Within the limits of the data from this study, it can be suggested that immediate placement and restoration of a single implant can be a valid and successful option of treatment in the case of single compromised teeth. Moreover, this treatment protocol eliminates the need for removable provisional restoration and seems to maintain the preexisting architecture of soft and hard tissues in most cases. Nonetheless, further prospective and long-term studies are required to obtain a better insight into the limitations of this protocol.

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M etal-free materials compared with metal-ceramic or other conventional all-metal materials for prosthodontic restorations Patient or population: adults (18 years of age or older) with prosthodontic restorations Settings: prim ary or secondary care Intervention: m etal-f ree m aterials Comparison: m etal-ceram ic or other conventional all-m etal m aterials This review is m ade up alm ost entirely of single-study com parisons of very sm all studies. For each com parison, the evidence f or the prim ary outcom es 'f ailure of the prosthesis', 'com plications' and 'aesthetic evaluation' at all tim es of assessm ent was rated as being very low quality. All bodies of evidence were downgraded by 1 level f or risk of bias and by 2 levels f or im precision (due to single-study com parisons with either very sm all sam ple sizes, low event rates, 95% CIs including the possibility of benef it f or both the test and control groups, or com binations of these problem s) This review has included studies assessing the f ollowing com parisons 1) M etal-f ree single crowns com pared to conventional crowns 2) M etal-f ree FDPs com pared to m etal-ceram ic FDPs 3) M etal-f ree cantilevered FDPs com pared to m etal-ceram ic cantilevered FDPs 4) M etal-f ree im plant-supported single crowns com pared to m etal-ceram ic im plant-supported single crowns 5) M etal-f ree abutm ents com pared to m etal abutm ents supporting single crowns 6) M etal-f ree im plant-supported FDPs m ade of dif f erent m aterials 7) M etal-f ree tooth-supported FDPs m ade of dif f erent m aterials CI: conf idence interval; FDPs: f ixed dental prostheses. GRADE Working Group grades of evidence High quality: f urther research is very unlikely to change our conf idence in the estim ate of ef f ect M oderate quality: f urther research is likely to have an im portant im pact on our conf idence in the estim ate of ef f ect and m ay change the estim ate Low quality: f urther research is very likely to have an im portant im pact on our conf idence in the estim ate of ef f ect and is likely to change the estim ate Very low quality: we are very uncertain about the estim ate B A C K G R O U N D Description of the condition Missing or severely damaged teeth may result in a functional and aesthetic deficit and have traditionally been replaced with fixed prosthodontic treatment (crowns or bridges). 4 Metal-free materials for fixed prosthodontic restorations (Review)

slower migration rate of osteogenic cells to the bone defect [2,3]. The underlying concept of GBR was first introduced more than 50 years ago, when cellulose acetate membranes were tested in the orthopedic field, for radial bone regeneration, rib and femoral bone defects [4,5]. Later, a series of animal studies provided evidence to show GBR concept can predictably facilitate healing of critical-sized bone defects or atrophic alveolar ridges prior to implant insertion [6,7]. Melchers hypothesis of selected cell repopulation formed the basis of the biological principle of guided tissue regeneration (GTR) [8]. These concept further evolved to a more compartmentalized principle of guided bone regeneration (GBR) developed by Nyman, Lindhe, Karring and Gottlow in the 1980s [2,3,9,10]. This introduced the importance of suitable environment for osteogenesis by excluding ephitelial and connective tissue cells from bone defects during the healing phase of the periodontal regeneration, faciliting the colonization of ligament cells, to form new connective tissue and alveolar bone.These concepts were later applied to bone regeneration and experimental studies [11] demonstrated that membrane can predictably faciltate bone regeneration by enhancing angiogenesis and osteoprogenitor cells proliferation. In the 1990s, thanks to many clinical trials [12][13][14][15], principles of GBR were applied to the atrophic jaws. Biological Bases of Guided Bone Regeneration (GBR)Bone regeneration with membranes focused on three main biological principles: 1. Cell occlusiveness 2. Wound stabilization 3. Space making and maintenance. Cell occlusivinessA physical barrier is necessary to prevent the proliferation of competing soft tissue cells from the mucosa into the defects.