ABSTRACT
This in vitro study was carried out to compare the cutting efficiency of diamond grinders on zirconia and resin-based composite materials. Grinders were employed with a special holder for the handpiece to apply a constant load (160 g) for resin-based composite (8 cuts, 40 s each) and zirconia materials (4 cuts, 5 min each; n = 10 for each material and grinder). To assess the efficiency of the grinders, weight measurements of the material were taken before and after the grinding process. Scanning electron micrographs were captured for instrument surfaces before and after testing and for the resulting surface of the materials. In the resin-based composite group, there were significant differences in weight removal between the burs for both the baseline (first cut; p = 0.009) and removal after the eighth cut (p = 0.049). Statistically significant decreases in weight removal compared to the baseline values were noted for the third, fourth, sixth, and seventh steps (p ≤ 0.046). For the zirconia group, significant differences existed in weight removal between the burs for the baseline (first cut; p < 0.001) and removal after the fourth cut (p < 0.001). A significant positive correlation was observed between removal and the number of cuts (Pearson: 0.673; p < 0.001). A statistically significant decrease in removal compared to the respective baseline value was found for the fourth step (p = 0.006). The initial wear removal and durability significantly differed between the grinders used on resin-based composite and zirconia. Achieving comparable weight removal took five times longer when grinding zirconia compared to the resin-based composite.
ABSTRACT
One therapeutical alternative in the treatment of functional disorders is the use of printed oral splints. The mechanical properties of these materials are highly essential to their clinical effectiveness, and their performance may vary depending on factors such as cleaning, post-polymerization, or their orientation during construction. The objective of this in vitro investigation is to evaluate the effectiveness of the selected materials in terms of their biaxial flexural strength in relation to the criteria listed above. Splint materials were used in the printing of 720 discs. The printing process was carried out in different orientations in relation to the building platform. Either an automatic or manual cleaning process was performed on the samples. For post-polymerization, either an LED or Xenon light was utilized. A piston-on-three-ball test was used to measure the biaxial flexural strength (BFS) of the materials after they were stored in water for either 24 h or 60 days. The homogeneity of the data was controlled by employing the Levene method, and the differences between the groups were analyzed using the ANOVA and Bonferroni methods. After being stored for twenty-four hours, the mean BFS ranged anywhere from 79 MPa to 157 MPa. Following a period of sixty hours, the BFS exhibited a substantial drop and revealed values that ranged from 72 to 127 MPa. There was no significant difference that could be identified between the materials or between the various cleaning processes. The results of post-polymerization showed that the LED light produced higher means than the Xenon light did. In terms of position, the mean values varied greatly, with 0°'s mean value being 101 MPa, 45°'s mean value being 102 MPa, and 90°'s mean value being 115 MPa. The use of a build orientation of 90° and post-polymerization with LED light resulted in significantly increased biaxial flexural strength. According to this study, this design should be implemented in order to ensure that splint materials have the highest possible strength.
ABSTRACT
Chipping of implant-supported molar crowns (iSCs) is a frequently reported complication. This study aimed to investigate the in-vitro aging and fracture resistance of iSCs with a CAD/CAM resin composite veneer structure fabricated with the Rapid Layer Technology (RLT) approach. Eight iSCs per group were fabricated by using two different CAD/CAM resin composites (Shofu Block HC: SH; Grandio blocs: GB) for veneer structures, and zirconia (ZrO2), polyetheretherketone (PEEK), and cobalt-chromium (CoCr; control) as framework materials. The surfaces to be bonded were sandblasted, cleaned in an ultrasonic bath, and a coupling agent was applied. A self-adhesive resin luting composite was used to adhesively lute the veneer structures to the frameworks. The crowns were semi-permanently cemented to the abutments. After storage in deionized water, iSCs were loaded in a chewing simulator (TCML, 10,000 thermal cycles 5 °C to 55 °C for 20 s, 1.2 million, loading force 50 N). Four ZrO2 and one CoCr crown did not survive the TCML. The fracture force was determined after 24 h storage in deionized water and yielded values of ≥974 N. Lowest fracture forces were yielded in the PEEK-SH group in comparison to CoCr or ZrO2 groups (p ≤ 0.031). For identical framework materials, no significant influence of the veneering material was observed. All PEEK-GB frameworks fractured, and chipping occurred for ZrO2-SH and all CoCr frameworks. PEEK-SH and ZrO2-GB presented both chipping and framework fractures. Within the limitations of this in-vitro study, the RLT with a CAD/CAM resin composite veneer structure might be a promising approach to veneer iSCs. Yet, the choice of the CAD/CAM resin composite and of the framework material determine the fracture resistance.
ABSTRACT
OBJECTIVES: To investigate stability and wear of tooth-supported zirconia single crowns with micro-layering in-vitro. MATERIALS AND METHODS: Molar crowns and specimens were fabricated from 5Y-TZP zirconia (Gen-X, Amann-Girrbach). Three groups were investigated: ML I: 0.1 mm cutback/painted/glazed (MiYO, Jensen); ML II: occlusal 0.3 mm cutback/painted/veneered/glazed (MiYO), and a monolithic control group (polished). After thermal cycling and mechanical loading (TCML), crowns were loaded to failure in a universal testing machine. Two-body wear test was performed. Wear (mean, maximum, antagonist) and roughness (Ra, Rz) were determined with a 3D laser-scanning-microscope. RESULTS: All crowns survived TCML. In the control (2501.5 N) and ML II group (1775.3 N) significantly lower fracture forces were observed than in ML I (3636.4 N) (p ≤ 0.003). Significant wear differences were found (p ≤ 0.001) but not for antagonist wear (p ≥ 0.202). Lowest wear was observed in the control group 10.2 ± 1.5 µm/28.8 ± 6.4 µm, ML I 112.8 ± 37.3 µm/152.9 ± 42.8 µm, and ML II 192.4 ± 49.1 µm/340.7 ± 54.2 µm. Roughness was characterized by a Ra from 1.6 µm (control) to 3.0 µm (ML II), and a Rz from 11.8 µm (Control) to 24.0 µm (ML II). Roughness significantly differed between control group and ML I (p = 0.002) as well as ML I and ML II (p = 0.020). CONCLUSIONS: Good in-vitro performance and fracture stability without chipping or fracture were found for all systems. Wear and roughness were comparable to conventional ceramic veneering systems. CLINICAL RELEVANCE: The micro-layering of zirconia restorations can be recommended, yet the micro-layering could be worn during clinical application.
Subject(s)
Crowns , Dental Porcelain , Ceramics , Zirconium , Materials TestingABSTRACT
Purpose To investigate aging and fracture resistance of screw-retained implant-supported single crowns (iSCs) fabricated from lithium disilicate containing virgilite (VLD). Materials and Methods iSCs were fabricated from VLD (CEREC Tessera, Dentsply Sirona) and lithium disilicate (control; n=8, e.max CAD, Ivoclar) and bonded to a Ti-base abutment. VLD crowns were luted either with (VLDc, n=8) or without (VLDw, n=8) a coupling agent. iSCs were cleaned, sterilized, and screw-retained on implants. Fracture force was determined after thermal cycling and mechanical loading (TCML). Results All crowns survived TCML. No significant differences in mean fracture forces were identified between VLDc 1583 N, VLDw 1694 N, and control 1797 N (P=0.639 ANOVA, P=1.000 Bonferroni). Conclusion Screw-retained iSCs fabricated from VLD provide acceptable stability, which is independent on the usage of a coupling agent for bonding to Ti-base abutments and sterilization. Int J Prosthodont 2023. doi: 10.11607/ijp.8369.
ABSTRACT
In the study the influence of different dental technical tools on the surface temperature and phase composition of fixed dental prostheses (FDPs) made of yttria-partially stabilized zirconia polycrystals (3Y-/4Y-/5Y-PSZ) was investigated. FDPs were fabricated by using computer-aided manufacturing (CAM). The FDPs were treated with a contra-angle handpiece equipped with different burs and polishers. The resulting surface temperatures were measured with a thermographic camera, and the resulting phase transformations were investigated by X-ray diffraction and quantified by Rietveld refinement. Processing with burs resulted in no phase transformation, but a preferred orientation shift. Using coarse polisher induced a phase transformation to the rhombohedral phase, while fine polishers produced no relevant phase transformations and no preferred orientation shift. Compared to the monoclinic phase (ca. 9% theoretical volume increase), which is associated with low-temperature degradation (LTD), the rhombohedral phase is much more voluminous (ca. 15% theoretical volume increase) and distorted and, therefore, has a greater degradation potential.
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Acid resistance of CAD/CAM resin composites. Erosion-related tooth surface loss is closely related to acid exposure, such as contact with acidic beverages or disease-related reflux. As a result, dental restorations in affected patients are also exposed to acids, which indicates that the performance and longevity of a dental restoration is impacted by the acid resistance of the individually employed restorative materials. However, unlike for ceramic materials, the acid resistance of CAD/CAM resin composites is not commonly evaluated by the manufacturers, and no standardised test methods have yet been established. Against this background, the present in vitro study aimed to examine the long-term resistance of CAD/CAM resin composites (Brilliant Crios, Cerasmart, Grandio blocs, Lava Ultimate, Shofu Block HC) against three acidic media (tonic water, acetic acid, hydrochloric acid) as well as demineralized water and to investigate potential damage mechanisms. Changes in surface roughness (Sa) were detected by confocal laser scanning microscopy (CLSM), and changes in surface hardness were measured using Vickers hardness (HV). The damage mechanisms were analysed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and micro X-ray computer tomography (µXCT). For each material, few changes in either Sa or HV were identified for at least one of the different media; for Cerasmart, the sharpest deterioration in surface properties was observed. SEM-EDS revealed leaching of barium, aluminium, and titanium from fillers in a 2 µm zone on the rough but not on the polished surface of the specimen. Within the limitations of the current study, it can be concluded that polished CAD/CAM resin composites can be recommended for clinical use in patients with erosive conditions.
ABSTRACT
Completely digital workflows for the fabrication of implant-supported removable restorations are not yet common in clinical dental practice. The aim of the current case report is to illustrate a reliable and comfortable workflow that reasonably merges conventional and digital workflows for the CAD/CAM-fabrication of implant-supported overdentures. The 53-year old patient was supplied with a digitally processed complete denture in the upper jaw and, simultaneously, with an overdenture supported by four interforaminal implants in the lower jaw. The overdenture included a completely digitally processed and manufactured alloy framework that had been fabricated by selective laser sintering. The case report indicates that digital manufacturing processes for extensive and complex removable restorations are possible. However, as it is currently not yet possible to digitally obtain functional impressions, future developments and innovations might focus on that issue.
