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At least 73 records · Page 4Linked to original sources
PubMed2000

Perturbative and nonperturbative parts of eigenstates and local spectral density of states: the wigner-band random-matrix model

The Wigner-band random-matrix model is studied by making use of a generalization of Brillouin-Wigner perturbation theory. Energy eigenfunctions are shown to be divided into perturbative and nonperturbative parts. Several perturbation strengths predicted by the perturbation theory are found to play important roles in the variation of the shape of the local spectral density of states with perturbation strength.

Journal Article↗
PubMedDate not supplied

A matrix solution for severly broken-down teeth.

A technique is described for preparation of a dead-soft copper band matrix for tooth restorations. Such a matrix is particularly useful in the restoration of teeth with significant variation in occlusogingival height.

Dental Amalgam↗
PubMed2006

Handling protocol of posterior composites--part 3: matrix systems.

Two of the major clinical problems related to direct posterior composite restorations are the clinician's inability to establish an ideal proximal contour and interproximal contact, which, in turn, can lead to continual food impaction and periodontal disease. The reason for this is that composites provide little internal force to counteract the force from the matrix. Therefore, unlike amalgams, which possess a very high resistance to deformation, composites are easily forced back into their original position by a tight circumferential matrix band. Thus, although tight contacts in small-moderate sized cavities may be possible for posterior composites using circumferential matrices, special matrix systems and wedging techniques are being required to establish a proper contact, especially when cavities with a wide buccolingual width are being restored.

Acrylic Resins↗
PubMed1987

Extraoral matrix for reconstruction of damaged teeth.

Conventional matrix bands are inappropriate for restoring extensively damaged teeth because of inadequate contact areas, inconsistent gingival margins, and undefined occlusal relationships. An extraoral matrix can be fabricated before intraoral reconstruction of the tooth.

Dental Instruments↗
PubMed2002

Modified Class II open sandwich restorations: evaluation of interfacial adaptation and influence of different restorative techniques.

The sandwich technique with resin-modified glass ionomer cement (RMGIC) has been proposed to relieve the contraction stresses of direct resin composite (RC) restorations. The aim of this study was to evaluate the interfacial adaptation to enamel and dentin of modified Class II open RMGIC/RC sandwich restorations and the influence of different light curing techniques and matrix bands. Forty box-shaped Class II fillings were placed in vivo in premolars scheduled for extraction after one month. In groups I and II, a metal matrix was used; RC was inserted with horizontal (group I) and diagonal (group II) increments and cured with indirect/direct light. Group III was performed as group II, but a transparent matrix was used. Group IV was as group II, but with a separating liner between RMGIC and RC. Group V was a closed sandwich restoration. Interfacial quality was studied using SEM replica technique. Gap-free interfacial adaptation to enamel was observed for RMGIC in 70%, for RC in 70% and to dentin for RMGIC in 81%, for RC in 56%. No significant differences were seen between the experimental groups. At the cervical margins, RMGIC showed significantly better adaptation to enamel than RC, 74% and 42%, respectively. In conclusion, the investigated restorations showed a high percentage of gap-free interfacial adaptation in vivo. Interfacial adaptation to dentin and to cervical enamel was significantly better for RMGIC than for RC.

Adolescent↗
PubMed2000

Correlated random band matrices: localization-delocalization transitions

We study the statistics of eigenvectors in correlated random band matrix models. These models are characterized by two parameters, the bandwidth B(N) of a Hermitian NxN matrix and the correlation parameter C(N) describing correlations of matrix elements along diagonal lines. The correlated band matrices show a much richer phenomenology than models without correlation as soon as the correlation parameter scales sufficiently fast with matrix size. In particular, for B(N) approximately sqrt[N] and C(N) approximately sqrt[N], the model shows a localization-delocalization transition of the quantum Hall type.

Journal Article↗
PubMedDate not supplied

Stable matrix for amalgam build-up.

A method is proposed of making amalgam build-ups for coronally debilitated teeth through the use of a stable matrix consisting of a disposable tray and polyvinylsiloxane occlusal registration material. For teeth with minimal remaining coronal tooth structure and/or the absence of adjacent teeth, this technique provides proper stabilization of the matrix band to permit adequate condensation of amalgam.

Dental Amalgam↗
PubMedDate not supplied

Modified matrix adaptation for sub-gingival Class II amalgam restorations.

Proper placement of the matrix and wedge is critical for the success of Class II amalgam restorations. Improper placement of matrix and wedges can result in poor contours or contacts, overhangs or weakness resulting from poorly condensed restorative material. This paper presents a technique for adaptation of a combination of matrix bands in cases where the gingival cavosurface margin extends deep sub-gingivally.

Dental Amalgam↗
PubMedDate not supplied

Establishing approximal contacts in Class 2 composite resin restorations.

Ensuring adequate approximal contacts when performing class 2 composite resin restorations is a significant challenge for the dentist. Fabrication of custom composite cylinders for placement into prepared cavity preparations enables the dentist to wedge the matrix band firmly against adjacent teeth, as well as eliminating the curing contraction variable that occurs when composite restorations are placed. Thus, predictable approximal contacts are obtained when class 2 composite restorations are completed.

Composite Resins↗
PubMed1980

Surface roughness of two dental amalgams after various polishing techniques.

1. In comparison with standard polishing after 24 hours, no advantage is gained by using an abrasive paste after 10 minutes. Polishing after 24 hours produced a significantly smoother surface for both amalgam alloys on both the simulated proximal and occlusal surfaces. 2. The standard polishing procedures after 24 hours produced a smoother surface than any of the immediate finishing procedures tested. 3. The high-copper amalgam was signijficantly rougher with initial carving and immediate finishing, but surfaces of both alloys were equally smooth when polished after 24 hours. 4. Both amalgam alloys, when condensed against a new matrix band lacked smoothness when compared to the surfaces obtained by finishing after 24 hours. 5. There was a high correlation between arithmetic average roughness and average maximum peak height as quantitative measurements of surface texture.

Chemical Phenomena↗
PubMed1996

An effective technique for extended proximal contacts in composite resin restorations.

Obtaining a firm anatomic contact has been a difficult criteria in placing Class II posterior composite restorations. Various techniques have been developed and a number of products marketed to accomplish this task, but none have combined the necessary qualifications of ease, simplicity, and effectiveness for consistent and predictable results. To address this challenge, two innovative devices--a precontoured (biplanar concave) sectional matrix band and a light--focusing tip-have been developed. Using a clinical case presentation, this article describes the application of these devices to obtain high quality proximal contacts, even in widely separated teeth. The learning objective of this article is to familiarize clinicians with this procedure. The technique is simple and universally applicable with a variety of posterior composite materials and placement methods.

Bicuspid↗
PubMed1991

Wedges in restorative dentistry: principles and applications.

Overhanging margins of proximal restorations are a well-known, iatrogenic cause of periodontal pathology. The high incidence of such findings in Western societies should arose the concern of the dental community. However, overhanging margins represent only part of the iatrogenic problem created by the misuse of wedges in restorative procedures. Other causes include incorrect proximal contouring, inadequate contact points and under- or overfilling the restorative material. The understanding of the variables associated with wedge selection and positioning has a major role to play in the prevention of iatrogenic periodontal pathology associated with restorative procedures. It is concluded that: (i) the occlusion of the matrix band to the remaining healthy tooth structure of the gingival cavosurface line angle should be achieved solely by the correct application of the wedges; (ii) the effect of the wedges on the proximal contour and contact area should be carefully re-evaluated prior to insertion of the restorative material; (iii) various sizes and shapes of wedges and a sharp knife for carving must be readily available.

Dental Caries↗
PubMed2001

Handling characteristics of a palladium-free gallium-based alloy compared with a high copper dental amalgam in a simulated clinical trial.

The aim of the current study was to compare the handling characteristics of a palladium-free gallium-based alloys (Galloy) with those of a high-copper amalgam (Permite C). The study had a particular interest in the evaluation of the direct placement delivery system used with both alloys. Ten dentists participated in the current study. Each placed two amalgam and two gallium-based alloy restorations in conventional class II cavities prepared in acrylic typodont teeth. None of the participating dentists had used the direct placement delivery system or had any previous experience with gallium-based alloy and no practice was allowed beforehand. The restorations were evaluated according to the following criteria: ease of loading the cavity (delivery system), ease of condensation, capacity to produce and sustain contact area, ease of carving, resistance to damage during removal of the matrix band, overall quality of the restoration and the available working time. Each criterion was given a score on a scale of 1-5 (1: very poor, 2: poor, 3: fair, 4: good, 5: very good). The results showed no statistically significant difference in the evaluated criteria between the two alloys (P > 0.05) except for criterion number 2 (ease of condensation, P=0.0005).

Acrylic Resins↗
PubMed1995

In search of a suitable denture marker.

The ID-Band (SDI AB, Sweden) has become the standard, internationally and FDI accepted denture marking system. In Australia however the strip is not easily obtainable and is expensive. Two other materials have been trialled as possible alternatives: (1) Titanium foil (9 microns) and (2) Ho Band (matrix) (3 microns) (Lorvic Corp, USA). All three bands were tested for tensile strength and elongation at temperatures: RT, 700 degrees and 900 degrees C. As the ID- and Ho Bands are both 18-8 stainless steel their performance was similar. The 18-8 was stronger, had a higher percentage break point and a higher elongation. The latter meant that it was softer and could be more easily inscribed and was therefore more suitable for denture marking. T1 is becoming increasingly used in dentistry but in spite of its abundance it is not likely to replace stainless steel for denture marking at present. On the other hand the Ho Band is cheaper, more readily available and it could replace ID-Band for use in Australia. An alternative paper based marking system is also presented together with the rationale for its use.

Denture Identification Marking↗