Cytotoxicity and degree of conversion of orthodontic adhesives.
OBJECTIVE
To test the hypothesis that there is no difference in the cytotoxicity related to the modes of polymerization of five commercially available orthodontic bonding resins, with and without an oxygen-inhibited layer (OIL), and to evaluate the degree of conversion (DC) of these resins and correlate this to cytotoxicity.


METHODS
Five commercially available orthodontic bonding resins were tested for cytotoxicity and DC. Thirty-six disks of standardized dimensions, for each resin, were used for cytotoxicity assessment. Half of them were washed with 99% acetone to remove the OIL (washed resins), and the remaining disks were left intact (intact resins). Glass disks were used as a control. Vero cells were exposed to intact and washed resins on day 1. Cell viability was determined by tetrazolium bromide reduction assay 1, 3, and 6 days after exposure. The DC of the adhesive specimens of each resin, prepared with a procedure identical to the clinical bonding process, was assessed by Fourier transform infrared spectroscopy.


RESULTS
Single-cured systems were comparatively less cytotoxic than dual-cured systems. With removal of the OIL, increased cell viability was noted only with two resins on all three days. Resins tested showed differences in DC. A positive correlation was demonstrated by two resins.


CONCLUSIONS
The hypothesis is rejected. Single-cured systems are superior to dual-cured systems in exhibiting comparatively less toxicity and higher DC. A significant positive correlation was not established between cytotoxicity and DC.
Department of Orthodontics and Dentofacial Orthopedics, Sri Ramachandra Dental College & Hospital, Sri Ramachandra University, Chennai, Tamil Nadu, India.
Nithya
N
Jagdish
Sridevi
S
Padmanabhan
Arun B
AB
Chitharanjan
J
J
Revathi
Gunasekaran
G
Palani
Mohana
M
Sambasivam
Khaleefathullah
K
Sheriff
K
K
Saravanamurali
D000096:Acetone / Q000737:chemistry; D000180:Acrylic Resins / Q000737:chemistry / Q000633:toxicity; D000538:Aluminum Silicates / Q000737:chemistry / Q000633:toxicity; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002522:Chlorocebus aethiops; D004396:Coloring Agents; D005899:Glass Ionomer Cements / Q000737:chemistry / Q000633:toxicity; D008422:Materials Testing; D009967:Orthodontic Appliances; D010100:Oxygen / Q000737:chemistry; D011108:Polymers / Q000737:chemistry / Q000633:toxicity; D019279:Resin Cements / Q000737:chemistry / Q000633:toxicity*; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013778:Tetrazolium Salts; D013844:Thiazoles; D013997:Time Factors; D014709:Vero Cells
D000180:Acrylic Resins; D000538:Aluminum Silicates; D004396:Coloring Agents; C095451:Fuji Ortho LC; D005899:Glass Ionomer Cements; D011108:Polymers; C090340:Reliance resin cement; D019279:Resin Cements; D012997:Solvents; D013778:Tetrazolium Salts; D013844:Thiazoles; C477790:Transbond XT; C045638:Unite dental cement; D000096:Acetone; C047484:heliosit; C022616:thiazolyl blue; D010100:Oxygen