Daisuke Kurihara

Effect of implant support on mandibular distal extension removable partial dentures: Relationship between denture supporting area and stress distribution

PURPOSE This study explored the relationship between implant support and the denture-supporting area by comparing the stability of an implant-supported distal extension removable partial denture and a conventional distal extension removable partial denture. METHODS A model simulating a mandibular bilateral distal extension missing (#34-37 and #44-47) was fabricated using silicone impression material as soft tissue (2 mm thick) on an epoxy resin bone model. The denture base was reduced by 5 mm cutting part of both the retromolar pad and the lingual border. Loads of up to 5 kg were applied, and the pressure and displacement of the RPDs were simultaneously measured and analyzed using the Wilcoxon test (α<0.05). RESULTS The pressure on the bilateral first molar and the middle areas of the implant-supported distal extension removable partial denture (ISRPD) was significantly less than on the conventional RPD (CRPD). As the supporting area of the denture base decreased, the pressure and the denture displacement of the CRPD were greater than for the ISRPD. CONCLUSION This study indicated that implant placement at the distal edentulous ridge can prevent denture displacement of the distal extension bases, regardless of the supporting area of the denture base.

In vitro assessment of mandibular single/two implant-retained overdentures using stress-breaking attachments.

Objective:This study investigated the strain surround implants and the pressure distribution of the alveolar ridge related to implant overdentures with stress-breaking ball (SBB) attachments. Methods:Simulation models of edentulous mandibles were embedded with 1 and 2 implants to simulate a single implant-retained overdenture (S-IOD) and a two-implant-retained overdenture (T-IOD), respectively. The implants were connected to the denture base with the following conditions: complete separation between the denture base and implant with cover screws as a conventional complete denture (CD), 3 types of settlements with an SBB attachment between them, and a conventional ball attachment (BALL). Strain surround the implant, pressure at 5 different soft tissue areas, and displacement of the denture base were measured with loading up to 50 N. Results:In S-IOD and T-IOD, the strain of each SBB attachment was less than the strain shown by the BALL. The pressure at each region of the SBB attachment was less than the pressure shown with the CD and BALL. Conclusions:SBB attachments prevented strain surround the implants in loading and provided optimal stress distribution.

An Experimental Study on the Relationship between the Denture Structural Designs and Pressure Distribution. The Effect of Retainer Designs.

Removable partial dentures should be designed to ensure efficient distribution of masticatory loads over the abutment teeth and alveolar ridge. The relationship between the denture stiffness and the various clasp designs on the pressure distribution to a single abutment tooth and the alveolar ridge was investigated in this study.The results were as follows:1. Regardless of the retainer designs, the pressure on the alveolar ridge was less when using a double structure than a skeleton type, and the pressure on the abutment tooth in the vertical direction was greater when supported by a double structure than a skeleton type.2. When a Konus telescope was applied as a retainer the pressure on the abutment tooth in the vertical direction was greater than an Akers or an RPI clasp.3. When an RPI clasp was applied as a retainer the amount of pressure on the alveolar ridge was maximum.4. The pressure on the abutment tooth in the lateral direction showed a greater tendency when an Akers clasp was applied.5. The displacement and strain of the denture were the least when a double structure design was applied.6. When a double structure design with Konus telescope was applied, the displacement of the denture was the least.

Fatigue Strength of the Metal Framework Structures for Removable Partial Dentures.

The structural design of the metal alloy framework for removable partial dentures is critical. A double structure framework was the representative of these designs, which enables the mechanical strength and durability to improve and the abutment teeth and alveolar ridge to protect. In this study, several structural designs (double structure, T-shapes, trussed structure, rectangular column, nonuniform section) including resin block as control were subjected to a load-controlled fatigue test. The benefits on fatigue strength of five types of structures were evaluated to record the number of cycles at catastrophic failure, to measure continuously displacement and strain under loads repeatedly, and to observe the fracture patterns.The results were as follows:1. Maximum stiffness of double structure and T-shapes was approximately 20 times that of rectangular column and nonuniform section by theoretical calculations.2. Fatigue strength of double structure was the highest, followed by that of trussed structure and T-shapes.3. Double structure was found to be the significantly lowest of both displacement and strain.4. Packed resin fracture was observed in all specimens except double structure.5. The interface of fractured specimen frameworks were revealed inherently with fatigue.