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Loading Protocols for the Mandibular Two-Implant Overdenture

Wherever possible, a one-stage surgical procedure with an early loading protocol (ie, 6 to 8 weeks) is the recommended technique for the two-implant overdenture. There may be instances when conventional loading (ie, 12 weeks) might be appropriate as well. A third “philosophical” variation on early and conventional loading protocols is immediate loading, in which final abutments are connected and retentive elements are activated at the time of implant placement. At present, immediate loading is not appropriate for the unsplinted two-implant overdenture design.

 

EARLY LOADING

In recent years, histological and experimental studies have demonstrated that newer implant surfaces may result in an increased and earlier bone-to-implant contact than was observed with conventional loading 12 weeks following implant placement.1-3 Such findings have led to the growing observance of “early loading” protocols when more ideal bone quality and quantity, more refined surgical and prosthetic protocols, and more advanced implant designs are available.

Currently, no consensus exists defining “early loading.” Studies evaluating early loading have demonstrated excellent success with a range of early loading from 3 to 8 weeks. Because of the larger body of research validating the success of early loading at 6 to 8 weeks postoperatively, the authors recommend this somewhat longer period as the technique of choice, pending additional empirical validation of an even shorter healing period. At this point, this is the least amount of time that will result in the highest level of predictability with the least amount of potential risks. Accordingly, early loading represents a significant paradigm shift in which the conventional 12-week healing period is dramatically shortened.

 

Indications For Early Loading

Early loading protocols may be considered when a one-stage surgical protocol has been achieved, which may include the following critical determinants:

  • Uncomplicated implant placement (eg, no hard or soft tissue grafting);
  • Adequate primary stabilization (eg, absence of micromotion at time of surgery);
  • Bone quality is Type I or II;
  • Implant length is a minimum of 10mm; and
  • Implant surface is osseoconductive.

 

Postsurgical Restorative Technique to Utilize Early Loading

Studies have demonstrated that patients may be permitted to wear their dentures immediately postsurgically--on the day of surgery--provided that the denture has been significantly relieved (minimally 3 mm) to provide adequate space for a soft reline material (Figures 1 and 2). The denture is relined and again relieved over the implants to minimize premature loading forces during this initial period of wound healing (Figures 3-4-5-6-7). During this initial period, follow-up is critical to avoid excessive loading and micromovement.

This postsurgical restorative technique (ie, providing a denture on the same day as surgery) is not defined as early loading (theoretically, it is a load-free period) but, rather, is part of the early load protocol.

Numerous studies demonstrate that the early loading of implants splinted or unsplinted (in the mandibular anterior region), utilized with overdentures at 6 to 8 weeks after implant placement, is an effective and predictable treatment for the edentulous patient and is the recommended loading protocol of choice where possible. Practically, it may be defined when the final connection of matrix and patrix has been established with the activation of retentive elements or when an implant restoration is in full function.

 

CONVENTIONAL LOADING

A stress-free, nonloaded healing period of 12 weeks in the mandible and 24 weeks in the maxilla has been recommended by Brånemark and coworkers as an accepted prerequisite to achieve bone apposition without interposition of a fibrous scar tissue.4 Following this principle both for submerged and nonsubmerged implants has resulted in high implant success rates.

Indications for Conventional Loading

Conventional loading protocols are indicated when the following conditions are present:

  • Bone quantity is >5 mm;
  • Bone quality is Type III or IV;
  • Bone augmentation is necessary;
  • Systemic conditions (eg,diabetes) are present;
  • A history of heavy bruxism exists; or
  • The clinician is less experienced in implant treatment.   

 

Procedure for Conventional Loading

Studies have shown that it is the excess of micromotion during the healing phase that leads to fibrous encapsulation and interferes with bone repair during the healing phase following implant surgery. A threshold of tolerated micromotion has been documented between 50 µm to 150 µm.5,6 In order not to exceed this threshold, patients undergoing conventional loading are instructed not to wear the denture for 10-14 days following implant placement. At the end of this time period, the denture is relined, relieved, and delivered. This approach may also be indicated for less experienced clinicians who are uncomfortable controlling these loading forces during the critical initial healing period.

The conventional loading protocol is the same whether one-stage or two-stage implant treatment is involved.

 

IMMEDIATE LOADING

The high levels of implant success and immediate restorations in the anterior mandible reported for more than two implants and a fixed connection of two or more interforaminal implants with  rigid overdenture connection should not be extrapolated to the unsplinted two-implant overdenture. Placement of two implants followed by final abutment connection and activation of the retentive components has not yet been successfully reported in the evidence-based literature. An assumption may be made that this prosthetic design and its non-rigid function may negatively effect wound healing and new woven bone formation in the first few weeks after surgery. 

 

References:

  1. Testori T, Del Fabbro, Feldman S, et al. A multicenter prospective evaluation of 2-months loaded Osseotite implants placed in the posterior jaws: 3-year follow-ups. Clin Oral Implants Res 2002;13:154-161.
  2. Bornstein MM, Lussi A, Schmid B, et al. Early loading of nonsubmerged titanium implants with a sandblasted and acid-etched (SLA) surface: 3-year results of a prospective study in partially edentulous patients. Int J Oral Maxillofac Implants 2003;18(5):659-666.
  3. Chiapasco M. Early and immediate restoration and loading of implants in completely edentulous patients. Int J Oral Maxillofac Implants 2004;19:76-81.
  4. Brånemark P-I, Hansson BO, Adell R, et al. Osseointegrated implants in the treatment of the edentulous jaw. Experience from a 10-year period. Scand J Plast Reconstr Surg 1977;16(Suppl):1-132.
  5. Soballe K. Hydroxyapatite ceramic coating for bone implant fixation. Mechanical and histological studies in dogs. Acta Orthop Scand 1993;255(Suppl):1-58.
  6. Vaillancourt H, Pilliar RM, McCammond D. Finite element analysis of crestal bone loss around porous-coated dental implants. J Appl Biomater 1995;6(4):267-282.
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