Stress Distribution Pattern in Mini Dental Implant-Assisted RPD with Different Clasp Designs: 3D Finite Element Analysis

Evaluation of the biomechanics of Aramany class I obturators of different designs using numerical and experimental methods. Part II: Stress distribution

STATEMENT OF PROBLEM

Evidence regarding stress evaluations of removable obturators with Aramany class I defects is lacking. Whether the stress distribution on Aramany class I prostheses can be improved by modifying the currently used designs is also unclear.

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.

Evaluation of the biomechanics of Aramany class I obturators of different designs using numerical and experimental methods. Part I: Retention and associated stress

STATEMENT OF PROBLEM

Studies on the biomechanics of obturators in the currently used designs of Aramany class I defect are lacking. Also, modifications of the designs presently used in unilateral palatal defects are needed to produce a prosthesis with more retention and less stress on the abutments.

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.

Implant-assisted removable partial dentures: Part I. a scoping review of clinical applications

PURPOSE

This scoping review aimed to systematically map research regarding implant-assisted removable partial dentures (IARPDs), and identify existing gaps in knowledge.

STUDY SELECTION

Two reviewers independently conducted a search of the MEDLINE-PubMed and Scopus databases according to the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) extension for Scoping Review and included articles published in English up to August 31, 2022, including human studies, reviews, and in vitro studies. Expert opinions, animal studies, and clinical studies involving complete overdentures were excluded, and ten aspects for establishing the treatment strategy for IARPDs were examined.

RESULTS

One hundred and twelve articles were chosen. There were two treatment modalities: IARPDs retained by implant- and tooth-supported surveyed single crowns (SCs) or fixed partial dentures (FPDs). In IARPDs retained by tooth-supported surveyed SCs or FPDs, the survival rate of dental implants for IARPDs was relatively higher with a wide range of marginal bone loss and many complications, but with improved functional performance, oral health-related quality of life, and patient satisfaction. There were limited data on survival or success rates and designs of IARPDs, attachment selections, length and diameter, inclination, placement sites, and loading protocols of implants, regardless of prosthetic types. There was limited information on maxillary IARPDs except for survival rates of implants.

CONCLUSIONS

Although IARPDs could become a useful treatment strategy, there is limited scientific consensus with gaps in knowledge about their use. Additional well-designed clinical and in vitro studies are necessary to scientifically establish IARPDs as definitive prostheses in implant dentistry.

Finite Element Analysis: Connector Designs and Pontic Stress Distribution of Fixed Partial Denture Implant-Supported Metal Framework

This virtual study was designed to evaluate the stress-deformation of a metal fixed partial dentures (FPDs) pontic under different loads using two different connectors. The STL file was generated for a RPD of two implant-supported restorations. The Co-Cr metal substructure was designed with two types of connector design. The pontic is connected to implant-supported crowns with square and round shape connectors. This study was designed for a cementless-retained implant-supported FPD. Finite element modeling (FEM) is used to assess the stress and deformation of the pontic within a metal substructure as the FEM might provide virtual values that could have laboratory and clinical relevance. The Co-Cr alloy mechanical properties like the Poisson ratio and modulus of elasticity were based on the parameters of the three-dimensional structure additive method. Nonparametric analyses (Mann-Whitney U test) was used. The use of square or round connectors often resulted in non-significant changes in stress, and deformation under either three or each loaded point on the occlusal surface of a pontic (P > 0.05). However, the deformation revealed distinct variations between loads of the three points compared to each loaded point (P ≤ 0.05). According to this study data, the pontic occlusal surface appears to be the same in stress and deformation under different loads depending on whether square or round connectors are used. While at the same connector designs, the pontic occlusal surface deformed significantly at three loaded points than it did at each point.

Mini-Implants Retaining Removable Partial Dentures in Subjects without Posterior Teeth: A 5-Year Prospective Study Comparing the Maxilla and the Mandible

Background and objectives: Long-term studies of clinical outcomes of mini-implants (MDIs) in the first premolar/canine sites retaining a bilateral free-ending removable partial dentures (RPD) in Kennedy class I subjects have not been well documented. The aim was to assess clinical outcomes in a prospective 5-year cohort study comparing the mandible and maxilla. Material and Methods: Participants (n = 92) who received two MDIs each and a new RPD were reviewed after one, three and five years. A total of 71 participants (82 mini-implants in the mandible; 58 in the maxilla) completed the study. Marginal bone level change, success, survival rates, Modified Plaque (MPI) and Bleeding Indices (MBI) were assessed. Results: The five-year success rate was 93.3% and 93.4% (p > 0.05), in the mandible and the maxilla, respectively. Mean peri-implant bone loss (MBL) increased significantly over five years (p < 0.01) to 0.50 mm in the mandible and 0.52 mm in the maxilla. Age had a significant effect on the MBL (higher rates in younger participants), while jaw of insertion, gender, and antagonistic jaw status did not. MPI and MBI were not significantly correlated with MBL. Conclusions: The insertion of two MDIs in previous first premolar/canine sites for retention of a free-end saddle RPD can be a successful treatment modality in subjects with narrow alveolar ridges.

Effect of Number and Location on Stress Distribution of Mini Dental Implant-Assisted Mandibular Kennedy Class I Removable Partial Denture: Three-Dimensional Finite Element Analysis

Purpose. To investigate effects of number and location on patterns of von Mises stress distribution and volume average stress on abutment tooth, edentulous ridge, mini dental implant, and surrounding bone of mini dental implant-assisted mandibular Kennedy class I removable partial denture. Materials and Methods. Eight three-dimensional finite element models of mandibular Kennedy class I with different numbers and locations of mini dental implants were constructed. Mini dental implants were generated in the area of second premolar, first molar, and second molar, respectively. A static load of 400 N was applied on all models. The von Mises stress and volumetric average stress were calculated by three-dimensional finite element analysis. Result. The minimum volumetric average stress of abutment tooth was found in the model, where there was one mini dental implant at the second molar position and 2 mini dental implants at first molar and second molar positions. The model with three mini dental implants had reduced volumetric average stress of abutment tooth, which was not different from the model with two mini dental implants. However, the minimum volumetric average stress of mini dental implant and surrounding bone were found when three mini dental implants were applied, followed by two and one mini dental implants, respectively. Conclusion. Placing at least one mini dental implant at a second molar position can help reduce stress transferred to the abutment tooth. Stresses around each implant and surrounding bone reduced with increased numbers of mini dental implants.