The effect of various interim fixed prosthodontic materials on the polymerization of elastomeric impression materials

Effect of freshly placed core buildup composites on setting of silicon impression materials

Aim:

The aim is to study the effect of freshly placed composite build-ups on setting of additional silicone impression materials.

Settings and Design:

In vitro - experimental study.

Materials and Methods:

Three composite materials; Build-It™ F. R™, Filtek™ Bulk Fill flow and Filtek™ Z350 and three light-bodied additional silicone impression materials; Elite HD+, Aquasil LV Ultra and Express™ were used. Cylindrical-shaped specimens were made of each material (diameter 15 mm and height 10 mm). The silicone specimens were brought into contact with the composite specimens, which were either freshly cured (9 groups, n = 90) or cured and then stored in normal saline for 1 week (9 groups, n = 90). Shore A hardness (SAH) scores of silicone surfaces were recorded following the ASTM D2240-5 standards for shore A Durometer testing. Six measurements were made per each silicone surface and medians were calculated. Kruskal–Wallis and Mann–Whitney tests (SPSS v20) were used to check statistical significant differences between all groups and paired comparisons, respectively (P < 0.05).

Statistical Analysis Used:

Kruskal-Wallis and Mann-Whitney tests.

Results:

The SAH scores of additional silicones in direct contact with freshly placed composites were significantly less than SAH scores of additional silicones in direct contact with composites specimens aged for 1 week in 7 out of 9 combinations (P < 0.05). Only when Express™ and Elite HD+ were applied over freshly placed Filtek™ Bulk Fill flow, the SAH scores difference was not statistically significant to SAH scores of matching combinations applied after 1 week of composite storage.

Conclusions:

Freshly placed composite might affect setting of additional silicone impression materials. Dentists should carefully assess final impression on areas of prepared teeth that have received composite fillings recently.

Effect of contemporary retraction agents and cleaning with hydrogen peroxide on the polymerization of elastomeric impression materials

The aim of the study is to investigate the polymerization inhibition of elastomeric impression materials vinylpoly siloxane (VPS) and polyether (PE) when used in combination with retraction materials with and without subsequent cleaning with hydrogen peroxide (H₂O₂). Methods: Seven stainless steel specimens were fabricated. Four hundred and twenty impressions were made with three different elastomeric materials (140 each) as follows: group 1: VPS-Panasil; group 2: VPS-Express; group 3: PE-Monophase. Each material group was further subdivided into seven subgroups, based on use of no retraction material (control), three different retraction materials [Retraction capsule (RC3M), Dryz, Expasyl], and two cleaning techniques (water and H₂O₂). All subgroups included 20 impressions, which were made by a single operator using an automix gun. Evaluations were made using a visual scale by three calibrated examiners blindly and independently. Subjective categorization of the impressions were made as inhibited and uninhibited. Data were analyzed using Fisher's exact test and significance was set at p < 0.05. Results: Inhibited impressions were lower than uninhibited impressions among VPS materials (Panasil and Express); Panasil and Express showed comparable (p > 0.05) impression retardation. PE showed significantly higher inhibition compared to VPS materials (p < 0.05). Expasyl showed significantly higher polymerization inhibition than other retraction materials (p < 0.05). The use of H₂O₂ for cleaning showed significant reduction in polymerization inhibition than cleaning with water for Expasyl (p < 0.05). Conclusion: Overall contemporary retraction materials showed low potential for polymerization inhibition of elastomeric impression materials. Expasyl should be cleaned with H₂O₂ prior to impression making. However, Dryz and RC3M can show accurate impressions with water cleaning alone.

Effect of Intraoral Mechanical Cleaning Techniques on Bond Strength of Cast Crowns to Metal Cores

PURPOSE

To evaluate the effect of cleaning of metal cores from provisional cement, using an intraoral airborne-particle abrasion method, on the bond strength of permanent resin cement with cast crowns to cores.

MATERIALS AND METHODS

Thirty stainless steel models of a standard complete crown tooth preparation were fabricated. Thirty Type III gold crowns were fabricated. Each cast crown corresponded to one stainless steel crown preparation model. All crowns were cemented with noneugenol zinc oxide cement and stored for 7 days at 37°C. All crowns were debonded, and the cement was cleaned with airborne-particle abrasion using 50 µm aluminum oxide at 4.1 bar (0.41 MPa) followed by ultrasonic cleaning. Based on the mechanical cleaning technique of the remaining provisional cement on surfaces of cast cores, specimens were equally divided into 3 groups: hand cleaning (HC) with a dental excavator, hand cleaning followed by polishing using a brush and pumice (BP), and hand cleaning followed by intraoral airborne-particle abrasion (APA). All crowns were then cemented to their corresponding cores using universal resin cement. All crowns were stored for 7 days at 37°C. An Instron universal testing machine was used to record the bond strength of crowns.

RESULTS

Airborne-particle abrasion method for intraoral mechanical cleaning revealed a statistically significantly higher bond strength compared to the other two methods.

CONCLUSIONS

When comparing the three methods of provisional cement cleaning from metal cores, airborne-particle abrasion resulted in the highest bond strength for cast crowns.

Predictable prosthetic space maintenance during staged complete-mouth rehabilitation

Staged complete-mouth rehabilitation to accommodate a patient's financial constraints during the course of treatment is presented. Clear acrylic resin added to the anterior cameo surface of the maxillary fixed complete denture (FCD) served as a space maintainer. The restoration of the maxillary FCD addressed the patient's chief complaint. By adding the space maintainer, supraeruption of mandibular anterior teeth and encroachment of the prosthetic space, which could have resulted in additional treatment, was avoided. During the second stage of the complete-mouth rehabilitation, zirconia restorations were used to restore the mandibular arch to the maxillary FCD after straightforward removal of the space maintainer. This allowed a smooth transition after a delay in treatment without having to modify the previous treatment.