Comparison of four novel customized implant abutments fabricated by pressing technology

Abstract

Restoring a dental implant in the esthetic zone can be challenging, especially if a metal implant abutment is directly visible or shows through the surrounding soft tissues. In addition, when esthetic demands justify the selection of ceramic crown materials, a low value, metal abutment is difficult to mask and with the harmful effects resulting from excess cement by hiding the margins subgingivallyallceramic abutments were evolved as a solution. The use of lithium disilicate with the pressed technique instead of zirconia allows elimination of purchasing CAD/CAM device besides the better sensitivity when exposed to wet environment, better material handling and better esthetics.

Therefore the aim of the present in vitro study was to compare the fracture resistance of four custom implant hybrid abutment restorations fabricated by Cementinge.max press to Ti Baseor pressing e.max on Ti base in both hybrid abutment crowns (HAC) and hybrid abutments (HA) designs.

Thirty two Ti bases (Sirona) compatible with 4.5-5 mm diameter analogs (Astra tech) were used to fabricate the custom implant hybrid abutments. One analog for each Ti base was mounted by a surveyor in acrylic resin and one was left dismounted to be used to fabricate the wax patterns. The Ti bases were divided into two major equal groups, the first group (n=16) was fabricated as cemented e.max press to Ti Bases (C). Half of the samples (n=8) were constructed cementing abutment crown to Ti base with abutment and crown are pressed as one unit (Cemented hybrid abutment crown CHAC). The other half (n=8) by cementing abutments to Ti base with separate cemented crown (Cemented hybrid abutment CHA).In the second major group (n=16) restorations were constructed as e.max press on Ti Bases (P). Half of the samples (n=8) were pressed abutment crown on Ti base with abutment and crown pressed on as one unit (Pressed hybrid abutment crown PHAC) and the other half (n=8) was constructed as pressed abutments on Ti base with crown cemented on as a separate unit (Pressed hybrid abutment PHA). In CHAC and PHAC groups a wax pattern of predetermined dimensions of an upper central incisor was built and standardized with the help of putty indices then either removed, invested, pressed and cemented on the Ti base in CHAC group or invested with its Ti base in PHAC.And in CHA and PHA groups wax patterns ofthe abutmentsonly was pressed either directly on the Ti base in PHA or separate and cemented on Ti bases in CHA. Then crowns of both CHA and PHA were constructed by building the crowns wax patterns after painting separating medium on the abutments and pressing them separately. All samples were loaded till failure at an angle of 30 degrees from the vertical long axis in a universal testing machine by a steel rod with a flat end on their incisal edges and the maximum load to produce fracture for each specimen was automatically recorded in Newtons using the computer software.

The obtained data were collected, presented and statistically analyzed using SPSS version 17 for Windows. The cemented samples (C) showed higher mean fracture resistance than pressed samples (P) regardless the study design variables. Regardless construction techniques, cement retained hybrid abutment samples (HA) showed higher mean fracture resistance than the screw retained hybrid abutment crown samples (HAC). The cemented hybrid abutments (CHA) showed the highest mean fracture resistance while the pressed on hybrid abutment crowns (PHAC) showed the lowest mean fracture resistance values. The pressing technique had a statistically significant effect over fracture resistance of custom hybrid abutment restorations regardless of restoration design; meanwhile neither restoration design alone nor technique design interactions had a statistically significant effect over the fracture resistance of the tested groups.