Clinical evaluation of a new laser‐ablated titanium implant for bone‐anchored hearing in 34 patients: 1‐year experience

Successful bone-anchored hearing implantation requires good osseointegration of the titanium implant in the temporal bone and low skin-related complication rates. The introduction of wider diameter implants, providing an enlarged bone-implant interface and thus a larger interface for osseointegration, has resulted in up to 3-year survival rates of >96% in healthy adult patients. Despite the low incidence of implant loss in healthy adults, in certain patient groups, ie patients with compromised bone quality or in children, the incidence is much higher, varying between 3.5%-10.5% even with these wider diameter implants. To improve implant survival in these populations as well, further optimisation of implant material, design and surgical technique remains needed. Based on dental research, modifications of the implant surface, eg physical topography and chemical properties, could play a pivotal role in further optimising the integration in the recipient’s bone. As such, a new implant for bone conduction hearing was developed in 2015. This implant is, in contrast to currently used implants, selectively laser-ablated within the thread valley. Combined with modified chemical properties, this has shown improved biomechanical anchorage in pre-clinical animal testing. In our clinical practice, before this implant is tested in patients with a higher risk of implant loss, it first has to be proven effective to use in healthy adults. This study, therefore, assesses retrospectively the performance of the new laser-ablated implant by reviewing implant survival, stability and soft tissue tolerability in healthy adults 1 year after surgery.

Clinical evaluation of a new laser-ablated titanium implant for bone-anchored hearing in 34 patients: 1-year experience 1

| INTRODUCTION
Successful bone-anchored hearing implantation requires good osseointegration of the titanium implant in the temporal bone and low skin-related complication rates. The introduction of wider diameter implants, providing an enlarged bone-implant interface and thus a larger interface for osseointegration, has resulted in up to 3-year survival rates of >96% in healthy adult patients. [1][2][3] Despite the low incidence of implant loss in healthy adults, in certain patient groups, ie patients with compromised bone quality or in children, the incidence is much higher, varying between 3.5%-10.5% even with these wider diameter implants. [4][5][6] To improve implant survival in these populations as well, further optimisation of implant material, design and surgical technique remains needed.
Based on dental research, modifications of the implant surface, eg physical topography and chemical properties, could play a pivotal role in further optimising the integration in the recipient's bone. 7 As such, a new implant for bone conduction hearing was developed in 2015. This implant is, in contrast to currently used implants, selectively laser-ablated within the thread valley. Combined with modified chemical properties, this has shown improved biomechanical anchorage in pre-clinical animal testing. 8 In our clinical practice, before this implant is tested in patients with a higher risk of implant loss, it first has to be proven effective to use in healthy adults. This study, therefore, assesses retrospectively the performance of the new laser-ablated implant by reviewing implant survival, stability and soft tissue tolerability in healthy adults 1 year after surgery.

| Ethical considerations
The ethics committee has passed a positive judgement on the study.

| Study population
The study was designed as a retrospective chart review approxi- To be included in the CMR-testing, patients had to be ≥18 years old and have no disease or treatment known to compromise the bone quality at the implant site. Exclusion criteria included inability to follow investigational procedure and any factor, at the discretion of the investigator, that was considered to contraindicate participation. As such, 34 healthy adult patients consented and received the laser-ablated implant between September 2015 and January 2016.
In all patients, a single-stage surgical procedure using a linear incision technique was performed under either local or general anaesthesia.
Subcutaneous soft tissue reduction during surgery was applied in one hospital, whilst subcutaneous soft tissue was preserved in the other two hospitals.

| Implant
The implant used was the wide Ponto BHX-implant (diameter, 4.5 mm; length, 3 or 4 mm)(Oticon Medical AB Askim, Sweden). This implant is, in contrast to traditional Br anemark type machined titanium implant surface, selectively laser-ablated within the thread valley to produce a microtopography with a superimposed nanotexture and a thickened surface oxide layer. Pre-mounted Ponto abutments of lengths 6, 9 and 12 mm were used, in case of tissue preservation depending on skin thickness measured during surgery. over time measured as Implant Stability Quotient (ISQ) were also noted. ISQ was assessed using resonance frequency analysis (RFA) at abutment level, using the Osstell ISQ and a SmartPeg (type 55) (Osstell AB, G€ oteborg, Sweden). 10 The highest and lowest values obtained from perpendicular measurements were recorded.

| RESULTS
All 34 subjects were eligible for review. However, in three patients, the last visit was performed by phone due to travelling issues. For these visits, only implant survival data were used in the analysis.
Demographics and baseline characteristics are summarised in Table 1

| Comparisons with other studies
Implant survival and soft tissue tolerability seem comparable to the standard wide-diameter implants used in healthy adults. 1-3 However, due to the retrospective, multicentre nature of this study, using multiple surgical techniques, caution is needed in drawing conclusions especially regarding soft tissue tolerability.
The use of ISQ to measure osseointegration has been discussed extensively and remains questionable. 10  torque measurements showed a 153% higher biomechanical anchorage of the laser-modified implants. 8 This underlines that ISQ might not reliably reflect actual osseointegration and that this implant might be beneficial for using in high-risk patients.

| Clinical applicability of the study
Despite these excellent results in terms of survival, prospective, long-term comparative research, using only one surgical technique, is needed to determine clinical usefulness of this implant. In addition, incremental cost-effectiveness has to be assessed, as the (head) room for improving implant survival compared to the standard widediameter implants seems to be limited. However, more headroom is present in high-risk patient groups. The current (retrospective) study F I G U R E 2 Implant Stability Quotient(ISQ)-low & ISQ-high over time per abutment length. The median follow-up for each visit (entire cohort) is stated in the round brackets F I G U R E 1 Holgers score per visit. The median follow-up for each visit (entire cohort) is stated in the round brackets. Missing data were caused by visit performed by phone or implant loss prior to visit