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Biomedical subjects

D McComb

Publications and source records attributed to D McComb.

17 recordsLinked to original sources
PubMed1991

Shear bond strengths of resin luting cements to laboratory-made composite resin veneers.

Retention problems have been reported with the clinical use of indirect microfilled resin veneers. This study used 24-hour shear tests to assess the bond strengths of such a resin veneer compared with other veneer types. The effect of different resin luting cements and resin veneer surface treatments were analyzed to elucidate factors by which retention could be increased. The six resin luting systems investigated showed a range of bond values. Debonding occurred primarily at the veneer/cement interface. G-Cera material produced the weakest bonds to Isosit-N resin. Surface treatment of Isosit-N veneers resulted in bond strength changes. Sandblasting reduced the force required for bond failure; Special Bond resin increased it slightly. Improving retention of prefabricated resin veneers proved difficult. Etched hybrid resin veneers delivered higher bond strengths than micro-filled resin veneers but not significantly. Etched porcelain veneers, however, provided consistently the strongest bond strengths with cohesive, as opposed to adhesive, bond failure.

Acid Etching, Dental↗
PubMed1991

Radiopacity of direct ceramic inlay restoratives.

The radiopacity of two new ceramic restorative materials (Dicor MGC and Cerec Vita Blocks) manufactured for use in producing direct inlays with the 'Cerec CAD-CAM' system was determined. Dicor MGC had a radiopacity significantly greater than that of enamel, while Cerec Vita Blocks had a radiopacity significantly less than that of dentine. It is concluded that Dicor MGC has a radiopacity suitable for its use as an intracoronal restorative for posterior teeth. The low radiopacity of Cerec Vita Blocks means that the use of radiopaque luting cement is essential to permit detection of secondary caries around restorations of this material. Furthermore, marginal overhangs around restorations made from Cerec Vita Blocks will be difficult to detect radiographically.

Analysis of Variance↗
PubMed1989

Physical properties of calcium hydroxide and glass-ionomer base and lining materials.

Compressive, diametral tensile and flexural strengths, moduli of elasticity, pH, and acid solubility values were compared for six calcium hydroxide cements, seven glass-ionomer cements, and one calcium aluminate cement. Results indicated that the glass-ionomer materials were generally stronger than the calcium hydroxide liners. Prisma VLC Dycal showed the lowest value for modulus of elasticity and the least acid solubility. The glass-ionomer materials were initially acidic, reaching a final pH between 5.4 and 7.3, whereas the calcium hydroxide and calcium aluminate cements were strongly alkaline at all time intervals.

Calcium Hydroxide↗
PubMed1987

Antimicrobial action of new, proprietary lining cements.

The antibacterial activity of innovative, commercial lining cements was investigated. A liner which contains calcium hydroxide and is polymerized by visible light (Prisma VLC Dycal) and a glass-ionomer lining cement (GC lining cement) were compared with two more established lining cements (Advanced Formula II Dycal and Life). Antibacterial activity and hemolysis-like agar change at 24, 48, and 72 hours were measured on blood agar plates inoculated with Streptococcus mutans KPSK 2 (serotype c), Lactobacillus casei ssp rhamnosus ATCC 11981, and chewing-stimulated saliva. Prisma VLC Dycal did not affect bacteria or agar. The glass-ionomer lining cement, with an acidic pH at setting, had the most pronounced effect on all test organisms and on the agar. Even after 48 hours' setting, it inhibited growth of S. mutans. The control lining cement (AFII Dycal) showed antibacterial activity toward both specific micro-organisms as well as some activity against the salivary organisms. The material Life showed only partial inhibition of microbial growth. For all lining cements, the hemolytic-like agar change correlated with antibacterial effects. The surface pH of the freshly-set cements containing calcium hydroxide was alkaline. It would seem that a simple correlation between high surface pH and antibacterial activity among these cements does not exist. Also, further biological characterization of new lining cements is required to direct their appropriate clinical use.

Anti-Infective Agents, Local↗
PubMed1979

Prospective study of maternal and infantile infection with Chlamydia trachomatis.

We examined the prevalence of chlamydial infection in a population of pregnant women and observed their infants to determine the risk of development of ocular or respiratory infection. We examined endocervical and serum specimens from 322 pregnant women for Chlamydia trachomatis and chlamydial antibody. The cultures were obtained at the first prenatal visit. Six (2%) of the women were infected with C trachomatis. Chlamydial antibody was present in the genital secretions of 47% and 73% of the serum samples. The six infants born to infected women, 61 infants born to women who were culture-negative, but local antibody-positive, and 28 control infants born to culture-negative, antibody-negative women were followed for up to six months. Four of six infants born to infected women developed chlamydial infection: two developed culture-positive conjunctivitis, one had asymptomatic nasopharyngeal infection, and one infant developed pneumonitis. Three of 61 infants born to mothers who were culture-negative and local antibody-positive developed conjunctivitis due to C trachomatis. None of the 28 control infants developed chlamydial infection. Most (79%) of the infants had chamydial antibody in their serum at 2 to 4 weeks of age. The correlation between maternal and infant serum antibody titer was r=0.71 suggesting that antibody was placentally transferred.

Adolescent↗
PubMed1978

Microbiology of the vagina in children: normal and potentially pathogenic organisms.

Vaginal cultures from 100 healthy girls, 2 months to 15 years of age, were examined for the presence of normal and potentially pathogenic microorganisms. Corynebacterium vaginale, yeast species, and genital mycoplasmas were isolated from vaginal cultures from 13.5 %, 28%, and 28% of the girls examined, respectively. Colonization with these organisms was not associated with signs or symptoms of vaginitis. Neisseria gonorrhoeae was isolated from a 4-year-old with purulent vaginitis. Trichomonas vaginalis was recovered from two 13-year-olds, both of whom had an abnormal vaginal discharge. Vaginal antibody to Chlamydia trachomatis was found in two girls 4 and 13 years of age. In neither girl was the organism recovered from the vaginal culture. Chlamydia trachomatis was recovered from the vaginal culture of another 4-year-old who had no abnormal findings on examination. Cultures from 59 of the girls were examined for aerobic and facultatively anaerobic bacteria. Diphtheroids and Staphylococcus epidermidis were the most frequently isolated organisms. Lactobacilli were isolated most frequently from the older girls, whereas enteric organisms were isolated most frequently from the younger girls.

Adolescent↗
PubMedDate not supplied

Physical properties of proprietary light-cured lining materials.

Physical parameters of four photopolymerized lining materials were evaluated for comparative purposes and to contribute to the understanding of these novel materials. Properties investigated included compressive, diametral and flexural strength, modulus of elasticity, fluoride and calcium release for four weeks, and pH values for 24 hours. In general Cavalite and TimeLine were significantly stronger than Vitrabond and XR-lonomer and were essentially neutral in pH. All the materials exhibited a yield upon compressive strength testing. The fluoride release was intermediate for TimeLine and negligible with Cavalite. Vitrabond and XR-lonomer released significant amounts of fluoride at all time periods. XR-lonomer was the only material investigated to have significant calcium release, and this may have been related to its visible dissolution in water. This material also showed a low initial pH of 2.2. It, along with Vitrabond, demonstrated a gradual increase in pH over time. The behavior of TimeLine and Cavalite is therefore more consistent with that of a modified composite resin, whereas Vitrabond and XR-lonomer are similar in nature to glass-ionomer liners.

Acrylic Resins↗
PubMedDate not supplied

Sealing efficacy of therapeutic varnishes used with silver amalgam restorations.

The sealing abilities of three therapeutic varnishes were compared with that of a conventional copal varnish in vitro under Tytin silver amalgam restorations. The therapeutic varnishes comprised two commercial fluoride varnishes and one experimental chlorhexidine-containing varnish. Leakage was traced using a basic fuchsin dye and was found to be considerable, particularly on root surfaces. The therapeutic varnishes performed as well as, and in some cases better than, the control. It is suggested that the use of preventive therapeutic varnishes in operative dentistry merits attention and further study.

Dental Amalgam↗