Effect of 30 Degree Taper on Molar CAD/CAM Crown Retention
Abstract
Objective: Evaluate the effect of molar 30 deg total occlusal convergence (TOC), at varying axial wall heights (AWH), on retention of adhesively bonded lithium disilicate CAD/CAM crowns. Methods: Sixty recently extracted third molars were divided into 5 groups (n=12). Each group received standardized 30 deg TOC all-ceramic crown preparations. Groups consisted of preparations with AWH 0-4mm. The surface area, mean AWH, and mean TOC for each preparation was determined using a digital measuring microscope (KH-7700, Hirox USA). The preparations were scanned (Sirona CEREC Omnicam AC/ CEREC MC XL), fitted with milled lithium disilicate crowns (IPS e.max CAD) and cemented with a dual cure self-adhesive resin cement (RelyX Unicem 2) following HF acid etching and silanation. All manufacturer recommendations were followed. Specimens were stored at 37 deg C/98% humidity for 24 hours and then tested to failure at a 45 deg angle on a universal testing machine. Failure load was recorded in Newtons (N) and failure stress calculated in megapascals (MPa) using the available bonding surface area with mean data analyzed using Kruskal-Wallis/Dunns post hoc test (p=0.05). Results: With regards to mean failure load, 2-4mm AWH preparations were statistically similar. Although failure stress was calculated, the research and clinical relevance of these values has yet to be determined.Conclusions: Within the limitations of this study, when preparing molar teeth for milled lithium disilicate crowns to be bonded with dual cure self-adhesive resin cement, an abutment height as minimal as 2mm provides adequate resistance form. However, total occlusal convergence appears to be more critical than abutment height.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 21, 2018
- Accession Number
- AD1128506
Entities
People
- Terrell M. Mitchell
Organizations
- Uniformed Services University of the Health Sciences