<jats:title>Abstract</jats:title><jats:sec><jats:title>Objectives</jats:title><jats:p>The main objective of the study was to compare the dimensional ridge changes and the histological composition after the use of an allograft or xenograft and a resorbable membrane in ridge preservation in molar sites and to evaluate the influence of bone plate thickness on dimensional changes and the need of lateral sinus augmentation following ridge preservation.</jats:p></jats:sec><jats:sec><jats:title>Materials and methods</jats:title><jats:p>Twenty‐four patients in need of maxillary or mandibular first or second molar extraction and subsequent implant placement were included and randomly assigned to a group; allograft or xenograft, plus a collagen membrane. Cone‐beam computed tomographies were obtained after molar extraction and after 5 months. A bone sample was harvested at the time of implant placement and analyzed by histomorphometry.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Bone ridge was reduced significantly. Major changes in width occurred at 1 mm from the bone crest (−2.93 ± 2.28 mm) (<jats:italic>p </jats:italic>= .0002), while in height, the greatest reduction occurred at the buccal area (−1.97 ± 2.21 mm) (<jats:italic>p </jats:italic>= .0006). However, differences between groups were not significant. Thicker buccal bone plates exhibited less bone remodeling, while histologically, both biomaterials resulted in similar tissue composition. The resulting available bone height in the implant site measured 7.30 ± 3.53 mm initially and 6.8 ± 3.61 mm after 5 months which allowed implant placement without the need for lateral sinus augmentation in all cases. Still, 55% of the preserved areas needed transcrestal sinus lift.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>Ridge preservation in molar sites using a mineralized allograft or xenograft provides similar dimensional and histomorphometrical results after 5 months.</jats:p></jats:sec>