Background/purpose No study has previously investigated and compared whether resin coating could prevent the effect of dehydration on flexural strengths and porosities of high powder-liquid and resin-modified glass ionomer cements (HPL-GIC and RM-GIC). The purpose of this study is to investigate the effect of resin coating on flexural strengths and porosities of HPL-GIC and RM-GIC under a dry condition. Materials and methods HPL-GIC ( Equia Forte Fil ) or RM-GIC ( Fuji II LC ) was mixed and loaded into a mold to create a bar-shaped specimen, n = 12 of each. The specimens were randomly divided into two groups, coated and uncoated , n = 6 of each. In the coated group, a resin coating agent ( Equia Forte Coat ) was applied and light cured for 20 s. After 72 h, each specimen was dried and scanned to detect porosities (% volume) using micro-computed tomography. After scanning, flexural strength (MPa) of the specimen was tested using a three-point bending method. Results Porosities of HPL-GIC were significantly higher than RM-GIC, either coated or uncoated group ( p < .05 ). Flexural strengths of coated and uncoated HPL-GIC were 41.47 ± 0.89 and 15.32 ± 1.15 MPa that were significantly lower than those of RM-GIC at 104.77 ± 3.97 and 52.90 ± 2.17 MPa ( p < .05 ). Flexural strengths of coated GICs were significantly higher than uncoated GICs ( p < .05 ). Conclusion Resin coating increased flexural strengths of GICs under dry condition. HPL-GIC had higher porosities and lower flexural strength than RM- GIC.

Aim To evaluate fracture resistance and gap/void presence of root‐filled mandibular molars restored with 2 bulk‐fill and 1 conventional resin composites, with or without a glass‐ionomer cement (GIC) base. Methods Coronal access and mesio‐occlusal (MO) cavities were prepared, then root canal treatment was performed on 30 mol/L. The teeth were randomly divided, according to the cavity volume, into 6 experimental groups (N = 5) and restored with conventional/light‐cured (Ceram‐X), bulk‐fill/light‐cured (SureFil SDR) or bulk‐fill/dual‐cured (Core‐X Flow) with/without a 2‐mm thick GIC base. Gaps and voids (%) were determined using microcomputed tomography. Intact teeth and unrestored teeth were used as negative and positive controls. Fracture load (N) was determined using a universal testing machine. Results No significant difference in fracture resistance or gap/void formation was found among the 3 resin composites. GIC‐base groups revealed significantly lower fracture strength than intact teeth, while fracture strengths of no GIC‐base groups were not significantly different from intact teeth. GIC‐base groups revealed significantly more gaps and voids in the area of the GIC than the resin composite. Conclusion Conventional and bulk‐fill resin composites provided similar fracture resistance and gaps/voids in root‐filled molars with MO cavities. Placing a GIC base decreased fracture resistance and increased gap/void formation.

This study compared shaping ability between two single‐file systems and before/after using supplementary file in untouched area, volume of removed dentin, maximum cut depth (the highest cut depth by main file) and remaining thinnest dentin (the thinnest root dentin after preparation). Ribbon‐shaped distal canals of mandibular molars were prepared with non‐adaptive core (WaveOne Gold) or adaptive core (XP‐endo Shaper) files (n = 15/group) and additionally prepared with a supplementary file (XP‐endo Finisher), and the shaping ability was investigated using micro‐computed tomography. XP‐endo Shaper group demonstrated significantly less overall untouched area than WaveOne Gold group (38.21 ± 6.98% vs. 47.68 ± 9.16%) (p < 0.05). No significant difference was detected between XP‐endo Shaper and WaveOne Gold groups in volume of removed dentin (1.85 ± 0.53 vs. 1.66 ± 0.33 mm3), maximum cut depth (0.10–0.28 vs. 0.10–0.29 mm) and remaining thinnest dentin (0.66–0.80 vs. 0.78–0.88 mm). Supplementary XP‐endo Finisher treatment significantly decreased untouched area (11%–23% reduction) (p < 0.05) with minimally cut root dentin (0.01–0.02 mm).