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Bicuspid Axial Wall Height Effect on CAD/CAM Crown Fracture Mode on Preparations Containing Advanced Total Occlusal Convergence
Author(s) -
Miller Matthew,
DuVall Nicholas,
Brewster John,
Wajdowicz Michael N.,
Harris Ashley,
Roberts Howard W.
Publication year - 2018
Publication title -
journal of prosthodontics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.902
H-Index - 60
eISSN - 1532-849X
pISSN - 1059-941X
DOI - 10.1111/jopr.12760
Subject(s) - cerec , materials science , crown (dentistry) , adhesive , composite material , ceramic , universal testing machine , acid etching , dentistry , orthodontics , medicine , layer (electronics) , ultimate tensile strength
Purpose To evaluate bicuspid axial wall height effect on the fracture mode of adhesively luted, all‐ceramic CAD/CAM crowns with a 20° total occlusal convergence (TOC). Materials and Methods Recently extracted premolars were randomly divided into 4 groups (n = 12) with all‐ceramic crown preparations accomplished using a high‐speed handpiece inserted into a milling device. Specimens were prepared containing occlusogingival axial wall heights of 3, 2, and 1 mm as well as a group containing a flat preparation surface with no axial wall height. All preparations contained a 20° TOC. Completed preparation surface area was determined, and preparation features confirmed using a digital measuring microscope. Scanned preparations (CEREC) were fitted with milled and crystallized lithium disilicate full coverage restorations and luted with a self‐etching adhesive resin cement after hydrofluoric acid etching and silanation. All manufacturer recommendations were followed. Specimens were stored at 37°C/98% humidity for 24 hours. Specimens were tested to failure at a 45° angle to the long axis of the tooth root on a universal testing machine. Failure load was converted to MPa using the available bonding surface area with mean data analyzed using Kruskal‐Wallis/Dunn's ( p = 0.05) Results The 3 mm preparation height specimens were similar to the 2 mm specimens, and both demonstrated significantly stronger failure load than the 1 mm axial wall height and flat preparation specimens. The flat preparation and 1 mm axial wall height specimens all failed adhesively, while the 2 mm and 3 mm specimens failed largely due to tooth fracture. Conclusions Further evidence is provided that CAD/CAM adhesive techniques may compensate for less than ideal preparation features. Under the conditions of this study, bicuspid preparations with a 20° TOC restored with adhesively luted, CAD/CAM e.max CAD crowns require at least 2 mm of axial wall height, but further planned fatigue studies are necessary before definitive recommendations can be made.