All-on-4 an introduction
In recent years, All-on-4 has gathered considerable interest in the part of the dental community involved with dental implants. This article, and those that follow, will explain where the term has arisen from, how the procedure differs from other techniques and the specific advantages and compromises to the patient that are necessary when electing to have this treatment option.
Securing a full arch bridge with four implants is not a new concept. The original Brånemark mandibular full arch implant protocol1, 2 outlined positioning five parallel implants between the mandibular foramen to secure a screw-retained cast beam veneered with acrylic and resin teeth (figures 1 and 2). The original protocol adopted by the Brånemark clinic was later adapted to four implants. This treatment option (with or without immediate loading) has for more than 30 years been the standard ‘fixed’ solution for the edentulous mandible when there is insufficient bone above the inferior dental canal for more posterior implants.
The situation has been more challenging in the maxillae. Due to the increased incidence of implant failure in the maxillae, and more specifically the posterior maxillae where the bone has less volume and is less dense, the treatment protocol was for the use of six or eight implants (fig 3). Eight implants is by no means the maximum number of implants that can be used in the maxillae and in their drive to seek the best long-term solution, some clinicians have advocated using 12 to 14 implants and cemented-bonded restorations.
As the number of implants increases, other problems appear: there is a need for more bone volume to retain the implants, time for surgery and restorative phases increases significantly, costs increase and maintenance becomes more difficult. Research in dental implants and the introduction of surface modifications have seen a reduction in failure rates3, and CAD/CAM technology being introduced for the fabrication of superstructures4.
As the confidence with dental implant success has grown, there has been a drive to provide patients with the results they seek more quickly. The conventional approach to managing the maxillae may take a year to 18 months from initiation to completion, allowing for healing after extraction, implant integration, second stage surgery and restoration fabrication, all the while the patient having to wear a complete upper denture, which they hate.
The challenge to reduce the cost and the time involved started with immediate loading protocols, which began in the mandible5, where success rates were already high and treatment time was the shortest. Single teeth immediate restoration in the upper arch came next and finally immediate full arch restoration. Initially, the number of implants remained the same, often with researchers placing ’sleeper implants’ in case of failure6, 7.
With so much at risk, biologically and fiscally, it is essential that general practice adopts protocols only after there is a body of evidence to suggest efficacy.
The evidence for management of the edentulous maxillae with four implants is now over 10 years. The concept of All-on-4 was created by Portuguese dentist Paulo Malo and development was carried out in the 1990s funded by Nobel Biocare, initially for the mandible and then the maxillae8, 9 (fig 4). The protocol is specific for Nobel Biocare implants and the term has been trademarked. Given the dramatic impact this treatment protocol has had, many other implant companies are now marketing that their systems are also suitable. Clinicians should be cautious as, in many instances, there is limited evidence to validate the claims.
The significant features with the All-on-4 concept are:
- Four, or more, Nobel Biocare implants to support a full arch maxillary or mandibular hybrid bridge (hybrid bridge = a fixed bar, usually of CAD/CAM titanium and veneered with acrylic resins and denture teeth [figs 5 and 6])
- The two most distal implants are angled in order to avoid anatomical structures (mental foramen and ID canal in the mandible, maxillary sinus in the maxilla), to allow implants of optimum dimensions in more dense bone and reduce cantilevering
- In the maxilla, the residual alveolar ridge is, in most instances, resected to increase the restorative space and hide the transition from restoration to patient under the upper lip (transition zone) (figs 7 and 8)
- Following insertion of the implants, a provisional bridge is immediately fabricated on site, and fitted, which acts to splint the implants together
- The bridge and implants are under functional immediate load
- The definitive hybrid bridge is fabricated following the required integration and healing period (usually not less than three months).
Successful application of this technique requires full understanding of many advanced and challenging principles, among which are:
- The fundamentals of comprehensive rehabilitation and aesthetic smile design
- Experience in managing the psychological aspects of providing full arch implant restorations
- Occlusal concepts including management of a patients occluso-vertical dimension in centric relation
- Intimate knowledge of the materials, techniques and recommended implant components required
- Experience in management of surgical and restorative implant complications and challenges
- Knowledge of laboratory techniques and materials with access to an onsite dental laboratory
- Comprehensive knowledge of the oral anatomy and advanced surgical planning techniques including CBCT interpretation
- Experience in advanced surgical techniques including mental nerve location, sinus mapping, alveolar ridge reduction and soft tissue resection
- Immediate extraction and implant placement techniques
- Design and use of radiographic and surgical guides
- Use of grafting materials and barrier membranes
- Achieving adequate primary stability in all bone types and immediate loading concepts
- Full arch bridge design concepts for long-term maintenance and oral hygiene
- Surgical and non-surgical management of soft and hard tissue implant complications.
Despite the challenges in providing this treatment option, there is significant marketing by dentists and implant companies alike about the concept. The reasons for this can be attributed to the significant advantages over previous options, which the patient may benefit from:
- Implants are placed and a bridge is fitted on the same day, avoiding the need for a complete denture
- There is only one surgical experience for the patient. Conventionally implants were covered under the gingivae and a second surgical appointment was required to uncover them
- Patients previously requiring sinus grafts or onlay grafts may now be treated in one visit more cost effectively and without the need for a two stage six to 10-month healing period
- In a periodontally or restoratively compromised dentition patients may proceed from dentate to implant supported bridgework without ever having to experience a denture
- A predictable long-term result
- With only using four implants costs can be significantly lower than previous full arch alternatives
- Maintenance and oral hygiene measures can be performed much more easily than on more conventional bridgework
- Significant aesthetic compromises can now be immediately improved and self confidence regained (figs 9 and 10).
Disadvantages specific to this technique are few, but need to addressed at the earliest opportunity:
- Realising expectations – the final restoration is, in effect, a screw-retained palateless denture. Patients need to be made aware that the procedure is not designed to give them their teeth back, but to offer them a replacement for having no teeth. Essentially, it is the replacement of a body part with a prosthesis in much the same way that a missing arm or leg may be replaced
- There may be short and long-term challenges such as failure to achieve the required primary stability for immediate loading, restoration fracture, speech and functional changes (fig 11)
- Despite being more cost effective than options involving more implants, a brief review of costs advertising the technique, using the recommended Nobel Biocare implant systems, shows costs in the region of £10,000 to £15,000. These are still significant and need to be carefully discussed and explained prior to any treatment being carried out.
Achieving a positive patient outcome requires careful planning and execution. We will over the next two articles review two cases showing how the treatment was planned and executed from consultation and differential treatment planning through surgical implant placement, final restoration and long term maintenance procedures.
About the author
This article is presented by Kevin Lochhead, specialist prosthodontist at Edinburgh Dental Specialists. Surgical expertise by Professor Glen Lello, Prof Lars Sennerby, Mr Martin Paley and Mrs Gillian Ainsworth. All laboratory work was carried out by the team at Edinburgh Dental Implant Laboratory.
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