Do thermal treatments affect the mechanical behavior of porcelain-veneered zirconia? A systematic review and meta-analysis.
OBJECTIVES
A systematic review of in vitro studies was conducted to assess the effect of thermal treatments on flexural strength or critical load to failure of porcelain-veneered zirconia (PVZ).


SOURCES
Literature searches were performed up to June 2018 in PubMed/MEDLINE, Scopus and Web of Science databases, with no publication year or language limits.


DATA
From 393 relevant studies, 21 were selected for full-text analysis, from which 7 failed to meet the inclusion criteria. The 14 remaining papers were included in the systematic review: 8 for meta-analysis and 6 restricted to descriptive analyses. Hand searching of reference lists resulted in no additional papers.


STUDY SELECTION
In vitro studies using PVZ specimens testing the influence of thermal treatments on the fracture resistance to monotonic or cyclic loading. Papers evaluating cooling rate were divided into those applying fast cooling from above the porcelain glass transition temperature (Tg), or from below it. Meta-analyses were performed separately for flexural strength and critical load to failure, using random effects at a 5% significance level.


CONCLUSIONS
Delaying furnace opening at a temperature below the porcelain Tg is advised for PVZ restorations, in order to improve their fracture resistance. Additional information is required to confirm the apparent beneficial effect of self-glaze and repeated veneer firings on the mechanical properties of these restorations. Finally, in order to obtain conclusive and relevant evidence regarding thermal treatments and the fracture resistance of PVZs, future studies should concentrate on anatomically-correct crown specimens.
['Rodrigues|Camila da Silva|CDS|', 'Aurélio|Iana Lamadrid|IL|', 'Kaizer|Marina da Rosa|MDR|', 'Zhang|Yu|Y|', 'May|Liliana Gressler|LG|']
D003442:Crowns D003776:Dental Porcelain D003799:Dental Stress Analysis D003801:Dental Veneers D008422:Materials Testing D013314:Stress, Mechanical D013499:Surface Properties D015040:Zirconium
Porcelain-veneered zirconia Mechanical properties Cooling protocols Glaze firings Heat treatment Repeated firings