In vitro evaluation of CAD/CAM composite materials

A Comparison of the Shear Bond Strength between a Luting Composite Resin and Both Machinable and Printable Ceramic-Glass Polymer Materials

This study aims to compare the shear bond strength (SBS) and Weibull characteristics between a luting composite resin and both printable and two different machinable ceramic-glass polymer materials. A total of 36 substrates were prepared, with 12 in each group. Printable substrates (12 mm × 12 mm × 2 mm) were printed by using permanent crown resin (3D-PR). Machinable substrates were obtained from Cerasmart 270 (CS) and Vita Enamic (VE) blocks (2 mm in thickness). The bonding surfaces of substrates were polished and airborne abraded (50 µm Al2O3). A self-adhesive luting composite resin (RelyX U200, 3M ESPE, St. Paul, MN, USA, SLC) was applied on substrates with the help of a cylindrical (Ø3 × 3 mm) mold. The SBS test was conducted using a universal test machine. The SBSs of three materials were compared using a one-way analysis of variance (ANOVA) (α = 0.05). The Weibull modulus was calculated for each material. The Kruskal-Wallis and chi-square tests were carried out for the failure mode analysis. There was no significant difference between the SBSs of the three materials (p = 0.129). The Weibull modulus was 3.76 for the 3D-PR, 4.22 for the CS, and 6.52 for the VE group. Statistical analysis showed no significant difference between the failure modes of the groups (p = 0.986). Mixed-failure fractures were predominantly observed in all three groups. The results show that the SBS of the SLC to printable 3D-PR is comparable to that of CS and VE material. Failure modes of printable 3D-PR show similar results with two different machinable ceramic-glass polymers.

Comparative Strength Study of Indirect Permanent Restorations: 3D-Printed, Milled, and Conventional Dental Composites

Background/Objectives: Limited research has been performed to assess the strength of resin-bonded 3D-printed restorations. Based on that, this study investigates the impact of different manufacturing methods on the fracture load of indirect composite restorations (ICRs) following an aging process. Methods: Three manufacturing techniques-conventional (CRC), milled (MRC), and printed (PRC)-were evaluated using 60 specimens, each with a diameter of 10 mm and a thickness of 1.0 mm. Sandblasting with Al2O3 particles was employed to optimize the bonding process, significantly influencing surface roughness parameters (Ra, Rz, RSm). All specimens were bonded to the dentin analog using composite resin cement and subjected to either 10,000 thermocycles (TC) or storage (ST) at 37 °C in distilled water. Fracture load assessments were performed using a universal testing machine. A finite element analysis was conducted to assess stress distribution. Results: Two-way ANOVA results indicated that the manufacturing method significantly affected mean fracture load values (p < 0.001), with PRC showing the highest mean fracture load (4185 ± 914 N), followed by MRC (2495 ± 941 N) and CRC (599 ± 292 N). The aging protocol did not have a significant impact on fracture load. Conclusions: This study revealed that 3D-printed resin composite exhibited comparable strength to milled resin composite when adhesively cemented, suggesting it is a promising option for indirect composite restorations based on its mechanical performance. However, further research is needed to evaluate its bond strength and optimal surface treatment methods to prevent early debonding.

Translucency and colour masking ability of hybrid CAD/CAM materials with different thicknesses: in vitro study

OBJECTIVE

To evaluate effect of material thickness and translucency of two different hybrid CAD/CAM materials on their masking ability.

MATERIALS AND METHODS

40 rectangular-shaped specimens (12 × 14 mm) were obtained from Vita Enamic and Grandio blocks at 0.5 and 1 mm-thick (n = 10/group). Colour parameters of specimens were measured on PMMA tooth-coloured replica backgrounds (A2, C4) and black, white backings using dental spectrophotometer. Translucency parameter (TP) and masking ability (∆E00) values of tested materials with 0.5, and 1 mm thicknesses were calculated. Quantitative variables were compared between groups using student t-test.

RESULTS

TP and ∆E00 significantly decreased as thickness of tested materials increased. Grandio showed significantly higher TP values. There were significantly lower ΔE00 values for Vita Enamic compared to Grandio at 1 mm thickness and inversely insignificant at 0.5 mm. The 0.5 mm-thick ∆E00 of tested materials was above clinical acceptability threshold, whereas, 1 mm-thick did not exceed showing better masking properties.

CONCLUSIONS

Thickness is more effective for colour masking than translucency. In thin thickness, the masking ability is less effective, irrespective of tested materials. Translucency of tested materials was affected by their composition. Both hybrid CAD/CAM materials are promising alternatives for masking dark discolouration at 1 mm-thick.

Biomechanical reinforcement by CAD-CAM materials affects stress distributions of posterior composite bridges: 3D finite element analysis

OBJECTIVES

This 3D finite element analysis study aimed to investigate the effect of reinforcing CAD-CAM bars on stress distribution in various components of a posterior composite bridge.

METHODS

A virtual model mimicking the absence of an upper second premolar was created, featuring class II cavity preparations on the proximal surfaces of the adjacent abutment teeth surrounding the edentulous space. Five distinct finite element analysis (FEA) models were generated, each representing a CAD-CAM reinforcing bar material: 3-YTZP (IPS. emax ZirCAD MO; Zr), lithium disilicate (IPS e.max CAD; EX), nano-hybrid resin composite (Grandio Blocs; GB), Fibre-reinforced composite (Trilor; Tri), and polyetheretherketone (PEEK). A veneering resin composite was employed to simulate the replacement of the missing premolar (pontic). In the FEA, an axial force of 600 N and a transverse load of 20 N were applied at the center of the pontic. Subsequently, maximum von Mises (mvM) and maximum principal stresses (σmax) were computed across various components of the generated models. Additionally, shear stresses at the interface between the CAD-CAM bars and the veneering resin composite were determined.

RESULTS

CAD-CAM materials with high modulus of elasticity, such as Zr and EX, exhibited the highest mvM stresses and shear stresses while transferring the lowest stress to the veneering resin composite in comparison to other materials. Conversely, PEEK demonstrated the lowest mvM stresses but produced the highest stresses within the veneering resin composite. There was a uniform distribution of mvM stresses in the remaining tooth structure among all groups, except for a noticeable elevation in the molar region of Zr and EX groups.

SIGNIFICANCE

Reinforcing CAD-CAM bar materials with a high modulus of elasticity, such as Zr and EX, may result in debonding failures at the connector sites of posterior composite bridges. Conversely, GB, PEEK, and Tri have the potential to cause fracture failures at the connectors rather than debonding.

Biofilm Formation on Hybrid, Resin-Based CAD/CAM Materials for Indirect Restorations: A Comprehensive Review

Hybrid materials are a recent addition in the field of restorative dentistry for computer-aided design/computer-aided manufacturing (CAD/CAM) indirect restorations. The long-term clinical success of modern dental restorative materials is influenced by multiple factors. Among the characteristics affecting the longevity of a restoration, the mechanical properties and physicοchemical interactions are of utmost importance. While numerous researchers constantly evaluate mechanical properties, the biological background of resin-based CAD/CAM biomaterials is scarcely investigated and, therefore, less described in the literature. This review aims to analyze biofilm formation on the surfaces of novel, hybrid, resin-based CAD/CAM materials and evaluate the methodological protocols followed to assess microbial growth. It is demonstrated that the surface structure, the composition and the finishing and polishing procedures on the surface of a dental restorative material influence initial bacterial adhesion; however, most studies focus on in vitro protocols, and in vivo and/or in situ research of microbiomics in CAD/CAM restorative materials is lacking, obstructing an accurate understanding of the bioadhesion phenomenon in the oral cavity.

CAD-CAM resin composites: Effective components for further development

OBJECTIVE

This paper summarizes the effective components of computer-aided design and computer-aided manufacturing (CAD-CAM) resin composites that contribute to achieving greater mechanical properties and further development.

METHODS

In silico multi-scale analysis, in silico nonlinear dynamic finite element analysis (FEA), and artificial intelligence (AI) were used to explore the effective components of CAD-CAM resin composites. The effects of the filler diameter and silane coupling ratio on the mechanical properties of CAD-CAM resin composites have been clarified through multi-scale analysis. The effects of the filler contents, and filler and monomer compositions have been investigated by AI algorithms. The fracture behavior of CAD-CAM composite crown was analyzed using in silico non-linear dynamic FEA. The longevity of CAD-CAM composite crown was assessed through step-stress accelerating life testing (SSALT).

RESULTS

As the filler diameter decreases, there is an increase in elastic moduli and compressive strengths at the macroscale. At the nanoscale, a decrease in the filler diameter results in a decrease in the maximum value of the maximum principal strain. When the silane coupling ratio decreases, there is a decrease in the elastic modulus and compressive strength. According to the exhaustive search and feature importance analysis based on the AI algorithm, the combination of certain components was narrowed down to achieve a flexural strength of 269.5 MPa. The in silico non-linear FEA successfully detected the sign of the initial crack of the CAD-CAM composite molar crown. The SSALT revealed that CAD-CAM resin composite molar crowns containing nanofillers with a high fraction of resin matrix demonstrated great longevity.

SIGNIFICANCE

This paper summarized the effective components of CAD-CAM resin composites for their further development. The integration of in vitro and in silico approaches will expedite the advancement of CAD-CAM resin composites, offering benefits such as time efficiency and reduction of material waste for researchers and manufacturers.