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Biomedical subjects

J B Dennison

Publications and source records attributed to J B Dennison.

At least 55 records · Page 3Linked to original sources
PubMed1979

Clinical success and potential failure after single application of a pit and fissure sealant: a four-year report.

A single application of a filled chemically initiated BIS-GMA sealant to permanent first molars of children ranging in age from 5 to 8 years covered the original sites in 52.4% of the 185 teeth examined after four years. Retention of sealant is greater in mandibular (64.7%) than in maxillary (42.0%) molars. The rate of loss of sealant was greatest during the first year (20%), then less than 10% per year at the second, third, and fourth recalls. In comparison with two similar studies, the retention of sealant was 20% to 30% greater. Using the parameters of percent effectiveness, net gain, and DMF scores per 100 test and control teeth, the data from the current study indicate a continued positive effect substantially greater than that in other similar studies. Complete loss of sealant does not appear to predispose that surface to caries any more than its contralateral paired surface. However, a partial loss of sealant because of abrasive wear that results in the exposure of the terminal ends of a fissure is a potential failure in that it creates an environment conducive to caries. Thus, even the well-applied sealant does not necessarily constitute permanent obturation of pits and fissures. Periodic clinical observation is necessary to determine the success or potential failure of the sealant treatment.

Child↗
PubMed1978

Surface finish of dental composite restorative materials.

Five composite filling materials were finished using six finishing procedures currently in clinical use. The average roughness produced by each procedure was measured by means of a Surfanalyzer with four replications for each procedure on each of the five materials. Statistical analysis indicated that finishing with silicon carbide disks produced the smoothest surfaces. Acceptable surfaces were obtained with stones or with burs. Use of an alumina paste after a green stone-white Arkansas sequence did not produce a significant improvement. Two processes of filler particle abrasion were distinguished by means of electron microscopy: wear and shear. Fracture striations indicated particle shear. The roughest surfaces were produced by the use of a diamond instrument which is contraindicated. Acceptable finishing procedures for the composite materials tested include silicon carbide disks for accessible areas or 12 fluted finishing burs for more inaccessible areas.

Composite Resins↗
PubMed1978

Color of dental restorative resins.

The color of 7 composite resins, an unfilled restorative resin, and 3 glaze coatings was determined by reflection spectrophotometry and visually with Munsell color tabs. Statistically significant correlations existed between comparable parameters of the spectrophotometric and Munsell data. There was observable color variations among the 11 resins studied, but only 3 materials were within the range for natural tooth color.

Acrylic Resins↗
PubMed1978

Characterization of enamel surfaces prepared with commercial and experimental etchants.

Polished enamel surfaces were etched with various commercial and experimental etching solutions and evaluated for changes in surface profile and topography. Enamel surfaces that were exposed to solutions of phosphoric acid in a concentration between 37% and 50% for a minute gave the most suitable surfaces for retention of the polymer. Enamel surfaces that were roughened with a diamond stone were not etched uniformly. Enamel that was exposed to acid etching solutions was better protected by a polycarboxylate cement than by either calcium hydroxide or zinc phosphate.

Acid Etching, Dental↗
PubMed1977

Effects of design on stress distribution of intracoronal gold restorations.

Eight intracoronal and extracoronal designs for gold restorations with different tapers to the lateral walls were investigated to determine the most efficient design in distributing occlusal stresses. It was found that the occulusal wall of an inlay cavity with a 7 degree taper and no bevel resulted in a better stress distribution than a cavity preparation with a greater taper or a long bevel. It was shown further that a wide inlay preparation resulted in less stress if the cusps were protected by gold.

Crowns↗
PubMed1977

A filled pit and fissure sealant: 18-month results.

One hundred and forty-three patients ranging in age from 5 to 8 years participated in a pit and fissure sealant study using a half-mouth design. At the end of 18 months, for all permanent first molars, there was a 75.9% effectiveness with a net gain of 82, which was statistically significant. The sealant was present on the surfaces to which it was applied in 74% of the teeth. Application time was 8 minutes per quadrant and 5.5 minutes per tooth. The effect of treatment was similar to that reported for an unfilled BIS-GMA sealant in patients with similar teeth and similar ages. Loss of sealant from the permanent maxillary first molars did not appear to contribute to the initiation of dental caries. However, in 6 of 38 mandibular tooth surfaces, sealant loss may have been a factor.

Acrylic Resins↗
PubMed1976

Penetration of restorative resins into acid-etched human enamel.

In this investigation, the penetration of different resins into the etched enamel surface and the effect of their viscosity on the penetration of these materials were studied. Freshly extracted teeth were pumiced, rinsed, and dried. The enamel surface was etched by using a solution containing 50% phosphoric acid for one minute; in one group the teeth were etched for two minutes. A layer of enamel surface of another group of teeth was removed before etching; these teeth were etched for one minute. Three different resins--Nuva-Seal, Concise Enamel Bind, and Restodent--were applied to the acid-etched enamel surface for one minute. The Concise composite resin also was applied to the enamel surface of a group of teeth etched for the same period of time. Observations with SEM and polarized light microscopy showed penetration of all the materials into the etched enamel surface to be 5 mum to 10 mum, with a mean of 7 mum. There was no difference in the penetration of these materials despite their different viscosities. The removal of a layer from the enamel surface was not effective in the penetration of the materials.

Acid Etching, Dental↗
PubMedDate not supplied

Effects of cement bases on the stresses and deflections in composite restorations.

A model was used to investigate stresses and deflections in cement bases and in a composite restorative material induced in a posterior Class I restoration. Deflections in the composite were highest when it was supported by a base with a low modulus; however, the maximum tensile stress (12 MN/meter2) occurring in the composite restoration at the interface with the base was well below the maximum tensile strength of most composite materials (30 to 40 MN/ meter2). Tensile and shear stresses occurring in the cement bases were of sufficient magnitude to exceed the strength of the cement when a 1.5-mm layer of zinc phosphate cement (base consistency) was supported by a 0.5-mm layer of ZOE lining material. Lowest values of stress were observed when a 2-mm layer of a zinc polyacrylate base was used to support the composite restoration. An ideal situation would be to have a cement base with a modulus of elasticity equal to that of the composite material. Finally, the maximum stress and deflection values obtained here can be easily exceeded in a clinical situation when wider variations can be easily introduced, making the choice of a cement with the proper modulus even more critical.

Composite Resins↗
PubMedDate not supplied

Parameters that affect the color of direct restorative resins.

The effects of thickness, background color, specular reflection, and surface roughness on the color of five commercial restorative resins were studied by reflection spectrophotometry. As thickness increased, values of luminous reflectance and excitation purity increased for a black background but decreased for a white background. Opacity increased dramatically as thickness increased from 1.3 to 3.9 mm.

Acrylic Resins↗
PubMedDate not supplied

Color stability of restorative resins under accelerated aging.

The color stability of seven commercial composite resins, an unfilled resin, and three glazes was studied under conditions of accelerated aging by reflection spectrophotometry and visually with Munsell color tabs. After aging for 900 hours, most of the resins had lower values of luminous reflectance and excitation purity and higher values of dominant wavelength and contrast ratio compared to values at baseline.

Acrylic Resins↗
PubMedDate not supplied

A survey of failure modes in composite resin restorations.

This study was undertaken as a first step in identifying opportunities to decrease the need for replacement of class 3, 4, and 5 composite resin restorations. Data regarding the reasons for original placement or replacement of a restoration, the age of restorations at the time of replacement, and patient/doctor factors that may be associated with a decision to place or replace a restoration were recorded by use of a cross-sectional survey. During a 2-week period 108 dentists recorded reasons for placing or replacing 1360 restorations. Of the 1360 restorations, 42.8% were classified as primary placement and 57.2% as replacement restorations. Of the primary placements 80% were categorized as being due to caries; 9.1% fracture of tooth; 8.4% other (erosion lesions were specified 94% of the time). By class, caries was the dominant cause for class 3 (96.2%); caries and other (erosion) for class 5 (77.3% and 16.4%); fracture of tooth and caries (48.9% and 40.2%) for class 4 restorations.

Chi-Square Distribution↗
PubMedDate not supplied

The effect of pulpal fluid flow on tensile bond strength of a glass-ionomer cement: an in vivo and in vitro comparison.

Previous studies of the bonding capabilities of glass-ionomer cements have concentrated on the use of in vitro testing conditions. Since early moisture contamination appears to have adverse effects on the physical properties of glass-ionomer cements, and with the probability of pulpally derived dentinal fluid being present under in vivo conditions, the objective of this study was to compare in vivo tensile bond strength with in vitro tensile bond strength of a glass-ionomer cement to dentin utilizing the same teeth under similar test conditions. A glass-ionomer lining cement was placed on freshly exposed labial dentin of the maxillary incisor on 10 Rhesus monkeys. Immediately following placement, an orthodontic button was placed over the cement and left undisturbed for 1 hour. The teeth were then extracted and stored in 100% relative humidity for 23 hours. An Instron testing machine was used to register in kilograms the force required to cause tensile bond failure of the cement. Identical methodology was then used on the same teeth for in vitro testing. The concluding results indicate that a statistically significant difference (P < or = 0.05) exists between in vivo and in vitro tensile bond strengths of the glass-ionomer lining cement and that the bond failure was cohesive in character for all cases both in vivo and in vitro. These findings suggest that clinically, tensile bond strengths of glass-ionomer cements to cut dentin can be expected to be weaker in vital teeth than in devital teeth.

Animals↗
PubMedDate not supplied

Dentin bonding: SEM comparison of the dentin surface in primary and permanent teeth.

The literature suggest differences between primary and permanent teeth regarding the composition and morphology of the dentin. The purpose of this study was to compare the effect of two dentin conditioners on the micromorphology of the dentin surface of primary and permanent teeth. Human extracted and noncarious molars were divided into four groups and conditioned with either 10% phosphoric acid (All-Bond 2) or 10% maleic acid (Scotchbond Multi-Purpose) for different time periods. SEM photomicrographs (1500x) were taken from the conditioned dentin and evaluated blindly by three calibrated examiners. The results indicate that the smear layer was removed more easily from primary teeth than from permanent teeth (P = 0.0001), which suggests greater reactivity to acidic dentin conditioners. We also found that the longer the time of application of dentin conditioner the more smear layer is removed (P = 0.0094). In comparing primary and permanent dentin, the results of this study indicate that less time is required for appropriate acid conditioning of primary dentin surfaces. Such a differentiated protocol for bonding to primary tooth dentin results in surface morphological characteristics similar to those found in conditioned permanent teeth.

Acid Etching, Dental↗