Two Years Retrospective Study of Metalceramic Crowns with Nickelchromium Alloy

Crown and bridge stability in the human mouth is not easy to evaluate. The structure and quality of crown materials are directly connected with the hardness and composition of the surface. The aim of the study was to evaluate the long-term stability of 52 crowns (19 patients) made from ceramic material (Vita Omega, Vita) and nickelchromium ceramic bonding metal alloy (Wiron, Bego) in clinical practice. In accordance with the US Public Health Service System changes in occlusal anatomy, occlusal relief, marginal adaptation, material break age, changes of shape and color, were checked. Another objective of the study was to observe the two year clinical progress of attrition of crowns. Replica casts (Epoxy-die (Ivoclar) were prepared. A scanning electron microscope (JEOL ; JMS-5500 LV (JEOL) and standard model (Ivoclar - Williams) were used to evaluate the quality of restoration. No changes in the shape and color were found, postop sensitivity was present in 1.9 %, and caries presence has been detected in 1.9 %. After two years the labial or buccal coronal margin was recorded as being at the level ofthe adjacent gingiva for 34.6 % of the 52 crowns placed and above the gingival margin for 65.4% of the crowns. Marginal adaptation was rated as contiguous with the existing anatomic form in 71.2 %. Gingival health varied from 0 to 2 CPITN index.Abrasion in fissures was visible in the scanning electron microscope. The cusps were well formed. Two fractures of the ceramic layer were observed. A significant increase in the position of the gingival margins was found, and varied from 45.0 μm to 108.3 μm vestibular 89.1 (SE12.1) to 63 μm oral (SE 7.0)

Artifacts In Magnetic Resonance Imaging and Computed Tomography Caused By Dental Materials

BACKGROUND: Artifacts caused by dental restorations, such as dental crowns, dental fillings and orthodontic appliances, are a common problem in MRI and CT scans of the head and neck. The aim of this in-vitro study was to identify and evaluate the artifacts produced by different dental restoration materials in CT and MRI images. METHODS: Test samples of 44 materials (Metal and Non-Metal) commonly used in dental restorations were fabricated and embedded with reference specimens in gelatin moulds. MRI imaging of 1.5T and CT scan were performed on the samples and evaluated in two dimensions. Artifact size and distortions were measured using a digital image analysis software. RESULTS: In MRI, 13 out of 44 materials produced artifacts, while in CT 41 out of 44 materials showed artifacts. Artifacts produced in both MRI and CT images were categorized according to the size of the artifact. SIGNIFICANCE: Metal based restoration materials had strong influence on CT and less artifacts in MRI images. Rare earth elements such as Ytterbium trifluoride found in composites caused artifacts in both MRI and CT. Recognizing these findings would help dental materials manufacturers and developers to produce materials which can cause less artifacts in MRI and CT images

Implant radiography and radiology

The practitioner placing dental implants has many options with respect to pre-implant radiographic assessment of the jaws. The advantages and disadvantages of the imaging modalities currently available for pre-implant imaging are discussed in some detail. Intra-oral and extra-oral radiographs are generally low dose but the information provided is limited as the images are not three-dimensional. Tomography is three-dimensional, but the image quality is highly variable. Computed tomography (CT) has been the gold standard for many years as the information provided is three-dimensional and generally very accurate. However, CT examinations are expensive and deliver a relatively high radiation dose to the patient. The latest imaging modality introduced is cone beam volumetric tomography (CBVT) and this technology is very promising with regard to pre-implant imaging. CBVT generally delivers a lower dose to the patient than CT and provides reasonably sharp images with three-dimensional information. A comparison between CT and CBVT is provided. Magnetic resonance imaging is showing some promise, but the examinations are not readily available, generally expensive and bone is not well imaged. Magnetic resonance imaging is excellent for demonstrating soft tissues and therefore may be of great use in identifying the inferior dental nerve and vessels. All of the above technology is of little value if the information required is not obtained and so information is also provided on imaging of some of the vital structures. Of particular interest is the inferior dental canal, incisive canals of the mandible, genial foramina and canals, maxillary sinus and the incisive canal and foramen of the maxilla