Photoelastic stress analysis at the metal-enamel junction of the anterior adhesive bridge on non-prepared teeth in eccentric jaw position

To study the stress involved at the metal-enamel junction of an adhesive bridge during the eccentric movement of the mandible, the author calculated the values of principal stress and maximum shearing stress, and determined the stress distribution at the adhesive surface which exists between retainer and enamel, for which an unprepared canine and a centaral incisor, using a three-dimensional photoelastic experiment. Based on the assumed eccentric movement of the mandible, three models with loading at different parts of the adhesive bridge were used for the experiment: Model 1 with loading only on the central incisor, Model 2 with loading on the pontic of the lateral incisor and Model 3 with loading only on the canine. The results were as follows. (1) Models 1 and 3 showed stress concentration directly under the loading point, where the compressive stress was 610 kgf/cm2 in Model 1 and 610 kgf/cm2 in Model 3. (2) Model 1 showed distribution of stress of 30-80 kgf/cm2 at the metal-enamel junction of the canine, while in Model 3 the stress of 80-150 kgf/cm2 was distributed at the metal-enamel junction of the central incisor. Loading only on the canine produced higher levels and broader distribution of stress than loading only on the central incisor. (3) Model 2 showed distribution of stress of about 60 kgf/cm2 at the metal-enamel junction of the central incisor and canine. Extremely intense stress, 250 kgf/cm2, was noted in the canine slice contiguous to the pontic. Stress as high as 70 kgf/cm2 was also observed in the central incisor slice contiguous to the pontic. (4) The maximum shearing stress values were 305 kgf/cm2 in Model 1 and 325 kgf/cm2 in Model 3 at the sites directly under the loading point, showing similarly high levels. (5) A comparative investigation of the maximum shearing stress appearing at the metal-enamel junction among the models showed that the distributed maximum shearing stress in Model 3 was about twice that in Model 1. (6) Model 2 had the maximum shearing stress, which was located toward the pontic in the canine, with an intensity closed to the shearing strength of currently available adhesive resin cement, suggesting a high risk of desquamation at this site.     

Oral mucosal lesions in patients with acute leukemia and related disorders during cytotoxic therapy

This study reports the presence of oral mucosal lesions in 26 patients with acute leukemia during the initial weeks of treatment (induction period). For comparison, three groups of patients without malignant disorders (acute disorders, long-term hospitalization, antibiotic treatment) were included. All patients were treated at the University Hospital of Ume?, Sweden. During the period of hospitalization hemorrhages were seen in 14 of the 26 patients with leukemia. No specific location was found. A correlation between presence of hemorrhages and low platelet counts was noted. Eighteen of the patients revealed ulcerations during the period. Ulcerations were predominantly found on the buccal mucosa, the lips, and the tongue. A tendency to an increase in the number and severity of ulcers was noted during the period of induction therapy. A correlation between presence of ulcers and low granulocyte counts was found. Candidiasis-like changes were seen in eight of the patients with leukemia. Compared with the patients with leukemia the patients in the reference groups showed a low prevalence of oral mucosal lesions.     

Characterization of mineral-binding 40-kDa glycoprotein extracted from young adult rabbit alveolar bone.

A forty-kilodalton (40-kDa) protein was extracted from alveolar bone of young adult rabbit with 0.5 M EDTA after extraction with 4 M GuHCl, and purified by gel-filtration, anion-exchange and hydroxyapatite columns using a high-pressure liquid chromatography system under denaturing conditions. The purified 40-kDa protein was not susceptible to bacterial collagenase and thrombin, but was cleaved by cyanogen bromide. The protein was stained blue with Stains-all. Among various lectins, concanavalin A and lentil lectin agglutinin bound to this protein, but peanut agglutinin, Ricinus communis agglutinin, phytohemagglutinin-E and wheatgerm lectin agglutinin did not. Lectin binding assays showed that the protein is a glycoprotein containing large amounts of mannose and/or glucose residues, but is not a fragment of proteoglycan. The amino acid composition of the protein shows a characteristically high content of acidic amino acids. Therefore, the mineral-binding 40-kDa glycoprotein is considered to be osteonectin/secreted protein acidic and rich in cysteine (SPARC), in terms of similarities to bovine and porcine osteonectins with regard to molecular weight and contents of glycoses and amino acids.     

常用根管充填材料生物相容性研究

通过细胞附着实验和扫描电镜技术对四种常用根管封闭剂以及三种牙胶尖的生物相容性研究发现：所有充填材料甚至一直被 认为细胞毒性最小的牙胶尖均有明显的细胞毒性。因此，在临床上，为了避免材料对根尖周细胞产生机械刺激和减少细胞毒性作用，应尽量避免根管充填材料超填。本文还就氯仿是否可用于根管治疗进行了讨论。     

Possible role of apoptotic cells of the oral epithelium in the pathogenesis of aphthous ulceration

Electron microscopic examination of the normal oral mucosa of patients with recurrent aphthous ulceration or Beh?et's syndrome revealed that the degenerate dark prickle cells are apoptotic cells. Such dark prickle cells showed characteristic findings of apoptosis, such as the shrinkage of nucleus and cytoplasm and the formation of contraction vacuoles. The number of intraepithelial mononuclear cells phagocytosing apoptotic cellular debris increased remarkably at the preulcerative stage of the aphthous lesions. The apoptotic debris also attracted neutrophilic leukocytes in the prickle cell layer at the preulcerative stage but not in the normal oral epithelium. It is speculated that the onset of aphthous ulceration is closely related to phagocytosis of these apoptotic cells by intraepithelial mononuclear cells.     

FT-Raman spectroscopy of calcium hydroxide medicament in root canals

AIM: To investigate chemical changes in calcium hydroxide introduced into human root canals as a medicament using Fourier transform-(FT) Raman spectroscopy. METHODOLOGY: Ten necrotic maxillary anterior teeth were selected in 10 patients. The teeth were divided into five treatment groups, according to the survey time. Root canal instrumentation was performed with hand instruments until the master apical file was size 40. Calcium hydroxide paste, in a 1 : 1.25 mixture by weight of powder and distilled water, was introduced directly into the root canal with a lentulo-spiral filler and then condensed with a finger plugger. The access cavity was sealed with a temporary dressing. After 2 and 4 days, then 2, 4 and 6 weeks, the calcium hydroxide paste was sampled with a K-file and then analysed using FT-Raman spectroscopy. The excitation source was an Nd : YAG laser with an excitation wavelength of 1064 nm. All spectra were taken with a laser power of 200 mW, 275-1185 scans, and 4 cm(-1) resolution. The conversion of calcium hydroxide to calcium carbonate was calculated on the basis of the spectral data obtained from the mixtures of both compounds. RESULTS: The calcium hydroxide paste in the apical region showed weak bands at 1088 and 284 cm(-1), in addition to bands associated with calcium hydroxide. The weak bands, assigned to calcium carbonate, became stronger with time. Calcium carbonate content increased rapidly in the first 2 days and then tended to increase slowly. Approximately 11% of the calcium hydroxide at the apical portion of the canal was converted to calcium carbonate after 6 weeks. However, little alteration of the paste was noticed in the samples from the middle portion of the canal. CONCLUSIONS: Calcium hydroxide medicament in root canals became transformed into calcium carbonate in the apical region within 2 days. Although the transformation continued with time, approximately 90% of the calcium hydroxide remained unchanged after 6 weeks.