The effect of micro-topography of the implant surface on osteoblasts and bone formation

The surface of bone and dental implants plays an important role in osteoblast adhesion and bone growth. Many parameters affect the quality of osteointegration, including chemical composition and surface morphology [1]. The microtopography of the surface appears to be an important factor in determination of the level of biological interaction between tissues and biomaterials, and many methods are used to achieve surface roughness on the micro-and-nano scale [2]. In-vivo studies have shown that, while smooth surfaces encourage formation of fibrous tissue, surfaces with micrometer-scale roughness are more conducive for bone formation [3-5]. These studies established that certain surfaces regulate osteoblast adhesion, proliferation, mineralization and differentiation [6-9], and when osteoblasts interact with implant surfaces with micro-scale topography they differentiate to mature osteoblasts, producing increased levels of alkaline phosphatase, osteocalcin [1], growth factors, cytokines and prostaglandins, all of which promote osteoblastogenesis and inhibit osteoclast activity [10,11]. In addition, these surfaces exhibit improved contact with bone [12-14], provide more mechanical support and encourage osteointegration more quickly compared to implants with smooth surfaces [5,15-17].

Figure 1 [18] shows the surface morphology of four different Ti6Al4V discs: one is smoothed by a machine with average roughness (Ra) of 0.2 µm, and the others are grit-blasted with Ra of 2.0, 3.0 and 3.3 µm. While the smoothed disc exhibits a concentric pattern due to the smoothing process, the grit-blasted surfaces are uneven, containing grooves and cracks.

Fig. 1: Scanning electron micrographs showing the morphology of the surfaces of the Ti6Al4V substrates: machine-polished (a), grit-blasted with Ra values of 2.0, 3.0, and 3.3 µm (b, c, and d, respectively) (X1200).

Comparison to other companies rough surfaces Ra values Click For More Info

Dentalis Surface roughness is achieved by grit-blasting with a unique combination of HA,
alpha TCP, and beta TCP (soluble) particles with different size of grains (U.S. registered patented)
The roughening process produces a larger, uniform and cleaner surface without any contamination and use of acid.
This process provides the surface with its optimal structural roughness, and enables the
incorporation of biocompatible particles.

Conclusions:

Dentalis surface treatment enhances the biocompatibility and the surface area. This improves the stability of the dental implant because there is greater potential area of contact between the implant and bone. This micro roughness is a biomimetic surface for the osteoblasts that are similar to the bone treated by osteoclasts that proceeds osteoblasts arrival.

Dentalis surface has the ideal Ra (3-3.3µm), as well as a more uniform composition

References:

  1. Albrektsson T, Wennerberg A. Oral implant surfaces: Part 2--review focusing on clinical knowledge of different surfaces. Int J Prosthodont 2004 Sep;17(5):544-564.
  2. Davies JE. Understanding peri-implant endosseous healing. J Dent Educ 2003 Aug;67(8):932-949.
  3. Guizzardi S, Galli C, Martini D, Belletti S, Tinti A, Raspanti M, et al. Different titanium surface treatment influences human mandibular osteoblast response. J.Periodontol 2004 Feb;75(2):273-282.

The following third-party trademarks apply:
SLA™ is a trademark of Straumann® of Institut Straumann AG,
OsseSpeed™ is trademark of ASTRA TECH- DENTSPLY,
MTX™ is trademark of Sulzer Dental Inc-Zimmer dental,
TiUnite™ is a trademark of Nobel BioCare®,
Osseotite™ is a trademark of 3i® of Biomet Group

Cell morphology
Cellular morphology was sensitive to the disk surface properties. When osteoblast-like MG63 cells were grown on TCPS (data not shown) or smooth Ti alloy surfaces, the cells were spindle shape and elongated. In addition, they were aligned with the microgrooved structure of the machined disks (Figure 2). On the rougher, grit-blasted surfaces, most cells appeared triangular, polygonal, or rounded with cytoplasmic extensions into the pits of the blasted topography.


Scanning electron micrographs showing morphology of MG63 cells on microstructured Ti6Al4V substrates. MG63 cells were cultured on machined (a) or grit-blasted Ti6Al4V substrates with Ra of 2.0, 3.0 or 3.3 μm (b-d, respectively) for 6 days. The cell morphologies were observed by SEM (x 1,000).
The micro-topography of the implant surface also has an effect on the differentiation of the osteoblasts associated with the surface, as well as on the production of local factors. Figure 2 [18] shows the quantification of various factors secreted from the osteoblasts that underwent adhesion to the same surfaces shown in Figure 1. The number of cells and amount of alkaline phosphatase (early marker of osteoblast differentiation) were reduced on Ti6Al4V surfaces (compared to tissue-culture polystyrene), and both parameters were lower on surfaces with rough topography compared to smooth surface (data not shown). However, the amount of osteocalcin, a late differentiation marker of osteoblasts, both in the condition media (Fig. 2-a) and normalized per cell (Fig. 6-b), was higher on Ti6Al4V surfaces compared to TCPS, and increased significantly on roughened surfaces than on smooth surfaces. The same trend occurred when the amounts of osteoprotegrin (OPG) (Fig. 6-c), prostaglandin E2 (PGE2) (Fig.6-d), PGE2 normalized per cell (Fig. 2-e) and TGF-β1 (Fig. 2-f) were measured. These data suggests that despite the lower number of cells on surfaces with micro-topography, the osteoblasts attached to them are more differentiated and secrete more local factors.

In-vitro research on our surface provided favorable results:

Osteocalcin is a late marker of differentiation and increases as mineral is deposited. Osteoblasts cultured on the Dentalis surface displayed high levels of proliferation, differentiation, and osteocalcin production. The osteocalcin levels increased 4-, 6-, and 11-fold on rough surfaces compared to smooth surfaces.


PGE2 - Prostaglandin

is required for osteoblast activity and prostaglandins mediate cell response to surface structure. Studies show that levels of local growth factors like PGE2-prostaglandin are significantly increased when osteoblasts are cultured on Dentalis BAS surface , as compared to plastic or pre-treated titanium disks.

The RANKL-OPG system in the osteoblast osteoclast coupling

Physiologic and reactive bone remodeling relies on the tight communication (coupling) between osteoblasts and osteoclasts. A critical component of this communication depends on the RANKLOPG system. Both membrane bound and excreted RANKL (produced by the osteoblasts) mediate a signal for osteoclast formation through RANK (“RANKL receptor”) expressed on osteoclast progenitors. OPG (also produced and excreted by the osteoblasts) counteracts this effect by competing for and neutralizing RANKL. Tightly controlled bone remodeling is critical for the adaptation of bone to mechanical stresses and bone repair, including implant osseointegration.


TGF- β1 Production Local factor production

These growth factors stimulate matrix synthesis and differentiation of osteoblasts and also inhibit osteoclasts. Another major difference can be observed in TGF-β levels. Dentalis BAS surface lead to a ten-fold increase in TGF-β production, compared to the control group (plastic).

Comparison of TGF-β production by different surface Click For More Info

For comparison, cells grown on Straumann’s SLA surface produced similar levels of TGF-β as cells grown on the same control surface. The SLA Active surface presented a three-fold increase in TGF-β secretion levels compared to the control TGF- β1 Production Local factor production

Dentalis BAS surface lead to a ten-fold increase in TGF-β production, compared to the control group (plastic).

The following third-party trademarks apply:
SLA™ is a trademark of Straumann® of Institut Straumann AG

Fig. 2: Effects of surface roughness on osteoblast differentiation and local factor production. MG63 cells were grown on tissue culture polystyrene (TCPS), Ti6AVI4V surfaces with smoothed surface (0.2 µm) and Ti6AVI4V surfaces with various roughnesses (2.0 µm, 3.0 µm and 3.3 µm). *p < 0.05 compared to TCPS, #p < 0.05 compared with smooth surface, +p < 0.05 compared with 3.0 µm rough surface.
In-vivo experiments also confirmed the advantage of micro-topography of the implant surface in terms of osteoblast growth, adhesion and mineralized matrix production (Fig. 3) [18]. Although some bone was formed on the smooth surface implants, it was also covered with fibrous tissue (Fig. 3-a,b,c), which was detached from the surface during the histological processing. Some fibrous tissue was found also on roughened surfaces (Fig. 3-d,e,f), but it was thinner and more attached to the surface, so that the detachment was mostly within the bone rather than at the bone-implant interface. Bone cells were directly attached to the rough surfaces and produced mineralized matrix. This resulted as well in a significant difference in removal torque measurements between the smooth and rough surfaced screws. Smooth screws required 2.3 ± 0.3 Nm, while rough screws required 5.3 ± 0.4 Nm (p < 0.0001).


Fig. 3: histological sections oh bone formed on Ti6Al4V pedicle screws implanted in the L4 vertebra of sheep. The screws had smooth (a,b,c) or rough (c,d,e) surfaces.

These data confirms the fact that osteoblasts grow on a variety of surfaces, and will adhere and grow even on smooth surfaces; however, it supports once again the theory that micro-scale topography of the surface of bone implants promotes osteoblast adhesion, differentiation and activation – both in-vitro and in-vivo. Therefore, when parameters such as time, efficiency, and proper bone growth are taken into consideration, the optimal Ra micro-roughness surface improves bone-implant interactions, when compared to smooth surfaces or surface with other micro-roughness.

For more info about BAS ™ Surface and the Scientific Research
Documentation In vitro & In vivo experiments please contact your local distributor.

Abbreviations:
1a,25 (OH)2D3 1a,25-Dihydroxy vitamin D3

Ang-1 Angiopoietin 1

BIC Bone to implant contact

BMP-2 Bone morphogenetic protein 2

Cox Cyclooxygenase

CSR Cumulative success rate

DAG Diacylglycerol

EGF Epidermal growth factor

ERK1/2 Extracellular regulated kinase

FGF-2 Fibroblast growth factor 2 (basic fibroblastgrowth factor)

GFOGER Glycine-phenylalanine-hydroxyprolineglycine-glutamate-arginine

KRSR Lysine-arginine-serine-arginine

KSSR Lysine-serine-serine-arginine

LPA Lysophosphatidic acid

MAPK Mitogen-activated protein kinase

MSC Mesenchymal stem cell

OPG Osteoprotegerin

PA Phosphatidic acid

PC Phosphatidylcholine

PGE1 Prostaglandin E1

PGE2 Prostaglandin E2

PKC Protein kinase C

PLD Phospholipase D

RANK Receptor activator of nuclear factor k B

RANKL Receptor activator of nuclear factor k B ligand

RGD Arginine-glycine-aspartic acid

TGF-b1 Transforming growth factor b1

VEGF-A Vascular endothelial growth factor A

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