Flexural strength, fracture toughness, translucency, stain resistance, and water sorption of 3D-printed, milled, and conventional denture base materials.

PURPOSE: To compare mechanical, optical, and physical properties of denture base materials fabricated with various 3D printing systems to reference milled and conventionally heat-processed denture base materials. MATERIALS AND METHODS: Specimens of denture base materials were either 3D-printed (DLP in-office printer, CLIP laboratory printer, or material jetting laboratory printer), milled, or heat processed. 3-point bend flexural strength testing was performed after 50 hours of water storage following 1hour of drying (dry testing) or in 37°C water (wet testing). Fracture toughness was performed with a notched beam specimen after 7 days of water storage and tested dry. The translucency parameter was measured with 2 mm thick specimens. Stain resistance was measured as color change following 14 days of storage in 37°C coffee. Water sorption was measured following 7 days of storage in 37°C distilled water. RESULTS: For dry testing, all but one of the 3D-printed materials attained higher or equivalent flexural strength as the reference materials. For wet testing, all 3D-printed materials attained higher or equivalent strength as the reference materials and dry-tested materials. For 3D-printed materials, wet testing increased displacement before fracture whereas it decreased displacement for the reference materials. Only two of the 3D-printed materials had similar fracture toughness as the reference materials. One of the 3D-printed materials was more translucent and one was more opaque than the reference materials. Only one of the 3D-printed materials absorbed more water than the reference materials. CONCLUSION: 3D-printed denture base materials have mostly equivalent mechanical, optical, and physical properties to conventional and milled denture base materials.

The Effect of Restoration Thickness on the Fracture Resistance of 5 mol% Yttria-Containing Zirconia Crowns.

BACKGROUND: To determine what thickness of 5 mol% yttria zirconia (5Y-Z) translucent crowns cemented with different cements and surface treatments would have equivalent fracture resistance as 3 mol% yttria (3Y-Z) crowns. METHODS: The study included 0.8 mm, 1.0 mm, and 1.2 mm thickness 5Y-Z (Katana UTML) crowns and 0.5 and 1.0 mm thickness 3Y-Z (Katana HT) crowns as controls. The 5Y-Z crowns were divided among three treatment subgroups (n = 10/subgroup): (1) cemented using RMGIC (Rely X Luting Cement), (2) alumina particle-abraded then luted with the same cement, (3) alumina particle-abraded and cemented using a resin cement (Panavia SA Cement Universal). The 3Y-Z controls were alumina particle-abraded then cemented with RMGIC. The specimens were then loaded in compression at 30° until failure. RESULTS: All 5Y-Z crowns (regardless of thickness or surface treatment) had a similar to or higher fracture force than the 0.5 mm 3Y-Z crowns. Only the 1.2 mm 5Y-Z crowns with resin cement showed significantly similar fracture force to the 1 mm 3Y-Z crowns. CONCLUSION: In order to achieve a similar fracture resistance to 0.5 mm 3Y-Z crowns cemented with RMGIC, 5Y-Z crowns may be as thin as 0.8 mm. To achieve a similar fracture resistance to 1.0 mm 3Y-Z crowns cemented with RMGIC, 5Y-Z crowns must be 1.2 mm and bonded with resin cement.

Evaluation of Candida albicans Adherence to CAD-CAM Milled, 3D-Printed, and Heat-Cured PMMA Resin and Efficacy of Different Disinfection Techniques: An In Vitro Study.

PURPOSE: Candida albicans has been regarded as the most predominant oral fungal pathogen and the main cause of denture stomatitis. This study aimed to investigate C. albicans adherence to three types of denture base polymers: heat-cured polymethylmethacrylate (PMMA), CAD-CAM milled and 3D-printed. The efficacy of four common disinfection techniques, glutaraldehyde, brushing, microwave irradiation, and Polident overnight tablets, were also examined. MATERIAL AND METHODS: Sixty blocks of pink acrylic specimens were fabricated from each polymer group. To investigate the C. albicans adherence, as well as the efficacy of different disinfection techniques on removing the yeast from the different materials, specimens were cultured within the fungal culture overnight followed by disinfection. The adhered C. albicans on the materials were then obtained by vortexing in phosphate buffered saline (PBS), and the numbers of the yeast in the suspensions were evaluated by measuring the optical density and/or colony-forming units on agar plates. Data were expressed as mean ± SEM (standard error of the mean). Statistical differences were evaluated by one-way analysis of variance (ANOVA) followed by the post hoc Tukey HSD tests. RESULTS: Significant differences in C. albicans adherence to the three polymers were noted. CAD-CAM milled and heat-cured PMMA showed significantly less C. albicans adherence compared with 3D printed PMMA. No significant difference was noted between milled and heat-cured PMMA. In the disinfection test, microwave irradiation, mechanical brushing, and Polident tablets were found to be effective in removing fungal attachment on the different denture materials, while glutaraldehyde was found to be the least effective. CONCLUSION: C. albicans adherence to the polymers varies greatly based on the types of PMMA. 3D-printed had the highest fungal biofilm attachment. Microwave irradiation, mechanical brushing, and Polident overnight tablets had comparable results in removing C. albicans from all types of PMMA, while glutaraldehyde was not as effective.

Laboratory Trends for Removable Prosthodontics: A Comparison of Two Surveys.

PURPOSE:  The purpose of this survey was to assess dental laboratory technicians' perceptions of the quality of communication and techniques used when receiving removable prosthodontic cases. Additionally, responses were compared to a 2009 survey and changes in trends were evaluated. MATERIALS AND METHODS:    An eleven-question anonymous response survey was developed based on a 2009 survey that assessed dental laboratory technicians' perceptions.  The survey was distributed via Qualtrics to members of the National Association of Dental Laboratories (NADL) The survey included questions related to detail of instruction, quality of work received, design of the prosthesis, and type of articulator used.  Responses were compared to those received in 2009. RESULTS:  Fifty-two survey responses were received from dental laboratory technicians. Of these, 12 did not provide removable prosthodontics services and were excluded. The remaining 40 responses were analyzed. Of these, only 3.7% of the responding laboratory technicians reported receiving work authorizations from dentists that were complete enough to do their best work. While roughly half of the respondents (48.49%) expected a dentist to send a design for a cast partial denture framework, most respondents (72.5%) answered that they designed the majority of the partial denture frameworks they fabricated. The majority of respondents reported that complete denture impressions were not border molded in custom trays, and that most dentists did not rearrange or modify a wax setup for complete or partial dentures. These findings were consistent with the trends reported in the 2009 survey. CONCLUSIONS:  Most dental laboratory technicians answered that based on their selected techniques, dentists tend to complete clinical procedures that minimize patient chair time. While the surveyed technicians appeared satisfied with the quality of work they received, there was a consistent message that communication was frequently inadequate, limiting the technicians ability to fabricate their best work.

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.

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.

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.

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.

Fracture resistance and marginal discrepancy of porcelain laminate veneers influenced by preparation design and restorative material in vitro.

OBJECTIVES: The purpose of this investigation is to evaluate marginal discrepancy and fracture resistance of two veneering materials using two preparation designs. METHODS: Two veneer preparation designs (full and traditional) were restored with leucite-reinforced ceramic (ProCAD, Ivoclar Vivadent, Amherst, NY) milled by CAD/CAM (Cerec 3D milling system, Serona Dental Systems), and conventional sintered feldspathic porcelain (Noritake Super Porcelain EX3, Noritake Dental Supply Co). Forty-eight specimens were analysed with a sample size of n=12 per group. The thickness of each veneer was measured on four specific surfaces. Marginal discrepancy was evaluated with a replica technique and cross-sectional view using a digital microscope. The fracture resistance of veneers cemented on standardised composite resin dies was evaluated using a universal testing machine. Results were analysed with ANOVA, Tukey-Kramer post hoc testing, and linear regression. RESULTS: The results of this investigation revealed no correlation between the thickness and marginal discrepancy of the veneers. The full preparation design with ProCAD and the traditional preparation design with feldspathic porcelain manifested smaller gap. Fracture resistance was decreased for the full preparation design with feldspathic porcelain. CONCLUSIONS: In terms of marginal discrepancy and fracture resistance, the most favourable combination was a traditional veneer preparation design with conventional sintered feldspathic porcelain. For the full veneer preparation, a stronger ceramic material such as ProCAD is suggested.

Sectional impressions and simplified folding complete denture for severe microstomia.

A patient presenting with severe microstomia (PDI Class IV) was unable to insert a maxillary complete denture. Sectional final impressions were made using two impression materials and an interlocking custom tray. A folding record base was used for maxillomandibular relationship records. A novel folding maxillary denture with a custom hinge and plunger attachment to lock the denture in the open position was fabricated. The patient was able to insert the collapsed denture, open it intraorally, and enjoy successful masticatory function.

Comparison of the passivity between cast alloy and laser-welded titanium overdenture bars.

PURPOSE: The purpose of this study was to investigate the fit of cast alloy overdenture and laser-welded titanium-alloy bars by measuring induced strain upon tightening of the bars on a master cast as well as a function of screw tightening sequence. MATERIALS AND METHODS: Four implant analogs were secured into Type IV dental stone to simulate a mandibular edentulous patient cast, and two groups of four overdenture bars were fabricated. Group I was four cast alloy bars and Group II was four laser-welded titanium bars. The cast alloy bars included Au-Ag-Pd, Pd-Ag-Au, Au-Ag-Cu-Pd, and Ag-Pd-Cu-Au, while the laser-welded bars were all Ti-Al-V alloy. Bars were made from the same master cast, were torqued into place, and the total strain in the bars was measured through five strain gauges bonded to the bar between the implants. Each bar was placed and torqued 27 times to 30 Ncm per screw using three tightening sequences. Data were processed through a strain amplifier and analyzed by computer using StrainSmart software. Data were analyzed by ANOVA and Tukey's post hoc test. RESULTS: Significant differences were found between alloy types. Laser-welded titanium bars tended to have lower strains than corresponding cast bars, although the Au-Ag-Pd bar was not significantly different. The magnitudes of total strain were the least when first tightening the ends of the bar. CONCLUSIONS: The passivity of implant overdenture bars was evaluated using total strain of the bar when tightening. Selecting a high modulus of elasticity cast alloy or use of laser-welded bar design resulted in the lowest average strain magnitudes. While the effect of screw tightening sequence was minimal, tightening the distal ends first demonstrated the lowest strain, and hence the best passivity.

The effect of etching technique on the retention of adhesively cemented prefabricated dowels.

PURPOSE: To determine if etching technique influences the bond strength of resin cement to root canal dentin. MATERIALS AND METHODS: Fifty-five extracted teeth were endodontically treated, dowel space prepared, and divided into five groups. Each group was treated with different etchant consistencies: acid gel, semi-gel, low-viscosity gel, liquid, and a self-etching primer. After dowel cementation, four sections were removed from each root and a push-out test was performed. RESULTS: Significant effects were found for etching procedure and for location within the root canal. The apical segment produced the lowest bond strength. Self-etching primer showed the highest bond strength. CONCLUSIONS: The consistency of etchant material influenced the bond strength of a prefabricated dowel in the canal.

Precious metals in dentistry.

Precious alloys are an important material group in dentistry because of their ease of use, excellent compatibility, favorable mechanical and physical properties, and application in ceramometal bonding. Although new precious alloys have been introduced in the past decades, frequently because of economic pressure, gold-based alloys remain a popular choice. Researchers have suggested that alloys should be chosen based on an understanding of the alloy system, selection of proven alloys from quality manufacturers, and consideration of the requirements of a given clinical situation.