Direct answer
Frequently, yes. When the bone height above the inferior alveolar nerve is reduced, short implants make it possible, in many cases, to rehabilitate the posterior region of the mandible without a bone graft. There are also advanced surgical techniques, such as lateralisation of the inferior alveolar nerve, that allow implants to be placed without resorting to a graft.
This region has an anatomical feature that constrains the whole of the planning. The inferior alveolar nerve is a branch of the mandibular nerve, the third division of the trigeminal nerve, and it crosses the mandible inside a bony canal — the mandibular canal. This is the nerve responsible for sensation in the lower lip and the chin.
In planning implants in this region, the bone considered available for the rehabilitation is the residual bone situated above the mandibular canal.
When that height is reduced, there are four routes to consider in rehabilitating these situations.
They are placed in the bone available above the nerve, without touching it and without a prior graft. They are implants designed to obtain stability in a limited bone height.
Implants less than 10 mm in length are considered short. There are also implants of between 4 and 6 mm, referred to as extra-short.
The evidence has been accumulating in favour of this route. An umbrella review of systematic reviews, which brought together 595 implants in 281 patients, compared short implants with implants of conventional length placed after bone augmentation. It concluded that short implants may fail less in the first year, show less bone loss around the implant at 3, 5 and 8 years, and that they probably reduce complications in the tissues surrounding it — gum inflammation and associated bone loss — over all those periods [1].
A meta-analysis of randomised clinical trials, the study design with the greatest comparative value, reached matching conclusions: over the first five years the results are equivalent between the two routes, with fewer complications with short implants [2]. In other words, avoiding the graft does not mean, in these cases, accepting a poorer outcome.
Bone resorption is frequently accompanied by a reduction in the attached gingiva — the firm gum, fixed to the bone, that covers and protects the area around the implant. In many cases, augmentation of the attached gingiva, carried out at the time the implants are placed, contributes to the stability of the peri-implant tissues and to their maintenance in the long term.
These are advanced surgical techniques in which the nerve is moved from its path to allow the placement of longer implants, supported by the bone structure at the base of the mandible. In lateralisation, the nerve is moved aside laterally; in transposition, it is additionally released at its point of emergence and repositioned.
These are established procedures, with good implant survival results, applied in carefully selected cases. In a systematic review of 33 studies and about 950 procedures, 93% of patients had altered sensation in the immediate postoperative period; that alteration persisted in 6% of lateralisation cases and 15% of transposition cases [3]. This is information to weigh up at the moment of the decision.
In situations of very marked atrophy, where the routes above are not viable, customised implants may be used. From three-dimensional imaging, a titanium framework adapted to the patient's anatomy is designed and manufactured, which rests on and is fixed to the bone and allows the dental prosthesis to be connected.
It is an approach applicable both to the maxilla and to the mandible, and one that has evolved considerably in recent years: digital planning and additive manufacturing in titanium now make it possible to produce frameworks closely adapted to each patient's anatomy. Its indication calls for careful assessment of the alternatives and of the follow-up care required [4].
It consists of reconstructing bone height above the nerve, in order then to place implants of conventional length. It generally involves two procedures and a healing period between them.
It remains indicated in specific situations, notably when the rehabilitation calls for a position or a relationship with the opposing teeth that the existing height does not allow, or when there is a marked step in relation to the adjacent teeth.
The decision rests on the bone height available above the mandibular canal, on the width of the ridge, on the relationship with the opposing teeth and on the demands of the planned rehabilitation. The study is carried out by cone beam computed tomography — CBCT — which allows the position of the canal and the remaining bone to be measured accurately.
None of these routes is universally preferable. Each case should be assessed with a professional experienced in these rehabilitations, who can explain which solution is the most appropriate and why — seeking the one that offers the greatest predictability and durability.
References
The route indicated is determined by imaging assessment, case by case.
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