AbstractAim: To assess dimensional ridge alterations following immediate implant placement in molar extraction sites.Material and methods: Twelve subjects received 12 immediate transmucosal implants in molar extraction sites. Peri‐implant defects were treated according to the principles of Guided Bone Regeneration by means of a deproteinized bone substitute and a bioresorbable collagen membrane. Changes in vertical (IS‐BD, CREST‐BD) and horizontal distances (EC‐I, IC‐I) of alveolar bony walls to the bottom of the defects (BD) and to the implant surfaces (I) were compared between implant placement and surgical re‐entry at 6 months.Results: The implant survival rate at 6 months was 100%. Statistically significant differences (P<0.01) were observed in the mean changes in vertical distances IS‐BD and CREST‐BD between baseline and re‐entry. At re‐entry, all peri‐implant marginal defects assessed from the internal socket wall to the implant surface (IC‐I) were healed. The residual combined thickness of the buccal wall with the newly formed peri‐implant bone at sites with an initial thickness of 1 mm was statistically significantly smaller (P<0.05) compared with that of sites with an initial buccal thickness of 2 mm (2.50 ± 0.76 vs. 4±0 mm).Conclusions: The marginal defects around immediate implants placed in molar extraction sites were completely filled after 6 months of healing through de novo bone formation. Bone resorption was observed from the external aspects of the buccal and oral socket walls. Dimensional changes of the external socket walls were mostly pronounced at the buccal aspects.