Mutsuo Yamauchi

Leachability of denture-base acrylic resins in artificial saliva☆

We studied the influence of salivary acidity on leachability of denture-base acrylic resins with etiological interest in denture stomatitis because denture surfaces are frequently exposed to acidic conditions in the oral cavities. Auto-, heat-, and microwave-polymerized resins were immersed in artificial saliva with pH ranging from 4.0 to 6.8 at 37 degrees C, and leachables were pursued quantitatively with time. Methyl methacrylate, methacrylic acid, and benzoic acid leached from all resins. Their concentrations in the saliva were markedly high for auto-polymerized resins, while leachability of heat- and microwave-polymerized resins was so low that quantitative analysis of leachables was impossible. Lower pH showed higher concentrations of methyl methacrylate, although no apparent association was confirmed between salivary acidity and its own leachability. The concentrations of methacrylic acid increased remarkably with an increase in pH, which was probably due to hydrolysis of methyl methacrylate. These results suggest that chemotoxic actions of auto-polymerized resins are potentially ascribable to methyl methacrylate under more acidic conditions and to methacrylic acid under less acidic conditions.

In Vitro Comparison of Cone Beam Computed Tomography with Digital Periapical Radiography for Detection of Vertical Root Fracture in Posterior Teeth.

Statement of the Problem: The diagnosis of vertical root fracture (VRF) is a challenging task. Purpose: This in vitro study compared cone beam computed tomography (CBCT) imaging with digital periapical radiography (DPR) made by three different horizontal angels (20°mesial, 0° and 20° distal) for accurate diagnosis of VRF. Materials and Method: Among 120 posterior teeth included in this study, 60 were vertically fractured. Fractured and non-fractured teeth were randomly distributed into three groups defined as group 1 with no filling in the root canal, group 2 with gutta-percha in the canal, and group 3 with the intracanal post. All samples were placed in a dry mandible and imaged with CBCT and DPR techniques. Two blind observers investigated the images. Results: CBCT had higher sensitivity but lower specificity compared with DPR, except for the intracanal post group in which the sensitivity of DPR was higher; though the chi-square test showed the differences to be statistically insignificant. The sensitivity, specificity, and accuracy of CBCT and DPR were reduced in the cases that gutta-percha or post were present in the canal. Inter-observer agreement was higher for CBCT. A set of three DPRs with different horizontal angels were significantly more sensitive for VRF recognition than a single orthogonal DPR. Conclusion: Based on our results, there was no significant difference between CBCT and a set of three DPRs with different angulations for VRF detection in posterior teeth. Therefore, it is suggested to consider DPRs with three different horizontal angels (20°mesial, 0° and 20° distal) for radiographic evaluation before CBCT examination.

Clinical application of removable partial dentures using thermoplastic resin. Part II: Material properties and clinical features of non-metal clasp dentures

This position paper reviews physical and mechanical properties of thermoplastic resin used for non-metal clasp dentures, and describes feature of each thermoplastic resin in clinical application of non-metal clasp dentures and complications based on clinical experience of expert panels. Since products of thermoplastic resin have great variability in physical and mechanical properties, clinicians should utilize them with careful consideration of the specific properties of each product. In general, thermoplastic resin has lower color-stability and higher risk for fracture than polymethyl methacrylate. Additionally, the surface of thermoplastic resin becomes roughened more easily than polymethyl methacrylate. Studies related to material properties of thermoplastic resin, treatment efficacy and follow-up are insufficient to provide definitive conclusions at this time. Therefore, this position paper should be revised based on future studies and a clinical guideline should be provided.

Innervation of the tooth pulp by the mesencephalic trigeminal nucleus in the cat: a retrograde horseradish peroxidase study.

HRP was applied to the tooth pulp of 8 cats. Six were subjected to postoperative administration of the anti-inflammatory drug, prednisolone, whereas the remaining two were not. In all prednisolone-treated cats, labeled neurons were found in both the mesencephalic trigeminal nucleus and trigeminal ganglion, ipsilaterally. On the other hand, no labeled neurons were observed in the mesencephalic nucleus in cats receiving no steroid.

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.

Abrasion of Denture Base Resin by Denture Cleaning Paste.

Abrasion of denture base resin by dentifrice manufactured for dentures was compared with that by ordinary tooth paste.Denture base samples were prepared using microwave-polymerized base resin. Using a brushing abrasion tester, the samples were brushed one hundred thousand times to determine the amount of abrasion and the surface roughness. SEM observation was also carried out. In addition, the X-ray diffraction and thermal weight of the dentifrice were measured.Brushing with the dentifrice for dentures resulted in a larger amount of abrasion compared to the ordinary tooth paste. Thus denture base resin was found to be liable to be abraded by brushing with the dentifrice manufactured for dentures. SEM observation and measurement of the surface roughness demonstrated that the surface of denture base resin underwent large changes by brushing with the dentifrice manufactured for dentures.The results of this study by SEM observation, X-ray diffraction measurement, and thermal weight measurement suggested that the difference in abrasiveness was due to the differences in the kind and grain size of the polishing material contained in dental paste.

Study on the Usefulness of Scanora for the Application to the Prosthodontic Examination and Diagnosis.

A clinical application of multimodal radiography (Scanora) was reported, and the reproducibility of cross-sectional images depending on Scanora was examined.Since it is possible to take images of dentomaxillary cross-sectional tomography clearly and easily by Scanora, teeth and jaw can be shown three-dimensionally. Therefore, it was suggested that Scanora could be an efficient means to examine and make diagnosis. Since the reproducibility of the images was superb, it was suited for periodical X-ray taking.From the above-mentioned results, Scanora is thought to be a useful diagnostic equipment for prosthodontics.

Application of Scanora^【○!R】to the Examination of the Temporomandibular Joint

Recently, multimodal radiography system “Scanora®” was introduced to Japan. Scanora is small enough to set in the dental office. In this paper, the images of the temporomandibular joint by Scanora were compared to images by multidirectional tomography.It was possible to observe the morphology of the temporomandibular joint and joint spaces by Scanora. There were no differences of images between the multidirectional tomography and Scanora in most clinical cases.These results suggested that the tomograms of the temporomandibular joint by Scanora can be used clinically.