treatment plans related to key implant positions and implant number

7/29/2019 Treatment Plans Related to Key Implant Positions and Implant Number

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The Primary causes of complications in ImplantDentistry are related to Biomechanics( Application of Physics and Mechanicsto the study of Movement) . Early Loading failures outnumber SurgicalHealing Failures, especially in Soft bone When forcesare Greaterthan usual or Implant sizes are shorterthan 10mm.

An Introduction


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Misch developed a treatment plan sequence to

decrease the risk of Biomechanical overload,

consisting of following-


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Prosthesis Design.

Patient Force Factors. Bone Density in the Edentulous sites.

Key Implant Positions and Number.

Implant Size. Available Bone in the Edentulous Sites.

Implant Design.

Treatment Plan Sequence


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The Incidence of Decay on a tooth Splinted In FPDgenerates 22% complications within 10 years.

Individual crown have less than 1% risk of Decaywith in 10 Years.

Unrestored natural teeth have less risk of Decay.

--- And As we Know ---

Implants Stand UNDECAYED!

Epidemiology


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A second complication of Teeth Supported FPD

restoration is Endodontic related factors in 15% of cases

with in 10 years.

Implant abutments dont require Endodontic Procedures.


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When an Implant restoration is joined to a Natural tooth

an Increased risk of Abutment Screw loosening Implant

Marginal bone loss and unretained restoration occurs.

So The Ideal Treatment Plan is-

An Independent Implant Restoration for Partially

Edentulous Patient.


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Guidelines for Key Implant Positions.

1) No Cantilevers-

Cantilevers are force Magnifiers to the Implants,Abutment Screws, and Implant Bone Interface.

Ideal Key Implant Position Include the Terminalabutment Positions when adjacent teeth are missing.

Key Implant Positions


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Fig 8-2


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A cantilevered restoration on multiple Implants becompared with a Class 1 lever.

Extension of the Prosthesis from the Last abutment isthe Effort Arm of the lever.

The Last abutment next to the cantilever acts as afulcurum when a load is applied to the lever.

The Distance between the last abutment and thefarthest abutment from the end of the cantilever isResistance arm or A-P spread of Implants.


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Mechanical Advantage=

The length of Cantilever(Effort arm)/Resistance arm

=20/10=2.

25 lb force on Cantilever results 50 lb force on thefarthest abutment from cantilever.

Abutment closest to Cantilever receives force = Sum of(25+50 )lb force.

Hence Proved Cantilevers Magnify forces to all theAbutments.

Mathematically..


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The Key Implant Positions when one or two adjacent

teeth are missing indicates one Implant per tooth .

A Three to Four unit Prosthesis may be fabricated with

only these abutments when force factors are low and the

bone density is favorable.

Restorations of 5-14 units require additional abutments.


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When the Implants are in one Plane ,the cantilever should

rarely extend farther than the A-P distance .

When force factors are unfavourable the cantilever length

should be reduced or eliminated, Implant number

increased ,implant size increased or the Implant design

surface areas increased.


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When five or more implants are positioned around

an arch and several different plains exist because ofthe arch form of the splinted Implant the Cantilever

may extend as far as 2.5 times the A-P distance when

force factors are low and density is favourable .

N.BMore than two pontics are not Indicated on a Posterior Cantilever even

under Ideal conditions.


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In most Prosthesis designs three adjacent Pontics are

contraindicated on Implants just as on natural Abutments

Rationale: Adjacent abutments subjected to additionalforce when supported by 3 missing teeth.

A one Pontic span exhibits little flexure 8m or less under 25 lbload.

A two pontic Span flexes 8 times more than a one Pontic span.

And three pontic span flexes 27 times more than one PonticSpan.(Metal Flexure is related to cube of Distance).

No Three Adjacent Pontics


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In most Prosthesis design three adjacent Pontics arecontraindicated on Implants just as on natural

abutments .Rationale: Adjacent abutments subjected to

additional force when supported by 3 missing teeth.

A one Pontic span exhibits little flexure 8 micrometer

or less under 25lb load.A two pontic span flexes 8 times more than a one

pontic space.


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And three pontic span flexes 27 times more than oneMetal flexure is related to Cube of distance.

No 3 adjacent Pontic


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The Flexure of Materials in a long Span is more aproblem for Implants than Natural teeth. As natural

roots have mobility both Apically and laterally thetooth acts as Stress absorber and amount of materialflexure may be reduced .

Natural teeth Vs

Implants


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The Span of Pontics in the ideal treatment Plan is

limited to the size of two Premolars which is

13.5-16mm.When a 2nd Premolar and first molar are missingtreatment is Planned to replace three teeth rather thantwo.

N.B-

A missing tooth span is often related to the missingnumber of roots in the mandible and number of buccalroots in the Maxilla.


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This is more appropiate for greater Patient forces

(moderate to severe parafunction) or softer bone

types i.e (D a ) .An Edentulous Arch missing on 14 natural teeth may

have 18 potential Implant size.

When 4-14 missing adjacent teeth are to be replacedkey Implant positions are located in the Terminal

abutments and additional Pier or Intermediaryabutments are indicated to limit the Pontic Spans to 2premolar size Pontics or less.


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5-7 premolar sized unit Prosthesis has 3 Keyabutments ( 2 terminal and one Pier).

C i d Fi M l


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Canine and First MolarSites


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When the 1st premolar ,canine and lateral Incisors aremissing key Implant positions are

1st Premolar and the canine.This results in a cantilever on the restoration

Lateral Incisor is Smallest tooth.

Anterior region has less bite force.

Canine Implant is larger than a lateral incisor implantfor meeting the esthetic requirement of the

restoration.


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Occlusion is modified so that so that no occlusalcontact is present on the lateral incisor Pontic in

Centric occlusion or excursions of the mandible.

In addition.


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When the Central ,Lateral Canine and FirstPremolar are missing the ideal key Implant positions

are Central and First Premolar.Rule Followed: Rule 1 viz No Cantilever.

Schematic representation:A


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When the Central ,lateral Canine, FirstPremolar,second Premolar and first molar are

missing the three key Implant positions are theCentral and 1st molar sites.( Rule 1).

And the Canine site ( Rule 2 and 3, no 3 adjacentpontic and canine and first molar Position.

Schematic representation:B


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When the central , lateral ,canine and first premolarand second premolar are missing there are three key

Implant Positions: The Central and second premolar ( Rule 1: No cantilever and the canine position ( Rule

3 the Canine and 1st molar position.

Schematic representation:C


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When 8 adjacent teeth are missing from secondPremolar to opposite canine there are four key

Implant positions : The canine and second Premolar position( Rule 1).

The opposite canine ( Rule 3).

One of central incisor positions (Rule 2).

Schematic representation:D


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When 10 adjacent teeth are missing from secondpremolar to second Premolar there are five key

Implant positions: The 2 second Premolar sites.(Rule 1)

The 2 canine sites.( Rule 3)

One of Central Incisor positions( Rule 2).

Schematic representation:D


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A traditional Fixed Prosthetic axiom

It is contraindicated toreplace a canine and two

or more adjacent teeth.


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Implants are required when the following adjacentteeth are missing in either arch:

1st premolar, Canine and lateral incisor. 2nd premolar ,1st premolar and canine.

Canine,lateral and Central Incisor.

RATIONALE-


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The length of the Span is 3 adjacent teeth.

The lateral direction of force during mandibular

excursion increase the stress.Magnitude of bite force is incresed in canine region

as compared to anterior region.

Therefore two key Implant positions required to

replace three adjacent teeth usually in terminalposition of span ( mainly when one of the terminalabutments is the canine.)


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When the patient is missing four teeth from the 1stpremolar to second molar there are 3 key Implant

positions to replace four teeth- The 1st premolar and 2nd molar sites.( Rule 1)

And the 1st Molar position ( Rule 3).

Schematic representation:A


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When the Patient is missing 6 adjacent teeth from theCito the first molar there are 3 Key Implant

positions. The Central and 1st molar position.( Rule 1)

And the canine position (Rule 3).

When a larger Implant cannot be inserted in to the

molar site an additional implant is required to followRule 2.

Schematic representation:B


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When the patient is missing teeth from first molar tofirst molar there are five key Implant positions-

The two first molars( Rule 1) The two canines ( Rule 3)

And a central Incisor (rule 2).

Additional Implants in the posterior region are

Indicated when larger diameter Implants is notpositioned in the 1st molar sites.( Rule 2).

Schematic representation:C


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Implants in the second premolar sites are usuallyindicated when force factors are moderate or bone

density is D. Even more Implant support is suggested when force

factors are severe or bone density is D


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Schematic

representation:D


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Key Arch Positions


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When a patient is missing eight teeth from 1 st

Premolar to 1st Premolar there are 5 key positions-

The 1st

Premolar site ( Rule 1,no cantilever and Rule4 One Implant in each open Pentagon segment.

The two canines- Rule 3 the Canine and first molarrule and Rule 4 , an Implant in each Pentagonsegment.

And an Implant in one one of the CI position ( Rule2, no three adjacent pontics . And rule 4, an Implantin each open pentagon segment.


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When two or more segments of an arch areconnected the tripod effect is Greater and as a benefit

an A-P spread is created from the most distalterminal abutments to the Most anterior Pierabutment.


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Implant should be positioned at least 1.5mm from an

adjacent natural teeth and 3mm from an adjacentImplant, each 4mm diameter implant requires 7mmof mesiodistal space.

Therefore maximum number of Implants betweenadjacent teeth can be calculated by taking the crestmodule of an Implant and adding these dimensions-

Minimum mesiodistal dimension for 2 standard4mm diameter Implants is=1.5mm+4mm+3mm+4mm+1.5mm=14mm.


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Splinted Dental unit provide greater prosthesisretention and transfer less force to the cement

interface as a result restoration is less likely tobecome uncemented.

Specially when Abutments are short or lateral forcesare present.

Splinted Implants


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A single crown has an endodontic risk of 3-5.6%

Splinted teeth have an endodontic risk of 18%

As Implants dont decay or need endodontic therapyhence indepent units would not be required toaddress these complications.

Why Splinted Implants

are here to Stay!


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Splinted Implants increase functional surfsce area ofsupport , increase the A-P distance ( A-P Spread) to

resist lateral loads increase increase cement retentionof the prosthesis.

Decrese

the risk of abutment screw loosening .

Marginal bone loss. The risk of Implant component fracture.


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In addition to biomechanical reasons if IndependentImplants fail over time Implant is removed the site

bone is grafted , the site is reimplanted and a newcrown is fabricated . When multiple splintedImplants have an Implant that fails the affectedImplant may be cut below the crown and theImplant or crown side is converted to Pontic.

Conclusion:


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A biomechanical based treatment plan reduces

complications after Implant loading with theprosthesis.

To reduce stress conditions there are key Implantpositions for a prosthesis replacing missing teeth

1) No cantilevers should be ideally designed on therestoration.

2) 3 adjacent pontics should be eliminated. 3) The canine and first molar sites are important

positions in an arch.


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An arch is divided in to 5 segments when more than1 segment of the arch is being replaced ,a key

Implant position is atleast ONE Implant in eachmissing segment


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Increasing the number of Implants is the mostefficient method to increase surface area and to

increase overall stress.Therefore after the keyImplant positions are selected additional implantsare indicated to reduce the risks of overload frompatient force factors or Implant sites with reducedbone density.


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Dr. Carl E. Misch(PhD).

Reference:


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Thank You!

treatment plans related to key implant positions and implant number

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