An investigation on the retention of two different core materials to frc posts

Abstract. Back ground and purpose. The ability of a dowel-and-core restoration to survive masticatory forces and remain firmly sealed depends on retention of FRC to core material. If either the dowel and/or the core material fails, the crown will ultimately fail. the goal of this study was to compare the effect of 2 core materials on their retention to FRC posts. Materials and methods. this experimental study was performed on 30 translucent FRC posts (RTD) and divided into 2 groups (n=15) according to their core material. A cylandric plastic matrix (for premolar teeth) was placed around the sailanized post and posts were centered and filled with the restorative resin composite. Each sample was loaded to failure under tension ata cross head of 0.05mm/ min. One way t-test were used for statistical analysis. Results. Dowel-head Retention values (M pa) of tested core materials (Mean+SD) from the highest to the lowest were as follows: Core Max (291/54±8) Crystalline (240±8/165), t-test revealed significant differences between the core material groups.(P>0.05). Conclusions. The bond strength between Core Max and FRC posts is significantly higher than Crystalline.

Introduction. The retentive potential of core materials to dental posts specially FRC counts as an important characteristic in heir selection for the crown restoration. Failures in this bonding will result in the immediate failure of crown restoration. There have been plenty of suggestions concerning the increasing of post retention to core material, including the alterations of surface characteristics at the interface of dowel head and core material to increase chemically and micromechanically the Retention. Another approach is to improve the characteristics of core material to increase the quality of restoration and post and core. Also posts are manufactured in different head designs including smooth, spherical, dentate, etc, all contributing to further retention of core materials.

Recent studies have shown that core build-up and also hybrid composites are more appropriate for crown restoration compared to the flow composites. Though a good surface adaptation is achieved, bond strength between post and core material remains less than desirable. On the other hand, the most bond strength among flowable composites is provided by highly filled materials. This is because highly filled composites decrease in porosity and provide more adaptation. According to the insufficiency of the investigations on the retention of different core materials and FRC posts, this study aimed to compare two core materials regarding their retention potential to the FRC posts in Dentistry School, Azad University of Medical Sciences, Tehran, in 2006.

Materials and methods. In this experimental, in vitro study 30 fiberoptic glass posts (RTD, St. Egere, France), each 20mm long and with a 1.2mm diameter, were equally divided into two groups. In each group, one of the two core materials were applied: Core Max Composite and Crystalline Composite.

Each post was vertically securely mounted on a glass slap by wax. Gurasy method was applied [6]. A cylindrical plastic matrix (premolar-like) was placed around each post so that each post be located at the center of the model and 3mm of its length be placed in the core material matrix. Bonding agent was then applied on the post by a microbrush (single bond 3M ESPE) and cured for 20 seconds [8]. Composites were then placed in the models and separately cured based on the instructions of manufacturer (Coltolux 2.5 light cure unit, with an average output of 280mWatt/cm2) [6]. Flowable composites were also injected into the models and cured in the same way. Matrix was then removed and cured from downside to assure complete polymerization of the crown [5]. To facilitate the insertion of the cores in the device and standardization of the applied force, metal core holder were fabricated to enclose cores (figure 1).

Figure 1. Metal holderFigure	2. Prepared sample whith metal holder

Also to facilitate the placement of the posts in to the device, an acrylic base was provided for them. Instron device was used to measure the retentive strength of the post and core (figure2). Each piece was placed under traction (tensile force) with the speed of 0.05 mm/min till the separation of post from core is observed in one of the surfaces (figure3). Obtained data were then recorded in data sheets. Since the distribution of data was normal, t-test was used for statistical analysis.

Figure 3. A sample loaded in tension on the universal testing machine

Results. The Retentive strength of two core materials to FRC posts was measured and compared. There were 30 samples which were divided into 2 groups of 15 each. Samples were then placed under tensile force of 0.5mm/min provided by post and core. Following the completion of forms, the mean and standard deviation of each group were calculated. Table 1 presents these measures.

Table 1. The mean and standard deviation of the FRC post and core according to the core material type

Single-sample Kolmogrov-Smirnov test was then used to determine the goodness of fit of the distribution of core material retention to FRC posts in each group. Since p-value was more than 0.05 in each group, data adhere to the normal distribution. Next, to compare the retention of two groups, one way t-test was applied which revealed to be significant. Therefore post hoc Bonferroni test was used to compare pairs (p‹.001). Meier-Kaplan survival analysis was then used to determine the separation point.In each group 13 samples were separated completely from the core and in 2 case (in each group) the core was broken.

Discussion. This study revealed that the retention of Core Max 2 to FRC posts is significantly higher than crystalline. Our findings support the studies of Marco Ferrari in 2004 who showed the retention of build-up and core max 2 to be higher more than crystalline. Through a study in 2004 by masavuki microtensile bond strength between RTD post and cores material (included Core Max 2 and Crystalline) was compared. It was concluded in order to restore crown on FRC posts, Crystalline is more efficient.

Differences among results of this study is probably due to not mention of wide range of Bonding system using in the research (Post core Bond). Final preparation of CORE-MAX according to Yamada (1990) should be done a week later after first-visit preparation, because mechanical proprieties of aforementioned resin is unstable between a day to a week, so the final preparation and impression taking would be postponed until the next appointment. We used fourth generation of bonding system (Scotchbond 3M) including etching, primer, and adhesive, therefore, acidic monomers are in second bottle(primer) which will be coated by adhesive and then cured. So its acicid proprieties will not influence on light-cured composites and especially self-cured ones.

The difference between this study and our investigations could be due to the obscurity of the applied bonding agent. Also in our study, metal prefabricated dowel holder were used to place core materials in instron device and facilitate and applying and even distribution of force.

Conclusion. According to the conditions and limitations of this study, it may be concluded that the retentive strength of Core Max 2 to FRC posts is more than Crystalline. 

Refrences 

1. Cohen B.1., Pagnillo M.K., Newman. Pilot study of the cyclic Fatigue characteri stice of five endodontic post with four core materials. J. Oral Rehabil. 2000:83-92.
2. Gokan Aksoy., H.Serdar, Levent Korkut. Effect of an adhesive Resine lutting agent on the dowel head retention of three different core material. J. of prosthetic dentistry, 2005:439-445.
3. E.D.Bonilla,G.Madirossian. Fracture Toughness of various core build up materials. J. of prosthodontics 2000:14-18.
4. Fernando Tranchesi Sadak, Francesca Monticelli. Bond strength perfprmance of resine composite sused as core materials around fiber posts. Dental materials, 2007:95-9.
5. Moticelli,C. Gorraci, Sgrandini. Scanning electron microscopic evaluation of fiber post resin core units build up with different resin composite. AM. J. Dent. 2005:61-5.
6. J.Aksor Nmuang, R.M.Foxton, M.Nakajimia. Microtensile bond strength of a dual cure resine core material to glass and fiber posts. Dent. 2004:443-50.
7. C.Goraci, O.Raffaelli, F. Monticelli. The Adhesion between prefabricated FRC post and composite resine core microtensile bond stegh with and without post- sillanization. Dent. Matter, 2005:437-44.
8. Francesca Monticelli, M.Toledano, Frankline R., Tay Marco Ferrari. Post surface conditioning improves interfacial adhesion in post core restoration. Dental Materials, 2006:602-9.
9. Salameh Z., Papachini F. Adhision between prefabricated fiber- reinforced posts and different composite resin cores:microtensille bond strength evaluation. J. Adhed Dent. 2006 113-7.

to be continued. . .

Вопросы, ответы, комментарии