Effect of Tack Cure on Polymerization Shrinkage of Resin-based Luting Cements.

CLINICAL RELEVANCE: Self-cure after tack cure could result in a lower polymerization shrinkage in some resin-based luting cements, which is closely related to lower degree of cure.

Effects of a novel light-curable material on odontoblastic differentiation of human dental pulp cells.

AIM: To assess the biological effects, including odontoblastic differentiation of a novel light-curable material (TheraCal), on human dental pulp cells (hDPCs). METHODOLOGY: The hDPCs were isolated from freshly extracted, caries-free third molars. Ten discs of TheraCal and MTA (8 mm in diameter and 3 mm in height) were incubated in α-minimum essential medium (α-MEM) and the supernatant collected. Viability of hDPCs in response to TheraCal and MTA was measured using the WST-1 assay. RT-PCR and real-time PCR were used to detect the gene expression of dentine sialophosphoprotein (DSPP) and dentine matrix protein-1 (DMP-1). ALP staining and Alizarin red S staining were used to evaluate the expression of alkaline phosphatase (ALP) and mineralization behaviour. One-way analysis of variance and Tukey's post hoc test were used to determine the statistically significant differences as a result of the variation in test materials (P < 0.05). RESULTS: The effects of TheraCal and MTA on cell viability were similar except at the highest concentration. The mRNA level of DSPP increased significantly in the MTA group relative to the control at day 1 and 3 (P < 0.05). Also, the mRNA level of DSPP increased significantly in the TheraCal group relative to the control at day 3 (P < 0.05). The increased mRNA level of DMP-1 was 2.5-fold and 2.3-fold each in the MTA and TheraCal groups relative to the control (P < 0.05). Cells exposed to MTA exhibited a 1.4-fold increase of ALP staining relative to control (P < 0.05). In the mineralization assay, increased calcium nodule formation was twofold and 1.3-fold each in the MTA and TheraCal groups compared to the control (P < 0.05). CONCLUSIONS: TheraCal and MTA had the ability to induce odontoblastic differentiation and mineralization of hDPCs.

Polymerization shrinkage and depth of cure of bulk-fill resin composites and highly filled flowable resin.

The aim of this study was to evaluate the polymerization behavior and depth of cure (DOC) of recently introduced resin composites for posterior use: highly filled flowable composite and composites for bulk fill. A highly filled flowable (G-aenial Universal Flo [GUF]), two bulk-fill flowables (Surefil SDR Flow [SDR] and Venus Bulk fill [VBF]), and a bulk-fill nonflowable composite (Tetric N-Ceram Bulk fill [TBF]) were compared with two conventional composites (Tetric Flow [TF], Filtek Supreme Ultra [FS]). Linear polymerization shrinkage and polymerization shrinkage stress were each measured with custom-made devices. To evaluate DOC, the composite specimen was prepared using a mold with a hole of 4 mm depth and 4 mm internal diameter. The hole was bulk filled with each of the six composites and light cured for 20 seconds, followed by 24 hours of water storage. The surface hardness was measured on the top and the bottom using a Vickers microhardness (HV) indenter. The linear polymerization shrinkage of the composite specimens after photo-initiation decreased in the following order: TF and GUF > VBF > SDR > FS and TBF (p<0.05). The polymerization shrinkage stress of the six composite groups decreased in the following order: GUF > TF and VBF > SDR > FS and TBF (p<0.05). The mean bottom surface HV of SDR and VBF exceeded 80% of the top surface HV (HV-80%). However, the bottom of GUF and TBF failed to reach HV-80%. A highly filled flowable (GUF) revealed limitations in polymerization shrinkage and DOC. Bulk-fill flowables (SDR and VBF) were properly cured in 4-mm bulk, but they shrank more than the conventional nonflowable composite. A bulk-fill nonflowable (TBF) showed comparable shrinkage to the conventional nonflowable composite, but it was not sufficiently cured in the 4-mm bulk.