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

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Rationale for the Application of Immediate Load In Implant Dentistry: Part II
Date: 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 Implantation
Abstract:
Immediate loading of an implant interface has been used for completely and partially edentulous patients. A biomechanical rationale to decrease the initial risk of overload is reasonable, because implant failure and overload has been well established. This article addresses methods to decrease stress to the transitional restoration. Forces may be influenced by patient factors, implant position, cantilever forces, occlusal load direction, occlusal contact intensity, and diet. The surface area of load distribution may be increased by implant size, implant design, and surface condition of the implant body. A blend of these factors affects the amount of stress to the developing implant interface and hence may affect the risk of immediate occlusal loading for implant prostheses.
Immediate loading of a dental implant loads the implant with a provisional restoration at the same appointment or shortly thereafter. Immediate loading was the initial protocol suggested with dental implants.1-5 The patient does not need to wear a removable restoration during initial bone healing, which greatly increases comfort, function, speech, and stability and enhances certain psychologic factors during the transition period.6,7 Over the last few years, several authors have reported on immediate loading in the completely or partially edentulous patient, with 95% to 100% success rates.
Rationale for Implant Immediate Loading
Part I of this article presented a rationale to decrease strain to the immediate loaded implant-bone interface. This is important because the higher the microstrain in bone, the greater the bone turnover rate. This results in more reactive woven bone, which is weaker and has a lower modulus of elasticity (and biomechanical mismatch to titanium). One method to decrease the strain in the bone is to decrease the stress to the implant and/or prosthesis, because stress and strain are directly related. Stress equals force divided by area. As a result, conditions that increase area of support in the bone or methods to decrease force to the prosthesis are appropriate. Area may be increased by implant number, because a number of implants splinted together may decrease the risk of overload to each implant as a result of a greater surface area and improved biomechanical distribution. This concept was presented in the previous report.
Implant Size
In the partially edentulous patient, the number of implants is more difficult to dramatically increase, compared with the completely edentulous situation. The surface area of implant support may also be increased by the size of the implant. For example, the length of the implant in most systems increases in increments of 2 to 4 mm. Each 3-mm increase in length can increase surface area by more than 20% for a cylinder implant design69 (Fig. 1). Removal torque, pushout force values, and Periotest values have been highly correlated with implant size.70-72 Most of the stresses to an implant bone interface are concentrated at the crestal bone, so the increased implant length does little to decrease the stress that occurs at the transosteal region around the implant.73 However, because the immediately restored implant loads the interface before the establishment of a cellular connection, implant length is more relevant, especially in softer bone types. The benefit of increased length may not be found at the crestal bone interface, but rather in initial stability of the bone-implant interface. The remodeling of the interface does not occur uniformly around the implant. Instead, one region of the implant-bone interface remodels, whereas another remains stable. The additional length may allow the remodeling in one region while the other is able to stabilize the implant (Fig. 2-5). The additional implant length may also permit the implant to engage the opposing cortical plate, which also may increase initial implant stability. The cortical bone has a lower remodeling rate and further ensures a stable condition during the early loading period.
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