Amelogenesis imperfecta in a new animal model--a mutation in chromosome 5 (human 4q21)

Candidate genes for amelogenesis imperfecta (AI) and dentinogenesis imperfecta (DI) are located on 4q21 in humans. We tested our hypothesis that mutations in the portion of mouse chromosome 5 corresponding to human chromosome 4q21 would cause enamel and dentin abnormalities. Male C3H mice were injected with ethylnitrosourea (ENU). Within a dominant ENU mutagenesis screen, a mouse mutant was isolated with an abnormal tooth enamel (ATE) phenotype. The structure and ultrastructure of teeth were studied. The mutation was located on mouse chromosome 5 in an interval of 9 cM between markers D5Mit18 and D5Mit10. Homozygotic mutants showed total enamel aplasia with exposed dentinal tubules, while heterozygotic mutants showed a significant reduction in enamel width. Dentin of mutant mice showed a reduced content of mature collagen cross-links. We were able to demonstrate that a mutation on chromosome 5 corresponding to human chromosome 4q21 can cause amelogenesis imperfecta and changes in dentin composition.     

Dental caries in children with asthma undergoing treatment with short-acting beta2-agonists

AIM: This study sought to evaluate possible higher risk for dental caries among asthmatic children undergoing treatment with short-acting beta2-agonists. METHODS: Dental clinical assessments, saliva analysis and a questionnaire survey were carried out on 60 children aged 6-12, of whom 30 were asthmatic subjects undergoing treatment with short-acting beta2-agonists and 30 were used as controls. The obtained data for DMFT/dmft scores, Silness-L?e plaque index, buffer capacity and bacteria counts for Streptococcus mutans and Lactobacillus in the saliva, oral hygiene and dietary habits were compared using Student t-test and Pearson chi-square test. RESULTS: We registered a higher DMFT score among asthmatics of 1.2-/+1.8 (SD) and 0.3-/+0.8 among non-asthmatic patients (p<0.05), while comparison of dmft scores between the examined groups showed not significant (Student t-test). Saliva analysis revealed lower buffer capacity in 43.3% of the asthmatic children, followed by higher cariogenic bacteria counts in their saliva (p<0.05 Student t-test). These results show the lower plaque index in the asthmatic group (1.6+/-0.4) compared with the control (2.1+/-0.3). Asthmatic children expressed better oral-health habits with more frequent tooth- brushing and usage of fluorides. CONCLUSION: The results from our study suggest a higher caries-susceptibility among asthmatic children undergoing treatment with short-acting beta2-agonists, but a clear association between these drugs, salivary changes and dental caries among children, still remains to be demonstrated.     

High frequency ultrasound imaging of a single-species biofilm

OBJECTIVE: This study evaluated the feasibility of a high frequency ultrasound scan to examine the 3D morphology of Streptococcus mutans biofilms grown in vitro. METHODS: Six 2-day S. mutans biofilms and six 7-day biofilms were grown on tissue culture membranes and on bovine dentine discs. A sterile growth medium on the membrane and disc were used as controls. Surfaces were rinsed and then immersed in sterile saline. High-frequency ultrasound imaging system was used to scan these surfaces at 55MHz, and a computer program calculated the average thickness of the biofilm layer from the 3D images. RESULTS: 3D pictures of the biofilm layers were obtained. Different cross-sections and plains are easily demonstrated. The average thickness of the 7-day biofilm was significantly bigger than the 2-day on both the membranes and dentinal discs. No structures were observed on the sterile membrane or disc. CONCLUSION: Three-dimensional structural imaging in situ is possible without damaging the biofilm layer in a quick and easy manner and can therefore be used to evaluate biofilms longitudinally as a function of time.     

Recruitment and standardization of a group of Australian dentists for a multipractice study on dental caries prevention

BACKGROUND: This introductory paper details the recruitment and standardization of a group of dentists participating in a clinical trial. The trial is being undertaken to determine the cost-effectiveness of a structured preventive programme compared to standard care within private dental practices. We recruited private dental practitioners from a variety of locations in New South Wales (NSW) and the Australian Capital Territory (ACT). We sought to quantify the diagnostic reliability of dentists involved, and to define, quantify, and analyse standard care. METHODS: This is a multi-centre, clustered randomized controlled trial, where dentists are allocated to an intervention preventive or control group. Recruitment was facilitated with the support of key stakeholders and included oral presentations at divisional meetings of the Australian Dental Association, NSW Branch (ADA). A detailed time-in-motion study of 426 dental procedures was undertaken in order to define the parameters of standard care. The reliability study involved each dentist reading a set of 12 pairs of bitewing radiographs that had been produced and reviewed under standardized conditions. The reliability analysis was undertaken blind to allocation status of the dentist. RESULTS: Recruitment ceased three months into the planned six-month recruitment period, 31 practices having approached the researchers. Eight suburban, five Central Business District (CBD), five rural (in fluoridated communities), and four rural (in non-fluoridated communities) practices have been recruited. Standard care did not differ significantly between intervention and control practices (Mann-Whitney U: z = -0.50; P = 0.6). Diagnostic reliability was substantial (Kappa = 0.79 [range 0.73-0.811 and 0.78 [range 0.72-0.82]) in relation to the intervention and control practices, respectively; P = 0.6. CONCLUSION: The involvement of private dental practices in research is feasible and well supported by the profession. Standard care does not differ significantly between intervention and control practices. Inter- and intra-observer reliability was substantial, and not statistically different between the two arms of the trial.     

The dynamic range of TMJ sounds

It is of clinical interest to record the amplitudes of temporomandibular joint (TMJ) sounds. The aim was to test the hypothesis that sealing the meatus, when placing a microphone in the ear canal affects such recording by increasing the sound pressure level (SPL). Bilateral recordings of 249 TMJ clickings were made from three subjects, using sampling rates of 48 or 96 kHz and 24 bits A/D conversion, with and without the ear canals sealed by Silicone putty. The peak-to-peak equivalent sound pressure level (peSPL) was higher (P < 0.001) when the ear canal was sealed (range of mean differences was 8.3-24.9 dB peSPL). This means that the signal to noise ratio can be improved by sealing the meatus because the electronic noise level is not increased. Most important is that the dynamic range of the clicking sounds was 62 dB that is larger than the effective dynamic range of a 16 bits sound card. Future studies are needed to establish normative peSPL values. However, cards with at least 24 bits A/D conversion will be required, especially in patients with suspected disc displacement with reduction, where the difference in loudness between opening and closing clicking often is large.     

A general dental practice research network: impact of oral health in general dental practice patients

OBJECTIVE: To measure the subjective impact of oral health in a group of patients attending general dental practices in the North West of England and to investigate the attributes of dentists and practices in order to examine how such attributes might relate to patients' subjective perceptions of oral health. DESIGN: Fifteen general dental practices conducting a simultaneous survey of attending patients and 15 practitioners from these practices providing information about their attitudes to treatment, prevention and various aspects of their surgery. SETTING: General dental OUTCOME MEASURES: Patient subjective impact scores. Relationships between practice and practitioner variables and patients' subjectively perceived oral health. RESULTS: Fifteen practitioners with diverse practice attributes provided data on 718 patients. The mean total oral health impact score was 18.4. Twenty two per cent of patients had experienced pain in the four weeks before the survey and 11% had been unable to chew some foods. Fifty five per cent of the surveyed population had, in the previous year, worried about the appearance of their mouth and 65% had worried about their oral health in general. Dentists' beliefs were related to patient impact scores but practice attributes were not significantly associated with patients' impacts. CONCLUSIONS: Fourteen percent of the differences in patients' subjectively perceived oral health can be attributed to dentist attitudes and attributes. Further research regarding the influence of dentists personality and professional beliefs on patients well-being needs to be undertaken.     

Polymerization shrinkage and microleakage in Class II cavities of various resin composites

This study investigated the polymerization shrinkage of restorative materials and microleakage in the proximal box of Class II restorations. Twenty caries free extracted human molars were prepared on the mesial and distal, making 40 slot cavities. Groups (n=10) were classified as: Group 1: Single bond/Filtek Z-250; Group 2: Single Bond/Filtek Flow/Filtek Z-250; Group 3: Admira Bond/Admira; Group 4: Ariston Liner/Ariston. Dentin bonding systems and resin composites were applied according to the manufacturer's instructions. The specimens were stored in distilled water for one week at 37 degrees C, thermocycled (5 degrees-55 degrees C x 2000), stained with 50% aqueous silver nitrate, immersed in a diluted developer solution (24 hours), rinsed and sectioned in two pieces with a low speed saw (Isomet). Dye penetration (Score 0-4) was determined separately at the occlusal enamel margin and cementoenamel junction. The volumetric polymerization shrinkage of materials was determined with the apparatus of Watts and Cash (Watts Cash, 1991) for 300 seconds. Polymerization shrinkage results were as follows: Filtek Flow (3.5% +/- 0.1) > Admira (2.1% +/- 0.1) = Ariston AT (2.3% +/- 0.1) > Filtek Z-250 (1.8% +/- 0.1) (One-way Anova, post hoc Bonferroni test at p = 0.05 level). No statistical difference was found at the enamel margins for any of the materials (Score 0-1). At the cemento-enamel junction, all test groups showed significantly higher microleakage when compared to the enamel margins (Kruskal-Wallis test, Mann-Whitney U). Dye penetration results at dentin were as follows: Filtek Flow + Filtek Z-250 = Admira < Ariston AT = Filtek Z-250. microleakage than the ion-releasing and hybrid composites lined only with bonding agent at the cementoenamel junction in Class II cavities.     

Association between developmental defects of enamel and different concentrations of fluoride in the public water supply

OBJECTIVES: To compare the prevalence and severity of developmental defects of enamel (DDE) among subjects whose maxillary incisors developed during periods with different concentrations of fluoride in the public water supply. METHODS: Standardized intra-oral photographs of random samples of 12-year-old children were collected in 1983, 1991 and 2001 (n = 1,990) in Hong Kong and assessed for DDE by a trained masked examiner. The fluoride concentrations in the public water supply at the times when the enamel on their maxillary incisors developed were 1.0, 0.7 and 0.5 ppm, respectively. RESULTS: The mouth prevalence of DDE for these children (based on the maxillary incisors) were 92.1, 55.8 and 35.2% in the years 1983, 1991 and 2001, respectively (p < 0.001). Most of these children were affected by diffuse opacities (89.3% in 1983, 48.5% in 1991 and 32.4% in 2001, p < 0.001). Marked differences in the mean number of teeth affected by DDE (p < 0.001) and in the maximum extent of DDE (p 相似文献