PURPOSE: The purpose of part I of this study was to differentiate among Aramany class I obturators of 4 designs regarding retention and associated stress using numerical and experimental methods.
MATERIAL AND METHODS: Four finite element models and 36 different base obturators were fabricated and divided into 9 acrylic resin bases retained with Adams clasps and 9 linear, 9 tripodal, and 9 fully tripodal design obturators from casts obtained from a scanned skull. After modification, the prostheses were fabricated on the casts obtained from a 3-dimensionally printed cast. The retention was evaluated, and the data were collected and analyzed using a statistical software program (α=.05). The displacement and associated stress in the assorted casts were compared by using 5-N displacing force at 3 points using finite element analysis. The quantitative assessment was made by measuring the displacement and von Mises stress distribution on the prostheses and their supporting structures. The qualitative analysis was done by using a visual color mapping to depict stress location and intensity.
RESULTS: No significant differences were found between fully tripodal (4.478 ±2.303 MPa) and tripodal obturators (4.478 ±2.286 MPa; P=.153), although fully tripodal showed more resistance to anterior displacement (4.522 ±0.979 and 3.553 ±1.58 MPa for fully tripodal and tripodal designs, respectively; P=.007), and tripodal obturators produced more resistance to middle displacement (5.441 ±1.778 and 2.784 ±0.432 MPa for tripodal and fully tripodal design respectively; P=.001). The fully tripodal obturator showed more retention (3.736 ±1.182 MPa) than the linear one (2.493 ±1.052 MPa; P=.001). The maxillary central incisor was the most stressed abutment, followed by the lateral incisor, while the second molar was the least.
CONCLUSIONS: Regarding retention, the fully tripodal obturator produces retention comparable with the tripodal and significantly more than the linear. Acrylic resin prostheses retained with Adams clasps may be similar to metal-based prostheses regarding retention and stress distribution on the supporting structures.
PURPOSE: The purpose of part II of this study was to evaluate the stress distribution in different designs of Aramany class I obturators using finite element analysis (FEA) and photoelastic stress analysis.
MATERIAL AND METHODS: Four finite element and 8 photoelastic models, including 2 acrylic resin base obturators retained with 2 Adams clasps, 2 linear, 2 tripodal, and 2 fully tripodal design obturators, were used in this study. The frameworks were fabricated on the casts obtained from a modified printed model. Vertical and oblique loads were applied on 2 points (anterior and posterior) of the models. The quantitative measurement was done by measuring the fringe orders and von Mises values to compare the influences of occlusal forces on the obturator components and their supporting structures. The qualitative evaluation was done by visual color mapping to identify the stress concentration.
RESULTS: In the photoelastic analysis, the anterior abutments of the tripodal showed the highest stress, followed by the fully tripodal obturators, while, in FEA, the anterior abutments of the linear design received the most in both vertical and oblique load. The central incisor received the most stress in photoelastic (3 or more fringe orders) and FEA (687.3 and 150.1 MPa for vertical and oblique loads, respectively), followed by the lateral incisors. Upon posterior loading, the base of the defect of the linear design demonstrated the most stress in photoelastic (3 or more fringes) and FEA (94.3 and 130.5 MPa for vertical and oblique loads, respectively). The acrylic resin base obturator retained with Adams clasps demonstrated the lowest stress distribution in abutments and their supporting bone upon anterior and posterior loads.
CONCLUSIONS: Upon vertical and oblique load application, the fully tripodal design was comparable with the tripodal in terms of stress distribution. Both designs were better than the linear in response to the same loading. The stress was concentrated at the anterior palatal part of the obturator, the base of the defect, and the junction of the metal and acrylic resin part of the prostheses upon anterior and posterior loading, respectively.