This review was intended on major factors contributing to abutment screw loosening. A search of Pubmed and Google Scholar, as well as a manual search, was conducted. Publications and articles accepted for publication up to February 2020 were included. Out of 150 studies retrieved, a total of 57 were selected for this review. Dental implants are associated with a complexity of abutment screw loosening. Implantologists and prosthodontists should be aware of factors that contribute to this problem. In this review previously identified factors were collected, the consideration of which can help to reduce the frequency of abutment screw loosening.
PURPOSE To investigate the fracture resistance of monolithic CAD-CAM all-ceramic surveyed crowns with two different occlusal rest seat designs. MATERIALS AND METHODS Two maxillary first premolar were prepared for all-ceramic surveyed crowns with wide (2/3 rd of buccolingual width of an unprepared tooth) or narrow (1/3 rd of buccolingual width of an unprepared tooth) disto-occlusal rest seat (ORS) designs. Eighty monolithic CAD-CAM all-ceramic surveyed crowns were prepared and divided into 4 groups - Group CR, Composite resin material as a control; Group LDS, Lithium disilicate based material; Group ZIPS, zirconia-material (IPS ZirCAD); and Group ZLHT, zirconia- material (CeramillZolidht+). Crowns were cemented on an epoxy resin die with adhesive resin cement. The fracture resistance of crowns was tested with the universal machine. Univariate regression analysis was used. RESULTS The mean ± standard deviation of maximum failure force values varied from 3476.10 ± 285.97 N for the narrow ORS subgroup of group ZIPS to 687.89 ± 167.63 N for the wide ORS subgroup of group CR. The mean ± standard deviation of maximum force was 1075 ± 77.0 N for group CR, 1309.3 ± 283.9 N for group LDS, 3476.1 ± 285.97 N for group ZIPS, and 2666.7 ± 228.21 N for group ZLHT, with narrow occlusal rest seat design. The results of the intergroup comparison showed significant differences in fracture strength with various material groups and occlusal rest seat designs ( P <.001). CONCLUSION The zirconia-based all-ceramic surveyed crowns fractured at more than double the load of Lithium disilicate based crowns. The crowns with narrow base occlusal rest seat design had statistically significantly higher fracture resistance than surveyed crowns with wide occlusal rest seat design. The use of narrow occlusal rest seat design in CAD-CAM all ceramic surveyed crowns provides higher fracture resistance, and therefore narrow occlusal rest design can be used for providing esthetics with high strength.
BACKGROUND: The aesthetics and strength of anterior porcelain layered zirconia (PLZ) crowns are mainly affected by the zirconia (Zr) coping design. There is a need for a modified design to enhance aesthetics with strength. OBJECTIVES: The purpose of this study was to compare the fracture resistance of anterior PLZ crowns having modified CAD-CAM Zr coping designs (in terms of thickness and marginal collar designs) with standard Zr copings. METHODS: Fifty PLZ crowns were fabricated and divided into two groups: Gr 1: Standard Zr Coping (SZC) (control gr) with 0.5 mm thickness (Facial-F, Mesial-M, Distal-D, incisal-I, and Palatal-P) without a collar; Gr 2: Collar Zr Coping (CZC) (test gr) with 2.5 mm collar height on M, D, P and 0.2 mm F and variable facial wall thickness. Subgroups: Gr 2a: (CZC-0.5 mm) facial wall thickness 0.5 mm; Gr 2b: (CZC-0.4 mm) facial wall thickness 0.4 mm; Gr 2c: (CZC-0.3 mm) facial wall thickness 0.3 mm; Gr 2d: (CZC-0.2 mm) facial wall thickness 0.2 mm. The fracture load was determined and analysed using One-way ANOVA and Dunnet test. RESULTS: The minimum fracture load was 927.36 ± 127.80 N observed for Gr 2c (CZC at 0.3 mm) while the maximum fracture load was 1373.61 ± 146.54 N observed for Gr 2a (CZC at 0.5 mm). A highly significant difference in mean fracture load among various Zr coping groups (p< 0.001) was determined. CONCLUSIONS: Novel Zr coping design for anterior PLZ crowns can provide better aesthetics with strength. Reducing the thickness of Zr coping in the aesthetic zone to 0.2 mm and providing a modified collar design (2.5 mm collar height on M, D, P, and 0.2 mm F) would provide strength without jeopardizing aesthetics.
Microleakage is a persistent problem despite advancement in materials and techniques in fixed prosthodontics. This leads to the importance of sound crown foundation material and luting agents used to maintain the marginal seal. The literature is deficient with studies, comparing microleakage under various crown foundation materials and luting agents, especially with CAD-CAM (computer-aided design and computer-aided manufacturing) metal crowns. This study was aimed to compare microleakage in a nanocomposite/dentinal bonding agent and amalgam/cavity varnish as crown foundation materials luted with two different luting cements: resin-reinforced glass ionomer cement and self-adhesive resin cement, under both dry and contaminated conditions. A hundred intact, caries-free human molars were prepared to receive crown foundation material and extra coronal restorations. Amalgams with cavity varnish and nanocomposites with dentinal bonding agent in both ideal and contaminated conditions were used as crown foundation materials. After restoration, each sample was cemented with a CAD-CAM milled metal crown using two different luting agents—resin-reinforced glass ionomer cement and self-adhesive resin cements both in ideal and contaminated conditions. Cementation was followed by thermocycling of samples, immersion in erythrosine B dye, embedding in clear auto polymerizing acrylic resin and sectioning to evaluate microleakage using stereomicroscope. The mean microleakage between different luting cements on the experimental side of the facial surface was 137.64 μm and 211.01 μm for resin-reinforced GIC and for self-adhesive resin cement was 119.78 μm and 150.42 μm, under ideal and contaminated condition, respectively. There was a significant difference in mean micro-leakage between different crown foundation material and cement groups used in the study. The composites and amalgam, both when used as crown foundation material and luted with use of technically advanced CAD-CAM metal crown with self-adhesive resin cement (in both ideal or contaminated condition), showed less microleakage than in resin-reinforced glass ionomer cement. Overall, the self-adhesive resin cement showed comparatively reduced microleakage in all combinations with different crown foundations. Thus, this combination can be used in daily clinical practice to provide better protection from further decay.
Aim: This report describes the challenges experienced in a unique case involving dental esthetics, and the treatment provided to achieve satisfactory conservative treatment. Background: Even minor aspects of dental esthetics can significantly affect a patient's quality of life. Moreover, the patient's level of satisfaction with rehabilitative dentition and prosthetics affects oral health, daily living, and dental perceptions. It is not unusual for clinicians to encounter cases with complex esthetics that have affected the patient's life. Such cases need careful treatment planning to meet the patient's expectations. Conservative treatment should be the clinician's goal, because complex treatment may result in negative outcomes. Case description: Here, the patient exhibited severe bone loss due to cleft palate, as well as improper positioning of the teeth. He could not be treated with implants because of poor bone quality and quantity. Orthodontic treatment was performed, but did not improve the outcome. A wax-up was made for each of the three possible options, and then transferred to the patient's mouth by making a mock-up. This allowed the patient to clearly understand the results of each option. After selecting an option, we performed the procedure on the cast before it was undertaken in the patient's mouth. This helped us to precisely determine the preparation needed for all teeth. Teeth were saved where possible to preserve the remaining bone. The lost bone was replaced with pink porcelain. Treatment was conservative and the results were optimal for the patient and our clinical team. Conclusion: In some cases, clinicians may have few options available to achieve satisfactory results. However, the use of appropriate diagnostic tools, data collection, and conservative treatment procedures can help achieve these goals. Clinical significance: Fabrication of wax-ups and mock-ups can help the clinician and patient predict the results of dental treatment and ensure a conservative procedure.
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