Name of the authors

1. Dr. Anshul Chugh (MDS). Asst. Professor, Dept of Prosthodontics, Govt. dental college , Rohtak .
2. Dr. Jigyasa Duhan (MDS) Assoct. Professor, Dept of Operative Dentistry, Govt . dental college, Rohtak.
3. Dr. Divya Dahiya (MDS) Asst. Professor, Dept of Prosthodontics, Govt. dental college , Rohtak .

The name of the department and institution

Department of Prosthodontics & crown and bridge
Pt. B. D. Sharma PGIMS, Govt. dental college, Rohtak         

INTRODUCTION

Available bone describes the external architecture or volume of the edentulous area considered for implants; Bone density describes the internal architecture or strength of the bone.
The density of bone available in an implant site has primary influence on treatment planning, implant design, surgical approach, healing time and initial progressive loading during prosthetic reconstruction.

BONE DENSTY CLASSIFICATION SCHEMES

A. Linkow (1970) classified bone density into three categories;    
  Class I Bone structure: This ideal bone type consists of evenly spaced trabeculae with small       cancellated spaces.
 Class II Bone structure: The bone has slightly larger cancellated  spaces with less uniformity of  the osseous pattern.
  Class III Bone structure: Large marrow filled spaces exist between bone trabeculae.                                              
 B. LekhOlm and Zarb (1985) listed four bone qualities found in the
anterior regions of jaw bone
 Quality 1 - Composed of homogeneous compact bone
Quality2  -Thick layer of compact bone surrounding a case
of dense trabecular bone,
Quality3 -  Thin layer of cortical bone surrounding dense
trabecular bone of favourable strength.
Quality4 -  Thin layer of cortical bone surrounding a core of
dense trabecular bone.
C. Drs-Lekholm and Zarb (1985)
Lekholm-Zarb classification of edentulous anterior jawbone quantity and quality.
Types A through E reflect a range of resorptive patterns relative to the presumed demarcation of the alveolar and basal jawbone(dotted line). Quality (types I through 4) reflects a range of cortical and cancellous patterns ‘which have been consistently used in planning oral implant treatment
D. Misch Bone density classification (1988)

BONE DENSITY DETERMINATION

1. Tactile sense
2. Anatomic location of bone density
3. Radiographic bone density

The table shows the relation of different bone densities with different region of the mouth: (% occurrence)

RADIOGRAPHIC CONSIDERATIONS
Radiography is important in:

1.  Presurgical phase
2.  Intra-treatment phase
3.  Post-placement phase

VARIOUS   IMPLANT IMAGING MODALITIES ARE:

1. Conventional

   1. Periapical radiograph
   2. Occlusal radiographs
   3. Panoramic radiographs
   4. Cephalometric Radiograph
   5. MRI
   6. Conventional tomography (scanora multimodel imaging system)
   7. Computed Tomography (Dental scan, 3D Dental, Tooth Pix)

1. Recent Advances

   1. Tuned Apertures Computed  Tomography
   2. Digitai substaction radiography
   3. Reformatted CT Sim-Plant)

FIXTURE EVALUATION

1. Lack of radiolucency around the outline of the implant
2.  Vertical bone loss of 1.2 mm or less n the first year and,0.5 mm n each succeeding year

 To determine whether the fixture has osseointegrated, following signs Should be checked:

1.  Clinical absence of mobility

To view. the threads of fixtures accurately, the central ray of xray  beam should be directed perpendicular to the long axis of the fixture.

FLOW CHART SHOWING RADIOGRAPHIC PLANNING

REFERENCES

1. Linkow LI, Chercheve R. Theories and techniques of oral implantology, vol 1, St. Louis, 1970, Mosby.
2. Lekholm U, Zarb GA. Patient selection and preparation. In Branemark P-I, Zarb GA, Albrektsson T, editors: Tissue integrated prostheses: osseointegration in clinical dentistry, Chicago, 1985, Quintessance.
3. Misch CE, Kircos LT. Diagnostic imaging and techniques. In Misch CE, editor, Contemporary implant dentistry, ed 2, St Louis, 1999, Mosby.

ANATOMIC CONSIDERATIONS
IMPLANT  RECOMMENDATIONS  RELATED TO TOOTH ANATOMY

1. The selection of an appropriate implant to use as a root analogue is the first step in providing support for crown-and-bridge restoration. This will maximize aesthetics through the development of a proper emergence profile.
2. Two considerations are important:
3. 1. Mesiodistal size of the natural crown, which determines the space required for a restoration.
4. 2. Mesiodistal dimension of the tooth root which determines the size of the appropriate implant.

The attachment for natural teeth are found in the vicinity of CEJ ; as the people age, these mechanism recede. Therefore ,it has been concluded that CEJ minus 2mm is good anatomic location to assess the average size of tooth root and thus optimal implant size for replacing the tooth.( Kenneth S. Hebel and Reena Gajjar 1997

TOOTH	MESIODISTAL CORWN (mm)	MESIODISTAL CEJ (mm)	MESIODISTAL CEJ MINUS 2 mm	RECOMMENDED IMPLANT (mm)
Central	5.3	3.5	3.5	3.25
ateral	5.7	3.5	3.5	3.25
Cuspid	6.8	5.2	4.1	4.1, 4.3
1st premolar	7.0	4.8	4.5	4.1, 4.3
2nd Premolar	7.1	5.0	4.7	4.1, 4.3
1st Molar	11.4	9.2	9.0	4.1, 4.3, 5.0, 6.5
2nd  Molar	10.8	9.1	8.5	4.1, 4.3, 5.0, 6.5

PROPER POSITIONING OF DENTAL IMPLANTS
One step in quality implant treatment is selecting and positioning the proper implant to act as an analogue to replace a specific tooth. Precise positioning is particularly critical when the implant is to as used as support for a crown-and-bridge restoration. In such cases, proper spacing is essential to both establish- aesthetic relationship between the implant and the tooth and achieve a proper emergence profile of the final restoration.
Principles of Implant Positioning
1. Vertical positioning of the implant in the bone (i.e., how far below the gingival crest it is placed).
2. Buccolingual positioning of the implant in the bone.
3. Mesiodistal placement of the implant in the bone.
4. Trajectory or angle of the implant.

VERTICAL POSITIONING
In aesthetically demanding situations , implants must be placed below the crest of the gingiva at a level that respects biologic health and still proves the ability to create a proper emergence profile.
Recommendations for vertical positioning suggest that the top of the implant be placed 5mm or more below the CEJ of the adjacent tooth

MESIO-DISTAL POSITIONING
Ideal distance:
The ideal or anatomic distance between the centers of implants enables the_proper spacing of Implants for crown-and-bridge restorations on dental implants. The goal is to space implants mesrodistally so that an emergence profile can be created that, when viewed from the buccal perspective, has the appearance of natural teeth. This mesiodistal spacing is critical for aesthetic restorations The following formula can be used to calculate the ideal or anatomic distance for crown-and-bridge restorations:
 Width of tooth 1 + by2 + width of tooth 2 + by 2

IMPLANT POSITIONING
When an implant is placed next to a natural tooth, it is possible to use the formula for anatomic spacing.
    
An alternative approach is to leave 2mm between the implant and the adjacent natural tooth. The formula for this spacing is 2mm plus the radius of the implant.

There is often a requirement to place an implant between two natural teeth. In this circumstance, the formulas do not always apply. When considering the scenario in which an implant is being used to replace a congenitally missing lateral incisor in association with orthodontics, orthodontic treatment before implant placement seldom leaves the average space of 6.6mm routinely, 5mm or less of space remains. A smaller implant (e.g., 3.25mm or 3.5mm in diameter) must be chosen and placed precisely with little margin for error.

ANGULATIONS

It is generally accepted that implants are best loaded vertically. This suggests that implants should be angled perpendicular to the plane of occlusion .The bone of the maxilla and mandible is not always occlusion, especially in the mandibular posterior and the maxillary anterior. Angled abutment’s to correct the angulation.

DISCUSSION

DIAGNOSIS

1. Medical history :

The medical history is one of the most important and revealing aspects of patient evaluation (Laney, 1986).
   1. Determine if the patient is currently under the care of a physician. so, determine the nature of present illness and therapy.
   2. Determine if the patient has a history of any cardiovascular disease such as hypertension, rheumatic or congenital heart disease. rheumatic fever, angina, myocardial infarction, or arrhythmias..
   3. Determine if the patient has a history of diseases of the kidney; urinary tract, gastrointestinal system, respiratory system, edocrine system and nervous system.
   4. Determine if the patient has a history of allergies, such as senstivity to certain drugs and/or dental materials.
   5. Determine if the patient is abusing drugs, alcohol, or chemical substances.
   6.Determine if the patient is under care for psychological problems.
Dental history :

1. Intra oral examination should be carried out for evaluation of the following :

 1. Soft tissue condition
2. Remaining teeth condition
3. Edentulous areas for undercuts, pathology and size & shape of residual bone.
4. Present occlusion for interferences, occlusal wear, prematurities
5. Parafunctional habits 

Radiographic Examination

Radiographs determine the quantity and quality of residual bone.
Necessary radiographs include periapicals, occlusals, orthopantograph   and a cephalometric radiograph (Laney, 1986), The jawbone anatomy and bone tissue abnormalities can be seen with radiographs and aid in circumventing potential problems. Since a radiograph is two dimensional, the surgeon must visualize surgical sites in three dimensions. Computer tomography scanning has been proposed for use.

BONE DENSITY DETERMINATION

1. Tactile sense
2. Anatomic location of bone density
3. Radiographic bone density

Principles of Implant Positioning

1. Vertical positioning of the implant in the bone (i.e., how far below the gingival crest it is placed).
2. Buccolingual positioning of the implant in the bone.
3. Mesiodistal placement of the implant in the bone.
4. Trajectory or angle of the implant.

A correct diagnosis including complete evaluation of available bone and determining the proper placement on an dental implant is key to its success. All the factors mentioned should be considered before placing an implant in the oral cavity.

References

1. Linkow LI, Chercheve R. Theories and techniques of oral implantology, vol 1, St. Louis, 1970, Mosby.
2. Lekholm U, Zarb GA. Patient selection and preparation. In Branemark P-I, Zarb GA, Albrektsson T, editors: Tissue integrated prostheses: osseointegration in clinical dentistry, Chicago, 1985, Quintessance.
3. Misch CE, Kircos LT. Diagnostic imaging and techniques. In Misch CE, editor, Contemporary implant dentistry, ed 2, St Louis, 1999, Mosby.
4. Wheeler RC. A textbook of dental anatomy and physiology, ed 4, Philadelphia, 1965, Lea & Febiger.
5. Tarnow DP, Cho SC, Wallace SS. The effect of inter-implant distance on the height of inter-implant bone crest, J Periodontol 71:546-549, 2000.
6. Hebel KS, Gajjar R. Achieving superior aesthetic results: parameters for implant and abutment selection, Int J Dent Symp 4:42-47, 1997.
7. Woelfel JB. Dental anatomy its relevance to dentistry, ed 4, Philadelphia, 1990, Lea & Febiger.
8. deLange GL. Aesthetic and prosthetic principles for single tooth implant procedures.: an overview, Pract Periodontics Aesthet Dent 7:51-61, 1995.
9. Spielman HP. Influence of the implant position on the aesthetics of restoration, Pract Periodontics Aesthet Dent 8:897-904, 1996.
10. Frederiksen NL. Diagnostic imaging in dental implantology: Oral Surgery Oral Medicine Oral Pathology 1995;80:540-54
11. Potter BJ, Shrout MK. Implant site assessment using cross-sectional tomographic image: Oral Surgery Oral Medicine Oral Pathology 1997; 84:436-41. 
12. Reiskin AB. Implant imaging: DCNA 1998;42:47-56.