Attachment and Osteogenic Potential of Dental Pulp Stem Cells on Non-Thermal Plasma and UV Light Treated Titanium, Zirconia and Modified PEEK Surfaces

Abstract

Ultraviolet (UV) light and non-thermal plasma (NTP) treatment are chairside methods that can efficiently improve the biological aging of implant material surfaces caused by customary storage. However, the behaviors of stem cells on these treated surfaces of the implant are still unclear. This study aimed to investigate the effects of UV light and NTP treated surfaces of titanium, zirconia and modified polyetheretherketone (PEEK, BioHPP) on the attachment and osteogenic potential of human dental pulp stem cells (DPSCs) in vitro. Machined disks were treated using UV light and argon or oxygen NTP for 12 min each. Untreated disks were set as controls. DPSCs were cultured from the wisdom teeth of adults that gave informed consent. After 24 h of incubation, the attachment and viability of cells on surfaces were assessed. Cells were further osteogenically induced, alkaline phosphatase (ALP) activity was detected via a p-Nitrophenyl phosphate assay (day 14 and 21) and mineralization degree was measured using a Calcium Assay kit (day 21). UV light and NTP treated titanium, zirconia and BioHPP surfaces improved the early attachment and viability of DPSCs. ALP activity and mineralization degree of osteoinductive DPSCs were significantly increased on UV light and NTP treated surfaces of titanium, zirconia and also oxygen plasma treated Bio-HPP (p < 0.05). In conclusion, UV light and NTP treatments may improve the attachment of DPSCs on titanium, zirconia and BioHPP surfaces. Osteogenic differentiation of DPSCs can be enhanced on UV light and NTP treated surfaces of titanium and zirconia, as well as on oxygen plasma treated Bio-HPP.

Keywords: dental pulp stem cells; modified polyetheretherketone; non-thermal plasma; osteogenesis; titanium; ultraviolet light; zirconia.

Figure 1

Cell attachment and morphology on different surface treated titanium, zirconia and BioHPP after 24 h. Representative examples of cytoskeletons stained with phalloidin after 24 h of incubation on controls (A,E,I), UV light treated (B,F,J), oxygen plasma treated (C,G,K) and argon plasma treated (D,H,L) surfaces of titanium, zirconia and BioHPP using confocal microscopy with 60-fold objective lens. The actin cytoskeleton was marked phalloidin (green color) and the nucleus by DAPI (blue color). Compared to control groups, cells were more extended and flattened with a more widely spread cytoskeleton possessing elongated cytoplasmic extensions on UV light, oxygen and argon plasma treated surfaces.

Figure 2

Cell attachment and morphology of osteoinductive DPSCs on different surface treated titanium, zirconia and BioHPP after 21 days. The attachment of osteoinductive cells at 21 days of culture was observed using fluorescence microscopy (20×). Adhesion of cells was weak and cells were loosely distributed on untreated surfaces of titanium, zirconia and BioHPP (A,E,I). Either UV light or NTP treatment resulted in stronger cell adhesion and dense distribution (B–D,F–H,J–L), whereas argon plasma treatment led only to sparse cell adhesion (D,H,L).

Figure 3

Viability of DPSCs on different surface treated titanium, zirconia and BioHPP after 24 h. Viability of DPSCs on controls and surface treated titanium, zirconia and BioHPP disks after 48 h of incubation was shown. Compared to controls, the viability of DPSCs on UV light, oxygen and argon plasma treated surfaces of titanium, zirconia and BioHPP was significantly increased (p < 0.05). There were no significant differences between the treatments. * p < 0.05.

Figure 4

ALP activity of osteoinductive DPSCs on different surface treated titanium, zirconia and BioHPP after 14 and 21 days. ALP activity was increased in general after UV light and NTP treatment compared to control groups. The increase in ALP between the experimental groups and their corresponding control group was statistically significant except for the argon treated surface of titanium at 14 days and BioHPP at 21 days. * p < 0.05.

Figure 5

Mineralization of osteoinductive DPSCs on different surface treated titanium, zirconia and BioHPP after 21 days. Although any surface treatment led to increased mineralization on titanium, zirconia and BioHPP disks, differences were only significant after UV light and oxygen treatment on all three types of materials and argon treatment on zirconia (p < 0.05). * p < 0.05.