The new wide Ponto implant design clinical and surgical aspects

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1 The new wide Ponto implant design clinical and surgical aspects Partik Westerkull, MSc. Eng. Ph., Senior Research Consultant to Oticon Medical Lars Jinton, Director of Engineering, Oticon Medical With the new wide Ponto implant, the bone-to-implant contact surface is significantly increased (+10%) compared to any other similar implants on the market. The implant geometry offers also higher initial stability (ISQ value). The new Ponto implant is designed to offer increased implant stability that may specifically improve clinical outcome in patients with soft or compromised bone as well as offering increased implant stability margins for regular patients. Due to the unique OptiGrip geometry, it has also been possible to limit the diameter of the drill to offer less surgical trauma and less risk of overheating the bone. The countersink drilling removes 27% less bone than required for other comparable 4.5 mm diameter bone anchored implants. The new wide Ponto implant has been designed to offer a well-documented osseointegration for efficient long-term connection of the sound processor. The universal conical abutment fit and surface design offer a gentle soft tissue interaction. The new Ponto implant has undergone extensive testing of for example insertion torque, initial implant stability (ISQ) and analysis of bone and soft tissue interaction aspects. Introduction The new wide Ponto implant has been designed to optimize initial stability with the aim of improving implant success rates. This paper describes the requirement background, the implant design and some of the key verifications for long-term success of the new wide Ponto osseointegrated implant. Background It is well-documented that for the vast majority of patients, a traditional type of implant design forms a long-term stable fixation in the bone (Tjellström et al 2007). Retrospective clinical data confirms good clinical outcomes for Ponto implants and is described in a corresponding white paper (Babu et al 2012). However, increased implant stability may further improve clinical results, especially for patients with soft bone, for example children, and may also offer increased implant safety margins for the regular patients. In cases of implant failures at an early stage after surgery these may be caused by overheating of the bone tissue at surgical drilling or by a mobilized implant during the healing. During the first weeks after surgery, osseointegration has not yet started or is just about to start. At that stage, implant stability is a macroscopic mechanical stability that is dependent on the implant geometry and measures, and it is related to the initial bone-to-implant contact area. A recent scientific publication indicated that the sound processor can be fitted 3-5 weeks after surgery for adults operated with a traditional 3.75 mm Brånemark type implant without any observations of increased implant losses compared to patients fitted at later stages (Dun et al 2012). The consensus report from Snik et al 2005, states that the implant can be loaded 4-6 weeks after surgery. For children and patients with compromised bone, significantly longer healing time is always applied; however the implant success rate is still lower for these patient groups compared to regular adult patients. An implant design offering increased initial stability would reduce the risk of implant mobility not only short-term but also long-term. A wider implant generally requires a wider drill hole in the bone, so an efficient cutting geometry is important to limit the required diameter of the drill to avoid heat-induced bone tissue damages during the drilling procedure. Other important design aspects to consider in implant design are compatibility with existing components, possible soft tissue interaction and trauma safety. The new wide Ponto implant has been specifically designed to improve the results of above important aspects.

2 The new Ponto implants The new wide Ponto implant offers higher initial stability. Due to the unique patented OptiGrip cutting geometry, the required drill diameter is significantly smaller than for any other 4.5 mm wide implant, thus minimizing tissue trauma at drilling. The new wide Ponto implant has a significantly increased initial bone-to-implant contact surface, also when comparing with other 4.5 mm diameter implants, see fig 1. Ponto implant 3.75 mm Wide Ponto implant 4.5 mm BI300 by Cochlear BAS Initial implant surface in contact with bone achieved with three different bone anchored implants Fig 1. Views of the implant surface that is in bone contact after surgery. The new wide Ponto implant has 10% more contact surface compared to another 4.5 mm implant, the Cochlear BAS BI300. It has also 72% more initial contact surface than a Ponto 3.75 mm implant. The increased surface in contact with bone is achieved by a combination of a unique geometry with increased threaded area which is extended along the full length of the implant and exceptional cutting properties allowing for a smaller drill hole compared to other implants with the same diameter. The area of the implant that is in contact with the bone after surgery is a contributing factor to implant stability. The Ponto abutments are now equipped with an attachment for an Osstell SmartPeg which makes it possible to measure the resonance frequency ISQ-value of an implant in bone. This value is related to the stability of the implant seated in the bone. Figure 2 shows the implant stability for different types of implant designs. The new wide Ponto implant and the Cochlear BAS BI300 implant both have a diameter of 4.5 mm, however the new wide Ponto implant has a increased bone-to-implant contact surface. This is a result of the unique OptiGrip design. To achieve a high accuracy of the relative measurement regarding stability in fig 2, the testing was performed in artificial medium soft bone according to ASTM F , i.e. no osseointegration was present. Implant Stability Quotient (ISQ) Wide Ponto Implant 4.5 mm Implant stability comparison 60 Fig 2. Implant stability measurement (ISQ) for wide Ponto implant compared to another 4.5 mm diameter implant, the Cochlear BAS BI300. The result for a traditional 3.75 mm diameter implant is also shown. Measured with 6 mm abutment lengths in medium soft artificial bone according to ASTM F N=28 for each implant type. Increased mechanical stability in the bone reduces the risk of implant mobility initially (Östman et al 2006). The new wide Ponto implant is threaded all the way up to the flange, which means that it can use more of the stability of the outer cortical shell of the skull bone, which may even increase its stability further in a clinical situation. In figure 3, the load capacity of a traditional 3.75 mm and 3 mm long implant has been compared with the load capacity of a 3 mm long wide Ponto implant. The load capacity has been defined as the maximum side force that can be applied to the upper end of the abutment before the bone around the implant would fracture. This example shows the load capacity with 9 mm long abutments mounted on 3 mm long implants in bone since this is the least favorable loading condition that has been documented in the literature (Doshi et al 2010). The results are based on theoretical calculations BIA 300, Cochlear BAS Ponto implant 3.75 mm 2

3 Load capacity in bone (N) Abut. length (mm) Impl. diam. (mm) Impl. lengh (mm) With the OptiGrip design, the drill diameter was reduced to 3.75 mm compared to a 4.0 mm drill diameter that is required for a traditional implant design of a 4.5 mm diameter implant. It is the final countersink drilling that prepares the hole in the bone that will interact with the implant in the osseointegration process. For the 3.75 mm wide Ponto countersink drill, 27% less bone is removed compared to the 4 mm countersink used for the Cochlear BAS BI300 implant. The bone volume is directly related to the heat induced in the bone during drilling. Both drill systems include a guide drilling of 2.3 mm diameter before countersinking and both countersinks create cylindrical holes to allow implant insertion to various depths in case of thin bone. A smaller hole means less tissue trauma and less heating of the bone during drilling, which makes the surgery more gentle. Generally, any drill should still be moved up and down, to allow generous cooling to reach also the tip of the drill. Fig 3. The side force load capacity of a traditional 3.75 mm and 3 mm long implant compared with the load capacity of a 3 mm long wide Ponto implant, based on calculations in bone. The new wide Ponto implant is designed to improve implant success in patients with compromised bone such as in pediatrics, and to offer further stability margins for regular patients at stages during the osseointegration process. The new wide Ponto implant does not affect the strategy on how to use sleeper implants in children since there will still be an increased risk of trauma in children compared to adults. Wide Ponto BI300 Tissue trauma and drilling The OptiGrip design of the new wide Ponto implant has a unique new cutting geometry which means it cuts more efficiently into the bone tissue. The wide Ponto implant includes a new logarithmic conical shape of the thread itself which increases bone contact and also distributes the cutting force equally on the cutting edges for easy engaging. While offering a high initial bone contact and stability as described above, it also means that the diameter of the drilled hole in the bone can be reduced without making it harder for the implant to engage and be inserted into the hole. Figure 4. Drill hole sizes required for two types of 4.5mm diameter implants. The wide Ponto countersink drill ( 3.75 mm) removes 27% less bone than a Cochlear BAS BI300 countersink ( 4.0 mm) for Cochlear BAS BI300 implant. A smaller hole generally means less tissue trauma and less heating of the bone during drilling. OptiGrip design The OptiGrip design includes several new important geometrical design features that lead to the unique implant properties. One of the revolutionary new key features is the gradual relieving behind the cutting edge of the implant as shown in figure 5. 3

4 Cut No relieving gives high tissue pressure & friction Straight cut relieving Cut All gradual optimal relieving gives much less tissue pressure & friction able in the regular 4 mm length as well as in a shorter 3 mm length. The implants are available with premounted abutments of different lengths, as well as separately for cases requiring a 2-stage surgical procedure. Universal hexagon interface Bone Bone Micro groove under flange Conical seal Simple classical relieving as in Cochlear BI300 and previous BAHA and Ponto implants OptiGrip gradual relieving unique to the new wide Ponto implants Fully threaded t ofl a n g e Conical thread Optigrip cutting geometry Figure 5. The OptiGrip gradual relieving behind the cutting edge of the implant offers significantly less bone tissue pressure and friction compared to a classical relieving. Figure 6. The new wide Ponto implant geometry. Since bone is an elastic material in the cutting process, some sort of relieving is always included in the design of any self-tapping implant to reduce tissue pressure and friction behind the cutting edge. Although it has been well-known to the experts that a gradual relieving would be a preferred design, it has not been possible to realistically manufacture this. Hence other implants have had to stay with a simple straight relieving that cannot follow the contour of the flexing bone, and that type of relieving starts a little behind the cutting edge due to material limitations. However, due to a unique development progress, Oticon Medical has been able to include a fully gradual relieving that creates efficient and tissue friendly cutting. This patented design is one of the reasons why the new wide Ponto implant can be inserted into a smaller drilled hole and why it offers increased bone contact and improved initial implant stability. In figure 6, an overview of the features of the new wide Ponto implant is shown. The implant is equipped with a micro groove under the flange and a thread that goes all the way up to the flange with the aim of minimizing the risk of bone resorption and maximizing the stability of the implant in the outer cortical bone. Micro threads may reduce or delay bone resorption around the implant (Lee et al 2007). The implants are avail- Implant surface Except for the Brånemark surface, other modified and rougher surfaces are also used in the dental implant field, mainly for increasing implant success rate in the trabecular bone of the maxilla since the success rate there is lower compared to the mandible. There are animal studies showing improved medium term fixation with moderately rough titanium surfaces. There are also indications of improved clinical results in the maxilla, whereas in the cortical bone of the mandible the clinical success is very high and similar for any of the available titanium implant surfaces. The structure of the temporal bone generally corresponds more to the dense structure of the mandible than to the trabecular structure of the maxilla. In the scientific literature, Palmquist et al 2010 found that randomized controlled studies in the dental field showed no scientific evidence that any particular type of established dental implant surface has superior long-term success. If there would be any clinical benefits in the temporal bone with rougher titanium surfaces compared to the Brånemark surface, the difference would most likely be very small. The implant losses that occur for bone anchored hearing implants are mainly due to trauma, poor initial implant stability or long-term bone resorption (Reyes et al 2000). To improve 4

5 results in these situations, the macroscopic geometry of the implant is most certainly important based on the biomechanics, whereas it is more uncertain if the type of osseointegrating implant surface will make any difference. There are new generations of implant surfaces that do not only include a moderately rough titanium surface, but also a chemical or active modification of the surface, and perhaps these could be developed to contribute to further progress in the field. In the literature search, Palmquist et al 2010 found that more implants with rough surfaces were affected by peri-implantitis, which leads to bone resorption around the implant. However, this evidence is very limited and no decisive conclusions should be made based on this. A possibility is that bacteria and biofilm might adhere more strongly to rougher surfaces compared with smoother surfaces. Bone resorption may take place around the upper part of any type of implant. If bone resorption occurs, the implant surface that should have been imbedded in bone will be available for bacteria to grow on. This may cause interaction with the skin penetration or contribute to further bone resorption. It might be an advantage to avoid rougher surfaces in the proximity of the flange of the implant, for the same reason that a smooth surface is generally chosen for the surface of percutaneous abutments. More research is needed in this area. Since bone anchored hearing implants are much shorter than dental implants it may be at least as important to avoid bone resorption in this application. The Brånemark surface is the most well-documented implant surface for both dental implants as well as for bone anchored hearing applications. In fact, it is the only implant surface with long-term clinical documentation in extra oral percutaneous applications. The new wide Ponto implant is equipped with a Brånemark type implant surface that has now been combined with the unique new OptiGrip geometry designed for improved initial and long-term stability in the bone. Trauma safety and other patient related aspects Although Brånemark type implants have shown excellent longterm clinical results, long-term implant losses may occur and are mainly due to traumas or loss of integration due to bone resorption (Reyes et al 2000). The incidence of trauma is higher in pediatrics than in adults (Lloyd et al 2007). The new wide Ponto implant has the universal hexagon abutment interface, which offers easy removal and replacement for the clinician to minimize inconvenience for the patient. To ensure backward compatibility, the implant hexagon of the new wide Ponto implant is the same as for any other Ponto implants. Another important requirement on the implant-abutment interconnection is that there should be a tight seal between the two components to avoid micro-gaps for bacteria to grow and be transported in. The Ponto implant and abutment forms a tight conical seal between the two components. The abutment is slightly more conical than the implant, which is important to ensure that the seal takes place in the periphery of the interconnection. The interface seal between the Ponto abutment and the implant has been verified and approved using ASTM F intended to verify sterile package materials. More on ISQ The ISQ value generated by an Osstell equipment is a way of measuring implant stability in patients. The ISQ value represents the resonance frequency of the mechanical arrangement fixated in the bone. The value depends on how firm the fixation is and how hard the bone is. It also depends on the length and weight of the arrangement. Currently, it is mainly a tool for clinical studies and implant research and not so much a tool to be used for any regular clinical conclusions at the moment. There is for example no specific ISQ value that has been documented as an acceptance value for loading the implant. There may also be other factors to consider when deciding to load the implant. The level of osseointegration for different implants in different patients cannot be compared with ISQ, since a non-osseointegrated implant in hard bone may give a higher ISQ than an osseointegrated implant in soft bone. The ISQ measurement is however suitable for following the stability progress with time on one specific implant, which might be useful in some situations. It should be noted that the abutment length affects the ISQ value for a specific implant when an ISQ measurement is performed with an Osstell SmartPeg mounted on an abutment. In figure 7, the ISQ value for different abutment lengths mounted on one specific implant is shown. Note how much the ISQ value varies with the abutment length although the stability of the implant in the bone is the same. This is due to the fact that ISQ measures a resonance frequency which is dependent on the component length. 5

6 Implant Stability Quotient (ISQ) Implant stability comparison 54 6 mm 9 mm 12 mm Abutment lengh Fig 7. The ISQ value measured on the abutment depends on the abutment length, since the ISQ value represents the resonance frequency which depends on the length of the arrangement. 46 Conclusion The design of the new wide Ponto implant has an increased (+10%) initial bone-to-implant contact surface, compared to any other bone anchored hearing implant on the market, and is designed for increased initial implant stability. Increased stability of the implant in the bone may reduce the risk of implant mobility that may cause implant loss, especially in soft bone, for example children. Higher stability may also contribute to increased stability margins for regular adult patients as well as increased safety margins. Increased implant stability reduces the risk of implant mobility both long-term and short-term and may contribute to further increased implant success rates. Due to the unique new OptiGrip cutting geometry, the countersink drill diameter is significantly reduced (27% less bone volume removed compared to countersinks for other comparable wide implants), which contributes both to increased initial bone-to implant contact area, and to a reduced risk of heat induced bone tissue damage during the drilling procedure. The implant interface to the abutment includes a conical fit and, together with the Ponto abutments, it is designed to offer an efficient and tissue friendly skin penetration (Westerkull 2012), on the Ponto abutment system. The universal low profile hexagon fit offers backward compatibility which is important for practical and patient related aspects. The new wide Ponto implant includes a number of important biomechanical improvements designed to offer important clinical benefits for patients who may have an increased risk of implant failure. Possible improvements of actual clinical results with the new wide Ponto implant remains to be seen in future clinical studies. 6

7 References: 1. Babu S, Fucci M, Mckinnon B, Sockalingam R, Jernby K. The Ponto Bone Anchored Implant System: A Survey of Clinical Outcomes. Oticon Medical White Paper, February Tjellström A, Hakansson B, Granstrom G, Odersjö M: Survival rate of self-tapping implants for bone-anchored hearing aids. J Laryngol Otol 2007; 121:2: De Wolf M, Hol M, Mylanus E, Cremers C: Bone anchored hearing aid surgery in older adults: Implant loss and skin reactions. Ann Otol Rhinol Laryngol 2009 Jul:118/7: Östman P-O, Hellman M, Wndelhag I, Sennerby L: Resonance Frequency Analysis Measurements of Implants at Placement Surgery. Int J Prosthodont 2006; 19; pp Doshi J, McDermott A, Reid A, Proops D: The 8.5 mm abutment in children: the Birmingham bone-anchored hearing aid program experience. Otology & Neurotology; June 2010, Volume 31, Issue 4, pp Westerkull P: The Ponto abutment and skin penetration concept clinical, biomechanical and long-term safety aspects. Oticon Medical White Paper, Dun C, Faber HT, de Wolf M, Mylanus E, Cremers C, Hol M: Assessment of More Than 1,000 Implanted Percutaneous Bone Conduction Devices: Skin Reactions and Implant Survival, Otology & Neurotology, 33: , Lee D, Choi Y, Park K, Kim C, Moon I: Effect of microthread on the maintenance of marginal bone level: a 3-year prospective study. Clin Oral Implants Res 2007;18: Lloyd S, Almeyda J, Sirimanna K, Albert D, Bailey C: Updated surgical experience with bone-anchored hearing aids in children. The Journal of Laryngology Otology; September 2007, 121, pp Palmquist A, Omar M, Esposito M, Lausmaa J, Thomsen P: Titanium oral implants: surface characteristics, interface biology and clinical outcome. J R Soc Interface 6 October 2010 vol. 7 no. Suppl 5 S515-S Reyes R, Tjellstrom A, Granström G: Evaluation of implant losses and skin reactions around extraoral bone-anchored implants: A 0 to 8-year follow-up, Otolaryngol Head Neck Surg Feb;122(2): Snik A, Mylanus E, Proops D, Wolfaardt J, Dent M, Hodgetts W, Somers T, Niparko J, Wazen J, Sterkers O, Cremers C, Tjellstrom A: Consensus Statement on the BAHA System: Where Do We Stand at Present? Ann Oto Rhinol Laryn 2005; 114(12) Suppl. 195: page 7. 7

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