This article was written by Dr. Noumbissi and published in the January 2013 edition (International Section) for the Orofacial Chronicle Journal from Bhopal, India.

Background

Since Dr. Brånemark first introduced titanium dental implants, a variety of materials have been used successfully for about 40 years. Today implants are made either of commercially pure titanium (cpTi) or titanium alloys.  In addition to its biocompatibility, titanium was also initially believed to be inert, nontoxic and nonallergenic1,2. However, several drawbacks have been documented in the literature with the use of titanium and titanium alloys as implant materials in medicine and dentistry. High concentrations of titanium have been detected in tissue surrounding dental implants mostly as a result of wear or corrosion of the titanium implant surface.  In an animal study Weingart et al.3   showed that nine months after titanium implantation, titanium particles had spread and were found in adjacent lymph nodes. This indicates the possibility that phagocytes could transport titanium particles to the lymph nodes without any initial or immediate inflammatory response and potentially cause later immunologic reactions.

The Facts

An increasing number of people who suffer some form tooth loss are choosing to replace their teeth with dental implants. For the last thirty plus years the only and highly successful option for freestanding tooth replacement available in the United States and other countries has been titanium and titanium alloy dental implants. There are increasing reports both in dentistry and medicine of individuals developing sensitivity and allergies to titanium and/or titanium alloys. Even of more concern some of these implants are corroding once exposed to body fluids such as saliva and developing electrical activity when they are coupled with prosthetic components made of other metal alloys. Titanium implants as they corrode are known to release metal ions which create low level electrical currents through the body but also weakens the structural integrity of the implants. With recent advances in implantable biomaterials research and technology, bioceramics such as zirconia (zirconium dioxide) are now available and a new generation of modern implants is made of zirconia. Zirconium Silicate (ZrSO4) is mined and is treated and transformed into zirconium dioxide which is also called zirconia. Zirconia is the crystal form of the material zirconium which is a transitional metal. After mining and processing of zirconium silicate, zirconium is isolated and further processed under high temperature and pressure. Zirconium then undergoes an oxidation and crystallization process which allows it to transition into a structurally stable and inert crystal. This bioceramic crystal is called Yttrium Stabilized Tetragonal Zirconium Polycrystal (Y-TZP) also called zirconium dioxide. Therefore zirconium dioxide is not a metal and presents exceptional physical and biological properties. Zirconia can sustain an extreme load capacity, features a very long service life, and presents no conductivity or interference in the body’s meridian systems; it is the most hygienic, non-electricity conducting and stable material for dental implantology and orthopedics. Zirconia implants also present no danger of corrosion, something that is often a serious problem with metal based dental implants. Corrosion of a titanium dental implant occurs when it is coupled with the metal framework or abutment of the crown which more often than not is a less noble metal or alloy than that of the titanium implant. The implant and crown assembly bathes in saliva which is an electrolyte and a good conductor of electricity; this leads to all sorts of chemical and electrical imbalances in the body and to a phenomenon called “battery mouth”. Another advantage of zirconia is its low affinity for plaque (picture#1). Clinical observations and studies show that zirconia implants compared to or next to titanium implants accumulate much less plaque and allow for superior gingival health (picture #2).

Radioactivity and Zirconia Implants

There is a controversial and highly misunderstood aspect of zirconium dioxide in terms of its radiological output. Zirconium Silicate (ZrSO4) depending where it is mined can be contaminated with natural radioactive isotopes including radium (226Ra) and thorium (228Th). This was a major concern in the early 1990’s because the ores selected were contaminated. Today zirconium dioxide processing plants have the technology to remove these contaminants and are able to yield and use very pure powders. For example, the radiation emitted by a 3 mol% Y2O3-ZrO2powder was the same order of magnitude as alumina powder, both of which were several orders of magnitude less than that typically measured for water, vegetables and livestock. Zirconia hip ball replacements weigh approximately 100mg and have a natural radiological output of 1mSv per year. The average weight of a zirconia dental implant is 1g, translating into a natural radiological output of roughly 0.01mSv/year. Therefore the radiation risk of zirconia bioceramics is negligible and given that the World Nuclear Association states that the typical background radiation experienced by most people in North America is 3.4mSv, there is little concern for adverse biological effects on the implant recipient.

Conclusion

Zirconia dental implants are a sensible and clearly a healthier alternative to conventional and titanium implant bridges, partials or Overdentures. Furthermore zirconia by virtue of its translucency and all-white color makes it the most aesthetically pleasing option available today for tooth replacement (picture #3 & picture #4). This is a new era in implant dentistry and the science of oral implantology.

Referrences:

1-  Rabin, Steven I., MD; Calhoun, Jason H., MD, FACS, editor: Immune Response to Implants  

2- Allauddin A Siddiqi, Alan G T AG Payne,Warwick J WJ Duncan. Titanium allergy: could it affect dental implant integration? Clin Oral Implants Res 22(7):673-80 (2011)  

3- Weingart D, Steinmann S, Schili W, Strub JR, Hellerich U, Assenmacher J, Simpson J. Titanium deposition in regional lymph nodes after insertion of titanium screw implants in the maxillofacial region. Int J Oral Maxillofac Surg.1994 Dec:23 (6Pt2): 450-2  

4- Scarano A, Piattelli M, Caputi S, Favero GA, Piattelli A. Bacterial adhesion on commercially pure titanium and   zirconium oxide disks: an in vivo human study. J Periodontol. 2004 Feb;75(2):292-6

For more than four decades titanium implants have been and continue to be  mainstream in implant dentistry. Most dentists today are trained to use and offer titanium and titanium alloy dental implants which are all metal. However there are increasing clinical reports and scientific research on instances of allergic reaction to titanium implants with spontaneous immediate or delayed implant failures. Other studies have investigated the stability of titanium dental implants and the crowns and bridges placed over them in the oral environment.

Thanks to the stability of the TiO2 layer (oxide layer) on their surface, titanium alloys are exceptionally resistant to corrosion but they are not inert to corrosive attack.  When the oxide layer is broken down and then fails to reconstitute itself, titanium can be as corrosive as many other base metals.  There is increasing evidence that titanium implants when exposed to the oral environment can corrode and result in compromised structural integrity of the implant but also lead to implant loss and potentially life threatening health conditions.

What is Corrosion?

Corrosion can be defined as the graded degradation of materials by chemical or electrochemical attack. This phenomenon is of concern particularly when  metallic implants, metallic/silver fillings, or orthodontic appliances are placed in the hostile electrolytic environment provided by the human mouth. Corrosion can severely limit the fatigue life and ultimate strength of dental materials leading to mechanical failure.

What Type of Corrosion Occurs in the mouth?

The type of corrosive reactions that occur in the oral cavity are electrochemical and are also called wet corrosion. Electrochemical corrosion requires the presence of water or some other fluid electrolytes and in the oral cavity saliva plays that role. This general mode of corrosion is important for dental restorations, implant-to-abutment joints and abutment-to-restoration (crown, bridge, retentive bars etc) connections.  The complexity of the electrochemical process involved in the implant-to-implant superstructure joint and/or connection is linked to the phenomenon of galvanic coupling and stress and pit corrosion.

Galvanic Corrosion

Galvanic corrosion is an electrochemical corrosion, it is the most common form of corrosion that occurs with dental implants. The use and connection of dissimilar metallic restorative materials is called galvanic coupling and may also generate corrosion. Therefore there is a great amount of  concern regarding the types of materials used for suprastructures and crowns over titanium dental implants. When two or more dental prosthetic devices/restorations made of dissimilar alloys come into contact while exposed to oral fluids, the difference between their corrosion potential results in a flow of electric current between them. A galvanic cell is formed in the mouth and the galvanic current causes acceleration of corrosion of the less noble metal. High noble gold alloys are generally chosen as the material of choice for superstructures because of their excellent biocompatibility, corrosion resistance, and mechanical properties. However, these materials have become  very expensive and as a result new more affordable less noble alloys such as Ni-Cr, Ag-Pd, and Co-Cr alloys are used instead. These alloys have good mechanical properties, they are less noble than titanium and their biocompatibility and corrosion resistance are of concern.

The galvanic current passes through the metal/metal junction and also through tissues, which causes inflammation and pain in the soft tissue (gums) and bone. In such cases saliva and other fluids in bone and soft tissue become electrolytes and allow the corrosive galvanic currents to take hold. These events trigger immune responses and ultimately possible implant loss.

Stress and Pit Corrosion

This is the second type of corrosion that occurs at the joint of the implant and the implant superstructure. Implant restorations and abutments can have small microscopic pits and crevices on their surface.  With chewing cycles, implant and implant teeth (abutments and crowns) endure high forces stress of various types such as torsional compression and elongation  and as a result stress and pit corrosion occurs.

Microbial Corrosion

Although not fully proven, microbial corrosion is another type of corrosion that can occur in the oral cavity. Titanium and the various alloys that are used to make restorations on implants are prone to retain a great amount of plaque compared to ceramic/zirconia implants. Wherever there is plaque there is bacteria and microbes living in it, and these bacteria release by-products that destroy bone and make natural teeth loose over time if not removed. In the same manner with titanium implants, those microbes and bacteria by-products are acidic in nature and can potentially corrode the titanium and the metal alloys used for restoration over the implants.

Clinical Observations when Corrosion Occurs in The Mouth

As long as metallic dental restorative materials are employed, there will be galvanic currents associated with electrogalvanism  in the oral cavity. For some patients, especially after the placement of  a base metal restoration, pain caused by galvanic currents can occur and be a source of discomfort  and ultimate implant failure.  Corrosion leads to roughening metal surfaces, release of  ions from the metal or alloy, and toxic reactions. The liberation of elements can produce discoloration of the soft tissues around the implant and allergic reactions such as oral edema, perioral stomatitis, gingivitis. Extraoral manifestation such as eczematous rashes in susceptible patients can occur.  In a study by Kirpatrick, et al, it was found that the pathomechanism of poor wound healing is modulated by specific metal ions released by corrosion.

 Conclusion

The mouth is the portal entry of the human body. It is also the habitat of microbial species that are kept wet by saliva. Oral tissues are exposed to a veritable bombardment of both chemical and physical stimuli as well as metabolism of about 30 species of bacteria. Teeth and dental implants function in one of the most inhospitable environments in the body, they are subject to the most extreme temperature variations, enduring temperatures as low as 0°C to hot foods and beverages. Multiple factors such as temperature, saliva, plaque, pH, and the physical and chemical properties of food and liquids as well as oral health conditions may influence corrosion. Yet, for the most part, oral tissues remain healthy.  The combination of stress, ongoing corrosion, and bacteria contribute to implant structural failure and loss of bone integration.

As it has been the case in orthopedics for almost two decades, we now have alternatives in implant dentistry. Metal-free and metal alloy-free solutions are available for teeth replacement, from the implant embedded in bone to the visible crown in the oral cavity. Zirconia (ceramic) dental implants and all types of all-ceramic restoration (crown, bridge, retentive bars etc) are available. Futhermore bioceramics  accumulate very little plaque if at all thus reducing bacteria habitat, multiplication and by-products. Zirconia dental implants and restorations do not conduct electrochemical currents nor release ions to the oral cavity, surrounding bone and the rest of the body.

References:

Chaturvedi TP, Upadhayay SN. An overview of orthodontic material degradation in oral cavity.  Indian J Dent Res 2010 Apr-Jun;21(2):275-84.

Reed GJ, Willman W. Galvinism in the oral cavity. J Am Dental Assoc 1940;27:1471.

Tschernitschek H, Borchers L, Geurtsen W. Nonalloyed titanium as a bioinert metal: A review. Quintessence Int 2005;36:523-30.

Manaranche C, Hornberger H. A proposal for the classification of dental alloys according to their resistance of corrosion. Dent Mater 2007;23:1428-37.

Chang JC, Oshida Y, Gregory RL, Andres CJ, Thomas M, Barco DT. Electrochemical study on microbiology-related corrosion of metallic dental materials. Biomed Mater Eng 2003;13:281-95

Green NT. Fracture of dental implants: Literature review and report of a case. Imp Dent 2002;11:137-43.

Grosgogeat B, Reclaru L, Lissac M, Dalard F. Measurement and evaluation of galvanic corrosion between titanium/Ti6Al4V implants and dental alloys by electrochemical techniques and auger spectrometry. Biomaterials 1999;20:933-41.

Olmedo D, Fernadez MM, Guglidmotti MB, Cabrini RL. Macrophages related to dental implant failure. Implant Dent 2003;12:75-80.

Cortada M et al. Galvanic Corrosion behaviour of titanium implants coupled to dental alloys. J Mater Sci Mater Med 2000;11:287-93.

Lugowski SJ, Smith DC, McHugh AD, Van Loon JC. Release of metal ions from dental implant materials in vivo:    Determinations of Al, Co, Cr, Mo, Ni, V, and Ti in organ tissue. J Biomed Mater Res 1991;25:1443-58.

The placement of dental implants in the posterior maxilla can sometimes be complicated due to the loss of bone below the maxillary sinuses. This is very common after maxillary molars have been lost or extracted and no bone preservation procedures provided at the time of extraction. Sinus graft/lift procedures are then necessary in order to create a proper foundation for implant placement. This article, published in June 2010 pp 47-60 in the Journal of Implant and Advanced Clinical Dentistry (www.JIACD.com)compares the amount of new bone formation and residual graft material when mineralized human dried bone (allografts) are used versus bovine bone (xenografts) are utilized to increase bone volume in maxillary sinus.  Sammy Noumbissi DDS MS

Read more… http://www.nxtbook.com/nxtbooks/specops/jiacd_201006/index.php?startid=46

This is a case report published in Prexion3D’s December 2011 newsletter.  All phases of this case were completed by Dr. Noumbissi. A patient had a missing tooth in the anterior maxilla, 3D dental imaging technology (CBCT) and software (InVivo5) were utilized to adequately and accurately plan the placement and temporization of a metal free zirconia dental implant.

The  CBCT radiation from the Prexion is extremely low compared to medical CT scanners. The InVivo 5  software was used to perform virtual implant placement prior to surgery. From the  implant placement simulation a surgical guide was generated using CAD/CAM technology.  The surgical guide was then utilized to place the implant in a precise manner allowing for much safer and more predictable implant placement.
Sammy Noumbissi DDS MS

Using Cone Beam CT (CBCT) Technology to Plan Zirconia Implant Placement in a Bone Deficient Site.

This study was conducted by Dr. Noumbissi in 2000 and published in the Journal od oral Implantology in 2005. This project was part of Dr. Noumbissi thesis project while in training in dental implantology at Loma Linda University’s Graduate Program in Implant Dentistry in California.

This evaluation of one 100% mineralized bone allograft was the first of  its kind and the results were groundbreaking. An allograft is bone harvested from another individual of the same species, that means in this case that the material used was human bone.This article  is often referenced in implant publications by other authors. It is also widely quoted by lecturers and speakers around the world.

Please follow this link to read the article: Noumbissi et al Article JOI

Clinical Histologic, Histomorphometric Evaluation of Mineralized Solvent-Dehydrated Bone Allograft (Puros) …