J Korean Acad Prosthodont.  2021 Oct;59(4):395-404. 10.4047/jkap.2021.59.4.395.

Comparison of internal and marginal fit of crown according to milling order in a single machinable wax disc

• Song JB
• Lee J
• Ha SR
• Choi YS

• KMID: 2521833
• DOI: http://doi.org/10.4047/jkap.2021.59.4.395

Abstract

Purpose
The purpose of present study was to evaluate the effect of changing structural stability of wax disc on the fit of prosthesis when the milling proceeded in order.
Materials and methods
Prepared maxillary left first molar was used to fabricate a Ni-Cr alloy reference model. This was scanned to design crown and then wax pattern was milled, invested and cast to fabricate prosthesis. The wax patterns located in a row centrally within a single wax disc were set into a total of five groups ranging from WM1 group that was first milled to WM5 group that was last milled and the number of each group was set as 10. Silicone replica technique was used to measure the marginal gap, axial internal gap, line angle internal gap, occlusal internal gap. Data was evaluated with one-way ANOVA with significance level set at α = .05 and then Tukey HSD test was conducted for post analysis.
Results
Marginal gap measured in each group, it was 40.41 ± 2.15 µm in WM1 group, 40.44 ± 2.23 µm in WM2 group, 39.96 ± 2.25 µm in WM3 group, 39.96 ± 2.48 µm in WM4 group, and 40.57 ± 2.53 µm in WM5 group. No significant difference was found between groups. The significant difference between the groups was also not found in the axial internal gap, line angle internal gap, and occlusal internal gap.
Conclusion
Internal and marginal fit of single crown to the sequential order of milling processing in the single machinable wax disc did not seem to be affected by the sequence.

Keyword

CAD-CAM; Elastic deformation; Machinable wax disc; Marginal gap; Milling; Internal gap; Silicone replica