BONE REMODELING IN IMMEDIATELY LOADED AND UNLOADED TITANIUM DENTAL IMPLANTS: A HISTOLOGIC AND HISTOMORPHOMETRIC STUDY IN HUMANS

BONE REMODELING IN IMMEDIATELY LOADED AND UNLOADED TITANIUM DENTAL IMPLANTS: A HISTOLOGIC AND HISTOMORPHOMETRIC STUDY IN HUMANS
2005
Marco Degidi, MD, DDS
Antonio Scarano, DDS
Maurizio Piattelli, MD, DDS
Vittoria Perrotti, DDS
Adriano Piattelli, MD, DDS
BONE REMODELING IN IMMEDIATELY LOADED AND UNLOADED TITANIUM DENTAL IMPLANTS: A HISTOLOGIC AND HISTOMORPHOMETRIC STUDY IN HUMANS
KEY WORDS
Bone remodeling
Bone remodeling rate
Fatigue fracture
Lamellar bone
Tetracycline labeling
Woven bone
Remodeling is thought to prevent microdamage accumulation caused by repetitive loading and to increase the fatigue life of bone. The bone remodeling rate (BRR) is the period of time needed for new bone to replace the existing bone and to allow for the adaptation of bone to its environment. BRR is expressed as a percentage or volume of new bone within a specific time period. The aim of the present study was to evaluate bone remodeling events on submerged and immediately loaded dental implants. Twelve patients with edentulous mandibles participated in this study. All patients were rehabilitated with fixed mandibular prostheses, with 10 dental implants per patient. An additional implant was inserted in the most distal posterior mandibular jaw region. In 6 patients, these additional implants were loaded with a fixed provisional prosthesis the same day of the implant surgery and loaded. In the other 6 patients, the additional implants were left submerged and not loaded. After 6 months, all the additional implants were retrieved with a trephine. The percentage of woven and lamellar bone, number of osteoclasts and osteoblasts, and percentage of bone labeled by tetracycline at 0.5 mm and 2 mm from the implant surface were evaluated. The percentage of lamellar bone, number of osteoblasts, and percentage of bone tetracycline labeling was significantly higher in the loaded implants than in the unloaded implants (P = .0001). Also in the loaded implants, the percentage of woven and lamellar bone, number of osteoclasts and osteoblasts, and percentage of bone tetracycline labeling was significantly higher at 0.5 mm than at 2 mm from the implant surface (P = .0001). No such differences were found in unloaded implants (P = .377). In conclusion, we found that (1) loading appeared to stimulate bone remodeling at the interface, (2) a higher percentage of lamellar bone was found in loaded implants, (3) the percentage of bone labeling was higher at the interface of loaded implants, (4) no differences were found in the BRRs between immediately loaded and unloaded implants, and (5) immediate loading had not interfered on the lamellar bone formation at the interface and had not produced formation of woven bone at the interface.
INTRODUCTION
Few reports have been published on bone adaptation to oral implants.1 According to the mechanostat theory of Frost, bone adapts by different biological processes within 4 mechanical usage windows: trivial, physiological, overload, and pathological.2 The thresholds are defined by minimum effective strains for activating adaptive processes.2 Modeling is the result of independent sites of formation and resorption3,4 that add cortical and trabecular bone and reshape surfaces by resorption or lamellar formation drifts.2
Remodeling is a simultaneous process of resorption and formation that replaces previously existing bone,3,4 tends to remove or conserve bone, and is activated by reduced mechanical usage in the trivial loading zone or microdamage in the pathological loading zone.2,5ÇƒÏ7 The repair process is thought to prevent microdamage accumulation caused by repetitive loading and to increase the fatigue life of the bone.8,9 Long-term maintenance and success of osseointegrated implants involves continued remodeling activity at the periphery of the implant to avoid bone fatigue fracture10 and to replace bone that may have sustained microfractures as a result of cyclic loading.3,8,9 Load bearing is threatened by fatigue microdamage, and damaged bone must be promptly removed.5 Woven bone is produced in response to extraordinary loading conditions2 and provides a rapid, almost immediate increase in the sectional geometry of bone.2 The amount of new, less-mineralized bone at the interface as well as the type of bone (woven vs lamellar) influence the strength of the interface.11 The bone remodeling rate (BRR) or bone turnover is the period of time needed for new bone to replace the existing bone and to allow for the adaptation of bone to its environment.3 BRR has also been expressed as a percentage or volume of new bone within a specific time period.3 Lamellar bone forms at a rate of between 1 and 5 ¨µm each day, whereas woven bone can form at rates of more than 60 ¨µm each day; hence, a higher BRR is directly related to an increase in the amount of woven bone formation.3 Higher risks for the bone-implant interface are related to higher turnover rates because the bone is less mineralized, less organized, and weaker at the interface, and different BRRs are most likely related to the microdamage resulting from repetitive loading.3 A heightened remodeling of bone may occur after loading.3
The microstrain environment may affect the turnover rate of bone adjacent to an implant during prosthetic loading.3 The rate of bone turnover in the regional environment of an implant has a great clinical importance for the long-term maintenance of dental implants.11 Immediate loading of dental implants has been said to determine the formation of fibrous tissue at the interface. In reality, several histologic studies in humans and experimental animals have found that loading did not impede osseointegration and did not produce untoward effects on bone formation in a peri-implant location.12ÇƒÏ24 Also, clinical studies have shown very high success percentages for immediately loaded implants in different clinical situations.25ÇƒÏ37
The aim of the present study was to evaluate bone remodeling events around submerged and immediately loaded dental implants.
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