Bridge Design Notes

Bridge Design

I) Selection of Prosthesis Type

Missing teeth can be replaced by:
- Implant-supported F.P.D
- Tooth-supported F.P.D
  - Conventional F.P.D
  - Resin-bonded F.P.D
- Removable partial denture

Components of a Bridge

Pontic: The artificial tooth that replaces the missing tooth.
Abutment: The natural tooth that supports the bridge.
Retainer: The restoration that attaches the pontic to the abutment.
Connector: Connects the pontic to the retainer.
Superstructure
Substructure
Preparation
Framework
Edentulous Ridge
Span
Wing

Types of Dentures

Removable Complete Denture
Removable Partial Denture
Implant Over Denture

Deciding Factors for FPD/RPD Construction

Length of Edentulous Area
- Number of missing teeth anteriorly.
- Number of missing teeth posteriorly.
- The effect of arch curvature in FPD design.
Position of Edentulous Area
- Bounded or free-end saddle.
- Unilateral, bilateral, or multiple.
- Controversy regarding cantilever in restoring distal free-end edentulous area.
- Role of implant-supported restoration in the case of free-end saddle.
Abutment Alignment
- Tilted abutment more than 25 degrees $\Rightarrow$ R.P.D
- Widely divergent abutment $\Rightarrow$ R.P.D
Abutment Status and Periodontal Condition
- Vitality.
- Existing caries and remaining tooth structure.
- C/R ratio.
- Root configuration.
- Antes' Law.
- Mobility.
Occlusion
- Adaptation.
- Deep bite and para-functional habits effect on FPD design and implant.
Ridge Form
- Mild resorption.
- Moderate resorption.
- Severe resorption.
General Factors
- Age.
- Systemic condition.
- Dry mouth.
- Tongue size.
- Gagging reflex.
- Patient attitude to RPD.

Treatment Plan Selection Sequence

Implant is preferable if indicated at any situation.
Resin-bonded bridge is the 2nd choice $\rightarrow$ to restore missing one tooth (except missing lower two centrals).
From the 2nd premolar $\rightarrow$ R.B.Br comes after conventional designs because of ↓ retention and resistance.
Conventional bridge design.

A ) Implant – Supported F.P.D

►Indication:

Single tooth can be replaced with a single abutment $\rightarrow$ saving adjacent teeth from destructive preparation.
Span length of 2$\rightarrow$6 teeth $\rightarrow$ replaced by multiple implants either $\rightarrow$ single –unit restoration $\rightarrow$ implant-supported F.P.D.
In case of no distal abutment.
Full arch can be replaced by implant-supported complete prosthesis.
Sufficient alveolar bone density.
In case of compromised abutment which can not support long span prosthesis.
In dry mouth (better than natural teeth $\rightarrow$ otherwise caries).

B) Resin Bonded Tooth-Supported F.P.D

Indication:
- i) Defect-free abutment.
- ii) Patient with bounded edentulous area (single tooth loss→except missing lower two centrals).
- iii) Edentulous ridge with moderate resorption $\rightarrow$ & no gross soft tissue defects.
- iv) sufficient enamel for bonding.
- v) Young pt with large pulp $\rightarrow$ because It is conservative within enamel.
- vi) Pt with normal bite. $\rightarrow$ i.e deep vertical overlap is contra-indicated.

C) Conventional Tooth-Supported F.P.D

It is an artificial restoration spanning missing area in the dental arch.
It is fabricated either from metal/non metal/combined material.
It restore the masticating surface of posterior and anterior teeth.

Components of the bridge:

Abutment
- It is the natural tooth/teeth or roots which support the bridge from both or one end.
Retainer
- it is an artificial restoration rebuilding the prepared abutment tooth restoring function and esthetic + it retains the bridge in its position.
  - Requirements of ideal retainer:
    1. it should constructed from material with high mechanical properties
    2. it provide good retention
    3. provide good esthetic if used in anterior area
Pontic
- it is the suspended from the bridge which restore the coronal portion of the missing tooth/teeh restoring function and esthetic.
Connector
- it is that part of the bridge which connecting the retainer and the pontics . it is either :
  - rigid connector
  - non rigid connector.

Types of Conventional Bridges

a) Fixed–Fixed F.P.D:
- It is a F.P.D where retainer & pontic are soldered together at both end.
b)Fixed–Supported F.P.D ( fixed – movable bridge)
- It is a F.P.D where retainer & pontic are soldered at one end while at the other end joined together by non-rigid connector.
c)Fixed–Free F.P.D (cantilever)
- It is a F.P.D in which the pontic is fixed to one retainer while the other end is free.
d)Spring cantilever
- It is a F.P.D where the pontic is at the end of resilient curved arm deriving its support from remote abutment.
- (used in case of diastema)
e)Removable bridge: (Precision attachment bridge)
- It is a bridge in which the retainer consists of two parts $\rightarrow$ one cemented to the abutment tooth (coping) and one soldered/connected to the pontic (telescoping crowns).
- The two retainers are frictionally retained to each other.
- The bridge can be removed by the patient for cleaning purpose.

Indications

In general fixed-fixed bridge is Indicated for:
- missing two teeth post. (maximum)
- missing four teeth ant. (maximum)
- according to periodontal membrane area ( ante´ s law)
- Otherwise $\rightarrow$ R.P.D
In young patients because of large pulp size $\Rightarrow$ root canal treatment may be done.

D) R.P.D

Indicated for:

Edentulous spaces greater than $\rightarrow$two post. Teeth $\rightarrow$four ant. Teeth.
Edentulous space with no distal abutment.
Multiple edentulous space.
Bilateral edentulous space with more than 2 teeth missing on one side.
Insufficient number of abutments.
Severe edentulous ridge bone loss.
Patient with $\rightarrow$ advanced age. $\rightarrow$systemic health problem

Contra-Indicated in

Pt with large tongue
Pt with unfavorable response for R.P.D

II) Guidelines for Bridge Designing

Abutment Selection
- Abutment should be vital whenever possible….. BUT
  - If endodontically treated $\rightarrow$ it should be
    - i) asymptomatic
    - ii) good canal seal.
- Failure occur if abutments have
  - i)short root ( improper C/R)
  - ii)little remaining tooth structure
- Therefore: Added (secondary) abutment should be taken
- Pulp capped teeth should not be used as FPD abutments $\rightarrow$ because of ↑ risk that they will require RCT later $\rightarrow$ therefore destruction of tooth structure and the retainers.
- Abutment should have good periodontal condition + healthy attached gingival (3mm width at least).
- Abutment should have $\rightarrow$ no mobility $\rightarrow$ proper C/R i.e 2/3 $\rightarrow$ proper root configuration.
- Secondary(added) abutment:
  - Used in case of weak abutment or improper C/R
  - It should have proper C/R + ↑ root surface area + retentive retainer
  - WHY???
  - Because when pontic flexes $\rightarrow$ tensile forces will be applied to the retainer of the secondary abutment.
- Terminal abutment:
  - It is preferable to end the bridge on a strong abutment and not on a weak one e.g upper lateral / lower central $\rightarrow$ therefore added abutment is needed i.e adjacent central incisors.
- Third molar abutment:
  - Rarely used as abutments………..why?
    - i)They have short / fused root
    - ii)They usually show incomplete eruption
    - iii)They usually show mesial inclination due to absence of 7
    - iv)The unattached mucosal tissue that surround the distal of third molar will be inflamed even with well fitted crown.
- Endodontically treated abutment:
  - Should not be used as abutment for cantilever or long span bridges$\rightarrow$ because ↑ torque will result in their fracture.(i.e used only for short span bridge)
  - Poor prognosis if endodontically treated teeth have short root or with canals that cannot allow placement of post (therefore better used to support RPD.
Retainer Selection

Factors affecting retainer selection:
- a)Alignment of abutments:
  - If the abutment teeth are not parallel $\rightarrow$ complete crown retainer with a common path of insertion will not be possible unless RCT is done.
- SOLUTION:
  - i)Use partial coverage retainer
  - ii)Change bridge design.
- b)Appearance:
  - All ceramic restorations have better esthetic than metal ceramic restoration.
  - According to clinician judgment $\rightarrow$ in some cases full coverage retainers may have better appearance than partial coverage or resin bonded bridge.
- c) Condition of the abutment:
  - If abutment has intact facial surface / adequate height / and bulk$\rightarrow$ therefore partial coverage retainers can be used.
  - If the abutment has palatal enamel loss $\Rightarrow$ adhesive bridges (resin bonded retainers) should not be used.
  - If abutment has proximal caries $\Rightarrow$ therefore full coverage is recommended
- d)Occlusion:
  - In case of heavy occlusal forces / deep bite $\rightarrow$ resin bonded retainers are contraindicated.

Pontic Selection

Factors affecting pontic design selection:
- a)Cleansability: (Biological)
  - Gingival aspect of pontic should be cleansable……. therefore $\rightarrow$
    - i)It should highly polished or glazed
    - ii)Metal ceramic junction should be away from the ridge surface of the pontic
    - iii)It should be convex.
  - Embrasure should be smooth and cleansable.
  - In posterior non esthetic area $\Rightarrow$ hygienic pontic is indicated
- b)Appearance: (esthetic)
  - In esthetic areas $\rightarrow$ pontic should look like the tooth as possible $\Rightarrow$ modified ridge lap
    - ovate pontic (in case of recent extraction)
  - In posterior areas $\rightarrow$ compromise should be made between reasonable appearance and oral hygiene measures.
- c)Strength (mechanical)
  - Pontics should be designed to withstand occlusal forces
  - ↑ span length$\rightarrow$ ↑ pontic occluso gingival height $\rightarrow$ use metallic pontic rather than metal ceramic one.

Connector Selection

Connectors should be large to withstand occlusal forces but it should provide embrasure space for plaque control.
Rigid connector is usually used ………but non rigid connectors (e.g occlusal rest or key and keyway) are used in the following condition:
- i)↓ load on the abutment
- ii)Solve problems of malaligned abutments
In case of fixed supported bridge$\rightarrow$ the support must be placed on the anterior abutment with cast restoration (Inlay)
In case of multiple diastemas $\rightarrow$ fixed-fixed bridge can be used with palatal loop connector.

Material Choice

a)Metal only $\rightarrow$ in non esthetic areas
- $\rightarrow$ more conservative
b)Metal-ceramic $\rightarrow$ used when esthetic and strength are required.
- $\Rightarrow$ veneered restoration is more conservative than full full veneered one
- $\Rightarrow$ in case of deep bite$\Rightarrow$ insufficient space $\Rightarrow$ therefore veneered restoration is recommended
c)Non-metal only $\rightarrow$ in esthetic areas.
- $\rightarrow$ recently new high strength ceramic material with improved mechanical properties are introduced.