Introduction: Intraoral preparation of zirconia implant abutments creates deep surface defects making abutments susceptible to fracture during loading. 

Objective: Measure fracture strengths after preparation and after surface treatments to minimize or repair defects.

Methods: Seven groups (n=12/gp) of HIP-processed zirconia bars (Astra-Tech) were fabricated (20x2x2mm) to mimic prepable-abutment surface conditions and tested for surface flaw effects (3-point-flexure, Instron Model 4411, CHS= 0.1mm/min, age=2d, T=25°C, dry).  Control groups included no preparation (NP), dry preparation (DP, high-speed coarse diamond: Premier Two-Striper), wet preparation (WP), or wet preparation with 30d storage in water (WP+30d).  Subsequent mitigating treatments included (1) bonding films to fill surface defects (Optibold-Solo-Plus) (WP+B), (2) sandblasting (50 mm Al2O3) (WP+SB), or (3) polishing (low-speed Dialite burs) (WP+P).  Statistical analysis of results (ANOVA, p≤0.05, differences indicated by unshared letters) is reported below.

Specimen Group:	Prep Type:	Repair Treatment:	Group Goal:	3-Point-Flexure: (MPa±sd)
NP	None	None	Control (un-prepped)	1634±95	[a]
DP	Dry	None	Control (dry damage)	1144±109	[b]
WP	Wet	None	Control (wet damage)	1442±89	[c]
WP+30d	Wet	None (stored 30d)	Control (water effects)	1193±155	[b,d]
WP+B	Wet	Optibond-Solo+	Repair defects	1218±77	[b,e]
WP+SB	Wet	Sandblasted	Reduce large defects	1632±134	[a,f]
WP+P	Wet	Polished	Remove large defects	1664±176	[a,g]

Results:  NP established the strength for pristine zirconia bars.  DP, WP, and WP+30d groups had significantly (p£0.05) reduced strengths (-30%, -12%, -27%).  DP generated damaging surface flaws. WP mitigated some surface damage.  WP+30d may have expanded existing surface cracks.  This effect deserves further investigation. WP+B was not effective in counteracting cracks by filling them.  WP+SB or WP+P repairs were equally effective in recovering to original strengths (p<0.001).  Both removed larger defects and mitigated preparation effects. 

Conclusions:  Polishing or sandblasting of prepable abutments produced 100% recovery from bur damage during preparation. 

Acknowledgments:  Supported by materials contributed by AstraTech and a 3M-ESPE grant.