ABSTRACT
Statement of the Problem: Marginal fitness is the most important criteria for evaluation of the clinical acceptability of a cast restoration. Marginal gap which is due to cement solubility and plaque retention is potentially detrimental to both tooth and periodontal tissues
Purpose: This in vitro study aimed to evaluate the marginal and internal fit of cobaltchromium [Co-Cr] copings fabricated by two different CAD/CAM systems: [CAD/milling and CAD/ Ceramill Sintron]
Materials and Method: We prepared one machined standard stainless steel master model with following dimensions: 7 mm height, 5mm diameter, 90[degree] shoulder marginal finish line with 1 mm width, 10[degree] convergence angle and anti-rotational surface on the buccal aspect of the die. There were 10 copings produced from hard presintered Co-Cr blocks according to CAD/ Milling technique and ten copings from soft non- presintered Co-Cr blocks according to CAD/ Ceramill Sintron technique. Marginal and internal accuracies of copings were documented by the replica technique. Replicas were examined at ten reference points under a digital microscope [230X]. The Student's ttest was used for statistical analysis. p< 0.001 was considered significant
Results: Statistically significant differences existed between the groups [p< 0.001]. The CAD/milling group [hard copings] had a mean marginal discrepancy [MD] of 104 micro m, axial discrepancy [AD] of 23 micro m and occlusal discrepancy of 130 micro m. For CAD/Ceramill Sintron group, these values were 195 micro m [MD], 46 micro m [AD], and 232 micro m [OD]. Internal total discrepancy [ITD] for the CAD/milling group was 77 micro m, whereas for the CAD/Ceramill Sintron group was 143 micro m
Conclusion: Hard presintered Co-Cr copings had significantly higher marginal and internal accuracies compared to the soft non-presintered copings
ABSTRACT
The early computer-aided design/computer-aided manufacturing [CAD/CAM] systems were relied exclusively on subtractive methods. In recent years, additive methods by employing rapid prototyping [RP] have progressed rapidly in various fields of dentistry as they have the potential to overcome known drawbacks of subtractive techniques such as fit problems. RP techniques have been exploited to build complex 3D models in medicine since the 1990s. RP has recently proposed successful applications in various dental fields, such as fabrication of implant surgical guides, frameworks for fixed and removable partial dentures, wax patterns for the dental prosthesis, zirconia prosthesis and molds for metal castings, and maxillofacial prosthesis and finally, complete dentures. This paper aimed to offer a comprehensive literature review of various RP methods, particularly in dentistry, that are expected to bring many improvements to the field. A search was made through MEDLINE database and Google scholar search engine. The keywords; 'rapid prototyping' and 'dentistry' were searched in title/abstract of publications; limited to 2003 to 2013, concerning past decade. The inclusion criterion was the technical researches that predominately included laboratory procedures. The exclusion criterion was meticulous clinical and excessive technical procedures. A total of 106 articles were retrieved, recited by authors and only 50 met the specified inclusion criteria for this review. Selected articles had used rapid prototyping techniques in various fields in dentistry through different techniques. This review depicted the different laboratory procedures employed in this method and confirmed that RP technique have been substantially feasible in dentistry. With advancement in various RP systems, it is possible to benefit from this technique in different dental practices, particularly in implementing dental prostheses for different applications
ABSTRACT
Statement of the Problem: By introducing the coloring liquids, it is claimed that it is possible to make the color of frameworks fabricated from zirconium oxide extremely close to the natural tooth color.
Purpose: The purpose of this research was to evaluate the effect of two staining techniques on value changing in zirconia crowns.
Materials and Method: Three groups A, B, and C, each containing ten zirconia crowns, were used. The zirconium cores samples were fabricated by a CAD/CAM device. Group A was left uncolored, Groups B was submerged for two minutes in A2 coloring liquid and Group C was stained with brush. Then all cores were sintered and the porcelain was applied by using the layering technique. Ultimately, the crowns color was determined using a spectrophotometer. Their color changing [Delta E] and value changing [Delta L] in relation to A2 color were also assessed. The data were analyzed with one-sample t-test, post-hoc Tukey, and one-way ANOVA tests with significant level set at 0.05
Results: The mean value in all groups was higher than the value obtained from A2 color samples [p= 0.001]. The highest mean value was 78.31 +/- 1.22 belonging to group C [staining with brush] and the lowest mean value was 76.99 +/- 0.65 belonging to group B [submerging]. The results of post-hoc Tukey regarding both Delta E and Delta L variables showed a significant difference between groups A [uncolored] and C [staining with brush] with P Delta E=0.006 and P Delta L=0.039, respectively. A significant difference between group B [submerging technique] and C [staining with brush] were shown when these two variables were compared [P Delta E=0.001, P Delta L=0.015]
Conclusion: Due to the higher value increase in surface staining [brush], it is recommended to use the submerging technique for staining zirconia cores
ABSTRACT
PURPOSE: This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS: Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (alpha=.05). RESULTS: Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 microm) was higher than press-over (50.64 microm) and CAD-on (51.50 microm) veneered groups (P<.001). CONCLUSION: Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.
Subject(s)
Ceramics , Crowns , Dental PorcelainABSTRACT
In spite of ceramics' desirable esthetics and compressive strength, they are inherently prone to fracture and are weak against tensile and torsional loads. In-Ceram Alumina is a type of reinforced alumina which has been used as a core material for crowns and three units anterior bidges since 90s. Turkom-Cera is presented in the market recently which uses a simple method to produce single and multiple unit anterior and posterior restorations. The purpose of this study is to evaluate the fracture resistance of copings made by these systems. 40 brass dyes were prepared and divided into two groups. To make the copings, impression was taken and model dyes were made. 20 ceramic coping were prepared according to manufacturers instructions for each group, cemented to brass dyes and kept in 100% moisture for one week. Load to fracture test was performed by Universal testing machine and load was applied by a speed of 0.5 mm/min. Fracture load was recorded for each specimen. Data were collected and entered to the SPSS software and t-test was done. The average fracture load for Turkom-Cera was 1273 N and was 1079 N for In-Ceram Alumina. The maximum and minimum values for the first group was 2490, 530 N and for the second group was 1490, 714 N respectively. According to t-test results with P-value<0.05 there was no significant difference between the two groups. According to the close results for both groups, clinical performance of the Turkom-Cera ceramic copings would be similar to In-Ceram Alumina and a wide range of clinical use could be anticioated for this system