Introduction: We aimed to compare implant osseointegration with calcium phosphate (CaP) surfaces and rough subtractive-treated sandblasted/acid etched surfaces (SA) in an in vivo minipig mandible model. Materials and Methods: A total of 36 cylindrical press-fit implants with two different surfaces (CaP, n = 18; SA, n = 18) were inserted bilaterally into the mandible of 9 adult female minipigs. After 2, 4, and 8 weeks, we analyzed the cortical bone-to-implant contact (cBIC; %) and area coverage of bone-to-implant contact within representative bone chambers (aBIC; %). Results: After 2 weeks, CaP implants showed no significant increase in cBIC and aBIC compared to SA (cBIC: mean 38 ± 5 vs. 16 ± 11%; aBIC: mean 21 ± 1 vs. 6 ± 9%). Two CaP implants failed to achieve osseointegration. After 4 weeks, no statistical difference between CaP and SA was seen for cBIC (mean 54 ± 15 vs. 43 ± 16%) and aBIC (mean 43 ± 28 vs. 32 ± 6). However, we excluded two implants in each group due to failure of osseointegration. After 8 weeks, we observed no significant intergroup differences (cBIC: 18 ± 9 vs. 18 ± 20%; aBIC: 13 ± 8 vs. 16 ± 9%). Again, three CaP implants and two SA implants had to be excluded due to failure of osseointegration. Conclusion: Due to multiple implant losses, we cannot recommend the oral mandibular minipig in vivo model for future endosseous implant research. Considering the higher rate of osseointegration failure, CaP coatings may provide an alternative to common subtractive implant surface modifications in the early phase post-insertion.