Tooru Nagasawa

An evaluation of chewing function of complete denture wearers

Chairside scoring of chewing function of complete denture wearers has been difficult. This study presents a table for chairside evaluation of the chewing function of Japanese complete denture wearers. The concept can be effective in other countries and permit international comparisons among complete denture wearers.

Changes in retention of various telescope crown assemblies over long-term use

An investigation was done on the effect of crown height, angle (one-half taper) and number of removals on the retention of telescope crowns. Assemblies of inner and outer crowns were constructed on master dies. Crown heights of 4 mm, 5 mm, and 6 mm were used. Cone angles of 0, 2, 4, and 6 degrees were used for each of the three heights. The inner crowns were fixed to the dies with an adhesive agent. the outer crowns were set over them and placed in a clamp. Separation forces were tested with an Instron machine (Instron Corp., Canton, Mass.). They were measured initially and after numerous 100 insertion/separation cycles up to 1000 cycles and numerous 500 insertion/separation cycles up to 10,000 cycles. The results demonstrated that the cone angle of the inner crown was more important than its height for maximum retention. Retention is rapidly lost after the cone angle exceeds 2 degrees. It was also shown that an accessory device is necessary to maintain retention capabilities after long-term use.

The effect of anteroposterior inclination of the occlusal plane on biting force.

With the experimental design of this study the following conclusions were reached. 1. Biting force during maximum clenching was the greatest when the occlusal plane was made parallel to the ala-tragus line. It decreased when the occlusal plane was inclined about 5 degrees anteriorly or about 5 degrees posteriorly. 2. The efficiency of biting force exertion during maximum clenching showed the best value when the occlusal plane was made parallel to the ala-tragus line. 3. Muscle activity during clenching at various given forces was least when the occlusal plane was made parallel to the ala-tragus line. The anteroposterior inclination of the occlusal plane tends to affect the biting force, and the method with the ala-tragus line seems to be the most reasonable for occlusal plane orientation.

The role of the periodontal ligament in overdenture treatment

The results of this experiment suggest that the periodontal ligament plays a role in the efficiency of muscular activity during chewing in patients wearing overdentures. A masticatory index as an indicator of the efficiency of masticatory movement is proposed in this research.

A comparative evaluation of masticatory efficiency of fixed and removable restorations replacing mandibular first molars

Abstract In replacing a missing mandibular first molar, removable and fixed partial dentures were constructed for each of ten subjects. Masticatory function tests with peanuts were made before, immediately after, and one week and one month subsequent to insertion of both types of prostheses. Masticatory performance, the number of strokes, and chewing time until swallowing were similar with the removable and fixed partial dentures. One month after insertion, a slight but statistically significant decrease in the total time of mastication was observed. The electromyogram of the anterior belly of the temporal muscles made during peanut chewing was also analyzed. It was found that, as a result, the rhythm of the masticatory movement after the cementation of fixed partial denture was more regular and that the duration of movement bursts became shorter than that with the removable partial denture.

Masseteric Silent Period After Tooth Contact in Full Denture Wearers

The purpose of this study was to analyze the silent period of the masseter EMG in participants wearing full dentures. The experimental subjects were eight persons (three males and five females) from 44 to 64 years old. In four subjects, the effect of topically applied anesthetic on the silent period was studied. The anesthetics used were xylocaine jelly (2%) and xylocaine spray (8%) .a Each participant tapped his or her teeth together ten times at various rates with a metronome. The activity in the bilateral masseter was recorded and the moment of tooth contact recorded with a small crystal microphone applied to the forehead. At a normal tapping rate (72/min), the latency and duration of the silent period were constant, the silent period lasting approximately 20 msec. However, as the tapping rate was heightened to 96/min and 132/min, the durations of the silent periods were reduced to approximately 14 msec and 11 msec, respectively (Illustration). At the more rapid tapping rate, the electrical activity of the masseter EMG after tooth contact showed a downward trend and almost no perceptible silent period occurred. The range of the latency increased in accordance with tapping rate, though the mean of the latency of the silent period was unchanged (about 13 msec). After topical anesthesia was administered on the mucous membrane under the upper and lower dentures, the duration of the silent period of the masseter muscle was considerably prolonged. The duration of the silent period shortened as the rate of tapping movement was heightened after anesthesia.

Palatal gland distribution.

Discussions about the retention of complete upper dentures have stressed many factors. Although opinions still differ on the significance of these factors, cohesion by palatal fluid is widely accepted as one of the most important factors. The purpose of this investigation was to study the distribution of the orifices of palatal glands, because it may be an important factor in the satisfactory retention of complete upper dentures. Salivary secretion from palatal glands has been studied by using alginate impressions (OSTLUND, j Prosthet Dent 10: 658, 1960). However, the palatal droplets can be more clearly observed, in many instances, on the surface of rubber base impression material than on alginate impression material because the latter is hydrophilic. The patients were 20 men and 20 women aged 22 to 26 years. It was difficult to study the palatal gland distribution within the limited setting time of impression material because of the small quantity of resting secretion from the palatal gland. Therefore, taste stimulation (2.0 ml of a quarter M of tartaric acid for five minutes) was used to accelerate secretion. The peak secretion was observed three to five minutes after stimulation, and this period was within the

Conditions of Casting Au-Ag-Pd Alloy to an Embedded Keeper of Magnetic Attachment in Clinical Cases.

目的: われわれは先にキーパーと12%金銀パラジウム合金の鋳接状態について基礎的に検討し, 接合部には酸素を固溶した反応層と間隙 (黒色層) がわずかながら存在し, これは鋳型の係留温度や鋳造方法などによって影響を受けることを報告した.本報告では, 実際に口腔内に装着されたキーパー付き根面板における鋳接状態について検討した.方法: 被験歯数は7歯で, すべて歯周疾患によって抜去されたものである.鋳造用合金にはすべて12%金銀パラジウム合金が使用されていた.鋳造はすべて遠心鋳造機により行われていた.根面板を支台歯とともにレジンにて包埋し中央にて割断後, 金属顕微鏡および走査型電子顕微鏡にてキーパーと鋳造用合金との接合部を観察した.また, X線電子マイクロアナライザーによる分析を行った. これらを既報告で良好な鋳接状態が得られた条件における結果と比較した.結果: 金属顕微鏡観察からキーパーと鋳造用合金との接合部には黒色層が観察された. 黒色層は, 走査型電子顕微鏡およびX線電子マイクロアナライザー分析から, 間隙と反応層から構成されていた. この黒色層は基礎実験の結果に比べて厚く, 不均一であった.結論: キーパーの根面板への鋳接に際しては適切な鋳造条件を厳守する必要がある.

Antibacterial Activity of Newly Developed Adhesive Resin Cements against Oral Bacteria.

The antibacterial activity of newly-developed adhesive resin cement and primer on oral bacteria was investigated. Three types of adhesive resin cements and primers, and glass-ionomer cement as a control were used in the experiment.S. mutansATCC 25175, S. sanguisATCC 10556, S. mitisATCC 3339, S. salivariusATCC 25975, andB. gingivalisATCC 3327 were used as test strains. Antibacterial activity of the resin cement immediately after mixing, after setting and after immersion in artificial saliva for one week were tested. A pH and fluoride release from resin setting were measured, and elute from settings was also measured by high-performance liquid chromatography.Most resin cements and primers showed antibacterial activity against the Streptococci, but did not show antibacterial activity against the Bacteroides. Primers and resin cement immediately after mixing showed greater antibacterial activity compared to the settings of resin after immersion of artificial saliva. A pH and fluoride release of settings of resin cement were not related to the antibacterial activity. HEMA, Mac-10, MDP and Bis-GMA were identified from settings and primers by high-performance liquid chromatography.The results suggested that the antibacterial activity was produced by the monomer of resin cement and primer.

Usefulness of Scanora for the Examination of Edentulous Jaw.

A multipurpose, maxillofacial X-ray tomographic device, Scanora 6 (Soledex), which can be installed in dental clinics because of its small size compared to conventional CT, has been developed and introduced to Japan. In a previous study, we examined the basic performance of Scanora to assess its applicability to prosthodontic diagnosis and reported that Scanora permitted evaluation of the maxillofacial morphology and structure including jaw bone and temporomandibular joints, that X-rays obtained with Scanora were highly reproducible, and that it was a very useful instrument for examination of temporomandibular joints.In this study, prosthodontic diagnosis was carried out using Scanora in 5 patients with severe resorption or morphological abnormality of alveolar ridge in the area of defect.It was found relatively easy to derive clear-cut information on alveolar morphology, which is an important element in prosthodontic diagnosis, from tomograms obtained with Scanora.