# A one-part free radical initiator system to enable visible light-activated polymerization with post-exposure dark cure and extensive, athermal shadow cure behavior

> **NIH NIH R21** · UNIVERSITY OF COLORADO DENVER · 2020 · $187,715

## Abstract

With a majority of the more than 160 million dental restorative treatments performed in the US each year
involving the placement of resin-bonded composite materials, and the acknowledgement that a large portion of
a dentist’s time is consumed with revising and replacing these restorations, there is a clear need for materials
with improved clinical performance. The relatively short average clinical lifespan (~6 years), particularly for large
restorations, is not just inefficient and expensive, but each revision escalates to more invasive treatment. The
primary reasons for the failure rate of restorations are fracture or loss of the composite as well as secondary
caries. These problems are all potentially linked to inadequate curing during placement of the restoration since
polymer properties are correlated with degree of conversion while adhesion to the tooth and the associated
reinforcement of a compromised tooth are also dependent on the extent of cure of the composite resin. Uncured
monomer leaching from a restoration is known to promote more aggressive bacterial activity in the vicinity of a
restoration, which further underscores the need for well cured composites. It is notable that there are significant
discrepancies in the clinical service life of similar commercial composite materials, which indicates that the
reliable placement of the materials is highly technique sensitive. The goal here is to design novel photoinitiating
systems capable of delivering free radicals for reliable polymerization beyond the temporal and spatial footprint
of a visible curing light. The intended clinically relevant application is for the direct placement of dimensionally
thick, highly filled composite restorative materials in which substantial light attenuation and/or shadow
patterning is encountered. These heavy-body materials cannot be accommodated in dual-cure auto-mixing
syringes. The product of this proposal could alleviate all concern of incompletely photocured composite
restorations by development of completely new photo-activated redox polymerization initiation systems that in
one version can augment the initial cure in under-cured regions of a composite by engaging a dark curing process
that continues beyond exposure to the curing light. Our early results demonstrate limited photopolymerizations
reaching only 10% conversion during direct light exposure that can then progress to full conversion of colorless
polymer in the ensuing dark phase. Alternatively, another version of the initiator is expected to produce full
conversion following a brief activation by visible light even within regions that received no exposure from the
curing light. If successful, this demonstration project will introduce a breakthrough in photocuring that would
dramatically increase depth of cure and provide full assurance of complete conversion in dental composite and
resin cement photopolymerizations. In addition to the obvious benefits of assured full conversion and optimize...

## Key facts

- **NIH application ID:** 9903283
- **Project number:** 5R21DE028017-02
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** JEFFREY W. STANSBURY
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $187,715
- **Award type:** 5
- **Project period:** 2019-04-01 → 2022-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9903283

## Citation

> US National Institutes of Health, RePORTER application 9903283, A one-part free radical initiator system to enable visible light-activated polymerization with post-exposure dark cure and extensive, athermal shadow cure behavior (5R21DE028017-02). Retrieved via AI Analytics 2026-06-07 from https://api.ai-analytics.org/grant/nih/9903283. Licensed CC0.

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