Implant Biomaterials & Surfaces

Every endosseous implant is two things at once: a structural bulk material that gives it strength, and an engineered surface that bone actually contacts. The bulk determines whether the fixture survives masticatory load over decades; the surface determines how quickly and how completely the host integrates it. The clinician chooses both — often without realizing it — when selecting an implant system, and the two decisions answer different biological questions. This chapter separates them deliberately, because conflating "the material" with "the surface" is one of the most common conceptual errors in implant biomaterials.³

On the bulk side, the field is dominated by titanium — commercially pure (cp) titanium in four ASTM grades and the higher-strength Ti-6Al-4V alloy — joined more recently by the titanium-zirconium alloy marketed as Roxolid and, for esthetic and metal-free indications, by yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic.⁴ On the surface side, the field is organized around a single dominant variable — micro-roughness, quantified as the arithmetic mean height Sa — and a second modifier, wettability, that accelerates the earliest healing events. Wennerberg and Albrektsson's classification of surfaces by Sa band, with the moderately rough range (Sa 1.0–2.0 µm) emerging as the documented optimum, is the organizing framework for everything that follows.¹

What unites bulk and surface is the titanium-oxide layer. Titanium owes its biocompatibility not to the metal itself but to the self-passivating TiO₂ film that re-forms within milliseconds whenever the surface is breached. That oxide is what plasma proteins adsorb to, what osteogenic cells read, and what every surface treatment — blasting, etching, anodizing — ultimately modifies. Surface engineering is, in large part, oxide engineering.⁶

Commercially pure titanium is graded 1 through 4 by the ASTM standard, the grades distinguished principally by interstitial oxygen and iron content. As oxygen and iron rise from Grade 1 to Grade 4, tensile and yield strength rise with them, while ductility falls — Grade 4 cp titanium being the strongest of the unalloyed grades and a common choice for one-piece and narrow fixtures.⁴ All four grades share the same self-passivating TiO₂ oxide and the same decades-long clinical track record that made titanium the reference biomaterial of implant dentistry.³

Grade 5 titanium — Ti-6Al-4V — is the workhorse alloy, titanium combined with roughly 6% aluminum and 4% vanadium. It offers substantially higher strength and fatigue resistance than any cp grade, which is why it is so often used for abutments, screws, and components subject to concentrated stress. Grade 23 is its extra-low-interstitial (ELI) variant, with tighter limits on oxygen and iron for improved fracture toughness. The trade-off is composition: the alloying elements aluminum and vanadium have prompted long-running, if largely theoretical, concern about ion release, which is part of the motivation for the alloy described next.⁴

Titanium-zirconium (Ti-Zr, marketed as Roxolid) is a binary alloy of titanium with approximately 13–17% zirconium (nominally about 15%). Zirconium is itself a biocompatible, osseointegrating element, so the alloy raises tensile and fatigue strength above cp titanium without introducing aluminum or vanadium and without sacrificing osseointegration. Its practical payoff is mechanical headroom: the added strength permits reduced-diameter implants — useful in narrow ridges and constricted interdental spaces — where a cp-titanium fixture of the same diameter might be at higher fracture risk.¹⁰

Zirconia ceramic

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is the principal ceramic implant material — a metal-free, tooth-colored alternative valued in the esthetic zone and for patients who request or require a metal-free restoration. Its soft-tissue behavior is favorable: low plaque affinity and a good mucosal response, which makes it attractive in thin biotypes where a titanium shadow might show through.⁸ Zirconia does osseointegrate, and short- to medium-term survival approaches that of titanium. The caveats are real, however: zirconia is brittle relative to metal, carries a fracture risk that is concentrated in one-piece designs and after chairside grinding (which can trigger an unfavorable tetragonal-to-monoclinic phase transformation), and is supported by a thinner long-term evidence base.⁸

The surface is where biology happens. Micro-roughness — quantified as Sa, the arithmetic mean height of the surface measured in three dimensions — is the single best-characterized determinant of the bone response, and Wennerberg and Albrektsson's four-band classification is the framework every clinician should carry.¹ The headline finding is non-monotonic: bone response improves as the surface roughens from smooth through minimally rough into the moderately rough band, then plateaus. Beyond Sa 2 µm there is no further integration benefit, while metal-ion release rises and the rougher surface — once exposed to the oral environment — more readily accumulates biofilm and may predispose to peri-implant disease.¹¹ The moderately rough band (Sa 1.0–2.0 µm) is therefore the documented optimum, and "moderately rough, not as rough as possible" is the design principle that follows.¹

If roughness sets the ceiling for bone response, wettability (hydrophilicity) governs how fast the host reaches it. A highly wettable surface — the chemically modified SLActive surface approaches a contact angle near 0° — promotes immediate, conformational protein adsorption, blood-clot adhesion, and faster establishment of bone-to-implant contact in the first weeks.² The crucial nuance for the examination and the chairside alike: this is an early advantage. Hydrophilic and conventional moderately rough surfaces show measurably different bone-to-implant contact at 2–4 weeks, but the curves converge by roughly six weeks, and long-term survival is comparable. Wettability buys time, not a higher final ceiling — which is precisely why it underpins accelerated healing and earlier loading protocols rather than claims of superior longevity.²

Different processing routes produce different roughness, wettability, and osseointegration behavior even on the same bulk metal. Select any surface or material below to review its roughness band, wettability, supporting evidence, and current role.