

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

View Original Abstract

The aim of the presented study was a comparative analysis of the polymerization kinetics of dental resin-based composites currently used in dentistry in different environmental conditions (irradiance, activation time, layer thickness). The photopolymerization kinetics of eleven dental resins were investigated using a Woodpecker LED source. The DC was measured by FTIR in transmission mode and attenuated total reflection (ATR) from 5 s to 7 days. In the transmission mode, the spectra from parallel optical layers (about 0.2 mm thick) of samples placed between the KBr crystals were recorded. In the reflection mode, an ATR attachment with a diamond window was used. The DC calculation method was applied based on the application of a monomer absorption band at 1638 cm−1 (stretching vibration double bond C=C of the vinyl group) without using a reference band. The data were analyzed by performing an ANOVA test comparison between sample groups at the significance level α = 0.05. For all tested materials, the polymerization kinetics consist of three stages. The fastest stage occurs during the irradiation, and the achieved DC value is 70-75% of the maximum value 5 s after the irradiation. Another 15-20% DC increase at a moderate speed takes about 15-20 min. There is also a very slow further increase in DC of 5-10% within 5 days after irradiation. For 8 out of the 11 tested fillings, the optimal photopolymerization conditions are as follows: a power density of 400 or 1000 mW/cm2; an exposure time of 10 s; and a thickness of the irradiated resin layer of up to 2 mm. The influence of various conditions and factors on the reaction kinetics is dominant only in the early, rapid phase of the conversion. After longer times, the DC values gradually level out under different light conditions. The DC of the dental resins are dependent on the irradiance, light source, filler type, time after irradiance, and monomer thickness.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15175850

References

2011 - Resin composite restorative materials [Crossref]
2012 - In vitro comparison of mechanical properties and degree of cure of bulk fill composites [Crossref]
2013 - Progress in dimethacrylate-based dental composite technology and curing efficiency [Crossref]
2015 - Influence of irradiation time on subsurface degree of conversion and microhardness of high-viscosity bulk-fill resin composites [Crossref]
2015 - Pre-heating of high-viscosity bulk-fill resin composites: Effects on shrinkage force and monomer conversion [Crossref]
1997 - Resin composites in dentistry: The monomer systems [Crossref]
2011 - State-of-the-art: Dental photocuring—A review [Crossref]
2011 - Resin composite—State of the art [Crossref]