Evaluation of irradiation effects of near-infrared free-electron-laser of silver alloy for dental application.

In the application of lasers in dentistry, there is a delicate balance between the benefits gained from laser treatment and the heat-related damage arising from laser irradiation. Hence, it is necessary to understand the different processes associated with the irradiation of lasers on dental materials. To obtain insight for the development of a safe and general-purpose laser for dentistry, the present study examines the physical effects associated with the irradiation of a near-infrared free-electron laser (FEL) on the surface of a commonly used silver dental alloy. The irradiation experiments using a 2900-nm FEL confirmed the formation of a pit in the dental alloy. The pit was formed with one macro-pulse of FEL irradiation, therefore, suggesting the possibility of efficient material processing with an FEL. Additionally, there was only a slight increase in the silver alloy temperature (less than 0.9 °C) despite the long duration of FEL irradiation, thus inferring that fixed prostheses in the oral cavity can be processed by FEL without thermal damage to the surrounding tissue. These results indicate that dental hard tissues and dental materials in the oral cavity can be safely and efficiently processed by the irradiation of a laser, which has the high repetition rate of a femtosecond laser pulse with a wavelength around 2900 nm.

Coordinated features in jaw and neck muscle activities induced by chewing of soft and hard gum in healthy subjects.

BACKGROUNDS: Jaw and neck muscles may be activated by chewing load using a hard food. However, it remains unclear how effects the gum hardness to the coordinated features in jaw and neck muscle activities during chewing performance. OBJECTIVES: This study was conducted to quantitatively elucidate the effects of the hardness of the gum on coordinated features in jaw and neck muscle activities using intermuscular EMG-EMG transfer function and EMG-EMG coherence function analyses in 18 healthy subjects. METHODS: Jaw and neck muscle activities were aggregated into the first peak frequency of the power spectrum, and power, gain, phase, and coherence parameters between jaw and neck muscle activities were examined in the first peak frequencies during soft and hard gum chewing. RESULTS: The first peak frequency was not significantly different between soft and hard gum chewing. In contrast, power values of the jaw and neck muscles were significantly increased by chewing of hard gum as compared with soft gum, whereas gain, phase, and coherence were not significantly changed by gum hardness. CONCLUSIONS: The chewing rhythm, the quantitative and temporal coordination, and the functional coordination in jaw and neck muscle activities were not changed during soft and hard gum chewing, as well as increased jaw and neck muscles activities. It is therefore concluded that the chewing rhythmicity and jaw and neck muscles coordination accompanied with the increased jaw and neck muscle activities are maintained under the condition of the chewing load using gum hardness in the healthy individuals.

Effects from applying adhesive agents onto silanated porcelain surface on the resin bond durability.

This study examined the effects on the bond durability of resins arising from the application of adhesive agent on porcelain surface, silanated by a ceramic primer consisting of gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS), by comparing shear bond strengths before and after thermocycling. When an adhesive agent was applied to a porcelain surface which had been silanated by a ceramic primer for 10 seconds, a significant reduction in resin bonding durability was observed. Extending the silanating period of the ceramic primer to 60 minutes resulted in an increase in resin bonding durability to the porcelain surface. However, the effect on resin bonding durability resulting from the application of adhesive agent was nearly the same as that without adhesive agent application, even though the porcelain surface was silanated for 60 minutes. In other words, positive effects arising from adhesive agent application on resin bonding durability were not observed.

[Bonding of resin cement to bleached dental enamel].

PURPOSE: The effects of bleaching times, types of etching agent and storage period of bleached bovine tooth on the shear bond strength of resin cement to the enamel were examined. MATERIALS AND METHODS: Bovine teeth were repeatedly bleached 0, 1, 3, and 5 times then stored in 37 degrees C water for 1 week. The effect of bleaching number of the bovine tooth on the bond strength of resin cement to the enamel was investigated using 40% phosphoric acid (EG) etching technique. Next, the effects of types of etching agent and of storage period of bleached bovine tooth with three times in 37 degrees C water on the bond strength were studied using 10% citric acid-3% ferric chloride (10-3) or 10% citric acid (10-0) solution. RESULTS: The bleaching of bovine tooth allowed for a dramatic decrease in the bond strength from 18.3 MPa to 9.8 MPa (1 time), and 3.9 MPa (3 times), even though the bovine enamel was etched by EG. However, when 10-3 or 10-0 solution was applied to the three times bleached enamel, bond strengths were 13.9 and 10.0 MPa, respectively. Furthermore, prolonging of the storage period of the three times bleached bovine tooth in water to 2 months resulted in a increase in the bond strength from 3.9 to 10.1 MPa, even if bovine enamel was etched by EG, and close to that obtained from the 10-3 etching. CONCLUSION: To obtain the expected bond strength to bleached enamel, it is better to wait for 2 months for a restoration and use the 10-3 etching.

Pyogenic granuloma associated with Actinomyces israelii.

Peculiar findings of orofacial actinomycosis mimicking the clinical appearance of a tumor of the upper gingiva are reported. An 83-year-old man with bleeding of the gingiva visited our hospital. The clinical diagnosis was a benign gingival tumor, and the lesion was surgically removed. Histologically, the excised specimens showed an ulcerative granuloma lesion covered by bacterial colonies consisting of club-shaped filaments. DNA samples were extracted from paraffin sections and examined by polymerase chain reaction (PCR) for Actinomyces species. The PCR products examined by direct DNA sequencing demonstrated the presence of Actinomyces israelii. Finally, a pathological diagnosis was made of a pyogenic granuloma associated with actinomycosis. The PCR method aided the early and exact diagnosis of the paraffin-embedded sample of oral mucosal infectious diseases including actinomycosis.

[Improvement of aesthetics by porcelain laminate veneers].

PATIENT: The patient consulted our department with a chief complaint of aesthetic problems due to anterior tooth discoloration. Since improvement by bleaching was considered impossible, porcelain laminate veneer restorations were performed. DISCUSSION: Insertion took too long for the patient's satisfaction due to the repetition of color adjustment and recontouring. The veneer preparation area should be limited to enamel; however when dentin is exposed, it is important to treat with primer before adhesion. CONCLUSION: In this case, establishing a selection criterion for bleaching, a combined approach was also considered. Although the preparation area is limited to enamel, phosphoric acid etching should be avoided when dentin is exposed. The treatment process should be arranged so as to reduce the manipulation period.