An investigation on the retention of three 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 3 core materials on their retention to FRC posts. Materials and methods. This experimental study was perfomed on 30 translucent FRCposts (RTD) and divided into 3 groups (n=10) according to their core material. A cylandric plastic matrix (for primolar 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 ANOVA and 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: photocore, 86.93+9.09:3MZ250 (59.81+8.69); Tetric flow (23.49+5.20). One_way ANOVA revealed significant differences between the core material groups (p‹0.001). Coclusions. The bond strength between photocore and FRC posts is significantly higher than 2 other groups.

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. [1]. 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 [2]. Another approach is to improve the characteristics of core material to increase the quality of restoration and post and core [3]. Also posts are manufactured in different head designs including smooth, spherical, dentate, etc, all contributing to further retention of core materials [4].

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 [5]. According to the insufficiency of the investigations on the retention of different core materials and FRC posts, this study aimed to compare three 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 21mm long and with a 1.6mm diameter, were equally divided into three groups. In each group, one of the three core materials were applied: 3M Z250Composite, Photocore Composite, Tetric Flow 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) [8] and cured for 20 seconds. 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). Also to facilitate the placement of the posts I the device, an acrylic base was provided for them. Instron device was used to measure the retentive strength of the post and core (figure 2).

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

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 (figure 3). Obtained data were then recorded in data sheets. Since the distribution of data was normal, ANOVA test was used for statistical analysis.

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

Results. The retentive strength of three core materials (3M Z250, Photocore, and Tetric Flow) to FRC posts was measured and compared. There were 30 samples which were divided into 3 groups of 10 each. Samples were then placed under tensile force of 0.5mm/ min provided by Instron device till the separation of the post and core. Following the completion of forms, the mean and standard deviation of each group were calculated. Table 1 present s 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 three groups, one way ANOVA 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 for %25, %50, and %75 of the cases. With photocore, %25 of the cases showed separation at 94.26mpa and %75 at 84.40mpa. With 3M, however, Bond separation in %25 and %75 ofthe samples occurred till 67.23mpa and 55.40mpa. These measures for Tetric Flow were %27.3 and %19.04, respectively.

Discussion. This study revealed that the retention of photocore to FRC posts is significantly higher than

two other groups. 3M Z250 was also significantly more efficient than Tetric Flow regarding retention. Our findings support the studies of Trancheshi et al who showed the retention of core build-up and hybrid composites and FRC posts to be highly more than Flow composite [5]. Also study materials (core materials and RTD posts) and method (Guarcy) [6] is similar in two studies, which provided the possibility of comparison to a large extent. Coltolux 2.5 with an output of 280 mWatt/ cm² and VIP (Bisco, Inc.) with an output of 600mWatt/ cm² were used respectively in our study and Tranchesi’s.

Through other studies in 2006 by Salmeh et al., [7] microtensile bond strength between FRC posts and light/ dual cure composite core materials was compared (core materials included Tetric Flow, 3M Z250, Multicore Flow, and Tetric Ceram). It was concluded that bond strength in MPa with Multi Core Flow is highly more than Z250. Therefore they claimed that in order to restore crown on FRC posts, dual cure composites are far more efficient than light cures in this regard and flow composites are far more efficient than 3M Z250. 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 composite core materials in Instron device and facilitate applying and even distribution of force. Salmeh Z, however, fixed the composite core on the jig by means of cyanoacrylate glue. This may have resulted in uneven distribution of the forced applied.

Conclusion. According to the conditions and limitations of this study, it may be concluded that the retentive strength of Photocore to FRC post is significantly more than 3M Z250 which in turn possess a significantly higher retentive potential than Tetric Flow.

Refrences

1. Gokhan Aksoy. Effect of an adhesive resin luting agent on the dowel head retention of 3 different core materials. J. of prosthetic dentistry. 2005: may: 439-445.
2. Robert M Love, David G. Purton. The effect of serration on carbon fi ber posts retention within the root canal,core retention, post rigidity. The intern. Journal of Prosthodontics. 1996;9:484-8.
3. Cohen B.L..Pilot study of the cyclic fatigue characteristics of 5 endodontic posts with 4 core materials. J. Oral Rehabil. 2000:27;83-92.
4. Francesca Monticelli. Post surface conditioning improves interfacial adhesion in post/core restorations. Dental Materials, 2006;22:602-609.
5. Fernanda Tranchesi Sadak. Bond Strength performance of fi ber different resin composits used as core materials around fi ber posts. Dental Material, 2007;23:95-99.
6. C.Gorraci. The adhesion between prefabricated FRC posts and composite resin cores:microtensile bond strength with and without post_sillanization. Dent Mater, 2005, May;21(5):437-44.
7. Salameh Z, Pappacchini F. Adhision between prefabricated fi ber-reinforced posts and different resin cores:a microtensile bond strength evaluation. J. Adhes Dent.2006 Apr; 8(2):113-7.
8. Xibile AA. Effect of silica and silinization on fl exural and composite-resin bond strengths of zirconia posts:an invitro study. J. Prosthent Dent. 2006 Mar:95(3):224-9.

Вопросы, ответы, комментарии