Oxygen-inhibited layer in adhesion dentistry.
OBJECTIVE
Characteristics of the oxygen-inhibited layer, including bond strength, photoinitiator decomposition, and post-curing degree of conversion, were investigated.


METHODS
To investigate shear bond strength, BisCover (Bisco, Inc., Schaumburg, IL, USA) and D/E Resin (Bisco, Inc.) were placed on disks of Renew composite (Bisco, Inc.) and cured both with and without an oxygen-inhibited layer. Light-Bond composite (Reliance Orthodontic, Itasca, IL, USA) was placed in a gelatin capsule and light cured over the cured resin. After soaking in water for 2 hours at 37 degrees C, specimens were sheared to failure using a universal testing machine (Model 4466, Instron Inc., Canton, MA, USA). To investigate microtensile bond strength, composite substrates prepared using Renew A2 composite were light cured either in air or under nitrogen. Light-Core (Bisco, Inc.) was placed on each substrate and light cured. The resulting specimens were sectioned into composite beams and stressed to failure using a microtensile tester (built by Bisco, Inc.). To determine camphorquinone (CQ) decomposition, an experimental CQ resin was placed between two glass plates and irradiated for different time intervals. The absorption spectrum was obtained using a Cary 50 Bio UV-Visible Spectrometer (Varian, Mulgrave, Australia). To explore the degree of conversion, polyester film strips (Mylar, DuPont, Wilmington, DE, USA) coated with the CQ resin were pre-cured in air for different time periods, and then post-cured at low intensity for 5 minutes under nitrogen. A Spectrum 1000FTIR Spectrometer (Perkin Elmer, Norwalk, CT, USA) was used to measure the degree of conversion.


RESULTS
Bond strength tests resulted in no significant difference between samples with or without an oxygen-inhibited layer. The oxygen-inhibited layer contained reduced amounts of photoinitiator. The degree of conversion of post-cured oxygen-inhibited layers was lower than that for the control.


CONCLUSIONS
An oxygen-inhibited layer is not necessary for bonding with composite resin.


CONCLUSIONS
It was believed that an oxygen-inhibited layer was required for bonding of composite resin. Studies show that composites bond even in the absence of an oxygen-inhibited layer, including recent products that cure without an oxygen-inhibited layer. With many simplified adhesives, especially self-etching, all-in-one adhesives, the oxygen-inhibited layer is acidic. This acidity interferes with self-curing reactions, making these adhesives incompatible with self-cured composites.
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Bisco Inc., Schaumburg, IL 60193, USA. sales@bisco.com
D000134:Acid Etching, Dental / Q000379:methods; D000179:Acrylates / Q000737:chemistry; D000180:Acrylic Resins / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003799:Dental Stress Analysis; D006244:Hardness; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D010100:Oxygen / Q000037:antagonists & inhibitors / Q000737:chemistry; D044367:Phase Transition; D017319:Photosensitizing Agents / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D033081:Shear Strength; D013499:Surface Properties; D013718:Tensile Strength; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors
D000179:Acrylates; D000180:Acrylic Resins; C481141:BisCover; D003188:Composite Resins; D008689:Methacrylates; D017319:Photosensitizing Agents; C485364:Renew composite; D019279:Resin Cements; D013729:Terpenes; C074236:Pyrofil light bond; C100742:All-Bond 2; C048339:camphoroquinone; D010100:Oxygen