• Acute and terminal illness

• Pregnancy

• Uncontrolled endocrine disorders

• Patient on radiotherapy

• Patient with unrealistic expectation

• Improper patient motivation

• Lack of experience of clinician

• Inability to restore with a restoration

Advantages

• Preserves bone

• Improves masticatory efficiency

• Maintains proper vertical dimension

• Immune to dental caries

• High level of predictability

• Improves aesthetics and phonetics

• Increases retention and stability

Disadvantages

• High initial cost of treatment

• Involves surgical procedure

• Procedure depends on quantity and quality of bone

• Depends highly on clinician skills

• Limitations in placement in medically compromised patient

Limitations

Limitations of dental implant are given in Table 33-1.

TABLE 33-1

ANATOMIC LIMITATIONS TO IMPLANT PLACEMENT

Anatomic Structure Minimum Distance between Implant and Structure

Nasal cavity 1 mm

Buccal plate 0.5 mm

Lingual plate 1 mm

Maxillary sinus 1 mm

Inferior alveolar nerve 2 mm from superior aspect of the body canal

Mental nerve 5 mm from the anterior loop or bony foramen

Interimplant distance 3 mm between the outer edge of implant

Adjacent natural tooth 0.5 mm

Classification of dental implant

1. On the basis of placement of implants within the tissues

2. On the basis of type of material used

3. On the basis of treatment options of completely edentulous arches

4. On the basis of treatment options of partially edentulous arches

5. On the basis of treatment options

6. On the basis of their reaction to bone

On the basis of placement of implants within the

tissues

(a) Subperiosteal implants: In these implants, a framework derives its

support by resting over the bony ridge without penetrating it. G.S.

Dahl conceived the concept of the subperiosteal implants. N.I.

Goldberg and A. Gershkoff made subperiosteal implant with

vitallium in 1948 (Fig. 33-1).

(b) Transosteal implants: These penetrate both the superior and

inferior cortical plates passing through the entire thickness of the

mandible. Sollier, R. Chercheve and Small introduced the transosteal

implant in 1953 (Fig. 33-2).

(c) Endosteal implants: These can extend into the basal bone, usually

penetrates only superior cortical plate. It is of two types, root-form

implants and the plate-form implants (Fig. 33-3).

On the basis of type of material used

(a) Metallic implants: Titanium and its alloys, cobalt–chromium,

molybdenum alloy, iron–chromium–nickel-based alloys are some

examples of metallic implants.

(b) Nonmetallic implants: Ceramics and carbon are some examples of

nonmetallic implants.

On the basis of treatment options of completely

edentulous arches (Misch)

The completely edentulous jaw is divided into three segments. The

anterior component lies between the mental foramen or in front of the

maxillary antrum. The left and the right posterior segments

correspond to the left and right sides.

Type 1 div A: It has abundant bone in all the three segments.

Type 1 div B: It has adequate bone in all three segments; narrow

diameter root-form or plate-form implants are used.

Type 1 div C-w: It has inadequate bone width for implant placement;

augmentation with autogenous bone may improve the bone

category.

Type 1 div C-h: It has a crown–implant ratio greater than 1; for longterm success removable prosthesis is indicated; it is most commonly

found in posterior maxilla with subantral augmentation.

Type 1 div D: Severely atrophied edentulous arches; bone

augmentation or conventional dentures are indicated.

Type 2 div A, B: Anterior segment has abundant bone and the

posterior segment has adequate bone for narrow diameter implant.

Type 2 div A, C and Type 2 div A, D: As described in type 1.

Type 2 div B, C: It has two treatment options, since anterior div B is

not adequate, it is converted to div A by osteoplasty, posterior

segment requires subantral augmentation.

Type 2 div B, D: It presents advanced atrophy in the posterior

segments and adequate ridge width and height in the anterior

segment; this situation can occur in the maxilla but never in the

mandible.

Type 3 div A, B, D arch: It has abundant bone in anterior segment,

moderate bone in the posterior right side and severe atrophy in the

left posterior segment; sinus augmentation is commonly indicated

in posterior atrophied maxilla and in the atrophied mandible

additional anterior implants with cantilever is more suitable.

Type 3 div C, D, C: It presents severe atrophy in the right section and

moderate atrophy in the left section; mandibular arch uses the

anterior segment with cantilever design and in the maxilla posterior

segment is treated with subantral augmentation and anterior

segment is treated with subnasal elevation.

On the basis of treatment options for partially

edentulous arches (Misch CE)

Class I: Partially edentulous arch with bilateral edentulous areas

posterior to the remaining natural teeth.

Div A: Edentulous areas have abundant bone height (10 mm) and

length (5 mm) for endosteal implant.

• Crown–implant ratio is <1.

• Direction of load is within 30º of implant body axis.

• Root-form implants and independent prosthesis

often are indicated.

Div B: Edentulous areas have moderate bone width (2.5 mm) and

adequate bone height (10 mm) and length (15 mm).

• Direction of load is within 20º of implant body axis.

• Crown–implant ratio is <1.

• Surgical options include osteoplasty, narrow

diameter implants with/without augmentation.

Div C: Edentulous area has inadequate available bone for endosteal

implant with a predictable result, because of too little bone width,

height and length.

• Crown–implant ratio is >1.

• Surgical option such as osteoplasty or augmentation

is indicated.

Div D: Edentulous ridges are severely resorbed involving the portion

of the basal or cortical supporting bone.

• Crown–implant ratio is >5.

• Surgical options usually require augmentation

before implant placement.

Class II: Partially edentulous arch with unilateral edentulous area

posterior to remaining teeth.

Div A–D: Same as for class I.

Class III: Partially edentulous arch with unilateral edentulous area

with natural teeth remaining anterior and posterior to it.

Div A–D: Same as for class I.

Class IV: Partially edentulous arch with edentulous area anterior to

remaining natural teeth and crosses the midline.

Div A–D: Same as for class I.

On the basis of treatment options (Misch)

• C.E. Misch (1989) reported five treatment options of implants. First

three of the five options are fixed prosthesis that may be partial or

complete replacements depending on the amount of hard and soft

tissue structures that are replaced.

• The remaining two are removable prostheses that are classified on

the basis of support as follows:

FP1: Fixed prosthesis; replaces only the crown; looks like a natural

tooth.

FP2: Fixed prosthesis; replaces the crown and a portion of the root;

crown contour appears normal in the occlusal half, but is elongated

or hypercontoured in the gingival half.

FP3: Fixed prosthesis; replaces missing crowns and gingival colour

and portion of the edentulous site; prosthesis most often uses

denture teeth and acrylic gingiva, but may be porcelain to metal.

RP4: Removable prosthesis; overdenture supported completely by

implant.

RP5: Removable prosthesis; overdenture supported by both soft tissue

and implant.

On the basis of their reaction to bone

(a) Bioactive: Ability of the implant to simulate bone formation, e.g.

hydroxyapatite.

(b) Bioinert: These materials do not bond directly to the bone but are

mechanically held in contact to the bone.

FIGURE 33-1 Subperiosteal implants.

FIGURE 33-2 Transosteal implants.

FIGURE 33-3 Endosteal implants.

Radiographic planning of dental implants

Dental radiographs help the clinician to assess the bone levels

available for implant placement. Since they are two-dimensional

images, they do not indicate the bone width. Along with the clinical

examination, they are important aid in treatment planning of dental

implants. Recently introduced tomographic examinations (computed

tomography [CT] and cone beam computed tomography [CBCT])

provide cross-sectional and three-dimensional images which are

useful in assessing both the bone quality and quantity.

Radiographs are used in treatment planning, during the placement

of the implant or the prosthesis, postsurgery in assessing the

angulation and placement of the implant, to assess the

osseointegration and in long-term maintenance.

Role of radiographs in implant treatment

• To assess initial osseointegration

• To evaluate seating of abutments

• To assess fit of the restoration or prosthesis

• To evaluate baseline bone level after completion of the final

treatment

• For longitudinal evaluation of the bone levels

Various types of radiographs used in implant dentistry are

periapical radiographs, panoramic, lateral cephalometric and the

computed tomographic images. The radiographs are useful to

clinician:

• To assess the overall status of the teeth and the supporting bone

• To identify implant sites where implants can be placed without

using complex procedures

• To identify sites where implants are placed using complex

procedures

• To identify sites where implant placement is not advisable

• To assess the quality and quantity of bone

• To identify any anatomical anomaly or pathological lesion

Panoramic radiography

For screening of the implant cases, the panoramic radiographs are

radiographs of choice. These provide reasonably accurate

approximation of the bone height, the position of the neurovascular

bundle, size and position of the maxillary sinus and pathology, if any.

Advantages

• The radiation dosage is less than the full mouth periapical

radiographs.

• The associated anatomical structures are better identified than the

periapical radiographs but with less fine details of the teeth.

• Bone height can be assessed.

• Procedure is convenient, fast and easy to perform.

Disadvantages

• Nonuniform magnification of the images

• Geometric distortion, especially in the anteroposterior dimension

• Overlapping of images

Periapical radiography

• It is useful in assessing the length and height of the bone.

• It is indicated for placement of the single-tooth implant in patient

with minimal bone loss.

• Intraoral radiographs are taken with a long cone parallel technique.

• Paralleling technique reduces the geometric distortion, gives better

resolution and produces more accurate images.

Lateral cephalogram

• It is used to evaluate the vertical height, width and angulation of the

bone in the midsagittal region of the maxilla and the mandible.

• It also helps to evaluate the loss of vertical dimension, skeletal

interarch relationship, anterior crown–implant ratio and the

anterior tooth position.

Role of CT scans in implant dentistry

CT scan was first introduced to medical field by G.N. Hounsfield in

1942. CT uses X-rays to produce sectional images of high resolution by

scanning in the axial plane keeping thin sections.

• The radiation is detected by highly sensitive crystals or gas detectors

which are then converted into the digital data.

• This digital data is stored and manipulated by the computer to

reconstruct the image of the object.

• The patient head is aligned in the scanner with the help of light

markers.

• Mandible is scanned with the slices parallel to the occlusal plane

and maxilla is scanned using the occlusal plane or the plane parallel

to the base of the nose.