Implants : An Overview, Biomechanics & Treatment Planning

IMPLANTS : AN OVERVIEW, BIOMECHANICS AND TREATMENT PLANING

By Dibya Falgoon Sarkar (North Bengal Dental College & Hospital)

OVERVIEW OF IMPLANTS• Implantation: The process

of grafting/ inserting a material such as an inert foreign body (alloplast) or tissue within the body

• Endosteal Implants: A device placed into the alveolar bone and/or basal bone of mandible/ maxilla that transects only one cortical plate. (Anusavice)

TYPES OF IMPLANTS

COMPONENTS OF AN IMPLANTAn endosteal implant has mainly three parts :1. Implant Body (fixture) :It can be further divided into- apex, crest module , body. It can have different surfaces. Generally made of titanium alloys.2. Transmucosal Abutment3. Implant Prosthesis

ADVANTAGES OF IMPLANTS:1. Improved maintainence of bone at edentulous site

2. Improved esthetics

3. Improved stability and retention for cases of implant supported prostheses

4. Psychological advantage

DISADVANTAGES OF IMPLANTS:5. Implants are highly expensive

6. Technique sensitive and time consuming

7. Cannot be done in patients who do not recover quickly

BRIEF OVERVIEW OF PLACEMENT OF IMPLANTS

Most common method used for implant placement is the TWO-STAGE SURGICAL PROCESS :1. First stage involves the surgical part, where

implant is placed within the bone. It is left within the bone until initial bone healing has occurred.

2. A second stage surgery is then done where the soft tissue is reflected and the implant is uncovered to attach the permucosal abutment.

3. The restorative phase then follows wherein a crown, a partial denture, or a removable overdenture is constructed .

OSSEOINTEGRATIONTheories of Implant to tissue integration :1. Wiess’ theory of fibro-osseous integration :

• Proposed by Dr.Charles Wiess• Complete encapsulation of the implant with soft

tissues• Soft tissue interface could resemble the highly

vascular periodontal fibers of natural dentition2. Branemark’s theory of osseointegration :

• Osseointegration is characterized by direct contact between bone and the surface of a functional implant

• It have also been achieved by the use of bioactive materials that stimulate formation of bone

BRIEF OVERVIEW OF MECHANISM OF OSSEOINTEGRATION

• It includes a process wherein bone producing cells migrate along the implant surface through the connective tissue scaffolding that forms adjacent to the implant interface.

• At first woven bone forms which is converted to lamellar bone under load stimulation

• Implant’s surface topography influences the strength of attachment to the bone

STRESS TREATMENT THEOREM FOR IMPLANT DENTISTRY

• The most common implant related complications are biomechanical problems that occur after implant is loaded

• Thus the overall treatment plan should

1. Assess the greatest force factors in the system

2. Establish mechanisms to protect the overall implant-bone prosthetic system

TREATMENT PLANNING FOR IMPLANT DENTISTRY

Carl E. Misch developed a treatment plan sequence to decrease the risk of biomechanical overload, consisting of the following:1. Prosthesis Design 2. Patient force factors3. Bone density in edentulous sites4. Key implant position and number5. Implant size6. Available bone in the edentulous sites7. Implant design

PROSTHETIC OPTIONS IN IMPLANT DENTISTRY

• According to stress treatment theorem by Misch, the final restoration is planned, similar to the architect designing a building before making the foundation

• Only after this the abutments necessary to support the specific predetermined restoration can be designed

• An axiom for implant treatment is to provide the most predictable and cost-effective treatment that will satisfy the patient’s anatomical need sand personal desires

MISCH PROPOSED FIVE PROSTHETIC OPTIONS FOR IMPLANT DENTISRY

REMOVABLE PROSTHESES :TWO TYPES BASED ON

SUPPORT

RP-4 RP -5

PATIENT FORCE FACTORS RELATED TO PATIENT CONDITIONS

1. PARAFUNCTIONS – BRUXISM, CLENCHING, TONGUE THRUSTING

2. CROWN HEIGHT SPACE3. MASTICATORY DYNAMICS4. ARCH POSITION 5. NATURE OF OPPOSING TEETH

PARAFUNCTIONS • These forces are most

damaging to the implant

• Bruxism –Primarily concerns horizontal, non-functional grinding of teeth. Presents with wear facets on teeth

• Clenching – A habit that generates a constant force exerted from one occlusal surface to other without any lateral movement. Donot present wear facets but cause fatigue fractures in implants

• Tongue Thrusting Habit

TREATMENT PLANNING FOR PARAFUNCTION PATIENTS

• Bruxism – Treatment plan is modified primarily in two ways when implants are inserted in posterior regions:

1. Additional implants that are wider in diameter

2. The anterior teeth may be modified to recreate the proper incisal guidance and avoid posterior interferences during excursions.

• Clenching – Additional implants are indicated with greater diameter, narrow posterior occlusal tables, and mutually protected occlusion are inicated

CROWN HEIGHT SPACE • It is measured from the crest

of the bone to the plane of occlusion in the posterior region and incisal edge of the arch in question in the anterior region

• Ideal CHS for fixed implants is 8-12mm

• Removable prosthesis often require > 12mm CHS

• Excessive CHS can cause increased stress accumulation leading to crestal bone loss (e.g – atrophied bone)

TREATMENT PLANNING FOR EXCESSIVE CROWN HEIGHT SPACE

• Because CHS is a considerable force magnifier various methods are adopted to decrease the stress:

1. Shorten the cantilever length

2. Minimize offset loads to the buccal and lingual

3. Increase the no. of implants

4. Increase diameters of implants

5. Fabricate removable restoration which are less retentive & incorporate soft tissue support

6. For >15mm CHS eliminated all occlusal contacts in centric relation in most posterior parts

TREATMENT PLANNING BASED ON NATURE OF OPPOSING TEETH

• Highest forces are created by implant prostheses because proprioception is lost .

• Case 1- When opposing arch has a fixed implant prosthesis or natural teeth Thus, length of cantilever should be reduced and no. of implants are increased

• Case 2 –When opposing arch have a removable denture the bite force is minimum

BONE DENSITY: A KEY DETERMINANT IN TREATMENT PLANNING

• There is an indisputable influence of bone density on clinical success

• Wolff in 1892 told that “every change in form & function of bone is followed by certain definite changes in the internal architecture and equally definite alteration in external confirmation, in accordance with mathematical laws

• Bone density decreases in jaws after tooth loss due to less loading

• Bone density change is greatest after tooth loss in posterior maxilla and least in anterior mandible

TREATMENT PLANNING BASED ON BONE DENSITY

• As the bone density decreases the strength of the bone decreases.

• To decrease the incidence of microfracture of the bone we must reduce the stress/ the biomechanical load on the implants by:

1. Shorten the cantilever length2. Overlying prostheses should have

narrow occlusal tables 3. Removable prostheses like RP-4

types are preferred so that they can be removed at night.

This reduces the effects from nocturnal parafunctions4. For soft bone types we can go for bone augmentation

TREATMENT PLANS RELATED TO KEY IMPLANT POSITIONS AND

IMPLANT NUMBERMisch proposed 4 guidelines for key implant positions 1. Cantilevers should be reduced or preferably eliminated

from the prostheses. Terminal abutments acts as key positions 2. Three adjacent pontics should not be designed 3. Canine & molar sites are key positions when adjacent

teeth are missing4. Arch dynamics where he divided each arch into five

segments Distance of an implant from adjacent natural tooth =1.5mm and adjacent implant =3mm {Misch}

No Cantilevers

• Cantilevers in prostheses acts as force magnifiers to the implants

• Ideal treatment plan should eliminate cantilevers

• Howevers in cases where where bone height is not available in posterior mandible we give cantilever pontics

• Cantilevers act as class 1 levers

No Three Adjacent Pontics

• Three adjacents pontics are avoided in prostheses as it leads to flexure of implant abutments on loading

CANINE & FIRST MOLAR SITESAND KEY ARCH POSITIONS

• When multiple teeth are missing and the canine edentulous site is a pier abutment position, the canine position is a key implant position which helps disocclude the posterior teeth during excursions

• First molar is also a key implant site

• Misch said that when multiple missing teeth extend beyond one of the open pentagon segments, a key implant position needs to be situated in each segment

• Patient with missing teeth from first molar to first molar

IMPLANT BODY SIZE• The initial treatment plan

should include the ideal implant size based primarily on biomechanic and esthetic considerations

• The size of an implant used to be determined primarily by the existing bone volume height, width, and length

• Ideal implant length under normal conditions is 12mm and upto 15mm for softer bone types

• 4mm diameter implant is used in most situations

RATIONALE FOR SHORTER IMPLANTS

• When the existing bone is short, as in posterior maxilla we have to use shorter implants (<12mm)

Implant Diameter

IMPLANT DESIGN BASED ON ESTHETICS

Anterior Tooth Replacement

• The implant body should be of lesser width than the natural tooth crowns.

This helps in mimicking the emergence profile of a natural tooth as the implant emerges.

• For multiple anterior implants each implant should be at a distance of 3mm from each other

Posterior Tooth Replacement

CASES WITH INSUFFICIENT BONE IN THE EDENTULOUS

SITE• Available bone can be

adjudged as compromised when :

1. Ridge width is less than 2.5mm

2. Ridge height is less than 12mm

3. Angulation of Occlusal Load >30degrees

4. Crown Height Space >15mm

• Treatment Modifications :

1. Osteoplasty

2. Subperiosteal implants

3. Ridge Augmentation

4. Transosteal Implants

5. Ramus frame implants

DIAGNOSTIC TOOLS USED FOR TREATMENT PLANNING

REFERENCES

•Contemporary Implant Dentistry ---- Carl E. Misch•Phillip’s Science of Dental Materials ---- Anusavice