Strontium Effects on Human Gingival Fibroblasts
Strontium is a naturally occurring alkaline earth metal that has been shown to be useful not only in the treatment and prevention of osteoporosis but also in the treatment of dentinal hypersensitivity in the oral cavity; strontium is also an effective cariostatic, antiplaque, antigingivitis agent. Relatively little is known, however, about the effects of strontium on gingival fibroblasts. The purpose of the present investigation was to conduct in vitro studies on the potential for strontium to positively affect the activity of these cells such that it might be effective in the enhancement of gingival attachment to surfaces, such as healing abutments in implants in the oral cavity. The results indicate that strontium added as strontium citrate (0.5–1.0 mM), both in the absence and presence of a healing abutment, increases human gingival cell activity and decreases apoptosis in these cells. Scanning electron microscopy studies also reveal that the addition of strontium increases attachment of gingival fibroblasts to the surfaces of healing abutments. These studies provide the basis for further investigations on the use of strontium in the prevention and treatment of peri-implantitis by maximizing the formation of a peri-implant soft-tissue barrier.
Strontium can increase human gingival fibroblast (HGF) activity: tetrazolium salt sodium 3I-[1- phenylamino-carbonyl-3,4-tetrazolium]-bis (4-methoxy-6-nitro) benzene sulfonic acid hydrate) (MTT) assay. (a) HGF cells were seeded in HGF media containing strontium concentrations of 0.5–0.0075 mM or no added strontium for the controls. Results shown represent mean/culture well ± SEM (n = 3). *Significantly higher activity in the 0.5 mM strontium (STR) group compared with controls. There were no significant differences in the metabolic activities between the other groups. Analysis of variance: degrees of freedom (df) (4 between groups; 10 within groups); F = 10.50; P < .001; Tukey HSD post hoc = 0.5mM STR group compared with control; P < .004. (b) HGF cells were seeded in medium without added STR (control) and with 1 mM STR added (STR group). Results shown represent mean/culture well ± SEM (n = 3). *Significantly higher cell MTT activity in 1 mM STR group compared with controls. Student t-test: t = 4.242; df = 2; P < .023. (c) HGF cells were seeded with the healing abutment in medium alone and with 1 mM STR. Results shown represent mean/culture well ± SEM (n = 7). *Significantly higher cell activity in the HGF media with 1 mM STR compared with the control. Student t-test: t = 1.342; df = 6; P = .045.
Strontium decreases apoptosis in human gingival fibroblast (HGF) cells. Apoptosis assay using APO-live GLO assay. (a) HGF cells were seeded in medium alone (control) or with added 1 mM strontium (STR group). Results represent mean/culture well ± SEM (n = 4). *Significantly higher increase in apoptotic activity in the control group compared with the 1 mM STR group. Student t-test: t = 2.353; degrees of freedom (df) = 3; P < .050. (b) HGF cells were seeded with the healing abutment in medium alone or with 1 mM STR. Results represent mean/culture well ± SEM (n = 3). *Significantly higher increase in apoptotic activity in the control group compared with the 1 mM STR group. Student t-test: t = 4.242; df = 2; P = .013.
Adenosine triphosphate assay: human gingival fibroblast (HGF) cells were seeded in the presence of a healing abutment either in medium without added strontium (STR) (control) or with 1 mM STR added. Results are mean/culture well ± SEM (n = 3). *Significantly higher adenosine triphosphate production (four-fold) in the HGF cells treated with 1 mM STR in the medium compared with the control group without added strontium. Student t-test: t = 15.037; degrees of freedom = 2; P = .000114.
Scanning electron microscopy analysis: Strontium (STR) increased human gingival fibroblast (HGF) cells on the surfaces of the healing abutment surface. HGF cells were seeded at equal concentrations in HGF media alone and with 1 mM STR for 4 days. First and second rows represent 50× magnification and third row represents 200× magnification. (a,b,c) Surface of a healing abutment with no cell incubation (negative control). (d,e,f) Surface of a healing abutment incubated with HGF cells in media alone (positive control). (g,h,i) Surface of a healing abutment with HGF cells incubated in HGF media with 1 mM STR. Images shown are representative of 4 analyzed surfaces from each experimental condition.
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