Biomedical subjects

D Assif

Publications and source records attributed to D Assif.

At least 19 recordsLinked to original sources

PubMed1992

The cantilever fixed partial denture--a literature review.

The cantilever fixed partial denture (FPD) is a restoration with one or more abutments at one end and unsupported at the other end. Forces transmitted through the cantilevered pontics can cause tilting and rotational movements of the abutments. In a cross-arch unilateral cantilever FPD, the distal cantilevered unit is subjected to comparatively less force than the contralateral posterior abutment. The unilateral lack of terminal abutments causes lateral bending forces activate peripheral inhibitory feedback reactions from the periodontal and/or temporomandibular mechanoreceptors. The greatest strain in distal cantilevered FPDs is recorded mesial to the most distal retainer because most fractures occur in this location. To improve the prognosis of the FPD cantilever, the number of abutments should be increased and the number of pontics decreased. The abutment teeth need long roots and acceptable alveolar support. Prepared abutments require adequate length and parallel axial walls. An equilibrated and harmonious occlusion is necessary, as well as exemplary oral hygiene. A cantilevered FPD with adequate periodontal support can replace any tooth in the dental arch, but is especially useful as an alternative to a removable partial denture. The cantilevered FPD requires at least two abutment teeth. The only documented exception permitting a single abutment is the replacement of a maxillary lateral incisor with the canine as an abutment. An alternative to the cantilevered FPD is the osseointegrated implant. As osseointegrated implants become more popular, the need for the tooth-supported cantilevered FPD may decline, but it will remain an alternative treatment modality.

Biomechanical Phenomena↗

PubMed1992

The degree of zinc phosphate cement coverage of complete crown preparations and its effect on crown retention.

This investigation examined the amount of retentive area covered by cement under complete coverage crowns and its effect on retention. Sixty crowns of self-cured acrylic resin were prepared on 60 identical brass dies and were divided into six groups of 10 crowns each according to different cement applications. The results showed that retention was dependent on the amount of retentive area covered by the cement. The amount of cement in the occlusal part of the cementation space did not affect retention.

Acrylic Resins↗

PubMed1992

Comparative accuracy of implant impression procedures.

In this study, four impression procedures were assessed for accuracy in a laboratory model that simulated clinical practice. The accuracy of stone casts with brass implant analogs was measured against a standard framework. The fit of the framework on the casts was tested by manual and visual judgment and by microscopic measurement. The measurements supported the clinical judgments. When acrylic resin was used to splint transfer copings in an impression, all casts were acceptable and were more accurate than the best of the two other procedures, which did not use an acrylic resin splint. When an impression material was used to orient the transfer copings, the accuracy was better if undercut copings remained in the impression. When impressions were made by removing an impression from smooth transfer copings and replacing the copings in the impression, the majority of casts were unacceptable.

Analysis of Variance↗

PubMed1991

Restoring teeth following crown lengthening procedures.

Crown lengthening procedures are often necessary to successfully restore teeth that have been mutilated at or below the level of the bone crest. Forced eruption is preferred to surgical removal of supporting alveolar bone, since forced eruption preserves the biologic width, maintains esthetics, and at the same time exposes sound tooth structure for the placement of restorative margins. To properly construct a crown, the minimal distance from the alveolar crest to the coronal extent of sound tooth structure should be 4 mm. Before initiation of forced eruption, the restorability of the root after completion of the orthodontic phase must be considered. A technique is suggested to calculate the root-to-crown ratio that will be created after root extrusion with respect to the coronal level of sound tooth structure before treatment.

Dental Restoration, Permanent↗

PubMed1990

Cuspal flexure associated with amalgam restorations.

Cavity preparation causes cuspal flexure under simulated occlusal loads. During amalgam condensation, the dentist exerts forces on the tooth. After condensation, dental amalgam undergoes dimensional changes. We measured possible changes in the cuspal position of premolars during and after their restoration with dental amalgam. Strain gauges were attached to the buccal surfaces of the teeth, and a direct reading of the strain and a simultaneous time-strain curve were obtained. Measurements were taken at the onset of amalgam condensation and continued for 24 hours. The amalgam was then removed from the teeth, and a subsequent reading was made. On the basis of this model, we found that the use of amalgam as a restorative material caused a static load on the cusps of the teeth brought about their consequent permanent deformation. After amalgam removal, we observed complete elastic recovery for all the treated teeth.

Biomechanical Phenomena↗

PubMed1990

A controlled putty-wash impression technique.

A precise impression is imperative for the construction of an accurately fitting indirect cast restoration. The putty-wash technique is commonly used in making impressions with silicone elastomers. Errors in manipulation may lead to inaccurate impressions. A technique is presented ensuring exact reseating of the putty impression tray and creation of a uniform wash space, which are essential for accurate results.

Dental Impression Technique↗

PubMed1989

A rapid dowel core construction technique.

The use of composite resins for dowel cementation and core construction is well established. A short, easy, time-saving method is proposed for simultaneous dowel cementation and core fabrication using a composite core construction material.

Composite Resins↗

PubMed1989

Photoelastic analysis of stress transfer by endodontically treated teeth to the supporting structure using different restorative techniques.

A photoelastic model was used to examine the influence of different types of restorations placed following endodontic therapy, emphasizing the way in which forces applied to the occlusal surface were dispersed to the supporting structures of the teeth. Stresses were photographed in the polarized light field. Findings indicate that distribution and patterns of stresses vary depending on the direction of the loads and the nature of the involved restorative procedures.

Bite Force↗

PubMed1989

Diagnostic casts--an additional dimension.

The indications and usefulness of diagnostic casts are well documented in the literature. A method is presented that enables increased access to the lingual aspect of the casts by sectioning them in a midsagittal plane. The sectioned portions are held together in maximum intercuspation by acrylic keys. The interdigitated casts can thus be examined from all aspects, thereby deriving maximum benefit from them.

Acrylic Resins↗

PubMed1988

A new electromechanical device to measure the accuracy of interocclusal records.

A new electromechanical device was developed for measuring vertical dimension. This device monitored accuracy and vertical displacement of various dental materials during the transfer of interocclusal relationships to an articulator. Polyether was the most precise material tested. Its accuracy was in the 20 to 30 micron range and also recommended for use because of other desirable characteristics. The accuracy of the remaining materials from displacement were, in descending order, Dura-Lay acrylic resin, wax, and wax plus zinc oxide. The electromechanical system was tested and verified as accurate, reliable, convenient, and easy to use.

Acrylic Resins↗

PubMed1988