Differences between implants. How they differ from each other when it comes to shape

Using examples, and comparing the tapered and cylindrical shape of the implant, we will analyze whether there is an "ideal" shape for the implant. This article will be of interest to everyone who studies clinical implantology, as well as practicing dentists, orthodontists and dental surgeons.

Varieties of dental implants shapes

Unfortunately, there are many shapes and varieties of implants, as well as specifics of connecting them with abutments. Some shapes defy explanation, taking into consideration clinical indications or common sense.

This is due to the desire of manufacturers to stand out and present their product as unique and innovative. In reality, this leads to confusion, such “novelties” are often taken out of production after 3-5 years. As a result, implantologist then has a problem, because it is impossible to find a new abutment for the restoration of the bridge or crown. After all, this innovative platform had its own taper angle, which is not compatible with any of the well-known manufacturers. Therefore, we recommend that you cautious about new products and “unique solutions”.

1. In practice, there are only a few key features by which dental implants can be classified:
   The shape of the dental implant: tapered, cylindrical, spindle-shaped or cylindrical shape with a transition to the taper.
   In recent years, tapered shape has been the leading design. We will analyze what advantages it gives.
2. The presence of micro-notches (micro-threads) in the upper part, see the middle photo above. Such a notch (micro-thread) prevents overstressing in the cortical (the hardest) part of the bone. It is worth mentioning that clinical studies do not show much difference whether there are notches or not. But there is a difference, and it is preferable to use implants with micro-notches.
3. Profile and pitch of thread: aggressive, flat or rectangular. The shape of the thread affects the area of ​​contact between the implant and the bone and is the indicator of the primary stability of the implant. Aggressive threads are recommended for implantation into low hardness bone. However, here too nothing is, unambiguous and obvious. We will talk about this later.

As to the optimum length and diameter of dental implants, we discussed this topic in a separate article (a link to the article shall be given).

Optimum implant shape (tapered or cylindrical)

Let’s start with an unexpected fact. The shape of the implant is not essential in the long-term clinical picture. If good primary stability has been obtained, then implants of any shape will integrate well and take root. In principle, all implants that have been tested and certified in your country can be used.

The following nuances are more important for the implant survival in the coming 5-10 years or more: a correctly selected straight or angled abutment (the gap between the implant socket and the abutment should be minimal), as well as the screw must be manufactured with great precision. Despite the significant strength of medical titanium, there are cases of breakage or loosening of the screw due to large tolerances (permissible dimensional deviations) that occurred during the manufacturing process.

However, when we say that there is no significant difference or the shape of the implant is not essential, it does not mean that there is no difference at all. In 2014, a study was conducted where implants of two variants were installed, see the photo below (variants “a” and “b”), cylindrical and tapered, respectively.

The implants were installed and loaded. It transpired that tapered implants with a wide thread pitch and square coil geometry have a slight advantage. If we use them, it is much easier to get torque (primary stability), and it is more convenient to work with them in most cases. However, we see that most modern implants have a root (cylindrical) shape. This is no coincidence, as it means that dentists have voted with their wallets. Let’s take a closer look at what advantages the tapered shape of dental implants has:

1. The tapered shape is objectively more convenient, especially for the aspiring implant surgeon. The illustration below shows the risk of the apical part of the implant exiting through the bone in case of landing in a narrow ridge of the alveolar bone. Moreover, the preparation of the landing hole can be successful, and after that the implant itself with threads can come out at the site of narrowing of the alveolar bone (fenestration is most often carried out by the apical, less often medial part of the implant).
   It seems clear that the tapered shape of the dental implant dramatically reduces the risk of fenestration.
2. There are less anatomical restrictions. The tapered implant fits more easily between living roots in difficult cases, see illustration below.
   Such cases are not infrequent after orthodontic interventions, when the dentition has to be moved apart to tilt individual teeth, etc.
   For example, it happens that there is no second incisor (not even a tooth embryo) and the orthodontist prepares the space between the canine and the central incisor. In this case, the roots of living teeth converge as shown in the illustration above. The risk of hitting one of the roots with a parallel-walled (cylindrical) implant is noticeably higher compared to a tapered one.In addition, in the case of using a tapered implant, it is much more convenient for a specialist to bypass the sinuses, see the photo below. There is also less risk of injury to the nerve when it comes to the lower jaw.
3. The tapered apex of the implant ensures better primary stability by reducing the drilling diameter and increasing the compression. Please see the picture below. The difference is especially noticeable when working in a soft bone.
   When preparing a hole for the implant (osteotomy), we make a passage not with three drills, where each next drill is a little larger in diameter, but with two. We then put an implant, for example, a 4mm implant into a 3mm hole. Due to the gradual entry of the coils of the wider part of the implant, the effect of pressure (compression) and slight compaction of bone tissue is achieved in the middle part. This would not be possible with a parallel-sided implant, see the right side of the picture above.Due to the compression, the best primary stability is achieved, which is critical in cases where the insertion of the implant and the temporary crown is carried out on the same day along with the removal of the problem tooth. With good skills, it is possible to install a cylindrical implant with sufficient primary stability, but this procedure requires very confident and well-developed skills of working with a drill. After all, if the drill falters, we will get a hole of irregular shape and variable length. If there is no margin in diameter (the margin is when the diameter of the implant is slightly larger than the hole), then it is difficult to achieve normal integration with good stability. Conversely, as to the hard bone (class D1), it is easy to obtain hyper torque (excessive primary stability) with a cylindrical implant. Such difficulties do not occur with an implant that has narrowing in the apical part.Tapered dental implants are an excellent option for aspiring implantologists because they can help to avoid both insufficient primary stability and excessive hyper torque.

How can a tapered dental implant be installed using a set of cylindrical drills?

However, it is better to make a tapered-shape socket for the installation of a tapered implant. Tapered drills for dental implantation are not yet widely used. The navigational surgery kits contain only cylindrical drills of various lengths with a pitch that allows the placement of implants from 2.5 to 5 mm in diameter.

In addition, there is a herringbone drilling technique, see the illustration above. This is when the longest and thinnest drill first. Its diameter should be as close as possible to the apical (tail) part of the implant. Each next pass is made with a drill of a larger diameter, but of a shorter length. Thus, we get a stepped herringbone socket into which the tapered implant is screwed, see the illustration below.

The illustration shows that hyperfixation is achieved in the vicinity of the steps, which corresponds to the apical and medial parts of the implant. In other words, the maximum tightness is achieved in the cancellous part of the bone, whereas, the contact density is moderate and there is no risk of overstressing in the cortical part. That is good, because for the formation of secondary stability for the implant overgrowth with bone tissue, clots must develop, and this space between the body of the implant and the bone is perfect for this.

Using this technique, you can get excellent results in both soft and dense bones. This technique also requires practice and time to master the skills, which every implantologist can learn.

Previously, it was believed that it is necessary to achieve maximum primary fixation in the cortical part of the bone. At first glance, that’s clear, because this is the hardest part, and it seems logical. However, it’s not as easy as it sounds. The upper part of the ridge with the cortical part is most susceptible to resorption (loss of volume and density of bone tissue). Therefore, reliable integration of the implant into the cancellous bone is important. For the same purpose, it is recommended to use long (14 mm and more) implants for prosthetics, for example, of the upper incisors, whereas in most cases, 10-12 mm implants are enough. Of course, we must remember that bone is a living structure, unlike a concrete wall. Therefore, in response to the load it becomes denser and stronger at the points of contact with the implant. However, this happens later, but at the stage of installation it is the primary stability of the implant that is important.

What is the purpose of aggressive threaded dental implants?

Firstly, the problem of primary stability in a soft bone is resolved with the help of aggressive threads. Aggressive thread means wide petals with a sharp profile. Moreover, the shape of the thread is non-uniform, the coils have a rectangular geometry on the wide part, and they acquire their aggressiveness closer to the apical part.

This shape allows the implant to anchor in the cancellous bone and immediately withstand significant loads. The demand for aggressive threaded dental implants is driven by the proliferation of one-stage implantation procedures. In other words, within one day, the patient has a tooth removed, an implant is placed, an abutment is screwed in and a temporary, but in some cases a permanent crown, is cemented onto the abutment. In such cases, good primary stability is critical. After all, in the process of integration of a dental implant there is a partial loss of primary stability before acquiring a secondary one.

On the other hand, hyper torque can be obtained(excessive primary stability) when inserting an implant with an aggressive thread into the native bone of good density. The shape of the thread shown in the photo above can still be called universal to some extent, but the implant shown on the left side of the photo below is intended only for installation in a soft bone. It will cause hyper torque in the hard bone (class D1). The second variant (right side of the photo) is also designed to provide primary stability in soft bones, but does not cause excessive primary stability in hard bone.

We’d like to conclude by saying that there is no ideal shape or length for an implant. We agree that there are widely used variants that are considered classic, and there are variants with specialization. We mean situations when specific cases require the use of a certain thread shape, length, diameter, etc. However, the determining factor is the experience and skills of the dentist. Craftsmanship multiplied by a precisely matched dental implant platform accomplishes wonders.

We hope this article was useful to you.