Types Of Crowns Research Articles

Comparative Evaluation of the Effect of Implant Crown Materials on Implant Components and Bone Stress Distribution: A 3D Finite Element Analysis.

Choosing implant crown materials for restoration remains challenging in clinical practice. This study assesses the impact of all-ceramic restoration instead of porcelain-fused-to-metal (PFM) restoration on the stress distribution within implant components and the surrounding bone. Four 3D models of a mandibular second premolar were meticulously prepared. The study groups comprised zirconia, lithium disilicate, and zirconia lithium silicate monolithic ceramic crowns cemented onto a zirconia hybrid abutment. A PFM crown cemented onto a cementable abutment was chosen as the control group. A total vertical load of 583 N was applied to the occlusal contact areas. Stress distribution within the crown and implant components was analyzed using von Mises stress analysis. Principal stress analyses were employed to assess stress distribution in the peripheral bone. The PFM model exhibited the highest von Mises stress values for both the implant (428.7 MPa) and crown (79.7 MPa) compared to the other models. The all-ceramic models displayed the highest maximum von Mises stress within the abutment, approximately 335 MPa, compared to the PFM model. von Mises stresses of the abutment and implant in the all-ceramic models were 69% higher and 20% lower, respectively, than those in the PFM model. Screw stresses were relatively consistent across all groups. Principal stresses in spongy bone and minimum principal stress in cortical bone were consistent across all models. All-ceramic restoration with a hybrid abutment, as opposed to traditional PFM restoration with a cementable abutment, does not adversely affect the implant and abutment screw and reduces crown stresses. Stresses within hybrid abutments were notably higher than those within cementable abutments. Spongy bone stresses remained unaffected by the type of crown or abutment.

The Comparison of Fracture Resistance between Low Translucent and Ultra-High Translucent Monolithic Zirconia Crown

Abstract Objective From the beginning of its discovery, the monolithic zirconia crown was highlighted for its remarkable strength; therefore, only available in opaque color. During the past decade, the translucent monolithic zirconia crown was manufactured to meet the aesthetic and restoration demand but was thought to be the cause of decreasing its strength. This study aimed to compare the fracture resistance between two types of translucent monolithic zirconia crowns, that is, low translucent monolithic zirconia (LT) and ultra-high translucent monolithic zirconia (UHT). Material and Methods The premolar crown model was prepared using a computer-aided design/computer-aided manufacturing system, producing 1 mm of thickness. Ten crown samples were divided into LT and UHT. Then, each sample was measured for its fracture resistance using Universal Testing Machine until a fracture occurred. The differences in fracture resistance were analyzed using an independent t-test with p < 0.05. Result The LT showed a higher fracture resistance than UHT (p < 0.05). Conclusion The LT monolithic zirconia crown has strength and can be used for posterior crown restoration.

Evaluation of the marginal adaptation and debonding strength of two types of CAD-CAM implant-supported cement-retained crowns

BackgroundIn-vitro data from a clinically well-known lithium disilicate ceramic reference was used to assess the expected performance of resin-based materials in implant dentistry. The purpose of the study was to compare the bond strength and marginal adaptation of nano-ceramic hybrid composite crowns cemented to stock cement-retained abutments to lithium disilicate crowns.MethodsTwenty abutment analogs were embedded into auto-polymerizing acrylic resin blocks. The blocks were divided into 2 groups according to the restorative crown material. The 2 groups were divided as follows: Resin nano-ceramic group and lithium disilicate group. Abutment analogs in both groups were scanned using a laboratory scanner, and the restorations were designed, manufactured, and cemented with resin cement over the corresponding group. All samples were tested for marginal adaptation and bond strength after storage for 24 hours at 37 °C in 100% humidity. Data were collected, tabulated, and statistically analysed using the appropriate tests. Normality was checked using Shapiro Wilk test and Q-Q plots. Data were normally distributed. Variables were presented using mean, 95% Confidence Interval (CI) and standard deviation in addition to median and Inter Quartile Range (IQR). Differences between groups regarding debonding forces was assessed using independent t test. Two Way ANOVA was performed to assess the effect of material and bonding on marginal gap. All tests were two tailed and p value was set at < 0.05.ResultsMarginal gap and debonding force values were significantly different according to the type of material used (P < .05). Resin nano-ceramic crowns presented lower marginal gap values before (20.80 ± 8.87 μm) and after (52.11 ± 22.92 μm) bonding than lithium disilicate crowns. The debonding force value for resin nano-ceramic crowns (284.30 ± 26.44 N) was significantly higher than that for lithium disilicate crowns (253.30 ± 33.26 N). Adhesive failure mode was detected in all the specimens in both groups.ConclusionsThe type of material used for implant-supported cement-retained crowns had a statistically significant effect on marginal adaptation and bond strength. Resin nano-ceramic implant-supported cement-retained crowns had better marginal adaptation and higher bond strength than those manufactured using lithium disilicate.

Er:YAG laser debonding of zirconia and lithium disilicate restorations

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations of different formulations are being used increasingly in monolithic form for a range of clinical applications. Using rotary instruments to remove such restorations for any purpose is challenging, but they can be removed conservatively with erbium lasers. However, studies on how a laser penetrates different zirconias to break the cement bond between the tooth surface and the zirconia are lacking. The purpose of this in vitro study was to evaluate and compare the time required for an erbium-doped yttrium-aluminum-garnet (Er:YAG) laser to remove different types of zirconia and lithium disilicate crowns. Forty extracted premolar teeth were prepared, scanned, designed, and milled to fabricate 40 computer-aided design and computer-aided manufacturing (CAD-CAM) crowns, which were assigned to 4 groups (n=10): 3mol% Y-TZP, 4mol% Y-TZP, 5mol% Y-TZP, and lithium disilicate as a control. All crowns were bonded to the teeth with a self-adhesive resin cement (Panavia SA Cement Universal). Each specimen was irradiated with an Er:YAG laser with the following parameters: 300mJ, 15Hz, 5.0W, and a 50-microsecond pulse duration (supershort pulse mode). The irradiation time required for crowns to be retrieved successfully was recorded for each specimen. Data were statistically analyzed using analysis of variance and the Tukey honestly significant difference post hoc test (α=.05). The intaglio surfaces of the restorations were analyzed using scanning electron microscopy (SEM). The mean ±standard deviation times in minutes needed for crown debonding were 12.46 ±4.17 for the 3mol% Y-TZP group, 10.30 ±3.33 for the 4mol% Y-TZP group, 4.03 ±1.62 for the 5mol% Y-TZP group, and 2.08 ±0.92 for the lithium disilicate group. A statistically significant difference (P<.05) in the debonding time was found for all investigated groups, expect between the 3mol% and 4mol% Y-TZP groups and between the 5mol% Y-TZP and lithium disilicate groups. SEM analysis of the ceramic surfaces showed no visual damage associated with Er:YAG laser irradiation. Zirconia crown retrieval time with the Er:YAG laser was influenced by the yttria content of the zirconia, with decreasing retrieval time with increasing yttria content. Er:YAG laser debonding of zirconia crowns is a noninvasive, efficient, and rapid approach to the removal of crowns and could be applied in clinical practice.

Quality of post and core placement by final year undergraduate dental students.

The success of endodontic restoration of badly compromised teeth depends on the quality of post and core placement and the extra-coronal restoration. Ensuring that students place posts to acceptable quality standards is therefore essential. The aim of this study was to radiographically evaluate post placement by final year undergraduate dental students and to identify any predictors of performance. Two hundred retrospectively and randomly selected posts placed by sixth year students were evaluated radiographically. Data on student gender; number and quality of radiographs; periapical pathology; tooth location; root canal treatment quality; amount of remaining gutta percha; gap between gutta percha and post; post-to-root width; crown-to-root ratio; and types of core material and crowns were recorded. Four criteria were used to grade post placement quality: (i) amount of remaining gutta percha; (ii) gap between gutta percha and post; (iii) post width to root ratio; and (iv) crown-to-root ratio. Assessments were scored to produce final grades. Data are presented using descriptive statistics and the chi-squared test was used to investigate whether student gender or tooth location were associated with final grade. Post and core quality was acceptable in most cases (97.5% were graded as adequate), with no differences in quality between male and female students nor according to tooth location (anterior, premolar, and molar). Just over half of radiographs were adequate quality (53.5%), while just under half were assessed as less than adequate (46.5%) due to cone cutting, overlap, shortening or elongation, although this did not affect formal assessment of post quality. General outcomes of post and core placement by undergraduate students were good, with few errors that might affect the prognosis and long-term survival of treated teeth. Providing undergraduate dental students with clear guidelines on when and how to take radiographs throughout the procedure may improve the quality of post and core treatment and reduce the risk of multiple unnecessary radiographic exposures. From the clinical perspective, although dental students generally place high quality posts and cores, it remains important to monitor the quality and performance of post placement as this determines the survival of compromised teeth.

Clinical and radiographic performance of preformed zirconia crowns and stainless-steel crowns in permanent first molars: 18-month results of a prospective, randomized trial

BackgroundThe treatment of young permanent first molars with extensive carious tissue loss may often require restoration with preformed crowns. This study compared the clinical and radiographic performance of stainless-steel crowns (SSCs) and preformed zirconia crowns (ZCs).MethodsForty-eight molar incisor hypomineralisation (MIH)- or caries-affected permanent molars in 20 healthy patients between 6–13-year-old were randomly divided into ZC and SSC groups (n = 24 teeth/group) in a split-mouth design. The oral hygiene levels of patients were assessed using Greene and Vermillion simplified oral hygiene index (OHI-S). Plaque accumulation and gingival health were evaluated using the Silness&Löe plaque index (PI) and Löe&Silness gingival index (GI), respectively. Clinical retention, marginal extension level, marginal adaptation of crowns and wear of the antagonist teeth were assessed at baseline, 1, 6, 12 and 18 months. The radiological assessments for evaluating the marginal adaptation of crowns and periapical pathology of crowned teeth were performed at 6 and 12 months. The data were analyzed using Kaplan–Meier analysis, Mann–Whitney U test, and two-way ANOVA.ResultsA total of forty teeth in 17 children were evaluated for 18 months. ZCs had significantly lower gingival and plaque index values than teeth restored with SSCs during all evaluation periods (p < 0.05). Neither crown type resulted in clinically-detectable wear on opposing dentition or periapical pathology. One ZC was lost at 13 months, while all SSCs survived in function clinically. The cumulative survival rates of ZCs and SSCs were 95.2% and 100% respectively.ConclusionsBoth ZCs and SSCs showed high clinical retention rates in young permanent molars. ZCs had lower plaque accumulation and better gingival health than SSCs, which were consistently associated with mild gingival inflammation.Clinical Trial Registration NumberNCT05049694.

Strength and Surface Characteristics of 3D-Printed Resin Crowns for the Primary Molars.

Some resin polymers available for three-dimensional (3D) printing are slightly elastic, which may be advantageous when used for full crown coverage of the primary teeth. This study was performed to evaluate the mechanical properties of two types of 3D-printed resin crowns in terms of strength and surface characteristics. Polymer resins used for temporary crowns (TCs) and temporary flexible dentures (TFDs) were tested. Digitally designed crowns with different thicknesses (0.4 and 0.6 mm) were 3D-printed. Milled zirconia crowns were used as the control. The static and dynamic fracture loads of the crowns were measured. The crown surface was evaluated using scanning electron microscopy. The average strength did not differ between the types of crowns. The differences between the dynamic and static fracture loads were insignificant. In the TC group, thicker crowns showed lower strength both under static and dynamic loads. After thermomechanical loading, microcracks and dropouts of macrofillers were detected on the surface of all types of resin crowns. The deposition of abraded debris occurred more in the TFD group. The 3D-printed resin crowns were thought to endure biting forces in children. However, some limitations of the material itself should be improved for consideration as a new treatment option in pediatric dentistry.

Paleoenvironmental inferences on the Late Miocene hominoid-bearing site of Can Llobateres (NE Iberian Peninsula): An ecometric approach based on functional dental traits

Hispanopithecus laietanus from the Late Miocene (9.8 Ma) of Can Llobateres 1 (CLL1; Vallès-Penedès Basin, NE Iberian Peninsula) represents one of the latest occurrences of fossil apes in Western mainland Europe, where they are last recorded at ∼9.5 Ma. The paleoenvironment of CLL1 is thus relevant for understanding the extinction of European hominoids. To refine paleoenvironmental inferences for CLL1, we apply ecometric models based on functional crown type (FCT) variables—a scoring scheme devised to capture macroscopic functional traits of occlusal shape and wear surfaces of herbivorous large mammal molars. Paleotemperature and paleoprecipitation estimates for CLL1 are provided based on published regional regression models linking average FCT of large herbivorous mammal communities to climatic conditions. A mapping to Whittaker's present-day biome classification is also attempted based on these estimates, as well as a case-based reasoning via canonical variate analysis of FCT variables from five relevant biomes. Estimates of mean annual temperature (25 °C) and mean annual precipitation (881 mm) classify CLL1 as a tropical seasonal forest/savanna, only in partial agreement with the canonical variate analysis results, which classify CLL1 as a tropical rainforest with a higher probability. The former biome agrees better with previous inferences derived from fossil plants and mammals, as well as preliminary isotopic data. The misclassification of CLL1 as a tropical forest is attributed to the mixture of forest-adapted taxa with others adapted to more open environments, given that faunal and plant composition indicates the presence of a dense wetland/riparian forest with more open woodlands nearby. The tested FCT ecometric approaches do not provide unambiguous biome classification for CLL1. Nevertheless, our results are consistent with those from other approaches, thus suggesting that FCT variables are potentially useful to investigate paleoenvironmental changes through time and space—including those that led to the extinction of European Miocene apes.

Clinical outcome of three different types of posterior all-ceramic crowns. A 3-year follow-up of a multicenter, randomized, controlled clinical trial.

To assess and compare the clinical outcomes of three different types of all-ceramic posterior monolithic tooth-supported crowns. A total of 71 patients received 90 all-ceramic crowns randomized to be either high-translucency zirconia (ZC), high-translucency zirconia with a partial buccal veneer (ZC-V), or lithium disilicate glass-ceramic (LDS). All treatments were performed by four general dentists. Choice of material was blinded. Baseline and subsequent annual evaluation were based on modified California Dental Association (CDA) criteria. A questionnaire was used to include patient-reported outcomes and to compare them to the crown quality rating performed by dentists. A total of 66 patients with 84 crowns were examined after 3 years. The survival rate was 98.8%. No crowns fractured during the observation period. One ZC-V crown failed due to loss of retention, and three complications were noted: loss of retention occurred in one ZC crown, and two ZC crowns needed to be endodontically treated. There was no significant difference between the different crowns regarding marginal integrity, surface, or anatomical form. Both patients and examining dentists rated the crowns favorably regarding esthetics, patients more than dentists. Posterior lithium disilicate glass-ceramic crowns and translucent zirconia crowns with or without a partial buccal veneer show excellent and promising clinical outcomes from a short-term perspective. Patients and dentists rate the restorations favorably concerning esthetics and function.

Are pediatric preformed zirconia crowns comparable to preformed metal crowns? A real-life retrospective study.

Although minimally and noninvasive caries management are advocated in pediatric dentistry, extensive caries progression often requires endodontic treatment followed by crowning of the tooth. Thus, the aim of this study was to evaluate the success of esthetic preformed zirconia crowns (PZCs) compared to the standard preformed metal crowns (PMCs) after pulpotomy in primary molars retrospectively. Patients' digital records in a specialized pediatric clinic in Germany were analyzed to include 2- to 9-year-olds, who had received one or more PMCs or PZCs after a pulpotomy between 2016 and 2020. The main outcomes were success, minor failure (restoration loss, wear, or fracture), or major failure (need for extraction or pulpectomy). In total, 151 patients with 249 teeth (PMC, n = 149; PZC, n = 100) were included. The mean follow-up time was (19.9 months), with 90.4% of the crowns followed for at least 18 months. The majority of the crowns were considered successful (94.4%). The differences in the success rates between PMCs (96%) and PZCs (92%) did not reach the level of statistical significance (P = .182). All minor failures (1.6%) were in the PZC group and located in the maxilla. Independent of crown type, especially first primary molars were prone to failure (7.9%; second primary molars, 3.3%). PMCs and PZCs both show high clinical success rates as restorations of primary teeth after a pulpotomy. However, there was a tendency of greater minor or major failure in the PZC group.

Comparative Evaluation of the Survival Rates of Zirconia Crown and Stainless Steel Crown for Proximal Caries in Primary Molars: a Retrospective Study

Due to increasing demand for aesthetics, zirconia crowns have become a popular choice for treating primary molars. However, there is limited literature available comparing the survival rates of zirconia crowns with those of other restorative materials. The objective of this study was to compare the 36-month survival rates of zirconia crowns and stainless steel crowns for proximal caries, as well as to analyze failure types associated with each crown type. Electronic medical records and radiographs of 1,061 primary molars from 498 patients treated with 2 types of prefabricated crowns at Chosun University Dental Hospital and 2 private dental clinics between 2017 and 2019 were collected and analyzed. The survival rate of zirconia crowns was found to be lower compared to that of stainless steel crowns. Regarding the groups without pulp treatment, the survival rate of stainless steel crowns was significantly higher than that of zirconia crowns. However, in the groups that received pulp therapy, no significant difference in the survival rates was observed between the two preformed crowns. Notably, abnormal root resorption or periapical lesions were identified as the primary cause of restorative failure in stainless steel crowns, whereas loss of restoration was the predominant cause in zirconia crowns. This study holds valuable implications for clinicians when selecting preformed crowns for primary molars.

Restorasi Estetik dengan Strip Crown pada Gigi Anterior Desidui (Laporan Kasus)

Background: Anterior dental caries affect masticatory function and aesthetics. The most popular type of aesthetic crown for the restoration of deciduous incisors is the strip crown. Purpose: to report the case of restoration of an aesthetic restoration with a strip crown on anterior primary teeth. Case: A 5.5-year-old boy comes with his mother with complaints of tooth decay. He never hurts and has never been traumatized. A clinical examination revealed that the teeth 52, 51, 61, and 62 had extensive dentinal caries in all parts. Diagnosis based on ICDAS is caries class 5. Case Management: The teeth were subjected to crown-strip restoration in two visits. The first visit was for teeth 51 and 61, and the second visit was for teeth 52 and 62. The teeth were cleaned with carious tissue, lining, and application of flowable composite resin with strip crown, polishing, and finishing. Conclusion: Strip crown restoration can be an alternative choice for primary anterior teeth where caries extends throughout the crown and improves aesthetic results.

Accuracy and margin quality of advanced 3D-printed monolithic zirconia crowns

Nanoparticle jetting (NPJ) is a novel ceramic 3D-printing technology with high printing accuracy. However, studies reporting the accuracy of zirconia crowns manufactured by NPJ and comparing them with conventional zirconia crowns are lacking. The purpose of this in vitro study was to evaluate and compare the trueness, crown fit, and margin quality of monolithic zirconia crowns manufactured by NPJ with those milled by a computer numerical control system. A gypsum left mandibular first molar was prepared and scanned with an intraoral scanner (TRIOS 4). Three types of monolithic crowns were manufactured through 3D printing and subtractive manufacturing (SM): NPJ (3D printing), VITA (milling), UPCERA (milling). The crowns were scanned, and the dimensional deviation (trueness) was evaluated and compared by using a software program. The triple scan method was used to measure crown fit and uniform index through precise alignment in the software program, and margin quality was also observed with an optical microscope. The data were analyzed with 1-way analysis of variance and the Tukey post hoc test (α=.05). The NPJ group reported better trueness of all crown and axial surfaces compared with the other SM group (P<.001), but marginal trueness (P=.601), intaglio surface (P=.596), and occlusal surface (P=.641) were statistically similar compared with the Vita milled group. All 3 groups reported clinically acceptable crown fit and uniformity with statistically similar values (P>.05). The NPJ group had more crowns judged to have flawless margin quality compared with the milled groups. All 3 manufacturing methods can fabricate zirconia crowns with a clinically acceptable crown fit. The NPJ system could be used to manufacture monolithic zirconia crowns with better margin quality and proximal surface trueness than milled crowns.

Shear bond strength of orthodontic metal brackets bonded to two different types of zirconium crowns: An in-vitro comparative study

Shear bond strength of orthodontic metal brackets bonded to two different types of zirconium crowns: An in-vitro comparative study

Metal artifact reduction and clinical verification in oral and maxillofacial region based on deep learning

Objective: To construct a kind of neural network for eliminating the metal artifacts in CT images by training the generative adversarial networks (GAN) model, so as to provide reference for clinical practice. Methods: The CT data of patients treated in the Department of Radiology, West China Hospital of Stomatology, Sichuan University from January 2017 to June 2022 were collected. A total of 1 000 cases of artifact-free CT data and 620 cases of metal artifact CT data were obtained, including 5 types of metal restorative materials, namely, fillings, crowns, titanium plates and screws, orthodontic brackets and metal foreign bodies. Four hundred metal artifact CT data and 1 000 artifact-free CT data were utilized for simulation synthesis, and 1 000 pairs of simulated artifacts and metal images and simulated metal images (200 pairs of each type) were constructed. Under the condition that the data of the five metal artifacts were equal, the entire data set was randomly (computer random) divided into a training set (800 pairs) and a test set (200 pairs). The former was used to train the GAN model, and the latter was used to evaluate the performance of the GAN model. The test set was evaluated quantitatively and the quantitative indexes were root-mean-square error (RMSE) and structural similarity index measure (SSIM). The trained GAN model was employed to eliminate the metal artifacts from the CT data of the remaining 220 clinical cases of metal artifact CT data, and the elimination results were evaluated by two senior attending doctors using the modified LiKert scale. Results: The RMSE values for artifact elimination of fillings, crowns, titanium plates and screws, orthodontic brackets and metal foreign bodies in test set were 0.018±0.004, 0.023±0.007, 0.015±0.003, 0.019±0.004, 0.024±0.008, respectively (F=1.29, P=0.274). The SSIM values were 0.963±0.023, 0.961±0.023, 0.965±0.013, 0.958±0.022, 0.957±0.026, respectively (F=2.22, P=0.069). The intra-group correlation coefficient of 2 evaluators was 0.972. For 220 clinical cases, the overall score of the modified LiKert scale was (3.73±1.13), indicating a satisfactory performance. The scores of modified LiKert scale for fillings, crowns, titanium plates and screws, orthodontic brackets and metal foreign bodies were (3.68±1.13), (3.67±1.16), (3.97±1.03), (3.83±1.14), (3.33±1.12), respectively (F=1.44, P=0.145). Conclusions: The metal artifact reduction GAN model constructed in this study can effectively remove the interference of metal artifacts and improve the image quality.

An 8-year retrospective study of fixed prosthodontics clinical unit completions in a postgraduate prosthodontics program.

The range of aesthetic fixed prosthodontics materials utilizing digital manufacturing techniques has expanded in recent years ostensibly replacing traditional laboratory techniques and materials. This retrospective study conducted over eight consecutive years aimed to analyze the types of laboratory fabricated fixed prosthodontics clinical units completed in a postgraduate prosthodontics specialist training program and determine meaningful trends. The logbooks of eight postgraduate prosthodontics completions from 2014 to 2021 were reviewed and the different types of laboratory fabricated fixed prosthodontics units and total number of fixed prosthodontics units completed were recorded. The data was categorized and presented in tabulated and chart form using Microsoft Excel software (version 2016). Paired t-tests and Mann-Kendall trend tests were performed to analyze for statistical significance between the different restoration types across the program completions. Porcelain bonded to metal (PBM) crowns represented 42.05% of all fixed prosthodontics units completed over all study years followed by all-ceramic crowns (ACC) (18.14%) and full gold crowns (FGC) (10.70%). Jointly, PBM, ACC and FGC's encompassed 70.88% of all fixed prosthodontics units. Over the 8-year study period, there were observed trends of reduced use of PBM's, increased use of ACC's, statistically significant reduced use of FGC's (p = 0.035) and a statistically significant difference in the use of complete and partial coverage restorations (p < 0.001). PBM crowns were the dominant laboratory fabricated fixed prosthodontic clinical unit across postgraduate prosthodontics program completions. The trend in later years indicating ACC as the dominant crown type warrants further investigation.

Radiopaque properties of polyetheretherketone crown at laboratory study

ObjectivesThere have been no reports on the radiopaque properties of new polyetheretherketone (PEEK) crowns for locating crowns during accidental ingestion or aspiration and detection of secondary caries, which is essential information for clinical application. This study aimed to investigate whether the radiopaque properties of PEEK crowns could be used to identify the site of accidental ingestion or aspiration and detect secondary caries. MethodsFour types of crowns were fabricated: three non-metal crowns (PEEK, hybrid resin, and zirconia) and one full metal cast crown (gold-silver-palladium alloy). Initially, the images for these crowns were compared using intraoral radiography, chest radiography, cone-beam computed tomography (CBCT), and multi-detector computed tomography (MDCT); computed tomography (CT) values were calculated. Subsequently, the images for the crowns placed on the secondary caries model with two artificial cavities were compared using intraoral radiography. ResultsThe PEEK crowns displayed the lowest radiopaque properties on radiography and very few artifacts were observed on CBCT and MDCT. On the other hand, the CT values of the PEEK crowns were a little lower than those of the hybrid resin crowns and considerably lower than the zirconia and full metal cast crowns. The cavity could be detected in the PEEK crown-placed secondary caries model through intraoral radiography. ConclusionsThis simulated study of radiopaque properties with four types of crowns suggested that a radiographic imaging system can be used to identify the site of accidental ingestion and aspiration of PEEK crowns and to detect secondary caries of the abutment tooth within a PEEK crown.

Influence of Different Cements and Cement Thickness on the Stress Distribution under Occlusal Surfaces of Porcelain-fused-to-metal and Porcelain-fused-to-zirconium Crowns: A Finite Element Analysis.

The purpose of this study is to compare and evaluate the influence of two different cement space settings and two different cement types on the stress distribution under occlusal surfaces of tooth restored with two different types of crowns and studied by using three-dimensional (3D) finite element analysis (FEA). Eight 3D finite element models (FEMs) representing a mandibular first molar tooth restored with crowns of, porcelain-fused-to-metal (PFM) and porcelain-fused-to-zirconia (PFZ) crowns with two cement space settings (50 and 80 µm) and with two different types of cement were constructed, using an FEA software (ANSYS, version 10). Each model was subjected to a distributed load simulating normal masticatory bite force of 225 N and was applied axial direction. Also, von Mises stress of each individual part in the system of models was calculated. The PFM crowns undergo less stress distribution than the PFZ crowns. The PFM crowns are more compatible with self-adhesive cements, and the PFZ crowns are more compatible with resin-modified glass ionomer cements. The PFM crowns with G-Cem Link Ace with 50 µm and PFZ crowns with RelyX Luting Plus with 80 µm combinations displayed less amount of stress distribution under normal masticatory bite force. Self-adhesive resin cements with PFM crowns and PFZ with resin-modified glass ionomer cements show more benefits in stress distribution under occlusal surfaces under normal masticatory bite force.

Assessment of the Amount of Nickel and Chromium Released from Two Types of Stainless Steel Crowns

Purpose: Estimate the release of Nickel and Chromium from two types of commercially available stainless steel crowns in artificial saliva. Materials and Methods: Twenty stainless steel crowns of fixed size (lower left E4) from two manufacturers were immersed in 10 ml of artificial saliva and stored in separate tubes in an incubator at 37°C for 21 days. The crowns were removed from each tube on every seven days, and were placed in other tubes with fresh artificial saliva. Flame Type Atomic Absorption Spectrophotometer was used to check for the release of metal ions in the solution inside each tube at the end of 1, 7, 14 and 21 days. Results : ANOVA test was used for analysis of results for the estimation of released Nickel and Chromium among the crowns . There was statistically verified difference in the release of Nickel and Chromium on different days in each of the group of SSCs tested. However, no significant difference was seen in the release of both metals among the groups. Conclusion: In all the SSCs tested, there was the release of Nickel and Chromium, but the total release of both the metals was below the critical level to cause any toxic effects, so the release of metal ions should not be an alarming concern for the use of any of the group of SSCs.

Assessment of the Amount of Nickel and Chromium Released from Two Types of Stainless Steel Crowns

Purpose: Estimate the release of Nickel and Chromium from two types of commercially available stainless steel crowns in artificial saliva. Materials and Methods: Twenty stainless steel crowns of fixed size (lower left E4) from two manufacturers were immersed in 10 ml of artificial saliva and stored in separate tubes in an incubator at 37°C for 21 days. The crowns were removed from each tube on every seven days, and were placed in other tubes with fresh artificial saliva. Flame Type Atomic Absorption Spectrophotometer was used to check for the release of metal ions in the solution inside each tube at the end of 1, 7, 14 and 21 days. Results : ANOVA test was used for analysis of results for the estimation of released Nickel and Chromium among the crowns . There was statistically verified difference in the release of Nickel and Chromium on different days in each of the group of SSCs tested. However, no significant difference was seen in the release of both metals among the groups. Conclusion: In all the SSCs tested, there was the release of Nickel and Chromium, but the total release of both the metals was below the critical level to cause any toxic effects, so the release of metal ions should not be an alarming concern for the use of any of the group of SSCs.