Fracture Resistance of Esthetic Post and Core Systems

Fracture Resistance of Esthetic Post and Core Systems Comparison of fracture resistance of three recent esthetic post and core systems with cast metal post and core to compressive loading An in vitro Study ABSTRACT: Aim: To determine and compare the fracture resistance of three recently introduced esthetic post and core systems with a cast metal post and core to compressive loading using a clinically related test method. Materials and Methods: Forty maxillary central incisors were selected, sectioned and their roots endodontically treated and assigned to 4 experimental groups (n=10).The cast metal post and core (CMPC) served as control group.The other groups are zirconium dioxide post and ceramic core group (ZCER), zirconium dioxide posts and composite core group (ZCOM) and glass fiber post and composite core group (GFCOM).The post spaces were prepared, posts were seated and cores were formed. A compressive load was applied to the inclined surface on each specimen until failure occurred and measured in newtons. Results: CMPC and ZCER groups exhibited the highest resistance fracture and the values are : 680.6 N and 630.03 N respectively . ZCOM group exhibited fracture resistance greater than GFCOM but less than ZCER and CMPC. Conclusion: CMPC group and ZCER group were found to be more fracture resistant than the ZCOM group and GFCOM group. Aside from its desirable esthetic properties,the ZCER group demonstrated high resistance to fracture. Keywords: compressive loading, endodontic treatment, fracture resistance, post and core INTRODUCTION Endodontic therapy has provided dentistry the ability to retain teeth that just a few decades ago would have been extracted without hesitation.When there is substantial loss of coronal tooth structure due to caries, trauma or both, a post and core is often required to retain a definitive restoration. A post is usually placed in an attempt to strengthen the tooth.1,2,3 However, in vitro and in vivo studies have demonstrated that a post cannot reinforce endodontically treated teeth.4,5,6 Posts are required for supporting a core foundation when there is insufficient clinical crown remaining.4,5,6,7 Although cast post and core foundations are the gold standard for endodontically treated teeth, due to their superior physical properties and proven clinical effectiveness8 yet its mechanical properties may increase the risk of root fracture9. The esthetic properties of these materials are limited since the gray colored post is apparent when used to support translucent all ceramic restorations. Coupled with a high lip line, cast metal post and core foundation may create esthetic problems. In the recent times, there has been a tremendous increase in the use of all ceramic crowns, particularly for anterior teeth because of their superior natural appearance compared to metal ceramic restorations.10 Both the declining acceptance of cast post and core restorations as well as patients interest in dental esthetics has resulted in the development of esthetic posts, especially Glass Fiber and Zirconia Ceramics.These increase the transmission of light within the root and overlying gingival tissues, enhancing the esthetics. They also eliminate the potential hazards of corrosion and allergic hypersensitivity as they are metal free materials.11 Glass fibers such as silica or quartz reinforced epoxy resin posts have low modulus of elasticity similar to that of dentin.12 This property has been reported to reduce the risk of root fracture. 13,14 Glass fiber reinforced posts also have the advantage of easy removal if endodontic re-treatment is required. 15,16 A prefabricated zirconia ceramic post system has been introduced to satisfy esthetic needs presented by endodontically treated anterior teeth. The translucency of all ceramic crowns can be successfully maintained with the use of ceramic post and core materials. Moreover improvements in adhesive porcelain bonding systems have accelerated the trend toward the use of ceramic core materials. Many dentists prefer to use prefabricated post systems because they are more practical, less expensive and in some situations less invasive than customized post and core systems. They also save time and can provide satisfactory results. 17,18,19 The purpose of this in vitro study is to determine and compare fracture resistance of three esthetic post and core systems, Zirconia post and Ceramic core, Zirconia post and Composite core and Glass Fiber post and Composite core with cast posts under compressive loading. METHODOLOGY Forty extracted human permanent central incisors were selected based on similar dimensions,caries free,no restorations and cracks.The teeth were soaked in 3% sodium hypochlorite (Vishal Dentocare PVT LTD), for 6 hours. These forty teeth were divided into 4 groups: Group 1: Cast Metal post and core (CMPC) Group 2: Zirconia posts and Ceramic core (ZCER) Group 3: Zirconia posts and Composite core (ZCOM) Group 4: Glass Fiber posts and Composite core (GFCOM) The coronal aspect of each tooth was resected perpendicular to the long axis and 1mm incisal to the cementoenamel junction, with a diamond coated disc (Horico) mounted in a straight handpiece (NSK, Japan). Labiolingual and mesiodistal measurements of the sectioned tooth surfaces were made with a digital vernier calipers (Aero space, China).The roots were endodontically instrumented to the apex using protaper rotary instruments (Dentsply,Maillefer) till F3 and obturated with protaper GP points (Dentsply,Maillefer) using ZOE sealer. Procedure for fabricating standardized cores: To obtain standardized cores, a wax pattern was fabricated from casting wax (Sk Dental waxes, Bombay) which had 6.5mm diameter base, 7.3 mm diameter cervico incisally and 6.2mm buccolingually. Impression of the wax pattern was taken with rubber base impression material (Exaflex). Then dies were made from the impression material. Polyvinyl material was vacuum pressed on these dies.In this way a hollow matrix was fabricated which had the same dimensions as that of the wax pattern. The base of the matrix was fitted flush to the sectioned tooth surfaces. Then 1 mm of the matrix was cut at the open end so that it acted as an inlet for the placement of composite resin. Procedure for preparation of forty samples: For all the groups the post spaces were enlarged with peeso reamers no 2 and 3 (MANI CE 0197 Prime Dental Products PVT LTD) initially to a depth of 9mm. The final enlargements were accomplished with the 1.4 mm diameter drills that were specifically given with 1.4mm zirconia posts (Cosmoposts,Ivoclar Vivadent) and 1.4mm GF posts (Bioloren,Ammdent). All the posts have 1.4mm diameter and were sectioned to a standard length of 13mm using carbide fissure bur and high speed airotor handpiece The length of the posts was 4 mm from the finish line into the core.In groups 2, 3 and 4 all the post spaces were etched using 37% orthorphosphoric acid (3M ESPE), for 30 sec and bonding was done using a bonding agent (3M ESPE) polymerized for 20 sec. Cementation was done using dual curing resin luting agent ( Kerr,Orange,CA). Group 1: A direct technique was used. The post pattern was fabricated using inlay wax. For the core part ,the polyvinyl matrix was placed on the tooth, resin wax (Leva) was injected in to the matrix and polymerized. After polymerization, the matrix was removed from the molded core. Then the entire pattern was retrieved from the root, invested and cast. The cast post and core systems were then cemented into the roots using GIC. Group 2: Posts were seated into the prepared post space.Polyvinyl matrix was placed on the tooth surface, resin wax was then injected in to the matrix and polymerized for 20 sec to form the core. Matrix was then removed and retrieved post and core foundations from the roots were invested with a phosphate bonded investment (Deguvest). Wax was eliminated from the invested units in a pre heated furnace (Unident) (800ËÅ ¡C for 45 minutes). Cores around zirconia posts were prepared using ceramic ingots (e-max, Ivoclar vivadent) heat-pressing process (975ËÅ ¡C for 45 min.) in a heat pressing furnace (Ivoclar vivadent). The formed ZCER foundations were then cemented into the post spaces. Group 3: After etching and bonding,posts were cemented in to the prepared post spaces. The matrix was seated on the sectioned tooth surface and composite core material (Z350, 3M ESPE) was placed in 2mm increments and polymerized for 20 sec. After polymerization, the matrix was removed from the molded cores. Group 4: Following etching and bonding posts were cemented into the prepared post spaces. The matrix was placed on the sectioned tooth surface and composite was placed in 2mm increments and was then polymerized for 20 sec. After polymerization, the matrix was removed from the molded cores. LOADING PROCEDURE: Following thermal cycling (5000 cycles between 5ËÅ ¡C and 55ËÅ ¡ C with a dwell time of 30 second) a universal testing machine (Shimadzu, Japan) was used to apply a constant compressive load at a crosshead speed of 1mm/min, at a 130Â º angle to the long axes of the test specimens, until failure ocurred. The tip of the loading bar was positioned to contact the centre of the palatoincisal surface at an angle of 90Â ºC. The force at failure was measured in newtons. RESULTS One-way Analysis of Variance (ANOVA) with Post HocTukey test was used to compare the score between the groups. A 95% confidence level was used for the ANOVA test. Results showed that there was significant difference in the fracture resistance values obtained with different groups (p