Continuing Education (CE)
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Dr. Robert Hayes discusses a predictable novel treatment modality for treating failing dentitions, edentulous, and potentially edentulous patients
Based on studies from many authors over 5 decades (Lopes, et al., 2106; Drago, 2016; Meloni, et al., 2017; Chan and Holmes, 2015; Patzelt, et al., 2014; Francetti, et al., 2008), this article is written from long clinical experience and deep understanding of the biomechanics of immediate load full arch treatment to emphasize and establish important parameters for successful technique (Holtzclaw, 2016).
Educational aims and objectives
This article aims to explain the benefits of and protocols for successful immediate load full arch treatment planning.
Implant Practice US subscribers can answer the CE questions to earn 2 hours of CE from reading this article. Correctly answering the questions will demonstrate the reader can:
- Read about this protocol and be aware of the evidence base supporting it.
- Read about some history of the full arch implant.
- Identify some aspects of prosthesis design.
- Recognize some aspects of angulation and load that facilitate successful outcomes.
- Identify the process for establishing the shelf.
- Realize how to determine access position.
- Realize how to guard against destructive bruxism.
Following careful investigation of the patient’s medical history and a tooth-by-tooth analysis, a detailed discussion that covers all treatment options — from living with gaps to wearing removable dentures or utilizing natural teeth as fixed bridge abutments or supplementing with sectional implant prosthetics — must also cover the anticipated scenarios and lifelong costs associated with each option.
Analyzing these cases is rather like high-level chess — how many strong pieces should be sacrificed early in order to win the long game?
Full arch implant treatment
Full arch implant treatment has a number of attractions. By eliminating the teeth, it removes the risks of decay, pulp necrosis, and periodontal infection. The first case was undertaken in 1965 by Dr. Per-Ingvar Brånemark, and many studies report the unassailable long-term success rates. The implants are linked by a supragingival metal bar providing cross-arch bracing and splinting, so no implant is ever bearing load alone. Full arch treatment is also an opportunity to establish an idealized version of the patient’s occlusion with canine rise/group function, balance, and harmony while eliminating destructive features such as cross-arch interference.
Since the 1960s, it has been recognized how a high-quality acrylic occlusion can protect the metal elements and bone from overloading as it softens impact and wears harmoniously, preventing the development of occlusal interferences (Brånemark, et al., 1977).
Research has also shown the development of hemidesmosomal attachment to acrylic, which we now utilize to control bacterial ingress and protect the bone from peri-implantitis (Listgarten and Lai, 1975). Ongoing investigations are evaluating the effects of incorporating antimicrobial and antibiotic agents into the prosthesis (Nazirkar, et al., 2014).
The long established adsorption of chlorhexidine gluconate onto acrylic supports transferring the prosthesis from the laboratory in such a solution and establishing a home-care regime that will refresh the anti-microbial reservoir (Bonesvoll and Olsen, 1974).
Since postoperative resorption of bone is inevitable, this author favors replacing the initial prosthesis at 4 months with a milled-titanium acrylic wrap that can be relined for years, with the original acrylic bridge being refurbished on the definitive models to provide a spare during laboratory procedures. The model ridge is trimmed by 1 millimeter to provide controlled gingival compression and development of a gingival trough in intimate contact with the dense, highly polished convex underside of the prosthesis. High-quality pressure-formed acrylic is used with great care on choice of fully chemically compatible teeth, metal prime, bond, mechanical retention on the bar and the teeth to achieve strength and durability. The esthetic result from high-quality acrylic work is far superior and easier to achieve than any other ceramic or composite alternative, and reparations can be much more readily accomplished.
Angulation and load
Biomechanical research has clearly demonstrated the advantage of placing long tilted implants to resist the high posterior load in the human jaw. Since the human jaw is a Class 3 lever (as is a nutcracker), the highest forces are always on the posterior implants (Lopes, et al., 2016; Silva, et al., 2010; Agliardi, et al., 2010). Thus placing short upright posterior implants below the sinus or above the nerve is inviting failure. To understand something of this, imagine a high occlusal point force on a single vertical implant — the bone contact surface has to bear all the force directly to prevent the implant being driven in like a nail.
With a 45º tilted implant, imagine the bone providing only a midpoint support. The force on the abutment would push the abutment end down, and the apical end would rise. Actually, the implant doesn’t move because the bone below the abutment end provides resistance, just as the bone above the apical end prevents the tilt. The forces are equal and opposite, so the load at such a point on the bone is halved.
None of the force applied during function — or more importantly parafunction — is directly along the long axis of the implant, so the resultant vectors of force along this natural path of movement of the implant are minimal. This angulation contributes to the near 99% implant success rates repeatedly reported, and it is incumbent on surgeons to apply this knowledge to full arch cases (Bhering, et al., 2016; Afrashtehfar, 2016; Saleh Saber, et al., 2015; Li, et al., 2015; Khatami and Smith, 2008).
The anatomy of the maxillary sinus and the mental nerve also lends itself to providing a resistant cortical surface immediately distal to the distal tilted implant, further enhancing its use, along with the widely understood benefit of reducing the cantilever and increasing the anterior-posterior spread of the abutments.
In extreme cases, it will be necessary to cross the anterior aspect of the sinus, place a zygomatic implant, or provide a posterior tilt in the opposite direction into the pterygoid plate. The most extreme maxillary cases are treated with quad zygoma, but in the mandible almost all can be treated with intra foraminal All-on-4 (All-on-3 in extreme cases) (De Moraes, et al., 2016; Jensen, et al., 2014; Malo, et al., 2013; Bedrossian, 2011; Ferreira, et al., 2010).
Application in the maxilla
The All-on-4 concept is absolutely applicable to the maxilla, but it must be recognized that the original papers were specific to a population of edentulous Portuguese pensioners accepting of a short arch concept and a 10-year survival (Malo, et al., 2011). When applying the concept to immediate placement in younger individuals with greater demands, it is wise to take into account the additional factors, including the lower density and reduced reliability of maxillary bone.
In many cases, the classic two tilted posterior and two anterior vertical implants should be supplemented by a third or fourth anterior implant and immediate load applied to all cases so that the implants are immediately splinted (Tallarico, et al., 2016; Silva, et al., 2010; Pomares, 2009). Placement of the biomechanically derived implant array must be prosthetically driven using a clear acrylic duplicate stent that informs positioning in all three dimensions.
This approach is derived from treatment of longstanding edentulous cases where fully guided surgery is a viable option using clear stereolithographically produced CAD/CAM devices produced digitally from CBCT planning software. In immediate cases, the dimensions of the surgical field are altered by reflection of full arch flaps, removal of teeth, roots and a sufficient depth of bone to accommodate the prosthesis (Faeghi Nejad, 2016; Butura, 2011; Pomares, 2009).
Establishing the shelf
It is vital to assess all aspects of the smile at the records appointment to determine the correct level of the transition line between the artificial and real gingivae, so that this is never visible in any expression of the lips, either anteriorly or within the buccal corridor.
The consequent requirement for ridge reduction must be communicated to the technician to inform the initial model ridge trimming, which must be flat rather than socketed to create a smooth, cleansable prosthetic junction (Abi Nader, et al., 2015; Krenmair, et al., 2014). The average case will require 3 millimeters of bone removal in the region of the extraction sockets — more if a gummy smile is to be corrected, and less if there has been significant bone loss due to severe periodontitis or a longstanding area of edentulous ridge (Jensen, et al., 2011a; Jensen, et al., 2010).
As each implant approaches final torque, account needs to be taken of the rotational position of the internal flats as these will determine the eventual access position of the prosthetic screws, which ideally occurs in the cingulum of the anterior teeth and the occlusal surface of the premolar or molar. Any facial deviation from this will risk an unsightly buccal access, and any lingual or palatal deviation will adversely affect the bulk of the prosthesis.
Some surgeons find it easier to use an external hex implant to directly observe the flats, but most manufacturers provide implant placement devices marked to indicate the internal flats. With the common hex design, this gives six positions for placing a 17º or 30º degree multi-unit abutment, three of which will be potentially restorable, giving a facial, mid, and lingual choice to abutment insertion, which should be chosen with reference to the clear stent by carefully referencing it to the final restorative position immediately prior to abutment connection.
It is wise to initially slightly under-prepare the osteotomies so that high primary stability (35-65 Ncm) of each implant is produced as the final rotational position is achieved, and abutments should be tightened to 15 Ncm, confirming full seating, which may require bone removal around any subcrestal aspect of the implant (Babbush, 2011; Jensen, et al., 2011b; Butura, 2011).
Guarding against bruxism
It should be recognized that many patients presenting for immediate full arch have destructive bruxism (De Rossi, et al., 2014). This is often apparent as a battle between the upper and lower teeth with units failing until eventually there are no opposing teeth in contact.
The pattern varies but, for example, the upper right and lower left buccal segments may be edentulous; then the lower incisors fail, and eventually the upper canines. Each loss depletes the dentition, and posterior loss in particular limits the parafunctional force. The “bruxism center” of the brain is searching for satisfying feedback and immediately introduces high forces to the transitional prosthesis. Creation of a protective, minimal overbite, minimal overjet, and idealized, close to edge-to-edge occlusion limited to first molars will protect the screws and implants from overloading.
Tightening abutments to 15 Ncm gives a positive fit, which will hold in most circumstances but release with more active bruxism — immediately protecting the implant bone attachment and alerting the clinician at the 2-month review. Protective steps can then be taken: retightening the screw to 10 Ncm to avoid over-torquing the healing bone, reducing the molars out of contact, and possibly adding an anterior bite plane to convert the prosthesis to an effective Michigan splint during the first 4 months.
Immediate full arch
Once all multi-unit abutments are tight, temporary titanium abutments are attached at 10 Ncm, and the transparent surgical guide is used carefully again to note the exact positioning and inform the opening of insertion channels through the interim prosthesis. This must eventually seat freely onto the mucosa, exactly like an immediate denture without interference from metal components once all the channels are completed.
The final position can be checked visually, focusing on features such as an esthetic occlusal plane, incisal display, lip support, centric occlusion, and alignment of center lines or checked using a putty bite provided by the laboratory from the articulated setup.
The prosthesis is then washed and dried, and a bonding agent is applied to the channels. The prosthesis is then attached using an intraoral reline process and removed for extraoral final finishing by uncovering and counter rotating the screws, which have been protected by packing PTFE tape to the full height of each hollow abutment (Boulos, 2010).
The alternative to picking up all supragingival abutments intraorally is to just pick up the anteriors, take a full arch impression with multi-unit impression abutments, and transfer both to the laboratory to create the posterior access and finish the bridge on the resulting model.
The author finds this alternative keeps the patient in the chair longer, especially if inadvertent occlusal inaccuracies are introduced by the impression and model production — but in cases where the posterior abutments are at very divergent angles, it results in a stronger, neater interim prosthesis.
The resulting interim acrylic bridge is then inserted with the screws at 10 Ncm and the screw access protected with new PTFE tape packed firmly and finished a millimeter below the prosthetic surface and sealed over with color-matched glass ionomer or resin.
At 4 months, the occlusion is recorded. The bridges are removed and copied using putty. All abutment screws are tightened to 20 Ncm, impression copings are placed at 10 Ncm, and accurate open tray impressions are taken. The bridges are replaced at 10 Ncm, and the patient chooses the final shade and characterization for the definitive try-in.
Once the try-in is successful, the definitive model ridges are reduced by 1 millimeter so that controlled compression is achieved at the final fit. Specific oral hygiene instruction is delivered and emphasized with an illustrated leaflet, and all patients are recalled at 1 month for a 15 Ncm retightening of the prosthetic screws, review of oral hygiene, oral health, and esthetic and occlusal outcome. Patient-appropriate hygiene, screw checking, and radiographic reviews are organized, and feedback recorded.
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