South African medical schools: Current state of selection criteria and medical students' demographic profile.

BACKGROUND: Selection of medical students at South African (SA) medical schools must promote equitable and fair access to students from all population groups, while ensuring optimal student throughput and success, and training future healthcare practitioners who will fulfil the needs of the local society. In keeping with international practices, a variety of academic and non-academic measures are used to select applicants for medical training programmes in SA medical schools. OBJECTIVES: To provide an overview of the selection procedures used by all eight medical schools in SA, and the student demographics (race and gender) at these medical schools, and to determine to what extent collective practices are achieving the goals of student diversity and inclusivity. METHODS: A retrospective, quantitative, descriptive study design was used. All eight medical schools in SA provided information regarding selection criteria, selection procedures, and student demographics (race and gender). Descriptive analysis of data was done by calculating frequencies and percentages of the variables measured. RESULTS: Medical schools in SA make use of academic and non-academic criteria in their selection processes. The latter include indices of socioeconomic disadvantage. Most undergraduate medical students in SA are black (38.7%), followed by white (33.0%), coloured (13.4%) and Indian/Asian (13.6%). The majority of students are female (62.2%). The number of black students is still proportionately lower than in the general population, while other groups are overrepresented. CONCLUSION: Selection policies for undergraduate medical programmes aimed at redress should be continued and further refined, along with the provision of support to ensure student success.

Mandibular fractures: an epidemiological survey at the Oral and Dental Hospital, Pretoria.

OBJECTIVE: The objective of this retrospective analysis was to study the etiology, distribution, treatment modalities and complications of mandibular fractures of patients who attended the Maxillo-Facial and Oral Surgery (MFOS) unit at the School of Dentistry, University of Pretoria. METHOD: The records of a representative sample of patients who presented at the MFOS unit with mandibular fractures between January 1999 and December 2003 were captured on a data form specifically designed for this purpose. The data were then analysed using the Statistix 8 programme. RESULTS: Of the 501 patients who were included in the survey, 67.6% were in the age group 21 to 40 years. The majority of the patients (83.2%) were male. Assault (72.5%) was the most common cause of injury followed by road traffic accidents (14.2 %) and falls (8.8%). Of the 501 cases, 41.3% were bilateral, 32.7% on the left side and 26% on the right side. With regard to the location of the fractures, the majority occurred in the body of the mandible (411%), followed by those in the area of the symphysis/ parasymphysis (23.1%). In the majority of cases (51.7%) the treatment modality used was a closed reduction with intermaxillary fixation. Complications were reported in 14.6% of the 501 cases of which malunion (32%) was the most prevalent. CONCLUSIONS: Mandibular fractures are more common in males in the age range 21 to 40 years. Interpersonal violence is the main cause of these fractures. The majority of mandibular fractures occur in the body region while malunion is the most common complication.

A pilot study to determine the effects of skin contact on two commonly used dental impression materials.

Impression materials used in the analysis of bite marks are required to maintain their stability and integrity for extended periods. It has been observed that certain impressions taken of skin lose their properties with time, becoming sticky and unusable as evidence. The objective of this study was to investigate the onset of "stickiness" in two commonly used dental impression materials when brought into contact with skin. The two materials tested were Impregum and President. They were syringed into glass rings positioned on the upper arms of 28 volunteers. Changes in stickiness were monitored over a four-month period using a tensile testing machine. A metal plunger was lowered onto the impression material and then retracted measuring the adhesive force of the material to the lower surface of the plunger. Over the research period 17 of the 28 rings of Impregum became sticky and changed colour from purple to turquoise. The remaining 11 Impregum samples, all the President samples and all control samples remained unchanged over the 120 day period. The results of this study show that certain factors present in or on skin are responsible for the loss of surface integrity of Impregum. The factors responsible for these changes have not been established.

Shear bond strength of five porcelain repair systems on cerec porcelain.

The purpose of this in vitro investigation was to evaluate the shear bond strength of composite resin bonded to Cerec Vitablocs Mark II porcelain with four different porcelain repair systems. The systems evaluated in this study were Scotchbond/ RelyX Primer (S/ 3M), Ultradent Porcelain Repair Kit (U, Ultradent), Vivadent Ceramic Repair Kit (V, Vivadent) and Prime & Bond NT/ Calibra Silane Coupling Agent (P, Dentsply). Seventy five Cerec Vitablocks Mark II porcelain were embedded in metal rings, leaving 7 mm of porcelain exposed above the ring surface. Samples were ground wet on 400 grit SiC paper to roughen the surface and then screened for surface defects. The five porcelain repair agents were applied according to manufacturers' instructions and matching composite stubbs, then bonded onto 15 treated porcelain surfaces, using an Ultradent mould with a diameter of 2,38 mm. All samples were stored in distilled water for 24 hours at 37 degrees C before the bonds were stressed to failure, using a shear load in a Texture Analyser (TAXT2i) (Stable Micro Systems) Data was analyzed statistically (ANOVA). The effects of the pretreatments on the porcelain surfaces after treatment with the different systems were examined in a Scanning Electron Microscope (SEM), and the modes of fracture were assessed under a light microscope. The mean SBS (MPa) for the products in descending order were: U = 26.6 1.7; V = 20.9 3.4; C = 19.4 5.3; S = 18.0 2.0 and P = 15.9 2.1. The Student-t Test revealed a statistical significant difference (p < 0.05) between the mean shear bond strengths of P and U. There was also a statistical significant difference (p < 0.05) between the mean shear bond strengths of P and V. Most debonded specimens showed cohesive fractures in the porcelain. Significant shear bond strength differences were observed for the different repair systems. All the systems tested can probably be used to repair Cerec Vitablocs Mark II porcelain, with some systems providing higher bond strengths.

Anti-bacterial efficacy of new self-etching dentine bonding agent.

Since a perfect seal is not easily achieved during bonding procedures, any product which will limit or delay bacterial proliferation in the resulting micro-leakage spaces should extend the life span of bonded restorations. This study compared the antibacterial properties of an experimental, self-etching, fluoride-releasing, antibacterial bonding system (ABF) with two standard bonding systems (SE Bond and Scotchbond MP). Spread plates of three different bacteria (Streptococcus mutans, Lactobacillus paracasei and Actinomyces naeslundii) were prepared on Brain-Heart Infusion agar. Standardised, sterilised filtration paper disks were infiltrated with 20 microl of primer and then placed on the inoculated agar and incubated at 37 degrees C for 48 hours. The extent of the inhibition zones were measured at different positions and data were analysed using the Student t-test to determine significant differences. All three primers showed zones of inhibition for all three bacteria tested. Inhibition zones for ABF primer against S. mutans were significantly larger (p<0.05) compared to that of Scotchbond MP and SE Bond. In general the antibacterial activity of the three primers against the three bacteria tested varied, and the inhibitory effect for the experimental primer was significantly superior against S. mutans only.

Flexural properties of denture-base polymer reinforced with glass-fibre polysulphone composite.

The aim of this study was to determine the effect of glass-fibre composite reinforcement on the flexural strength and flexural modulus poly-methyl methacrylate (PMMA). Prefabricated electrical glass-fibre polysulphone composite rods (GF/PSu), 3mm in diameter, were incorporated in cylindrical, heat polymerizing PMMA specimens with diameters of 4, 5 and 6mm respectively (n = 10). These specimens were compared with PMMA control groups of similar dimension. A three point loading test was performed in air after storage of specimens in water at 37 degrees C for 8 weeks. The following variables were measured : Flexural Strength (FS) and Flexural Modulus (FM). The data were analyzed using one way analysis of variance (ANOVA). After testing, the fracture zone was evaluated using a scanning electron microscope (SEM). The glass-fibre reinforcement used in this study significantly enhanced both the FM and FS values of PMMA. This enhancement was, however, progressively reduced in relation to an increase in cross-sectional dimension of the specimens. SEM evaluation revealed delamination and fracture of the glass-fibres in the polymer matrix.

Effect of biological contamination on dentine bond strength of adhesive resins.

The purpose of this in vitro study was to determine the effect of saliva (S) and blood (B) contamination on the dentine bond strength of two single-component dentine bonding systems. The occlusal thirds of 120 recently extracted, human molars were removed with a low speed saw and subsequently embedded in Bencor rings by means of self-curing, acrylic resin. The occlusal surfaces were ground wet on 600-grit silicone carbide paper in a polishing machine to expose superficial dentine and to create a smear layer. The teeth were randomly divided into 12 groups (n = 10). All the dentine surfaces were etched with 34% phosphoric acid for 15 seconds rinsed with water, air-dried for 3 seconds, leaving the surfaces visibly moist. For the control groups (C) the etched dentine surfaces were treated with either, Scotchbond 1 (SB1, 3M) or Prime & Bond NT (PBNT, Dentsply) according to the manufacturer's instructions. In the contaminated groups, the saliva or blood was applied by means of a disposable brush, left undisturbed for 1 minute, and the excess then thinned by air spray. The dentine bonding systems were then applied, also according to manufacturer's instructions. Composite (Z250 and TPH) and Compomer (F2000 and Dyract AP (D-AP)) stubs were packed and cured incrementally to the corresponding pretreated dentine surfaces. All specimens were stored for 24 hours under water at 37 degrees C. The bonds were then stressed to failure with a Zwick testing machine, operating at a crosshead speed of 0.5 mm/min. Fractured samples were examined in a Scanning Electron Microscope. The data were statistically analysed (Student-t test). The mean SBS (MPa) were. SB1 with Z250: C = 19.1 +/- 4.4; S = 17.3 +/- 3.5; B = 2.6 +/- 0.9; SB1 with F2000: C = 11.8 +/- 3.3; S = 9.7 +/- 1.8; B = 4.7 +/- 1.6. PBNT with TPH: C = 9.2 +/- 3.2; S = 6.5 +/- 3.0; B = 4.3 +/- 1.5; PBNT with D-AP: C = 10.2 +/- 3.6; S = 9.3 +/- 2.9 and B = 7.3 +/- 2.5. There was no statistical significant difference in shear bond strengths between the control and the saliva-contaminated samples for both systems. There was, however, a significant difference in bond strengths between the control and the blood-contaminated samples. Blood contamination negatively influenced bond strength of bonding systems to dentine.

Evaluation of a novel heminested PCR assay based on the phosphoglucosamine mutase gene for detection of Helicobacter pylori in saliva and dental plaque.

A novel heminested PCR protocol was developed for the specific detection of Helicobacter pylori at low copy numbers. A set of primers specific for the phosphoglucosamine mutase gene (glmM) of H. pylori produced a 765-bp fragment that was used as template for the heminested primer pair delineating a 496-bp fragment. By using agarose gel electrophoresis for detection of the heminested PCR-amplified products, amplification of H. pylori genomic DNA was achieved at concentrations as low as 0.1 pg, equivalent to 5 x 10(2) bacteria. A study was subsequently undertaken to evaluate the heminested PCR for detection of H. pylori in dental plaque and saliva. Specimens collected from 58 individuals were cultured, and PCR was subsequently performed on the oral cultures. Identification of H. pylori in the same series of saliva and dental plaque specimens was carried out with PCR using a primer pair specific for the H. pylori urease B gene and by the heminested PCR assay. The identity of the amplified products was confirmed by DNA sequencing. Our results demonstrate that the heminested PCR assay was specific for detection of H. pylori, yielding no false-positive results, and that H. pylori had a low prevalence (approximately 3%) in specimens obtained from the oral cavity.

Caries prediction factors in children with primary dentition.

Previous studies have indicated an association between the dmft and the lactobacilli counts in small children. This study evaluated and compared a number of salivary factors that could have an effect on caries progression in two groups of children with primary dentition (group 1 = 3-6 years; group II = 9 years). The average dmft score was higher for group II. The dmft score of group I consisted mainly of a large dt component, while in group II a large ft component was found. Lactobacilli were present in 44.83% of group I and in 77.27% of group II. Significant positive correlations were found for group I between the dt component of the dmft and lactobacilli count (P < 0.05, r = 0.48) as well as the total dmft and lactobacilli count (P < 0.05, r = 0.45). Significant positive correlations were found for group II between the dmft and lactobacilli count (P < 0.05, r = 0.39) and the plaque index and lactobacilli count (P < 0.05, r = 0.31). Significant correlations between the dmft and the prevalence of lactobacilli in the oral cavity were also indicated (group I: P < 0.05, r = 0.45; group II: P < 0.05, r = 0.36). Significant correlations confirmed the association of lactobacilli with the caries process and indicated the reliability of lactobacilli counts to determine caries activity. Correlations between the dmft and the prevalence of lactobacilli in the oral cavity indicated the possibility of an excellent but simple test for the prediction of caries susceptibility in children.

In vitro cytotoxicity of chlorhexidine gluconate, benzydamine-HCl and povidone iodine mouthrinses on human gingival fibroblasts.

Mouthrinses are frequently prescribed for the treatment of ulcerative diseases of the oral mucosa. In this study the in vitro cytotoxic effect of 0.2% chlorhexidine gluconate in water, 0.15% benzydamine-HCl in 8.5% ethanol and 1% povidone iodine in 10% ethanol were determined. Results of photographs and cell counts revealed that all the cells exposed to chlorhexidine gluconate, benzydamine-HCl and povidone iodine were immediately fixated onto the tissue culture surfaces. The three agents were then diluted in phosphate buffered saline to concentrations varying between 10% and 90% and fibroblasts were once again exposed to the dilutions of the test agents. Photographs were taken and cell concentrations in the wells were determined immediately after exposure and after 2, 4 and 24 hours. Results indicated that cells were immediately fixated by 10% chlorhexidine gluconate in water, 20% povidone iodine and 70% benzydamine-HCl. Fibroblasts survived and recovered from the exposure to 8.5% and 10% ethanol, which indicated that the fixation effect is not the result of the ethanol, but should be ascribed to the activity of the active ingredients in the mouthrinses.

Lactobacillus species associated with active caries lesions.

Lactobacilli that are most frequently associated with active caries lesions in dentine were isolated and identified as part of a research project which aims to determine the role of the predominant species of these organisms in the carious process. Samples of carious dentine were collected from 12 patients with open caries lesions (Group A) and stimulated saliva samples were collected from 12 patients with a DMFT = 0 and confirmed presence of lactobacilli in the oral cavity (Group B). After serial dilutions samples were plated on Rogosa agar and incubated anaerobically at 37 degrees C for 48 hours. Representative colonies were isolated from each sample, using Harrison's disc and species were identified by classical taxonomy. A total of 153 isolates were identified. The redefinition and description of lactobacilli species in recent systematic literature resulted in a new and different species composition of oral lactobacilli as shown in this study, namely: homofermentative species (Group A = 82 per cent; Group B = 90 per cent) were predominantly Lactobacillus paracasei (Group A = 39 per cent; Group B = 30 percent) and Lactobacillus rhamnosus (Group A = 31 per cent; Group B = 41 per cent). Heterofermentative species (Group A = 18 per cent; Group B = 10 per cent) were predominantly Lactobacillus fermentum (Group A = 68 per cent; Group B = 100 percent).

Anaerobic bacteria in orofacial abscesses.

Obligate anaerobic bacteria were cultured from 15 orofacial abscesses. Bacteroides species constituted 43 per cent, Clostridium 21 per cent, Fusobacterium 14 per cent, Peptostreptococci 11 per cent, peptococci 7 per cent and Veillonella 4 per cent of the isolates. This study confirms the polymicrobial nature of orofacial infections. Sensitivity to antibiotics was unpredictable. Clostridium difficile, Clostridium tetani, Peptostreptococcus productus and Veillonella parvula showed resistance to some of the most frequently used antibiotics. Ampicillin and tetracycline were the most effective antibiotics and the highest resistance was shown against erythromycin.

Oral lactobacilli isolated from teenage orthodontic patients.

Orthodontic bands form retention areas which create favourable conditions for growth of lactobacilli. This study deals with the numbers and specific species of lactobacilli in the oral cavity of teenage orthodontic patients. High numbers of lactobacilli were obtained (log 6.398 +/- 0.761 cfu/ml) and the buffer capacity of saliva indicated a high caries risk amongst these individuals but the actual DMFT values were relatively low. Homofermentative lactobacilli predominated in both plaque and saliva and particularly L. salivarius and L. casei. These two lactobacilli species indicated that these patients are at a high caries risk. Several other homofermentative and heterofermentative lactobacilli were isolated which indicated the complexity of the oral lactobacilli community in saliva and plaque.

Preservation of the quantity of lactobacilli in samples from the oral cavity.

Transport media for the preservation of streptococci from oral samples have been described, but a suitable transport medium for the preservation of lactobacilli in oral samples is yet to be established. In this study MRS, ROGOSA, and modifications of these media were evaluated as transport media for the quantitative preservation of oral lactobacilli. Results indicated a survival of ca. 100 per cent oral lactobacilli for both media when stored at 4 degrees C for up to 72 h. A decrease in the survival rate was obtained upon storage at -196 degrees C and growth occurred upon storage at 20 degrees C. It was evident throughout that carbohydrate-free modifications of both media best supported the quantitative survival of oral lactobacili. Carbohydrate-free modifications of both MRS and ROGOSA are therefore recommended as preservative transport media for the quantity of oral lactobacilli in oral samples for limited time periods.

Physiology of Sporolactobacillus strains isolated from different habitats and the indication of in vitro antagonism against Bacillus species.

In an ecological study only low numbers of Sporolactobacillus were found in habitats such as the faeces of herbivores, the rumen of cattle and the final waste water of an abattoir. Their presence in the final waste water of an abattoir indicates their possible association with food, and, more specifically, with meat. Differences were found in some physiological characteristics. One isolate (L2404) differed from the authentic Sporolactobacillus ATCC 15538 by its inability to ferment inulin, its growth in presence of 6.5% NaCl and in 0.2% tellurite, by the isomer(s) of lactic acid produced and the mol% G + G in the DNA. One Sporolactobacillus isolate (L2407) showed antagonism against Bacillus cereus, Bacillus cereus var, mycoides, Bacillus megaterium and Bacillus subtilis.

Resistance of vegetative cells and endospores of Sporolactobacillus to gamma-irradiation.

Vegetative cells of Sporolactobacillus showed average resistance to gamma-irradiation compared to other vegetative bacteria with D10 values ranging from 0.350 to 0.525 kGy. Endospores of Sporolactobacillus showed higher resistance to gamma-irradiation than most Bacillus species but were close to that of Clostridium species. The average D10 value for Sporolactobacillus endospores was 2.5 kGy.

Effect of reduced water activity on vegetative growth of cells and on germination of endospores of Sporolactobacillus.

Growth of vegetative cells and germination of endospores of Sporolactobacillus at reduced water activity (aw) values were studied with NaCl and glycerol as humectants, and compared with Bacillus cereus and Clostridium sporogenes. With NaCl the highest aw for complete inhibition of both growth of vegetative cells and germinated spores of Sporolactobacillus was 0.955. With glycerol, growth of vegetative cells was completely inhibited at 0.905 as compared to 0.880 for vegetative growth resulting from germinated endospores. The mechanism of this phenomenon cannot be explained yet. NaCl appeared to have a toxic effect, in addition to inhibition by reduced aw per se.