The influence of simulated masticatory loading regimes on the bi-axial flexure strength and reliability of a Y-TZP dental ceramic

OBJECTIVES: The purpose of the current study was to examine the influence of simulated masticatory loading regimes, to which all-ceramic crown or bridge restorations will routinely be subjected during their service-life, on the performance of a yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) dental ceramic. METHODS: Ten sets of 30 Y-TZP ceramic discs (13 mm diameter, 1.48-1.54 mm thickness) supplied by the manufacturer were randomly selected. Six groups were loaded for 2000 cycles at 500 N (383-420 MPa), 700N (536-588 MPa) and 800 N (613-672 MPa) with three groups maintained dry and the remaining three groups loaded while immersed in water at 37+/-1 degrees C. A further two groups underwent extended simulated masticatory loading regimes at 80 N (61-67 MPa) for 10(4) and 10(5)cycles under dry conditions. The mean bi-axial flexure strengths, standard deviations and associated Weibull moduli (m) were determined. The surface hardness was also determined using the Vickers hardness indentation technique. RESULTS: No significant difference (P>0.05) was identified in the bi-axial flexure strength of the simulated masticatory loading regimes and the control specimens loaded dry or wet. A significant increase in m was identified for the Y-TZP specimens following loading while immersed in water (8.6+/-1.6, 8.5+/-1.6 and 10.3+/-1.9) compared with the control (7.1+/-1.3). However, the extended loading regime to 10(5)cycles resulted in a significant reduction in the m of the Y-TZP specimens (5.3+/-1.0) compared with the control. Localised areas of increased surface hardness were identified to occur directly beneath the spherical indenter. CONCLUSIONS: The occurrence of localised areas of increased surface hardness could be the result of either a transformation toughening mechanism or crushing and densification of the material beneath the indentor manifested as the formation of a surface layer of compressive stresses that counteracted the tensile field generated at the tip of a propagating crack which increased the Weibull modulus of the Y-TZP specimens. The reduced reliability of the Y-TZP specimens loaded to 80 N for 10(5)cycles was associated with the accumulation of subcritical damage as a result of the extended nature of loading.     

Periodontitis is associated with preeclampsia in pregnant women

BACKGROUND: Recent investigations have demonstrated a positive association between periodontitis and pregnancy complications. The purpose of this study was to determine the effect of periodontitis and the subgingival microbial composition on preeclampsia. METHODS: A case-control study was carried out in Cali, Colombia that included 130 preeclamptic and 243 non-preeclamptic women between 26 to 36 weeks of pregnancy. Sociodemographic data, obstetric risk factors, periodontal status, and subgingival microbial composition were determined in both groups. Preeclampsia was defined as blood pressure>or=140/90 mm Hg, and >or=2+ proteinuria, confirmed by 0.3 g proteinuria/24 hours of urine specimens. Controls were healthy pregnant women. Odds ratios (ORs) for periodontitis and subgingival microbiota compositions were calculated. RESULTS: A total of 83 out of 130 preeclamptic women (63.8%) and 89 out of 243 controls (36.6%) had chronic periodontitis (OR: 3.0; 95% confidence interval (CI): 1.91 to 4.87; P<0.001). Clinical attachment loss increased in the case group (4.0+/-0.10 mm) compared to the control group (3.0+/-0.08 mm) (P<0.001). The average newborn birth weight from preeclamptic mothers was 2.453 g, whereas in controls was 2.981 g (P<0.001). Two red complex microorganisms, Porphyromonas gingivalis and Tannerella forsythensis, and the green complex microorganism Eikenella corrodens were more prevalent in the preeclamptic group than in controls (P<0.01). CONCLUSIONS: Chronic periodontal disease and the presence of P. gingivalis, T. forsythensis, and E. corrodens were significantly associated with preeclampsia in pregnant women. Further research is needed to establish pathogenic mechanisms of active periodontal disease and subgingival periodontopathogens related to preeclampsia development.     

Assessment of ST segment depression in patients with cardiac disease after local anesthesia

This study found that dental treatment with 2% lidocaine with 1:100,000 epinephrine did not provoke myocardial ischemia, as assessed by greater than or equal to 1 mm of ST segment depression. Although in some cases systolic and diastolic blood pressure and rate pressure product increased slightly after local anesthetic administration, these changes were not statistically significant. Because these patients were medically supervised and compliant with cardiac therapy, this study suggests that such patients are not at great risk while receiving local anesthesia with 1:100,000 epinephrine for routine dental care.     

Colorado pit and fissure sealant survey: attitudes toward and use of pit and fissure sealants by Colorado general dentists

The purpose of this study was to conduct a survey of Colorado general dentists regarding the use of and attitudes toward pit and fissure sealants. The survey consisted of a questionnaire to determine the utilization levels of sealants by general dentists, reasons for limited placement or non-utilization of sealants, whether sealant placement was delegated to dental auxiliaries or not, and if continuing education courses on sealants had been attended by the dentists and/or their dental auxiliaries. A total of 544 completed questionnaires were available for study. The results indicated that sealants were used by 82.7% of the dentists. Approximately 70% of the practitioners reported that they utilized sealants either routinely or occasionally. Reasons for limited placement or non-utilization of sealants were, in descending order: 1) Not covered by insurance; 2) Inadvertent sealing in of caries; 3) Sealants do not last; 4) Sealants too expensive; 5) Not familiar with sealant technique; 6) Sealants not effective. Placement of sealants was delegated as follows: 1) Dentists, 64.8%; 2) Hygienists, 17.8%; 3) Assistants, 17.4%. Continuing education courses had been attended by 29.1% of the dentists surveyed. Only 6.6% of the dentists indicated that their staff had attended continuing education courses on sealant placement. A relatively high percentage of Colorado dentists are utilizing sealants on a frequent basis. Major reasons for limited usage or non-utilization of sealants relates to lack of insurance coverage and concern regarding sealing in of caries. A need for continuing education courses on sealants appears to exist.     

Infection control in general dental practice

A postal survey of 600 dental practitioners in New South Wales was conducted in 1986 to establish a data base on current infection control protocols as they apply to everyday dental practice. Three hundred and sixty-three replies (60 per cent) were returned, representing approximately 16 per cent of Australian Dental Association members in New South Wales (1987).     

Kinetics of acquisition and loss of calcium fluoride by enamel in vivo

Two in vivo experiments were performed, concerning (1) the kinetics of the acquisition of calcium fluoride on enamel during daily rinses with a solution of 0.023% F as sodium fluoride, and (2) the loss of calcium fluoride from enamel slabs which had been topically treated with a neutral solution containing 0.9% F as sodium fluoride. Enamel slabs were carried in the mouth by 6 volunteers for 8 days in both experiments. Sound and etched enamel were included. (1) During mouthrinses moderate amounts of fluoride were acquired by sound enamel, and more as calcium fluoride than as fluoridated apatite, whereas on etched enamel, more fluoride was deposited as fluoridated apatite. On etched enamel there was also a tendency that the deposition of calcium fluoride levelled out whereas the incorporation of firmly bound fluoride continued. This may indicate that calcium fluoride was transformed into fluoridated apatite, probably through remineralization during pH cycling in plaque covering the etched enamel. (2) After single topical application, it was found that etched enamel initially took up more calcium fluoride than sound enamel, but also lost more during the 1st day of in vivo exposure. The loss of calcium fluoride was arrested after 1-2 days, on sound enamel at 70% and on etched enamel at 40% of the original level. It is suggested that the increased amounts of firmly incorporated fluoride in enamel originated from calcium fluoride on enamel, and that calcium fluoride is an important and clinically significant source of fluoride ions on enamel.     

The elimination of cross-infection in dental practice--a 5-year follow-up

A survey in 1983 showed that 16% of general dental practitioners in the Lothian Region wore operating gloves when treating patients; 9% wore them continually and 7% only when performing dento-alveolar surgery. Twelve per cent replied that they would not consider wearing operating gloves and 72% stated that they might consider their use. A similar survey has now been completed 5 years later, involving practitioners in the Lothian and Borders regions. This shows that 163 (97%) of the 168 practitioners who replied now wear operating gloves; 51% restrict their use to the treatment of 'potentially infectious patients' and dento-alveolar surgery; 46% wear them continually. The main objections given to wearing gloves continually were loss of tactile sensation (67%) and cost (13%). The most difficult task to perform wearing gloves was root canal therapy (56%). The majority of practitioners (84%) believed that gloves reduced the dangers of cross-infection. The methods stated to be available for instrument sterilisation in 99.5% of practices were acceptable. This paper proposes that to eliminate cross-infection and protect the dental practitioner, operating gloves should be worn when treating all patients.     

Microbiological and immunological studies of adult periodontitis in patients with noninsulin-dependent diabetes mellitus

The subgingival microflora and serum antibody response was examined in periodontitis patients with noninsulin-dependent diabetes mellitus (NIDDM), impaired glucose tolerance (IGT), and normal glucose tolerance (NGT). The predominant cultivable microflora was determined for subgingival plaque sampled from two deep periodontal pockets in each of eight adult periodontitis patients with NIDDM. Indirect immunofluorescence for Bacteroides intermedius, Bacteroides gingivalis, and Haemophilus actinomycetemcomitans was used to examine these same samples as well as 186 additional subgingival plaque samples from 47 patients with moderate to severe generalized periodontitis including 25 subjects with NIDDM, six subjects with IGT, and 16 subjects with NGT. Serum antibody levels to 13 microorganisms including seven oral bacterial species and one nonoral control species were measured by enzyme-linked immunosorbent assays (ELISA) in 377 subjects including 84 normal subjects without periodontal disease, 112 normal subjects with periodontitis, 19 periodontally normal subjects with IGT, 65 periodontitis patients with IGT, 15 periodontally normal subjects with NIDDM, and 82 periodontitis patients with NIDDM. Three hundred eighty-two bacterial isolates were recovered from the eight patients. B. intermedius was the most frequently isolated microorganism constituting 16% of the total isolates followed by Wolinella recta and B. gingivalis, which each accounted for 13% of the total. Streptococcus sanguis was the most prevalent microorganism, which was found in 75% of the sites. Subgingival plaque samples examined by immunofluorescence demonstrate a high prevalence of black-pigmented Bacteroides and suggest that the proportion of B. gingivalis but not B. intermedius is higher in NIDDM with periodontitis than in other groups.(ABSTRACT TRUNCATED AT 250 WORDS)