Effect of ring length and diameter on effective radial setting expansion

Area of Science:

• Dental Materials Science
• Casting Technology
• Biomaterials Engineering

Background:

• Previous research indicated an inverse relationship between MOD inlay casting flaring and casting ring diameter.
• The precise mechanisms driving this inverse proportion, particularly the role of investment setting expansion, required further investigation.

Purpose of the Study:

• To ascertain if radial setting expansion of investment is the main cause of the inverse proportion observed in casting ring diameters.
• To further characterize the fluid mechanics of setting expansion by measuring it in casting rings of varying lengths and diameters.

Main Methods:

• MOD inlay wax patterns with radiopaque markers were invested in plastic casting rings of different lengths and diameters.
• Specimens were imaged using xeroradiography at set intervals during setting, with dimensions measured from the images.
• Statistical analysis was performed to determine the significance of observed differences in setting expansion.

Main Results:

• No significant differences in total effective setting expansion were found in casting rings of varying lengths (p > 0.05).
• Setting expansion decreased proportionally with increasing ring diameter, ranging from 1.3% to 1.5% in 28-mm diameter rings.
• Significant differences in total expansion were observed with varying ring diameters (p < 0.001), showing an inverse proportion (p < 0.001).

Conclusions:

• Investment setting expansion is identified as the primary determinant of mold expansion in dental casting.
• The diameter of the casting ring significantly influences setting expansion, with smaller diameters yielding greater expansion.
• Understanding these fluid mechanics is critical for optimizing the accuracy of MOD inlay castings.