***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: STATEMENT OF PROBLEM It is important that artificial crowns fit the prepared tooth accurately , as marginal deficiencies are predisposed to plaque accumulation and lead to increased risk of periodontal disease . Various methods of evaluation for marginal fit are described in the literature , but most approaches are limited by destructive methods of assessment and /or small points of measurement . PURPOSE This study compared , in vitro , the marginal fit of 4 types of complete crowns on human premolar teeth with the use of nondestructive profilometry . This method determined whether fit was influenced by type of crown or surface morphology of the tooth , namely , grooved or ungrooved surfaces . MATERIAL AND METHODS Four groups of specimens were prepared for complete crowns : group BA , bonding alloy with chamfer finish line ; group G , gold alloy with chamfer finish line ; group PC , porcelain with a chamfer finish line ;  and group PS , porcelain with a shoulder finish line . Two profiles of grooved mesial and ungrooved distal surfaces of the teeth were performed : ( 1 ) teeth prepared for each type of crown and ( 2 ) teeth with crowns seated but not cemented . Marginal fit ( absolute marginal discrepancy ) from the finish line edge of the tooth preparations to crown edges ( CE ) and leading edges ( LE ) of crowns were measured . RESULTS A 2-way analysis of variance for crown type and tooth surface morphology revealed significant differences between crown types for all measurement parameters , except vertical LE . The effect of surface morphology was not significant , except for vertical LE ( P<.05 ) . For all parameters , except vertical LE , the ranking of marginal fit discrepancies from greatest to least was as follows : group PC , G , BA , and PS . For vertical LE distances , the ranking was PS , BA , G , and PC ( P<.05 ) . CONCLUSION Profilometry was used as a nondestructive , accurate method of evaluating the absolute marginal fit of different types of crowns . Marginal fits varied continuously around the circumference of each crown and made clinical assessment of fit accuracy subjective and arduous OBJECTIVES This study evaluated the marginal misfit and microleakage of cement-retained implant-supported crown copings . METHODS Single crown structures were constructed with : ( 1 ) laser-sintered Co-Cr ( LS ) ; ( 2 ) vacuum-cast Co-Cr ( CC ) and ( 3 ) vacuum-cast Ni-Cr-Ti ( CN ) . Sample s of each alloy group were r and omly luted in st and ard fashion onto machined titanium abutments using : ( 1 ) GC Fuji PLUS ( FP ) ; ( 2 ) Clearfil Esthetic Cement ( CEC ) ; ( 3 ) RelyX Unicem 2 Automix ( RXU ) and ( 4 ) DentoTemp ( DT ) ( n=15 each ) . After 60 days of water ageing , vertical discrepancy was SEM-measured and cement microleakage was scored using a digital microscope . Misfit data were subjected to two-way ANOVA and Student-Newman-Keuls multiple comparisons tests . Kruskal-Wallis and Dunn 's tests were run for microleakage analysis ( α=0.05 ) . RESULTS Regardless of the cement type , LS sample s exhibited the best fit , whilst CC and CN performed equally well . Despite the framework alloy and manufacturing technique , FP and DT provide comparably better fit and greater microleakage scores than did CEC and RXU , which showed no differences . CONCLUSIONS DMLS of Co-Cr may be a reliable alternative to the casting of base metal alloys to obtain well-fitted implant-supported crowns , although all the groups tested were within the clinical ly acceptable range of vertical discrepancy . No strong correlations were found between misfit and microleakage . Notwithst and ing the framework alloy , definitive resin-modified glass-ionomer ( FP ) and temporary acrylic/urethane-based ( DT ) cements demonstrated comparably better marginal fit and greater microleakage scores than did 10-methacryloxydecyl-dihydrogen phosphate-based ( CEC ) and self-adhesive ( RXU ) dual-cure resin agents Numerous reports have suggested a relationship between marginal adaptation of dental castings and periodontal tissue health , and this study examined this relationship quantitatively . Forty-two crown restorations in 29 r and omly selected patients were selected for this study using three criteria . ( 1 ) The crowns were placed at the University of North Carolina School of Dentistry ; ( 2 ) the crowns were in service for a minimum of 4 years ; and ( 3 ) the crown margins were within the intracrevicular crevice ( subgingival ) . Replica impressions of the facial margins of specific crowns were made with a vinyl polysiloxane impression material , and poured casts were prepared for scanning electron micrograph evaluation . Marginal discrepancy measurements were identified on each micrograph at 10 equally spaced locations along the margin and averaged for each specimen . Periodontal indices of pocket depths , crevicular fluid volume , and gingival index were accumulated for clinical measurements . Pearson correlation and Bonferroni adjusted probability tests were performed , but no significant correlation was found between marginal discrepancy ( 0.16 + /- 0.13 mm ) and pocket depth ( 2.4 + /- 0.9 mm ) . However , a strong correlation ( p less than 0.001 ) existed between marginal discrepancy and gingival index ( 2 + /- 0.8 ) and between marginal discrepancies and crevicular fluid volume ( 49.9 + /- 31.1 ) . These results established that a significant quantitative relationship existed between the marginal discrepancy and periodontal tissue inflammation for subgingivally located crown margins PURPOSE This study evaluated the marginal fit of  experimental and custom-made fixed prosthetic restorations  through a new 360-degree external examination . The minimum number of gap measurements required to produce relevant results for gap analysis was also investigated . MATERIAL S AND METHODS The marginal fit of six experimental and eight custom-made crowns  was observed microscopically by means of a mechanical device , and software was employed to measure the gap . Two crowns , chosen from among the 14 previously evaluated , were reanalyzed to determine the minimum number of gap measurements required to produce significant results for gap analysis . RESULTS The precision obtained with the custom-made crowns differed from that of the experimental specimens . The minimum number of measurements required to produce a sample mean value within + /- 5 microm of the mean , calculated over 360 measurements , taking st and ard error of the means < or = 4 microm , was 18 for experimental and 90 for custom-made crowns , for both equidistant measurement spacing and r and omly selected points . CONCLUSION Differences in fit between experimental specimens and custom-made ones showed that experimental results might not always be obtained in clinical practice . Within the limitations of the protocol of this study , the minimum number of measurements required to ensure relevant results for gap analysis was 18 for experimental and 90 for custom-made crowns OBJECTIVE The aim of the present work was to compare the marginal precision of titanium frameworks for a complete arch-fixed prosthesis fabricated using five different methods . METHODS A prospect i ve study was design ed . Fifteen titanium frameworks for totally edentulous upper or lower jaws , each supported by five to nine implants , were assigned to five study groups , so as to have three frameworks in each group for each technique : ( 1 ) lost wax technique frameworks , ( 2 ) cast titanium sovrastructures laser welded to prefabricated titanium copings , ( 3 ) Procera Implant Bridge , ( 4 ) Cresco Ti System and ( 5 ) CAM StructSURE Precision Milled Bar . The microgap between the framework and the shoulders of implant analogues was measured on the master cast with a stereomicroscope at a magnification of 100 x at four different locations , yielding a total of 364 data points on 91 implants . Data were analyzed using an ANOVA and a Tukey post hoc test ( P=<0.05 ) . RESULTS The mean values for the microgap were 78 microm ( SD+/-48 ) for lost wax technique frameworks , 33 microm ( SD+/-19 ) for cast titanium sovrastructures laser welded to titanium copyings , 21 microm ( SD+/-10 ) for the Procera implant bridge , 18 microm ( SD+/-8 ) for the Cresco Ti System and 27 microm ( SD+/-15 ) for the CAM StructSURE . The differences among the mean values were statistically significant ( P<0.01 or P<0.05 ) . The comparisons among groups 3 , 4 , and 5 and between groups 2 and 5 were not significant ( P>0.05 ) . CONCLUSION The computer-aided procedures analyzed in the present study were able to produce a precision-fitting framework , with no significant differences among them and , at the same time , showed a greater precision compared with the traditional casting methods or with the use of prefabricated titanium copings . However , it should be noted that , even if group 2 frameworks were not as accurate as groups 3 and 4 , cast titanium sovrastructures laser welded to prefabricated titanium copings showed significantly better marginal precision than the frameworks produced with the lost wax technique PURPOSE The aims of this r and omized-controlled clinical trial were to compare marginal and internal adaptation of  all-ceramic crowns fabricated with CAD/CAM and heat-pressed ( HP ) techniques  before luting and to evaluate the clinical outcomes at baseline and at 6 , 12 , and 24 months after luting . MATERIAL S AND METHODS Fifteen CAD/CAM ( CC ) and 15 HP all-ceramic crowns were placed in 15 patients . A silicone replica was obtained to measure marginal and internal adaptation of each all-ceramic crown before luting , and they were sectioned buccolingually and mesiodistally . Marginal and internal adaptations were measured using computerized light microscope at 40 × magnification . Clinical evaluations took place at baseline ( 2 days after luting ) and at 6 , 12 , and 24 months after luting . Replica scores were analyzed with Mann-Whitney U and Student 's t-test ( α = 0.05 ) . Survival rate of crowns was determined using Kaplan-Meier statistical analysis . RESULTS The median marginal gap for the CC group was 132.2 μm and was 130.2 μm for the HP group . The mean internal adaptation for the CC group was 220.3 ± 51.3 μm and 210.5 ± 31 μm for the HP group . There were no statistically significant differences with respect to marginal opening ( Mann-Whitney U test ; p = 0.95 ) and internal adaptation ( Student 's t-test ; p = 0.535 ) between the 2 groups . Based on modified Ryge criteria , 100 % of the crowns were rated satisfactory during the 2-year period . CONCLUSION In this in vivo study , CAD/CAM and HP all-ceramic crowns exhibited similar marginal and internal adaptations . A 100 % success rate was recorded for the 15 CAD/CAM and for the 15 HP all-ceramic crowns during the 2-year period The objective of this study was to measure marginal fit of  castable ceramic versus gold crowns . Full veneer gold and ceramic crowns were made on Ivorine dies . Crowns were cemented , embedded , sectioned faciolingually and mesiodistally , and photographed for measurement of absolute marginal discrepancies ( cavosurface angle to casting margin ) to evaluate fit . Results revealed no statistically significant differences in fit among four locations around the margins of either ceramic or gold crowns . There was no statistically significant difference in the combined absolute marginal discrepancy ( fit ) between ceramic and gold crowns . The variance of the combined absolute marginal discrepancy ( fit ) of the ceramic crowns was significantly different than that of the gold crowns ( p = 0.01 level ) . The st and ard deviation ( variability ) of the gold crowns was more than twice that of the ceramic crowns . R and omized block ANOVA demonstrated statistically significant differences among individual gold crown specimens , but none among individual ceramic crown specimens 
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Results : Of the 55 included comparative studies , 28 compared CAD‐CAM technology with  conventional fabrication techniques  , 12 contrasted CAD‐CAM technology  and copy milling  , 4 compared CAD‐CAM milling with direct metal laser sintering ( DMLS ) , and 22 investigated the performance of a CAD‐CAM system regarding marginal adaptation in restorations/infrastructures produced with different restorative material s. Conclusions : Most of the CAD‐CAM restorations/infrastructures were within the clinical ly acceptable marginal discrepancy ( MD ) range .
The performance of a CAD‐CAM system relative to marginal adaptation is influenced by the restorative material .
Compared with CAD‐CAM , most of the heat‐pressed lithium disilicate crowns displayed equal or smaller MD values .
Slip‐casting crowns exhibited similar or better marginal accuracy than those fabricated with CAD‐CAM .
Cobalt‐chromium and titanium implant infrastructures produced using a CAD‐CAM system elicited smaller MD values than zirconia .
The majority of cobalt‐chromium restorations/infrastructures produced by DMLS displayed better marginal accuracy than those fabricated with the casting technique .
Compared with copy milling , the majority of zirconia restorations/infrastructures produced by CAD‐CAM milling exhibited better marginal adaptation .
No clear conclusions can be drawn about the superiority of CAD‐CAM milling over the casting technique and DMLS regarding marginal adaptation