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8/13/2019 FPD Lecture 2009-2
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FIXED P RTI LDENTURESTreatment Planning andBiomechanics
Donna N. Deines, DDS, MS
Resources: Shillingburg, et alRosenstiel, et al
Components of the FPD
Abutment: tooth serving as attachment for FPD
Retainer: extracoronal restoration cemented to abutment
Pontic: artificial tooth suspended from abutments
Connector: 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
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
Indications for a Fixed Partial Denture
Replace function of missing teeth
Stabilize occlusion (drifting, prematurities)
Improve stress distribution
Provide esthetics and phonetics
Comfort
Contraindications for FPD
Too great a span length
Long edentulous space at the end of an arch
Tipped abutments, divergent alignment
Non-restorable abutment teeth or periodontium
Severe loss of tissue in the edentulous ridge
(Limited financial ability / advanced age or
systemic (terminal) illnesses)
Stress Distribution in Fixed Partial Dentures
An FPD distributes forces favorably by directing
forces in the long axis of the abutment teeth.
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
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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
Span length limited by availability of bone / ridge configuration
Implant-Supported Fixed Partial Dentures
Prosthesis is usually not attached to adjoining natural teeth.
Implant-supported fixed prosthesis placed in a totally edentulousmandible
Limitations of Implant Placement
Amount of bone may severely limit potential for
implant placement - maxillary sinus / mandibular canal
Precise abutment alignment and positioning for
occlusal forces
Implant-Supported Fixed Partial Dentures
Insufficient number of abutment teeth
Lack of distal abutment
Connection of implants / natural teeth can be compromised
Indications for Removable Partial Dentures
Periodontally involved teeth
Tilted molar abutments
Multiple edentulous spaces
Edentulous space with no distal abutment
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Treatment Options for Tooth Loss
Removable Partial Denture (RPD)
Gross soft tissue defects
Traumatic injury
Ablative surgery
Disadvantages of Removable Prostheses
Soft tissue irritation of edentulous ridge
Less comfortable than FPD
Esthetics often inferior to FPD
Fixed partial dentures are preferred for
comfort and estheticsCase Presentation
Present treatment options
Advantages / disadvantages
Patient input esthetics, finances
Agree on definitive treatment
plan Understanding of risks /
responsibilities
No prosthetic treatment Unrealistic expectations
Do no harm
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Abutment Evaluation
Caries
Existing restorations Endodontic assessment
Periodontal health
Orthodontic position
Occlusion
Abutment Evaluation: Remove all caries, oldrestorations, base; then evaluate.
Pulp exposure? Symptomatic? PA pathology?
Proximity of cavity depth to alveolar crest
Biologic width
Pulpal Health: Vital or Endodontically Treated -Asymptomatic with sound tooth structure remaining.
Questionable / pulpal exposure RCT before FPD
Evaluation of Diagnostic Casts:AccurateMounted on semi-adjustable articulator w/ facebow / CR
Edentulous spaces and span
length
Curvature of the arch
Occlusocervical dimension
Inclination of the abutment
teeth
M-D drifting, rotation, F-L
displacement of abutments
Interocclusal relationships
Abutment Alignment and Path of InsertionEvaluation of the path of insertion
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Discrepancies in the long axes of abutment teeth
Complicates the ability to prepare parallel paths of
insertion.
Facio-lingual and mesio-distal inclinations
Evaluation of Interocclusal Relations
Interocclusal space is necessary to re-establish a
proper occlusal plane.
The occlusion may be acceptable or changes may
necessary.
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
Abutment Evaluation: Crown-Root Ratio
Crown - Root Ratio
Length of tooth occlusal to the alveolar crestcompared with the length of root embedded in bone
Optimum C:R is 2:3
Minimum C:R is 1:1
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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
Periodontally compromised
Abutment Evaluation: Root Configuration
Favorable: elliptical; widely
separated roots; curvature in
apical 1/3
Unfavorable: round; fused roots;
conical taper
Well aligned tooth provides
better support than a tilted one.
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.
Generally successful
Antes Law: The root surface area of the abutment teeth should
equal or surpass that of the teeth being replaced with pontics.
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Deflection of the FPD relates to span length
The deflection is proportional
(varies directly) to the cube
of the length of its span.
Law of Beams
Bending also varies inversely with the cube of the
occlusogingival thickness of the pontic / connector
Design pontic/connector with adequate O-G thickness
Use alloy with high yield strength
BIOMECHANICAL CONSIDERATIONS
Bending or deflection of the FPD
Abutments and retainers receive greater
torque than a single crown
Modify preparations to increase retention and
resistance
Place boxes / grooves in response to direction of
anticipated torque
Dislodging forces on an FPD
Occlusal forces can act in a M-D direction on an FPD.
Forces at an oblique angle or outside the center of the
restoration cause F-L dislodgement .
FPD and Dislodging Forces
Grooves / boxes resistance to dislodgement.
Place boxes / grooves in response to direction of
anticipated torque.
Use retainer with appropriate retention / resistance.
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.
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Criteria for secondary abutments:
Root surface area and C:R must = 1o abutments
2o retainers must have retention of 1o retainers
Long crown length and adequate interproximalspace for connectors
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 toothstructure
Is splinting necessary here?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
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 retainers
and abutments; intrusion of abutments under
loading
Differences in retentive capacities between
abutments (relative to size)
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FPD #4-6-8 (Pier abutment #6)
Rigid Connectors
Extensive caries through crown
resulting from #6 retainer
debonding from abutment.
Non-Rigid Connector Non-Rigid Connector / Pier Abutment
Criteria for use: Short span length Non-mobile abutments
Equal distribution of
occlusal force
Location:Location:
Within distal surface of pier retainerWithin distal surface of pier retainer
((mesialmesial seating action of posteriors)seating action of posteriors)
Non-rigid connector (stress breaker)Special Problem: Pier Abutment
Where periodontal support is adequate, a simpler
approach could be a mesial cantilever pontic.
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Implant supported FPD #5-#6-#7 SPECIAL PROBLEMS: Tilted Molar Abutment
Discrepancy between long axis of molar
and premolar abutments
25o - 30o - maximum angle of tilting
SPECIAL PROBLEMS: Tilted Molar Abutment
Mesial wall must be over-reduced ( resistance)
Distal adjacent tooth may intrude on the path of insertion
SPECIAL PROBLEMS: Tilted Molar Abutment
Plan path of insertion / preparation design on diagnostic
cast.
Surveyor may help in determination
SPECIAL PROBLEMS: Tilted Molar Abutment
Occlusal reduction is not always the same as clearanceneeded.
Remove only enough to provide necessary space forthe restoration.
Allows for longer axial wall length.
SPECIAL PROBLEMS: Tilted Molar Abutment
Molar uprighting Places abutment in better position for preparation
Distributes forces under loading through long axis oftooth (helps eliminate mesial bony defects)
Enables replacement of optimum occlusion
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Orthodontic Movement: Molar UprightingTilted Molar Abutments: Proximal Half Crown
Proximal Half Crown does not involve distal wall
A 3/4 crown rotated 90o
Requirements:
Caries-free distal surface
Low incidence of caries
Even marginal ridge height
Proximal Half
Crown Retainer
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 crown
Tilted Molar Abutments: Non-Rigid Connector
Allows slight movement - short span
Keyway in distal of premolarto avoid intrusion ofmolar (mesial seating action)
Must prepare box in distal of premolar preparation
Canine Replacement FPD (Complex)
Pontic lies outside the inter-abutment axis
Stress is greater on maxillary arch Forces inside arch (weak - tension)
Stress more favorable in mandibular arch Forces outside arch (strong compression)
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Resin-bonded hybrid cantilever
Full crown retainer central incisor #9
Resin-bonded wing / mesial preparation #7
Favorable occlusion
Cantilever FPD:
Replacement of First Premolar
Limit pontic occlusion to distal fossa.
Use full veneer retainers on the 2nd premolar
and 1st molar.
Cantilever: First Premolar
Resin-bonded retainer on canine
(mesial rest)
When using a rest on a cantilever pontic, always
place a rest prep in a restoration on the abutment.
Caries
Missing tooth less than space
Change proximal contour / occlusion
Button pontic
Importance of resistance form: clinical crown length;
facial lingual grooves; minimal taper
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Cantilever FPD: Molar Replacement
Very Unfavorable
Extreme forces generated by posterior position(Class 2 lever)
Occlusal forces place tensile stress on 2o retainer
Cantilever FPD: Replacement of First MolarUnfavorable
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