MY TAKE ON MINI-IMPLANTS

Recently there has been a resurgence in the use of mini-implants (1.8-2.4mm in diameter). These implants were originally introduced as temporary implants and are now being used as a final solution for patients. This “new idea” is being promoted by some opinion leaders as an inexpensive solution for patients. My only experience with mini-implants has been the removal of fractured mini-implants, so the idea of taking a one or two-day course and starting to place these flaplessly left me scratching my head.

Keeping an open mind, I read a recent article* in Compendium. I would like to share my feelings after reviewing the article. The article tracked an impressive number of implants (2,514) over a 5-year period with an average evaluation period of slightly under 3 years. The average reported survival rate was 94.2%. While impressive, it falls about 3.5% shy of our 10-year survival rate with standard and wide-diameter implants. That represents a greater than 100% increase in failure rate. Additionally, 20 implants fractured during placement and were not included in the survival analysis. If included, that would increase the failure rate by an additional 0.8%. Furthermore, the authors preclude the placement of these mini-implants in type-4 bone and D-quantity bone. These criteria represent areas where most failures occur with standard implants. If I removed short implants and implants placed in poor quality bone and include immediately loaded mandibular implants, my published survival rate jumps to 99.38%** That represents about a 500% increase in failure rate using mini-implants.

Upon further review, the article stated that the average time period for failure was about 6.4 months. Today most standard implants are loaded at about 8 weeks. Published data with standard implants demonstrate that most failures occur during the 8-week period immediately following placement. This means that most failures occur with standard implants prior to fabrication of the prosthesis, while most mini-implant failures may occur during or after prosthesis fabrication.

Several other interesting facts surfaced. First, it took three years’ experience with MDI placement to achieve success rates over 90%. Second, mini-implants were far more successful supporting fixed bridges, which is an expensive restoration. Third, mini-implants used to support existing dentures had only an 88% survival rate. Fourth, a larger number of mini-implants are suggested as compared to standard diameter implants. Fifth, implants placed in the posterior maxilla were 3.3 times more likely to fail. Sixth, this implant is contraindicated in extraction sockets and, therefore, should not be used for immediate placement. Finally, mini- implants placed to support removable prostheses were 4.3 times more likely to fail.

After reviewing this article, I remain of the opinion that the use of standard implants will remain my treatment of choice. Let us never forget that there are patients attached to these implants, and the best way to manage a complication is to avoid it in the first place.

I compliment the authors for a well-written objective publication.

* Mini Dental Implants For Long Term Fixed and Removable Prosthetics. Shatkin TE, etal. Compendium, Vol 28, Number 2 pp 92-99.

** A 5 Year Life Table Analysis Of A Multi Center Study Involving Immediately Loaded Implants In The Edentulous Mandible. Testori T and Meltzer AM. Clin Oral Implant Research, Vol.115, 2004.

ENCODED ABUTMENTS

In this newsletter I would like to introduce a new concept in implant restoration. From this point forward it is no longer necessary to use an impression coping or snap cap to fabricate an implant restoration. We have worked closely with Biomet-3i to develop an encoded healing abutment system. Let me explain how this system works.

Following our usual protocol, either at the time of implant placement or at second-stage surgery, our office will install a healing abutment. The healing abutment will appear completely normal to you with the exception of some small “hieroglyphics” carved in the occlusal surface of the healing abutment. These markings carry a very specific code, which describes the exact location of the implant in four dimensions: buccal-lingual, mesial-distal, apical-occlusal as well as the timing of the internal hex.

When the patient arrives in your office, all that you need to do is rinse and dry the healing abutment in place. This will ensure a clean and accurate impression. Then, simply take a vinyl polysiloxane impression of the arch in a stock impression tray.

Take an alginate impression for a counter model, as well as providing a bite and shade. Forward the materials to your laboratory. They will pour and mount the casts. The material will be sent to 3i and then scanned. At 3i a virtual model is made and a custom abutment generated. Additionally, the encoded abutment data will permit 3i to fabricate a master cast.

The abutment and master cast are returned to the laboratory. The lab now fabricates a crown or crowns to exactly fit the cast and custom abutment(s). The abutment(s) can be made to your exact specifications or to a set of default specifications.

The master cast, crown and custom abutment are returned to you for installation. All you need to do is remove the encoded abutment for the first and only time, install the custom abutment, torque the abutment screw to 20 n/cm and cement the crown(s).

I hope this new innovation is both better for your patients as well as your practice.

Editorial Correction of Immediate Loading Update

Graph was mislabeled in the original letter sent last week. The corrected graph is below. Please reread the newsletter referring to the graph.

Editorial

As many of you are aware, Nobel Biocare has presented a technique which they call Teeth in an Hour™. This technique has been heavily marketed and involves the production of a computer-generated surgical guide which may then be used to direct the placement of implants into either an edentulous mandible or maxilla. Following the placement of implants and the placement of abutments, a prefabricated final bridge is immediately placed. The technique, which combines computerized surgical and prosthetic treatment planning coupled with flapless surgery and the immediate placement of a final prosthesis in one sitting, seems on the surface to be a major step forward in implant dentistry. Some of its advantages include a one-stage flapless procedure, limited bleeding and post-operative pain, and the potential to treat fragile patients. However, there has been limited data to support this innovative approach. Preliminary data demonstrated success rates in the 95% range.

Recently at the Fifth World Congress of Osseointegration, which was held in Venice, Italy on February 15-17, 2007, Professor Bjorn Klinge presented a study on Nobel Biocare’s Teeth in an Hour™ concept. The presentation was titled “Success and Failure Following Computer-Assisted Virtual Treatment Planning in Immediate Loading of Edentulous Patients.” It should be noted that Professor Klinge of the Karolinska Institute is one of three independent MPA panelists for the NobelDirect™ implant investigation in Sweden. Professor Klinge’s single-centre data showed a 29% complication rate with up to three years follow-up. His data were based on the treatment of 31 arches and 175 implants. Professor Klinge went on to say that the 71% success rate remains an over estimate of true success since the current data are only clinical in nature and do not include radiographic data. Therefore, the true success rate is expected to be less than 71%. Dr. Klinge states that this technique remains in the exploratory phase.

I applaud Nobel Biocare’s visionary approach. However, considering that the gold standard for implant success remains in the 95% range, I personally have a difficult time adding this technique (71% success) to my implant protocol. It is my opinion that accelerated computer-guided implant protocols seem to be of clinical value. However, the practitioner must always perform a risk-benefit analysis prior to performing treatment. It appears to me that increasing failure rates by about 500% in an effort to accelerate treatment is not something with which I am comfortable.

In our practice we continue to offer immediate implant placement and immediate fixed provisionalization using an approach supported by published clinical data. In one such paper published in COIR¹, Dr. Testori and I demonstrated a 99.38% implant success rate over a five-year period with immediate placement and restoration. While we continue to research combining computer-guided implant surgery and restoration, it remains part of a research protocol within our practice and should not be viewed as the standard of care until sufficient data are available.

Let us never lose sight as we move forward that there are people attached to these implants.

Note: NobelGuide™, Teeth in an Hour™ and NobelDirect™ are trademarked by Nobel Biocare.

¹Testori T, Meltzer A, Fabbro MD, Troiano M, Francetti L, Weinstein RL. Immediate occlusal loading of Osseotite implants in the lower edentulous jaw: A multicentre prospective study. Clin Oral Impl Res 2004; 15:278-284.

This monograph will address crestal bone preservation techniques. As I discussed in my last newsletter, when an implant is exposed to the oral environment there is a natural adjustment in the position of the crestal bone. The bone adjusts apically and laterally about 1.5 millimeters. This has been classically described as “bone loss to the first thread.” As discussed previously, this natural phenomenon impacts soft tissue morphology and aesthetics.

One way to overcome this problem is through the use of platform switching. Platform switching is defined as the placement of an undersized prosthetic component on an oversized or expanded platform.

Notice the classic formation of biologic width on the mesial implant. Bone remodeling has moved the point of bone to implant contact to the first thread. Note how the bone level on the distal implant holds at the platform level due to the impact of platform switching on the formation of biologic width.

How does platform switching alter the formation of biologic width?

By moving the implant abutment junction away from the edge of the implant, a space is provided to shield the bone from the inflammatory process associated with the junction. This physiologic inflammatory process has been described and documented by Ericsson and others. It is this inflammatory reaction which is the trigger for the formation of biologic width. Platform switching provides a space for the inflammatory cells to reside without impacting the bone. Therefore, platform switching eliminates crestal bone remodeling, providing additional bone to implant contact and eliminating changes in soft tissue morphology usually associated with the formation of biologic width.

The classic location of the inflammatory cells.

The location of inflammatory cells with platform switching. Note how the platform provides a space for the inflammatory cells so it does not impact the crestal bone.

The behavior of bone around and between adjacent implants:

When an implant is exposed to the oral environment, there is classically bone loss to the first thread associated with the formation of biologic width. This genetically ordained formation of biologic width has two components which are described as horizontal and vertical. Each component measures about 1.5 millimeters.

If adjacent implants are greater than 3 millimeters apart, the horizontal components of biologic width fail to overlap and a bridge of bone will remain between them. This bridge of bone will support the soft tissue.

If adjacent implants are less than 3 millimeters apart, then, as biologic width forms, the horizontal components of biologic width overlap and destroy the interproximal bridge of bone, eliminating the required soft tissue support producing a significant black triangle.

Preserve the inter-implant bone and support the soft tissue.
Remember only 3.5 millimeters of soft tissue covers the inter-implant bony crest

A method of reducing the impact of the formation of biologic width through the use of platform switching will be explored in my next monograph.

Photos courtesy of Dr. R. Coucchetto-Italy

In this issue I will explore the formation of papilla between adjacent implants. As you may recall from my previous monograph, when a single tooth implant is placed the formation of the papilla is controlled by the distance from the crest of bone on the adjacent natural teeth to the crown contact points. The general rule is as long as the distance from the tooth contact point to the crest of bone on the adjacent teeth is 5 millimeters or less there is an excellent chance the papilla will form. Simply stated, the fate of the papilla is controlled by the attachment level of the tissue to the natural tooth and not by the situation associated with the implant side of the interproximal space.

In the case of adjacent implants, there is no tooth-associated supracrestal fiber system to support the inter-implant papilla. Additionally, in this case the position of the contact point is completely within the control of the restorative dentist and laboratory since these adjacent implants are restored by crowns. Therefore, the measure used is simply the thickness of tissue covering the interproximal bone. The average tissue thickness is 3.5 millimeters. It is for this reason that adjacent implants frequently produce black triangles rather than full papilla.

This aesthetic dilemma remains one of the great challenges of implant dentistry. When one replaces two central incisors, symmetry can be maintained as long as the inter-implant distance is greater than 3 millimeters (see my next monograph for further explanation). The true problem surfaces when one needs to replace either a central incisor and its adjacent lateral incisor or a canine and adjacent lateral incisor. When the implant side is compared with the opposite tooth side, there will be an obvious difference in soft tissue morphology creating an aesthetic compromise. One can expect only 3.5 millimeters of soft tissue over the bone between implants, while 5-6 millimeters or more can be expected between natural teeth. This requires the restorative dentist to alter tooth form or create a black triangle.

Note the lack of symmetry of the central lateral papilla (#7 and #8 are adjacent implant crowns compared to natural teeth #9 and #10)

What is the best solution? Place one implant and cantilever off the lateral incisor. This solution works because the edentulous lateral incisor site can be augmented at the time of implant replacement. Connective tissue augmentation of the pontic site can produce almost 7 millimeters of soft tissue thickness compared to 3.4 millimeters between implants. The use of a properly placed wide-diameter implant in either the canine or central incisor site is suggested. A lateral incisor can be cantilevered off either the canine or central incisor as required. An implant with an internal connection is suggested to insure abutment stability.

In this monograph, I will explore the fate of the mid-facial free gingival margin around single tooth implants. As stated at the conclusion of the last monograph, papillae either stay the same over time or improve, while the mid-facial worsens over time.

How much worse does the mid-facial become over time? It is a well-documented fact that over a 12 to 24 month period the mid-facial will recede approximately 1 millimeter. The degree of recession is generally more pronounced in a thin periodontium than in a thick one.

Why does this happen? A tooth has the ability to form a periodontal supracrestal fiber attachment while implants do not. This variation in the formation of biologic width from supracrestal around teeth to crestal-subcrestal around implants is responsible for the aesthetic compromise.

How can this problem be overcome? The solution requires over-correction of the mid-facial either prior to tooth extraction, at the time of tooth extraction, or at the time of implant placement. Available techniques may include orthodontic extrusion prior to extraction, soft tissue augmentation, hard tissue augmentation or some combination of the above. It is because of this mid-facial aesthetic issue that immediate placements are generally contraindicated in thin periodontal biotypes with high smile lines and high aesthetic demands. This special requirement is not an implant integration problem, but rather an aesthetic issue. Correcting this deficiency after the implant and restoration have been placed is extremely difficult and in some cases impossible.

Does grafting the socket at the time of tooth extraction solve this problem? No. While socket grafting is necessary in the aesthetic zone at the time of tooth extraction, it must be combined with other clinical approaches to maximize the aesthetic outcome. Remember that socket preservation is not the answer to this mid-facial problem; overcorrection is required.

In this third monograph, I will explore the subject of the interdental papilla with focus on the single tooth implant.

How close can a dental implant be placed to a natural tooth root? It is well documented that an implant should be placed no closer than 1 millimeter from a natural tooth root (green arrow) or the implant will compromise the bone support on the adjacent natural tooth. The generally accepted distance is approximately 1.5millimeters.

What is the minimal width of an interdental space required for implant placement? The average width of most standard sized dental implants is about 4 millimeters. Therefore, the minimal width is 7 millimeters.This allows 4 millimeters for the implant and 1½ millimeters mesially and distally for root clearance.

What about the use of narrow diameter implants? Most dental manufacturers produce narrow diameter implants. Most have a prosthetic platform in the 3.4 millimeter range (3.25 mm implant with a 3.4 mm prosthetic seating surface). This would reduce the interdental minimal width requirement to 6 millimeters. There are some narrower implants (3 millimeter range) but the potential risk of metal fatigue and implant fracture must always be taken into consideration. These specialized narrow implants should only be used in areas of minimal occlusal stress such as upper lateral incisors or lower incisors.

How can the loss of papillary tissue be predicted? Once again, it is a well-documented fact that this aesthetic dilemma can be evaluated preoperatively.

The key measurement involves evaluating the periodontal health of the adjacent natural teeth. If one measures the distance from the contact point to the crest of bone on the adjacent teeth (red arrow) this will accurately give you the ability to predict the chances of maintaining or regenerating the papilla.

If the distance from the contact point to the crest of bone on the teeth adjacent to the proposed implant site is 4 to 5 millimeters, you have an almost 100% chance of regaining the papilla. If the distance is 6 millimeters you have about a 50% chance of getting the papilla back. If the distance measures 7 millimeters the odds fall to roughly 25%.

Note: Papillae either stay the same over time or improve. The mid-facial either stays the same over time or worsens. The mid-facial dilemma will be the subject of my next monograph.

In this monograph, I will explore the role of immediate implant placement in the dental implant armamentarium.

Definition of immediate implant placement: The placement of an implant in an extraction socket at the time of extraction or explantation.

Can this be done with success? YES, it is a well-documented fact that implants can be placed at the time of extraction with extremely high success (survival) rates. The complete answer is that immediately placed implants survive well, but there are numerous aesthetic issues which can be created using this approach. The current state of the art dictates that immediate placements should not be the treatment of choice in aesthetically demanding cases.

Does the placement of an implant at the time of extraction preserve bone? NO, the placement of an implant in a socket at the time of extraction has nothing to do with bone preservation.

What are some of the contraindications to immediate placement? Infected sockets or pockets, poor primary implant stability, aesthetically demanding cases. Patients who present with an allergy to penicillin seem to have a higher complication rate with immediate placement.

If the socket is intact, how wide a gap can be left between the socket wall and the implant wall? If the residual defect between the socket wall and the implant surface exceeds 2 millimeters, then that portion of the implant will not integrate unless it is filled with a bone graft and protected by a regenerative membrane.

What if the bony walls of the socket are fully or partially absent? Immediate placement can still produce high survival rates as long as infection is controlled, a bone graft and/or regenerative membrane is used, and good primary stability is achieved.Additionally, it is prudent only to use this approach in patients with low aesthetic demand or areas where aesthetics are not a major consideration.

Why is immediate placement a poor choice in aesthetically demanding areas? When a tooth is extracted, the bone remodels regardless of whether an implant is placed immediately or not. The thin buccal plate, even if intact, undergoes palatal and apical resorption. This moves the free soft tissue margin apically and palatally leaving a tooth which appears longer than its neighbors. The facial collapse produces an unaesthetic emergence. It is well documented that this mid-facial tissue will recede approximately 1 millimeter over a 12-24 month period. While papillary areas have the potential to stay the same over time or improve, the mid-facial rarely stays the same and usually worsens (recedes) over time. This issue occurs with all implant systems.

The solution to this complex dilemma will be the subject of my next monographs.