Inlay–onlay grafting for three-dimensional reconstruction of the posterior atrophic maxilla with mandibular bone

Abstract

This prospective study describes and evaluates a surgical approach for 3D reconstruction of the posterior maxilla with autogenous mandibular bone in 16 patients (mean age 51 years). Bone blocks were harvested from the mandible and used as lateral or vertical block grafts (onlay); they were also partially milled and used for sinus elevation (inlay). In 4 cases, anorganic bovine bone was added at the periphery of the blocks. 4 months after grafting, implants were placed in a second operation and loaded after 12 weeks. Lateral and vertical augmentations were measured immediately after grafting and at re-entry for implant placement. Mean lateral augmentation performed was 5.5 mm, reduced to 4.3 mm ( p < 0.01) after 4 months’ healing. Mean vertical augmentation was 3.2 mm, reduced to 2.1 mm ( p < 0.01) after healing. The amounts of lateral and vertical graft resorption were similar (1.2 mm vs. 1.1 mm) but were different when compared with the original graft (22% vs. 34%). 49 implants were placed 4 months after grafting. Implant parameters were evaluated after 32–48 months follow up and demonstrated 100% survival rates. The use of mandibular bone grafts for 3D augmentation of the posterior maxilla has shown good results and minor complications.

Horizontal and vertical bone resorption may be seen after tooth loss in the posterior maxilla. The deficient edentulous ridge may interfere with the insertion of implants of adequate length placed in the correct position and with the ideal inclination. Bone resorption in the posterior maxilla takes place in three directions: bone may be resorbed in a bucco-palatal direction, resulting in a narrow ridge displaced towards the palate; bone resorption may have a vertical apical direction, resulting in reduced ridge height and increased inter-occlusal distance; atrophy may be caused by the increase in the volume of the maxillary sinus (sinus pneumatization) that reduces residual bone volume in an occlusal direction by causing a downward displacement of the floor of the sinus . Most of the cases show a combination of the former situations resulting in various types of atrophies. Some authors have attempted to classify these clinical situations .

The reconstruction of the posterior maxilla before or at the time of implant placement by means of sinus floor elevation via a crestal or lateral approach is considered a safe and effective procedure . These procedures are not designed to augment the residual alveolar crest in a lateral or downward direction. Some procedures have been described to achieve a three-dimensional (3D) reconstruction of the posterior maxilla with intra-oral or extra-oral bone grafts .

The combination of sinus floor elevation and a sagittal osteotomy of the anterior maxilla to achieve widening of the crest in the premolar region has been described, but only a few cases are reported . Some authors have described the combination of sinus floor elevation and vertical augmentation of the residual ridge in one case series; guided bone regeneration (GBR) was used with the aid of non-resorbable titanium reinforced membranes and mandibular bone grafts mixed with bovine bone mineral .

A minimally invasive technique has been designed to achieve crestal bone widening and elevation of the sinus floor, in the same surgical session, with the use of osteotomes and green-stick fracture of the alveolus . This technique does not allow downward grafting of the residual ridge, and adequate residual horizontal bone width is needed to achieve implant primary stability.

A combination of horizontal augmentation and sinus floor elevation in edentulous patients has been described by R aghoebar et al., with excellent long-term results and few complications. In this retrospective study the authors analyzed different donor sites (mandible or iliac crest) and different treatment modalities . Iliac bone has been used alone or in combination with beta tricalcium phosphate in the inlay–onlay reconstruction of edentulous maxillae .

Most of the studies report results on different types of defects, treated with different surgical approaches, so it is difficult to draw conclusions regarding treatment outcomes related to the different types of atrophies in the posterior maxilla.

The aim of the present study is to focus on 3D reconstruction of the posterior maxilla without the use of extra-orally harvested bone. In this cohort, maxillary reconstruction was achieved by means of sinus floor elevation combined with autogenous mandibular bone grafted in block to achieve vertical and/or horizontal enlargement of the deficient ridge.

Materials and methods

Patients referred from January 2004 to June 2005 were enrolled consecutively in this prospective study if they required a surgical procedure that included a combination of the elevation of the floor of the maxillary sinus with a lateral approach (inlay procedure) and a horizontal or a vertical augmentation of the residual ridge (onlay grafting). Patients treated with minor augmentation procedures such as sinus floor elevation with the osteotome technique or guided bone regeneration techniques for dehiscence or fenestrations at implant sites were excluded from the study. All patients treated with autogenous bone harvested extra-orally were excluded from the evaluation. Surgical reconstructions of the deficient alveolar segments were planned if patients were healthy, if no contraindications to implant surgery were present, if they were smoked fewer than 10 cigarettes per day and if no signs of active periodontal disease were present.

In the study recruitment period, of 86 patients requiring bone augmentation procedures in the posterior maxilla only 16 (19% cases) required inlay–onlay reconstruction and were thus included in the study. They included 12 females and 4 males with a mean age of 51 years (range 38–67 years). All the patients included in the study were treated according to the following diagnostic and surgical rationale.

Diagnosis

Clinical records including digital photographs, panoramic and intra-oral X-rays and CT scans were recorded. The residual ridge was considered reduced in width if the bucco-palatal dimensions measured on reformatted CT scans were less than 4 mm in the premolar or molar region. Ridge width was measured with a ruler directly on CT scans on reformatted oblique axial cuts of the maxillae at the premolar and molar regions. Measurements of bony width and height were taken directly during the surgical stages and the measurements on CT scans were taken only in the diagnostic phase to decide the allocation of the patients to the present study.

Vertical bone augmentation in the occlusal direction was planned to correct the increased inter-arch dimension if the distance from the edentulous ridge to the lower occlusal plane was greater than 12 mm.

Surgical rationale

Sinus floor augmentation was performed with mandibular bone harvested in blocks and then milled and grafted into the sinus. In some cases, if the bone was considered not sufficient, some anorganic bovine bone (ABB; Bio-Oss, Geistlich AG, Wolhusen, Switzerland) was mixed with milled bone and grafted into the sinus. All the patients included in this study presented sinus pneumatization, so sinus lift was always performed.

Vertical onlay augmentation was performed with bone blocks grafts. Vertical onlay augmentation was used in cases of vertical resorption of the alveolar ridge with increased inter-arch distance in the premolar and/or molar area.

Lateral onlay augmentation was performed with bone blocks in cases with a residual alveolar width of 4 mm or less. Lateral onlay augmentation was used in cases of horizontal resorption of the alveolar ridge in the premolar and/or molar area. In some cases ABB was added to increase the volume of the graft or at the periphery of the bone blocks. When ABB was used in conjunction with block grafts for onlay augmentation the entire reconstruction was covered with a resorbable collagen membrane (Bio-Gide, Geistlich AG, Wolhusen, Switzerland).

Surgical technique

Recipient site

Following local anesthesia a midcrestal incision was designed continuing into the gingival sulcus of the most distal remaining tooth, two vertical vestibular releasing incisions allowed the elevation of a broad mucoperiosteal flap. After exposure of the alveolar ridge, measurements were taken to assess the effective bony width. The need for vertical augmentation was confirmed at this stage if the bone crest was positioned 3 mm or more apically when referred to the interproximal bony peak of the mesial tooth. If vertical atrophy was less than 3 mm compared with the bone peaks of the adjacent teeth, no vertical augmentation with bone blocks was performed. The vertical level of the residual crest was taken directly in the patient’s mouth with the aid of two periodontal probes. The reference line used was the one connecting the cusps of the 2 teeth adjacent to the bone defect.

After evaluation of the bone defects, a bony window was designed on the lateral wall of the sinus and was removed or elevated towards the medial wall. Dissection of the sinus membrane was accomplished to prepare the inlay grafting of the sinus floor . The choice of the donor site was made by the clinician on the basis of his evaluation of the amount of bone necessary. Generally, the ramus was preferred because the harvesting procedure is associated with minor morbidity , but if a large amount of bone was required the chin was chosen as the donor site.

The bone blocks were secured to the recipient site with the aid of one or two titanium lag screws 1.5 mm in diameter (Modus Straumann AG, Basel, Switzerland) for each block. Great care was taken to place lag screws in pristine bone with no violation of the sinus. The sinus was then augmented. Periosteal releasing incisions allowed tension-free closure of the flaps with complete closure of the grafted site.

Donor site

To harvest bone from the mandibular ramus and body ( Fig. 1 a and b ) a retromolar incision at least 3 mm from the mucogingival junction was made from first molar to the coronoid process. After reflection of a full thickness mucoperiosteal flap, two bone cuts involving only the buccal cortical plate of the mandible were made with a Lindemann bur beginning at the external oblique line and carried obliquely towards the mandibular angle. They were connected superiorly and the cortical plate out fractured with a straight chisel. The incision was closed in layers with resorbable sutures (Vycril, Ethicon, Somerville, NJ, USA).

Fig. 1
Bone harvesting from the mandibular ramus (a and b) and from the chin (c and d).

To harvest bone from the anterior mandible ( Fig. 1 c and d), a horizontal incision 7–10 mm away from the mucogingival junction was performed in the buccal vestibule from cuspid to cuspid and the incision was deepened in an oblique posterior direction in the muscular layer towards the periosteum. The anterior mandible was exposed and trephine burs of various diameters (7–12 mm) were used to harvest 2–4 bony cylinders of different diameters and depth, depending on the graft needed. Great care was taken to leave at least 4 mm of intact bone below the roots of the mandibular teeth. A collagen sponge was placed in the donor site (Spongostan, Ethicon, Somerville, NJ, USA) and the wound was closed in layers with resorbable sutures (Vycril, Ethicon, Somerville, NJ, USA). A compressive external dressing was applied and kept in place for 24 h.

Postoperative medication

Antibiotics (amoxicillin plus clavulanic acid 2 g endovenous) were administered during surgery, and amoxicillin plus clavulanic acid, 1 g every 12 h, was prescribed for the following 5 days (Augmentin, Glaxo Smithkline, Brentford, UK). Nimesulide, 100 mg twice daily, was used for pain control when needed (Aulin, F. Hoffmann – La Roche AG, Basel, Switzerland). Ice packs were used for 24 h and the patient was instructed to use 0.2% clorhexidine mouthwash twice daily for the first 3 weeks (Corsodyl, Glaxo Smithkline). Patients were seen every 3 weeks after suture removal to ensure adequate tissue healing.

Implant placement

Occasionally, some of the implants could be placed at the time of grafting in association with the inlay procedure (for example if the width of the crest at the molar site was adequate but needed horizontal or vertical augmentation in the premolar area). Implant placement was never performed simultaneously to grafting in the location where the block grafts were used. 4 months after bone augmentation, after a clinical and radiological examination, a second surgical procedure was performed. For implants placed at the time of reconstruction, healing abutments were connected at this time during the completion of implant insertion.

A standard surgical procedure was used to place implants, but the lag screws used for graft fixation were removed before implant bed preparation. Standard screw implants 4.1 or 4.8 mm (standard or wide neck) in diameter, with Sandblasted – Acid etched surface (SLA), at least 10 mm long were used (Institut Straumann AG, Basel Switzerland). Implants were submerged or non-submerged according to the esthetic situation.

Implant loading and follow up

Implants were loaded 12 weeks after insertion. Follow up visits were performed every 6 months after implant loading; the last follow up visit was planned for all patients between May and June 2008.

Measurements

Direct bony measurements of the alveolar ridge width were taken with a millimeter graduated caliper. They were taken during the first operation immediately before grafting (baseline) and immediately after grafting, and during the second operation immediately before implant placement .

A reference line connecting the vestibular cusps or the incisal edges of the 2 teeth mesial to the site to be augmented was used for measurements related to crestal height. The vertical distance between the bone crest and this reference line was measured with a UNC 15 periodontal probe before grafting (baseline), immediately after bone grafting and immediately before implant placement at the time of re-entry for implant insertion. These measurements were taken only when vertical onlay grafts were undertaken. Increases in width and height at the crestal level were then calculated easily. The amount of horizontal and vertical augmentation was calculated comparing baseline values and measurements taken immediately after grafting. Graft resorption was determined by comparing measurements taken immediately after grafting and the same measurement taken immediately before implant placement. The final bone gain obtained with the graft was calculated by comparing the amount of augmentation and the amount of graft resorption.

When vertical augmentation was accomplished, the horizontal increase was measured at the crestal level. The number of bone blocks, donor sites and number of implants inserted in each augmented site were also recorded.

Clinical parameters such as Bleeding on Probing (BOP), Probing Depht (PD), and absence of infection or suppuration were recorded. X-rays (digital panoramic or intra-oral) were taken, as in any standard implant case at implant loading, 1 year after loading and at the latest follow up visit. Implants were considered successful if there was absence of persistent pain or peri-implant infection with suppuration, absence of implant mobility or peri-implant radiolucency and if peri-implant bone resorption was less than 1.5 mm in the first year of function and less than 0.2 mm in the following years .

The bone level measured on the radiographs taken immediately after implant placement was considered the baseline for further measurements. The measurements were recorded to the nearest 0.5 mm.

Adverse events were systematically recorded in the charts and were reviewed at the last follow up visit.

Statistical analysis

Statistical analysis was performed by comparing horizontal and vertical bony measurements at baseline, immediately after graft and immediately before implant placement, by means of the Wilcoxon test. The level of significance was set at p < 0.05.

Results

Depending on the type of atrophy present at the time of reconstruction, slightly different surgical approaches were used ( Figs 2–4 ). Types of procedure used (including type of treatment, donor site, number of implants inserted at the first or second operation and the use of membranes or xenografts) are described in Table 1 . Table 2 gives the patients’ demographic data and the timing of surgical sessions. Mandibular autogenous bone in blocks was used for onlay augmentation in all cases in combination with sinus floor elevation: 11 patients received horizontal onlay augmentation; 2 received vertical onlay grafts; and 3 received combined horizontal and vertical onlays.

Fig. 2
Inlay–onlay grafting in the posterior maxilla of a 53-year-old female patient with a failing prosthesis (a). The bony width was insufficient for the placement of implants (b and c). The bony height was not sufficient because of sinus pneumatization. The inter-arch distance was not increased. An inlay–onlay graft was prescribed: three blocks were harvested from the chin. One was milled and the resulting particulated bone was grafted into the sinus and two blocks were secured to the alveolar ridge for horizontal augmentation (d). Bone substitute was added at the periphery of the blocks and two layers of a collagen membrane were used to protect the graft (e). 4 months later a re-entry was performed: the augmented bone (f) permitted the placement of two implants. After their safe healing (g), a new prosthesis was delivered to the patient (g).

Fig. 3
Radiographic images of the patient depicted in Fig. 2 before and after treatment. Panoramic X-ray and CT scan showed alveolar bone atrophy before treatment (a and b). Panoramic and periapical X-rays after treatment showed the perfect integration of the implants in the augmented bone (c and d).

Fig. 4
Inlay–onlay grafting in the posterior maxilla of a 48-year-old female patient. The bony width in the canine and premolar region was not sufficient (a). The bony height was not sufficient because of sinus pneumatization and vertical resorption of the alveolar ridge with increased inter-arch distance in the first molar area. An inlay–onlay graft was planned: a block was harvested from the ramus and separated into three pieces: one was milled and the resulting particulated bone was grafted into the sinus, another was secured to the alveolar ridge for horizontal augmentation in the canine and premolar area, and the last block was secured in the molar area for vertical augmentation (b). 4 months later a re-entry was performed: the augmented bone showed only minimal resorption and allowed the placement of three implants in the canine, first premolar and first molar sites (c and d).

Table 1
Treatments performed in the present study.
Patient Type of treatment No. of bone blocks Donor site Membrane and or bone substitute Implant sites
Sinus elevation Premolar region
Vertical onlay Lateral onlay
1 × × 2 Chin 24,25,26
2 × × × 3 Chin 24,25,26
3 × × 3 Chin Bone substitute and membrane 25,26
4 × × × 3 Chin Bone substitute and membrane 24,25,26,27
5 × × 2 Chin 26,27
6 × × 3 Chin 14,15,17
7 × × 3 Chin 14,15,16
8 × × 1 Ramus 14,15,16
9 × × 3 Chin 14,15,16
10 × × × 3 Ramus 26,24,23
11 × × 3 Ramus Bone substitute and membrane 26,25,24
12 × × 4 Chin 14,15,16,17
13 × × 2 Chin 14,15,16
14 × × 3 Ramus 24,25,26,27
15 × × 3 Chin 15,14
16 × × 3 Ramus Bone substitute and membrane 27,25,24
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Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Inlay–onlay grafting for three-dimensional reconstruction of the posterior atrophic maxilla with mandibular bone
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