By Dr. Wally Renne
(Originally posted in the Keep CEREC’ing Facebook Group)
Why do a printed onlay? Why not just squirt some direct resin in the tooth? I get this a lot from people. Afterall the materials at first glance are similar.
The next question I get is , if I’m going to do an indirect why not just mill it? I have an entire 2hr presentation on this topic with a deep dive into the literature with over 100 references but let’s discuss a few major differences between a direct resin and indirect.
By moving to indirect you almost completely eliminate polymerization shrinkage stress on the tooth. Shrinkage stress is the force placed in the tooth and adhesive as the composite undergoes polymerization and subsequent contraction towards the light source. This is a big deal as most of the issues with direct resins can be partly attributed to polymerization shrinkage stress such as leakage, cusp fracture, recurrent decay.
The publication below compares direct and indirect resins and show that much more force is placed on the tooth and adhesive interface not only during polymerization, but it remains. Furthermore, we see how the different materials restore the tooth during function. Indirect resin restores the tooth to the unrestored strength. Direct resin does not.
This can explain why in a recent systematic review and meta analysis indirect resins restorations performed just as well compared to indirect ceramics, both dramatically preforming better then direct resins.
Bustamante-Hernández N, Montiel-Company JM, Bellot-Arcís C, Mañes-Ferrer JF, Solá-Ruíz MF, Agustín-Panadero R, Fernández-Estevan L. Clinical Behavior of Ceramic, Hybrid and Composite Onlays. A Systematic Review and Meta-Analysis. Int J Environ Res Public Health. 2020 Oct 19;17(20):7582. doi: 10.3390/ijerph17207582. PMID: 33086485; PMCID: PMC7589045.
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