Operative dentistry aje qualtrough, jd satterthwaite la morrow, pa brunton

65
: 357–64.
21.
Ostlund L.E. Cavity design and mathematics: their effect on gaps at the
margins of cast restorations. Oper Dent, 1985; 10: 122–37.
22.
Craig R.G. and Farah J.W. Stress analysis and design of single restora-
tions and fixed bridges. Oral Sci Rev, 1977; 10: 45–74.
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6
Indirect restorations – 
further considerations
MATERIAL TYPE
Essentially the primary factors influencing choice of restorative 
material are the mechanical and aesthetic properties of the available
materials in relation to the clinical situation. The main important 
factors to consider are:
• Functional demands
• Space
• Aesthetics
• Patient wishes
Functional demands
The need to consider the functional demands on a restoration is
mainly related to the potential for wear and/or fracture, and the abil-
ity of the available materials to resist these. The principal influences
on functional demand are mainly related to the occlusal relationships
(see Chapter 1). More specifically, these are:
• Nature of movement from the intercuspal position (ICP) during excursive
movements. If teeth are separated as soon as an excursive move-
ment begins (termed immediate disclusion or point centric), then
the degree to which opposing teeth will rub over each other is 
minimised, hence reducing the propensity for wear. If there is 
some ‘rubbing’ contact between opposing teeth before disclusion
(delayed disclusion or long/wide centric), then it would be wise to
choose materials for the functional surfaces that are more able to
resist this wear, i.e. metal.
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Chapter 6
• Nature and type of tooth contact during excursive movements. If only a
pair of canines contact during excursive movement and all other
teeth are separated (i.e. they disclude) they ‘provide the guidance’,
and this relationship is termed canine guidance. If more teeth are
involved in guidance, this relationship is termed ‘group function’.
It is widely thought that canine guidance will result in less wear 
of the posterior teeth and will also protect the posterior teeth from
lateral loads. Although little evidence exists to support this view,
separation of the posterior teeth during excursive movements 
will allow more flexibility in choice of material used to restore the
posterior teeth. Similarly, contacts between opposing teeth on the
non-working side may place high lateral loads on teeth. If such
teeth are to be restored, and these contacts cannot be removed, then
a material that is better able to withstand these lateral loads should
be used, i.e. metal.
• Parafunctional habits. Opposing teeth are normally only in contact
for a short time, typically during mastication and swallowing.
Habits such as bruxism/grinding or clenching will dramatically
increase the contact time and hence increase the propensity for
wear. In addition, as well as an increase in contact time, higher
loads are usually placed on the teeth. In a patient who has a bruxist
or clenching habit, it would be wise to carefully consider the likeli-
hood of fracture before placing all ceramic restorations. Generally
in these situations, restorations are more likely to last if functional
and guiding surfaces are in metal.
• Opposing dentition. When planning a restoration, the potential 
for the opposing dentition to become worn or to wear the restora-
tion should be considered. In general terms ‘matching’ materials
are best if the opposing teeth have previously been restored. 
Metal (especially gold) is the least abrasive to opposing tooth 
structure
1
, though in most situations ceramics may be employed,
provided there is not a high potential for wear, as discussed 
above. Obviously, if there is no opposing tooth contact then 
there will be no (or minimal) load on the restoration and no 
concerns regarding wear and the choice of restorative material 
may be made with impunity. The ability to achieve stable occlusal
contacts with available materials should also be considered. In 
situations in which many occlusal surfaces are to be restored, then
multiple contacts will need to be provided in order to achieve or
maintain occlusal stability. Ideally, this should not influence material
choice. However multiple contacts are hard to obtain with ceramic
restoration and require the skills of a highly competent technician.
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Indirect restorations – further considerations