Dentistry case study: All-on-4 protocol

All GDPs know how difficult it is to manage a patient through the psychological and physical trauma of a clearance and the provision of an immediate denture.

The advent of implants has increased patients’ options, with studs and bars to help retain loose dentures, or fixed implants to support bridgework. While the extent of bone loss from progressive periodontal disease in terminal dentition cases can pose problems in identifying potential implant sites, it is often possible to replace lost bone in suitable locations with cortical and sinus grafts.

However, many patients do not have the financial resources or the inclination to undergo this type of surgery.

Even if they consent, the periodontal pathology must be managed, clearance must still be achieved, and the immediate denture stages undergone. Patients must also suffer the embarrassment and inconvenience of not being able to wear their dentures after each surgical intervention. The all-on-4 approach overcomes these difficulties to provide ‘same day’ patient satisfaction.

This article seeks to offer experience-based advice and tutorial on the application of the all-on-4 technique, widely acknowledged to be a difficult procedure, to the replacement of the  periodontally compromised terminal dentition, thus enabling an increased success rate and more predictable outcomes. We shall introduce implant surgeons and technicians to the Lymm technique of registration using modified Nobel Biocare components.

The all-on-4 protocol
The all-on-4 protocol developed by Paulo Malo provides immediate, temporary fixed bridgework for the edentulous mandible1 and edentulous maxilla [2], which is then converted to definitive bridgework after six-12 months.

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Figure 2: Lip line smiling

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Figure 3: Class II div II set up

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Figure 4: High lip line, class II, div II

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Figure 5: Dental panoramic tomograph (DPT)

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Figure 6: Bone removal lines, DPT

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Figure 7: Bone removal lines (patient’s mouth)

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Figure 8: Positioning of virtual implants

The essential features of the protocol are maximising the distal position of the posterior implants using angled implants and abutments to avoid the mental foramina and maxillary sinuses (Figures 9 and 10) and the immediate provision of a temporary acrylic bridge extending to the posterior implant without cantilever (Figures 11 and 12). This is replaced by a definitive bridge after six months with a metal framework to splint the implants and provide bilateral distal cantilevers. A major advantage of this protocol is the facility to wear the temporary bridge again while the definitive bridge undergoes repair or restoration after several years of wear.

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Figure 9: Implant position in mandible

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Figure 10: Implant position in maxilla

Studies have shown a success rate of around 97% for the edentulous mandible, with only five implants lost in five out of 44 patients in the first six months and with all prostheses surviving after one year[1]. Similar results (97.6% success) were achieved for the edentulous maxilla, with only three Branemark implants lost in three out of 32 patients. This study revealed a loss of marginal bone level averaging 0.9mm (SD 1.0mm) from the implant abutment junction after one year[2].

The success rate improved to 98.9% when Nobel Biocare Speedygroovy implants were used in both maxilla (44 patients) and mandible (nine patients). Two implants were lost in two patients, who showed an increase in the loss of marginal bone level to on average 1.2mm (SD 1.4mm) from the implant abutment junction after one year[3].

In a six-year study, Malo reviewed the placing of implants in periodontally compromised sites in two groups of patients which included 90 full arch fixed immediate bridges using the all-on-4 technique. The first group comprised mainly machined Branemark implants placed over five years with a 91% success rate, where 13 of 165 implants were lost in nine out of 81 patients. There was an increase in the loss of marginal bone level to on average 1.2mm (SD 0.9mm) from implant abutment junction after one year.

The second group were all oxidised implants placed prospectively over a year with a 100% success rate. 103 patients were treated with 268 implants using a standardised surgical and maintenance protocol. There was a loss of marginal bone level of on average 1.1mm (SD 1.1mm) from implant abutment junction after one year. The surgical protocol included a regenerative surgical technique, antibiotics and corticosteroid anti-inflammatory medication, with anti-inflammatory agents used in regression mode.

The maintenance protocol included the use of hyaluronic acid in the first two months and chlorhexidine between two and four months.  Malo concluded: ‘Implants may be successfully placed in periodontally compromised situations so long as oxidized surface implants are used and specific clinical protocols are followed, coupled with standardised surgical and maintenance procedures.’[4]

Patients with healthy edentulous arches can benefit from advances in guided surgery using bone and tissue borne stents because of the stability of the reference points5, whereas the mobility of the teeth and the irregular pattern of bone loss associated with periodontally compromised terminal dentition prevents the use of surgical guides.

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Figure 11: Temporary bridge, mandible

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Figure 12: Temporary bridge, maxilla

The success of our own treatments over the last four years compares favourably with results of Malo’s study. We have carried out 97 immediate fixed bridges in periodontally compromised patients using the all-on-4 technique since July 2006, following the basic all-on-4 protocol but with subtle differences (to be detailed later).

Only one implant out of a total of 392 for the 97 patients failed within six months, a success rate of 99.8%. This implant has now been replaced without further problems. Any complications we have experienced are discussed below.

Patient assessment
Every case must begin with an assessment of the patient’s overall well-being as well as a scrupulous examination of each potential implant site. It is vital to maximise the implant surface area available for bone integration and to optimise the position of the implant in relation to anatomical restrictions, the overlying bridgework and surrounding soft tissues. The periodontal pathology also needs to be assessed, managed and monitored as part of a standard protocol. We follow a standard assessment format, which includes comments relevant to the all-on-4 technique.
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Figure 13: Posterior implant position, maxilla

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Figure 14: Posterior implant position, mandible

History of present complaint
The most successful clinicians are those who respect each patient as an individual and offer emotional support for those who are perhaps in denial, distressed or traumatised by the prospect of losing their teeth. The surgeon must attend to the patient’s concerns by listening to their own assessment of the situation as well as explaining the procedures.

Such support is best offered away from the dental chair but with an illustrative device to hand – a monitor or X-ray viewer for example – and perhaps a cup of tea and a supply of preferably non-surgical tissues. It’s important to have the patient ‘onside’ and committed to the treatment as a major factor contributing to an improved quality of life post completion.

Medical history
The usual medical considerations for placing multiple implants apply to the all-on-4 technique. The irregular nature of the bone loss in periodontally compromised patients and the need to establish a clean level of bone for osteotomy often requires a significant amount of bone removal with rongeurs and burs. We therefore use IV sedation, administered by a qualified third party, and the patients need to be assessed, informed and give their consent.

Dental history
A common predisposing cause of terminal, periodontally compromised dentition is failure to pursue an adequate oral hygiene regime, and as the condition develops
so this situation becomes self-perpetuating. Patients are discouraged when their teeth still appear
unattractive even after cleaning, or their teeth have become too loose or too painful to clean.

Some patients will have avoided going to the dentist for regular check-ups or declined periodontal therapy because of the painful sequelae. The implant surgeon needs to gently encourage the patient to understand and accept the need for preliminary periodontal care and for a strict post-operative maintenance and monitoring programme.

Extraoral  
The presence of mobile, over-erupted and protruding teeth can complicate assessment of the free way space (FWS), lip support and smile lines. Photographs at rest (Figure 1) and full smile (Figure 2), with and without a denture if applicable, are essential for planning and to allow the technician to relate to the case. The planned implants and abutments must, where possible, be above the smile line to hide the transition from acrylic gumwork to mucosa. This determines the amount of bone to be removed and by inference the height of bone available for placement. The skeletal relationship is important in determining the correct occlusion and tooth set-up, especially where teeth have drifted or been replaced with Class 1 dentures. Patients with Class 2 div II jaws often have narrow anterior ridges (Figure 3), and high lip lines (Figure 4) also make implant placement and planning more difficult.

Intraoral  
This is the point when mobility and CPITN scores need to be recorded. The periodontal condition inevitably dictates a full periodontal charting according to the CPITN. The patient can be spared the trauma of pocket depth measurements of the teeth that are Class 3 mobile and clearly to be extracted. The usual indicators of bleeding and plaque should be carried out for any teeth that will remain to determine the future periodontal plan and serve to motivate the patient’s hygiene regimen.  The presence of sinuses and any signs of acute infection should be noted, especially in potential implant sites.

The condition of the pre-existing teeth must be assessed on two counts. The first is how they will impact on measuring FWS, recording lip support, midline position and line of arch for construction of the temporary bridge. The second is how the teeth remaining after extraction will occlude against the bridge in terms of FWS, mobility, posterior support, anterior guidance, over-eruption and longevity.

Edentulous saddles in the premolar area of the opposing arch should be assessed to restore posterior support where necessary.

Details of the occlusion need to be noted and indicators of disharmony such as facets and abfraction lesions recorded. The temporary bridge should follow the anterior and lateral guidance prescription of the natural teeth as far as possible.

The labio/bucco-lingual/palatal ridge width is recorded at each site between the first molars. The ridge width is palpated at a higher, more apical, level to ensure adequate width for the full length of the proposed implant site. Palpation can normally be carried out with finger and thumb pressure. The degree of loss of buccal cortical plate over a compromised tooth can be assessed by moving the tooth laterally during palpation.
 
Radiographic examination
A panoral radiograph (Figure 5) can be regarded as part of the routine assessment for this type of case. It not only provides essential data but is a useful aid for explaining problems and treatment planning to the patient.

The height of the alveolar ridge is recorded between the first molars taking account of the maxillary sinuses, nasal cavity and inferior dental canals. A large incisive canal will also impact on possible implant placement. The extent of bone loss due to periodontal and periapical lesions is noted. Even advanced periodontal bone loss has little impact on implant placement if the patient has a high lip line and the ridge has to be recontoured above the affected bone, so long as sufficient bone volume remains to allow placement. Extensive periapical or buccal bone loss may mean that an adjacent site needs to be chosen, or indicate the need for augmentation.

Periapical radiographs are required when the DPT does not provide sufficient definition for accurate diagnosis. A CT scan is mandatory if the examination indicates inadequate alveolar ridge volume. The patient must understand that the scan may show there is inadequate bone volume for the all-on-4 procedure to be viable, and an alternative, possibly unacceptable, surgical approach may be indicated.

To avoid unnecessary exposure, CT scans should only be taken after the patient has indicated a clear wish to continue with the all-on-4 plan, and understands the procedure, the time frame and financial implications.

Treatment options and provisional plan
As part of the dentist’s medico-legal and ethical responsibilities, the patient must be made aware of all the possible treatment options. Anatomical models of the mandible and maxilla (Salvin dental specialities) and the sinus lift model (Trycare) are helpful as educational aids and we also use a maxillary model with four Speedygroovy dummy implants and multiunits in place. We provide a short Powerpoint presentation showing the Nobel Biocare all-on-4 slides with clinical photographs as well as radiographs of our own cases. We also keep a list of previous all-on-4 patients who are happy to talk to prospective patients to allay their fears and provide a patient’s perspective of the treatment process.

Type of implant
The all-on-4 protocol recommends the use of a minimum 4.0mm diameter Nobel Biocare Speedygroovy implants whose solid nature and aggressive thread provide a robust primary fixation. The Tiunite surface has been shown to be reliable in these types of cases4. These implants are available in convenient lengths of 7, 8.5, 10, 11.5, 13, 15 and 18mm. The full Speedygroovy range includes 5.0 and 6.0mm diameter units although the 3.5mm diameter implants are only supplied in lengths of 10, 11.5, 13 and 15mm. We keep a stock of four of each length of the 4.0mm regular platform (RP) with two 3.5mm length 13mm and one length 15mm for situations where the ridge proves to be narrower than foreseen.
The multiunit abutments are specific for each diameter and are available as either straight, 17° or 30° options. There are limited multiunit gingival height options available for the narrow and wide platforms and these are shown in the table below.

It would be extremely expensive to maintain a complete stock of four of each choice, we do keep four each of the RP straight 2mm, RP 17° 2mm and RP 30° 4mm platforms with three 17° 2mm abutments for the narrow platform (NP) emergency implants.
 
Planning implant sites
Manipulating digital radiographs using software such as Kodak’s dental imaging version 6,6,3,0 allows the surgeon to alter the position, angulation, length and diameter of virtual implants on the screen in two dimensions. This not only simplifies planning but also helps to explain the procedure to the patient.

CT scan software such as Simplant offers the same facility in three dimensions and also provides a bone density reading in the proposed implant site.
Nobel Biocare produces an acetate for Speedygroovy implants magnifications of 100%, 130% and 170%. Wherever possible, 5mm ball bearings should be used to calibrate DPTs at each implant site, but the angled nature of the posterior implants means that the guides should remain merely guides and not be taken entirely on trust.

If digital imaging software is not available, a print should be made of the DPT and used as the basis for construction drawings. Conventional DPT radiographs can be covered with a fixed sheet of transparent paper for the same purpose.

The starting point for planning implant placement is to use the diagrams or monitor to draw a real or virtual line at the level to which the bone will be trimmed. In the mandible the level is found after the alveolar bone supporting the periodontally compromised teeth is removed. The same procedure applies to the maxilla but the level must always be just above the smile line to ensure the acrylic gumwork – mucosa junction is hidden (Figures 6 and 7). This consideration occasionally applies to the mandible when patients reveal their lower anterior teeth and gum when speaking.

Further bone reduction is indicated if there is insufficient inter-maxillary space, although this can be limited below the sinus.

The position of the implants is then determined using the new baseline and the previous labio/bucco-lingual/palatal dimension readings. The posterior implants are positioned as far distally as possible and mesial to the anterior wall of the sinus in the maxilla, and mesial to the mental foramen and anterior loop of the ID canal in the mandible, using a maximum angulation of 45° with 30° abutments. Their length is determined by the sinus and floor of the nose in the maxilla and the lower border in the mandible (Figures 13 and 14).

Ideally, the anterior implants will be positioned in the lateral incisor sites for more even support of the future bridgework and to allow sufficient bulk of acrylic between the abutments to prevent the temporary bridge fracturing under load (Figure 8). The angulation of the anterior implant abutments is decided by the patient’s skeletal relationship and the position of the remaining ridge relative to the cingula of the incisor teeth of the bridgework. The cingula are the optimum point of access to the retaining screws because this minimises the bulk of supporting acrylic around the temporary abutments and maintains the integrity, and therefore the aesthetics, of the labial face of the incisor teeth.

The bulk of acrylic is difficult to avoid in extreme Class 2 div 1 cases where it is necessary to provide a bite plane for occlusion with the lower incisors. The retroinclined nature of the incisors in a pronounced Class 2 div 2 set up also complicates the planning of the implant position relative to the cingulae and the choice of mutiabutment abutment, and this is not made easier by the narrow nature of the ridge in this type of skeletal relationship.

In cases with limited bone volume in the maxilla it may be necessary to shorten the posterior implant to prevent contact with the anterior implant, and this will mean planning an abutment with a different angle.

When there is limited bone volume in the mandible there is often little available bone above the mental foramen. In such cases the angulation of the posterior implants is planned primarily to avoid the anterior loop of the IDB/c with the appropriate (usually straight or 17°) angled abutments.

At this point the patient needs to be informed of the costs and different characteristics of the materials available for construction of the definitive bridgework, and give written consent for the actual treatment to begin. 

References
1. ‘All-on-four’ immediate function concept with Brånemark System implants for completely edentulous mandibles: A retrospective clinical study. Maló P, Rangert B, Nobre M. Clin Implant Dent Relat Res 2003;5 (suppl. 1):2-9
2. ‘All-on-four’ immediate function concept with Brånemark System implants for completely edentulous maxillae: A 1-year retrospective clinical study. Maló P, 3. Rangert B, Nobre M. Clin Implant Dent Relat Res 2005; 7(suppl 1): S88-S94
Clin Implant Dent Relat Res 2006; 8 (4) 223-32
4. Maló P, Nobre M, Rangert B. Implants placed in immediate function in peridontally compromised sites: A 5-year retrospective and a 1-year prospective study. J Prosthetic Dent 2007; 97 (suppl 1): 86-95
5. Maló P, Nobre M, Lopes A. The use of computer-guided flapless implant surgery and 4 implants placed in immediate function to support a fixed denture: Preliminary results after a mean follow-up period of 13 months. J Prosthetic Dent 2007; 97 (suppl 1) : 26-34.

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