[Introduction of a technique for fabrication of an implant-supported fixed temporary prosthesis]

In fully edentulous patients, reconstruction with implant-supported fixed prosthesis is a complicated treatment. In conventional technique, after the placement of the implants, fixed temporary prosthesis is fabricated with no consideration of the removable prosthesis that the patient has used yet. Therefore, the logical relation of the phases of treatment is lost and the points such as vertical dimension occlusion and centric relation are not recorded exactly. The purpose of this article is to introduce a technique in which a fixed temporary prosthesis is fabricated by use of patient's full denture. In this study, a 60-year-old patient with complete edentulous in the mandible was referred to Dental School. He has used a complete jaw denture in the mandible. The complete denture especially in the lower jaw has caused destructions to the remaining ridge. Due to the patient's condition and the existing circumstances, the treatment design of implant-supported fixed prosthesis was accepted by the treatment team. Prior to the surgery, assessments of the bone quality and quantity, force factors, the number of the implants, their lengths and angles were done and the complete denture was converted to implant-supported fixed temporary prosthesis. The fabrication of conversion prosthesis was introduced with implant-supported metal ceramic restoration

[Marginal discrepancy in two kinds of finishing line for full veneer crown prior to porcelain application [simulation method]]

One of the most important criteria for clinical acceptance and longevity of cast restorations is marginal accuracy. Marginal discrepancy causes cement layer exposure, increases risk of cement wash out leading to plaque accumulation, recurrent caries and gingival tissue inflammation. This study assessed the effect of finishing line preparation design on marginal discrepancy. In this experimental invitro study, three metal dies were prepared using simulation method with beveled shoulder, chamfer and combination of both [buccal beveled shoulder encounters palatal chamfer] that addressed groups A, B and C respectively. Seven wax patterns for each die were cast in Wiron 99 [Basemetal Alloy]. After seating the frameworks, marginal discrepancy was measured in two horizontal and vertical dimensions. The data were analyzed by one way ANOVA and Tukey multiple comparisons tests. The significant differences of horizontal marginal opening were found among three groups in buccopalatal and mesiodistal directions [P<0.003, P<0.0001]. Also, significant differences found between pair groups except to A and C in buccopalatal and A and B in mesiodistal directions. The vertical marginal opening in three groups was statistically different at mesial, distal and palatal directions [P<0.05] but not at buccal side. The vertical marginal opening differences of pair groups [A and C, B and C] at mesial, distal and palatal directions were significant [P<0.05]. Within the limitation of this study, finishing line, preparation design significantly affects the marginal discrepancy, the least and most horizontal marginal opening was produced in beveled shoulder and the combined preparation of beveled shoulder and chamfer, respectively. Chamfer preparation caused minimum vertical marginal opening while the beveled shoulder was in the next rank with no significant statistical differences

[Effect of smear layer on the retention of custom made posts luted with two different cements]

Post retention has a considerable effect on restorative treatments and is influenced by various factors. The purpose of this study was to evaluate the effect of dentinal smear layer on the retention of custom-made posts luted with composite resin and zinc phosphate cements. Forty single-rooted lower premolars were decoronated, filed and filled with gutta-percha and divided into 4 equal groups. Post spaces were prepared to a length of 8 mm. Direct post patterns were made with acrylic resin and castings were fabricated using Ni-cr alloy. In Groups A and C, the post spaces were rinsed with 2 ml of 0.9% normal saline. The specimens in Groups B and D were rinsed with 1 ml of 17% EDTA followed by 1 ml of 5.25% Naocl and 10 ml distilled water. After drying, ZPC [Dentsply] was used for cementation in groups A and B. The samples in Groups C and D were luted with Panavia F[2.0]. Retention was measured on a Universal Testing Machine at 0.5 m/min. Data were subjected to statistical analysis using ANOVA. The mean amount of retention was 19.66 +/- 1.98 kg, 19.72 +/- 2.08 kg, 20.99 +/- 2.08 kg and 22.17 +/- 3.66 kg in groups A, B, C and D, respectively. There was no significant difference between the groups, but the mean value was highest in group D. The use of resin cement provided greater retention for custom-made posts compared to ZPC. Removing dentinal smear layer did not significantly affect the retention of custom-made posts cemented with ZPC or Panavia F[2.0]

[Silane and bonding of resins to ceramic]

When bonding between two different dental materials is impossible due to structural dissimilarity, a third material can be used at the interface to achieve the desired bond. Silanes have been developed for this purpose and can improve bonding strength in dental restorations by preventing debonding at the interface region. The present study reviewed the relevant publications in order to determine the effect of silane on the bond strength of ceramic to resin restorations. Multiple internet search engines including Google, AltaVista, and the archives of related Journals were used in order to access information on the properties of silane. Application of silane increases the bonding strength between composite and resin by approximately 25%, regardless of different fabrication and testing methods. Etching with phosphoric acid and treatment with silane emerged as the two most significant factors in the improvement of the bonding strength of cements. However, using an appropriate coupling agent even without etching has also been shown to produce an acceptable bonding strength. Hydrolyzed silanes do not produce methanol and therefore cannot completely vaporize the water generated during chemical reactions. On the other hand, non-hydrolyzed silanes vaporize surface water by producing 3 methanol molecules and thus do not interfere with bonding of adhesive systems. Therefore the bonding strength of non-hydrolized silanes is greater than hydrolyzed silanes. In conclusion, the type of silane [hydrolyzed, non-hydrolyzed], the adhesive used and the technique of its application are considered to be three of the most important factors affecting bond strength

[Effect of different sprue designs on the internal porosity of cast titanium crowns]

Porosity is a frequently observed casting defect in titanium dental casting. This study measured the effects of different sprue design on the internal porosity of cast titanium crowns. Sixty complete veneer crowns were fabricated on a stainless steel die with a 150- degree sloping shoulder using customized wax patterns. All wax patterns were sprued with 3 different sprue design [Reservoir, Runner bar and Rousseau] and were invested with an alumina- magnesia investment. Castings were made with commercially pure titanium [CP Ti [grade II]] according to the manufacturer's instructions. The castings were carefully cleaned. Internal porosities were quantified with photographs and radiographs by computerized image analyses. Data were analyzed with an ANOVA with a confidence level of 95%. There were statistically significant differences in the values of porosity between 3 types of sprue design. The reservoir sprue design had the least internal porosity comparing to the other designs. Improvements in the porosity of titanium crowns was the result of the Reservoir sprue design with vent. Effects of Different sprue designs on internal porosity and their effects on casting accuracy and marginal adaptation of cast titanium crown and bridges must be evaluated to achieve better evidence and clinical relevance