A Gupta, M Dhanraj, G Sivagami
adhesion molecules, bone implant interface, hydroxyapatite coating, sputtering, surface chemistry, surface topography
A Gupta, M Dhanraj, G Sivagami. Implant surface modification: review of literature. The Internet Journal of Dental Science. 2008 Volume 7 Number 1.
The attachment of cells to titanium surfaces is an important phenomenon in the area of clinical implant dentistry. A major consideration in designing implants has been to produce surfaces that promote desirable responses in the cells and tissues. To achieve these requirements, the titanium implant surface can be modified in various ways. This review mainly focuses on the surface topography of dental implants currently in use, emphasizing the association of reported variables with biological outcome
Major advances have occurred over the last 3 decades in the clinical use of oral and maxillofacial implants. Statistics on the use of dental implant reveals about 100,000 to 300,000 dental implants are placed per year, 1 which approximates the numbers of artificial hip and knee joints placed per year 2 . Implants are currently used to replace missing teeth, rebuild the craniofacial skeleton, provide anchorage during orthodontic treatments, and even to help form new bone in the process of distraction osteogenesis.
Despite the impressive clinical accomplishments with oral and maxillofacial implants—and the undisputed fact that implants have improved the lives of millions of patients—it is nevertheless disquieting that key information is still missing about fundamental principles underlying their design and clinical use. With some important exceptions, the design and use of oral and maxillofacial implants has often been driven by an aggressive, “copycat” marketing environment, rather than by basic advances in biomaterials, biomechanics, or bone biology.
Controlling the bone implant interface by biomaterial selection and modification
Different approaches are being used in an effort to obtain desired outcomes at the bone-implant interface. As a general rule, an ideal implant biomaterial should present a surface that will not disrupt, and that may even enhance, the general processes of bone healing, regardless of implantation site, bone quantity, bone quality. As described by Ito et al 3 the approaches can be classified as physicochemical, morphologic, or biochemical.
Two categories of surface characteristics 6 commonly cited for determining tissue response are:
Surface topography/ morphological characteristics
A. Wennerberg and coworker 10 have classified implant surfaces as:
1.) Minimally rough (0.5-1µm)
2.) Intermediately rough (1-2µm)
3.) Rough (2-3µm)
B. Based on texture obtained
1.) Concave texture (mainly by additive treatments like HA coating and titanium plasma spraying)
2.) Convex texture (mainly by subtractive treatment like etching and blasting)
C. Based on orientation of irregularities 11
1.) Isotopic surfaces: have the same topography independent of measuring direction.
2.) Anisotropic surfaces: have clear directionality and differ considerably in roughness.
Increased surface area of implant adjacent to bone
Improved cell attachment to bone
Increased bone present at implant interface
Increased biochemical interaction of implant with bone
Methods to increase surface roughness
It is mainly done by Al2O3 68 and TiO2 with particle size ranging from small, medium to large grit. Roughness depends upon particle size, time of blasting, pressure and distance from the source of particle to the implant surface.
Studies have shown that it allows adhesion, proliferation and differentiation of osteoblasts 52 and also it has been found that fibroblasts adhere to the surface with difficulty and hence could limit soft tissue proliferation 13 and increase bone formation.
Al2O3 particles are left after blasting. Studies have shown mixed results regarding its presence, in some it has been shown to have catalyzing Osseointegration 14 and in some it has been shown to impair bone formation by a possible competitive action on calcium ions.
Metallic implant is immersed into an acidic solution, which erodes its surface, creating pits of specific diameter and shape 15 .
Concentration of acidic solution, time and temperature are factor determining the result of chemical attack and microstructure of the surface.
Higher adhesion and expression of platelet and extracellular genes even which helps in colonization of osteoblasts at the site and promote osseointegration.
A secure 3-D interlocking interface with bone is observed
Predictable and minimal crestal bone remodeling
Short healing time
Provide space, volume for cell migration and attachment and thus support contact osteogenesis
Reported to increase the surface area of bone implant interface and act similarly to 3D surface, which may stimulate adhesion osteogenesis
Surface area to increase by 600%
Increases tensile strength of bone implant interface 21
Improves primary stability
For type 4 bone
Fresh extraction sites
Newly grafted sites
HA coating can lower the corrosion rates of same substrate alloys
HA coating can be credited with enabling to obtain improved bone implant attachment 2425
Have higher success rates in maxilla
Being osteoconductive in nature, more bone deposited is noted.
Disadvantages 60 :
Delamination of coating leads to failure of implant 26 .
Dissolution/ fracture of HA coating results in failure.
Predisposes to plaque retention.
Various methods of coating:
high deposition rates.
Ease of sputtering of the most of the materials.
High purity films.
Extremely high adhesion of the films.
Excellent coverage of highly difficult surface geometry.
Ability to coat heat sensitive substrates.
Ease of automation and excellent uniform layers.
Surface chemistry/ chemical topography
Commercially pure titanium and Ti-6Al-4V are commonly used dental implant materials, although new alloys containing niobium, iron, molybdenum, manganese and zirconia are developed.
Biomaterial surface interacts with water, ions and numerous biomolecules after implantation. The nature of these interaction such as hydroxylation of the oxide surface by dissociative adsorption of water, formation of an electrical double layer and protein adsorption and denaturation, determine how cells and tissues respond to the implant.
The goal of biochemical surface modification is to immobilize proteins, enzymes/ peptides on biomaterial for the purpose of inducing specific cells and tissue response or in other words to control the tissue implant interface with molecules delivered directly to the interface 66 .
Two main approaches have been suggested to achieve the above stated goal:
First approach mainly directed to control cell-biomaterial interaction utilizing cell adhesion molecules 59 . A particular sequence i.e. Arg-Gly-Asp(RGD) has been known as mediator of attachment of cells to several plasma and extracellular matrix proteins including osteopontin, bone sialoprotein, fibronectin etc. researchers are trying to deposit this particular sequence on to implant to modulate the interface.
Second approach mainly deals with the biomolecules with demonstrated osteotropic effects. Molecules like interleukin, growth factor 1 and 2, platelet growth factor, BMP etc are known to have this effect.
Dental implants are valuable devices for restoring lost teeth. Implants are available in many shapes, sizes and length using a variety of materials with different surface properties. Among the most desired characteristics of an implant are those that ensure that implant-tissue interface will be established quickly and can be maintained. Because many variables affect oral implant, so it is difficult to assess whether various modification in the latest implant deliver improved performance.
The continuing search for osseoattractive implants is leading to surface modification involving biological molecules 41 . By attaching these molecules desired cell and tissue response can be obtained. In future, similar approaches may also be used to promote interaction of mucosal and sub mucosal tissues with dental implant.