Assessment of All-Ceramic Dental Restorations Behavior by Development of Simulation-Based Experimental Methods

New dental materials are often introduced into the market and especially in the current practice, without a basic understanding of their clinical performance because long‐term controlled clinical trials are required, which are both time consuming and expensive. Ceramic materials are known for their relatively high fracture resistance and improved aesthetics, but brittleness remains a concern. The stressed areas of the materials are key factors for the failure analysis, and numerical simulations may play an important role in the understanding of the behavior of all‐ceramic restorations. Simulation‐based medicine and the development of complex computer models of biological structures are becoming ubiquitous for advancing biomedical engineering and clinical research. The studies have to be focused on the analysis of all‐ceramic restorations failures, investigating several parameters involved in the tooth structure–restoration complex, in order to improve clinical performances. The experiments have to be conducted and interpreted reported to the brittle behavior of ceramic systems. Varied simulation methods are promising to assess the biomechanical behavior of all‐ceramic systems, and first principal stress criterion is an alternative for ceramic materials investigations. The development of well‐designed experiments could be useful to help to predict the clinical behavior of these new all‐ceramic restorative techniques and materials

Optical Properties and Color Stability of Dental PEEK Related to Artificial Ageing and Staining

Considering that the processes of PEEK discoloration caused by either intrinsic or extrinsic factors require elucidation, the aim of this study was to investigate the long-term effect of the combined action of ageing and immersing solutions on the optical properties and color stability of PEEK material, related to surface processing (polishing or glazing). (2) Methods: This study aims to determine the influence of different ageing and staining protocols on optical properties, color changes, and surface roughness of a reinforced PEEK material (bioHPP, Bredent, Senden, Germany). For ageing, specimens were submitted to 5000 cycles in a 55 °C bath and a 5 °C bath filled with distilled water. For staining, thermal cycling was performed in a hot coffee bath (55 °C) and a bath filled with distilled water (37 °C) and in a cold juice bath (5 °C) and a bath filled with distilled water (37 °C). Translucency (TP) and opalescence (OP) parameters were determined, the total color change value (ΔΕ*) was calculated, specimens’ surface roughness was analyzed, and statistical analyses were performed. (3) Results: The mean TP values of the studied samples were in the interval of 1.25–3.60, which is lower than those reported for natural teeth or other aesthetic restoration materials. The OP values of PEEK were registered in the range of 0.27–0.75, being also lower than those of natural teeth or other aesthetic restoration materials. OP has a very strong positive relationship with TP. The mean registered Ra values for all subgroups were below 0.13 µm. Artificial ageing and staining in hot coffee proved to increase the roughness values. (4) Conclusions: The glazing of PEEK has a favorable effect on surface roughness and opalescence, irrespective of the artificial ageing or staining protocols. Artificial ageing damages the color stability and roughness of PEEK, regardless of surface processing, and decreases the translucency and opalescence of glazed surfaces. Immersion in hot coffee leads to perceivable discolorations

OCT and SEM imagistic investigations of composite resin-IPS empress ceramic interfaces

The purpose of this in vitro study is to evaluate the quality of repaired all ceramic IPS Empress e.max crowns. Excellent esthetics of all ceramic crowns is well known. One disadvantage of all ceramic restoration is the susceptibility to fracture due to brittle character of ceramic materials. Fracture of ceramic veneer may be repaired with composite resin or special designed ceramic material. Twenty four all ceramic crowns were made with IPS Empress e.max system. Fracture of ceramic veneer happens in the cervical, incise or functional (occlusal) area of metal-ceramic and all ceramic crowns. For simulating the fracture of ceramic veneers, defects of 2×2cm were made with a grinding instrument in the 1/3 incise area, on facial surface of each crown. All defects were repaired with Filtek Supreme (3M ESPE) composite resin. Samples were imagistic investigated by Optical Computer Tomography- Time Domain and Scanning Electron Microscopy. The interested areas were ceramic- composite resin interfaces. Longevity of all repaired ceramic crowns depends on interfaces integrity. Apparently intact, the ceramic-composite resin interface may display microscopic material defects which may lead to failure. Optical Coherence Tomography and Scanning Electron Microscopy are identifying and validate the micro-defects

Qualitative study of repaired metal ceramic crowns

The purpose of this study is to investigate the reparation of metal ceramic crowns with ceramic mass. 30 metal ceramic crowns which restore the upper first central incisor (2.1) were divided in three groups. Each group was repaired with a different ceramic material. Group 1- In Line (Ivoclar Vivadent) ceramic, the second group was repaired with D. Sign (Ivoclar Vivadent) and for the last group was used VMK. Master (Vita). All the repaired crowns were investigated through imagistic non-invasive methods. The metallic infrastructure of the samples was made from Ni-Cr alloy and the porcelain mass was Kiss (D. Sign). Defects were made on the buccal surface of each crown. The ceramic mass and the opaque were removed and the metallic infrastructure was exposed. Size defects has 3Ã?3mm and it is situated on incise and 1/3 medium buccal surface. The defect was made with a green grinding instrument under air-water cooling. All the samples were conditioned and repaired with ceramic mass. The reparations were investigated with two noninvasive imagistic methods Rx and Optical Coherence Tomography Time Domain in order to detect de reparation's defects. The investigation methods may spot the presence or absence defects localized at the interface between the two materials and those localized in the ceramic mass

Optical imaging of oral pathological tissue using optical coherence tomography and synchrotron radiation computed microtomography

The efforts aimed at early diagnosis of oral cancer should be prioritized towards developing a new screening instrument, based on optical coherence tomography (OCT), to be used directly intraorally, able to perform a fast, real time, 3D and non-invasive diagnosis of oral malignancies. The first step in this direction would be to optimize the OCT image interpretation of oral tissues. Therefore we propose plastination as a tissue preparation method that better preserves three-dimensional structure for study by new optical imaging techniques. The OCT and the synchrotron radiation computed microtomography (micro-CT) were employed for tissue sample analyze. For validating the OCT results we used the gold standard diagnostic procedure for any suspicious lesion - histopathology. This is a preliminary study of comparing features provided by OCT and Micro-CT. In the conditions of the present study, OCT proves to be a highly promising imaging modality. The use of x-ray based topographic imaging of small biological samples has been limited by the low intrinsic x-ray absorption of non-mineralized tissue and the lack of established contrast agents. Plastination can be used to enhance optical imagies of oral soft tissue samples

Imagistic evaluation of matrix bone interface

The problematic elements of bone regenerative materials are represented by their quality control methods. The defects repaired by bone grafting material were evaluated by en face optical coherence tomography and by synchrotron radiation micro-CT. The images obtained by efOCT show defects in some of the investigated samples, at the bone interface with different osteoconductive bone substitutes and we were able to detect gaps as small as 50 μm. After the common synchrotron radiation micro-CT investigations, the slides were reconstructed and the 3D model was obtained. Along with the possibility of navigating inside the structure, one big advantage of this technique was pointed out: the remaining regenerative materials can be separated from the normal bone and the new bone can be visualized. Optical coherence tomography can be performed in vivo and can provide a qualitative and quantitative evaluation of the bone augmentation procedure. © 2014 Copyright SPIE

Analysis of dental abfractions by optical coherence tomography

Aim and objectives. Abfraction is the pathological loss of cervical hard tooth substance caused by biomechanical overload. High horizontal occlusal forces result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause microfractures in the dental hard tissues, eventually resulting in the loss of cervical enamel and dentin. The present study proposes the microstructural characterization of these cervical lesions by en face optical coherence tomography (eFOCT). Material and methods: 31 extracted bicuspids were investigated using eFOCT. 24 teeth derived from patients with active bruxism and occlusal interferences; they presented deep buccal abfractions and variable degrees of occlusal pathological attrition. The other 7 bicuspids were not exposed to occlusal overload and had a normal morphology of the dental crowns. The dental samples were investigated using an eFOCT system operating at 1300 nm (B-scan at 1 Hz and C-scan mode at 2 Hz). The system has a lateral resolution better than 5 μm and a depth resolution of 9 μm in tissue. OCT images were further compared with micro - computer tomography images. Results. The eFOCT investigation of bicuspids with a normal morphology revealed a homogeneous structure of the buccal cervical enamel. The C-scan and B-scan images obtained from the occlusal overloaded bicuspids visualized the wedge-shaped loss of cervical enamel and damage in the microstructure of the underlaying dentin. The high occlusal forces produced a characteristic pattern of large cracks, which reached the tooth surface. Conclusions: eFOCT is a promising imaging method for dental abfractions and it may offer some insight on the etiological mechanism of these noncarious cervical lesions

En face OCT imagistic evaluation and laser microspectral analysis for assessing microleakage at the prosthetic interfaces

The microleakage at the prosthetic interface, for example between the metallic framework and the veneering part of the fixed partial prostheses (FPP's) is a common problem in dentistry. Optical tomographic techniques are of particular importance in the medical imaging field, because these techniques can provide non-invasive diagnostic images. En-face OCT is preferred for microscopy as it can provide real time images with similar orientation as that of microscopy images. The purpose of this study is to detect and analyze the possible defects at the interface of several FPP's using en face optical coherence tomography (efOCT) and laser microspectral analysis, a method which allows to investigate small quantities of materials of around 0.1 μg and to establish the content of atoms and molecules and to perform semi-quantitative and quantitative analysis. By this method it is possible to establish trace elements, i. e. with concentration of ppm (parts per million). The advantages of the OCT method consist in non-invasiveness and high resolution. En face OCT investigations permit to visualize a more complex stratified structure at the interface metallic framework/veneering material

IMAGING EVALUATIONS OF UNICA CERAMICS UNDER THERMAL CYCLE CONTROL CONDITIONS

Aim of the study: To evaluate the efficacy of Optical Coherence Tomography (OCT) in non-invasively monitoring temperature variations during ceramic sintering for dental prosthetics, emphasizing the importance of precise temperature control for optimal material properties and structural integrity. Materials and Methods: The study utilized OCT to examine 17 metal-ceramic restorations at various sintering temperatures (standard, 80°C below, and 50°C above the standard). The method involved generating 61 cross-sectional images per prosthesis to identify defects and structural changes. Results: OCT revealed significant insights into the impact of temperature deviations on ceramic microstructure, including uniform grain sizes at standard temperatures and areas of reduced retention at elevated temperatures, highlighting the technology’s potential in quality control. Conclusions: OCT offers a rapid, accurate, and non-destructive means to assess sintering temperatures and detect defects in dental ceramics, facilitating improvements in dental prosthetics’ fabrication process. The study advocates for OCT’s integration into routine dental laboratory practices to enhance prosthesis quality and reliability

Morphological characterization of dental prostheses interfaces using optical coherence tomography

Fixed partial prostheses as integral ceramic, polymers, metal-ceramic or metal-polymers bridges are mainly used in the frontal part of the dental arch (especially the integral bridges). They have to satisfy high stress as well as esthetic requirements. The masticatory stress may induce fractures of the bridges. These may be triggered by initial materials defects or by alterations of the technological process. The fractures of these bridges lead to functional, esthetic and phonetic disturbances which finally render the prosthetic treatment inefficient. Dental interfaces represent one of the most significant aspects in the strength of the dental prostheses under the masticatory load. The purpose of this study is to evaluate the capability of optical coherence tomography (OCT) to characterize the dental prostheses interfaces. The materials used were several fixed partial prostheses integral ceramic, polymers, metal-ceramic and metal-polymers bridges. It is important to produce both C-scans and B-scans of the defects in order to differentiate morphological aspects of the bridge infrastructures. The material defects observed with OCT were investigated with micro-CT in order to prove their existence and positions. In conclusion, it is important to have a non invasive method to investigate dental prostheses interfaces before the insertion of prostheses in the oral cavity