The clinical durability of restorations made using water-based materials depends upon the type of material used. Current specification tests cannot predict durability, possibly because these are carried out on samples matured for 24 hours whereas longer maturation times may be more relevant. The lactic acid jet test was selected as a test method, being believed capable of ranking materials in the same order of erosion resistance in vitro as found in vivo. The powder/liquid interaction (glass or zinc oxide with polymeric or phosphoric acid) was investigated by selecting glass-ionomer, zinc polycarboxylate, silicate and zinc phosphate cements, with emphasis placed on glass ionomers. Two test times, 24 hours and 2 months, were chosen, with eight samples for each material tested at each time. All glass ionomers showed a significant reduction in erosion rate with time; two zinc polycarboxylates also showed some reduction but not to a significant degree. The silicate and zinc phosphate cements increased in erosion rate but not significantly. It was concluded that materials using polymeric acids had erosion rates which reduced with time, significantly so for glass ionomers. This might explain their longevity over silicate cements.

Dental Cements↗

PubMedDate not supplied

The effect of variable energy input from a novel light source on the photoactivated bactericidal action of toluidine blue O on Streptococcus Mutans.

Although the combination of toluidine blue O (TBO) dye and laser light at a wavelength of 633 nm has a bactericidal effect, light from laboratory lasers can only be directed externally at a bacterial colony or suspension. In this study a novel delivery system guided the laser light to an 800-micrometer diameter spherical tip (an isotropic tip) from which light radiated producing a uniform sphere of light within the colony or suspension. The system was highly effective in killing TBO-treated Streptococcus mutans NCTC 10449 in stirred planktonic suspension, killing at least 10(9 )cfu/ml. Antibacterial action increased as the delivered energy dose increased. Energy doses of 1.8 J or more produced 100% kills and log reductions of 8-10 cfu/ml. Neither TBO dye nor light alone had a significant antibacterial effect under the experimental conditions used. The existence of a threshold energy, i.e. a minimum energy required before bactericidal action occurred, could not be demonstrated.

Colony Count, Microbial↗

PubMedDate not supplied

The photo-activated antibacterial action of toluidine blue O in a collagen matrix and in carious dentine.

The main aim of this study was to determine the susceptibility to photo-activated disinfection (PAD) of Streptococcus mutans when the organism was present in a collagen matrix--an environment similar to that which would exist within a carious tooth. In addition, the susceptibility to PAD of bacteria present in carious human teeth was also determined. Light was delivered to the collagen and teeth using a system comprising a 0.8-mm diameter isotropic tip emitting light at 633 +/- 2 nm. A single concentration of TBO (10 microg/ml) was used with both collagen and dentine. Two contact times, 30 and 180 s, were evaluated in intact collagen and additionally, for 180 s only, in collagen partially disrupted by shredding. The effect of energy doses from 1.8 to 14.4 J on the kills attained was assessed by determining the number of surviving viable bacteria. In carious dentine, two contact times, 30 and 60 s and one energy dose, 4.8 J, were used. Antibacterial effects were less than those obtained using planktonic suspensions with a maximum mean log reduction of 1.4 in shredded collagen and dentine. Increasing contact time increased the antibacterial effectiveness in both substrates although this was not always of statistical significance. Shredding the collagen resulted in significantly increased bacterial kills compared to those obtained in intact collagen for the 30-second contact time. The collagen matrix appeared to be a suitable model for carious dentine with advantages of availability and reproducibility. The results of this study have shown that PAD can achieve appreciable kills of oral bacteria, including S. mutans, when the organisms are embedded in a collagen gel or are present in carious teeth.

Animals↗

PubMedDate not supplied

An in vitro investigation of the temperature rises produced in dentine by Nd:YAG laser light with and without water cooling.

Infrared lasers are reported to have thermal side effects which may damage pulp tissue. This study investigated the thermal effects of the pulsed Nd:YAG laser. Prepared, extracted teeth were measured prior to irradiation. Temperature was recorded using a thermocouple/data logging system. Laser irradiation was carried out with or without water spray for an exposure time of ten seconds. Results indicated that dry irradiation produced unacceptable temperature rises with dentine thicknesses used. Wet irradiation produced a significantly lower temperature rise. It was concluded that the Nd:YAG laser produced thermal effects which could potentially cause pulpal trauma. A water coolant was effective in reducing these thermal effects, but the temperature rise achieved whilst using water coolant may still cause pulpal damage.

Dental Cavity Preparation↗

PubMedDate not supplied

The influence of cement thickness on the tensile strength of two resin cements.

This study evaluated the influence of varying the cement thickness upon the tensile strength of nickel-chromium specimen cylinders cemented with Panavia Ex or Panavia 21 resin cements. A decrease in mean tensile strength of the resin-nickel-chromium alloy composite structure was recorded with an increasing cement thickness for both resin cements. Panavia 21 exhibited a significantly greater mean tensile strength than Panavia Ex at all cement thicknesses tested (P < .01).

Cementation↗