الفهرس 
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Abstract
This study was conducted to evaluate biological dentin posts in primary anterior teeth in comparison to fiber posts and composite resin posts in terms of fracture resistance as well as bond strength to root dentin.
Specimens were divided into three main groups according to the type of post used:
group I: in which biological dentin posts were used.
group II: in which fiber posts were used.
group III: in which composite resin posts were used.
Sixty extracted primary anterior teeth were collected from the outpatient clinic of Pediatric Dentistry and Dental Public Health Department. Ten extracted premolars were collected from the outpatient clinic of Oral and Maxillofacial Department. Both departments are in Faculty of Dentistry, Ain Shams University. The teeth were selected according to certain criteria to be used in this study.
The premolars were freshly extracted for orthodontic reasons and were used for preparation of biological dentin posts. Each tooth was decoronated then sectioned longitudinally into two halves along the root canal. Each half was then fixed in acrylic resin block. The milling was then accomplished using CNC milling machine to generate dentin posts of standardized shape and dimensions similar to the red color-coded Easy posts that were used in the study (Kathuria et al., 2011). The prepared dentin posts were all autoclaved at 121°C for 20 minutes before use (Swarupa et al., 2014).
Composite resin posts were prepared using a specially constructed split Teflon mold with six holes; each has the same dimensions as the red color-coded easy posts used in this study. Prior to cementation, the posts were etched for 30 seconds then washed and dried (Borges et al., 2011).
The red color-coded Easy postsTM (DENTSPLY, Maillefer, USA) were used for this study. They were silanized before cementation by applying silane for 1 minute then left to dry according to the manufacturer’s instructions.
The measurements of fracture resistance and push-out bond strength were performed at Faculty of Dentistry, Ain shams university; Dental Biomaterials Department using a universal testing machine (Hampshire,UK, LLOYD, LR 5K).
Regarding the fracture resistance testing, thirty primary anterior teeth were cross-sectioned 1 mm above the CEJ. Each root canal was filed, irrigated with normal saline solution and then dried with paper points. Metapex was then injected into the canal space. Glass ionomer lining cement (GC Equia, Tokyo, Japan) was then inserted into the canal space and adjusted to a thickness of 1 mm. The post space inside the root canal was 3 mm (Baghalian et al., 2014),(Seraj et al., 2015).
Ten posts from each of the three groups of posts in the study were cut so as to obtain the length of 6 mm for each post (n=10 for each experimental condition). Three millimeters of each post was inserted inside the root canal and cemented with self adhesive resin cement (GC G-cem, Tokyo, Japan) according to the manufacturer’s instructions, leaving 3 mm coronally for crown building up. The crowns build-up was performed using cellioloid strip crowns filled with flowable composite resin (Filtek Z350 XT). All the specimens were mounted in self-cured acrylic resin and then thermocycled. The fracture resistance was measured using the universal testing machine. The specimens were loaded at a cross head speed of 1 mm/min. The values obtained at fracture were recorded in Newtons.
As for push-out bond strength testing, thirty primary anterior teeth were cross-sectioned 1 mm above the CEJ. Each root canal was filed, irrigated with normal saline solution and then dried with paper points. Ten posts from each of the three groups were cemented into the root canals of the primary anterior teeth with self adhesive resin cement (G-cem, GC, Tokyo, Japan) according to the manufacturer’s instructions.
The roots were then embedded in self-cured acrylic resin. The acrylic resin blocks were then sectioned perpendicular to the long axis to create 2 mm thick slice from the coronal third from each root (Ranjithkumar et al., 2012). One specimen was obtained from each root, in such a way, the number of specimens for each experimental condition equals 10 (n=10). The push-out tests were performed at a cross head speed of 0.5 mm/min using the universal testing machine. The maximum load was recorded in time of post dislodgement in Newton (N) and the bond strength in MPa was calculated by dividing the applied load by the bonded area (S).
After testing, the mode of failure was determined for each group under a stereomicroscope (SZ-PT, Olympus, DP10, Japan). The failure modes were categorized as adhesive, cohesive or mixed.
The fracture resistance measurements showed that there was no statistically significant difference between the different post types. As for bond strength testing, pair-wise comparisons between the post types revealed that there was no statistically significant difference between biological and composite posts; both showed the statistically significantly highest push-out bond strength values. Fiber post showed the statistically significantly lowest push-out bond strength. The microscopic images showed that the mode of failure in all biological and composite resin post specimens was mixed failure, where the resin cement was present on both the post and the walls of the root canal. As for the fiber post specimens; 8 of them showed mixed failure, while 2 of them showed adhesive failure between the post and the cement.