First results from the Thomson scattering diagnostic on proto-MPEX

A Thomson scattering (TS) diagnostic has been successfully implemented on the prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory. The diagnostic collects the light scattered by plasma electrons and spectroscopically resolves the Doppler shift imparted to the light by the velocity of the electrons. The spread in velocities is proportional to the electron temperature, while the total number of photons is proportional to the electron density. TS is a technique used on many devices to measure the electron temperature (T_e) and electron density (n_e) of the plasma. A challenging aspect of the technique is to discriminate the small number of Thomson scattered photons against the large peak of background photons from the high-power laser used to probe the plasma. A variety of methods are used to mitigate the background photons in Proto-MPEX, including Brewster angled windows, viewing dumps, and light baffles. With these methods, first results were measured from argon plasmas in Proto-MPEX, indicating T_e ∼ 2 eV and n_e ∼ 1 × 10¹⁹ m^-3. The configuration of the Proto-MPEX TS diagnostic will be described and plans for improvement will be given.

A periodontal attachment mechanism without alveolar bone. Case report

A 22-year-old black male was referred for periodontal therapy because of radiographic evidence of advanced bone loss associated with the posterior teeth. Clinical examination revealed gingivitis, normal sulcus depths, and minimal loss of clinical attachment. Complete blood counts, serum chemistry, and neutrophil function were within normal limits. Histological, histochemical and ultrastructural analysis of an extracted tooth revealed no loss of attachment; large areas of the cementum were collagen-poor and, ultrastructurally, resembled afibrillar cementum. It is proposed that the periodontal attachment mechanism present in this case was associated with a localized failure in normal periodontal development.

Associations between crestal lamina dura and periodontal status

The purpose of the present study was to investigate associations between radiographic crestal lamina dura and the clinical periodontal status of the corresponding interdental area. The population consisted of 90 individuals (53 females and 37 males), ages 21 to 45 years (mean 31 years), who underwent a comprehensive periodontal examination. Buccal and lingual to the contact point at each interdental area four different clinical criteria were scored as being present or absent: (i) visual inflammation, (ii) bleeding after probing with 25 gm force, (iii) pocket depth greater than 3 mm after probing with 50 gm force, (iv) loss of connective tissue attachment. Bite-wing and full-mouth periapical radiographs were taken and processed using standardized techniques. Each interdental crestal area on the radiographs was examined and scored for presence or absence of an intact lamina dura. Statistical analyses were undertaken using correlated means to compare the presence or absence of lamina dura with the individual and simultaneous clinical criteria. No significant differences were obtained between any of the comparisons and, in addition, there was no correlation between lamina dura images on periapical and bite-wing radiographs. The results indicated that crestal lamina dura on radiographs did not appear to be related to the presence or absence of clinical inflammation, bleeding upon probing, periodontal pockets or loss of attachment.

Co-destructive factors of marginal periodontitis and repetitive mechanical injury

When repetitive mechanical injury was produced in combination with marginal periodontitis a significant loss of connective tissue attachment did not occur as compared with specimens in which periodontitis alone was produced. It seems unlikely, therefore, that there is a "co-destructive" factor effect on the loss of connective tissue attachment. The amount of alveolar bone lost as a result of marginal periodontitis was increased by the addition of repeated mesiodistal jiggling of the teeth. This could represent an irreversible "co-destructive" effect or could merely be a functional adaptation of the periodontium.