Lower border bone onlays to augment the severely atrophic (class VI) mandible in preparation for implants: a preliminary report

Abstract

We present the preliminary results of a study involving a group of consecutive patients who underwent lower border onlay grafting, limited to the symphyseal area, in preparation for implant insertion. This technique allows for maximum-sized implants, followed by prosthetic rehabilitation. The main advantage of this method is the minimal risk of damage to the mental nerve. Sixteen patients were followed for a period of 6 months to 4 years and all were free of neurosensory disturbances. Eight had a removable overdenture placed and were satisfied with the result. This surgical approach allows the patient to wear their dentures during the healing period. A further advantage of lower border grafting over intraoral upper border grafting is that mucosal dehiscences are not seen.

Despite the advances made in the treatment of patients with severely atrophic mandibles (Cawood and Howell, class VI), the thin mandible remains a challenge for which no definitive solution has yet been found. Several authors recommend ultra-short implants, whilst others advocate augmentation before implants are to be inserted or combined with implant placement. All options have their specific advantages and disadvantages.

Although with decreasing height, measured at the mandibular symphysis, the body of the mandible becomes wider, a recent study based on an inventory among Dutch oral and maxillofacial surgeons showed that mandibles with a height of less than 10 mm are at risk of fracture when short implants are used. These fractures do not necessarily occur immediately after insertion, but may take place years later. Short implants may be unfavourably loaded because of the increased leverage caused by the increased intermaxillary distance.

Augmentation by building up an ‘alveolar process’ via an intraoral route also has its shortcomings, in that neurosensory disturbance in the area of the mental nerve is not always avoidable. This happens both when onlay grafting is used and in cases of sandwich osteotomies. It is not uncommon when dealing with thin mandibles to find that the inferior alveolar nerve is located on top of the mandible, completely embedded in connective tissue. Dissecting this nerve free may itself cause a nerve neurosensory disturbance. Distraction might be another option, but in common with surgery to the ‘upper border’, nerve neurosensory disturbance may occur for the same reason as mentioned previously because the same ‘sandwich cut’ has to be made. This comes on top of the possible complications that may occur when the vector of the vertical distraction does not coincide with the planned vector, or when other complications occur, such as fracturing of the mandible.

A somewhat forgotten technique that was proposed at the time when pre-prosthetic surgery was evolving is inferior border grafting. Although grafting of the lower border will circumvent the above-mentioned problems, a visible scar is the main disadvantage of this technique. It is thought that in the older population, the resulting submental scar might not be too much of a problem, particularly when weighed against the chances of permanent neurosensory disturbance of the lower lip or chin. The fact that the denture to be made will be supported by two implants of maximum length is reason to believe that sufficient retention and stability can be achieved without risk of early implant loss because of unfavourable loading.

In this report, we present the preliminary results of a study involving a group of 17 consecutive patients who underwent lower border onlay grafting, limited to the symphyseal area, in preparation for implant insertion.

Materials and methods

Patient selection

Seventeen edentulous patients (11 females and 6 males) aged 50–84 years (mean 66.7 years) with class VI mandibles, treated at the study medical centre from 2007 to 2010, were included in this study. All mandibles had a height of 9 mm or less in the bilateral canine region, as measured on cone beam computed tomography (CBCT) scans (i-Cat; Imaging Sciences International, Hatfield, PA, USA). Patient details are given in Table 1 . All patients were informed about the procedure and the advantages and disadvantages were explained; alternative options were offered. The final choice of treatment was left to the patient.

Table 1
Relevant patient data.
Patient Age, years Gender Follow-up after augmentation (months) Neurosensory disturbance Dehiscence Implants in place (months) Types of implant a and lengths, mm, right/left
1 57 F 12 Normal 10 RP 11.5/11.5
2 69 F 38 Normal 28 RP 15/NP 15
3 b 75 F 4 NA NA NA
4 50 F 20 Normal 12 RP 15/15
5 64 F 18 Normal 13 RP 11.5/11.5
6 68 M 20 Normal 19 RP 15/15
7 64 F 29 Normal 22 NP 13/13
8 73 F 33 Normal 27 RP 11.5/11.5
9 79 M 16 Normal 22 RP 13/13
10 69 M 15 Normal 6 RP 13/13
11 69 M 15 Normal 35 RP 13/13
12 84 M 41 Normal 38 NP 13/13
13 71 M 58 Normal 38 NP 11.5/11.5
14 75 F 46 Normal 34 NP 13/13
15 61 F 24 Normal 19 RP 13/13
16 60 F 22 Normal 13 RP 13/15
17 51 F 25 Normal 17 RP 13/13
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Jan 19, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Lower border bone onlays to augment the severely atrophic (class VI) mandible in preparation for implants: a preliminary report
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