Scanning Experience Affects Fit of E4D CAD/CAM All-Ceramic Crowns

Objective: To compare the in vitro fit of all-ceramic crowns produced by experienced and inexperienced scanners using the E4D Dentist^TM (D4D Technologies) CAD/CAM system.

Methods: Typodont tooth #14 was prepared per standard specifications to receive an all-ceramic crown. The preparation had well-defined, rounded shoulder, ~2 mm occlusal reduction, rounded internal angles, and less than 20° total occlusal convergence. Small indentations were made on root of tooth as a plane of sectioning. Thirty impressions of prepared typodont tooth were taken using PVS and 30 die stone models poured. Dies were placed in full-dentate typodont and scanned with E4D laser by two different users. Experienced user was dental assistant who had completed three full training sessions and scanned with system in private practice for one year. Inexperienced user was dentist who had completed one half-day training session and had no prior experience with system. IPS e.max® CAD LT A1/C14 crowns (Ivoclar Vivadent) were fabricated per manufacturer's instructions. Crowns were cemented using Multilink® Automix (Ivoclar Vivadent) under constant pressure of 100N. Samples were embedded in clear acrylic resin and sectioned buccolingually in a consistent plane using the root indentations as guidance (Isomet 1000, Buehler). Sections were evaluated under digital microscope with 10X objective (Olympus) and measured using OmniMet software (Buehler) on 3 locations per buccal and lingual side of section: marginal-edge, mid-axial wall, and cusp-tip. One measurement was made on occlusal table. Mean thicknesses at each location were calculated and compared between experienced and inexperienced users. Statistical analysis was done by one-way ANOVA. Statistical different was predetermined at P<.05.

Results: Mean fits at various locations of prep are shown in Table 1.

Table 1: Cement thicknesses measured at marginal and internal locations of prep (n=15)
Measurement Location	Buccal				Lingual
	Margin	Mid-Axial	Cusp	Occlusal Table	Margin	Mid-Axial	Cusp
Experienced User Mean Thickness (µm ± SD)	44.88 ± 32.06	120.45 ± 45.95	95.47 ± 59.99	161.05 ± 29.11	39.07 ± 32.44	154.60 ± 57.94	95.00 ± 34.53
Inexperienced User Mean Thickness (µm ± SD)	113.77 ± 68.54	111.65 ± 44.97	67.53 ± 47.30	159.37 ± 60.03	61.71 ± 36.80	145.45 ± 57.07	80.43 ± 38.75
P value	0.0021	0.6	0.1676	0.9238	0.2861	0.6662	0.0847

Conclusions: Marginal thicknesses of crowns produced by experienced user were significantly less than those of crowns produced by inexperienced user.