Newly-developed all ceramic and metal ceramic crowns are alternatives to conventional porcelain jacket crowns (PJC) and porcelain fused to metal crowns (PFM). Two types of metal ceramic crowns, made ...by sintering precious metals, were investigated as to adaptation and strength in clinical applications. The results were as follows: 1. The prime factors in adaptation of crowns are the method of impression used for making a duplication die with the HERATEC (HT) system, and the method of applying the bonding agent between duplication die materials and the metal of the DEGUSINT (DG) system. 2. The strengths of these new metal ceramic crowns depend on the thickness of the sintered metal layer. 3. The strength of the HT crown is equal to the value of PJC and is one-third that of PFM, while the strength of the DG crown is two times that of the HT crown and the PJC and 0.7 times that of PFM. 4. To increase the strength of these new crowns, with the HT system, the thickness of the sintered metal layer and the mechanical strength of Au-Pd layer must be increased, and the number and the diameter of bubbles in the metal ceramic conjunction layer, should be decreased. With the DG system, it is necessary to increase the mechanical strength of the sintered metals. Thus it is necessary to investigate the sintering conditions.
Objectives
The purpose of this clinical study was to describe outcome variables of all‐ceramic and metal‐ceramic implant‐supported, single‐tooth restorations.
Materials and methods
A total of 59 ...patients (mean age: 27.9 years) with tooth agenesis and treated with 98 implant‐supported single‐tooth restorations were included in this study. Two patients did not attend baseline examination, but all patients were followed for 3 years. The implants supported 52 zirconia, 21 titanium and 25 gold alloy abutments, which retained 64 all‐ceramic and 34 metal‐ceramic crowns. At baseline and 3‐year follow‐up examinations, the biological outcome variables such as survival rate of implants, marginal bone level, modified Plaque Index (mPlI), modified Sulcus Bleeding Index (mBI) and biological complications were registered. The technical outcome variables included abutment and crown survival rate, marginal adaptation of crowns, cement excess and technical complications. The aesthetic outcome was assessed by using the Copenhagen Index Score, and the patient‐reported outcomes were recorded using the OHIP‐49 questionnaire. The statistical analyses were mainly performed by using mixed model of ANOVA for quantitative data and PROC NLMIXED for ordinal categorical data.
Results
The 3‐year survival rate was 100% for implants and 97% for abutments and crowns. Significantly more marginal bone loss was registered at gold‐alloy compared to zirconia abutments (P = 0.040). The mPlI and mBI were not significantly different at three abutment materials. The frequency of biological complications was higher at restorations with all‐ceramic restorations than metal‐ceramic crowns. Loss of retention, which was only observed at metal‐ceramic crowns, was the most frequent technical complication, and the marginal adaptations of all‐ceramic crowns were significantly less optimal than metal‐ceramic crowns (P = 0.020). The professional‐reported aesthetic outcome demonstrated significantly superior colour match of all‐ceramic over metal‐ceramic crowns (P = 0.015). However, no significant differences in the other aesthetic parameters at various restoration materials were registered. After 3 years, the patient‐reported outcome variables at different restoration materials were not significantly different.
Conclusion
The biological outcomes at the zirconia and metal abutments were comparable. All‐ceramic crowns demonstrated better colour match, but higher frequency of marginal discrepancy compared to metal‐ceramic crowns. Generally, the patients noticed no difference in aesthetic outcome of all‐ceramic and metal‐ceramic restorations.
The dental bridges are often used to replace missing teeth. Currently, the most common are the metal-ceramic structures, which have the high mechanical properties and are aesthetic and functional, ...because they restore chewing efficiency by 85-100% and provide a high level of adaptation to them. However, in the presence of metallic and combined prostheses in the oral cavity, the pathological changes may occur, taking into account that in the oral cavity, the non-removable dentures are foriegn bodies affecting the tissues and the environment of the oral cavity. The effect of almost all artificial bridges on the tissues of the marginal periodontal disease depends on the level of the location of the bridge margin and the depth of the immersion under the gum. In the presence of such processes, the main factor is the specific antimicrobial protection, which is carried out by immunoglobulins; in the oral cavity, there are present only IgA, IgG, IgM of six classes. Thus, in the prosthetic dentistry one of the important problems is the connection of prosthetic constructions and the state of the oral cavity – homeostasis. The dental prostheses activate the lipid peroxidation and reduce the antioxidant defense factors. On the 7th day after bridge fixation, there is a significant decrease in the level of antioxidant enzymes and immunoglobulins and high concentrations of anti-inflammatory cytokines and interleukins. It is found that on the first stage of dental prosthesis the activity of lysozyme is sharply reduced and then restored very slowly. There is reduced not only non-specific reactivity (lysozyme), but also specific (lgA, IgG, and IgE) affected by dental prostheses, in particular, from acrylic plastics.
The clinical data of 46 patients, age between 29 – 73 years old (56% of women, 44% of men), which had the non-removable metal ceramic crowns and bridge prostheses, and the indicators of immune markers in the oral fluid were used. In a determination of IL-1β concentration in the saliva of the tested patients, there was found a significant increase by a factor of 12 in the control parameters, it indicates on the high activity of the monocyte-macrophage lineage cells. In the saliva, the increased content of IL-1β confirms its role in the local inflammatory process and indicates the activation of endothelial cells and connective tissue. In the group of patients, IL-6 salivary content exceeds the level in healthy people by 3.66 times, indicating a protective mechanism that is necessary for the initial phase of inflammation. The IL-6 high level is a prognostic adverse factor, which can indicate the progression of the inflammatory process and the increase of membrane-destructive disorders in the cells.
Monocytes and macrophages, activated by periodontopathogenic microbes, produce all cascade of proinflammatory interleukins, causing an imbalance between them. The damage of the periodontal tissue and resorption of the alveolar bone occur. In periodontal disease, the most damaging effect is characteristic for IL-1β and TNF-α.
In the saliva of patients, there was detected an increased TNF-α level by 2.89 times compared to control, that has a negative inotropic effect, stimulates apoptosis, and increases vascular wall permeability. In prolonged prosthesis in the saliva of patients, there was found the higher level of IL-4 than in healthy individuals by 1.24 times. IL-4 is an anti-inflammatory cytokine, an activator and chemokinetic factor for phagocytes.
The cytokines ensure the consistency and completeness of the immune response. Most of them induce inflammatory reaction and acute phase response of the organism and can exhibit the immunopathological effect on the tissues. At the systemic level, cytokines modulate the key protective reactions of the organism.
To radiographically evaluate the proximal marginal fit of the clinically acceptable metal-ceramic crowns.
The prospective study was conducted at the dental clinics of Aga Khan University, Karachi, ...from July to December 2018, and comprised metal-ceramic crowns that were evaluated prior to the cementation. Clinical examinations were conducted by seating the crown on the tooth preparation and visual assessment was done using sharp explorer along the margins. Clinically acceptable crowns were then evaluated on the bite-wing radiograph. Any horizontal or vertical inaccuracy of >0.5mm at the proximal margins was recorded as 'discrepancy'. Data was analysed using SPSS 22.
Of the 230 interproximal margins of 115 crowns evaluated, 113(49.1%) sites had marginal discrepancies; 44(19.1%) horizontal discrepancies, 58(25.2%) vertical discrepancies, and 11(4.8%) having both horizontal and vertical discrepancies. Horizontal crown margin discrepancies were most associated with the mesial site of the maxillary crowns, while vertical discrepancies were commonly associated with the distal aspect of all crowns (p<0.050).
Almost half of the crowns that were considered clinically acceptable had some vertical or horizontal marginal discrepancy on radiographic evaluation.
To evaluate the long-term clinical outcome of posterior metal-ceramic crowns fabricated with CAD/CAM-based laser-sintering technology (BEGO Medical, Bremen, Germany).
Sixty posterior crowns were ...placed in 39 patients. After tooth preparation, impression taking and model casting, the stone dies were scanned to create STL data, followed by manufacturing of crown frameworks with laser-sintering technology. A base metal alloy (CoCr) and a precious alloy (AuPt) were used for 31 and 29 posterior crowns, respectively, which were veneered using the layering technique. All crowns were cemented using glass-ionomer cement.
The mean observation period was 10.5 ± 3.9 years. Six patients with 10 crowns were regarded as dropout. Nine crowns had been removed, three of them were intact but they were removed due to a new prosthetic treatment plan. The cumulative survival rate of all crowns was 81% after 14.7 years. When comparing the survival rates related to the alloy used, the Gehan-Wilcoxon test showed no significant differences between both alloys. Biological complications were most commonly reported, while technical complications did not affect the function of the crowns.
The long-term clinical outcome of posterior metal-ceramic crowns fabricated with CAD/CAM-based laser-sintering technology is very promising, so that this novel technique could be an alternative to the traditional lost wax casting process.
Introduction: Marginal adaptation is the most critical item in long-term prognosis of single crowns. This study aimed to assess the marginal quality as well asthe discrepancies in marginal integrity ...of some PFM single crowns of posterior teeth by employing parallel radiography in Shiraz Dental School, Shiraz, Iran. Methods: In this descriptive study, parallel radiographies were taken from 200 fabricated PFM single crowns of posterior teeth after cementation and before discharging the patient. To calculate the magnification of the images, a metallic sphere with the thickness of 4 mm was placed in the direction of the crown margin on the occlusal surface. Thereafter, the horizontal and vertical space between the crown margins, the margin of preparations and also the vertical space between the crown margin and the bone crest were measured by using digital radiological software. Results: Analysis of data by descriptive statistics revealed that 75.5% and 60% of the cases had more than the acceptable space (50µm) in the vertical (130±20µm) and horizontal (90±15µm) dimensions, respectively. Moreover, 85% of patients were found to have either horizontal or vertical gap. In 77% of cases, the margins of crowns invaded the biologic width in the mesial and 70% in distal surfaces. Conclusion: Parallel radiography can be expedient in the stage of framework try-in to yield some important information that cannot be obtained by routine clinical evaluations and may improve the treatment prognosis
The aim of the present study was to objectively assess the variability in color reproduction of metal-ceramic (MC) single crowns fabricated by blending different color of opaque and body ceramic in ...order to point out which shade of the ceramic layers influences mostly the final color of the restorations. Eight nickel-chromium ceramic metal alloy copings were fabricated, on the same cast, following by blending the ceramic for the specific A3 color as follows: one reference ceramic (R) was blended, according to the producer s recommendation, and seven tests crowns have been build-up by considering as variables each one of the two uniform opaque layers, and dentin layer. Color of each manufactured crowns was measured after the three important steps of the technological workflow: the last opaque layer, enamel-dentin correction and final glaze firing using Vita Easyshade spectrophotometer. The best final color match (color difference of deltaE=0.8) was obtained for specimen no. 5, with a lighter opaque firs layer (A1). Fabricated specimens of all groups, except for no.4, with a darker dentin layer (A 3.5), showed deltaE values between 0.8 and 2.8, in the limit of the threshold perception in the oral cavity, and were scored as good. Within the limits of the present study, we can conclude that the dentin-enamel layer mostly influences the final color of the MC crowns.
(1) Background: Traditional metal-ceramic restorations are considered as a standard in the evaluation of new technologies. A critical factor in their longevity is represented by their adaptability; ...The purpose of this study was to evaluate the marginal and internal gap of ceramic-fused to metal crowns with frameworks obtained by additive manufacturing (AM) technologies and the influence of veneering process on their fit; (2) Methods: Metal-ceramic crowns have been produced by conventional lost-wax technology (T), digital milling (F), selective laser sintering (SLS) and selective laser melting (SLM). The adaptability was assessed using silicone replicas before and after ceramic veneering; (3) Results: The best values were obtained for the milled group followed closely by SLM and SLS, and a significantly higher gap for casted copings. The veneering process did not significantly influence the adaptability of the crowns, regardless of the manufacturing process used for frameworks. The present study promotes additive technologies (AT) as a fast, efficient, and cost-effective alternative to traditional technology. There are fewer steps in which errors can occur when digital technologies are used and the risk of distortion is diminished. (4) Conclusions: CAD/CAM technologies, both additive and subtractive, represent an excellent option to produce time-effective, precise metal-ceramic crowns with excellent adaptation.
Ceramic restoration experiences the non-linear wear process during the chewing simulation, which contains running-in, steady and severe wear stages. However since various levels of contact stress may ...be applied on the occlusal surface during chewing, the cycle-dependent wear behaviors of ceramic crowns may differ. The aim of this study was to investigate the effect of contact stress on the development of wear behavior, as tested in a chewing simulator.
Thirty-six anatomical metal-ceramic crowns using Ceramco III as the veneering porcelain were randomly assigned to two groups based on the contact stress applied in the wear testing. Stainless steel balls served as antagonists. The specimens were dynamically loaded in a chewing simulator up to 2.4×106 loading cycles, with additional thermal cycling between 5 and 55℃. For each group, several checkpoints were employed to measure the substance loss of the crowns’ occlusal surfaces and to evaluate the microstructure of the worn areas.
After 2.4×106 cycles, the ceramic restorations with lower contact stress demonstrated a long steady wear stage following the running-in, but without the severe wear stage. And a slowly microstructural degradation was observed that the subsurface defect could not be seen until final. With higher contact stress, however, the ceramic restorations experienced a faster transition from running-in to severe wear stage that the steady wear stage nearly disappeared. And an early formation of subsurface defects and the deterioration of microstructure were observed.
Contact stress is a key factor affecting the wear development of ceramic restoration. The higher contact stress promotes the veneering porcelain to evolve into severe wear stage. In contrast, lower contact stress is prone to keep the veneering porcelain operating in steady wear stage, which delays the arrival of severe wear region.
Display omitted
•The wear processes of porcelain in PFM crowns with different stresses were studied.•Contact stress is a key factor affecting the cycle-dependent wear behavior.•Higher contact stress promotes the porcelain to evolve into severe wear stage.•Lower contact stress is prone to keep the porcelain operating in steady wear stage.
PDF
