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Chewing efficiency and occlusal forces in PMMA, acetal and polyamide removable partial denture wearers

Macura-Karbownik A., Chladek G., Żmudzki J., Kasperski J.

Acta of Bioengineering and Biomechanics

2016

Vol. 18, no. 1

137--144

Purpose: Thermoplastic materials, such as acetal (AC) and polyamide (PA), constitute an alternative to polymethyl methacrylate (PMMA) based resins as the materials for removable partial dentures. However, none of the previous studies compared chewing efficiency and occlusal forces in the wearers of dentures made of various materials. Therefore, the aim of this study was to determine and compare the chewing efficiency and occlusal forces in PMMA, PA and AC RPDs’ wearers. The hypothesis was that the type of denture base material shows a significant effect on chewing efficiency (expressed as a degree of food fragmentation) and occlusal force. Methods: The experiment included the group of 30 patients using removable partial dentures. The dentures made of PMMA, acetal and polyamide were tested in each patient. Each denture was worn for 90 days, with a random sequence of the denture manufacturing and insertion. After 7, 30 and 90 days of each denture wear, chewing efficiency coefficient was determined with the aid of a sieving method, and occlusal force was measured with a dynamometer. Results: The use of dentures made of PMMA or acetal was reflected by a marked increase in chewing efficiency and occlusal force. None of these parameters changed significantly with the time of denture wear. Moreover, no significant correlation was found between chewing efficiency and occlusal forces. Conclusions: Denture base material exerts significant effects on the degree of food fragmentation and the level of occlusal forces. The use of dentures and clasps made of materials with lower modulus of elasticity is associated with lower chewing efficiency and lower occlusal forces.

Occlusal load transfer in full-contour ceramic implant fixed denture

Żmudzki J., Chladek G., Krawczyk C.

Archives of Materials Science and Engineering

2015

Vol. 72, nr 2

61--68

Purpose: Many clinicians use dentures with metallic core due to fears of insufficient strength of ceramic bridges. The aim of work was finite element strength analysis of fullcontour ceramic implant supported denture in lateral region. Design/methodology/approach: Finite element analysis (Solidworks) of occlusal load transfer in all-ceramic implant supported denture for missing second premolar, first molar and second molar teeth was made. Bridgework from zirconia was supported on two implants 4x12 mm (diameter x length) placed in bone with good quality and quantity. Model was loaded with lateral maximal occlusal force of 800 N. Findings: In the bridgework in the connector with premolar tooth Huber-Mises stress reached 375 MPa. Stress in implants was about 1000 MPa and small plastic deformation zones can occur close to the implant edge under pressure of abutment. Stress in abutment screw reached about 800 MPa in the first thread root and up to 400 MPa in the shank. Stress in bone tissues around implant neck and slightly lower of the beginning of the thread exceeded 140 MPa. Research limitations/implications: Linear isotropic behavior of materials and tied contact between components were assumed in the model. Practical implications: Detrimental effect of maximal occlusal force on the osseointegration between implant and bone showed that patients must be warned against loading of the denture over normal mastication. Stress in the abutment screw reached dangerous value and specific design to prevent fatigue failure is required. Originality/value: An impact of torsion and oblique bending are rarely considered in investigations. This result is relevant for the design of bridgeworks and graded materials for ceramic restoration.