78 Chapter 3.2 Traditional air conduction hearing aids have their own limitations in this group of children and include narrow ear canals and impaction of wax, both of which may create significant rates of complications including infection and further conductive losses. In addition, any learning difficulties may influence the child’s acceptance and tolerance of wearing any traditional hearing aid. The use of a bone anchored hearing implant (BAHI) and hearing device as an alternative aiding system has been shown to be a very acceptable form of hearing rehabilitation in this patient group [17,18] and with those with learning difficulties [19]. In 2009, Oticon™ Medical introduced the 4.5 mm Ponto wide bone anchored hearing implant (BAHI) [20] and this was later replaced in 2015 by the Ponto Biohelix (BHX) Oticon™ of the same 4.5 mm diameter which utilises OptiGrip™ Geometry and laser-ablated surface to improve stability and promote osseointegration. The application of wider diameter implant was initially shown to improve outcomes in dental implantation with lower implant failure rates [21,22]. Application of this wider BAHI has been found to have comparable skin reaction rates to the previous 3.75 mm implants and in addition it was noted to be associated with increased survival [23–26]. The wider diameter of these implants increases the surface area contact between the implant and temporal bone providing a greater stability which results in a reduction in spontaneous fixture loss. Recent meta-analysis by Kruyt et al. supports these finding in children demonstrating a 17.1% loss in small-diameter implants compared to a 5.9% for wide-diameter implants [27] although many of the studies included in this utilised a differently designed wide implant. As a result of this evolving evidence, some centres advocate early loading of processors in adults as early as 3 weeks [27–30] and at 6 weeks in children [31]. Complications associated with previous generations of narrow paediatric BAHI, particularly peri-abutment soft tissue reactions and fixture (implant) loss through both trauma and failed osseointergration, have been demonstrated to be higher in paediatric populations [32]. With specific regards to the wider (4.5 mm) implants, failure rates of 2.6–4.2% are reported in the adult population [23,26,29,33] and 5.9% in children [27]. In 1996 resonance frequency analysis (RFA) was introduced as a non- invasive, objective method to clinically test implant stability in-vitro and in-vivo. It measures the resonance frequency of a small transducer attached to an implant. A strong correlation (r = 0.94, p < 0.01) was observed between the observed frequency and the height of implant fixture exposed. A significant increase in resonance frequency was observed related to the increase in stiffness on implants in-vivo and the results correlated with the in-vitro findings [34].
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