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All-On-4 Treatment Concept: A Viable treatment modality or under engineering in biomechanics?

November 1, 2012
by Mark Lin, BSc, DDS, MSc (Prostho), FRCD(c)


Dr. Mark Lin: Dr. Bongard, thank you for taking the time to participate in this interview on the “All-on-4” treatment concept. Please tell us about your educational background.

Dr. Steven Bongard: I graduated from the University of Toronto in 1986 and presently maintain a private practice in Toronto that is limited to the placement and restoration of dental implants. Since 1995 my interest has been concentrated on all aspects of implant dentistry. I have extensive experience in implant placement and bone grafting procedures as well as the prosthetic component of implant restoration. I have published and lectured both nationally and internationally on implant placement, “guided” implant surgery, as well as alternative implant solutions and their restoration. My recent focus has been on developing innovative implant solutions for predictable same day treatment of the severely atrophic edentulous patient.

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Lin: What is this treatment concept called “All-on-4”?

Bongard: All-on-4® is an over-simplified term for a concept developed by Dr. Paulo Malo that has been trademarked by Nobel Biocare. It is a concept whereby a patient receives same day surgical and prosthetic full arch rehabilitation utilizing four or more implants to support a fixed, immediately functional and highly aesthetic prosthesis.

Lin: How does the All-on-4 concept compare to the conventional approach to treatment for full-mouth rehabilitations? Can you highlight some of the key differences?

Bongard: From a clinical perspective, the main difference between All-on-4 and traditional approaches in treating the completely edentulous patient is in the approach to implant placement. In the posterior maxilla, the implants are placed on an angle, just anterior to the maxillary sinus, into the more dense bone of the pre-maxilla. This avoids the need for sinus augmentation while still allowing for a shortened posterior cantilever. In the mandible, implants are placed between the mental foramina, angled in the posterior, engaging the more predictable dense bone of the anterior mandible.

From a patient’s perspective, the differences are quite significant. Conventional treatment of the full arch would most often require extensive bone grafting which is associated with significant morbidity and a long awkward transitional period. With the All-on-4 treatment, the less invasive nature of the procedure reduces morbidity, and the immediately fixed transitionals allow for significantly less disruption to a patient’s life. Also, the aesthetics of this treatment are much more predictable and favourable. There is far less cost to the patient for a full arch solution using All-on-4 compared to traditional approaches. The bottom line is a consistently high level of patient satisfaction.

Lin: Please share with us the extent of your clinical experience with this concept.

Bongard: I began treating patients with this concept in 2005 and since that time we’ve treated well over a thousand cases with this approach. Patient satisfaction has been outstanding and the overall complication rate has been very low. Surgical complications are rare and are mainly related to traditional implant related risk factors. Short-term implant survival rates are comparable to the traditional two-stage approach and most prosthetic concerns involve breakage of the transitional all-acrylic prosthesis. Modifications to our prosthetic protocols over time have reduced the prosthetic complications considerably.

Lin: What does the literature show on an international or worldwide level? Are there other doctors performing All-on-4? What does their data reflect?

Bongard: In March 2011 Dr. Paulo Malo, in Lisbon Portugal, published a 10-year follow-up study in the Journal of the American Dental Association, (A longitudinal study of the survival of All-on-4 implants in the mandible with up to 10 years follow-up. Malo et al JADA 2011;142(3):310-320) that showed a 95% survival rate for four implants supporting a full arch restoration.

Other studies that confirm the present technique can be considered a viable treatment option for the immediate rehabilitation of both mandible and maxilla include:

• Agliardi E, Panigatti S, Clericò M, Villa C, Malò P. Immediate rehabilitation of the edentulous jaws with full fixed prostheses supported by four implants. Interim results of a 5-year single cohort prospective study. Accepted for publication in Clin Oral Implants Res.

• Clin Implant Dent Relat Res. 2008 Dec;10(4):255-63. Epub 2008 Apr 1. Immediate rehabilitation of the mandible with fixed full prosthesis supported by axial and tilted implants: interim results of a single cohort prospective study.

• Francetti L, Agliardi E, Testori T, Romeo D, Taschieri S, Fabbro MD. Int J Oral Maxillofac Implants. 2012 May;27(3):628-33.

• Francetti L, Agliardi E, Testori T, Romeo D, Taschieri S, Fabbro MD. Immediate rehabilitation of the mandible with fixed full prosthesis supported by axial and tilted implants: interim results of a single cohort prospective study. Clin Implant Dent Relat Res 2008; 10(4):255-263.

• Khatami AH, Smith CR.”All-on-Four” immediate function concept and clinical report of treatment of an edentulous mandible with a fixed complete denture and milled titanium framework. J Prosthodontics 2008;17(1):47-51.

• Maló P, de Araujo Nobre M, Rangert B. Implants placed in immediate function in periodontally compromised sites: a five-year and one-year prospective study. J Prosthet Dent 2007; 97:86-95.

• Pomares C. A retrospective clinical study of edentulous patient rehabilitated according to the all-on-four or the all-on-six immediate function concept Eur J Oral Implantol 2009; 2 (1):55-60.

• Testori T, Del Fabbro M, Capelli M, Zuffetti F, Francetti L, Weinstein RL. Immediate occlusal loading of tilted implants for the rehabilitation of the atrophic edentulous maxilla: 1-year interim results of a multicenter prospective study. Clin Oral Implants Res 2008 Mar; 19 (3):227-32

Lin: The name All-on-4 implies the use of only four implants. Please elaborate on this point.

Bongard: To my understanding, there are clinics that provide this treatment utilizing four implants exclusively. Our protocols, however, differ in that we will often use more than four implants depending on patient-specific circumstances. Immediate function requires good primary stability and on occasion, in softer bone, more implants are required to help ensure sufficient prosthesis stability during healing Very often in the maxilla, depending on: the quality and distribution of available bone, the patient’s masticatory biomechanics, and para-functional considerations; four, five, or even six implants are used. Regardless of the number of implants placed, we still consider it the All-on-4 concept.

Lin: So what are the clinical parameters that would help you determine the use of four, five or six implants per arch?

Bongard: It is always our intention to attempt to provide an immediate fixed transitional prosthesis for our patients and well over 95% of the time we are able to do so. It is well understood that successful implant integration depends on limiting implant micro-movement during the early stages of integration, so it is not uncommon for us to add additional implants to aid in the overall initial stability of the structure. Of course, bone quality and the anticipated bite forces generated by the opposing arch are significant considerations as well.

Lin: The traditional philosophy is that, if and when possible, we would like to promote axial loading of the implants. In juxtaposition to the traditional ph
ilosophy, All-on-4 calls for the placement of tilted implants. Please share your thoughts concerning the tilting of implants with regard to All-on-4.

Bongard: Tilted implants are one of the key elements of the All-on-4 concept. There are several well-documented advantages to tilting implants. We tilt the implants to shorten cantilevers greatly improving force distribution, to avoid the antrum eliminating the need for sinus augmentation procedures, to allow engagement of the more dense anterior bone, and to be able to use longer implants in areas of limited vertical bone.

Lin: We instinctively suspect that tilting implants will cause an unfavourable bone reaction and/or introduce problems interacting with prosthetic components. What has been your experience with the tilting of posterior implants?

Bongard: That was my initial concern when I first heard of this concept. It is important to understand, however, that when we are talking about tilting implants with this concept we are only referring to implants that are rigidly connected to other implants, and that allows for a totally different force dynamic in comparison to a single off-angle implant. Our experience has been very favourable, as we have not seen any significant difference in bone reaction compared to implants placed in a more axial inclination under such conditions.

Lin: Are you aware of any literature that gives a little bit more of a historical perspective on tilted implants?

Bongard: There is a Swedish study: Bone level changes at axial and non-axial positioned implants supporting fixed partial dentures. A 5-year retrospective longitudinal study. (Koutouzis and Wennstrom 2007) which failed to support the hypothesis that implant inclination has an effect on peri-implant bone loss. Clin Oral Implants Res. 2007 Oct;18(5):585-90. Epub 2007 Jun 30.

A different 5-year study on tilted implants in both jaws (Tilting of posterior mandibular and maxillary implants for improved prosthesis support. Krekmanov et al International Journal of Oral and Maxillofacial Implants 2000) found a 98% success rate for tilted implants in the maxilla and a 100% in the mandible.

A number of bench top or computer simulation studies of the mechanics have been done as well that show a favourable biomechanical situation:

1. Stress Patterns around Distal angled abutments in the All-On-4 concept configuration Begg et al International Journal of Oral and Maxillofacial Implants 2009) found that implants placed at 15 and 30 degree angles there was little difference in stress between the central straight and the distal angled implant;

2. Tilting of splinted implants for improved prosthodontic support: a two-dimensional finite element analysis. Zampelis et al J Prosthetic Dent. 2007; 97:s35-s43 and 3. Effect of cantilever length and inclined implants on axial force and bending moment in implant-supported fixed prostheses. Geremia et al Rev Odonto Cienc. 2009;24(2):145-150

Last but not least, there was a study published in 1999 (Implant Treatment without bone grafting in severely resorbed edentulous maxillae; Mattson et al International Journal of Oral and Maxillofacial Surgery with a 10 year published follow-up (Implant Treatment without bone grafting in severely resorbed edentulous maxillas: a long-term follow-up study Rosen and Gynther IJOMS 2007) that showed a high success rate for tilted implants from surgeries that were done in the early nineties, almost 20 years ago.

Lin: The third component of this All-on-4 concept is the immediate loading of these implants. Please give us more perspective on immediate loading. How do the differences in bone density and bone quality affect your approach?

Bongard: It is our intention, when going into every surgery, to immediately load each case. Being able to provide patients with an implant-supported immediate transitional is an important part of the patient expectation at our clinic. Our surgical protocols are designed to try to maximize primary stability to allow for this to occur predictably. In the maxilla the implants are angled to avoid the less dense posterior bone. The pre-maxilla, for the most part, has fairly dense bone and has sufficient bone quality similar to the bone found in the intra-foramina region of the mandible. We haven’t seen any significant difference in survival rates for either arch.

Lin: What are the clinical parameters or prerequisites to consider when providing immediate load, and in which cases will you instead perform a second stage uncovering procedure and load after 4-6 months?

Bongard: One of the keys to the All-on-4 concept from the patient’s perspective is the convenience of receiving teeth on the same day as the surgery. Our protocols for the mandible or the maxilla call for at least 35 Ncm of initial stabilization on at least 4 implants to enable us to immediately load.

Lin: Assuming you achieved initial implant stability of greater than 35 Ncm and were able to immediately load the prosthesis, what are some of the instructions that you would suggest for your patients in terms of post-op instructions?

Bongard: We instruct our patients to eat a somewhat modified normal diet for the first 3 months after implant placement; food with a softer consistency, such as fish or pasta. Our protocols include occlusal adjustments and checks initially, at day of surgery at 2 weeks and followed up again at 6 weeks. At the two-week postoperative appointment, we introduce oral hygiene with a waterpik. A properly adjusted and well-balanced occlusal scheme is very important clinically, as well as to our patients’ continued comfort with their new prosthesis. Therefore, we pay close attention to each patient’s occlusal scheme, meticulously evaluating and adjusting it, utilizing the T-scan computerized analysis system at 2 weeks and re-verified at 8 weeks post-operatively.

Lin: You mentioned something about the meticulous, careful attention to the details of the occlusal scheme. Can you comment on what it is that you look for or follow up on in these patients again at 1 week, and 2 weeks because, when you have the patients back, specifically what type of occlusal schemes are you looking to achieve?

Bongard: Our protocols call for bilateral, simultaneous, equal intensity posterior contacts in the maximal intercuspation position. We want to avoid contact in the cantilever portion and we want to avoid premature contacts. We take the time to verify all contact with a t-scan to ensure its accuracy.

Lin: It sounds like you are trying to achieve a mutually protected occlusal scheme in which when the teeth are in the Maximal Intercusp (MIP) position, there are posterior equal intensity simultaneous contacts in which there are little to no contacts to the anterior teeth. In excursive movements of protrusion and/or lateral excursions the anterior teeth will provide guidance where there is immediate disclusion of the posterior teeth.

Bongard: That is correct, however, our protocols call for more anterior contact than you described. We actually have the front teeth equally contributing to the MIP. The front teeth contribute equally with the back teeth. Since we are talking about the implants that are placed primarily in the anterior maxilla, we include contact with the anterior teeth in MIP.

Lin: Dr. Bongard, I can see that in certain clinical cases of fully edentulous residual ridge resorption, we would consider this All-on-4 concept. What are some of your clinical experiences with cases where the patient presents with poor prognosis of the remaining teeth and/or teeth that are not salvageable?

Bongard: It has been our experience that over 60% of our cases are patients that have failing teeth that are to be extracted. Motivated by t
rying to reduce the number of total surgeries for a patient and the unpleasant or awkward transitional period, it is our intention to extract the teeth, immediately place the implants, and immediate load these implants with the All-on-4 all acrylic transitional prosthesis. We have found that this sequence of treatment has equivalent overall success rate, provided that we have achieved initial stabilization of the implants in the same parameters as we discussed earlier.

Lin: During the immediate provisionalization of the All-on-4 concept, can you describe for us what types of prostheses are inserted on these implants that have achieved initial fixation?

Bongard: The initial prosthesis, or what we call ‘the transitional prosthesis’, is an all-acrylic, screw-retained, fixed, provisional prosthesis. We wait 4-6 months before we fabricate a second or final prosthesis. During that time, we measure the implant –stability –quotient (ISQ) at regular intervals to ensure that implant integration is progressing successfully. Our final restoration is a hybrid type of a restoration, which is a screw-retained, milled, titanium bar with premium acrylic teeth attached.

Lin: So, in the final prosthesis, it sounds like there is an acrylic base and also the denture teeth. What are your thoughts on using porcelain for the final teeth?

Bongard: Porcelain is an option that is certainly available. In our office, we prefer acrylic teeth for several reasons, including the predictability and ease of repair. Patients are very satisfied with the aesthetics of the high-end acrylic teeth that are now available on the market. The repair and maintenance are much easier with acrylic than with porcelain teeth.

Lin: Once the final prosthesis has been fabricated and inserted, what type of maintenance protocol or recall do you provide for your patients?

Bongard: Similar to natural teeth, the maintenance of the final prosthetic is somewhat case specific depending on the patient’s willingness and ability to maintain plaque control.

Lin: And I would assume that in these recall appointments you would verify and check the occlusion?

Bongard: Correct. The occlusion is checked, the implants are evaluated, and the tissue surfaces are examined for health. This is usually done back at the referring dentist’s office.

Lin: What are some of the risk factors you would consider in evaluating a patient as a potential candidate for this All-on-4 treatment concept?

Bongard: As in all implant placement surgical modalities; there are several factors that could potentially compromise a successful outcome. These factors include: smoking, immunosuppressive medications, radiation therapy to the affected area, poorly controlled diabetes, para-function, and other systemic conditions that can adversely affect healing.

Lin: What are some of the contra-indications that you would say prohibit patients for this type of treatment modality?

Bongard: Medically or psychologically unstable patients or patients who are unwilling or unable to consent to treatment.

Lin: What are the clinical contra-indications or minimal requirements to consider in this treatment modality?

Bongard: Patients are considered ideal for this treatment if they have 5mm of bone width and 10 mm of bone height between the canines in the maxilla, and 5mm of bone width and a minimum of 8 mm of bone height intra-foraminally in the mandible. However, there is a significant population of patients that, due to early tooth loss, present with significantly less bone then just described. We have been working on some new protocol modifications for these “extreme cases” that are showing very favourable outcomes in the short-term.

Lin: In conclusion, as a general wrap up, there seems to be a tremendous patient benefit in terms of this treatment modality. Can you comment on what these patients have shared with you regarding their experiences?

Bongard: What’s consistent is the very high level of patient satisfaction that we are able to achieve. The combination of simpler surgery and immediate loading of the prosthetics allows the patient to leave the clinic with aesthetic, fixed teeth with which they can begin to chew and confidently resume the rest of their lives. They report incredible improvement in the quality of their lives, including an immediate improvement in aesthetics, an immediate improvement in phonetics, an immediate improvement in their ability to function and chew, and the confidence that having fixed, non-removable teeth provides them in social situations. All of these factors contribute to achieving a patient satisfaction rate that is far beyond any other treatment modality I have ever been able to offer as a dentist.

Lin: Dr. Bongard, thank you for your valuable expertise and for sharing your experience with us.

Bongard: Dr. Lin, you are welcome. It has been my pleasure to share my clinical experience and knowledge with my professional colleagues and to have this interview published in Oral Health.OH

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Oral Health welcomes this original article.

Dr. Lin is Assistant Professor, Co-director of Post Graduate Prosthodontics Program and Implant Prosthodontic Unit, Prosthodontics, University Of Toronto. In addition, he maintains a full time specialty practice as a Prosthodontist at Dr. Mark Lin Prosthodontic Center

Dr. Lin is one of the instructors for Nobel Biocare and both he and Dr. Bongard teach courses for Nobel Biocare and the All-On-4 Concept. Neither were paid to generate this article.