Episode 9: Bonding vs Cementing a Single Unit Crown

composite

Dr. Nate Lawson, a professor at University of Alabama, set out to answer a clinical question: When and why do dentists choose to bond a single unit crown compared to cementing? The data came from an enormous clinical practice study conducted by the National Dental Practice Based Research network. 

Main Findings: 

Dr. Lawson and his team found that dentists primarily chose to either bond or cement a crown based on the type of material the crown was made of. Lithium disilicate crowns were bonded 70% of the time, whereas 70% of zirconia crowns were cemented with RMGI cement. There was no correlation for dentists choosing to bond a crown if the prep was under reduced. On the other hand, if the prep was excessively short, there was a correlation with dentists choosing to bond the crown. There was no correlation to bond based on if adequate isolation could be achieved. 

Can zirconia crowns actually be bonded? 

Lab studies have shown that it’s possible to bond zirconia. It’s probably not needed due to zirconia’s natural strength. A time when bonding zirconia might be very useful is short 2nd molar crowns, especially when the dentist wants the strength from zirconia in the crown but the prep is short and non retentive. 

Why are clinicians more apt to bond lithium disilicate?

Bonding E-max lithium disilicate is a good choice because it is not as strong of a material as zirconia. New guidelines state that 1mm of occlusal reduction yields enough material thickness to bond. Without bonding, lithium disilicate needs 1.5mm of occlusal reduction for strength. Bonding increases the overall strength of the crown. This is because the bond transfers stresses to the substructure, a property not present with RMGI cements. A bonded resin cement is stronger than a glass ionomer cement because resin contains stronger filler particles. Resin cements also form hybrid layers between the resin and demineralized collagen in dentin.  

What other clinical situations would be good to bond?

Onlays are completely reliant on bonding. Dr. Lawson prefers onlays in situations where the patient presents with failed MOD’s, but the buccal and lingual surfaces are completely intact. This technique preserves more tooth structure compared to a traditional crown prep. 

How is moisture control different with bonding versus cementing?

Moisture control is more important when a clinician bonds a restoration. To combat this, Viscostat is great for controlling heme, and Isolite’s can be a good tool for saliva control. The posterior mandible is the hardest area to keep isolated. Dr. Lawson and a colleague just finished a study on the effects of saliva contamination with RMGI cement. They found there was no effect on cementing a crown covered in saliva if the dentist used a RMGI cement. In other words, a dentist does not have to worry about great isolation when using a RMGI cement.

Is the property of fluoride release a good reason to use RMGI cement, especially in high caries risk patients? 

Yes, there is local protection from demineralization around the crown margins with RMGI cement.

Hannah Wilken

This article was written by Hannah Wilken.

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