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H C Clark

Publications and source records attributed to H C Clark.

6 recordsLinked to original sources
PubMed2004

A prospective comparison between findings from a clinical examination and results of bitewing and panoramic radiographs for dental caries diagnosis in children.

AIM: To compare the findings of a clinical examination with those from bitewing (BW), panoramic (Pan) and panoramic plus bitewing (PanBW) radiographs for dental caries in children. METHOD: A population of 39 children, aged 3.8 to 11.9 years, who required radiographs as part of their initial assessment for care in the Department of Paediatric Dentistry (Leeds), was selected. Each subject was examined clinically for dental caries. Subsequently, a paediatric dentist and a specialist in dental radiography read the radiographs. ANALYSIS: A database in Microsoft Access was used to compare the examiners readings for each radiographic view; agreements were taken to be a consensus. Disagreements were re-viewed by both examiners to arrive at a consensus. Radiographic results were compared with those of the clinical examination. RESULTS: The clinical examination identified 6.0% (95% CI 4.1 to 7.8, p<0.001) more carious surfaces than Pan. Clinical examinations also identified more carious surfaces than BW 1.2% (95% CI -0.7 to 3.2, p<0.247) and PanBW 0.6% (95% CI -1.1 to 2.3, p<0.533) but these differences were not statistically significant. When occlusal surfaces only were compared, the clinical examination identified significantly more carious occlusal surfaces then BW (15.2%, p<0.001), Pan (17.1%, p<0.001) and PanBW (13.5%, p<0.001). Comparing the approximal surfaces only, the BW and PanBW identified significantly more carious surfaces than the clinical examination, 5.1% (p<0.001) and 4.3% (p<0.001) respectively. CONCLUSION: The use of a clinical examination with PanBW provided the maximum information on dental caries in the primary and mixed dentitions, particularly for approximal surfaces. This is important in planning comprehensive dental care for children.

Chi-Square Distribution↗
PubMed1983

Chemical mechanism of the Gram stain and synthesis of a new electron-opaque marker for electron microscopy which replaces the iodine mordant of the stain.

Crystal violet (hexamethyl-para-rosaniline chloride) interacts with aqueous KI-I2 during the Gram stain via a simple metathetical anion exchange to produce a chemical precipitate. There is an apparent 1:1 stoichiometry between anion (I-) and cation (hexamethyl-para-rosaniline+) during the reaction and, since the small chloride anion is replaced by the bulkier iodide, the complex formed becomes insoluble in water. It is this same precipitate which forms in the cellular substance of bacteria (both gram-positive and gram-negative types) and which initiates the Gram reaction. Potassium trichloro(eta 2-ethylene)-platinum(II), as an electronopaque marker for electron microscopy, was chemically synthesized, and it produced an anion in aqueous solution which was compatible with crystal violet for the Gram stain. It interacted with crystal violet in a similar manner as iodide to produce an insoluble complex which was chemically and physically analogous to the dye-iodide precipitate. This platinum anion therefore allows the Gram staining mechanism to be followed by electron microscopy.

Bacillus subtilis↗
PubMedDate not supplied

The mechanism of transcatheter electrocoagulation (TCEC).

This study was performed to evaluate the temperature, pH change, and electrolysis products at the anode during transcatheter electrocoagulation (TCEC). Stainless steel and platinum anodes insulated by standard angiographic catheters were placed in renal dialysis tubing. The tubing, filled with either saline solution or plasma, was placed in a water bath (25 degrees C) containing a cathode. Temperature was recorded at the tip of the anode, placed in saline solution, using 15 ma for 20 minutes (n = 5 for each wire and current). pH was measured during applications of 15, 30, and 60 ma for 20 minutes (n = 6 for each current, anode, and solution). The solutions were analyzed for products of electrolysis. The temperature remained constant. The pH declined to 1.5 +/- .3 (mean +/- SEM) with the platinum electrode and to 2.5 +/- .5 with the stainless steel anode. Metallic elements and oxygen were the electrolysis products recovered from the stainless steel experiments. Chlorine gas was the major product recovered from the platinum studies. These results confirm that during TCEC there is no thermal injury. The pH change at the anode is probably a major mechanism in TCEC. Different types of reactions take place at platinum and stainless steel anodes, which may account for differences between TCEC with these two electrodes.

Catheterization↗