Current techniques used for characterising the geometry of the tooth-crown interface lack accuracy and inter-specimen reproducibility and repeatability. The aim was to test the accuracy, repeatability and reproducibility of a new interface measurement technique that uses micro-CT imaging and computational analysis.
Method:
An all-ceramic crown preparation was prepared on a typodont maxillary first premolar in accordance with the manufacturer’s guidelines (Ivoclar-Vivadent AG). 15 dies were duplicated from the master and divided into 5 equal sets. Lithium-disilicate glass ceramic crowns (IPS e.max®; Ivoclar Vivadent AG) were fabricated for each die using 5 different techniques: Manually-applied wax spacer and pressed-crown; vacuum-formed 0.1mm spacer (Isofolan®, Scheu Dental GmbH) and pressed-crown; 3D-printed wax pattern (Solidscape D76PLUS, Solidscape Inc.) and pressed-crown; digital scan and machined-crown (CEREC-inLab® v3.6 Sirona AG), digital scan and machined-crown (Zirkonzahn-5TEC®, Zirkonzahn GmbH). The fitting surface of the crowns was unaltered and the crowns were cemented with a resin-based cement (Panavia F2.0®, Kuraray Dental) mixed with barium sulphate to improve the contrast ratio. The cementation technique was standardised using a universal testing machine (Lloyd LRX®, Lloyd Materials Testing Inc). The samples were micro-CT scanned (Skyscan 1172®, Bruker-Micro CT), a 3D digital model was constructed (MIMICS 14.1, Materialise Co., Ltd) and the digital model was segmented into its component parts; the ceramic crown, resin cement and tooth. A technique was developed to accurately measure the interface dimensions in multiple planes with a resolution of 1µm for all specimens in a reproducible manner.
Result:
One-way ANOVA (p ≤ 0.05) indicated a significant difference in interface thickness between the five groups. Tukey’s HSD multiple comparisons indicated a significantly more homogenous interface width for the ‘manually-applied wax and pressed-crown’ group.
Conclusion:
This technique enabled high accuracy and intra- and inter-specimen measuring reproducibility and repeatability with effective 3D comparison of the interface geometry.