Preparation of dentine surface and contamination with sealer
The enamel layer in the occlusal area of the primary teeth, which was stored in a 0.1% thymol solution at 4°C until use, was removed in a low-speed rotating water-cooled Isomet device (Isomet Low Speed Saw; Buehler Ltd, Lake Bluff, IL, USA) in Selcuk University Faculty of Dentistry Research Laboratory. The materials used in this study are shown in Table 1.
Table 1
Materials used in this study
Materials | Composition | Application mode |
Root canal sealers | MTA Fillapex | Salicylate resin, diluting resin, natural resin, bismuth trioxide, nanoparticulated silica, MTA, pigments | It was applied to the dentine with help of dry cotton pellet |
AH Plus | A patı: Epoxy resin B patı: amine derivatives | It was applied to the dentine with help of dry cotton pellet |
Irrigations | NaOCI | 2.5% in intensity | Applied with the help of cotton pellet |
Ethanol | 95% in intensity | Applied with the help of cotton pellet |
Bonding | Prime & Bond Universal; Dentsply, Germany | Diamine Bis Acrylic; Water; Propanol; Dihydrogen Phosphate Methacrylate; Penta; Bis Acrylic Propylamine; Camphorquinone; HexaFluorPhosphate; Benzonitrile Dimethylamino; Hydroquinone. | Bond was applied and waited for 20 seconds, the air was dried with water spray for 5 seconds and light was applied for 10 seconds |
Composite | Nova Compo C | Dimetakrilat, ba-glass, yiterbiyum triflorur, prepolimerized filler, catalyst, stabilizer, ULS monomer | The resin composite was applied and light was applied for 20 seconds |
The teeth, which were then washed and dried with air‒water spray, were randomly divided into three main groups to canal sealers:
Group 1: Control group. The root canal sealer and irrigation solution were not applied.
Group 2: AH Plus paste (AH Plus; Dentsply, Konstanz, Germany) was applied to the dentin surface with a dry cotton pellet for five minutes.
Group 3: MTA Fillapex paste (MTA-FILLAPEX (MTA Fillapex; Angelus, Londrina, Brazil) was applied to the dentin surface with a dry cotton pellet for five minutes.
The root canal paste was applied once to cover the dentin surface after contacting the dry cotton pellet.
The main groups (2 and 3) were further divided into four subgroups depending on the irrigation solution:
Subgroups 2a: Contaminated dentin was cleaned with cotton pellets soaked in saline.
Subgroups 2b: Contaminated dentin was cleaned with cotton pellets soaked in 2.5% NaOCl.
Subgroups 2c: Contaminated dentin was cleaned with cotton pellets soaked in saline after 24 hours. Samples were kept at 37°C for 24 hours.
Subgroups 2d: Contaminated dentin was cleaned with cotton pellets soaked in 95% ethanol.
Subgroups 3a: Contaminated dentin was cleaned with cotton pellets soaked in saline.
Subgroups 3b: Contaminated dentin was cleaned with cotton pellets soaked in 2.5% NaOCl.
Subgroups 3c: Contaminated dentin was cleaned with cotton pellets soaked in saline after 24 hours. Samples were kept at 37°C for 24 hours.
Subgroups 3d: Contaminated dentin was cleaned with cotton pellets soaked in 95% ethanol.
** All samples were cleared for one minute.
*** The manufacturer stated that the setting time for MTA Fillapex is more than two hours. For AH Plus, this is approximately eight hours. From this point of view, we set a waiting period of 24 hours in Subgroups 2c and 3c. When the recommended waiting times are applied in line with the recommendations of the manufacturer, a 24-hour waiting period is deemed appropriate to prevent patients from being kept in the clinic for a long time. Then, the restoration phase was initiated.
Bonding and restoration procedure
After removing the sealer, the teeth were restored with self-etch adhesive (Prime & Bond Universal Dentsply) and composite (Nova Compo C Composite Imicryl Corporation, Konya, Turkey) following the manufacturer's recommendations. In delayed restoration, the bonding and composite of the specimens were restored after they were kept in a humid environment at 37°C for 24 hours. Composite material with 2 mm thickness was placed using the incremental technique on the bonded dentin surface and cured with an LED curing unit (VALO Cordless, Ultradent, US) according to the manufacturer’s instructions.
Preparation of samples and micro tensile testing
After the composite was applied in the study, the samples were kept in a humid environment at 37°C for 24 hours. Horizontal sections of approximately 1 mm2 thickness were taken from the restored dental crowns mesiodistally and buccolingually under a water-cooled Isomet saw (Isomet Low Speed Saw; Buehler Ltd, Lake Bluff, IL, USA). Sticks that were broken or attached to the enamel area during sectioning were removed from the study group and a total of 30 sticks were obtained in each group (270 sticks in total). The area of the beams was calculated by measuring with an electronic caliper (Starret 727-6/150; Starret, San Paulo, Brazil). The bonded sticks were attached to a loading jig with cyanoacrylate resin glue (Akfix; Akfix Trade Ltd. Co., Istanbul, Turkey). Subjected to tensile force in a universal testing machine (Microtensile Tester; Bisco Inc., Schaumburg, IL, USA) at a tensile force with a speed of 1 mm/min. A microtensile load was applied until specimen failure. The bond strength was recorded in Newtons (N) and calculated as megapascals (MPa).
One-way ANOVA was used to determine whether there was a difference between the groups, and the Tukey test, which is one of the multiple comparison tests, was used to compare the group averages.
The failure modes for all specimens were evaluated at 100x magnification with scanning electron microscopy (SEM: Zeiss EVO LS10; Oberkochen, Germany). Failures were classified as adhesive failure, cohesive failure (between the resin and dentin), or mixed failure (in the dentin and adhesive material or composite resin).