Investigation of the Type of Angled Abutment for Anterior Maxillary Implants: A Finite Element Analysis.

PURPOSE: The optimal abutment material and design for an angled implant-abutment connection in the esthetic zone is unclear. The purpose of this finite element analysis (FEA) study was to compare different abutment models by evaluating the stress values in the implant components and strain values on the simulated bone around an anterior maxillary implant with different angled abutment models and loading conditions. MATERIALS AND METHODS: One Ø3.5×12-mm implant was placed in 3D FEA models representing the anterior left lateral segment of the maxilla. Three different contemporary implant models were created with 17° or 25° angled abutments (Ti base abutment, zirconia abutment, and titanium abutment) and 3D-modeled. The implant abutment model was an angled Ti base abutment (TIB), an angled zirconia abutment (ZIR), or an angled titanium abutment (TIT). Vertical and oblique loads of 100 N for the central incisors were applied as boundary conditions to the cingulum area and incisal area in a nonlinear FEA. RESULTS: The TIB model resulted in reduced stress conditions. According to the von Mises stresses occurring on the screw, abutment, crown, and implant, especially under oblique loads, the TIB model was exposed to less stress than the ZIR or TIT models. Strain values in simulated cortical and trabecular bones were obtained lower in the TIB model. CONCLUSIONS: When a standard implant was placed in the esthetic zone at an increased angle, the implants, abutments, and screws had more unfavorable stress levels; therefore, using a Ti-base abutment may reduce stress. The amount of contact surface of the implant with the simulated cortical bone is also an important factor affecting stress and strain.

Effect of coating on the color and surface hardness of the surface of dental ceramics.

BACKGROUND: The aim of this study was to investigate whether boron nitride (BN) and BN-chromium (BN-Cr) coatings applied with the sputtering method would change the characteristics of hardness and discoloration of the ceramic veneer surface. MATERIALS AND METHODS: In this experimental study, thirty disc-shaped cores (10 mm in diameter and 0.8 mm in thickness) were prepared. Three different ceramic systems, IPS Empress (E) (Ivoclar Vivadent, Schaan, Liechntenstein), IPS e.max Press (EP) (Ivoclar Vivadent, Schaan, Liechntenstein), and Turkom Cera (T) (Turcom-Ceramic SDN-BHD, Kuala Lumpur, Malaysia), were tested, each with n = 10. The specimens were divided into two subgroups (n = 5) according to the coating on the veneering ceramic: BN or BN-Cr. The Vickers hardness and color differences (ΔE) values were measured before and after coating. Surface analysis was performed with X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopic. The Wilcoxon signed-rank test was performed to compare hardness values. The Kruskal-Wallis test was performed to compare ΔE values among all groups. The post hoc tests was used after Kruskal-Wallis, with level of statistical significance set at P ≤ 0.05. RESULTS: BN-Cr coating statistically significantly increased the hardness of all types of ceramics (P < 0.05). BN coating did not change the hardness statistically significantly (P > 0.05). The mean ΔE values indicated clinically noticeable (over the limit of 3.7) color change in all groups except for the EP-BN and T-BN groups. CONCLUSION: Although BN-Cr coating in this thickness had a negative effect on color, it increased the hardness of the ceramics and could be useful in the palatal region.

Evaluation of the color stability of temporary materials produced with CAD/CAM.

BACKGROUND: If a temporary restoration is in the esthetic area and needs to be worn for a long time, the color stability of temporary materials becomes an important factor. OBJECTIVES: The aim of this in vitro study was to evaluate the long-term effects of various staining solutions on the color stability of different temporary materials produced with the computer-aided design and computer-aided manufacturing (CAD/CAM) technology. MATERIAL AND METHODS: In the study, the following materials were used: VITA CAD-Temp® (group 1); Ceramill® Temp (group 2); and Telio® CAD (group 3). Forty disk-shaped specimens (10 mm in diameter, 2 mm in thickness) of each material (N = 120) were produced with a CAD/CAM system. Staining solutions - of tea (A), of coffee (B) and cola (C) - and distilled water (D, control) were used, and color was evaluated before and after storing the samples in the solutions. Measurements were taken with a spectrophotometer and the color parameters (L*, a*, b*, and ΔE) were calculated according to the Commission internationale de l'éclairage system (CIELab). The results were evaluated with the two-way analysis of variance (ANOVA) and Tukey's tests (α = 0.05). RESULTS: Clinically perceivable (ΔE00 > 0.8) and statistically significant (p < 0.001) color differences were detected in all specimens. The highest ΔE00 value was found in the Ceramill Temp specimens. In addition, the highest ΔE00 values were noted for the specimens stored in cola and the coffee solution for all groups. The lowest ΔE00 value was observed for the groups stored in the tea solution. CONCLUSIONS: Clinically perceivable color changes were observed in all the specimens kept in the solutions. Color changes were greater for cola and coffee as compared to tea.

Incorporation of Hydroxyapatite into Glass Ionomer Cement (GIC) Formulated Based on Alumino-Silicate-Fluoride Glass Ceramics from Waste Materials.

Glass ionomer cement (GIC) is a well-known restorative material applied in dentistry. The present work aims to study the effect of hydroxyapatite (HA) addition into GIC based on physical, mechanical and structural properties. The utilization of waste materials namely clam shell (CS) and soda lime silica (SLS) glass as replacements for the respective CaO and SiO2 sources in the fabrication of alumino-silicate-fluoride (ASF) glass ceramics powder. GIC was formulated based on ASF glass ceramics, polyacrylic acid (PAA) and deionized water, while 1 wt.% of HA powder was added to enhance the properties of the cement samples. The cement samples were subjected to four different ageing times before being analyzed. In this study, the addition of HA caused an increment in density and compressive strength results along with ageing time. Besides, X-ray Diffraction (XRD) revealed the formation of fluorohydroxyapatite (FHA) phase in HA-added GIC samples and it was confirmed by Fourier Transform Infrared (FTIR) analysis which detected OH‒F vibration mode. In addition, needle-like and agglomeration of spherical shapes owned by apatite crystals were observed from Field Emission Scanning Electron Microscopy (FESEM). Based on Energy Dispersive X-ray (EDX) analysis, the detection of chemical elements in the cement samples were originated from chemical compounds used in the preparation of glass ceramics powder and also the polyacid utilized in initiating the reaction of GIC.

Effect of different design of abutment and implant on stress distribution in 2 implants and peripheral bone: A finite element analysis study.

STATEMENT OF PROBLEM: How adjacent dental implants with different sizes, designs, and abutment connection shapes affect stress on the prosthetic structure is unclear. PURPOSE: The purpose of this finite element analysis (FEA) study was to analyze stress distribution around bone and around 2 implants with different sizes, diameters, shapes, and loading directions placed next to each other in splinted and unsplinted prostheses. MATERIAL AND METHODS: On 3D FEA models representing the posterior right lateral segment of the mandible, 1 implant (Ø3.5×12 mm) and 1 implant (Ø5.5×8 mm) were placed adjacent. Three different contemporary implant models were created with different teeth, pitch, spiral numbers, and self-taping features, and different abutments for them were modeled in 3D. The implant-abutment connection was internal hexagonal (MIH), stepped conical (MSC), and internal conical (MIC). Vertical and oblique loads of 365 N for molar teeth and of 200 N for premolar teeth were applied as boundary conditions to the cusp ridges and grooves in a nonlinear FEA. RESULTS: The MIH implants resulted in improved stress conditions. According to the von Mises stresses occurring on the screw, abutment, and implant, especially under oblique loads, MIH was exposed to less stress than MSC, and MSC was exposed to less stress than MIC. CONCLUSIONS: When a standard implant and a short implant were placed adjacent and splinted by crowns, the implants, abutments, and screws had unfavorable stress levels; therefore, adjacent splinted implants should be of similar size. The form of the implant-abutment junction is also an important factor affecting stress.

A comparison of the fracture resistance of premolars without a ferrule with different post systems.

STATEMENT OF PROBLEM: Which type of post improves the performance of endodontically treated mandibular premolars without a ferrule remains unclear. PURPOSE: The purpose of this in vitro study was to compare the restoration of endodontically treated mandibular premolars without a ferrule by using different post systems. MATERIAL AND METHODS: Thirty extracted mandibular premolars were endodontically treated, and their crowns removed. They were divided into 3 groups with different post systems (n=10): zirconia ceramic posts (ZRPs), fiber posts (FPs), and bundled glass fiber-reinforced composite resin posts (GTPs). After post placement and core fabrication, computer-aided design and computer-aided manufacture (CAD-CAM) lithium disilicate crowns were cemented. The specimens were subjected to thermocycling and mastication simulation before a fracture test in a universal testing machine. The maximum load at which the fracture occurred was recorded, and the fractured specimens were examined by using an optical microscope. The data were analyzed for statistical differences with a 1-way ANOVA and the Tukey honestly significant difference post hoc test (α=.05). RESULTS: No statistically significant difference in fracture strength was found among the groups (P=.970). From the light microscopy examination, catastrophic failure was observed in all specimens, and there was no failure of the ceramic crowns. CONCLUSIONS: Based on the findings of this in vitro study, the choice of post material with a low or high modulus of elasticity did not prevent catastrophic failures in endodontically treated teeth without a ferrule.

Effect of Different Surface Treatments on Bond Strength of Resin Cement to a CAD/CAM Restorative Material.

PURPOSE: To investigate the effects of various surface treatment methods on the shear bond strength of self-adhesive resin cement to a novel CAD/CAM hybrid ceramic material. MATERIALS AND METHODS: A novel hybrid ceramic restorative material (Vita Enamic) was used in this study. Sixty resin block specimens were prepared and separated into six groups for each surface treatment method (n = 10); group 1: control group, no treatment applied; group 2: sandblasted by 30 µm silicate-coated alumina particles (CoJet Sandblasting); group 3: 50 µm Al2 O3 sandblasting; group 4: 10% hydrofluoric acid; group 5: no surface treatment + universal adhesive (3M Single Bond Universal); group 6: 200 mJ, 10 Hz 2W Er,Cr:YSGG laser treatment. For each specimen, surface roughness measurements in noncontact mode were taken after the surface treatments using a portable surface texture-measuring machine. A self-adhesive resin cement (3M U200) was applied on every surface treated with the help of a cylindrical mold (2 × 4 mm) and was filled gradually. Shear bond strength was measured using a universal test machine, and one-way ANOVA and a Duncan test (p = 0.05) were used to analyze the data. RESULTS: Mean values of the shear bond strength varied between 7.75 and 10.73 MPa. Bond strength values were enhanced by all surface treatment methods compared to the control group. The difference between group 5 and the control group (p < 0.05) was statistically significant, whereas there were no considerable differences between other treatment methods. CONCLUSION: Surface treatments of hybrid ceramic resin blocks could enhance the bond strength to resin cement; however, using Single Bond Universal without surface treatment showed a higher bond strength value.

Evaluation of thermal conductivity and flexural strength properties of poly(methyl methacrylate) denture base material reinforced with different fillers.

STATEMENT OF PROBLEM: Poly(methyl methacrylate) (PMMA) is widely used in prosthodontics as a denture base material. However, it has several disadvantages, including low strength and low thermal conductivity. PURPOSE: The purpose of this in vitro study was to evaluate thermal conductivity and flexural strength after adding powdered Ag, TiO2, ZrO2, Al2O3, SiC, SiC-nano, Si3N4, and HA-nano in ratios of 10 wt% to PMMA. MATERIAL AND METHODS: A total of 144 specimens were fabricated and divided into 18 groups. Specimens were left in water for 30 days. Thermal conductivity values were measured using a heat flowmeter, flexural strength was measured with a 3-point bend test, and specimens were investigated with environmental scanning electron microscopy. One-way ANOVA was used to compare means followed by using Duncan multiple range test (α=.05). RESULTS: The thermal conductivity value of PMMA increased significantly after the addition of Si3N4, SiC, Al2O3, SiC-nano, TiO2, ZrO2, HA-nano, and Ag. Progressive increases in thermal conductivity were observed in Si3N4, SiC, and Al2O3 fillers. Flexural strength values of the control group were not significantly different from those of the SiC, Al2O3, or Ag group (P>.05). In the other groups, flexural strength values decreased significantly (P<.05). On the basis of electron microscopy, we observed that Si3N4, SiC, and Al2O3 powders had higher thermal conductivity values that are dissipated more homogeneously in PMMA. CONCLUSIONS: Although the addition of 10 wt% SiC, Al2O3, and Ag powder to PMMA significantly increased thermal conductivity, the flexural strength values of PMMA were not significantly changed.

Effect of different post space irrigation procedures on the bond strength of a fiber post attached with a self-adhesive resin cement.

STATEMENT OF PROBLEM: The effects of different post space irrigation procedures on the bond strength of a self-adhesive resin cement to the root canal dentin are still unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effects of alternative post space irrigation procedures on the cement strengths of posts attached with a self-adhesive resin cement. MATERIAL AND METHODS: Forty single-rooted teeth were selected, and after root canal preparation and obturation, post spaces were prepared. The teeth were divided into 4 groups corresponding to the post space irrigation procedure and treated as follows: the distilled water (DW) group (control) received 15 mL of distilled water; the NaOCl+ethylenediaminetetraacetic acid (EDTA) group was treated with 5 mL of 5.25% NaOCl, 5 mL of 17% EDTA, and 5 mL of distilled water; the chlorhexidine (CHX) group was treated with 15 mL of 2% chlorhexidine solution; and the phosphoric acid (PA) group treatment consisted of etching the walls of the prepared post holes with 35% phosphoric acid. Fiber posts were attached with a self-adhesive resin cement, and specimens were cut horizontally for push-out testing. The statistical evaluation consisted of 1-way ANOVA with the post hoc Tukey honest significant differences test (α=.05). RESULTS: The NaOCl+EDTA treatment yielded a significantly higher bond strength than those used in the other 3 groups (P=.003). No statistically significant differences were found among any of the other groups, as different root regions showed similar bond strength values (P>.05). CONCLUSIONS: The results showed that EDTA in combination with NaOCl could be advantageous for post space irrigation when fiber posts are bonded with a self-adhesive resin cement.

Effect of sealer coating and storage methods on the surface roughness of soft liners.

STATEMENT OF PROBLEM: A soft lining is applied under a removable prosthesis for various reasons. The porosity of the lining material may increase colonization by microorganisms and cause tissue inflammation. PURPOSE: The purpose of this in vitro study was to evaluate the effect of sealer coating on the surface roughness of soft lining materials under 4 different conditions. MATERIAL AND METHODS: A total of 125 specimens were prepared. One high-temperature silicone-based soft lining material and 2 room-temperature-polymerized soft lining materials (1 silicone-based and 1 methacrylate-based) were used. Twenty-five specimens of each room-temperature soft lining material were coated with 2 layers of surface sealer. Additionally, 5 specimens of each material were stored in either distilled water, Coca-Cola, denture cleanser, saliva, or air. The surface roughness was measured at baseline and after 1, 7, 14, and 28 days. Surface roughness values were analyzed with repeated measures analysis of variance, and the Bonferroni multiple comparison test was performed using time-dependent groups and storage methods. RESULTS: In the time-dependent groups, methacrylate-based sealer-coated soft liners exhibited a significant increase in roughness (1.74-2.09 µm, P<.001), and silicone-based sealer-coated soft liners exhibited a decrease in roughness, but it was not significant (2.16-2.02 µm, P>.05). Therefore, the sealer coating was not effective in reducing surface roughness. Among the time-dependent storage methods, the denture cleanser exhibited an almost significant increase in roughness (1.83-1.99 µm, P=.054). Coca-Cola and artificial saliva did not show a significant difference (P>.05). However, a significant decrease in roughness was found with distilled water (P=.02) and air (P<.001). CONCLUSIONS: Statistically significant differences in surface roughness were found among the different types of soft liners. The sealer coating had no significant effect, and denture cleanser slightly increased the surface roughness. Contrary to expectations, the roughness did not increase in all groups over time.

Comparison of the metal-ceramic bond after recasting and after laser sintering.

STATEMENT OF PROBLEM: Failure of the bond between metal and ceramic is common with metal ceramic prostheses. PURPOSE: The purpose of this in vitro study was to investigate how recasting affects the metal-ceramic bond strength for 1 base metal and 1 noble alloy compared with laser-sintered Co-Cr alloy by using a procedure based on ANSI/ADA Specification No. 38. MATERIAL AND METHODS: One laser-sintered (Co-Cr) and 2 metal (Co-Cr, Pd-Ag) alloys were used. Metal strips (25 × 3 × 0.5 mm) were obtained with 2 different methods: torch melting and laser sintering. Twelve alloy specimens were processed for each group. Vita VM13 porcelain layers (8 × 3 × 1.1 mm) were fabricated at the centers of the metal frameworks. Specimens containing 100% fresh alloy were used in the first casting group (control). Metal ceramic specimens were prepared for each alloy, and no new metal was added to the second and third castings. The findings were statistically analyzed and compared with a 2-way analysis of variance (ANOVA). RESULTS: The second casting of the noble alloy-ceramic specimen had the highest mean metal-ceramic bond strength in flexure. No significant differences were found between the laser-sintered Co-Cr and the Pd-Ag metal ceramic specimens after the first and third castings. CONCLUSION: All groups had adequate porcelain bond strength, except C2 (second casting of Co-Cr alloy) and C3 (third casting of Co-Cr alloy). Co-Cr alloy fabricated with new laser-sintering techniques is a promising alternative for metal ceramic restorations. Further research is needed before its use can be advocated in the dental laboratory.