Effects of shade and thickness on the translucency parameter of anatomic-contour zirconia, transmitted light intensity, and degree of conversion of the resin cement

Statement of problem Anatomic-contour zirconia prostheses are usually cemented with resin cement. However, information regarding the effects of the zirconia shade and thicknesses on the translucency of the prosthesis, the intensity of the transmitted light beneath the prosthesis, and the subsequent degree of conversion in the resin cement is sparse. Purpose The purpose of this in vitro study was to investigate the translucency parameter in 3 anatomic-contour zirconia specimens of 2 shades at 5 different thicknesses and to investigate the transmitted light intensity and degree of conversion of the resin cement beneath the ceramic specimens by using a traditional zirconia and a lithium disilicate glass ceramic as controls. Material and methods Ceramic specimens from 1 anatomic-contour zirconia in a generic shade (CAP FZ) and 2 anatomic-contour zirconias in A2 shade (Zirlux and Luxisse) were used. Lithium disilicate in HT A2 shade (IPS e.max CAD) and traditional zirconia in a generic shade (CAP QZ) were used as controls. A total of 125 ceramic specimens (n=25) were fabricated to a final specimen dimension of 12×12 mm and in thicknesses of 1.0, 1.25, 1.5, 1.75, and 2.0 mm according to the manufacturers’ recommendations. The CIELab color space for all specimens placed against a white and black ground was measured with a spectrophotometer (CM-2600D), and the translucency parameters were calculated for the materials at various thicknesses. A light-polymerizing unit (DEMI LED) was used to polymerize the resin cement (Variolink II) placed beneath the ceramic specimens. Transmitted light intensity from the polymerization unit beneath the ceramic specimens was measured by using a spectrophotometer (MARC Resin Calibrator), and the transmittance of each specimen was calculated. The coefficient of absorption of each material was calculated from the regression analysis between the natural log of transmittance and specimen thickness. The degree of conversion of resin cement was measured by using a Fourier transformation infrared (FTIR) spectrophotometer. The results were analyzed by using 2-way ANOVA (α=.05). The relationship between the transmittance and the translucency parameter was evaluated by plotting the transmittance against the translucency parameter value of each specimen. Results The translucency parameter decreased with increasing thickness in all 5 material groups. All anatomic-contour zirconia had lower translucency parameters than e-max CAD (P<.001). The same results were found for the intensity of the transmitted light (P<.001). Both A2 shade anatomic-contour zirconia (Zirlux and Luxisse) showed significantly lower light transmittance than a generic shade anatomic-contour zirconia (CAP FZ) (P<.001). The coefficients of absorption were found to range from 0.63 to 1.72 mm-1, and reflectance from 0.10 to 0.25. The results from the degree of conversion of resin cement after polymerization through 1 to 2 mm of specimens showed a significantly higher degree of conversion in the e.max group than in all other groups (P<.001). The correlation between translucency parameter and the intensity of the transmitted light suggested that the relationship was shade dependent. Conclusions The translucency parameter and the transmitted light intensity of ceramic material were influenced by the type of ceramic and the shade and thickness of the ceramic. The combined effects of layer thickness and the intensity of the transmitted light in the A2 shade anatomic-contour zirconia (Zirlux and Luxisse) resulted in a lower degree of conversion in resin cement than in a generic shade anatomic-contour zirconia (CAP FZ) at layer thicknesses of 1.75 and 2 mm

Fracture Resistance Behaviors of Titanium-Zirconium and Zirconia Implants

Purpose To evaluate the fracture resistance behaviors of titanium-zirconium, one-piece zirconia, and two-piece zirconia implants restored by zirconia crowns and different combinations of abutment materials (zirconia and titanium) and retention modes (cement-retained and screw-retained zirconia crowns). Material and Methods Three research groups (n=12) were divided according to combinations of abutment material, retention mode, and implant type. In the control group (TTC), titanium-zirconium implants (∅ 4.1 mm RN, 12 mm, Roxolid; Straumann USA) and prefabricated titanium abutments (RN synOcta Cementable Abutment, H 5.5 mm; Straumann USA) were used to support cement-retained zirconia crowns. In the second group (ZZC), one-piece zirconia implants (PURE Ceramic Implant Monotype, ∅ 4.1 mm RD, 12 mm, AH 5.5 mm; Straumann USA) were used to support cement-retained zirconia crowns. In the third group (ZTS), two-piece zirconia implants (PURE Ceramic Implant, ∅ 4.1 mm RD, 12 mm) and prefabricated titanium abutments (CI RD PUREbase Abutment, H 5.5 mm) were used to support screw-retained zirconia crowns. All zirconia crowns were manufactured in the same anatomic contour with a 5-axis dental mill and blended 3 and 5 mol% yttria-stabilized zirconia (LayZir A2). Implants were inserted into specimen holders made of epoxy resin-glass fiber composite. All specimens were then subject to artificial aging in an incubator at 37 C° for 90 days. Fracture resistance of specimen assemblies was tested under static compression load using the universal testing machine following ISO14801 specification. The peak fracture loads were recorded. All specimens were examined at the end of the test microscopically at 5 × and 10 × magnification to detect any catastrophic failures. Comparisons between groups for differences in peak fracture load were made using Wilcoxon Rank Sum tests and Weibull and Kaplan-Meier survival analyses (α = .05). Results The TTC group (942 ±241 N) showed significantly higher peak fracture loads than the ZZC (645 ±165 N) and ZTS (650 ±124 N) groups (p < .001), while there was no significant difference between ZZC and ZTS groups (p = 0.940). The survival probability based on the Weibull and Kaplan-Meier models demonstrated different failure molds between titanium- zirconium and zirconia implants, in which the TTC group remained in the plastic strain zone for a longer period before fracture when compared to ZZC and ZTS groups. Catastrophic failures, with implant fractures at the embedding level or slightly below, were only observed in the ZZC and ZTS groups. Conclusions Cement-retained zirconia crowns supported by titanium-zirconium implants and prefabricated titanium abutments showed superior peak fracture loads and better survival probability behavior. One-piece zirconia implants with cement-retained zirconia crowns and two-piece zirconia implants with screw-retained zirconia crowns on prefabricated titanium abutment showed similar peak fracture loads and survival probability behavior. Titanium-zirconium and zirconia implants could withstand average intraoral mastication loads in the incisor region. This study was conducted under static load, room temperature (21.7 °C), and dry condition, and full impacts of intraoral hydrothermal aging and dynamic loading conditions on the zirconia implants should be considered and studied further

Fatigue Failure Load of Lithium Disilicate Restorations Cemented on a Chairside Titanium‐Base

PurposeTo evaluate the fatigue failure load of distinct lithium disilicate restoration designs cemented on a chairside titanium base for maxillary anterior implant‐supported restorations.Materials and MethodsA left‐maxillary incisor restoration was virtually designed and sorted into 3 groups: (n = 10/group; CTD: lithium disilicate crowns cemented on custom‐milled titanium abutments; VMLD: monolithic full‐contour lithium disilicate crowns cemented on a chairside titanium‐base; VCLD: lithium disilicate crowns bonded to lithium disilicate customized anatomic structures and then cemented onto a chairside titanium base). The chairside titanium base was air‐abraded with aluminum oxide particles. Subsequently, the titanium base was steam‐cleaned and air‐dried. Then a thin coat of a silane agent was applied. The intaglio surface of the ceramic components was treated with 5% hydrofluoric acid (HF) etching gel, followed by silanization, and bonded with a resin cement. The specimens were fatigued at 20 Hz, starting with a 100 N load (5000× load pulses), followed by stepwise loading from 400 N up to 1400 N (200 N increments) at a maximum of 30,000 cycles each. The failure loads, number of cycles, and fracture analysis were recorded. The data were statistically analyzed using one‐way ANOVA, followed by pairwise comparisons (p < 0.05). Kaplan‐Meier survival plots and Weibull survival analyses were reported.ResultsFor catastrophic fatigue failure load and the total number of cycles for failure, VMLD (1260 N, 175,231 cycles) was significantly higher than VCLD (1080 N, 139,965 cycles) and CDT (1000 N, 133,185 cycles). VMLD had a higher Weibull modulus demonstrating greater structural reliability.ConclusionVMLD had the best fatigue failure resistance when compared with the other two groups.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152519/1/jopr12911_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152519/2/jopr12911.pd