Effects of various beverages on characteristics of provisional restoration materials.

OBJECTIVE: To investigate the effect of common beverages on four currently used provisional restoration materials: Protemp®4, Integrity®, polymethyl methacrylate (PMMA) block, and acrylic resin. Flowable resin composite is included as a control group. MATERIALS AND METHODS: Each material was formed into disks of 10-mm diameter and 4-mm thickness (N = 40) by loading the material into acrylic molds. The exposed surface in the mold was covered using a glass slide to prevent an oxygen inhibition layer, and polymerization then proceeded. The solidified disks were placed in distilled water for 24 h. These samples (n = 8) were then immersed for 14 days in one of four different beverages: water, orange juice, cola, and coffee. Changes in color dimension, hardness, and roughness were observed and then analyzed using two-way repeated analysis of variance. RESULTS: The provisional materials had more obvious changes in all three color dimensions than the flowable resin composite. Integrity showed the biggest changes, followed by acrylic resin and PMMA block, whereas Protemp had the smallest changes. The hardness of all the materials significantly decreased after immersion in any of the beverages for 14 days. There were no changes in surface roughness when the materials were immersed in distilled water. The surface roughness of the PMMA block significantly decreased in orange juice whereas that of Integrity and acrylic resin significantly increased in cola. CONCLUSION: Different kinds of provisional materials had different degrees of staining due to their composition. Moisture had a significant influence on the hardness of materials, and the acidity of cola significantly roughened the surface of the provisional materials.

Fracture resistance of bonded ceramic overlay restorations prepared in various designs.

This study investigates fracture resistance of adhesive ceramic overlays of various designs. Forty-eight upper premolar teeth were divided into eight groups. The variations were: shoulder margins on the buccal and lingual surfaces with axial wall heights of 1, 2, or 3 mm; one shoulder margin with axial wall height of 1, 2, or 3 mm on the lingual surface and one contrabevel margin on the buccal surface; contrabevel margins on the buccal and lingual surfaces; and a control of sound teeth. Overlays were designed and fabricated with CAD/CAM using zirconia-reinforced lithium disilicate ceramic and bonded with resin cement. Samples underwent thermocycling and dynamic fatigue equivalent to 6 months of use. Compressive loading was applied until fracture, and fracture mode was analyzed. Results showed no statistical difference in fracture resistance between designs, and the fracture pattern of most was involvement of pulp tissue and below the CEJ. Fracture resistance of the restored teeth was also not statistically different from the control. All control fractures were within the dentin and above the CEJ. Overlay restorations were therefore effective in strengthening damaged teeth and imparting fracture resistance equal to sound teeth, and axial wall heights and margin types did not influence this result.

Influence of restorative material translucency on the chameleon effect.

Blending of artificial restoration materials to the natural tooth is challenging. Beyond just color, optical properties, particularly translucency, substantially influence the final appearance. The more chameleon effect that the restorative materials exhibit, the more natural looking restorations. The purpose of this study is to investigate the influence of restorative material translucency on the chameleon effect. Five types of resin composite in three different shades as well as one shade of conventional glass ionomer cement were fabricated into disks. To analyze the chameleon effect, glass ceramic blocks were milled to create four wells in each block. The restorative materials were filled into the wells. The color was measured with CIE L*a*b* every 6 months. Statistical analysis was conducted using Two-Way Repeated Measures ANOVA. The material with the highest translucency was flowable resin composite. The high translucency materials exhibited an immediate chameleon effect, as did the bulk-fill resin composites, which are low translucency. Both high and low translucency materials exhibited a delayed chameleon effect for 3 years, except for the bulk fill resin composites. The translucency of the restorative materials had a 68% positive correlation with their chameleon effect. The age of the restoration is one important factor influencing the color blending.

Effect of Prebiotics-Enhanced Probiotics on the Growth of Streptococcus mutans.

Streptococcus mutans predominantly creates an acidic environment in an oral cavity. This results in dental demineralization and carious lesions. The probiotics are beneficial microorganisms that modulate the bacterial balance in the digestive system. Prebiotics are defined as nondigestible oligosaccharides that are utilized for the selective stimulation of the beneficial microorganisms. The objective of this study was to evaluate the efficacy of the prebiotics, galactooligosaccharides (GOS) and fructooligosaccharides (FOS), for enhancing the probiotic Lactobacillus acidophilus ATCC 4356, for inhibiting Streptococcus mutans (A32-2) for the prevention of dental caries. The growth rate of the S. mutans significantly decreased when cocultured with L. acidophilus in the GOS-supplemented medium at 3%, 4%, and 5%. In the FOS-supplemented medium, the growth rate of S. mutans significantly decreased in all concentrations when cocultured with L. acidophilus. There was no significant difference in the growth rate of L. acidophilus in all concentrations of either GOS or FOS. It can be concluded that the growth rate of S. mutans was significantly retarded when cocultured with L. acidophilus and the proper concentration of prebiotics. These prebiotics have potential for a clinical application to activate the function of the naturally intraoral L. acidophilus to inhibit S. mutans.

The inhibition of Caco-2 proliferation by astaxanthin from Xanthophyllomyces dendrorhous.

PURPOSE: To investigate the efficiency of natural astaxanthin that has been extracted from Xanthophyllomyces dendrorhous in inhibiting the proliferation and viability of colorectal adenocarcinoma cell line (Caco-2; colon cancer cells). METHODOLOGY: Caco-2 cells and normal human oralkeratinocytes (NOKs) were treated with different concentrations of extracted astaxanthin, ranging from 0.075 to 10 mg ml-1, for 24, 48 and 72 h. The number of cells was determined via MTS assay and the proliferating cells were investigated by bromodeoxyuridine (BrdU) assay.Results/Key findings. Of the Caco-2 cells, 30-50 % remained viable, while the NOKs showed 110-120 % survival when treated with 5 mg ml-1 astaxanthin. The Caco-2 cells showed distinct structural shrinkage when treated with the same concentration of astaxanthin. Fluorescent labelling of the DNA of the proliferative cells with BrdU showed a significant decrease in the number of the proliferative Caco-2 cells when the concentration of astaxanthin was increased to 5 mg ml-1. CONCLUSION: The natural astaxanthin from X. dendrorhous, at an appropriate concentration, is effective in terminating the viability of, or retarding the proliferative activity of, Caco-2 cells, without harmful effects on NOKs.

Surface modification for bonding between amalgam and orthodontic brackets.

OBJECTIVE: Testing of methods to enhance the shear bond strength (SBS) between orthodontic metal brackets and amalgam by sandblasting and different primers. MATERIALS AND METHODS: Three hundred samples of amalgam restorations (KerrAlloy®) were prepared in self-cured acrylic blocks, polished, and divided into two groups: nonsandblasted and sandblasted. Each group was divided into five subgroups with different primers used in surface treatment methods, with a control group of bonded brackets on human mandibular incisors. Following the surface treatments, mandibular incisor brackets (Unitek®) were bonded on the amalgam with adhesive resin (Transbond XT®). The SBS of the samples was tested. The adhesive remnant index (ARI) and failure modes were then determined under a stereo-microscope. Two-way analysis of variance, Chi-square, and Kruskal-Wallis tests were performed to calculate the correlations between and among the SBS and ARI values, the failure modes, and surface roughness results. RESULTS: There were statistically significant differences of SBS among the different adhesive primers and sandblasting methods (P < 0.05). The sandblasted amalgam with Assure Plus® showed the highest SBS (P < 0.001). Samples mainly showed an ARI score = 1 and mix-mode failure. There was a statistically significant difference of surface roughness between nonsandblasted amalgam and sandblasted amalgam (P < 0.05), but no significant differences among priming agents (P > 0.05). CONCLUSIONS: Using adhesive primers with sandblasting together effectively enhances the SBS between orthodontic metal brackets and amalgam. The two primers with the ingredient methacryloxydecyl dihydrogen phosphate (MDP) monomer, Alloy Primer® and Assure Plus®, were the most effective. Including sandblasting in the treatment is essential to achieve the bonding strength required.

The Rho-GEF Kalirin regulates bone mass and the function of osteoblasts and osteoclasts.

Bone homeostasis is maintained by the balance between bone resorption by osteoclasts and bone formation by osteoblasts. Dysregulation in the activity of the bone cells can lead to osteoporosis, a disease characterized by low bone mass and an increase in bone fragility and risk of fracture. Kalirin is a novel GTP-exchange factor protein that has been shown to play a role in cytoskeletal remodeling and dendritic spine formation in neurons. We examined Kalirin expression in skeletal tissue and found that it was expressed in osteoclasts and osteoblasts. Furthermore, micro-CT analyses of the distal femur of global Kalirin knockout (Kal-KO) mice revealed significantly reduced trabecular and cortical bone parameters in Kal-KO mice, compared to WT mice, with significantly reduced bone mass in 8, 14 and 36week-old female Kal-KO mice. Male mice also exhibited a decrease in bone parameters but not to the level seen in female mice. Histomorphometric analyses also revealed decreased bone formation rate in 14week-old female Kal-KO mice, as well as decreased osteoblast number/bone surface and increased osteoclast surface/bone surface. Consistent with our in vivo findings, the bone resorbing activity and differentiation of Kal-KO osteoclasts was increased in vitro. Although alkaline phosphatase activity by Kal-KO osteoblasts was increased in vitro, Kal-KO osteoblasts showed decreased mineralizing activity, as well as decreased secretion of OPG, which was inversely correlated with ERK activity. Taken together, our findings suggest that deletion of Kalirin directly affects osteoclast and osteoblast activity, leading to decreased OPG secretion by osteoblasts which is likely to alter the RANKL/OPG ratio and promote osteoclastogenesis. Therefore, Kalirin may play a role in paracrine and/or endocrine signaling events that control skeletal bone remodeling and the maintenance of bone mass.

Osteoblast differentiation and migration are regulated by dynamin GTPase activity.

Bone formation is controlled by osteoblasts, but the signaling proteins that control osteoblast differentiation and function are still unclear. We examined if the dynamin GTPase, which is associated with actin remodeling and migration in other cells, plays a role in osteoblast differentiation and migration. Dynamin mRNA was expressed in primary osteoblasts throughout differentiation (0-21 days). However, alkaline phosphatase (ALP) activity, a marker of osteoblast differentiation, was decreased in osteoblasts over-expressing dynamin. Conversely, ALP activity was increased following shRNA-mediated knockdown of dynamin and in osteoblasts treated with the dynamin inhibitor, dynasore. Dynasore also reduced c-fos and osterix expression, markers of early osteoblasts, suggesting a role for dynamin in pre-osteoblast to osteoblast differentiation. Since dynamin GTPase activity is regulated by tyrosine phosphorylation, we examined the mechanism of dynamin dephosphorylation in osteoblasts. Dynamin formed a protein complex with the tyrosine phosphatase PTP-PEST and inhibition of phosphatase activity increased the level of phosphorylated dynamin. Further, PTP-PEST blocked the Src-mediated increase in the phosphorylation and GTPase activity of wild-type dynamin but not the phosphorylation mutant dynY231F/Y597F. Although ALP activity was increased in osteoblasts expressing GTPase-defective dynK44A, and to a lesser extent dynY231F/Y597F, osteoblast migration was significantly inhibited by dynK44A and dynY231F/Y597F. These studies demonstrate a novel role for dynamin GTPase activity and phosphorylation in osteoblast differentiation and migration, which may be important for bone formation.

Polymersome-mediated intracellular delivery of antibiotics to treat Porphyromonas gingivalis-infected oral epithelial cells.

The gram-negative anaerobe Porphyromonas gingivalis colonizes the gingival crevice and is etiologically associated with periodontal disease that can lead to alveolar bone damage and resorption, promoting tooth loss. Although susceptible to antibiotics, P. gingivalis can evade antibiotic killing by residing within gingival keratinocytes. This provides a reservoir of organisms that may recolonize the gingival crevice once antibiotic therapy is complete. Polymersomes are nanosized amphiphilic block copolymer vesicles that can encapsulate drugs. Cells internalize polymersomes by endocytosis into early endosomes, where they are disassembled by the low pH, causing intracellular release of their drug load. In this study, polymersomes were used as vehicles to deliver antibiotics in an attempt to kill intracellular P. gingivalis within monolayers of keratinocytes and organotypic oral mucosal models. Polymersome-encapsulated metronidazole or doxycycline, free metronidazole, or doxycycline, or polymersomes alone as controls, were used, and the number of surviving intracellular P. gingivalis was quantified after host cell lysis. Polymersome-encapsulated metronidazole or doxycycline significantly (P<0.05) reduced the number of intracellular P. gingivalis in both monolayer and organotypic cultures compared to free antibiotic or polymersome alone controls. Polymersomes are effective delivery vehicles for antibiotics that do not normally gain entry to host cells. This approach could be used to treat recurrent periodontitis or other diseases caused by intracellular-dwelling organisms.