Comparison of retention of monolithic zirconia crowns with alumina airborne-particle abraded and nonabraded intaglio using three different cements: A clinical simulation.

STATEMENT OF PROBLEM: The necessity of roughening the intaglio surface of zirconia crowns to achieve adequate retention is unclear. PURPOSE: The purpose of this clinical simulation study was to evaluate the retention of airborne-particle-abraded and nonabraded monolithic zirconia crowns using 3 different cement types. MATERIAL AND METHODS: Extracted human molars were used and prepared with a 10-degree taper. Impressions were made of the prepared teeth with a polyvinyl siloxane (PVS) material, and dies were made with Type 4 gypsum. Each die was scanned with a NobelProcera 1G Scanner, and the standard tessellation language (STL) files were transferred electronically to the Nobel Biocare production site, where a bar was added virtually on top of each crown and parameters were set for milling. Seventy-two Procera zirconia crowns were generated, of which half were airborne-particle abraded on the intaglio surface with 50-µm alumina particles at 400 to 500 kPa for 15 seconds. The other 36 received no intaglio treatment other than cleaning. Both groups of 36 crowns were divided into 3 subgroups of 12 specimens. The area of each preparation was calculated using a computer-aided design software program. The specimens were distributed to attain similar mean surface areas among the cementation groups. The crowns were cemented onto the specimen with a controlled force of 196 N. The 3 cements used were self-adhesive, modified resin RelyX Unicem Aplicap, resin-modified glass ionomer RelyX Luting, and a composite resin, Panavia F2.0 with ED Primer A & B. All specimens were thermocycled (5 °C to 55 °C) for 5000 cycles and then removed axially with a universal testing machine (Instron Model 5585H) at a crosshead speed of 0.5 mm/min. The removal force was recorded, and stress of dislodgement was calculated for each crown. A 2-way analysis of variance was used for statistical analyses. The type of failure was analyzed with the chi-squared test of association for independent samples (α=.05 for all tests). RESULTS: The mean dislodging force for crowns with airborne-particle abraded intaglio was 5.4 MPa, which was statistically greater than the mean of 3.2 MPa for nonabraded specimens (P<.001). No significant differences related to the dislodging stresses were detected among the 3 cements (P=.109). The mode of failure was similar whether abraded or not, with 50% of specimens retaining cement in the crown after separation. CONCLUSIONS: Alumina airborne-particle abrasion of the intaglio of zirconia to create surface roughness is beneficial in retaining the crowns, regardless of the cement type. The nonabraded crowns demonstrated significantly lower retentive stress with crown removal. The principal mode of failure was similar whether the zirconia intaglio was airborne-particle abraded or not. The most common mode of failure (>50% of specimens) was at least three-fourths of the cement remaining within the crown.

Accuracy of a new ring-opening metathesis elastomeric dental impression material with spray and immersion disinfection.

STATEMENT OF PROBLEM: A new elastomeric impression material has been formulated with a ring-opening metathesis chemistry. In addition to other properties of clinical significance, the impression accuracy must be confirmed. PURPOSE: The purpose of this study was to compare the accuracy of the new elastomeric impression material with vinyl polysiloxane and polyether following both spray and immersion disinfection. MATERIAL AND METHODS: Impressions of a modified dentoform with a stainless steel crown preparation in the lower right quadrant were made, and type IV gypsum working casts and dies were formed. Anteroposterior (AP), cross-arch (CA), buccolingual (BL), mesiodistal (MD), occlusogingivobuccal (OGB), and occlusogingivolingual (OGL) dimensions were measured using a microscope. Working cast and die dimensions were compared to those of the master model. The impression materials were a newly formulated, ring-opening metathesis-polymerization impression material (ROMP Cartridge Tray and ROMP Volume Wash), vinyl polysiloxane (VPS, Aquasil Ultra Monophase/LV), and a polyether (PE, Impregum Penta Soft/Permadyne Garant L). Fifteen impressions with each material were made, of which 5 were disinfected by spray for 10 minutes (CaviCide), 5 were disinfected by immersion for 90 minutes (ProCide D), and 5 were not disinfected. There were significant cross-product interactions with a 2-way ANOVA, so a 1-way ANOVA and Dunnett's T3 multiple comparison test were used to compare the dimensional changes of the 3 impression materials, by disinfection status and for each location (alpha=.05). RESULTS: For ROMP, there were no significant differences from the master, for any dimension, when comparing the control and 2 disinfectant conditions. No significant differences were detected among the 3 impression materials for CA, BL, and MD. The working die dimensions of OGB and OGL for VPS with immersion disinfection were significantly shorter than with PE and ROMP (P<.05). Overall, the AP dimension was more accurate than CA, and the BL of working dies was 0.040 mm greater in diameter than MD. CONCLUSIONS: The accuracy of gypsum working casts and working dies from the new and 2 existing types of impression material were similar, for both spray and immersion disinfection. Judicious application of a die spacer can compensate for the small differences observed. VPS may require additional laboratory accommodation to compensate for a shorter working die.