Rationale for the Application of Immediate Load In Implant Dentistry: Part I

Rationale for the Application of Immediate Load In Implant Dentistry: Part I
September 2004
By: Misch, Carl E. DDS, MDS; Wang, Hom-Lay DDS, MDS; Misch, Craig M. DDS, MDS, Sharawy, Mohamed BDS, PhD; Lemons, Jack PhD; Judy, Kenneth W. M. DDS
LWWOnline / The International Journal of Oral Implantology
Immediate loading in implant dentistry is increasing in popularity as a clinical procedure. A scientific rationale of immediate occlusal loading of the implant support system should emphasize methods to decrease surgical trauma during implant placement and to decrease bone loading trauma during the early loading period. The surgical trauma may be reduced by decreasing heat generation and pressure necrosis. The early loading trauma may be decreased by decreasing the bone strain adjacent to the implant interface. Greater microstrain conditions in bone increase the remodeling rate of bone. The higher the remodeling rate, the weaker the bone and the more risk of occlusal overload. Occlusal overload may lead to implant failure. Since strain is directly related to stress, methods to decrease stress are beneficial. In the present report, the stress-reducing influences include increasing the number of implants.
Predictable formation of a direct bone-to-implant interface is one treatment goal in implant dentistry. The two-stage surgical protocol established by Branemark et al. 1 to accomplish osseointegration consisted of several prerequisites, including 1) countersinking the implant below the crestal bone; 2) obtaining and maintaining a soft-tissue covering over the implant for 3 to 6 months; and 3) maintaining a minimally loaded implant environment for 3 to 6 months. 1 The primary reasons cited for the submerged, countersunk surgical approach to implant placement were 1) to reduce and minimize the risk of bacterial infection, 2) to prevent apical migration of the oral epithelium along the body of the implant, and 3) to minimize the risk of early implant loading during bone remodeling. 1 After this procedure, a second-stage surgery was necessary to uncover these implants and place a prosthetic abutment. Predictable long-term, clinical rigid fixation has been reported after this protocol in both completely and partially edentulous patients.
Surgical Trauma
The immediate implant loading concept challenges the conventional healing time of 3 to 6 months of no loading before the restoration of the implant. Often, the risks of this procedure are perceived to be during the first week after the implant insertion surgery. In reality, the bone in the macroscopic thread design is stronger on the day of implant placement compared with the 3 months later, since there is more mature lamellar bone in the threads of the implant. 37 However, the cellular connection of the implant surface condition does not yet exist. On the day of surgery, there is residual cortical and trabecular bone around the implant. When the implant is inserted, it has some contact with this prepared bone. Early cellular repair is triggered by the surgical trauma and begins to form an increased vascularization and repair process to the injured bone. Woven bone formation by appositional growth may begin to form as early as the second week after insertion at a rate of 30 to 50 microns per day. The implant-bone interface is weakest and at highest risk of overload at approximately 3 to 5 weeks after surgical insertion, since the implant-bone interface is least mineralized and unorganized during this time frame. A clinical report by Buchs et al. found that immediate loaded-implant failure occurred primarily between 3 to 5 weeks postoperative from mobility without infection.
The implant-bone interface will have a larger zone of repair when the implant is significantly compressed against the bone. For example, a self-tapping implant may cause greater bone remodeling (woven bone) around the implant during initial healing compared with a bone tap and implant placement technique. 44 The implant should be non-mobile upon insertion, but excess strain within the bone from additional torque and space filling may also increase the risk of microdamage at the interface. A proposed protocol for immediate load has been to insert the implant within the bone to 45 to 60 Ncm. 28,45 This concept helps ensure that the implant has relatively rigid fixation in good quality bone. However, the additional torque used to secure or evaluate fixation of an implant in bone may actually result in pressure necrosis and/or increase the strain magnitude at the interface and therefore increase the amount of damage and remodeling, which could decrease the strength of the bone implant interface. Periostest and various frequency signal values have been used to evaluate implants at the time of insertion as an indication of whether fixation was adequate for immediate load. 21 An alternative approach is to use a reverse torque test of 20 Ncm to evaluate the quality of the bone and interface initial fixation, first suggested by Sullivan et al. for evaluating delayed healing. 46 As described previously by Palti, if the implant does not unthread at 20 Ncm, the resistance indicates that the bone is of sufficient density to consider immediate loading.
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