Oversized Surgical Preparation of the Implant Site: Systematic Review and Meta-analysis of Preclinical Studies.

PURPOSE: To answer the following focus question: In preclinical in vivo experimental models, do oral implants placed in overdimensioned (OD) sites present greater biomechanical properties and histomorphometric parameters of osseointegration compared to implants placed in standard or undersized implant sockets? MATERIALS AND METHODS: Online databases were searched for controlled animal studies reporting on OD sites up to February 2023. The relative implant- final drill discrepancy (IDD) was used to categorize the control and test groups according to surgical drilling protocol: (1) control: undersized (IDD > 0.5 mm) or standard (IDD = 0.2 to 0.5 mm); and (2) test OD: stress-free oversized (IDD = 0.0 to -0.1 mm); test GAP: friction-free oversized (IDD ≤ -0.1 mm). Random-effects meta-analyses were performed for the outcomes of insertion and removal torque values (ITV and RTV, respectively), bone-to-implant contact (%BIC), and bone density (%BD) for short- (0 to 2 weeks), intermediate- (3 to 4 weeks), and long-term (≥ 5 weeks) healing periods. RESULTS: Of the 527 records identified, 13 studies met the eligibility criteria. Histologically, the OD and GAP groups prevented ischemic necrosis and extensive bone resorption at the bone-implant interface in both the marginal cortical layer and the trabeculae. Faster and increased rates of bone formation, characterized by primary osteons and highly vascularized tissue, took place in OD sites between 1 and 5 weeks of healing. Meta-analyses indicated statistically significant benefits in favor of (1) control vs OD for short-term healing in extraoral sites, with pooled estimates (weighted mean difference) of ITV = 25.35 Ncm, %BIC = 2.10%, and %BD = 26.19%; (2) control vs OD for long-term healing in intraoral sites, with %BD = 11.69%; (3) control vs GAP for intermediate-term healing in extraoral sites, with %BD = 3.03%; and (4) control vs GAP for long-term healing in extraoral sites, with RTV = 5.57 Ncm. CONCLUSIONS: Oversized surgical preparation of the implant site does not seem to provide any additional benefit compared to standard or undersized sites regarding quantitative parameters of osseointegration. However, it does minimize marginal bone resorption and yields better-quality bone healing, despite the comparable results among different experimental animal models in the late postoperative period.

Effect of ionizing radiation after-therapy interval on bone: histomorphometric and biomechanical characteristics.

OBJECTIVES: This study aimed to evaluate the effects of radiotherapy on biomechanical, histomorphometric, and microstructural characteristics of bone, in diverse periods, compared with intact bone tissue. MATERIALS AND METHODS: Eighteen adult male New Zealand rabbits were treated with a single radiation dose of 30 Gy. The animals were randomly divided into six groups: NoIr, control group, no radiation, and five irradiated groups sacrificed after 24 h (Ir24h), 7 (Ir7d), 14 (Ir14d), 21 (Ir21d), and 28 (Ir28d) days. After these periods, the animals were sacrificed and their tibias (n = 6) evaluated using three-point bending test to calculate the ultimate force, work to failure, and bone stiffness. Dynamic indentation test was used to quantify Vickers hardness and elasticity modulus of bone tissue. Micro-CT was used to analyze the cortical volume (CtV), cortical thickness (CtTh), and porosity (Ct.Po). Histomorphometric assessment was based on the lacunarity of bone tissue. Data were analyzed using one-way ANOVA and Kruskal-Wallis tests followed by Tukey, Dunnet, and Dunn's post-tests (P < 0.05). RESULTS: The ultimate force, work to failure, stiffness, elastic modulus, and Vickers hardness values of irradiated bone were significantly lower that non-irradiated bone. Irradiated bone showed significantly lower CtTh and CtV values and higher CtPo than non-irradiated bone. No significant difference was found for lacunarity between non-irradiated bone and irradiated bone. CONCLUSIONS: Ionizing radiation decreases normal anisotropy on microarchitecture of cortical bone, and increases bone fragility compared with non-irradiated bone. Further, these changes were seen after longer periods (e.g., 14 and 21 days), and not immediately after radiation therapy. CLINICAL RELEVANCE: The radiotherapy reduces bone mechanical properties and the normal structure of organic and inorganic bone matrix. For studying the protocols to protect the radiotherapy effect using rabbit model, the use of the sacrificing period between 14 and 21 days is recommended.

Interfacial biomechanical properties of a dual acid-etched versus a chemically modified hydrophilic dual acid-etched implant surface: an experimental study in Beagles.

BACKGROUND: The high survival clinical success rates of osseointegration are requisites for establishing a long-term biomechanical fixation and load-bearing potential of endosseous oral implants. The objective of this preclinical animal study was to evaluate the effect of surface microtopography and chemistry on the early stages of biomechanical rigidity with a sandblasted, dual acid-etched surface, with or without an additional chemical modification (SAE-HD and SAE, respectively), in the tibia of Beagle dogs. METHODS: Two pairs of implants, with the same macrogeometry but different surface technology ((a) dual acid-etched surface treatment with hydrochloric and sulfuric acid followed by microwave treatment and insertion in isotonic saline solution to increase hydrophilicity (SAE-HD) (test, n = 12) and (b) dual acid-etched surface (SAE) (control, n = 12)), were installed bilaterally in the proximal tibia of six Beagle dogs. In order to determine the effect of surface modification on biomechanical fixation, a test protocol was established to assess the torque and a complete set of intrinsic properties. Maximum removal torque (in N cm) was the primary outcome measure, while connection stiffness (N cm/rad) and removal energy (× 10-2J) were the secondary outcome measures and were assessed after 2 and 4 weeks in vivo. A general linear statistical model was used and performed for significant differences with the one-way ANOVA followed by Tukey post hoc test (P < 0.05). RESULTS: The removal torque values did not reveal significant statistical differences between SAE-HD and SAE implants at any observation times (P = 0.06). Although a slight increase over time could be observed in both test and control groups. SAE-HD showed higher removal energy at 4 weeks (999.35 ± 924.94 × 10- 2 J) compared to that at 2 weeks (421.94 ± 450.58 × 10- 2 J), while SAE displayed lower values at the respective healing periods (P = 0.16). Regarding connection stiffness, there were no significant statistical differences neither within the groups nor over time. There was a strong, positive monotonic correlation between removal torque and removal energy (=0.722, n = 19, P < 0.001). CONCLUSIONS: In this study, no significant differences were observed between the specific hydrophilic (SAE-HD) and hydrophobic (SAE) surfaces evaluated, in terms of biomechanical properties during the early osseointegration period.

Histomorphometric evaluation of a dual acid-etched vs. a chemically modified hydrophilic dual acid-etched implant surface. An experimental study in dogs.

OBJECTIVE: The aim of this preclinical in vivo study was to compare histologically and histomorphometrically osseointegration of dual acid-etched vs. hydrophilic implants. MATERIAL AND METHODS: Two pairs of implants (Neodent, Curitiba, Brazil), with same macrogeometry but different surface technology (i) dual acid-etched surface (SAE) treatment with hydrochloric and sulfuric acid followed by microwave treatment and insertion in isotonic saline solution to increase hydrophilicity (SAE-HD) (test, n = 12); (ii) dual SAE (control, n = 12) were installed bilaterally in the proximal tibia of six beagle dogs. Histologic and histomorphometric evaluation was performed after 2 and 4 weeks in vivo, on non-decalcified sections. Percentages of bone-to-implant contact (BIC) and bone density (BD) were estimated and tested for significant differences with the Wilcoxon signed-rank test for paired samples (P < 0.05). RESULTS: In general, new bone formation along and in contact with the implant surface could be observed irrespective of the experimental group and observation period. Most of the bone was woven but small quantities of lamellar bone, mainly in close proximity to the cortex could also be observed. BIC at 2 weeks was 19.57 ± 13.57 and 20.33 ± 7.99 (P = 0.75), and at 4 weeks was 42.80 ± 14.48 and 40.25 ± 9.45 (P = 0.65) for SAE-HD and SAE implants respectively. BD at 2 weeks was 24.85 ± 16.31 and 25.66 ± 8.59 (P = 0.35) and at 4 weeks 44.13 ± 6.46 and 40.13 ± 6.46 (P = 0.25) for SAE-HD and SAE implants respectively. CONCLUSION: Bone-to-implant contact and BD increased with time in both SAE-HD and SAE implants. No significant differences were observed between the two different implant surfaces for any of the evaluated parameters and at any observation time-point.