ABSTRACT
Statement of Problem: Metal-ceramic crowns are most commonly used as the complete coverage restorations in clinical daily use. Disadvantages of conventional handmade wax-patterns introduce some alternative ways by means of CAD/CAM technologies
Purpose: This study compares the marginal and internal fit of copings cast from CAD/CAM and conventional fabricated wax-patterns
Materials and Method: Twenty-four standardized brass dies were prepared and randomly divided into 2 groups according to the wax-patterns fabrication method [CAD/CAM technique and conventional method] [n=12]. All the wax-patterns were fabricated in a standard fashion by means of contour, thickness and internal relief [M1- M12: representative of CAD/CAM group, C1-C12: representative of conventional group]
CAD/CAM milling machine [Cori TEC 340i; imes-icore GmbH, Eiterfeld, Germany] was used to fabricate the CAD/CAM group wax-patterns
The copings cast from 24 wax-patterns were cemented to the corresponding dies. For all the coping-die assemblies cross-sectional technique was used to evaluate the marginal and internal fit at 15 points. The Student's t- test was used for statistical analysis [alpah=0.05]
Results: The overall mean [SD] for absolute marginal discrepancy [AMD] was 254.46 [25.10] um for CAD/CAM group and 88.08[10.67] um for conventional group [control]
The overall mean of internal gap total [IGT] was 110.77[5.92]um for CAD/CAM group and 76.90 [10.17] um for conventional group. The Student's t-test revealed significant differences between 2 groups. Marginal and internal gaps were found to be significantly higher at all measured areas in CAD/CAM group than conventional group [p< 0.001]
Conclusion: Within limitations of this study, conventional method of wax-pattern fabrication produced copings with significantly better marginal and internal fit than CAD/CAM [machine-milled] technique. All the factors for 2 groups were standardized except wax pattern fabrication technique, therefore, only the conventional group results in copings with clinically acceptable margins of less than 120um
ABSTRACT
Statement of Problem: After 30 years of intermittent reports in the literature, the use of fiber-reinforcement is just now experiencing rapid expansion in dentistry. However, there are some controversy reports in the amounts of flexural strength of fiber reinforced composites to use them as bridges
Purpose: The purpose of this study was to evaluate the flexural strength of three commercially available fiber-reinforced composites including Belle Glass, GC Gradia, and Signum
Materials and Method: Thirty uniform bars of 25x2x2 mm [10 for each group] were fabricated as their manufacturers recommended. Then all specimens were loaded to failure using a three-point bending test and flexural strength was determined
Results: The mean flexural strength of Belle Glass [386.65 MPa] was significantly [p < 0.0001] higher than that of GC Gradia [219.25 MPa] and Signum [172.89 MPa]. There was no significant difference between GC Gradia and Signum in flexural strength
Conclusion: On the basis of these findings, Belle Glass can be used in clinical practice with greater confidence compared to GC Gradia and Signum
ABSTRACT
A 22 year old female with chief complaint of tenderness of the masticatory muscles and joint sound referred to Prosthodontic Department of Shiraz Dental School. The patient expressed the history of nocturnal bruxism and pain in the masticatory muscles in early morning that decreased with time. In extraoral examination, there was no facial asymmetry and masseters of both sides were tender with palpation. In intraoral examination, excessive wear of the anterior and posterior teeth and several wear fascets on the posterior teeth wear were found. Overjet was 0 mm and overbite was -1mm which was due to excessive wear of the anterior teeth. There was a single click while opening and closing the mouth in the right TMJ, but both right and left TMJs were tender during examination. There were interferences in the centric relation both in the arc of closure and line of the closure. At first, stabilization appliance was made for the patient to relax the masticatory muscles and to reduce their pain. The patient wore the appliance for 4 months. Then occlusal equilibration was done for her in order to achieve bilateral, even and simultaneous contacts in the centric relation. After that without increasing the OVD, the upper and lower anterior teeth were reconstructed with composite resin so that in the excursive movements the anterior teeth could exclude the posterior teeth out of the occlusion. This treatment approach is affordable for patients because it minimizes the need for orthodontic and extensive prosthodontic treatments
ABSTRACT
Statement of Problem: Zirconia has been introduced as an appropriate structure for fabricating metal free copings. A major advantage of such restorations is esthetic concerns; however, due to its high strength, zirconia can also be used in posterior areas. One of the recent methods of making these restorations is CAD/CAM machines
Purpose: This study aimed to evaluate the fracture resistance of zirconia copings fabricated by two methods, CAD/CAM and slip casting
Materials and Method: 32 brass dies were fabricated for this study and divided into two groups of 16 dies each. Zirconia copings were made by CAD/CAM machine for one group and by slip casting method for the other. The copings were cemented to dies by a resin-modified glass ionomer [GC plus]. A hardened steel ball with a diameter of 5 mm was used to apply the load to the copings in the long axis of the dies at a crosshead speed of 0.5 mm/min. Then the amount of force needed to fracture each coping was recorded. Independent Sample T-test was used to compare the two groups
Results: The average of fracture resistance for the CAD/CAM group was 1411+/- 424 N and for the slip cast group it was 1542+/-412 N, having no significant difference [p > 0.05]
Conclusion: Zirconia copings made by CAD/CAM and slip casting methods have no significant difference in fracture resistance
ABSTRACT
The ability to produce multiple accurate casts from a single impression has been evaluated in a few impression materials. The aim of this study was to evaluate the effect of multiple casting in specific time intervals with three different elastomeric impression materials, on the dimensional accuracy. A stainless steel model composed of two dies with precut molar and premolar teeth were used in this study. The bigger die had a notch to reproduce undercut in order to study the elastic recovery. Seven impressions were made from this model by each of the following impression materials: Correct plus, Panasil [addition-cured silicones] and Speedex [condensation-cured silicone] according to manufacturer's instructions. The 21 impressions were poured in 30, 90, 150 minutes and 24 hours after impression taking. The stone casts were measured in six dimensions by an optical traveling, high precision [0.001 millimeter] microscope. The mean dimensions were compared with each other and the stainless steel model. For statistical analysis, Two-way ANOVA and Post Hoc tests were used to determine the significance levels. There were significant changes in most of the dimensions between the metal model and the first cast, but these changes were within the acceptable limits, according to ANSI/ADA Specification No. 19 for impression materials. No significant difference was observed between almost all of the dimensions of the second, third and fourth casts when compared with the first cast of each impression material [P>0.05]. The only significant difference was detected between the fourth cast and the first cast of Speedex in one dimension. Based on these results, four casts from Correct plus and Panasil as well as three casts from Speedex could be considered as acceptable from clinical stand points
Subject(s)
Dental Impression Materials , Molar , BicuspidABSTRACT
Statement of problem: Surface changes of ceromers caused by tooth brushing are well established, meanwhile they have been improved and are now widely used for various kinds of prosthetics restorations. These materials have lower surface hardness than porcelain and may induce discoloration due to surface roughness. Since it is an important clinical problem, more investigations are needed to evaluate their surface roughness
Purpose: The aim of this study was to evaluate the effect of tooth brushing on abrasive wear and surface roughness of two current used ceromers
Material and Method: Ten specimens of each type of the ceromer [Belleglass and Gradia] were prepared. All the specimens were examined and surface roughness [Ra] of each was recorded. Then tooth brushing abrasion test were performed with 500 gr weight applied, using a dentifrice containing calcium carbonate as the abrasive material. The surface roughness of each specimen after 20000 strokes were determined with Talysurf 10. Data were analyzed with two sample T test and non parametric Wilcoxon test
Results: Mechanical toothbrushing decreased the surface roughness of Gradia [p<0.05], but did not have any effect on the surface roughness of Belleglass [p>0.05]
Conclusion: The results of this study showed that Belleglass is more resistant to abrasive wear but Gradia is a more polishable ceromer
ABSTRACT
In this article, a telescopic implant- supported fix partial denture, and its seven years follow-up is reported. A 42 years old lady with edentulous free end space in the right quadrant of her lower jaw was refferd for construction of implant supported prosthesis. After implant insertion and osseointegration, the implants showed severe mesiodistal and buccolingual tiltation in the manner that might not be corrected by extensive preparation or using angled abutments. Telescopic copings were made to correct the angulation of the abutments and the path of insertion in order to allowed the construction of a suitable prosthesis. The prosthesis is functional and healthy after seven years follow-up
Subject(s)
Humans , Female , Dental Prosthesis, Implant-Supported/methods , Follow-Up Studies , Severity of Illness IndexABSTRACT
Background: The most important factor in fabrication of a perfect crown is having a perfect margin, which matches completely with finish line preparation and has a good situation in relation to the alveolar bone crest. To control the quality of the fixed prostheses made in a dental clinic in Shiraz, there was an attempt to assess the quality of their margins
Materials and Method: Radiography was used to check this quality. Parallel periapical radiography was made from the 102 crowns and bridges after cementation and before discharging the patients. To measure the magnification, a metal ball with 4mm diameter was attached on the crowns at the line of their proximal margins before taking images. To obtain more exact and detailed information, a projector was used to increase the magnification of the images. The distance between the crown's margin and finish line in horizontal and vertical aspects and also the distance to the alveolar bone crest were measured
Results: The statistical analysis of the data revealed that in 76.5 percent of the cases the crowns had more gap in the vertical aspect than the acceptable range [50 micro meters]. In 60.8 percent of the cases there was a gap in the horizontal aspect. In 11 percent of the cases, a ledge was seen in the horizontal aspect and by combining the gaps in both horizontal and vertical aspects, it was seen that, as a whole, 92.2 percent of the crowns had more gaps than the acceptable range. Also it was seen that in 77 percent of the cases in the mesial and 64.5 percent in the distal part, the crown's margin had invaded to the biologic width
Conclusion: It is concluded that it would be worthwhile to make radiographic image to check the framework, thereby important errors, which are difficult or impossible to discover by clinical examination will be shown