Impact of artificial aging by thermocycling on edge chipping resistance and Martens hardness of different dental CAD-CAM restorative materials

Impact of liner treatment on the translucency of CAD/CAM multi-colored lithium disilicate and multi-layered zirconia implant-supported crowns, and evaluation of fracture strength of ceramic crowns

This study aimed to evaluate the optical properties of liner-treated CAD/CAM Multi-colored lithium disilicate (Amber Mill Direct; AMD) and multi-layered zirconia (Omega multi; OM) implant-supported crowns, as well as their effect on the fracture strength of Ti or Zr abutments to which they were applied. After sintering AMD and OM ceramic blocks, they were classified into three groups: untreated, liner-treated, and liner-treated with added color. Optical properties were evaluated by analyzing color differences using background materials to assess translucency and the masking ability of liner-treated ceramics. Subsequently, the fracture strength of implant-supported crowns applied to Ti or Zr abutments was measured, and statistical analysis was conducted using Weibull statistics. Untreated AMD exhibited the highest translucency. Liner treatment reduced translucency in both ceramics, while color-added liner treatment increased translucency. Liner-treated AMD showed greater color difference compared to OM, whereas color-added liner treatment reduced the color difference. Fracture strength was highest in Ti abutment-OM crowns (548.03 N) and lowest in Zr abutment-AMD crowns (283.58 N). Additionally, the Weibull coefficient was over twice as high in Ti abutment-AMD crowns (m = 17.500). Color liners can adjust the high translucency of lithium disilicate ceramics to block discoloration, providing natural tooth-like color and enabling the creation of esthetic restorations. Furthermore, lithium disilicate ceramic crowns applied to Ti abutments exhibited high Weibull coefficients and fracture strengths.

Performance Assessment of Three Similar Dental Restorative Composite Materials via Raman Spectroscopy Supported by Complementary Methods Such as Hardness and Density Measurements

(1) Background: A widespread problem in oral health is cavities produced by cariogenic bacteria that consume fermentable carbohydrates and lower pH to 5.5-6.5, thus extracting Ca2+ and phosphate ions (PO43-) from teeth. Dental restorative materials based on polymers are used to fill the gaps in damaged teeth, but their properties are different from those of dental enamel. Therefore, a question is raised about the similarity between dental composites and natural teeth in terms of density and hardness. (2) Methods: We have used Raman spectroscopy and density and microhardness measurements to compare physical characteristics of several restorative dental composites at different polymerization intervals. (3) Results: XRVHerculite®, Optishade®, and VertiseFlow® showed the very different characteristics of the physical properties following four polymerization intervals. Of the three composites, OptiShade showed the highest polymerization rate. (4) Conclusions: Only fully polymerized composites can be used in teeth restoring, because incomplete polymerization would result in cracks, pitting, and lead finally to failure.

The Influence of Polishing and Artificial Aging on BioMed Amber® Resin's Mechanical Properties

Currently, 3D print is becoming more common in all branches of medicine, including dentistry. Some novel resins, such as BioMed Amber (Formlabs), are used and incorporated to more advanced techniques. The aims of the study were to check whether or not polishing and/or artificial aging influences the properties of the 3D-printed resin. A total of 240 specimens of BioMed Resin were printed. Two shapes (rectangular and dumbbell) were prepared. Of each shape, 120 specimens were divided into four groups each (with no influence, after polishing only, after artificial aging only, and after both polishing and artificial aging). Artificial aging took place in water at the temperature of 37 °C for 90 days. For testing, the universal testing machine (Z10-X700, AML Instruments, Lincoln, UK) was used. The axial compression was performed with the speed of 1mm/min. The tensile modulus was measured with the constant speed of 5 mm/min. The highest resistance to compression and tensile test were observed in the specimens that were neither polished nor aged (0.88 ± 0.03 and 2.88 ± 0.26, respectively). The lowest resistance to compression was observed in the specimens that were not polished, but aged (0.70 ± 0.02). The lowest results of the tensile test were observed when specimens were both polished and aged (2.05 ± 0.28). Both polishing and artificial aging weakened the mechanical properties of the BioMed Amber resin. The compressive modulus changed much with or without polishing. The tensile modulus differed in specimens that were either polished or aged. The application of both did not change the properties when compared to the polished or aged probes only.

Martens Hardness of CAD/CAM Resin-Based Composites

(1) Background: The properties of CAD/CAM resin-based composites differ due to differences in their composition. Instrumented indentation testing can help to analyze these differences with respect to hardness, as well as energy-converting capabilities due to viscoelastic behavior. (2) Methods: Eleven materials were investigated using instrumented indentation testing. Indentation depth (hr), Martens hardness (HM), indentation hardness (HIT), indentation modulus (EIT), the elastic part of indentation work (ηIT), and indentation creep (CIT) were investigated, and statistical analysis was performed using one-way ANOVA, Bonferroni post-hoc test, and Pearson correlation (α = 0.05). (3) Results: All of the investigated parameters revealed differences between the analyzed materials. Besides the differences in hardness-associated parameters (hr, HM, and HIT), instrumented indentation testing demonstrated differences in energy-converting properties. The subsequent one-way ANOVA revealed significant differences (p < 0.001). A significant (p < 0.01, Pearson correlation >0.576) correlation between the materials and HM, HIT, or EIT was identified. (4) Conclusions: Due to the differences found in the energy-converting properties of the investigated materials, certain CAD/CAM resin-based composites could show superior stress-breaking capabilities than others. The consequential reduction in stress build-up may prove to beneficial, especially for implant-retained restorations or patients suffering from parafunctions.

Bending moment of implants restored with CAD/CAM polymer-based restoration materials with or without a titanium base before and after artificial aging

OBJECTIVES

To test and compare two types of implant systems restored with four monolithic polymer-based materials with regard to their bending moments (BM) before and after aging.

METHODS

A total of 192 tissue-level implants (TRI Dental Implants) differing in the presence (TiB, Octa line, n = 96) or absence (NTiB, Matrix line, n = 96) of a titanium base were restored with mandibular right first molar crowns manufactured from composite (CC), polymer-infiltrated ceramic (VE), PMMA (PM) and a 3D printed resin (ND) (n = 24). Half of the specimens (n = 12) were loaded for 1,200,000 cycles (50 N, 1.3 Hz, TC: 5/55 °C, 6000×) and examined for failures. Fracture load was measured according to ISO standard 14801, BM was calculated, and fracture types were examined. Data were analyzed using parametric statistics (p < 0.05).

RESULTS

No failures were observed after 600,000 cycles. After 1,200,000 cycles, wear traces were recorded in all groups except PM, VE and CC on TiB implants. In group CC on NTiB implants, three specimens were rated zero in BM testing as they showed fracture of the screw. Regarding BM, TiB implants exhibited higher values than NTiB implants with aged CC (p = 0.023), aged PM (p < 0.001), initial PM (p = 0.011) and initial VE (p < 0.001). No differences occurred among the implant types with initial CC, initial ND, aged ND and aged VE. With regard to initial BM values, NTiB implants showed higher values for ND and CC compared with PM and VE (p < 0.001). No differences in initial BM values were found for the tested materials on TiB implants (p > 0.116). When aged, restoration material had no impact on the BM values of NTiB implants (p ≥ 0.233). Aged TiB implants showed higher values in combination with CC than with ND (p = 0.001). PM and VE showed similar values as ND and CC. Artificial aging led to a decrease of BM within PM, CC and ND on NTiB implants and ND on TiB implants. The majority of failures after testing were characterized by crown fractures in two to four pieces. Fractures in more pieces with smaller fragments occurred primarily for ND.

SIGNIFICANCE

The use of NTiB implants with the polymer-based materials tested can only be recommended for clinical use as interim prostheses. CC seems to show a positive effect on the BM. Clinical research investigating the in vivo behavior is necessary to confirm these findings.

Methodology investigation: Impact of crown geometry, crown, abutment and antagonist material and thermal loading on the two-body wear of dental materials

OBJECTIVES

To investigate the impact of crown geometry, crown/abutment/antagonist material and thermal loading on the two-body wear of dental materials caused by chewing simulation.

MATERIALS AND METHODS

For the crown geometry, crowns (polymethylmethacrylate (PMMA), polyetheretherketone (PEEK) and silicate ceramic (SiO₂)) were milled with a flat, steep, or medium cusp inclination (CINC). For the crown/abutment material, crowns (PMMA, PEEK and SiO₂) were combined with PMMA, polymer-infiltrated-ceramic-network (PICN), cobalt-chrome alloy (CoCr) and natural teeth (ENAM) abutments. For the antagonist material, antagonists were fabricated from PICN, CAD/CAM resin composite (RECO), steatite (STEA), steel (STL) and ENAM and tested against flat specimens (substrates) made of veneering ceramic (VC). For thermal loading, the duration (30 s, 60 s, 120 s) and presence of temperature changes (37 °C versus 5 °C/55 °C) was varied. Material losses were determined by matching scanned specimens before and after aging (400,000 chewing cycles, 50 N, 1.3 Hz). Martens parameters were determined for the antagonists/substrates. Data were analyzed using Kolmogorov-Smirnov-test, Kruskal-Wallis H, Scheffé-Post-Hoc-tests, pairwise comparisons, Bonferroni correction, one-way ANOVA, Mann-Whitney-U and Spearman rho.

RESULTS

PMMA crowns presented the highest and PEEK the lowest material losses. Flat CINC showed the lowest material losses for PEEK and SiO₂ crowns. CoCr and ENAM abutments presented material losses in the same range. Antagonist and cumulative material losses for RECO and ENAM were similar. Thermal loading did not influence material losses.

SIGNIFICANCE

Crown geometry influences the crown and antagonists wear, with an increased cusp inclination entailing increased wear. For in vitro set-ups, CoCr abutments and RECO antagonists present valid alternatives to natural teeth. For polymers, in vitro chewing simulations may be performed at a constant temperature (37 °C).

Evaluation of the damping capacity of common CAD/CAM restorative materials

OBJECTIVES

To evaluate and quantify the damping capacities of common CAD/CAM restorative materials (CRMs) and to assess their energy dissipation abilities by comparing loss tangent and Leeb hardness data.

METHODS

Leeb hardness (HLD), together with its deduced energy dissipation data (HLD_dis), and loss tangent values recorded via dynamic mechanical analysis (DMA) were determined for 4 ceramic, 13 composite, and 2 polymer-based CRMs as well as 1 metal. For Leeb hardness, ten indentations per material were performed on two separate specimens (12.0 × 12.0 × 3.5 mm³) after water storage (24 h; 37.0 ± 1.0 °C). For DMA, ten specimens (16.00 × 4.00 × 1.00 mm³ ± 0.05 mm) per material were investigated in distilled water (37.0 ± 0.5 °C) with a dynamic force of 1 N at 1.5 Hz. Each data set was analyzed using two-way analysis of variance (ANOVA) with material type and material nested in material type as factors. Post-ANOVA contrasts were performed using a Bonferroni adjustment for multiple comparisons (α = 0.05). Correlations between different parameters were tested (Pearson, α = 0.05).

RESULTS

HLD_dis data revealed the significantly highest damping capacity for metal and the lowest values for ceramics with composites and polymers in between. However, for loss tangent, the metal together with lithium disilicate glass-ceramics exhibited the lowest damping effects and polymer materials the highest results with composites likewise in between. A strong dependency of the loss tangent results on the filler content of the investigated CRMs was indicated (r = - 0.822, p < 0.001), while a positive and only moderate correlation between loss tangent and HLD_dis was observed (r = 0.565, p < 0.001), which conversely revealed a very strong correlation (r = 0.911, p < 0.001) if the metal was excluded from the calculation.

CONCLUSIONS

Although HLD_dis and loss tangent values both allowed a distinct differentiation of the damping capabilities of various CRMs and the respective material types, HLD_dis data appeared to more accurately describe the damping capacity of CRMs as the energy dissipation mechanism of permanent plastic material deformation, that is commonly observed for metals and some composite-based CRMs, is equally captured. This finding could be particularly interesting for the future development of new CRMs with improved mechanical properties as HLD_dis data determination in principle is a very efficient and simple technique to entirely specify unknown damping capacities of materials.

Effect of repeated ultrasonic instrumentation on single-unit crowns: a laboratory study

OBJECTIVES

This laboratory study aimed to assess the effects of ultrasonic instrumentation, simulating 10 years of supportive periodontal therapy (SPT), on single-unit crowns.

MATERIALS AND METHODS

Standardized crowns were fabricated from porcelain-fused-to-metal (PFM) (n = 12), zirconia (ZrO₂) (n = 12), lithium disilicate (LDS) (n = 12), feldspar ceramic (FSFC) (n = 6), and polymer-infiltrated ceramic network material (PICN) (n = 6). The crowns, luted on PICN abutments with resin-based luting material (RBLM), and if applicable glass ionomer cement (GILC), underwent thermal cycling and trimonthly ultrasonic instrumentation. After 1 and 10 years of simulated SPT, restoration quality assessments were performed, comprising profilometric surface roughness measurements, marginal integrity evaluations, and scores for luting material remnants and visible cracks. The statistical analysis included multiple logistic regressions with nested designs (α = 0.05).

RESULTS

During simulated SPT, bulk fractures (n = 2) and a de-cementation failure (n = 1) of LDS and ZrO₂ crowns were observed. No significant change in roughness was detected after 10 years (p = 0.078). Over time, marginal defects increased (p = 0.010), with PFM crowns showing the highest rate of chippings at sites with a narrow shoulder. Fewer marginal defects were detectable on crowns luted with RBLM compared with GILC (p = 0.005). Luting material remnants decreased during SPT (p < 0.001). Ultrasonic instrumentation caused cracks in most crown materials, in particular at sites with a narrow shoulder and in PFM crowns.

CONCLUSIONS

Repeated ultrasonic instrumentation may damage single-unit crowns. PFM crowns with a narrow, all-ceramic margin are especially prone to defects.

CLINICAL RELEVANCE

Frequent ultrasonic instrumentation of restoration margins of fixed dental prostheses, PFM crowns in particular, ought to be avoided.