Implant Fixtures With Horizontal Microthreads

Horizontal grooves or mini-threads near the top of the implant reduce concentrations of stress in this area as shown on photoelastic studies, and that is the theory behind why they may reduce bone loss, but most bone loss is due to a thin labial plate and not stress under function.

I've been installing Astra Tech ST 4.5 fixtures since 1993. I can confirm that the loss of bone around the collar of these fixtures is actually is the slightest I've ever found in implant dentistry. The average crestal bone resorption is less than 1 mm, if present, in 13 years. You can find the microthreads features reading the papers published by Michael Norton and Stig Hansson on JOMI (PubMed).

About this, read the follwing paper on JOMI 2006/5: The International Journal of Oral & Maxillofacial Implants September/October 2006 Volume 21 , Issue 5 Radiographic Evaluation of Marginal Bone Level Around Implants with Different Neck Designs After 1 Year Young-Kyu Shin, DDS / Chong-Hyun Han, DDS, MSD, PhD / Seong-Joo Heo, DDS, MSD, PhD / Sunjai Kim, DDS, MS / Heoung-Jae Chun, PhD

Regarding the absences of bone loss, the Microthreads is only part of the solution. The success Astra has achieved is based on the Whole and not just the Parts. Others have copied parts of the system and have failed to yield the same results as Astra. It is the combination of rough surface, microthreads and most importantly the conus abutment

Dr Lupo is parroting Astra's Marketing story... "The success Astra has achieved is based on the Whole and not just the Parts. Others have copied parts of the system and have failed to yield the same results as Astra. It is the combination of rough surface, microthreads and most importantly the conus abutment." This goes far beyond speculation. Firstly, where are the side by side clinical studies that support the claim that other systems have failed to yeild the same results as Astra. Other systems have horizontal grooves or microthreads. Other systems have rough surfaces to the crest of the ridge and other systems have stable connections. The conus abutment contributing to reduced micro-leakage thus reducing bone loss is the basic myth on which Astra advocates use to claim less bone loss, since micro-leakage with stable internal connections is of no consequence if it exists at all.

The only way you will ever truly determine if microthreads aid in reducing crestal bone remodeling is to manufacture a clone of Astra without the microthreads and then compare the two side by side as Bio-Lok did with their Laser Lock trials. Simply comparing system to system with and without grooves is garbage science - too many other variables to contend with.

What is the cause of the bone loss. If....then If there is no bone loss with the internal morse taper and the external hex shows bone loss....what conclusion can we draw...or I am being just too simple

Bio mechanical stress breaking is vital as is supracrestal placement...I have a case that in 3 years has gained 1mm of bone and it is a cantilever bridge!!!! so you never know.The story that you will lose 1mm of bone is mainly due to deep placement, the crestal plate is vital as it is the "armour" to the cancelous bone.Microthreads possibly help stabilise this crestal bone.

I have not worked much with Astra, but I have colleagues that do, and they have stated that they see crestal bone levels maintained with this particular implant. I have been working with the 3i system for a number of years and have enjoyed the same success with their Prevail implant that incorporates the "platform switching" method. The goal of this particular design is to medialize the implant abutment junction. The medialization of the IAJ moves the IAJ away from the implant shoulder and shields the bone from any potential irritants. The bone stays up and so does the soft tissue. The implant works great in aesthetic areas. The funny thing is that 3i discovered this method by accident about 15 years ago. This is pretty helpful though because that have a significant amount of data and research already collected. That's all I know about implants maintaining crestal bone. Sorry I couldn't be more help with additional Astra info.

Astra has beautiful micro threads but this a implant that has restrictions.the first is that it is not a good immediate load implant. The most stress on bone is crestal. The Astra has no significant fixation threads to stabilize the implant to immediate occlusal forces(even if taken out of occlussion since the bolus of food will load it) Second problem is in infracturein the floor of the sinus and immediate placement in lateral wall sinus lift cases where the crestal screw threads will hold the implant from falling into the sinus.However, Astra was the pioneer in micro threads that all implants are going to to help adhere the gingival circular fibers. Every implant has is its pluses and minuses. No implant is perfect for every spot.

I have never had a problem with Astra during immediate loading, but I admit it is very skill sensitive system.

I have been using the microthread implants for the last eight years and I have never seen the usual yearly crestal bone loss(1.2mm first year and 0.5mm every year).Not at all.It is amazing.

I have seen similar crestal presevation results on Bicon and Ankylos(Dentsply) implants,besides Astra. But they all shre the comon feature of conical morse tapered abutment design.Ankylos and Bicon ,however do not have crestal microthreads design. I'm more favorable to the conical morse tapered abutment design that may contribute to the crestal bone preservation then the mirothread theory. One more thing, Ankylos implants have more than 16 years of clinical result on this issue, The Germans have been doing this for more than 16 years already.

Back to the basics basically indicates that crestal bone loss is usually due to some source of persistant irritation, usually from microgaps harbouring microorganisms that are present in crowns. Gave rise to the term "biological width", first coined in the field of crown and bridge work. It was observed that bone always resorbed 1 to 2 mm away from the crown-tooth cervical margin. That is why we try to extrude a tooth fractured at the gum level in order to distance the expected crown-tooth margin at least 1 to 2 mm away from the crestal bone level. Microthreads may mainly be just cosmetic or a seemingly good idea or a convenient selling point by manufacturers running out of selling points. At the microscopic level, osteoblasts probably don't care a damn whether it is macro or micro threads. What is more relevant may be the microscopic pore size on the implant surface below 50 microns in width, considering that osteoblasts/osteoclasts are about 10 to 20 microns in size. And a system that avoids microgaps where microorganisms can thrive occult from the immune system will be more significant in our quest to avoid bone resorption on implants that haunted our predecessors and for some time was even assumed to be inevitable.

I liked all the comments by Dr Ordonez and agree with much of them. I have let the mini's integrate also and have then again seen failures in the maxillary arch. I have also seen failures some months following placement with the mini's loaded-of course the soft tissue/ridge should provide the support; the implants the retention.I too have replaced those that have failed; again some are lost. I think it is difficult to predict success in the maxillary arch. At some point you start to lose money and patient confidence by continuing to replace those lost. I will do them if the patient really understands the risk; otherwise I think root form with attachments is a better coice in the maxilla.

My personal opinion is that it is better to have a microthread or microgrooves on the implant's neck then just a textured surface. But why to do it "micro" ? Because of the thickness of the wall around the conical or any other internal connection. Take a look at Astra 4.0 straight and 4.5 flared implants. The hights of the microhtreaded region is different. Quite different. 4.5 has about 30%more microthreads. Again, it relates to the thickness of the wall. 4.0mm implant has a much smaller platform than 4.5mm implant, plus 4.5 tapers in to 3.5mm diameter, so the regular depth thread can be positioned closer to the implant's platform. This leads to a question - how much of a microthread is good? The answer is - as little as possible. Microthread might be almost as good as a regular thread in a cortical bone, but definitely not as good in cancellous bone. The thickness of cortical bone is around 1.0mm. My point is - microthreads were invented because there is not enough of the wall thickness for regular thread around the internal connection. External morse taper post connection with regular size threads to the neck of the implant provides for an ideal stress distribution and gives you a "conical fit". Hope Nobel gets FDA approval soon for Active external. With all limitations it is a step forward.

There's actually very little conclusive evidence that micro-threads are the reason for minimal bone loss. A number other factors, surface type, biomechanical design and position of implant/abutment junction, etc etc, all contribute. So it's not as easy as listening to a marketing pitch and figuring that microthreads are the reason for bone preservation. Microthreads simply reduce stress peaks, which could be done without any threads at all. Look at Straumann's implants, they have no thread at the coronal portion and bone maintenance is superb. And the threads on the rest of the implant do a great job of giving me primary stability, even in immediate placement cases. I've worked with Astra too and found the primary stability to be far less favorable. As for "grooves" on an implant thread (Nobel), I had even more bone loss with them than without. With one study supporting their claim (on rabbits), it's not surprising.