Goro Nishigawa

In situ microsampling technique for identification of elements of a restoration with exposed metal to identify potential allergens.

STATEMENT OF PROBLEM For clinical investigations of allergic reactions to dental materials, it is necessary to know the type of metal used in restorations in the mouth of the patient. However, an intraoral method of sampling the dental alloy without removing the metal restoration has not yet been established. PURPOSE This study attempted to establish a clinically serviceable method for microsampling dental alloy. MATERIAL AND METHODS A piece of silicone sampling tube is held on the surface of the metal restoration. This surface was ground with a carbide bur through the sampling tube, and the ground metal particles were then recovered from the inner surface of the tube. The recovered sample was subjected to energy-dispersive x-ray microanalysis. The percentage recovery of ground alloy by this microsampling method, which was the ratio of the recovered weight of metal to the total weight of the metal ground, was evaluated using 3 mm diameter x 1 mm thick disk-shaped specimens of Ag-Au-Pd and Ni-Cr alloys. RESULTS Elemental analysis of the retrieved alloys identified the component elements in the alloy compositions. The percentage recovery by this microsampling method was 75.0% for Ag-Au-Pd alloy and 69.9% for Ni-Cr alloy, respectively. CONCLUSIONS The microsampling method demonstrated a relatively high percentage recovery of the ground alloy particles. This microsampling method would be of great benefit clinically to patients who have allergic reactions to dental materials.

The Design of Non-Occlusal Intraoral Appliances on Hard Palate and Their Effect on Masseter Muscle Activity During Sleep

Abstract This study aimed to reveal whether masseter muscle activity during sleep is affected by the difference in design of non-occlusal intraoral appliances on hard palate. Eight healthy Japanese participants were selected and wore each of the four types of appliances (horse shoe, thin, thick and medium thick) during sleep for one week with a one week interval without appliance during sleep. A masseter muscle electromyograph (EMG) was recorded during sleep. The EMG activities were analyzed by calculating the number of bursts per hour, episodes per hour, and bursts per episode. The EMG parameters with the thick type appliance were significantly lower than the baseline condition without appliance. In this study, it is suggested that a thick type appliance has an active effect on suppression of masseter muscle activity.

Vertical and horizontal polymerization shrinkage in composite restorations

OBJECTIVE Polymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold. METHODS Vertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured. RESULTS There was a significant correlation between vertical and horizontal polymerization shrinkage (r=0.647, p=0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r=-0.697, p=0.025) and dentin (r=-0.752, p=0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r=0.829, p=0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p>0.05). SIGNIFICANCE During the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.

Efficacy of tray adhesives for the adhesion of elastomer rubber impression materials to impression modeling plastics for border molding

STATEMENT OF PROBLEM Tray adhesive, which is used for the adhesion of elastomer rubber impression materials to a custom resin tray, lowers the retention of the impression materials to the impression modeling plastics, as some ingredients of tray adhesive make the impression modeling plastic soft and tacky. PURPOSE The efficacy of tray adhesive, which is used for the adhesion of elastomer rubber impression materials to a custom resin tray, on the adhesion between elastomer rubber impression material and impression modeling plastic was investigated. MATERIAL AND METHODS Four silicone rubber impression materials (two addition reaction types and two condensation reaction types), two polysulfide rubber impression materials, and one impression modeling plastic were used in this study. Tensile strength between elastomer rubber impression material and impression modeling plastic with or without the application of tray adhesive was evaluated. RESULTS Although tray adhesives for both addition reaction type and both condensation reaction type of silicone impression materials and one tray adhesive for polysulfide rubber impression material increased the tensile strength between the impression material and impression modeling plastic, one tray adhesive for polysulfide rubber impression material decreased the tensile strength when sufficient drying time was not applied.

Salivary stress biomarker levels during speech in patients with maxillectomy defect

After resection of maxillofacial tumors, severe functional problems related to mastication, deglutition, and speech are observed in addition to the changes in appearance and psychosocial functioning. Although speech outcome is recovered with prosthetic treatments, patients sometimes complain of continued dissatisfaction with their speech. The purpose of this study was to evaluate the potential dissatisfaction of patients with maxillectomy defects during speech.

Lateral Forces Exerted on Abutment Teeth of Removable Partial Denture : Part I. Clinical Measuring method

有床義歯に作用 した咬合力は,人 工歯 の咬合面形態 や 対合 関係 ならびに顎堤 の形態に よって さまざまな方向の 分力に変化 し,こ れ によって義歯の移動な らびに回転が 生 じる.部 分床義歯 では このよ うな動 きを鉤歯 に負担 さ せ ることによって防止す るため,鉤 歯は垂 直方向の力の み ならず側方力や回転力を受け,こ れが過 大な場合は, 早期に抜歯 に至 る場合 が多い.し たが って,鉤 歯 に伝達 され る力をコン トロール し,そ の保全 を図る ことは義歯 の設計を考 える上で きわめて重要 なことである,こ の課 題 に対 してシ ミュ レー ター を用 いた 力学的研究4~6)や歯 の動揺度に関す る研究1,2)や病理学的研究9)が行われ てき た.さ らに従 来維持歯に対 して最 も悪い影響 をおよぼす と考 えられ ている側方力 に関 しての臨床例に よる研 究と してKyddら7)の 報告がみ られ るが,機 能時の維 持歯 に 作用す る側 方力の大 きさやその発現パターンについて明 らかにした報告はみ られ ない. そ こで,著 者 らは口腔内において機能時の維持歯に作 用する側方力 を測定 し,そ の大 きさやエネルギー量,な らびに発現パ ター ンなどを分析 し,義 歯設計に際 しての 基礎資料 を得 ることを目的 として以下の研究を行 った. 今回第1報 として.機 能時の維持歯に作用す る側方 力 の測定が可能 なtransducerを 開発 したので,そ の構造 と特徴な らびに これ を用いて測 定を行 った測定例につい て報告す る.

Longitudindinal investigation on occlusal force distribution in removable partial denture - Part I. Method of vertical force measurement in vivo.

有床義歯 に作用 した咬合力は歯根膜 と顎堤粘膜 とに配 分 され るが,こ の両者の被圧変位量 には大 きな差 がある ので,こ れ をどの ように調整 して歯 と粘膜への負担の平 衡 を図るか は義歯の構成 を考える上 で重要な 問 題 で あ る.こ の点に関 して,補 綴臨床においては粘膜加圧印象 や維持装置 と義歯 との連結方法を考慮するな どの方法が 行われ てお り,一 方基礎的研究 としてはシ ミュ レー ター または天然歯に よる歯の動揺 に関す る研 究1~8),光弾性 による力学的研究9),あ るいは病理学的研究10)などがな され てきた.し かしなが ら,生 体が咀嚼 とい うきわめて 複雑 な運動 を行 うことや,顎 堤の吸収11~13)や慣れ14と いった経時的変化 を伴 うことから,本 研 究は機能時の維 持歯に作用する力の経時的な観察 を行い,こ れ らに作用 す る力の配分の方法についての資料 を得 ん とす るもので ある. 本論文では第1報 として,機 能時の維持歯 に作用する 垂直力 を経 時的に測定す る ことが可能 なtransducerを 作製 したので,そ の構造 と測定方法 ならびに測定例 につ いて報告する.