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1. Title A STUDY TO EVALUATE AND COMPARE THE SHEAR BOND STRENGTH OF DIFFERENT CORE MATERIALS – AN INVITRO STUDY .

2. introduction An abutment tooth provides such a foundation for fixed prosthesis, and there is a need to restore this abutment with a core material. Core build- up is a restoration placed, in a grossly destructed tooth to restore the bulk of the coronal portion so as to facilitate the subsequent restoration by means of an indirect extra coronal restoration. The goal of a core build-up material is to provide satisfactory strength and resistance to fracture during and after crown preparation. A core restoration should provide sufficient strength and contribute to the retention and support of the prosthesis. The core material should also have sufficient compressive strength to resist intraoral forces and flexural strength to prevent core dislodgement during function.

3. The success of the core material depends on its strength to withstand axial and lateral loads, and its ability to retain and support, provisional crown and long term definitive restoration. The ideal requisite of any core materials is its strength. This is because stronger the core material greater the resistance to deformation and fracture which provides more equitable stress distribution, reduced probability of tensile or shear failure, greater stability, and greater probability of clinical success Hence, this study was done to evaluate and compare the shear bond strength of different types of core materials.

4. Need for the study The purpose of the study was to evaluate and compare the shear bond strength of different core buildup materials .

5. aim To evaluate and analyse the shear bond strength of different core materials.

6. objectives 1.To evaluate the shear bond strength of resin modified glass ionomer cement and composite resin core materials. 2. To compare the shear bond strength of resin modified glass ionomer cement and composite resin core materials.

7. RESEARCH HYPOTHESIS THE NULL HYPOTHESIS There is no significant difference in the mean shear bond strength (in MPa ) of three core materials i.e. µ1=µ2=µ3 THE ALTERNATE HYPOTHESIS There is a significant difference in shear bond strength (in MPa ) of three core materials i.e. µ1≠µ2≠µ3.

8. MATERIALS AND METHODOLOGY Materials Three commercially available brands of core materials. 1.ParaCore(COLTENE) 2. MultiCoreFlow ( Ivoclar ) 3. Resin Modified Glass ionomer cement (GC) Prisma universal bond etchant Prisma universal bond adhesive Auotopolymerising pink acrylic resin (DPI) Lubricant- vaseline . 600 grit silicone carbide strips.

9. Armamentarium Poly vinyl chloride pipe (3 cm x 5 cm) 5mm x 5mm cylindrical Stainless Steel mold secured by custom made Teflon sleeve Small ball end condenser Porcelain jar Mixing pad Agate spatul a EQUIPMENTS: Composite Light Curing unit ( Ledition Ivoclar Vivadent Schaan Liechtenstein) Three-point bending apparatus jig ( Mecmesin ) Universal testing machine ( Mecmesin ) Scanning electron microscope (Ultra 55, field emission scanning electron microscope, Karl Zeiss )

10. METHODOLOGY SOURCE OF DATA The present in vitro study will be conducted in the Department of Prosthodontics, Crown and Bridge and Implantology, Pacific Dental College, Hospital ,Udaipur. To evaluate and compare the shear bond strength of four different core materials. Sixty extracted non-carious permanent first molar teeth will be collected from the Department of Oral and Maxillofacial surgery, Dental College and Hospital, Udaipur. All the sixty extracted non-carious permanent first molar teeth were randomly selected and embedded in an auto polymerizing pink acrylic resin. All the mounted specimens were divided into four equal colour coded groups that will be assigned to four different core materials (n=20).

11. Sample size determination Level of Significance: α=0.0001 STATISTICAL TESTS USED: one-way Analysis of variance (ANOVA), Bonferroni multiple comparison Post – Hoc tests A total of 60 extracted teeth were divided into 4 groups of 20 specimens each .

12. Grouping of samples Group I - 20 mounted specimen’s with ParaCore (COLTENE) as a core material. Group II- 20 mounted specimen’s with MultiCoreFlow ( Ivoclar ) as a core material. Group III-20 mounted specimen’s with Resin Modified Glass Ionomer (GC) as a core material.

13. Preparation of samples Sixty (N=60) extracted non-carious permanent first molar teeth used in this study were cleaned and stored in distilled water. polyvinyl chloride pipe was cut to make a cylinder measuring 5cm in length and 3 cm in diameter. Auto polymerizing pink acrylic resin powder and monomer in a ratio of 3:1, was mixed in a porcelain jar. Autopolymerising acrylic resin was then added on to the polyvinyl chloride mould in a dough stage and the molar teeth were embedded. All the 60 teeth were mounted in the same manner to obtain 60 specimens. The acrylic resin blocks were then trimmed and polished. Each molar teeth was flattened horizontally at cemento -enamel junction to expose the dentinal surface using 600 grit silicone carbide bur to create an uniform flat surface. The dentin surface of the tooth were treated according to the manufacturer’s instructions

14. test Sher bond strength will be evaluated By Universal Testing Machine [MECMESIN]

15. Statistical analysis Data of the shear bond strength values are entered in Microsoft Excel and statistically analysed using One Way Anova . In order to find out among which pair of materials there exists a significant difference with respect to the strength, multiple comparisons will be done using Bonferroni test.

16. PROPOSED CONCLUSION Higher mean shear bond strength will be recorded for MultiCore Flow ( Ivoclar ) group followed by ParaCore (COLTENE) Lowest shear strength was recorded for RESIN MODIFIED GIC Resin modified glass ionomer cement can be used as a core build up material in situations where the tooth structure lost is minimal, as it had the least shear bond strength and its use may be limited to anterior esthetic zone.

17. Review of literature Kovarik RE et al (1992), compared the fatigue life of three core materials under simulated chewing conditions. Two types of prefabricated posts were placed in extracted teeth, followed by core buildups in amalgam, composite resin, or glass ionomer. The teeth were prepared for full cast crowns with the margins of the crown preparation extending 0.5 to 1.0 mm below the margins of the core buildup. Crowns were fabricated and cemented with zinc phosphate cement. A custom-designed chewing machine was used to cyclically load the teeth with vertical and horizontal forces for one million cycles or until failure occurred. The results of this study showed that amalgam cores had the lowest failure rate, followed by composite resin cores. Glass-ionomer core buildup had the highest failure rate .

18. Levartovsky S, Kuyinu E et al (1994), compared three mechanical properties of two recently introduced core materials, a light-activated glass ionomer cement ( VariGlass VLC) and a fluoride-release dual cure composite resin ( FluoroCore ), with those of a conventional silver-reinforced glass-ionomer cement (Miracle Mix). Seventy-two samples (eight per product for each property) were prepared for testing diametral tensile strength, flexural strength, and compressive strength. The specimens were cured and stored for 24 hours at 37 degrees C in 100% humidity, and tested with the use of an Intron universal testing machine. The results of this study showed that the diametral tensile strength, flexural strength, and compressive strength of FluoroCore and VariGlass VLC materials were significantly higher than those of the conventional Miracle Mix. The values obtained with FluoroCore material were higher than those obtained with VariGlass VLC material.

19. A study done by Cohen BI, Puntillo M et al (1997), to compare the fracture strength of three core restorative materials, lanthanide reinforced composite ( Ti -Core Natural), silver amalgam (Titin), and hybrid glass ionomer (Advance), supported by either a multitier, threaded split-shank post (Flexi-Flange) or with a dentin spur without a post. This study showed that all failures occurred either when the core material fractured or when the tooth fractured. No post failures were observed in this study. The result showed that there was a statistically significant difference between core materials. Ti -Core Natural material [composite] had a significantly larger mean failure threshold for fracture than either Tytin silver amalgam or Advance material. There was no statistical difference between Ti -Core material with and without a post.

20. A study was done by Shaini FJ, Fleming et al (1997) to compare the mechanical properties of a palladium free gallium-based alloy ( Galloy ) with a spherical highcopper amalgam ( Tytin ). Cylindrical specimens were mechanically condensed, to measure compressive strength, Vickers hardness test, static creep and dimensional change on setting. Disc and beam shaped specimens were manually prepared to assess the diametral tensile and flexural strengths of the investigated alloys. The galliumbased alloy investigated showed superior mechanical properties when compared with high copper amalgam alloy. There was a significant reduction in the mean compressive fracture strength and hardness identified for Galloy when compared with Tytin , the results of this study has concluded that galloy is better than tytin with respect to mechanical properties, however its effect on the oral environment should be studied further.

21. references Combe EC, Shaglouf AM, Watts DC, Wilson NHF: Mechanical properties of direct core materials. Dent Mat 1999;15:158-65. 2. Medina Tirado JI, Nagy WW, Dhuru VB, Ziebert AJ. The effect of themocycling on the fracture toughness and hardness of core buildup materials. J Prosthet Dent 2001;86:474-80. 3. Jayanthi N, Vinod V. Comparative evaluation of compressive strength and flexural strength of conventional core materials with nanohybrid composite resin core material an in vitro study. J Indian Prosthodont Soc July-sept 2013; 13(3):281-89. 4. ADA council on scientific affairs. Dental Amalgam: Update on safety concerns. J Am Dent Assoc 1998;129;494-503.