The dental implants are similar to a natural tooth which can be surgically inserted into the alveolar bone followed by the fabrication of a prosthesis
What are Dental Implants?
Dental implants are prosthetic devices made up of alloplastic material implanted into the oral tissue below the mucosa or periosteal layer within the bone to provide retention and support for a fixed or removable dental prosthesis. The dental implants are similar to a natural tooth which can be surgically inserted into the alveolar bone followed by the fabrication of a prosthesis. It acts as a substitute for the natural root of the tooth. Most implants used today are mainly made up of titanium in the form of pure titanium or Ti-Al-V Alloys.
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| (A-D) Restoration of partially edentulous space with implants. |
Indications for Dental Implants
It is mainly used in the replacement of the single tooth of the patient who lost their teeth and it is the best alternate option for removable partial denture (RPD) for loss of single tooth. In distal extension cases also we can use dental implants instead of fixed partial dentures (FPD) and removal partial dentures (RPD). Removal partial dentures (RPD) are also suggested for patients who cannot afford dental implants. In completely edentulous patients, dental implants are used in the form of overdenture. If there is a limitation in placing a fixed partial denture (FPD) due to weak or unfavourable abutments, the dental implant is indicated. In the patient where the conventional complete denture is not to be done because of poor muscular coordination, low tolerance of mucosal tissue, not well denture supporting area, and parafunctional habits ( like tongue thrusting, lip biting ), hyperactive gag reflex, the psychological inability of the patients.
Contraindications of Dental Implants
ABSOLUTE CONTRAINDICATIONS- Dental implants are strictly avoided in these patients due to unavoidable risks. They are,
- Patient history of taking Anti-angiogenic drugs and bisphosphonates.
- Patient with cerebral palsy, blood dyscrasias, poorly controlled diabetes, immunocompromised states, regional malignancy and ischemic heart diseases.
- For patients with irradiated jaw bone less than 1 year before implant placement, if the implant is placed it may lead to osteoradionecrosis.
- Acute bone resorption and psychotic disorders.
- Reduced mouth opening due to Oral submucous fibrosis.
- During pregnancy, the implants are avoided.
- Patients with metabolic disorders, musculoskeletal disorders, and focal and systemic disorders.
- Patients with renal osteodystrophy.
- Alcohol and drug dependence.
RELATIVE CONTRAINDICATIONS- Dental implants are indicated once the patient's conditions are controlled.
Patient with uncontrolled diabetes mellitus, significant history of smoking, endocrine disorders disturbances like hyperparathyroidism etc.., history of taking antidepressants, and anticoagulant drugs, abnormal oral habits including bruxism and tongue thrusting.
Advantages of Dental Implants
Dental implants help in the Preservation of the alveolar bone thereby maintaining the esthetics and vertical dimension of the patients. It is used in the establishment of the proper occlusion followed by improvement in the mastication of foods. It provides better stability and retention to the prosthesis.
Disadvantages of Dental Implants
- It is too expensive.
- It takes more treatment time.
- It involves surgical procedures.
Types of Dental Implants
Based on their design and location
1. Endosteal Implants
A dental implant is inserted into the alveolar bone of the mandible or maxilla and transects one cortical plate is called an Endosteal implant. This implant is based on osseointegration. It is the most commonly used type of dental implant. The type of implant selected is based on the amount of bone, the quality of the bone and the expectations of the patients. The minimum amount of bone required vertically for placing endosteal implants is 8mm. The minimum amount of bone required for buccal and lingual aspects of a dental implant is 1mm. Therefore for a 4mm implant, 6mm of bone width is necessary. It consists of
- Blade forms
- Root forms
- Spiral
- Tripod
- Plates
- Endodontic
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| Blade form implants with (a) Single abutment. |
Root forms are of 2 types depending on the shape and connection of abutments
Based on shape, it is
I. Cylindrical (press-fit)- threaded and nonthreaded.
II. Tapered or Screw shaped- threaded and nonthreaded.
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| (A) Cylinder (B) Tapered |
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| (A) Threaded (B) Nonthreaded |
On the connection with the abutment. It is
I. One-piece abutment- When the fixture and abutment are joined together they are termed as one-piece implants.
II. Two-piece abutment- When the fixture and abutment are separable, they are termed as two-piece implants. Two-piece implants are classified based on whether the connection to the abutment is within the implant or outside as
- External connections
- Internal connections
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| (A) External connection (B) Internal connection |
2. Transosteal Implants
A dental implant that is penetrated in both cortical plates and passes entirely (full thickness) into the alveolar bone. It is also called a staple bone implant. The main disadvantage is it can't be widely used because it damages the infra bony soft tissue like nerves and vessels. It is also known as Staple bone plates. Transosteal implants are inserted by placing an extraoral insertion under the chin and connected through the bony plates which rest on the inferior of the mandible. It is mostly used in the anterior mandible in situations like atrophy of the mandible.
3. Eposteal/Subperiosteal Implants
It receives primary support by resting upon the bone. This is the implant that is placed beneath the mucoperiosteum by overlying a bony cortex. It is also known as Subperiosteal Implants. It is available as complete/unilateral eposteal implants. Subperiosteal implants are used when there is inadequate bone is present which limits the placement of the endosteal implants.
4. Mucosal Implants
The metal form is attached to the tissue surface of a removable dental prosthesis that engages the undercut in a surgically prepared mucosa. Also called a subdermal button implant (or) Intramucosal insert.
Based on the Exposure During Surgery
SUBMERGED IMPLANT
Submerged implants are not exposed to the oral cavity. It is seen in two-stage surgery, which means the first surgery is to place the implant followed by a second surgery to expose them and proceed with impression-making. Hence, it is termed a two-staged implant.
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| (A) Implant placed along with cover screw. |
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| (B) Flap is sutured over the implant so that the implant is not exposed to the oral cavity. |
NON-SUBMERGED IMPLANT
The implant is left exposed to the oral cavity after the first surgery. So that the second surgery is avoided. Hence it is called a one/ single-staged implant.
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| Cover screw left exposed after the implant placement surgery. |
Based on function
- Retentive implants
- Supportive implants
Based on implant materials
- Polymer implants
- Ceramic implants
- Metallic implants
- Vitreous carbon implants
Based on the Implant design
- Branemark implant- Threaded screw
- Core-vent implant- Open basket with vents combined with threads
- IMZ implant- Rough plasma sprayed implant surface
- Stryker implant- Fluted design
Based on the loading protocol
- Conventional loading/ delayed loading/two-stage loading- seen in submerged implants.
- One-stage protocol: Immediate loading and Early loading- seen in non-submerged implants.
BIOLOGICAL CONSIDERATION OF IMPLANT-TISSUE INTERFACE
- SOFT TISSUE-IMPLANT INTERFACE
Like natural teeth, dental implants also have the
junctional epithelium which is the specialized structure for dental apparatus.
It maintains the integrity of the natural tooth as well as implants. The
collagen fibres at the junctional epithelium run perpendicular to the implant
surface. The connective tissue fibres run parallel to the implant surface and support the junctional epithelium which forms the effective tight seal to peri-implant pocket formation and bone loss
- BONE-IMPLANT INTERFACE
The bone-to-implant contact is important for the success of
the implants. The recent discoveries are based on this to improve the surface
area of the implants. There are two basic theories regarding the bone-implant
implant interface. They are
1. Fibro-osseous integration (Linkow 1970, James 1975, and Weiss 1986)
The presence of collagen fibres between
the dental implant and bone is a peri-implant membrane with an osteogenic effect. The
collagen fibres around an implant are arranged regularly and parallel and are different from the collagen fibres arranged in periodontal ligaments as
perpendicular. Fibro-osseous integration is seen in implant systems as a good
initial success rate but the success rate may fall in the long term.
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| (A) Comparison of attachment of normal teeth and the implant. 1. Natural tooth crown. 2. Artificial tooth crown. 3. Gum tissue. 4. Implant abutment. 5. Gum tissue. 6. Screw type implant. 7. Bone. 8. Periodontal Ligament Fibres. 9. Bone attaches directly to implant (Osseointegration) (B) Histopathological image showing osseointegration. |
2. Osseointegration
(supported by Branemark, Zarb, and Albrektsson 1985)
Branemark theory of osseointegration
The osseointegration is defined as the direct structural and functional connection between the ordered, living bone and the surface of load carrying implant. The bone is laid very close to the implant without intervening with the connective tissues. The titanium oxide is permanently fused with the bone. With osseointegration, root-form implants are the most dominant design. In dentistry, osseointegration is undoubtedly one of the significant discoveries in the past 10- 20 years.
PARTS OF DENTAL IMPLANTS
1. Main component
- Implant body or fixture
- Abutment
- Superstructure
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| (1) Implant fixture, (2) Abutment (3) Superstructure. |
2. Accessory Components
SURGICAL
- Cover screw
- Gingival former or Healing abutment
PROSTHETIC
- Implant analogue
- Impression Coping/ Transfer coping
1. MAIN COMPONENTS
IMPLANT FIXTURE/ BODY
A component that is surgically placed into the alveolar bone. It is also termed an implant body. It also has three parts namely,
- Body
- Crest module
- Collar
Crest Module
It is used to retain the prosthetic component of the two-piece system. The abutment connection area has a platform on which the abutment is set. The platform offers resistance to occlusal loads. The crest module is often smoother to avoid plaque retention and prevent crestal bone loss. It represents the transition zone from the implant body design to the transosteal region of the implant at the crest of the ridge. The platform contains the connection to the abutment which is present above or below the crestal bone level. If it is present above, it is termed as an External Connection and if present below, it is termed as an Internal Connection. The various types of anti-rotational features are incorporated in internal connections such as hexagons, octagons, morse tapers, grooves, etc.
Body of the implant
As mentioned earlier, it is either screw or cylindrical. It also has many variations.
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| Parts of Implant Fixture (a) Body, (b) Collar, (c) Crest module |
IMPLANT ABUTMENT
A part of the dental implant that supports any fixed or removable dental prosthesis is called an Abutment or Fixed prosthesis
1. Definitive
A) Prefabricated
Solid abutment
Hollow (straight, angled)
B) Custom-made
Castable abutments
CAD-CAM abutments
2. Abutments for a removable prosthesis (overdenture prosthesis)
Stud attachments
Bar attachments
Magnetic attachments
Telescopic attachments
Bar attachments
Magnetic attachments
Telescopic attachments
IMPLANT SUPERSTRUCTURE
It is the prosthesis that is fabricated with the support of dental abutment it is classified as,
1. Fixed prosthesis
Crowns and Bridges
2. Removable prosthesis
Overdenture
3. Fixed detachable prosthesis
Hybrid denture
ACCESSORIES
1. SURGICAL
a) Cover screw
After the surgical placement of the dental implant, a cover screw is placed in the superior aspect of 2 piece implant to cover the connection for abutment during the healing also, it is called a healing screw.
b) Gingival former/ Healing abutments
This is required only for two-stage implants. After the second surgery to expose the implant, the cover screws are removed and gingival formers which can be available at different heights, are placed on the implant fixture they extend above the soft tissue into the oral cavity and form a gingival cuff around the implant. It is usually in place for 2-5 weeks which depends on the healing following which they are removed and impression procedures are commenced. They will be replaced by the abutment in the final
restoration. They are also termed Healing abutments or per mucosal extensions. A replica of the entire dental implant, not intended for human implantation. This component is the same as the implant but is used in the model to fabricate the prosthesis in the laboratory.
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| (A) Cover screw (B) Healing abutment/ Gingival former. |
2. PROSTHETIC
IMPLANT ANALOGUE
A replica of the entire dental implant is similar to the implant fixture but used as a model to fabricate the prosthesis in the laboratory.
IMPRESSION COPING
The component of the dental implant system provides the spatial relationship of an endosteal dental implant to the alveolar ridge and adjacent dentition. It is used as a transfer impression to transfer the location of the implant body or abutment to the dental cast. It is also called an impression pin or transfer coping.
IMPLANT TREATMENT PROTOCOL
The implant treatment protocol is the step-by-step evaluation of the implant site for dental implant placement.
- Diagnosis
- Treatment planning
- Surgical phase
- Prosthetic phase
DIAGNOSIS
MEDICAL EVALUATION
Medical evaluation should be done for implant patients. systemic diseases should be ruled out and a history of any condition that contraindicates surgery should be noted. Vital signs, respiratory rate, height, and weight should be noted. A complete Blood count should be checked before the surgery.
DENTAL EVALUATION
An articulated diagnostic cast is essential for diagnosis and treatment planning. It provides information regarding,
1. Occlusal plane
2. Arch location for abutment
3. Opposing dentition.
4. Bone mapping.
5. Missing teeth.
6. Inter-arch space.
7. Position and morphology of natural abutment.
8. Direction of force in the implant site.
9. Relation of the edentulous ridge to adjacent teeth and opposing arches.
10. Arch form
RADIOGRAPHIC EVALUATION
It may provide information about,
1. Quantity, and angulation of the bone
2. Presence or absence of diseases
The following radiographs such as
Periapical radiograph – which gives information regarding the quality of bone.
Radiovisiography(RVG)- are used to verify the location of the implant in a critical anatomical structure like the maxillary sinus.
Occlusal radiograph- provides information regarding the width of bone and density of bone.
Lateral cephalogram- provides information regarding the angulation of bone and skeletal arch relationship.
Orthopantomogram(OPG)- It provides information regarding height, quality, and relation to the critical structure.
Computed tomography (CT)- very accurate information regarding width, and critical anatomical structure. 3D model can be fabricated with CT Scan.
Treatment planning
• For single tooth replacement
• Partially edentulous
• Completely edentulous
The treatment plan for the single-tooth edentulous area requirements is as follows,
1. Emergence profile
2. Diameter of the implant
3. Gingival papilla –contour
4. Gingival zenith
5. Need for augmentation
6. Selection of abutments
1. Emergence profile
The emergence profile is defined as the position and relationship of the crown to the underlying mucoperiosteum and the bone, which gives the illusion of the crown emerging from the gingiva as seen in the natural tooth. It is based on the location of the head of the implant and the perimucosal extension of the abutment.
2. Diameter of the implant
It plays an important role in the aesthetic and selection of implants which mainly depends on the mesio-distal width of the edentulous area. There must be a clear gap of 2 mm between the implant and the natural tooth abutment roots. The implant with optimum diameter is chosen otherwise it has adverse effects on the emergence profile.
3. Gingival papilla and contour
Gingival papilla must be preserved if it is absent it should be developed using multiple and sequential use of acrylic prosthesis. Normally it takes about 3 to 4 weeks to develop gingiva.
4. Gingival zenith
It is formed by the cervical one-third contour of the crown.
4. Need for augmentation
If the bone is deficiently placed, the deficient bone may be horizontal or the augmentation needs to be performed with the bone graft (allograft or autograft).
5. Selection of abutment
The abutment can be made of metal or zirconium. Generally, metal abutments are used for thick biotypes and zirconium for thin biotypes for partially edentulous.
For partially edentulous patients
Fixed prostheses are indicated with the prosthesis may be,
1. Fixed partial denture supported by natural teeth and implant
2. Fixed partial denture supported by the implant
3. Independent crown supported by an implant with or without splitting
Indications
For class I, II, and posterior class III.
Contraindications
Anterior tooth as heavy lateral force involved.
For completely edentulous patients
Both fixed and removable dentures are treatment planning for the completely edentulous patient.
1. Removable prosthesis(overdenture)
2. Fixed prosthesis
i) Full arch crowns/bridge
ii) Hybrid denture(fixed detachable bridge)
These are screw-retained complete dentures that cannot be removed by the patients but can be removed by the dentist.
Advantage of overdenture compared to fixed implant prosthesis
1. Fewer implant
2. Good hygiene and maintenance
3. Good aesthetics
4. Less cost
5. Less specific placement
Disadvantage
1. Psychological ( need for fixed teeth)
2. Space requirement
3. Food impaction
Surgical procedure for dental implant placement
The placement of implants is done in two phases.
PHASE- I
Local anesthesia is injected in the implant placement area. Then the area is incised slightly buccal to the alveolar crest in the mandible or palatally on the maxillary crest. The full-thickness flap is raised with the help of a periosteal elevator. After adequate exposure and retraction of the surgical site, remove any bony irregularities with the help of the bone rongeur or round bur. Transfer the surgical stent/ templates to the mouth for the placement of the implant in the correct direction and angulation. During the drilling of the bone, preparation should involve sterile water irrigation. The RPM of drilling the bone should not exceed 1000rpm in high motor mode and should not exceed 40-50rpm. The osteotomy site is enlarged at the alveolar crest with the help of a guide drill. The osteotomy site is then gradually enlarged with sequence drills. If multiple implants are placed, then the parallel pins are placed in the implant site to maintain the parallelism with other implants during placement. If the implants are placed in the dense mandibular bone, the implant site is pre-threaded or tapered with thread former at low speeds to create threads at the low osteotomy site. The contamination of the implants is avoided before the insertion into the prepared site. The carrier is removed and the implant is seated in its final position. The operative site is thoroughly irrigated and all sharp bony edges are smoothened.
PHASE- II
After 3-4 months, the abutment analogue is attached to the transfer coping and the cast is poured. The superstructure or prosthetic restoration is constructed on the implant or abutment and delivered to the patient. The prosthesis is fixed to the abutment either by screw or luting.
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| TWO-STAGE SURGICAL PROCEDURE FOR IMPLANT PLACEMENT. Stage- I (A-G) Stage-II (H-O) |
IMPLANT PLACEMENT
Implant surgery is performed in a sterile environment to avoid contamination of the implant fixture because contamination of the implant fixture results in a lack of osseointegration. Once the implant is seated firmly, the cover screws are placed into the implant body. The surgical site is irrigated, and the mucosal flap is sutured and closed with 3-0 black silk. The sutures are removed after 7-10 days. Following implant surgery, patients are prescribed antibiotics and analgesics.
FEATURE OF SUCCESSFUL IMPLANTS
- The implant should be immobile or mobile with less than 1mm when tested clinically.
- Vertical bone loss should be less than 0.2mm annually following the implant's first year of service.
- Paraesthesia, infections, neuropathies, and violations of anatomic structures such as maxillary sinus, nasal passage or mandibular canal should be absent.
- Success rates should be 85% after 5 years and 80% after 10 years.
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