Surgical Placement of Implants

Results of a 15-year study on Br£ne-mark implants, published by Adeil et al in 1981,' included details of a definitive surgical procedure essential to the long term viability of the osseointegrated implant. This procedure, which previous articles had identified as encouraging an intimate connection between an implant, of defined geometry and surface preparation, with living bone2*4 remains the key to a predictable osseointe-gration technique.

With implant manufacturers presenting fixtures of varying specification, the surgical protocol varies to allow for design specificity. By way of an example, the preparation for a hollow basket implant requires the use of a trephine drill rather than a solid drill. However, a common theme that exists throughout, is the aim to inflict minimal physical and thermaltrauma to vital osseous tissues and to encourage close apposition of the fixture to bone for effective primary fixation. A surgical protocol that breaches this theme will likely result in a fibrous encapsulation of the implant, which is then less able to withstand biomechanical and microbial insult.5' 6

The importance of minimal heat production during bone preparation has been highlighted by Eriksson, whose thesis7 and subsequent publications8*10 established a threshold temperature of 47°C for one minute, if bone was not to be irreversibly damaged. Implant companies have endeavoured to design drills that impart minimal heat through cutting, introducing concepts of internal and external irrigation. Research has failed to show any significant advantage between the techniques11' 12 but emphasises the need for an efficient supply of copious saline irrigation. This would suggest that the most important piece of equipment ts the drill unit which should allow low cutting speeds, with a facility to pump saline directly onto or through the drill.

The surgical protocol presented below, which aims to reflect the nature of this general theme, is specific to the Astra Tech Implant System (Astra Tech AB, Molndal, Sweden). It will be used throughout this text since this is the system used by the author. An effort will be made to point out variations that may occur with other implant systems, but this chapter is not intended to be a definitive source for the surgicai protocol. The reader is encouraged to seek a more detailed protocol from the specific manufacturer of the implant system of their choice.

General Surgical Protocol

As part of the routine pre-operative requirements, all patients are given prophylactic antibiotics of choice and are asked to rinse out their mouth with 0.2% w/v chlorhexidine mouthwash (Corsodyl-SmithKline Beecham Ltd, Brentford, UK) for one minute.

There may be a need to establish an anaesthetic protocol for patients who request that they be unconscious during surgery. Sedation by intravenous titration of 10-1 5 mg of Midazolam (Hypnovel® Roche Products Ltd, England) or a similar anxiolytic is often sufficient to sustain a peaceful response and a degree of short acting amnesia. The option of a general anaesthetic should only be considered in advanced surgical cases, since this is essentially a minor operative procedure. It is important that prior consent always be obtained and that an appropriately trained clinician be responsible for the anaesthetic induction and maintenance.

Local anaesthetic (Xylocaine-Adren-aline 2%, Astra AB, Sodertalje, Sweden) is administered via infiltration and/or regional blocks, accord ing to the surgical requirement. In working towards a sterile environment, it is required that the patient should be swabbed with 0,1% w/v chlorhexidine and then draped. Both surgeon and nurse should scrub and gown up, making sure that the surgical gloves are non powdered since this may contaminate the implant surface (Fig 2-1). It is useful to have an unscrubbed runner, to avoid unnecessary contact with non sterile items.

The incision is normally placed either in the buccal sulcus so that the line of incision is distant from the surgical site, or is placed along the crest of the ridge (Fig 2-2), which facilitates surgical access, and reduces postoperative haematoma. However a crestal incision may increase the risk of implant fenestration, with subsequent infection. It may be that the ideal solution is a paracrestal incision offset to the palatal or lingual side.

In raising the flap it is essential that a sound mucoperiosteum is stripped from the bone (Fig 2-3) with limited exposure of the underlying alveolus, allowing an appreciation of ridge contours, particularly buccal and lingual concavities. Excessive damage to the periosteal lining will likely result in marginal bone resorption around the implants with soft tissue downgrowth which may compromise osseointegration. The use of high quality, sharp surgical instruments is to be commended. Clearly an awareness of the surgical field, anatomical boundaries such as

Medical Augmented Reality

Fig 2-1 Surgical Protocol requires that an aseptic technique should be employed when placing dental implants.

Epithelial Tissue Deep Wound

Fig 2-2 The incision is placed according to the surgeon's preference. In the case shown, the incision has been placed Imgually to avoid direct trauma to the superficial inferior alveolar nerve.

Harbin Ice Festival

Fig 2-3 A sound mucoperiosteum is raised, with limited elevation that should provide adequate visual and instrument access. Over stripping of the periosteum will delay healing and may compromise bone vitality

Fig 2-4 When placing mandibular implants it is necessary to carry out blunt dissection to localise and isolate the neurovascular bundles (arrow), as they emerge from the mental foramen or superficial canal floor of riose or antrum and knowledge of vital structures is essential. In the mandible, it is necessary to carry out blunt subperiosteal dissection to locate the exiting neurovascular bundle from the mental foramen (Fig 2-4) in order to avoid traumatising this vital structure, Identification of the nasopalatine neurovascular bundle is also necessary when placing implants in the pre-maxilia, A breach of anatomical boundaries or an encroachment of vital structures without forethought, will likely result in implant failure, or complications such as paraesthesia or anaesthesia of the mental nerve distribution. There is a clear need to be aware of the anatomy of any surgical field even if simply assessing the case for referral and the reader is encouraged to pursue a refresher course on this subject. In light of the above, it would be prudent to approach the placement of implants in the posterior maxilla and mandible with caution, since damage to the maxillary antra and the inferior dental nerve are to be avoided. Notwithstanding this statement, it is imperative that an adequately trained surgeon should utilise all available clinical and radiographic data to ensure a margin of safety when implants are utilised in the posterior regions. Prior to surgical preparation of the bone for implant insertion, it may be necessary to alter the morphology of the crestal bone, reducing any "knife edge" ridge and creating an even contour with an adequate bone width. This will depend on the width of implant to be used. The use of bone files is perhaps preferable to the large bone burs, since they offer greater control over ridge reduction and allow the early harvesting of autogenous bone, which may be of value for grafting purposes, later in the procedure (Fig 2-5). The surgical template is now placed in situ (Fig 2-6), ensuring that it is correctly seated. In the partially dentate patient the template should always be tooth borne so that the seating is not interfered with by soft tissue flaps.

In order to prepare implant sites in the host bone, efficiently and atraumatically. it is essential to use the recommended instrumentation (Fig 2-7). It is wise for all members of staff to familiarise themselves with this instrumentation and be aware of handling and storage instructions which will vary between manufacturers. The improper handling of instrumentation may well compromise surgical success. Common to all systems is the gradual preparation of implant sites with a series of drills which increase in width (Fig 2-8), and which are used at speeds ranging from 500-2000 rpm under copious saline irrigation. The first of these drilling steps is the guide drill, a small rosehead bur used to pierce the outer cortex, marking the implant site for preparation (Fig 2-9), as indicated by the surgical stent. It is at this early stage that the surgeon first appreciates the true nature of bony quality.

Fig 2-5 The knife-edged ridge will always require either augmentation or reduction to create adequate crestal bone to circumscribe the fixture. In reducing the ridge the use of a bone file is effective and allows the bone chips to be harvested lor future use, if indicated.

Fig 2-6 To ensure that the implants are positioned in a manner that relates to the final prosthesis, it is essential to use a surgical template (stent) to guide the preparation of fixture sites.

Fig 2-7 All implant manufacturers recommend that only approved instrumentation be used to guarantee precise and atraumatic preparation of the fixture sites.

Fig 2-8 The Astra Tech Tiger™ Drills are laser banded to correspond to available implant lengths allowing easy assessment of preparation depth and are available in a range of widths and lengths to aid precise preparation.

Fig 2-9 The rosehead bur or guide drill is used to perforate the outer cortex thus indicating implant position. It also provides the surgeon with an opportunity to assess bone quality.

Fig 2-10 Preparation of the fixture sites will determine implant angulation and inclination. Control over fixture positioning and their relationship to one another is aided by the use of direction indicators.

Fig 2-11 Preparation depth can be confirmed by use of a depth gauge, which in this case utilises the same laser bands as on the Tiger™ Drills.

Subsequent drilling steps will determine implant length, position and inclination. The relative position of one implant to another may have considerable bearing on the prosthetic reconstruction and all systems recommend the use of direction indicators to help In judging the ideal relation of one implant to another (Fig 2-10). If using a self tapping implant it should be possible, having assessed bone quality, to select the appropriate final preparation width to provide optimal primary fixation. In contrast, the preparation of bone for press fit or non self tapping implants requires a definitive preparation width, regardless of bone quality. The use of trephines, canon drills, or twist drills will depend on implant design, but all systems provide a measuring facility to ensure accuracy of preparation depth (Fig 2-11), and a range of drills to select appropriate preparation width.

The design of a drill should encourage maximum bone cutting efficiency at low speeds and should ensure that saline irrigation is directed to the tip of the drill, where control of heat production is critical (Fig 2-12). Ideally the drill should encourage the flushing out or collection of bone debris which not only leaves a patent preparation, but if harvested as autogenous bone mush can be used as bone grafting material, if required at a later stage (Fig 2-13).

For the standard Astra implant shown in Fig 2-14 there are no further preparatory drilling steps, as the

Fig 2-12 Whether using internal or external irrigation, the drill design and saline distribution should predictably direct maximum irrigation to the cutting tip, which is most a! risk of causing thermal trauma to surrounding bone.

Astra Implant Drilling

Fig 2-13 The drill should encourage complete removal of bone debris from (he preparation site Ideally such bone should be removed in a way that it can be harvested for future use, if indicated, as autogenous bone graft.

Fig 2-14 The standard Aslra Tech Denial Implant is a self tapping titanium fixture, which is available in seven lengths, 8,9,11,13,15, 17, 19 mm (only six lengths shown) and two diameters 3.5 and 4 0 mm (3.5 mm diameter pictured).

Fig 2 -15 The countersink preparation removes additional crestal bone in order that the fixture site is able to receive the head of an implant which may, by design, be wider than the implant body.

Fig 2-16 Other additional preparatory measures may be necessary to customise fixture sites to the design of an implant. The use of trephines is required for hollow implants and pictured here; a conical drill preparation is essential to receive the flared head of (he Astra Single Tooth Implant.

Fig 2-17 The insertion of any dental implant should be carried o.ut in an atraumatic and controlled manner, either using a reducing handpiece running at 20 r.p.m. or as shown here, using a hand driven ratchet wrench. The need for irrigation is of course paramount.

implant has parallel sides. However for some implants there may now be one or two final preparatory steps in the surgery. A term often mentioned when discussing Implant surgery is countersinking, which refers to the need to crater the crestal bone (Fig 2-15), in order to receive the head oi an implant which is, by design, wider than the implant body. When using the Astra single tooth implant, it is necessary to flare the coronal third of the Implant preparation in order to receive the single tooth implant, which is flared to improve the aesthetic contour of the cervical margin of a single tooth restoration (Fig 2-16).

For screw type implants that are not self tapping, it is necessary as a final step to tap the bone prior to implant insertion. This tapping which cuts a thread into the bone, needs to be done at low speeds of 15-20 rpm. Likewise when inserting a self tapping implant, this should also be carried out at equivalent low speeds, which are controlled by using a hand ratchet instrument (Fig 2-17), or a high torque low speed handpiece to insert the implant. For press fit implants an instrument is usually provided to gently tap the implant into the bony socket.

It is now necessary to cover or occlude the implant surface which will interface with the transmucosa! component (abutment), i.e. that component that relates the position of the implant into the oral cavity for bridge support. This is necessary to prevent bony overgrowth and subsequent seating problems

Generally speaking there are two types of interface, internal or external. The external interface is usually associated with a flat topped implant that has a small hexagon, forming a butt joint with the cover screw and subsequent transmucosal components (Fig 2-18). The internal interface is usually of an hexagonal design as with the Screw Vent implant (Dentsply ""/Implant Division, California, USA) or a conical or tapered design, as is presented by ITI implants (Institute Straumann AG, Waldenburg, Switzerland) and the Astra Tech Implant System (Astra Tech AB, Molndal, Sweden) (Fig 2 -19). Having secured these protective cover screws {Fig 2-20), the insertion procedure is complete.

Suturing

Prior to suturing, the surgical area is thoroughly irrigated and debrided. In suturing the wound, it is necessary to ensure that flaps are correctly repositioned, and that mattress sutures are employed to help evert the edges. The suture material of choice Is somewhat subjective, but a 3/0 or 4/0 resorbable polyglactin suture (Vicryl® Ethicon Ltd, Edinburgh, UK) is very suitable (Fig 2-21). The patient is now provided with an analgesic or non steroidal antiinflammatory like Ibuprofen and asked to gently apply pressure to the wound with a damp gauze swab.

Fig 2-18 Insertion of the cover screw on a Br&nemark implant, which demonstrates the externa! butt joint interface.

Fig 2-19 Both the Astra Tech Dental Implant and the ITI Im-implant advocate an internal conical or tapered interface which is occluded during healing by the insertion of a protective cover screw.

Fig 2-20 Five mandibular implants are shown, with their respective cover screws In situ. Nole that the autogenous bone mush harvested earlier in the procedure has been used to patch up some of the crestai labial plate dehiscence that occurred during preparation.

Buttock Implant Been Inserted

Fig 2-21 Tight and reliable suturing is essential. Multiple interrupted mattress sutures will ensure eversión of the edges and healing through primary intention. A weak suture will encourage exposure of the fixture heads through the overlying mucosa, which is contra-indicated in a two stage implant system.

Postoperative Management

This will include a prescription for antibiotics comparable to a 7 day course of Penicillin V, 250 mg QDS, analgesics when indicated, and a Chlorhexidine mouthwash. The patient should be aware that there may be a need to leave the surgical site unencumbered by overlying prostheses, and as such it may be necessary not to wear dentures for a short period of time. Recommendations vary from two weeks to a few days, depending on whether the implants are proud of the marginal bone, or indeed left exposed in the mouth (see Chapter 3). However, ail agree that it is necessary to thoroughly relieve that part of the prosthesis overlying the implants and in the case of a denture, this should be relined with a soft tissue con ditioner like Viscogel® (De Trey Division. Dentsply Ltd., Surrey, England).

Though many general dental practitioners will refer patients for their implant surgery, they may well retain responsibility for overseeing the postoperative management of the patient. It is essential therefore to be aware of the exact position of the implants so that correct relief and relining can be effected. Sutures are removed at one week and an assessment of sofl tissue healing is noted. The patient should not now be neglected over the period of osseointegration but encouraged to attend clinic at least twice during this time to allow the dentist to oversee the healing of soft tissues and, in particular, to note the presence or absence of soft tissue perforation.

References

1 Adeli. R. Lekholm. U„ Rockier. 8., Bräne-mark. PL A 15-year study of osseointe-gralect implants in the treatment of the edentulous jaw. Int J Oral Surg 1981; 10: 387-416.

2 Bränemark, P.-!., Breine. U.. Adell, R.. Hans son. BO. Lind ström, J, Olsson, A Intra-osseous anchorage of dental prostheses. t. Experimental studies. Scand J Plast Reconstr Surg 1969: 3 81 -100.

3 Bränemark, P-t., Hansson, S.O., Adell, R,, Br elm, U„ Lindström, J,, Hallen, 0„ Öhman, A. Osseolntegrated implants In the treatment of the edentulous jaw. Experience from a 10-year period. Scand J Plast Reconsir Surg 1977. 11 Suppl 16

4 Albrektsson, T. Bränemark. P.-I., Hansson. H.A., Lindström, J. Osseomt eg rated titanium implanfs Acta Orthop Scand 1981. 52: 155-170.

5 Cranin, N.A., Rabkin, M.F., Gartlnke!, L. A statistical evaluation of 952 endosteal implants in humans. J Am Dent Assoc 1977; 94 315-320

6 Zarb, G.A., Smith, D.C., Levant, H.C., Graham, S.S. Zing, G.W The effects of cemented and un cemented end osseous implants J Prosthet Dent 1979; 42 202-210

7 Eriksson. R A Heal induced bone tissue injury An in vivo investigation of heat tolerance ot bone tissue and temperature rise In the drilling of cortical bone. Thesis, University of Göteborg 1984.

8 Eriksson. R.A, Albrektsson, T. Temperature threshold levels for heat-induced bone tissue injury A vilal microscopic study in the rabbit J Prosthet Dent 1983; 50 101-107.

9 Eriksson, R A., Albrektsson, T. The effect of heat on bone regeneration. J Oral Maxil-lofac Surg 1984; 42: 705-711

10 Eriksson, R A.. Adel!. R, Temperatures during drilling for the placement of implants using the osseomtegration technique. J Oral Maxillofac Surg 1986. 44 4-7

11 Watanabe, F, Tawada. Y, Komatsu, S. Hala. Y. Heat distribution in bone during preparation ot implant sites Heat analysis by real-time thermography. Int J Oral Maxil lofac Implants 1992; 7: 212-219.

12 Haider, R.. Watzek. G„ Plenk, H Effects ot drill cooling and bone structure on IMZ implant fixation, int J Oral Maxitlofac Implants 1993; 8; 83-91

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