Journal List > J Korean Acad Prosthodont > v.54(3) > 1034875

Ko, Kim, and Cho: Comparison of micro CT and cross-section technique for evaluation of marginal and internal fit of lithium disilicate crowns

Abstract

Purpose

The purpose of this study was to evaluate the adaptation of lithium disilicate crowns fabricated by CAD-CAM (computer aided design-computer aided manufacturing) and heat-press technique to compare two different measurement methods in assessing fit of the ceramic crowns: micro CT and cross-section technique.

Materials and methods

A prepared typodont mandibular molar for ceramic crown was duplicated and ten dies were produced by milling the PMMA (polymethylmethacrylate) resin. Ten vinyl polysiloxane impressions were made and stone casts were produced. Five dies were used for IPS e.max Press crowns with heat-press technique. The other five dies were used for IPS e.max CAD crowns with CAD-CAM technique. Ten lithium disilicate crowns were cemented on the resin dies using zinc phosphate cement with finger pressure. The marginal and internal fits in central buccolingual plane were evaluated using a micro CT. Then the specimens were embedded and cross-sectioned and the marginal and internal fits were measured using scanning electronic microscope. The two measurement methods and two manufacturing methods were compared using Mann-Whitney U test (SPSS 22.0).

Results

The marginal and internal fit values using micro CT and cross-section technique were similar, showing no significant differences. There were no significant differences in adaptation between lithium disilicate crowns fabricated with CAD-CAM and heat-press technique.

Conclusion

Both micro CT and cross-section technique were acceptable methods in the evaluation of marginal and internal fit of lithium disilicate crown. There was no difference in adaptation between lithium disilicate crowns fabricated with CAD-CAM and heat-press technique except occlusal fit. (J Korean Acad Prosthodont 2016;54:226-33)

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Fig. 1.
Prepared resin master die.
jkap-54-226f1.tif
Fig. 2.
Micro CT analysis of adaptation.
jkap-54-226f2.tif
Fig. 3.
Eight reference points showing sites of marginal fit (1, 8), cervical fit (2, 7), axial fit (3, 6) and occlusal fit (4, 5).
jkap-54-226f3.tif
Fig. 4.
Cross-sectioning of resin die-ceramic crown complex.
jkap-54-226f4.tif
Fig. 5.
SEM analysis of adaptation. LDS: lithium disilicate.
jkap-54-226f5.tif
Table 1.
Descriptive statistics of internal adaptation according to fabricating method using micro CT and cross section technique
Reference point Group Micro CT Cross section technique
Median (㎛) Mann-Whitney U P Median (㎛) Mann-Whitney U P
Marginal fit CAD-CAM 130.5 48.5 .909 136 43 .597
Heat-press 170.5     185.5    
Cervical fit CAD-CAM 121.5 39.5 .426 142.5 46 .762
Heat-press 161.5     180    
Axial fit CAD-CAM 67.5 37 .322 86 33.5 .212
Heat-press 84     104.5    
Occlusal fit CAD-CAM 206 33 .198 222 25 .059
Heat-press 143.5     155    
Table 2.
Descriptive statistics of internal adaptation of lithium disilicate crowns according to measurement method
Reference point Group CAD-CAM Heat-press technique
Median (㎛) Mann-Whitney U P Median (㎛) Mann-Whitney U P
Marginal fit Micro CT 130.5 47 .821 170.5 44 .649
Cross section 136     185.5    
Cervical fit Micro CT 121.5 43 .596 161.5 48 .880
Cross section 142.5     180    
Axial fit Micro CT 67.5 48 .880 84 31.5 .160
Cross section 86     104.5    
Occlusal fit Micro CT 206 48 .879 143.5 48 .879
Cross section 222     155    
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