Types of implant: titanium, zirconia, one-piece, two-piece

Counting implant types in a single list is misleading, because the same implant falls into more than one class at once. An implant made of titanium, in two pieces, with a standard diameter and placed in the bone the teeth sit in is the description of the type most commonly used today. Each word in that description answers a separate question: what it is made of, how many pieces it has, how big it is and where in the bone it anchors.

Let us start with the material. The great majority of modern implants are pure titanium or a titanium alloy. Titanium has been used for decades because it can bond to the bone surface and is considered compatible with the body's tissues. Titanium alloys, mixed with other metals to increase strength, are also used; these are preferred especially for thin implants. We deal with the question 'Is a titanium implant harmful?' separately below.

A zirconia implant is made of a white ceramic that contains no metal. Its main strengths are that it does not show the grey shadow of metal in patients with thin gums, and that it is an option for patients who do not want metal. In return, the data behind it is not as broad as for titanium. A review pooling five-year observational studies reports reliable results; another review, directly comparing the two materials, notes that randomised studies of this kind are few and their follow-up periods short.

The second criterion is design. Most implants used today are two-piece: a body that goes into the bone and an abutment screwed on top. With this design, the angle or height can be adjusted later by changing the abutment. In a one-piece implant, the body and the abutment part are a single block; there is no screw or join between them, but the scope for adjusting it later is limited and the planning has to be right from the first day. For a long time zirconia implants were made only in one piece; today there are two-piece versions too.

The third criterion is size. Alongside standard-diameter implants there are also narrow-diameter and short implants. Narrow-diameter implants are used when there is little space between the teeth or the bone is thin. A comprehensive review found that survival of implants 3–3.5 millimetres in diameter was no different from that of standard implants, but was significantly lower for mini implants under three millimetres. Short implants are considered in some cases as an alternative to adding bone when the bone has lost height.

The fourth criterion is the one patients know least about but that changes the outcome most: where in the bone the implant anchors. A conventional implant is placed in the upper bone, which holds the teeth and shrinks after tooth loss. The type known as a subperiosteal implant is a metal framework that sits on top of the bone and was described for patients without enough bone height. When the bone in the upper jaw has shrunk very severely, long implants reaching into the cheekbone come into the picture. In the approach known as corticobasal or strategic, the implant is placed so that it locks into the hard layer deep in the jaw, which resists resorption.

In practice these four criteria are not chosen separately; each one limits the others. If the bone is thin, the diameter gets smaller; the smaller the diameter, the more the strength of the material matters; if the bone has shrunk, the place to anchor changes; and when the place to anchor changes, the design changes too. That is why corticobasal implants have thin bodies and are made in one piece. So the question 'which type is better' cannot be answered on its own. The right question is which type has been chosen for your bone, and on what grounds.

The first list describes the situations in which each type comes to the fore, the second the combinations that call for caution. The decision is made with a CBCT scan and an examination; the list is not a menu to choose from.

The type is not something picked from a catalogue; it is the result of the sequence below. Each step builds on the answer to the one before.

1. 1

   Measuring the bone

   A three-dimensional CBCT scan measures the height, width and density of the bone. If the bone is wide, a standard diameter is discussed; if it is thin, a narrow diameter; if it lacks height, a short implant or a different place for anchorage.

2. 2

   Deciding where the tooth will go

   First the position of the tooth in the mouth is planned, and the angle of the implant is worked out from that. If the direction of the bone and the direction of the tooth do not match, this directly affects the choice of design.

3. 3

   Working out the load to be carried

   Will it carry a single tooth, a bridge or a full mouth? What is in the opposite jaw? Do you grind your teeth at night? The greater the load, the more the diameter and number of implants and the strength of the material matter.

4. 4

   Talking through your health and expectations

   A suspected reaction to metal, the thickness of the gums, smoking and diabetes are put on the table here. In areas that show when you smile, your aesthetic expectations can affect the choice of material.

5. 5

   Putting the choice in writing, with the reasons

   Which type was chosen, in which diameter and length, and why, should be shared in writing. When treatment is finished, you should be given a record of the type, system and dimensions of the implants; this information is needed for any procedure carried out years later.

None of the types below is superior to the others in every case. Each was developed as the answer to a particular problem and loses its advantage in a mouth that does not have that problem.

These are the topics patients ask about most often, and the ones most often explained wrongly online.

The course of healing is set as much by the condition of the bone and the loading decision as by the type. Below are the points where the type has the most visible effect on the timeline.

1. The day of surgery

   A two-piece implant can be covered over with gum, or a healing cap is fitted on top. With a one-piece implant, the abutment part sits in the mouth from the first day.

2. The first weeks

   It is important that no uncontrolled load falls on the part of a one-piece implant that is in the mouth. So it is either protected or joined to the other implants in a bridge so that the load is shared.

3. The fusion period

   On the conventional route, months of fusion are expected for both titanium and zirconia implants. In areas where bone has been added, this period is longer.

4. The long term

   Whatever the type, the gum around an implant can become inflamed if it is not kept clean. How often you have check-ups is set not by the type but by the condition of your mouth.

There are no figures on this page, but the effect of the choice of type on the scope of the plan is concrete. These are the items that set the scope:

Whether bone needs to be added

A short implant, a narrow-diameter implant or an implant anchored in the deep layer removes the bone grafting step from the plan in some cases. When that step is removed, the timeline gets shorter too.

Material

The parts of zirconia and titanium implants, and the teeth made on top of them, are different. Which material is chosen, and why, should be discussed along with the scope.

Continuity of the system

With two-piece systems, an abutment or screw may need changing years later. Whether parts for the system used can still be obtained in future affects the scope in the long run.

Number of implants and the load to be carried

The difference between a single tooth and a full-mouth bridge is bigger than the difference between types. As the load increases, so do the number and diameter of the implants; the type is chosen as part of this decision.