Evaluation of various denture cleansers on color stability and surface topography of polyetherketoneketone, polyamide, and polymethylmethacrylate.

The aim of this study was to evaluate the effect of sodium perborate effervescent tablets and citric acid solution on the color stability and surface topography of a new generation of high-performance polymer polyetherketoneketone (PEKK), thermoinjection-molded polyamide, and polymethylmethacrylate (PMMA). Fifty disc-shaped specimens were fabricated (10 mm × 2 mm) from PEKK (P group), polyamide (D group), and PMMA (M group). These groups were divided into five subgroups (n = 10) according to the storage media. The test groups were immersed in the following solutions: distilled water (Control), Corega, Protefix, Perlodent, and Curaprox. The color stability values (ΔE) were measured using a spectrophotometer before and after immersion in distilled water and four different denture cleansers for 8 hr/day for 140 days. Topography alterations after treatments were assessed with scanning electron microscopy (SEM). Data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey's Honest Significant Difference test. The p < .05 was considered significant. All denture cleansers increased the ΔE values relative to the baseline values in the M, D, and P groups (p < .05). The Perlodent denture cleanser demonstrated the highest ΔE value in all groups, which was unacceptable. Curaprox denture cleanser showed the lowest ΔE value in the M and D groups (p < .05). Curaprox in all groups showed a ∆E value less than 3.7. For patients who have PEKK- and polyamide-based prosthesis, the use of citric acid-based cleansers may be more recommended than sodium perborate-containing cleansers because of its clinically acceptable color changes on polymers in terms of color stability.

Effect of mucosa thicknesses on stress distribution of implant-supported overdentures under unilateral loading: Photoelastic analysis.

INTRODUCTION: The aim of this study was to evaluate the effect of different heights of attachment and mucosa thicknesses on the stress distribution of two implant-retained mandibular overdenture designs under loading using the photoelastic stress analysis method. MATERIALS AND METHODS: Six photoelastic models of an edentulous mandibula were fabricated with two solitary implants that were placed in the canine regions. The attachment systems studied were ball and locator stud attachments. Both the ball and locator groups included three models that had different residual ridge heights so as to provide different mucosa thicknesses (1 mm-1 mm, 1 mm-2 mm, 1 mm-4 mm). A static vertical force of 135 N was applied unilaterally (each on the right then the left side) to the central fossa of the first molars. Models were positioned in the field of a circular polariscope to observe the distribution of isochromatic fringes around the implants and the interimplant areas under loading. The photoelastic stress fringes were monitored and recorded photographically. RESULTS: The ball attachment groups showed higher stress values than did the locator groups under loading. Both attachment systems produced the lowest stress values in stimulated 1 mm-1 mm mucosa thickness models. The models with 1 mm-2 mm mucosa thicknesses showed higher stress values than did other models for both attachment systems. The highest stress value observed around both attachment systems was the moderate level in all test models. CONCLUSION: In different height mucosa thicknesses, locator attachment models distributed the load to the other side of the implant and its surrounding tissue, whereas the ball attachment did not. Regardless of mucosal thickness and attachment type, the implant on the loading side was subjected to the highest stress concentration.

Evaluation of Stress Distribution on Mandibular Implant-Supported Overdentures With Different Bone Heights and Attachment Types: A 3D Finite Element Analysis.

The biomechanical behavior of the edentulous mandible with bone irregularities that has been rehabilitated with implant-supported overdentures has become an important factor for treatment planning. Restorative options, including dental implants with various attachments, affect the stress distribution. The purpose of this study was to evaluate the stress distribution of cortical bone around the implant neck and implant structures in overdentures with two different attachment types at the edentulous mandible and with different bone heights using three-dimensional finite element analysis. Five three-dimensional models of an edentulous mandible were designed and implemented. Ten models were constructed with ball and locator attachments. Static bilateral and unilateral vertical and oblique occlusal loads with magnitudes of 100 N were applied to the overdentures. The principal stresses were higher in the presence of oblique loads compared to vertical loads in all the analyzed models. Maximum principal stresses were observed around the mesial side of the contralateral implant, and the minimum principal stresses were noted around the distal side of ipsilateral implant during unilateral vertical loading. These patterns were reversed during oblique loadings. The ball attachment models yielded lower von Mises stress values than the locator models at all the loading conditions, while the stress distributions were similar in the models with the same and different bone levels. Correspondingly, bone corrections due to irregularities may not be necessary in terms of biomechanics. The results of this study may provide clinicians a better understanding for the mandibular overdenture design in the cases at which different bone heights exist.

Effect of cleansers on denture base resins' structural properties.

INTRODUCTION:: We assessed the effect of different available denture cleansers on the roughness and hardness of polyetherketoneketone, thermoinjection-molded polyamide, and polymethylmethacrylate. MATERIALS AND METHODS:: A total of 150 disc-shaped specimens were fabricated (10 mm × 2 mm) from these three denture base resins, and divided into five subgroups ( n = 10) according to immersion procedures. One of these groups subjected to distilled water served as control, whereas other groups were subjected to daily cleansing with four denture cleansers (Corega, Protefix, Curaprox, and Perlodent) for 8 h a day for 140 days. The surface roughness and hardness values of specimens were recorded by measuring twice at baseline, and again after application of chemical solutions. Topography alterations after treatments were assessed with scanning electron microscopy. The data were subjected to statistical analysis and comparison among groups was done using Kruskal Wallis and Wilcoxon Signed Ranks tests. P-value <0.05 was considered significant. RESULTS:: The surface roughness of polyetherketoneketone, polymethylmethacrylate, and polyamide dentures was increased significantly by chemical solutions of denture cleansers. While the hardness value of polyetherketoneketone was not affected significantly after immersion in denture cleansers, those of polymethylmethacrylate and polyamide decreased significantly. Compared with Curaprox, the effervescent tablets significantly altered the surface hardness and roughness of polyamide. CONCLUSION:: Denture cleansers can considerably alter the surface roughness and hardness of denture base resins and should be used carefully depending on the material.

The influence of the irrigant QMix on the push-out bond strength of a bioceramic endodontic sealer.

PURPOSE: The aim of this study was to evaluate the effect of a commercially available irrigant, the Qmix 2 in 1, on the push out bond strength of Endosequence BC which is a bioceramic based root canal sealer. MATERIAL AND METHODS: Sixty extracted maxillary central incisors were prepared with Protaper Next rotary instrument up to X4 (# 40). The specimens were randomly divided into four groups of equal sample size (n=15), according to the final irrigation regimen as follows: Group 1: 2.5% sodium hypochloride (NaOCl) (control), Group 2: 17% ethylenediaminetetraacetic acid (EDTA), Group 3: 2% Chlorhexidine (CHX), Group 4: QMix 2 in 1. After rinsing, teeth were obturated using gutta-percha with Endosequence BC sealer. Slices were obtained from coronal, middle, and an apical section of the root canal. Push-out test was performed to evaluate the bond strength between the root canal dentin and the sealer. Data was statistically analyzed. RESULTS: The push-out bond strength of the root canal sealer was significantly affected by the type of irrigation solution. Highest bond strengths were found in canals irrigated with Qmix solution, and these results were regardless of anatomical section of the root canal (p< 0.05). CONCLUSION: Final irrigation of the root canals with QMix had a positive effect on the bond strength of Endosequence BC sealer throughout the root canal.

Effect of Different Surface Treatments on Porcelain-Resin Bond Strength.

PURPOSE: The aim of this study was to evaluate the effects of various surface treatments on the surface structure and shear bond strength (SBS) of different ceramics. MATERIALS AND METHODS: A total of 192 disk-shaped cores were prepared using two all-ceramic systems, of which 168 were submitted to SBS tests, and 24 were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The ceramics used were IPS Empress e.max (EX) lithium glass-ceramic and Vita In-Ceram Zirconia glass-infiltrated zirconia (ICZ). The specimens were randomly divided into seven groups (n = 12) on the basis of the surface treatment used: control; SB-sandblasting with 50 µm Al2 O3 particles; CJ-chairside silica coating with 30 µm SiO2 particles and silanization (Clearfil Porcelain Bond Activator); HF-etching in 5% hydrofluoric acid and silanization; ER-etching with an Er:YAG laser (10 W); ND-Nd:YAG laser etching (0.8 W); and FS-etching with a femtosecond laser (860 mW). A luting cement (Clearfil Esthetic) was photopolymerized on each treated ceramic disk. After subjecting the specimens to thermocycling (1000 cycles, 5°C to 55°C), SBS tests were performed using a universal testing machine. The data were analyzed with two-way ANOVA and Tukey's tests using a significance limit of 5%. RESULTS: Among the EX ceramics, the CJ (29.10 MPa) and HF (26.07 MPa) specimens had statistically higher SBS values. For the ICZ ceramics, the highest value (28.08 MPa) was obtained for the CJ specimens. CONCLUSIONS: Silanization after coating with silica improves the bond strengths of both EX and ICZ specimens, while HF etching is favorable only for the EX specimens.

Effect of sodium ascorbate on the bond strength of silorane and methacrylate composites after vital bleaching.

We investigated the effect of sodium ascorbate (SA) on the microtensile bond strengths (MTBSs) of different composites to bovine enamel after vital bleaching with hydrogen peroxide (HP) or carbamide peroxide (CP). Thirty bovine incisors were randomly divided into five groups and treated with no bleaching application (control), 35% HP alone, 35% HP+10% SA for 10 minutes (HP+SA), 16% CP alone, or 16% CP+10% SA for 10 minutes (CP+SA). Specimens were restored with Silorane adhesive and Filtek Silorane composite (designated as S/group) or with Clearfil SE bond and Filtek Supreme XT (designated as F/group). Composite build-up was created on the enamel. Sectioned specimens (n=10 per group; 1 mm2; cross-sectional area) were created and stressed in a universal testing machine at 1 mm/min crosshead speed. The application of 10% SA immediately after bleaching with 16% CP or 35% HP increased the enamel MTBS, regardless of the adhesive/composite resin used. The resulting MTBS values were similar to those of the control groups. Use of 16% CP and 35% HP alone decreased the enamel MTBS, regardless of the adhesive/composite resin used, with F/CP+SA=F/HP+SA=F/CP=S/CP+SA=S/HP+SA=S/C>S/CP=S/HP=F/CP=F/HP (p<0.05). We concluded that the application of SA for 10 minutes immediately after vital bleaching increases the enamel BS for dimethacrylate- and silorane-based composites.

Effect of Nd:YAG laser bleaching and antioxidizing agents on the shear bond strength of brackets.

OBJECTIVE: The aims of this study were to evaluate the effect of hydrogen peroxide bleaching agents, both nonactivated and activated by a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser, and of antioxidant treatment on the shear bond strength (SBS) of orthodontic brackets. BACKGROUND DATA: Nd:YAG laser activation is expected to accelerate the bleaching therapy without decrease shear bond strength. MATERIALS AND METHODS: Ninety extracted maxillary central incisors were divided into two experimental groups and a control group. Group I was the control group, Group II was bleached with 35% hydrogen peroxide and had no photoactivation, and Group III was bleached with 35% hydrogen peroxide with activation by a Nd:YAG laser (4.0 W, 60 Hz frequency, 1 mm distance, 20 sec). Each group was divided into two subgroups: Subgroup A was immersed in artificial saliva for 2 weeks, and then bonded using the total etch system, whereas subgroup B was treated with an antioxidant agent (10% sodium ascorbate) and then bonded using the same system. The samples were stored in water for 24 h at 37°C, and thermocycled. The SBS in megapascals (MPa) was determined by a shear test with 1 mm/min crosshead speed, and failure types were classified with modified adhesive remnant index scores. The data were analyzed with two way analyses of variance, Tukey, and χ(2) tests at the α = 0.05 level. RESULTS: In both Groups II and III, the SBSs of brackets bonded after bleaching (Group II 15.16, Group III 17.50 MPa) were significantly lower than those of brackets in the bonded unbleached group (Group I 22.13 MPa); however, sodium ascorbate treatment significantly increased the SBSs of brackets in the bleached groups (Group II 21.52, Group III 22.43 MPa), but had an insignificant effect on the SBS of the control group (Group I 23.66MPa). CONCLUSIONS: Hydrogen peroxide bleaching agents reduce the SBSs both with and without Nd:YAG laser activation; however, treatment of the bleached enamel surface with 10% sodium ascorbate prior to bonding negates the effect.

Effect of sodium ascorbate on the bond strength of silorane and methacrylate composites after vital bleaching

We investigated the effect of sodium ascorbate (SA) on the microtensile bond strengths (MTBSs) of different composites to bovine enamel after vital bleaching with hydrogen peroxide (HP) or carbamide peroxide (CP). Thirty bovine incisors were randomly divided into five groups and treated with no bleaching application (control), 35% HP alone, 35% HP + 10% SA for 10 minutes (HP + SA), 16% CP alone, or 16% CP + 10% SA for 10 minutes (CP + SA). Specimens were restored with Silorane adhesive and Filtek Silorane composite (designated as S / group) or with Clearfil SE bond and Filtek Supreme XT (designated as F / group). Composite build-up was created on the enamel. Sectioned specimens (n = 10 per group; 1 mm2; cross-sectional area) were created and stressed in a universal testing machine at 1 mm/min crosshead speed. The application of 10% SA immediately after bleaching with 16% CP or 35% HP increased the enamel MTBS, regardless of the adhesive / composite resin used. The resulting MTBS values were similar to those of the control groups. Use of 16% CP and 35% HP alone decreased the enamel MTBS, regardless of the adhesive / composite resin used, with F / CP + SA = F / HP + SA = F / CP = S / CP + SA = S / HP + SA = S / C > S / CP = S / HP = F / CP = F / HP (p < 0.05). We concluded that the application of SA for 10 minutes immediately after vital bleaching increases the enamel BS for dimethacrylate- and silorane-based composites.