in the past , traditional dental luting agents such as zinc phosphate were commonly used 
 for cementation of crowns . in spite 
 of disadvantages , such as solubility , lack of retention and low ph , this luting agent has been successfully 
 used and was the most 
 researched cement for over a century . nowadays , some new adhesive luting agents have 
 been tested in order to reduce microleakage , increase retention , and improve physical 
 properties . currently , vegetable polyurethanes , which combine the versatility of polymer formulation 
 with the global concern in producing new biomaterials through resources that preserve 
 the environment , became one of the main studied categories of materials . in dentistry , membrane 
 material , sealers and irrigating 
 solution additionally , since this polyurethane 
 has been described as being biocompatible , osteoconductor , osteoinductor , antimicrobial , 
 osseointegrable and absorbable , it has been used in bone prosthesis , 
 alveolar healing and plastic surgery . in a study conducted by camargo , et al . ( 2010 ) , the castor oil bean showed less inflammatory 
 response in subcutaneous tissue of rats when compared with calcium hydroxide cement . this polyurethane has elasticity , good compatibility , versatility , composition and 
 structure that can be modified in accordance with specific requirements , characteristics that enable great 
 applicability in the biomedical area and open a new field to the development of dental 
 luting agents . in addition to the innumerable uses of the castor oil , the plant from 
 which it is extracted can be found in many parts of the world . it is greatly exploited 
 in brazil and india , and can be 
 produced on a large scale , which makes it interesting from an economic and ecological 
 point of view . in the oral environment , dental luting agents must withstand masticatory and 
 parafunctional stresses in different clinical situation . they should 
 maintain their integrity while transferring stresses from crowns or fixed partial 
 dentures to tooth structure . once the retention of crowns is intimately related to 
 mechanical properties of the dental luting agents , the strength of these materials 
 associated to the ability of resisting crack propagation , which causes ruptures , can predict the clinical success . resistant dental luting agents provide better stress distribution , less probability of 
 compressive or tensile failures and great probability of clinical success . diametral tensile strength ( dts ) is a mechanical property that must be 
 assessed because several 
 cements are extremely friable and have a susceptibility to mechanical failure . this test is widely used due to its 
 relative simplicity and reproducible results . additionally , it is the most common method 
 for assessing the tensile strength of friable materials because it avoids the 
 difficulties inherent to the flexural tensile strength test . in addition to the mechanical properties , physical properties , such as film thickness 
 ( ft ) of luting agents , can directly affect long - term clinical success . current iso standards require a ft at the time of 
 seating inferior to 25 m for water - based luting cements , and no greater than 50 m for resin - based 
 cements . low ft can improve 
 seating and decrease marginal gaps ; whereas improved marginal adaptation can also reduce 
 plaque accumulation , periodontal disease and cement dissolution . so , the purpose of this study was to 
 compare the dts and ft of an experimental polyurethane dental luting agent derived from 
 castor oil with traditional zinc phosphate cement . experimental groups , manufacturers and compositions of materials used in this 
 study cop= castor oil poliurethane ; mdi= methylene diphenyl disocyanato the castor oil polyurethane ( cop ) was supplied in sachet . pure cop contained the 
 prepolymer and polyol separately , while cop 10% and cop 50% included another separation 
 containing 10% or 50% in weight of filler ( calcium carbonate - caco3 ) , 
 respectively . the quantity of filler , in % weight , was determined by the manufacturer in 
 relation to the sum of the polyol and the prepolymer weights . the mixing method of cop 
 groups includes 2 min of manual mixing into the sachet and other 2 min of mixing with a 
 spatula on a teflon plate to obtain the final material ( figure 2 ) . homogeneous paste of castor oil polyurethane ( cop ) obtained after manual mixing 
 and mixing with a spatula on a teflon plate zinc phosphate was mixed within 90 s with a spatula following the incremental technique . the proportion of 1.4 g/0.4 ml recommended by the manufacturer was converted to 1.4 g of 
 powder/1.54 g of liquid . dts test : it was conducted with 40 cylindrical specimens ( 6.0 mm in 
 diameter x 3.0 mm in height ) divided into the 4 experimental groups ( n=10 ) . immediately 
 after the mixing , the materials were inserted in a teflon mold , which was put in a 
 mechanical press under constant load in an atmosphere of 100% relative humidity at 37c 
 for 1 h. subsequently , all specimens 
 were finished and polished with 400-grit abrasive sic papers ( buehlermet abrasive 
 papers , buehler , lake bluff , il , usa ) and were stored in distilled water at 37c for 24 
 h before the mechanical test . the specimens were subjected to a compressive load ( 10 kn ) 
 in a universal testing machine ( mts-810 material test system , eden praire , mn , usa ) at a 
 crosshead speed of 0.5 mm / min until fracture . the results were recorded and transformed 
 in tensile values ( mpa ) by the computer software ( test star ii , international business 
 machines corporation - ibm , armonk , ny , usa ) , connected to the system . the results were 
 submitted to one - way anova and tukey 's test ( =0.05 ) in order to compare the values of 
 dts among the 4 experimental groups . ft test : it was conducted with 40 specimens divided into the 4 
 experimental groups ( n=10 ) . the method for determining ft was described in iso 
 9917 . for pure cop , cop 10% 
 and cop 50% , immediately after the mixing , the dental luting agent was sandwiched 
 between two uniform thickness glass plates ( 2 cm ) with faces precisely 
 parallels . a load of 15 kg was applied vertically on the top of the glass plate . after 
 10 min , the thickness of the two plates with cement was determined using a micrometer 
 ( absolute digimatic micrometer 227 , mitutoyo sul america ltda , suzano , sp , brazil ) . the 
 ft of the cement was calculated by subtracting the thickness of the glasses without the 
 mixed material from the overall thickness . for zinc phosphate group , after 3 min of the 
 beginning of the mixture , the cement was inserted between the two glass plates and 
 submitted to the ft test as cited above . dts and ft values of each material are given in tables 
 1 and 2 . diametral tensile strength ( mpa ) of dental luting agents and standard 
 deviations different uppercase letters indicate significant differences by one - way anova 
 followed by hsd tukey test one - way anova ( p=1.01e-4 )   cop = castor oil polyurethane dts= diametral tensile strenght film thicknesses ( m ) of dental luting agents and standard deviations different uppercase letters indicate significant differences by one - way anova 
 followed by hsd tukey test one - way anova ( p=2.4e-10 ) cop = castor oil polyurethane   according to the statistical analysis , all cops ( pure cop , cop 10% and cop 50% ) 
 demonstrated significantly higher ( p<0.05 ) dts than zinc phosphate . the addition of 
 the filler ( caco3- 10% and 50% w / w ) increased dts . no significant differences 
 ( p>0.05 ) were found between the dts values of cop 10% and cop 50% . as shown in table 2 , ft values of cop 10% , cop 
 50% and zinc phosphate were inferior to 25 m ; only the pure cop exceeded this value . there was a positive influence of filler addition in the ft , since the comparisons pure 
 cop vs. cop 10% , pure cop vs. cop 50% , cop 10% 
 vs. cop 50% were minor than 0.05 i.e. , the mean values of ft 
 diminished as the quantity of filler was incorporated . this research assessed dts and ft of an experimental polyurethane dental luting agent 
 derived from castor oil , pure or with different quantities of caco3 , 
 comparing then with zinc phosphate cement . the zinc phosphate cement and cop differ each other because their viscous and elastic 
 components ; zinc phosphate is water - based cement which is more friable after the final 
 setting reaction , while cop is a polymer similar to resinous cements . when submitted to 
 tensile forces , cop shows a curve characteristic of polymers that undergo flow after the 
 linear region of elasticity , with plastic deformation occurring until rupture . the results showed that the addition of caco3 improves the dts of cop 
 independently of its percentage . calcium carbonate diminishes the plastic deformation of 
 cop causing an increase in the final resistance since this filler can fill any pores in 
 the matrix , allowing the cement resists to higher loads . the presence of 
 caco3 was also proven interesting because it provides radiopacity without 
 affecting biocompatibility . zinc phosphate cement had the lower dts ( 4.88 mpa ) when compared with cop . dts of cops 
 ( cop 10% and cop 50% ) was higher than values of glass ionomer cement ( 18 mpa ) and seems to be more close to the 
 literature results of resin cements which ( 40 - 45 mpa ) . with respect to ft , there is no agreement on its minimum value , but values between 
 50 - 100 m seem convenient . the 
 american dental association specification n. 8 restricts the zinc 
 phosphate ft ranging from 25 m to 40 m , but literature values of ft of a number of luting materials show 
 that it can range from 10 m to 152 m , depending on the nature of the 
 material . the results of this study showed that all evaluated dental luting agents , except pure 
 cop , had ft means inferior to 25 m , meeting the relevant iso standard . the differences found among the ft of 
 the evaluated materials may be explained by the nature and composition of them . while 
 the setting of zinc phosphate cement occurs by means of a water - based reaction with the 
 growth of the crystalline network of the zinc phosphate , the polymerization of cop includes a moisture curing 
 kinetics which is determined by a reaction between the isocyanate and hydroxyl groups , 
 showing a volumetric expansion and consequently higher ft . the obtained results of zinc 
 phosphate ( 20.04 m ) are in agreement previous studies . ft of cop diminished with the addition of caco3 making it lesser than that of 
 some resin cements . considering that 
 the volumetric expansion is linked to the quantity of organic matrix and that the 
 experimental cement may be composed by only organic matrix ( pure cop ) or by an organic 
 matrix with mineral filler ( cop+caco3 ) , the incorporation of filler 
 diminishes the expansion and consequently provides better ft values . despite the clinical importance of the two properties evaluated in this study , the 
 assessment of single properties is not sufficient to identify the best dental luting 
 agent . however , if an experimental dental luting agent does not have appropriate ft and 
 dts it will not allow the prosthesis serves the functions adequately over a long period . 
 among the various materials used for cementing indirect restorations and fixed dental 
 prostheses , although one of the experimental materials tested in this study provided better 
 results compared with zinc phosphate cement , further research is required . comparison 
 with other cements and evaluation of other properties , such as adhesion , hydrolytic 
 degradation and microleakage , can be the focus of future researches . finally , the 
 introduction of new materials , particularly those not derived from petroleum will enrich 
 the available arsenal of luting materials . within the limitations of this study , it was conclude that : 1 ) the polyurethane dental luting agent derived from castor oil ( cop ) with the addition 
 of caco3 filler showed better values of dts and ft when compared with zinc 
 phosphate cement . 2 ) for both dts and ft , the best composition of the experimental polyurethane dental 
 luting agent was the one with the addition of 50% w / w of caco3 . the authors of this paper thank to fapesp for financial support ( grants 06/02821 - 8 ; 
 06/00082 - 3 ; 07/02441 - 3 )