FACULTY OF ORAL AND DENTAL MEDICINE CAIRO UNIVERSITY AMIRA ALI AHMED ZAIED THESIS SUBMITTED TO B.D.S 1997-M.SC 2006

Transcription

1 VALIDITY OF COMPUTER GUIDED BONE DENSITY MEASURE MENT AS A PREDICTOR FOR IMME DIATE LOADING OF MAXILLARY DENTAL IMPLANT THESIS SUBMITTED TO The Faculty of Oral and Dental Medicine, Cairo University in partial fulfillment of the requirement of doctoral degree in Oral and Maxillofacial surgery BY AMIRA ALI AHMED ZAIED B.D.S 1997-M.SC 2006 FACULTY OF ORAL AND DENTAL MEDICINE CAIRO UNIVERSITY 2012

2 SUPERVISORS DR. HATEM ABDUL RAHMAN PROFESSOR OF ORAL AND MAXILLOFACIAL SURGERY FACULTY OF ORAL AND DENTAL MEDICINE CAIRO UNIVERSITY DR. AHMED ABDEL MONEM BARAKAT PROFESSOR OF ORAL AND MAXILLOFACIAL SURGERY FACULTY OF ORAL AND DENTAL MEDICINE CAIRO UNIVERSITY DR. SAMEH TAREK MEKHEMER PROFESSOR OF ORAL AND MAXILLOFACIAL SURGERY FACULTY OF ORAL AND DENTAL MEDICINE CAIRO UNIVERSITY DR. ASHRAF ABDEL MONEM AMER PROFESSOR OF PROSTHODONTICS FACULTY OF ORAL AND DENTAL MEDICINE CAIRO UNIVERSITY

3 L I S T O F F I G U R E S FIG (1) FIG (2) Showing Muco-periostium covering edentulous area was free form any signs of inflammation, ulceration or scar formation Preoperative screening digital panoramic radiograph showing tracing of vital structures and preliminary treatment plan FIG (3) Showing the study models. 32 FIG (4) Showing the waxing up. 32 FIG Showing the vacuform stent constructed on the waxed up model 32 (5 a & b): FIG (6) Picture showing radiopaque acrylic resin in place of missing 33 teeth& the reffex is fixed on the stent FIG (7) Showing the locations of titanium master pins 33 FIG (8) showing that the accepted denture was duplicated using 34 laboratory duplication silicone (putty consistency) FIG (9 ) showing the replica produced is a patient radio-opaque denture 34 and that is could be used as a radiographic stent FIG (10) showing the stent constructed then poured by stone to get the cast that would be seated on the conagyx machine 34 FIG(11) showing Gonyx machine prepared so that all the angels adjusted 35 precisely in( zero degree FIG(12) Showing the mounting table carrying the study model depending on the orientation of 35 the pins three titanium pins. fig (13) showing the study model fixed in position to the mounting ring using 35 plaster of paris. fig (14) showing Radiographic stent after trimming, finishing and polishing 35 FIG (15) showing that Data were uploaded to the work station for inter active manipulation in dental C.T program 36

4 FIG(16) FIG (17) FIG (18) FIG (19) showing that the patient data was visualized as cross-sections in userdefinable directions, and visualized as 3D renderings, together with the grayscale values. showing a series of points along the dental arch were selected to define the panoramic curve. This was used to generate a panoramic view showing cross-sections of CT data and implants renderings of anatomy with implants. showing that Implants shown in all viewports where modification of location and orientation are carried out FIG (20) showing that the mean bone density value of each implant 40 recipient site was recorded in Hounsfield units (HU) at fixed distance 1 mm around the whole implant length. FIG (21) showing that the reference pins were marked and the implant 41 was localized in the reference to those registered pins FIG (22) showing that the readings of an implant to be adjusted on the 41 gonyx machine FIG (23) showing that After the gonyx machine adjusted to the required 42 readings; start drilling trough the stent fabricating the surgical stent, FIG (24) showing holes in the surgical stent to guide orientation and position 42 FIG (26 ) showing the surgical stent was seated in place 43 FIG (27) showing that Drilling was started using the pilot drill guided by the 43 surgical stent to create the osteotomy hole FIG (28) ) showing Placing the parallel pin to check the orientation 44 FIG (29) ) showing The osteotomy hole was enlarged to the planned size using sequential 44 drilling FIG (30) ) showing The fixture 1 was placed in its prepared osteotomy 44 FIG (31) showing that the torque increasing by hand device in 5 Ncm increments until total implant insertion 44

5 FIG (32) showing)that the resonance frequency values are automatically converted into an arbitrary index called implant stability quotient (ISQ). 45 FIG (33. A) showing implants in place in the day of surgery 47 FIG (33.B) showing healing abutment inserted until the prosthetic parts needed to be 47 adjusted FIG (34 ) showing the impression coping was snapped on with caps 47 FIG (35) showing the impression was taken using the appropriate materials 47 FIG (36) ) showing the position of the abutment transferred using the snap-on coping 47 FIG (37 ) showing that the abutment is placed and secured with a screw and torqued if 48 required by the manufacturer FIG (38) ) showing Provisional prosthesis were cemented temporarily 48 FIG (39) ) showing Finalize abutment preparation 48 FIG (40) ) showing Metal try in patient mouth. 48 FIG (41 A) showing Patient mouth before implant insertion 48 FIG (41 B) Patient mouth after cementation of final restoration 48 FIG (41C) showing Pre-operative Panorex Radiographic picture 49 FIG (41 D) showing Post-operative Panorex Radiographic picture(12 months) after immediate loading 49 FIG (42A&B) showing standardized Intraoral radiograph immediately after loading with provesional restorations and with the definitive prosthesis. After 1- year 50 Figure (43) Bar chart representing implant site distributions in males and females 53 Figure (44) Bar chart representing bone density in anterior and posterior maxilla 54 Figure (45) Bar chart representing insertion torque in anterior and posterior maxilla 55

6 Figure (46) Scatter diagram showing positive (direct) correlation between torque and density 55 Figure (47) Scatter diagram showing positive (direct) correlation between density and implant stability quotient (ISQ) of all surfaces 56 Figure (48) Scatter diagram showing positive (direct) correlation between torque and implant stability quotient (ISQ) of all surfaces 57 Figure (49) Scatter diagram showing positive (direct) correlation between torque and density in anterior maxilla 59 Figure (50) Scatter diagram showing positive (direct) correlation between torque and implant stability quotient (ISQ) in anterior maxilla 59 Figure (51 ) Scatter diagram showing positive (direct) correlation between density and implant stability quotient (ISQ) in anterior maxilla 59 Figure (52) Scatter diagram showing positive (direct) correlation between torque and density in posterior maxilla 61 Figure (53) Scatter diagram showing positive (direct) correlation between torque and (ISQ) in posterior maxilla 61 Figure (54) Figure (55) Scatter diagram showing positive (direct) correlation between density and (ISQ) in posterior maxilla Bar chart representing amount of bone loss around implants with immediate or delayed loading 61 62

7 INTRODUCTION T he use of dental implants in oral rehabilitation has currently been increasing since clinical studies with dental implant treatment have revealed successful outcomes. The successful outcome of any implant procedure requires a series of patientrelated and procedure-dependent parameters. The volume and quality of the bone, which determine the type of surgical procedure and the type of the implant, are associated with the success of dental implant surgery. Mechanical & Physiologic behaviors of the bone are important factors in the successful osseointegration, several classification methods were suggested for assessing the Bone Quality. However, many studies have included the evaluation of bone quality either at the time of osteotomy preparation or subsequent to implant insertion, which may provide valuable knowledge of the bone density but their benefit to both the clinician and the patient is limited because osteotomies have already been completed or implants have already been placed. To remove the above limitations, a method using computerized tomography (CT) scans for pre-operative quantitative assessment of dental implant patients that is more objective and reliable has been developed. P R I M A R Y STABILITY having a basic role in successful osseointegration is a function of local bone quality and quantity, the geometry of an implant, and the placement technique used. Non-invasive clinical test methods (i.e., insertion torque, the periotest, vibration methods) and invasive research test methods (i.e., removal torque) are available for implant stability measurements. The insertion torque method, which records the torque during implant placement, provides valuable information about the local bone quality. 1

8 Another quantitative method is the resonance frequency (RF) analysis technique where the implant stability is recorded using a machine and a transducer including piezo-ceramic elements. In implant dentistry, an undisturbed healing period was always required to ensure osseointegration. A modified protocol with Early or Immediate Loading has been tested to satisfy the demand of more rapid treatment and to reduce discomfort of wearing removable appliances during the healing period. in addition, elimination of the healing period offers advantages in terms of cost of therapy. O n e - S t a g e surgical procedures and immediate loading of implants at the time of placement have shown promising clinical results. Immediate /e a r l y loading procedures have been applied to rehabilitate the edentulous mandible with high predictability and have shown their success, especially in fixtures that were connected with cross-arch appliances. I M M E D I A T E LOADING of implants supporting a full arch prosthesis in the edentulous maxilla also showed high success rates, similar to those using standard 6-month osseointegration protocols. Provided that the implant has primary stability, studies have shown that the survival of loaded dental implants can be analogous to the unloaded protocol. Although there are many studies utilizing Ct for Assessing Bone Quality And Other Clinical Studies On The Relationship between Ct Values and Initial Implant Stability, the clinical studies evaluating the correlations between the bone densities, implant stability parameters and early loading protocol outcomes are few. However the study was conducted in promising era for prediction of the successes rate of the implant before implant insertion, it will satisfy the demands of both clinician and the patient 2

9 T H I S C L I N I C A L S T U D Y A I M E D T O Determine the bone density in dental implant recipient sites using computerized tomography (CT) and a specialized implant planning computer soft ware. Evaluate a possible correlation between bone densities and implant stability parameters (fastening torque and the resonance frequency analysis measures). Establish a lower threshold value of bone density for immediate/early loading protocols in maxilla. 3

10 R E V I E W O F L I T E R A T U R E The implant-supported oral restoration has become an increasingly used treatment option for edentulous and partially edentulous patients with successful outcomes. (1, 2) Even in patients with severe bone atrophy and in locations previously considered unsuitable for implants, implant treatment has been made possible through sophisticated reconstruction techniques, including sinus augmentation, distraction osteogenesis, bone grafting, and tissue regeneration.(3-5) The successful outcome of any implant procedure requires a series of patientrelated and procedure-dependent parameters. (6) The quality and the volume of bone available are highly associated with the type of surgical procedure and the type of implant, and both of these factors play a vital role in the success of dental implant surgery. (7) Historically, dental surgeons tended to place implants where the greatest amount of bone was present, with less regard to placement of the definitive restoration. The clinical outcome and long-term prognosis of implant-supported oral restorations largely depends on the stable and firm fixation of dental implants in the bone. However, disregarding prosthetic demands often leads to a compromised definitive prosthesis with a jeopardized occlusal scheme, poor esthetics, or unfavorable biomechanics.(8,9) More than 30 years of experience have refined the material involved as well as the planning and surgical procedure, a philosophy of prosthodontic-driven implant placement has been adopted as a treatment modality that combines functional and esthetic concepts. (10, 11) In prosthodontic-driven implant placement, diagnostic casts and the diagnostic wax-up of the prosthodontic restoration guide the planning of the positions of the proposed implants. To precisely transfer the plan to the operative site, customized radiographic and surgical templates have become a routine part of treatment.(12-15) 4

11 Conventional dental panoramic tomography and plain film tomography are usually performed with the patient wearing a radiographic template with integrated metal spheres at the position of the wax-up. Based on the magnification factor and the known dimensions of the metal sphere, the depth and dimensions of the implants are planned. However, radiography, which is widely used, has important diagnostic limitations, such as expansion and distortion, setting error, and position artifacts. Radiography does not show blood vessels or provide complete 3-dimensional (3D) information of the dental arch.(16,17) Although conventional surgical templates will allow guiding the bone entry of the drill, they do not provide exact 3D guidance. The templates are fabricated on the diagnostic cast without knowledge of the exact anatomy below the surface. Thus, when conventional implantation techniques are used, the clinical outcome is often unpredictable, and even if the implants are well placed, the location and deviation of the implants may not meet the optimal prosthodontic requirements. To overcome these limitations, computed tomography (ct), 3d implant planning software, image guided template production techniques, and computer- aided surgery have been introduced.(16-20) In CT, multi-planar reformatting (MPR) allows one to reformat a volumetric dataset in axial, coronal, and sagittal cuts and to build multiple cross-sectional and panoramic views.21 Shaded surface display (SSD) and volume rendering methods generate 3D reconstructions of the complete dental arch and relevant structures, including nerves. These advantages make dental CT the most precise and comprehensive radiologic technique for dental implant planning.( 21) Special Planning Software has been adapted to allow practitioners to virtually plan location, angle, depth, and diameter of virtual implants, which are superimposed on the 3D data set. Following backward planning, the diagnostic wax-up has to be visualized on the CT scan through radiographic templates.(22) 5

12 The Radiographic Templates are fabricated based on the desired prosthetic end result and is supported with different radiopaque markers such as gutta percha balls and stripes,metal pins and tubes,radiopaque varnishes, or lead foil.(23) Based on the information of the visible wax-up, dental implants are planned on the CT data with respect to vital structures such as the mandibular nerve, the maxillary sinus, and the roots of adjacent teeth. Different approaches to image-guided dental implant placement have been introduced to precisely transfer the planning data to the operative sits Mechanical Positioning Devices or drilling machines convert the radiographic template to a surgical template by executing a computerized transformation algorithm CAD-CAM (computer-aided design/computer-aided manufacturing)(24) Rapid Prototyping Techniques generate stereolithographic templates.(25,26) Bur Tracking allows for intra-operative real-time tracking of the drill according to the planned trajectory.in addition, surgical microscopes and head-mounted display are used to project the virtual plan into the real optical path; the displayed target structures are then followed with the bur drill.(27) Bur tracking and image-guided template production have been clinically tested and are on the way to being established as routine clinical treatment options.(28) In evaluating the precision of transfer of a computer based three-dimensional plan for dental implants, the most frequently used method is the matching of the pre- and postoperative CT scans. In most reported cases, this method was applied in experimental studies conducted with human cadaver mandibles to evaluate the accuracy of computer-aided surgery systems.(29,30) Recently published studies with matching of pre- and postoperative CT scans indicate that the use of computer- aided surgical techniques result in an average 6

13 precision within 1 mm of implant position and within 5 degrees of deviation for implant inclination.(29,31-32) ASPECTS OF ACCURACY OF AN IMAGE-GUIDED PROCEDURE Accurate assessment of bony architecture and measurements of anatomic structures are prerequisites for appropriate implant planning. In general, the quality of CT data depends on the slice thickness and the influence of possible artifacts. The thinner the slice thickness and the smaller the voxel size, the higher the resolution and accuracy of measurements of delineated structures.movement and metallic artifacts of dental restorations may lead to geometric distortions and invalid data acquisition (31) Cavalcanti concluded No significant differences in precision (reproducibility) or accuracy (validity) of 3D volume rendered images from multislice spiral CT data sets (slice thickness 0.5 mm, 0.5 mm table feed, and 0.5-mm interval reconstructions) were observed between either inter- or intraobserver measurements or between in vitro and in vivo measurements,so multislice spiral CT is the most accurate radiographic means for dental implant planning.(32,33) The precise transfer of virtual planning to the surgical site depends on the accuracy of the registration procedure. This is known as the Image-To-Physical (Ip) Transformation. It depends on 1-to-1 mapping between the coordinates in 1 space (image data) and those in another (physical space; the patient); points in the 2 spaces that correspond to the same anatomic point must be mapped to each other. production differs from IP transformation for bur tracking. The patient s dental stone cast is registered rather than the patient. Building blocks, reference tubes, or pins are integrated in a registration template and are recognized by the software in the CT scan. The 3D implant planning is transferred into a surgical template by a mechanical positioning device, by a drilling machine, or by rapid prototyping, which executes a computerized transfer algorithm or specific 7

14 angular measures. So safety pins must be used to independently check the registration accuracy.(34) ACCURACY OF SURGICAL TEMPLATE PRODUCTION The precision of the surgical transfer itself depends on the systematic and application accuracy of the individual technique used. Most studies were evaluated by comparing the postoperative CT data with the planning data set through image fusion using the mutual information technique. In this technique, the scans are interpolated to isotropic voxel size and matched by comparing the similarity of neighboring voxels in the volume image,they found mean accuracies of surgical templates obtained by a drilling machine of 0.6 mm for the maxilla and 0.3 mm for the mandible, with a maximum deviation of 1.5 mm. as well they reported mean accuracies of rapid prototyping templates of 0.8 mm at the base and 0.9 mm at the tip of the implant.(31) In image-guided template production, errors may be the result of unstable fixation of the surgical template. Precise mechanical fitting of the template into the patient s mouth (or to the dental stone cast in case of an in vitro study) is of major importance, as the template is fabricated using the dental stone casts of the patient. Naturally, accurate dental impressions and dental stone casts are required. For appropriate use in edentulous patients or in extensive distal free-end situations, it is necessary to secure the templates to the underlying bone by fixation screws.(35) As the implants are planned on the computer, familiarity with the system is needed for routine application. Specialized software optimized for dental implant surgery which is intuitive and easy to use can significantly reduce time and expenditure. Despite the expense, compared to the conventional technique, computer-aided implant surgery seems to be superior on account of its potential to eliminate possible manual placement errors and to systematize reproducible treatment success. The protection of critical anatomic structures and the esthetic and 8

15 functional advantages of prosthodontic-driven implant positioning must also be considered.(36) Furthermore, the available bone can be fully utilized, which allows for longer implants (and thus superior implant stability) and perhaps the omission of additional surgical effort such as bone grafting or sinus augmentation (37). Dental restorations with poor esthetics and functionality originating from suboptimal implant positioning may lead to discomfort and additional surgical effort, which means higher costs and a greater burden for the patient. Considering these advantages, image guidance may have a positive cost/effort benefit ratio, depending on the individual situation. Ewers et al (36) stated that the application of this technology offers essential improvement in outcome and intra-operative safety with a considerable technical expenditure (substantially depending on the software used). A further beneficial aspect of the use of computer-aided technology is the associated automatic and complete electronic documentation of the intervention (28) QUALITY OR DENSITY OF BONE The density of available bone in an edentulous site is a determining factor in treatment planning, implant design, surgical approach, healing time, and initial bone loading during prosthetic reconstruction. (38) Clinical reports suggested that dental implants for the mandible have higher survival rates than those for the maxilla, especially for the posterior maxilla whether restored by immediate or delayed loading protocol Clinicians generally consider that the basic cause of the difference in the survival rates between maxilla and mandible is bone quality. Higher failure seems to be associated with the implants in which the surgeon observes a poor degree of bone mineralization or limited bone resistance by tactile assessment while drilling. it is typical that the bone around the implant has better quantity and quality in the mandible than the maxilla.(39,40 9

16 The internal structure of bone is described in terms of quality or density, which reflect a number of biomechanical properties, such as strength and modulus of elasticity. The external and internal architecture of bone control virtually every facet of practice of implant dentistry. BONE is an organ able to change in relation to a number of factors, including hormones, vitamins, and mechanical influences. However, biomechanical parameters, such as duration of edentulous state, are predominant. Awareness of this adaptability has been reported for more than a century. Parfitt have reported on the structural characteristics and variation of trabeculae in the alveolar regions of the jaws. For example, maxilla and mandible have different biomechanical functions.(41) MANDIBLE is an independent structure; it is designed as a Force- Absorption Unit. Therefore when teeth are present, the outer cortical bone is denser and thicker and the trabecular bone is more coarse and dense. MAXILLA is a Force-Distribution Unit. Any strain to the maxilla is transferred by the zygomatic arch and palate away from the brain and orbit, the maxilla has a thin cortical plate and fine trabecular bone supporting the teeth. Others demonstrated a decrease in the trabecular bone pattern around a maxillary molar with no opposing occlusion, compared with a tooth with occlusal contacts on the contralateral side. (42) BONE DENSITY in the jaws also decreases after tooth loss. This loss is primarily related to the length of time the region has been edentulous and not loaded appropriately, in general, the density change after tooth loss is greatest in the posterior maxilla and least in the anterior mandible(43) Cortical and trabecular bone throughout the body are constantly modified by either modeling or remodeling. However these adaptive phenomena have been associated with the alteration of the mechanical stress and strain environment within the host bone. 10

17 MODELING has independent sites of formation and resorption which results in the change of the shape or size of bone. REMODELING is a process of resorption and formation at the same site that replaces previously existing bone and primarily affects the internal turnover of bone, including that region where teeth are lost or the bone next to an endosteal implant. Bone modeling and remodeling are primarily controlled, in part or whole, by mechanical environment of stress and strain(44). BONE CLASSIFICATION SCHEMES RELATED TO IMPLANT DENTISTRY Because mechanical behavior of bone seems to be a vital factor in the achievement of osseointegration, several classification systems and procedures were suggested for assessing bone quality (45-48) the most popular method of bone quality assessment is that developed by lekholm and zarb, who introduced a scale of 1 4, based on both the radiographic assessment, and the sensation of resistance experienced by the surgeon when preparing the implant site, with this classification, jawbone quality is divided into four quality groups based on the amount of and proportion of trabecular and compact bone.(45) Grading system for bone quality assessment (lekholm & zarb 1985) The grading refers to individual experience, and furthermore, it provides only a rough mean value of the entire jaw. Therefore, their classification has recently been questioned due to poor objectivity and reproducibility (49) 11

18 In 1999, Misch proposed four bone density groups independent of the regions of the jaws, based on macroscopic cortical and trabecular bone characteristics. the regions of the jaws with similar densities were often consistent. Furthermore suggested treatment plans, implant design, surgical protocol, healing and progressive loading time spans have been described for each bone density type(50). Dense or porous cortical bone is found on the outer surface of bone and includes the crest of an edentulous ridge. Coarse and fine trabecular bone types are found within the outer shell of cortical bone and occasionally on the crestal surface of an edentulous residual ridge. These four macroscopic structures of bone may be arranged from the least dense to the most dense, as first described by roberts and frost.these four increasing macroscopic densities constitute four bone categories described by Misch (D1, D2, D3, And D4) located in the edentulous-areas of the maxilla and mandible(51) Attempts have been made to classify jawbone tissue before implant treatment on the basis of Hounsfield units as measured in CT examinations Norton and Gamble et al 2007 reported that the mean bone density from CT was 682HU for 139 sites. They reported that the mean bone densities in the the anterior maxilla, and the posterior maxilla were 970, 669, 696, and 417 HU, respectively and they also reported a strong correlation between the bone density and the regions within the mouth (52) Another study to correlate the Hu values with a visual evaluation of the same ct images using the lekholm and zarb classification.(49) Subjective bone quality assessments during surgery were also made on autopsy specimens, and the assessments were correlated with ct-determined bone density measurements. (53) Furthermore studies attempted to correlate calculations of bone mineral density from Hounsfield with assessments of bone quality and implant stability during 12

19 surgery and with marginal bone loss assessment has concluded that computed tomographic examination can be used as a preoperative method to assess jawbone density before implant placement, since density values correlate with prevailing methods of measuring implant stability.(54) BONE DENSITY & COMPUTERIZED TOMOGRAPHY Location of bone density may be more precisely determined by radiographs; especially computerized tomography produces axial images of the patent's anatomy, perpendicular to the long axis of the body. CT axial image has 260,000 pixels and each pixel has a ct number (hounsfield) related to the density of the tissues within the pixel. in general, the higher the ct number, the denser the tissue. Modern CT scanners can resolve object less than 0.5 mm apart. In addition, software is available to electronically position the implant on the CT scan and evaluate to Hounsfield (HU) numbers in contact with the implant. In a retrospective study, kirkos and misch established a correlation between CT hounsfield units and density at the time of surgery, and the misch bone density classification may be evaluated on the CT image by correlation to a range of hounsfield units (HU) (55) DETREMINATION OF BONE DENSITY ON CT IMAGE D1: 1250 Hounsfield units D2: 850 to 1250 Hounsfield units D3: 350 to 850 Hounsfield units D4: 150 to 350 Hounsfield units D5: 150 Hounsfield units Table 1 : Classification puplished by Mich CE where the different bone types correlated to a range of hounsfield units obtained from the CT image 13

20 The introduction of computerized tomography (CT) in implant therapy by (Schwarz et al. 1987) allowed a tridimensional visualization of bone, especially in the bucco-lingual direction, which was not available on traditional panoramic images.(56,57) Recording bone mineral density and subsequent translation into Hounsfield units (HU) also became possible, provided that the necessary calibration had been carried out previously by (Kalender & Suess1987; Nickoloff et al. 1988; and Hill et al in 2005) (58-60) and especially after the development of reliable low-dose scan protocols (Ekestubbe et al in 1996 & Loubele et al. in 2005) (61,62) CT can be considered as an acceptable tool for implant therapy besides the cone beam technology, So far, a few studies have assessed the relationship between CT parameters and bone density and they were on cadavers (63) one of this study conducted by Beer et al reported that the bone density values ranged from 51 to 529 HU in the mandible, and from 186 to 389HU in the maxilla for a 72-year-old male cadaver. (64) On the other hand the study reviewed by Shapurian et al. (2006) reported that the average bone density values in the anterior mandible, the anterior maxilla, and the posterior maxilla, the posterior mandible were 559, 517, 333, and 321HU for 219 implant sites.(49) However Turkyilmaz et al. reported for 158 implant recipient sites that the mean bone densities in the anterior mandible, the posterior mandible, the anterior maxilla, the posterior maxilla were 912, 698, 751 and 467 HU respectively(39) BONE DENSITY AND BONE-IMPLANT CONTACT PERCENTAG the relations between bone density and bone-implant contact percentage could be highlighted by misch research in 1990 explain how the bone density influences the amount of bone in contact with implant surface, not only at first stage surgery, but also at the second stage uncovery and early prosthetic loading. 14