An Advanced Fiber-Reinforced Composite Solution for Gingival Inflammation and Bone Loss Related to Restorative Crowns.

Soaring gold prices have created an almost impossible void in the Dental Materials supply reserves for affordable patient posterior crowns. Fortunately, aerotech fiber-reinforced composite (FRC) materials in use for many diverse structural applications can be developed for dentistry to replace gold with computer-assisted design/computer-assisted manufacture (CAD/CAM) technology. Current dental ceramics or high-strength oxide ceramics like alumina and zirconia available for CAD/CAM have extremely poor fracture-toughness properties and can propagate microscopic cracks rapidly to sudden adverse brittle failure. As a highly promising alternative, exceptional FRC fracture toughness properties counteract brittle failure with high-strength fibers that act as major barriers to crack propagation. In addition, excellent rapid FRC CAD/CAM machining can offer one-patient appointments for single crowns. FRCs have high-strength fibers coupled into a polymer matrix with the ability to form strong covalent bonds with resin adhesives whereas ceramics do not bond well and oxide ceramics have non-reactive inert surfaces making resin bonding extremely difficult. Prominent adhesive free-radical covalent bonding by FRCs then provides a great opportunity to achieve a crown marginal reline directly on the patients clinical tooth for possible near zero-gap defect tolerances. To place crown gingival marginal defects in proper perspective, gaps between the tooth and crown expose luting cements that can wash out and provide space for microbial plaque growth. Bacterial toxins released from a crown-tooth interface can subsequently produce secondary decay, gingival inflammation and eventually under severe plaque environments breed periodontal disease with bone loss.

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.

Retentive Force of Zirconia Implant Crowns on Titanium Bases Following Different Surface Treatments.

PURPOSE: Screw-retained zirconia implant crowns with an internal titanium base have favorable mechanical properties compared with single-piece zirconia implant crowns; however, the screw-retained implant crowns require adequate bonding between the zirconia crown and the titanium base. This study measured the retention between a titanium base and a full-contour zirconia implant crown following different surface treatments of their bonded surfaces. MATERIALS AND METHODS: Full-contour screw-retained zirconia implant crowns were fabricated to fit a titanium base. The crowns were bonded to the titanium bases following one of four treatment protocols (n = 15 per protocol group): no surface treatment (Control), 10-methacryloyloxydecyl dihydrogen phosphate (MDP) primer on the intaglio of crown and exterior of base (MDP), alumina airborne-particle abrasion of the intaglio of crown and exterior of base (Alu), and alumina airborne-particle abrasion and an MDP primer on the intaglio of crown and exterior of base (Alu+MDP). All crowns were bonded to the base with resin cement. Specimens were stored in water for 24 hours at 37°C and then thermocycled in water, with a temperature range of 5°C to 55°C, for 15,000 cycles with a 15-second dwell time. Crowns were separated from the titanium bases using a universal testing machine. The four treatment protocols were compared using one-way analysis of variance (ANOVA), followed by Tukey post hoc tests (P < .05). Sectioned specimens were examined with scanning electron microscopy (SEM). RESULTS: Retention forces for Control (737.8 ± 148.9 N) and MDP (804.1 ± 114.5 N) were significantly greater than Alu+MDP (595.5 ± 122.2 N), which was significantly greater than Alu (428.2 ± 93.8 N). Visual inspection of the debonded specimens showed that the majority of the cement remnants were seen on the external surface of the titanium bases. Microscopic examination of the interface between the crown and the unaltered base shows that the cement gap is approximately 13 µm at the crest of the microgrooves and 50 µm within the channel of the microgrooves. After airborne-particle abrasion, the microgrooves became significantly dulled, and the cement gap increased to 27 to 40 µm at the crest and 55 to 58 µm in the channels. CONCLUSION: Airborne-particle abrasion of titanium bases that contain retentive microgrooves prior to bonding is contraindicated. Application of an MDP primer demonstrated limited improvement in the retention of the zirconia implant crowns.

Fiber-Reinforced Composites: A Breakthrough in Practical Clinical Applications with Advanced Wear Resistance for Dental Materials.

Newer dental fiber-reinforced composites can provide service with less wear than enamel. Further, fibers in bulk molding form pack oriented parallel to the occlusal-dentinal floor planes that wear by uniform thinning into micrometer-sized fiber remnants and subsequent flat plate-like particulate bond by compression back into the polymer matrix. The fiber wear-in process is accomplished by creating fine crystalline chemically resistant nanoparticulates that become an exceptional polishing agent. Resulting consolidation by the underlying fiber network squeezes plasticized polymer and partially hydrolyzed polymer chains along with residual monomer, pendant methacrylate groups and nano-sized particulate to the surface that surround larger exposed micrometer-sized particulate and smallest fiber remnants. Eventually consolidation of the polymer matrix overall squeezes up and engulfs the top particulate or fiber remnants forming a smooth polished hard polymer-matrix composite wear surface probably filled with small nanoparticulate. The final hardened polymer surface may show particulate from worn fibers, but displays no signs of the original fibers after an in vitro wear simulator test comparable to 3 years of clinical service. Nanoparticulates formed from the fibers that have broken down generally reconsolidate back in to the top surface for a polished toughened polymer surface or behave as a polishing agent. The underlying fiber-reinforced composite network supports wear loads to greatly reduce wear especially as fibers extend well beyond a critical length that prevents fiber debonding from the matrix. Further, fiber-reinforced composite consolidation can aid in cavity molding placement by applied pressure to squeeze monomer, resin and particulates from the fiber network toward collapsing or filling in voids and removing entrapped air.

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.

Mechanical Properties Comparing Composite Fiber Length to Amalgam.

Photocure fiber-reinforced composites (FRCs) with varying chopped quartz-fiber lengths were incorporated into a dental photocure zirconia-silicate particulate-filled composite (PFC) for mechanical test comparisons with a popular commercial spherical-particle amalgam. FRC lengths included 0.5-mm, 1.0 mm, 2.0 mm, and 3.0 mm all at a constant 28.2 volume percent. Four-point fully articulated fixtures were used according to American Standards Test Methods with sample dimensions of 2×2×50 mm3 across a 40 mm span to provide sufficient Euler flexural bending and prevent top-load compressive shear error. Mechanical properties for flexural strength, modulus, yield strength, resilience, work of fracture, critical strain energy release, critical stress intensity factor, and strain were obtained for comparison. Fiber length subsequently correlated with increasing all mechanical properties, p < 1.1×10-5. Although the modulus was significantly statistically higher for amalgam than all composites, all FRCs and even the PFC had higher values than amalgam for all other mechanical properties. Because amalgams provide increased longevity during clinical use compared to the standard PFCs, modulus would appear to be a mechanical property that might sufficiently reduce margin interlaminar shear stress and strain-related microcracking that could reduce failure rates. Also, since FRCs were tested with all mechanical properties that statistically significantly increased over the PFC, new avenues for future development could be provided toward surpassing amalgam in clinical longevity.

3D-WOVEN FIBER-REINFORCED COMPOSITE FOR CAD/CAM DENTAL APPLICATION.

Three-dimensional (3D)-woven noncrimp fiber-reinforced composite (FRC) was tested for mechanical properties in the two principal directions of the main XY plane and compared to different Computer-Aided-Design/Computer-Aided-Machining (CAD/CAM) Dental Materials. The Dental Materials included ceramic with Vitablock Mark II®, ProCAD®, InCeram® Spinel, InCeram® Alumina and InCeram® Zirconia in addition to a resin-based 3M Corp. Paradigm® particulate-filled composite. Alternate material controls included Coors 300 Alumina Ceramic and a tungsten carbide 22% cobalt cermet. The 3D-woven FRC was vacuum assisted resin transfer molding processed as a one-depth-thickness ~19-mm preform with a vinyl-ester resin and cut into blocks similar to the commercial CAD/CAM Dental Materials. Mechanical test samples prepared for a flexural three-point span length of 10.0 mm were sectioned for minimum-depth cuts to compare machinability and fracture resistance between groups. 3D-woven FRC improved mechanical properties with significant statistical differences over all CAD/CAM Dental Materials and Coors Alumina Ceramic for flexural strength (p<0.001), resilience (p<0.05), work of fracture (p<0.001), strain energy release (p<0.05), critical stress intensity factor (p<0.001) and strain (p<0.001).

Restoring Congenitally Missing Maxillary Lateral Incisors Using Zirconia-Based Resin Bonded Prostheses.

OBJECTIVE: This clinical report describes an alternative treatment modality for the replacement of congenitally missing maxillary lateral incisors in a 17-year-old patient. CLINICAL CONSIDERATIONS: Zirconia-based resin-bonded fixed partial dentures (RBFPDs) were selected as a viable and conservative treatment option in a young individual with highly aesthetic expectations. Fabrication of all-ceramic RBFPDs followed specific preparation design and features to accommodate two retainers. The zirconia frameworks with bilateral wings were digitally designed and then milled by a computer-aided design and computer-aided manufacturing (CAD/CAM)-controlled milling machine. Zirconia surface was treated with a two-step chairside tribochemical silica-coating/silane coupling surface treatment protocol, and adhesive resin luting cement was used to achieve micromechanical and chemical bonding. Completion of the treatment resulted in a functional and aesthetic successful outcome and a 17-month follow-up presented uneventful. CONCLUSION: Contemporary adhesive techniques involving resin-bonded zirconia-based prostheses can be utilized successfully and predictably in young patients with single missing teeth when implant therapy is currently not a treatment of choice and a less invasive approach is desired. CLINICAL SIGNIFICANCE: The zirconia-based resin-bonded prosthesis constitutes a viable and conservative treatment modality for the replacement of missing teeth either congenitally or from another etiology in young patients in which implant therapy and a fixed partial denture are currently contraindicated.

The Effect of Contamination of Implant Screws on Reverse Torque.

PURPOSE: To determine if contamination of abutment screws with titanium nanoparticles affects the preload by measuring the reverse torque after multiple cycles of screw closing-opening. MATERIALS AND METHODS: The study included 30 internal hex implants, titanium abutments, and titanium abutment screws. Fifteen abutment screws were contaminated with 60- to 80-nm titanium nanoparticles (contamination group), and the remaining 15 screws did not receive titanium nanoparticle contamination (noncontamination group). Each abutment screw was initially tightened to 25 Ncm with a digital torque gauge to stabilize the abutment to the implant. The second torque, 25 Ncm, was applied 10 minutes after the initial torque. After an additional 5 minutes, the screw was loosened to measure the reverse torque. Ten cycles of screw insertion and removal were conducted, and reverse torque values were measured in each cycle. Repeated measures analysis of variance and the Student t test were used for statistical analysis. The level of significance was set at α = .05. After 10 cycles of closure-opening, abutment screw threads were observed under ×40 magnification. RESULTS: Abutment screws at every cycle generally showed preload values less than the initial applied torque. The mean reverse torque values in both groups had a tendency to decline as the test cycle progressed, except at the 6th, 9th, and 10th cycle in the contamination group. The noncontamination group always had higher mean reverse torques than the contamination group at the same test cycle with significant differences at the 1st, 2nd, 4th, 5th, 7th, and 8th cycles. The preload loss in percentages were 7.83% and 12.57% after the 1st cycle, 14.48% and 19.77% after 5 cycles, and 18.83% and 19.83% after 10 cycles in the noncontamination and contamination group, respectively. Abutment screws in both groups showed various degrees of wear and metal debris on screw surfaces. CONCLUSION: Contamination of abutment screws with titanium nanoparticles decreased screw reverse torque values because of a settling effect, though this effect seemed minimal after five cycles. A future clinical study is indicated to validate if cleaning of contaminated screws before the delivery of the prosthesis will increase preloads.

Effect of imaging powder and CAD/CAM stone types on the marginal gap of zirconia crowns.

OBJECTIVE: To compare the marginal gap using different types of die stones and titanium dies with and without powders for imaging. METHODS: A melamine tooth was prepared and scanned using a laboratory 3-shape scanner to mill a polyurethane die, which was duplicated into different stones (Jade, Lean, CEREC) and titanium. Each die was sprayed with imaging powders (NP, IPS, Optispray, Vita) to form 15 groups. Ten of each combination of stone/titanium and imaging powders were used to mill crowns. A light-bodied impression material was injected into the intaglio surface of each crown and placed on the corresponding die. Each crown was removed, and the monophase material was injected to form a monophase die, which was cut into 8 sections. Digital images were captured using a stereomicroscope to measure marginal gap. Scanning electron microscopy was used to determine the particle size and shape of imaging powders and stones. RESULTS: Marginal gaps ranged from mean (standard deviation) 49.32 to 1.20 micrometers (3.97-42.41 µm). There was no statistical difference (P > .05) in the marginal gap by any combination of stone/titanium and imaging powders. All of the imaging powders had a similar size and rounded shape, whereas the surface of the stones showed different structures. CONCLUSIONS: When a laboratory 3-shape scanner is used, all imaging powders performed the same for scanning titanium abutments. However, there was no added value related to the use of imaging powder on die stone. It is recommended that the selection of stone for a master cast be based on the hysical properties. PRACTICAL IMPLICATIONS: When a laboratory 3-shape scanner is used, the imaging powder is not required for scanning die stone. Whenever scanning titanium implant abutments, select the least expensive imaging powder.

Influence of implant angulation on the fracture resistance of zirconia abutments.

PURPOSE: To investigate the effects of abutment design to correct for implant angulation and aging on the fracture resistance of zirconia abutments. Greater understanding of the fracture strength of the zirconia abutments under various clinical conditions may lead to improvement of clinical protocols and possibly limit potential failures of implant prosthetics. MATERIALS AND METHODS: Test specimens consisted of an implant-zirconia abutment-zirconia crown assembly with implant apex positioned at 0°, 20° to the facial (20F), and 20° to the lingual (20L) with respect to a constant crown contour. To keep the abutment design as the only variable, CAD/CAM technology was used to generate monolithic zirconia crowns identical both in external and internal dimensions and marginal contours to precisely fit all the abutments in an identical fashion. The monolithic zirconia abutments were designed to fit the constant crown contours and the internal connection of the implant at the three angulations. The customized abutments for the three implant angulations varied in emergence profile, screw hole location, and material thickness around the screw hole. Half the specimens from each group were subjected to steam autoclaving and thermocycling to simulate aging of the restorations in vivo. To mimic the off-axis loading of the central incisor, the specimens were loaded at the recommended cephalometric interincisal relationship of 135° between the long axis of the crown supported by the implant and the Instron force applicator simulating the mandibular incisor. The force applicator was positioned 2 mm from the incisal edge and loaded at a 1 mm/min crosshead speed. Data were evaluated by 2-way ANOVA (α = 0.05) and Tukey's HSD. RESULTS: The 20F group had the highest fracture values followed by the 0° group, and the 20L group had the lowest fracture values. Aging did not yield any significant difference in fracture force magnitudes. CONCLUSION: Within the limitations of this study, tilting the implant apex to the lingual significantly reduced the fracture strength of angle-corrected zirconia abutments. Accordingly, while the angle between the occlusal force application and the long axis of the implant decreases, the resistance (force) to fracture decreases.

Effect of Luting Agents on Retention of Dental Implant-Supported Prostheses.

To evaluate the retentive strength of 7 different luting agents in cement-retained implant abutment/analog assemblies. Fifty-six externally hexed dental implant abutment/analog assemblies and cast superstructures were divided randomly into 7 groups for cementation with each of the 7 luting agents. Five definitive cements tested were zinc phosphate cement, All-Bond 2, Maxcem, RelyX Luting cement, HY-Bond, and two provisional cements, ImProv and Premier. Cast superstructures were cemented onto the implant abutments and exposed to 1000 thermal cycles (0°C-55°C) and 100 000 cycles on a chewing simulator (75 N load). A universal testing machine was used to measure cement failure load of the assembled specimens. Cement failure load was evaluated with 1-way ANOVA and Duncan's multiple range analysis. Significant differences in cement failure loads were measured (P < .0001). Post hoc testing with Duncan's multiple range indicated 4 separate groupings. Maxcem and All-Bond 2 were comparable, having the greatest load failure. RelyX and zinc phosphate cement were analogous, and higher than HY-Bond. Improv and Premier constituted a pair, which demonstrated the lowest retentive values. Within the limitations of this in vitro study, Maxcem and All-Bond 2 are good candidates for cement-retained implant prostheses while concerning retention.

Influence of surface treatment of yttrium-stabilized tetragonal zirconium oxides and cement type on crown retention after artificial aging.

STATEMENT OF PROBLEM: Information about the influence of zirconia crown surface treatment and cement type on the retention of zirconia crowns is limited. It is unclear whether zirconia crowns require surface treatment to enhance their retention. PURPOSE: The purpose of this in vitro study was to evaluate the effect of surface treatment on the retention of zirconia crowns cemented with 3 different adhesive resin cements after artificial aging. MATERIAL AND METHODS: Ninety extracted human molars were prepared for ceramic crowns (approximately 20-degree taper, approximately 4-mm axial length) and were divided into 3 groups (n=30). Computer-aided design and computer-aided manufacturing zirconia copings were fabricated. Three surface treatments were applied to the intaglio surface of the copings. The control group received no treatment, the second group was airborne-particle abraded with 50 µm Al2O3, and the third group was treated with 30 µm silica-modified Al2O3, The copings were luted with a self-etch (RelyX Unicem 2), a total-etch (Duo-Link), or a self-etch primer (Panavia F 2.0) adhesive cement. They were stored for 24 hours at 37°C before being artificially aged with 5000 (5°C-55°C) thermal cycles and 100,000 cycles of 70 N dynamic loading. Retention was measured on a universal testing machine under tension, with a crosshead speed of 0.5 mm/min. Statistical analysis was performed with 1-way and 2-way ANOVA. RESULTS: Mean retention values ranged from 0.72 to 3.7 MPa. Surface treatment increased crown retention, but the difference was not statistically significant (P>.05), except for the Duo-Link cement group (P<.05). Analysis of the adhesives revealed that the Duo-Link cement resulted in significantly lower crown retention (P<.05) than the other 2 cements. CONCLUSION: For zirconia crowns, retention seems to be dependent on cement type rather than surface treatment.

Maxillary cement retained implant supported monolithic zirconia prosthesis in a full mouth rehabilitation: a clinical report.

This clinical report presents the reconstruction of a maxillary arch with a cement retained implant supported fixed prosthesis using a monolithic zirconia generated by CAD/CAM system on eight osseointegrated implants. The prosthesis was copy milled from an interim prosthesis minimizing occlusal adjustments on the definitive prosthesis at the time of delivery. Monolithic zirconia provides high esthetics and reduces the number of metal alloys used in the oral cavity.

Managing dislodged locator from a titanium alloy implant bar in an implant-supported bar overdenture: a clinical report.

An implant-supported prosthesis is a successful treatment option for edentulous patients. This article reports on a case that has not been documented in the literature involving complications in a maxillary implant-supported bar overdenture, followed by the management of the complications.

A technique for verifying implant analog positions in the definitive cast.

This article introduces a procedure that allows the clinician to verify the 3-dimensional spatial orientations of implant analogs in the definitive cast for a cement-retained, implant-supported prosthesis with engaging abutments. Multiple interlocking puzzle pieces are used with engaging interim abutments to verify the accuracy of the impression.

The failure load of CAD/CAM generated zirconia and glass-ceramic laminate veneers with different preparation designs.

STATEMENT OF PROBLEM: Fracture of feldspathic porcelain laminate veneers represents a significant mode of clinical failure. Therefore, ceramic materials that withstand a higher load to fracture, especially for patients with parafunctional habits, are needed. PURPOSE: The purpose of this study was to examine the correlation of material (zirconia, TZP, glass-ceramic, IEC, and feldspathic porcelain, FP) design (incisal overlapped preparation, IOP, and three-quarter preparation, TQP), and fracture mode to failure load for veneers supported by composite resin abutments. MATERIAL AND METHODS: A typodont tooth prepared with 2 designs (IOP, TQP) and the corresponding 2 definitive dies were used to fabricate the composite resin abutments (30 for IOP and 30 for TQP). Ten veneer specimens for each system (Y-TZP, IEC, and FP), were fabricated for each design. The veneers were cemented, invested, and tested in compression until failure by using a universal testing machine. Significant differences were evaluated by 2-factor ANOVA (α=.05). RESULTS: No statistical mean load difference was noted between the preparation designs for Y-TZP (IOP: 244 ±81 and TQP: 224 ±58 N), IEC (IOP: 306 ±101 and TQP: 263 ±77 N), and FP veneers (IOP: 161 ±93 and TQP: 246 ±45 N). No statistical difference in the mean load was found among the 3 veneer materials for each preparation design except between IEC (306 ±101 N) and FP (161 ±93 N) veneers for TQP. CONCLUSIONS: Preparation design did not influence the failure load of the veneer materials. Zirconia veneers were the least likely to fracture but the most likely to completely debond; feldspathic porcelain veneers exhibited the opposite characteristics.

Evaluation of the optical properties of CAD-CAM generated yttria-stabilized zirconia and glass-ceramic laminate veneers.

STATEMENT OF PROBLEM: When feldspathic porcelain (FP) laminate veneers are used to mask tooth discoloration that extends into the dentin, significant tooth reduction is needed to provide space for the opaque layer and optimize the bonding of the restoration. PURPOSE: The purpose of this study was to investigate the color effect of trial insertion paste (TP), composite resin abutment (CRA), and veneer regions on the optical properties of feldspathic porcelain (FP), yttria-stabilized zirconia (Y-TZP), and IPS e.max CAD HT (IEC) veneers. MATERIAL AND METHODS: A melamine tooth was prepared for a laminate veneer on a model, and a definitive cast was made. The definitive die was scanned by using the TurboDent System (TDS), then 30 CRA were machined and 10 veneers were fabricated for each ceramic material (FP, Y-TZP, IEC). The optical properties of different veneer materials, CRA (A(1), A(2), A(3)) and TP (bleach XL, opaque white, transparent, and yellow) were evaluated in the cervical, body, and incisal regions with a spectrophotometer. Results were analyzed by using 1-way ANOVA (.05). RESULTS: The color difference for all the veneers was affected by TP and CRA colors in different regions. The mean values for the Y-TZP veneer color coordinates (L*: 74 ±0.34, a*: 0.09 ±0.20, and b*: 17.43 ±0.44) were significantly different (P<.001) from those of IEC veneers (L*: 70.15 ±0.23, a*: -0.69 ±0.073, and b*:11.48 ±0.30) and FP veneers (L*: 70.00 ±0.86, a*: - 0.28 ±0.203, and b*: 13.86 ±1.08). There was no difference between IEC for L* and FP. Significant difference was detected (P<.001) in color coordinates among the 3 veneer materials for a* and b*. CONCLUSIONS: The TP color affected the color difference for all veneer materials except the Y-TZP, while there was no effect on the CRA color. The magnitude of color coordinates changed as a function of TP color and veneer material.

Influence of low-temperature environmental exposure on the mechanical properties and structural stability of dental zirconia.

PURPOSE: The effect of dental fabrication procedures of zirconia monolithic restorations and changes in properties during low-temperature exposure in the oral environment is not completely understood. The purpose of this study was to investigate the effect of procedures for fabrication of dental restorations by low-temperature simulation and relative changes of flexural strength, nanoindentation hardness, Young's modulus, surface roughness, and structural stability of yttria-stabilized zirconia. MATERIALS AND METHODS: A total of 64 zirconia specimens were prepared to simulate dental practice. The specimens were divided into the control group and the accelerated aging group. The simulated group followed the same procedure as the control group except for the aging treatment. Atomic force microscopy was used to measure surface roughness. The degree of tetragonal-to-monoclinic transformation was determined using X-ray diffraction. Nanoindentation hardness and modulus measurements were carried out on the surface of the zirconia specimens using a nanoindenter XP/G200 system. The yttria levels for nonaged and aged specimens were measured using energy dispersive spectroscopy. Flexural strength was determined using the piston-on-three-ball test. The t-test was used to determine statistical significance. RESULTS: Means and standard deviations were calculated using all observations for each condition and evaluated using a group t-test (p < 0.05). The LTD treatment resulted in increased surface roughness (from 12.23 nm to 21.56 nm for Ra and 15.06 nm to 27.45 nm for RMS) and monoclinic phase fractions (from 2% to 21%), with a concomitant decrease in hardness (from 16.56 GPa to 15.14 GPa) and modulus (from 275.68 GPa to 256.56 GPa). Yttria content (from 4.43% to 4.46%) and flexural strength (from 586 MPa to 578 MPa) were not significantly altered, supporting longer term in vivo function without biomechanical fracture. CONCLUSION: The LTD treatment induced the tetragonal-to-monoclinic transformation with surface roughening in zirconia prepared using dental procedures.

The effect of different fabrication steps on the marginal adaptation of two types of glass-infiltrated ceramic crown copings fabricated by CAD/CAM technology.

PURPOSE: Marginal adaptation is an important factor affecting the longevity of all-ceramic restorations, although the effects of different fabrication steps on marginal adaptation at various stages of fabrication are not fully understood. The purpose of this study was to assess with an in vitro model whether In-Ceram alumina (IA) or In-Ceram zirconia (IZ) copings produced by the CAD/CAM method would be clinically acceptable, and to evaluate the effect of each fabrication step (post-milling, post-trimming, and post-glass infiltration) on the marginal discrepancy of the coping. MATERIALS AND METHODS: A melamine tooth was prepared, duplicated, poured with inlay wax, and then cast with metal to fabricate a master die. An InLab 3D system was used to scan the master die and to design and mill the copings. Thirty IA and IZ copings each were developed with thicknesses of 0.6 mm and a 30-µm thick computer luting space. Epoxy resin replicas of the master die were fabricated, and the vertical and horizontal marginal discrepancies were measured using a Micro-Vu optical microscope at three stages of the fabrication (post-milling, post-trimming, post-infiltration). One-way ANOVA was used to analyze the data between the three stages of fabrication for each marginal discrepancy, and a t-test was used to compare vertical and horizontal marginal discrepancies (after glass infiltration) between IZ and IA copings RESULTS: There were no significant differences (p > 0.05) in the vertical marginal discrepancies (µm) between IA (36 ± 14) and IZ (40 ± 14) copings after glass infiltration. ANOVA (comparing three stages within horizontal marginal discrepancy for IZ copings) showed that post-milling (40 ± 26) > post-trimming (23 ± 11) = post-infiltration (19 ± 13). ANOVA (comparing three stages within vertical marginal discrepancy for IZ copings) showed that post-milling (53 ± 12) = post-trimming (47 ± 13) > post-infiltration (36 ± 14). ANOVA (comparing three stages within horizontal marginal discrepancy for IA copings) showed that post-milling (52 ± 28) > post-trimming (30 ± 16) > post-infiltration (30 ± 16). ANOVA (comparing three stages within vertical marginal discrepancy for IA copings) showed that post-milling (54 ± 13) = post-trimming (56 ± 26) > post-infiltration (40 ± 14). CONCLUSION: There was no significant difference in the marginal adaptation of both material copings. After the trimming process, the glass infiltration firing cycle improved the vertical marginal discrepancy for both IZ and IA copings. Clinical implications. IA and IZ copings fabricated by CAD/CAM technology have an acceptable marginal fit as documented in the literature, and the glass infiltration process improves the marginal fit after machining.