Kjell Randow

Technical failures and some related clinical complications in extensive fixed prosthodontics: An epidemiological study of long-term clinical quality

Three hundred and sixteen fixed partial dentures made in 1975-1976 by 112 general practitioners in Malmö, Sweden, were selected for a questionnaire study of the technical failure rates after 6-7 years. Cariologic, periodontal, endodontic, and esthetic complications were also identified, as were those appearing in the stomatognathic system. The total material consisted of three groups with an approximately equal number of reconstructions. One group consisted of fixed partial dentures with distal abutment teeth, another was formed of fixed prostheses with single cantilever pontic/pontics, and a third consisted of double cantilever pontics. Excluding the 26 reconstructions, which had been made for patients who died (24) or emigrated (2) during the observation period, data was obtained for 97% of the selected restorations. The results showed high rates of cariologic (18-31%), endodontic (5-23%), periodontal (7-12%), esthetic (10-16%), and technical (8-34%) complications. Differences were noted between the groups. For all types of technical failures (fractures and loss of retention) higher frequencies were related to the extent of cantilevering. Direct relationships were found between the technical failure rate and the time in service, the sum of all cantilever extension pontics in the reconstructions, and the state of the pulps of the distal abutments. No relationship was found between the technical failure rate and the status of the dentition in the opposing jaw. The clinical significance of the results obtained is discussed.

On cantilever loading of vital and non-vital teeth An experimental clinical study

Three healthy subjects with neighboring or contralateral vital and root-filled teeth requiring crown therapy were selected as test persons. All teeth had optimal alveolar bone support. The root-filled teeth were furnished with individual cast posts and cores, and veneer crowns were made on both the vital and non-vital teeth. Buccal extension bars were then soldered to the occlusal surfaces of these crowns, and weights were applied in different positions along the bars until the test persons experienced pain. The experiments were repeated under local anesthesia. The results showed that non-vital teeth had mean pain threshold levels that, on cantilever loading, were more than twice as high as those of their neighboring or contralateral vital teeth. The positions of the centers of rotational deformations of the loaded teeth, which were assumed to be mainly rotational, were calculated and found to be located inside the peripheries of the crowns for the vital teeth but extracoronally in markedly more peripheral positions for the non-vital teeth.

On functional strain in fixed mandibular reconstructions I. An in vitro study

Six linear strain gauges and one rosette strain gauge were used on three different types of models prepared from one partially dentate subject, to study loading deformation in a six-unit fixed mandibular bridge. The bridge was mounted on each of the models on an adjustable articulator and loaded in a universal testing machine at loading levels ranging from 0 to 491 N. The results showed considerable differences between the three types of model, with regard to both the magnitude of the recorded strains for the individual gauges and the calculated direction of the principal strains under the rosette gauges. The findings indicate that the mechanical properties and the design of the supporting structures have a major influence on the functional deformation of fixed dental appliances.

On the clinical deformation of maxillary complete dentures: Influence of denture-base design and shape of denture-bearing tissue

This paper aimed to study the influence of denture base design and the shape of the denture-supporting area on the functional deformation of maxillary complete dentures. Six strain-gauged duplicate maxillary dentures were made for the study of two test subjects with different shapes of the palatal vault. Each subject was supplied with two polymethyl methacrylate dentures, one with a 1-mm-thick palatal base and the other 2 mm thick. A third denture was constructed with a cobalt-chromium base. The functional loading tests included maximum biting and the chewing of the food test samples. An analysis based on chewing time and total number of chewing cycles per test piece was also made. The results showed that surface straining is highly complex at the anterior part of the maxillary dentures constructed from polymethyl methacrylate and that increasing the denture thickness per se might not be accompanied by a reduction of strain. The results also suggest that high thrust to the supporting tissue is produced with high palatal vault dentures made in polymethyl methacrylate. The study proposes that cobalt-chromium bases may be used in maxillary dentures to reduce functional deformation and thrust to the supporting tissues at the anterior part of the maxilla.

On Functional Strain in Fixed and Removable Partial Dentures: An experimental in vivo study

Three rosette strain gauges were attached to a fixed bilateral cantilevered crossarch maxillary bridge and one linear strain gauge to an attachment-retained removable partial denture (RPD), to study the functional deformation pattern in this combined reconstruction. The deformation under clinical conditions at maximum habitual biting and at maximum unilateral loading was very complex, with both elongation and contraction in different parts of the fixed reconstruction. Even though this complexity in the functional deformation was found both with and without the RPD incorporated, the RPD seemed to provide a more even and favorable distribution of the masticatory forces in the fixed reconstruction.