Case Report
Anorganic Bone Matrix Retrieved 14 Years After
a Sinus Augmentation Procedure: A Histologic
and Histomorphometric Evaluation
Giovanna Iezzi,* Marco Degidi,*
†Antonio Scarano,* Giovanna Petrone,* and Adriano Piattelli*
Background: Anorganic bone matrix (ABM) is reported to have osteoconductive properties. No in-flammatory or adverse responses have been reported when this material is used in sinus augmentation pro-cedures. ABM is said to be a bioabsorbable biomate-rial, but histologic data seem to suggest that the resorption process is slow. Long-term histologic data in humans are lacking. The aim of this case report was to evaluate the bone response to ABM used in maxillary sinus augmentation and retrieved 14 years after surgery.
Methods:Titanium dental implants were inserted in two sinuses augmented with ABM. The implants were osseointegrated and functioned well for 14 years. After this period of loading, the connecting screw of one of the implants inserted in the left maxilla broke, and it was necessary to remove the implant. A bone core of the augmented area was harvested sepa-rately during the implant removal.
Results:A very high quantity of mature, compact bone and a small percentage of residual grafted bio-material were found. About 5% to 7% of the bone was undergoing remodeling. In most cases, residual ABM particles were surrounded by marrow spaces. In other areas, lamellar bone was found in tight con-tact with the particle surfaces. Histomorphometry showed that the mean amount of mature, compact bone was 71.0% – 2.28%, the mean amount of ABM was 22.1% – 3.18%, and the mean amount of marrow spaces was 11.2% – 5.42%.
Conclusions:ABM seemed to resorb very slowly; after 14 years, only a small quantity of residual grafted particles was present. ABM is an effective graft material for sinus augmentation procedures. Vital, mature bone was formed and maintained over a long period with no chronic inflammatory cell infil-trate, foreign body response, or other adverse effects. J Periodontol 2007;78:2057-2061.
KEY WORDS
Biomaterial; bone matrix.
T
he resorption time and the ultimate replace-ment of some graft materials with newly formed bone are still not understood fully, but these materials have a relevant role in clinical practice.1 For example, conflicting data are present in the literature about the performance of anorganic bovine bone over the long term, and human histologic re-ports are quite rare in the literature.2Resorption or a decrease in the density of the grafted area has been reported to occur over time,3,4 whereas otherre-searchers found a lack of breakdown of the mate-rial.5-14Anorganic bovine bone particles were present
after 4.5 years without evident signs of resorption.14
Anorganic bone matrix (ABM) is a xenograft ob-tained by steam heating bovine bone at 1,100C to remove all organic material.15 ABM is a porous,
non-ceramic hydroxyapatite manufactured in sizes between 250 and 420 mm.16Compared to
hydroxy-apatite, ABM is calcium deficient, has hydroxyl vacancies, and has less carbonate on the surface.15 ABM particles present a very rough surface with peaks, ranging from 0.5 to 2.0 mm in width, and pits.15 The material appears to be composed of a network of spherical bodies and shows a porous appearance un-der scanning electron microscopy.17,18The network
of crystallites observed under transmission electron microscopy gives a porous pattern under scanning electron microscopy.18The resorption time of ABM
has been estimated at 2 to 3 years.17ABM, in
combi-nation with a synthetic peptide,‡19,20has been used in
several clinical conditions.21-27
The aim of the present case study was a histologic and histomorphometric evaluation of ABM retrieved 14 years after a sinus augmentation procedure.
MATERIALS AND METHODS
In 1992, a 52-year-old male patient with extreme atrophy of the posterior maxilla underwent a bilateral sinus augmentation procedure in the private practice
* Dental School, University of Chieti-Pescara, Chieti, Italy.
† Private practice, Bologna, Italy. doi: 10.1902/jop.2007.070062
of one of the authors (MD) in Bologna. The average thickness of the subantral bone was 1.5 to 3 mm.
Under local anesthesia, a crestal incision was per-formed slightly palatally, which was supplemented with two buccal releasing incisions mesially and dis-tally. Full-thickness flaps were elevated to expose the alveolar crest and the lateral wall of the maxillary sinus. Using a round bur under sterile saline solution irrigation, a trap door was made in the lateral sinus wall. The door was rotated inward and upward, with a top hinge, to a horizontal position. The sinus mem-brane was elevated with curets of different shapes, un-til it became detached completely from the lateral and inferior wall of the sinus. The ABM grafting material§
was mixed with venous blood and packed carefully in the sinus cavity, especially in the posterior and an-terior parts. Flaps were sutured. Antibiotics and anal-gesics were given for 1 week. Sutures were removed 2 weeks after surgery. After 6 months of healing, five ti-tanium implantsi were inserted. After an additional period of 6 months, a fixed prosthesis was placed on all of the implants. The implants were osseointe-grated and functioned well for 14 years. After this period of loading, the connecting screw of one of the implants inserted in the left maxilla broke, and it was necessary to remove the implant. A bone core of the augmented area was retrieved during the im-plant removal. This core was harvested separately from the implant. No histologic evaluation of the im-plant was carried out. Subsequently, a new imim-plant was inserted, and a new prosthesis was placed.
Processing of Specimens
The specimen was immediately stored in 10% buff-ered formalin and processed to obtain thin ground sections with the cutting-grinding system.¶The spec-imen was dehydrated in an ascending series of alcohol rinses and embedded in a glycolmethacrylate resin.# After polymerization, the specimen was sectioned longitudinally along the major axis of the implant with a high-precision diamond disk at ;150 mm and ground down to ;30 mm. Three slides were obtained. The slides were stained with acid fuchsin and toluidine blue. A double staining with von Kossa and acid fuch-sin was done to evaluate the degree of bone mineral-ization; after polishing, one slide per implant was immersed in AgNO3for 30 minutes and exposed to
sunlight. Then the slides were washed under tap wa-ter, dried, immersed in acid fuchsin for 5 minutes, washed, and mounted.
Histomorphometry of percentage of bone, residual grafted material, and marrow spaces was carried out using a light microscope** connected to a high-reso-lution video camera††and interfaced to a monitor and
personal computer.‡‡This optical system was
associ-ated with a digitizing pad§§and a histometry software package with image-capturing capabilities.ii
RESULTS
At low-power magnification, it was possible to see that mature, compact bone occupied most of the speci-men (Fig. 1). The bone in contact with the grafted par-ticles was mainly lamellar without osteonic structures and with small osteocyte lacunae (Fig. 2). Some grafted particles were joined by bone. In some areas of the bone–biomaterial interface, many osteocytes were in close contact with the particles’ surface. No
Figure 1.
At low-power magnification, it was possible to see a large quantity of mature, compact bone and black biomaterial particles (acid fuchsin–toluidine blue; original magnification ·6).
Figure 2.
The bone in contact with the grafted particles was mainly lamellar bone. No gaps or connective fibrous tissue is present at the interface (arrows) (acid fuchsin–toluidine blue; original magnification ·200).
§ Osteograf, Ceramed, Lakewood, CO. i Friadent, Mannheim, Germany.
¶ Precise 1 Automated System, Assing, Rome, Italy. # Technovit 7200 VLC, Kulzer, Wehrheim, Germany. ** Laborlux S, Leitz, Wetzlar, Germany.
†† 3CCD, JVC KY-F55B, JVC, Yokohama, Japan. ‡‡ Intel Pentium III 1200 MMX, Intel, Santa Clara, CA. §§ Matrix Vision, Oppenweiler, Germany.
ii Image-Pro Plus 4.5, Media Cybernetics, Bethesda, MD; Immagini & Computer, Milan, Italy.
cement or reversal lines were observed between the grafted particles and bone. About 5% to 7% of the bone was undergoing remodeling (Fig. 3). Some grafted particles appeared to be partially resorbed (Fig. 4). In most areas, newly formed bone was ;100 to 200 mm away from the particle surfaces (Fig. 5). Small capillaries, monocytes, and myelocytes were visible in the space between the bone and the grafted particles (Fig. 5). No chronic inflammatory cell infil-trate or foreign body reaction was present. No gaps or connective fibrous tissue were present at the bone–biomaterial interface (Fig. 6). No osteoclasts, osteoblasts, or macrophages were present. Histomor-phometry showed that the mean amount of mature, compact bone was 71.0% – 2.28%, the mean amount of ABM was 22.1% – 3.18%, and the mean amount of marrow space was 11.2% – 5.42%.
DISCUSSION
An understanding of the mechanisms of graft material resorption rates, especially of xenografts, plays a relevant role for the clinician.28Histologic evaluation of the newly formed tissues in sinus augmentation procedures is very helpful to understand issues such as the nature and amount of newly formed bone and remnants of grafting material. Long-term results in humans are crucial; it is important to understand whether grafted particles in the regenerated area can interfere with the long-term prognosis of dental im-plants that are inserted into this bone-graft composite.28
Figure 3.
An area undergoing remodeling. Newly formed bone, more strongly stained with acid fuchsin, is present (arrows) (acid fuchsin–toluidine blue; original magnification ·100).
Figure 4.
Some grafted particles (arrows) appeared to be partially resorbed (acid fuchsin–toluidine blue; original magnification ·200).
Figure 5.
In most areas, newly formed bone was ;100 to 200 mm away from the particle surfaces. Small capillaries (green arrow) and monocytes and myelocytes (black arrows) are visible in the space between the bone and the grafted particles (acid fuchsin–toluidine blue; original magnification ·40).
Figure 6.
No gaps or connective fibrous tissue was present at the bone– biomaterial interface. Compact bone (B) is present. Many osteocyte lacunae (arrows) are present near the bone–biomaterial interface (acid fuchsin–toluidine blue; original magnification ·200).
To the best of our knowledge, the present case report evaluates the histologic results of a retrieved xeno-graft after the longest period of time in the human body. Reports29,30have shown that, even if the anor-ganic bovine bone particles are not resorbed com-pletely and replaced by newly formed bone, there will be no adverse effects on the osseointegration of implants inserted into a site grafted with this material because no contact between the grafted particles and the implant surface was present.
Anorganic bovine bone resorption does not seem to be an essential prerequisite for the predictable os-seointegration of dental implants in grafted areas, and its continued presence does not lessen the adaptive capability of the newly formed bone.29 Moreover,
the slow resorption rate of some materials, e.g., anor-ganic bovine bone, could have positive effects. This is in contrast to autografts, which, after 8 months of healing, have shown resorption of >50% of the original volume.1The stability of the regenerated area seems to be a very important factor for the patient.31It also is possible that the mechanical properties of the bone formed around the xenograft particles will improve over time in relation to bone remodeling and to the replacement of woven bone by lamellar bone.1
The present histologic data showed that ABM ap-peared to have, in some areas, a close contact with bone; the xenograft did not appear to inhibit the nor-mal activity of bone cells on its surface or to disturb the natural bone-remodeling processes occurring around it. The continued presence of ABM particles inte-grated into the bone architecture 14 years after the surgical procedure probably can be explained by the fact that osteoclastic degradation of the grafted material is related to its degree of solubility, which re-sults in the formation of resorption lacunae. The most important factor regulating osteoclastic activity prob-ably is the microenvironment of the osteoclast–sub-stratum interface. In this sealed compartment, acid secretion by osteoclasts causes mineral release from the substratum surface, leading to an increase in Ca2+
ions in the compartment.32,33A high concentration of
Ca2+ions produces an increase in the intracellular
cal-cium levels with an inhibition of osteoclastic bone re-sorption and detachment of the osteoclast from the bone surface.32,33The size of the present graft
mate-rial varies, according to the manufacturer, from 250 to 420 mm; in the present specimen, the particles varied from 40 to 400 mm, with most being close to 400 mm. This fact seemed to show that the particle size likely did not change much over time.
Therefore, the incomplete resorption of the ABM particles, even after a long period, might be due to the high calcium concentration present on the bio-material surface that could inhibit the osteoclastic resorption.32,33
The ABM particles incorporated into compact, mature bone seemed to form a network that could strengthen the bone tissue mass and its ability to with-stand loading forces. The long-lasting ABM particles also might be explained by a bonding mechanism able to maintain the biomechanical integrity of bone/ biomaterial during remodeling/repair processes. Fur-ther investigations are needed to clarify this aspect.
CONCLUSIONS
The present histologic results support the fact that ABM is an effective graft material for sinus augmenta-tion procedures. Vital, mature bone was formed and maintained over a long period, with no chronic inflam-matory cell infiltrate, foreign body response, or other adverse effects.
ACKNOWLEDGMENTS
This work was supported, in part, by the National Re-search Council, Rome, Italy; the Ministry of Educa-tion, University and Research, Rome, Italy; and the Research Association for Dentistry and Dermatology, Chieti, Italy.
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Submitted January 29, 2007; accepted for publication March 19, 2007.
