Preliminary assessment of metal-porcelain bonding strength of CoCrW alloy after 3wt.% Cu addition.

In this work, a novel Cu-bearing CoCrW alloy fabricated by selective laser melting for dental application has been studied. For its successful application, the bonding strength of metal-porcelain is essential to be systematically investigated. Therefore, the aim of this study was to evaluate the metal-porcelain bonding strength of CoCrWCu alloy by three-point bending test, meanwhile the Ni-free CoCrW alloy was used as control. The oxygen content was investigated by an elemental analyzer; X-ray photoelectron spectroscopy (XPS) was used to analyze the surface chemical composition of CoCrW based alloy after preoxidation treatment; the fracture mode was investigated by X-ray energy spectrum analysis (EDS) and scanning electron microscope (SEM). Result from the oxygen content analysis showed that the content of oxygen dramatically increased after the Cu addition. And the XPS suggested that Co-oxidation, Cr2O3, CrO2, WO3, Cu2O and CuO existed on the preoxidated surface of the CoCrWCu alloy; the three-point bending test showed that the bonding strength of the CoCrWCu alloy was 43.32 MPa, which was lower than that of the CoCrW group of 47.65 MPa. However, the average metal-porcelain bonding strength is significantly higher than the minimum value in the ISO 9693 standard. Results from the SEM images and EDS indicated that the fracture mode of CoCrWCu-porcelain was mixed between cohesive and adhesive. Based on the results obtained in this study, it can be indicated that the Cu-bearing CoCrW alloy fabricated by the selective laser melting is a promising candidate for use in dental application.

Assessment of Posterior Teeth Preparations for Metal-Ceramic Crowns.

OBJECTIVES: To evaluate teeth preparation designs for metal-ceramic crowns in private dental practice in Jordan. MATERIALS AND METHODS: One-hundred and seventy two dies were included. Different aspects of tooth preparations were quantified, analyzed and compared with the recommended guidelines. RESULTS: Almost 64% of preparations finish lines were positioned subgingivally. Shoulder finish lines were observed in 74.4% where-as 22.7% showed chamfer finish lines. Total occlusal convergence angles were 29.8 degrees in BL plane, 247 degrees in MD plane. CONCLUSIONS: Dental practitioners in private practice in Jordan did not fully adhere to the recommendedguidelines for tooth preparations for MCRs.

Students' self-assessment: a learning tool and its comparison with the faculty assessments.

OBJECTIVE: This study compared the student's self-grades versus the examiners grades, inter examiner grades and grades of anterior with posterior teeth in a preclinical prosthodontic course. METHODS: 75 students and 2 examiners participated in the study. The students prepared one anterior (upper central incisor) and one posterior (lower first molar) teeth for full veneer crowns in allocated time of 2 hours and 30 minutes. After the preparations, the students self-graded their preparations based on criteria-based evaluation forms. The examiners also completed the grading for the prepared teeth. All the grades were recorded, comparisons were made using SPSS version 21 and results tabulated. RESULTS: The means of grades (8.32) by the students themselves were found to be higher compared to the examiners grades (7.3) for the anterior as well as posterior teeth. Comparison of the grades for the anterior/posterior teeth and the overall grades showed a statistically significant difference (p=0.000). A moderate correlation (0.399) and a strong correlation (0.601) were found between the grades of the faculty and the students for the anterior and posterior teeth respectively. The overall grading for the anterior and posterior teeth by the two faculty members showed no statistically significant difference (p=0.053) and a very strong correlation (0.784). The results of the test showed a significant difference (p=0.001) between the overall grading for anterior and posterior teeth. CONCLUSION: Students tended to grade their teeth preparations higher compared to the examiner grades, inter examiner variation in the grades existed and the grades of the anterior teeth were higher compared to the posterior teeth.

Digital data acquisition for a CAD/CAM-fabricated titanium framework and zirconium oxide restorations for an implant-supported fixed complete dental prosthesis.

This dental technique report describes a digital workflow with digital data acquisition at the implant level, computer-aided design and computer-aided manufacturing fabricated, tissue-colored, anodized titanium framework, individually luted zirconium oxide restorations, and autopolymerizing injection-molded acrylic resin to fabricate an implant-supported, metal-ceramic-resin fixed complete dental prosthesis in an edentulous mandible. The 1-step computer-aided design and computer-aided manufacturing fabrication of titanium framework and zirconium oxide restorations can provide a cost-effective alternative to the conventional metal-resin fixed complete dental prosthesis.

Recreating an esthetically and functionally acceptable dentition: a multidisciplinary approach.

Patients today demand a youthful, attractive smile with comfortable functional acceptance. The complete oral rehabilitation of patients with a functionally compromised dentition frequently involves a multidisciplinary approach and presents a considerable clinical challenge. To a great extent, proper patient selection and careful interdisciplinary treatment planning, including acknowledgment of the patient's perceived needs, reasons for seeking services, financial ability, and socioeconomic profile, can govern the predictability of successful restorations. This clinical report describes a successful interdisciplinary approach for the management of a severely worn dentition with reduced vertical dimension of occlusion. Treatment modalities included periodontal crown lengthening procedures, endodontic treatment followed by post and core restorations, and prosthetic rehabilitation for severe tooth surface loss and reduced vertical dimension of occlusion comprising metal-ceramic restorations in esthetic zones and full-metal restorations in posterior regions.

Maximum dislodging forces of mandibular implant-assisted removable partial dentures: in vitro assessment.

PURPOSE: The initial retention of implant-assisted removable partial dentures (IARPDs) is unknown. The purpose of this in vitro study was to compare maximum dislodging forces of distal extension mandibular IARPD with two different attachments and three clasp designs. MATERIALS AND METHODS: A simulated class I partially edentulous mandible was prepared with two screw-type 3.75 × 12 mm implants in the first molar regions and 2 metal-ceramic crowns on distal abutments. Fifteen bilateral distal extension frameworks were conventionally fabricated in three clasp designs (suprabulge, infrabulge, no clasp). Locator attachments were connected to the 15 denture bases with autopolymerized resin. Each specimen was subject to four types of retention pulls (main, anterior, posterior, unilateral pull) five times with a universal testing machine. Locator attachments were replaced with O-ring attachments, and the same procedure was performed. Therefore, the study groups included: IRPD with Locator attachment and suprabulge clasp (group 1), IRPD with Locator attachment and infrabulge clasp (group 2), IRPD with Locator attachment and no clasp (group 3), IRPD with O-ring attachment and suprabulge clasp (group 4), IRPD with O-ring attachment and infrabulge clasp (group 5), IRPD with O-ring attachment and no clasp (group 6). Data were analyzed using one-way ANOVA, two-way ANOVA, and Tukey tests. RESULTS: The highest mean value was 22.99 lb for prostheses with a Locator attachment and suprabulge clasp. The lowest retentive values were recorded for IARPDs with O-ring attachments. CONCLUSION: The results of this in vitro study suggest that the precise selection of attachments with or without clasp assemblies may affect the clinical success of mandibular IARPDs.

Assessment of convergence angle of full-coverage porcelain fused to metal crowns in clinical practice.

BACKGROUND: Full-coverage porcelain fused to metal crowns is commonly recommended for restoration of extensively damaged teeth. Ability of the dentist to adequately prepare teeth is fundamental to success and longevity of these restorations. AIMS: This study was designed to compare recommended convergence angle and taper values of tooth preparation with clinically practiced values and to assess the factors such as tooth position, operator experience, vitality, and restorative status on convergence angle of prepared teeth. SETTING AND DESIGN: It was a descriptive, cross-sectional study design and held at The Aga Khan University Hospital, Dental Section, for a period of 1 year. MATERIALS AND METHODS: A minimum of 197 crown preparation models of molar and premolar teeth prepared by residents and specialists were collected in order to achieve the objectives of the study on the basis of convenient sampling technique. STATISTICAL ANALYSIS: One sample t-test used to compare the mean practiced convergence angle values with its recommended values. Independent sample t-test and one-way ANOVA was used to see difference in the convergence angle values of the teeth prepared by different operators, tooth type, vitality status, and restorative status of teeth. RESULTS: Mean reported convergence angle and axial wall taper values were 23.7° ± 8.9° and 11.3° ± 7.8°, respectively, which is significantly greater (P<0.001) than the recommended values. Convergence angle values were greater for molars as compared to premolars. CONCLUSION: There was a considerable disparity between the convergent angles values recorded in this study and the recommended guidelines and are affected by tooth type, vitality, and restorative status of tooth.

Current paradigm shifts in dentistry.

It is a time of revolution and innovation in dentistry. Many of the ongoing changes are significant, while others are less influential. I have discussed numerous observable and inevitable paradigm shifts. Dentists are advised to note the ongoing trends, become educated about them, evaluate the importance of the changes in their individual practices and to their patients, and to integrate these changes into practice.

Avaliação das condutas adotadas por profissionais na utilização de coroas metalo-cerâmicas / Assessment of clinical proceedings adopted by dental professionals regarding the employment of ceramic fused to metal crowns

A fim de avaliar a opinião da classe odontológica sobre a utilização das coroas metalo-cerâmicas na prática odontológica, aplicou-se um questionário de 20 questões a cirurgiões-dentistas da cidade de Aracaju - SE, e a cirurgiões-dentistas e estudantes de pós-graduação em odontologia, na área de prótese dental, da cidade de Bauru-SP. Concluiu-se que: 1. As coroas metalo-cerâmicas são o tipo de restauração protética mais empregado em Odontologia. 2. A maioria dos dentistas refere-se às coroas metalo-cerâmicas como restaurações bem sucedidas, indicando superfícies oclusais metálicas para a maioria dos pacientes. 3. Apesar da maior parte dos profissionais utilizar as ligas de níquel-cromo nas coroas metalo-cerâmicas de seus pacientes, os mesmos prefeririam que ligas nobres ou semi-nobres fossem empregadas em suas próprias restaurações. 4. A maioria dos entrevistados emprega as coroas metalo-cerâmicas na restauração de dentes anteriores (57,23 por cento). Entretanto, esse valor se deve à preferência dos dentistas de Aracaju (78 por cento) por esse tipo de restauração, ao passo que, em Bauru, prevaleceu o número de respostas favoráveis às coroas de porcelana pura. 5. O cimento de fosfato de zinco foi o cimento de escolha da maioria dos profissionais. 6. A preferência da maior parte dos entrevistados, com relação à porcelana utilizada foi pela porcelana Vita (34,34 por cento), em comparação às porcelanas Noritake e Dulceram Plus (13,86 por cento). 6. Ficou evidente o desejo dos entrevistados quanto ao desenvolvimento de mecanismos que facilitem o reparo das coroas metalo-cerâmicas.

The confusing array of tooth-colored crowns.

The venerable PFM crown or fixed prosthesis still dominates the tooth-colored restoration market. However, use of PFMs is declining slightly, as the many new all-ceramic and resin-based composite crowns and fixed-prosthesis products flood the market. Several situations may indicate the use of materials other than PFM. They include patients requiring a high level of esthetic acceptability, patients with proven or perceived allergies to the metals used in dentistry and bruxing or clenching patients with metal allergies or desire to eliminate metal from their mouths. PFM restorations have been proven during 40 years of successful use. They provide acceptable esthetics for most situations, minimal fracture during service, proven ability to serve in multiple-unit situations and excellent fit, and the profession has detailed knowledge of these restorations' advantages, disadvantages and physical characteristics. PFM restorations have only a few well-known negative characteristics. Be cautious as you elect to move from the reliability and positive history of PFM to relatively unknown types of restorations.

New die design for dimensional accuracy assessment of crown castings.

PURPOSE: The aim of this study was to introduce a newly designed die for ceramometal restoration, and to compare the dimensional accuracy with the traditional complete-crown design. Two methods of dimensional accuracy assessment, vertical axial discrepancy and transverse diametral percentage, were compared. MATERIALS AND METHODS: Patterns were prepared from two different die designs--complete crown and ceramometal. Two investments available for titanium crown casting were used, Titavest CB and T-invest C & B. Titanium castings were made from each investment with a high-pressure casting machine. Vertical axial discrepancy of casting was determined by measuring the discrepancy for each set of wax patterns and their castings on the same die under a traveling microscope. Dimensional accuracy was expressed as vertical axial discrepancy and by transforming the vertical axial discrepancy into transverse diametral percentage. RESULTS: Both dies produced undersized castings with T-invest C & B and oversized castings with Titavest CB. Dimensional accuracy assessment of the two different types of crown casting design showed no significant difference in vertical axial discrepancy. CONCLUSION: Compared to the traditional transverse diametral percentage calculation, the vertical axial discrepancy assessment is independent of the die's dimensions. The two types of investment materials studied resulted in castings with different dimensional accuracies.

Assessment of clinical preparations for single gold and ceramometal crowns.

OBJECTIVE: Single-crown preparations at a dental teaching hospital were compared with guidelines advocated in the dental literature. METHOD AND MATERIALS: Sixty-three single complete gold crown and 151 single ceramometal crown preparations were evaluated. Impression silhouettes were measured for occlusal and axial wall tooth reductions, shoulder widths, internal shoulder angles, and axial wall convergence angles. Marginal designs, the presence of retention grooves and undercuts, and the types of cores present were also recorded. RESULTS: Cuspal reduction was generally inadequate for the ceramometal crowns, and central fossa reduction was insufficient for both complete gold crowns and ceramometal crowns. The facial shoulder widths were also generally underprepared for the ceramometal crowns. Axial wall convergence angles for both complete gold crowns and ceramometal crowns were generally much greater than recommended. Large faciolingual convergence angles for anterior ceramometal crowns were associated with the absence of cingulum walls. Few preparations had retention grooves or undercut areas. CONCLUSION: Although strict guidelines for tooth preparations for complete crowns are available and well known to dentists, the preparations in this study did not always conform to these recommendations.

Approaches for intraoral repair of ceramic restorations.

Ceramic-based restorations are an important part of a dentist's armamentarium for durability and esthetics. Because of the brittle nature of ceramic materials, these restorations have the potential to fracture. Repairing ceramic-based restorations can increase the clinical longevity of failed restorations and offer the dentist and patient a cost-effective alternative to replacement. Newer porcelain repair systems show excellent adhesion durability of resin-based composites to the fractured ceramic and exposed metal surfaces. This article reviews the basic principles of ceramic repair and details the use of five intraoral porcelain repair systems.

Gold color in dental alloys.

This article will help the dental laboratory with alloy selection by exploring how the relationship among color, ductility and strength applies to gold and how color can be quantified. Because higher quality materials translate into higher profits, upselling to the dentist and patient is also discussed.

Alternatives to gold.

Despite, or perhaps because of, its antiquity the lost wax casting process which we use in dentistry still produces the most accurate and durable restorations in our armamentarium. Although high-gold content alloys still act as the benchmark of quality, fit, and durability in the aggressive conditions of the mouth, their inherent cost, high density and low modulus have stimulated a search for alternatives. This has ranged widely through the metallurgical world and across the periodic table of the elements. As a result dental alloys for casting into inlays, crowns and bridges (with or without facings of dental porcelain) have become incredibly complex. This article will explain some of the reasons behind the developments.