A Novel Concept for Developing a Precise and Predictable Post and Core Complex Using the Injectable Resin Technique (Part 2).

Post and core systems have long been used in dentistry for the purposes of replacing missing coronal tooth structure, retaining the core, and providing sufficient retention and resistance form to the final restoration to re-establish original form and function. While Part 1 of this two-part article provided a history of post and core systems and materials and discussed empirical data regarding fiber-reinforced post systems, this second part of the article focuses on an alternative approach for developing a fiber-reinforced post and core system using a monoblock system via the injectable resin technique and a recently developed fiber-optic post. The present article explains the concept of a ferrule effect and demonstrates the novel restorative procedure.

A Novel Concept for Developing a Precise and Predictable Post and Core Complex Using the Injectable Resin Technique.

Post systems have long been used in the roots of teeth to retain dental restorations. The primary objectives of current post and core systems are to replace missing coronal tooth structure, retain the core, and provide sufficient retention and resistance form to the final restoration to restore original form and function. Many varieties of user-friendly post and core systems are available today for different endodontic, restorative, and esthetic requirements. The present article provides a history of post and core usage in dentistry, describes various systems and materials for this purpose, and discusses empirical data regarding fiber-reinforced post systems.

In vitro inhibition of demineralization from bioglass-containing adhesive and composite.

PURPOSE: To measure and compare the area of inhibition around a bioglass-containing adhesive and resin-based composite following an in vitro artificial caries model in human extracted teeth. METHODS: Preparations were made at the CEJ of extracted human molars (40, n=10/material) and restored with combinations of a bioglass-containing adhesive (BA, Regen), a reference adhesive which served as a negative control (RA), a bioglass-containing composite (BC, Regen), and a reference composite which served as a negative control (RC): BABC, RABC, BARC, RARC. All materials were light-cured and then finished with a polishing disc. Teeth were incubated (37°C) for 24 hours in water. A demineralization solution composed of 0.1 M lactic acid, 3 mM Ca3(PO4)2, 0.1% thymol, and NaOH (to adjust pH= 4.5) and a remineralization solution composed of 1.5 mM Ca, 0.9 mM P, and 20 mM Tris(hydroxymethil)-aminomethane (pH= 7.0) were prepared. Specimens were placed in the demineralization solution for 4 hours followed by a remineralization solution for 20 hours and cycled daily for 30 days. The specimens were embedded, sectioned into 100 µm sections, and the interface between the adhesive/composite and root dentin margin was viewed with polarized light. A line was drawn parallel with the zone of demineralization for each tooth. The area of "inhibition" (defined as the area external to the line) or "wall lesion" (defined as the area internal to the line) was traced with internal image evaluation software and measured. Areas of inhibition were measured as positive values and areas of wall lesions were measured as negative values. RESULTS: A one-way ANOVA found significant differences between materials for "inhibition/wall lesion" areas in root dentin (P< 0.001). Tukey post-hoc analysis ranked materials (µm2, mean± SD): BABC (3590± 2847)a RABC (1903± 1025)a, BARC (-792± 850)b, RARC (-2544± 1760)b. CLINICAL SIGNIFICANCE: The use of bioglass-containing resin-based composite with or without a bioglass-containing adhesive demonstrated inhibition of demineralization at the restoration margin.

Effect of Surface Treatment and Cement on Fracture Load of Traditional Zirconia (3Y), Translucent Zirconia (5Y), and Lithium Disilicate Crowns.

PURPOSE: To determine if surface treatment and cement selection for traditional 3 mol% yttria partially stabilized zirconia (3Y-PSZ), "translucent" 5 mol% yttria-stabilized zirconia (5Y-Z), or lithium disilicate crowns affected their fracture load. MATERIALS AND METHODS: Crowns with 0.8 mm uniform thickness (96, n = 8/group) were milled of 3Y-PSZ (Lava Plus), 5Y-Z (Lava Esthetic), or lithium disilicate (e.max CAD) and sintered/crystallized. Half the crowns were either particle-abraded with 30 µm alumina (zirconias) or etched with 5% hydrofluoric acid (lithium disilicate), and the other half received no surface treatment. Half the crowns from each group were luted with resin-modified glass ionomer (RMGI, RelyX Luting Plus) and half were luted with a resin cement (RelyX Unicem 2) to resin composite dies. Crowns were load cycled (100,000 cycles, 100 N force, 24°C water) and then loaded with a steel indenter until failure. A three-way ANOVA examined the effects of material, cement, and surface treatment on fracture load. Post-hoc comparisons were performed with the Tukey-Krammer method. RESULTS: Fracture load was signficiantly different for materials and cements (p < 0.0001) but not surface treatments (p = 0.77). All lithium disilicate crowns luted with RMGI failed in fatigue loading cycling; 3Y-PSZ and 5Y-Z crowns luted with resin showed a higher fracture load compared with RMGI (p < 0.001). With resin cement, there was no signficant difference in fracture load between 5Y-Z and lithium disiliciate (p = 1) whereas 3Y-PSZ had a higher fracture load (p < 0.0001). CONCLUSIONS: Cement type affected fracture load of crowns but surface treatment did not. The 0.8 mm uniform thick crowns tested benefited from using resin cement regardless of type of ceramic material. Crowns fabricated from 5Y-Z may be particle-abraded if luted with resin cement.

Comparison of the mechanical properties of translucent zirconia and lithium disilicate.

STATEMENT OF PROBLEM: Three mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) possesses excellent mechanical properties but is relatively opaque. Five mol% yttria-stabilized zirconia polycrystal (5Y-ZP) offers improved translucency, but many of its clinical properties have not been compared with those of 3Y-TZP and lithium disilicate. PURPOSE: The purpose of this in vitro study was to compare the flexural strength, translucency parameter, bond strength, and enamel and material wear of 5Y-ZP (Katana UTML) with 3Y-TZP (Katana HT) and lithium disilicate (e.max CAD). MATERIAL AND METHODS: Flexural strength bars were sectioned (n=10, 25×4×2 mm), sintered or crystallized, polished, and fractured at 1 mm/min. Translucency specimens (1 mm thick) were fabricated (n=10). Their L*a*b* values were measured against a black-and-white background with a spectrophotometer, and ΔE00 was calculated. Zirconia bond strength specimens were airborne-particle abraded with 50 µm alumina followed by the application of a 10-methacryloxydecyl dihydrogen phosphate-containing primer (Clearfil Ceramic Primer). Lithium disilicate bond strength specimens were etched with 5% hydrofluoric acid followed by application of a silane-containing primer (Clearfil Ceramic Primer). A Tygon tube filled with resin cement (Panavia SA) was fixed to the surface of the ceramics and light-polymerized. After 1 day or 150 days of water storage, the resin cement was debonded in a macroshear test (n=10). The cusps of extracted human molars were isolated and mounted into the University of Alabama at Birmingham wear-testing device. Wear testing was performed with a 20-N load for 300000 cycles in 33% glycerin. The volumetric wear of polished zirconia, lithium disilicate, and enamel were measured along with the wear of the opposing enamel cusps using a noncontact profilometer (n=8). The data were compared by ANOVA and Tukey-Kramer analysis (α=.05). RESULTS: No statistical difference was seen between the bond strengths (P=.155) or the opposing enamel wear (P=.533) of different ceramics. A statistically significant difference was seen between the flexural strength (P<.001), translucency parameter (P<.001), and wear (P<.001) of the materials. The flexural strength values (MPa) were 1194 ±111 (Katana HT), 688 ±159 (Katana UTML), and 450 ±53 (e.max LT). The translucency parameter values were 6.96 ±0.53 (Katana HT), 8.30 ±0.24 (Katana UTML), 9.28 ±0.36 (e.max LT), and 12.64 ±0.48 (e.max HT). Bond strength values (MPa) at 1 and 150 days were 34.22 ±5.14 and 28.37 ±6.03 (Katana HT), 35.04 ±5.69 and 25.03 ±6.44 (Katana UTML), and 35.50 ±3.45 and 22.32 ±3.45 (e.max LT). Material and enamel wear (mm3) were 0 and 0.24 ±0.19 (Katana HT), 0 and 0.23 ±0.09 (Katana UTML), 0.28 ±0.13 and 0.31 ±0.10 (e.max CAD), and 0.09 ±0.03 and 0.31 ±0.14 (enamel). CONCLUSIONS: 5Y-TZP has a flexural strength and translucency parameter between those of 3Y-TZP and lithium disilicate. Both the short-term and long-term bond strength of 5Y-ZP and 3Y-TZP was shown to be similar to lithium disilicate. 5Y-ZP demonstrated no measurable material wear and opposing enamel wear similar to that of all the other materials tested.

Light-transmitting fiber optic posts: An in vitro evaluation.

STATEMENT OF PROBLEM: The clinical challenge of adhering cement to intracanal dentin is transmitting light to the most apical parts of root canals to allow more efficient polymerization of the cement. PURPOSE: The purpose of this in vitro study was to compare the cement-polymerizing ability, microstructure, and radiopacity of a new fiber optic post (iLumi fiber optic Post) with a clinically successful fiber post (DT Light Post). MATERIAL AND METHODS: Polymerizing ability was compared using a modified depth-of-polymerization protocol. A split aluminum mold with a 12-mm cylindrical hole (diameter=4.7 mm) was filled with light-polymerized resin cement (Variolink Esthetic LC). Each fiber post (n=12) was positioned and light-polymerized on the coronal end for 60 seconds with a light-emitting diode polymerization light. Unpolymerized resin was dissolved with an organic solvent, and the weight and length of the polymerized resin cement were measured. Scanning electron microscopy was used to examine vertical and horizontal cross-sections. The radiopacity values of both the posts and 5 additional reference posts were evaluated using an aluminum step wedge. RESULTS: The weight and length of the polymerized resin cement were significantly greater (P<.05) with the fiber optic post, which scanning electron microscopy showed to have a higher density of parallel fibers. The iLumi post demonstrated greater radiopacity among the tested fiber posts and a titanium alloy post. CONCLUSIONS: The iLumi fiber optic posts have a unique structural fiber composition and excellent radiopacity and light-transmitting ability that produce more complete polymerization of the resin cement than the DT Light posts.

Microleakage around Class V Composite Restorations after Ultrasonic Scaling and Sonic Toothbrushing around their Margin.

OBJECTIVES: To measure microleakage around class V composite restorations after piezoelectric ultrasonic scaling and sonic toothbrushing. METHODS: 3 mm × 2 mm × 1.5 mm boxes were prepared on buccal and lingual surfaces of extracted molars centered on the cementum-enamel junction. Half the preparations were beveled (0.5 mm). Preparations were restored with composite and polished. Restorations on one side of the teeth were either traced with an ultrasonic scaler (60 seconds, n = 16) or brushed in a sonic toothbrushing machine (2 hours, n = 16). After thermocycling (10,000 cycles/5-55°C), specimens were immersed in 5 wt% Fuchsine solution (24 hours). Samples were sectioned and evaluated for percentage of dye penetration. Data were analyzed with an exact Wilcoxon rank-sum test and exact Wilcoxon signed-rank test (alpha = 0.05). RESULTS: Microleakage was observed at the cementum-composite interface but not the enamel-composite interface. There was not a statistically significant effect of the bevel for ultrasonic scaling or for sonic toothbrushing. Data obtained with and without a bevel were combined and a statistically significant difference in microleakage between the treatment and control sides of the tooth were found for ultrasonic scaling (32.5%±44.9%, n = 16; p = 0.016) but not sonic toothbrushing (2.5% ± 41.2%, n = 16; p = 1.0). CONCLUSIONS: Piezoelectric ultrasonic scaling increased microleakage at cementum-composite interface and there was no difference in microleakage with the use of a bevel. CLINICAL SIGNIFICANCE: Piezoelectric sonic scaling around Class V composite restorations with margins in cementum should be avoided. Beveled margins will not reduce the incidence of microleakge resulting from ultrasonic scaling in Class V restorations. Placing the apical margin of the restoration in enamel should be attempted whenever possible to prevent future microleakage. (J Esthet Restor Dent 29:41-48, 2017).

Wear, strength, modulus and hardness of CAD/CAM restorative materials.

OBJECTIVE: To measure the mechanical properties of several CAD/CAM materials, including lithium disilicate (e.max CAD), lithium silicate/zirconia (Celtra Duo), 3 resin composites (Cerasmart, Lava Ultimate, Paradigm MZ100), and a polymer infiltrated ceramic (Enamic). METHODS: CAD/CAM blocks were sectioned into 2.5mm×2.5mm×16mm bars for flexural strength and elastic modulus testing and 4mm thick blocks for hardness and wear testing. E.max CAD and half the Celtra Duo specimens were treated in a furnace. Flexural strength specimens (n=10) were tested in a three-point bending fixture. Vickers microhardness (n=2, 5 readings per specimen) was measured with a 1kg load and 15s dwell time. The CAD/CAM materials as well as labial surfaces of human incisors were mounted in the UAB wear device. Cusps of human premolars were mounted as antagonists. Specimens were tested for 400,000 cycles at 20N force, 2mm sliding distance, 1Hz frequency, 24°C, and 33% glycerin lubrication. Volumetric wear and opposing enamel wear were measured with non-contact profilometry. Data were analyzed with 1-way ANOVA and Tukey post-hoc analysis (alpha=0.05). Specimens were observed with SEM. RESULTS: Properties were different for each material (p<0.01). E.max CAD and Celtra Duo were generally stronger, stiffer, and harder than the other materials. E.max CAD, Celtra Duo, Enamic, and enamel demonstrated signs of abrasive wear, whereas Cerasmart, Lava Ultimate, Paradigm MZ100 demonstrated signs of fatigue. SIGNIFICANCE: Resin composite and resin infiltrated ceramic materials have demonstrated adequate wear resistance for load bearing restorations, however, they will require at least similar material thickness as lithium disilicate restorations due to their strength.

Cleaning Methods for Zirconia Following Salivary Contamination.

PURPOSE: To determine the best method of cleaning saliva-contaminated zirconia in preparation for resin bonding. MATERIAL AND METHODS: Flat blocks of zirconia were particle abraded with aluminum oxide and divided into eight groups (n = 10). Groups 1 to 4 were first treated with one coat of an MDP primer (Z-prime Plus) and groups 5 to 8 were left untreated. A thin coat of fresh whole saliva was painted on all specimens (except the control, group 1) and left in contact for 3 minutes. The specimens were then cleaned by rinsing with water for 20 seconds (groups 2 and 5), or cleaned with 35% phosphoric acid for 20 seconds and rinsed (groups 3 and 6), or cleaned with a zirconia cleaning solution (Ivoclean) for 20 seconds and rinsed (groups 4 and 7), or abraded with aluminum oxide particles and rinsed (group 5). Following the cleaning procedure, groups 5 to 8 were treated with one coat of Z-prime Plus. A 2.5 mm diameter tube was filled with composite (Z100), affixed to the zirconia surface, and light-cured. Specimens were stored in water (37°C for 24 hours) followed by thermocycling (5°C to 55°C for 10,000 cycles). Shear bond strength testing was performed at a crosshead speed of 1 mm/min. Bond strength values were compared to the control using a Dunnett's test (alpha = 0.05). Contact angles of the zirconia specimens with and without Z-prime Plus were measured with water using a goniometer. RESULTS: Groups 2, 5, and 8 were not significantly different from the control. Application of Z-prime made the zirconia surface more hydrophobic. CONCLUSIONS: If salivary contamination occurs after MDP application, rinsing off the saliva with water will preserve bond strength. If salivary contamination occurs prior to MDP application, particle abrasion or cleaning with Ivoclean will preserve bond strength.

Factors influencing the progression of noncarious cervical lesions: A 5-year prospective clinical evaluation.

STATEMENT OF PROBLEM: The etiology (chemical, friction, abfraction) of noncarious cervical lesion (NCCL) progression is poorly understood. PURPOSE: The purpose of this 5-year prospective clinical trial was to measure the relationship between NCCLs and various etiologic factors. MATERIAL AND METHODS: After review board approval, 29 participants with NCCLs were enrolled. Polyvinyl siloxane impressions were made of each NCCL, and casts were poured at baseline, 1, 2, and 5 years. The casts were scanned with a noncontact profilometer, and 1-, 2-, and 5-year scans were superimposed over baseline scans to measure volumetric change in NCCLs. T-scan and Fujifilm Prescale films were used to record relative and absolute occlusal forces on teeth with NCCLs at the 5-year recall. Participant diet, medical condition, toothbrushing, and adverse oral habit questionnaires were given at the 5-year recall. Occlusal analysis was completed on mounted casts to determine the presence of wear facets and group function. Volumetric lesion progression from 1 to 5 years was correlated to absolute and relative occlusal force using mixed model analysis. The Kruskall-Wallis and Mann-Whitney analyses compared lesion progression with diet, medical condition, toothbrushing, adverse oral habits, wear facets, and group function. RESULTS: The NCCL progression rate over 5 years was 1.50 ±0.92 mm(3)/yr. The rate of progression of NCCLs was related to mean occlusal stress (P=.011) and relative occlusal force (P=.032) in maximum intercuspation position. No difference was seen in NCCL progression between participants with any other factors. CONCLUSION: Heavy occlusal forces play a significant role in the progression of NCCLs.

Gloss and Stain Resistance of Ceramic-Polymer CAD/CAM Restorative Blocks.

OBJECTIVE: To evaluate the gloss and stain resistance of several new ceramic-polymer CAD/CAM blocks MATERIALS AND METHODS: Specimens (4 mm) were sectioned from: Enamic (polymer-infused ceramic), LAVA Ultimate (nano-ceramic reinforced polymer), e.max (lithium disilicate), Paradigm C (porcelain), and Paradigm MZ100 (composite). Specimens were wet polished on a polishing wheel to either 320 grit silicon paper (un-polished, N = 8) or 2000 grit silicon carbide papers followed by a 0.05 µm alumina slurry (polished, N = 8). Initial gloss and color (L*a*b*) values were measured. Specimens were stored in a staining solution at 37°C in darkness for 12 days (simulating 1 year). After storage, L*a*b* values re-measured. Change in color was reported as ΔE00 based on the CIEDE2000 formula. Gloss and ΔE00 were analyzed by two-way analysis of variance (ANOVA) (alpha = .05). Separate one-way ANOVA and Tukey post-hoc analyses were performed for both polish conditions and all materials. RESULTS: Two-way ANOVA showed that factors material, polish and their interaction were significant for both gloss and ΔE00 (p < .01). Post-hoc analysis reveals that polished specimens had significantly less color change than un-polished specimens for Paradigm C and LAVA Ultimate. E.max had significantly higher gloss and less color change than all other materials. CONCLUSION: The composition and polish of CAD/CAM materials affects gloss and stain resistance. CLINICAL SIGNIFICANCE: Ceramic-polymer hybrid materials can achieve the high gloss required for esthetic restorations. These materials should be polished in order to minimize staining. If polished, all of the tested materials exhibited clinically acceptable color changes at 1 year of simulated staining. (J Esthet Restor Dent 28:S40-S45, 2016).

Effect of grain size on the monoclinic transformation, hardness, roughness, and modulus of aged partially stabilized zirconia.

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 2 bar pressure for 5 h. X-ray diffraction (30 mA, 40 kV) 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 (0.350 µm, 0.372 µm, 0.428 µm, and 0.574 µm). 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.

Two-year clinical trial of a universal adhesive in total-etch and self-etch mode in non-carious cervical lesions.

OBJECTIVES: To compare the clinical performance of Scotchbond™ Universal Adhesive used in self- and total-etch modes and two-bottle Scotchbond™ Multi-purpose Adhesive in total-etch mode for Class 5 non-carious cervical lesions (NCCLs). METHODS: 37 adults were recruited with 3 or 6 NCCLs (>1.5mm deep). Teeth were isolated, and a short cervical bevel was prepared. Teeth were restored randomly with Scotchbond Universal total-etch, Scotchbond Universal self-etch or Scotchbond Multi-purpose followed with a composite resin. Restorations were evaluated at baseline, 6, 12 and 24 months for marginal adaptation, marginal discoloration, secondary caries, and sensitivity to cold using modified USPHS Criteria. Patients and evaluators were blinded. Logistic and linear regression models using a generalized estimating equation were applied to evaluate the effects of time and adhesive material on clinical assessment outcomes over the 24 month follow-up period. Kaplan-Meier method was used to compare the retention between adhesive materials. RESULTS: Clinical performance of all adhesive materials deteriorated over time for marginal adaptation, and discoloration (p<0.0001). Both Scotchbond Universal self-etch and Scotchbond Multi-purpose materials were more than three times as likely to contribute to less satisfying performance in marginal discoloration over time than Scotchbond Universal total-etch. The retention rates up to 24 months were 87.6%, 94.9% and 100% for Scotchbond Multi-purpose and Scotchbond Universal self-etch and total-etch, respectively. CONCLUSIONS: Scotchbond Universal in self- and total- etch modes performed similar to or better than Scotchbond Multipurpose, respectively. CLINICAL SIGNIFICANCE: 24 month evaluation of a universal adhesive indicates acceptable clinical performance, particularly in a total-etch mode.

Contact angle of unset elastomeric impression materials.

STATEMENT OF PROBLEM: Some elastomeric impression materials are hydrophobic, and it is often necessary to take definitive impressions of teeth coated with some saliva. New hydrophilic materials have been developed. PURPOSE: The purpose of this in vitro study was to compare contact angles of water and saliva on 7 unset elastomeric impression materials at 5 time points from the start of mixing. MATERIAL AND METHODS: Two traditional polyvinyl siloxane (PVS) (Aquasil, Take 1), 2 modified PVS (Imprint 4, Panasil), a polyether (Impregum), and 2 hybrid (Identium, EXA'lence) materials were compared. Each material was flattened to 2 mm and a 5 µL drop of distilled water or saliva was dropped on the surface at 25 seconds (t0) after the start of mix. Contact angle measurements were made with a digital microscope at initial contact (t0), t1=2 seconds, t2=5 seconds, t3=50% working time, and t4=95% working time. Data were analyzed with a generalized linear mixed model analysis, and individual 1-way ANOVA and Tukey HSD post hoc tests (α=.05). RESULTS: For water, materials grouped into 3 categories at all time-points: the modified PVS and one hybrid material (Identium) produced the lowest contact angles, the polyether material was intermediate, and the traditional PVS materials and the other hybrid (EXA'lence) produced the highest contact angles. For saliva, Identium, Impregum, and Imprint 4 were in the group with the lowest contact angle at most time points. CONCLUSION: Modified PVS materials and one of the hybrid materials are more hydrophilic than traditional PVS materials when measured with water. Saliva behaves differently than water in contact angle measurement on unset impression material and produces a lower contact angle on polyether based materials.

Fracture load of ceramic restorations after fatigue loading.

STATEMENT OF PROBLEM: A clinician must decide what ceramic coping and veneer material to prescribe based on the amount of tooth reduction possible and the desired esthetic outcome of the restoration. PURPOSE: The purpose of this in vitro study was to compare the fracture strength of monolithic and bilayered lithium disilicate (IPS e.max) and zirconia (LAVA) crowns at clinically relevant thicknesses after load cycling. MATERIAL AND METHODS: Crowns (n=8) were fabricated from 6 groups: 1.2-mm monolithic lithium disilicate, 1.5-mm monolithic lithium disilicate, 1.5-mm bilayered lithium disilicate with hand-layered veneer, 0.6 mm monolithic zirconia, 1.2-mm bilayered zirconia with hand-layered veneer, and 1.2-mm bilayered zirconia with milled veneer (dimension represents thickness at the occlusal pit). Crowns were cemented to identical milled resin dies with resin-modified glass ionomer cement. Cemented crowns were stored at 37°C for 24 hours and load cycled for 200,000 cycles at 25 N at a rate of 40 cycles/minute. The ultimate fracture load for each specimen was measured in a universal testing machine. Data were analyzed with a 1-way ANOVA and Tukey honest significant difference post hoc analysis (α=.05). RESULTS: Mean ±SD fracture load values were 1465 ±330 N for monolithic lithium disilicate (1.2-mm thickness) and 2027 ±365 N (1.5-mm thickness) and 1732 ±315 N for bilayered hand-veneered lithium disilicate (1.5-mm thickness). Fracture loads were 1669 ±311 N for monolithic zirconia crowns (0.6mm thickness), 2625 ±300 N for zirconia milled-veneered (1.2-mm thickness), and 2655 ±590N for zirconia hand-veneered crowns (1.2mm thickness). One-way ANOVA showed a statistically significant difference among the groups (P<.01). Veneered zirconia crowns showed the highest fracture strength, 1.2-mm hand veneered zirconia was similar to that of 1.5-mm monolithic zirconia, and all other groups were not statistically different. CONCLUSIONS: Crowns of 1.2-mm bilayered zirconia had higher fracture loads than 0.6-mm zirconia or 1.2-mm lithium disilicate monolithic crowns.

Bonding a veneered zirconia anterior fixed partial denture.

This case report documents the rationale and procedure for bonding a veneered zirconia restoration. A three-unit zirconia fixed partial denture (FPD) was fabricated with facial and incisal porcelain veneering. The intaglio surface of the prosthesis was abraded with 50-µm aluminum oxide (Al2O3) particles and coated with one layer of a 10-methacryloxydecyl dihydrogen phosphate (MDP) primer. The FPD was tried into the mouth and occlusal adjustment was performed with a fine grit diamond, and then it was polished with zirconia polishing points. The intaglio surfaces of the abutment crowns were cleaned with 37% phosphoric acid and rinsed. A self-etch adhesive was applied to the tooth preparations and light-cured, and the crowns were filled with cement and seated. Excess cement was immediately wiped away with a brush, followed by spot-curing of the margins. The case demonstrates that, when properly designed, veneered zirconia restorations offer acceptable esthetic and mechanical properties for anterior FPDs.

Clinicians reaping benefits of new concepts in impressioning.

While conventional elastomeric impression materials are still being used to generate excellent impressions, the future of impression-taking is undoubtedly with digital intraoral scanners. Advances in scanning systems are making this technology easier to use and more practical for dentists.

Phase transformation of dental zirconia following artificial aging.

AIMS: 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. METHODS: 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. RESULTS: 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. SIGNIFICANCE: 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.