3.5 fixed partial dentures

parts of fixed partial dentures and what they do

• Retainer - part that seats on the abutment tooth

• Pontic - suspended member of FPD that replaces the missing tooth

• Connector - provide connection between the retainer and pontic

• Abutment tooth - the tooth that provides support for the retainer

what can happen to the structural integrity of the dental arch when a tooth is lost?

• disrupts structural integrity of dental arch

• can lead to realignment of teeth as new state of equilibrium is achieved

• Adjacent and opposing teeth may move into edentulous space, with some drifting bodily and some tilting.

• These changes can affect morphology and cuntion of dentition

what are types of abutments of FPDs?

• natural teeth

• implant abutments

types of connectors of FPDs

• fixed - adhesive and via screw

• removable - joint and free

• combined - fixed and removable

types of retainers of FPDs

• full crown

• partial crown

• post-crown - cemented in root canal or screwed to the implant

types of pontics of FPDs

• hygienic

• non-hygienic - saddled

• semi-hygienic - convex

types of durations (as per designation) of FPDs

• temporary

• permanent

types of materials of FPDs

• metal - gold, non-precious alloy, precious alloy

• composite fibre reinforced

• ceramics

• combined (metal plastic, metal composite, metal ceramic)

types of manufacturing of FPDs

casting

sintering

modes of retentions of FPDs

• simple - fixed, fixed supported, fixed-free, spring-cantilever

• compound - more than one of the simple types

according to site of FPDs

• anterior

• posterior (uni-lateral (midline), bilateral (canine))

• complex

how is a tooth evaluated to be an abutement?

• Crown-root ratio: Evaluates the proportion between the height of the tooth's crown and the length of its root. Around 2:3 or 1:1

• Root configuration: Considers the shape and structure of the tooth's root for support.

• Periodontal ligament area (Ante's law!): The combined surface area of abutment teeth should be equal to or greater than the missing tooth/teeth being replaced.

what is the affect of having longer span on flexing of abutement teeth ?

• longer spans, meaning longer sections between abutement teeth are generally less rigid and more prone to flexing (deforming and bending of prosthesis)

• To minimise flexing, pontic designs with greater occlusalgingival dimensions (from biting surface to gum line) can be chosen

• Excessive flexing under occlusal loads may cause failure of long span FPD

How does material of the prosthesis affect the strength and stability?

using an alloy with higher yield strength, such as nickel-chromium, can provide increased strength and stability

how does arch curvature affect pontics?

• when pontics are positioned outside interabutment axis line (line connecting abutement teeth) they can act as a lever arm.

• Can potentially create a torquing movement, which may affect the stresses occurring in the FPD

what is the difference of replacing a maxillary and mandibular canines with FPD?

replacing a maxillary canine with FPD can experience more stress compared to replacing mandibular canine due to outward forces exerted on the maxillary arch

what is the best option when restoring an edentulous space caused by loss of canine and two adjacent teeth?

RPD or implants

In what form is the strength of pontics tripled?

strength of pontics is tripled when its form is convex and oval as opposed to sharp and concave

how is occlusal forces reduced of pontics?

reduce vertical-lingual dimensions

what can canines be secondary abatements for?

• Canines can be used as secondary abutements to first premolars primary abutement

• But it is unwise to use lateral incisors as secondary abutements to canines

what is non-rigid connectors used for?

• they transfer shear stress to supporting bone

• prevent stress concentration in connectors

• allow some movement in abutements

• design helps distribute forced evenly and reduces the risk of complications

• helps in tilted FPD abutement

define an abutement

tooth or portion of tooth, or that portion of a dental implant that serves to support/retain a prosthesis

What are complications of tilted molar abutement?

• common problem

• second molar in lower jaw tilts into space where first molar used to be.

• Second molar being tilted makes it difficult or even impossible to create a satisfactory FPD cause the positional relationship is no longer allows for parallel path of insertion without interfering with adjacent teeth

• If third molar present, it can further complicate issue. Tipped third molar’s mesial surface can block insertion path of a fixed partial denture

what is a cantilever fixed partial denture?

• they replace only one tooth but have at least two abutments

bridge designs

types of FPD depending on number of teeth

• Two units FPD

• Three units FPD

Fixed-fixed bridges

• rigid connectors are present at both ends of pontics

• maximum retention and strength

• long span bridges

• All retainers are major retainers and require extensive preparation reduction of the abutment

• one path of insertion, with preparation of both abutments being parallel

• entire occlusal surface of both abutements should be covered with the retainer to distribute occlusal forces evenly

• All retainers should have approx same degree of retention to minimise risk of dislodging a weak retainer

• More tooth structure reduction leads to more destruction and trauma to pulp

• Abutement teeth are splinted together which is beneficial for mobile teeth

• This type of bridge is cemented as one piece

Fixed free bridges

• has rigid connector (major) at distal end of pontic and a mobile connector (minor) mesially

• more conservative to tooth structure compared to fixed-fixed because the minor retainer requires less reduction

• allows for minor tooth movement, both laterally and vertically

• limited to one missing tooth and has span length (distance between abutment teeth) limitation

• parts of bridge can be cemented separately, so lab construction is complex and difficult

• preparation of abutement does not need to be parallel

• Fixed-free is indicated for use in cases of divergent abutment teeth (unparallel), when pier abutment is present (complex bridge) and for aesthetic considerations (such as a class III inlay on distal of canine)

Simple cantilever

• this design provides support for the pontic at only one end

• pontic can be attached to one or two retainers

• abutment tooth is either mesial or distal to the span

• most conservative design when only one abutment tooth is available

• It’s a successful design for replacing a lateral incisor using the canine as an abutment, especially when the occlusion is favourable

• The design can also be used to replace upper or lower first premolars and second molars

Spring cantilever

• abutement tooth is usually posterior and should be a tooth that needs restoration

• pontic is connected to retainer by long flexible metal bar

• design is contraindicated is cases of a V-shaped or narrow palate and is not recommended for the lower arch

• Indicated for replacing a missing upper incisor when adjacent teeth are healthy, in cases of midline diastema (gap between the two upper front teeth (maxillary central incisors)) or when posterior teeth need crowns

• Not advised for the lower arch due to the stability of the sub-mucosal tissue and potential for plaque and calculus deposition

Combination design (complex or compound bridge)

• incorporates two or more conventional bridge designs into one

• examples - fixed-fixed with simple cantilever and fixed-fixed with fixed mobile

• benefit - easier repair work as only small parts of the bridge may need to be disturbed

• Construction steps are simplified and the strain on patient is reduced with shorted, more comfortable visits

FFD (fixed-fixed design) pontics

• pontic is part of a fixed partial denture that replaces missing teeth

• pontics are usually connected to retaining crowns, which fit onto abutment teeth

factors when making pontic form

1. edentulous ridge, esthetic considerations and patient homecare + hygiene

2. edentulous ridge - shape, width and current condition should be taken into account

3. Estehtic considerations - determining appropriate pontic shape and restorative material

requiremnet of pontics

• pontic should challenge the gingiva where indicated by pontic design to prevent food entrapment under the pontic

• Pontics should be as smooth as possible especially on the gingival surface to reduced the amount of plaque

what are different pontic designs?

• saddle

• modified ridge lap

• hygienic

• ovate

• bullet

Pontic design - Saddle

• Full contour buccal and lingual to edentulous ridge

• + full contour gives nice facial and lingual esthetics

• - difficult patient homecare under pontic

Pontic design - Modified ridge lap

• Full contour on buccal side but tissue contact only to one millimetre lingual to the crest of edentulous area

• + provides adequate facial aesthetics and increases buccolingual access to gingival

• - decreased lingual contour and increased possibility of food entrapment

Pontic design - Hygienic

• Totally open access under the pontic for hygiene

• + 3 mm space gives simple access for hygiene and decreases the possibility of food entrapment

• - Esthetics due to lack of facial and lingual contour

Pontic design - Ovate

• Egg-shaped end that protrudes into concavity in edentulous tissue

• + super esthetics due to mimicked papillary form which is usually lost post-extraction due to bone deterioration

• - Requires a wide ridge, possibly indicating ridge augmentation surgery

Pontic design - Bullet

• Comes to a pointy area like the more pointed end of an egg which challenges the tissue

• + increased hygienic access to buccal and lingual surfaces. Can be used against a variety of ridges

• - Decreased aesthetics due to lack of full contour on the facial and lingual

Patient homecare for cleaning underneath pontics

1. Items used commonly - floss, floss threaders and super floss

2. Floss and floss threader are helpful for cleaning between pontic and adjacent teeth

3. Superfloss is a specialised floss that has stiff end fro threading underneath pontic

4. Proxybrushes can also be sued to clean around and underneath the pontic