When it comes to the fundamentals of dental prosthetics, the possibilities are virtually, limitless. Today, dental prosthesis reach far beyond the simple replacement of a missing tooth or covering up tooth defects. While this is and always will be the objective of the prosthesis itself, there is no modern dentistry without implantology – the procedures that involved both tooth replacement and restoration by embedding dental implants.
Whether you're an experienced clinician or a novice, if you're new to the world of oral implantology, it's important to understand the critical steps involved in the procedure. No less important, is that the procedure also results in a satisfied patient, now with an attractive, esthetically-pleasing smile.
The prosthetic stage should be considered at a very early stage of treatment planning, long before the implants are placed in the patienwhent's mouth. Therefore, we will not focus on implant placement surgery, but rather on the planning that precedes it, and the restorative treatment that follows.
Dental implant restoration procedure consists of the following steps:
Pre-surgical prosthetic planning is best defined as the process of accumulating diagnostic information to determine which course of treatment should be considered for the patient. Prosthetic planning includes these steps:
In cases of immediate loading, the soft tissues stabilize and conform from the moment of placing the implant, a temporary abutment, and temporary teeth. According to the traditional approach, after the implantologist has confirmed the implant osseointegration, an implant uncovering surgery takes place. This usually occurs 3-4 months after the implants were placed in the maxilla, and 3 months after mandibular placement. A healing abutment is then placed, and it's recommended that you wait 15-20 days for the soft tissues to become stable.
There are two main types of implant prosthesis – provisional and definitive.
Provisional prosthesis are placed either in the implant-placement surgery stage. This technique is referred to as immediate provisionalization for a single tooth or immediate loading for multiple tooth replacement, or in the second (uncovering) surgery stage, instead of placing a healing abutment.
Provisional prosthesis can be screw or cement-retained, and can be made from titanium or PEEK (polyetheretherketone).
In immediate loading, the provisional prosthesis is placed on an implant without reaching occlusal contact with the antagonist teeth. Immediate loading is performed to meet the patient's aesthetic requirements. It can be used in implants with good primary stability, especially with a single tooth or short-span bridges. In some cases, real immediate occlusal loading can be performed, where there will be contact between provisional and antagonist teeth to enable proper mastication, e.g. in full-arch implant restorations. For immediate loading, the implant should achieve suitable primary stability exceeding 35 Ncm.
Definitive prosthesis can also be screw or cement-retained. Cement-retained prosthesis will be used in cases with adequate gingivo-occlusal and interproximal spaces (at least 7mm), and unfavorable implant angulation. In cases with lower spaces, a screw-retained prosthesis is sufficient, however, in this case, the angulation of the implant should be favorable to enable aesthetic positioning of the screw channel (on the occlusal or lingual surface of the restoration).
For cement-retained prosthesis, machined (straight or angled) or castable (UCLA) abutments can be used. Straight machined abutments are used when the implant emergence is ideal. In cases where the emergence is not ideal, an angled abutment should be used to prevent the crown from over-contouring. The most widely-used angled abutments have angles of 15° or 25°, however, a new 35° angled abutment is also available.
The fundamental difference between machined and cast abutments is the adaptation with the prosthetic implant base. Machined abutments offer very good adaptation and fit, providing excellent marginal seal, and a very good transmission of forces. Cast abutments do not have the same precision and fit, and they generate larger gaps and deficient force transmission, particularly when cast in Ni-Cr alloy. To reduce the lack of precision in cast abutments, abutments with a Co-Cr metal base or multi-unit abutments can be used. Similarly, multi-unit abutments provide perfect adaptation and adjustment, as they are machined. Further, multi-unit abutments take the interface with the cast metal above the gingiva, thereby lowering the risk of soft tissue inflammation.
Passivity is a key property of prosthetic structures, essentially allowing them to sit correctly on the implants without exerting permanent tension on the implant bone interface. If the prosthetic structure lacks passivity, the following complications may arise – bone resorption, soft tissue inflammation, lack of adaptation, and loosening of the prosthetic fixation screws. For passive adaptation, machined prosthetic elements or metal-base castable abutments should be used. In restoration involving multiple implants, the most common technique to obtain passivity is to segment multiple metal structures, and then weld them. Dividing the prosthesis into a mesostructure and suprastructure reduces the possibility of dimensional variation due to volume, therefore, increasing passivity when installing the prosthesis.
When it comes to improving implantology procedures, the overall patient experience, and the esthetic results, proper prosthetic restoration planning and implementation is essential.
As we consistently strive for better results based on enhanced diagnoses and techniques, as professionals, we continue to learn – and we never stop learning. Oftentimes, it's the most challenging cases that become our very best teachers.