In vitro effect of humidity on dentin bond strength of two universal adhesives.

Description :

Samples preparation: Sound human molars (N=40; age range: 18–30 years) will be stored after extraction in a solution of de-ionized water and sodium azide (0.2%) at 4 ◦C to inhibit microbial growth and will be used within 1 month from the start of the experiments. Next, all these teeth will be used for determining μTBS. Afterwards, the dentine will be exposed by cutting the enamel using a precise cutting machine (Exact Technologies Inc., Kg of Norderstedt, Germany). Smear layer will be standardized by grinding the surface with 320-grit silicon carbide paper using the variable speed grinder-polisher (Buehler Ltd., Lake Bluff, IL, USA) at a motor speed 70 rpm for 1min under water irrigation. Adhesive treatment and preparation of μTBS specimens will be performed according to relative humidity (50 ± 3%) and temperature (37 ± 2 ◦C) simulating the use of rubber dam with absolute isolation of the operatory area or at an increased humidity (90 ± 3%) and same temperature (37 ± 2 ◦C) simulating the oral environment without rubber dam. These values will be chosen according to Bicalho et al. [8] In order to simulate the temperature and humidity of the mouth a Plexiglas incubator will be performed with a humidifier and temperature controller (277 Stage LED Fogger with LED, Thermo control + humidity incubator220v, Adapter Sing24v 1000MA SMPS) which can be modified as needed. In addition, an air/water blow gun will be used for bonding procedure and 2 lateral hand holes to work inside the incubator. -Bonding procedure The teeth will be randomly divided into 4 groups (n = 10/each group): • Group 1: control group: under 37 ± 2 ◦C and 50 ± 3% relative humidity, simulating the use of rubber dam with absolute isolation of the operatory area; Prime&Bond activeTM (Dentsply) will be applied in self-etching mode. • Group 2: under 37 ± 2 ◦C and 90 ± 3% relative humidity, simulating the oral environment without rubber dam; Prime&Bond activeTM (Dentsply) will be applied in self-etching mode. • Group 3: control group: under 37 ± 2 ◦C and 50 ± 3% relative humidity, simulating the use of rubber dam with absolute isolation of the operatory area; Scotchbond universal (3M) will be applied in self-etching mode. • Group 4: under 37 ± 2 ◦C and 90 ± 3% relative humidity, simulating the oral environment without rubber dam; Scotchbond universal (3M) will be applied in self-etching mode. The adhesive systems will be applied according to the manufacturers’ instructions, then will be restored with restorative composite Filtek Z250 (3M ESPE, St. Paul, MN, USA). Composite will be applied in 2 increments of 2mm each and will be light cured for 20 s using a LED curing unit Elipar S10 (3M ESPE; St. Paul; MN; USA). After bonding, the specimens will be stored in distilled water for 24h at 37 ◦C. All bonding procedures will be carried out by a single operator.