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Authors:Dr. Happy Bajaj, Dr. Anmol Mahajan

Abstract:

Dental implantology has proven to be a predictable method of restoring function in oral cavity. But the placement of implants in the posterior region of jaw is often associated with anatomic complications. Hence the concept of using two axially implants in the anterior region and two tilted posterior implants has been popularized as the All On four concept. The purpose of this article is to review the advantages, indications and prosthetic considerations for placing dental implants with immediate loading using the All-on-Four concept.

Key words: All-on four concepts, Tilting posterior implant, Severe atrophy maxilla and mandible, Full arch rehabilitation

Introduction:

Partial or complete edentulism leads to compromised masticatory efficiency and impaired quality of life leading to significant oral health burden 1-2. Complete edentulism can result from various factors such as periodontitis, dental caries, trauma, intentionally removed or lost post surgical or after radiotherpeutic dose in oral carcinoma etc3. The edentulous condition has an negative impact on oral health quality of life, to improve the quality of life and increase the life expectancy need to fabricate prosthesis that provides a replacement for the loss of natural teeth.
The recent advances in dental implant have improved the treatment option for patient by providing a fixed prosthesis. The common complaints associated with conventional complete denture are pain, discomfort, gagging, poor retention, stability, decrease masticatory performance and decrease oral – sensory function4,5.
In recent times, osseointegrated implant retained prosthesis improves the quality of life of patient as compared to conventional complete denture. The conventional way of treating edentulous patient with full mouth implant supported fixed prosthesis may require placement of multiple number of implants, bone augmentation procedures, longer treatment span and multiple number of surgical procedure.
Thus, such techniques are not always comfortable to patients. But the stress analysis studies have demonstrated that four implants placed as corner stone:- two posteriorly and two anteriorly, with good anterioposterior distance (A-P spread) is an optional number for complete arch prosthesis. This concept of using 2 axially placed implants in the anterior region and two tilted implant in posterior region has been popularized as All on four concept6,7,8.

Treatment concept 5,9,10,11:

The “All-on Four” treatment concept was developed by Paul Malo (1990) and encompasses an immediately loaded full arch fixed prosthesis anchored with four implants in either maxilla or mandible utilizing immediate function full arch prosthesis in maxilla and mandible has been documented as a predictable and successful procedure based on long term results.
After teeth has been lost in completely edentulous jaw, there is often significant bone loss due to resorption resulting in minimal bone volume, poorer quality bone, need bone grafting to be carried prior to implants. Such procedures are more intensive, require multiple surgical steps, elongate the time of treatment and cause tissue morbidity to some extent.
Dental implants traditionally have been placed axially, along the long axis of the desired tooth to accept forces axially down the implant. In the completely edentulous jaw, there is often insufficient vertical height after bony resorption in the posterior regions. This may be due to bone resorption after teeth removal and the proximity of the inferior dental nerve in the lower jaw and the maxillary sinus in the upper jaw.
Historically, there would be a need for bone grafting to augment the posterior regions to build vertical height for adequate implant length, adding significant time, morbidity and cost to the procedures. In the maxilla, sinus augmentation with a lateral window approach is necessary with an extended treatment time of up to 5 months.
In the mandible, bone augmentation with onlay grafts or nerve transposition could be carried out to allow placement of implants posteriorly. Other alternatives to overcome limitation in bone quantity have been the use of long distal cantilevers, short implants or implants placed into the zygoma or pterygoid plate. These procedures have their own advantages, risks and complications and require significant expertise for predictable success.

The “All-on-4” concept utilises:
 
  • Two axially orientated implants in the anterior region; and
  • Two tilted posterior implants

The All-on-4 technique involves tilting the posterior implants, allowing the clinician to avoid anatomical structures. It also enables the placement of longer implants into better quality bone anteriorly. When used in the mandible, tilting of the posterior implants makes it possible to achieve good bone anchorage without interfering with the mental foramina. In severely resorbed maxillae, the tilted implants are an alternative to sinus floor augmentation.
Biomechanical measurements reported by Krekmanov et al indicate that tilted implants as part of a prosthetic support do not have any negative impact on load distribution. Tilted distal implants facilitate a better spread of the implants along the alveolar crest. This feature is beneficial for load distribution and allows the final prosthesis to hold as many as 12 teeth with only short cantilevers. This advantage of tilted implants in minimizing cantilevers is significant, as a longer cantilever can produce significant biomechanical stress on the implants. Furthermore, tilted implants allow an increased interimplant space congenial for oral hygiene procedures.
Capelli et al showed that marginal bone loss is similar between tilted and axially placed implants.'" Thus, angulating implants causes no deleterious effects to the osseointegration process Furthermore, the All-on-4 concept is associated with a cumulative implant survival rate of 92.2% to 100%

Indication 9: All on 4 concept indicated in those patient who met with following criteria:
  1. Maxillary/ mandibular bone quality which allows for placement of at least four implants of at least 10mm in length in either healed or immediate extraction sites.
  2. No medical history, good systemic health with satisfactory oral hygiene.
  3. Implant should attain a sufficient stability for immediate function.

Contraindication4:
 
  1. If there is insufficient bone volume, irregular or thin bone crest.
  2. Remaining teeth that interfere with the planning of implant placement.
  3. In patients with insufficient mouth opening it is difficult to accomoate a surgical instrument in limited mouth opening.

Treatment Planning12-15:

After medical evaluation patient has to undergo various examinations and protocols for the placement of implant which are listed as below:
Examination:
1. Extraoral Examination:
  1. Smile line: high or low smile line which reveal the visibility of transition zone between the junction of the soft tissues and bridge.
  2. Lip support and length: patient should be assessed that they require a flange or lip support or not.
  3. Vertical dimension of occlusion: determine the lower facial height of patient.

2. Intraoral Examination:
  1. Thickness of mucosa and kertinization of tissue.
  2. Inter arch relationship: bone resorption occurs as that the ridge is located palatally in the maxilla and more buccally in the mandible which often leads to a class III relationship for fully edentulous patient.
  3. Sign of parafunction or dental disease.

3. Radiographic Examination: a computed tomography scan should be taken to assess bone volume. The prognosis is good for implant placement when ridge height is 10 mm for both maxilla and mandible and ridge width is 6mm for maxilla and 5 mm for mandible.
Surgical Protocol:
  1. Prophylactic antibiotic and preoperative anti-inflammatory and oral hygiene instruction are recommended to patient before and after the surgical procedures.
  2. Local anesthetic injection (both nerve block and infiltration) are given to patient in combination with sedation if required.
  3. Full thickness flap with mid- crestal incision was given to raise the flap to expose the ridge. Minor alveolectomy procedures can be carried out with bone ronguers or bur to level the ridge.
  4. For the placement of implant, surgical guide was used for correct positioning, angulation and emergence of implant.
  5. In maxilla two distal implants were placed in posterior region and tilted anterior to maxillary antrum, at an angle of 30-450. Two straight implants were placed in anterior maxillary region stabilized by nasal floor.
  6. In mandible implants are positioned anterior to mental foramina and inserted at an angle of 30-450 and two straight anterior implants are placed in anterior mandible.
  7. As implant of appropriate diameter and length was placed, Abutment straight, 170 multiunit abutment, 300 angulated abutment with different collar heights are placed into implants.


Prosthetic protocol:
Procedural steps for provisional and final prosthesis protocol are attained below:
 
  1. Open tray multiunit impression copings are used which are splinted with low shrinkage autopolymerising resin or wire to attain a passive fit of prosthesis.
  2. Impression made with polyvinylsiloxane to record the implant position and soft tissue.
  3. Heat cure provisional restoration was fabricated and delivered to the patient on the same day of implant placement. Provisional restoration was tightened to 15Ncm.
  4. Provisional restoration which is delivered to the patient should have short cantilever to minimize load and possibility of fracture of prosthesis.
  5. Occlusion is carefully adjusted so that there is contact only in intercanine region and no premature contact posteriorly.
  6. Instruction are given to the patient for maintenance for oral hygiene with a chlorhexidine mouth wash, as well as soft diet for a period of 6 weeks to minimize the micromotion. Definitive prosthesis was delivered after 3-4 months of surgical procedures.


Final prosthesis protocol:

Implants should be assessed for oseointegration, esthetic and provisional restoration should be checked for esthetic and occlusion to check for any modification required. Final impressions made with a heavy or rigid body VPS material. The final impressions can then be verified using verification jigs to ensure accuracy and complete passive fit of the models. Following final prosthesis options are:
  1. CAD/CAM designed fixed prosthesis with zirconia and titanium frameworks. Individual crowns are cemented to the final bridge frameworks.
  2. Fixed prosthesis with CAD/CAM designed titanium or zirconia frameworks with acrylic veneering.
  3. Fixed prosthesis with cast metal and veneering porcelain.
  4. Removable fixed prosthesis :- e.g. milled bar overdenture / MK1 attached overdenture.


Occlusal scheme which is to be used for prosthesis:
  1. Bilateral balanced occlusion with an opposing complete denture
  2. Group function occlusion with shallow anterior guidance when opposing natural dentition
  3. No working and balancing contact on a cantilever.

Advantages of all–on- four concepts 9:
 
  1. Angled posterior implants avoid damage to anatomical structures
  2. Angled posterior implants allow longer implants anchoraged in better quality bone.
  3. Reduces posterior cantilever
  4. Eliminates bone graft in the edentulous maxilla and mandible in majority of cases
  5. High success rates
  6. Implants well-spaced, good bio –mechanics, easier to clean
  7. Immediate function and esthetics
  8. Final restoration can be fixed or removable
  9. Reduced cost due to less number of implants and avoidance of grafting in the majority of cases.

Discussion:

The All-on-Four concept is a highly successful treatment option for the edentulous patient with excellent clinical outcomes without major grafting, low cost and less surgical morbidity. As Malo P et al has popularized and published the All-on-Four concept, with good cumulative survival rates. He also did studies on immediate loading of four implants placed in edentulous mandible and concluded that immediate loading protocol had 96.7%-98.2% implant cumulative survival rate 16.

Krekmanov L and Bellini CM in their studies on stress analysis on tilted implants have shown no signicant difference between tilted or non-tilted implants 11, 17. Antonios Zampelis evaluated the tilting of splinted implants, whether it affects stress distribution in the bone surrounding the implant and also investigated that distally tilted implant is biomechanically superior to use of distal cantilever, using two dimensionally finite element analysis. He found that there is no stress distribution on bone with tilted implants and there is biomechanics advantage of using tilted distal implants rather than distal cantilever units 18.

Kyer Soon Kim found that use of tilted implants reduced the maximum stress in the distal crestal bone of the distal implant by approximately 17% relative to the axial implants 19. Kan et al said that combining these 2 concepts, the all-on-four immediate function concept is a simple, safe and effective surgical and prosthetic protocol for immediate function (within 2 hr) of four implants supporting a fixed prosthesis in completely edentulous mandible.

Recently, reported the integration of the all-on-four immediate function concept with computer aided guided implant placement for the rehabilitation of completely edentulous jaws showed that this treatment modality can be predictable with a high implant survival rates 20. There is a opinion of few practitioners for all-on-four concept is that this concept required a specialized implants and specialized trained professional, which turn out to be a expensive procedures than conventional implant prosthesis. But babbush in his study revelaed a significantly higher decrease in cost for the all-on-four procedures compared to conventional implant restorations 21.

Conclusion:

All-on-four concept has proven as a clinically effective technique for completely edentulous patients, cumulative survival rates. Marginal bone loss and other bio-mechanical factors are similar to better than that of conventional implant treatment. This concept can be adopted by implant dentists as a standardized dental procedure and can be routinely performed to most of the edentulous patient to deliver a short treatment procedures and an immediate functional full arch prosthesis in place of implant insertion surgery.

References:
 
  1. Muller F, Naharro M, Carisson GE. What are the prevalence and incidence of tooth loss in the adult and elderly population in Europe? Clin Oral Impiants Res. 2007;18(suppl 3):2-14.
  2. Wu B, Liang J, Plassman BL, et al. Edentulism trends among middle aged and older adults in the United States: comparison of five racial/ ethnic groups. Community Dent Orai Epidemioi. 2012;40(2):145-153.
  3. Singh AV, Singh S. Tilted Implant Concept for Full Mouth Immediate Loading Restoration. Int J Oral Implantol Clin Res 2014;5(1):12-23.
  4. Malo P, de Araujo Nobre M, Lopes A. The use of computer-guided flapless implant surgery and four implants placed in immediate function to support a fixed denture: preliminary results after a mean follow- up period of thirteen months J Prosthet Dent. 2007;97(6 suppl):S26–34.
  5. Capelli, M., Zuffetti, F., Testori, T. & Del Fabbro, M. (2007) Immediate rehabilitation of the com- pletely edentulous jaws with fixed prostheses supported by upright and tilted implants. A multi- center clinical study. The International Journal of Oral & Maxillofacial Implants 22: 639–644.
  6. Thomason JM, Feine J, Exley C. Mandibular two implantsupported overdentures as the first choice standard of care for edentulous patients. Br Dent J 2009 Aug 22;207(4):185-186.
  7. Singh AV, Singh S, Rojo AV. Quality life for elderly edentulous patients with implant over dentures, implantology section. Dental Practice 2013 May-June;11(6):22-25.
  8. Duyck J, Van Oosterwyck H, Vander Sloten J, De Cooman M, Puers R, Naert I. Magnitude and distribution of occlusal forces on oral implants supporting fixed prostheses: an in vivo study. Clin Oral Implants Res 2000; 11:465–475.
  9. Christopher C K. Implant rehabilitation in edentulous jaw: the All-on-four immediate function concept. Australian dental practice march/april 2012
  10. Christopher CK. , Grad Dip Clin Dent, M Ciin Den, Sascha A Jovanovic The "All-on-4" Concept for Implant Rehabilitation of an Edentulous Jaw Compendium 2014; 35 (4): 255-259.

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