Brian Nattress

ARCHITECTURE OF INTACT NATURAL HUMAN PLAQUE BIOFILMS STUDIED BY CONFOCAL LASER SCANNING MICROSCOPY

Determination of the structure of human plaque will be of great benefit in the prediction of its formation and also the effects of treatment. However, a problem lies in the harvesting of undisturbed intact plaque samples from human volunteers and the viewing of the biofilms in their natural state. In this study, we used an in situ device for the in vivo generation of intact dental plaque biofilms on natural tooth surfaces in human subjects. Two devices were placed in the mouths of each of eight healthy volunteers and left to generate biofilm for 4 days. Immediately upon removal from the mouth, the intact, undisturbed biofilms were imaged by the non-invasive technique of confocal microscopy in both reflected light and fluorescence mode. Depth measurements indicated that the plaque formed in the devices was thicker round the edges at the enamel/nylon junction (range = 75-220 μm) than in the center of the devices (range = 35-215 μm). The reflected-light confocal images showed a heterogeneous structure in all of the plaque biofilms examined; channels and voids were clearly visible. This is in contrast to images generated previously by electron microscopy, suggesting a more compact structure. Staining of the biofilms with fluorescein in conjunction with fluorescence imaging suggested that the voids were fluid-filled. This more open architecture is consistent with recent models of biofilm structure from other habitats and has important implications for the delivery of therapeutics to desired targets within the plaque.

AN IN VITRO STUDY OF THE USE OF PHOTODYNAMIC THERAPY FOR THE TREATMENT OF NATURAL ORAL PLAQUE BIOFILMS FORMED IN VIVO

Seven-day oral plaque biofilms have been formed on natural enamel surfaces in vivo using a previously reported in situ device. The devices are then incubated with a cationic Zn(II) phthalocyanine photosensitizer and irradiated with white light. Confocal scanning laser microscopy (CSLM) of the biofilms shows that the photosensitizer is taken up into the biomass of the biofilm and that significant cell death is caused by photodynamic therapy (PDT). In addition, the treated biofilms are much thinner than the control samples and demonstrate a different structure from the control samples, with little evidence of channels and a less dense biomass. Transmission electron microscopy (TEM) of the in vivo-formed plaque biofilms reveals considerable damage to bacteria in the biofilm, vacuolation of the cytoplasm and membrane damage being clearly visible after PDT. These results clearly demonstrate the potential value of PDT in the management of oral biofilms.

Penetration of Fluoride into Natural Plaque Biofilms

Caries occurs at inaccessible stagnation sites where plaque removal is difficult. Here, the penetration through plaque of protective components, such as fluoride, is likely to be crucial in caries inhibition. We hypothesized that topically applied fluoride would readily penetrate such plaque deposits. In this study, plaque biofilms generated in vivo on natural enamel surfaces were exposed to NaF (1000 ppm F−) for 30 or 120 sec (equivalent to toothbrushing) or for 30 min. Biofilms were then sectioned throughout their depth, and the fluoride content of each section was determined with the use of a fluoride electrode. Exposure to NaF for 30 or 120 sec increased plaque fluoride concentrations near the saliva interface, while concentrations near the enamel surface remained low. Fluoride penetration increased with duration of NaF exposure. Removal of exogenous fluoride resulted in fluoride loss and redistribution. Penetration of fluoride into plaque biofilms during brief topical exposure is restricted, which may limit anti-caries efficacy.

A Method for the Quantitative Site-Specific Study of the Biochemistry within Dental Plaque Biofilms Formed in vivo

The study of plaque biofilms in the oral cavity is difficult as plaque removal inevitably disrupts biofilm integrity precluding kinetic studies involving the penetration of components and metabolism of substrates in situ. A method is described here in which plaque is formed in vivo under normal (or experimental) conditions using a collection device which can be removed from the mouth after a specified time without physical disturbance to the plaque biofilm, permitting site-specific analysis or exposure of the undisturbed plaque to experimental conditions in vitro. Microbiological analysis revealed plaque flora which was similar to that reported from many natural sources. Analytical data can be related to plaque volume rather than weight. Using this device, plaque fluoride concentrations have been shown to vary with plaque depth and in vitro short-term exposure to radiolabelled components may be carried out, permitting important conclusions to be drawn regarding the site-specific composition and dynamics of dental plaque.

Site-specific variations in the concentrations of substances in the mouth

Estimates of the concentration of soluble substances in the oral fluids have generally been obtained by the analysis of whole saliva, either mixed in the mouth or obtained directly from the salivary duct. Such values may give little indication of concentrations at any particular site in the mouth. This is partly because substances do not always move easily about the mouth and also because there are large regional differences between the rates of oral clearance or retention of substances dissolved in saliva. Differential patterns therefore develop and are related, via the patterns of salivary flow, to the anatomy and physiology of the mouth. There are general features in these patterns common to all mouths and variations, which relate to characteristics of the individual, which may influence the rates of reactions occurring at different sites. The patterns may be associated with the site-specific patterns of dental disease, and they may have implications with regard to the best use of pharmaceutical agents. This paper describes some of the more recent data, problems and future possibilities in this hitherto unexplored area of oral physiology

Control of microbial contamination in dental unit water systems using tetra-sodium EDTA

Aim:  To examine the efficacy of tetra‐sodium EDTA in controlling microbial contamination of dental unit water systems (DUWS).

Determination of volumes of fluid in the mouth by fluoride dilution.

A dilution technique, with fluoride as a marker, has been developed to measure the volume of saliva and other fluids in the mouth. Immediately after swallowing, a small amount of fluoride solution is placed in the mouth, mixed with the oral fluids, and expelled from the mouth. The fluoride concentration of the expelled oral fluid is measured and the volume of fluid in the mouth at the time of spitting calculated from the fluoride dilution. Mean values of 0.75 +/- (SD) 0.28 ml for males and 0.72 +/- (SD) 0.16 ml for females were recorded. The accuracy of the volume determination is about +/- 0.10 ml in vivo. This technique has provided a convenient and rapid means of determining saliva volumes. It could also be used to determine rates of secretion and may prove useful in the clinic for assessing a patients salivary competence.

Minimizing prion risk without compromising the microbial composition of biofilms grown in vivo in a human plaque model

Aims:  To determine whether the stringency of sterilization procedures for biological components of in vivo dental plaque‐generating devices based on enamel can be increased to minimize prion risk without compromising natural biofilm composition.

Removable partial dentures: The clinical need for innovation

Statement of problem. The number of partially dentate adults is increasing, and many patients will require replacement of missing teeth. Although current treatment options also include fixed partial dentures and implants, removable partial dentures (RPDs) can have advantages and are widely used in clinical practice. However, a significant need exists to advance materials and fabrication technologies because of the unwanted health consequences associated with current RPDs. Purpose. The purpose of this review was to assess the current state of and future need for prosthetics such as RPDs for patients with partial edentulism, highlight areas of weakness, and outline possible solutions to issues that affect patient satisfaction and the use of RPDs. Material and methods. The data on treatment for partial edentulism were reviewed and summarized with a focus on currently available and future RPD designs, materials, means of production, and impact on oral health. Data on patient satisfaction and compliance with RPD treatment were also reviewed to assess patient‐centered care. Results. Design, materials, ease of repair, patient education, and follow‐up for RPD treatment all had a significant impact on treatment success. Almost 40% of patients no longer use their RPD within 5 years because of factors such as sociodemographics, pain, and esthetics. Research on RPD‐based treatment for partial edentulism for both disease‐oriented and patient‐centered outcomes is lacking. Conclusions. Future trials should evaluate new RPD materials and design technologies and include both long‐term follow‐up and health‐related and patient‐reported outcomes. Advances in materials and digital design/production along with patient education promise to further the application of RPDs and improve the quality of life for patients requiring RPDs.

An overview of electronic apex locators: part 2

To effectively carry out root canal therapy, the clinician must accurately determine the apical limit of the root canal system as well as the position of the canal terminus. Its position can be estimated using a variety of techniques, including radiographs, tactile feedback from endodontic instruments and electronic apex locators. This article describes the micro-anatomy of the apical terminus, different methods of measuring root canal system length and how a tooth can function as an electrical capacitor. This capacitor model represents a starting point upon which all apex locators are based. An understanding of this model can help the practitioner to optimise the use of apex locators, understand their limitations and avoid errors that can occur.