Tokyo Medical and Dental University (TMDU) researchers developed a new cross-linker for dental cement that breaks down under UV light, making treatments easier to reverse.
Tooth Enamel Safe Adhesive
The new cross-linker is ideal for dental procedures that require non-permanent adhesion to the tooth surface, such as the fixing of orthodontic brackets. Removing adhered materials after such procedures generally requires mechanical detachment that can damage tooth enamel.
Efforts to improve removal processes have produced materials that are weakened by triggers, such as heat or electric currents. However, approved sources of these stimuli are not readily available in standard dental clinics. The researchers therefore focused on UV light-responsive materials that can be triggered by the UV sources widely used by dentists to cure resin cements and composites.
The toughness of many dental cements is a result of mixing them with a cross-linker that locks the cement molecules to each other to form a stable network. The researchers have introduced a chemical ‘switch’ into a new cross-linker that opens when UV light is shined on it.
Accessible Method for Removing Dental Adhesives
To facilitate the debonding of dental restorative materials adhered on tooth surfaces, UV light-embrittled dental resin cement containing photodegradable polyrotacane (PRX) cross-linkers was developed. PRX is a supramolecular interlocked polymer composed of α-cyclodextrin threaded on a linear polymer chain capped with bulky stopper molecules.
The photodegradable PRXs containing photolabile o-nitrobenzyl ester was newly designed and used as a cross-linker of dental resin cements. The UV irradiation cleaves o-nitrobenzyl ester and the PRXs are dissociated, leading to decreasing the adhesive force of the dental resin cements. The plastic block was adhered on to the surface of bovine dentin using adhesive resin cement cross-linked with photodegradable PRXs, and the adhesive strength between plastic and dentin was clinically acceptable value.
By contrast, the adhesive force was decreased by approximately 60 percent through the irradiation of UV light for 2 min, due to the photodegradation of PRX cross-linkers. This result suggests that the adhesive resin cement containing photodegradable PRX cross-linkers is a promising candidate for facilitating the debonding of dental materials from tooth surfaces via UV light irradiation.
“The cross-linker structure resembles rings threaded onto a piece of string with bulky stoppers at each end. We have added a section to the string—an o-nitrobenzyl ester group—that breaks under UV light causing the rings to slide off. This has a significant effect on the stability of the cement material the cross-linker is holding in place,” said study lead author Atsushi Tamura.
“We are very encouraged by the initial findings using our cross-linker. Although the UV wavelength used to disrupt the material was not clinically appropriate in this case, we intend to develop the chemistry of our internal switch so that it can provide a facile and readily accessible method of removing adhesives in the clinic,” said study corresponding author Nobuhiko Yui.
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