Issues with Hexed Implants and Bone Loss

In a perfect world there would be only one implant system on the market and it would satisfy the needs of every implant case that presents to the dental office. Unfortunately, that world does not exist. There are virtually hundreds of implant companies across the globe manufacturing implants with the intended purpose of satisfying the clinical challenges that clinicians see in practice every day. Many of these companies have been in business for decades, while others are relatively new to the market. I suspect every implant manufacturer is trying to produce a superior product as compared to its competitors. Currently there are so many implant products available it can be very confusing to the dental practitioner when trying to determine which system to purchase and use in their respective offices.

The fundamental question that seems to come up over and over again from doctors that want to get involved in implant dentistry is simply, “what is the best system on the market, or what system should I buy?” To answer that question one must first understand the basic challenges clinicians try to resolve with an implant system, and how a particular system may be the solution. In other words, what are the characteristics of an ideal implant system?

When considering implant characteristics it is safe to say that there is considerable disagreement amongst manufacturers and clinicians on what characteristics are of most importance. For example:

I purchased my dental practice in 1993 from a clinician that was soon retiring. He was placing and restoring implants in his clinical practice for over 25 years. The purchase of his practice came with hundreds of active implant patients. I chose to follow his lead and for the last 16 years have placed and restored a significant number of dental implants. In fact, today, my practice is limited to implant dentistry. I share this story because I have had a unique opportunity to observe, and work with a significant number of implant systems.

Some systems have been around longer than I have been in practice and other systems have come and gone. I have certainly had the experience of working with implant cases that were highly successful over time and others that were not. The biggest challenge I have had in implant dentistry is maintaining bone support around implants. Crestal bone loss, or die back of bone down to the first, second or third thread was not an uncommon event in some of my predecessor’s cases as well as mine. All of those cases are compromised and require a significant amount of time and energy to maintain a less than desirable outcome.

Another challenge that I have had in my implant journey was trying to pre-determine which cases would be successful long-term versus the cases that were going to result in clinical compromises both functionally and aesthetically. Ideal clinical outcomes were not routinely predictable. It appears that dental implants can fail to maintain proper bone support for a whole host of reasons. Some of the most common causes are overloading of the implant too early in the healing phase. An overload can cause rapid bone loss, or even loss of the implant fixture. Excessive load of the implant following integration eventually can lead to the same result. Inappropriately sized implants, or implants too close to each other or adjacent teeth routinely caused bone loss. Poorly positioned implants with excessive off-axis loading of the implant restoration appear to cause significant bone loss as well. In retrospect, in those types of compromised cases proper protocols were not followed and bone loss could have been predicted. 

A lack of experience and understanding was a major contributing factor to the compromised results. However after observing clinical cases that have been in my practice for as long as 30 to 40 years, where it appeared all fundamental implant protocols were followed, some implant cases showed significant bone loss, while others showed none. The clinical results were vastly different and a complete mystery to me for many years. Fortunately that mystery has now been resolved, and I will share that understanding over the next few paragraphs.

It has become apparent to me that bone loss can be caused by the implant design itself, in certain clinical situations. Let us first look at a brief history of dental implants in the North American market. In the 1930s, the Strock implants were introduced.

In the 1960s and 70s the Linkow, Subperiosteal and Blade implants were introduced. All of those previous implants systems had some success. For example, I have patients in my practice currently that had blade implants placed by my predecessor almost 40 years ago and are still functioning very well, yet those implants are hardly ever used today. Subperiosteal implants are also rarely used today. It was my experience that when Subperiosteal implants worked, they worked well but when they failed, they failed ugly. As a result, Subperiosteal implants have lost favor in the market. The market is constantly changing. Heavy hitters in the market today are the root form implants, most of which are either externally hexed implants or internally hexed implants. Most of my clinical experience has come from using those hexed implants, and as a result most of my clinical challenges are also coming from those implant systems.

The hexed implant systems I suspect have taken over the market mostly because they are mechanically simple and quite easy to use both from the surgical and restorative side of implant dentistry. There are many well documented cases using hexed implants that have been successful for many years providing excellent clinical results both functionally and aesthetically. Unfortunately there are also many documented cases that show significant bone loss around these hexed implants over time. So, that raises the question; why do these implants work well in some cases and not in others? That was a clinical mystery to me for at least 10 years in my practice. What I have discovered has been a well guarded secret for entirely too long. It is a clinically significant issue.

The North American market is currently changing. A circular or conical connection of the implant abutment junction is becoming more popular. These implant systems were introduced into the North American market approximately five years ago. The tapered connection, in some of these systems, allows placement of the implant below the crest of bone and significantly deeper into the soft tissue. These implants have been on the European market for over 20 years. There is a significant amount of clinical research and data that shows dramatically healthier tissue is that the implant abutment junction (I.A.J.) or the connection between the implant and the abutment is a critical factor in implant success and bone health.

In any two piece implant system the implant abutment junction has a microgap, with some associated micro movement between the implant in the abutment under occlusal load. The microgap on any hexed implant is a reservoir for bacteria because the gap is always bigger than .8 μ which is the normal size of oral bacteria. It is virtually impossible to reduce the gap to less than .8 μ when manufacturing an abutment with six-eight sides that needs to be inserted into an internally hexed implant with six-eight sides. The resultant microgap has to be accessed and cleaned by the patient in order for that implant to hold bone. If it is not accessible to daily hygiene maintenance those implants will always lose bone. In other words, if the implant abutment junction is too far sub gingival for mechanical cleaning, or worse yet below the crest of bone, the clinical result will always be bone loss down to the connection or even the first, second or third thread of the implant.

Furthermore the patient will generally have a variety of symptoms which could include swollen tissue, excessive periodontal pocketing, bleeding, exudates and odor – an unrelenting persistent periodontal problem. On the other hand if the implant abutment junction is accessible to daily hygiene bone loss does not occur and the implants will be highly successful for many years. I suspect the previous explanation of bone loss around implants almost seems too simple to be true. If that is the case for you, I would challenge you not to just believe what you just read, but go back into your practice and look at your implant cases. After reviewing radiographs, you will find that hexed implants that are placed too far sub gingival or subcrestal always lose bone, there are no exceptions.

All hexed implants have a distinctive clinical odor when taking off the healing cap or the abutments. That odor is caused by the bacteria trapped inside the connection which is deleterious to the bone. If an implant representative claims that their particular hexed implants have no microgap or micro movement and bone loss is never an issue, believe me they are being disingenuous. Your clinical results will not support their position. Any clinician involved in implant dentistry is very familiar with the foul odor that is evident whenever taking off a healing cap or an abutment from a integrated implant. That odor, which is very common with most systems, is nothing more than bacterial byproduct trapped in and around the implant abutment junction. If that odor is present in your implant cases those implants have the potential for bone loss. The microgap is obviously bigger than the size of oral bacteria or the connection would have no distinctive odor. I am not saying that hexed implants are not quality implants; I am simply saying that they have to be used appropriately to gain optimal results. I still use these implants in my practice today when appropriate. It is my opinion that the microgap issue on these implants has and bone around these implants even when the connection is not accessible to oral hygiene. The improved clinical results are achieved simply because of the conical type connection. This connection provides a smaller microgap between the implant and the abutment.

The conical connection is tapered and not hexed, which affords a tighter connection between the implant and the abutment. They do not have sharp line angles to close in the connection between the implant in the abutment as compared to any hexed implant system. The microgap in the tapered implants are significantly smaller and do not harbor bacteria. Subsequently there is no clinical odor when removing healing caps or abutments from these implants. The tapered implants hold bone when placed significantly sub gingival or subcrestal. Hygiene access to that connection is no longer required with these implants. The size of the microgap is less than .8 μ and bacteria cannot invade the connection. There is a distinct advantage in being able to place implants below the crest of bone and have the bone grow over the top of the implant rather than watching the bone pull back. I have been using these conical connection types of implants in my practice for the past five years. The clinical results have been very impressive. Moreover these implants have a platform switched abutment which also allows the implants be placed closer to each other without strangulating the tissue between the implants.

In the immediate extraction cases this implant design also has some significant advantage. When extracting a tooth, the bone around the extraction site is almost never level or flat. When using a hexed implant the manufacturer’s recommendation is to place the implant at the crest of bone or above the crest, but never below the bone crest. For extraction cases the clinical options for hexed implant is often to flatten the bone by removing some vertical height, or place the implant above the crest of bone which is usually on the facial aspect. Doing so can be an aesthetic challenge when restoring the implant and attempting to hide the metal around the implant crown interface.

With a conical type connection one can simply place the implant at the lowest crest of bone level, which is usually on the facial aspect of the extraction site. The implant generally would then be placed subcrestal on the mesial, distal and lingual aspect. By not re-contouring the bone the hard tissue will better support the soft tissue and the aesthetics will be superior. Those common dark triangles, created in implant dentistry or between the implant and the adjacent teeth, will not develop. Bone re-contouring in the immediate extraction cases and also in cases where the teeth have been missing for some time, is almost never required. Surgically these cases are simpler with predictably better aesthetics results after healing because bone was not reshaped or recontured. In summary the implant market is changing and evolving to meet the clinician’s requirements.

Recently more implant companies in North America are providing tapered implant connections, and I expect that trend will continue. I will predict that in a short time, most implant manufacturers will rise to the challenge and produce similar implants for their customers.

The implant companies that offered a tapered implant abutment connection in Europe over 20 years ago produced a very robust implant system. These implant systems maintain hard and soft tissue integrity very well over a long period of time, which is well documented in the literature. If you are looking to integrate implants into your practice or improve your clinical implant cases, I would take a hard look at these implant systems. They have solved some persistent clinical challenges in my practice, and can do the same in yours as well. Change is on the horizon and change is good.

Dr. Leo Malin graduated from Marquette University in 1991. He maintains a private practice in LaCrosse, WI where he has been utilizing occlusal based dental concepts since 1998. With the help of other experts in the fields of radiology and occlusion, he has developed an implant placement technique which focuses on occlusion (and cosmetics) for implant placement and crown restoration. Dr. Malin lectures throughout North America on full mouth reconstructions and implant placement