Abstract
Orthodontic clear aligner treatment is gaining tremendous popularity. The world market leader is Align Technology® and its product Invisalign®. Although numerous patients are treated with Invisalign® aligners, only little is known about the cellular effects of aligner material on oral epithelial cells. In the present study, we aimed to investigate the effects of SmartTrack® clear aligner material on directly cultured primary human oral keratinocytes (HOKs). Cell morphology and behavior were investigated by scanning electron microscopy and bright field microscopy. Aligner effects on viability were detected by cell-counting-kit (CCK)-8 and live/dead staining. Gene expression of several inflammatory and barrier proteins was assessed by qPCR. Cells cultured on tissue culture plastic served as control. Cell proliferation/viability was significantly lower in cells cultured on aligner material (p < 0.05) in comparison to control. Live/dead staining did not reveal an increase in the number of dead cells on aligner surfaces. After two and seven days of incubation, interleukin (IL)-6 expression decreased, and IL-8 expression increased in HOKs cultured on aligner surfaces. The expression of intercellular adhesion molecule 1 (ICAM-1) significantly decreased after seven days. Gene expression of epithelial barrier markers showed that integrin (ITG)-α6 significantly decreased after two and seven days. A significant decrease in ITG-β4 and E-cadherin expression levels compared to control could only be seen after seven days. We did not find any cytotoxic effect, but alterations in the cell’s barrier functions and inflammatory reaction were obvious. Clinical studies are required to give further insights into clinical reactions on the underlying aligner material of this quickly expanding orthodontic appliance.
Highlights
Since clear aligners are directly in contact with oral epithelial structures and no data existed on the behavior of oral cells directly grown on solid clear aligner specimens, we described in a previous in vitro study the effects of SmartTrack® material on human oral epithelial cells directly grown on the material [19]
Since epithelial defense is realized by means of the inflammatory response and mechanical barrier, we have focused on the inflammatory parameters interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, IL-8 and intercellular adhesion molecule (ICAM)-1, as well as proteins involved in barrier function integrin (ITG)-α6, ITG-β4, and E-cadherin
human oral keratinocytes (HOKs) show a lower cell density on aligner surfaces compared to tissue culture plastic (TCP) at both time points
Summary
Reinforced by the patients’ request for less visible orthodontic devices and a systematic promotion policy of aligner companies, an increased demand for clear aligner treatment took place in the last decade [1,2,3]. This led to an intensified development and application of this orthodontic treatment modality [4]. Based on increasing ranges of aligner application, orthodontists and general dentists use aligner techniques to treat orthodontic patients [7,8]
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