Romanian Biotechnological Letters Vol. , No. x, Copyright © 2016 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER Polyspecies biofilm formation involved in overdenture peri-implantitis Received for publication, December 10, 2015 Accepted, December 19, 2016 LIGIA MUNTIANU 1* , IOANA SUCIU 1 , CORINA CIRCEI 2 , SORIN PENTA 1 , ION VIOREL 3 ,CARMEN CURUTIU 4 , IRINA GHEORGHE 4 , ANCA MARIA RADUCANU 1 1Dentistry Faculty Carol Davila, Bucharest, Romania 2Dentistry Faculty Titu Maiorescu, Bucharest, Romania 3Smile Focus Dental Cabinet, Bucharest, Romania 4 Faculty of Biology, University of Bucharest; ICUB, University of Bucharest, Romania *Correspondent author: Ligia Muntianu, Tel 0736 476 484Email: ligia.muntianu@gmail.com Abstract This report describes the investigation of potential causal factors involved in producing or promotion of peri-implantitis in a complex case with periodontal history, mixed prosthetic rehabilitation including maxillary implant overdenture and a partially edentate mandible. Biological harvests were sent to two different laboratories for cross checking the results. The results identified the presence of a polymicrobial biofilm with a mixture of species, predominantly anaerobic Gram negative rods, but some rare components of oral microbiota, as Streptococus thoralensis were also identified. Keywords:peri-implantitis, implant overdenture, Streptococcus thoralensis 1. Introduction Prosthetic rehabilitation of partial or complete edentulous patient using implants has updated to modern the prosthodontic techniques. Implants integrate by bone growth around implant body. At gingival level, there is never achieved a perfect seal as the epithelial junction in natural tooth. Thus, microorganisms could penetrate the tissue and in time could determine gingival retraction, bone resorption, peri-implantitis and finally implant loss (MADER & al. [1]). This happens more if personal hygiene is poor as in old people or children with brackets and orthodontic mini-implants (FERREIRA& al. [2]). Peri-implantitis represents in fact a progressive and irreversible disease of hard and soft tissues that surround implant and conduct in the end to bone resorption, decreased osseointegration, increased pocket formation and purulence (SMEETS& al. [3]). Dental plaque and biofilms develop in the mouth even if all teeth are lost (LUPPENS& al. [4]). The biofilm formation is a natural process and its composition could be related by inflammation of soft and hard tissue in different conditions of mouth health state (ADELL& al. [5], ALBRECKTSON &ISIDOR [6]). Prevention of biofilm development imply identifying the pathogen microorganisms involved in soft tissue inflammation and bone resorption. We analyzed a complex clinical case with maxillary overdentures on implants and partially edentulous in the mandible with periodontal disease history. We found a mixed pathogenic microbial species as we expected according studies reported in the literature (TORTAMANOA& al. [7], DE FREITAS & al.[8]) but we also found some interesting and rare bacteria that were not usually associated to oral microbiota. 2. Experimental procedure First step: Beginning 2 months before starting the procedure of implantation, patient should not be going to have dental scaling. With 14 days before starting patient is informed