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At least 883 records · Page 49Linked to original sources
PubMed1991

[Longevity of restorations in composite and etched porcelain].

Due to continuing alterations in composition of dental products and materials, prognoses about longevity of restorations in composite or etched porcelain are extremely difficult to make. Strength, wear resistance and resistance against disintegration determine durability of stress bearing restorations. Elasticity in combination with bond strength are determinant for prevention against premature leakage. Indication, cavity form and careful handling of the materials are prerequisites for longevity of the restoration. The prognosis of the favourably located but stress bearing class IV is far better than that of the unfavourable located, non stress bearing class V-composite restoration. For the etched porcelains, the veneers offer the best perspectives with respect to durability thanks to the favourable shrinkage pattern.

Acid Etching, Dental↗
PubMedDate not supplied

The effect of cross-sectional area on transverse strength of Amalgapin-retained restorations.

The transverse strength of large amalgam restorations retained by amalgapins of varying diameter and number was evaluated. Restorations with amalgapin retention fractured with greatest frequency parallel to the pulpal floor through the amalgapin at the amalgam-tooth interface. The findings indicate that the geometric configuration and number of amalgapins was of greater importance to the transverse strength of amalgapin-retained restorations than the total cross-sectional area.

Analysis of Variance↗
PubMedDate not supplied

Amalgam buildups: shear strength and dentin sealing properties.

The retentive strength and sealing properties of amalgam buildups were compared in vitro in three groups of specimens. All teeth were prepared with flat, nonretentive surfaces. In the first group, the amalgam buildups were retained by four self-threading Minim pins. In the second group, retention was provided by a circumferential slot prepared in the dentin just inside the DEJ. The third group utilized an adhesive resin for retention. Dentin permeability was measured as a hydraulic conductance before and after placement of the amalgam buildups and before and after thermocycling. All methods of retention sealed dentin very well even in the absence of cavity varnish. The 90 degree retentive strength was: pins, 10.3 +/- 0.9 MPa; slots, 4.1 +/- 0.5 MPa; resin, 3.1 +/- 0.8 MPa (mean +/- SEM).

Adolescent↗
PubMed1991

Comparison of resistance features for complex amalgam restorations.

This study evaluated the resistance provided to complex Dispersalloy amalgam restorations by pins (Group 1), amalgapins (Group 2), and a peripheral shelf or shoulder (Group 3) or in combinations of pins plus peripheral shelf (Group 4), or amalgapins plus peripheral shelf (Group 5). The occlusal surfaces of 50 extracted maxillary molar teeth were ground to a flat surface 2 mm occlusal to the CEJ, and the roots were matched and embedded in acrylic resin 2 mm apical to the CEJ. The greatest faciolingual and mesiodistal dimensions of each tooth at the level of preparation were recorded and these two measurements were multiplied to give a product for each specimen. The teeth were then sorted by tooth sizes and equally distributed among the five groups. Each group of flattened teeth received a different resistance form configuration. Amalgam was condensed using a matrix; the bands and excess amalgam were removed 24 hours later and each amalgam "occlusal" surface was ground flat to standardize the restoration at a 4 mm occlusal height. A 1 mm 45 degrees bevel was prepared on the facio-occlusal angle of the amalgam, and each specimen was loaded in compression at 45 degrees in an Instron at a crosshead speed of 1 mm/min. The groups and their mean (SD) failure loads in Newtons were: Group 1: 1515 (274); Group 2: 1521 (244); Group 3: 578 (175); Group 4: 1199 (229); and Group 5: 1691 (298). A one-factor ANOVA and a Tukey B post-hoc analysis showed no differences between Groups 1, 2 and 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1991

A technique for making porcelain facings.

New improved refractory die materials are now being introduced onto the UK market which make it possible to construct porcelain facings and inlays directly onto refractory dies. From previous experience with several refractory die facing systems, it was decided that the Flexo-Ceram system should be used. This is because the porcelain is matched to the full Vita shade range and the materials are relatively easy to handle.

Adult↗
PubMed1991

[Optimized pin geometry for improved retention of parapulpal pins in amalgam].

The retentive part of parapulpal pins is often very bulky, and this may compromise the strength of the amalgam restoration. This in turn may considerably limit the range of applications of parapulpal pins. For this reason the geometry of the retentive pin portion was optimized with the aid of a finite element analysis. This manoeuvre resulted in a better stress distribution and improved retention, although the pin size was reduced. In clinical terms this implies a wider range of possible applications, because these pins allow safe anchorage of extensive amalgam restorations and do not affect the strength of the restoration.

Dental Amalgam↗
PubMed1991

[Rehabilitation of partially edentulous cases with telescope crowns: modified, fully veneered tapered crowns].

Telescope crowns are well established as prosthodontic retainers for removable partial dentures. After a short review of the advantages and disadvantages of telescope crowns, the specifies of tapered crowns are described. By the use of appropriate tooth preparation and the fabrication of modified, fully resin-veneered tapered crowns, it is possible to improve on the crown contours and the aesthetics provided by conventional tapered crowns. Periodontal prophylactic conditions are also considered.

Aged↗
PubMed1991

[The hydrodynamic behavior of dentinal tubule fluid under occlusal loading].

In an in-vitro study, the fluid movements were quantitatively recorded in natural teeth incorporated rigidly in a closed measuring system and exposed to an occlusal load of 122.6 N. Fluid movements under load are the result of elastic deformations of the tooth. Occlusal loads which were repeated within a short period of time caused a reversible plastic deformation. In comparison to the unfilled tooth the placement of an MOD restoration combined with a glass ionomer cement base caused the following alterations in fluid movements: composite inlay -24.7%, ceramic inlay +34.7%, MOD amalgam -3.1%; the placement of the base per se induced a reduction of -12.7%. In this in-vitro study, the physical properties of the restorative materials governed the magnitude of the fluid movements under load. The results are in contradiction to clinical findings and favor the pulpitis-related genesis of postoperative sensitivity. The intratubular and intrapulpal fluid movements under occlusal load simply seem to trigger the pain sensation.

Biomechanical Phenomena↗
PubMedDate not supplied

Wear measurements in clinical studies of composite resin restorations in the posterior region: a review.

During the last twenty years, wear-evaluation methods have changed, with newer techniques developed to determine the extent of loss of material in posterior composite resin restorations functioning in the mouth. These included: direct clinical evaluation; marginal evaluation on models; heights of exposed cavity walls; volumetric assessment of impressions; profilometry and artificial or natural references; section measurements; coordinate measuring device, contact and noncontact scanning; measuring microscope; photogrammetry; moiré topography; laser interferometry; scanning electron microscopy; and optical scanning. A laser scanning technique appears to hold great potential in clinical research.

Bicuspid↗
PubMedDate not supplied

Fracture surface analysis of dental ceramics: clinically failed restorations.

Fractography was used to study all-ceramic restorations that had failed clinically. Some basic tenets of fracture mechanics and fractography are reviewed and related to the examination of clinically failed all-ceramic restorations. Dicor and Cerestore restorations that had failed either at trial placement or 17 to 36 months postcementation were evaluated. Failed Dicor restorations were studied to determine the origin of failure and calculate the intraoral stress at failure. Descriptive information regarding crack origin and crack path were obtained from failed restorations constructed of first-generation Cerestore. A majority of the crowns apparently failed from the internal surface, indicating this as the highest tensile surface and/or the location of the largest flaws. Flaws were identified as being related to fabrication or inherent in the ceramic microstructure.

Aluminum Oxide↗