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.

There is limited knowledge about the effects of ultrashort pulsed laser on zirconia ceramic surfaces. The aim of this study was to evaluate the effects of ytterbium (Yb)-doped fiber laser and other surface treatment methods -namely, sandblasting with 110 µm aluminum oxide or 30 µm silica-coated alumina on shear bond strength (SBS) of zirconia to tooth surface. A total of 128 zirconium oxide disks were made by using CAD-CAM technology. Disk surfaces were sandblasted with Al2O3 particles or silica-coated alumina or irradiated with Yb-doped fiber based nanosecond pulsed laser at 85W output power at 25 kHz. Disks were luted to dentin using two different resin cement. SBS of each specimen was measured. Results were statistically analyzed using two-way analysis of variance (ANOVA) and Bonferroni and Dunnett tests (p<0.005). Highest bond strength was obtained when zirconia surface was pretreated with Yb-doped fiber-based nanosecond pulsed laser regardless of the resin cement used.

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PURPOSEThe 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 METHODSTwo 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.RESULTSThe 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.CONCLUSIONThe 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 IMPLICATIONSThese results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.

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Dental ceramics have superior characteristics for fixed restorations. However, crack propagation and chipping are also common problems. Repair availability of a restoration would be advantagous for both clinician and patient.The aim of this study was to compare different repair techniques and materials. M Ma at te er ri ia al l a an nd d M Me et th ho od ds s: : Fifty specimens were fabricated from feldspathic ceramic. The specimens were divided into 5 groups (n=10) for different repair techniques. For the direct repair, a repair set was used and composite resin was applied using a silicone matrix. For indirect repair, the composite resin and ceramic repair components were prepared. All ceramic surfaces were etched with 40% phosphoric acid. For cementation of the repair ceramic and repair composite resin, a dual polymerized composite resin or a commercial cyanoacrylate (CA) was used. After cementation/CA application, all specimes were thermocycled. The shear test was performed with 5-mm/min crosshead speed. The shear bond strength values were recorded in Newton and converted into megapascal (MPa). Data (MPa) were analyzed using Kruskal-Wallis non-parametric test, and for the multiple comparisons, the Dunn test was used with Benforrini corrections (α=.05). R Re es su ul lt ts s: : The higher mean shear bond strength values were observed with the direct composite resin repair technique (20.73MPa), composite resin applied with CA (14.77 MPa), and ceramic cemented with dual-polymerized composite resin (14.98 MPa), The lowest shear bond strength value was observed with the ceramic-to-ceramic bonding with CA (8.59 MPa). C Co on nc cl lu us si io on n: : Direct repair technique showed the best shear bond strength values while other techniques can be used for interim solutions. K Ke ey yw wo or rd ds s: : Fixed partial denture; dental ceramics; repair; shear bond strength; cyanoacrylate Ö ÖZ ZE ET T A Am ma aç ç: : Dental seramikler sabit restorasyonlar için üstün özelliklere sahiptir. Ancak çatlak oluşumu ve kırıklar genel problemlerdendir. Restorasyonun tamir edilebilir olması hem klinisyen hem de hasta için avantajlı olacaktır. Bu çalışmanın amacı farklı tamir yöntemleri ve materyallerini karşılaştırmaktır. G Ge er re eç ç v ve e Y Yö ön nt te em ml le er r: : Feldspatic seramikten elli örnek hazırlanmıştır. Örnekler tamir yöntemlerine göre 5 gruba (n=10) ayrıldı. Direkt tamir yöntemi için tamir seti kullanılarak silikon matrix ile kompozit rezin uygulanmıştır. İndirekt tamir yöntemi için kompozit rezin ve seramik parçalar hazırlanmıştır. Tüm seramik yüzeylere %40 fosforik asit uygulanmıştır. Tamir seramiğini ve tamir kompozit rezini, dual polimerize kompozit rezin veya ticari siyanoakrilat (CA) ile siamnte edilmiş/yapıştırılmıştır. Tüm örneklere termosiklus uygulanmıştır. Makaslama testleri 5-mm/dak. hızda yapılmıştır. Makaslama kuvvetleri Newton cinsinden ölçülmüş daha sonra megapaskal (MPa) cinsine çevrilmiştir. İstatistiksel analizler (MPa) Kruskal-Wallis non-parametrik testi ile değerlendirilmiş, karşılaştırmalar...

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