Implant-supported fixed restorations for patients with no teeth at all.
In dental implantology, cases are assessed differently from both a surgical and a prosthetic point of view, according to their degree of difficulty. In general, all cases are classified as simple, advanced or complex. Surgically, cases with no bone defects and no anatomical structures that adversely affect the case are classified as simple, while cases where bone problems occur in the area where the implant socket is to be placed are assessed as surgically complex and advanced. From a prosthetic point of view, all implant cases are graded by difficulty depending on the number and area of missing teeth. For example, posterior cases that have lost a single tooth are classified as simple, while anterior cases that have lost a single tooth are classified as advanced and complex. From this point of view, completely edentulous cases that must be rehabilitated with fixed restorations on implants throughout are the most difficult cases in implantology.
In such cases, the doctor's knowledge and experience play a key role in success.
To make implant-supported fixed restorations fully complete, the appearance of the final restorations on completion must be determined during treatment planning. Sufficient information on this can be obtained from the impressions taken from the patient, the diagnostic models produced, and the wax models to be made on them. While this procedure is important for planning, it also gives the doctor very important guidance on how to position the implants during surgery.
For a fully edentulous upper and lower jaw, 6 or 8 implants are used for the fixed restoration on implants, depending on the size of the dental arches. While 6 are sufficient for very small dental arches, it is more appropriate to use 8 implants for normal or larger arches. In addition to the biomechanical advantages it brings, the increase in the number of implants allows the final restoration to be made in smaller sections. Where 6 implants are used, the restoration is made in two sections at most, while where 8 implants are used, the restoration can be divided into 4 sections.
Because the number of implants changes with the size of the dental arches, the position of these implants in the arch also changes. In patients with 6 implants, the implants are ideally placed in the central incisor, canine and first molar regions, and where 8 implants are used, the implants are ideally placed in the central incisor, canine, first premolar and first molar regions. Where a single jaw is completely edentulous, the number of implants is determined according to the quality and quantity of bone, the size and shape of the arch, the amount of lost tissue, the distance between the arches and the opposing teeth, phonetics, aesthetics inside and outside the mouth, hygiene requirements and, finally, the angulation of the implant.
The most important factor in choosing implants in edentulous cases is the size of the implant. The dimensions of the chosen implants must meet the biomechanical requirements and must not lead to iatrogenic errors during and after implant surgery. We must remember that choosing implants of short and narrow diameter will make surgery easier from a biomechanical point of view, but will pose problems when long-term success is considered. However, using implants with a wider diameter than necessary in the upper jaw and the anterior region, where aesthetics are very important, will later lead to bone resorption, resulting in very serious aesthetic problems. Ideally, when the implant is placed in the bone, at least 1 mm of vestibular and lingual bone tissue should remain. Considering all these factors, an implant diameter of about 4 mm and a length of at least 10 mm can be regarded as optimal from a biomechanical point of view. If placing short, narrow-diameter implants is unavoidable because of the circumstances of the case, increasing the number of implants would be a more suitable approach.
Difficulty
The greatest difficulty in completely edentulous cases arises from the relationship between the jaws or from resorption. After the loss of natural teeth, resorption occurs in different directions in the two jaws. In the lower jaw, resorption occurs downwards, while in the upper jaw it occurs upwards and backwards. Over time, therefore, such cases develop into a Class III jaw relationship, even if they were not one in the past. This means that an implant-supported fixed restoration on the upper jaw is made quite differently from natural teeth. The differences are as follows:
1. Lengthening of the crown
2. Placing the teeth at a right angle to the lips
3. The contours in the cervical embrasure areas, where physiological tooth cleaning cannot be done very easily.
The loss of bone, and therefore of gum levels, caused by resorption over time can only be compensated for by lengthening the crowns during restorative work. Otherwise, the vertical dimension of occlusion would be reduced in these patients. Again, because resorption in the upper jaw occurs upwards and backwards, in the resulting Class III relationship the upper teeth of the restoration are inclined towards the lips in order to bring the lower teeth into proper occlusion. For the same reason, the cervical contours in particular must be quite different from natural crowns. To avoid these situations, implants should be placed immediately after the loss of natural teeth if possible, or ideally immediately after tooth extraction. As time passes, resorption inevitably presents the difficulties mentioned above. While fixed restorations made on implants placed immediately or straight after tooth extraction look the same as natural teeth, fixed restorations made in cases of long standing inevitably look different.
In implantology, it is possible to make restorations on implants with ideal aesthetics and function in all cases of tooth loss, but only if ideal conditions exist. It is almost impossible to find optimal conditions for a completely edentulous patient who lost their teeth long ago. Immediate placement of the implant during the extraction session reduces the number of surgical procedures that must be performed on the patient, reduces socket resorption at the level of the alveolar crest and shortens the overall duration of treatment. However, surgeons must pay particular attention to the position of the natural tooth to be extracted in such cases. If the position of the natural tooth adversely affects the ideal placement of the implant, they must revise the treatment plans accordingly. Otherwise, we must remember that we will be faced with irreparable aesthetic problems in the future.
In completely edentulous cases, in addition to the difficulties caused by resorption and the relationship between the jaws, there are also difficulties relating to the papillae. Today, although advanced surgical techniques and materials have developed considerably, it is still not possible to create an ideal papilla between two implants. For this reason, interdental contact surfaces should be made rather than contact points, so that there are no dark triangular areas between the teeth that would disturb the aesthetic form, especially in the anterior regions.
All the principles of implant placement in the anterior region of the upper jaw apply to the final aesthetics of implant prostheses in edentulous patients. For this reason, it is necessary to pay attention to the choice of implant, the three-dimensional position of the implant in the bone socket and the angular values of the alveolar bone, especially when working in the upper jaw. All these factors have a great effect on the ideal aesthetics of the restoration. We should never forget that aesthetics is one of the greatest challenges when making a fixed full-arch implant-supported restoration in patients with poor dentition. Complete removal of residual cement makes it more reliable for clinicians to secure restorations to screw-retained abutments.
In principle, if the top of the implant lies less than 3 mm below the gum, it should be cemented, and if it lies 3 mm or more below, it should be screw-retained. However, if a cemented restoration is planned in edentulous patients, it is very important to be able to divide this restoration into several sections in a single jaw. It is also a fact that fixing full-arch bridges, which can be made in one piece or two pieces at most, will lead to difficulties in solving problems in the future. As a result, fully cemented restorations can be made, although this is not very common, if the restoration is multi-section and if the implants are not very deep below the gum level.
An important issue in this regard is the fit of the restoration to the abutments. In full-arch bridges, where a metal-ceramic restoration is almost always made, the alignment can be affected by the casting shrinkage that can occur. For this reason, great importance must be attached to fit when cementing or screwing. Passive fit of the bridges is the most important factor in preventing mechanical problems that may arise later. We must not forget that visible loosening of the screws after fixation and loss of retention due to deterioration of the seal are warning signs of such situations. Particularly in long-span bridges, great importance must be given to fit.
It is not yet scientifically sound to speak of a particular occlusal concept for implants. In general, assessments of occlusion on implanted teeth do not differ from those on natural teeth.
In completely edentulous cases, two occlusal concepts stand out during the fixed restoration on the implant. These are:
- Providing lateral guidance on the working side
- Elimination of balancing contacts
Lateral guidance on the working side is provided either by canine-guided occlusion or by group function. Although canine-guided occlusion is easier to create than group function, it is generally undesirable because it places more force on the implant in the canine region. In all possible cases, group function guidance in lateral movements is a more suitable approach in terms of transferring forces to other implants.
Conclusion
Despite all its complexity and difficulty, in cases that have lost all their natural teeth, being able to carry out a complete fixed implant-supported rehabilitation of the mouth, with an error-free diagnosis and treatment plan, offers significant advantages in terms of bone resorption, as well as many other benefits such as comfort in functional, aesthetic and social life.
