THE BASIS FOR USING MINI DENTAL IMPLANTS

THE BASIS FOR USING MINI DENTAL IMPLANTS

While I would like spend a lot of time reading up all the journals I can lay my hands on and including all their references as part of this book, I realize as a clinician with a busy practice and a large family commitment, my time has to be prioritized carefully.

However, the need for this book cannot wait. There is a huge debate currently on whether or not mini implants or small dental implants or as I prefer to call them MOSTDIS (Minimised Osseointegrated Screw Titanium Dental Implants) should or should not be used for the long term fixation of crowns and bridges.

In the last few years, there has been a widespread concession that mini-implants can be used for denture stabilization. I use the word “concession” as (opposed to “consensus”) because previous to that, mini-implants were frowned upon as transitionals pretending to be “genuine” implants. Historically, mini-implants were used as transitionals that were placed between the conventionally sized dental implants to hold the temporary prosthesis while waiting for the conventional implants to osseointegrate. When the time came to remove the temporary prosthesis, some of the transitionals were found to have osseointegrated  and were impossible to unscrew. Often, the head of such osseointegrated mini-implants were cut off and the endosseous part left in situ. Over time, it occurred to some practitioners that transitories or mini-implants can be used in a more permanent or long term manner.

Initially, mini-implants were used more for denture stabilization. Subsequently, some practitioners tried cementing crowns and then bridges on top of the mini-implants and more often than not were found to be successful, especially in the mandible. Such practices were frowned upon and even condemned by oral implantologists because of several reasons:-

(1) Mini-implants were considered too small in diameter and therefore its ability to withstand masticatory forces over long periods of time were doubtful.

(2) Mini-implants were used originally as transitories and therefore should remain so.

(3) The surface area of mini- implants compared to a conventional implant is too small and therefore the amount of osseointegration is insufficient to withstand masticatory forces.

(4) Mini- implants do not osseointegrate.

(5) It goes against the original tenets laid down by Professor Branemark where it is accepted wisdom that the size of the implant fixture should imitate the size of the root of the tooth that it is replacing.

(6) The emotional element also comes into play, as in, “How can oral implantology be so simple and easy to do?” Emotionally it is difficult to accept that a previously complex procedure can be bypassed with a simple approach.

(7) How can you load mini-implants so routinely when conventional implants usually cannot be loaded immediately, and when done so, only progressively?

These reasons why can be readily addressed when the facts are laid down clearly:-

(1) Mini- implants are made of titanium alloy, i.e. is size for size, 1.6 times stronger than commercially pure titanium. The diameter of mini- implants range between 2.0mm to 3.0mm. Mini- implants are actually less prone to fracture because it is solid. Conventional implants are more prone to fracture because they consist of 2 pieces with a connecting screw in between. If a conventional implant is 4.0mm in diameter and the abutment with the connecting screw together is 2.0mm in diameter. The thickness of the remaining wall of the implant fixture is only 1mm. Compare this to the mini implant which is 2.5mm in diameter or thickness, which is stronger? The mini- implant…… believe it or not is stronger than the conventional implant! It is less prone to fracture than the conventional implant.

(2) Additionally, the 2 piece conventional implant is connected by a screw which has a tendency to come loose and even fracture. Also, there is a microgap between the 2 pieces of the conventional implant which harbour microorganisms that causes bone resorption and sometimes peri-implantitis. Such a chronic source of pathogens in the body may cause coronary artery disease with the accompanying sequelae.

(3) Just because mini implants were designed to be transitionals should not mean that they cannot be used permanently. Many mini- implants have been used for crowns and bridges in the last 10 years successfully. The concept that an implant root should imitate the root size of the tooth it is replacing is largely an assumption by the pioneers of implantology. The basis should have been a study of how much osseointegrated surface is required to withstand the masticatory forces of a particular tooth. It should be reasonable to assume that the surface area of osseointegration can be designed to be less than the surface area of the periodontal ligament of the tooth to be replaced , since osseointegration square mm to square mm is much stronger a bond than the bond of the periodontal ligament, although without the shock-absorbing ability of the periodontal ligament. It is much more easier to extract a tooth than an osseointegrated implant. In fact, you cannot extract an osseointegrated implant. It is reasonable again therefore, to assume that an implant that is half the size of a tooth root will give sufficient surface area of osseointegration to carry the tooth and support it’s masticatory functions.

(4)  Actually, it is the titanium oxide layer on both pure titanium and titanium alloy that is biocompatible and integrates and not pure titanium. Titanium, whether pure or alloy is covered with a layer of titanium oxide immediately on exposure to air. It follows then that both titanium and its alloy will osseointegrate.

(5) The whole world of surgery is moving relentlessly towards minimal invasiveness as shown by the rapid change towards laporoscopy and closed surgery as far as possible. Why should’nt we, as responsible professionals, not make oral implantology less invasive and as simple as possible?  This will not only lower costs, it would decrease clinical time for the doctor and recovery time for the patient. On top of it, such procedures have  proven to be relatively pain free and heals rapidly.

(6) One reason why mini- implants can be loaded immediately as a matter of routine is because there is minimal trauma to the bone. As such, the process of osseointegration begins immediately on implantation. There is no transitional margin of necrosis between the implant and bone which is found in conventional implant placement. Also, because the mini-implant is small, the healing challenge to the surrounding tissue is correspondingly small, the tissue heals rapidly. The healing challenge to the surrounding tissue in the case of the conventional implant is much more and therefore requires a longer time, thus immediate loading of conventional implants often is less successful.

(7) The actual surface area of minis are actually comparable to the surface area of conventional size dental implants. This is because minis are usually placed deeper and therefore longer than conventionals, thus increasing the effective surface area available for osseointegration.

• A conventional sized dental implant 4mm diameter and 10mm long has a surface area of about 125 sq mm.
• A reduced diameter dental implant 2.5mm diameter and 10mm long has a surface of about 80sq mm.
• A reduced diameter dental implant 2.5mm diameter and 13mm long has a surface of about 100sq mm.
• A reduced diameter dental implant 2.5mm diameter and 16mm long has a surface of about 125 sq mm.
• A reduced diameter dental implant 2.5mm diameter and 19mm long has a surface of about150 sq mm.

Note: The actual surface area for all threaded screw implants will be 30 to 50% more than the figures above, taking into consideration that the surface of the threads will be more than that of a simple cylindrical surface.

Thus  a mini that is 2.5mm diameter and 16mm long in its threaded area has a surface area equivalent to a conventional sized dental implant 4mm diameter and 10mm long.

In my experience, this length is one of the most common mini used and very often 2 minis are used to restore one molar. Two minis 2.5mm diameter and with the threaded part 10mm long has a surface area of 160 sq mm! This is more than that of a conventional 4mm diameter and 10mm long. Two minis 10mm long is more than adequate for one molar since very often one molar is restored by a conventional that has a surface area of only 125 to 150sq mm.

How I Got Hooked

Before I could bring myself to place in the first dental implant into my patient’s jaw, I had to overcome the difficult mental block of believing that it is actually possible for a missing tooth to be replaced by an artificial implant.

Throughout my dental school training and into my subsequent years of treating various types of dental diseases, the incessant mantra that was emphasized again and again and again was the need to prevent inflammation of the tissues in the mouth, especially the soft tissue. Time and time again, I observed how vulnerable teeth can become once the gums have become inflamed. Inevitably, the inflammation was associated with foreign elements like pathogenic bacteria in plaque attached to teeth and fillings and prostheses. The idea of a foreign element being embedded into the gums and bones, sticking out into the mouth, then expecting them to stay there and undergo continued stress and hoping that they will be maintained there for years was considered a pipe dream.

In order to overcome the mental block, I decided to read as much about dental implants as possible. I paid special attention to the landmark discoveries and writings of Professor Branemark of Sweden.  I spent a small fortune buying his books and others like it and reading them all. This intellectual exercise helped me to substantially overcome the deep seated skepticism that I felt towards dental implants to the point that I felt that I was ready to take on my first patient. Having convinced my first patient to have dental implants placed in her mouth, I proceeded to do a sinus lift simultaneously with 3 conventional implants placed on the upper left maxilla! I planned carefully and worked down all the steps required and read up all I could to prepare for my first implant surgery.

Then I followed the steps faithfully and stitched up the wound. Four months later I placed in some healing caps and a week later removed them. The sight of a well formed crater in the gums lined by healthy-looking pink mucosa, at the bottom of which I could see the shiny surface of the titanium fixture was something I can never forget. There was little or no inflammation and no bleeding. It struck me convincingly and clearly that titanium is biocompatible with the bone and mucosa of the human body.

From that moment on, I was hooked. Dental implants work!