Measurement of the strength of brittle materials, such as resin composites, is extremely difficult. Micro-indentation hardness testing is a convenient way of investigating the mechanical properties of a small volume of material. In this study, the mechanical properties of five commercially available flowable resin composites were investigated by the dynamic micro-indentation method. Additionally, the effects of inorganic-filler content on the dynamic hardness and elastic modulus of flowable composites obtained by this method were investigated. The weight percentages of the inorganic fillers in the resin composites were determined by the ashing technique. The results indicate that the mechanical properties of flowable composites are affected by not only the filler content but also the properties of the resin matrix. In conclusion, the dynamic micro-indentation method is a useful technique for determining the mechanical behavior of dental resin composites as brittle material.

We designed three experimental 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based one-step (EX) adhesives consisting of MDP, urethane dimethacrylate, and triethylene glycol dimethacrylate adhesives with different water contents (98.4, 196.8, and 294.4 mg/g), and 4-methacryloyloxyethyl trimellitic anhydride (4-META) or 2-hydroxyethyl methacrylate (HEMA)-containing onestep adhesive. The effect of the amount of MDP-calcium (MDP-Ca) salt produced through demineralization of enamel and dentin on the bonding performance was examined. The efficacy of 4-META and HEMA was then discussed. When the amount of water in EX adhesive was increased, the production amount of MDP-Ca salt of enamel increased, but not the dentin. The enamel bond strength slightly increased with increasing the production amount of MDP-Ca salt, in contrast to the dentin. However, addition of 4-META in the EX adhesive (water content=98.4 mg/g) increased both bond strengths, although the production amounts of MDP-Ca salt significantly decreased. The 4-META enhances both bond strengths more effectively than the HEMA.

Background: With transitions in the disease concept of orthokeratinized odontogenic cyst (OOC), the pathogenesis and etiology have not been sufficiently elucidated. Objectives: OOC cases were reclassified and observed to understand the clinico-histopathological characteristics. In addition, literature review of OOC was performed to better organize the pathology. Materials and methods: Subjects with jawbone cysts lined by keratinized stratified squamous epithelium from 2005 to 2018 were reclassified, and clinico-histopathological findings were analyzed. Previous reports of OOC/orthokeratinized-type odontogenic keratocyst (OKC) from 1980 to 2019 were organized. Results: Five cases of OOC were diagnosed, representing 2.1% of odontogenic developmental cysts (total, 239 cases). Mean age was 37.6 years, with a female predominance. The mandibular molar area was the frequent site, and all cysts were solitary. Sixty percent involved an impacted tooth. Mean maximum diameter of the cyst was 2.2 cm. Histopathologically, 4 cases were unilocular, and partial palisading of the basal layer and scattered epithelial islands were observed in 2 cases each and formation of daughter cysts was noted in 3 cases. Previous papers described that most were unilocular and related to impacted teeth. Mean age ranged between 20 and 40 years, and the mandibular molar region was dominant. Recurrence rates were low. Conclusion: OOC shows a different biological attitude to OKC and is closer to dentigerous cyst. Meanwhile, OOC shows a similar histology of epidermoid cysts accompanying the granular layer. We thus surmised that OCC represents an independent concept as an odontogenic developmental cyst.

Background: Silane coupling agents are used as a bonding agent between ceramics and resins in dentistry. The effectiveness of these agents is often enhanced by the addition of acid or by heat treatment. Objective: This study aimed to evaluate, the clinical characteristics, TBS (tensile bond strength) and water resistance of eight commercial ceramic primers (seven silane coupling agents and one alumina zirconia primer). Method: Glass plates were used as the adherent. The TBS of the resin composite and the wettability of the resin monomer to glass surfaces treated with ceramic primers was investigated, with 3-MPS (methacryloxypropyltrimethoxysilane) used as a control. The values obtained from the experiments were analyzed using one-way ANOVA followed by Tukey's multiple comparison tests (p < 0.05). Results: No significant differences in TBS were observed between the commercial products and MPS, except for the alumina zirconia primer. However, four products (three of the seven agents and the alumina zirconia primer) exhibited significantly lower TBS values after application of thermal stress when compared with those stored in water (p < 0.05). All but one of the eight primers displayed significantly higher contact angles between the treated glass and the resin monomer when compared with MPS (p < 0.05). These results suggest that some commercial ceramic primers may contribute to increased strength and durability.