Neil Pender

Aspects of Oral Health in Orthodontic Patients

A longitudinal and transverse study has been carried out on 22 orthodontic patients during their first year of treatment to assess levels of plaque control and gingival inflammation. The scores were of full data and the patients randomly arranged on a split mouth cross-over design to study the effects of patient oral care and selective tooth cleaning on levels of oral health. The results are analysed in respect of upper fixed, lower fixed and upper removable appliances, comparing and contrasting quadrants that have been treated differently. Plaque levels appear constant, whereas levels of gingival inflammation are consistently worse during treatment but only in certain areas of the mouth. Levels of plaque and gingivitis are well controlled. There appears to be no hygiene disadvantage to an upper removable appliance when compared with an upper fixed appliance though the effect differs in relation to the tooth aspect considered. The significance of the findings is discussed.

Validation of enamel erosion in vitro

OBJECTIVES Many tools are available to quantify dental erosion, but each technique has its own inherent disadvantages. This study aims to validate the use of quantitative light-induced fluorescence (QLF) and non-contacting surface profilometry compared to the gold standard transverse microradiography (TMR) for the quantification of enamel erosion in vitro. METHODS This was an in vitro laboratory based study. 60 bovine incisors were divided into 6 groups of 10. Each tooths labial surface was completely varnished except for a window of enamel approximately 3mmx5mm. Each was baseline imaged with QLF and non-contacting surface profilometry before being subjected to an erosive solution (pH 3.4) for up to 36h. The lesions were imaged using non-contacting surface profilometry and QLF, sectioned and analysed with TMR. Correlation coefficients were calculated to assess the validity of the methods of measurement as compared to TMR. RESULTS A range of lesion severities resulted. Mineral loss measured as DeltaQ (QLF) and step height (profilometry), was recorded and confirmed by TMR. A correlation was found between DeltaZ (TMR) and profilometry lesion depth of r=0.648 (p<0.001). A poorer correlation was found between DeltaZ and DeltaQ: r=0.217 (p=0.096). CONCLUSIONS Profilometry lesion depth and DeltaZ correlated significantly. Both methods allow for quantification of erosive crater depth. QLF correlated poorly with DeltaZ, but is useful for measuring subsurface loss of mineralisation. TMR is valuable but is destructive and can only be used in vitro. Currently only QLF can be used in vivo. Advances in these technologies may allow the development of non-destructive in vivo measurements of mineral loss, combining the positive features of each measurement method.

An in vitro study of the bond strength of two light-cured composites used in the direct bonding of orthodontic brackets to molars

This study examines methods of improving the bond strengths of the light-activated composites, Heliosit-orthodontic, and Transbond. Begg brackets were bonded onto each of the four surfaces of 50 molar teeth that had been previously extracted. The bonding systems used were Right-on (R), Heliosit-orthodontic (H), Heliosit with a precured composite resin on the mesh (HPC), Heliosit with a precured intermediate bonding resin on the mesh (HPR), Transbond (T), and Transbond with a precured layer of resin on the mesh (TPC). The shear bond strengths were tested on a M5K tensile tester, crosshead speed 0.5 mm/min. After bracket removal, the enamel surface of the bonding site was examined and assessed with the adhesive remnant index (ARI). The shear bond strength in mean mPa +/- 1 SD was found to be significantly greater for HPC, HPR, and TPC than for H (P < 0.001). The ARI scores suggest that bond failure is associated more with the micromechanical bond with enamel for HPC and HPR. The results indicate that the chemical properties of the two light-activated adhesives were improved by precuring on the mesh base of the bracket before bonding.

Enamel demineralisation assessed by computerised image analysis of clinical photographs.

OBJECTIVES To investigate the use of computerised image analysis to measure the area of demineralisation on the buccal surface of a tooth and to analyse the effect on that measurement of varying the angle at which a photographic image of the buccal surface of a tooth is taken. METHODS Twenty-two teeth with areas of incremental demineralisation on the buccal surface were photographed perpendicular to the buccal surface and at angles of 20 and 40 degrees, above (Cuspal) and below (Gingival) the perpendicular. The images were captured and analysed using computerised image analysis. RESULTS The Gingival views showed lower limits of agreement than the Cuspal views, probably due to the positioning of the masking on the lower part of the flash, to reduce reflection. There was a significant difference between the areas of demineralisation measured for the three angles from the Gingival views (p<0.001). The mean differences in areas measured were not linear, but there was a significantly greater reduction in area measured for the 40 degrees views. CONCLUSIONS Computerised image analysis to measure areas of demineralisation from a captured 35mm slide is reproducible. The position of the masking on the camera flash and the angle of the camera makes a difference to the area measured and the grey scales recorded. Images taken at a larger angle than 20 degrees to the perpendicular will record a significantly reduced area of demineralisation. Standardisation of photographs with the use of calibration markers and manipulation of images is discussed.

Preclinical studies of streptolysin-O in enhancing antisense oligonucleotide uptake in harvests from chronic myeloid leukaemia patients

Antisense oligodeoxyribonucleotides (ODN) have been shown to produce a sequence-specific cleavage of BCR-ABL mRNA. They may therefore have clinical potential for purging harvests from chronic myeloid leukaemia (CML) patients, prior to autografting. Whilst ODN are highly effective in cell-free systems, their uptake into intact cells is very poor. We have previously reported that reversible permeabilisation of CML cell lines with Streptolysin-O (SL-O) can dramatically increase intracytoplasmic and nuclear ODN uptake. In this study, we examined whether SL-O permeabilisation could be used to enhance ODN uptake into bone marrow (BM) and peripheral blood stem cell (PBSC) harvests from CML patients, without undue toxicity. All 19 harvests studied were from patients in stable chronic phase of CML. Samples studied were either fresh BM harvests following leucoconcentration, fresh PBSC collections, or from previously cryopreserved harvests. Cells were permeabilised by SL-O to load them with fluorescein-labelled ODN. The proportion of permeabilised and viable cells was assessed by fluorescein uptake and propidium iodide exclusion, respectively, by flow cytometry. The effect of SL-O on ODN uptake and cell toxicity was unpredictable on simple mononuclear fractions of harvests. In contrast, SL-O consistently significantly enhanced ODN uptake in samples which were first selected for CD34-positive cells, and this was achieved without either direct toxicity or inhibition of CFU-GM growth. The SL-O concentration required for optimal permeabilisation varied considerably from case to case, in line with previous data on cell lines. PBSC harvests positively selected for CD34-positive cells tended to achieve superior permeabilisation to CD34 positively selected BM harvests. SL-O can be used to safely enhance the intracellular uptake of antisense ODN. This is best achieved on harvests which are first selected for CD34-positive cells.

Morphometric assessment of enamel demineralisation from photographs

OBJECTIVES To investigate the validity and reproducibility of a method of morphometric assessment of enamel demineralisation. METHODS An in vitro investigation was carried out on 22 human teeth. One investigator coated the crowns of the teeth with an acid-resistant varnish, leaving a small window on the buccal surface. This was incrementally occluded by varnish over a 14-day period, during which the teeth were placed in a demineralising gel at pH 4.5. After varnish removal, a second investigator blindly quantitated the demineralised area by three methods of examination; direct visual, microscopic and from photographs. The microscopic and photographic measurements were carried out using a morphometric assessment with a 121-dot array. Photographs and assessments were repeated after 1 week. The readings were analysed using the kappa statistic, the limits of agreement and the coefficient of repeatability. RESULTS Photographic assessments demonstrated excellent agreement for grid positioning (kappa > 0.81) and substantial agreement for reading reproducibility (kappa = 0.61-0.80). The coefficients of repeatability were found to be the same for repeat readings of the same slide and the repeated slides (5.0 mm2). They were higher for the microscopic technique (6.8 mm2) and for the direct visual technique (7.8 mm2). The limits of agreement are presented graphically. CONCLUSIONS The photographic technique used was a reproducible method of measuring artificial enamel demineralisation. Measurement from photographs was more reproducible than direct measurement with the naked eye. Subjectiveness of the index leads to most variation and more objective means of assessing enamel demineralisation need to be found.

Histamine stimulates exocytosis in a sub-population of bovine adrenal chromaffin cells

Both nicotinic stimulation and histamine are able to raise cytosolic free calcium concentration in the majority of cells in a population of bovine adrenal medullary chromaffin cells to comparable levels. Nevertheless, histamine induces much less catecholamine secretion than does nicotine. In order to test whether this is due to heterogeneity in the responses of chromaffin cells to histamine we examined exocytosis in response to nicotine and histamine using an immunofluorescence method based on staining with anti-DBH to detect inserted secretory vesicle membrane. The results show that while up to 98% of the chromaffin cells in culture undergo exocytosis in response to nicotine, histamine stimulates exocytosis in only a sub-population of cells.

Application of biophysical technologies in dental research

There is a wealth of evidence to indicate that if dental caries can be recognized at an early stage, it is possible to halt its progression or even reverse it. This has led to an increased interest in the development of diagnostic techniques capable of visualizing caries at an early stage in addition to providing clinicians with an aid to diagnosis. Several techniques are available for research and clinical applications for detecting early demineralization. This manuscript has reviewed some of the techniques currently available to determine their advantages, whether they have any limitations and their applicability to dental research and clinical dentistry. Not one method is the perfect choice in all situations, but what is clear is that the development and application of biophysical technologies have allowed major advances to be made in dental research as well as in clinical dentistry. With continued developments these technologies will play an important role in the future management of dental disease.

Evaluation of the co-existence of the red fluorescent plaque bacteria P. gingivalis with S. gordonii and S. mutans in white spot lesion formation during orthodontic treatment

BACKGROUND Early detection of white spot lesions (WSLs) around brackets during orthodontic treatment is important for treatment and prevention. But it is unclear whether red fluorescent plaque (RFP) bacteria Porphyromonas gingivalis and its co-existence with Streptococcus mutans and Streptococcus gordonii has any significant influence on this. Therefore the role of this bacterial co existence and WSLs formation during one year of fixed orthodontic therapy was evaluated. METHODS Fourteen 12 to 22 year old (mean 15 ± 3 years) consecutive patients attending the University of Liverpool dental hospital were recruited for this study. Quantitative Light-induced Fluorescence (QLF) was used to identify RFP and enamel demineralisation, respectively, on anterior labial surfaces before and after placement of fixed orthodontic appliances. Bacterial composition was determined by denaturing gradient gel electrophoresis (DGGE) following nested PCR amplification of the 16S rRNA V2-V3 hypervariable region. RESULTS WSLs were recorded on 4.2% of tooth surfaces and WSL development was not associated with RFP bacteria P. gingivalis presence. Differences in RFP bacteria P. gingivalis presence with S. mutans and S. gordonii, were observed before and after appliance placement. Intra subject changes in plaque flora between visits were not significantly associated with WSL development (p > 0.05). However, DGGE profiles indicated that apart from S. mutans, S. gordonii might also have a role in human enamel demineralisation. CONCLUSIONS Fixed orthodontic brackets in adolescents may play a role in altering bacterial composition around brackets during orthodontic treatment and it is plausible that S. gordonii also have a role in human enamel demineralisation. Combinatorial approach of QLF technology and DGGE may be useful in determining bacterial composition during orthodontic therapy which could inform clinical interventions.

A Report of Orthodontic Undergraduate Education in Two Dental Schools: Toronto, Canada and Liverpool, England

The undergraduate orthodontic courses at Toronto and Liverpool are compared. Each course comprises more than 250 hours of teaching and within that, more than 100 hours involve clinical tuition. Both courses contain laboratory modules for the teaching of removable and fixed appliance technique. Undergraduates treat their own patients with both simple and complex appliances, within their clinical training period which extends over at least 2 years. Liverpool undergraduates treat more patients per student than their counterparts in Toronto (P<0·05). During the third year of study, the clinical experience of the Liverpool students (P<0·001) is made up of a greater proportion of patients treated with removable appliances. In both centres, senior students treat patients with a greater preponderance of fixed appliance techniques and two-arch treatments.