Composition, tensile strength, and elastic modulus of Orden as cast post alloy

Post is one element of the fixed restorations that is generally used to restore endodontically treated teeth at Prosthodontic Installation of Oral and Dental Hospital (RSGM) Faculty of Dentistry Universitas Padjadjaran, whereas Orden alloy is still used as cast post material. The faculty supplies Orden without packaging or manuals, so the information about its composition and mechanical properties are not available. This study was conducted to search the composition, tensile strength, and elastic modulus of Orden. For the composition test, specimen with size 20x20x2 mm3 was tested with Optical Emission Spectroscopy (OES). For tensile test, 6 specimens were made according to ASTM Standard E8. While for bending test, 6 specimens were made according to ASTM Standard E855. The Universal Testing Machine Instron 1195 was used to test the tensile strength and elastic modulus. The value of tensile strength of Orden was compared to gold alloy type III and the value of elastic modulus of Orden was compared to dentin. Composition test found that Orden was a brass with the largest ingredient of copper 53.76 wt%, followed by zinc 44.94 wt%, and alumunium 1.17 wt%. The statistic calculation showed that tensile strength of Orden was lower than gold alloy type III and the elastic modulus of Orden was higher than dentin.


INTRODUCTION
Post crown is one of fixed restoration which is commonly used to repair teeth that have undergone endodontic treatment.However, not all teeth that have been endodontically treated should be restored by making post crown.The use of post is an indication when the anatomic crowns have been damaged badly. 1,2n Prosthodontic Installation of RSGM Faculty of Dentistry UNPAD, clinic and preclinic students must meet the requirements for making cast post crowns on anterior teeth.The kind of metal commonly used for making cast post is Orden.
According to Martanto 3 , Orden is a base-metal alloy that is considered as soft metal.This metal is used because it is relatively cheap and easy to manipulate so that it is beneficial to patients and operators.
The metal used for post must have similar elastic modulus to dentin in order to evenly distribute the stress to the root, thus reducing the possibility of root fracture. 4,5The same opinion was also suggested by Akkayan 2 , Elias 6 , and Martinez-Inzua et al. 7 They stated that the posts that have the same elastic modulus as dentin can reduce the risk of root fracture. 2,6,7here are several types of posts, based on the manufacturing proces, posts can be divided into prefabricated posts and cast posts.Cast post is made by dentists by making appropriate wax patterns in the root canal preparation which is then casted with metal, while prefabricated post is made by manufacturers, available in various shapes, sizes, and materials. 3,8�ased on the type �ased on the type of the material, prefabricated post can be divided into stainless steel post, zirconium post, titanium post, and fiber post. 8he advantage of cast post is its good adaptation to the root canal walls because it is fitted to the shape of its root canal preparation. 2,9owever, cast post also has a disadvantage.The failure that might occur when using a cast post is the root fracture because the cast post itself has a high resistance against fracture. 10,11Several studies showed that a restoration with cast post can caused a high internal stress on the root. 10Martinez-Inzua et al. 2 reported that the magnitude of the fracture load of cast post was higher than fiber post. 12f a structure consisting of two different materials (such as post and dentine) receives a force, the material with higher elastic modulus will be able to withstand towards larger forces without changing the shape. 1,5,11,13����� ����� ����� ����� higher elastic modulus than that of dentin tend to cause root fracture, because the stress will be distributed and is concentrated in the roots that are less stiff. 1,5,11Posts that have lower elastic Posts that have lower elastic modulus than dentin tend to protect the dentin from fracture. 9,13trength is also very important in post metal selection, this correspond to post diameter. 1,5,8,146][17] Cast post is made in small diameter, Cast post is made in small diameter, not more than 1/3 of root diameter. 3With such a small diameter, the post must be able to withstand the chewing force. 1,14For reference, the strength For reference, the strength of Orden can be compared to gold alloy type III which is commonly used for posts based on the specifications of American Dental Association (ADA) No.5. 18rden used in Prosthodontic Installation of Oral and Dental Hospital (RSGM) Faculty of Dentistry Universitas Padjadjaran does not come with packaging and brochures, so the information about the composition of this metal cannot be obtained.Whereas, the composition of a material greatly affects its mechanical properties including its tensile strength and elastic modulus. 17Due to Due to the facts, the author is interested in studying the composition, tensile strength and elastic modulus of Orden in order to get information to consider the selection of this metal for a cast post.

MATERIALS AND METHODS
The research method used for composition test is a descriptive study.As for testing tensile strength and elastic modulus, pre-experimental research, called the one-shot case study was used. 19 The population of the research was Orden alloy supplied by Faculty of Dentistry of Universitas Padjadjaran.The samples were drawn randomly from the population according to the number needed to make research specimens.
This study used the specimens as follows: For composition test, one piece of metal specimen size 20x20x2 mm 3 (Fig. 1a); For tensile strength test (tensile test), 6 pieces of metal specimens with the shape and size in accordance with ASTM standard E8 (Fig. 1b). 20For elastic modulus test (bending test), 6 pieces of metal specimens size 80x13x0, 6mm 3 in ASTM standard E855 (Fig. 1c). 21he research procedure consisted of the manufacturing procedure for the test specimen and the testing procedure.The test specimen's production was using the "lost wax technique" casting method.The test procedures consisted of the composition test, tensile strength test and bending test.For the composition test procedure, the test specimen is inserted into the Optical Emission Spectroscopy (Fig. 2), and then it was shot with photon ray at 3 different points locations.Test results could be viewed at the computer print out.For tensile strength test procedure, calculate the width and thickness of each tensile test specimen to determine cross-sectional area.The specimen was placed on the test machine (Fig. 3), then was pulled with the speed of 1 mm/minute (Metallurgy Laboratory IT�).The results could be viewed on the computer in the form of load curve (kg) to the length elongation (mm).Perform data processing, the load curve to the elongation was processed into stress-strain curve.Tensile strength was determined from stress-strain curve by observing the maximum stress before the specimen fractured.
For the bending test procedure, calculate the width and thickness of each bending test specimen.The specimen was placed on the test machine (Fig. 4), then compressed at the speed of 0.5 mm/min (Laboratory of Metallurgy IT�).The results could be viewed on a computer in the form of load curve (kg) to the deflection (mm).Elastic modulus was determined using the following formula: Where: L = length of the specimen (mm) P = force (N) b = width of the specimen (mm) h = thickness of the specimen (mm) δ = deflection (mm) When the tensile strength and elastic modulus datas have been obtained, the average value and the standard deviation were determined.Then by using the t test, the tensile strength of orden was compared to the tensile strength of gold alloy type III, whereas the elastic modulus was compared to the elastic modulus of dentin.

RESULTS
�ased on the spectroscopy test result (Table 1), it was found that Orden was a copper-zincaluminum (Cu-Zn-Al) alloy.][24] The tensile strength of Orden was presented at Table 2. �ased on Table 2 the average value of the tensile strength of Orden was 300.6632MPa.The average value of the tensile strength of Orden was then compared to the tensile strength of gold alloy type III which was 448 MPa. 25 The test was done using t test one sample.it was found that the tensile strength of orden was lower than the tensile strength of gold alloy type III.�ased on the bending test data processing results the elastic modulus of orden was presented at Table 2. �ased on Table 2, the average value of elastic modulus was 80.2299 GPa.The average value of the elastic modulus of orden was compared to the elastic modulus dentin, which 17 GPa. 21The test was conducted using the t test one sample and it was found that the elastic modulus of orden was higher than dentin.It means orden cast post was stiffer than dentin.

DISCUSSION
Copper is a ductile and maleable metal. 17,23,24The addition of zinc increases the strength and zinc serves also as a deoxidizing agent that will prevent corrosion. 16,17,22Nickel increases the strength, hardness, and resistance to abrasion and corrosion. 15,17,23Aluminum (Al) increases the strength and resistance to corrosion. . 17,24ilicon (Si) increases the strength, hardness, resistance to corrosion, increases fluidity, and castability. 17,22Lead (Pb) increases the machinability. 234] Magnesium (Mg) increases the fluidity and castability. 17ure copper has a tensile strength of 200 MPa. 22From the results of this study; the tensile strength of orden was 300.66 MPa.�ased on these data, it can be concluded that addition of other metals can improve the tensile strength of copper.This is in line with some theories that explain the influence of the addition of other metals to copper.According to Johnson, the mixture of zinc and copper up to 45 wt% will increase the tensile strength. 23] One of the requirement for post metal alloy is that it should be made in the minimum diameter.It will be possible if the alloy has a high strength so that it will be strong enough to resist chewing forces. 1,9,14The higher the strength of the post, the smaller the diameter it can be mode. 8�ased on the result of statistical analysis, it was known that orden has a lower tensile strength than gold alloy type III.However, the usege of Orden as a cast post on the anterior teeth can still be considered if it is made with maximum root diameter of 1/3.To develop orden alloy, further research on the addition of other metals that can increase tensile strength needs to be conducted so that the tensile strength of orden can be similar to the gold alloy.
Pure copper has elastic modulus of 110 GPa. 26 While the results of this research noted that elastic modulus of orden was 80.22 GPa.�ased on the data, besides increasing the tensile strength, the addition of other metals to copper can also reduce the elastic modulus.However, based on the result of statistical analysis the elastic modulus of orden was still higher than that of dentin.Further research on addition of other metals which can reduce the elastic modulus of orden to be closer to dentin needs to be conducted.Thus, Orden can be more qualified to be used as post metal in terms of the modulus of elasticity.
6]12 �ased on this study, Orden has a higher elastic modulus than of dentin.Post with higher elastic modulus tends to cause root fracture because the strees will be distributed and is concentrated in the less stiff roots compared to the post, this should be avoided in the usage of a post. 1,5,11

CONCLUSION
The conclusions drawn from this study are as follows: Orden is the alloy of Cu-Zn-Al; Orden has a tensile strength of 300.66 Mpa; Orden has a lower tensile strength than gold alloy type III; Orden has elastic modulus of 80.22 GPa; Orden has a higher elastic modulus than that of dentin.

Figure
Figure 4. Bending test using Universal Testing Machine instron 1195.
Data of tensile strength test results and the elastic modulus were analyzed with t test.This research was conducted in the Prosthodontic Installation of Faculty of Dentistry, Universitas Padjadjaran, Laboratory of Metallurgy of Ministry of National Education Polytechnic of Manufacture �andung, and Metallurgy Laboratory of Institut Teknologi �andung.The research was conducted in November 2007 to March 2008.