Comparison of push out bond strength of various root perforation repair materials

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Introduction
Root perforation connects spaces of root canal with periodontal tissues.The connection may happen due to iatrogenic etiologies during root canal therapy or during prosthetic treatment of post canal penetration.It can also introduce by the external resorption of the root or by caries process.[1,2,3] Root perforation could be sealed either with external surgical access or intracoronally.In both methods better sealing should be achieved between periodentium and tooth structure, which could be influenced by operative procedure , the location and size of perforation , and features of materials that utilized for prevent contamination.[4] Different materials has been used for perforation repairs, which include: zinc oxide eugenol (EBA and IRM), Mineral trioxide aggregate (MTA), glass iomomer (GIC), gutta percha, and calcium hydroxide (Ca(OH) 2 ).[5,6,7,8] MTA show superior bonding ability and biocompatibility compared to many other root perforation materials [9,10]

Prepared samples:
Forty lower premolars with a straight single root canal and mature apex were used and kept in formalin "10%".Then, the teeth decorated at and Nekoofer 16 .Sample diameter was checked using Motic Image software connecting to digital stereomicroscope (Motic, Taiwan).The samples were placed in 17% EDTA for 3 minutes followed by 2.5% NaOCl for the same time, and then immediately rinsed with distilled water for 2 minutes and dried.
After that, specimens were divided randomly into 4groups with 10 specimens in every group as follows: Group I: BIO (Septodent, France).

MDJ
Comparison of push out bond strength of various root perforation repair materials 349 Solutions, Goias Londrina PR Barazil).

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In each group the materials were mixed following the manufactures recommendations, and then the mixture was placed into cavities and condensed with plugger.
Material access was removed from the specimens surface with scalpel.
Photographed was taken for both coronal and apical surfaces of each discs using computerized stereomicroscope "X 40" (Motic; Taiwan)and viewed prior testing for excluding any defects, cracks, and spaces between dentin wall and material (Figure 1).All samples were then stored at 37 o C and 100% humidity for one week.

Push out bond strength (PBS):
PBS was achieved using a

Results
One  (22) .The highest mean values of PBS of Bio seen in the current study may be related to that Bio contains highest amount of products that release Calcium and stimulate the generation of tag-like structures at the dentincement interface, this lead to increase the resistance to load of dislodgement when compared to MTA [23].
In MTA some of the particles size is smaller than the dentinal tubule diameter and this might play an important role in good adhesion of MTA to dentin.[24] This agree with finding of study down by Majeed and AlShwaimi 2016, they compared the PBS of Calcium Silicate based materials and found that BIO showed significantly higher push out bond strength than MTA.[25] But this result disagree with finding of Nikhade et al., 2016; they found that the differences was not between the PBS of BIO and MTA.[26] Under the conditions of our study, GI showed greater resistance to push-out forces than Ca(OH) 2 .The differences in PBS might be related to the particles size of the material.It is well known that the differences in particles size of the test materials are of great importance for mechanical properties of the materials tested.[19] GI is a material with important

Conclusions
Within the limitations of this study, it was found that the force required for the dislodgment of BIO from root dentine was significantly greater than that necessary for the dislodgment of MTA, GI, and Ca(OH) 2. Therefore, BIO can be used successfully for repair of root perforation.

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15 mm" from the root apex by diamond disc (KG Sorensen SP, Brazil), and the middle third of the roots were cut perpendicular to their long axis by using mintom (Struers, Denmark) in order to obtain sections with 1 mm thick.Instrumentation for the canal of the dentin discs with Gates Glidden burs (Dentsply/Maillefer/Switzerland), from sizes 2-5 to result into standardized cavities with 1.3 mm diameter as described by VanderWeele et al. [15] computerized universal testing device (TERCO, MT 3037, Sweden)Figure( 2): a. Specimens were placed over a hole of 1.5 mm in the center of block of an acrylic (15 mm diameter and12 mm thickness).Load was exerting by applying downward pressure on the surface of the filling material utilizing a cylindrical plunger with "1.2mm" diameter that provided full cover over the filling material without contacting the canal wall (Figure 2:b).PBS preformed at cross-head speed "0.5mm / min".Greatest reading obtained once debonding happen was recorded, and this reading represent the PBS.Surface area subject to force measured from 2πrh (r= radius, h= height).PBS in Mpa was estimated by dividing the force (N) by the area in mm 2 .[15,16,17,18] Mode of Failures: Every specimen was viewed by digital stereomicroscope at 40X magnification to evaluate the mode of failure and placed into one of the following: (1) Adhesive at the dentine surface and tested material interface (2) Cohesive within the tested material, and (3) Mixed in both cohesive and adhesive failures.[15]

Table 1 : One Way Analysis of Variance for the differences on PBS between tested materials.
* * P ≤ 0.05 mean there is significant variation.Table(2): Mean of PBS differences among tested materials.*The