Abstract
Alveolar bone splitting and immediate implant placement have been proposed for patients with severe atrophy of the maxilla in the horizontal dimension. A new modification of the classical alveolar bone splitting for the treatment of the narrow ridge in the maxilla is provided. Thirty-three dental implants in eight consecutive patients were evaluated retrospectively following the described modified split-crest osteotomy. Inclusion criteria were: inadequate maxillary buccolingual dimension, 3–4 mm of crestal width, and sufficient height from alveolar ridge tip to maxillary sinus floor. Primary stability was calculated using resonance frequency analysis (RFA). Alveolar bone height was measured in the panorex pre- and postoperatively. Histological bone examination was assessed following trephine bone harvesting during the second operation. Mean follow-up was 28.33 months. Bone regeneration of the inter-cortical gap occurred in 98% of implant sites (implant survival rate 100%). Mean implant stability quotient (ISQ) for the whole series of implants was 69.48. At the second operation, mean loss of the alveolar bone height was 0.542 mm. Predictable results are obtained using the modified split-crest osteotomy. This technique provides an acceptable inter-cortical gap, decreases the risk of necrosis of the outer cortex, and provides a firm-wall box for the placement of particulate bone grafting.
Horizontal and vertical atrophy of the alveolar ridge are usually present in severe edentulism, corresponding to classes IV to VI according to C awood & H owell . In these cases, vertical and horizontal augmentation of the alveolar ridge is mandatory to allow adequate implant insertion. In the severely atrophied maxilla, alveolar ridge augmentation by means of bone grafting, guided bone regeneration or distraction osteogenesis is mandatory previous to the placement of endosseous implants. Specific disadvantages have been reported for each technique, such as: resorption, limited amount of bone, damage to the adjacent teeth and sensory nerve disruption, in bone grafting; tissue dehiscence, membrane displacement and membrane collapse, in guided bone regeneration; and inadequacy of the distraction vector, bone resorption, absence of bone formation and prolonged time for implant placement, in alveolar distraction.
Alveolar bone splitting and immediate implant placement have been proposed for patients with severe atrophy of the maxilla in the horizontal dimension. O sborn described the ‘extension plasty’, a two-staged method for splitting and extending the alveolar crest and filling the expanded space with hydroxyapatite or autogenous bone, while insertion of the implant was performed 8–12 weeks later. N entwig & K niha reported the bone splitting technique in 1986, as a one-staged method that allowed extension of the alveolar crest and insertion of the implant at the same time. These classical approaches for the splitting technique were generalized with the use of osteotomes. Since then, several modifications have been reported for the classical technique, such as the use of ultrasonic surgery or the staged ridge splitting technique . C hiapasco et al. cited the technique of sagittal osteotomy of the anterior maxilla with preservation of the buccal cortex periosteum and vascularization with a half-thickness flap, stating that this technique results in a better outcome than other techniques.
Otherwise, it is thought that implant primary stability plays a major role in successful osseointegration. It depends on the quality and quantity of the bone, the implant geometry and the technique for preparation of the implant site . Volume and quality of bone are important factors in determining the surgical process and the type of implant to be used, and are related to the success of implant surgery. The technique of resonance frequency analysis (RFA) measures the stability of the implant as a function of the rigidity of the complex bone/implant. The frequency of the resonance (in Hz) in a transducer is established by means of the implant stability quotient (ISQ), and typically ranges between 45 and 85. Although the use of RFA was primarily introduced to help in the decision of when to use implants with the immediate load technique, its use in other scenarios makes it possible to evaluate the primary stability of implants placed on atrophic crests undergoing previous augmentation procedures.
The authors describe a modification of the classical alveolar bone splitting technique for the treatment of the narrow ridge in the maxilla, bearing in mind the degree of implant primary stability measured by RFA.
Patients and methods
33 dental implants in 8 consecutive patients (mean age 53 years; range 38–69 years) with severe atrophy of the alveolar maxillary ridge were evaluated in this retrospective study ( Fig. 1 ). The study was carried out at the Centro de Implantología y Cirugía Oral y Maxilofacial CICOM, Badajoz, Spain. The study was approved by the Ethical Committee. All the patients underwent a modified split-crest technique with immediate implant insertion. Implant placement was conducted through a conventional two-step procedure, and a second stage surgical procedure to place the abutments was performed following the healing process 4 months later. Patients were selected using the following inclusion criteria: inadequate maxillary buccolingual dimension, 3–4 mm of crestal width; and sufficient height from the tip of the alveolar ridge to the floor of the maxillary sinus, to allow immediate implant placement without the need for an associated sinus lift procedure. Panoramic radiography and dental CT scans were used to assess the preoperative conditions. Implant stability was measured using the RFA with the Ostell™ Mentor (Integrations Diagnostics AB, Savedalen, Sweden) in ISQ units. The pre- and postoperative alveolar height measurements were made in relation to implant sites. Height of the maxillary bone was measured from the head of the implant (postoperatively) or from the tip of the alveolar ridge at implant site (preoperatively) to the cortical bone corresponding to the floor of the maxillary sinus or the nasal cavity. The loss or increase of alveolar height was expressed as the difference between pre- and post-operative heights.
Adequate bone formation was assessed by histological examination of specimens obtained with a trephine drill during the second operation. The biopsy was taken with a 2.0 mm diameter trephine introduced within the grafted bone in the vicinity of the implant. Special care was taken not to disturb the architecture of the bone around the implant. Specimens were washed and immediately fixed in 10% formalin following biopsy. Conventional histological examination with haematoxylin–eosin was performed once the bone was completely decalcified with a freshly prepared aqueous solution of CH 2 O 4% and HCl 10%. A physical method (needle prick) was used to confirm adequate decalcification of the specimen, taking care to use it away from the site of interest to avoid artifacts. The specimens were rinsed to wash away the acid. The sections were processed and embedded in paraffin blocks.
All patients were clinically followed for at least 24 months postoperatively ( Fig. 2 ), although mean postoperative follow-up for the whole series was 28.33 months. Panorex radiography was performed for each patient to assess postoperative alveolar bone height in the site of implant placement. Panorex radiography obtained at month 24 was compared with that for preoperative evaluation in terms of alveolar bone height at the implant site.
Surgical technique
A buccal mucoperiosteal flap was elevated following mid-crestal and intracrevicular incisions. No palatal flap was harvested in order to maintain adequate irrigation of the alveolar ridge. First, a mid-crestal osteotomy with a reciprocating saw or a diamond disc was performed into the alveolar ridge ( Fig. 3 A) . This osteotomy was extended as far as the narrow alveolar crest was present. Two vertical cuts were then performed on the proximal and distal ends of the mid-crestal osteotomy ( Fig. 4 ). The cephalad ends of the vertical cuts were connected with a horizontal corticotomy by means of a piezosurgical device ( Fig. 5 ). Vertical osteotomies were deepened 3 mm through the cortical bone, with preservation of intact cancellous bone. The authors only used the piezosurgical device to make the corticotomy that connected both vertical osteotomies. This was because a careful cut to cortical bone was selectively required at this point, in order to create a green-stick fracture and avoid a complete fracture of the buccal plate. The other osteotomies required deeper cuts, and a diamond disc ( Fig. 3 A) or a reciprocating saw was used.
A green-stick fracture of the cephalad horizontal corticotomy was performed carefully with the introduction of a thin chisel ( Fig. 4 ). Following this manoeuvre, progressive introduction of thin osteotomes between buccal and palatal cortical plates was performed in order to obtain the desired widening of the inter-cortical gap ( Figs 3B,4 and 5 ). The sequential introduction of the osteotomes from a minor to a major diameter allowed safer and more controlled splitting. Following splitting of the outer cortex, implants were placed in the cancellous bone without saline irrigation ( Figs 6 and 7A ). Primary implant stabilization was assessed with the ISQ values. Subsequent filling of the gap with particulated bone graft was carried out ( Figs 3C and 7B ). It was composed of a mixture of autogenous bone graft obtained from the vicinity with a bone scraper and the allogenic bovine particulated bone graft Laddec ® (Transphyto, France). A re-absorbable membrane Gore Resolute ® (W.L. Gore & Associates, Inc, Newark, Delaware, USA) was used to cover the graft. Finally, the mucoperiosteal flap was repositioned and fixed with a 4/0 Gore-tex ® suture (W. L. Gore & Associates, Inc, Newark, Delaware, USA) ( Figs 3D and 7C ). The degree of ossification in the inter-cortical gap was assessed by histological analysis of bone biopsies adjacent to implants obtained during the second operation ( Fig. 8 ).
