Thomas J Lucas’s research while affiliated with University of Alabama at Birmingham and other places

Attempting endodontic access through ceramic or veneering porcelain can be wrought with challenges. Clinicians must take every precaution to assist patients who are in pain without causing harm through chipping or fracturing the restoration. This article discusses strategies clinicians can consider when facing the task of achieving endodontic access through an all-ceramic crown.

Objectives: To compare the fracture load of zirconia and lithium disilicate crowns prepared with endodontic access with fine and coarse diamond instruments. Materials and methods: 0.8 mm (3Y zirconia) or 1 mm (lithium disilicate) crowns were luted to resin composite dies with resin-modified glass ionomer (zirconia) or self-adhesive resin (lithium disilicate) cement. A 2.5 mm endodontic access hole was placed in each crown with fine (8369DF.31.025FOOTBALL) or coarse (6379 DC.31.023FOOTBALL) diamond instruments and restored with composite. A control group was prepared without access holes. Crowns were thermocycled for 10,000 cycles (5-55°C) and tested in compression with a steel indenter until failure (n = 8/group). A one-way ANOVA and Dunnett 2-sided test (alpha = 0.05) compared differences in fracture load between groups. Results: For zirconia, there was no statistical difference between the control group (2335 ± 160 N) and coarse diamond group (2345 ± 246 N); however, the fine diamond group (2077 ± 216 N) was significantly lower. For lithium disilicate, there was no statistical difference between the control group (2113 ± 183 N) and the fine (2049 ± 105 N) or coarse (2240 ± 118 N) groups. Conclusions: 3Y zirconia crowns became weaker when accessed with a fine diamond instrument. There was no negative effect of the endodontic access with bonded lithium disilicate crowns. Clinical significance: Conservative endodontic access openings in high-strength ceramic restorations do not have a negative effect on their static fracture load. The coarse zirconia-cutting diamond rotary instrument is more efficient and has a less detrimental effect on the strength of the crowns than a fine diamond rotary instrument.

Objective: Low-temperature-degradation (LTD) has been reported to cause property changes in yttria-tetragonal zirconia polycrystals (Y-TZP). The current study measured monoclinic phase transformation of Y-TZP with different grain sizes and corresponding property changes due to artificial aging. Null hypothesis: the grain size of aged Y-TZP will not influence its transformation, roughness, hardness or modulus of elasticity. Methods: Four groups of Y-TZP were examined with differing grain sizes (n=5). The line intercept technique was used to determine grain sizes on SEM images (100,000×). Artificial aging was accomplished by autoclaving at 2bar pressure for 5h. X-ray diffraction (30mA, 40kV) was used to measure tetragonal to monoclinic transformation (t→m). Surface roughness analysis was performed using a non-contact surface-profilometer. Nano-hardness and modulus of elasticity were measured using nano-indentation. Results: SEM analyses showed different grain sizes for each sample group (0.350μm, 0.372μm, 0.428μm, and 0.574μm). The fraction of t→m transformation increased as grain size increased; furthermore, aging of zirconia caused increased roughness. Modulus and hardness after aging displayed no significant correlation or interaction with grain size. Significance: Smaller grains caused less transformation, and aging caused increased roughness, but grain size did not influence the amount of increased surface roughness. Future studies are needed to determine the effects of grain size on the wear and fracture properties of dental zirconia.

Low-temperature degradation (LTD) of yttria-stabilized zirconia can produce increased surface roughness with a concomitant decrease in strength. This study determined the effectiveness of artificial aging (prolonged boiling/autoclaving) to induce LTD of Y-TZP (yttria-tetragonal zirconia-polycrystals) and used artificial aging for transformation depth progression analyses. The null hypothesis is aging techniques tested produce the same amount of transformation, transformation is not time/temperature dependent and LTD causes a constant transformation throughout the Y-TZP samples. Dental-grade Y-TZP samples were randomly divided into nine subgroups (n = 5): as received, 3.5 and 7 day boiling, 1 bar autoclave (1, 3, 5 h), and 2 bar autoclave (1, 3, 5 h). A 4-h boil treatment (n = 2) was performed post-experiment for completion of data. Transformation was measured using traditional X-ray diffraction and low-angle X-ray diffraction. The fraction of t → m transformation increased with aging time. The 3.5 day boil and 2 bar 5 h autoclave produced similar transformation results, while the 7 day boiling treatment revealed the greatest transformation. The surface layer of the aged specimen underwent the most transformation while all samples displayed decreasing transformation with depth. Surface transformation was evident, which can lead to rougher surfaces and increased wear of opposing dentition/materials. Therefore, wear studies addressing LTD of Y-TZP are needed utilizing accelerated aging. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2014. Copyright © 2014 Wiley Periodicals, Inc.

Objective: Low-temperature-degradation (LTD) in partially stabilized zirconia (PSZ) has been reported which results in property changes. LTD is known to begin at the surface and progress inward, producing possible increased surface roughness. The current study measured transformation of PSZ with differing grain sizes and the corresponding property changes due to artificial accelerated aging. Null hypothesis: the grain size of the PSZ will influence the amount of transformation, and more transformation will result in greater property degradations. Methods: Two groups of PSZ materials were provided from two manufacturers, with differing grain sizes (4 groups n=5). SEM images were used to determine grain sizes using line intercept technique. Artificial accelerated aging was accomplished using a MidMark M11 Ultraclave Automatic Sterilizer for 5 hours. A Siemens D500 XRD device with Cu-K-alpha radiation was used to measure tetragonal to monoclinic transformation (t→m). Surface roughness analysis was performed using Scantron Proscan 2000, a non-contact surface-measuring instrument. Nano-hardness and Modulus of Elasticity were measured using MTS Nano G200. Results: Grain sizes, monoclinic transformations, surface roughness, modulus, and nano-hardness values are indicated below for each group. Grain Size (μm) Aging Transformation(%Tm) Surface roughness (Ra) Modulus (GPa) Hardness (GPa) LK Group 1 0.224 (0.019) Before 0 0.204(0.054) 241.2(3.63) 15.9(0.61) After 0.39(0.46) 0.324(0.142) 267.7(2.82) 16.6(0.32) LK Group 2 0.239 (0.015) Before 0 0.328(0.089) 266.7(5.37) 16.6(0.50) After 2.54(0.61) 0.360(0.161) 270.8(4.61) 15.6(0.33) Lava Plus 0.274 (0.013) Before 0 0.156(0.051) 299.6(5.39) 17.0(0.32) After 4.03(0.54) 0.184(0.047) 269.4(12.9) 16.4(1.05) Lava 0.368 (0.035) Before 0 0.168(0.075) 285.1(5.34) 16.4(0.26) After 6.64(1.01) 0.220(0.082) 276.3(4.81) 16.5(0.42) Conclusions: Within the limits of this study, the monoclinic transformation decreases with smaller grains and the zirconia samples experienced a surface roughening upon aging. Furthermore, the modulus and hardness decreased after aging in all but one group. However, grain size did not appear to influence the amount of roughening.

Objective: A depth study was performed on yttria-stabilized-zirconia to observe the depth progression of transformation as a function of artificial aging time/treatment. Hypothesis: tested aging conditions of stabilized zirconia have the similar influence on depth progression of t → m transformation and cause the surface layer to transform first followed inward progression of transformation. Methods: The aging treatments chosen were prolonged boiling (40 hours, 3.5 and 7 days) and autoclaving under 2 bar of pressure (1, 3, and 5 hours). These tests efficiently accelerate the aging process of Y-TZP and provide observable patterns in the progression of transformation depth as time increases. Transformation (t→m) was measured using Xray-diffraction – Siemens D 500 XRD device with Cu K-alpha radiation. Scans were performed at 40 kV, 30 mA, 0.02 degrees/step from 27-33, with 12s/step dwell time. Seven settings for the x-ray incident-angle were used to analyze the sample: 1,2,3,5,8,10, and varied (θ/2θ). Results: Amount of monoclinic phase present and the corresponding x-ray incident angle and penetration depth is shown below. Incident Angle X-ray Penetration Depth (µm) 2-bar 5-Hour 2-Bar 3-Hour 2-bar 1-Hour 7-Day Boil 3.5-Day Boil 40-Hour Boil Theta-2-Theta 6.05 17.54 14.3 3.61 32.6 21.0 13.7 1 0.85 52.2 53.2 13.7 57.2 59.1 39.8 2 1.65 45.4 42.0 8.90 51.6 56.4 30.0 3 2.35 38.8 39.3 8.22 47.8 50.6 26.5 5 3.55 29.3 36.7 5.73 41.3 34.7 20.2 8 4.95 22.7 18.9 4.28 36.3 27.2 16.9 10 5.55 20.1 17.5 3.98 33.0 23.4 14.5 Theta-2-Theta rerun 6.05 16.9 14.9 3.36 33.6 21.2 14.2 Conclusions: As the aging time was increased the t→m transformation increased. The surface layer underwent the most transformation displaying decreasing transformation with depth progression. This implies transformation saturation at the surface, which can lead to rougher surfaces. Supported by NIDCR-5T32DE017607DART.

Recently full contour partially-stabilized-zirconia (PSZ) crowns have been introduced rather than feldspathic porcelain layered PSZ restorations. As zirconia ages it transforms from a partially stabilized tetragonal to a monoclinic phase with an accompanying increase in surface roughness. This transformation may be accelerated by boiling or autoclaving the yttrium stabilized zirconia. OBJECTIVES: Methods of accelerating the aging process should be investigated since the transformation could increase wear on teeth opposing the zirconia. To determine the effectiveness of artificial aging by prolonged boiling and autoclaving to induce the tetragonal-to-monoclinic phase transformation of partially-stabilized-zirconia. The null hypothesis is that both aging techniques will produce the same percentage of transformation. METHODS: The PSZ was randomly divided into 7 subgroups: as received, storage at ambient conditions for 3months, 3.5 day boiling, 7 day boiling, 1 hour autoclave (temperature 250F, pressure- 1bar), 3 hour autoclave, and 5 hour autoclave. Before and after x-ray diffraction patterns were measured using a Siemens D500 X-ray Diffractometer (30mA, 40kV) from 25-33, 0.02 step-size, and a dwell time of 8 seconds. 90% of diffraction information is obtained within 5 microns of the surface. Phase transformation was calculated using the relative percentage of monoclinic peak area present after aging compared to before aging. RESULTS: The following table shows each PSZ group and the amount of monoclinic phase after the two types of accelerated aging. Material 3M Lava Type of Aging Percent Monoclinic After Treatment 1 As Received 0.00 2 Stored 2.44 3 3.5 Day Boil 22.58 4 7 Day Boil 33.24 5 1 Hour Autoclave 1.77 6 3 Hour Autoclave 5.70 7 5 Hour Autoclave 4.90 CONCLUSIONS: The Lava samples had no monoclinic present as-received but transformed after boiling and autoclaving. Boiling produced more transformation than autoclaving. Funding provided by NIDCR Grant DEO17607. Zirconia supplied by 3M ESPE.

Objectives: Measure color change produced with three thicknesses of two ceramics with one total-etch resin-cement (Variolink II) compared to the original ceramic color. The null hypothesis is both ceramics covering the cured cement will have no color change at any thickness. Methods: ProCAD-100/I14 ceramic blocks were sectioned into three thicknesses: 0.59, 1.1, 2.1mm. Vita-Mark-II-A1C/I12 ceramic blocks were also sectioned into three thicknesses: 2.1, 1.05, 0.62mm. A thin layer (approximately 0.1 mm) of resin-cement (Variolink Veneer, shade-value +3) was applied to the ceramic and light cured for 30s (3M ESPE Elipar S10-1030mW/cm2). Color change was observed using a Konica-Minolta 700d Spectrophotometer at 0 and 90 using white and black backgrounds. L*a*b* values were recorded and ΔE calculated: ΔE=(ΔL*2+Δa*2+Δb*2)1/2. The cement thickness was measured using a .001 micrometer caliper. The cementing procedure was repeated until n≥5 for each ceramic material. Results: The ΔE values for white and black backgrounds are displayed below. The data were analyzed (General Linear Models) using SAS-9.3 to determine intergroup differences (p=0.05). There was no statistical significant difference in measurements made at 0and 90. Significant differences were observed when comparing ProCad-0.59 to ProCad-1.14, ProCad-0.59 to ProCad-2.1, and Vita-0.62 to Vita-1.05 (p<.05). Ceramic Ceramic Thickness (mm) Average Cement Thickness (mm) White-Background Average ΔE Black-Background Average ΔE ProCad 0.59 0.1350.0077 0.7710.175 5.1710.326 ProCad 1.14 0.1220.0032 0.5900.039 1.4350.142 ProCad 2.10 0.1340.0038 0.4290.106 1.0430.141 Vita MII 0.62 0.0980.0012 0.6490.195 3.8020.351 Vita MII 1.05 0.0910.0053 0.4660.099 1.6750.201 Vita MII 2.12 0.1210.0060 0.3050.132 0.7460.146 Conclusions: As ceramic thickness increased to 2 mm, the ΔE values decreased showing that the color of a 2mm thick ceramic is difficult to alter with a thin (120μm) thickness of cement. However, the color of 0.6-1mm thick ceramics can be altered with a resin cement. SUPPORTED BY NIDCR GRANT DEO17607.

Objectives: To evaluate the property degradation of partially stabilized zirconia (PSZ) due to mechanical fatiguing both before and after aging. Methods: 20 partially stabilized zirconia bars (2x2x21) were separated into 4 groups: as-received, aged, fatigued, and aged-and-fatigued. Five partially stabilized zirconia discs (20 mm X 5mm) of the same material were aged. X-ray diffraction (XRD) was conducted on the discs before and after aging. Aging involved boiling the samples for 7 days in a soxhlet device. The partially stabilized zirconia bars (2x2x21) were fatigued by repeatedly loading the samples with 10N for 20,000 cycles at a 1second/cycle frequency. The bars were then tested for flexural strength and modulus using a three-point bend test (Instron-5565) at a 1 mm/minute crosshead speed until failure. Scans were run on the partially stabilized zirconia discs using a 3D non-contact surface profilometer (Proscan 2000) to determine the surface roughness (Ra). Results: Strength and modulus data is displayed below (MeanSD). The data were analyzed using ANOVA and Tukey-Kramer tests to determine intergroup differences (p=.05). No significant differences were seen for flexural strength between groups (p>.05). Aged-and-fatigued and fatigued groups showed a significantly higher modulus compared to as-received group (p<.05). Values show that a phase transformation appears to take place causing the increase in modulus. The XRD indicated that a 13% volume fraction increase occurred due to the aging process. The Ra increased after aging for the partially stabilized zirconia discs. Count Strength (MPa) Modulus (GPa) As received 5 812.53106.0 123.275.44 Aged 5 896.42112.9 134.679.03 Fatigued 5 935.10133.2 147.379.20 Aged & Fatigued 5 931.85123.2 144.115.65 Conclusions: Results of this study indicate that the modulus of PSZ is increased by fatigue and ageing and fatigue testing. A phase transformation from tetragonal to monoclinic was the cause of the changes, which also led to rougher surfaces.