Yoshihiko Okuno

Clasping system with rotational path of insertion. Part 1. Retention of denture

The rotational path of insertion differs substantially from the conventional path or the straight path of insertion. In the use of the rotational path, one segment of the partial denture is seated first, then the remainder of the prosthesis is rotated into position. One segment of this system is the rigid retentive component with long rest and the other the conventional clasp.This study examined the influence of point and direction of displacing force and the proximal undercut of rigid retainer on retention of this system. Then this system was applied in clinical field. The following results were obtained:1) Retention of denture is the smallest when displacing force was applied at the conventional clasp part.2) Direction of displacing force (± 10deg;) has no significant effect on the retention.3) The value of retention showed a tendency to increase in order when proximal undercut of rigid retainer was 0.3, 0.7 and 1.0 mm respectively.4) The effects of the point and direction of displacing force on retention of mesio-disto rests and reciprocal arms design are similar to those of original long rest design.5) When a severly tilted posterior tooth is used as an abutment tooth, this system could provide adequate retention.

Effect of Resilient Lining Material of Denture Base. Clinical Investigation and Model Experiment on Occlusal Force Distribution.

Resilient denture lining materials have been known as one of the effective measures for treating cases with severely atrophic mandible or with constant pain on residual ridge. The effective method of application and the mode of action of these materials, however, have not been clearly demonstrated yet. The main objective of this study was to investigate the influence of these materials on occlusal force distribution using T-Scan system. The study was carried out on six volunteer edentulous manidble patients using resilient polyolefin lining materials with two different hardness (soft and hard) . Following results were obtained. 1. In dentures with the soft resilient lining material, comparing with the hard one or the conventional resin base, the number of occlusal contact points increased and the location of contacts more widely spread within dental arch. 2. Despite the use of soft lining material, pain and discomfort were not eliminated in some subjects. Orthopantomography of these subjects suggested the topography of mandibular bone cloud has significant effect on these incidences. 3. Occlusal adjustments should be carefully performed after the insertion of denture with soft lining material.

Evaluation of Soldering Procedure in Fabrication of Wrought Wire Clasp. Differences in Temporary Attachment and Soldering.

Most wrought wire clasps are attached to the framework of removable partial dentures by soldering. The purpose of this study is to investigate the influence of soldering procedures on deformation and mechanical properties of clasp arms and strength of jointing parts.In this study, circular clasp arms were made from Co-Cr alloy wires and soldered to supporting parts with a silver solder. Two kinds of temporary attachments, investing and spot welding, and two kinds of soldering methods, torch and electric resistance soldering were applied. These temporary attachment and soldering methods were combined, then four different procedures were compared.The results were follows.1. The change of distance between clasp tips during soldering procedure was smaller for temporary attachment by investing than spot welding, and for electric soldering than torch soldering.2. By any soldering procedure, load required for 0.1 mm deflection of clasp arms increased significantly and permanent deformation after 0.5 mm deflection of them decreased considerably.3. In both tensile strength and fatigue profile of jointing part, combination of spot welding and electric soldering was the best of all procedures.These results indicated that without the deformation of clasp arms, combination of spot welding and electric resistance soldering was the most effective procedure in wrought wire clasp construction.

Survey on denture weathers. Cleaning of denture at home and outside home.

Denture wearers have different problems from non-denture wearers in terms of maintaining oral health.In this study, we attempted to find out specific difficulties of denture wearers with questionnaires about social life problems as well as oral hygiene problems. Our results indicate that about the half of the patients we surveyed remembered the instruction for denture cleaning methods. Most of the denture wearers considered the cleaning of denture was essential to maintain their oral health, though methods they employed showed a great deal of difference.Also denture wearers cared much about for other peoples attention and felt much difficulties in cleaning their dentures when they were not at home.

Development of a computer system for determining retentive force of cast clasps

The purpose of this study is to develop a rational fabricating system for determining retentive force of cast clasps. The radius of curvature of a circumferential clasp arm is considered to be one of the important factors affecting dynamical properties of cast clasps. In this study, a device for determining the radius of curvature and a computer system for Akers clasps and I-bar clasps were developed. It was suggested to be very significant in partial denture designing, that the retentive force and the bending rigidity required according to various conditions around abutment teeth can be easily obtained by using a personal computer, and that the proper part of a commercially available clasp pattern required to fabricate cast clasps providing rational retentive forces can be determined in this system.

Clinical studies on crevicular fluid of abutment tooth. Part II. Gingival condition around proximal area adjacent to edentulous spaces

Sixty subjects (42 subjects with dentures and 18 subjects without dentures) were participated in this study. Crevicular fluid flow (Periotron unit: GCF), gingival index (GI), plaque index (PH) and probing depth (PD) of 209 marginal gingiva around natural and crowned abutment teeth were measured to evaluate gingival condition.The following results were obtained.1. The GI, PII and PD in subjects with dentures were higher than those in subjects without dentures. The GCF in subjects with dentures was inclined to be high comparing with those in subjects without dentures.2. The GCF, GI and PD of crowned teeth in the subjects with dentures were higher than those of natural teeth. On the other hand, the GCF, GI and PD of crowned teeth in the subjects without dentures were almost equal to those of natural teeth.3. The coefficient of correlation between GCF and other indices (GI, PII, PD) were+0.66 (p<0.01), +0.38 (p<0.01) and+0.38 (p<0.01), respectively.

[Caries-reduction of overdenture abutment. Part 2. Solubility of the embedded tannin-fluoride preparation].

We tried to embed HY-preparation with the zinc oxide eugenol cement as the base material to the inner surface of denture base to which the abutment might contact. We reported that it was useful to prevent caries of the overdenture abutment teeth. But we anticipated solubility of the embedded HY-preparation might gradually decrease.In this study we measured the F-ion solubility in the HY-preparation and examined the gradual change of its solubility in vitro, and examined clinically the caries activity of five subjects with overdenture and obtained the following results.1) The F-solubility in both distilled water and artificial saliva almost had the same increasing tendency.2) The F-solubility of the preparation, with zinc oxide eugenol cement in powder-liquid ratio of 6: 1 and 12: 1, had almost the same increasing tendency.3) The solubility of HY-preparation to artificial saliva per day was larger in the early stage and gradually decreased thereafter, but after 24 weeks the solubility was almost nil. The solubility period of R2-group with larger surface area was longer than that of R1-group.4) We examined clinically caries activity with the Cariostat. It was lower after 3 months than on the time we had embedded the HY-preparation in the cavity.

[Filling materials with a tannin-fluoride preparation in denture base. Part 1. In relation to the mixing ratio of preparation to the autopolymerizing resin].

We embedded tannin-fluoride preparation with the zinc oxide eugenol cement as the filling material to the inner surface of denture base to which the abutment might contact, and reported that it was useful to prevent caries of the overdenture abutment teeth. But we anticipated the weakness of mechanical strength of the denture.In this study we produced autopolymerizing resin containing the preparation, and the F-ion solubility, setting time, Knoop Hardness, adhesive strength and compressive strength were measured. The following results were obtained:1) The F-ion solubility was increased as the mixing ratio increased.2) Setting time was increased as the mixing ratio increased.3) The values of Knoop Hardness from 10 to 50% groups were lower than that of 0% group, and there was no statistical difference between the values from 10 to 50% groups.4) The values of adhesive strength of mixing ratio from 10 to 30% groups showed almost the same value as that of 0% group.5) The values of proportional limit of compressive strength of 10 and 20% groups showed almost the same value as that of 0% group.

[Mechanical studies on cast clasps of a superelastic Ni-Ti alloy. Part 2. Deflection behavior caused be repeated bending forces].

The purpose of this study is to investigate mechanical properties of a superelastic Ni-Ti alloy for cast clasps. Bending properties of other alloys (Co-Cr, Au-Pt, Au-Ag-Pd) have been examined by the use of a universal testing machine to be compared with that of the Ni-Ti alloy which was examined in part 1. In this paper, repeated bending forces were applied on the tip of specimens supposed clasp arms by the use of a fatigue testing machine, then permanent deflections were measured by the use of a surface-shape recorder. It can be concluded that:(1) The force required to produce the deflection in 0.1mm (P0.1: bending rigidity) of the Ni-Ti alloy was smaller than other alloys.(2) After repeated deflections (30, 000 times) of 0.25-1.00mm, specimens of the Ni-Ti alloy produced less permanent deflections than other alloys. In clinical cases, it is supposed that large amount of undercut is available by the use of a superelastic Ni-Ti alloy for cast clasps.

[Laboratory-made stud attachment. Report II. Effect of cycle of engaging and disengaging on fatigue]

A number of engaging and disengaging of retainers induce those fatigue and consequent decrease in retentive force. In this study on the laboratory-made stud attachment consisting of a male (Type IV gold) like a snap and a female with semi-loop and linear portion made by bending a wrought gold wire, the maximum buldges of males, the distances between the female tips, and the retentive forces were measured before and after each stage of engaging and disengaging of predetermined cycles (10: initial, 1, 000, 3, 000, 5, 000, 10, 000). The males had 0.25 mm undercut. The females were 0.8mm in diameter and 3, 5, 7 and 10mm in length from the contact points with the males at the semi-loop portion to the points fixed in the resin base at the linear portion.Results:1. The initial retentive force, the abrasion of male, the permanent deformation of female and the decrease in retentive force all increased with the shorter female.2. 5mm-length female kept the most amount of retentive force of approximately 380 to 190g during 1, 000 to 10, 000 cycles.