Effect of Fabrication Technique and Thermal Cycling on the Bond Strength of CAD/CAM Milled Custom Fit Anatomical Post and Cores: An In Vitro Study

Abstract

Purpose This study is to investigate the effect of milling custom fit anatomical post and cores from fiber reinforced composite and high‐density polymer blocks using CAD/CAM technology on the bond strength to root canal dentin compared with prefabricated fiber posts, and to evaluate the influence of thermal cycling on the push out bond strength of the tested materials. Materials and Methods Eighty extracted single‐rooted premolars, endodontically treated and prepared to receive the posts, were randomly divided into four groups (n = 20): BLC: Custom‐milled fiber‐reinforced composite posts and cores (Trilor, Bioloren), AMC: Custom‐milled high‐density polymer posts and cores (Ambarino, Creamed), BLP: Prefabricated fiber‐reinforced composite posts and composite core buildups (Bioloren; Filtek Bulk Fill Posterior, 3M). The posts used have the same matrix and fiber composition as BLC, RXP: Prefabricated posts and composite core buildups (RelyX fiber post, 3M; Filtek Bulk Fill Posterior); used as a control group. All of the posts were cemented using a self‐adhesive resin cement (RelyX U200, 3M). Half of the sample was randomly assigned to thermal cycling in distilled water for 6,000 cycles to simulate aging, while the other half was tested for bond strength without thermal cycling. A push‐out test was conducted using a universal testing machine until failure. Bond strength values were calculated in megapascals (MPa). The mode of failure was observed using a stereo microscope. Results were analyzed by two‐way ANOVA followed by a Bonferroni post hoc test for comparison. The level of significance was set at p < 0.05. Results Push‐out bond strength was significantly higher (p <0.001) in the CAD/CAM post groups than in the groups with prefabricated posts regardless of the post material, while aging of the teeth did not significantly affect the push‐out strength (p = 0.536). Failures were adhesive between cement and dentin for all groups except for AMC, where adhesive failure between the cement and the post was also observed. Conclusion The CAD/CAM manufacturing technique was proved to ameliorate the retention of the post and cores in the root canal. Thermal cycling did not affect the bond strength of the tested groups.

<p>CAD/CAM Customized Glass Fiber Post and Core With Digital Intraoral Impression: A Case Report</p>

“…After processing 3d images and CAD design of the pieces a custom glass fiber post and core (Trilor Bioloren, Saronno, VA, Italy) 34 was manufactured by a CAM milling machine (Roland DWX-50, Irvine, CA, USA) 35 as well as a provisional composite resin crown (Figures 3 and 4). Trilor was chosen as it is a multidirectional fiber-reinforced resin material approved for definitive CAD-CAM prosthetic appliances and its mechanical characteristics are close to natural dentin as it has an elastic modulus of 26GPa (manufacturer data) and it was purposed as a promising material by Ruschel et al in 2018.…”

“…35 The milled post and core was realized with 80µm tolerances to ensure a proper fit without interfering with cementation procedures. 34 After fitting and adaptation check to ensure the necessity of only a light force to complete sitting, no adjustment was needed, the surface of the custom post to be cemented was cleaned, etched with 37% orthophosphoric acid (Ivoclar Vivadent, Italy) and silanized (Monobond Plus Ivoclar Vivadent, Italy) to prepare it for the following adhesive procedures. 37 All dental surfaces were pretreated for adhesive procedures with 37% orthophosphoric acid (Ivoclar Vivadent, Italy).…”

Fabrication of Custom Post‐And‐Core Using a Directly Fabricated Silicone Pattern and Digital Workflow

“…[1][2][3] Even though custom cast post-and-cores require an additional patient visit, provisionalization, and a laboratory fee, they have two important advantages over prefabricated postsystems. 4,5 First, they are customized to fit the existing root canal morphology, requiring little preparation of radicular dentin. 1 Second, because custom cast post-and-cores are monolithic, the strength of the post-core interface is enhanced.…”

“…1 Second, because custom cast post-and-cores are monolithic, the strength of the post-core interface is enhanced. 5,6 These advantages make custom cast post-andcores more apt for restoring structurally compromised teeth that have flared (extreme taper), noncircular cross section canals, or very small canals (lower anterior teeth). 1 Custom cast post-and-cores are also the treatment of choice to restore structurally compromised teeth that are subject to heavy functional loads or teeth for which a change in the emergence profile is required for esthetic reasons.…”

“…10 Custom post-and-core can now be fabricated not only from cast alloys but also from many contemporary (CAD/CAM) dental materials such as zirconia, nanoceramic resin composite, fiber-reinforced composite and high-density polymers. 5,11,12 Historically, auto-polymerizing acrylic resin pattern material has been the most commonly used material to direct pattern fabrication; it sets quickly with minimal heat generation and shrinkage, is dimensionally stable, is strong and rigid, and is easy to cast using conventional casting technique (lost wax technique) as it leaves no residue after burnout. 13 However, direct pattern fabrication with acrylic resin carries the risk of inadvertently locking into undercuts within the postspace, which is very hard to remove and may lead to root fracture or root perforation, and may leave residual resin debris inside the canal.…”