Pressure distribution of implant-supported removable partial dentureswith stress-breaking attachments
K.Kono1, Y. Suzuki2, M. Sato1, C. Ohkubo1, M. Takahashi3
1

Department of Removable Prosthodontics, Tsurumi University
Division of Oral and Maxillofacial Implantlogy, Tsurumi University
3
GC Corp2

Introduction
The implant has been placed in the edentulous ridge to support and stabilize the removablepartial denture (RPD) and minimize the rotational movement1,2) (Fig.1). As a result, less bone
resorption, fewer numbers of relining and minimum decrease of retentive force of precisionattachments would be expected. There are remarkable differences between implant mobility and soft
tissue displacement under occlusal force. Therefore, the implant might undergo excessive pressure
with a conventional RPD during masticatory function. The stress-breaking attachment for implant
has been developed to prevent the excessive and harmful occlusal forces.

Fig.1 The implant has been placed in the edentulous ridge to support and stabilize the removablepartial denture (RPD) and minimize the rotational movement

Objective
This study investigated the pressure distribution of the implant-supported RPDs with the stressbreaking attachment under the occlusal force.

Materials and Methods
A model simulating a mandibular bilateral distal extension missing (#34 to #37 and #44 to #47)
was fabricated using silicone impression material (FIT CHECKER® GC CORPORATION, Tokyo,Japan) as soft tissue (2.0 mm thick) on an epoxy resin bone model (Fig. 2). Five small pressure
sensors (4.2mm diameter, PS-10KA, PS-10KB, Kyowa, Tokyo, Japan) were attached near the left

and right first molars, first premolars and medio-lingual alveolar crest (ML). The sensor at themedian was positioned beneath the lingual bar when the RPD was set on the modified models. Fivebilateral distal extension RPDs with a lingual bar and Akers clasps on both canines were designed
and formed like an occlusion rim without any denture teeth. Co-Cr frameworks were conventionally
cast, and then heat-cured denture base resin was packed and polymerized (Fig. 3). Two implants(SLA® implant, standard φ4.1mm 10mm, straumann japan, Osaka, Japan) were placed at thebilateral second molar regions (#37 and #47). Implant-supported RPDs, with the non stress-breaking
connection (healing cap: HC) and the two stress-breaking connection (SBB attachment, GC, Tokyo:SBB, Magfit IPS, Aichi Steel Corp, Aichi: MG) were fabricated. For a conventional RPD (CRPD),
healing screws were placed without being connected to the implants (Fig. 4,5). Loads up to 5kg wereapplied, and the pressure and displacement of the RPDs were simultaneously measured and analyzed
using the Wilcoxen test (α=0.05).

Results
The pressure on #36 and #46 of HC and MG was significantly less than SBB and CRPD (p<0.05).
In contrast, the pressure on #34 and #44 of SBB and the MG were slightly greater than HC andCRPD. The pressure of CRPD indicated approximately one half times to three times at ML,
compared with HC and MG, SBB (Fig.6). The amount of total pressure of HC and MG was
significantly less than for SBB and CRPD (p<0.05) (Fig.7). The denture displacement of HC andMG tended to be less than for CRPD and SBB. There were approximately 20-40μm differencesamong HC, MG and CRPD (p<0.05) (Fig.8).

Discussion
The results of this study indicated that implant placement at the distal edentulous ridge canprevent the denture displacement of the distal extension bases. Note that the pressure at the distal
regions (#36 and #46) decreased compared with the mesial regions (#34 and #44) by implant support.
The pressure differences of the alveolar ridge, the SBB attachment tended to be greater than Healing
cap and magnetic attachment. The buffer action of magnetic attachment was less than SBB
attachment in vertical direction. Because the SBB attachment is stress breaking attachment until thedenture displacement was 0.3mm. The selection of SBB attachment should be considered so that theocclusal force can be equally distributed between alveolar ridge and implants.

Conclusion
Within the in vitro limitations, precise denture settlements and pressure distribution under thedenture base could be controlled using a SBB attachment. SBB attachment might be able to protect
the implant from harmful force.

References
1. Ohkubo C, Effect of implant support on distal extension removable partial dentures: in vitroassessment, J Oral Rehabili 34(1):52-56, 2007.
2. Ohkubo C, Effect of implant support on distal-extension removable partial dentures: in vivo
assessment, Int J Oral Maxillofac Implants 23(6):1095-1101, 2008.