Vibration analysis of maxillary removable partial denture frameworks

Structural stability of posterior retainer design for resin-bonded prostheses: a 3D finite element study

The purpose of this in vitro study was to compare the stress distribution and natural frequency of different shape and thickness retainer designs for maxillary posterior resin-bonded prostheses using finite element (FE) method. A 3D FE model of a three unit posterior resin-bonded prosthesis analysis model was generated. Three different shaped retainer designs, viz. C-shaped (three axial surface wraparounds), D-shaped (three axial surface wraparounds with central groove) and O-shaped (360° wraparounds), and three different thicknesses, viz., 0.4, 0.8, and 1.2 mm, resin-bonded prostheses were used in this study. The resin-bonded prosthesis analysis model was imported into an FE analysis software (ANSYS 10.0, ANSYS, USA) and attribution of material properties. The nodes at the bottom surface of the roots were assigned fixed zero displacement in the three spatial dimensions. A simulated angle of 45° loading of a 100 N force was applied to the node of the pontic lingual cusp surface. The stress distributions and corresponding natural frequencies were analyzed and resolved. The C-shaped retainer for 0.4 mm thickness recorded the greatest von Mises stresses of 71.4 MPa for all three groups. C-shaped, D-shaped and O-shaped retainer presented natural frequencies 3,988, 7,754, and 10,494 Hz, respectively. D-shaped retainer and O-shaped retainer increased natural frequencies and structural rigidity over the traditional C-shaped retainer. The maximum von Mises stresses values of the remaining tooth and prosthesis decreased with greater retainer thickness. D-shaped retainer and O-shaped retainer increased natural frequencies and structural rigidity over the traditional C-shaped retainer.

In-vivo modal analysis of maxillary dentition in a maxillectomy patient wearing buccal flange obturator prostheses with different bulb height designs

PURPOSE

The purpose of this study was to apply in vivo modal analysis to the maxillary dentition of the maxillectomy patient using obturator prostheses which were different in lateral wall height of the bulb: specifically a high type (H type), middle type (M type), and low type (L type).

METHODS

The left central incisor was struck with an impact hammer, and the response at each measurement point was detected using a Laser-Doppler vibrometer. The transfer function was then obtained from each measurement point using a fast Fourier transform analyzer. Finally, a computer analysis and simulation were performed based on the measured transfer functions to obtain the natural frequency, modal shape decay rate (DR), and maximum displacement (MDP).

RESULTS

The results showed that the natural frequency was different between with and without obturator prostheses, that the modal shapes with M and L type obturator prostheses are more suitable than that with H type. The DR of the maxillary dentition with the L type was significantly higher than that with the H or M types, and the MDP of the maxillary dentition with an obturator prosthesis was significantly lower than without an obturator prosthesis.

CONCLUSION

From the standpoint of vibratory characteristics, the L type obturator prosthesis is the most suitable bulb design for the patient of the three types obturator prostheses. This is the first report to apply in-vivo modal analysis to the maxillary dentition of the maxillectomy patient using obturator prostheses and clarify the vibratory characteristics of the dentition.

The vibratory characteristics of obturators with different bulb height and form designs

The aim of the present study was to investigate whether the vibratory characteristics of obturator prostheses are affected by bulb design, i.e.: the hollow or buccal flange type, and different lateral and medial bulb heights. Buccal flange and hollow bulb obturator prostheses were fabricated with two different lateral bulb wall heights and two different medial bulb wall heights. Ultimately, eight obturator prostheses were prepared for evaluation of their vibratory characteristics. The frequency-response functions were recorded on an FFT analyzer to identify their vibratory characteristics. A transient response simulation was carried out in which an impact was applied to the non-defect side. The decay rate, damping time and maximum amplitude of the retainers were statistically analysed by anova with Scheffé's test (P < 0.05). The decay rate of every buccal flange type was higher and damping time was shorter than those of every hollow type, except between a pair with low lateral and low medial bulb walls. The maximum amplitude values of four obturators with low medial bulb walls were significantly lower than those of four obturators with high medial walls. The buccal flange obturator prosthesis with high lateral and low medial walls showed the maximum decay rate and the minimum amplitude of the retainers on molars. Vibration analysis suggests that a buccal flange obturator prosthesis with high lateral and low medial walls is preferable.