The Effect of Denture Cleansing Solutions on the Retention of Precision Attachments: An In Vitro Study.

This study aimed to investigate the effect of different cleansing solutions on the retention of precision attachments. A precision attachment patrix was embedded into acrylic resin and the matrix was placed onto the patrix. The red (high retention, 8 N), yellow (regular retention, 6 N), and green (reduced retention, 4 N) plastic matrixes of the attachments (n = 32) were soaked in three different denture cleansing solutions (sodium laureth sulfate, sodium bicarbonate-sodium perborate, sodium bicarbonate) for a duration simulating 6 months of clinical use. The control group was soaked in tap water. A universal testing machine was used to measure the retention values of attachments after they were soaked in denture cleansers. The retention values were compared among the groups with repeated-measures analysis of variance followed by the Tukey HSD test (p = 0.05). Yellow attachments were affected by sodium laureth sulfate, sodium bicarbonate-sodium perborate, and water (p = 0.012). Green attachments' retention increased after immersion in sodium laureth sulfate (p = 0.04) and water (p = 0.02). Red attachments' retention increased after immersion in sodium laureth sulfate or sodium bicarbonate-sodium perborate (p = 0.045). Water did not affect the retention of red attachments. Because sodium bicarbonate tablets did not affect the retention of attachments, clinicians may recommend their use as a cleanser. Clinicians also may inform patients using fixed and removable partial prostheses with precision attachments of a possible increase in retention after the use of sodium laureth sulfate or when using sodium bicarbonate-sodium perborate with yellow and red attachments.

Wear of monolithic zirconia against different CAD-CAM and indirect restorative materials.

STATEMENT OF PROBLEM: The wear of monolithic zirconia against enamel has been widely studied, but how zirconia affects different opposing restorative materials is not clear. PURPOSE: The purpose of this in vitro study was to investigate the depth of wear and volumetric loss of different restorative materials opposed by monolithic zirconia. MATERIAL AND METHODS: Sixty-six Ø10×3-mm specimens (n=11) were fabricated from monolithic zirconia, zirconia reinforced ceramic, lithium disilicate ceramic, feldspathic ceramic, ORMOCER, and ceramic optimized polymer. A 2-body pin-on-disk wear test was performed by using monolithic zirconia pins. The specimens were scanned with a noncontact profilometer after the tests. The scan parameters were a frame size area of 1.5×1.5 mm, frequency of 400 Hz, and scan sensitivity of 2 µm. After the evaluation of depth and volume loss, the specimens were analyzed with a scanning electron microscope. The Kruskal-Wallis test was used to analyze the differences in wear values across the specimen groups, and pairwise comparison tests were performed with a post hoc test (α=.05). RESULTS: Maximum depth of wear was 257.55 ±18.88 µm for lithium disilicate ceramic, 295.36 ±14.46 µm for zirconia reinforced ceramic, 421.82 ±214.49 µm for ORMOCER, 333.73 ±79.09 µm for ceramic optimized polymer, 146.27 ±22.86 µm for feldspathic ceramic, and 41.55 ±5.04 µm for monolithic zirconia. The depth of wear was not significantly different among lithium disilicate, zirconia-reinforced ceramic, ORMOCER, and ceramic optimized polymer (P<.05). However, the depth of wear of monolithic zirconia and feldspathic ceramic was less than that of other materials (P<.001). Volume loss of lithium disilicate was 1.68 ±0.25 mm3, 1.08 ±0.35 mm3 for zirconia reinforced ceramic, 4.29 ±2.91 mm3 for ORMOCER, 2.46 ±0.63 mm3 for resin ceramic, 1.07 ±0.09 mm3 for feldspathic ceramic, and 0.19 ±0.02 mm3 for monolithic zirconia. Feldspathic ceramic and monolithic zirconia had significantly less volume loss than the other groups (P<.001), and the difference between them for volume loss was statistically insignificant (P>.05). CONCLUSIONS: The tested ceramic-based materials had favorable wear resistance compared with the tested composite resin-based ones. However, the ceramics tended to crack formation than the composite resins.

Effect of Various Treatment Modalities on Surface Characteristics and Shear Bond Strengths of Polyetheretherketone-Based Core Materials.

PURPOSE: To investigate the effect of different surface treatments on the surface roughness (Ra), wettability, and shear bond strength of polyetheretherketone (PEEK) to composite resin. MATERIALS AND METHODS: One hundred ninety eight PEEK specimens were divided into six groups (n = 33). Specimen surfaces were treated with the following surface treatment modalities: silicoating (CoJet), acetone treatment, acid etching (H2 SO4 ), airborne particle abrasion (Al2 O3 ), laser irradiation (Yb:PL laser), and the nontreated surface serving as the control. Surface roughness was measured with an profilometer (n = 11) and a goniometer was used to measure the surface wettability through contact angle (θ)(n = 11). PEEK surfaces were veneered with a composite resin (n = 11). The specimens were then thermocycled for 10,000 cycles at 5 to 55°C. Shear bond strengths between the PEEK and composite resin were measured with an universal test machine. One-way ANOVA was used to analyze the data. Tukey's post-hoc test was used to determine significant differences between groups (α = 0.05). RESULTS: Surface roughness and wettability of PEEK surfaces along with shear bond strength of PEEK to composite resin were influenced by the surface treatments. (p < 0.01) Highest mean Ra values were obtained for PEEK surfaces treated by laser irradiation (2.85 ± 0.2 µm) followed by airborne particle abrasion (2.26 ± 0.33 µm), whereas other surface treatment modalities provided similar Ra values, with the acid-etched PEEK surfaces having the lowest mean Ra values (0.35 ± 0.14 µm). Silicoating provided the most wettable PEEK surfaces (48.04 ± 6.28º), followed by either acetone treatment (70.19 ± 4.49º) or acid treatment (76.07 ± 6.61º). Decreased wettability was observed for airborne particle abraded (84.83 ± 4.56º) and laser-treated PEEK surfaces (103.06 ± 4.88º). The highest mean shear bond strength values were observed for acid-etched PEEK surfaces (15.82 ± 4.23 MPa) followed by laser irradiated (11.46 ± 1.97 MPa), airborne particle abraded (10.81 ± 3.06 MPa), and silicoated PEEK surfaces (8.07 ± 2.54 MPa). Acetone-treated (5.98 ± 1.54 MPa) and untreated PEEK surfaces (5.09 ± 2.14 MPa) provided the lowest mean shear bond strengths. CONCLUSIONS: The highest mean shear bond strengths were observed for acid-etched PEEK surfaces, followed by laser-irradiated, airborne particle abraded, and silicoated PEEK surfaces providing similar mean shear bond strengths. Since shear bond strengths higher than 10 MPa are considered acceptable, acid etching, laser irradiation, and airborne particle abrasion of PEEK surfaces may be considered viable surface treatment modalities for the PEEK material tested.

Effect of heat polymerization conditions and microwave on the flexural strength of polymethyl methacrylate.

OBJECTIVE: The objective of this study is the effect of different heat polymerization conditions on the strength of polymethyl methacrylate (PMMA) resin base is unknown. Distinguishing one method that provides improved mechanical properties may be beneficial to the clinical success of complete and partial dentures and overdentures. The purpose of this study was to evaluate the effect of different polymerization methods on the flexural strength of a dental PMMA resin. MATERIALS AND METHODS: Forty PMMA specimens (64 mm × 10 mm × 4 mm) were prepared with 4 different polymerization methods (n = 10); heat polymerization at 74°C for 9 h, at 100°C for 40 min, and with 620 kPa pressure at 100°C for 20 min. The remaining group of specimens was microwave polymerized at 180 W for 6 min. All specimens were thermocycled at 5°C and 55°C for 5000 times. Three-point flexure test was used to measure the flexural strength of specimens. One-way ANOVA and Tukey Honestly Significant Difference were applied to analyze the differences in flexural strengths (α = 0.05). RESULTS: The flexural strength of heat-polymerized groups was similar. The flexural strength of microwave polymerized group was significantly different and lower than the other groups (P < 0.05). CONCLUSION: Polymerizing conventional heat-polymerizing PMMA resin with microwave energy resulted in a significant decrease in flexural strength. The results of this study suggest that clinicians may benefit from using heat polymerization when processing PMMA denture bases instead of microvawe polymerization when tested brand is used.

Effect of restoration material on stress distribution on partial crowns: A 3D finite element analysis.

BACKGROUND/PURPOSE: Various restoration materials have been used to restore as onlay materials to restore highly defected molar teeth. Different mechanical and physical properties of these materials may affect the success or survival of the restoration. The purpose of this study was to evaluate the restoration materials effects on stress distribution. MATERIALS AND METHODS: Three dimensional finite element analysis (FEA) was used to evaluate the stress concentrations and distributions at the restoration and the tooth. Maxillar first molar tooth constructed to evaluate the stress distribution and concentration levels at the restorations and the tooth structure. Two kinds of restoration materials, bulkfill composite and conventional hybrid composite was evaluated for direct method, while full ceramic and indirect composite was used for indirect method. A load of 200 N was applied on the restorations and stress levels were calculated by von Mises stress values. RESULTS: Highest stress concentration was observed at the ceramic restoration (3.77 GPa). Stress levels were 2.90 GPa for bulkfill composite and 2.14 GPa for direct and indirect composite. At the tooth structure the stress levels were 3.33 GPa, 3.18 GPa and 2.48 GPa for bulkfill, direct and indirect composites respectively. The lowest stress values was observed with the porcelain restoration (1.69 GPa). Stress concentrations at the adhesive system were 2.10 MPa for bulkfill composite, 1.35 MPa for direct and indirect composites and 1.25 Mpa for porcelain restoration. CONCLUSION: The restoration material affects the stress levels at the restoration and the tooth while the stress concentration areas remained nearly the same.

Effect of different housing retaining materials on the flexural strength of an acrylic resin overdenture base.

STATEMENT OF PROBLEM: An attachment housing inside an overdenture may weaken the acrylic resin base. The type of housing retaining material may affect the strength of the housing retaining material-acrylic resin base assembly. The effect of different housing retaining materials on the strength of acrylic resin base is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the effects of different materials used to retain the housing on the flexural strength of a poly(methyl methacrylate) (PMMA) resin base. MATERIAL AND METHODS: Sixty PMMA specimens (64×10×4 mm) were prepared with a clearance inside to allow the insertion of overdenture housings. Five different materials were used for housing orientation: an autopolymerizing composite resin, an acrylic resin reline material, a heat-polymerized PMMA, an autopolymerizing PMMA (n=10), and a control group (n=10) were prepared without any preparation or housing. The specimens were thermocycled 5000 times between 5°C and 55°C. The flexural strength data were analyzed by an analysis of variance using the maximum likelihood estimation method to eliminate the needs for normality within the groups and for equality of variances between the groups. If statistically significant, resolution of the significance factor was obtained by pairwise comparisons using the Tukey adjustment (α=.05). RESULTS: The fracture values were statistically significantly higher (P<.05) for the control group (90.22 ±12.46 MPa) than the test groups (heat-polymerized, 27.36 ±4.86 MPa), the autopolymerizing material (26.78 ±6.72 MPa), the acrylic resin reline material (16.94 ±4.38 MPa), the Ufigel (16.07 ±3.40 MPa), and the autopolymerizing composite resin (19.37 ±3.13 MPa). Heat- and autopolymerizing PMMA groups were significantly different from acrylic resin-based hard reline materials (P<.05). However, the remaining groups were not significantly different from each other. All fractures included both the PMMA and retaining material except for one of the hard reline groups, which separated from the PMMA. CONCLUSIONS: The tested retaining materials significantly reduced the flexural strength of PMMA denture base. The flexural strength of the resin base with housing was significantly higher when PMMA-based retaining materials were used than when acrylic resin-based hard reline materials were used.

Surface roughness and adaptation of different materials to secure implant attachment housings.

STATEMENT OF PROBLEM: Various materials are available to secure implant attachment housings in overdentures. Surface roughness and the adaptation of these materials to the denture base and the housings may increase the microcracks and bacterial adhesion at the interfaces in the long term. The surface characteristics of the interface between the denture base orientation material and the attachment housing have not been extensively studied. PURPOSE: The purpose of this in vitro study was to evaluate the surface roughness and the adaptation of 5 different housing orientation materials to the housings and the denture base. MATERIAL AND METHODS: Fifty-five poly(methyl methacrylate) (PMMA) specimens (15 mm in diameter and 4 mm in height) were prepared with a clearance inside to allow the insertion of overdenture housings. Five different materials were used for housing orientation (Quick Up, Ufi Gel Hard, Tokuyama Rebase II Fast, Meliodent, and Paladent). The specimens were thermocycled 5000 times between 5°C and 55°C. The surface roughness (Ra values) of the specimens was measured with a noncontact profilometer. Scanning electron images were made in order to inspect the PMMA-orientation material-housing interfaces. The Kruskal-Wallis test was used to investigate the differences between the surface roughness values of the orientation materials, and the Iman-Conover test was used for pairwise comparisons (α=.05). RESULTS: The surface roughness values significantly differed between Quick up and Ufi Gel orientation materials only, and Quick up had smaller surface roughness values than Ufi Gel (P=.009). Microcracks were observed among the groups only at the junction of the orientation material and the housing after thermocycling. CONCLUSIONS: Ufi Gel Hard showed the roughest surfaces around the overdenture attachment housings. The adaptation between the orientation material and the housing may deteriorate, and increased surface roughness and microcrack formation may be seen around the housings.

The Effect of Ytterbium-Doped Fiber Laser with Different Parameters on Physical Properties of Zirconia Surface.

OBJECTIVE: Laser irradiation is an alternative surface treatment method for roughening zirconia surfaces. The aim of this study was to evaluate the effects of ytterbium-doped fiber laser (YbPL) on zirconia. BACKGROUND: Zirconia surfaces are resistant to many surface treatment methods, but surface roughness is crucial for adhesion of veneering materials and cements to zirconia. METHODS: The zirconia discs were prepared and divided into four groups according to the power of the laser irradiation (5, 12, 17, and 20 W). These groups were divided into five subgroups according to the frequency (25, 40, 60, 80, and 100 kHz). Surface roughness values were measured with a noncontact profilometer, and the mean Ra values were calculated. Wettability was measured with a goniometer. The surface morphology was observed with a scanning electron microscope (SEM). The changes in the surface crystalline structure were analyzed with X-ray diffractometry. RESULTS: Ra values of all groups were higher than the control group. The highest surface roughness value was at 20 W and 100 kHz. Best wettability characteristic was observed at 5 W and 60 kHz. The correlations between Ra and wettability were low but significant. SEM examination of 5 W with different frequencies showed no microcracks, however, melted areas were observed. Remaining groups had microcracks and melted layers. A significantly lower T/M-phase transformation was observed in some groups. CONCLUSIONS: YbPL irradiation was effective at roughening the zirconia surface. Although laser treatment affected zirconia surfaces and provided surface roughness, the power and frequency should be adjusted to achieve optimum results.

Effects of crown retrieval on implants and the surrounding bone: a finite element analysis.

PURPOSE: The aim of this study was to observe stress concentration in the implant, the surrounding bone, and other components under the pull-out force during the crown removal. MATERIALS AND METHODS: Two 3-dimensional models of implant-supported conventional metal ceramic crowns were digitally constructed. One model was designed as a vertically placed implant (3.7 mm × 10 mm) with a straight abutment, and the other model was designed as a 30-degree inclined implant (3.7 mm × 10 mm) with an angled abutment. A pull-out force of 40 N was applied to the crown. The stress values were calculated within the dental implant, the abutment, the abutment screw, and the surrounding bone. RESULTS: The highest stress concentration was observed at the coronal portion of the straight implant (9.29 MPa). The stress concentrations at the cortical bone were lower than at the implants, and maximum stress concentration in bone structure was 1.73 MPa. At the abutment screws, the stress concentration levels were similiar (3.09 MPa and 3.44 MPa), but the localizations were different. The stress at the angled abutment was higher than the stress at the straight abutment. CONCLUSION: The pull-out force, applied during a crown removal, did not show an evident effect in bone structure. The higher stress concentrations were mostly observed at the implant and the abutment collar. In addition, the abutment screw, which is the weakest part of an implant system, also showed stress concentrations. Implant angulation affected the stress concentration levels and localizations. CLINICAL IMPLICATIONS: These results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.

Macro design effects on stress distribution around implants: a photoelastic stress analysis.

OBJECTIVES: Biomechanics is one of the main factors for achieving long-term success of implant supported prostheses. Long-term failures mostly depend on biomechanical complications. It is important to distinguish the effects of macro design of the implants. MATERIALS AND METHODS: In this study, the photoelastic response of four different types of implants that were inserted with different angulations were comparatively analyzed. The implant types investigated were screw cylinder (ITI, Straumann AG, Basel, Switzerland), stepped cylinder (Frialit2, Friadent GmbH, Manheim, Germany), root form (Camlog Rootline, Alatatec, Wilshelm, Germany), and cylindrical implant, with micro-threads on the implant neck (Astra, AstraTech, Mölndal, Sweden). In the test models, one of the implants was inserted straight, while the other one was aligned mesially with 15° angles. The superstructures were prepared as single crowns. A 150N loading was applied to the restorations throughout the test. RESULTS: A comparison of the implant designs showed that there were no significant differences between the straight implants; however, between the inclined implants, the most favorable stress distribution was seen with the stepped cylinder implants. The least favorable stress concentration was observed around the root formed implants. Microthreads around the implant neck appeared to be effective in a homogenous stress distribution. Observations showed that misaligned implants caused less stress than straight implants, but the stress concentrations were not homogenous. CONCLUSION: As there were observable differences between the implant types, straight placed cylindrical implants showed better stress distribution characteristics, while inclined tapering implants had better stress distribution characteristics.