We would like to thank Nobel Biocare for their generous sponsorship of speaker Steve Hurson for our March meeting of the Conejo Simi Implant Study Club. Steve is a mechanical engineer by education who graduated from Cal Poly San Louis Obispo and has over 30 years of experience in the implant field.
Mr. Hurson brought to us knowledge that he has accumulated from a long and industrious career at Nobel Biocare, spearheading the science behind the product line. His topic today was to inform us on how we can increase long term success by understanding the importance of proper screw preload, properly matched components and an occlusal scheme that will not deteriorate the system.
The original implants were all CP 1 (commercially pure grade). Now the implants are CP 4. Large diameter fixtures have a CPA value of 680 and all the other have a CPA 0f 750. The manufacturer starts with a large bar that is cold worked into a smaller and smaller size. This creates a work hardened bar stock. As the oxygen and hydrogen and nitrogen levels go up the bar gets stronger. There will also be trace amounts of iron in the implants. Some other companies use annealing to create their bar stock.
You can never overstretch a prosthetic screw, this is a myth. It will break before it stretches. You can’t make it too tight. Steve described the preload of a screw to a stiff spring, like an old garage spring, we try to tighten it to 75% of its induced tension of yield. Today’s springs can be tightened 3 x tighter due to the stronger material used as compared to 25 years ago. A problem with Ti screws in Ti implants is the galling of the surfaces as they rub against each other. Each time the screw is tightened it galls more and weakens the screw. This led Nobel to develop Torqtite coated screws. Each tightening leads to the small deposit of material and the screw can be tightened more. This coating lasts for up to five tightenings before the coating wears off.
Screw loosening many times relates to poor management of occlusal forces. The longer the tooth the more negative impact the horizontal forces will have on the screw system. Best results will come from loading implants on their long axis in the posterior jaw, even if this requires the use of shorter implants to achieve the proper position. Angled implants will place detrimental horizontal forces on the screw system. As a side note, this does not relate to all on four cases since this load is held by the framework and dispersed over all the implants. It is important to note that aftermarket screws do not have the high preload which will lead to a rocking motion and screw failure. The tribe connection has a longer screw and tube that goes 4mm into the implant so it is less likely to rock. The conical connection is even better as it has a 12-degree taper that stretches the implant wall and hermetically seals the micro gap. These connections are all tested at over 5 million cycles with torqtite screws. Overall, screw loosening can be attributed to occlusal overload, lack of screw preload and misfit components.
He advised all the attendees to purchase a 10x loupe so they can evaluate the lab work prior to delivery. Always wash all the component with soap and water and rinse in saline when they come from the lab, even sterilize if you can. Do not use peridex as it will cause the periodontal tissues not to adhere to the abutment surface. Furthermore, do not allow the lab to glass bead or grit blast the component. It will create high points that can eventually lead to loosening. The but joint is the best connection to the implant for multiple units as it sits passively on the shoulder of the implant. It is even better to use multiunit abutments and move the micro gap further from the bone level, especially with the conical connections that can be hermetically sealed. Additionally he advised against probing around implants, as the hemidesmisomal seal is broken each time and contaminated. This attachment is much different than the bone implant level that consists of a 100 angstrom protein layer that the bone adheres to.
Steve then spent time discussing the soft tissue seal around dental implants and how important it is for good bone health and the prevention of perimplantitis. He reviewed the role of the hemidesmosmal attachment that occurs. There are three materials that soft tissue will adhere to: Titanium, Zirconia, and PEET. It will not adhere to gold. This means that some sort of abutment is needed to provide the best seal. Try to eliminate anything that would prevent cell adherence to the restorative components. So make sure the components are cleaned with soap and water and rinsed with saline. Sterilize if possible. Do not use peridex as a cleaner for final abutments of temporary abutments as it will inhibit cell adhesion. A mirror finish is no better than a machined surface in this regard. He is not an advocate of probing around implants as he feels this leads to inoculation of the area with bacteria.
I hope this information helps to build a better understanding of osseointergrated implants.