1 FP2 FPD Lecture 2011pdf

7/29/2019 1 FP2 FPD Lecture 2011pdf

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FIXED PARTIALDENTURESTreatment Planning and Biomechanicsreatment Planning and Biomechanics

Donna N. Deines, DDS, MSResources: Shillingburg, et al. Fundamentals of Fixed Prosthodontics

Rosenstiel, et al. Contemporary Fixed ProsthodonticsAquilino & Gratton, ACP Prosthopaedia

Goodacre, Principles of Tooth Preparation DVD

Pontic Retainer

Connector

Abutment

Abutment

Preparation

AbutmentPreparation

EdentulousRidge

Abutment

Abutment: natural tooth/implant serving as attachment for FPDRetainer: extracoronal restoration cemented to abutmentPontic: artificial tooth suspended from abutmentsConnector: rigid or non-rigid metal connecting pontics / retainers

Treatment of Tooth Loss

Caries

Periodontitis

Trauma, congenital Decision to remove tooth

Careful assessment

Replacement decision

Consequences of tooth loss:

Supra-eruption

Tilt ing

Loss of proximal contact

Disruption of occlusion

Restoration of the Occlusal Plane

Occlusal interferences are produced when FPD is made to a

supraerupted opposing dentition.

Opposing tooth restored to correct occlusal plane

May require RCT; periodontal surgery; orthodontics; extraction

Prevents occlusal interferences in restored dentition

Shillingburg

Relation of Tooth Loss to the Edentulous Ridge

Alveolar ridge resorption results vary due to individual

patient factors length of time, existence of periodontal

disease, trauma, arch, etc.


2/15

Relation of Tooth Loss to the Edentulous Ridge

Knife-edge ridge

Loss of interdental papillae

Gross soft tissue defects

Traumatic injury

Ablative surgery

Indications for a Fixed Partial Denture

Replace function of missing teeth

Stabilize occlusion drifting, prematurities

Provide esthetics and phonetics

Comfor t

Properly distributed abutments Both ends of edentulous space

Reasonable span length

Biomechanically solid abutments Restorable

Periodontally stable

No apical pathosis (vital or RCT)

Contraindications for Fixed Partial Dentures

Long edentulous spans / no distal abutment / non-restorable abutment

Poor 1o abutments: tipped teeth / divergent alignment / periodontallyweakened / short clinical crowns / insufficient # abutments

Unresolved periodontal disease / high caries index and risk

Severe loss of tissue in edentulous ridge

Minimally restored teeth where an implant retained restoration ispreferable.

Selection of the Type of Prosthesis for

the Partially Edentulous Patient

Removable Partial Denture

Tooth-Supported Fixed Partial Denture (FPD)

Resin-Bonded Fixed Partial Denture

an ever xe ar a en ure

Implant-Supported Fixed Partial Denture

Factors to consider

Biomechanical, periodontal, esthetic, financial

Treatment simplification

Treatment Options for Tooth Loss

Removable Partial Denture (RPD)

Long edentulous spans / no distal abutment / multipleedentulous spaces

Tipped / widely divergent abutments / few abutments

Periodontally weakened 1o abutments

Severe loss of tissue in residual ridge


3/15

Disadvantages of Removable Prostheses

Soft tissue irritation of edentulous ridge / dry mouth

Less comfortable than FPD Large tongue

Unfavorable attitude toward RPD

Esthetics often inferior to FPD

Conventional Fixed Partial Denture

Abutment on each end

Periodontally sound abutments, straight alignment

No gross soft tissue defect

Dry mouth increases risk of failure


Conservative, enamel preparation

Single missing tooth; slight - moderate tissue resorption

Good axial alignment and light occlusal stresses Especially indicated for younger patients Aquilino & Gratton,


Conservative, enamel preparation

Single missing tooth; slight - moderate tissue resorption

Good axial alignment and light occlusal stresses

Especially indicated for younger patients

Posterior Resin-Bonded FPD

Occlusal rests; 180o encirclement of axial tooth structure.

Single molar replacement requires minimum occlusal load.

Implant-Supported Crown / Fixed Partial Denture

Indications: insufficient abutments / no distal abutment

Single tooth implant saves virgin adjacent teeth

Limitations: availability of bone / ridge configuration


4/15

Implant-Supported Fixed Partial Dentures

Prosthesis is usually not attached to adjoining natural teeth.

Implant-supported fixed prosthesis placed in a totally

edentulous mandible

Limitations of Implant Placement

Amount of bone may severely limit potential for implantplacement - maxillary sinus / mandibular canal

Precise abutment alignment and positioning for favorableocclusal forces

Vertical forces prevent unfavorable lateral loading ofimplants

Implant-Supported Fixed Partial Dentures

Insufficient number of abutment teeth

Lack of distal abutment

Connection of implants / natural teeth can be compromised

Biomechanical differences due to lack of PDL in implants

Case Presentation

Present treatment options

Advantages / disadvantages

Patient input esthetics, finances

Understand risks / responsibilities

Informed Consent

No prosthetic treatment

Unrealistic expectations

Do no harm

Abutment Evaluation

Coronal Tooth Structure

Pulp Status / Endodontic Assessment

Periodontal Health / Support

u men nc na on

Orthodontic position

Occlusion

Coronal Tooth Structure

Clinical exam, radiographic exam, diagnosticcasts (mounted)

Adequate retention and resistance form? Is the tooth restorable as is?

If not, can it be gained with foundation or modification ofpreparation?

What is the apical extent of caries orrestoration?


5/15

Abutment Evaluation: Remove all caries, oldrestorations, base; then evaluate.

Pulp exposure? Symptomatic? PA pathology?

Proximity of cavity depth to alveolar crest

Biologic width

Adequacy of retention / resistance form

Pulpal Health: Vital or Endodontically Treated

Asymptomatic with sound tooth structure remaining

Questionable / pulpal exposure RCT before FPD

Radiographic Evaluation for FPDs Caries

Un-restored proximal surfaces

Recurrent restorations

Periapical lesions

Existence / quality of previous RCT

C:R / length, configuration, direction of roots

Widening of PDL (w/ occlusal prematurities)

Thickness of cortical plate; trabeculation

Presence of root tips / other pathology

Thickness of soft tissue edentulous ridge

Maxillary sinus; TMJ; third molars

Evaluation of Diagnostic Casts:AccurateMounted on semi-adjustable articulator w/ facebow / CR

Edentulous spaces and span

length

Curvature of the arch

nc na on o a u men ee

M-D drifting, rotation, F-L

displacement of abutments

Occlusocervical dimension

Interocclusal relationships

Abutment Inclination / Alignment: Path of Insertion

Axial walls of abutment

teeth must be aligned

w/o any undercuts.

Discrepancies in the long axes of abutment teeth

Complicates the ability to prepare axial walls with a

common path of insertion.

Mesio-distal and Facio-lingual inclinations


6/15

Abutment InclinationAbutment Inclination

Adjacent tipped tooth can prevent FPD from

seating in the common path of insertion.

Path of Insertion: Diagnostic Cast / Surveyor

Useful for:

Pre-preparation planning

During preparation phase

Evaluation

Evaluation of Interocclusal Relations

Interocclusal space is necessary to re-establish a proper

occlusal plane.

Thickness of pontics/ connectors for strength

Room for artificial teeth / framework (FPD, implants, RPD)

The occlusion may be acceptable or changes maynecessary.

Diagnostic waxing: visualize problems and results

Diagnostic Waxing and Case Planning

OR

Healthy periodontium: a prerequisite for all fixed

prosthodontic restorations

No mobility / zone of attached tissue / good oral hygiene

Additional abutment evaluation of the periodontium:

Crown-root ratio

Root configuration

Periodontal ligament area


7/15

Abutment Evaluation: Crown-Root Ratio

2

3

1

1

Ratio of the portion of tooth occlusal to the alveolar crest (CROWN)VS. the portion of tooth embedded in bone (ROOT)

Optimum C:R is 2:3

Minimum C:R is 1:1

Periodontal Disease - Horizontal bone loss

dramatically reduces supported root surface area

Conical root shape diminishes actual area of support morethan expected from the height of bone.

The center of rotation (R) moves apically and the lever arm(L) increases, magnifying the forces on the supportivestructure.

Rosenstiel

A crown-root ratio 1:1 may be adequate if:

Opposing occlusal force is

diminished

Artificial teeth Dentures, RPD

er o on a y comprom se

opposing dentition

Root ConfigurationAbutment Evaluation: Root Configuration

Broader facial-lingual than mesio-distalpreferred to round

Multi-rooted better than single, conical root

Single-rooted teeth with irregularconfiguration or curvature preferable

to perfect taper

Widely separated better than fused roots

Long roots

Root Morphology

2nd molar long, separated roots;

1st molar extensive caries and positioned

against adjacent tooth.

Abutment Evaluation:

Root Surface (Periodontal Ligament) Area

Antes Law: The root surface area of the abutment

teeth (embedded in bone) should equal or surpass that of

the teeth being replaced with pontics.

Rosenstiel


8/15

Generally successful

Antes Law: The root surface area of the abutment teeth should

equal or surpass that of the teeth being replaced with pontics.

Shillingburg

Probably, but limit is being approached

Antes Law: The root surface area of the abutment teeth should

equal or surpass that of the teeth being replaced with pontics.

Shillingburg

Generally unacceptableAny FPD replacing more than 2 posterior teeth - risky

Maxillary arch more often possible than mandibular (when all

conditions ideal) - longer clinical crowns / less abutment inclination

Shillingburg

Anterior FPD replacing incisors

Most common FPD to replace more than two

teeth with success

Antes Law A guideline with validity

(More than just overloading the PDL)

Long span FPDs fail due to abnormal stress attributed to:

1) Leverage and torque

2) Material failure

Bio-mechanical Considerations

Simple:

1 or 2 teeth missing

2 abutments

Complex:

, , or grea er an a u men s splinted or pier abutments

more than 3 missing teeth

non-parallel abutments

combined anterior and posterior FPDs


9/15

Biomechanical Problems:

Bending or Deflection of the FPD

Fracture of porcelain veneer

Connector breakage

Retainer loosening and caries

Unfavorable tooth or tissue response

Deflection of the FPD relates to span length

The deflection is proportionalto the cube of the length of

its span (varies directly).

Deflection = Load (Length)3

4eWidth (Height)3

FPD flexure varies directly by x3

where x is the inter-abutment

distance, therefore:

2p = 8 times increase in flexure

3p = 27 times increase in flexure

Rosenstiel

Deflection and FPD Span Length

S.A.A. U of I

Deflection of the FPD relates to OG Dimension

(Pontic / Connector Thickness)

Deflection = Load (Length)3

4eWidth (Height)3

FPD flexure varies inversely by t3 where t is the height(or thickness) of the connector, therefore:

1/2t = 8 times increase in flexure

1/3t = 27 times increase in flexure

Deflection and Height of Connector / Pontic Thickness

Design pontic/connector with adequate O-C thickness

(Plan ahead with diagnostic waxing abutment evaluation)

Use alloy with high yield strength

BIOMECHANICAL CONSIDERATIONS

Deflection of the FPD

Abutments and retainers receive greater

dislodging forces than a single crown

Magnitude and direction Modify preparations to increase retention

and resistance form / structural durability

Place boxes / grooves in response to

direction of anticipated torque


10/15

Dislodging forces on an FPD

Occlusal force on pontics can cause M-D torque.

Forces at an oblique angle or outside the center of the

restoration cause F-L torque (around M-D axis of rotation) .

Shillingburg

FPD and Dislodging Forces

Grooves / boxes 8resistance to dislodgement. Place boxes / grooves in response to direction of anticipated torque.

Use retainer with appropriate retention / resistance

Wall length / occlusal convergence / geometric resistance form

Effect of Arch Curvature on FPD Deflection

Pontics lying outside the inter-abutment axis act as a leverarm torquing movement.

Additional resistance in opposite direction from lever arm;

distance = to length of the lever arm (2o

abutments)

Shillingburg

Double abutments (splinting) can help problems

caused by poor crown-root ratio and long spans.

Double abutments help stabilize the prosthesis by

distributing forces over more teeth.

Periodontally weakened teeth

Criteria for (splinted) secondary abutments:

Root surface area and C:R must = 1o abutments

2o retainers must have retention of 1o retainers

Long crown length and adequate interproximal space forconnectors

Shillingburg

Long-term periodontal splint

Bone loss and increased physiologic movement

Deflection / torque microleakage / debonding

Caries involvement of abutment teeth

Fracture of RCT abutment with large amount of missing tooth

structure


11/15

SPECIAL PROBLEMS: Pier Abutments

An edentulous space on both sides of a lone free-

standing abutment

Physiologic tooth movement

direction and amount varies from anterior to posterior

SPECIAL PROBLEMS: Pier Abutments

Cause of failure - loosened retainer

Prosthesis flexure / movement of teeth

Tensile stresses between terminal retainersand abutments; intrusion of abutments under

Differences in retentive capacities between

abutments (relative to size)

Extensive caries through crown

resulting from #6 retainer de-

bonding from abutment.

Non-Rigid Connector

Rosenstiel

Non-Rigid Connector / Pier Abutment

Criteria for use:

Short span length

Non-mobile abutments

Equal distribution ofocclusal force

No edentulous space / RPD

Location:Location:

Within distal surface of pier retainerWithin distal surface of pier retainer((mesialmesial seating action of posteriors)seating action of posteriors)

Special Problem: Pier Abutment

Where periodontal support is adequate, a simpler

approach could be a mesial cantilever pontic.

Rosenstiel


12/15

Implant-supported Cantilever FPD #5-#6-#7 SPECIAL PROBLEMS: Tilted Molar Abutment

Discrepancy between long axis of molar

and premolar abutments

25o - 30o - maximum angle of tilting

Stress Distribution in Fixed Partial Dentures

An FPD distributes forces favorably by directing forces in

the long axis of the abutment teeth.

Well-aligned abutment teeth provide better support than

tipped abutment teeth. Non-axial loading proximal crestal bone loss

SPECIAL PROBLEMS: Tilted Molar Abutment

Generally poor abutments

Mesial wall must be over-reduced ( resistance)

Distal adjacent tooth may intrude on the path of insertion

Mesial surface may need re-contouring or restoration

Rosenstiel


Plan path of insertion / preparation design on diagnostic

cast.

Surveyor may help in determination of preparation design

for common path of insertion.

Rudd & Morrow Rosenstiel


Occlusal reduction is not always the same as clearanceneeded.

Remove only enough tooth structure to providenecessary space for the restoration.

Allows for longer axial wall length.

Shillingburg


13/15


Molar uprighting optimum

Places abutment in better position forpreparation

Distributes forces underloading through long axis oftooth (helps eliminate mesial bony defects)

Enables replacement ofoptimum occlusion

Rosenstiel

Tilted Molar Abutments: Proximal Half Crown

Proximal Half Crown does not involve distal wall

3/4 crown rotated 90o

Requirements: Caries-free distal surface

Low incidence of caries

Even marginal ridge height

Short span length

RosenstielShillingburg

Tilted Molar Abutments:

Telescopic Coping and Crown

Full crown preparation and coping

with path of insertion in long axis of

tooth

Full coverage crown compensates

for discrepancy in paths of insertion

Must over-reduce molar to

accommodate the thickness of

coping and crownShillingburg

Tilted Molar Abutments: Non-Rigid Connector

Allows slight movement - short span

Keyway in distal of premolarto avoid intrusion ofmolar (mesial seating action)

Must prepare boxin distal of premolar preparation (To accommodate the female / keyway)

Too much inclinationShillingburg

Canine Replacement FPD (Complex)

Pontic lies outside the inter-abutment axis

Stress is greater / less favorable on maxillary arch Forces inside arch (weak - tension)

Stress more favorable in mandibular arch Forces outside arch (strong compression)

Shillingburg

Canine Replacement FPD

Pontic lies outside the inter-abutment axis

Adjacent teeth are weakest possible abutments

Should not replace more than one additional tooth

Canine plus 2 contiguous teeth poor prognosis

restore with implants if possible

(Splint central incisors and premolar / molar)

Shillingburg


14/15

SPECIAL PROBLEMS: Cantilever FPD(Potentially destructive lever arm)

Replace only 1 tooth, andhave at least 2 abutments

Long root w/ good configuration

Long clinical crown

Favorable crown:root ratio and

healthy periodontium

Shillingburg

Conventional FPD

Conventional FPD (replacing lateral incisor)

Shillingburg

Cantilever FPD

Cantilever FPD (replacing lateral incisor)Cantilever FPD:

Replacement ofmaxillary lateral incisor

Only the canine should be used as a solo abutment

Rest should be placed on mesial of pontic against a restprep in a restoration in the distal of the central incisor

Good clinical crown length / orthodontic position

Shillingburg

Unfavorable Occlusion: deep vertical overlap(Cantilever FPD or Resin-Bonded FPD)

Maximum Intercuspation

Lateral Excursive Canine Guidance

Unfavorable Cantilever:

Lateral incisor abutment

Severe vertical overlap

Unfavorable Central Incisor Cantilever Pontic FPD

Solution:

1) Conventional FPD #8-#102) Single implant-retained crown


15/15

Cantilever FPD:

Replacement ofFirst Premolar

Use full veneer retainers on the 2nd premolarand 1st molar.

Limit pontic occlusion to distal fossa.

Shillingburg Rosenstiel

Cantilever FPD: First PremolarMetal-ceramic crown retainer 2nd Premolar

Mesial rest on pontic

Resin-bonded rest seat on canine

When using a rest on a cantilever pontic, always

place a rest seat in a restoration on the abutment.

Caries can develop due to inadequate cleansability.

Caries

Cantilever FPD: Molar ReplacementVery Unfavorable

Extreme leverage forces generated by posterior position

Occlusal forces place tensile stress on 2o retainer

Shillingburg

Cantilever FPD: Replacement ofFirst Molar

(Unfavorable)

Pontic size small (premolar)

Light occlusal contact; no excursive

contact Pontic and connector

Maximum O-G height for rigidity

Good crown:root ratio of abutments

Clinical crowns - maximum preparation

length and resistance form

Shillingburg

1 FP2 FPD Lecture 2011pdf

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