title: Finite element method analysis of stress distribution to supporting tissues in a Class IV Aramany removable partial denture (Part II: bone and mucosal membrane).
abstract: OBJECTIVE
  One of the most important issues in the design of removable partial dentures (RPD) is the location of retentive arms to provide sufficient support. This is a critical factor in patients with less supporting tissue and abutment teeth. Patients classified as Class IV Aramany need special attention in this area of RPD design to minimize the stress distribution in bone and mucosal membrane. Using the finite element method, the aim of this study was to analyze the distribution stress to supporting tissues when a Class IV Aramany RPD is worn. The data presented in this report are the effects of the stress on bone and mucosal membranes. Results on teeth and the periodontal ligament have been previously reported.
  
  
  METHODS
  Three dimensional finite element models were constructed using normal dimensions. Exact physiology and morphology of teeth and the remaining palate were simulated to that of a maxillectomy patient. Three RPD designs with circumferential cast retainers were examined: buccal retention and palatal reciprocation (P1); palatal retention and buccal reciprocation (P2); and buccal and palatal retention (P3). After completion of the models and remaining palate, each RPD design was loaded under 53N and stress was applied in three different directions: vertical to the posterior teeth (premolar and first molars) of the RPD (F1); at a 33 masculine angle to the posterior teeth (premolar and first molars) of the RPD (F2); and vertically on the anterior teeth (central incisors) of the RPD (F3). The stress distribution in the RPD models on cortical and cancellous bone and the mucosal membrane was analyzed using von Mises criterion.
  
  
  RESULTS
  The maximum tension in cortical bone (70.84 Mpa) was observed when a 53N force was applied in a vertical direction to posterior teeth (F2) using buccal and palatal retention (P3). Minimum tension (15.73 Mpa) in cortical bone was observed using the F3 load on the P2 design. Similar results were seen in cancellous bone, with the highest stress (8.01 Mpa) observed using F2 load on the P3 design and the lowest stress (3.04 Mpa) observed using the F3 load on the P2 design. For mucosal membrane, the maximum (3.57 Mpa) and minimum (3.05 Mpa) stress was observed using the F3 load on the P3 design and the F1 load on the P2 design, respectively. The average stress in all RPD designs was 3 Mpa.
  
  
  CONCLUSIONS
  The design demonstrating the least tension in cortical and cancellous bone and mucosal membrane was the P2 design, a RPD with palatal retention and buccal reciprocation.
  
  
  CONCLUSIONS
  Palatal retention and buccal reciprocation (P2 design) is recommended for patients with maxillofacial RPDs.
authors.affiliation: Department of Prosthodontics of the School of Dentistry, Dental Research Center, at Mashhad University of Medical Science in Mashhad, Khorasan Iran. dr_gharechahi@yahoo.com
authors.forename: Jafar
authors.initials: J
authors.lastname: Gharechahi
authors.forename: Esmael
authors.initials: E
authors.lastname: Sharifi
authors.forename: Saeid
authors.initials: S
authors.lastname: Nosohian
authors.forename: Nafiseh Asadzadeh
authors.initials: NA
authors.lastname: Aghdaee
mesh_terms: D000539:Alveolar Process / Q000502:physiology*; D003198:Computer Simulation; D003799:Dental Stress Analysis / Q000379:methods*; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation; D003832:Denture, Partial, Removable; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006801:Humans; D008437:Maxilla / Q000601:surgery; D009061:Mouth Mucosa / Q000502:physiology*; D019647:Oral Surgical Procedures / Q000534:rehabilitation; D010158:Palatal Obturators