ABSTRACT
A three-dimensional finite-element model of a human mandible is presented, and the stresses and deformations computed for loading states induced by two different gnathologic reconstructions using six and four implants are discussed. Occlusal canine guidance and posterior and anterior group functions on cantilevered and distally supported prostheses have been simulated. The stress distributions generated by the different loading conditions on either the osseointegrated prosthesis or the bone tissue surrounding the implants are described. The analysis of the stress distribution on the working side reveals that the posterior group function undergoes a reduction in stress intensity on the cortical bone surrounding the implants (especially for the distal implant) compared with the anterior group function and canine guidance in both gnathologic reconstructions.
ABSTRACT
The kinetic behaviour of dental composite is traditionally studied, considering only the isothermal behaviour, whereas a fast and highly non-isothermal bulk polymerization is expected as a consequence of the significant heat developed due to the exothermic nature of the polymerization reaction. In this paper the photopolymerization kinetics of a commercial dental composite activated by visible light are analysed by differential scanning calorimetry. This technique is applied to determine the degree of reaction and the glass transition temperature of thin layers of the composite matrix, at different isothermal cure temperatures. A phenomenological kinetic model is then integrated with an energy balance in order to analyse the cure behaviour of thicker composite layers. The full model results indicate that non-isothermal cure conditions may be achieved, obtaining higher values for the glass transition temperature and the degree of reaction.
Subject(s)
Composite Resins/chemistry , Dental Materials/chemistry , Polymers/chemistry , Calorimetry, Differential Scanning , Chemical Phenomena , Chemistry, Physical , Hot Temperature , Kinetics , Mathematical Computing , Models, Chemical , Photochemistry , Temperature , ThermodynamicsABSTRACT
We have studied hemoglobin concentration in saliva of anti-HIV positive and anti-HIV negative intravenous drug abusers (IVDA) and normal controls and the relationship between hemoglobin concentration in saliva and number of CD4+ cells and clinical status of AIDS in anti-HIV positive IVDA. 120 anti-HIV positive IVDA, 112 anti-HIV negative IVDA and 116 normal healthy subjects not belonging to any risk group for HIV infection completed the study. Saliva was collected at awakening before brushing teeth and the concentration of hemoglobin was determined. Hemoglobin concentration in saliva in basal conditions is higher in anti-HIV positive IVDA with respect to anti-HIV negative IVDA (p less than 0.05) and controls (p less than 0.01). In anti-HIV positive IVDA hemoglobin concentration in saliva is higher in subjects with CD4+ cells less than 200/10(6) l with respect to subjects with CD4+ greater than 200/10(6) l (p less than 0.05) and in subjects with ARC/AIDS with respect to subjects with PGL or who are asymptomatic (p less than 0.01). Subjects with ARC/AIDS have a mean concentration of hemoglobin of 19 micrograms/0.1 ml saliva (range 0-153) which corresponds to 1.3 microliters of blood/ml saliva. If 10 ml of saliva are exchanged during kissing an average of 13 microliters of blood are transferred (110 microliters of whole blood at extreme range). Blood of symptomatic patients has an HIV titer of 7 TCID/microliters which for 10 ml saliva containing an average of 1.3 microliters blood/ml saliva corresponds to an average of 90 TCID (770 TCID at the extreme range).(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Acquired Immunodeficiency Syndrome/transmission , HIV Seropositivity/blood , Hemoglobins/analysis , Saliva/chemistry , Substance Abuse, Intravenous/complications , Adolescent , Adult , Female , Humans , Male , Stomatitis/etiologyABSTRACT
The importance of perfect knowledge of the anatomy and physiology of the stomatognathic complex for any understanding of the aetiopathogenic mechanisms behind temporomandibular joint pain dysfunction syndrome is emphasised and the fundamental concepts underlying the use of the bite plane as a valuable aid in the diagnosis and initial treatment of articular dysfunction are described.
