Influence of Implant Angulation With Different Crowns on Stress Distribution Eduardo Piza Pellizzer, DDS, MSc, PhD,* Rosse Mary Falco ´n-Antenucci, DDS, MSc, Paulo Se ´rgio Perri de Carvalho, DDS, MSc, PhD,Þ Daniela Mayumi Inatomi Kavano Sa ´nchez, DDS, Gabriel Augusto Tozo Rinaldi, DDS, Carolina Calles de Aguirre, DDS, and Marcelo Coelho Goiato, DDS, MSc, PhD* Abstract: The aim of this study was to perform a photoelastic analysis of stress distribution on straight and angulated implants with different crowns (screwed and cemented). Three models were made of photoelastic resin PL-2: model 1: external hexagon im- plant 3.75 Â 10.00 mm at 0 degrees; model 2: external hexagon im- plant 3.75 Â 10.00 mm at 17 degrees; model 3: external hexagon implant 3.75 Â 10.00 mm at 30 degrees. Axial and oblique (45 degrees) load (100 N) was applied with a universal testing machine. The pho- toelastic fringes on the models were recorded with a digital camera and visualized in a graphic software for qualitative analysis. The axial loading generated the same pattern of stress distribution. The highest stresses were concentrated between medium and apical thirds. The oblique loading generated a similar pattern of stress distribution in the models with similar implant angulation; the highest stress was located on the cervical region opposite to implant angulation and on the api- cal third. It was concluded that the higher the implant angulation, the higher the stress value, independent of crown type. The screwed pros- theses exhibited the highest stress concentration. The oblique load generated higher stress value and concentration than the axial load. Key Words: Dental implant, implant angulation, cement retention, screw retention, photoelasticity, biomechanics (J Craniofac Surg 2011;22: 434Y437) I n general, the implants are inserted with an ideal angulation for prosthetic rehabilitation. However, in some cases, the anatomy and morphology of residual ridge may dictate an undesirable implant an- gulation for prosthetic restoration. 1,2 Considering that the mesiodistal angulation of implants is an aesthetic and technical complication, angulated abutments are presented as a clinical solution 1 to overcome anatomic limitations. 3,4 The abutment angulation is a mechanical variable in implantology 5 that may influence the internal and external structure of bone tissue. 6 So, the bone behavior is related to the stress and deformation applied on it. 1 The maximum angulation between implants using regular abutments is 30 to 40 degrees according to the design of settlement surfaces. 3 The angulated abutment is available with 15 and 25 degrees of angulation for cemented segmented prostheses and with 17, 25, 30, and 35 degrees for screwed segmented prostheses. 7 The treatment planning for implant-supported fixed prosthe- sis should present the retention screw access hole in the occlusal surface of posterior teeth or in the cingulum region of anterior teeth. 3 The implant-supported fixed prosthesis may be segmented or non- segmented. 8 The nonsegmented prosthesis is a 2-piece structure with implant and crown (UCLA-type abutments), whereas the segmented prosthesis includes 3 components (implant, abutment, and crown). In addition, the segmented prosthesis can be screw-retained, with the prosthesis attached to the abutment by a titanium or gold screw; or cemented, with the prosthesis fixed to the abutment using cement. Clelland and colleagues 1,9 evaluated the stress distribution on angulated abutments through photoelasticity, strain gauges, and clinical studies. The authors determined that stress in peri-implant region increased with abutment angulation with stress concentra- tion surrounding the abutment. Similar results were found by Brosh and colleagues, 10 comparing straight and angulated abutments through photoelasticity and strain gauges. A finite element analysis performed by Kao and colleagues 11 demonstrated that an abutment angulation superior to 25 degrees increases stress in 18% and micromovement in 30%. However, prospective and clinical studies 12,13 including clin- ical, periodontal, and radiographic evaluations of straight and angu- lated abutments in maxilla and mandible demonstrated no difference between the abutments regarding function, aesthetics, and long-term implant success. Considering the lack of information on biomechanical be- havior of angulated implants restored with different crowns, the aim of this study was to perform a photoelastic analysis of stress dis- tribution on straight (0 degrees) and angulated (17 and 30 degrees) implants with different crowns (screwed and cemented). MATERIALS AND METHODS A wax matrix simulating a hemimandible was used to fabri- cate a silicone mould (Sapeca artesanato, Bauru, Sa ˜o Paulo, Brazil) poured with dental stone type IV (Durone; Dentsply, Petro ´ polis, Rio de Janeiro, Brazil) to obtain 3 models. Implant analogs were inserted in the models corresponding to a premolar using a dental surveyor and an angulated silicone matrix (17 and 30 degrees). After dupli- cation of these models, other model was fabricated with implants (Conexa ˜o Sistemas de Pro ´tese, Sa ˜o Paulo, Brazil) inserted with dif- ferent angulations and filled with photoelastic resin (PL-2; Vishay ORIGINAL ARTICLE 434 The Journal of Craniofacial Surgery & Volume 22, Number 2, March 2011 From the Departments of *Dental Materials and Prosthodontics and †Sur- gery, Ara0atuba School of Dentistry, Sa ˜o Paulo State UniversityYUNESP, Sa ˜o Paulo, Brazil. Received March 25, 2010. Accepted for publication July 4, 2010. Address correspondence and reprint requests to Eduardo Piza Pellizzer, DDS, MSc, PhD, Rua Jose ´ Bonifa ´cio 1193-Vila Mendon0a, Postal Code 16015-050, Ara0atuba, Sa ˜o Paulo, Brazil; E-mail: ed.pl@uol.com.br Dr. Falco ´n-Antenucci is a postgraduate student and Drs. Sa ´nchez, Rinaldi, and de Aguirre are students at Ara0atuba School of Dentistry, Sa ˜o Paulo State UniversityYUNESP, Brazil. The authors report no conflicts of interest. Copyright * 2011 by Mutaz B. Habal, MD ISSN: 1049-2275 DOI: 10.1097/SCS.0b013e318207477c Copyright © 2011 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.