Oral epithelial cell reaction after exposure to Invisalign plastic material

doi:10.1016/j.ajodo.2013.09.011

American Journal of Orthodontics and Dentofacial Orthopedics

Volume 145, Issue 1, January 2014, Pages 64-71

https://doi.org/10.1016/j.ajodo.2013.09.011 Get rights and content

Introduction

Invisalign plastic aligners (Align Technology, Santa Clara, Calif) are used to correct malocclusions. The aligners wrap around the teeth and are in contact with gingival epithelium during treatment. The purpose of this study was to evaluate the cellular responses of oral epithelium exposed to Invisalign plastic in vitro.

Methods

Oral epithelial cells were exposed to eluate obtained by soaking Invisalign plastic in either saline solution or artificial saliva for 2, 4, and 8 weeks. Cells grown in media containing saline solution or saliva served as controls. Morphologic changes were assessed by light microscopy. The 3-[4, 5-dimethythiazol- 2-yl]-2, 5-diphenyl tetrazolium bromide assay and flow cytometry were used to determine cell viability and membrane integrity, respectively. Cellular adhesion and micromotion of epithelial cells were measured in real time by electrical cell-substrate impedance sensing.

Results

Cells exposed to saline-solution eluate appeared rounded, were lifted from the culture plates, and demonstrated significantly increased metabolic inactivity or cell death (P <0.05). Saliva eluates did not induce significant changes in cell viability compared with untreated cells. Flow cytometry and electric cell-substrate impedance sensing showed that cells treated with saline-solution eluate exhibited compromised membrane integrity, and reduced cell-to-cell contact and mobility when compared with saliva-eluate treatment.

Conclusions

Exposure to Invisalign plastic caused changes in viability, membrane permeability, and adhesion of epithelial cells in a saline-solution environment. Microleakage and hapten formation secondary to compromised epithelial integrity might lead to isocyanate allergy, which could be systemic or localized to gingiva. However, these results suggest that saliva might offer protection.

Section snippets

Material and methods

The human keratinocyte N/ TERT-1 cell line was used in this study. Cells were maintained according to the protocol provided by the James Rheinwald Laboratory, Harvard Skin Disease Research Center (Boston, Mass), where the cell line was purchased. An immortalized cell line was chosen for this study because primary keratinocyte cell lines have limited replicative life spans in culture. Also, it has been reported that this immortalized human keratinocyte cell line initiates the program of

Results

When viewed under a light microscope, keratinocytes treated with saline-solution eluate exhibited rounding and were detached from one another, compared with the untreated cells (Fig 2). Interestingly, cells treated with saliva eluate behaved like the control cells.

Colorimetric MTT assay was used to estimate the number of active and viable cells. The results indicated that cells exposed to 1:1 and 1:3 dilutions of 8-week saline-solution eluate had significantly reduced optical density compared

Discussion

Invisalign plastic is polyurethane, a product of 4,4′-methylene diphenyl diisocyanate and 1,6-hexanedial precursors.¹⁴ When isocyanates come into contact with tissues, they rapidly bind to proteins and other biomacromolecules.15, 16, 17 This reaction forms immunogenic haptens that can lead to sensitization in humans. Relatively few studies have reported dermal uptake of isocyanates and consequent toxicity,17, 18, 19 although contact allergic reactions to isocyanate exposure have been reported.20

Conclusions

This is the first study to report the effect of contact with Invisalign plastic on oral keratinocytes. Unwanted effects were demonstrated when epithelial cells were treated with eluates obtained from soaking Invisalign plastic in saline solution. However, when exposed to artificial saliva, the cells behaved normally or even showed increased cell-to-cell contact. Saliva might play an important role in maintaining epithelial cell integrity. Keeping in mind that it is difficult to simply equate

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: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported.

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Original articleOral epithelial cell reaction after exposure to Invisalign plastic material

Introduction

Methods

Results

Conclusions

Section snippets

Material and methods

Results

Discussion

Conclusions

Am J Orthod Dentofacial Orthop

Exp Cell Res

Biophys J

Biosens Bioelectron

Toxicol Appl Pharmacol

Orthodontic Waves

Chem Biol Interact

Toxicol Lett

J Prosthet Dent

Brain Res

Chest

Dermal and inhalation exposure to methylene bisphenyl isocyanate (MDI) in iron foundry workers

Ann Occup Hyg

Identification of human lung and skin proteins conjugated with hexamethylene diisocyanate in vitro and in vivo

Am J Respir Crit Care Med

Original article
Oral epithelial cell reaction after exposure to Invisalign plastic material