The findings of this study suggest that an increase in the thickness of monolithic lithium disilicate or anterior monolithic zirconia restorations can significantly decrease the microhardness of the dual-cure resin cement polymerized beneath the restoration. Dual-cure resin cements can be used for the cementation of anterior monolithic zirconia restorations up to 2 mm thickness and for monolithic lithium disilicate restorations up to 2.5 mm thickness. However, for lithium disilicate restorations with a ≥2.5 mm thickness and zirconia restorations with a ≥2-mm thickness, different cementation approaches must be further studied, such as: extended light curing; the use of dual-cure resin cement with a higher self-curing component than the ones used in this study; or a self-cure resin cement.

Lower depth of cure was observed as the amount of transmitted light decreased in the investigated materials. In clinical practice, light-cured resin cements may result in inadequate polymerization for ceramic materials with lower TP values. Zirconia-reinforced lithium silicate and nanoceramic resins may be reliable restorative materials for a restoration with both optimal esthetics and sufficient mechanical strength resulting from proper polymerization.

With the introduction of dental implants to the market, varying restorative options have been successfully added for restoring the function and esthetics of both completely and partially edentulous patients. Accurate prosthodontic rehabilitation is the key factor for providing the long-term success and the survival of osseointegrated implants. Implantsupported restorations can be fabricated with different techniques. The prefabricated abutments provided by the implant companies are accepted as the gold standard because of their biocompatibility and advanced mechanical properties. However, especially for the anterior restorations, they are increasingly being replaced by custom abutments ideally prepared with CAD/CAM techniques; due to disadvantages of prefabricated abutments such as esthetic flaws, mechanical insufficiency resulting from implant placement, unacceptable emergence profile, and unhygienic regions formed under angled abutments. Currently, custom abutments are reported to have functional and esthetic advantages over prefabricated abutments. In this chapter, indications for proper abutment selection, contemporary production techniques, and different abutment materials will be stated, and the current research on the subject will be discussed.

Purpose The aim of the present study was to investigate the effects of the type and thickness of the zirconia material on the microhardness of the underlying dual-cure resin cement. Materials and Methods Eight disk-shaped zirconia specimens with a 4-mm diameter and four varying thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were fabricated from two different monolithic zirconia materials: posterior monolithic zirconia (Prettau) and anterior monolithic zirconia (Prettau Anterior). Dual-cure resin cement specimens with a 4-mm diameter and 5-mm height were prepared using Teflon cylinder molds and activated by light beneath the eight zirconia disks and without any zirconia disk for 20 s (n=12). A total of 108 specimens were embedded in acrylic. Vickers hardness of each specimen was measured at three different depths using a microhardness device with a 50-g load. All data were statistically evaluated using three-way ANOVA, one-way ANOVA, independent samples t-tests, and Bonferroni corrected post hoc tests (α=.05). Results Dual-cure resin cement's microhardness was significantly higher for the samples polymerized beneath anterior monolithic zirconia compared to posterior monolithic zirconia. The hardness decreased as the thickness increased for both types of zirconia; the latter was attributed to an attenuated curing efficiency. Conclusion Microhardness of the dual-cure resin cement is influenced by both the type and the thickness of the monolithic zirconia restoration. Polymerization efficiency for resin cement cured under anterior monolithic zirconia may be superior to cured beneath posterior monolithic zirconia.

This study aimed to investigate the effects of the different dental implant neck designs, diameters, and inclinations, on the stress distributions at the mandibular crestal bone and implant-abutment complex, using three-dimensional (3D) finite element stress analysis (FEA) method. Finite element models of three-unit fixed partial dentures supported with two same length implants (10 mm), placed on the second premolar and second molar regions, were designed. Eight different models were designed according to the implants’ neck designs (platform switching/traditional), diameters (4.1 mm/4.8 mm) and the tilting angles of the posterior implants (0°/15°). The anterior implants’ widths were 4.1 mm and the neck design of the anterior implants matched the posterior implants. Two types of 100-N loads in vertical and 30° oblique directions were applied separately onto each central fossae and functional cusps of the fixed partial dentures crowns. Algor Fempro Software was used for the simulation and evaluation of the stress levels at the implant-abutment complex and the crestal bone. Stress levels measured at the crestal bone were found to be lower for the platform switching models. However, the platform switching design generated higher stress magnitudes within the implant-abutment complex. Inclined placement of posterior implants increased the amount of stress at the crestal bone around both implants. Biomechanically, selection of the largest diameter possible when using tilted platform switched implants may be recommended at the posterior mandible.

ÖZET Amaç: Bu in vitro çalışmada; farklı "computer aided design/computer aided manifacturing (CAD/CAM)" materyallerinden hazırlanan implant destekli tam seramik kronların tutuculuk özelliklerinin incelenmesidir. Gereç ve Yöntemler: Her bir grupta 8 adet olacak şekilde 4 farklı CAD/CAM materyalinden (IPS e-max CAD-IPS, Vita Suprinity-VS, Vita Enamic-VE ve Vita YZ ST-ST) toplam 32 adet kron hazırlandı. Kronlar, zirkonya "abutment"ler üzerine rezin siman ile simante edildi. Kronların tutuculuk özellikleri, universal test cihazında her bir krona dikey yönde 1,0 mm/dk çekme hızıyla ayırma kuvveti uygulanarak test edildi ve desimantasyona sebep olan maksimum kuvvet belirlendi. Elde edilen veriler tek yönlü varyans analizi (ANOVA) ve post-hoc Tukey HSD testleri kullanılarak istatistiksel olarak karşılaştırıldı. İstatistiksel anlamlılık düzeyi p<0,05 olarak değerlendirildi. Bulgular: Gruplar arasındaki retansiyon kuvveti değerleri karşılaştırıldığında anlamlı farklar saptanmıştır (p<0,05). En yüksek retansiyon kuvveti VS grubunda elde edilmiş ve onu sırasıyla IPS, VE ve ST grupları izlemiştir. Sonuç: İmplant destekli tam seramik kronların tutuculuk özellikleri, protetik restorasyon için kullanılan materyal tipinden etkilenmektedir.Anah tar Ke li me ler: İmplant destekli kuron; tam seramik; retansiyon ABS TRACT Objective: The purpose of this in vitro study was to investigate the retention properties of implant supported full ceramic crowns prepared from different CAD/CAM restorative materials. Material and Methods: A total of 32 crowns, 8 in each group, were prepared from 4 different CAD/CAM materials (IPS e-max CAD-IPS, Vita Suprinity-VS, Vita Enamic-VE and Vita YZ ST-ST). Crowns were cemented on zirconia abutments with resin cement. The retention properties of the crowns were tested in a universal testing machine by applying a separation force at a cross-head speed of 1.0 mm/min in vertical direction and the maximum force leading to decementation was determined. The obtained data were statistically compared using oneway analysis of variance (ANOVA) and post-hoc Tukey HSD tests. Statistical significance was determined at p<0.05. Results: Significant differences were found among the groups with respect to the retention strengh values (p<0.05). The highest retention strength was obtained in the VS group followed by the groups IPS, VE, and ST, respectively. Conclusion: The retentive properties of implant supported full ceramic crowns were affected by the type of material used for prosthetic restoration.