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Biomedical subjects

J B Dennison

Publications and source records attributed to J B Dennison.

At least 19 recordsLinked to original sources
PubMed2003

Adhesive resin induces apoptosis and cell-cycle arrest of pulp cells.

The application of an adhesive resin near or directly over the pulp was shown to induce pulp inflammation and lack of dentin regeneration. We hypothesize that the absence of dentin bridging is due to adhesive-resin-induced apoptosis of cells responsible for pulp healing and dentin regeneration. Mouse odontoblast-like cells (MDPC-23), undifferentiated pulp cells (OD-21), or macrophages (RAW 264.7) were exposed to SingleBond polymerized for 0-40 seconds. Annexin V and propidium iodide assays demonstrated that SingleBond induced apoptosis of MDPC-23, OD-21, and macrophages. The proportion of apoptotic cells was dependent on the degree of adhesive resin polymerization. Adhesive-resin-induced death of pulp cells was associated with activation of the pro-apoptotic cysteine protease Caspase-3. Interestingly, most cells exposed to adhesive resin that did not undergo apoptosis showed cell-cycle arrest. We conclude that an adhesive resin induces apoptosis and cell-cycle arrest of cells involved in the regeneration of the dentin-pulp complex in vitro.

Analysis of Variance↗
PubMed2001

A clinical evaluation of air-abrasion treatment of questionable carious lesions. A 12-month report.

BACKGROUND: The efficacy of treating questionable incipient lesions early with air abrasion, a modality used by many practitioners, has not been adequately demonstrated. METHODS: The authors enrolled 223 teeth, each with a questionable incipient pit-and-fissure carious lesion, from 93 dental patients in a projected five-year randomized clinical trial. Caries was defined as softness, decalcification or cavitation at the base of a pit or fissure or radiographic evidence of caries. Each tooth was randomly assigned to either a treatment group (n = 113 teeth) or a control group (n = 110 teeth) (which was observed but left untreated until the definition of caries was met). Each tooth in the treatment group was air-abraded and restored with a flowable resin-based composite. The authors re-examined teeth in both groups every six months; they evaluated the restorations using a modified set of Ryge criteria and inspected teeth for caries using radiographs, mirrors and standardized explorers. RESULTS: Of the 113 teeth with questionable incipient carious lesions air-abraded in the treatment group, 50 had caries extending into dentin. After 12 months of clinical service, there were three sealants that exhibited a partial loss of sealant which did not require any re-treatment. Two restorations with penetrating staining were re-treated. In the control group at the end of 12 months, only nine of the 86 recalled teeth were diagnosed with pit-and-fissure caries and were treated with air abrasion and restored with flowable resin-based composite. There was no statistically significant difference between the volume of the treatment and control preparations. CONCLUSION: After 12 months of clinical service, two preventive resin-based composite restorations in the treatment group required re-treatment. Fewer teeth than expected in the control group were diagnosed as having caries and were treated. CLINICAL IMPLICATIONS: The merit of treating questionable incipient pit-and-fissure carious lesions early with air abrasion has not been demonstrated after 12 months in this clinical study.

Adolescent↗
PubMed2000

Effect of variable light intensity on composite shrinkage.

STATEMENT OF PROBLEM: Polymerization shrinkage is a critical limitation of dental composites and may contribute to postoperative pain, tooth fracture, microleakage, and secondary caries. Polymerization with high-intensity light sources has been related to increased depth of cure and improved mechanical properties. However, high-intensity light initiation has also been associated with greater polymerization shrinkage. PURPOSE: The purpose of this study was to investigate the effect of sequentially increasing light intensity on the polymerization shrinkage of 2 composites, a hybrid and a microfil. A Knoop hardness test was used to evaluate effectiveness of the cure with each intensity increase. MATERIAL AND METHODS: Four groups of 12 samples were measured for polymerization shrinkage by using a linometer. Light intensity curing sequences were as follows: full-intensity control (100% intensity for 40 seconds), low-intensity control (25% intensity for 40 seconds), test group 1 (25% intensity for 20 seconds, 50% for 10 seconds, 100% for 10 seconds), and test group 2 (25% intensity for 10 seconds, 50% for 10 seconds, 100% for 20 seconds). Statistical comparisons were made using a 1-factor ANOVA and a Tukey multiple comparisons test within each material. RESULTS: Results showed a significant difference (P<. 05) in mean linear shrinkage between the full-intensity control group and the other 3 sequences for both composites. No difference existed within the other 3 groups for either composite. Knoop hardness was similar for the full-intensity control and test group 2. The low-intensity control group and test group 1 were also similar but significantly lower. CONCLUSION: Curing composites for 10 seconds at 25% intensity, 10 seconds at 50%, and 20 seconds at 100% significantly reduced polymerization shrinkage while not compromising depth of cure.

Analysis of Variance↗
PubMed2000

Effectiveness of sealant treatment over five years in an insured population.

BACKGROUND: The authors analyzed an insurance claim database to evaluate the use and effectiveness of placing sealants on first and second permanent molars of children in private dental practices. METHODS: A retrospective study was conducted using an insured population with sealant coverage at 70 percent of the usual fee in a preferred provider organization than that limited reapplication to once every three years. Children were selected who were eligible for sealant benefits from July 1, 1990, to June 30, 1991. Two groups were selected for analysis, based on age, as determined by permanent molar eruption dates. Children who received sealants were compared with those who did not to determine post-sealant restorative outcomes after five years. RESULTS: During the full year of coverage, sealants were used in only 16.3 percent of first permanent molars and 11.6 percent of second permanent molars. The five-year incidence of an occlusal restoration having been placed was 13.7 percent and 20.8 percent, respectively, on nonsealed first and second molars and 6.5 percent and 10.4 percent, respectively, on sealed first and second molars. From years three to five, sealant placement provided only nominal additional preventive effect. CONCLUSIONS: In the population selected, both the incidence of occlusal caries and the use of sealants were lower than expected for both age groups. However, within these groups, molar occlusal surfaces were only half as likely to have been restored in sealed teeth than in nonsealed teeth after five years. CLINICAL IMPLICATIONS: Based on the five-year data from a population with a low incidence of caries, the authors found that 15 sealed first permanent molars or 10 sealed second permanent molars prevented placement of one occlusal restoration. Therefore, sealants are more effective when placed in patients with risk factors for occlusal caries.

Adolescent↗
PubMed1998

Fluoride release and re-uptake in direct tooth colored restorative materials.

OBJECTIVES: Glass ionomers may be "recharged" through topical fluoride (F-) treatments; however, this reported "recharging," may be attributed to surface changes after F- treatment. This study examined differences in F- release and re-uptake among dual-cured and chemically-cured glass ionomers, and a photo-cured F- releasing composite. A secondary goal was to determine if tensile strength or surface roughness changed due to F- release, or F- re-uptake and re-release. METHODS: In Phase 1, initial surface roughness and diametral tensile strength were measured. F- release was measured for 30 days. Strength and roughness were then remeasured. In Phase 2, surface roughness was measured, then materials were treated with a 5000 ppm neutral F- gel, the same gel without F-, or phosphoric acid. F- release was measured for 30 days, then final surface roughness and strength were determined. RESULTS: Significant differences were found in amount and rate of F- release, and F- re-uptake and re-release among study materials and enamel controls (p < 0.001). The amount and rate of F- re-release after NaF treatment differed significantly from F- release after acid treatment in glass ionomers, although both groups showed increased F- release after surface treatment (p < 0.001). There were no significant changes in tensile strength or surface roughness after F- release or F- re-uptake and re-release as determined by ANOVA. SIGNIFICANCE: The results of this in vitro study indicate that applications of neutral 5000 ppm F- gel to aged glass ionomer restorations results in a significant fluoride uptake and subsequent release. The data suggest that the application of neutral fluoride gel to glass ionomer restorations in situ may result in increases in oral fluoride concentrations, without affecting the restoration's surface roughness or tensile strength.

Analysis of Variance↗
PubMed1998

Shear bond strength of a resin cement to densely sintered high-purity alumina with various surface conditions.

Procera Sandvik AB is now manufacturing a densely sintered high-purity alumina core for an all-ceramic crown designed for anterior and posterior restorations. Whereas the material holds promise on the basis of in vitro strength tests, the ability to alter the surface and use conventional bonded resin cements has not been reported previously in the literature. Samples of the core were treated by means of one of four methods routinely used for all ceramic restorations, and then a commercially available resin cement was bonded to the surface. A shear bond test of the adhesion showed that the highest shear bond strengths of 11.99 +/- 3.12 MPa were obtained with air abrasion at 80 psi and 50-microm alumina particles.

Acid Etching, Dental↗
PubMed1998

Resistance to fracture of three all-ceramic systems.

All-ceramic restorations have become an attractive alternative to porcelain-fused-to-metal crowns, but their strength is still an important issue. The purpose of this study was to compare the in vitro fracture resistance of three all-ceramic systems: IPS Empress, In-Ceram, and Procera AllCeram. Thirty dies were replicated from a master die using high filler resin with a modulus of elasticity similar to dentin. Ten cores each of In-Ceram and Procera were fabricated to a thickness of 0.5 mm. The remaining porcelain was applied using a sculpting device to produce a crown with a final thickness of 1.0 mm axially and 2.5 mm occlusally. Ten IPS Empress crowns were mixed to the same dimensions and were pressed by the manufacturer. The internal surfaces of all the crowns were etched and silanated prior to cementation with a resin cement (Panavia 21). The cemented samples were loaded in an Instron machine until fracture. The mean fracture loads were: IPS Empress, 222.45 (+/- 49) kg; In-Ceram, 218.8 (+/- 36) kg; Procera AllCeram, 194.20 (+/- 37) kg. Tukey's test showed no statistically significant differences among the three all-ceramic systems at p < .05.

Aluminum Oxide↗
PubMed1997

Effect of adding opaque porcelain on the final color of porcelain laminates.

STATEMENT OF PROBLEM: Increasing the opacity of porcelain laminates is one of the techniques most commonly used to mask the color of darkly stained teeth. PURPOSE OF STUDY: Two different brands of porcelain (Fortune and Optec) disks that contained various amounts of modifying porcelains to alter opacity were cemented with untinted resin cement to a dark colored substrate. MATERIAL AND METHODS: The color of the substrate was measured before and after cementation and the change in color was calculated. RESULTS: Fortune porcelain showed a progressive increase in the amount of change produced as the modifying porcelain was increased, whereas Optec porcelain showed a decrease in the amount of change as modifying porcelain was increased. CONCLUSION: A progressive increase of yellow was exhibited in the samples as the amount of opacity is increased.

Analysis of Variance↗
PubMed1996

Dentin bonding: SEM comparison of the resin-dentin interface in primary and permanent teeth.

Previous studies have suggested minor differences between primary and permanent teeth in terms of dentin composition and morphology. Other reports indicated lower bond strengths of resin composites to dentin of primary teeth compared with dentin of permanent teeth; however, no information is available regarding differences in the micromorphology of the resin-dentin interface that may explain these lower bond strengths. Therefore, the purpose of the present study was to compare primary and permanent teeth in terms of the thickness of the hybrid layer developed with two bonding systems. Our hypothesis was that bonding differences previously reported between primary and permanent dentin would be reflected in hybrid layer differences observable in SEM analyses. Twenty human extracted and non-carious teeth were divided into 4 groups: 5 primary and 5 permanent teeth restored with All-Bond 2/Bisfil P system; and 5 primary and 5 permanent teeth restored with Scotchbond Multi-Purpose/Z100. The sample area available on each tooth was divided for the two dentin conditioning times (7 and 15 sec). Measurements of hybrid layer thickness were performed by means of SEM at x13,000. The results of this study indicated that the hybrid layer produced is significantly thicker in primary than in permanent teeth (p = 0.0001), suggesting that primary tooth dentin is more reactive to acid conditioning. No difference was observed in the hybrid layers produced by the two adhesive systems (p = 0.7920). The increased thickness of the hybrid layer in primary teeth (25 to 30%) and the subsequent lack of complete penetration of adhesive resin into previously demineralized dentin may contribute to the lower bond strengths to primary dentin reported in the literature. If a narrower hybrid layer more uniformly infused with resin is the goal of dentin bonding, it is concluded that a differentiated protocol for bonding to primary dentin (with shorter time for dentin conditioning) can be used as a means to reproduce the hybrid layer thickness seen in permanent teeth.

Acid Etching, Dental↗
PubMed1995

Cytotoxic interactive effects of dentin bonding components on mouse fibroblasts.

Previous studies have shown a wide range of pulpal reactions to dentin bonding systems and a poor correlation between in vitro and in vivo toxicity of dentin bonding agents. Because dentin bonding agents are composed of multiple components which may diffuse through dentin, we hypothesized that these components may cause cytotoxicity through interactive (synergistic) effects. We investigated the cytotoxicities of four dentin bonding components--HEMA, Bis-GMA, TEGDMA, and UDMA--and interactive effects for three binary combinations of the dentin bonding components--HEMA and Bis-GMA, Bis-GMA and TEGDMA, and TEGDMA and UDMA. Cytotoxicities to Balb/c 3T3 mouse fibroblasts were measured by the MTT assay. Concentrations which caused 50% toxicity compared with controls (TC50 values) were compared, and the interactive effects were determined by evaluation of the differences between observed and expected MTT activities of the cells. The ranks of toxicity of the dentin bonding components in terms of TC50 values were as follows: Bis-GMA > UDMA > TEGDMA >>> HEMA (least toxic) after 24- and 72-hour exposures. As binary combinations, the three combinations of dentin bonding components interacted in three ways--synergism, additivism, and antagonism--which were influenced by the concentrations of both components. The longer period of exposure resulted in a significant increase in the cytotoxicity of the dentin bonding components and combinations. The findings indicate that both exposure time and the interactions between the dentin bonding components may be important parameters in determining the cytotoxicity of dentin bonding agents in vivo.

3T3 Cells↗
PubMed1992

Physical properties and repair bond strength of direct and indirect composite resins.

Use of composite resins now includes indirect curing methods. Surface chemistry, repair bond strength, plus location of failure and five physical properties of two direct and three indirect composite resins were determined. There were statistically significant differences in flexural strength of materials and in hardness values. Repair bond strength failures were not significantly different; failures occurred primarily at the interface. Multiple internal reflection spectroscopy confirmed the presence of unpolymerized material after cure in all products. Indirect cure of the direct composite resin increased the degree of cure.

Absorption↗
PubMed1990

Evaluating tooth eruption on sealant efficacy.

For patients aged 5 to 9 and 11 to 14, 100 occlusal surfaces on newly erupting permanent molars were treated with a self-curing pit and fissure sealant. All teeth were categorized according to stage of eruption and sealant thickness of the coating applied. After 36 months, 75 surfaces were examined for a final evaluation; 52 surfaces (70%) did not need retreatment. Of the 23 surfaces retreated as a result of sealant loss or marginal deterioration, 18 were retreated only once in the six recall evaluations. Those molars treated originally with the operculum covering the distal marginal ridge of the occlusal surface had twice the probability for retreatment as teeth not treated until the entire marginal ridge was exposed. The thickness of the sealant coating did not affect the early signs of sealant failure.

Adolescent↗
PubMed1989

Parameters affecting in vitro bond strength of composites to enamel and dentin.

In vitro tensile bond strengths of Photo Clearfil Bright (PB) and Clearfil Photo Posterior (CP) with Clearfil Photo Bond to human enamel and dentin were determined by a truncated cone bond test. Parameters tested were: four substrates (etched enamel; unetched dentin, D1; dentin conditioned with 10% polyacrylic acid, D2; and dentin etched with phosphoric acid, D3); two techniques (bonding agent prepolymerized, and bonding agent and composite polymerized together); and two storage times in 37 degrees C water (one day and one week). Bond strengths of PB and CP to enamel ranged from 15 to 25 MN/m2 and 19 to 24 MN/m2, respectively. Bond strengths of PB to dentin ranged from 10.2 to 13.6 MN/m2 for D1, 8.2 to 10.5 MN/m2 for D2, and 5.5 to 7.8 MN/m2 for D3. Bond strengths of CP to dentin ranged from 7.6 to 12.3 MN/m2 for D1, 6.8 to 9.5 MN/m2 for D2, and 4.6 to 6.7 MN/m2 for D3. Bond strengths were higher to enamel than to dentin. The highest bond strengths to dentin were to unetched dentin, followed by conditioned dentin, and then etched dentin. Polymerization techniques and storage times did not affect the bond strengths.

Composite Resins↗
PubMed1989

Thermal expansion of visible-light-cured composite resins.

Linear coefficients of thermal expansion were measured on seven visible-light-cured composite resins from 0 to 60 degrees C. The values ranged from 29.0 to 83.5 x 10(-6)/degrees C at 37 degrees C. Statistical analysis revealed significant differences among temperature ranges and products and between runs. Significant correlation was not found between the coefficient of thermal expansion and volume fraction of filler particles.

Chemical Phenomena↗
PubMed1989

Quantitative evaluation of approximal contacts in Class 2 composite resin restorations: a clinical study.

The purpose of this study was to develop an accurate and reproducible intraoral method of measuring the distance between two teeth, and to conduct a clinical pilot study of the effect of placement of a class 2 posterior resin restoration upon this intertooth dimension. A Kaman Sciences KD-2611 noncontact displacement measuring system with a 1U unshielding sensor, based upon the variable resistance of eddy current, was used for the intraoral measurement. Seven patients requiring conservative interproximal restorations (initial placements or replacements) on the premolars were selected. Addition silicone impressions were taken of the posterior quadrants from which low-fusing metal (Cerrolow-136) casts were made. Composite resin copings constructed on modified rubber dam clamps were fabricated for the restoration and adjacent teeth upon these metal casts. Aluminum targets and Plexiglas holders for the sensor were attached to the bow of the rubber dam clamp with light-activated composite resin. Quantitative measurements of intertooth distance were made preoperatively, postoperatively, and at one-week and 4 1/2-month recalls after placement of class 2 composite resin restorations for 11 teeth. Four unrestored premolars served as a control. The data were tabulated and analyzed using one-way analysis of variance. The results indicated that the mean postoperative intercoping distance for restored teeth increased after a multiple wedging technique had been applied during restorative procedure. At the one-week recall, these distances had decreased. The 4 1/2-month measurements showed a further decrease with an average loss of 15 microns from the preoperative baseline.

Analysis of Variance↗
PubMed1988

Clinical evaluation comparing sealant and amalgam after 7 years: final report.

A study compared two alternative methods for the clinical treatment of occlusal pits and fissures in the early posteruption state. On contralateral pairs of permanent first and second molars, one molar was given a preventive treatment with pit and fissure sealant, and the paired molar surfaces were restored with amalgam. The retreatment rate for sealant was highest after 6 months (20%) and declined to 11% or less during the 7 years. A generalized margin deterioration was seen in more than 50% of amalgam restorations, whereas 55% of the sealant margins remained not detectable clinically. The data from this study support the application of pit and fissure sealant as a treatment within the specific limitations of a controlled preventive program and professional supervision.

Child↗