Sample size calculation:
The study was approved by the Research Ethics Committee (REC) at the College of Dentistry of Suez Canal University, ( registered No. 327/2021). All steps were accomplished in accordance with the relevant guidelines and regulations. The sample size was obtained by using the G* power software statistical analysis (Latest ver. 3.1.9.7; Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany) according to D'Aviz et al [11]. One hundred and twenty teeth were sufficient to detect the effect size of 0.4 and a power (1- β) of 80% at a significant level of (α) level of 0.05.
Teeth selection:
The present study was conducted on 120 single-rooted extracted human anterior teeth. Teeth were selected from the oral surgery clinic at the College of Dentistry, Suez Canal University. The teeth were collected from unknown patients irrelevant to the study that had extraction due to periodontal problems. The teeth were radiographed to exclude cracks and caries. The selected teeth were soaked in 2.5% sodium hypochlorite for 2 hours to enable disinfection.
Preparation for the pulp exposure:
One hundred and twenty teeth were subjected to a class V preparation on their labial surface coronal to the gingival margin. Inverted cone bur size 1 (Dentsply Maillefer, Tulsa, Oklahoma, USA) at high speed (30,000 rpm) contra-angle handpiece (NSK, Tokyo, Japan) was used under a water coolant until an exposure was noticed at the floor of the cavity. The tested materials were applied on the exposure site and then final restoration was placed using Inter mediate Restorative Material (IRM) (Dentsply, Charlote, U.S.A).
Sample randomization and grouping :
Randomization was utilized using Microsoft Excel. Later, blind allocation was performed where the samples were coded and placed in opaque envelopes. The samples were divided into three main groups utilizing the three materials: WMTA Angelus (Angelus, Londrina, Brazil); GSE (Nu Sci, HerbStore, USA); MTA+GSE with 40 samples for each group. Samples were then divided into two subgroups, each with 20 samples, based on time intervals (1 month, 3 months). Subsequently, 10 samples for each subgroup were examined independently for the push out bond strength and dentinal penetration.
Preparation of the GSE :
The GSE powder was made by hot water extraction, and its molecular weight is 590.581 g/mol, corresponding to the manufacturer’s recommendation [11].
Preparation of the mixture of MTA and GSE:
At room temperature, an electric balance was used to weigh out the powder and water. On the glass slab, the powder was divided into four equal amounts GSE was blended 25 % by weight into MTA where the powder constituents were vibrated in a mixer for an hour. The initial quantity of the powder was inserted into the bath to begin the mixing process. The distilled water was added to the resulting mixtures. In order to obtain the required consistency, the powder was blended into the water to achieve a uniform mix. As a result, the water/powder ratio was 1:3:3 where the weight of GSE was equal to MTA.
Push out bond strength
A total of 60 dentin discs with a thickness of 1.50.2 mm and a lumen of 1.3 mm were employed using an IsoMet diamond saw (Buehler, Lake Bluff, NY, USA). The disc was embedded in a polyvinyl ring with self-curing acrylic resin (Prothyl repair EVO, Zhermack, Badia Polesine, Italy). The dentin surface was polished with 600-grit silicon carbide paper and later cleaned in an ultrasonic cleanser for 10 min. The samples were randomly divided into three groups, 20 of each, according to tested capping materials ( MTA, GSE and mixture of MTA and GSE). Twenty samples of each examined material were further divided into two subgroups (n = 10) for push out bond strength testing at 1 and 3 months. The tested materials were mixed according to the manufacturers’ instructions. Each sample was compressed after being mounted in a loading fixture using a computer-controlled materials testing machine (Model LRX-plus; Lloyd Instruments Ltd., Fareham, UK) with a load cell of 5kN. Using computer software, the data was captured and loaded at a crosshead speed of 0.5 mm/min (Nexygen-MT; Lloyd Instruments). Plungers apply a load of diameter-size (1 mm). Only the filling is contacted to move it downwards, according to the plunger diameter chosen. The bond intensity was considered from the observed peak load divided by the measured surface area as defined by the following formulation: Bond = F/A = π h 2 (r). Where π is the 3.14 constant, the sample thickness in millimeters is the radius of r1 and h. Extrusion of the filling material indicated failure, which was confirmed by a dramatic drop in the load-deflection curve of the computer program.
Penetration depth measurements:
SEM was accustomed to assess the amount of capping material diffusion into the dentinal tubules. A #2 diamond disc was used to cut the crowns of the teeth at the cemento-enamel junction. The samples were sliced with a diamond disc under sprayed water after the capping materials were applied. The bottom 3mm of the cervical region is left. The sample was then dehydrated for 10 minutes in a succession of solutions with ethanol concentrations ranging from 50% to 100% in 10% increments, before being dried for 24 hours at room temperature in a closed jar containing silica gel. In the upper notch, a chisel and hammer were used to cut cross-sections, which were then coated by ion sputtering with Pt (E-1030, Hitachi High Technologies, Tokyo, Japan. Photographs of the coronal part were taken using a scanning electron microscope (SEM) at magnifications of X 500, 1000, and 1500, depending on the degree of material diffusion (SU-8220, Hitachi High Technologies, Tokyo, Japan). The general penetration of the substance in the images was tested using Adobe Photoshop 7.0.0.
Statistical analysis:
The statistical package for the social sciences (SPSS) version 26 was used to code and enter the data (IBM Corp., Armonk, NY, USA). The mean and standard deviation were used to summarize the data. Data were investigated for normality using Kolmogorov-Smirnov and Shapiro-Wilk tests. Data displayed normal distribution. The analysis of variance (ANOVA) with multiple comparisons post hoc test was used to compare the groups. The paired t test was used to compare the two timings in each group. Correlations between quantitative variables were done using Pearson correlation coefficient. Statistical significance was defined as a P-value of less than 0.05.