The interaction of various liquids with long-term denture soft lining materials.

OBJECTIVES: To study the uptake of liquids, representative of those encountered orally, by long-term denture soft lining materials, and analyze the data in terms of appropriate theories. METHODS: Four proprietary and one experimental soft lining material were investigated, and the weight change presented as a function of time in both aqueous and organic fluids over the course of a year. A separate experiment determined the equilibrium swelling in ethanol of poly(ethyl methacrylate) and poly(methyl methacrylate). RESULTS: Uptake date for the five soft lining materials in various aqueous solution, coconut oil and HB307 are reported. The experimental value for the equilibrium swelling of poly(ethyl methacrylate) and poly(methyl methacrylate) in ethanol was reported to indicate the solubility parameter of the system. SIGNIFICANCE: The results have been analyzed by relevant theoretical models, which have been shown to explain the experimental data.

In vitro colonization of an experimental silicone by Candida albicans.

Denture soft-lining materials are exposed to the oral cavity for long periods and are in continuous contact with saliva, subject to inhibition of liquid molecules, and susceptible to colonization by microorganisms. The opportunist yeast Candida albicans is of particular concern in this context, being associated with denture plaque and denture-related stomatitis. In this study, penetration of C. albicans into an experimental silicone elastomer soft-lining material was investigated under batch and continuous culture conditions. A model "denture plaque" microcosm was also used. Increasing the filler concentration within the elastomer decreased penetration under both batch and continuous culture conditions. In continuous culture, C. albicans penetration was significantly greater in pure culture than in the presence of bacteria after 72-h incubation (p < 0.05).

Kinetics of fluoride release from glass components of glass ionomers.

OBJECTIVES: To compare the F release from glass ionomer glasses (GICs) into water changed periodically with release into an unchanged "sink" [Williams JA, Billington RW, Pearson GJ. The glass ionomer cement: the sources of soluble fluoride. Biomaterials 2002;23:2191-200]. To evaluate the effect of replacing Ca wholly or partially by Sr. To compare two different methods of decomplexing F containing species. METHODS: All four glasses contained Al, Si, P, O and F. Glass AH2 (Advanced Healthcare Ltd.) had Na and Ca, LG26 (Advanced Healthcare Ltd.) had Ca, LG26Sr (ULTRASET project) had Ca and Sr, and LG125 (ULTRASET project) had Sr. Glasses were tested: after ball-milling, after washing in dilute acid, and W mixed with 35% acetic acid to form a "pseudo-cement". F(-) release was from 130mg samples into 10ml of deionised water changed at 1, 3, 7, 14, 21, 28, 35, and 42 days. Analysis was carried out: (a) using ISE without decomplexing, (b) using TISAB buffer, and (c) acid hydrolysis+TISAB (after Hattab). RESULT: The cumulative release rates from all glasses and treatments are linear with respect to t(1/2) with r=0.97 or greater (p=<0.001). F release into a "sink" showed no such correlation. The higher release rate from AH2 is more than accounted for by its higher F content. Most F release is not complexed except of AH2. AH2 has 20% of complex fluoride from raw glass, 44% from acid-washed glass and 51% from pseudo-cement. More fluoride is released after acid treatment from all 4 glasses, these are on average 4.4 times higher from acid-washed glass and 5.3 times higher from pseudo-cement. For TISAB fluoride release, LG26Sr is 26% more than LG26. Hattab fluoride>TISAB fluoride only for raw glasses. CONCLUSIONS: Changing water produces diffusion controlled kinetics. Acid treated will increase the complex fluoride from AH2. Replacing Ca by Sr enhances F release rate slightly.

Current clinical applications of photo-activated disinfection in restorative dentistry.

UNLABELLED: The traditional treatment of dental caries has been limited to bulk removal of the diseased tissue. Recently, disinfection rather than the removal of all the carious tissue has been advocated with the aim of more effective and conservative treatment. In endodontics, prognosis is dependent on the complete disinfection of the root canal system. Evidence exists that Photo-Activated Disinfection is more effective than traditional chemo-mechanical canal preparation. Photo-Activated Disinfection may also have a place in the treatment of other infective oral conditions, including periodontal disease. CLINICAL RELEVANCE: Removal or disruption of micro-organisms and their ecosystem is important in many branches of restorative dentistry. A novel disinfection system is now available which has the potential to improve treatment methods and prognoses.

Interoperator variability during polishing.

OBJECTIVE: The object of this study was to establish the 3 variables used in polishing by measuring the range of loads, speeds, and times used by practitioners when finishing and polishing samples of amalgam, resin composite, and glass-ionomer cement. These parameters could then be used to establish clinically relevant values that might optimize clinical finishing techniques. METHODS AND MATERIALS: Samples of the 3 materials were attached to the load cell of a universal testing machine that was attached to an X-Y plotter. Practitioners were asked to finish the samples using 4 grades of a polishing disk system. Prior to using each grade of disk, the practitioner selected a speed. The sample was finished using one grade of disk until the practitioner was satisfied with the finish achieved. The process was then repeated with the next grade of disk. From the tracings for each disk the load and time were calculated. RESULTS: There was a wide variation in the loads, speeds, and times used by the practitioners to finish the 3 materials, and it was not possible to find any relationship among the 3 variables. It appeared that practitioners finished the materials in an arbitrary manner. CONCLUSION: No clear evidence was obtained to determine optimal combinations of load, speed, and time for finishing of amalgam, resin composite, or glass-ionomer cement. However, the results of this study indicate a range of values commonly used for each parameter in clinical practice, which could be useful for manufacturers in providing finishing instructions for their products.

Antibacterial action of photoactivated disinfection {PAD} used on endodontic bacteria in planktonic suspension and in artificial and human root canals.

OBJECTIVES: To measure antibacterial action of photoactivated disinfection (PAD) on endodontic bacteria in planktonic suspension and root canals. METHODS: Four bacteria, Fusobacterium nucleatum,Peptostreptococcus micros, Prevotella intermedia and Streptococcus intermedius, were tested in suspension. After mixing equal volumes of Tolonium chloride and bacterial suspension for 60s, each 200 microL of concentration (>10(6)cfu mL(-1)) was irradiated with light at 633+/-2 nm. Each energy dose/Tolonium chloride concentration combination was tested eight times, with controls. Prepared root canals in Training Blocs and extracted human teeth were inoculated with S. intermedius followed by 10 mg L(-1) Tolonium chloride or saline. Bacteria in canals were sampled before and after light irradiation. Student t-test assessed significance of changes in viable bacteria produced by treatment of either light or Tolonium chloride alone and light/Tolonium chloride combinations. RESULTS: In suspension, reductions in bacteria were highly significant (P<0.01) for light/Tolonium chloride combinations compared to light or Tolonium chloride alone. Maximum mean log reductions of 1.14 (P. intermedia), 2.48 (P. micros), 2.81 (F. nucleatum) and 6.73 (S. intermedius) were at 4.8 J/20 mg L(-1). Antibacterial action was increased by energy dose increase (not always significantly), but not by Tolonium chloride concentration. In control canals mean log reductions of 0.42 (Blocs) and 0.38 (teeth) from initial levels were not significant. PAD mean log reductions of 2.40 (Blocs) and 2.01 (teeth) were highly significant. Changes for PAD/energy dose combinations were not significant. CONCLUSION: PAD killed endodontic bacteria at statistically significant levels compared to controls. Kills varied with bacterial species.

The effect of the disc support system on biaxial tensile strength of a glass ionomer cement.

OBJECTIVE: This was to examine how varying the type of support, from a complete ring to a series of point supports, affected the biaxial tensile strength of one glass ionomer cement. METHOD: Three support diameters from 11.5 to 28.6 mm were achieved using 3 mm ball bearings as point supports equidistantly spaced around the diameter. From 3-30 point supports were used depending on diameter. At the maximum number of point supports for each diameter the support points were 3 mm apart. After 24h storage in water at 37 degrees C the biaxial tensile strength of 1 mm thick glass ionomer restorative cement discs was measured using a loading rate of 1 mm min(-1). The load at break was converted to biaxial tensile strength using the Timoschenko and Woinowsky-Kreiger equation using a Poisson's ratio value of 0.30. The mean strength of six specimens tested per support regime was calculated. RESULTS: Comparison with the mean result obtained from using a continuous knife-edge support showed there to be no significant difference (unpaired t-test) between the different support systems except in two cases, both being when a four-point support was used. Neither the support diameter nor the number of point supports was crucial. SIGNIFICANCE: Results from studies where different systems have been used to support brittle cement discs may be compared.