Fixed prosthodontics(The principles of tooth replacement)

Edited by Dr. Ahmed SaidBDS , MFDS RCSEd

Edited by Dr. Ahmed SaidBDS , MFDS RCSEd

Factors that govern the clinical decision on type of prosthesis

• Dental factors:– Abutment teeth present– No. of teeth lost– Position– Periodontal consideration– Conservation– Root treatment required– Quality of bone and ridge– Presence of any pathology– Occlusion

• Canine guided-group function• Opposing teeth

Factors that govern the clinical decision on type of prosthesis

• Patients’ factors– Wishes and expectations– Age– Medical conditions– Social factors

• Smoking • Alcohol • cost

Principles of tooth preparation

• Mechanical:– Retention– Resistance performance– Resistance to deformation

Principles of tooth preparation

• Biological:– Conservative– Supra-gingival margins– Correct contours– Tooth protection from fracture

Principles of tooth preparation

• Aesthetic– Adequate thickness of porcelain– No metal– Colour matching

Check list prior to clinical bridge procedure

• All preparatory conservative work completed• Good plaque control /periodontal condition• Abutments tested for vitality• Relevant radiographs• Occlusion assessed• Diagnostic wax up• Selection of abutments• Trial preparations on mounted casts• Design• Integrate design to existing /anticipated treatment

needs

Short anterior teeth causing an aesthetic problem

Diagnostic wax-up of a Case

Meta-analysis

• Conventional bridge survival rate• At 5 years recall : 4-5 % failure• 15 years recall : 25-30 %• Loosening-recurrent caries

Fibre – reinforced composite bridge

• Well suited to single visit immediate tooth replacement

• Improved aesthetics• Long term provisional• Suitable for young and elderly• Wear is kind• Low treatment costs• Readily repaired

Resin bonded bridges

• Are the best treatment option for many cases• Meta analysis: 4 years survival rate -> 25% • Appropriate case selection -> 10 years recall ->

90% success rate

Requirements for RBB’s

• Space for aesthetics pontics• Sufficient area of surface enamel -> bonding• Abutments -> unrestored +sound • Occlusion favourable• Rubber dam

Hybrid bridge

• Sound abutment on one end & heavily restored on the other

• Resin bonded retainer + conventional bridge retainer

• Common problem after many years: debonding on the resin retained side and patient ignorance -> caries

Pontics : optimal design• Biological:

– No presurre on the ridge– Tissue surface cleansable– Access to abutments

• Mechanical:– Rigid – Strong– Correct framework design

• Aethetic– Shade matched– Appear to ‘grow out’– Porcelain bulk

Pontics : types

• Saddle X• Modified ridge lap • Mandible: hygienic, wash through or sanitary

pontic(non-ceramic)• Anterior region ->ceramic• Posterior region-> Gold

Occlusal considerations

• Group function• Canine guided• ICP• Retruded contact position• Centric stops

Canine guidance

Group function

• Functional occlusion: smooth gliding movements without interferences

• Balanced occlusion: contacts on working and non-working side

Ante’s Law

States that the total periodontal membrane area of the abutment teeth should be equal to or exceeds the teeth to be replaced

UK-> Non-applicable

Ante’s law has no specific bases & no longer has place in contemporary bridge work design, it doesn’t take into account that we are dealing with a biological system

As the load is high on the abutment teeth a biological feedback mechanism operates to cause reduction in this load

All ceramic crown

• Inceram (celay systems)• Empress• Procera• Cerec systems

• High strength alumina core ceramic can be used as posterior bridge

The press ceramic furnace used for the construction of injection moulded IPS Empress crowns (Courtesy of Ivoclar).

A Captek coping for a ceramo-metal restoration of a central incisor.

Bridge failure

• Most common reasons:– Loss of retention– Mechanical failure # of the casting– Problems with the abutment teeth

Specific design problemsPeriodontally involved abutments

• First control periodontal disease.• Then ? • bridge indicated. Fixed-fixed type of design

preferable to splint teeth together.

Specific design problemsPier abutments

• This is the central abutment in a complex bridge that supports pontics on either side, which are in turn anchored to the terminal abutments.

• pier abutment can act as a fulcrum and when one part of the bridge is loaded the retainer at the other end experiences an unseating force which can lead to cementation failure.

• Solution :stress-breaking element must be introduced, e.g. fixed-movable joint, or avoid pier abutments by simplifying the design.

Specific design problemsTilted abutments

This occurs most commonly following loss of a molar. Solutions:• Orthodontic treatment to upright abutments.• Two-part bridge, e.g. fixed-movable.• Telescopic crowns-placement of individual gold shell crowns

on abutments, over which telescopic sleeves of bridge fit.• Partial veneer preparations in which pins or slots are

prepared to compensate for slight mal-alignment of abutments (least satisfactory).

• Precision attachments-a precision screw and screw tube can be incorporated into a two-part bridge. After cementation the screw is inserted, which effectively converts the bridge to a fixedfixed design.

Specific design problemsCanines

• The canine is often the keystone of the arch, and a very difficult tooth to replace.

• The adjacent teeth are poor in terms of the amount of retention and support that they offer and the canine is often subject to enormous stresses in lateral excursion (in a canine-guided occlusion).

• If a canine is to be replaced with a bridge the occlusal scheme should be designed to provide group function in lateral excursion-never canine guidance.

Planning treatment

Information gathering

Make a diagnosis

Consider all options for treatment

Adapting treatment options for individual setting

Patients’ culture

In the third world, missing teeth are associated with poverty and misery

Patients’ culture

In the developing world, discoloured teeth are synonymous with misfortune

Patients’ culture

In some African cultures, anterior gold dental prostheses signify prosperity

Fashion trends influence provision of oral jewellery

Treatment options

• Ideal• Acceptable compromised• No treatment – is an option as well