The conventional treatment for mucocele is excision with a scalpel. Recently, however, CO2 laser has been used for excising mucocele because it has many advantages: the surgical technique is simple, the total treatment time is shorter, the wound is left open without sutures, intraoperative and postoperative bleeding are decreased, and there are almost no critical complications. In addition, the rate of recurrence is thought to be low. This paper describes 40 patients at various sites. The results suggested that CO2 laser is very effective for the treatment of oral mucocele.
The production of new dentures imposes financial and physical burdens on elderly patients; it is preferable for them to keep wearing their old dentures after remodeling and repair. In such denture cases, metal part welding technology may be a problem. Laser welding is frequently applied to the junction of dental cobalt-chromium alloy, considering the shortness of the welding time and narrowness of the heat-affected zone (HAZ). However, welding defects, such as cracks and porosities, occasionally develop in the welding area. Therefore, this study investigated the influence of the casting of dental cobalt-chromium alloy on the occurrence of cracks. Cobalt-chromium alloy ingots for casting (Cobaltan) and castings were used in this study. Using a phosphate bonded investment material (Snow white), castings were produced using a casting machine (Argon caster AE). A dental Nd:YAG laser welding apparatus (Alpha Laser ALP50) was used for welding. The irradiation energy was set to 10.6 or 30.2 J/pulse, and spot welding areas were formed in an argon gas atmosphere. Thereafter, to evaluate the occurrence and causes of cracks, metal tissues of the base material and welded areas were observed using an optical microscope. The fracture surface was observed using a scanning electron microscope (SEM). Element concentration analysis was performed using an energy dispersive X-ray spectrometer (EDX). The metal tissue of the welded area was finer than that of the base material. When the irradiation energy was 10.6 J/pulse, cracks were found in 5 of 15 spots on the ingots, and in 14 of 14 spots on the castings. When the irradiation energy was 30.2 J/pulse, cracks were observed in 1 of 14 spots on the ingots, and in 16 of 18 spots on the castings. Cracks in the welds were more frequently observed in the castings than in the ingots. Observation of the metal tissue and fracture surface showed that those cracks were solidification cracks. It was concluded that casting was the main cause of the solidification cracks. Furthermore, phosphorus may be a cause of the solidification cracks.
Dentures are comprised of resin and metal materials. These materials are joined using chemicals or mechanically by making under-cuts, but spaces remaining between the materials cause denture fracture and oral bacterial infection. To solve this problem, we performed a basic study to evaluate the applicability of laser-assisted metal and plastic (LAMP) joining for the direct joining of cobalt-chromium alloy for casting (COBALTAN, Shofu Inc., Kyoto, Japan) and acrylic resin for a thermoplastic base (ACRYJET, High-Dental Japan, Osaka, Japan). LAMP joining is a technique that facilitates the laser joining of resin and metal and was developed by the Laser Welding and Materials Processing, Welding Research Institute, Osaka University. LAMP joining achieves a very strong joint between acrylic resin and cobalt-chromium alloy. As a result, most samples of thermoplastic acrylic resin for denture suffer plastic deformation in tensile shear tests, and some samples broke at a position away from the joint interface on thermoplastic acrylic resin for dentures, prior to fracture at the joint interface. Although it was not possible to measure the bonding strength to line profile, in this experiment, the joints possessed very strong tensile shear strengths of not less than 4.9 MPa. Sufficient bonding strength was obtained between the thermoplastic acrylic resin for dentures and the cobalt-chromium alloy for casting by LAMP joining. When the bonded interface was observed under SEM, fine air bubbles characteristic of LAMP joining were observed, and no micro-level space was present in the bonded interface. It is suggested that cobalt-chromium alloy for casting and acrylic resin for a thermoplastic base can be joined with no space in the bond interface by using LAMP joining without special surface processing.
Optical coherence tomography (OCT) is a new biomedical imaging modality which can generate high-resolution, cross-sectional images of microstructures in biological systems. One of the most attractive features of OCT is that it uses safe near-infrared light instead of hazardous ionizing radiation. Furthermore, resolution on the order of 10 micrometers can be obtained. The optical accessibility of clinically relevant structures in the oral cavity makes it a particularly attractive location for the application of OCT imaging techniques. Our National Center for Geriatrics and Gerontology has developed a new swept-source optical coherence tomography (SS-OCT) system through joint research with industry and the public sector. In this study, this new SS-OCT system was applied to cross-sectional imaging of dental caries, resin based composite restorations, periodontal disease, oral cancer and finished dentures. It is concluded that our new SS-OCT system is a promising new and useful alternative imaging technique which can safely provide much more definitive information on oral structures at far higher resolution than is possible by conventional clinical imaging methods. The National Center for Geriatrics and Gerontology received the world's first production unit of this new dental SS-OCT system.
The application of optical equipment during examinations enables general dental practitioners to conduct simple and low-invasive screening for oral mucosal diseases. Use of these devices has recently become widespread in North America and South East Asia, with the most common device being the VELscope system. The present study investigated the feasibility of using the VELscope in fluorescent screening for oral mucosal diseases and to determine the extent of resection for oral cancer. VELscope application has been indicated and approved for aiding in the early detection of oral mucosal diseases and determining the extent of resection for oral cancer; approximately 2,000 units were distributed in North America during 2008. The American Academy of Oral Medicine and other scientific societies and bodies hold training sessions for general dental practitioners on how to use the VELscope for early-stage diagnosis of oral cancer. The general principle of screening based on oral mucosa observation using fluorescence involves exposing the tissue to shorter-wavelength blue light and observing the reflected longer-wavelength green light to determine whether the mucosa is normal or has atypical epithelium. Healthy tissue emits green fluorescence while atypical epithelium loses this characteristic. With the VELscope, mucosa is exposed to blue light from a metal-halide lamp (wavelength, 400-460 nm; output, 500 mW) and a real image derived from the reflected light, including that emitted from within the tissue, can be visually observed via a half mirror or a filter that blocks wavelengths exceeding that of the irradiating light. In cases of atypical epithelium and malignant tumor, the observation of decreased fluorescence from the lesion site and the surrounding tissue affected by epithelial dysplasia indicated the effectiveness of the VELscope in screening for lesions. However, care is required when analyzing screening results as decreases in fluorescence cannot be observed in cases of deep-seated tumors. By appropriately adjusting the device settings, the present system can also be used to determine the extent of tumor resection.