History of Dental Implants
Dental Implants possibly date back to Egyptian times. It is thought that seashells were trimmed and shaped, then hammered into the jaw to replace a patient’s missing teeth!41 Interestingly, these predecessors to modern-day dental implants were effective to a degree as they were composed of calcium, as is our bone, of course, and therefore the shell-based implants at times were able to fuse together with the jawbone. This technological advance was perhaps cutting edge in ancient Egypt, however the birth of modern day dental implants as we know them actually starts in the 1950’s.
Dr. Per-Ingvar Brånemark of Gothenburg, Sweden is credited as the father of dental implantology as we know it today, as his concept of osseointegration using titanium-based dental implants was proven to be the best initial answer to the question of material choice. Previously, blade implants and transosteal implants were the only options. The best initial lecture given on this concept was not until years later, in 1982. In Toronto, Canada, Brånemark presented work that he had begun 15 years earlier—his discovery and application of osseointegration. This concept is basic: the biological fusion of bone to a foreign material (in this case, titanium). This lecture was unparalleled and scientific documentation of implantology had never before been gathered by others.
The name Biotes was given to the first commercially sold implants, however this name was soon changed to “Brånemark implants” after the creator of the concept now nearly universally accepted. Today, nearly all implants are made from titanium, however a small but growing share of implants are comprised of zirconia.
Dental implants have exploded in terms of popularity over the years. Consider that there are approximately 200 million adults in the United States, and that approximately 178 million of these adults are missing at least one tooth! This warrants a predictable, effective, conservative, and esthetic option for the replacement of a tooth or teeth—and dental implants have become the gold standard in many situations. In general, dental implants have a much higher success rate than other types of dental work. The survival rates of dental implants over a ten year period have been reported to be as high as 98%42; however this number has been disputed and debated.
What is known, however, is that the success of dental implants has been found to be higher than the success rate of restoring severely compromised teeth that would require significant dentistry in order to save. For example, in a patient with a tooth that requires a root canal, post and core, and crown, it seems today that a dental implant would be a better option from both a cost-analysis and longevity standpoint. There is no better choice that maintaining natural teeth, however many patients find themselves needing replacement of teeth, and today implants are usually the best option.
In recent history, dental bridges have been used for single and multiple tooth replacements. Today, if a patient is to lose a single tooth for whatever reason, a bridge is still considered a viable option. However, there are a growing number of dentists who feel that choosing a bridge over an implant for replacing a single tooth is an inferior option. Suppose a patient had virgin adjacent teeth, and a bridge could be performed by preparing crowns on these teeth to replace the missing middle tooth. The three tooth bridge would then be cemented to these two abutment teeth. The issues arising from this scenario include the possibility that decay may eventually occur on one of the abutment teeth requiring replacement of the entire three tooth bridge. Next, the adjacent teeth are typically not in need of restorations, so “cutting down” these teeth seems unwarranted if avoidable. Finally, if a patient cannot clean around their teeth and dental work easily, then it is probable that decay or periodontal disease can begin. A bridge is much more challenging to clean around then an implant, as the bridge is connected together, and an implant is like an individual tooth.
There are risks of having dental implants placed. Once restored, residual cement left around the implant has been shown to cause inflammation and even the eventual loss of an implant.45 If a patient is a heavy smoker or uncontrolled diabetic, the success rates of dental implants have been found to be substantially lower.43, 44 In addition, if a patient is undergoing bisphosphonate therapy at higher doses (for chemotherapeutic reasons, for example), it is not advisable to have dental surgery of any kind, including dental implants. Finally, implants are invasive intentionally, in order to engage the bone they are placed into. With this in mind, there are important anatomical structures in the mouth including blood vessels and nerves that can be severed when an implant is placed. Today, with 3D scans, such as cone beam computed tomography (CBCT), these important anatomical structures can be easily avoided. Many clinicians, including this author, feel that CBCT scans are a standard of care diagnostic procedure in dental implantology today. The radiation exposure is very limited with a CBCT scan, yet the ability to avoid complications with the information these scans provide is quite profound and impressive.
Dental Implants are confusing to dentists, let alone patients because of the variety of restoration choices that can come from having an implant or implants placed. Technically speaking, dental implants have nothing to do with teeth. Most dental implants have three parts: the implant itself, the abutment, and the crown. This is of course if you are replacing a single tooth in the mouth, which is the most common use for implants today. Once placed, an implant typically receives a healing abutment (cover screw) that helps to guide the healing gum tissue around the implant, and keeps the gum tissue from growing down into the inner implant threads. In addition, there are laboratory analogs which are an exact replica of the implant in the bone which are utilized within a stone model for the laboratory technician to complete build the restoration. There are also special abutments that are used to take the impression of the implant, called impression copings. Today, there is also CAD CAM technology that can be used to actually scan the implant cover screw in lieu of impressions. Implant technology is changing all of the time, however many of these components will be used indefinitely.
The implant itself is a titanium or zirconia screw that is surgically placed into the bone. This screw merges with the bone (osseointegration) over time, and can then be used to function (chew). Implants can also be mini-implants, which are used for anchoring dentures or in orthodontics to pull teeth in a certain direction, but not to replace a tooth. Additionally, very short dental implants can be used in unusual situations where there is not enough vertical bone, and these implants are wide and short. There are also very long dental implants used in unusual situations where alternative bones in the skull must be accessed from the mouth, such as the zygoma, when severe atrophy of the maxillary bone has occurred. However, despite these aforementioned possibilities, the main implants used today range in size from about 3-5 mm in width at the gum line, and range in length from about 10-12 mm from the gum line to the bottom of the implant.
In general, the longer and wider the implant, the more surface area will make contact with bone, and the more stable the implant will be. However, from the restoring dentist’s perspective, a wide implant placed in a location where a smaller tooth should eventually be presents significant esthetic challenges. In addition, the placement accuracy of the implant usually has a specific and direct correlation to how effective the eventual restoration will be. It is imperative that restorative dentists and implant surgeons communicate the specifics of the case goals prior to any patient undergoing treatment with implants.
The dental implant abutment is a specific part that connects the implant to a prosthesis (dental crown, denture, or bridge). The abutment in most cases is a separate component from the implant, although some implants have an attached abutment, and other systems have the abutment connected to a crown. Abutments are usually screwed into the inner threading of an implant. While an implant has threads on the outside that can be seen, there are also inner, unseen threads that are used to connect the abutment with a special screw at a specific torque. It is imperative that this screw connection is the correct tightness, and that the abutment be fully seated and placed correctly onto the implant. Each implant system has a different internal or external configuration such as hexagonal, square, or triangular that is designed to help with the seating and anti-rotational characteristics of the abutment on the implant. However, this can mean there are up to six ways in which the implant abutment can be seated onto the implant—yet only one way is correct! The possibility of screw-loosening between the implant and abutment is actually one of the main complications that occur with implant restorations.
Implant abutments can be made from a variety of materials, but most often are a form of metal, such as gold, titanium, or a combination of metals. Other abutment materials used are zirconia and lithium disilicate in growing numbers, due to the esthetic limitations of metal, as well as the rising costs of gold. If a single tooth implant is being restored in the anterior area of the mouth, cosmetic dentists are often inclined to select an abutment that mimics the true color of what a real tooth would look like in this region, so that an esthetic and translucent restorative material can be used for the crown. This is most commonly zirconia for Dr. Brent Engelberg, for example. If a metal abutment is utilized, then this metal must be masked somehow, otherwise the restoration placed on top of the abutment will show through and look unattractive or phony.
Implant abutments can be either stock or custom abutments. Over the years, the vast majority of implant abutments that have been restored with crowns have been stock abutments. These abutments are ordered from the implant manufacturer, and are somewhat less expensive for the dentist and laboratory. These stock abutments are prepared by the dentist or more commonly a laboratory technician, and are screwed into the implant prior to a crown being seated. The limitations are that these abutments are, of course, designed for an average implant, placed perfectly, and all of the stock abutments are the same core shape prior to preparation at the laboratory. If an implant is placed at a slightly varied angle or a bit high or low, a stock abutment leaves several compromises to the final restorative outcome.
Custom abutments were invented to help offset any placement and hygiene issues created when the implant was placed. In addition, the esthetics and tissue contours that can be created by custom abutments are typically superior. The disadvantage of custom abutments, as one can imagine, is that they must be expertly designed by a qualified laboratory technician or via CAD CAM technology, and are therefore much more labor intensive and thus proportionally more expensive. Custom implant abutments involve separate materials and a significant time investment to complete properly, however are usually worth the extra effort, especially in an esthetic implant case. A combination of excellent diagnostic protocols coupled with dentist-surgeon-laboratory communication can minimize the need for custom abutments, but in some situations they are necessary for the ideal final result.
Implants are restored by connecting a dental prosthesis to the implant or abutment. There are a myriad of options to restore implants, but the most common restoration is a single tooth replacement with a single abutment and crown restoration connected to an implant either by cementing the crown onto an abutment, or screwing the abutment-crown combination to an implant. If a patient is missing several teeth in a row, multiple implants can be placed and a bridge can be fabricated to restore this missing section of teeth, often with fewer implants than teeth being replaced. Additionally, if all of the teeth are missing in an arch, implants with an implant-supported denture can be placed to help restore the arch with more comfort and stability than a denture alone.
Typically, the less implants placed, the more removable and tissue-supported the prosthesis will be. Conversely, the more implants placed in an edentulous arch, the more fixed and less tissue-supported the dental prosthesis tends to be. It is a misconception that to replace fourteen teeth, for example, that fourteen implants must be placed. For example, in a lower arch, in which a patient is completely edentulous, two implants can be placed, and abutments can be connected to these implants that resemble spheres (male portion of the attachment). The underside of a denture can be fitted with components that resemble O-rings (female portion of the attachment), that snap the denture into place. In this situation, the denture is still removed daily to clean, however it has a much more solid fit and substantially less looseness than without the implants.
If a patient has four to six implants placed in the lower arch, then a fixed prosthesis can be fabricated that cannot be removed by a patient. For example, if five lower implants are placed, a supportive framework can be made that supports the denture teeth and screws directly into the five dental implants. The five screw access holes are then covered, and a patient has a fixed screw-retained prosthesis that does not need to sit on the gum tissue whatsoever. This is an outstanding option for patients who would like to have a more permanent solution for missing teeth. Additional major benefits of this prosthesis are that it can be unscrewed and cleaned periodically, as well as easily removed and sent to a laboratory for any minor repairs. A similar prosthesis can be made that is cemented, however this is not as easily retrieved should modifications need to be made in the future. Benefits of the cemented prosthesis are that the locations of the implants are not as important, and the prosthesis can be a little less bulky.
Bone Grafts are used commonly prior to implant placement, or as an adjunct procedure. A bone graft procedure is simply used to add bone to an area in order to increase the success rate of an implant. Typically, the greater volume of bone that is present in an edentulous zone, the greater the stability of a future implant. Bone grafts are usually done with freeze dried bone particles, or a matrix of bony particles mixed with the patient’s blood components, such as platelet rich plasma. On occasion, bone can be harvested from an alternative area in a patient’s body, such as the chin, and used for a block graft elsewhere in the mouth where implants are to be placed. In general, most bone grafts are actually resorbed by the patient’s body and replaced over time with the patient’s own bone.
Sinus Lifts are performed only in the upper arch when the position of a patient’s sinus is such that it limits the desired length of an implant to be placed. Everyone has sinuses, which are simply epithelial lined cavities in our heads that are full of air. The sinuses keep our heads lighter in weight, as opposed to our heads being comprised of solid bone. When a patient has been missing a tooth for an extended period of time, allowing the bone to atrophy, or if the sinuses are a bit low relative to where an implant is to be placed, a sinus lift is used before or during implant placement. A sinus lift sounds like an invasive procedure, however it is actually quite simple in the majority of cases. The surgeon simply pushes on and tacks the floor of the sinus up vertically and fills this space in with a bone grafting material. This allows for an implant to be placed without puncturing through the floor of the sinus, in addition to allowing for a longer implant that is likely to be more successful.
Socket Preservation procedures are similar to bone graft procedures, but are done at the time of an extraction. Immediately after an extraction, bony matrix materials and/or a scaffolding material is placed into the extraction socket to preserve the alveolar ridge. Without this procedure, the bone will resorb, and placing a future dental implant becomes much more challenging. The additional fee for socket preservation with an extraction is usually well worth the cost, as there is truly no better opportunity to add bone to a future implant site than at the time of an extraction.
Ridge Augmentation procedures are also used to increase the volume of bone prior to implant placement. Ridge augmentation procedures differ from socket preservation procedures, as the ridge is augmented long after a tooth has been removed. The augmentation procedures are often more complex, as there is not fresh surrounding bone as there would be in a socket preservation procedure, and the surgeon usually has to utilize more intricate techniques to develop adequate volumes of bone. These procedures are done to increase either the bone height, width, or combination of the two to permit sufficient bone for dental implant procedures.
A very important decision that was made in the acceptance of dental implants was the US Food and Drug Administration’s (US FDA) 510K ruling which stated that any implant which was fabricated from titanium and was of a screw design could be given approval for use as a human dental implant device. This caused a major escalation in designs from manufacturers who claimed to have the next best product in dental implantology. Alas, this created a problem that even today plagues the dental community: there are so many dental implant companies, many of which claim to have a “special” feature, but will not work with the other systems. It has become difficult as implant companies have been bought and sold over the years to track down old components when replacement of specific implant parts is required.
Today, there are hundreds of implant manufacturers, however in the United States, the top dental implant companies are Nobel Biocare, Straumann, Astra (now Dentsply Implants), Biomet 3i, Zimmer Dental, Camlog Implants, and Biohorizons, however there are dozens more “major players,” including Implant Direct, who basically copies the major systems and sells the components for less money (generic implants). Many of these brands have unique screwdrivers, specific torque requirements, and precise components that a restorative dentist must have on hand to work with correctly.
Overall, this author has had success with nearly all of these aforementioned systems. Today, as long as a high quality implant is placed, the brand of implant matters far less than the surgeon’s placement abilities and restorative dentist’s skill and experience completing dental work on implants. Typically, the surgeon (often a periodontist or oral surgeon) placing the dental implant has the first choice of which system to use. The restoring dentist might have a preference or comfort level with a particular system that dictates which implant system to use. The reality is that there are more similarities between systems then differences, and once a restoring dentist is comfortable with a couple of dental implant systems, any new system presenting to that dentist would be possible to understand with some thought.
All companies have their own abutments, screws, parts, impression components, specific sizes and surface finishes, and proprietary nuances that must be understood by the dentist. It is of course important that all details of what was used in each case be accurately recorded if and when the time comes where a specific part must be replaced or reordered. Older implant parts are often hard to locate, especially when a company that once existed was purchased by a larger implant company, and these parts are now sold under a new name—this makes searching for and finding replacement parts an arduous task for the dentist. An important key is selecting a skilled and experienced dentist with a comfort level in working with implants.
Who places dental implants? Usually, in the United States, dental specialists such as periodontists (gum surgeons) or oral surgeons (tooth-extraction experts) have placed dental implants over the years. There is a debate over which specialist is the better choice, however as in nearly every field, the pure talent, compassion and concern level, and detailed-orientated nature of the doctor placing the implant will outweigh the title. In fact, many general dentists have started placing dental implants themselves for a variety of reasons, including increasing their revenue, ease of placing most simple dental implants, and the claim of convenience and cost-savings for the patient. This author prefers to work with dental specialists (periodontists or oral surgeons) to place all implants, for several reasons, including increased expertise, ability to deal with complications, clinical accuracy, increased success rates, and shared accountability. Most importantly, in the opinion of this author, some dentists have become a “jack of all trades but a master of none.” It is essential that dental implants be treated as complex medical devices, and often a specialist is the best choice for the surgical portion of the procedure.