Evaluation of the accuracy of interocclusal records in relation to two recording techniques.

PURPOSE: The accuracy of interocclusal records influences the relationship of the working casts and therefore the success of the prosthesis. The aims of this study were to determine the accuracy of the fit of interocclusal records on the working casts and to compare the accuracy between a classic and modified recording technique, which is described in this article. METHODS: The modified technique uses a metal apparatus that represents opposing arches. Bite registration polyether was used as the recording material and epoxy resin was used as the working cast material. RESULTS: The results indicated that the presence of the recording material produced vertical discrepancies on the interocclusal relationships of the casts. Repositioning or transferring of the records enhanced these discrepancies. CONCLUSIONS: The proposed modified technique reduced the inaccuracies but did not completely eliminate them.

Finite element analysis of ceramic abutment-restoration combinations for osseointegrated implants.

All-ceramic restorations can solve many esthetic problems associated with implant-supported prostheses. This study evaluated stress concentration and distribution in implant abutments under normal masticatory forces using computer simulations. Two-dimensional finite element analysis was used to study four different abutment-restoration combinations using Brånemark implants. The models considered two positions of the fastening screw, two positions of the crown margins, cemented versus screw-retained prostheses, and clinical loads of 200 N. Models having screws on top of abutments had the lowest stresses (3.1 to 4.8 MPa) and best stress distribution. Screw-retained prostheses and short crown margins increased overall stresses (9.9 to 11.4 MPa).

Strength and mode of failure of single implant all-ceramic abutment restorations under static load.

The strength and mode of failure of three different designs of custom-made all-ceramic implant abutments fabricated by milling of In-Ceram sintered ceramic blocks were compared with the conventional CeraOne system under static load. Four test groups were formed with different locations of abutment screws. In three test groups, In-Ceram crowns were fabricated for placement on the all-ceramic abutments, and in one test group, a veneer porcelain was fired directly on the abutment; crowns in the control group were fabricated using the CeraOne system. Ten-mm-long Brånemark implants were placed into a brass block that allowed loading at a 30-degree angle to the long axis. The test group in which the veneer porcelain was fired directly on the all-ceramic abutments was the weakest, and it showed fractures at a mean value of 236 N. The fracture strength of the three other test groups was dependent on the extension of the crown margin relative to the location of the screw head. The test group that had the screw on the top compressing the entire ceramic abutment showed a mean value of 422 N that was similar to the results that were achieved with the CeraOne system (427 N). The weakest link in the all-ceramic single implant restorations was the abutment screw in which the bending began at approximately 190 N.

Clinical study of location and reproducibility of three mandibular positions in relation to body posture and muscle function.

Clinical studies have confirmed the adequate reproducibility of both centric occlusion and centric relation when used as reference positions during treatment; however, the reproducibility of the neuromuscular position has been found inadequate. This study evaluated the location and reproducibility of these three mandibular positions in relation to body posture, sitting and supine, and bilateral muscle activity before and after the insertion of a flat mandibular positioning device equilibrated to balance the muscle functions, as shown by two electromyography biofeedback instruments. Intraoral recordings were made in 11 young subjects with complete natural dentition. Acrylic resin clutches that supported a screw point in the maxillary arch and painted glass in the mandibular arch were used and positioned not to interfere with the occlusion. The distances of the screw scratch from two of the edges of the painted glass were used to measure the anteroposterior and mediolateral locations with a micrometer. The reproducibility was evaluated by measuring the scratch surface by measuring the weight of the print cutouts made from photographs of the scratches taken with a stereoscope. The location and reproducibility of centric occlusion and centric relation were not affected by body posture. A more precise posterior neuromuscular position was obtained in the supine position. The insertion of a mandibular positioning device did not affect centric occlusion but gave a more precise centric relation. Neuromuscular position became as precise as centric occlusion and was located anteroposteriorly between centric occlusion and centric relation.

Perio-prosthetic management in restoring teeth with reduced clinical crown in children.

The purpose of this article is to underline the importance and to discuss the indications and techniques of crown lengthening procedures prior to prosthetic treatment of mutilated or undererupted permanent teeth of children. The aim of surgical crown lengthening is the exposure of at least 3 to 4 mm of healthy tooth structure coronally to the alveolar crest, length that will allow the formation of the new epithelial attachment and the existence of 1 to 2mm of tooth structure for the construction of a biologically acceptable crown margin. If the margin of the defect is inadequate distance from the alveolar crest the surgical procedure involves reduction of the attachment complex and is limited to the soft tissues only (a gingivectomy, apically repositioned full thickness flap, distal wedge). When the margin of the defect is close to the alveolar crest, less than 3 mm, the surgery involves also modification of the hard tissues of the periodontium (apically repositioned full thickness flap with ostectomy-osteoplasty). Although cases of children generally call for a conservative approach, the necessity for harmony between restorative procedures and materials with the supporting structures make surgical intervention inevitable.

[Amalgam build-up for endodontically treated posterior teeth with intraradicular extension]. / Anasystase apo amalgama endodontika therapeumenon opisthion dontion me endorrhizike epektase.

Prosthetic treatment of endodontically treated teeth usually involves the use of pins, prefabricated or cast posts that basically aim to protect the tooth from horizontal or vertical fractures. Nevertheless, according to the current way of thinking, the most important factors against tooth fractures are the preservation of as much as possible sound tooth structure as well as the use of full coverage. The amalgam coronal-radicular dowel and core technique is described in this paper. The method has been tested successfully in recent studies, both in vitro and in vivo. Its advantages are that it requires less sound tooth structure removal, involves uniform material for both the dowel and the core, is accomplished in a single chair side session and can be easily removed. It can accordingly be used as a complete crown build up in cases where prosthetic treatment has to be postponed for various reasons.

[Surgical crown lengthening procedures. Preparatory step for fixed prosthesis]. / Cheirourgike auxese tes klinikes myles: proparaskenastiko stadio gia ton akinete prosthetike apokatastase.

Necessary restorative requirements for full coverage are adequate axial wall height of the preparation for retention as well as sufficient vertical width of sound tooth structure cervically for the crown margins. In cases where adequate healthy tooth structure does not exist coronally to the epithelial attachment due to various crown damages, the margins of the crown might traumatize the periodontal attachment and the periodontium will be jeopardized iatrogenically. Teeth with inadequate axial Reight of the clinical crown, subgingival caries, vertical or horizontal fractures will require surgical crown lengthening procedures before prosthetic treatment is performed. These procedures may either involve only the soft tissues or bone remodeling as well. Irrespective of the procedure, crown lengthening must be performed with the objective of at least 3 mm. of healthy tooth structure coronally to the bone. This width will permit the formation of a new dentinogingival junction and the existence of 1-2 m.m. of sound tooth structure coronally to the new attachment line for the construction of a biologically acceptable crown margin. The purpose of this article is to discuss the clinical problem and underline the importance of crown lengthening procedures as a preparatory step for prosthetic treatment in fixed partial dentures.

[Shade selection in fixed prosthodontics]. / E epiloge tou chromatos ten akinete prosthetike.

Shade selection is a crucial clinical step during prosthetic treatment. Nevertheless, because it is based on subjective criteria, very often the esthetic result is compromised due to inadequate color reproduction. In order to explore this complicated problem, this paper attempts to analyse it as scientifically as possible. Initially, the physical phenomenon of "Color" is analysed. Color depends upon the light source, the object and the observer. Metamerism is the fatal enemy in shade matching. Shade selection through the use of shade guides is inadequate due to lack of standardization. Therefore the possibilities of improved application of the available materials are thoroughly explored for both simple and more complicated cases. Best results can be achieved by segmental color selection (separately for dentin and enamel).