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.
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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
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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
Resin-Bonded Fixed Partial Denture
Conservative, enamel preparation
Single missing tooth; slight - moderate tissue resorption
Good axial alignment and light occlusal stresses Especially indicated for younger patients Aquilino & Gratton,
Resin-Bonded Fixed Partial Denture
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
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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?
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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
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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
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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
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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
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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
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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
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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
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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
SPECIAL PROBLEMS: Tilted Molar Abutment
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
SPECIAL PROBLEMS: Tilted Molar Abutment
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
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SPECIAL PROBLEMS: Tilted Molar Abutment
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
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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
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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
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