RESTORATION OF ALVEOLAR DEFECTS USING ALLOGENIC BONE BLOCKS

'Essentuki department of Stavropol State Medical University of the Ministry of Health of Russian Federation, Stavropol, Russian Federation. 2Department of General Dentistry and Pediatric Dentistry Stavropol State Medical University of the Ministry of Health of the Russian Federation, Stavropol, Russian Federation. 3The Peoples' Friendship University of Russia, 6 Miklukho-Maklaya St., Moscow, 117198, Russian Federation


Introduction
Bone deficiency in the maxillofacial region is a situa tion that the dental surgeon encounters on a daily basis in his office. Such conditions as: bone atrophy in the m axil lary sinus area, alveolar ridge, intraosseous defects of the jaws, cortical plate defects in the form of dehiscence and fenestration, furcation defects require some kind of bone augmentation [4,5,6,7,8,9].
We conducted a retrospective analysis of the treatment and rehabilitation of patients with partial and complete tooth loss in the conditions of alveolar bone deficiency. We analyzed 62 sources on the use of alloblocs for bone augmentation, published for the period from 2001 to 2018. This allowed us to summarize the information on this issue.
According to the classification of Cawood J. I. & How ell R. A. 1998 Grade 4 -6 alveolar ridge atrophy requires bone augmentation not only horizontally, but also vertically.
To date, a variety of forms and types of bone replacement materials have been proposed for the reconstruction of bone defects. For hard tissue replacement, in addition to autotis sues, materials of other origin are used. Allostomy, xenograft (denatured bovine or porcine bone), bioactive glass (coral structures), synthetic bone substitutes such as hydroxyapatite, tricalcium phosphate are possible alternative materials for use in hard tissue augmentation.
Although the use of the aforementioned bone substitutes is a routine procedure, it has become commonplace to write and say that autologous bone is the «gold standard» in bone augmentation.
Either extra-oral or intra-oral donor sites are used for au tologous bone donation. Typical extra-oral donor sites include iliac crest, parietal bone, tibia, and rib. On the one hand, the extra-oral donor sites allow for large bone acquisition, but on the other hand, such operations require general anesthesia and hospitalization, which makes it impossible to use such technologies in outpatient dental practice.
Bone harvesting from intraoral donor areas does not usually require anaesthesia and is perform ed on an out patient basis. The best known intraoral donor sites are the m andibular symphysis, the zone of the external oblique line of the mandible, the zygomatic-alveolar counterfort and the m axillary cusps. But taking from these areas in volves a number of difficulties. A complication in taking bone from the region of the subm andibular sym physis can be im pairm ent o f the tactile sensitivity in the chin region and cosm etic defects. Bone extraction from the area of the external oblique line is associated with the risk of m andibular nerve damage; in addition, the block itself is usually hom ogeneous, containing only cortical bone, which significantly limits the use of such a block. W hen bone is taken in the area of the zygomatic-alveolar buttress, the surgical risk is m inim al, but the volume is small for the reconstruction of defects longer than two teeth. The volume of bone taken in the cusp area is very limited and can only be used for small bone defects. In addition, taking bone in the cusp area leads to a deformation of the alveolar ridge in this area.
With any technique, the main disadvantage of autologous bone sampling is additional trauma to the patient. Reducing the invasiveness of surgical steps is especially relevant in elderly patients with comorbidities.  The aim of our work is to demonstrate the potential of allogen ic bone blocks for jawbone reconstruction in the rehabilitation of patients with partial and complete tooth loss.

M aterials and methods of the clinical study.
This study was based on a clinical analysis of the results of allogeneic bone blocks of 8 persons (4 men and 4 women) from 2010-2014.
The age of the patients ranged from 52 to 68 years. The patients suffered from one or another somatic pathology. In all cases, we used alloblocs in conditions of grade 4 alveo lar ridge atrophy (according to Cawood J. I. & Howell R. A classification). There were 4 patients with complete tooth loss, 2 patients with partial tooth loss, and 2 patients with single tooth loss.
In the preoperative period, clinical and laboratory exam ination of the patients was performed. X-ray examination of the teeth and jaws was performed (targeted intraoral pictures, orthopantomograms, computer tomograms with three-dimen sional image reconstruction).
The size of the used block was decided based on the sim ulation of the situation dictated by the conditions in the oral cavity and the condition of the bone tissue of the implant bed. For this purpose, the size and topography of the alveolar ridge defect, the degree of atrophy of the alveolar process, the type of bite, the shape of the occlusal surface, etc. were determined using models. In addition, the following parameters were evaluated during the examination with CT scanning: • the height and thickness of the alveolar processes of the jaws; • condition of the alveolar process of the maxilla in relation to the floor of the alveolar bay of the maxillary sinus; • condition of the alveolar process of the lower jaw in re lation to the upper wall of the mandibular canal bottom; • condition of the marginal regions of the alveolar process around the retained teeth; • the shape of the elements of the temporomandibular joint.
In the preoperative period, a thorough sanitation of the oral cavity and the necessary prosthodontic preparation were performed. In this case, the future location of the implant and its superstructure was taken into account and it was performed by the same team (orthopedic-dental technician) that performed prosthetics after the dental implant surgery.
After the investigations and determination of the diagnosis, a treatment plan was drawn up, including bone augmentation surgery, implantation followed by prosthodontic treatment.
Total and subtotal tooth loss is often accompanied by marked atrophy of the alveolar ridge. Bone loss in periodontitis or when the supporting teeth are overloaded with dentures is particularly intense.
A s an example, we present the following clinical case. Patient X, aged 63 years, came to us with complaints of loss of masticatory teeth in the lateral parts of both upper and lower jaw s, m obility of the rem aining teeth in the frontal parts of both jaws, failure of removable and fixed dentures. Tooth loss occurred during 30-35 years of life due to complicated forms of caries and periodontitis. Past m edical history -the patient suffers from hypertension II-III stages.
On examination: there is a bridge structure on the upper jaw with 1.3 to 2.2 teeth with supports on teeth 1.2 and 2.1. Partial removable plate denture. Mobility of teeth 1.2 and 2.1 of grade III.
On the lower jaw, from 3.3 to 4.4 teeth with all teeth supported by a bridge. Partial removable plate prosthesis. Degree II-III tooth mobility, crown destruction of teeth 3.3, 3.2 under the crowns (Fig.1, 2).
The study of alveolar ridges revealed a complete absence of alveolar ridge in the area of m axillary and mandibular molars, which corresponds to degree 5 of atrophy, the ridge width of 2-3 mm in the area of maxillary premolars -degree 4 of atrophy, in the area of remaining teeth bone deficit in the area of the walls of cavities.
The overall level of risk according to the SAC system (ITI recommendations, 2009), was considered by us to be high (Table 1).
Due to the presence of concomitant general somatic pa thology, the treatment plan was developed according to the principles of reduced invasiveness of surgical stages.
The following treatment plan was formulated:       m issing tooth 2.1 to 1.5 to 2 mm, in the area of the m issing tooth 23 to 5 mm.In the first segment, a provisional implant was placed in the area of tooth 1.3 and a provisional im plant in the area of tooth 1.1 (Fig. 4). Because the alveolar ridge was hourglass-shaped, there was a digiscence in the apical area (Fig. 5).
In the second segment a provision al implant was also placed in tooth 2.3 and a permanent implant in tooth 2.3. The alveolar ridge was augmented in the first and second segm ents using fragm ents o f allogenic bone blocks th a t w ere fix ed w ith m in i screw s (Fig. 6, 7).
The gaps betw een the g raft and the bed were filled with allo-and au tograft. The augm entation area was closed with a collagen membrane and sutures were applied. In the postop erative period, there was a moderate swelling of the soft tissues, analgesics were used for not more than 2 days, the patient felt satisfactory. One week after implant placement, a provision al fixed metal acrylic prosthesis was fabricated (Fig. 8).
Three months after augmentation, clinical and radiological signs of bone engraftment and osseointegration in the implant area 1.3 and 2.3 were observed. (Fig. 9,10).
Permanent implants were placed in the area of teeth 1.4 and 2.4. D uring implant placement, good engraftment of the bone block was observed with preservation of the volume and shape o f the augm entation. M ini screw s were removed during this operation (Fig. 11,12).
After an additional 3 months of os seointegration (Fig. 13), the implants in areas 1.4 and 2.4 were opened and a permanent bridge supported on implants 1.4, 1.1, 2.1 and 2.4 was placed.

Conclusions
The use o f allogenic bone blocks is indicated in cases o f pronounced atrophy o f b oth the upper and the lower jaw.
The use o f allogenic bone blocks significantly reduces the pain and du ration of surgical intervention due to the absence of the need for donor bone sampling.
s Fig. 10. Radiological follow-up 3 months after Fig. 11. Placement of the implant in the area surgery. Osteointegration in the area of the of tooth 1.4. permanent implants is detected.  The use of allogenic bone provides an opportunity to form bone blocks of any shape, for any part of the jaw.
The use of allogenic bone material and collagen membrane prevents early resorption of alloblocs.

Recommendations
The use of allogenic bone blocks requires a surgeon with the appropriate manual skills and a thorough understanding of the principles of bone tissue regeneration.
The use of allogeneic bone blocks requires careful preoperative planning.
Fixation of allogenic bone blocks should ensure their maximum stability and immobility in the augmentation zone.
Due to the probable resorption of the augmentate, it is necessary to introduce an excessive volume of particulated graft in the form of a mixture of allo-(xeno-) and autograft.
The mucosal-periosteal flaps should cover the augmentation area without tension. It is categorically not recommended to subject the augmentation area to any kind of stress in the postoperative period.
Implants should preferably be placed using a delayed protocol for allogeneic bone augmentation.

Conclusion
The use of alloblocs is the method of choice for rehabilitation of elderly patients with somatic diseases in alveolar ridge augmentation of the jaws in conditions of bone deficit.