zirconia has excellent aesthetic quality , biocompatibility , and mechanical property . in addition , the price of zirconia is inexpensive compared to gold . thus , zirconia is getting attention as a proper material for posterior teeth restoration to replace the existing ceramic.123 commercialization of zirconia is closely linked to the development of cad / cam introduced to the dental industry 20 years ago.456 recently , the introduction of new cad / cam milling technology and new zirconia made it possible to manufacture anatomic contour zirconia crown , enabling the forming of occlusal surface anatomically instead of in the form of porcelain veneer.78 anatomic contour zirconia crowns have excellent fracture resistance property because it does not have superstructure . in addition , it has higher strength even when the volume of tooth preparation is small during the manufacture of a crown.9 however , long - term clinical success of dental restoration is influenced not only by mechanical property , aesthetic quality , and biocompatibility , but also by marginal fit . large marginal gap causes failure of a crown by dissolving dental cement so quickly that plaques easily accumulate , leading to marginal leakage and secondary caries.1011 through in vitro and in vivo studies on marginal fit of dental restorations , marginal fit has been proven to be one of the major factors causing secondary caries and periodontal diseases.1213141516 it has been proven by mclean in 1971 that clinically allowable marginal fit is within 120 m range when fabricating a dental restoration.17 martnez - rus has reported that cad / cam ceramic crown has clinically allowable marginal fit within the range of 17 to 118 m.18 chamfer margins and shoulder margins were recommended to fabricate the precise anatomic contour crowns.19 although computer - controlled technique is used in producing dental restoration in order to improve the accuracy during the manufacturing process , not enough studies have been conducted on the marginal fit of anatomic contour zirconia crowns fabricated using cad / cam system . therefore , the objective of this study was to compare the marginal fit of anatomic contour zirconia crown to that of lithium disilicate glass ceramic crown regarding the finish line configuration and fabrication systems . null hypotheses for this experiment are as follows : ( 1 ) finish line configuration has no influence on the marginal fit of anatomic contour crowns ; ( 2 ) fabrication systems do not affect the marginal fit of anatomic contour crown . an acrylic resin model of maxillary first premolar ( columbia dentiform corp , long island city , ny , usa ) was prepared . tooth reduction was uniformly conducted with hand piece mounted in a milling machine ( f4 basic , dentsplydegudent , germany , fig . an occlusal reduction of 1.5 mm at the center of the occlusal surface was executed . the definitive die had a 1 mm shoulder and deep chamfer margin on each mesiodistal and buccolingual marginal surface ( fig . four reference points were formed at the middle of the buccal , palatal , mesial , and distal root surface of tooth margin for later measurements . the width of each margin was managed by keeping it no wider than half of the diamond tip used for preparation . a flat - end diamond bur with 2.3 mm in diameter ( komet 6848.314.023 ; gebr . a tapered diamond bur with 2.1 mm in diameter ( komet 6856.314.021 ; gebr.brasseler gmbh & co kg ) was used for the chamfer margin . the widths of the margins were measured with a 3-dimensional measuring microscope ( measuring microscope ; mitutoyo , kawasaki , japan ) to determine whether planned dimensions ( 1 mm shoulder and chamfer ) were achieved . forty eight impressions of the resin tooth were obtained from the definitive die by using a light viscosity and putty vinyl polysiloxane ( exaflex and exafine ; gc corporation , tokyo , japan ) . forty eight impressions were poured with type iv die stone ( suprastone , kerr corporation , orange , ca , usa ) . each stone die was carefully removed from the impression and examined for the presence of air bubbles or other defects . two cad / cam system ( prettauzirconia ; zirkonzahn gmbh ; gais , italy / zenostarzr translucent ; wieland dental gmbh , pforzheim , germany ) zirconia crowns and ips e.maxpress ( ivoclarvivadent ag , schaan , liechtenstein ) lithium disilicate glass ceramic crowns were divided into three groups according to fabrication methods ( n=16 ) . each group was sub - categorized into two groups ( shoulder margin , chamfer margin ) based on the finish line configuration . therefore , a total of 6 groups were used in this study ( n=8 , table 1 ) . all crowns were fabricated with anatomical shape according to the directions of manufacturing companies for each fabrication system ( fig . 3 ) . the 5-tec cad / cam system ( zirkonzahn gmbh ; gais , italy ) was used to fabricate the prettauzirconia crowns . the dies were scanned sequentially with a scanner s600 arti ( zirkonzahn gmbh ; gais , italy ) . zirkonzahnarchiv software ( zirkonzahn gmbh ; gais , italy ) was used to design anatomic contour zirconia crowns . the simulated die spacer was programmed at 30 m , starting at 1 mm ahead from the margin . the prettau zirconia blocks were milled with m5 milling machine ( zirkonzahn gmbh ; gais , italy ) . all specimens were fired in a furnace ( zirkonofen600 ; zirkonzahn gmbh ; gais , italy ) at 1600. the zeno tecsystem ( zenotec ; wieland dental gmbh , pforzheim , germany ) was used to fabricate the zenostarzr translucent crowns . the dies were scanned sequentially with 3shape d250 ( wieland dental gmbh , pforzheim , germany ) . anatomic contour zirconia crowns were designed with design software ( dental designer ; wieland dental gmbh , pforzheim , germany ) . this information was transmitted to a milling machine ( zenotec t1 ; wieland dental gmbh , pforzheim , germany ) . the crowns were produced by milling the zenostar zr translucent block and firing ( zenotec fire ; wieland dental gmbh , pforzheim , germany ) at 1450. the ips e.maxpress lithium disilicate glass ceramic crowns were fabricated using the lost wax technique . two coats of die spacer were applied to the stone dies20 1 mm above the cervical end of the preparation to ensure good marginal fit . the crowns were fabricated by pressure injection of ceramic ingots in the programatep5000 furnace ( ivoclarvivadent ag , schaan , liechtenstein ) following the manufacturer 's recommendations . forty eight crowns were luted with resin cement ( rely x unicem , 3 m espe , seefeld , germany ) on the stone dies , respectively . all crowns that were completely bonded to stone dies were embedded with acrylic resin ( caulk , dentsply , milford , de , usa ) for observation . cured resin blocks were cut in the middle of buccopalatal and mesiodistal directions using linear precision saw ( isomet 5000 ; buehler ltd . , lake bluff , il , usa ) referring to four reference points . each reference point of every sample was measured three times using a light microscope equipped with a digital camera ( leica dfc295 ; leica microsystems ltd . , the marginal gap and the absolute marginal discrepancy were measured . the perpendicular measurement from internal surface of the crown to the edge of the tooth finish line the distance from the edge of the crown to the edge of the tooth finish line was defined as absolute marginal discrepancy ( fig . two - way analysis of variance ( anova ) and post - hoc tukey 's hsd test were conducted to analyze significance of crown marginal fit regarding the finish line configuration and the fabrication system . the mean marginal gap of shoulder and deep chamfer finish line configurations was 118.8  78.2 m and 109.0  83.3 m in the prettauzirconiagroup , 91.5  43.7 m and 84.7  41.5 m in the zenostarzr translucent group , 41.2  31.0 m and 40.5  42.9 m in the ips e.maxpress group , respectively ( table 2 ) . the two - way anova showed that the fabrication system significantly influenced the marginal gap ( p<.05 ) . there was no significant difference in marginal gap depending on the finish line configuration , and in the interaction between the fabrication system and the finish line configuration ( p>.05)(table 3 ) . according to tukey honestly significant difference ( hsd ) test results , the mean absolute marginal discrepancy of shoulder and deep chamfer finish line configurations was 73.9  32.9 m and 37.8  37.1 m in the prettauzirconia group , -14.3  61.2 m and -51.3  66.9 m in the zenostarzr translucent group , 29.4  19.1 m and 22.5  20.5 m in the ips e max press group , respectively ( table 4 ) . zenostarzr translucent had under - extended margin , whereas prettauzirconia and ips e.maxpress had over - extended margin . the two - way anova analysis results showed that both the fabrication system and the finish line configuration significantly influenced the absolute marginal discrepancy ( p<.05 ) . tukey honestly significant difference ( hsd ) test indicated a significant difference between ips e.maxpress and zenostarzr translucent , and also between prettau zirconia and zenostarzr translucent ( p<.05 ) . this study examined the marginal fit of two cad / cam anatomic contour zirconia crowns ( prettauzirconia of zikozahnandzenostarzr translucent of wieland dental ) and lithium disilicate glass ceramic crowns ( ips e.maxpress of ivoclarvivadent ) which are widely used clinically . the null hypothesis that the fabrication system has no influence on marginal fit of anatomic contour crowns was rejected , whereas the other null hypothesis that the finish line configuration has no influence on marginal fit of anatomic contour crown was accepted . each crown was sectioned at the same position with four reference points . to simulate the cementation of the clinical situation , finger pressure was applied to each of the crowns for ten minutes . in general , sectioning embedded specimens22232425 and direct visualization2627 are the two methods used to measure marginal fit . direct visualization has an advantage that it is measurable without destroying specimens , making it applicable under clinical situation . however , it is hard to obtain precise measurements by direct visualization.24 the sectioning method was used in this study in order to measure marginal fit precisely . our results revealed that the maximum marginal gap was 118.8  78.2 m when shoulder margin was formed on crowns using prettauzirconia . the amount of marginal gap was in the clinically acceptable range according to martnez - rus.18 the marginal fit of restoration manufactured by cad / cam system was increased compared to the ips e.maxpress system . procedures added on computers caused some errors , although handwork errors were reduced by the cad / cam system.28 the large marginal gap compared to other studies are due to shrinkage error that could increase before and after sintering due to the larger material volume of anatomic zirconia crowns than zirconia copings . the differences in marginal fit between each system result from zirconia blocks with various shrinkage rates depending on manufacturing company , scanning process , size of milling bur used , and the number of milling axis . therefore , the use of a loading device is needed to apply uniform load on all crowns . in addition , stone dies instead of teeth were used to evaluate marginal fit of anatomic contour crown . although stone dies or resin dies have been allowed to be used for evaluating marginal fit,2429 the use of human tooth would be ideal to simulate clinical procedure . the results of this study suggest that ips e.maxpress is better than prettauzirconia regarding the marginal gap when fabricating an anatomic contour crown . further study and clinical applications should be performed to compensate for the shrinkage of zirconia that might happen during the fabricating procedure . the development of cad / cam technology is needed to produce more accurate milling process . within the limitations of this study , we have the following conclusions : 1 ) ips e.maxpress had significantly smaller marginal gap than prettauzirconia ; 2 ) finish line configuration did not show significant influence on the marginal gap ; 3 ) in terms of absolute marginal discrepancy , zenostarzr translucent had under - extended margins , whereas prettau zirconia and ips e.maxpress had over - extended margins ; 4 ) the measured marginal gaps of the two cad / cam anatomic contour zirconia crown and lithium disilicate glass ceramic crown were within the range of clinical acceptance .
purposethis study was to evaluate the marginal fit of two cad - cam anatomic contour zirconia crown systems compared to lithium disilicate glass - ceramic crowns.materials and methodsshoulder and deep chamfer margin were formed on each acrylic resin tooth model of a maxillary first premolar . 
 two cad - cam systems ( prettauzirconia and zenostarzr translucent ) and lithium disilicate glass ceramic ( ips e.maxpress ) crowns were made ( n=16 ) . 
 each crown was bonded to stone dies with resin cement ( rely x unicem ) . marginal gap and absolute marginal discrepancy of crowns were measured using a light microscope equipped with a digital camera ( leica dfc295 ) magnified by a factor of 100 . 
 two - way analysis of variance ( anova ) and post - hoc tukey 's hsd test were conducted to analyze the significance of crown marginal fit regarding the finish line configuration and the fabrication system.resultsthe mean marginal gap of lithium disilicate glass ceramic crowns ( ips e.maxpress ) was significantly lower than that of the cad - cam anatomic contour zirconia crown system ( prettauzirconia ) ( p<.05 ) . both fabrication systems and finish line configurations significantly influenced the absolute marginal discrepancy ( p<.05).conclusionthe lithium disilicate glass ceramic crown ( ips e.maxpress ) had significantly smaller marginal gap than the cad - cam anatomic contour zirconia crown system ( prettauzirconia ) . in terms of absolute marginal discrepancy , 
 the cad - cam anatomic contour zirconia crown system ( zenostarzr translucent ) had under - extended margin , whereas the cad - cam anatomic contour zirconia crown system ( prettauzirconia ) and lithium disilicate glass ceramic crowns ( ips e.maxpress ) had overextended margins .