Lectures 1-4

Lecture 1: Fundamentals of Fixed Partial Dentures

Fixed Partial Denture (FPD)

aka “bridge”
naming/describing: material+ FPD + designate pontic with “p” [ex: metal ceramic FPD #18-19p-20]
goes on teeth or implants to replace missing teeth in a partially edentulous arch; CANNOT be removed by the patient
comparing tooth replacement options:
- FPD: tooth supported fixed partial denture (bridge)
- Implants: either an implant supported single crown OR implant supported fixed partial denture
- RPD: removable partial denture
functions of FPD
- to replace missing teeth
- provide proper occlusal function
- maintain arch integrity/tooth position
- maintain occlusal relationship
- restore function, esthetics, and speech
Defining terminology
- abutment= a tooth/implant serving as an attachment for a fixed partial denture (Bridge)
- pontic= the artificial tooth on a FPD that replaces the missing natural tooth to restore function
- retainer= extra-coronal restorations that are cemented to or otherwise attached to the abutment teeth or implants in a FPD
- connectors= the portion of a fixed partial denture that unites the retainers and the pontic
Types of Pontics
- saddle
- modified ridge lap
- ovate
- conical
- hygienic

refers to the part in contact with the edentulous ridge

bounded vs cantilevered pontics
- bounded=supported on both ends; both ends are retainers
- cantilevered= supported on one end but not the other
Connectors
- the part connecting the retainer tot he pontic
- rigid vs non-rigid connector

Principles of Tooth Preparation

in tooth supported FPDs the abutments (tooth) must be prepared to receive the retainers (crown)
preservation of tooth structure
- aims to preserve as much sound tooth structure as possible and preserve the pulpal vitality
- we must remove structure for caries and defects, to provide room for the restoration bulk, for proper POI retention and resistance, and for esthetics
outline of preparation
- clinically the outline will be determined by existing restorations, caries, defects, esthetics, and retention
- sim lab: 0.65mm supraginigival, 0.5mm gingival separation, and no damage to adjacent teeth or gingiva
internal reduction
- avoid unnecessary removal of sound tooth structure but prep must also provide space for the necessary bulk of the restorative material
marginal integrity
- margin of restoration closely adapted to finish line of the preparation= margins sealed when restoration is fully seated
- finish line must terminate on sound tooth structure
- appropriate margin design/configuration
- well supported, clear, smooth and continuous
preservation of the periodontium
- we prevent over-contouring by reduce enough gingival-axially which gives space for the material
  - over-contouring causes food impaction & irritation to the periodontium
- supra-gingival finish lines aid in visual accessibility
- sub-ginigval finish lines irritate the periodontium and cause plaque accumulation bc its harder to clean
  - sub-gingival finish lines acceptable- caries or defect go below the gingiva; to aid in retention for wall height
- must be wary when placing sub-gingival finish lines- sealing the margins; invasion of biological width (avg 2mm)
retention and resistance
- retention- prevent displacement along path of insertion
- resistance- prevent displacement along planes outside of POI
- factors that contribute to retention: taper, surface area, surface roughness, wall height
- treat the entire FPD like one big tooth; most look at convergent/divergent walls across BOTH abutments
  - extra-coronal element- convergence
  - intra-coronal element- divergence
- properly tapered walls 6-10 degrees (M/L and B/L walls)
- wall height 3.0mm ideal; minimum 2.5 mm
- no undercuts or parallel walls; no undercuts between abutments
- secondary features properly placed
- ***the most important walls for FPD retention are the M wall of the mesial abutment and the D wall of the distal abutment; for longer span FPD more inclination of the distal wall may be necessary to get the draw
- note: dislodging forces on a FPD tend to act in the M/D direction
FPD path of insertion
- FPD preparation is one big tooth!! we prep similar planes at the same time (lingual on one tooth and lingual on the other)
- POI follows the long axis of the smaller abutment
  - adjacent tooth can be used as reference/guide for the POI of the smaller tooth
- POI must be coincident between the abutments; so POI of larger abutment will be parallel to the POI of the smaller abutment
- do NOT change angulation of the bur between abutments; therefore all gauging grooves placed should be parallel to each other
- buccal and lingual walls converging on each abutment
- order: buccal/lingual walls —> proximal reduction (outer walls) —> occlusal reduction —> inner walls proximal reduction —> second and third planes

Lecture 2: FPD Provisionals & Pontic Design

Pontics

definition: an artificial tooth on a fixed partial denture that replaces a missing natural tooth, restores its function, and usually restores the space previously occupied by the clinical crown
ideal characteristics:
- restore function of the tooth it replaces
- smooth and polished pontic surface for tissue health
- mostly convex to allow for proper cleaning
- restore esthetic contours confluent with the adjacent teeth
- positive contact with ridge
- pontic design varies based on the ridge configuration
Siebert Classification of Ridge Defects
- Class I: horizontal defect —> loss of facio-lingual width with normal ridge height
- Class II: vertical defect —> loss of ridge height with normal width
- Class III: combination defect —> loss of both height and width of the ridge

Pontic Designs

saddle pontic
- aka “ridge lap”
- any extension of the pontic past the crest of the ridge still constitutes a saddle
- large concave contact with ridge
- more difficult to clean, may cause tissue inflammation
- esthetic replacing all contours of the missing tooth
modified ridge lap pontic
- gives illusion of a tooth but nearly all convex surfaces for ease of cleaning
- lingual has a deflective contour to prevent food impaction and minimize plaque accumulation
- should not extend further lingually than the middle of the crest
- slightly concave contacting the ridge to the buccal
- indicated for esthetic zone maxillary and mandibular FPDs
Ovate
- rounded-end design
- indicated where esthetics is primary concern
- for broad, flat ridge, gives appearance of emerging out of the ridge
- tissue-contacting area of pontic is bluntly rounded, it seats into a concavity in the ridge
- concavity can be created by placement of FPD with pontic into socket immediately after extraction of tooth, or surgically on an edentulous ridge
- surgical preparation for ovate pontic
  - egg shaped
  - contour residual ridge with round/football diamond bur
  - buccal center 0.5-1.5mm below the buccal emergence profile
  - inter-proximal measurement can be as deep as 3-4mm depending upon the proximal papilla
Conical Pontic
- indicated for thin mandibular ridges
- rounded and easy to clean
- not indicated in broad ridges since it creates areas of food trap
Hygienic Pontic
- also known as “sanitary pontic”
- no contact with the edentulous ride, all aspects are convex
- used for non-esthetic area (mandibular first molar) gingival thickness of pontic must be at least 3mm
- access for hygiene but may become a food trap
- not commonly used
Lab Rx for Pontics
- step 6 of the USC lab slip
- can choose what style of pontic you want (modified ridge lap, ovate, saddle, conical, hygienic)
- can choose how much compression you want (not applicable for hygienic style pontic

Connectors

def: the portion of a FPD that unties the retainers and pontic
a rigid connector must be rigid enough to prevent movement and bending
Law of Beams: bending or deflection varies directly with the cube of the length and inversely with the cube of the occlusoginigval thickness of the pontic span

connector dimensions
- as tall and wide as possible
- increasing height has greater effect on reducing deflection
- the longer the span, the greater the cross section of the connector is required

Preparing for FPD Provisional

goal: maximize connector cross section for fracture resistance
wax-up lingual embrasures to increase the width for the strngth of the connectors
additional wax up margins on the abutment teeth (same as single unit)
on long span FPD provisional a metal or fiber reinforced FPD may be needed

Provisional:

definition= fixed or removable prothesis designed to enhance esthetics, stabilization, and/or function for a limited period of time, after which is to be replaced by a definitive prothesis
functions:
- provides the template for the final restoration
  - assist in the determination of the therapeutic effectiveness or the form and function of the planned definitive prothesis
  - allows for evaluation of parallelisms of the abutment
  - allows for evaluating an occlusal schemes before the definitive restoration
- provides patient comfort and pulpal protection of the abutment teeth
- maintains positional stability of the abutments
- restores occlusal function and esthetics
- favorable for periodontal health (non-impinging margins, proper gingival embrasures to facilitate cleaning)
Provisional Materials
- self-cure/dual-cure composite resin
  - ex: bis-acrl
- light-cure composite resin
  - ex: Fermit-N
- acrylic resin
  - material w/ high strength and fracture resistance required
  - ex: polymethyl methacrylate (PMMA)
    - advantages: good margin adaptation, good strength, good polish-ability, easy repair, esthetic
    - disadvantages: exothermic rxn, volumetric polymerization shrinkage ~6-7%, soft tissue/pulpal irritation w/ excess free monomer, allergic reactions to monomer
    - provisional fabrication techinque = indirect-direct technique
  - ex: polyethyl methacrylate (PEMA)
    - advantages: minimal exothermic heat, good stain resistance, good polishability, low shrinkage
    - disadvantages: lower strength, lower fracture toughness, poor wear resistance, poor color stability
  - ex: CAD/CAM Acrylic Resin
    - advantages: high flexural strength, less porosity (pre-polymerized), color stability, good abrasion resistance
    - disadvantages: CAD/CAM digital workflow, time consuming, expensive, require specific thickness (occ. 1.5mm and margins 0.8mm)

Indirect-Direct PMMA Shell Provisional

1) Shell Fabrication
- done prior to pt tooth prep appt
- requires prep of teeth on a plaster cast
- indirect technique PMMA shell fabrication
- shell provides the contours for the provisional
- separators: alcote or vaseline
- pressure pot —> 20PSI for 5 mins
2) Shell Adjustment
- intra-oral try-in shell adjustments
- shell proximal contacts and internal may require additional relief so shell will seat passively and allows for relining material
- no hyper-occlusion prior to relining!!
3) Shell Reline
- reline is done direct intra-orally by adding mix of PMMA to adjusted shell
- pt closes in MIP during initial setting of material
- need to use air-water to control the heat from exothermic rxn during setting
- intermittently pump up and down to avoid locking
- remove the relined shell before complete setting
4) Provisional
- inspect that margins and details have been captured
- trim in same sequence as the single unit
- additional trimming of the gingival embrasures
  - should be open for cleaning and gingiva health
  - lingual embrasures- over contoured to maintain width of connector for strength
  - buccal embrasures- trimmed and defined for esthetics
- occlusal contacts hold mylar on the adjacent teeth and on the retainers of the FPD [for anterior FPD, drag mylar]

FPD Provisional Pontic

should have the prescribed design
must be smooth and polished
- important for tissue health
must have positive contact with the ridge
should challenge the tissue and drag mylar
template for definitive restoration
- esthetic changes made on provisional for patient approval
- take alginate impression of approved provisional and pour up cast for lab tech to use as reference for final rest.
- communicates: contour, shape and size; embrasures, line angles and texture; incisal length and position; midline and symmetry; occlusion and function

**Patient receives post op instructions for cleaning = use floss threader or super floss to clean

Lecture 3: Treatment Planning Considerations for Tooth Replacement

treatment plan = the sequence of procedures planned for the treatment of a patient after diagnosis
data collection & diagnosis = chief complaint, health history and dental history, intra-oral examination and periodontal charting, diagnostic casts, radiographs// diagnosis & diagnostic wax-up, treatment plan & treatment sequence, interdisciplinary approach to patient care (referrals)
developing a treatment plan: begins with looking at individual teeth, in which each tooth should be considered as a piece of the overall patient-centric treatment plan
Consider these:
- why is the pt missing teeth? history of tooth loss, non-restorable tooth, caries, trauma, bruxism, drugs, extrinsic factors, periodontal disease
- what is the condition of the other teeth? intact adjacent teeth, caries and existing restorations, super-erupted opposing teeth, positions of remaining teeth
- what are the patients constraints? medical limitations, financial constraints, fixed vs removable, declines surgical procedures
What are my treatment options for replacing a missing tooth: fixed implant supported crown, fixed partial denture, removable partial denture, no treatment
Implant Supported Crown
- advantages: most conservative to the adjacent teeth, restores function and esthetics, fixed prosthesis with high survival rate, good option for high caries risk
- disadvantages: requires surgical procedure for placement, longer time to delivery of final crown, anatomical limitations for implant placement, possible peri-implantitis with bone loss
Fixed Partial Denture
- advantages: restores function to some extent (Kennedy Classification), replaces missing teeth
- disadvantages: higher plaque index caries prone, stresses to the abutment teeth, abutment teeth need preparation of rests and guiding planes, abutment teeth may need crowns to support the RPD, removable prosthesis, may not be esthetic metal clasps visible
No Treatment
- advantages: less costly for now, no additional time spent for now
- consequences of not replacing a missing tooth: alters future space for restorations, supra-eruption of opposing teeth, teeth shifting into space, tilting and rotation of adjacent teeth, ridge resorption, may alter esthetics, decreased function?

Survival Rates of FPDS

10-year success 71.1-81.1%; 10-year survival: 89.1-92%
Biological Complications: caries > loss of vitality
technical complications: loss of retention > abutment tooth fracture > fracture of framework/ceramic
FPD opposing complete dentures had longest survival rate ~16 years

Considerations when planning for a FPD

evaluate edentulous space:
- span lengths —> posterior 2 or fewer; anterior 4 or fewer
- span configurations —> distal abutment or short cantilever
- patient factors —> finances or xerostomia

additional treatments (interdisciplinary approach to patient care):
- endodontic tx, core build-up with or without a post, crown lengthening or other periodontal tx, orthodontic tx, correction of occlusal plane
evaluate abutment teeth:
- occlusal plane, crown to root ratio, root surface area, periodontal health, tooth vitality
- multi-rooted teeth with separated roots are better at displacing occlusal load than teeth with fused roots
- teeth w/ a winder BL dimension than MD have a greater ability to handle load than conically shaped roots
- larger teeth have a greater root surface area (the area of periodontal ligament attachment of the root to bone) and are better abutments for FPD
- Ante’s Law: the root surface area of the abutment teeth has to be equal or greater than that of the teeth being replaced with pontics
existing restorations and caries:
- ask: direct/indirect existing restorations, intact or defective
- remove defective restoration and caries clean out
- evaluate remaining tooth structure for restorability check, additional endo treatment/perio surgery may be needed, additional restorative core build up with or without post may be needed
tooth vitality:
- preferable vital abutment tooth, RCT teeth are not a contraindication for FPD so long as they are asymptomatic, complete obturation, good apical and coronal seal, sufficient remaining tooth structure
periodontal health:
- supporting tissue surrounding the abutment must show no inflammation, periodontally involved teeth may not have enough support to withstand the occlusal forces; abutment tooth mobility=poor prognosis
- optimum corwn:root ratio 2:3
  - minimum acceptable is 1:1
edentulous space and biomechanical considerations
- deflection of the FPD; the longer the span the more the deflection
- law of beams: bending or deflection varies directly with the cube of the length (p) and inversely with the cube of the occlusoginigval thickness (t) of the pontic span
- MUST compensate by increasing thickness
  - amount of restorative space limits how thick you can make it
- or we can fabricate of an alloy with a higher yield strength such as nickel-chromium
- ALL FPDs regardless of span will flex to some extent
- FPD dislodging forces tend to act in a M/D direction
  - factors that minimize dislodging forces
    - abutment preparation height
    - proper taper of the opposing walls
    - secondary BL retentive grooves
  - secondary abutment must have at least as much root surface area and must be at least as retentive as the primary abutment
  - the secondary retainers are placed in tensions when the pontic flexes; the primary abutments act as fulcrums (dislodging forces)
- Pier Abutment
  - =an edentulous space lies one each side of the middle abutment
  - middle abutment acts as a fulcrum for displacing forces causing failure of the retainer
  - non-rigid connector transfers forces to the supporting bone
occlusal plane evaluation
- movement of adjacent teeth after tooth loss causing a discrepancy in the occlusal plane and decreased restorative space
- the malpositioned adjacent/ opposing teeth may compromise the restoration
- opposing tooth may be treated via orthodontic movmnt and/or restoration
occlusal schemes
- must propose an occlusal scheme for the final FPD
  - mutually protected occlusion, group function occlusion, balanced occlusion (complete dentures)
- 1) mutually protected
  - anterior teeth protect posterior teeth during movmnt and posterior teeth protect anterior teeth in MIP from vertical occlusal forces
  - canine guidance —> canine disocludes posterior teeth in excursive mvmnts of mandible
  - anterior guidance —> ant teeth disoclude all posterior teeth in excursive mvmnt of mandible
- 2) group function
  - aka posterior group function
  - multiple contact relations between the max and man teeth in lateral mvmnts on the working-side whereby simultaneous contact of several teeth acts as a group to distribute occlusal forces
  - **not all posterior teeth need to guide to be considered group function
  - indications: severe class II, III occlusion; mandible cannot be guided by anterior teeth due to missing anteriors, open bite or compromised anterior dentition; force distribution for long span FPD or compromised abutments