12 January 2021

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Ceramic laminate veneers: influence of preparation design and ceramic thickness on margin quality and fracture resistance of the restorations

Co-authors: A. Comba, F. Del Bianco

Lorenzo Breschi

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Ceramic veneers are considered an excellent choice for anterior restorations, especially when high aesthetic demand is needed. The literature in the field reveals different annual failure rates for anterior veneers, ranging from 0 to 5% . Clinical trials often lack exact documentations of preparation designs and extents of dentin exposure

Doctor Blunck from University of Berlin decided to  evaluate:
- the influence of (1) invasiveness of preparation designs,
- (2) the amount of dentin exposure during preparation,
- (3) the thickness of the veneer
- (4) the  preexisting resin composite restorations on (a) margin quality and (b) facture resistance of ceramic veneers.

Material and Methods

To conduct the study the German research Group collected eighty human central incisors randomly assigned to 10 groups (n = 8) with five different preparation designs: non-prep (NP), minimally invasive (MI) = exclusively enamel-bonded, semi-invasive (SI) = 50% bonded in dentin, invasive (I) = 100% in dentin, and semi-invasive with two additional class III composite resin restorations (SI-C). IPS InLine veneers were, then, fabricated in two thicknesses (L1 = 0.2–0.5 mm; L2 = 0.5–1.2 mm). After adhesive luting (OptiBond FL, Variolink Veneer),light curing and polishing, specimens were st ored in distilled water at 37 °C for 21 days and thermocycled (2000 cycles between + 5 and + 55 °C), and mechanically loaded at the incisal edge with an angle of 45° for 2,000,000 cycles at 50 N and further 1,000,000 cycles at 100 N. The authors took Impressions initially, after thermocycling, and after every 250,000 mechanical cycles in order to evaluate cracks and margin quality under SEM. The veneers were evaluated with a light microscope (× 20) for cracks, chippings, partial, and catastrophic fractures.

Results
The result obtained bu the group of Dr. Blunck et.al showed found no significant differences in marginal quality at T0 between the tested  groups (p = 0.14).
After three million cycles marginal integrity revealed medians for continuous margin of 82–95% without significant differences among groups, neither at the ceramic/composite (p = 0.943) nor at the tooth/composite interface (p = 0.571).
During visual inspection of the ceramic veneers Blunk et al noticed 22 cracks, 11 chippings, 4 partial and 4 catastrophic fractures  in 38 out of 80 veneers, and group with more invasive preparations suffered more alterations when the veneers were thinner.

Conclusion
The authors of the present in vitro research concluded that after three million mechanical load cycles including one million at 100 N, all groups showed high amounts of good marginal integrity.
However, fracture risk for thin veneers with preparations characterized by a significant dentin exposure, suffer higher fracture risk compared with restoration luted on enamel or with thicker material luted to exposed dentin. Furthermore the authors concluded that pre-existing composite resin restorations had no adverse effect on the outcome.

For additional information: Ceramic laminate veneers: effect of preparation design and ceramic thickness on fracture resistance and marginal quality in vitro