Expansion of the alveolar bone crest in two stages: two clinical cases

Oral Surgery ISSN 1752-2471 CASE REPORT ors_1102 30..34 Expansion of the alveolar bone crest in two stages: two clinical cases J. Cano1, J. Campo1 & R. Ewers2 1 Department of Buccofacial Medicine and Surgery, Universidad Complutense de Madrid, Madrid, Spain Head of Department of Oral and Craniomaxillofacial Surgery, University of Vienna, Vienna, Austria 2 Key words: corticotomies, crest expansion, dental implants Correspondence to: Dr J Cano Department of Buccofacial Medicine and Surgery Faculty of Dentistry – Universidad Complutense de Madrid Plaza Ramón y Cajal s/n Madrid-28040 Spain Tel.: 913941912 Fax: 913941910 email: jo.cano@wanadoo.es Abstract Alveolar crest expansion is a surgical approach used to remedy width defects and represents a predictable alternative procedure to guided tissue regeneration and autologous onlay grafts. Clinical and experimental results underscore the benefits of non-mechanical implant bed preparation in bones with very low density. We report two clinical cases in which crest expansion was conducted in two stages: corticotomies in alveolar crest and then, after a 28-day interval, crest expansion and implant placement, permitting revascularisation of the buccal cortical bone. Accepted: 2 September 2010 doi:10.1111/j.1752-248X.2010.01102.x Introduction In 1981, Albrektsson stated that reliable osseointegration depended on the biocompatibility, implant design, implant surface, state of host bed, surgical insertion technique and subsequent loading conditions1. All of these factors have been the subject of continuous research and innovation. Novel developments in relation to the host bed and surgery include the application of growth factors and the use of bone condensation techniques in the implant bed and the application of expansion techniques for very thin crests (split crest). The objective of these techniques is to increase bone density and avoid the cortical bone loss produced by drilling, thereby, favouring primary implant stability and earlier prosthodontic implant loading. Radiological and histological studies have demonstrated that the trabecular bone on which an implant is placed becomes denser at the point of union. The biomechanical resistance of the bone-implant union depends on the percentage bone-implant contact (%BIC) and the morphology of the adjacent bone 30 (thickness of trabeculae and presence of cortical bone). It has also been reported that maintenance of the cortical bone in the coronal area is highly favourable for subsequent load transmission2. Bone bed preparation by drilling causes adjacent bone necrosis with a width proportional to the heat produced, usually around 1 mm under normal drilling conditions3,4. The regeneration rate of this necrotic area affects the timing of implant loading and depends on the cellular and vascular state of the adjacent bone. Thus, the healing of this area was reported to be earlier in trabecular versus cortical bone because of the greater and more rapid vascular growth in the former4. In mandibular (types I and II) bone, drilling is the bed preparation procedure of choice. In maxillary (types III and IV) bone, however, the loss of tactile sensitivity produced by drilling may have undesirable effects, e.g. accidental entry into the sinus, bed over-preparation or the removal of scarce cortical bone indispensable for primary implant stability. These complications contribute to the high implant failure rates in type IV bone, reported to be 44% by one study5. Expanders or Oral Surgery 4 (2011) 30–34. © 2010 John Wiley & Sons A/S Cano et al. condensers are used for implant bed preparation to avoid drilling in poor quality bone and these adverse effects6. Reports on bone resorption patterns in the alveolar crest after dental loss7 have described atrophy of the maxilla with resorption of buccal cortical bone, producing a more horizontal than vertical loss. Restoration of the edentulous crest with implants frequently requires previous crest widening to obtain the desired functional and aesthetic outcomes. Four techniques are used for this purpose: guided tissue regeneration, onlay grafts, alveolar distraction and ridge expansion In the crest expansion technique, osteotomes (including the threaded type) are used to progressively widen the bone, permitting simultaneous implant placement8. There are two main approaches: one is trabecular bone condensation in the implant bed with no expansion or widening of the crest, while the other is a combination of bone condensation with crest expansion or widening (split crest), which may or may not be accompanied by a green-stick fracture of buccal cortical bone. Maintenance of the periosteum in place permits blood supply, holds fractured fragments in a stable position and forms a barrier against soft tissue migration, and it also contains bone progenitor cells9. We report the application of a novel crest expansion technique in two patients. It is performed in two stages in order to avoid cortical resorption due to periosteal detachment in buccal cortical bone of the alveolar crest (Fig. 1). Case 1 A 32-year-old female with posterior mandibular edentulism came for implant treatment. She had no systemic disease of interest. It was decided to place three implants in each posterior sector to support a fixed implant. Scarce horizontal bone availability (4 mm in coronal area) did not permit the predictable insertion of 4.5 mm implants. Consequently, a two-stage crest expansion technique was agreed with the patient. In the first stage, supracrestal incision and elevation of the buccal mucoperiosteal flap was followed by a sagittal corticotomy in the coronal area of the alveolar crest and a second sagittal corticotomy, but in a lower (basal) position and two vertical corticotomies in the buccal wall, using a contra-angle handpiece (Frios MicroSaw, Dentsply Friadent, Mannheim, Germany). The wound was closed with interrupted suture, followed by a 28-day interval for periosteal revascularisation of buccal cortical bone. In the second stage, a minimal mucoperiosteal elevation was performed. Adequate crest expansion Oral Surgery 4 (2011) 30–34. © 2010 John Wiley & Sons A/S Alveolar crest expansion Figure 1 Technique sequence: 1.1 coronal and buccal corticotomies; 1.2 flap closure; 1.3 revascularisation period; 1.4 flap reopening; 1.5 crest expansion without buccal detachment; 1.6 implant placement. was achieved without compromising cortical vascularisation by utilising a combination of scalpel, thin chisels and threaded osteotomes. Internal connection threaded screw implants were then placed (Xive, Dentsply Friadent, Mannheim, Germany), with diameters of 4.5 mm for the central implant and 3.8 mm for the other two. Implant sockets were made using a conventional drill sequence according to implant size. Implants were inserted by using a mechanical system initially and final turns were completed with a manual wrench. Immediate stability was evaluated clinically and all implants had insertion torque bigger than 25 N/cm. The gap was filled with coralline hydroxyapatite (Frios Algipore, Friadent, Mannheim, Germany). Individual fixed rehabilitations were cemented after a 3-month healing period (Fig. 2). Case 2 A 42-year-old male with posterior maxillary edentulism came for implant treatment. He had no systemic disease of interest. He had undergone maxillary sinus floor augmentation 4 months earlier. It was decided to place three implants in each posterior sector for subsequent implant-supported fixed rehabilitation. Predictable placing of 3.8 mm implants was not possible due to the scarce horizontal bone availability. 31 Cano et al. Alveolar crest expansion Figure 2 Mandibular case: upper-left, CT image showing alveolar width deficit; upper-middle, sagittal and vertical corticotomies; upper-right, crest expansion after 28 days with mucous membrane covering; lower-left, implants in place; lower-middle, space filling with coralline hydroxyapatite; lowerright, panoramic X-ray at 1 year. After supracrestal incision and elevation of the buccal mucoperiosteal flap, sagittal corticotomy was performed in the coronal area of the alveolar crest and another sagittal and two vertical corticotomies were performed in the buccal wall using a contra-angle handpiece (Frios MicroSaw, Dentsply Friadent). The wound was closed by interrupted suture and was followed by a 28-day interval to permit periosteal revascularisation of buccal cortical bone. In the second stage, minimal periosteal elevation was performed, and the desired crest expansion was achieved by using a combination of scalpel, thin chisels and threaded osteotomes without compromising cortical vascularisation. Internal connection threaded implants were placed (Xive, Dentsply Friadent, Mannheim, Germany), with diameters of 3.4 mm for the mesial implant and 3.8 mm for the other two. Implant sockets were made using a conventional drill sequence according to implant size. Implants were inserted by using a mechanical system initially and final turns were completed with a manual wrench. Immediate stability was evaluated clinically and all implants had insertion torque bigger than 25 N/cm. The gap was filled with coralline hydroxyapatite (Frios Algipore, Friadent, Mannheim, Germany). Soft tissue augmentation was achieved with a pedicle flap of 32 palatal connective tissue transposed to the buccal area. After a 3-month healing period, two splinted fixed rehabilitations were cemented in each posterior sector (Fig. 3). Discussion Bone expansion technique has become a genuine alternative to guided tissue regeneration procedures or onlay block grafts. The elasticity and compression properties of the bone create an optimal membrane for bone regeneration in the chamber left by the expansion. Onlay grafts are associated with a higher morbidity in relation to the donor site and with an elevated frequency of resorption, and they require the removal of fixation systems. Further advantages of the bone expansion method are the shorter overall treatment time and lower costs in comparison to the other approaches. The stability of the expanded fragment is of major importance for osteogenic differentiation. The displaced bone must remain anchored on basal bone by a bone pedicle (green-stick fracture) that facilitates fracture callus stability and osteoblastic rather than fibroblastic/centroblastic differentiation of undifferentiated mesenchymal cells. Stabilisation measures by Oral Surgery 4 (2011) 30–34. © 2010 John Wiley & Sons A/S Cano et al. Alveolar crest expansion Figure 3 Maxillary case: upper-left, sagittal and vertical corticotomies; upper-middle, expansion with threaded osteotomes after 28 days; upper-right, implants in place; lower-left flap of palatal connective tissue; lower-middle, flap suture; lower-right, clinical image of prosthodontic rehabilitation at 1 year. osteosynthesis or cover membrane are required in cases of fracture and high mobility of the displaced fragment. Some authors advocate this technique without periosteal elevation, favouring subsequent regeneration of the area, or without vertical osteotomies8,10,11. In our view, visualisation of fracture areas allows the implant position to be guided and reveals the spaces to be filled with graft material. Furthermore, vertical release osteotomies allow control over the site of the fracture. However, the expanded cortical is vascularised from the periosteum and not from the medullar. Consequently, this technique should not be performed in a single stage if the expanded fragment is very thin or highly porous. Revascularisation of the cortical bone should be permitted before expansion to avoid resorption of the buccal plate. As stated above, the heat and mechanical effects generated during bed drilling creates a necrotic area that delays peri-implant bone healing. Nkenke et al.12 compared BIC values between beds prepared with osteotomes and drilling in rabbit femoral condyles and reported higher values for osteotome-prepared beds at 2, 4 and 8 weeks after peri-implant healing, with a statistically significant difference at 2 weeks (55.0 ⫾ 7.1% vs. 29.2 ⫾ 4.8%). Fluorochrome studies also demonstrated an earlier and stronger signal for the osteotome technique. The predictability of the crestal expansion technique is supported by various reports on its medium-term clinical outcomes. Sethi and Kaus8 described a 5-year survival rate of 97% for 449 implants placed by Oral Surgery 4 (2011) 30–34. © 2010 John Wiley & Sons A/S crest expansion with osteotomes; interventions were performed without periosteal elevation, allowing vascularisation of fractured buccal bone areas. The periimplant bone healing period was around 6 months. Scipioni et al.13 reported a 98.8% 5-year survival rate for 329 implants placed with crestal expansion; flaps were partial-thickness and the healing time was 4–5 months. The drawback of single-stage techniques without periosteal elevation is the lack of control over the expansion and fracture areas, limiting the possibilities of widening as well as increasing the risk of fenestration and dehiscence. Scipioni et al.11 studied the histological characteristics of the bone formed in the post-expansion chamber, finding. At 40 days of healing, they reported an immature bone (possibly immature woven bone) with abundant presence of osteoblasts and osteoid formation; transmission electron microscopy revealed a predominance of collagen fibres with small deposits of calcium salts. At 90, 120 and 150 days they observed more mature bone (possibly immature parallel-fibre bone) and the appearance of osteocytes. At 480 days, they found organised mature bone (possibly laminar bone). References 1. Albrektsson T, Bränemark PI, Hansson HA, Lindström J. Osseintegrated titanium implants. Requirements for ensuring a long-lasting direct bone anchorage in man. Acta Orthop Scand 1981;52:155–70. 33 Cano et al. Alveolar crest expansion 2. Ivanoff CJ, Sennerby L, Lekholm U. Influence of initial implant mobility on the integration of titanium implants. An experimental study in rabbits. Clin Oral Implants Res 1996;7:120–7. 3. Roberts WE, Garetto LP, Brezniak N. Fisiología Y Metabolismo Óseo. 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