Microhardness of light- and dual-polymerizable luting resins polymerized through 7.5-mm-thick endocrowns.
BACKGROUND
The complete polymerization of luting resins through thick indirect restorations is still questioned.


OBJECTIVE
The purpose of this study was to evaluate the degree of polymerization of light- and dual-polymerizable luting resins under thick indirect composite resin and ceramic endocrowns by means of Vickers microhardness measurements.


METHODS
The Vickers microhardness measurements of a light-polymerizable microhybrid composite resin and a dual-polymerizable luting cement directly polymerized in a natural tooth mold for 40 seconds with a high-power light-emitting diode lamp (control) were compared with measurements after indirect irradiation through 7.5-mm-thick composite resin and ceramic endocrowns for 3 × 90 seconds. A test-to-control microhardness values ratio of 0.80 at a depth of 0.5 mm below the surface was assumed as the criterion for adequate conversion.


RESULTS
For the Vickers microhardness measurements of a dual-polymerizable luting cement, no differences (P>.05) were found between Vickers microhardness control values and values reported after polymerization through composite resin and ceramic endocrowns. For The Vickers microhardness measurements (±SD) of a light-polymerizable microhybrid composite resin, control values were significantly (P<.05) higher (111 ±3.3) than those reported after polymerization through composite resin (100.5 ±3.8) and ceramic (99.7 ±2.3) endocrowns. However, the hardness values of The Vickers microhardness measurements of a light-polymerizable microhybrid composite resin polymerized through the endocrowns were approximately 10% to 12% lower than those of the control values. Two-way ANOVA showed the influence of the luting material on the Vickers microhardness values (P<.05). The effect of endocrown material was not significant (P>.05).


CONCLUSIONS
Under the conditions of this in vitro study, Vickers microhardness values of the dual-polymerizable resin cement and the light-polymerizable restorative composite resin irradiated for 3 × 90 seconds with a high irradiance light-emitting diode lamp through 7.5-mm-thick endocrowns reached at least 80% of the control Vickers microhardness values, which means that both materials can be adequately polymerized when they are used for luting thick indirect restorations.
Senior Lecturer, Division of Cariology and Endodontology, Dental School, University of Geneva, Switzerland.
Ladislav
L
Gregor
Associate Professor, Division of Cariology and Endodontology, Dental School, University of Geneva, Switzerland.
Serge
S
Bouillaguet
Senior Lecturer, Division of Cariology and Endodontology, Dental School, University of Geneva, Switzerland.
Ioana
I
Onisor
Senior Lecturer, Division of Cariology and Endodontology, Dental School, University of Geneva, Switzerland.
Stefano
S
Ardu
Professor and Chair, Division of Cariology and Endodontology, Dental School, University of Geneva, Switzerland.
Ivo
I
Krejci
Senior Lecturer, Division of Cariology and Endodontology, Dental School, University of Geneva, Switzerland. Electronic address: Giovanni.rocca@unige.ch.
Giovanni Tommaso
GT
Rocca
D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003442:Crowns; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation / Q000379:methods*; D008422:Materials Testing; D058105:Polymerization; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D055116:Self-Curing of Dental Resins / Q000295:instrumentation / Q000379:methods*; D013053:Spectrophotometry / Q000379:methods; D013499:Surface Properties; D019553:Tooth, Nonvital / Q000628:therapy; D015040:Zirconium / Q000737:chemistry
D000538:Aluminum Silicates; D003188:Composite Resins; D003764:Dental Materials; D017680:Potassium Compounds; D019279:Resin Cements; C090969:Tetric; C082340:Vita Mark II; C452079:paradigm MZ100; D003776:Dental Porcelain; C016447:feldspar; C103502:Variolink; D015040:Zirconium