Surgical principles in oral implantology are returning to a paradigm of early or immediate loading of dental implants[i]. Respect for both prosthetic and biologic principles is imperative. When a dental implant is placed, the bone to implant interface is weaker at two weeks immediately after implant insertion because of an inflammatory cascade and catabolic events which result in bone breakdown and remodeling[ii]. This places the implant at risk if it is placed in immediate function or in an extraction site with a significant defect. Previous implant coatings, such as plasma-sprayed HA, have attempted to address this breakdown phase with mixed success[iii]. Earlier amorphous HA coatings were highly osteoinductive because of the bioavailability of free calcium ions[iv]. Studies of HA coated implants in the 1980’s clearly demonstrated earlier osseointegration and a higher bone-to-implant contact[v]. However, the low crystallinity of the HA coating led to fractures of these coatings and severe peri-implant infections after loading[vi]. For over a decade, clinicians avoided HA coatings. In an attempt to eliminate these clinical problems, manufacturers subsequently changed the HA formulation to approximately 97% crystallinity. This solved the fracture problem but had the opposite effect on osteoinductivity. Highly dense HA does not resorb to any significant degree. This dramatically reduces the bioavailability of free calcium from the implant surface. Therefore, current HA surfaces have limited biologic interaction when compared to newer acid-etched titanium surfaces and no longer offer any significant clinical advantage[vii].
In 1991, the concept of “bone-bonding” was first described[viii]. Different from the type of interface originally described by Branemark and known as osseointegration, bone-bonding is characterized as an interfacial bond between the bone and implant surface that exceeds the cohesive strength of either bone or implant[ix]. A chemical interaction occurs between bone and implant that enhances both bone cystallinity and adhesion, and can be demonstrated when calcium phosphate materials are present in the correct concentrations[x]. The introduction of a nanotextured surface, further enhanced by molecular impregnation with calcium phosphate, has been shown to significantly enhance osteoblastic activity and thereby eliminate the catabolic phase of bone remodeling[xi]. (Figure 1)
Figure 1. SEM of Ossean™ surface at high magnification (50,000X)
In addition, the Ossean™ surface dramatically increases the rate of osteoblastic synthesis of type I collagen, thus promoting osseointegration and reducing the chances of early failure of immediately loaded implant[xii]. Even distribution of the calcium phosphate surface is critical to control the physiology of osteoblasts. (Figure 2)
Figure 2. Auger spectroscopy demonstrating even distribution of the calcium phosphate surface
This increase in bone-bonding strength is clearly demonstrated in a study conducted by Coelho P, et al, where Intra-Lock™ implants with and without the Ossean™ surface were tested in a reverse torque pullout study[xiii]. The Ossean™ surface implants at 2 weeks exhibited a 100% greater bone adhesion than the implants without the surface modification. In a second study, implants from two other competing manufacturers were tested against a similar macro-architecture Intra-Lock® implant. In this study, when compared to a particulate calcium phosphate coating and a TiO blasted + HF etched surface, at one week the Intra-Lock® implants had a 500% greater bone-bonding shear strength as demonstrated in a reverse torque pullout study[xiv]. The conclusion reached by both studies is that there is a limitation of biologic activity on purely etched surfaces and there is also a qualitative difference in some nanotextured + calcium phosphate impregnated surfaces. The Ossean™ surface is clearly biologically active in the sense that bone goes directly to the anabolic phase without intervening bone breakdown. This is extremely important in immediate load cases and for extraction site defects where the percentage of initial bone-to-implant contact is compromised[xv].
[i] Castellon P, Blatz MB,, D.M.D., Dr.Med.Dent., Block MS, Finger IM, Rogers B. Immediate loading of dental implants in the edentulous mandible. J Am Dent Assoc 2004 Vol 135, No 11, 1543-1549.
[ii] Albreksson T, Johansson C. Quantified bone tissue reactions to various metallic materials with reference to the so-called osseointegration concept. In: Davies JE, ed. The Bone-Biomaterial Interface 1991; Toronto: University of Toronto Press:357-363.
[iii] Block MS. Advantages and disadvantages of hydroxylapatite-coated implants. Oral MaxillofacSurg Clin of North America 1991;3:835-851.
[iv] Gerner BT, Arth E, Alberktsson T, Ronningen H, Solheim LF, Wie H. Comparison of bone reactions to coated calcium phosphate and pure titanium dental implant in the canine iliac crest. Scan Journ of Denta Res1988; 96:143-148.
[v] Engquist B, Bergendal T, Kallus T, Linden U. A retrospective Multicenter evaluation of osseointegrated implants supporting overdentures. Intl J Oral Maxillofac Impl 1988: 3:129-134.
[vi] MacDonald DE, Betts F, Stranick M, Doty, Boskey AL. Physicochemical study of plasma-sprayed hydroxyapatite-coated implants in humans. Journal of Biomed Mat Res 2000 Vol. 54(4):480-490
[vii] Dalton JE,, Cook SD.In vivo mechanical and histological characteristics of HA-coated implants vary with coating vendor. Journal of Biomedical Maerialst Research 2004 Vol. 29(2): 239 – 245
[viii] Lee SC, Song WS. Histomorphometric and Removal Torque Values Comparision of Rough Surface Titanium
Implants. J Korean Assoc Maxillofac Plast Reconstr Surg. 2001 Sep;23(5):396-405
[ix] Mendes VC, Moineddin R, Davies JE. The effect of discrete calcium phosphate nanocrystals on bone bonding.
[x]Zhamg Y, Yokogawa Y, Kameyama T. Bimodal porous bi-phasic calcium phosphate ceramics and its dissolution in SBF solution. Key Eng Mat 2007 Vol. 330-332;91-94
[xi] Coelho P, Freire J, Coelho A, etal. Nanothickness bioceramic coatings: Improving the host response to surgical implants. In: Leipsch D, ed. World Congress of Biomechanis Conference Proceedings. Munich:Medimont.2006;253-258
[xii] Anselme K. Osteoblast adhesion on biomaterials. Biomaterials 200; 21:667-681
[xiii] Marin C, Granato R, Suzuki M, Gil JN Piattelli A, Coelho PG. Removal torque and histomorphometric evaluation of bioceramic grit-blasted/acid-etched and dual acid-etched implant surfaces. An experimental study in dogs. J Perio 2009 Vol. 79(10):1942-1949
[xiv] Coelho PG, Personal communication, Manuscript in preparation, 2008
[xv] Susarla SM, Chuang SK, Dodson TB. Delayed versus immediate loading of implants: survival analysis and risk factors for dental implant failure. J Oral Maxillofac Surg. 2008;66:251