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Biomedical subjects

H W Denissen

Publications and source records attributed to H W Denissen.

At least 19 recordsLinked to original sources
PubMed1999

[CAD/CAM-copings for partial coverage].

Aim of the study was to evaluate the Computer Integrated Ceramic Reconstruction (CICERO)-system and the Ceramic Reconstruction (CEREC)-system for the production of all ceramic copings for partial coverage. Posterior teeth were prepared and the stone dies were made. Accuracy analyses were performed on ceramic restorations made by means of the CICERO and by means of the CEREC technique. The marginal gaps were compared to that of a control cast metal restoration. The results demonstrate that the marginal gaps of the CICERO and CEREC copings varied respectively for the premolar 58-80 microns (mean 69 microns) and 71-91 microns (mean 81 microns). For the upper molar 63-92 microns (mean 78 microns) and 68-110 microns (mean 89 microns) and for the lower molar 54-98 microns (mean 76 microns) and 73-99 microns (mean 86 microns). Control cast metal partial coverage restorations showed marginal gaps of 33, 49 and 41 microns. It is concluded that computers can produce copings for partial coverage preparations on stone dies with a mean marginal gap for CICERO copings of 74 microns and for CEREC copings of 85 microns. These values were obtained before optimizing the marginal fit by means of porcelain veneering.

Ceramics↗
PubMed1999

[Reproducible marginal gap measurements of partial ceramic crowns].

Aim of this research was to test the hypothesis that marginal gap measurements by a digital microscopic image processing computer are reproducible. Light microscopic images of the margins of Artglass partial crowns on stone dies were obtained with a 3CCD color video camera, digitized and processed. Ten measuring points were painted on a 0.5 mm section of the finish line of the preparation. The opposite corresponding measuring points on the margin of the partial crown were painted as well. The distance (marginal gap) between two corresponding points was painted and calculated by the computer. Reproducibility (precision) is reflected in the ability to reproduce the same measurement results in repeated measurements (n = 5). The reproducibility error was expressed as the coefficient of variation (CV) in percent (%). The localization of the corresponding measurement points and the calculation of the marginal gap were performed without errors. For a marginal gap between 15-50 microns the average measurement error was 3% or 0.45-1.5 microns. It was concluded that the measurement of the gap between two points by the digital image processing computer was reproducible. The measurement error was neglectable given that a clinically acceptable marginal gap is 100 microns.

Ceramics↗
PubMed1993

Five-year study of all-porcelain veneer fixed partial dentures.

Improvements in enamel-dentinal bonding systems combined with the introduction of new ceramics have encouraged replacement of missing anterior teeth in specific patients with porcelain veneer fixed partial dentures. Metal substructures are not needed, and more natural tooth structure can be preserved because the preparation of abutments is conservative. Twelve porcelain veneer fixed partial dentures were monitored for 5 years, and fractures attributed to degradation of the gingival margins occurred in the veneer surface of the fixed partial dentures. The success rate of 75% was dependent on rigid patient selection criteria, strength of the major connectors, and precise adjustment of occlusion to prevent overloading. The failing margins were attributed to the degeneration, attrition, and deterioration of the composite resin cements. Despite these limitations, patients were extremely satisfied with the esthetics. Improvement in the mechanical properties of composite resin cement will ameliorate the prognosis with this approach.

Composite Resins↗
PubMed1993

Preventive goals in oral implantology.

Preventive dentistry is mainly concerned with caries and periodontal disease and little or no attention is paid to the prevention of alveolar bone loss. An overdenture contributes to the preservation of alveolar bone and offers a number of advantages in comparison to a conventional complete denture. After tooth extraction the atrophy of edentulous lower jaws can be prevented or delayed by using implants supporting an overdenture or a fixed mandibular prosthesis. Hydroxyapatite implants have been studied as submerged tooth root substitutes and have proven to be able to preserve the bulk of the alveolar ridge. A drawback of this submucosal implant is that the ridge maintenance depends solely on the physical presence of the hydroxyapatite implants. If implants support an overdenture or a fixed prosthesis they also play a role in maintaining the function of the bone in the different stages of reduction of the mandible. In this paper a classification for the different resorption stages of the mandible is presented and is used to determine the correct moment for preventive implantology. In addition the use of a lingualised occlusion is discussed as a contribution to the preventive goals in oral implantology.

Alveolar Bone Loss↗
PubMed1993

Anatomic consideration for preventive implantation.

The aim of preventive implant therapy is to prevent or delay loss of alveolar ridge bone mass. For use in an anatomic study of 60 mandibles, resorption of the alveolar ridge was classified into four preventive stages: (1) after extraction of teeth; (2) after initial resorption; (3) when the ridge has atrophied to a knife-edge shape; and (4) when only basal bone remains. Implantation in stage 3 necessitates removal of the knife-edge ridge to create space for cylindrical implants. Therefore, implantation in stage 2 is advocated to prevent the development of stage 3. The aim of implantation in stage 4 is to prevent total loss of function of the atrophic mandible.

Alveolar Bone Loss↗
PubMed1991

Dutch consensus on guidelines for superstructures on endosseous implants in the edentulous mandible.

This consensus report has been reached under the authority of the Dutch Society for Oral Implantology and the Dutch Society for Prosthetic Dentistry by a panel of Dutch dentists and prosthodontists (listed above) who are involved in the treatment of patients with oral implants, either via practice or via research. They were commissioned with a task to "formulate guidelines for the prosthetic treatment of edentulous patients receiving oral implants in the mandible".

Dental Implantation, Endosseous↗
PubMed1991

Preventive implantations.

Preventive implantology is concerned with the preservation of the alveolar ridge of the (edentulous) jaw. Maintaining the volume of the alveolar ridge is a major problem in the prevention of oral disease. Loss of teeth and tooth roots leads to resorption of residual ridges. This being so, it is a logical approach to substitute artificial analogues for lost tooth roots. Hydroxyapatite implants have been studied as submerged tooth root substitutes and shown to maintain the bulk of the alveolar ridge. A drawback of the implants is that the ridge maintenance depends solely on the physical presence of the hydroxyapatite implants. No physiological influence on bone preservation can be attributed to the implants. However, long term research indicates that 75 per cent of the implants survive under full lower dentures and 100 per cent of the implants under fixed partial dentures.

Alveolar Process↗
PubMed1990

[Classification of edentulous mandibles in preventive implantology].

The aim of preventive implantology is to prevent or delay the resorption of edentulous alveolar ridges. The classifications of the resorption stages of the mandible which are now in use, are not applicable to preventive implantology. After anatomic research it was concluded that the resorption of the alveolar ridge of the mandible should be classified in three stages. Loaded as well as unloaded implants can function as tooth root analogues in maintaining the volume of the edentulous ridge.

Alveolar Bone Loss↗
PubMed1989

Eleven-year study of hydroxyapatite implants.

An 11-year clinical research study was conducted with both unloaded bulk hydroxyapatite implants and loaded hydroxyapatite-coated titanium implants. A total of 102 submerged bulk hydroxyapatite implants were placed after extraction of teeth to maintain the volume of the residual alveolar ridge by their physical presence. All 21 implants under fixed partial dentures and 51 of 81 implants under lower complete dentures remained submucosal. A total of 71 hydroxyapatite-coated titanium implants were connected with permucosal superstructures by use of a two-stage method. Modifications in design and in implantation technique were required. This long-term research indicates that cylindrical hydroxyapatite implants are reliable devices as natural tooth root substitutes that bond directly to bone instead of simply being osseointegrated.

Dental Abutments↗
PubMed1989

[Implants with plasma spray coatings of hydroxyapatite: an experimental study in alveolar bone].

Sintered hydroxyapatite ceramic can be coated to a titanium core by means of a high temperature plasma spray procedure. The biological response of alveolar bone to an implant with such a coating of hydroxyapatite was evaluated in an animal experimental study. The results indicated that the plasma spray coating gave a very strong and direct bonding to cortical alveolar bone. The shear strength between bone and ceramic was greater than the shear strength between ceramic and titanium. From a radiological, macroscopic and microscopic point of view the conclusion could be drawn that the biological properties of a plasma spray coating of hydroxyapatite are the same as the properties of bulk hydroxyapatite ceramic. The outermost layer of the hydroxyapatite coating appeared to be unstable under the experimental conditions.

Animals↗