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Biomedical subjects

R B Johns

Publications and source records attributed to R B Johns.

At least 37 records · Page 2Linked to original sources
PubMed1975

The epithelium contiguous with the neck of intraosseous dental implants.

There are three distinct regions with which a wedge shaped dental implant is in contact; the intraoral, transitional and intraosseous portions. The environment of each of these is different and will require special consideration. This investigation compares the epithelium found associated with a natural tooth to that which is found contiguous with the transitional region of an implant. The possibility of a pseudojunctional epithelium being formed in association with a glass collar processed onto the neck of a wedge shaped implant is examined. The histological appearance of a specimen in situ for 11 months shows an altered epithelial structure compared to that found adjacent to the neck of an unmodified titanium wedge shaped implant. Because the implant and glass must be mechanically separated from the tissue being examined, the value of demeneralized histological sections is limited. However, examination by a Scanning Electron Microscope of the surface of the glass after removal reveals an area of clear glass in the deeper region of the collar. Above this there is a deposit, the exact nature of which is unknown, but which migth be interpreted as the contents of the gingival crevice. Although this might be interpreted as a type of epithelial attachment, other factors are necessary to ensure close gingival adaptation and limitation on epithelial downgrowth.

Animals↗
PubMedDate not supplied

Distribution of load in an oral prosthesis system: an in vitro study.

Although the long-term success of osseointegrated endosseous implants for the support of fixed dental prostheses has been reported, the increasingly routine and widespread use of implant-supported prostheses has led to problems associated with their structural integrity. To assess the service life of the components of the prosthetic system, a knowledge of the loads transmitted through the system is needed. This paper reports in vitro findings for forces and bending moments transmitted through the abutments from a fixed dental prosthesis to its supporting implants. The results have been compared to previous theoretical analyses that generally overestimate the maximum tensile forces. The effect of the length of distal cantilevers and of missing gold screws as the result of loosening or fracture is also considered. It is proposed that bending moments may play a larger role in failures than previously believed.

Bite Force↗
PubMedDate not supplied

Factors related to success and failure rates at 3-year follow-up in a multicenter study of overdentures supported by Brånemark implants.

An international prospective study of Brånemark implants retaining overdentures was conducted at nine clinical centers. One hundred thirty-three subjects were recruited in a 12-month period and provided with 510 implants, 117 of which were in maxillae and 393 were in mandibles. This study reports the 3-year follow-up status of 120 overdentures and 444 implants. There were 11 overdenture failures (9.2%). Maxillary overdenture failure rates (27.6%) were nearly nine times greater than mandibular overdenture failure rates (3.3%). Maxillary overdenture treatment was less successful than previously reported fixed implant-supported restorations. However, their mandibular counterparts had success rates slightly higher than those reported for fixed implant-supported restorations. At 3 years, 150 implants remained submerged and 66 implants had been withdrawn because the subjects discontinued study participation. Eleven mandibular and 29 maxillary implants had failed and had been removed from 21 subjects. Logistic regression with forward model selection indicated that one two-way interaction was significantly related to implant failure. At highest risk were the subjects who possessed dental arches with bone quantity E and bone quality 4. Subjects with one implant failure were likely to have more than one failure. The Generalized Estimating Equation was used to adjust for the cluster effect in this population because multiple implants (2 to 6) were placed and evaluated in each of the 133 subjects.

Adult↗