Influence of Bone Quality, Drilling Protocol, Implant Diameter/Length on Primary Stability: An In Vitro Comparative Study on Insertion Torque and Resonance Frequency Analysis
The aim of this study was to evaluate the influence of bone quality, drilling technique, implant diameter, and implant length on insertion torque (IT) and resonance frequency analysis (RFA) of a prototype-tapered implant with knife-edge threads. The investigators hypothesized that IT would be affected by variations in bone quality and drilling protocol, whereas RFA would be less influenced by such variables. The investigators implemented an in vitro experiment in which a prototype implant was inserted with different testing conditions into rigid polyurethane foam blocks. The independent variables were: bone quality, drilling protocol, implant diameter, and implant length. Group A implants were inserted with a conventional drilling protocol, whereas Group B implants were inserted with an undersized drilling protocol. Values of IT and RFA were measured at implant installation. IT and RFA values were significantly correlated (Pearson correlation coefficient: 0.54). A multivariable analysis showed a strong model. Higher IT values were associated with drilling protocol B vs A (mean difference: 71.7 Ncm), implant length (3.6 Ncm increase per mm in length), and substrate density (0.199 Ncm increase per mg/cm3 in density). Higher RFA values were associated with drilling protocol B vs A (mean difference: 3.9), implant length (1.0 increase per mm in length), and substrate density (0.032 increase per mg/cm3 in density). Implant diameter was not associated with RFA or IT. Within the limitations of an in vitro study, the results of this study suggest that the studied implant can achieve good level of primary stability in terms of IT and RFA. A strong correlation was found between values of IT and RFA. Both parameters are influenced by the drilling protocol, implant length, and substrate density. Further studies are required to investigate the clinical response in primary stability and marginal bone response.
(a) Three-dimensional representation of the prototype implant used in the experiment. (b) Schematic outline of the prototype implant used in the experiment. The image is referred to a 5.1 × 15 mm implant. The outer profile of the apical portion is tapered (10°). The implant presents a variable thread design from the coronal to the apical area: the thread depth progressively increases, due to a reduction of the minor diameter; the crest width reduces from 0.17 to 0.11 mm.
Experimental set up tested in the study. The osteotomies were performed using a handpiece mounted on a vertical drill press. Polyurethan blocks were fixed to the drill basis.
The figure illustrates the discrepancy between the implant diameter and the drill size for Group A (left) and Group B (right). The implant outer diameter outline is depicted by a black line, the implant inner diameter outline is depicted by a red line, and the drilling osteotomy line is depicted by a dotted black line. IDD indicates implant-drill discrepancy.
Box plots representing RFA and IT results based on the substrate density (PCF) comparing two different drilling techniques: a non-undersized drilling (Group A) and an undersized drilling (Group B).
Contributor Notes