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At least 685 records · Page 38Linked to original sources
PubMed1994

Marginal castability of two different materials (a comparative study).

Achieving a clinically acceptable margin is a conspicuous objective to any practicing dentist. The main concern is the space existing between the margin of the prepared tooth and that of the final restoration. Marginal fit has been measured and evaluated in a variety of methods., and a gap of approximately 50 microns is usually considered acceptable. While inlay wax is the material commonly used in the wax-up stage when fabricating crowns and bridges, Duralay (methylmethacrylate) is a material widely used nowadays in the field of fixed prosthodontics. Due to the ease of using this material intra-orally to form margins, an attempt is made to compare the castability of margins made out of inlay wax to the ones made out of Duralay.

Crowns↗
PubMed1986

Slicing technique for tooth specimens in histological preparation.

A slicing technique for the preparation of a tooth specimen is described. A low speed saw (ISOMET) was used for this modified technique. It is a slicing machine fitted with a diamond-impregnated cutting disc of 0.5 mm in thickness. The formalin was used for lubrication to serve as both a coolant and a fixative simultaneously. It is thought that the preparation will not damage or disturb the surface of the tooth specimen by careful management under 200 rpm with a loading of 50 grams. The cutting of slices can be controlled by adjusting the specimen arm with a micrometer to the desired thickness. A high quality histological preparation can be obtained when the specimen is sliced as mentioned above soon after it is removed from the living body before decalcification. By the observation of specimens such as the resected jaw bone or other large hard tissue specimens, it is suggested that the sliced specimens of 2 mm in thickness can be obtained routinely for histological study by using this method.

Animals↗
PubMed2001

Mechanically induced EPR signals in tooth enamel.

Sample preparation of tooth enamel for electron paramagnetic resonance (EPR) dosimetry usually involves mechanical operations. The present study shows that mechanical operations performed without water cooling generate a paramagnetic center inducing a stable isotropic EPR signal with g-value of 2.00320 and linewidth of about 0.1 mT. Using EPR spectrum simulation, the similarity between the mechanically induced signal and the signal generated when the enamel is heated in air at a temperature above 600 degrees C was investigated. Results indicate that the mechanically induced signal is related to sample temperature increase during mechanical friction.

Adult↗
PubMed2002

Histologic and radiographic assessment of caries-like lesions localized at the crown margin.

STATEMENT OF PROBLEMS: Little is known about the impact of crown margins on the demineralization and remineralization process or on the interpretation of radiographs for the detection of early secondary caries. PURPOSE: The aim of this study was to correlate the findings from 2 different radiographic techniques with the results of a histologic assessment of carieslike lesions at the crown margin. MATERIAL AND METHODS: Ten fully impacted third molars were extracted and restored with complete metal crowns with chamfer preparations. For each tooth, the prepared margin ended in enamel on one side and extended into cementum/dentin on the other. After being thoroughly cleaned, the teeth were covered with wax except for a 2- x 3-mm window at the crown margin in each of 2 test areas localized at the interproximal enamel and cementum/dentin junction. During demineralization with 6% hydroxyethyl cellulose gel at pH 4.9, direct digital radiographs or conventional radiographs were made at baseline and after 7, 14, 21, and 28 days. Each radiograph was blinded and examined for the presence/absence of lesions by 3 calibrated observers who used predetermined criteria required for receiver operating characteristic (ROC) analysis. After 28 days, the teeth were imbibed with methyl methacrylate and serially ground sectioned for assessment of the lesions in polarized light. Morphometric analysis of lesion extension included the calculation of mean values and standard deviations. Kappa and ROC analysis were applied to assess radiographs made at different demineralization time periods, localization of the crown margins in enamel or cementum/dentin, and direct digital and conventional radiographs. Data were tested for normal distribution (QQ plot), and statistical differences were calculated with Tukey's honestly significant difference post hoc test. RESULTS: Radiographic evaluation revealed only slight interexaminer agreement (Kappa) for enamel lesions (direct digital 0.19, conventional radiographs 0.2) and a fair interexaminer agreement for cementum/dentin lesions (direct digital 0.35, conventional radiographs 0.33). ROC analysis revealed no differences between the radiographic techniques. Lesions localized in cementum/dentin (direct digital 0.86 +/- 0.14, conventional radiographs 0.86 +/- 0.09) were diagnosed more reliably than those in enamel (direct digital 0.79 +/- 0.05, conventional radiographs 0.72 +/- 0.10). As microscopically assessed, the depth of lesions in enamel was less than that of lesions in cementum/dentin (49.3 +/- 7.3 microm vs 89.5 +/- 13.2 microm). Erosions were found in cementum/dentin (depth 25.2 +/- 5.3 microm). CONCLUSION: Within the limitations of this study, small artificial lesions were detected equally well by conventional and direct digital radiography. However, because of low interexaminer agreement, the radiographic assessment did not reproduce true histopathologic lesion characteristics documented by morphometry of serial ground sections.

Adolescent↗
PubMed2005

Remaining tooth structure associated with various preparation designs for the endodontically treated maxillary second premolar.

Existing literature suggests a relationship between the amount of remaining tooth structure and the fracture resistance of the restored endodontically treated tooth. This study investigated the amount of tooth structure remaining following various tooth preparations used in the restoration of the endodontically treated maxillary second premolar. Illustrations of the maxillary second premolar in buccopalatal, mesiodistal and occlusal sections were drawn to scale. Outlines of various intra- and extracoronal preparations were superim-posed on the illustrations to reveal the amount of tooth tissue remaining in each case. Preparations for a ceramic inlay, inlay with palatal cusp coverage and onlay left 2.0-2.5mm of tooth structure buccally and palatally. Following preparation for a metal-ceramic crown, approximately 1.0mm of tooth structure remained buccally, and between 1.6mm-1.8mm palatally. Preparation for an all-ceramic crown was observed to leave 1.0mm-1.2mm of tooth structure surrounding what remained of the endodontic access cavity. It was concluded that decisions as to the type of definitive restoration to restore the endodontically treated maxillary second premolar may be influenced, amongst other factors, by information on the amount of tooth tissue remaining following preparation.

Bicuspid↗
PubMed1988

Temperature gradients at two locations within the tooth during cavity preparation in vitro.

An improved method has been developed to measure temperature at both the DEJ and the PDJ during cavity preparation. This method allows a more realistic determination of the effects on the pulp tissue of various tooth reduction procedures. In future studies, the same method could also be used to determine pulpal effects from various restorative materials.

Body Temperature↗
PubMed1989

[Preparation of hard tooth structure with Excimer lasers. In vitro study].

The present study will show, that caries removal and conditioning of tooth surfaces by an (ArF)*-Excimer-Laser is an alternative to conventional preparation methods without thermal and mechanical irritations. This promises caries removal without pain to the patient. The photoablative process leads to retentive surfaces of the treated cavities. These findings promise good results in adhesive techniques. In vitro studies show, that photoablation of dental tissue is effective enough to make clinical usage possible.

Dental Caries↗
PubMed1991

Biomechanics of the intact, prepared and restored tooth: some clinical implications.

The practice of restorative dentistry has changed for many and varied reasons. They include changes in the epidemiology of dental caries due to fluoridation, and availability of new equipment and techniques for cavity preparation and new or improved restorative materials. Changes driven by these 'new' materials frequently do not provide the benefits anticipated. In the context of this paper, it is argued that, regardless of restorative materials and techniques, the biomechanics of intact, prepared and restored teeth must be understood to attain a satisfactory clinical outcome.

Biomechanical Phenomena↗
PubMed1993

Minor axial tooth movement in preparation for fixed prostheses.

In this first of two articles the theory and practice of creating occlusal clearance for restorative procedures without the removal of tooth tissue is discussed. Earlier techniques for producing minor axial tooth movement are reviewed, together with the relevant literature on continuous eruption and occlusal stability. The indications for axial tooth movement and alternative treatment options are also considered.

Dental Occlusion, Balanced↗
PubMed1989

[Preparation of hard tooth structure with Excimer lasers].

In this study the possible application of photoablation with an Excimer UV laser for the creation of retentive surfaces was studied as an alternative to conventional enamel conditioning methods using acids. Surfaces of untreated enamel and of prepared cavities were irradiated with an argon fluoride Excimer laser at a wavelength of 193nm and evaluated in a scanning electron microscope. The bond strength of composites to these surfaces was measured in tear tests. "Laser conditioning" left the surfaces similarly roughened as chemical etching. The variable extension of the laser field allows a sharp delineation of the area to be conditioned. The tear tests with human tooth enamel showed bond strength values corresponding to approx. 75% of those obtained by acid etching techniques. The question if these bonds are durable is the subject of current studies.

Adhesiveness↗