In the case of removable dentures, connective elements transfer forces and flexural moments to a different extent to the implants. This is due to the different construction characteristics.
With hybrid dentures, the desired extent of retention depends on various factors:
- Number of implants or pillars
- Their distribution throughout the jaw
- Curvature of the jaw
- Size and type of anchor elements
- Bar length and number of matrices
- Degree of atrophy and jaw extension
Available elements are single anchors or bars.
Functions may be rigid or flexible.
Single anchors are the easiest and cheapest method for fixing a hybrid denture.
They can be inserted directly in the dental practice, a laboratory is not required. If correctly made dentures exist, the respective denture parts are removed.
The healing caps are removed from the implant and exchanged, for instance, by ball-head anchors.
The male parts are then put on and the undercuts blocked out with wax.
After that, the male parts are fixed in the denture with cold polymerisate.
A ball-head anchor is a flexible retention mechanism.
The matrix can only exert its full retentive function if it is positioned in a circle around the abutment equator.
Abutment equators should therefore be positioned at the same level.
Bars may be pre-fabricated, cast or milled.
Flexible bars are round and the oval Dolder bars.
The U-type bar (bar attachment) is inflexible.
According to a study, the horizontal forces working on implants are not higher with U-type bars than when round bars are used (Mericske-Stern 1997). However, round bars require more control than U-type bars (bar matrix activation).
- A bar should exactly follow a horizontal course,
- follow the course of the alveolar ridge,
- consider the form of the hybrid denture, and
- be easily cleanable with interdental brushes.
The Dolder bar remains in the mouth
- The space between the Dolder bar and the gingiva below it must be carefully blocked out with wax.
If this is not done, the impression material flows around the bar and the lining will be damaged at the time of removal.
- Then the base of the total denture is filled with impression material as usual and put back into the mouth.
After curing, it is lined in the laboratory.
The Dolder bar remains in the impression
- Holes must be drilled through the denture in order to be able to position the impression screws.
- Impression screws replace the occlusal screws of the Dolder bar while the impression is taken.
- Impression compound is applied to the denture base that is then positioned correctly in the mouth.
- After curing of the material, the impression screws are loosened; the Dolder bar is now in the denture, surrounded by impression compound.
Advantage of this method:
The bar's rider can again be exactly positioned.
Mucosal resilience is taken into consideration when the distance between rider and bar are determined.
They can be lined directly.
Ball-head anchors have parts subject to wear and tear which must be replaced according to the manufacturer's instructions.