Implant Stability and Histomorphometric Analysis Comparing Two Different Implant Macrogeometries Placed in Fresh Sockets: An Experimental Study in Sheep

Purpose: To examine the impact of two implant designs that promote different insertion torque values on implant stability and to histomorphometrically evaluate the bone healing after immediate implant placement in fresh sockets in a sheep model. Materials and Methods: Twelve female sheep (mean weight: 35.0 ± 5.0 kg) were included in the study. Additionally, 48 conical Morse taper dental implants were included, comprising two groups (n = 24 per group): Group 1, where the implant design can provide high insertion torque values; and Group 2, where the implant design can provide low insertion torque values. Both had the same surface treatment and dimensions (4.0 × 10 mm). The mandibular first and second molars on both sides were extracted carefully. Sequentially, osteotomies were made in the mesial socket of each molar tooth. The final implant position was 2 mm below the buccal bone crest level. On the right side, a Group 1 implant was placed anteriorly, with a Group 2 implant in the posterior position; on the left side, the Group 2 implant was anterior and the Group 1 implant was posterior. A digital torque meter was used to measure the maximum final insertion torque value (f-IT). The initial implant stability quotient (ISQ) was measured immediately after implant insertion (T0) and immediately after the euthanasia and removing the mandibles. The animals were euthanized (n = 6 animals/ time) at 21 days (T1) and 35 days (T2). To compare statistical differences for each analyzed intragroup parameter, t-test was used. Pearson’s correlation was used to analyze possible correlations: f-IT and percentage of bone-to-implant contact (%BIC), f-IT and ISQ, and ISQ and %BIC. Results: Group 1 presented higher insertion torque values than Group 2, with a statistically significant difference (P < .0001). The ISQ mean values were higher in the buccolingual direction than those obtained in the mesiodistal direction for both groups. Higher %BIC measurements were seen in Group 2 than Group 1 samples at both times and in both directions. There were statistical differences between groups for new bone, medullary spaces, and collagen matrix at each evaluation time. Conclusions: Using implants with a modified macrogeometry plays a significant role in implant stability and bone tissue healing around the implant. It is important for clinicians to carefully consider implant macrogeometry when planning implant surgery to achieve optimal implant stability and successful osseointegration, mainly in cases of immediate implant placement.