Читать книгу Endodontic Materials in Clinical Practice - Группа авторов - Страница 41

GICs form as a result of an acid–base reaction between a weak polymeric acid and powdered glass, which is basic in nature. Curing occurs in concentrated solutions of water, and the final structure contains unreacted glass particles, which act as a filler, reinforcing the material. Resin‐modified glass ionomer cements (RMGICs) were developed to provide command set in an attempt to decrease setting time/moisture sensitivity [190]. Ostensibly, they are a hybrid of glass ionomers and resin composite.

These materials are not traditionally thought of as an option for directly interfacing with the vital pulp tissue, due to their cytotoxicity. Conventional glass ionomers tend to be less toxic than the resin‐modified formulations [191, 192]. Due to their ability to chemically bond to tooth structures, they provide an excellent bacterial seal [193] and show good biocompatibility when used in close approximation – but not direct contact – with the pulp [75].

When RMGICs were compared to calcium hydroxide in deep nonexposed cavities, a quantitative systematic review could not demonstrate superiority in terms of pulp response with either agent [194], and although histologically RMGICs showed more damage in the short term, this decreased over time, with both RMGICs and conventional GICs performing similarly [195].

Activa Bioactive base/liner (Pulpdent, Watertown, MA, USA) was launched in 2014. It has the mechanical strength, aesthetics, and physical properties of composites and the increased release and recharge of calcium, phosphate, and fluoride. Pulpdent suggests that it is a light‐cured resin‐modified calcium silicate, but this is misleading – it is much more indicative of an RMGIC [196]. The material has three setting mechanisms: glass ionomer (acid–base reaction), light composite resin, and self‐cure composite resin; however, there is a suggestion that the self‐cure reaction does not occur [197]. The bioactive properties of this material are based on a mechanism whereby changes in pH result in the release and recharge of significant amounts of calcium, phosphate, and fluoride [198]. Although this material is suggested for use in indirect and direct pulp therapies, there is insufficient evidence at this stage to support its placement directly against the pulp.

GICs are thus considered indirect pulp‐capping agents rather than as suitable for direct placement on to the pulp itself. A high‐quality randomized controlled clinical trial has shown them to be as effective as Biodentine in treating a deep carious lesion with reversible pulpitis when used in the former mode [27, 199]. Meanwhile, the European Society of Endodontology recommends either a glass ionomer or an HCSC be used as an indirect pulp‐capping agent [1].