Evaluation of resin infiltration for inhibiting initial caries progression: An in vitro study using Micro-Computed Tomographic analysis.

Objective: To evaluate the changes in lesion depth and mineral density of resin infiltration-treated white spot lesions against a simulated oral environment using thermal and acidic challenges in vitro. Materials and methods: Two enamel slabs were prepared from each buccal surface of permanent human premolars, for a total of 56 slabs. Artificial white spot lesions were induced. One specimen was treated with resin infiltration, while the other was used as an untreated control. A micro-CT was used to assess the lesion depth and mineral density of each specimen. Subsequently, all specimens were subjected to 10,000 cycles of thermocycling and pH cycling for 10 days before being re-evaluated using the micro-CT. Lesion depth and mineral density were examined and compared between before and after aging procedures within each group by the paired sample t-test. The independent samples t-test was utilized to compare lesion depth progression and percentage change of mineral density between groups. Results: After aging, there was both a significant lesion depth progression and a mineral loss in the control and resin infiltration groups. Mean lesion depth progression was 132.88 ± 4.18 µm for the control group and 52.31 ± 4.16 µm for resin infiltration group. Percentage mineral density loss as a percentage for the control and resin infiltration groups were 16.1 ± 0.64 % and 8.83 ± 0.30 %, respectively. The resin infiltration group demonstrated a significantly lower mean lesion depth progression and percentage changes in mineral loss compared to the control group. Conclusions: The lesion depth and mineral density changes in the resin infiltrated-treated group were lower than untreated white spot lesions after aging procedures using thermal and acidic challenges. Clinical significance: Resin infiltration is a promising approach to inhibit the progression of white spot lesions related to the initial stage of dental caries.

Finite Element Analysis of the Mechanical Performance of Non-Restorable Crownless Primary Molars Restored with Intracoronal Core-Supported Crowns: A Proposed Treatment Alternative to Extraction for Severe Early Childhood Caries.

Early childhood caries (ECC) involve extensive coronal tooth structure loss, and tooth reconstruction remains highly challenging. To fulfill preclinical assessment, the present study investigated the biomechanics of non-restorable crownless primary molars that were restored by stainless steel crowns (SSC) using different composite core build-up materials. Computer-aided design-integrated 3D finite element and modified Goodman fatigue analyses were performed to determine stress distribution, risk of failure, fatigue life and dentine-material interfacial strength for the restored crownless primary molars. A dual-cured resin composite (MultiCore Flow), a light-cured bulk-fill resin composite (Filtek Bulk Fill posterior), a resin-modified glass-ionomer cement (Fuji II LC) and a nano-filled resin-modified glass-ionomer cement (NRMGIC; Ketac N100) were used as core build-up composite materials in the simulated models. The finite element analysis showed that types of core build-up materials affected the maximum von Mises stress only in the core materials (p-value = 0.0339). NRMGIC demonstrated the lowest von Mises stresses and revealed the highest minimum safety factor. The weakest sites were along the central grooves regardless of type of material, and the ratio of shear bond strength to maximum shear stress at the core-dentine interface of the NRMGIC group was lowest among the tested composite cores. However, all groups provided lifetime longevity from the fatigue analysis. In conclusion, core build-up materials differentially influenced the von Mises stress (magnitude and distribution) and the safety factor in crownless primary molars restored with core-supported SSC. However, all materials and the remaining dentine of crownless primary molars provided lifetime longevity. The reconstruction by core-supported SSC, as an alternative to tooth extraction, may successfully restore non-restorable crownless primary molars without unfavorable failures throughout their lifespan. Further clinical studies are required to evaluate the clinical performance and suitability of this proposed method.

Primer application technique and remaining dentin thickness affected microtensile bond strength of contemporary dentin adhesives under simulated pulp pressure.

OBJECTIVES: To evaluate the effect of application techniques, type of adhesives and remaining dentin thicknesses on microtensile bond strength (µTBS) of 3 adhesive systems. MATERIALS AND METHODS: 112 flat occlusal dentinal surfaces of third molar were randomly allocated into 16 groups based on 2 remaining dentin thicknesses (RDT), 2 application techniques, and 3 adhesive systems (Optibond FL, OFL; Clearfil SE Bond, CSE; and Single Bond Universal, SB); SB was applied in either etch-and-rinse (ER) or self-etch (SE) mode. Simulated pulpal pressure was performed during restorative procedure and water storage. The stick-shaped specimens from each tooth underwent µTBS testing. The data were evaluated using a paired t test and ANOVA followed by a post hoc test. The fractured specimens were evaluated for mode of failure using a stereomicroscope. RESULTS: The mean µTBS values were significantly affected by RDT, application technique, and types of adhesives. Neither RDT nor application technique affected µTBS of SB in ER mode, whereas application technique affected both conventional and universal self-etch adhesives. RDT also influenced µTBS of OFL. CONCLUSIONS: RDT and application technique differently affected the µTBS of dentin bonding which was product-related. Etch-and-rinse systems had higher bond strength to superficial than to deep dentin, whereas self-etch systems were more sensitive to both RDT and application technique. CLINICAL RELEVANCE: The universal adhesive is less sensitive to intrinsic wetness and can be used according to manufacturer's instructions.

Cyclic tensile force-upregulated IL6 increases MMP3 expression by human periodontal ligament cells.

OBJECTIVE: Cyclic tensile force (CTF) modulates physiological responses of periodontal ligament (PDL) cells. PDL cells are mechanosensitive and are able to maintain tissue homeostasis; a process mediated by the expression of particular cytokines including interleukin 6 (IL6). It is unknown whether CTF-induced IL6 regulates the expression of MMPs, enzymes needed for tissue remodeling. DESIGN: Human PDL cells were subjected to 10% elongation strain of CTF at a frequency of 60 rpm continuously for 6 h. RNA and proteins were extracted and analyzed for IL6 and MMP expression by quantitative real-time PCR and ELISA, respectively. Using a neutralizing anti-IL6 antibody and addition of recombinant human IL6 at concentrations of 0.1, 1, 10 ng.mL-1 were performed to clarify whether CTF-upregulated IL6 increased MMP expression. Inhibitors of intracellular signaling molecules were employed to reveal possible pathway(s) of IL6-induced MMP expression. RESULTS: CTF-induced IL6 expression coincided with an increased MMP3 expression. A neutralizing anti-IL6 antibody attenuated the CTF-increased MMP3 expression, whereas stimulating the cells with recombinant human IL6 increased MMP3 expression. Both PI3K and MAPK pathways were essential in the IL6 induced expression of MMP3. CONCLUSION: Our findings suggest a role of CTF in the modulation of expression of IL6 and MMP3 and thus in the regulation of homeostasis and remodeling of the periodontal ligament.

Cyclic tensile force stimulates BMP9 synthesis and in vitro mineralization by human periodontal ligament cells.

Periodontal ligament (PDL) cells are mechanosensitive and have the potential to differentiate into osteoblast-like cells under the influence of cyclic tensile force (CTF). CTF modulates the expression of regulatory proteins including bone morphogenetic proteins (BMPs), which are essential for the homeostasis of the periodontium. Among the BMPs, BMP9 is one of the most potent osteogenic BMPs. It is yet unknown whether CTF affects the expression of BMP9 and mineralization. Here, we demonstrated that continuously applied CTF for only the first 6 hr stimulated the synthesis of BMP9 and induced mineral deposition within 14 days by human PDL cells. Stimulation of BMP9 expression depended on ATP and P2Y 1 receptors. Apyrase, an ecto-ATPase, inhibited CTF-mediated ATP-induced BMP9 expression. The addition of ATP increased the expression of BMP9. Loss of function experiments using suramin (a broad-spectrum P2Y antagonist), MRS2179 (a specific P2Y 1 receptor antagonist), MRS 2365 (a specific P2Y 1 agonist), U-73122 (a phospholipase C [PLC] inhibitor), and thapsigargin (enhancer of intracytosolic calcium) revealed the participation of P2Y 1 in regulating the expression of BMP9. This was mediated by an increased level of intracellular Ca 2+ through the PLC pathway. A neutralizing anti-BMP9 antibody decreased mineral deposition, which was stimulated by CTF for almost 45% indicating a role of BMP9 in an in vitro mineralization. Collectively, our findings suggest an essential modulatory role of CTF in the homeostasis and regeneration of the periodontium.