The All-on-4®fixed implant-borne total rehabilitation procedure for the mandible 22 January 2018

The All-on-4® treatment concept (Nobel Biocare) within the framework of fixed implant-borne total rehabilitation for the maxilla and mandible has become a scientifically proven and clinically prescribed therapy.

The All-on-4® surgical protocol, developed at the end of the 1990s by Paolo Malo, provides simple and immediate full-arch rehabilitation for edentulous patients with 12 fixed teeth on just 4 implants, with immediate loading, no later than 24 hours after the operation.

In the clinical study chosen for this issue of the "IFCIA Newsletter", we
provide a stage-by-stage description of mandible rehabilitation development using a fixed prosthesis based on a simple, accurate and standard protocol and quick execution, restoring the patient's masticatory function and aesthetics.  

Case history and x-ray

An 85 year-old woman, with no medical history and no general contraindications, comes for a consultation for fixed mandibular rehabilitation.

Clinical observation showed a maxillary implant-borne bridge with which the patient is happy. The patient is interested in a partially removable  mandibular prosthesis. The prosthetic space seems suitable without having to lose the VDO, as it is maintained by the three residual teeth: 34, 35 and 48. The edentulous ridge is thin and irregular and the periodontal biotype is thin (Figures 1, 2, 3).

 

 

 Figure 1: Regarding implant-borne maxillary reconstruction, the removable mandibular prosthesis is continually unstable and uncomfortable for the patient. The stability of maxillary soft tissue regarding the buccal denture flange, associated with the regular patient care, lead us to suggest a fixed implant-borne mandible reconstruction.

 

Figure 2: Despite partial dentition, the VDO remains due to the presence of 3 residual teeth. The available prosthetic volume associated with weak antero-posterior variation of the mandibular base, enables us to consider the final, suitable prosthetic outcome.

 

Figure 3: The edentulous ridge is thin, but it is a rounded semi-circle shape. This shape is suitable for obtaining a significant distance between the anterior and posterior implants, thus constituting a large support polygon.

 

 

The x-ray examinations—panoramic x-ray and cone beam CT—show knife-edge ridge form (Cawood and Howell IV classification) and the presence of a residual root in site 33 (Figures 4, 5 and 6).

 

 

Figures 4, 5 and 6: Despite significant mandibular osseous volume on the panoramic x-ray, the CBCT shows class 4 bone resorption (Cawood et al.) right mandibular sector. This poor bone height shall be further lowered with the bone adjustment necessary prior to implantation.

 

Therapeutic decision and operative procedure:

The patient chooses the All-on-4®   fixed implant-borne total rehabilitation of the mandible.

The protocol shall involve pre-prosthetic guiding assembly which shall be validated for aesthetic and functional aspects in the mouth prior to the surgical phase. At the end of this test, the surgical phase will entail extraction of teeth 34, 35 and 48 and the root of 33, and 4 simultaneous implants in the symphyseal area and filling the extraction sockets.

For immediate loading, an impression is taken just after surgery by using a surgical guide like the dental implant tray and preserving the previously recorded intermaxillary relation.  The provisional resin implant-born prosthesis shall be fitted within 24 hours of the operation. The immediate prosthesis, designed and produced using CAD/CAM software (Procera Implant Bridge®, Nobel Biocare), shall be made from a titanium framework and resin teeth. It shall be fitted 3-6 months later.

 

Pre-prosthetic stage:

A topographic analysis including the arch shape, residual osseous volume, anatomic variations, lip support, tooth-to-tooth proportions and their positions is essential for the calculation of the prosthetic space available and preview the final aesthetics. The outcome of the combination of these elements will result in the prosthesis being fitted immediately with or without a buccal denture flange (Figures 7 and 8).

Figures 7 and 8: A new prosthetic mounting guide is aesthetically and functionally prepared and checked.  The teeth distribution is regular and consistent with 34, 35 and 47 which shall be extracted. The incisors are delicately placed in front of the crest thus reducing anterior projection in the absence of osseous foundation variation.

 

Surgical stage:

Here is a reminder of the steps in this stage:

1- Extraction of residual teeth

2- Implant fitting

3- Abutment connection

4- Extraction socket filling

5- Impression coping connection

6- Sutures

First, after local anaesthesia, the residual teeth were extracted. A crestal incision in the keratinized gingiva layer extended by two small releasing incisions in the posterior areas enables us to carefully uncover the mental foramen, major antonomical bodies in this zone. Two implants are inserted in site 32 and 42. They are spaced 12mm apart. These are the most anterior implants. The meeting of these two implants with an imaginary line shall determine the anterior limit of the support polygon. The next stage involves fitting the posterior implants honouring the buccal corridor developed by the guide. They are distally tilted at a 30º angle with a crestal emergence profile above the mental foramen. The meeting of these two implants with an imaginary line shall determine the posterior limit of the support polygon. This position, respecting the All-on-4® protocol, allows us to increase the support polygon and reduce the maximum prosthetic cantilever. To avoid weakening this whole structure, the recommended length of this extension should not exceed 1.5 times the antero-posterior distance of the polygon. The surgical insertion torque for all of the implants surrounding the 40N.cm allows us to securely tighten the 1.5mm straight multi-unit abutments at 35Ncm on the anterior implants and 35N.cm on the 2.5mm straight abutments on the posterior implants. 

At this stage, before closing the sites with simple sutures, the extraction sockets are filled with Bio-Oss® (Geistlich) and the impression coping is connected (Figures 9 and 10).

 

  

Figures 9 and 10: A full-thickness crestal incision on the keratinized gingiva facilitates the closure of the wound. The adjustment of the crest, even though the bone height availability has decreased, allowed us to fit the implants without a bone graft. The copings are immediately fitted to take the impressions and it is sutured.

 

Figure 11: The post-operative panoramic X-ray allows us to view the symmetrical distribution of the symphyseal sutures of the 4 implants (Nobel Replace CC PMC of 4.3x13mm, Nobel Biocare). The approx. 15° inclination on the posterior implants only allowed us to use 2.5mm straight abutments in this clinical situation.

Post-operative impression and immediate loading

After adjusting the height of the impression copings in order to avoid any kind of interference with the opposing prosthesis during recording, a dental dam is interposed on top of the gingiva giving protection to the sutures and preventing the expansion of the recording product around the base of the copings. The impression is taken in occlusion with a bisacryl resin by using the surgical guide. Respecting industrial instructions, in terms of the duration of polymerisation, interest in using this product lies in getting the position of copings to fix rigidly and a recording of the post-operative gingival relief. The prosthesis prepared in the lab is fitted to the mouth the following day (Figures 12 to 14).

 

 

 

Figures 12 and 13: The impression is immediately loaded with the surgical guide which is a transparent resin duplicate of the prosthetic project. It is performed in occlusion and with a bisacryl resin. The regular emergence profile of the prosthetic screws at occlusal surface level can be observed.

 

Figure 14: The prosthesis is carefully prepared in the laboratory (Laboratoire Stéphane Hurtado - Paris), then fitted to the mouth the same day or 24 hours (max.) following surgery. A small space at intrados level may be considered at this stage in order to facilitate hygiene and avoid tissue compression in the healing process.

 

 

Prosthetic stage: Screw-retained implant-born immediate prosthesis

Three months after surgery, the provisional prosthesis is removed and the osseointegration of the implants is checked (Figure 15). A plaster impression is made with the copings in place. Despite the precision of this technique, in order to minimise the adjustments, a plaster core shall be used to check this stage.

 

Figure 15: The provisional prosthesis is removed. The straight abutments are tightened to 35 N.cm. The healing process and remodelling of the keratinized tissue and the osseointegration of the implants are checked and validated. An impression, in the plaster of preference, is taken in order to gage the exact position of the implants and ensure a passive framework.  

Once the aesthetic teeth arrangement has been confirmed again, production of the titanium framework using CAD/CAM software can begin. This machining method provides an accurate fit compared with a cast framework while guaranteeing excellent biomechanical properties.

The final prosthesis is made. It is essential that its passive insertion, the functional and aesthetic parameters are checked, in accordance with the provisional bridgeworks data. If required, occlusal stability is refined in the mouth (Figures 16, 17 and 18).

Once the whole process is done and checked, the prosthesis screws are tightened to 15N.cm and the screw channels are filled with a composite material over the Teflon bands. A reference X-ray control is performed (Figure 19).

 Figures 16, 17 and 18: The final prosthesis is made using the CAD/CAM software with a titanium framework (PIB - Procera Implant Bridge, Nobel Biocare) and precast filled resin teeth. It is fitted to the mouth and the occlusion is refined. Harmonious integration is successful. The patient is completely satisfied with the restoration of the aesthetic and masticatory function (Prosthesis: Dr Richard Massihi, Laboratoire Stéphane Hurtado).

 

Figure 19: The reference X-ray shows perfect stability at bone level. At maxillary level, the current data guides us towards reconstructions on implants 4 to 6.

Discussion:

Due to its hardiness and efficiency, implant-borne rehabilitation of the mandible with only 4 implants—the ALL-on-4® approach—has become a common and frequent indication. After just a few sessions and for a reasonable cost, worried and disconcerted patients regain their masticatory, taste, aesthetic and phonetic functions, which were often troubled in the past. Beyond its incredible clinical triumphs and high levels of success reported in different literature, the scientific basis of this approach lies in capitalising on abundant and regular publications (1, 2, 3, 4).  However, only excellent consideration, a pre-project study and respect for protocols lead to a successful, expeditiously concluded job.

The retention guaranteed by an immediate provisional prosthesis relying on implants distributed throughout the largest possible support polygon, associated with increased primary stability obtained through a surgical torque (minimum insertion 35N.cm), and limited, low intensity micromovements not exceeding 150µ around the implants, promote stable bone contact and facilitates osseointegration. Drilling under implant sites and the use of conical implants on rough surfaces helps improve the post-operative histological remodelling process (5, 6).

In the mandibular posterior regions, the inclination of the two implants with distal emergence profiles avoids the mental foramen. The posterior ridges at this level are most often resorbed in patients with older tooth loss. In terms of the maxilla, the use of 4 to 6 implants in the intersinus area with two posterior implants (equally inclined), justifies the space between the sinus lift operations.

The inclination of these implants allows cantilevers limited to 10 to 12mm, thus increasing the length of the arch consisting of 12 teeth for the final prosthesis. These cantilevers are advised against in retained provisional prostheses loaded immediately after surgery. The bone reaction around angled implants and their clinical stability, though sometimes controversial, may justify their use in the framework of overall retention (7, 8, 9, 10).

Regarding the choice of occlusal concepts, a universal consensus does not currently exist. Various factors must be taken into account since the perception threshold of the contacts varies based on the opponents (11). This includes the presence of natural teeth, implant-borne teeth and a full removable denture. For certain authors, canine functions, or even group functions are advised; for others, balanced occlusions are recommended (12, 13, 14).

 

Conclusion

The main purpose of such prosthetic rehabilitation is the patient's satisfaction at functional and aesthetic levels. A preliminary pre-prosthetic project is essential. It shall determine the direction of the treatment plan.

The experience and understanding of the surgical-prosthetic team along with that of the prosthetist will be key to the success of this type of treatment.

For long-lasting, stable results, it is necessary to monitor recovery. The prosthestic concept should be designed to facilitate effective daily cleaning without any constraints for the patient. The practitioner, in turn, checks the stability of the osteointegration and occlusion by eliminating all risk factors; check up may be bi-annual or annual, it is adapted to suit the candidate (15).

The application of the All-on-4® concept has allowed us to treat elderly patients. They benefit from fixed rehabilitation according to their main wish. Given its reliability and simplicity the All-on-4® approach means avoiding extensive bone reconstruction, thereby reducing the overall cost of the treatment. A well-mastered All-on-4® approach ensures quick clinical execution, with only a few sessions required in the practice.

 

Bibliography:

 

1 - Malo P, de Araujo Nobre M, Lopes A, Moss SM, Molina GJ. A longitudinal study of the survival of All-on-4 implants in the mandible with up to 10 years of follow-up. J Am Dent Assoc 2011;142:310-20

2 - Balshi TJ, Wolfinger GJ, Slauch RW, Balshi SF. A retrospective analysis of 800 Brånemark System implants following the All-on-Four™ protocol. J Prosthodont. 2014 23:83-8

3 - Soto-Penaloza D1, Zaragozí-Alonso R2, Penarrocha-Diago M3, Penarrocha-Diago M4. The all-on-four treatment concept: Systematic review. J Clin Exp Dent. 2017 Mar 1;9(3):e474-e488.

4 - Mozzati M, Arata V, Gallesio G, Mussano F, Carossa S. Immediate postextractive dental implant placement with immediate loading on four implants for mandibular full-arch rehabilitation: a retrospective analysis. Clin Implant Dent Relat Res 2013;15:332-40

5 - Cordioli G, Majzoub Z, Piattelli A, Scarano A. Removal torque and histomorphometric investigation of 4 different titanium surfaces: an experimental study in the rabbit tibia. Int J Oral Maxillofac Implants. 2000 Sep-Oct;15(5):668-74.

6 - Gotfredsen K1, Berglundh T, Lindhe J. Anchorage of titanium implants with different surface characteristics: an experimental study in rabbits. Clin Implant Dent Relat Res. 2000;2(3):120-8.

7 - Francetti L, Romeo D, Corbella S, Taschieri S, Del Fabbro M. Bone level changes around axial and tilted implants in full-arch fixed immediate restorations. Interim results of a prospective study. Clin Implant Dent Relat Res 2012;14:646-54

8 - Zeynep Gümrükçü Z., Korkmaz Y., Korkmaz F.  Biomechanical evaluation of implant-supported prosthesis with various tilting implant angles and bone types in atrophic maxilla: A finite element study  Computers in Biology and Medicine 86 (2017) 47–54

9 - Maminskas J, Puisys A, Kuoppala R, Raustia A, Juodzbalys G. The Prosthetic Influence and Biomechanics on Peri-Implant Strain: a Systematic Literature Review of Finite Element Studies J Oral Maxillofac Res 2016;7(3):e4

10 - Testori T, Galli F, Fumagalli L, Capelli M, Zuffetti F, Deflorian M, Parenti A, Del Fabbro M. Assessment of Long-Term Survival of Immediately Loaded Tilted Implants Supporting a Maxillary Full-Arch Fixed Prosthesis. Int J Oral Maxillofac Implants. 2017 Jul/Aug;32(4):904-911.

11 - Jacobs R, van Steenberghe D. Comparative evaluation of the oral tactile function by means of teeth or implant-supported prostheses. Clin Oral Implants Res. 1991 Apr-Jun;2(2):75-80.

12 - Rilo B, da Silva JL, Mora MJ, Santana U. Guidelines for occlusion strategy in implant-borne prostheses. A review. Int Dent J. 2008 Jun;58(3):139-45

13 - Kim Y, Oh TJ, Misch CE, Wang HL. Occlusal considerations in implant therapy: clinical guidelines with biomechanical rationale. Clin Oral Implants Res. 2005 Feb;16(1):26-35.

14 - Ravel M., Sousa, & al. Influence of connection type and implant number on the bioméchanical behavior of mandibular  full arch rehablitation .  IJOMI  2016,31, 750-760

15 - Sojod B., Abillama T.M. La maintenance péri-implantaire, le fil dentaire,2013 Sept ;26 :26-29

 

Key words:

All-on-4®, aesthetic, fixed bridge, inclined implants, angled implants, cantilever, prosthetic extension, support polygon, screw-retained prosthesis, overall rehabilitation.