Marginal and Internal Adaptation of CAD/CAM Endocrown Preparation Designs

Objectives: This in vitro study evaluated the marginal fit and internal adaptation of chairside CAD/CAM endocrowns (monolithic core and crown restoration) fabricated using different preparation designs.

Methods: Four different preparations were performed on tooth #14, each with a 3mm extension into the pulp chamber.  The internal walls of the pulp chamber are used for adhesive retention of the restoration, eliminating the need for a core to be placed.  Ten epoxy models were made for each master preparation.  Each model was imaged, designed, and a crown was milled from ceramic (IPS EmpressCAD/Ivoclar) using a Cerec AC unit (Sirona) with v3.80 software.

Group 1: 130 degree sloped shoulder margin; rounded internal line angles

Group 2: 90 degree shoulder margin; rounded internal line angles

Group 3: 90 degree shoulder margin; sharp internal line angles

Group 4: 90 degree shoulder margin; circumferential ferrule  

The endocrowns were bonded to the epoxy models using a self-etching resin cement (SpeedCEM/Ivoclar).  The crowns were sectioned faciolingually with a diamond saw and adaptation was measured at the cavosurface margins, internal walls, and pulpal wall with a measuring microscope (Nikon) at 20x.

Results:

(microns)	Margin	Internal Wall	Pulpal Wall
Group 1	49.34±7.79     a	151.94±13.89   a	220.59±25.13   a
Group 2	65.74±13.42   b	176.12±22.18   b	210.89±56.11   a
Group 3	70.06±10.78   b	139.77±8.30     a	225.47±22.29   a
Group 4	102.64±12.28  c	194.25±19.96   b	229.79±35.17   a

The data was analyzed using a one-way ANOVA and significant differences were determined with a Tukey test.  Letters identify significantly different groups (p<0.05). 

Conclusion: The sloped shoulder margin with rounded internal line angles resulted in the best marginal fit, while the 90 degree shoulder margin with rounded and sharp internal line angles produced marginal adaptation values that were clinically acceptable.  The circumferential ferrule resulted in a large enough marginal gap that it should be avoided in endocrown preparation design.