Basis of Immediate Loading and the Biomechanics of Graft-Less Solutions

Fig. 6.1

Screw-retained, cross-arch-stabilized interim prosthesis to be immediately loaded

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Fig. 6.2

Interim prosthesis with adequate AP spread and minimal cantilever

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Fig. 6.3

Interim prosthesis intra-orally with minimal vertical and horizontal overlap

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Fig. 6.4

Requirements of immediate loading

6.3 Specific Elements of Immediate Loading

Immediate loading is considered the establishment of occlusal function of implants during the first week after implant placement [3]. The timing of when the prosthesis is delivered after the surgical placement of the implants is important, as it relates to the bone healing around the dental implants, and the continued stability of the implants in the osseous structure. Glauser et al. [19] have established that the primary initial stability that is attained at the time of surgical implant placement decreases significantly after 1 week. Furthermore, it has been shown that bone remodelling begins to significantly occur at the 1-week time point [2023]. This helps to establish the first week after surgical placement of the dental implants as the safest time to deliver the immediate prosthesis. However, it must be stated that on a cellular level, osteoclasts have been shown to be present on the surface of the cut native bone surrounding the implant 4 days after implant placement [20]. Thus, it may be advantageous to place the immediate interim restoration as soon as possible after the implants have been surgically placed.

6.4 Occlusion

Agreement on the occlusal scheme to be utilized in the interim prosthesis has not been established in the literature [6]. There is no evidence to show that one occlusal scheme is superior to another, one type of tooth form is more efficient than another or one type of occlusal scheme is preferred by patients.

Most occlusal schemes advise on avoiding non-axial loading on implants. If we evaluate the recommendations critically we become aware that axial loading of implants almost never occurs along the long axis of the implant. Instead function occurs on various areas of the prosthesis with the development of complex bending moments within the restorative implant components and within the surrounding bone.

Factors that affect distribution of occlusal forces include but are not limited to

  1. (a)

    Number of implants involved

     
  2. (b)

    Biomechanical design of the implant

     
  3. (c)

    Nature of the bolus of food

     
  4. (d)

    Design and fit of the prosthesis

     
  5. (e)

    Nature of the opposing occlusion

     
  6. (f)

    Deformation of the bone and the prosthesis

     
During the immediate load phase, management of the occlusion for force distribution and protection of the existing implants becomes very critical [6, 24, 25]. Unfortunately an evidence base does not exist which guides the clinician in developing an occlusal scheme. The following are generalized guidelines for immediate loading in a patient with a class 1 incisor relationship:

  1. 1.

    Posterior cusps flattened to minimize bending and torsional forces.

     
  2. 2.

    Evaluation of the opposing occlusion—If the full-arch interim prosthesis opposes natural teeth, it may be feasible to adjust the natural teeth to minimize steep inclines and lateral forces.

     
  3. 3.

    Bilateral simultaneous contact.

     
  4. 4.

    Shallow protrusive disclusion.

     
  5. 5.

    Anterior group function.

     
  6. 6.

    Steep anterior disclusion is not recommended as this may create destructive deflective forces which may result in prosthesis fracture.

     
  7. 7.

    No cantilevers—Although no evidence-based consensus has been established regarding cantilevers, it is the overall recommendation that distal cantilevers are minimized or eliminated from the interim prosthesis. Cantilevers have been found to create greater risk in restoration fracture and implant failure, when utilized in the interim restoration [2629].

     
  8. 8.

    Definitive contacts on canine to canine with lighter contacts on posterior teeth: The rationale for the above is that the further posterior the tooth, the higher the occlusal forces. The implants in the posterior part of the mouth are also in the weakest quality bone. As clinicians, our goal in the immediate load phase is to minimize occlusal load on the implants that are more posteriorly positioned and in the poorest quality bone.

     
  9. 9.

    Use of a night-time appliance.

     

From a clinician’s perspective one aspect that must be considered is the relationship between occlusion loading and mechanical complications. As resin fracture and tooth fracture are the most common types of prosthetic complication in these types of prostheses [6], the design and namely the rigidity of the interim hybrid prosthesis have been suggested to aid in the strength and resilience during the healing phase [30]. Furthermore, increased rigidity of the interim prosthesis is also suggested to aid in successful osseointegration by reducing load-induced implant micro-movement during healing [3133]. The rigidity of the interim restoration is increased through dimensional thickness. Appropriate restorative space must be created by the surgeon to fulfil the biomechanical requirements of the specific restoration treatment planned.

One of the main methods in which rigidity can be improved is through reinforcement of the interim hybrid prosthesis. Patient advantages include less breakage and a longer lasting provisional restoration. Clinician advantages include fewer unscheduled visits and reduced chairtime. One material that has shown to increase flexural strength is fibre [32]. This material type has also been suggested to increase fracture toughness in provisional restorations [6, 31, 33] (Figs. 6.5, 6.6, 6.7, 6.8 and 6.9).

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Fig. 6.5

Fibre reinforcement requires an indirect technique with impressions and tooth set-up

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Fig. 6.6

Putty matrix of tooth position in relation to the temporary cylinders

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Fig. 6.7

Fibre tied in a specific manner to provide support for the teeth, processed provisional

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Fig. 6.8

Clinical delivery

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Fig. 6.9

Provisional restoration intra-orally, note minimum vertical overlap of anterior teeth

6.5 Optimal Number of Implants

The number of implants needed to successfully and routinely rehabilitate an edentulous arch utilizing an immediate loading protocol has been debated for some time in the literature. Classically, the use of five mandibular implants for a full-arch rehabilitation has been advocated. However, recently, 2–3 implants have been advocated for the fixed rehabilitation of a dental arch utilizing an immediate loading protocol [3436]. With the introduction of full-arch fixed rehabilitation on four implants [37, 38] the conceptual requirement of increased implant numbers for full-arch fixed rehabilitation was put into question. With continued research being conducted in this area, it can be stated that the use of 4–6 implants for fixed full-arch rehabilitation utilizing an immediate loading protocol is evidence based.

When deciding the optimal number of implants, we must give the term optimal a broader definition. The clinician should consider not just the number of implants, but where in the jaw they are placed and the quality of bone in which they are placed [39]. The magnitude of stresses that develop in the bone, the implant and the prosthesis and the relationship of the stresses and strains to thresholds for damage to the bone and prosthetic components should also be given consideration. The treatment plan must be developed biomechanically (Fig. 6.10).

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Fig. 6.10

Advantages of tilted implants

When looking at the literature in this arena three types of study have been completed:

  1. 1.

    Mathematical models

     
  2. 2.

    3D finite element analyses

     
  3. 3.

    Intra-oral strain gauge studies

     

When attempting to predict forces on 4, 5 or 6 implants with the above studies extrapolation becomes very difficult. What makes this problem difficult to solve is the fact that each implant is connected to both the bone and the prosthesis; computing the loads (and stresses and strains) in each part of the structure is a problem that is not solvable by statics alone, but also requires data on the material properties of the implants, bone and prosthesis as well as their stress-strain behaviours. Prosthesis rigidity, bone implant stiffness and deformation of the mandible also come into consideration. The use of fewer implants to rehabilitate an edentulous patient has been established and the need for reserve implants is no longer considered necessary.

6.6 Axial vs. Tilted Implants

The introduction of a tilted implant protocol in full-arch fixed rehabilitation utilizing immediate loading puts into question the need for universal axial implant placement. Since that time, these two implant positioning regimens have been compared throughout the literature [4045]. However it is clear that in many instances tilting of posterior implants in full-arch rehabilitations provides significant benefits [45] (Table 6.1).

Table 6.1

Benefits of Tilted Posterior Implants [4050]

1. Implants are placed into more dense and better quality bone

2. Longer posterior implants can be utilized through tilting

3. Tilting posterior implants allows for greater distribution of the implant connections

4. Larger anterior-posterior spread of implants decreases cantilever lengths needed

5. Marginal bone levels are maintained around tilted implants

6. Similar success and survival rates when compared to axial implants

7. Vital anatomical structures are avoided by tilting posterior implants

8. Tilting posterior implants minimizes the need for grafting procedures

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Dec 6, 2018 | Posted by in General Dentistry | Comments Off on Basis of Immediate Loading and the Biomechanics of Graft-Less Solutions
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