Torsional testing of Canal Master U hand instruments.

Ten each of size 25, 30, 35, 40, and 45 Canal Master U hand instruments were tested for torsional failure and revolutions to failure. In addition, the point at which separation occurred was measured on the instrument shaft. An Instron 1125 machine was used for all torsion testing. The mean torque failure value for size 25 and 35 Canal Master U instruments exceeded the ADA specification No. 28 minimum values while sizes 30, 40, and 45 were below the ADA minimum average values. All Canal Master U averages for revolutions to failure exceeded the ADA minimums. Although size 25 was above the minimum average, due to a wide range of values, 5 of the 10 were below the ADA specification No. 28 values. The point of instrument separation was 0.325 to 1.575 mm behind the cutting head. Due to the structural design differences of endodontic files versus Canal Master U, it is suggested that an additional category of ADA specification be introduced for Canal Master endodontic instruments.     

The carcinostatic effects of 1-(2-tetrahydrofuryl)-5-fluorouracil and uracil (UFT) on tongue carcinoma induced by 4-nitroquinoline 1-oxide (4NQO) in rats.

UFT is a carcinostatic agent used in adjuvant chemotherapy for head and neck cancer. In the present study. UFT was given orally to treat tongue carcinoma in rats induced by 4-nitroquinoline 1-oxide. The antitumor effects of UFT were studied macroscopically and histologically. In addition, the antitumor effects of UFT were evaluated in relationship to lesions of the clinical and, invasive types, and to there vascular structure. In clinical lesions, the antitumor effect of UFT was higher in extrovert tumor-mass lesions and lower in ulcerous lesions. With regard to vascular structure, the effect was higher in cases demonstrating irregular net-like patterns and branch-like patterns and lower in cases in which the pattern had been destroyed. There was a correlation between antitumor effect and invasive type. As invasive tendency the 3H-thymidine labeling index, and mitotic index increased, antitumor effect and degree of tumor cell degeneration decreased.     

Effect of orthodontic forces on blood flow in human gingiva.

The relationship of gingival blood flow to the magnitude and duration of applied force was studied in humans using Laser Doppler flowmetry. The sample consisted of five adult volunteers with interdental space between their maxillary central incisors. The labial surface of each central incisor was bonded with a buccal tube and a spring force was applied to close the space. The forces applied were 50 g, 80 g, 120 g, and 250 g. Each force was applied for 30 seconds, 60 seconds, 90 seconds, 5 minutes, and 10 minutes. The blood flow signals were recorded continuously using a pen recorder. Measurements indicated that blood flow was negatively correlated to the amount of force applied. The duration of reactive hyperemia was positively correlated to the duration of force. Laser Doppler flowmetry measures blood flow in superficial periodontal tissues. Yet, the relationship of blood flow changes to the magnitude and duration of orthodontic force suggests that measurements of gingival blood flow may provide a means of estimating physiologic orthodontic forces.     

Ultrastructural differentiation in the distal ends of ameloblasts from the presecretory zone to the early secretory zone

Morphological differentiation of the distal ends of ameloblasts (AMs) from the late presecretory to early secretory zones of the rat upper incisor was studied by electron microscopy. Preameloblasts (PAs) showed a high columnar shape, with the nucleus located in the basal portion. The Golgi apparatus occupied the supranuclear region with type-1 vesicles, and microvilli were present at the distal cell membrane. Coarse-textured material was observed inside the type-1 vesicles and in the lateral intercellular spaces as well as along the distal cell membrane, whereas fine-textured material was found along the distal cell membrane. Near the region of initial enamel formation, large matrix islands were found in the lateral intercellular space. A thin electron-dense layer was observed on the dentin surface. This layer might have occurred as a result of diffusion after degradation of the coarse- or fine-textured material into a finer substance in the extracellular spaces. In the region of initial enamel formation, the distal cell membrane of AMs was flat, but shallow and narrow membrane invaginations were associated with the cell membrane close to the matrix islands. In the region of inner enamel formation, a cone-shaped Tomes' process was formed between large matrix islands which had developed in the intercellular spaces between the lateral portions of the distal ends of AMs. It was considered that the membrane invaginations which had existed at the distal end of PAs moved lower toward the distal terminal bar, thereafter becoming microvilli.     

Accuracy of complete dental arch impressions and stone casts using a three-dimensional measurement system. Effects on accuracy of rubber impression materials and trays

The purpose of this study was to investigate and compare the accuracy of complete dental arch impressions and stone casts made with two kinds of impression materials (addition-type silicone and polysulfide rubber) and trays (custom tray and modified custom tray). In addition, the effect of the quantity of stone was examined. Impressions were made from a metallic model of a simplified maxillary dentition. Impressions and stone casts were measured respectively with a three-dimensional measuring microscope. The results were as follows: 1. Distortions of impressions were so small that the reproducibilities of impressions were superior three-dimensionally. These kinds of impressions and trays did not influence the accuracy of impressions. 2. The setting expansion of the stone in the impression occurred in the outward direction and was affected by the kinds of impressions and trays. 3. The arch widths and lengths of the stone casts tended to increase in number. 4. Stone casts made with addition-type silicone impression material and a custom tray were the most accurate because the combination of the impression material and tray effectively suppressed the setting expansion of stone. 5. The accuracy of stone casts could be improved by controlling the quantity of stone.     

An in vitro study of the effect endodontic access preparation and amalgam restoration have upon incisor crown retention

Endodontic access preparation leads to a significant reduction in crown retention. This study sought to determine whether this retention can be regained after access. Eighteen extracted human maxillary incisors had PFM crowns fabricated. Crowns were cemented, retention measured, recemented, access preparations cut, and retention once again measured. Then, crowns were recemented and accesses restored with dental amalgam and new retention measured. This format allowed each crown to be used as a control of itself. For crowns cemented with zinc phosphate cement and restored with amalgam, a 126% increase over original retention was measured. For crowns cemented with polycarboxylate cement and restored with amalgam, a 237% increase over original retention was measured. For crowns cemented with polycarboxylate cement and restored with amalgam, a 237% increase over original retention was measured. These results suggest that recementing crowns secondary to endodontic access and restoring the access with amalgam regains and even surpasses the original retention.     

Intranodal injection of anticancer drugs into fixed cervical metastatic lymph nodes

OBJECTIVE: In patients with head and neck carcinoma, fixed enlarged metastatic lymph nodes (LNs) are sometimes inoperable and carry an increased risk of mortality. To control metastatic LNs, we attempted intranodal injection of anticancer agents.
SUBJECTS AND METHODS: Fifteen patients with squamous cell carcinoma arising in the gingiva (8), tongue (3), floor of the mouth (1), or maxillary sinus (3) were enrolled. These patients consisted of two groups, those in the early era in which the fixed LNs of six patients were treated with ⁶⁰Co (RA group) and those in the late era in which both radiation and intranodal injection of anticancer agents were administered to nine patients (IN group). Intranodal injection consisted of peplomycin, 5-fiuorouracil, and cis-diamminedichloroplatinum.
RESULTS: In the IN group, LNs regressed from about 40% to nearly 100%, although two patients showed no appreciable response. The LNs treated by combination therapy regressed considerably while LNs in the same patients treated with ⁶⁰Co alone showed a minor response or grew gradually. In three patients, the LNs regressed sufficiently to be extirpated safely. The good clinical response in the locally injected LNs was histologically associated with distinct evidence of tumor cell degeneration. In the RA group, none of the LNs responded to radiation with ⁶⁰Co; one LN exhibited slight regression, but the others enlarged during and soon after the radiation. Compatible with the clinical effects, many patients in the IN group demonstrated a good prognosis; three are alive without disease, and four survived for prolonged periodS. However, all patients in the RA group died due to progression of the positive LNs or pulmonary complication within 10 months.
CONCLUSION: These results indicate that intranodal injection of anticancer drugs is useful for the management of fixed enlarged LNs.     

Leaching of hydrogen peroxide from bleached bovine enamel.

Accurately weighed bovine enamel slabs were individually immersed in 2 ml of 35% hydrogen peroxide for 1, 3, 5, 30, or 60 min. A control group was obtained by individual immersion of bovine enamel slabs in 2 ml of saline for 60 min. All samples were washed, dried, acid-etched with 37% phosphoric acid for 60 s, then washed and dried again. Two milliliters of double-distilled water were used for individual sample leaching. Leaching was done for 1, 5, 10, 20 min, or 7 days for the experimental groups and for 7 days for the control group. The samples of one of the experimental groups were leached for a second time for 1 min. A total of 112 samples was used in this study. Hydrogen peroxide was spectrophotometrically identified and quantified in all leaching solutions based on the oxidation reaction of leuco-crystal violet buffer solution by hydrogen peroxide, a reaction catalyzed by horseradish peroxidase. The results revealed a significant difference in the quantity of leached peroxide between bleached samples (irrespective of the duration of leaching) and control, saline-treated ones. No difference was observed in the quantity of leached peroxide between releached samples and control, saline-treated ones. However, these were small, random, and numerically insignificant. Statistically significant differences were also noted among some of the experimental groups. They were thought to hold no clinical significance. The results suggested that upon immersion, the complete leaching of peroxide from bleached enamel occurs rapidly.     

A survey of disease changes observed on dental panoramic tomographs taken of patients attending a periodontology clinic.

Dental panoramic tomographs (DPTs) were taken consecutively of 500 patients referred to a specialist periodontal department by general dental practitioners in order to assist in the diagnosis of the severity of the periodontal disease. Analysis of these DPTs showed 316 (63.2%) of these patients to have some form of dental abnormality unrelated to periodontal disease. The DPT was shown to be a valuable screening technique for clinical practice.