About 95 percent of all implants are still intact after 5 to 10 years - the success rates of implantologists are impressive, the loss rates are less than five percent. Significantly worse is the balance on the crowns, bridges and prostheses on the implants, which are referred to in the jargon as a superstructure: in 20 to 25 percent of cases in the first five years repairs or even new productions are required, explains Professor Manfred Wichmann, Erlangen, at the 20th Annual Congress of the German Society of Implantology in Munich. Too powerful a bite of the patient, especially when teeth grinding, overwhelmed the materials. Biting back powerfully - that's what patients want after tooth loss, which has problems with conventional dentures. Implant-supported dentures make this powerful biting possible again.
The dark side of the chewing force
Due to the regained chewing capacity, there are also downsides - at least for the prosthetic materials: "Since the ability to chew with implants is much better than with a conventional prosthesis, people bite much harder, putting a strain on the materials of the crowns, bridges and prostheses Implants more than conventional prosthetic restoration, "explains Professor Manfred Wichmann of the Department of Prosthodontics, University of Erlangen-Nuremberg.
With a bridge anchored to natural teeth, patients notice very quickly when a nut is too hard for the dentition and overwhelms the chewing forces: the own tooth registers the chewing forces via specific receptors in the periodontium much more sensitive than an implant. Protective reflexes then limit the forces of the masticatory muscles. This information flow is cut off on implants. Accordingly, the powerful bite of the implant wearer puts the materials of the superstructures under stress.
Materials under stress
Investigations show that complications - for example breaks of the tooth-colored ceramic veneering layer in bridges - occur on own teeth only in about three percent of the patients. In implant-borne constructions, however, this complication is five times more common at 15 percent. The chewing forces are particularly strong in people who press or grind their teeth during the night. This phenomenon is called by dentists "bruxism" and occurs in about 10 percent of the population. "Forces act on the dentures, which can significantly exceed the arbitrary maximum chewing force, " says Wichmann. For example, chewing forces of up to 800 Newton have been measured on teeth-crunchers (a weight of 1 kg develops a pressure or pull of 9.8 Newtons.) These forces are up to seven times higher than the forces of chewing food. By comparison, depending on the food consistency, the chewing force people have to eat is usually between 50 and 100 Newtons. An ingrown implant in the bone usually holds this out: it does not break out of the bone until forces of more than 1500 Newton are applied. But the maximum chewing force may well overwhelm the materials and components of the prosthetic superstructure.
Consider teeth grinding
Therefore, when patients grind their teeth, this has to be taken into account in the prosthetic restoration with implant-supported dentures: "In planning, the positioning of the implants, their number, length and shape can increase the load capacity of the subsequent superstructure, " says Wichmann. "With prosthetic restoration, the material selection, the type of attachment (cemented / screwed), the design of the frameworks and occlusal surfaces as well as the connection of the implant with each other avoid peak loads and have a positive effect on the resistance of the construction." Wichmann also sees material development R & D requirements: "Ceramics with better fracture resistance would be helpful." Even advanced composite materials, predicted by the Erlangen prosthetist, "could lead to a renaissance of veneering resin plastics if they wear less and age less than the materials available to date. "
Advantage: Repairable dentures
But even at the onset of the superstructure, mistakes can occur that affect durability. Wichmann: "When tightening the screws, the torque specified by the manufacturer must be strictly adhered to, otherwise the screw connection may loosen." It makes sense, too, especially to plan larger superstructures so that they can be unscrewed if necessary and are not made of one piece. In case of problems they can be repaired easier. Wichmann: "A cementation is not useful in large reconstructions, so complete restorations of the entire jaw."