DENTAL IMPLANTS PART I

DEFINITION-Implant is something that replaces a natural tooth.
Implantation should be differentiated from other two terms-Replantation and Transplantation
Replantation-its the reinsertion of a tooth back into its socket after accidental or intentional removal from the socket.
Transplantaion-Its the insertion of body part from one site to another.
CLASSIFICATION OF DENTAL IMPLANTS-

1. ENDOSTEAL
2. SUBPERIOSTEAL
3. TRANSOSTEAL
4. EPITHELIAL IMPLANT

ENDOSTEAL IMPLANT-Its an implant that is directly placed into the bone like a natural teeth.
SUBPERIOSTEAL IMPLANT-In this a custom cast framework is placed directly beneath the periosteum,overlying the bony cortex.Its used in cases where there is excessive bone loss.
TRANSOSTEAL IMPLANT-It combines both subperiosteal and endosteal components.this implant passes through the full thickness of the alveolar bone.This type of implants are restricted to be used in anterior area of mandible and provide support for tissue borne overdentures.
EPITHELIAL IMPLANT-Inserted into oral mucosa.
Titanium is the most common material that is used for dental implants.Reasons behind this are-
*high heat resistance of titanium
*High strength of titanium
*Resistance to corrosion
*Biocomaptible


Various implant materials that have been used in the market till date are-

1. Ti-6Al-4V (most biocompatible)
2. CP Titanium (cp-commercially pure)
3. Ti-6Al-4V ELI (Extra low interstitial)
4. Stainless steel
5. Aluminium oxide
6. Zirconia

ATTACHMENT MECHANISM-Dental implants mostly get attached to the cortical bone by the process called as osseointegration.
Osseointegration is a process in which living bony tissues come under the direct connection of the implant surface without any intervening fibrous connective tissue,making it structural and functionally stable.
Implant surfaces can be of threaded,grooved,perforated,plasma sprayed or coated type.
MODIFICATIONS-Metallic implants can modified by following processes- 

1. PASSIVATION-Enhancment of the oxide layer to prevent the release of the metallic ions as a result of surface breakdown,this makes implant more biocompatible.
2. Anodization-In this current is passed through the implant.This adds oxide layer to the implant surface that is much more thicker as compared to the one produced by passivation.It helps to prevent corrosion of implant surface.
3. Surface texturing-Its a process of increasing surface roughness to aid in surface area for bone attachment.This can be attained by acid etching or by blasting with aluminium oxide or any other ceramic material.

BIOACTIVE/BIOCONDUCTIVE Materials-They are the variety of inorganic materials that can stimulate adhesion and bonding to bone.These materials can either be coated on implant surface or they can be plasma sprayed on implant surface. 
Calcium Hydroxyapatite(HA) and Tricalcium phosphate are two commonly used bioactive materials.
The major advantage of these coatings is that they stimulate the bone formation.
There are some disadvantages associated with bioactive materials,which are-
 *The long term stability of HA coated implants is still controversial.The interface between the HA and implant surface can be unstable
* Microorganisms can adhere to the HA surface leading to peri-implantitis  
Thus Bioactive coated implants to be used in cases where there is less bone available for implant placement. 
Clinical Success of an Implant-Criteria of Albrektsson et al

1. Implant must be immobile when tested clinically
2. no sign of periapical radiolucency
3. Vertical bone loss less than 0.2mm annually  following the implants's first year of service
4. absence of any signs of inflammation like pain,infection etc

Reference-Phillips 11TH Edition

SUBPERIOSTEAL IMPLANT

ENDOSTEAL IMPLANT