PURPOSE: To compile the current evidence on biomechanical, biologic, and clinical outcomes of undersized surgical preparation protocols in dental implant surgery. MATERIALS AND METHODS: An electronic search using three different databases (PubMed, Web of Science, and Cochrane Library) and a manual hand search were performed including in vitro, animal, and clinical studies published prior to October 2015. Studies in which an undersized drilling protocol was compared with a nonundersized drilling protocol were included. RESULTS: From an initial selection of 1,655 titles, 29 studies met the inclusion criteria, including 14 biomechanical, 7 biologic, 6 biologic and biomechanical, and 2 clinical. Due to methodologic variation, meta-analysis was not performed. Several studies showed that implants inserted with an undersized drilling approach reached a significantly higher insertion torque value than conventional drilling in low-density substrates, while this effect is less evident if a thick cortical layer is present. Similar results in terms of boneto-implant contact (BIC) were achieved in the longer term between implants inserted with undersized and nonundersized protocols. Results in the short term were inconclusive. Clinical studies did not show negative outcomes for undersized drilling, although clinical evidence was sparse. No data are available on marginal bone loss. CONCLUSION: From the biomechanical standpoint, an undersized drilling protocol is effective in increasing insertion torque in low-density bone. Biologic response in long-term healing after undersized implant placement is comparable to that in the nonundersized surgical drilling protocol. Clinical studies indicate that performing an undersized drilling protocol on low-density bone is a safe procedure; however, more extensive studies are needed to confirm these data.

Purpose: To evaluate insertion torque value ( ITV) and marginal bone loss (MBL) of an implant system after a clinically perceived bone quality-adapted drilling. Materials and Methods: This multicenter retrospective study included patients treated with implants, conventionally loaded, in completely healed sites. Operators customized the osteotomy preparation according to radiographic assessment and their perception of bone quality. Drilling sequence, bone quality, and ITV were recorded at the time of surgery. Radiographs were taken at the time of implant placement and permanent restoration. MBL between implant placement and permanent restoration was calculated. The implant was used as the statistical unit. Demographic and implant characteristics were shown by means of descriptive statistics. Outcome values were compared using analysis of variance (ANOVA) and Kruskal-Wallis tests. Multiple regression models were used to test the effect of independent variables on ITV and MBL. Results: One hundred eighty-eight implants placed in 87 patients were included in the analysis. The mean observation period was 144 +/- 59 days. The mean ITV was 30.8 +/- 15.1 Ncm. ITV differed significantly based on arches (mandible/maxilla) (P = .001), bone quality (P < .001), implant diameter (P = .032), and drilling protocol (P = .019). Median MBL was 0.05 mm (0.00; 0.24). A significant difference was found between the mandible and maxilla (P = .008) and between drilling protocols (P = .011). In particular, significantly higher MBL was found in the undersized drilling protocol. Multiple regression analysis showed that ITV was influenced by bone quality and implant diameter. MBL was influenced by bone quality, implant diameter, ITV, and the interaction between bone quality and ITV. It was estimated that MBL was greater with increased bone density and ITV. Conclusion: Excessive ITV in dense bone can cause negative marginal bone responses. A presurgical radiographic assessment and the perception of bone quality are necessary to select an optimal drilling protocol and to minimize surgical trauma.

ObjectiveThe aim of this study was to investigate the extent of cortical bone remodeling between two different drilling protocols by means of histomorphometric, mu-CT, and biomechanical analyses. Material and methodsA total of 48 implants were inserted into the mandible of six sheep following two drilling protocols: Group A (Test, n=24), undersized preparation; Group B (Control, n=24), non-undersized preparation. The animals were euthanatized to obtain 5 and 10weeks of implantation time. Removal torque (RTQ) was measured on 12 implants of each group and the peri-implant bone was mu-CT scanned. Bone volume density (BV/TV) was calculated in pre-determined cylindrical volumes, up to 1.5mm from implant surface. Non-decalcified histology was prepared on the remaining 12 implants from each group, where total bone-to-implant contact (totBIC) and newly-formed BIC (newBIC) was measured. Bone Area Fraction Occupancy (BAFO) was determined in pre-determined areas up to 1.5mm from implant surface. Paired sample t test or Wilcoxon signed-rank test was used to investigate differences between the groups. ResultsGroup A presented significantly increased RTQ value at 5weeks, while no difference was observed at 10weeks. Group B presented increased BV/TV value at 5weeks. Both groups showed comparable values for totBIC at both time-points. However, Group A presented significantly lower newBIC at 5weeks. Higher BAFO was observed in Group B at 5weeks. ConclusionsImplants inserted into undersized sites has an increased biomechanical performance, but provoked major remodeling of the cortical bone during the early healing period compared to non-undersized preparations. After 10weeks, no difference was observed.

PURPOSE: The aim of this multi-scale in silico study was to evaluate the influence of resorption cavities on the mechanical properties and load distribution in cortical bone after implant placement with two different drilling protocols.

MATERIAL AND METHODS: Two different micro-scale bone structures were assessed: cortical bone models with cavities (test) and without cavities (control) were designed from μCT data. In a macro-scale model, representing a mandibular ridge, oblique load of 150 N was applied on the implant-abutment. Maximum principal stress/strain, and shear stress/strain were calculated in the macro- and micro-scale models.

RESULTS: Test presented anisotropic material properties. In tests, significantly greater maximum values of Maximum principal stress/strain were calculated in micro-scale model. These values were located at the implant neck area in the macro-scale model and in the proximity of cavities in the micro-scale model respectively. Greater values of shear stress/strain were found in the test along the mandibular horizontal plane.

CONCLUSIONS: Cortical bone with resorption cavities following undersized drilling showed an impaired load distribution compared with bone without cavities. Subsequently, stress/strain distribution suggests that this bone model is more prone to microdamage, thus delaying the healing process.