Osseointegration of immediately loaded dental implants in the edentulous jaws. A study of the literature. Summary

Transcription

1 Osseointegration of immediately loaded dental implants in the edentulous jaws. A study of the literature. Johan Olsson, Nathon Stearns Institute of Odontology Karolinska Institute Summary Clinical studies have indicated the possibility of osseointegration following one-stage surgery and immediate loading of titanium implants in edentulous jaws. However, there is little long-term data comparing this method to the conventional two-stage technique. Based on these observations the objective of the present study was to describe the biology of osseointegration and the scientific background for the healing of implants prior to occlusal loading. The authors also present a study of the literature of new clinical methods for immediate loading in edentulous jaws as well as a description of these techniques. Literature for both the classic two-stage protocol, as well as immediate loading techniques, such as the LITORIM and Novum implant systems, were studied and their respective implant survival rates were compared. The results of the literature study indicate that the implant survival rate of the classic two-stage surgery and the delayed loading of implants can be used as the standard to which all other methods should be compared. The results of one-stage surgery and immediately loaded implants have been promising but have not achieved the same rate of success as the classic twostage protocol. The literature study demonstrated the need for more long-term clinical studies using a higher number of human test subjects in order to make any statistically significant conclusions. However, considering the debilitating nature of complete edentulism, both functionally and aesthetically, as well as the increasing number of elderly patients, immediately loaded dental implants may be thought of as the treatment of choice for those patients whom demand a quick and efficient treatment. Introduction Osseointegration i.e. the establishment and maintenance of a direct bone to implant anchorage grows from the experimental and clinical work by P-I Brånemark and collaborators during the 1960s (1,2). In 1977, they described their findings in the first long-term clinical report of tissue-integrated prostheses in completely edentulous mandibles (3). Characterisation of the direct functional and structural connection between living bone and the surface of a load bearing implant was confirmed by morphological studies (4-7). Since the beginning of the 1980 s dental implants have become a routine method for the rehabilitation of partly and completely edentulous cases (8-13). Approximately 6 % of the Swedish population aged are edentulous. Individuals between years of age have lost 5 teeth in average. Above 70 years of age, 75% have less than 10 remaining teeth (14). In the original two-stage surgical protocol, a two-piece dental implant is inserted at two separate surgical sessions with healing periods of 3-6 months in between. To minimise the risk of implant failure, the fixtures are kept load-free during the initial healing period and submerged under the oral mucosa. During healing a temporary removable prosthesis is used. At the second stage surgery, a cylinder penetrating the oral mucosa is 287

2 connected to the osseointegrated fixture. The final prosthetic suprastructure is then fabricated to fit these cylinder abutments. Including extractions of severely damaged teeth and healing after fixture insertion the full treatment may require up to 12 months before completed. Although the original two-stage surgical method remains the most reliable procedure for achieving osseointegration shown in numerous long-term clinical studies it would be beneficial for patients if the healing period could be shortened without jeopardising the final results. The traditional empirically based healing periods before loading of fixtures has therefore been questioned (15). Several reports have indicated that a one-stage procedure with delayed, early or immediate loading can provide satisfactory results (16). Manufacturers of dental implants hope that through these developments implants will become less expensive, reduce chair time and therefore more available and desirable to an increasing number of patients (17). In edentulous mandibles/maxillas there are several different methods of directly/immediately loaded implants. The NobelBiocare Novum concept is one example of directly loaded implants in patients who meet specific selection criteria (16). LITORIM (Leuven Information Technology-based Oral Rehabilitation by means of Implants) is another novel method, which uses data acquired from a spiral 3-D CT of the jaws to customise implant placement and optimise prosthodontic precision (18). These methods are still being clinically and scientifically evaluated. The objective of the present study was to describe the biology of osseointegration and the scientific background for healing of implants before occlusal load. New clinical methods for immediate load in edentulous jaws are described and the literature reviewed. Biology of Osseointegration The concept of osseointegration in oral implants was first described by P-I Brånemark in the early sixties. Although unaccepted at the time, it was later proven through the work of A. Schroeder that a direct bone to implant contact was possible (19). The direct connection of living bone to load bearing endosseous implants is defined as osseointegration. Healing of tissue defects have been analysed using a vital microscopic chamber technique. Initially, the defect is filled with a fibrin network, derived from plasma, which leaks from a damaged blood vessel at the defects edge. After 6 to 10 hours granulations cells are present in the wound. These cells send out cytoplasmatic projections while still moving in the fibrin network. 3 to 4 days after later erythrocytes perfuse the healing defect and thereby establishing an open circulation. In the next phase granulation cells stop moving in the wound and their projections connect with each other to form a cellular network, which is still perfused with erythrocytes from blood vessels. At the same time newly formed capillaries and finally, 5 to 6 days after the original defect, the wound is perfused by a large number of broad, winding, thin walled newly formed capillaries. Within 3 to 4 weeks these blood vessels will reduce in number and diameter, creating a characteristic capillary network for connective tissue (20). Into this capillary network, fibroblasts from the periosteum, endosteum and red bone marrow invade and produce a network of collagen. Into this network chondrocytes develop from osteogenic cells and begin to produce a fibrocartilaginous callus. This stage lasts for about 3 weeks. Osteogenic cells then develop into osteoblasts, which begin to produce spongy bone trabeculae and is referred to as a bony callus, which lasts for 3 to 4 months. In the final phase or after roughly 4 months, spongy bone is gradually replaced by compact bone around the periphery (21). The histologic description of bone includes lamellar bone, woven bone, composite bone, and bundle bone. The first three of these bone types are often found next to an osseointegrated dental implant (22). Composite bone is a combination of lamellar and woven bone, which 288

3 forms primarily on the endosteal and periosteal surfaces of cortical bone. Lamellar bone is the most organized, highly mineralised, and strongest of the bone types and is the most desired next to an implant (23). Woven bone is also called immature bone since it is unorganised, less mineralised, and has less strength than the other types. These histologic terms may be used to describe the microscopic bone types of cortical and trabecular bone (24). Anatomical congruence between bone and marrow tissue and synthetic components with continual remodelling of bone has been shown in clinical long-term studies to give a predictable prognosis without significant complications. Reliable stability is achieved through the incorporation of anchoring element in normal bone tissue in such a way that the functional load can be absorbed and is distributed in the surrounding tissues resulting in adequate bone remodelling. Penetration through skin or mucosa to allow a connection of the external prosthesis demands that a biological barrier can be established between external and internal environments in the anchoring region. An anchoring unit is constituted of a non-biological anchoring element as well as hard and soft tissue anchoring (24). Fig. 1: Schematic summary of the biology of osseointegration A. The screw-thread seats cannot initially be made to be congruent with the dental implant. The importance of the threaded implant is to create immediate stability after insertion and during the initial healing phase. (1) Contact between the fixture and bone (so called immobilization). (2) Hematoma in a confined cavity, which is bordered by the fixture and bone. (3) Bone, despite careful preparation is thermally and mechanically damaged. (4) Unmolested bone tissue. (5) Fixture. B. During the initial healing phase the haematoma is transformed into new bone through in situ bone formation. (6) Damaged bone tissue heals through revascularisation, demineralisation and remineralisation. (7). C. After the initial healing phase vital bone is in direct contact with the surface of the fixture without any intermediary tissue. (8) Border zone is remodelled in response to functional loading. D. In the case of osseointegration failure, non-mineralised connective tissue forms in the border zone in contact with the implant, (9) which can be considered a form of pseudoarthrosis. This situation can occur as a result of trauma during bone preparation, infections, early functional loading during initial healing phase, prior to adequate mineralisation and the organization of hard tissue, as well as later in the process, through supra-laminal loading, occasionally several years after initial osseointegration has been achieved (20). Factors of importance for initial healing and osseointegration Osseointegration is dependent upon four main factors: a biocompatible implant material, a high level of precision between the implant and the site of insertion in the bone, the use of surgical techniques which minimize traumatic tissue damage, the post-operative loading conditions. 1. The material selected for dental implants must not induce a host immune response. 289

4 Pathogens and allergens induce the host body to surround the foreign body with granulation tissue and a connective tissue capsule if it is not biologically inert. Titanium and certain calcium-phosphate ceramics are biocompatible and do not stimulate a foreign body rejection reaction. 2. Osseointegration is dependent upon the precision of the prepared bone site and the dental implant to be inserted. A large discrepancy in the gap between the implant and the host bone can lead to implant failure. A cylindrical preparation and precision instrumentation provide the most predictable outcomes of implant surgery. 3. Surgical techniques, which minimize traumatic thermal and mechanical damage aid in integration of the fixture. Temperatures over 47 C can damage osteocytes. An intermittent drilling technique, adequate saline irrigation as well as sharp burrs prevent higher temperatures. The experience and skill of the surgeon have an equally important roll in the end result. 4. The importance of allowing a healing phase from 3 to 6 months before functional loading with a permanent prosthetic replacement is considered optimal. It is thought, supported by recent research, that directly loading implants following fixture placement surgery provides equal levels of osseointegration and moreover may stimulate osseointegration and resist osteolysis (20). Primary stability Stability of the implant following surgery is most important determinant for osseointegration (25). During treatment planning it is important to ensure a sufficient number and spread of implants as well as the stability of adjacent teeth. It may be necessary to minimize or reduce occlusal tables. Rigid splinting should be used whenever possible. It is important to maximize the spread and distribution of contacts and to recheck the occlusion during the first days and weeks after immediate/early loading. Use the best positions for the permanent implants and place any provisional or reserve implants in the left over sites (17). Therefore rigid splinting of the prosthesis can provide an advantageous force distribution to all abutments. Some micromotion is thought to be beneficial by stimulating osteoblasts, but this micromotion should not be greater than 100µm while micromotion over 150µm is thought to be detrimental to osseointegration (25). The effect on cells from micromotion, termed strain, is the relative elongation of cells and is calculated by the ratio between the initial cell length and the final length obtained. Strain incurred during immediately loaded implants can stimulate bone healing similar to that of fracture healing where cyclic micromovements elicit a more physiologic pattern of tissue regeneration (26). The mechanical environment of strain or deformation of the bone cells largely determines the cellular behaviour of bone cells. It is speculated that the source of energy to open the ion membrane channels in the bone cell membrane is the microstrain in the cells as a result of the load applied to the bone. (24). It is thought that 2-stage surgery can apply rotational forces on the osseointegrated implants during prosthesis placement (27). The direction, magnitude and repetition rate of biomechanical forces can influence the modelling and remodelling processes in bone surrounding endosseous implants. Bone can resist rapidly applied loads and bone quality is increased under repetitive load forces. If the implant surface is titanium plasma-sprayed or hydroxylapatitite-coated, sandblasted, etched or etched-sandblasted can increase significantly bone metabolism with a resulting increase in implant-bone contact (28). Adequate initial implant stability is considered important for a successful outcome. Controlled occlusal loads for full arch cases and non-occlusal loads for short span bridges and single teeth replacements are considered important for a successful outcome. Site evaluation for bone density/volume and controlled infection and inflammation are considered important for a successful outcome (17). 290

5 Primary stability measurement Resonance frequency analysis (RFA) employs small Piezo-electric transducer, which may be attached to an implant fixture directly. The transducer is excited electrically and its response is measured as a function of resonance frequency and damping. However, there is insufficient data at the present time to provide definitive values of what are safe initial stability measurements. An insertion torque value between 30 to 50 Ncm before the implant is fully seated appears to provide required stability (17). Patient selection It has been suggested that patient selection for immediate/early loading is not significantly different than for conventional implant treatment protocols (17), which are listed below. Smoking has in recent publications been found to negatively affect the long-term prognosis of osseointegration as well as the marginal bone remodelling around the implants (29,30). Furthermore it has been reported that if the patient can stop smoking just during healing, the implant survival rate may improve (31). Systemic diseases such as developing cancer and AIDS should be taken into account. Even HIV positive patients ought not to be considered, as there may be future complications due to their impaired immunologic defence mechanisms, resulting in increased risk of infections and impaired healing around the implants (32). Infection is considered a risk factor for failures at immediate and early loading (17). In the case of diabetes, when there may be an increased risk for infection and reduced healing, it is still possible to perform implant surgery if the operation is carried out under antibiotic cover, and provided that diabetic condition can be controlled via insulin medication and/or via the diet (32,33). However, if unregulated diabetes is present, implant surgery should be avoided. Irradiation of the jaw may be another potential risk factor for implant treatment, specifically if the jaw has been exposed to irradiation over the level of 50 Gy, due to the risk of developing osteoradionecrosis (34). However, it has been suggested that with the use of hyperbaric oxygen treatment preceding implant therapy, the failure rate can be reduced from around 60% down to 5% (35). Deficient hemostasis and blood dyscrasias, such as hemofilia, thrombocytopenia, acute leukemia, and agranulocytosis, are situations, which present risks for bleeding or may limit the healing capacity of the tissues. If these conditions are suspected, the patient should be checked via laboratory tests. Anticoagulant medication or any medication leading to impaired hemostasis, such as ASA, may result in the extended pre- and postoperative bleeding as well as enlarged postoperative hematoma. If anamnestic information regarding such medication is at hand, test of coagulation and and/or primary hemostasia should be carried out, and the medication be interrupted, if implants are to be inserted (36). Knowledge of maxillary growth is important before considering implants in the young patients. The risk of alteration in the maxillary growth, as well as the functional and aesthetic facial complications, is considerable in the child. The long-term prognosis of an implant positioned in the child is very uncertain. It is advised to wait until the end of growth for the placement of dental implants in the young patient. Implants may be considered on average after 15 years in the female and after 18 years in the male (37). There is no upper age limit in implant placement patients (38), however, it is thought that there is a longer healing phase and in some patients a greater succeptability to infection (39,40). The minimum bone volume needed for standard implants (10mm long and 3.75mm in diameter) is where the bone height is 10mm and the buccolingual width amounts to at least 6 mm. When working above the inferior alveolar nerve, a minimum height of 12 mm is needed for a standard implant. If less height is present, no standard implant can be placed without damaging the nerve, as the drills extend about 2mm deeper than the length of the implant. In the buccolingual width a minimum of 1mm of bone around the entire fixture is required and 291

6 an interdental space of at least 7mm is needed. A minimum of 6mm is required between implants when more than one fixture is placed. Anatomical structures may limit the length of the fixture to less than 10mm, it is therefore recommended to use larger diameter implants or a greater number of implants to provide sufficient anchoring surface area (41). To compensate for lack of bone volume implants may be angulated or be placed in the zygomatic bone to achieve the desired bone anchorage. Bone grafts or bone augmentation surgery may be considered to increase bone volume prior to implant placement surgery. Bone is classified into 4 groups (42). Type 1 consists of mostly homogenous compact bone. Type 2 consists of a thick layer of compact bone surrounding a core of dense trabecular bone. Type 3 is a thin layer of cortical bone surrounding a core of dense trabecular bone and type 4 is composed of a thin layer of cortical bone with a core of low-density trabecular bone. Type 4 bone is by far the worst possible bone environment for implant placement because of inadequate stability and poor bone quality (43). A grading into five groups depending on the resorption rate has been presented for the residual jaw shape (42). Site evaluation for bone density and volume is important for a successful outcome. Low bone volume and density as well as poor bone quality are risk factors; in combination they seem to be the reasons for failures at immediately and early loading (17). During the radiographic examination, the location of important anatomical structures is very important prior to planning implant placement. The inferior borders of the maxillary sinuses, the foramen incisivum and the inferior limit of cavum nasi, the inferior alveolar nerve and the foramina mentale are important to locate both before and during surgery. Parafunctional habits such as bruxism, tongue pressing and teeth pressing can be considered contraindications for implant placement, especially in immediately loaded implants (17,44). For a successful treatment outcome the patient s cooperation is vital for both the biological aspects, such as osseointegration, and the completed prosthetic denture. The patient's expectations must be realistic and it is therefore important to carefully explain to the patient what is possible during the treatment planning stage (36). The surgeon should evaluate the clinical and radiographic information obtained whether suggested positions and directions are possible in the relation to the available anatomy. Possible obstacles for surgery must be identified, and alternative solutions suggested in case it turns out to be impossible to perform the first alternative during implant placement. The skill and experience of the surgeon will thereby be of importance, when having to improvise during the stage 1 operation. Ongoing oral pathologies must be resolved prior to implant placement surgery to avoid greater risks of complications. Psychological diseases may carry potential risks as well as such patients often have difficulty cooperating and/or lack interest in maintaining sufficient oral hygiene. They may also be using medication, which could interfere with the anaestesia needed during the surgical procedure. Surface Properties/Implant Design Several studies including in vivo experiments have reported that a better bone fixation (osseointegration) will be achieved with implants with an enlarged, isotropic surface as compared to implants with a turned unisotropic surface structure. In some studies a positive correlation was found between increasing surface roughness and degree of implant incorporation (45), while in other studies no such correlation was observed (19). Since the early 1980 s, several groups have attempted to improve implant surface properties by adding new materials on the surface, titanium plasma spray (TPS) or hydroxyapatite (HA) (46,47). Other types of surface processing have also been suggested, 292

7 such as sandblasting and acid etching (HCL-H2SO4, HF-NO3). The aim of these technologies is to improve the quality of osseointegration and to increase the implant surface area. Treatment of the implant surface is divided into two processes: the addition process and the subtraction process. The TPS and HA techniques alter the implant surface using additive processing. The aim is to optimise the biologic and physical characteristics of the bone-to-implant contact surface. The techniques using acid etching or sand blasting are subtractive processes that eliminate microscopic particles from the implant surface, thus creating an irregular morphology of the titanium. The subtractive methods increase the implant surface area without any contamination from added microparticles. Titanium can establish direct bone contact. It is not titanium itself, which is in direct contact with bone but rather the oxides, which are always present on its surface. It is therefore the oxide layer s biocompatibility, which is a determining factor in osseointegration. Contamination of the oxide surface layer decreases the level of ossoeintegration, which makes a contamination free handling of the implant absolutely necessary (48). The standard implant diameter is mm but may vary between 3mm and 6mm, dependent upon the manufacturer, and is to be used according to the location in the jaw and bone quality at the surgical site. The optimal length of dental implants is 10mm or longer but shorter implants may be indicated dependent upon anatomical structures, but with shorter implants there is a poorer prognosis (49). Screw thread design varies greatly by manufacturer but all are to increase fixture stability and induce osseointegration. Many types of screw design have been introduced claiming that substantive research to be unnecessary since the new designs are based upon the original well-documented Swedish Brånemark titanium implant. This reasoning is based on the opinion that oral implants represent generic products, a misconceived notion at this stage. The various look-alike implants differ from one another with respect to titanium composition, thread configuration, and surface topography (50). Indeed, the observed differences in surface topography alone are such that they will clearly influence the results in experimental studies. At present there is insufficient knowledge about what governs the incorporation of an oral implant and we lack a great deal of information about optimal composition of the biomaterial, the design and the surface finish of an implant. Therefore every oral implant must be supported by clinical documentation of the specific product without reference to any other implant of assumed similarity (51). Method for reduced healing periods and immediate/early loading of edentulous jaws Definitions of surgical protocols and loading schemes A. Surgical Protocols: Two-stage surgery: The first stage consists of fixture placement surgery and cover screw placement. Second stage surgery begins with the reflection of a mucoperiosteal flap followed by placement of a soft tissue-guiding abutment. A healing abutment, or in the case of immediately loaded fixtures, a final prosthesis is placed. One-stage surgery: consists of fixture placement surgery followed by healing abutment placement and gingival correction. In immediately loaded fixtures the healing abutment is replaced by the final prosthesis. B. Loading schemes: Delayed loading: The prosthesis is attached at the second procedure after a conventional healing period of 3 to 6 months. 293

8 Early loading: The prosthesis is attached during a second procedure, earlier than the conventional healing period of 3 to 6 months. Time of loading should be stated in days to weeks. Immediate/Direct loading: The prosthesis is attached to the implants the same day the implants are placed. (17). Brånemark Novum System This technique was specifically designed for edentulous mandibles with Angle Class I and Class III occlusal relationships with the finished prosthetic replacement affixed on the day of implant placement surgery. Class II occlusion may present with aesthetic and functional difficulties using this system. A minimum mandibular height of mm and a width of 6-7 mm are needed. A minimum of 50 mm vertical height is needed in order to obtain complete access to the oral cavity prefabricated surgical and prosthetic components are used in a predetermined precision protocol. Immediate and permanent loading is possible using a bar system for the rigid connection of the implants at the time of the implant placement. A prefabricated bridge framework eliminates the need for conventional impression procedures. The Novum System relies on a jig to ensure exact implant position with a prosthesis supported by a machined titanium superstructure that is placed the same day as the implants. Conventional pre-operative examinations, including clinical and radiographic assessments, are performed prior to treatment. As always a complete treatment plan includes the opposite jaw and any ongoing pathology in the oral cavity must be treated prior to implant surgery. Impressions are taken in both jaws to fabricate study models. Radiographic evaluation: A panorama radiograph, a profile radiograph as well as intra-oral radiographs are needed to judge bone quality, height, thickness, as well as to find the location of anatomical structures. Tomography is usually not needed. Before operating, the surgeon is recommended to carefully check the jaw form in the occlusal plane as well as in the profile. U-formed jaws are not expected to pose any major challenge (42). Jaws that are broad or straight between the mental foramina, or belong to shape group A, are also possible to treat, albeit with surgical precautions. The most difficult situation involves the narrow D-shaped jaw, which should be treated with extreme caution. Pronounced V-formed mandibles are currently regarded as contraindicated for the Novum System. The surgical protocol involves the following steps: sedation and local anesthesia, incision reducing the height of the alveolar crest, fixture placement, suturing and attaching the prosthetic substructure If necessary, the height of the alveolar crest is reduced on order to accommodate the prefabricated titanium bar and the three specially designed fixtures. The adaptation is performed with forceps and/or twist reamer drills under perfuse irrigation with the saline solution until the alveolar crest platform is approximately 6-7mm wide. The areas distal to the mental foramina must also be included to create room for the prosthetic supra-structure. Installation begins by placing the guide template over the jaw. The positions of the threeimplant sites are marked through the template holes in order to clarify whether fixtures can be inserted without thread exposure between the buccal and lingual sides of the jaw. Optimal positions of the fixtures in the middle of the crestal platform and between the two cortical plates are also assessed. The three sites are marked with a guide drill, which is then expanded using a 2mm twist drill aimed at the optimal direction in relation to the buccolingual surface and the opposite jaw. The evaluation template is used to evaluate the direction of the sites in relation to the anatomy. The positioning template or stent is attached to the mandible via guide pin placed in the two distal sites. The template is used to prepare the central site. 294

9 After the central fixture has been placed the V-template is loosely attached to the inserted fixture using a temporary screw. Stabilizing screws adjacent to the central fixture are attached. There should be no contact between bone and the template in the distal area of the template. The distal fixtures are now placed. When the bar to bone distance is acceptable the mucosa is contoured around the implants and sutured back into positions, using a resorbable suture material (3-0 monocryl). A silicon sheet is applied on top of the readapted soft tissues to protect and compress them during the initial healing period and to prevent edema formation. The sub-structure is attached permanently with lower bar screws starting with the central site and the tightening the distal screws alternately. The screws are tightened manually at first and then tightened by machine to 45 Ncm. After surgery the prosthetic protocol starts by checking the fit of the sub-structure to the fixtures. A prefabricated titanium supra-structure, the upper bar, is then temporarily attached to the sub-structure, the lower bar, with two titanium Unigrip prosthetic screws. A registration of jaw relations is made with a rigid, fast set silicone putty material or with wax in order to establish the correct vertical and horizontal dimensions of the jaws. The jaw relation index and the prefabricated titanium supra-structure are then sent to the dental laboratory for further processing. The patient is allowed to rest until the bridge is delivered later the same day. Early loading of dental implants In early loading of dental implants the technique is such that an incision is made in the gingiva under anaesthesia and the jawbone is exposed. Holes are then drilled in the jawbone and the fixture is then placed. In those cases where an abutment is needed it is then attached to the fixture. The gingiva is sutured back in place around the implant, which now will protrude a few millimeters over the gingival margin. A dental impression is taken directly after the operation. A dental technician then fabricates a prosthetic construction (crown or bridge), which is attached to the implants. During the following months the implants will osseointegrate in the jawbone while simultaneously they can have masticatory function as usual. In some cases a temporary bridge or crown is attached to the implants. The final prosthetic construction is fabricated and then attached following osseointegration. The time it takes for osseointegration to take place depends upon the jawbone quality and the implants surface properties among other things. It often takes longer time for implants to osseointegrate in the maxilla than in the mandible (especially between the metal foramina) because the maxilla is comprised of more spongious bone (52). Leuven Information Technology Based Oral Rehabilitation by Means of Implants (LITORIM) Encouraged by reports indicating that early and immediate loading can result in osseointgration, a new approach has been developed, based on a high-precision threedimensional (3D) computer tomographic (CT) image implant planning system which is applicable in both jaws (53,54). The LITORIM concept was developed in order to provide patients with edentulous jaws with a complete fixed denture at the same time that a flapless dental implant surgery is performed. The process begins with a CT-scan of the patients jaw. Then a CT-scan is taken of the prosthesis with an x-ray contrasting material, such as gutta percha, to provide reference coordinates. The two images are then fused together using a 3D-software package. The combined image allows a virtual reality model displaying the patients bone anatomy and future prosthetic design. It is then possible to ascertain optimal implant placement and implant length. Using Procera technology the dental technician can then produce a surgical guide template for the surgeon as well as the completed fixed denture. Therefore, both the surgeon 295

10 and the dentist have all that they need in time for the surgical procedure. After placement and adaptation of the drill guide on the alveolar crest, three horizontal fixation pins are drilled into the jawbone. A drill is used to remove the gingival tissue at the sites of implant placement. Implants are placed on each side of the arch to provide stability during the placement of the rest of the fixtures. To prevent soft tissue collapse around the installed implants, fixture mounts are placed. The template can now be removed. The elapsed time to this point has been less than one hour. Abutment placement is done at the same time as final prosthesis placement. The most important aspect of the procedure is the correct placement of the surgical template. The framework of the prosthesis is made of fibre-reinforced carbon that provides more rigidity than steel and is important for the uniform loading of the implants. Uniform loading is essential in immediately loaded implants. The first human patient to undergo the LITORIM surgical protocol was in 1998 and since then 120 patients have undergone the LITORIM implant procedure. Up to this date, there have been 2 failures in which the fixtures have failed to osseointegrate. A larger study is now underway to evaluate this procedure. The advantages of the LITORIM concept is: less chair time for the patient, roughly 4 hours compared with 9 for a classic treatment; the surgery can be meticulously planned; a higher level of precision is achievable with CT-scan radiography; the surgery is flapless which means a less traumatic procedure for the patient; all information is digital and can therefore be easily transported from one location to the other. Reduction in costs for the patient is difficult to determine. There is less chair time for the patient but a more complicated and thorough planning and examination stage as well as more advanced technology involved (30,55). It has been impossible to assess how well the implants have achieved osseointegration, since this would require removal of the cemented prothesis to check for immobility of the unconnected implants (56). The use of screw-retained prosthetic bridges, however, does allow the prosthesis to be removed and stability of the fixtures to be ascertained at a later date. Results Success Criteria Albrektsson et al in1986 evaluated whether a dental implant is osseointegrated into the bone and suggested certain success criteria. They are as follows: clinically immobile, no associated pain or sign of infection, no peri-implant radiolucency is present, marginal bone loss does not exceed 1 mm after the first year and 0.2 mm in the following years (57). Failing Implant Biological failure can be defined as the inadequacy of the host tissue to establish or maintain osseointegration. Such failures can further be divided chronologically into early, or primary failures (failure to establish osseointegration i.e. an interference with the healing process) and into late, or secondary failures (failure to maintain the established osseointegration i.e processes involving a breakdown of osseointegration). One way to chronologically discriminate early from late failures may be to confine all implants removed before bridge insertion (or after an "appropriate" healing period) to the group of early failures. Similarly, all failures occurring after the prosthetic rehabilitation may belong to the group of late failures (58). Early failures occur within weeks to a few months after implantation and late failures, which occur much later (8,9,10). According to another source implant failure may occur at three distinct times. 1) At the time of, or shortly after the stage two surgery, 2) approximately eighteen months after stage 296

11 two surgery, and 3) more than eighteen months after stage two surgery. A few implants will fail to integrate. This failure will be identified at the time of, or shortly after stage II surgery. Failure in this period may be related to a variety of factors. Overheating of bone during placement or failure to achieve a precise implant fir with primary stability may lead to failure of integration. Postoperative infection, excessive pressure on the integrating implant with movement of the implant, or wound-healing problems may also jeopardize implant integration. After loading the prosthesis, bone loss will occur for approximately eighteen months after which a steady state will be achieved. During this eighteen months period, additional implant failure may occur (59). Failure during this period is often associated with excessive biomechanical forces on the implant or compromised peri-implant soft tissue health resulting from lack of attached tissue, poor hygiene, or both. Smoking is also associated with increase failure in this period and later periods (29). Later failure (i.e., more than eighteen months after placement of the prosthesis) may also occur. Results of published reports The traditional method of establishing osseointegration through a non-loaded healing period of between 3 to 6 months has been met with a high degree of success (3,8,60). The fifteenyear cumulative survival rate of 99% (61), obtained when a 2-stage protocol is used, can be the standard to which all other methods can be compared. In the classic two-stage technique, a stress free healing period is considered to increase the possibility for the fixtures to ossointegrate into jawbone (5,7,8). This treatment method has been well documented in a large number of scientific articles, and has been shown to be very successful with patients whom are totally edentulous (9,11,62,63,64). There is much interest and discussion regarding the efficacy of placing cylindrical implants in a single surgical phase and loading them at the time of implant placement. It has been concluded, based on the results of several studies that the immediate loading of multiple implants rigidly splinted around a completely edentulous arch can be a viable treatment modality (65,66,67). Another clinical study demonstrated that it is, at least on an 18-month observation period with a 100% implant survival rate, possible to successfully load titanium implants immediately following installation via a cross-arch supraconstuction and recommended such an approach be limited to the inter-foramina area of the edentulous mandible only (68). However, in one study the ten-year survival rate of immediately loaded implants was 84.7% and 100% survival rate in submerged implants (69). The author of that study concluded that although mandibular implants can be successfully placed into immediate function in the short term, however, the long-term prognosis is guarded for those implants placed into immediate function distal to the incisor region and therefore be submerged during a three month healing period (69). Except in two cases reported (70), posterior mandibular placement has been avoided in most studies because of poor bone quality in this region was expected to result in high failure rates (65). According to Aparicio et al 2003, immediate/early loading of the full arch mandibular fixed prosthesis and overdentures supported by implants placed in healed sites are accepted clinical procedures with adequate clinical documentation (17). Maxillary bone is, in contrast to the interforamina region of the mandible, frequently characterised by lower density. In fact, in a 3-year follow up study (71), the implant failure rate was 3.3% in the case of mandibular implant-supported overdentures, whereas it was 27,6% for maxillary overdentures. The results from one study of edentulous maxillas with implant supported fixed prostheses showed an implant survival rate of 93.4% after one year of loading (72). Following extraction of the remaining anterior mandibular teeth, 18 Brånemark implants, including two zygomatic and two pterygoid implants were installed in both arches and a screw-retained prosthesis was placed for immediate loading. Only 1 of 18 immediately 297

12 loaded implants failed to osseointegrate three years after completion of treatment (73). In another study using flapless surgery, three-dimensional soft tissue and bone models, a survival rate of 94% was achieved with splinted immediately loaded implants in the maxilla (74). Several studies have not only reported on edentulous mandibles but also on immediate loading on edentulous maxillae (65,75,76,77). Tarnow and coworkers (Tarnow et al 1997) inserted a minimum of ten Brånemark system implants per jaw, of which at least five implants were used for immediate loading. There 1- to 5-year results revealed a 97% implant survival rate, independent of jaw type. They, therefore, stated that by using the wide anteriorposterior distribution of the implants in order to resist critical micro-movements of the implants, it is possible to achieve the same good success rate in the maxillae as in the mandibles (65). Although these results are promising, the possible application of immediately loaded implants in the maxilla has to be further investigated (78). Discussion It has been shown that immediate loading of dental implants, even in the posterior regions of the jaw bones, hadn t caused untoward effects on the formation of the mineralized tissues at the interface, producing, on the contrary, a higher bone-implant percentage than in submerged implants, and thus, immediate loading can be a possible alternative procedure in implant dentistry (79). The classic 2-stage protocol is associated with long treatment time and high treatment costs, and elimination of the healing period offers advantages in terms of cost of treatment and convenience to patients (80), and avoiding the need for complete dentures while undergoing implant therapy can be a distinct advantage. Complete dentures may create functional and psychological problems (81). It has been reported that, with immediately loaded implants, patients resumed function quickly and that masticatory function was uniformly judged to be superior to pretreatment time. Any reduction in the number of the surgical procedures necessary or a decrease in the healing period is certainly very well welcomed by clinicians and patients (82). In the posterior areas of the jaws, and especially in the maxilla, several demanding preconditions require considering insufficient bone volume, poor bone quality, and high functional forces. When immediately loaded implants reach a state of osseointegration clinically, they have a long-term predictability similar to those of conventionally loaded implants (83). Moreover, immediate loading shortens the total rehabilitation time, with an increased patient satisfaction and the avoidance of delays in the final rehabilitation with the accompanying difficulty of wearing the conventional denture during the healing phase. Rigid splinting and minimal lateral forces are critical factors for success (81,83). Primary stability is a key factor in the success of immediately loaded implants because a high degree of primary stability helps to resist micromotion. Micromotion is the relative movements between the implant surface and the surrounding bone during functional loading. The surface of the implant plays a relevant role in implant long-term success, particularly in very demanding situations such as immediate loading in posterior jaw regions. The roughened surface of the implants helps to stabilize the initial blood clot and wound against the titanium surface, and that results in an enhanced bone-to-implant contact (84). Moreover, this surface may stimulate cell differentiation of osteoblast like cells, and the larger dimensions of roughness created by the sandblasting may provide pockets of bony in-growth that may function as a series of mini-retentive grooves (84). Several studies have reported a higher bone-to-implant contact percentage from immediate loading implants compared to classical implant loading schemes (85). These results could be explained by the fact that functional loading stimulates bone apposition. Wolff formulated his theory according to the idea that there is a direct link between mechanical loading and bone 298

13 formation. Wolff s law would imply that increased stresses act as a stimulus for new bone formation while reduced stress tends to produce bone loss (86). It must, however, be borne in mind that the number of specimens studied in most clinical studies of immediate loaded implants are too small to draw definitive conclusions on the influence of loading in the peri-implant bone response. Additional studies, with a larger and significant number of implants, are certainly needed (79). The level of scientific knowledge supporting one-stage immediately or directly loaded dental implants is insufficient (52). The LITORIM system offers the advantage of providing optimal aesthetics and phonetics utilizing a custom fit approach. However, in contrast to the Brånemark Novum system, where both surgical and prosthetic hardware are standardized and prefabricated, the LITORIM approach uses custom fit prefabricated hardware. The technology is not in the stage that makes a proper comparison between the two systems possible (55). Indeed the two-stage approach will be difficult to match considering the documented fifteen year 99% cumulative success rates obtained with the screw type machined implant configuration (61). However, the treatment option under consideration (LITORIM) could be used for patients in whom the number of surgeries should be limited because of general health problems, or for those who need an expedited oral rehabilitation for personal reasons. (55). In the course of evaluating the current literature available on immediately loaded dental it is important to consider that the literature published on immediately loaded dental implants is often based on animal research rather than on human test subjects. The research that has been performed on humans has included too few test subjects and with too few implants. Furthermore, the length of the studies on immediate loading longitudinal has not been longer than 5 years. It is, therefore, difficult to draw any statistically significant conclusions based on the human research or make any correlations from research on animal subjects to humans. Longitudinal studies with control groups in order to examine if complications can occur in the long-term with immediately loaded implants (87). Many consider complete edentulism to be a handicap, both functionally as well as socially. Therefore, immediately loaded dental implants can be thought of as the treatment of choice for patients with demands for a quick, efficient treatment, as well as the elderly and disabled, whom several treatment sessions may be impractical or whose general health may deteriorate more rapidly. Recently in Sweden, a program of subsidizing fixed prosthodontic treatment for pensioners has increased demand for dental implants. Taken this into consideration, dental implants will most likely only increase in demand in the future. This new policy may convince many general practice dentists to perform dental implant surgery in order to offer their patients a broader range of treatment. This program of subsidization will only fund implant treatment in the mandible and maxilla where the fixtures are placed between the mental foramina in the mandible or mesial to the second premolar region in the maxilla, those distal to these regions are paid for completely by the patient. Therefore, a fewer number of fixtures may be placed which then may lead to lower survival rates in both jaws. Although LITORIM may become the new standard in treating patients with complete edentulism, it is still relatively unproven, technically complex, and potentially expensive to acquire the necessary equipment. 299

14 Acknowledgements We wish to express our sincere gratitude to our supervisor Margareta Hultin who helped us with our literature study, and to Professor Björn Klinge for allowing us to observe the LITORIM surgery at the Karolinska Institute, Institute of Odontology, Huddinge. References 1. Brånemark PI, Adell R, Breine U, Hansson BO, Lindström J, Ohlsson A. Intraosseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg 1969;3: Brånemark, PI. Osseointegration and its experimental background. J Prosthet Dent 1983;50: Brånemark P-I, Hansson BU, Adell R, Biene U, Lindström J, Hallen O, Öhman A. Osseointegrated implants in the treatment of the edentulous jaw: Experience from a 10-year period. Scand J Plast Reconstr Surg 1977;2(suppl. 16): Schroeder A, van der Zypen, E, Stich, H, Sutter F. The reactions of bone, connective tissue, and epithelium to endosteal implants with titanium-sprayed surfaces. J Maxillofac Surg 1981;9: Albrektsson T, Brånemark PI, Hansson HA, Lindström J. Osseointegrated titanium implants. Requirements for ensuring a long-lasting, direct bone-toimplant anchorage in man. Acta Orthop Scand 1981;52: Albrektsson T, Hansson H.A., Ivarsson B. Interface analysis of titanium and zirconium bone implants. Biomaterials 1985;6: Albrektsson T,Hansson HA. An ultrastructural characterization of the interface between bone and sputtered titanium or stainless steel surfaces. Biomaterials 1986;7: Adell R, Lekholm U, Rockler B, Brånemark PI. A 15 year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10: Adell R, Eriksson B, Lekholm U, Brånemark P, Jemt T. A long-term follow-up study of osseointegrated implants in the treatment of the totally edentulous jaws. Int J Oral Maxillofac Implants 1990;5: Albrektsson T, Dahl E, Enbom L et al. A swedish multicenter study of 8139 consecutively inserted Nobelpharma implants. J Perodontol 1988;59:

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