What are the pro and cons for placing 6 mm implants?

Wow, great question. I can't wait to hear responses. I once heard a "pro" argument for 6 mm implants that made a lot of sense to me and I saw this example play out on my own driveway... I had basketball backboard and pole installed. The pole was 11 to 12 feet tall with a heavy backboard and rim cantilevered off of it (not to mention countless teenage boys hanging on the rim). When the hole was dug for the concrete I looked at it and said, "That's it?" It looked to be only about 30 inches deep and 2 feet in diameter. I didn't think it was big enough. That pole lasted over 15 years with heavy use and horrible weather conditions and was incredibly hard to remove when the boys were grown and gone. The analogy I heard was if a dentist was going to install a basketball backboard and pole the pole would be dug 50+ feet deep and 5 feet wide! Maybe our implants are unnecessarily too long. Aren't we just inviting trouble by going deeper than necessary?

I have placed and followed 135 Straumann Tissue Level 6mm length implants for up to a 20 year follow-up and compared the survival rates (not cumulative) to the Straumann 8mm and 10-16mm lengths. I published in JOMI in 2006 on the up to 7 year follow up time when I only had 35 implants of 6mm length in the study. Currently the survival rates are 91.1% for 6mm (N=135), compared to 96.1% for 8mm (N=383) and 95.4% for the 10 to 16mm (N=763). The vast majority of the 6mm implants were in the posterior mandible and most were splinted. I strongly suspect the failure rates would be higher in the maxilla especially for unsplinted implants. So my conclusion is that 6mm implants offer an alternative to advanced augmentation procedures where the short implants can be placed in reasonably good bone quality, but one should expect about a 100% higher failure rate compared to 8mm or longer implants (in my data failure rates of 8.9% compared to 3.9% for 8mm and 4.6% for 10 to 16mm)

In response to Dr. Chris Forte: The comparison of a ground post and an implant is somewhat comical (please take it as a comment not criticism). Dirt and concrete cannot be compared to bone biology and I hope we agree. I call myself a woodworking hobbyist and many times I think of comparisons of various woods and screws that evolved over the years. Regardless of my observation I have to remember that I am a dental professional and that biology is where the answers lie. Sometimes I wonder about the huge number of implant designs and each with their own claim of superiority. Craft is craft and dentistry is dentistry. Implants fail not because they tip over or the bone erodes around them because of force. Perhaps it does happen at times but many other potential factors need to be included. A simple calculation without consider the diameter of the implant, a one millimeter loss of bone in the case of a 6 mm implant is over 16 percent loos of support while in the case of 8mm implants a 1 mm bone loss is Over 12 percent. Is it significant? In end we deal with half mm and we worry, in implants we don't know when to worry. Surface area is also a consideration which means diameters of implants matter. That is why we don't see a 2mm implant.

If enough force is applied to any implant it will fail. When using short or narrow implants, inclined planes and off center loads need to be minimized ever more so than with longer wider implants. Careful planning for placement and load must be done before the case is started. An implant that is not subject to destructive force is not likely to fail even if it is short or narrow. Bicon has been selling short implants for several years and has stats that are rather favorable; but why would you place a 6mm instead of a 10mm implant implant when you have bone for a 13mm implant? Does any one know how to test and measure the load limits of the bone before implants are placed? We know what type of forces can be the most destructive to our implants. Just minimize these forces with good planning and careful execution. Reserve the use of ultra short and narrow implants to those places where they are needed.

In my opinion we must consider the amount of bone around the implants.In other words should be right placing a 4 mm. Implant long and 4 mm. wide when you have more than 2mm. of bone around it.I think that the lenght of implants could be inversely proportional to the amount of surrounding bone .

This is a tough one. Most implants are tapered so in a 6 mm implant , if and when you loose the first mm of cervical bone you are loosing a lot of BIC area, arround 22% and that is catastrophic( and is just 1mm).During the old times, Branemark times, 7 mm where the ultra short and they fell out like crazy (up to 50% depending on the study). Most short implants are placed because there is no other choice or the other choice would take too long or too much money or... so they are usually not in the best position (too deep) that means long crowns, that is a longer force arm against a shorter resistance arm so mechanically its hell for the little implant, I have seen 18mm crowns on top of 6mm implants. In this situation cervical bone tends to go, and fast. Other thing to consider is that normally 6mm implants start at 4,2 mm diameter and up, but usually we start with 5mm diameter, that means you need a lot of width and usually is not the case and lots of new grafted bone is not the same as nice mature mandibular bone. There are extra short implants like Bicon, Endopore or OTmedical, and having used them a lot, due to their design and or surface, they work fine, untill they don´t and in those cases it looks like you dropped a grenade in there.... I would say no to stand alone implants, and yes to splinted and or terminal implants, at least in our experience, under those conditions they do work, nicely too.

I forgot the name but what about the company that made short wide implants? Are they still in business?

First of all I want to state that I have a vested investment in Quantum dental Implants, I am the president of the Company. To remove any bias from my posting I will mention that we also manufacture and sell implants as long as 14 mm. Going a step further Bicon has also a wonderful 6 mm implants. When I first started placing implants many many years ago I favored long implants, and little by little I have completely changed my mind. The results that I have experience with short implants are equal or even sometimes better than with longer implants, and I have placed implants from a lot of different manufacturers. A lot has to do with the fin and thread designs of short implants, and with the sloping shoulders at the crest of the implants. Go to our web page and under advantages look for short implants. The same advantages apply to Bicon, and if you chose Bicon it is ok with Quantum, we have so much demand that sharing success with another company for the betterment of Implantology is in itself rewarding. Raul

I am neither a dentist nor without commercial interest. Two considerations are that if you use a cylinder as an approximation of an implant then the surface area of implanted titanium (the walls and one end) is about the same for a 10x3.5 implant as for a 6x6. As a previous commentator said. Bone loss around the larger diameter implant will be more critical than with longer, smaller diameter implant. How about bone loss? Partially or predominantly non resorbing graft materials have and may still be predominant. Are they implicated? Is bone generated with non resorbing graft material more likely to become infected and lost etc. etc.? It seems logical that the area surrounding the implant will have reduced blood supply directly in proportion to the amount of residual graft proximal to the implant. If this is the case then would the prognosis for short implants be improved with full resorption? Phil

Happy to receive direct comments re my above comments. Phil

Because of my engineering background i tend to look at implant placement and selection from a mechanical perspective. Hopefully someday someone will research the relationship of implant length, diameter, bone density and implant design. All these factors are intertwined in the proper selection of an implant. All of this can most likely be established from some principles of mechanics with consideration of the different qualities of living bone vs. other materials. As it is right know dentists select implants based on gut feeling being aware of implant length, diameter and implant design. One wonders if such study will ever come about. We should perhaps look at orthopedics and learn how they go about selecting various mechanical implants like hip and knee. One thing is for sure in my mind, length matters because our role is to assure to the degree we are capable, the most predictable results. In the event of bone attrition which happens invariably, what is left to support the implant matters. Nature designed teeth roots with lengths well over 6 mm for a very good reason. Traditionally when we see teeth with short roots like post orthodontics, we think of poor prognosis. We should keep that in mind when we select implants.

The literature is replete with studies of successful short implants. Early studies revealing higher failure rates of short implants involved implants without surface treatment. Additionally, occlusal forces have been shown to be concentrated within 5-6mm of the coronal aspect of implants. These facts likely account for the success reported for shorter implants. However, it is well pointed out that crestal bone loss should also enter the calculation in planning.

I agree with Gregg about the research. It is the configuration and the placement technique followed to make a short implant successful, and Bicon implant system has a perfect solution. I have been watching Bicon since they were introduced. Was reluctant to use it for a while until a few years back. They are successful if placed at a proper level and with a friction grip. They are technique sensitive. Check their site.

In life....length is not everything........ and implants have to be included in this axiom. Diameter and design of the threads are a consideration..... these factors add to the surface area in contact with the bone. Proper placement and control of stress factors such as proper occlusion, adequate number of fixtures are considerations as well. So if the bone will only allow shorter fixtures.... go for it.