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Busting Myths In Dentistry

Myth #1
“You CAN’T bond to zirconia like you can to porcelain.”
It is possible to get the same bond strength to zirconia as you can to porcelain, but only if the proper surface treatment is used. Initially, CoJet and silane treatment was the recommended protocol for bonding to zirconia, but BISCO studies showed1 that sandblasting with CoJet was ineffective at permanently embedding zirconia surfaces with ceramic particles, which could be rinsed off with water spray. In addition, studies showed2 that zirconia is contaminated with phosphates ions (found in saliva) during try-in, and if the surface is not decontaminated, restorations would not chemically bond and may result in de-bonding.
 
Good chemical bonding to zirconia is achieved between MDP and zirconia ions via an addition reaction. This bond between zirconia and resin is as strong and stable over time as the bond provided by silane to glass ceramics. In fact, data shows that the long-term durability of the chemical bond to zirconia is more stable than the silane bond to glass ceramics*.
 
Myth #2
“You shouldn’t place resin directly on a pulp exposure.” 
All resin (monomers) are toxic/irritants, and if the resin is not light-cured properly, it can be toxic to pulp tissue. However, an alkaline material that is properly polymerized has been proven to have a therapeutic effect and achieve a positive response from the pulp. On the other hand, RMGI contains resin and polyacrylic acid, which is intrinsically acidic. This acidic nature of RMGI can generate a detrimental response from the pulp and should not be used for direct pulp capping.
 
Myth #3
“You must use products from ONE company in order to ensure compatibility.” 
Compatibility between adhesives and restorative materials are not brand dependent, but pH dependent. In general, all L/C adhesives will be compatible with all L/C composites. However, any adhesive that has a pH less than 3 (highwater content) will not be compatible with any dual-cured (or self-cured) material without a separate activator. The low pH will inhibit proper chemical polymerization, thus leading to low bond strengths.
 
Myth #4
“If a material contains calcium, it must release calcium”
For calcium to be released, the material must allow for ion exchange to occur. If the matrix of the calcium-containing material is too hydrophobic, then calcium will not be released due to a lack of ion exchange. The matrix needs to be relatively hydrophilic for ion exchange (and calcium release) to occur.
 
Myth #5
“Not all MDP is created equal.”
Some companies claim their MDP is superior to others. However, 10-MDP is a chemical monomer, it is what it is, like all H2O is water. What makes the biggest difference in efficacy is the formulation and the amount of MDP - the ratio between MDP, solvent (ethanol) and water. That is what differentiates adhesive formulations, not the MDP itself.
 
Myth #6
“You don’t need to cure the adhesive layer under indirect restorations.”
If the adhesive is light-cured, it MUST be fully polymerized BEFORE seating the indirect restoration for the highest bond strength. If the adhesive is left uncured, the result will be a lower bond strength between the tooth preparation and the restorative surface. If a clinician wants to avoid light curing the adhesive under indirect restorations, a dual-cured adhesive should be used.
 
 
1. Evaluation of silica-coating techniques for zirconia bonding Liang Chen 1, Byoung In Suh, Jongryul Kim, Franklin R Tay American Journal of Dentistry. Vol 24. No. 2. April 2011.
2. Influence of saliva contamination on zirconia ceramic bonding B Yang 1, H C Lange-Jansen, M Scharnberg, S Wolfart, K Ludwig, R Adelung, M Kern Dent Mater 2008 Apr;24(4):508-13
 
* Data on file.
 
First published in the Fall 2020 BisDent Globe.
 

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