Stress in bone adjacent to dental implants

Finite element analysis (FEA) was employed to assess patterns of stress in bone adjacent to an implant after application of loads through an attached distal extension cantilever. Under all loading conditions, the highest stresses occurred at the distal cervical bone margin adjacent to the cantilever. In clinical studies, this is not consistently the site of the greatest bone changes seen radiographically. This suggests that extrapolation of FEA studies to clinical implantology should be approached with caution until further data become available on both mechanical properties of bone and patterns of bone remodelling induced by defined functional stresses in mandible and maxillae.     

Variability of hydroxyapatite-coated dental implants

Uniformity, surface roughness, and chemical phase structure are all important features of implant coatings. While the first two variables are important for implant placement, the phase structure affects implant fixation. This study examined the coating morphology and the amount, size, and distribution of crystalline regions of press-fit and screw-type dental implants. Implants obtained from five commercial vendors were sectioned sagittally, mounted, and polished to reveal the coating microstructure. The crystalline phase content varied depending on the implant supplier; however, general trends were observed. Amorphous regions were predominantly found at the metal interface and decreased toward the outside of the coating, producing a crystallinity graded coating. The distal end of the implant, where heat build-up was more likely during the coating procedure, displayed a higher crystalline content and larger crystalline regions. Similarly, the thread apex consisted of more of a crystalline phase. The results of this study of coating microstructure may be used to improve the quality and performance of implants and may help to explain different in vivo responses to the many available varieties of hydroxyapatite-coated dental implants.     

Experimental peri-implant tissue breakdown around hydroxyapatite-coated implants

Factor V Leiden mutation was initially detected in thrombophilic patients and relatives by PCR RFLP (Restriction Fragment Length Polymorphism) according to Bertina (1). This technique presents some drawbacks and the current trend is to simplify the diagnosis. We describe a technique of Allele Specific Amplification (ASA) which is optimized in terms of reliability: an additional mismatch in antepenultimate position enables to obtain the same specificity as PCR RFLP. Furthermore, coamplification of internal control warrants an optimal sensitivity. All the PCR have been simplified: the DNA extraction improvement allows to analyse the genotype with only a few microliters of whole blood whatever the anticoagulant and the procedure of preservation (freezing, dried blood spots, storage at +4 degrees C for several days). This technique saves time. Moreover, full automation of the ASA technique may be shortened thanks to the lack of extraction and the positive/negative reading of the PCR signal.     

Effects of guided bone regeneration around commercially pure titanium and hydroxyapatite-coated dental implants. II. Histologic analysis

The purpose of this study was to determine which treatment of a large osseous defect adjacent to an endosseous dental implant would produce the greatest regeneration of bone and degree of osseointegration: barrier membrane therapy plus demineralized freeze-dried bone allograft (DFDBA), membrane therapy alone, or no treatment. The current study histologically assessed changes in bone within the healed peri-implant osseous defect. In a split-mouth design, 6 implants were placed in edentulous mandibular ridges of 10 mongrel dogs after preparation of 6 cylindrical mid-crestal defects, 5 mm in depth, and 9.525 mm in diameter. An implant site was then prepared in the center of each defect to a depth of 5 mm beyond the apical extent of the defect. One mandibular quadrant received three commercially pure titanium (Ti) screw implants (3.75 x 10 mm), while the contralateral side received three hydroxyapatite (HA) coated root-form implants (3.3 x 10 mm). Consequently, the coronal 5 mm of each implant was surrounded by a circumferential defect approximately 3 mm wide and 5 mm deep. The three dental implants in each quadrant received either DFDBA (canine source) and an expanded polytetrafluoroethylene membrane (ePTFE), ePTFE membrane alone, or no treatment which served as the control. Clinically, the greatest increase in ridge height and width was seen with DFDBA/ePTFE. Histologically, statistically significant differences in defect osseointegration were seen between treatment groups (P < 0.0001: DFDBA/ePTFE > ePTFE alone > control). HA-coated implants had significantly greater osseointegration within the defect than Ti implants (P < 0.0001). Average trabeculation of newly formed bone in the defect after healing was significantly greater for HA-coated implants than for titanium (P < 0.0001), while the effect on trabeculation between treatments was not significantly different (P = 0.14). Finally, there were significantly less residual allograft particles in defect areas adjacent to HA-coated implants than Ti implants (P = 0.0355). The use of HA-coated implants in large size defects with DFDBA and ePTFE membranes produced significantly more osseointegration histologically than other treatment options and more than Ti implants with the same treatment combinations. The results of this study indicate that, although the implants appeared osseointegrated clinically after 4 months of healing, histologic data suggest that selection of both the implant type and the treatment modality is important in obtaining optimum osseointegration in large size defects.     

Functional osseointegration of hydroxyapatite-coated implants in a weight-bearing canine model

The serotonin3 receptor antagonist ICS 205-930 (ICS) may act peripherally to attenuate the anorectic response of rats given an imbalanced amino acid (IMB) diet. Rats were divided into four groups: SHAM+saline (sal); SHAM+ICS; total liver denervation (TLD) + sal; and TLD+ICS. Rats were then given a purified basal diet for 16 days. Next, the groups were injected with sal or 9 mg/kg BW of ICS at 0800 h and at 0900 h (lights out) an isoleucine IMB diet was presented. By 12 h postinjection, the food intake (FI) of TLD and SHAM rats receiving ICS was similarly higher (p < 0.02) than sal-injected counterparts whose FI was also similar; BW followed FI. By day 3, the SHAM groups had similar low FI, whereas the FI of the TLD groups was increasing. The above study was repeated with similar results. Liver innervation is not required for ICS attenuation of IMB diet-induced hypophagia. Also, while sal-injected TLD rats show a normal attenuation of consumption of the IMB diet on the first day of exposure, they subsequently consume more of the IMB diet than SHAM rats. The reason for this difference in TLD rats is not clear but may be related to metabolism of the IMB diet or possibly learning.     

Loaded and nonloaded titanium versus hydroxyapatite-coated threaded implants in the canine mandible

A commercially pure titanium threaded implant was compared to a hydroxyapatite-coated threaded implant of similar geometric design and dimensions in the canine model. Bilateral posterior implants supported fixed prostheses, and some implants in the same mandibles served as unloaded control implants. Implants were evaluated clinically, radiographically, and histomorphometrically at the light microscope level to detect any differences in bone response to loaded conditions. No statistically significant differences were found between the two implant designs under loaded or nonloaded conditions with regard to mobility, probing depth, percentage of osseointegration, and crestal bone position.     

Histological and mechanical comparison of hydroxyapatite-coated cobalt-chrome and titanium implants in the rabbit femur

The purpose of this study was to compare hydroxyapatite (HA)-coated titanium (Ti) and HA-coated cobalt-chrome (CoCr) implants in the distal femur of the rabbit by evaluating bone apposition and interfacial shear strength. Bilateral cylindrical implants with a plasma sprayed 50-microns thick HA coating were press-fit into the metaphyseal cancellous bone of the lateral femoral condyles in a transverse fashion, and the animals were sacrificed at 2, 4, and 8 weeks postimplantation. Mechanical strength of the interface between HA and bone was measured using the pushout method. For histologic analysis, the fractional linear extent of bone apposition was quantitated. No differences were found in the interfacial shear strength between the Ti and CoCr at any time period. The amount of bone apposition increased significantly at each time interval for both substrate metals, but there were no significant differences between the two substrates at any of the time periods studied. The HA-coated CoCr implants performed in a similar manner to the HA-coated Ti implants, both mechanically and histologically, suggesting that HA-coated CoCr implants deserve further study as a viable alternative to Ti for the biological fixation of total joint components in orthopaedic surgery.     

Histological and biomechanical analysis of bone and interface reactions around hydroxyapatite-coated intramedullary implants of different stiffness: a pilot study on the goat

We hypothesized that reduced stem stiffness of orthopaedic implants contributes to a high risk of loosening, since interface stresses and relative motions may exceed a tolerable range. To study this hypothesis, three types of load-bearing implant with different stiffnesses were inserted into the tibia of the goat. Histological analysis was performed of bone repair after insertion of the implant, bone ingrowth, interface disruption and loosening. A finite element model of the configuration provided the quantitative range of interface stresses and relative motions for the present experiment. The implants were made out of stainless steel, hollow titanium and a thin titanium core covered with a polyacetal coating. The stiffness ratios of these implants were approximately 10:4:1, respectively. All implants were coated with a layer of hydroxyapatite (HA) in order to minimize the possible biological effects of the different implant materials. Irrespective of the type of implant, there was a repair phase that lasted 6-12 weeks. The stiff implants functioned well. Large areas of bone bonding to the HA layer were found after the repair phase at 12 weeks postoperatively. After 24 weeks, some signs of loosening were observed. More loosening occurred with the hollow titanium and polyacetal implants, mainly during the repair phase. Three hollow titanium and three polyacetal coated implants survived this period, and were killed after 24 weeks. The integrity of the HA layer at the bone-implant interface of the titanium implants was good. In the polyacetal implants, the repair reaction of the cortical bone was incomplete. Bone ingrowth into HA was largely lacking. In conclusion, we found significant differences in the repair and interface reactions around implants of different stiffness. Stiff implants showed favourable initial interface conditions for bone ingrowth. Intermediate and flexible implants provoked unfavourable interface conditions for initial bone ingrowth. The finite element study showed that the flexible stems produce larger micromotions and higher interface stresses at the bone-prosthesis interface than the stiff stems, indicating an explanation for the histological findings.     

Impaired osteoclastic bone resorption leads to osteopetrosis in cathepsin-K-deficient mice

Cathepsin K is a recently identified lysosomal cysteine proteinase. It is abundant in osteoclasts, where it is believed to play a vital role in the resorption and remodeling of bone. Pycnodysostosis is a rare inherited osteochondrodysplasia that is caused by mutations of the cathepsin-K gene, characterized by osteosclerosis, short stature, and acroosteolysis of the distal phalanges. With a view to delineating the role of cathepsin K in bone resorption, we generated mice with a targeted disruption of this proteinase. Cathepsin-K-deficient mice survive and are fertile, but display an osteopetrotic phenotype with excessive trabeculation of the bone-marrow space. Cathepsin-K-deficient osteoclasts manifested a modified ultrastructural appearance: their resorptive surface was poorly defined with a broad demineralized matrix fringe containing undigested fine collagen fibrils; their ruffled borders lacked crystal-like inclusions, and they were devoid of collagen-fibril-containing cytoplasmic vacuoles. Assaying the resorptive activity of cathepsin-K-deficient osteoclasts in vitro revealed this function to be severely impaired, which supports the contention that cathepsin K is of major importance in bone remodeling.     

Macrophage activation results in bone resorption

Monocytes or macrophages from important accessory cells in the regulation of bone metabolism and destruction. Cells of the mononuclear phagocyte lineage form the precursor cells of the osteoclasts. Soluble products produced by activated macrophages regulate progenitor cell proliferation, recruitment, differentiation, and activity of osteoblasts and osteoclasts. After osteoclasts are removed from the resorption site, macrophages process bone surfaces and create a cement line before osteoblasts enter to form new bone. Although osteolysis associated with normal bone remodeling is seen as an osteoclast driven process, it may be that in chronic inflammation macrophage activation and vascular derangements lead to low pH, local bone demineralization (acid attack), and H+ mediated stimulation of the primary afferent nociceptive nerve fibers (bone pain). Osteoclasts are not able to attach to demineralized bone or to osteoid surfaces. However, if macrophages degrade the demineralized organic bone matrix, chemotactic factors and attachment sites for osteoclasts are produced. In such a scenario, the osteoclast-osteoblast mediated activation, resorption, and formation cycle would be secondarily activated. Such events may play a role in the most common orthopaedic problem related to macrophage activation, aseptic loosening of orthopaedic joint implants, which is secondary to a chronic foreign body reaction and to micromovement.     

Pharmacologic inhibition of particulate-induced bone resorption

The traditional hospital-based approach to Australian nurse education curricula was primarily based on the medical model and directed towards the preparation of nurses who were able to give care to individual clients. The major focus was on the needs of the individual. A notable absence in curricula was any consideration of the role or importance of families to individual and family health. This was despite the continuing involvement that nurses have in their practice with the families of their clients. This paper describes the experiences of introducing a family nursing subject in an undergraduate, preregistration nursing programme which focuses on the family as a unit of care. Educational strategies, clinical experiences, and evaluation of the unit of study are discussed.     

Cortical bone resorption secondary to endodontic-implant pathology. A case report

A single implant was inserted to replace the mandibular right lateral incisor in a 50-year-old Caucasian woman. After one month, an endodontic lesion formed on the adjacent canine, which went on to engulf the fixture. Even though endodontic therapy was instituted expeditiously on the canine, the implant exfoliated spontaneously the following month. There was a large radiolucency afterwards, suggesting resorption of both the labial and lingual cortical plates. A follow-up radiograph four months later revealed a residual detect along with delayed wound repair.     

Urinary N-telopeptides to monitor bone resorption while on GnRH agonist therapy

A 25-year-old woman complained of coughing for over 8 weeks. The coughing was not relieved by a bronchodilator (beta 2-adrenoceptor agonist; clenbuterol), and anti-allergic agent (azelastine), or an inhaled corticosteroid. The thromboxane synthetase inhibitor ozagrel completely abolished her cough. In this case, thromboxane A2 may have contributed to the coughing.     

Participation of cathepsin L on bone resorption

The proteinase responsible for bone collagen degradation in osteo-resorption was examined. The bone pit formation induced by parathyroid hormone (PTH) was markedly suppressed by leupeptin, E-64 and cystatin A, while no inhibition was observed by CA-074, a specific inhibitor of cathepsin B. Pig leucocyte cysteine proteinase inhibitor (PLCPI), a specific inhibitor of cathepsin L, and chymostatin, a selective inhibitor of cathepsin L, completely inhibited the pit formation. Cathepsin L activity in osteoclasts was much higher than the other cathepsin activities. Serum calcium in rats placed on a low calcium diet was decreased by treatment of E-64 or cystatin A, but not by CA-074. These findings suggest that cathepsin L is the main proteinase responsible for bone collagen degradation.     

Dissociation between bone resorption and bone formation in osteopenic transgenic mice

Bone mass is maintained constant in vertebrates through bone remodeling (BR). BR is characterized by osteoclastic resorption of preexisting bone followed by de novo bone formation by osteoblasts. This sequence of events and the fact that bone mass remains constant in physiological situation lead to the assumption that resorption and formation are regulated by each other during BR. Recent evidence shows that cells of the osteoblastic lineage are involved in osteoclast differentiation. However, the existence of a functional link between the two activities, formation and resorption, has never been shown in vivo. To define the role of bone formation in the control of bone resorption, we generated an inducible osteoblast ablation mouse model. These mice developed a reversible osteopenia. Functional analyses showed that in the absence of bone formation, bone resorption continued to occur normally, leading to an osteoporosis of controllable severity, whose appearance could be prevented by an antiresorptive agent. This study establishes that bone formation and/or bone mass do not control the extent of bone resorption in vivo.     

Whole body bone resorption in the growing pig

Our knowledge of total body bone resorption during growth is limited. The primary purpose of this study was to determine if a commercially available bone resorption assay, developed for measuring human bone resorption, could be used to measure whole body bone resorption in young, growing pigs. A secondary purpose was to evaluate if this method could detect changes in bone resorption in response to certain dental appliances which have been shown to change mandibular and maxillary growth. Five growing 4-month-old male Hanford minipigs (Sus scrofa) were housed in metabolic cages for 24 h, every other day, over a period of 1 month. Three of the animals were fitted with a mandibular protrusive orthodontic appliance. Total 24 h urines were collected in which the concentration of creatinine and collagen type I N-telopeptide crosslinks (NTx, a marker of bone resorption) were measured. The NTx immunoassay was originally developed for the analysis of human urine. Pig bone was powdered, defatted, and decalcified, and the resulting powder digested with bacterial collagenase. The digest was screened for NTx content, in the same fashion as the pig urines. Bone extract and pig urines were cross-calibrated to a standard of adolescent human urine. This allowed calculation of the daily quantity of pig bone resorbed. Daily metabolite excretion was quite variable in these growing animals; for NTx the CV was 31%, for creatinine the CV was 25%. The mean daily quantities of bone resorption ranged between 26 and 46 grams of bone which amounted to 1.2-1.7% of estimated total skeletal mass. The protrusive appliances increased bone resorption significantly during the first two weeks of the trial. In conclusion: the NTx assay can be used to measure bone resorption in pigs; the assay is sensitive enough to indicate changes in bone resorption, such as those caused by an orthodontic mandibular protrusive appliance. During growth, bone resorption varies greatly from day to day. On average, every 24 h, 1.4% of the skeletal mass is resorbed.     

Exposure of macrophage-like cells to titanium particles does not affect bone resorption, but inhibits bone formation

Endocrine tumours of the pancreas, even in case of liver involvement, are generally characterized by a slower evolution and a better prognosis, if compared with ductal carcinoma. This fact gives reason to a radical surgical approach, whenever possible, and to the research of any effective adjuvant treatment. For this purpose, hepatic transarterial chemoembolization (TACE) has been proposed in recent years for the treatment of metastatic endocrine tumours. Out of 80 patients suffering from endocrine tumours of the pancreas, observed between January 1985 and December 1996, 28 (35%) presented liver metastases at the time of diagnosis. Twelve of these patients were submitted to palliative resection of pancreatic tumour and one or more cycles of TACE. Overall survival was 50% (6/12); median survival was 35.4 months (range 4-75). These results suggest that chemoembolization, combined with surgical resection of primary malignancy, appears to be able to control the disease for a certain time and to increase the survival rate.