To compare clinically practiced convergence angle values of tooth preparation with recommended values, and also the effect of tooth position and operator experience on convergence angle.
Analytical ...study.
The study was carried out at the Dental clinic, The Aga Khan University Hospital, Karachi, from January to June 2007.
A minimum of 75 crown preparation dies including 25 dies in each group of teeth (anterior, premolars and molars) were collected retrospectively which were prepared by residents and specialists of operative dentistry. AutoCAD 2007 software was used for measurement of convergence angle. One sample t-test was applied to compare the mean practiced convergence angle values with its recommended values. Two way ANOVA was applied to measure difference in convergence angle values with respect to operator experience and tooth type with the level of significance being α=0.050.
Mean reported convergence angle value was 22.72°, which was significantly greater (p < 0.001) than the recommended values. Statistically significant difference in convergence angle was found between anterior vs. molar teeth and between premolars vs. molar teeth (p=0.0001 and p=0.002, respectively).
There was a considerable disparity between the convergent angles values recorded in this study and the recommended guidelines. Measured convergence angle values were greater for posterior teeth as compared to the anterior teeth.
Key Clinical Message
This case shows an excellent esthetic treatment outcome using implant‐retained crowns replacing maxillary laterals and canines in hypodontia patient with unusual incidence of ...spontaneous diastema closure after the placement of implants. To our knowledge, this is the first case report showing maxillary midline diastema closure after implant placement.
This case shows an excellent esthetic treatment outcome using implant‐retained crowns replacing maxillary laterals and canines in hypodontia patient with unusual incidence of spontaneous diastema closure after the placement of implants. To our knowledge, this is the first case report showing maxillary midline diastema closure after implant placement.
The purpose of this study was to evaluate the fit of metal ceramic crowns cast in Au-1.6
wt% Ti alloy and investigate the effect of abutment finish line curvature on the fit of crowns.
Three types of ...finish line curvature abutments were prepared (1, 3 and 5
mm-curvature). For each type of abutment, five metal ceramic crowns of the facial veneered type were fabricated, which were cast in Au-1.6
wt% Ti alloy. Used as controls, another fifteen specimens were made from a commercially available gold alloy. The fit was measured in the as-cast and after porcelain application.
In the as-cast specimens, the greater the finish line curvature was, the larger the gaps exhibited at the mesial and distal margins of copings, compared with labial and lingual margins. The distal margin of copings for 5
mm-curvature abutments showed the largest gap (35 (7)
μm). After porcelain application, the greater was the finish line curvature, the larger the labial marginal gap became (mean 44, 34, 25
μm, respectively, for 5, 3, 1
mm-curvature). However, there was no significant difference on marginal gaps between specimens of Au-1.6
wt% Ti alloy and control gold alloy.
This study indicated that the metal ceramic crowns cast in Au-1.6
wt% Ti alloy had equivalent accuracy to those that cast in control gold alloy, and the abutment finish line curvature had a significant effect on the marginal fit of metal ceramic crowns.
In an effort to improve health care outcomes, there has been a focused movement by national organizations such as the American Dental Association (ADA) to embed the principles of evidence-based ...dentistry (EBD) into mainstream care delivered by private practicing dentists. Although many dentists may garner benefits from EBD, some may encounter barriers including the time it takes to review evidence or identifying reliable resources. However, recent advances in electronic clinical decision support (CDS) have enabled busy and even novice EBD practitioners to implement the foundational elements of EBD and evidence-based decision making (EBDM) into clinical care. Evidence identified using CDS tools can be applied to implant and restorative dentistry treatment planning in the clinical setting and results discussed with patients during information-sharing doctor-patient consultations to make sound EBD-based health care decisions.
Long-term clinical failures of cemented prosthesis depend, to a large extent, on the integrity of the luting agent. The causative factors that lead to microfracture and, hence, failure of the luting ...agents are the stresses acting inside the oral cavity. Therefore, the present study was designed to develop an understanding of the relationship between stresses in the tooth and the failure potential of the luting agent. Two-dimensional finite element stress analysis was performed on the mandibular second premolar. The behavior of zinc-phosphate and glass-ionomer were studied under different crowns (metal-ceramic and metal crown) and loading conditions (mechanical force of 450 N acting vertically over the occlusal surface, thermal loads of 60° and 0°C). It was observed from the study that failure threshold of the luting agent was influenced both by the elastic modulus of the luting agent and by the type of the crown.
Amelogenesis imperfecta has been described as a complex group of hereditary enamel defects that disturbs the enamel structure and exists independent of any related systemic disorder. A 24-year-old ...male patient presented with discolored and hypersensitive teeth. The aim of the treatment was to reduce dental hypersensitivity and restore esthetics and masticatory function. The maxillary and mandibular teeth were prepared and metal ceramic crowns were cemented on the prepared teeth. The final treatment result provided the patient with improved dental esthetics and functional efficiency that enhanced his self-image.
The purpose of this investigation was to document the failure rate and length of service of crowns and fixed partial dentures (FPDs) fabricated in a Nigerian dental school. The reasons for failure of ...the initial restorations and their length of service were also ascertained. Also, the numbers of retainers, pontics, and the types of restoration were recorded. Poor esthetics was the most frequent cause of failure, 66 units (40.5%); followed by fracture, 58 units (35.6%); and dental caries, 25 units (15.4%). These outcomes were contrary to findings previously reported in studies from western countries where dental caries was principally responsible for failures (22.0% to 38.0% of cases). The resin-retained FPDs had the shortest mean years of service at 2.7 years, while the three-unit metal-ceramic FPDs had the greatest longevity at 8.6 years. The overall mean years of service for replaced restorations were 5.6 years. The study found a decrease in the mean years of service as the number of units in the fixed-fixed partial dentures increased. This is in sharp contrast to previous reports where no relationship existed between length of service and the number of units in a FPD.
A metal-ceramic crown used in the clinical stage is manufactured by burning the dental porcelain on the metal coping. Then the deformation of the crown is occurred by a hardening shrinkage and ...thermal shrinkage. Therefore, a study on deformation of the metal coping in the making of metal-ceramic crowns had been done by using the finite element method (FEM). As a result, the following conclusions were obtained. (1) Neighborhoods of ends of the collar extended into outsides of the crown. In particularly, the largest deformation was observed at ends of the collar. (2) Extension of neighborhoods of end of the collar increased with increasing the length of the collar. These results coincide with results of experiment.
Thirty-three crowns of similar size and shape were constructed to fit a standard brass die. Eleven crowns were manufactured from each of the following groups of materials: metal-ceramic, aluminous ...porcelain and a new all-ceramic system based on a glass infiltrated alumina coping. The overall fitting accuracy of each crown was determined using a low viscosity silicone paste, prior to cementation onto brass dies with zinc phosphate cement. The average film thickness was 95, 154 and 123 microns respectively. Each cemented crown was loaded to fracture. The mean load to failure of the glass infiltrated alumina crowns was significantly greater than that of the aluminous porcelain jacket crowns (P < 0.0001), but not significantly different from the metal-ceramic crowns.
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