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Abstract
Statement of problem
There are common clinical cases in which the mandibular first and second molars are missing unilaterally.
Purpose
This study was designed to compare and evaluate the magnitude and distribution of stress produced by four kinds of mandibular unilateral free-end removable partial dentures that could be applied clinically in Kennedy class II cases.
Material and methods
Four unilateral free-end removable partial dentures using clasp, Konus crown, resilient attachment, and flexible resin were fabricated on the photoelastic models of the Kennedy class II cases. The vertical load of 6㎏ was applied on the central fossa of the first molar of every removable partial denture in the stress freezing furnace and the photoelastic models were frozen according to the stress freezing cycle. After these models were sliced mesio-distally to a thickness of 6mm, the photoelastic isochromatic white and black lines of the sliced specimens were examined with the transparent photoelastic experiment device and photographs were taken with a digital camera. The fringe order numbers at eight measuring points in the photograph were measured with the naked eye.
Results
The maximum fringe order number of each sliced specimen and the fringe order number at the residual ridge just below the loading point were in the decreasing order of the unilateral removable partial dentures using flexible resin followed by clasp, resilient attachment, and Konus crown. The fringe order number at the root apex of the second premolar was in the decreasing order of the unilateral removable partial dentures using clasp followed by flexible resin, Konus crown, and resilient attachment.
Conclusion
The removable partial denture using Konus crown showed the most equalized stress distribution to the supporting alveolar bone of abutment teeth and residual ridge under the vertical loads. The removable partial denture using flexible resin can be applied to the case that has a better state of residual ridge than abutment teeth.
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Fig. 4.
Unilateral free-end removable partial dentures on the photoelastic model. A: Partial denture using the clasp (C-URPD), B: Partial denture using the Konus crown (K-URPD), C: Partial denture using the resilient attachment (ReA-URPD), D: Partial denture using the flexible resin (F-URPD)
Fig. 7.
Measuring points of the fringe order number in the sliced specimen. A: Central fossa just below the 2nd molar artificial tooth, B: Central fossa just below the 1st molar artificial tooth (loading point), C: Distal side (middle) of the root of the 2nd premolar, D: Root apex of the 2nd premolar, E: Mesial side (middle) of the root of the 2nd premolar, F: Distal side (middle) of the root of the 1st premolar, G: Root apex of the 1st premolar, H: Mesial side (middle) of the root of the 1st premolar
Fig. 9.
Photoelastic isochromatic white & black fringe pattern of the sliced specimens produced by the unilateral free-end removable partial dentures under the vertical loading. A: C-URPD, B: K-URPD, C: ReA-URPD, D: F-URPD.
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