Radiation Chemical Yields of 7-Hydroxy-Coumarin-3-Carboxylic Acid for Proton- and Carbon-Ion Beams at Ultra-High Dose Rates: Potential Roles in FLASH Effects.

It has been observed that healthy tissues are spared at ultra-high dose rate (UHDR: >40 Gy/s), so called FLASH effect. To elucidate the mechanism of FLASH effect, we evaluate changes in radiation chemical yield (G value) of 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), which is formed by the reaction of hydroxyl radicals with coumarin-3-carboxylic acid (C3CA), under carbon ions (140 MeV/u) and protons (27.5 and 55 MeV) in a wide-dose-rate range up to 100 Gy/s. The relative G value, which is the G value at each dose rate normalized by that at the conventional dose (CONV: 0.1 Gy/s >), 140 MeV/u carbon-ion beam is almost equivalent to 27.5 and 55 MeV proton beams. This finding implies that UHDR irradiations using carbon-ion beams have a potential to spare healthy tissues. Furthermore, we evaluate the G value of 7OH-C3CA under the de-oxygenated condition to investigate roles of oxygen to the generation of 7OH-C3CA effect. The G value of 7OH-C3CA under the de-oxygenated condition is lower than that under the oxygenated condition. The G value of 7OH-C3CA under the de-oxygenated condition is higher than those under UHDR irradiations. By direct measurements of the oxygen concentration during 55 MeV proton irradiations, the oxygen concentration drops by 0.1%/Gy, which is independent of the dose rate. When the oxygen concentration directly affects to yields of 7OH-C3CA, the rate of decrease in the oxygen concentration may be correlated with that of decrease in the G value of 7OH-C3CA. However, the reduction rate of G value under UHDR is significantly higher than the oxygen consumption. This finding implied that the influence of the reaction between water radiolysis species formed by neighborhood tracks could be strongly related to the mechanisms of UHDR effect.

DNA strand break induction of aqueous plasmid DNA exposed to 30 MeV protons at ultra-high dose rate.

Radiation cancer therapy with ultra-high dose rate exposure, so called FLASH radiotherapy, appears to reduce normal tissue damage without compromising tumor response. The aim of this study was to clarify whether FLASH exposure of proton beam would be effective in reducing the DNA strand break induction. We applied a simple model system, pBR322 plasmid DNA in aqueous 1 × TE solution, where DNA single strand breaks (SSBs) and double strand breaks (DSBs) can be precisely quantified by gel electrophoresis. Plasmid DNA were exposed to 27.5 MeV protons in the conventional dose rate of 0.05 Gy/s (CONV) and ultra-high dose rate of 40 Gy/s (FLASH). With both dose rate, the kinetics of the SSB and DSB induction were proportional to absorbed dose. The SSB induction of FLASH was significantly less than CONV, which were 8.79 ± 0.14 (10-3 SSB per Gy per molecule) and 10.8 ± 0.68 (10-3 SSB per Gy per molecule), respectively. The DSB induction of FLASH was also slightly less than CONV, but difference was not significant. Altogether, 27.5 MeV proton beam at 40 Gy/s reduced SSB and not DSB, thus its effect may not be significant in reducing lethal DNA damage that become apparent in acute radiation effect.

Significant changes in yields of 7-hydroxy-coumarin-3-carboxylic acid produced under FLASH radiotherapy conditions.

FLASH radiotherapy appears to kill off tumor cells while sparing healthy tissues, by irradiation at ultra high dose rate (>40 Gy s-1). The present study aims to clarify the mechanism of the sparing effect by proton irradiation under the FLASH conditions from a viewpoint of radiation chemistry. To do so, we evaluate radiation chemical yields (G values) of 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), which is produced by water radiolysis using coumarin-3-carboxylic acid (C3CA) solution as a radical scavenger of hydroxyl radicals. We shoot 27.5 MeV protons in the dose rate ranging from 0.05 to 160 Gy s-1. The recombination process of hydroxyl radicals produced is followed by varying the concentration of C3CA from 0.2 to 20 mM, which corresponds to the scavenging time scale from 7.1 to 714 ns. The G value of 7OH-C3CA produced decreases with increasing dose rate on the same scavenging time scale. Additionally, the trend of the relative G value normalized at a scavenging time scale of 100 ns, where radical-radical reaction subsides, is consistent in the examined dose rate range. This finding implies that G values of 7OH-C3CA produced reduce with increasing dose rate due to the oxygen depletion. We experimentally present that the sparing effect for healthy tissues would be seen even with a proton beam under the FLASH conditions due to the depletion of oxygen.

A simple algorithm for beam profile diagnostics using a thermographic camera.

A new algorithm for digital image processing apparatuses is developed to evaluate profiles of high-intensity DC beams from temperature images of irradiated thin foils. Numerical analyses are performed to examine the reliability of the algorithm. To simulate the temperature images acquired by a thermographic camera, temperature distributions are numerically calculated for 20 MeV proton beams with different parameters. Noise in the temperature images which is added by the camera sensor is also simulated to account for its effect. Using the algorithm, beam profiles are evaluated from the simulated temperature images and compared with exact solutions. We find that niobium is an appropriate material for the thin foil used in the diagnostic system. We also confirm that the algorithm is adaptable over a wide beam current range of 0.11-214 µA, even when employing a general-purpose thermographic camera with rather high noise (ΔT(NETD) ≃ 0.3 K; NETD: noise equivalent temperature difference).

(11)CH4 molecule production using a NaBH4 target for (11)C ion acceleration.

Solid-state materials suitable for use as proton irradiation targets were investigated for producing high-purity (11)CH4 molecules for heavy-ion cancer therapy. The radioactivity of gas produced by proton irradiation was measured for several target materials. Also, the radioactive molecular species of the produced gas were analyzed by radio gas chromatography. We found that 5 × 10(12) (11)C molecules could be collected by proton irradiation on a NaBH4 target. We also found that the (11)CH4 molecules were produced and collected directly from the irradiated target, owing to the hydrogen atoms bound in the solid-state NaBH4.

Impact of facial form on the relationship between conventional or implant-assisted mandibular dentures and masticatory function.

STATEMENT OF PROBLEM: It is not clear if the interaction of craniofacial form with type of prosthetic restoration (conventional or implant-assisted) is related to masticatory function in complete denture patients. PURPOSE: The purpose of this study was to investigate the relationships among facial form, skeletal class, alveolar residual ridge heights and masticatory function in subjects treated with implant-assisted or conventional mandibular dentures with lateral cephalometric evaluation. MATERIAL AND METHODS: Data from a previously reported randomized controlled clinical trial were accessed to compare treatment success rates, functional and perceptual outcomes, dietary intake, and craniofacial relationships between mandibular complete dentures and implant overdentures in edentulous diabetic subjects. Evaluation of the digitized post-insertion lateral cephalometric radiographs provided measures of facial form (mesocephalic "medium", brachycephalic "broad and square", dolichocephalic "vertical and long"), skeletal class (Class I, Class II, Class III), and alveolar ridge height (mm), which were compared to results of standardized masticatory tests as evaluated using MANOVA and REGW post-hoc evaluation (α=.05). RESULTS: Masticatory performance on the preferred side was slightly reduced in the dolichocephalic group, compared to brachycephalic and mesocephalic groups (P=.085). Swallowing threshold performance was significantly less in skeletal Class II subjects compared to Class I (P=.034). Maxillary residual alveolar ridge height was significantly less in the brachycephalic group compared to the dolichocephalic group (P<.001). No differences in mandibular ridge height were seen associated with facial form or skeletal class groups. CONCLUSIONS: Facial form may be related to masticatory function with conventional and implant-assisted mandibular dentures, but larger controlled studies are needed to confirm this relationship. Alveolar ridge height is reduced in edentulous subjects with a brachycephalic facial form.

Bone quality of mandibles reconstructed with particulate cellular bone and marrow, and platelet-rich plasma.

The purpose of this study was to evaluate the bone quality of mandibles reconstructed with particulate cellular bone and marrow (PCBM) and platelet-rich plasma (PRP). We compared the bone mineral density (BMD) and microstructure of PCBM and PRP-reconstructed bone and normal bone in patients. Bone biopsies were taken of 11 samples of PCBM and PRP reconstructed bone and 16 samples of normal bone using a trephine bur. BMD and microstructures were assessed using microcomputed tomography. The compact bone resulting from the PCBM and PRP reconstruction was extremely thin. Analysis of the microstructures, showed statistically significant differences only in trabecular bone number and trabecular bone spaces between PCBM and PRP-reconstructed bones and normal bones. In the case of BMD, no statistical differences were found between the two groups. Lamellar structures and osteocytes were observed histologically in the trabecular bone in both groups. In conclusion, the BMD and microstructures of the cancellous bone in the PCBM and PRP-reconstructed mandibles resembled those in the normal mandibles.

Polishing of dental porcelain by polycrystalline diamond.

Polycrystalline diamond (PCD) exhibits excellent abrasive characteristics and is commonly used as loose grains for precision machining of hard ceramics and other materials that are difficult to grind and polish. In the present study, we investigated using bonded PCD for polishing dental porcelain, for which a lustrous surface is difficult to obtain by polishing. We compared the surface texture and characteristics of dental porcelain after polishing with bonded PCD with that obtained using bonded monocrystalline diamond (MCD), which is commonly used for this purpose. Polishing was performed at various pressures and rotational speeds on a custom-built polishing apparatus using bonded PCD or MCD with grain sizes of 3.92 µm on specimens consisting of VITA Omega 900 dentin porcelain after firing and then glazing to a specified surface roughness. The surface roughness of the polished porcelain and the abrasion quantity in terms of its polishing depth were measured, and its surface texture and characteristics were investigated. At low polishing pressures, PCD yielded a finer polished surface than MCD. The polishing depth after polishing for 20-30 min was approximately 2-3 µm with PCD and 1-2 µm with MCD. The polished surface was more uniform and smooth with PCD than with MCD.

The effect of surface roughness on the Weibull distribution of porcelain strength.

The purpose of the present study was to test the hypothesis that glazing will affect the Weibull modulus or the mean flexural strength of dental porcelain. Four groups (n = 30) of specimens were prepared from feldspathic body porcelain (Vita VMK 68). The specimens were tested in groups: original glazed condition (control), and after grinding separately with 1,000-grit, 600-grit, and 100-grit silicon carbide abrasive. A three-point flexure test was undertaken for each specimen. The flexural strength of porcelain and the Weibull modulus were then obtained using a computer program and load-to-failure data. Flexural strength decreased as surface roughness increased, and the differences were significant (p < 0.05), as determined by Tukey's multiple range test, except between the 600-grit group and the 100-grit group. The Weibull modulus of the glazed group was the largest (16.3), and the surface roughness was found to influence the Weibull modulus.

Bonding strength of autopolymerizing resin to nylon denture base polymer.

This study aimed to investigate the shear bond strength of an autopolymerizing resin to a nylon denture base polymer (Lucitone FRS: LT) subjected to different surface treatments, and the results thereof compared with a heat-polymerizing resin and a polycarbonate polymer. Specimens were divided into five groups according to the surface treatment method: polishing (#600), sandblasting, adhesive primer application (resin primer), sandblasting + adhesive primer application, and tribochemical coating (Rocatec system). Following which, specimens were subjected to a shear bond strength test and Si concentrations were measured using an electron probe microanalyzer (EPMA). On shear bond strength, that of LT with tribochemical coating was significantly higher than the other groups. On EPMA results, the surface of LT with tribochemical coating was found to be covered with a silica film. Therefore, findings in this study indicated that silica-coating by Rocatec system was effective in improving the bond strength of nylon denture base polymer to autopolymerizing repair resin.

Effects of thermal cycling and surface roughness on the Weibull distribution of porcelain strength.

The objective of this study was to test the hypothesis that thermal cycling weakens the flexural strength of porcelain. Specimens of Deguceram Gold and Vita Omega 900 were tested in four groups of 30 specimens each: in the original glazed condition versus being ground with 1000-grit, 600-grit, and 100-grit silicon carbide abrasives. Corresponding to these four types of surface treatments, four groups of 30 specimens per group received 5,000 times of thermal cycling. Flexural strength was measured using a four-point flexural test, and Weibull modulus was calculated. Within each type of surface treatment, the thermal cycling treatment did not result in any decrease in flexural strength although it caused the Weibull modulus to become smaller - except for the control and thermal-cycled groups of 600-grit surface treatment.

Usefulness of noninjectable anesthetic gel for intraperiodontal gingival retraction.

This study aimed to determine the efficacy of local anesthesia using Oraqix for gingival retraction in 35 healthy adult patients. The median visual analogue scale value was 20.5 +/- 24.2 (range: 0 to 81) for pain encountered during the procedure. In most patients, a lower verbal rating scale value corresponded with a lower visual analogue scale value. More than 80% of the operators evaluated the procedure as simple to perform, and more than 65% considered it useful compared with conventional injectable anesthesia. The results suggest that Oraqix is an attractive alternative to injectable anesthesia generally performed for gingival retraction at dental clinics.

Influence of simplified silica coating method on the bonding strength of resin cement to dental alloy.

This study evaluated the effectiveness of a simplified silica coating method (CoJet System) on the bonding strength of resin cements to dental alloy. Bonding strength of the specimens treated with metal primer after alumina sandblasting was compared with those treated with silica coating and silane coupling agent after alumina sandblasting. Furthermore, the influence of silane coupling agent on bonding strength was compared between one-liquid and two-liquid silane coupling agents. Measurement of shear bond strength before and after thermal cycling revealed that the group treated with silica coating in one step without alumina sandblasting yielded high bonding strength. As for the influence of silane coupling agent, treatment with two-liquid silane coupling agent achieved higher mean shear bond strength than with one-liquid silane coupling agent. Findings in this study indicated that silicatization by means of this simplified silica coating method was effective in improving the bonding strength to dental alloy.

A study of the effects of irradiation on the polymerization of dual-cured self-etching bonding system using electron spin resonance (ESR) spectroscopy.

The purpose of this study was to investigate the effect of irradiation on the polymerization behavior of a bonding agent of a dual-cured self-etching bonding system. By means of electron spin resonance spectroscopy, it was shown that the concentration of polymer radicals in samples cured chemically without irradiation was closely similar to that in samples dual-cured under irradiation. There was no significant difference in the time required to reach the maximum spin concentration between these two sample groups, thereby showing that the radical generation rates were similar. Findings of this study revealed that the dual-cured self-etching bonding system tested in this study was effective in polymerization in regions where irradiated light could hardly reach.

Photoelastic analysis of the effect of palatal support on various implant-supported overdenture designs.

STATEMENT OF PROBLEM: The effect of palatal support on various types of implant-supported maxillary overdenture designs has not been sufficiently assessed. PURPOSE: The purpose of this study was to photoelastically evaluate the palatal support of 3 designs of maxillary implant-supported overdentures. MATERIAL AND METHODS: A photoelastic model of an edentulous maxilla was fabricated with four 3.75 x 13-mm 3i implants. Three maxillary overdenture designs were fabricated: a splinted Hader bar incorporating 2 distal ERA attachments with anterior clips; non-splinted Zaag 4-mm direct abutments and attachments; and nonsplinted Locator 2-mm direct abutments and attachments. All restorative components and attachments were fitted and observed for passivity of fit and alignment. The overdentures were first tested with complete palatal coverage. Unilateral 25-lb loads were applied at the left and right first molars and the incisive papilla area. The photoelastic effects were monitored and recorded photographically. The palatal area was removed from the 3 overdentures and the loading regimens were repeated. RESULTS: The highest stresses under central loading were seen with the splinted Hader bar and complete palatal coverage, followed by similar levels of stress with either Zaag or Locator attachments. After removal of the palate, the center load demonstrated greater differences between designs. The highest stresses were observed with the Hader bar, followed by the Zaag and then Locator attachments. Lack of palatal coverage demonstrated higher levels of stress around implants and visible supporting tissues. The unilateral load produced the highest stress for the splinted Hader bar, followed by Locator, and then Zaag. CONCLUSIONS: Removal of the palatal support produced a greater effect and more concentrated stress difference for maxillary overdentures than differences between the attachment designs tested.