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he replacement of a single tooth or multiple teeth with implant-supported restorations in the esthetic zone will be successful if the clinician follows the guidelines for correct implant placement and the adjacent hard and soft tissues of the mouth are intact. The esthetic zone is defined as those teeth that are visible when one is facing an individual, that usually includes the upper front teeth from canine to canine. When we are facing the situation of replacing multiple teeth in the front of the mouth, the success of implant-supported restorations is more difficult to predict than in the back of the mouth. This is due to the potential loss of bone in the areas to be restored as well as the importance of getting the esthetics right. Another difficult issue is how to deal with the lack of soft tissue between the implants that are being restored in the esthetic zone. This is why it is important to retain as much bone as possible between the implants and the areas where the previous teeth were lost.
Pontics and Cantilevers
One way that way that clinicians deal with the lack of space for multiple implants is through the use of pontics or cantilevers. A dental pontic is an artificial tooth on a fixed prosthesis in the mouth that replaces a missing natural tooth and is supported on either side by the natural teeth or a dental implant. A dental cantilever is when we are replacing a missing tooth but there is only one adjacent supporting tooth so it only supported on one side. Previous studies have shown that there are no differences in the outcomes when we are using one implant with a crown and a cantilever as compared to two implants with crowns as long as important risk factors are controlled for.
It is important that when we are planning to restore a limited space with an implant and pontic or implant and cantilever, we use a prosthodontic mock up to properly evaluate implant locations and available space. We must also incorporate cone-beam computed tomography and three-dimensional modeling of the implant positions with the appropriate software at the planning stage before the implant is placed.
Bone Grafting
Sufficient bone is needed in esthetic areas to ensure the best outcomes and when there is not enough bone, a variety of grafting materials and methods can be considered. When it comes to grafting, the gold standard is the autologous bone graft. This is a surgical procedure that involves transplanting bone from one part of the body to another. This is the gold standard because the tissues are biocompatible and all the available biological factors for growth are there. An allogenic bone graft involves taking bone from a donor and transplanting it into a recipient. There are also synthetic bone grafts that use artificially produced materials made from a variety of porous substances. The bone graft can also be utilized with a membrane. The membrane is a tarp that is placed over the bone graft to help with the regeneration of the bone and there are two types of membrane: non-resorbable and resorbable. Non-resorbable membranes need a second surgery to be removed while resorbable membranes dissolve in the mouth over time.
Another factor to consider when restoring an area with an implant is the timing of the placement of the implant after the tooth has been lost. There is a classification system that is used based on desired levels of healing. Type 1 is the placement of an implant into the tooth socket when the tooth is removed/extracted and is called “immediate implant placement”. Type 2 refers to the placement of an implant after the soft tissue has time to heal after an extraction but before clinically significant bone filling has occurred at the extraction site. Type 3 refers to placement of an implant after significant bone filling in the extraction site. Types 2 and 3 fall into the category of “early implant placement”. Finally type 4 refers to placement of an implant into fully healed bone long after the tooth has been extracted, and is known as “late implant placement”.
There are specific advantages and disadvantages that must be considered when we talk about implant placement times. When it comes to immediate implant placement, the combination of tooth extraction and implant placement at the same visit reduces the number of visits the patient must undertake. One disadvantage of immediate implant placement is that there is an increase in the risk of the soft tissue receding and as a result additional tissue grafting procedures may be needed in the future. With early implant placement, there is a chance for improved esthetic outcomes with regards the soft tissue. Another advantage of early implant placement that occurs 4 to 8 weeks after tooth extraction is that it allows pathology such as an infection around the extracted tooth to heal before implant placement. With late implant placement, the likelihood of needing bone grafting prior to implant placement is increased because of bone resorption that would have occurred over time where the tooth was extracted.
Computer Planning in Implant Surgery
Computer navigated “Dynamic” surgery includes the use of a surgical navigation system that reproduces the implant position directly using cone-beam computed tomography (CBCT) and that allows the surgeon to make changes in implant position during the surgical procedure. In contrast, a static surgical template does not allow the surgeon to make changes in implant position during the surgical procedure. The benefit of dynamic surgery is that it can reduce complications and lead to better prosthetic and surgical outcomes. The downside of dynamic surgery is that the learning curve is more complicated than using a static surgical template.
Risk Assessment
It is also important to create a risk profile for each patient to help predict the likelihood of success for each case. Factors that come into play include but are not limited to the patient’s medical status, smoking habits, the patient’s expectations, the presence or absence of infections at the implant site, the amount of bone present and the status of the neighboring teeth.
Prosthodontic Planning
When planning to replace multiple adjacent teeth in the front of the upper jaw, a diagnostic wax-up, described in detail in my previous blog, is important. This diagnostic wax up allows the clinician and the patient to evaluate the esthetics and function in detail before the procedure is started. This will help in the decision-making process about what implants to use and where they should be placed in the front of the mouth. Usually when replacing upper central incisors or canines, standard platform (regular neck) implants will suffice. When dealing with narrow spaces such as the upper lateral incisors, narrow neck implants may be a better choice. The decision about whether to use bone-level or tissue-level implants also depends on how much soft tissue is available. Bone-level implants may be the better choice if the gum tissue is thinner and bone grafting procedures are required for the patient. Bone-level implants are fully submerged in the bone as opposed to tissue-level implants which have a polished collar that comes out of the bone.
Cement versus Screw Retained Implants
The final implant crown and abutment may be connected through the use of a screw retained process or through the use of cement. Cemented restorations are easier to fit and simpler to use. The biggest disadvantage of cement retained restorations is the difficulty of removing excess cement and the problems that can occur if the excess cement is not removed. Another disadvantage of cemented restorations is the difficulty of removal of the implant crown if it needs to be replaced. Screw-retained restorations are usually the better choice in the front of the mouth as long as the screw holes do not interfere with the patient’s bite. Finally, some studies suggest that screw-retained might also be better for the overall health of the gums.
The Choice of the Abutment Under the Crown
The dental abutment is the connector that connects the dental implant in the bone to the crown, bridge or denture that is replacing the missing tooth or teeth. Abutments are usually made of titanium, gold, zirconia or ceramics. The abutment may be prefabricated or customized but customized abutments give the dentist more options for the position and angulation of the final restoration and gives superior esthetics. Implants that are placed too deep in the bone will necessitate the use of custom abutments.
The Choice of Material for the Crown
For the selection of the crown that goes over the abutment, the choice is either an all ceramic or porcelain fused to metal (PFM) crown. Factors to consider when making the choice include the patients’ habits and esthetics. If the patient grinds their teeth heavily, a PFM crown may be indicated with the areas where the teeth contact with the contact in metal. A PFM may also be indicated if there is limited space as all ceramic restorations need more room. However, all ceramic restorations offer superior esthetics so if there are no grinding issues, all ceramic restorations are the standard of care for restorations in the esthetic zone or front of the mouth. Screw retained restorations are preferred over cement retained in the front of the mouth if possible.
The importance of the patient’s bite/dental occlusion
Dental occlusion is the way the patient’s teeth come together. This is especially important when it comes to dental implants. Natural teeth have a built in shock absorption in the surrounding tissues, dental implants lack this natural protection, so it is crucial to ensure that the pressure that the front teeth are under with dental implants is reduced to a minimum.
Brian Laurence
Much of the information was taken from “ITI Treatment Guide: Volume 6, Extended Edentulous Spaces in the Esthetic Zone by JG Wittneben and HP Weber”
