Effect of material and connector position on the accuracy of CAD-CAM milled posts.

STATEMENT OF PROBLEM: Subtractive manufacturing is a popular technique for custom post-and-core fabrication. Milling accuracy affects restoration-root canal fit; however, the inherently slender structure of posts may cause machining deviations, and the effects of material properties and connector position on accuracy remain unclear.

PURPOSE: The purpose of this in vitro study was to evaluate the effects of material properties and connector position on the manufacturing accuracy of milled posts.

MATERIAL AND

METHODS

A digital reference model was created based on a standard prefabricated fiber post. Two connector positions were designed: a coronal third connector (CTC) and a middle third connector (MTC). Polyetheretherketone (PEEK) and fiber-reinforced composite (FRC) milling blanks were used to fabricate specimens using a 5-axis milling machine (n=10). The specimens were scanned using a desktop scanner. The obtained standard tessellation language (STL) files were imported into a reverse engineering software program for alignment and 3-dimensional (3D) deviation analysis with the reference model. Root mean square (RMS) values were calculated for trueness and precision. Additionally, maximum positive and negative deviations were recorded. Data were analyzed using 2-way ANOVA and post hoc tests (α=.05).

RESULTS

Material and connector position each had significant main and interaction effects on trueness and precision (P<.05). Overall, PEEK showed higher trueness than FRC. FRC-CTC showed the lowest trueness (70.0 ±6.9 μm), while PEEK-MTC achieved the highest precision (13.5 ±3.7 μm). For maximum positive deviation, both FRC and the CTC design caused higher values (P<.05), with the highest found in FRC-CTC (162.8 ±17.3 μm). For maximum negative deviation, the highest value was found in PEEK-CTC (157.5 ±29.9 μm). The connector position significantly influenced this deviation for PEEK (P<.001), but not for FRC (P>.05).

CONCLUSIONS

Material properties and connector position significantly influenced the milling accuracy of posts. PEEK showed superior trueness and precision compared with FRC. The MTC design significantly improved milling accuracy for slender post structures.