Assessing the cutting efficiency of different burs on zirconia substrate.

Cutting dental zirconia for endodontic access preparation is difficult. Therefore, this study aimed to determine cutting efficiency of various burs when cutting this material. An air turbine handpiece was used in a customised test rig to cut sintered zirconia specimens, using a conventional blue band diamond, two different zirconia-cutting diamond and a zirconia-cutting tungsten carbide bur. Position and speed of the bur were continuously determined using wireless data acquisition over two successive five-minute runs. Differences in cutting efficiency were statistically analysed. Burs were examined using light and scanning electron microscopy (SEM). All diamond burs cut zirconia more efficiently than the tungsten carbide bur. Overall, all burs showed decreasing cutting efficiency over time. SEM images showed discernible wear and damage to the cutting portion of each bur head. It is concluded that zirconia-cutting burs are advantageous regarding durability, and carbide burs are rather ineffective against carbide substrate.

PEDF promotes self-renewal of limbal stem cell and accelerates corneal epithelial wound healing.

Limbal epithelial stem cell (LSC) transplantation is a prevalent therapeutic method for patients with LSC deficiency. The maintenance of stem cell characteristics in the process of culture expansion is critical for the success of ocular surface reconstruction. Pigment epithelial-derived factor (PEDF) increased the numbers of holoclone in LSC monolayer culture and preserved the stemness of LSC in suspension culture by evidence of ΔNp63α, Bmi-1, and ABCG2 expression. BrdU pulse-labeling assay also demonstrated that PEDF stimulated LSCs proliferation. In air-lift culture of limbal equivalent, PEDF was capable of increasing the numbers of ΔNp63α-positive cells. The mitogenic effect of PEDF was found to be mediated by the phosphorylations of p38 MAPK and STAT3 in LSCs. Synthetic 44-mer PEDF (residues 78-121) was as effective as the full length PEDF in LSC expansion in suspension culture and limbal equivalent formation, as well as the activation of p38 MAPK and STAT3. In mice subjecting to mechanical removal of cornea epithelium, 44-mer PEDF facilitated corneal wound healing. Microscopically, 44-mer PEDF advanced the early proliferative response in limbus, increased the proliferation of ΔNp63α-positive cells both in limbus and in epithelial healing front, and assisted the repopulation of limbus in the late phase of wound healing. In conclusion, the capability of expanding LSC in cell culture and in animal indicates the potential of PEDF and its fragment (e.g., 44-mer PEDF) in ameliorating limbal stem cell deficiency; and their uses as therapeutics for treating corneal wound.