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At least 1,063 records · Page 59Linked to original sources
PubMed1990

A comparative study of porcelain repair materials.

Intra-oral fracture of metal-ceramic restorations sometimes occurs when clinical and laboratory techniques have been inadequate. Removal and refabrication of the prosthesis is the ideal solution, but may not always be practical. Recently, several products have been marketed for expediting the repair of fractured restorations in the mouth. This study compared the effectiveness of three of these repair systems (Super-C, Command Ultrafine and 3M Porcelain Repair Kits) with a control group of porcelain-fused-to-metal specimens. Measurement of failure load of each material being tested was carried out in compression using a universal testing apparatus and a specially designed jig. Each experimental and control group contained ten specimens. Each material was tested individually for repairs against metal and against porcelain. A comparison of the failure load values indicated that the control samples gave the highest mean value of 881.6 +/- 192.9 N, while that of Super-C against metal was the lowest at 385.4 +/- 102.4 N. The Command Ultrafine Repair Kit was the strongest of the repair systems studied.

Analysis of Variance↗
PubMed1982

Thiamine pyrophosphatase activity of the prenatal mouse molar. A histochemical investigation.

Thiamine pyrophosphatase (TPPase), an enzyme associated with the Golgi apparatus, has been implicated in the regulation of cellular oxidation as well as of transport across cell membranes. This enzyme has been localized in odontogenic tissues of the postnatal mouse and it was the intent of the present study to localize TPPase during prenatal odontogenesis. Mouse fetuses (CDI, Charles River) 14 through 19 days postconception were decapitated, the heads were frozen and mounted on the chuck of a cryostat. Frontal sections, 14 micrometers thick, were air-dried and incubated for TPPase activity. Subsequent to incubation the activity was visualized by immersion in 1% ammonium sulfide. The degree of enzyme activity varied not only with the chronological age of the fetus but also as a function of the tissue's metabolic state. Regions, such as the dental lamina, evidenced decreased TPPase activity with increasing age, while tissue layers such as the IEE displayed greater enzyme activity with increasing age.

Animals↗
PubMed1995

In vitro radiographic representation of the extent of voids within obturated root canals.

The aim of this study was to determine whether radiographs provide an accurate representation of the degree of root canal obturation following a cold lateral condensation technique. A total of 40 extracted single-rooted lower premolar teeth were prepared using either a standardized step-back technique or an ultrasonic device by one of two operators. The four groups each of 10 teeth were obturated using lateral condensation by a third operator. To assess apical leakage the obturated teeth were coated with nail varnish to within 2 mm of the apex and immersed in methylene blue for 48 h. The teeth were then radiographed in bucco-lingual and mesio-distal planes prior to subsequent sectioning in a bucco-lingual plane. Sections and radiographs were analysed using an image analysis apparatus to determine the proportion of root canal occupied by gutta-percha, void and/or sealer. Mean percentages of void calculated from the bucco-lingual radiographs, mesiodistal radiographs and tooth sections were 4.14%, 5.98% and 4.98%, respectively. Statistical analysis showed no significant differences between the radiographic views and the tooth sections (P > 0.05). Both planes of radiograph accurately represented the proportion of void when compared with the tooth section.

Analysis of Variance↗
PubMed1989

[The ultrastructure of human enamel organs].

The ultrastructural features of enamel organs from 3 human fetus were examined in this study. There were few and simple organelles in the inner enamel epithelium, this imply that these cells were not active ones. Comparing with the inner enamel epithelium, the ameloblasts showed active functional condition. They had a large amount of mitochondria, enlarged rough endoplasmic reticulum and well developed Golgi apparatus in the distal cytoplasm. On the top of the ameloblasts, Tomes' processes were formed. In the Tomes' processes, there were numerous vesicles containing "stippled material". This kind of material also could be seen in the spaces between the Tomes' processes and the enamel matrix, and in the vesicles of the Golgi apparatus. Ultrastructurally, each enamel matrix invagination received a large part of process of an ameloblast and a small part of another ameloblast. But the meaning of this structure were unclear. Tight junctions were found at the distal part of the ameloblasts. The stratum intermedium cells, beside the ameloblasts, had a lot of small processes protecting into the intercellular spaces. Gap junctions were found between all enamel organ cells, and illustrated that there were active material transmissions between these cells.

Ameloblasts↗
PubMed1985

Machinability of some dentin simulating materials.

Machinability in low speed drilling was investigated for pure aluminium, Frasaco teeth, ivory, plexiglass and human dentin. The investigation was performed in order to find a suitable test material for drilling experiments using paralleling instruments. A material simulating human dentin in terms of cuttability at low drilling speeds was sought. Tests were performed using a specially designed apparatus. Holes to a depth of 2 mm were drilled with a twist drill using a constant feeding force. The time required was registered. The machinability of the materials tested was determined by direct comparison of the drilling times. As regards cuttability, first aluminium and then ivory were found to resemble human dentin most closely. By comparing drilling time variances the homogeneity of the materials tested was estimated. Aluminium, Frasaco teeth and plexiglass demonstrated better homogeneity than ivory and human dentin.

Aluminum↗
PubMed1999

The influence of luting cements on the fermentation of sucrose by oral microorganisms.

OBJECTIVES: Three luting cements based on zinc oxide phosphate, glass ionomer or composite resin were compared with respect to their influence on the anaerobic fermentation of sucrose by human oral bacteria. METHODS: Fifteen standardized samples of each of the three luting cements were prepared according to the manufacturer's instructions and stored for 72 h at 37 degrees C in distilled water, which was also used as elution medium. After removing the samples solutions were incubated with human fasting saliva, sucrose and a bicarbonate buffer in a Warburg apparatus. Intermediary organic acids resulting from anaerobic fermentation of sucrose were quantified indirectly by manometric measurement of CO2, released from the buffer. RESULTS: The materials did not indicate either an accelerating or an inhibiting effect on the formation of organic acids from sucrose. CONCLUSION: In the case of bacterial microleakage along the interface between cavity and luting cement, an inhibition of acid induced dentin or enamel demineralisation--using the materials investigated--cannot be expected.

Analysis of Variance↗
PubMed2004

Measurement of the setting expansion of phosphate-bonded investment materials: part II--An evaluation of the Casting-Ring Test at 10 laboratories.

The Casting-Ring Test has the potential to fulfil the requirement for a reliable 'Standard' test to measure the setting expansion of phosphate-bonded investment materials. The purpose of this study was to investigate the reproducibility of the measurements and the value that is produced at 10 test sites. The Casting-Ring Test apparatus, three phosphate-bonded investment products and one ring liner product were sent to the 10 participants, together with a detailed test protocol. Participants were asked to use their normal vacuum mixers. Reproducibility at individual sites was good. However, there were significant differences between test sites for the mean setting expansions, attributed to the range of vacuum mixers employed. From these results, the Casting-Ring Test appears to satisfy the requirements for adoption as an ISO standard test. The effect produced by different vacuum-mixer models would be manifest in any test. Not only does this have implications when determining the value of setting expansion for product information, but such a range of setting expansions will also be reproduced during production of moulds in commercial dental laboratory practice. However, for any specific product and vacuum-mixer combination, the setting expansion will be consistent and will not vary from mould to mould.

Chemical Phenomena↗
PubMed2003

Wear and superficial roughness of glass ionomer cements used as sealants, after simulated toothbrushing.

The purpose of this study was to evaluate, in vitro, the properties (wear and roughness) of glass ionomer cements that could influence their indication as pit and fissure sealants. The utilized materials were Fuji Plus, Ketac-Molar and Vitremer (in two different proportions: 1:1 and :1). The resin-based sealant Delton was used as control. By means of an electronic balance (precision of 10-4 g), wear was measured in function of weight loss after simulated toothbrushing. Superficial roughness was determined by means of a surface roughness-measuring apparatus. The results revealed that diluted Vitremer and Fuji Plus were less resistant to toothbrushing abrasion and had the greatest increase in superficial roughness. Although in clinical situations luting or diluted ionomer cements are often utilized as alternatives to resin-based sealants, the resultsof this study revealed that the properties of those cements are worse than those of restorative ionomers, whichpresented results similar to those of the evaluated resin sealant.

Dental Restoration Wear↗
PubMed1978

[Food and water intake of the rat in a recording device].

Knowledge of the normal eating and drinking habits of the rat is indispensable for comparative experiments concerned with the cariogenicity of different diets. At a time six rats were maintained individually in a registration apparatus (Hofer, Switzerland). Food (basal diet "ssniff") and normal tap water was made available ad libitum. The amounts of food and water, as well as the frequency and duration of food intake, were registered by a pen recorder, which was connected to an electronic balance. The experiment began with three week old rats, and lasted 9 weeks. Conclusions on the procedure of short term caries experiments with rats could be drawn from the results.

Animal Feed↗
PubMed1988

Localization and synthesis of type III collagen and fibronectin in human reparative dentine. Immunoperoxidase and immunogold staining.

The injury of dental pulp tissue, following caries, is accompanied by the deposit of a typical hard scar tissue known as reparative dentine which should be regarded as the mineralization of a new organic matrix. Highly purified antibodies were used in combination with immunoperoxidase or immunogold technique at the ultrastructural level to reveal the distribution and synthesis of types I and III collagen and fibronectin elaborated by typical matrix-forming cells in the new tissue. Specific immunoperoxidase labelling, on demineralized teeth, clearly demonstrated that type I collagen represents the main type of collagen (88%). It is associated with bundles of fine striated fibrils of type III collagen and in close vicinity with fibronectin and constituted, at least, the new organic matrix of reparative dentine. Immunogold staining gave precise localization mainly over Golgi apparatus for the 3 components, thus suggesting that the cells concerned should not be considered as new odontoblasts but rather as pulpal cells in the process of differentiation participating in the formation of new dentine. Moreover, these events are very similar to those observed during wound healing in other tissues.

Collagen↗
PubMed1996

The effect of plasma-treated polyethylene fiber on the fracture strength of polymethyl methacrylate.

The effect of a plasma-treated polyethylene fiber on the fracture strength of polymethyl methacrylate was evaluated in this study. Sixteen treated and 16 untreated polymethyl methacrylate bars were tested by use of a three-point compression loading apparatus. Under the conditions of this experiment the treated bars showed a mean fracture strength of 12.56 MPa compared with 9.81 MPa for the untreated samples. In addition to the increased fracture strength, the treated bars also demonstrated resistance to crack propagation. The bars remained in one piece, held together throughout the compression loading by the polyethylene fiber. The clinical implication of these findings is a reduced incidence of fixed provisional restoration failure.

Chemical Phenomena↗
PubMed2003

An oral surgeon's evaluation of Emdogain.

A product developed by researchers in Sweden (Biora AB Malmo, Sweden) has been approved by the United States Food and Drug Administration for use in the regeneration of periodontal attachment apparatus. Enamel matrix protein (Emdogain) has been shown to be effective in animal and human studies. This report documents a series of 19 clinical trials to help retain "hopeless" teeth referred for extraction. It was offered as an alternative to extraction. The techniques used involved a departure from the method specifically recommended by the manufacturer. Seventeen of the 19 teeth treated showed significant improvement with decreased mobility, improved attachment levels and new bone on follow-up radiographic examination.

Alveolar Bone Loss↗
PubMed1992

Dentin wetness, permeability and thickness and bond strength of adhesive systems.

This study evaluated the shear bond strength of Scotchbond 2, Clearfil PhotoBond, Tenure, All-Bond and Vitrabond and their sensitivity to dentin permeability, wetness and thickness. Occlusal dentin was prepared from extracted human teeth that were connected to a hydraulic pressure apparatus. Dentin permeability was calculated as a fluid flow rate and dentin surface wetness was evaluated using the Periotron device. Dentin thickness was measured using a pincer caliper. Shear bond strength was tested after 24 hours storage under hydrostatic pulpal pressure. Several significant correlations were found between dentin wetness, dentin permeability and remaining dentin thickness and the shear bond strengths of Scotchbond 2, Tenure and All-Bond/no etch. No apparent correlations were observed for the other adhesive systems.

Acid Etching, Dental↗
PubMed1990

[Linearity and error correction of the Meyer/dal Ri hinge axis measurement system].

Measurement errors inherently related to the instrument and those due to external factors were analysed for the SAS hinge axis measurement system in conjunction with the digital recording system. An optical bench served as measurement apparatus. Linearity errors are substantially less than 0.1 mm and thus of no clinical relevance. A slight reduction in the size of the movement coordinates imaged with slight incongruences of the six measurement canals results from erroneous calibration. The recording system proves to be insusceptible to interference by external factors in practical application. The projection error correction we investigated experimentally was satisfactory. Merely the processing quality of the electrical wiring attached to the measuring foils was not fully satisfactory.

Dental Articulators↗
PubMed2001

Size discrepancy of apical bases and treatment success in angle Class III malocclusion.

The aim of this retrospective clinical study was to measure the apical bases and determine their size relationship in Class III malocclusion cases before and after orthodontic treatment, in order to evaluate their significance for the treatment success. Maxillary and mandibular apical bases were measured on study models of 104 Class III cases treated by conventional orthodontics, using a specifically constructed conveyance apparatus, and related to each other as an index. Treatment success was quantitatively assessed as the percentage change of PAR scores obtained from the pretreatment and posttreatment study models. Statistically significant relationships were disclosed between the measurements of the apical bases and several other evaluated parameters. The results obtained indicate a high prognostic value of the size relationship of the apical bases for the treatment success of Class III malocclusion.

Adolescent↗
PubMed1989

Physical and mechanical properties of elastomers in orthodontic positioners.

Elastomers for conventional Kesling-type tooth positioners are relatively inelastic and are primarily indicated as finishing devices. However, new materials, first described in the Japanese literature, with claims of a greater range of tooth movement warrant a comparison with conventional materials. Physical and mechanical property testing of positioner elastomers has not been reported in the orthodontic literature. This investigation compared properties of a high temperature vulcanizing (HTV) Japanese silicone (Orthocon) to three traditional polyurethane and vinyl-based polymers and five experimental silicone elastomers. Fourier transform infrared spectroscopy established the definitive chemical composition of the urethane and vinyl materials obtained from a commercial positioner laboratory. Tear strength, tensile strength, tensile stress at selected elongations, and ultimate elongation of all materials were evaluated at 37 degrees C in an aqueous environment. Hardness and water sorption values also were determined and an in vitro force measurement apparatus was fabricated to determine force levels exerted by positioner materials at low displacements. Orthocon was statistically different (Duncan's multiple range test, p less than 0.05) from the traditional commercial urethane and vinyl materials. Orthocon had lower tear strength than the traditional materials. It also demonstrated lower stress values below 100% elongation. The parameters of tensile stress at 50% elongation and ultimate elongation were statistically identical for Orthocon and one experimental silicone material.

Absorption↗
PubMed1999

Coronal leakage of two root canal sealers containing calcium hydroxide after exposure to human saliva.

This in vitro study evaluated the coronal leakage of human saliva into root canals filled by lateral condensation of gutta-percha using two root canal sealers containing calcium hydroxide. Obturated canals with gutta-percha and either Sealapex of Sealer 26 were mounted in an apparatus and then exposed to saliva. The number of days required for total recontamination of the root canal was recorded. Evaluation was conducted for 60 days. Thirty-five percent of the specimens of the Sealer 26 group showed entire recontamination at 60 days. Eighty percent of the root canals obturated with Sealapex showed complete recontamination at 60 days. Sealer 26 presented significantly less leakage than Sealapex (p < 0.01).

Bismuth↗
PubMed2005

Chewing gum of antimicrobial decapeptide (KSL) as a sustained antiplaque agent: preformulation study.

The purpose of this study was to investigate the potential of KSL, an antimicrobial decapeptide, which has been shown to inhibit the growth of oral bacterial strains associated with caries development and plaque formation, to act as an antiplaque agent in a chewing gum formulation. A reversed-phase high-performance liquid chromatography method was developed for KSL and found to be stability-indicating. KSL was stable in acetate buffer at pH 4 and artificial saliva. On the affinity of KSL to tooth-like materials, the KSL showed favorable interaction with hydroxyapatite discs pretreated with human saliva. A chewing gum formulation of KSL was prepared based on conventional procedures and the release of KSL from the gum was studied in vitro using the chewing apparatus and in vivo by a chew-out method. The gum formulations showed promising in vitro/in vivo release profiles, in which 70-80% KSL was released in a sustained manner over 20 min of chewing time. This study suggests that KSL in a gum formulation is suitable for the delivery in the oral cavity, thereby serving as a novel antiplaque agent.

Anti-Bacterial Agents↗