Biomechanical aspects of two different implant-prosthetic concepts for edentulous maxillae.

Two essentially different implant-prosthetic concepts are known for the treatment of edentulous maxillae. One concept propagates a "concentrated" arrangement of four to six implants in the premolar and anterior regions with a fixed cantilever superstructure. An alternative is a "spread-out" implant arrangement of six implants placed in the tuberosity, premolar, and anterior regions. The prosthetic rehabilitation consists of a fixed horseshoe-shaped bar and a removable prosthesis. A cantilever situation is avoided. The biomechanical aspects of these implant-prosthetic concepts were studied with clinical strain-gauge measurements and theoretical three-dimensional analysis using the finite element method. Results revealed that the distribution of bone stresses is more favorable with a spread-out implant arrangement than with a concentrated implant arrangement and cantilever restoration. The resistance to bending of a superstructure has an influence on bone stress concentration that should not be ignored. Stresses are controlled not only by the number or distribution of implants, but also by the material and design of the superstructure.

Changes in chewing patterns after implantation in the edentulous mandible.

Almost all edentulous patients with implant-supported prostheses in mandibles describe an improvement in their chewing function and quality of life. This was reason to believe that an implant prosthetic treatment actually influences mandibular border movements, as well as the chewing patterns. The present study compares border movements and chewing patterns in 15 patients recorded with the Sirognathograph. The first measurements were made with existing complete dentures. After implantation and rehabilitation with a Dolder-bar and clip-to-bar overdenture, the movements were recorded again. The measurements revealed an improved guidance of the mandibular movements and larger borderline patterns following stabilization of the complete denture with the bar. This leads to more harmonic shapes in the movements and better chewing efficiency.

Implant and prosthetic treatment of the edentulous maxilla using a bar-supported prosthesis.

Functional and anatomical considerations led to a new concept of an implant-supported bar prosthesis in the edentulous maxilla. The cantilever situation is avoided by the placement of endosseous cylindrical implants (type IMZ) in the maxillary tuberosities distal to the maxillary sinus. Full arch support is provided by the symmetrical insertion of six IMZ implants in the tuberosity, canine, and incisor regions. After 4 months of healing, a milled precision bar and removable prosthesis are fabricated and supported by the implants.

[Comparison of two computer-aided recording systems: MT 1602 and Compugnath]. / Vergleich der computerunterstützten Registriersysteme MT 1602 und compugnath.

Two computer-aided jaw movement recording systems were compared with each other. The results showed that both systems work satisfactorily for use in reconstructive dentistry and TMJ diagnosis. It is, however, emphasized, that there are a number of shortcomings which may have a negative effect on the recordings.

[Functional status of patients prior to and after orthognathic surgery]. / Funktionelle Befunde bei Patienten vor und nach kieferorthopädisch-chirurgischer Operation.

The functional status of 12 patients was evaluated before and after orthognathic surgery for a malocclusion. The results of surgical intervention showed distinctive differences in the status of the temporomandibular joint and masticatory musculature. The number of tender muscles on palpation and the occurrence of temporomandibular joint sounds was reduced to approximately one third. However, the number of joints showing pain on palpation increased. Axiographical recordings of movement paths shawed normal values in 2 patients postoperatively. Chewing patterns were generally more harmonious, but the size of the chewing field was smaller.

[Plaque-accumulation on galvano-ceramic crowns]. / Plaqueanlagerung an glavano-keramischen Kronen.

48 patients treated with galvano-ceramic crowns and bridges were evaluated as to their plaque indices according to Silness and Löe (PI) and their papillary bleeding indices (PBI) according to Mühlemann. The mean values of PI and PBI were determined for all teeth as well as for defined groups of teeth: sound teeth, teeth with galvano-ceramic crowns and other restorative materials. Galvano-ceramic crowns showed the least plaque accumulation. Their PI was lower than the PI of sound teeth. Resin-veneered crowns and full cast crowns exhibited significantly higher PI-values in the posterior area. Crowned teeth had a higher PBI than sound teeth, but galvano-ceramic crowns showed lower PBI-values than crowns of other restorative materials.

[Radiosterilization of impressions]. / Strahlensterilisation von Abformungen.

Dimensional stability and mechanical properties of addition-silicone impression materials were tested after sterilisation with gamma rays. There were no clinically relevant changes to not sterilized materials.

Complete dentures fixed on dental implants: chewing patterns and implant stress.

Electrognathographic measurements on 18 patients with implant-attached mandibular complete dentures showed larger and more stable chewing patterns compared to their former dentures without implants. Strain gauge measurements revealed mechanical stress acting on the implants even during the fixation of the bar. In addition to simulating the periodontal ligament, the intramobile element (IME) of the IMZ system compensated minor, clinically undetectable mismatches inherent with technical procedures (casting, soldering). Although the implants are loaded with tensile and compressive stress, tensile stress dominated during the chewing process. The implants were also loaded during swallowing. This load reached half of the value of the chewing loads.