Magnus Jacobsson

Bone-metal interface in osseointegration

D ental implants have been used clinically for more than 30 years with a variety of implant materials and different designs, and with poorly described surface properties and surface structures, without the benefit of scientific: experience and investigation. Furthermore, clinical follow-up of the patients has been of unacceptably poor quality with inadequately defined success criteria. In a recently published article, American, Japanese, and European dental implant systems were evaluated against a strictly defined success protocol.’ The conclusions were alarming. Of all the currently used dental implants, only two passed the defined success criteria: the Small transosteal implant2 and the Branemark osseointegrated screw.3 In addition, a few directly bone-anchored systems including the IMZ implant (Friedrichsfeld BmBh, Mannheim, Germany) of commerical pure CP titanium, the IT1 CP titanium screw (Inst. Straumann, Waldenburg, Switzerland),5 and the Frailit-Tubingen aluminum oxide implant6 (Friedrichsfeld BmBh) were investigated scientifically with promising results. However, they were not followed up for an adequate time period, which Albrektsson et al.’ defined as minimally 10 years. Commonly used dental implants including blade-vents, subperiosteal implants, or the Core-Vent system (CoreVent Corp.., Encino, Calif.) were found to be poorly investigated or with unacceptable clinical results. The clinical success achieved with the Brinemark osseointegrated, titanium screw is based on a meticulous method of follow-up and a thorough scientific examination of relevant background factors of a functioning dental implant. Many articles have been published in refereed journals on various aspects of the implantation procedure and the clinical results of the Brinemark screw.3’7 An essential reason for the observed clinical success is the interface that is established between oral hard and soft tissues and the Brinemark implant. The present article reviews important implant parameters determining the bone-metal interface reactions used around an inserted titanium screw. The concept of

Integration of Titanium Implants in Irradiated Bone Histologic and Clinical Study

Nine patients who had undergone combined surgical and radiologic treatment for malignant tumors had skin-penetrating titanium implants inserted in the bone tissue in the treated region at various time intervals after irradiation. The absorbed dose to the implant region varied between 25 and 86 Gy normalized to five fractions of 2.0 Gy/wk, according to the cumulative radiation effect formula. The time interval between irradiation and fixture insertion varied from 9 months to 37 years. Of the 35 fixtures installed, only five were lost because of lack of osseointegration. The follow-up time from implant insertion ranged from 15 to 44 months.

Present clinical applications of osseointegrated percutaneous implants.

Altogether, 389 screws of commercially pure titanium have been inserted at various locations in the facial skeleton of 174 patients. The indications for treatment have been stable anchorage of an external hearing aid or a facial episthesis, in the latter case to restore the facial contours after congenital disorders or status after trauma or cancer surgery. All implants have been inserted in a two-stage procedure, the first being anchorage of the titanium elements in the bone, the second, minimally 3 months later, being establishment of a permanent skin penetration. The outcome of every inserted implant has been analyzed. Only six implants failed to become integrated in bone and had to be removed. Five of these failures occurred in previously irradiated bone, where the success rate was estimated to 85.3 percent. In nonirradiated bone, 354 of 355 inserted implants became osseointegrated, i.e., anchored in bone in a stable manner. The soft tissues were without any adverse reactions in 92 percent of the 951 clinical observations, whereas potentially serious skin complications were observed in only 2.8 percent. Presently, the longest clinical follow-up is 8 years, and 37 implants have been followed for more than 5 years. We believe that this clinical material is the first in which an uneventful bone anchorage and skin penetration have been demonstrated in consecutively operated upon clinical cases. The implants used for anchoring an external hearing aid were also successful in the sense that the patients gained 15 dB (average) in hearing threshold and showed a significantly improved discrimination score. The implants inserted to hold facial epistheses resulted in considerably improved retention and a good cosmetic outcome for the patients.

Short- and long-term effects of irradiation on bone regeneration

The aim of the present study is to quantify bone-regenerative capacity directly and 1 year after administration of 15 Gy 60Co irradiation. A titanium implant, the bone growth chamber, which in nonirradiated cases becomes filled with newly formed bone over a 4-week period, was inserted into each tibial metaphysis of 20 rabbits. In 10 animals the chambers were installed directly after irradiation, while in 10 other rabbits the implants were installed 1 year after the 60Co trauma. In both groups the bone-forming capacity on the irradiated side was compared to that of the contralateral, nonirradiated, control tibia. The amount of bone formed was determined by microradiography and microdensitometry. It was found that bone regeneration was depressed by 70.9 percent within a 4-week period after irradiation. At a follow-up of 1 year, the average depression of bone-forming capacity was only 28.9 percent. This means a recovery by a factor of almost 2.5. The clinical implications of these findings are discussed.

Dose-response for bone regeneration after single doses of 60Co irradiation

The Bone Growth Chamber (BGC) methodology was used to establish a dose-response relationship for regeneration of mature bone tissue after irradiation of 5, 8, 11, 15 and 25 Gy single dose 60Co. The BGC, which is a titanium implant, was inserted in the proximal tibial metaphyses, bilaterally, of a rabbit immediately following local irradiation to one tibia. Each animal thus served as its own control. During a healing period of 4 weeks, the two canals penetrating the implant became filled with more or less newly formed bone. At the end of the healing period, the implants were removed and taken apart and the newly formed bone was collected and its volume measured by microradiography and microdensitometry. It was found that in the dose range of 5 to 8 Gy bone regeneration was reduced by about 20% as compared to non-irradiated controls. Between 8 and 11 Gy, there was a critical range in that a small increase in dose resulted in a greatly reduced bone formation. At 11 Gy and above, the depression in bone formation, as compared to non-irradiated controls, was about 65 to 75%.

Alterations in Bone Regenerative Capacity after Low Level Gamma Irradiation: A Quantitative Study

In the present study the influence of single 2.5 and 5 Gy doses of irradiation on the regenerative capacity of mature bone tissue has been investigated. To the knowledge of the present authors, no quantitative analysis of bone repair after low doses of irradiation has been presented previously. The experimental model used was the Bone Growth Chamber (BGC), which is a porous implant made of titanium. Each one of twenty animals was irradiated with 2.5 or 5 Gy to one tibial metaphysis. Directly after irradiation each animal had BGC:s inserted bilaterally into the tibial metaphyses. Thus, each animal served as its own control. Four weeks after irradiation the BGC:s were removed and the newly formed bone was collected from the implant pores and was analyzed by microradiography and quantified by microdensitometry and histology. It was found that 2.5 Gy irradiation led to no statistically significant alteration in bone formation as compared to non-irradiated controls. At the 5 Gy dose level, however, there was a significant reduction of bone formation as compared to non-irradiated controls.

The effect of static bone strain on implant stability and bone remodeling

Bone remodeling is a process involving both dynamic and static bone strain. Although there exist numerous studies on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain has yet to be clarified. Hence, for this purpose, the effect of static bone strain on implant stability and bone remodeling was investigated in rabbits. Based on Finite Element (FE) simulation two different test implants, with a diametrical increase of 0.15 mm (group A) and 0.05 mm (group B) creating static strains in the bone of 0.045 and 0.015 respectively, were inserted in the femur (group A) and the proximal tibia metaphysis (groups A and B respectively) of 14 rabbits to observe the biological response. Both groups were compared to control implants, with no diametrical increase (group C), which were placed in the opposite leg. At the time of surgery, the insertion torque (ITQ) was measured to represent the initial stability. The rabbits were euthanized after 24 days and the removal torque (RTQ) was measured to analyze the effect on implant stability and bone remodeling. The mean ITQ value was significantly higher for both groups A and B compared to group C regardless of the bone type. The RTQ value was significantly higher in tibia for groups A and B compared to group C while group A placed in femur presented no significant difference compared to group C. The results suggest that increased static strain in the bone not only creates higher implant stability at the time of insertion, but also generates increased implant stability throughout the observation period.

Provoked Repetitive Healing of Mature Bone Tissue Following Irradiation a Quantitative Investigation

A titanium implant, the bone harvest chamber (BHC), was used to investigate the regenerative capacity of mature bone after irradiation. One BHC was inserted in each proximal tibial metaphysis of a rabbit. One of these implant sites was irradiated (60Co single dose) to either 15 or 25 Gy while the other served as control. Newly formed bone grew through a canal that penetrated the implant. This newly formed bone was harvested from the implant every three weeks following irradiation and then quantified by microradiography and computer-assisted densitometry. In this way a ratio between bone formed on the irradiated side in comparison with the control could be established. An immediate depression in bone formation compared with the non-irradiated controls, was seen at both dose levels. A recovery in bone regenerative capacity was seen at 15 weeks after 15 Gy while the decrease in bone formation remained constant after 25 Gy during the 30 week follow-up period.

Soft Tissue Infection Around a Skin Penetrating Osseointegrated Implant: A Case Report

A case is reported where a female patient with bilateral otosclerosis received a bone-anchored and skin-penetrating titanium implant on which a hearing aid was mounted to improve conductive hearing loss. The patient developed an infection that did not cease despite intensive local treatment and skin-grafting. Eventually the implant was removed. The histological examination of the interface between implant and surrounding bone and soft tissues showed an inflammatory reaction in the superficial parts of the soft tissues whereas the deeper portions of the soft tissues and all of the bone tissue were free of inflammation. It is concluded that it is possible to maintain osseointegration in spite of an aggressive soft tissue infection around the implant.

Implant stability and bone remodeling after 3 and 13 days of implantation with an initial static strain.

OBJECTIVE Bone is constantly exposed to dynamic and static loads, which induce both dynamic and static bone strains. Although numerous studies exist on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain needs further investigation. Therefore, the effect of two different static bone strain levels on implant stability and bone remodeling at two different implantation times was investigated in a rabbit model. METHODS Two different test implants with a diametrical expansion of 0.15 mm (group A) and 0.05 mm (group B) creating initial static bone strains of 0.045 and 0.015, respectively. The implants were inserted in the proximal tibial metaphysis of 24 rabbits to observe the biological response at implant removal. Both groups were compared to control implants (group C), with no diametrical increase. The insertion torque (ITQ) was measured to represent the initial stability and the removal torque (RTQ) was measured to analyze the effect that static strain had on implant stability and bone remodeling after 3 and 13 days of implantation time. RESULTS The ITQ and the RTQ values for test implants were significantly higher for both implantation times compared to control implants. A selection of histology samples was prepared to measure bone to implant contact (BIC). There was a tendency that the BIC values for test implants were higher compared to control implants. CONCLUSION These findings suggest that increased static bone strain creates higher implant stability at the time of insertion, and this increased stability is maintained throughout the observed period.