As most of us know, zirconia crowns and bridges are healthy, esthetic, and nearly indestructible. However, in certain conditions, long term cement retention can be unpredictable. This is especially true if the internal surfaces have been exposed to saliva. Unfortunately, there is not a lot of information about the best ways to eliminate contamination. Below, we try to bring more clarity to this topic.
Aladag, et al conducted research to determine the effect of saliva on the cementing surface of untreated zirconia. They reported that different cleaning methods, water spray, sodium hypochlorite, or Ivoclean® produced few improvements to bond strengths. The first point to note is that in this investigation, the tested zirconia surface was not air abraded.
Tunc’s team obtained different results from Aladag’s. Their research included Ivoclean, phosphoric acid, alcohol , water rinsing, steam cleaned, and air abrasion (after) saliva contamination. Their findings proved air abrasion to be best followed closely by Ivoclean. But that doesn’t answer the question about saliva contamination after zirconia has been air abraded.
Wille’s prosthodontic team from Germany tested the affect saliva has on zirconia surfaces that have been air abraded prior to contamination. Their testing included silicone disclosing agents, GC Fit Checker white or GC Fit Checker II for checking the fit of zirconia copings. Uncontaminated zirconia surfaces used as controls were compared to contaminated copings cleaned with “…water spray or ultrasonically in 99% isopropanol or using a newly developed cleaning paste (Ivoclean® from Ivoclar) .” Their findings showed that using a secondary application of isopropanol increased reduction of carbon residuals on the zirconia surfaces, more so than did an additional application of Ivoclean. However, none of the cleaning agents or additional applications removed all the silicone contaminants. This could be due to air abrasion increasing retention of the contaminants.
Feitosa’s group also looked at saliva contamination, but included the effects of aging on resin bond strengths. Their investigation included “one hundred and eighty zirconia specimens sandblasted with 50 μm aluminum oxide particles, immersed in saliva for one minute (with the exception of the control group, [C]), and divided into groups according to the cleansing method, as follows: water rinse (W); 37% phosphoric acid gel (PA); cleaning paste (ie, Ivoclean®) containing mainly zirconium oxide (IC); and 70% isopropanol (AL).” Resin SBS was evaluated “…after 24 hours, 5000 thermal cycles (TC), or 150 days of water storage.” The results”…showed that PA < AL and W < IC and C. SBS ranged from 10.4 to 21.9 MPa (24 hours), from 6.4 to 14.8 MPa (TC), and from 2.9 to 7.0 MPa (150 days). Failure analysis revealed a greater percentage of mixed failures for the majority of the specimens and a smaller percentage of adhesive failures at the ceramic-resin cement interface,” and that Ivoclean® was able to sufficiently clean saliva contaminated zirconia surfaces to maintain acceptable long term bond strengths.
Kim, et al’s research, in 2015, also examined saliva contamination of air abraded zirconia surfaces. Their testing included cleaning with “…water-spray rinsing (WS), additional air abrasion (AA), and cleaning with four solutions (Ivoclean® [IC]; 1.0 wt% sodium dodecyl sulfate [SDS], 1.0 wt% hydrogen peroxide [HP], and 1.0 wt% sodium hypochlorite [SHC].” A sample with no contamination (NC) was used as the control. Each zirconia sample was bonded to resin with Panavia F 2.0 prior to aging with 5000 thermocycles. Their results showed “…groups NC, AA, IC, and SHC had hydrophilic surfaces. Groups IC and SHC showed statistically similar bond strengths to groups NC and AA (P>.05), but not groups SDS and HP (P<.05). For groups WS, SDS, and HP, blister-like bubble formations were observed on the surfaces under SEM. Test results reiterated the cleaning effectiveness of Ivoclean®, and also supported the use of sodium 1.0 wt% hypochlorite.