Step-wise analysis of the dental implant insertion process using the finite element technique

OBJECTIVES: Using the finite element method (FEM), the insertion process of a dental implant into a section of the human mandible is analysed. The ultimate aim of this article is to advance the use of an innovative engineering approach in dental practices, especially in the process of dental implantation. MATERIAL AND METHODS: The FEM and analysis techniques are used to replicate and evaluate the stress profile created within the mandible during the implantation process. RESULTS: The von Mises stress profiles in both cancellous and cortical bone are examined during implant insertion. The applied torque and the insertion stage are found to strongly influence the resulting stress profile within the surrounding jawbone. CONCLUSIONS: Through the combination of both dental and engineering expertise, a simplified and efficient modelling technique is developed. This improves the understanding of the biomechanical reaction that the jawbone exhibits due to the insertion of implant. The current research is a pilot study using the FEM to model and simulate the dental implantation process. The assumptions made in the modelling and simulation process are: (1) the implantation process is simulated as a step-wise process instead of a continuous process; (2) the implant is parallel threaded and the implant does not rotate during insertion into the jawbone. Although the modelling and simulation techniques had to be simplified, a significant amount of information is gained that helps lay a good foundation for future research. Recommendations for future studies include the variation of the torque applied during the implantation process and upgrading the software capabilities to simulate the full dynamical process of implantation.     

Influence of leucite content on slow crack growth of dental porcelains.

OBJECTIVES: To determine the stress corrosion susceptibility coefficient, n, of seven dental porcelains (A: Ceramco I; B: Ceramco-II; C: Ceramco-III; D: d.Sign; E: Cerabien; F: Vitadur-Alpha; and G: Ultropaline) after aging in air or artificial saliva, and correlate results with leucite content (LC). METHODS: Bars were fired according to manufacturers' instructions and polished before induction of cracks by a Vickers indenter (19.6N, 20s). Four specimens were stored in air/room temperature, and three in saliva/37 degrees C. Five indentations were made per specimen and crack lengths measured at the following times: approximately 0; 1; 3; 10; 30; 100; 300; 1000 and 3000 h. The stress corrosion coefficient n was calculated by linear regression analysis after plotting crack length as a function of time, considering that the slope of the curve was [2/(3n+2)]. Microstructural analysis was performed to determine LC. RESULTS: LC of the porcelains were 22% (A and B); 6% (C); 15% (D); 0% (E and F); and 13% (G). Except for porcelains A and D, all materials showed a decrease in their n values when stored in artificial saliva. However, the decrease was more pronounced for porcelains B, F, and G. Ranking of materials varied according to storage media (in air, porcelain G showed higher n compared to A, while in saliva both showed similar coefficients). No correlation was found between n values and LC in air or saliva. SIGNIFICANCE: Storage media influenced the n value obtained for most of the materials. LC did not affect resistance to slow crack growth regardless of the test environment.     

Unilateral ligature-induced periodontitis influences the expression of neuropeptides in the ipsilateral and contralateral trigeminal ganglion in rats

OBJECTIVES: Expression of neuronal neuropeptides in inflammatory conditions is altered. The changes in expression of substance P (SP) and calcitonin gene-related peptide (CGRP) in ipsilateral and contralateral trigeminal ganglion (TG) neurons were investigated by immunohistochemistry one week after unilateral ligature-induced periodontitis in rats. DESIGN: A retrograde nerve tracer Fluorogold (FG) was applied into the gingival sulcus of the second maxillary molar to identify the neurons in TG that specifically innervate the inflamed gingivomucosa. In addition, neurons from the corresponding maxillary and the adjacent mandibular-ophthalmic regions in TG were analysed. RESULTS: Statistically significantly higher frequencies of CGRP-positive neurons, regardless of their size, were found in TG ipsilateral to the periodontitis (83% and 73% in FG-labelled and maxillary regions, respectively) than in the control group without periodontitis (52% and 42% in FG-labelled and maxillary regions, respectively). The frequency of small FG-labelled SP-positive neurons in the ipsilateral TG (60%) was significantly higher than in the control TG (25%). In the contralateral TG the frequency of CGRP-positive neurons in maxillary region (66%) was significantly higher than in the control group. Surprisingly, the number of SP-positive neurons in all regions of contralateral TG decreased when compared to control and ipsilateral TGs. CONCLUSIONS: Taken together, these results implicate a role of neurogenic component in the pathogenesis of periodontitis. The contralateral response in the TG could be mediated through the transmedian neurological pathways crossing in the trigeminal nuclear complex or through the systemic inflammatory reaction and the activation of the so called "neuro-immune axis".     

Knowledge of and attitudes about blood-borne viruses and infection control in Brazilian dental practice

OBJECTIVE: To determine whether there were any recent changes in hepatitis B immunisation of dental staff, infection control or understanding of viral infections in Brazilian dentists.
DESIGN: A randomised survey was conducted on 740 dentists attending the National Dental Congress in Sao Paulo, Brazil in 1994.
SUBJECTS AND METHODS: The 740 dentists were questioned as to the presence of various viruses in saliva, the perceived risks of dental staff and long-term sequelae, the availability and uptake of vaccines, willingness to treat virus-infected persons, and means of infection control. Nearly 69% of respondents were female dentists, of mean age 30 years. Results were compared with a similar survey from 1990.
RESULTS: Most respondents knew that HIV and hepatitis viruses could appear in saliva and almost all knew of infective risks from hepatitis B (HBV), and the availability of the vaccine. Less than half knew of the association of HBV with liver cancer. There was a four-fold increase in those vaccinated against HBV since the low figure of 9% in 1990. Nearly two-thirds of respondents perceived an occupational risk to dental staff from HIV, and a similar proportion were also unwilling to treat virus-infected persons. A similar proportion also used chemical disinfection for some dental instruments.
CONCLUSIONS: The results show little improvement over a 4-year period except a much greater proportion of dentists were immunised against HBV. However, still only one third of dentists had been vaccinated, in a country with a high prevalence of infection in the general population.     

A new ultrasensitive chemiluminescent assay for the site-specific quantification of alkaline phosphatase in gingival crevicular fluid

The search for markers of periodontal disease activity and progression has accelerated over the last decade, in an effort to replace existing subjective clinical measures of periodontal health status. Research is being aimed at establishing more objective and quantitative methodology, capable of rapid diagnosis prior to the appearance of clinical signs of destructive disease. Such tests need to be sensitive enough to evaluate individual periodontal sites in health as well as disease states. We report the development of a new chemiluminescent assay for the enzyme alkaline phosphatase, that is capable of quantifying the enzyme in sub-microliter volumes of gingival crevicular fluid and serum. The technique will measure alkaline phosphatase (ALP) whilst immobilised on paper strips, without the need for an elution stage. It is simple, versatile and amenable to chair-side use. We discuss in detail the assay procedure and have examined levels of ALP in 11 adult volunteers with clinically healthy periodontal tissues. The mean ALP concentration was 2135 IU/L for GCF and 183 IU/L for serum, a 12-fold difference. There also appeared to be an "oral pattern" of enzyme distribution in healthy periodontal sites, with levels being higher in the anterior region of the mouth and highest in the lower anterior region.     

Relationship of occlusal vertical dimension to the health of the masticatory system

Changes in occlusal vertical dimension have been claimed to cause masticatory system disorders. Early articles on this subject were mainly limited to clinical case reports, and the more recent clinical studies have been flawed by the lack of control groups, blind evaluation, and by poor definition of criteria for evaluating the health of the masticatory system. Research with humans and animals has shown that if increases in occlusal vertical dimension are not extreme and the appliance used covers most of the dentition, there is a good possibility of adaptation. Current scientific knowledge does not support the hypothesis that moderate changes in occlusal vertical dimension are detrimental to the masticatory system.     

Power spectral analysis of electromyographic signal of masticatory muscles at rest position and habitual clench

Thirteen normal subjects were selected for this investigation. At the vertical dimension of rest position and habitual clench, their myoelectric activities of the masseter, anterior and posterior temporal, and digastric muscles on the left and right sides were simultaneously sampled and processed by computer, and the mean power frequency (MPF) and the mean amplitude (MA) of the myoelectric signal were calculated. At rest position, the temporal muscles were major muscles and the MPF differences of various masticatory muscles were not significant. At habitual clench, with the increase in MA, the MPF of various muscles increased. The results show that MPF may have application in describing a central tendency of myoelectrical signal frequency distribution and in evaluating recruitment of motor units. MPF and MA are the quantitative indices reflecting masticatory muscle function.