In the present study, the implants were positioned in the crestal bone level, by following Bornstein et al. [34, 35] which reported that the implants are often inserted within the bone crest. Tomasi et al. [36] in a clinical trial observed that the implant position conditioned the amount of buccal crest resorption. Moreover, the thickness of the buccal bone plate and the tridimensional positioning of the implant must be considered because these are important factors that influence the response of hard tissues during healing. In this sense, each animal was performed a surgical guide, based in the previous natural teeth, to position the implants in all groups and conditions in the same place because mainly in the site with the presence of alveolus post-extraction, this condition induces the error of the ideal position during the implant osteotomy.

In relation to the non-submerged implants, it has become a widely reported practice with success rates ranging from 82.9 to 95.7% [37,38,39]. Theoretically, submerged implant during the osseointegration period are less susceptible to complications; however, some studies comparing submerged implants and non-submerged showed no difference in the implant failure rate, postoperative infection, and marginal bone loss [40]. In the present study, the two groups with non-submerged implants compared between them (groups 1 vs 2 and, groups 3 vs 4), the bone height was smaller, which is likely related to the presence of micromovements generated during mastication during the initial period of osseointegration [41].

Today, implants with expanded platform have demonstrated better crestal bone preservation. Then, in this study, it was carried out by the insertion of implants with an expanded platform and a surface characterized for presenting light roughness in the upper part of the neck, different parts of the body, and apical portion where showed a highly roughness. Previous studies had established that the use of implants with a rough surface may influence the amount of bone regeneration and the values of BIC during healing [9, 20, 42]. Different studies have assessed that implants presenting a rough surface may influence the degree of bone regeneration and the percentages of BIC during healing [9, 43, 44]. Calvo-Guirado et al. [31, 45] concluded that the surface treatment can reduce the crestal bone resorption. Cooper [46] found that an increased surface roughness improves bone integration of the implant, increases osteoconduction, and increases osteogenesis.