Influence of retainer design on two-unit cantilever resin-bonded glass fiber reinforced composite fixed dental prostheses: an in vitro and finite element analysis study.
OBJECTIVE
The aim of this study was to evaluate in vitro the influence of retainer design on the strength of two-unit cantilever resin-bonded glass fiber-reinforced composite (FRC) fixed dental prostheses (FDP).


METHODS
Four retainer designs were tested: a proximal box, a step-box, a dual wing, and a step-box-wing. Of each design on 8 human mandibular molars, FRC-FDPs of a premolar size were produced. The FRC framework was made of resin impregnated unidirectional glass fibers (Estenia C&B EG Fiber, Kuraray) and veneered with hybrid resin composite (Estenia C&B, Kuraray). Panavia F 2.0 (Kuraray) was used as resin luting cement. FRC-FDPs were loaded to failure in a universal testing machine. One-way ANOVA and Tukey's post-hoc test were used to evaluate the data. The four designs were analyzed with finite element analysis (FEA) to reveal the stress distribution within the tooth/restoration complex.


RESULTS
Significantly lower fracture strengths were observed with inlay-retained FDPs (proximal box: 300 +/- 65 N; step-box: 309 +/- 37 N) compared to wing-retained FDPs (p < 0.05) (step-box-wing: 662 +/- 99 N; dual wing: 697 +/- 67 N). Proximal-box-, step-box-, and step-box-wing-retained FDPs mainly failed with catastrophic cusp fracture (proximal box 100%, step-box 100%, and step-box-wing 75%), while dual-wing-retained FDPs mainly failed at the adhesive interface and/or due to pontic failure (75%). FEA showed more favorable stress distributions within the tooth/restoration complex for dual wing retainers.


CONCLUSIONS
A dual-wing retainer is the optimal design for replacement of a single premolar by means of a two-unit cantilever FRC-FDPs.
Keulemans
Filip
F
Department of Dental Material Sciences, Academic Centre for Dentistry Amsterdam (ACTA). f.keulemans@acta.nl
De Jager
Niek
N
Kleverlaan
Cornelis J
CJ
Feilzer
Albert J
AJ
D001641:Bicuspid; D001696:Biomechanical Phenomena; D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D000044:Dental Abutments; D003764:Dental Materials / Q000737:chemistry*; D019232:Dental Restoration Failure; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation*; D016379:Denture, Partial, Fixed, Resin-Bonded; D020342:Finite Element Analysis; D005898:Glass / Q000737:chemistry*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008954:Models, Biological; D008963:Molar; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength
D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; C438843:Panavia-Fluoro; D011140:Polyurethanes; D019279:Resin Cements; C009753:fiberglass; C091839:urethanetrimethacrylate