[Matt Nejad]
[Dr. Matt Nejad] Hi, I'm Dr. Matt Nejad and in this video I'm going to be talking about the
tooth cycle of death which describes a process or cycle that occurs very commonly in restorative
dentistry and it's basically a series of different interventions and failures that culminates in
loss of teeth and we're going to be reviewing this so that we can understand
how changing the approach can minimize this and help us preserve and keep teeth for life. So
the tooth cycle of death of course begins with a natural intact tooth and it's very important to
understand and appreciate how the natural intact tooth really has optimal structure and properties
which gives it the best chance of succeeding long-term and minimizing complications and
leading to failures. We have enamel which forms a very stiff, strong, rigid outer shell of the tooth.
Then you have dentin which is the dampening inner core like the shock absorber of the tooth which
receives stresses and transmits them through the root of the tooth or the roots of the teeth.
The important thing is that enamel and dentin have pretty
significantly different properties, one being significantly stiffer than the other
and if these two materials are not joined together strongly, there'll be
a lot of failures and cracks and fractures, but the dentin enamel junction forms a strong biological
bond that brings these two different materials together in a way that allows stresses to flow
fluidly through and that's very important because, as a structure, the tooth is only successful
because of the combination of these properties. If the tooth was made entirely out of enamel,
then it would be too stiff and it would fracture and crack and fail all the time and if it was
made entirely of dentin, then it wouldn't be wear-resistant enough and it would also have problems
and failures long term. It's the combination of the properties that makes the tooth so successful
and keep that in mind because that means when we restore the tooth, we want to be able to
mimic and restore these properties as well. So once you have an initial cavity, then you need to
restore the tooth. Now while the tooth is extremely strong in its ability to withstand mechanical
pressure and loads, it's still susceptible to failure from cavities and cavities form from
acid dissolution of the enamel, the enamel is susceptible to an acidic caries process especially
when the conditions are not favorable, when there's poor plaque control, when there is inadequate
hygiene and so on. So once a cavity forms, an initial filling must be placed and traditionally
the filling was an amalgam filling or a silver filling and this type of filling requires
significant additional removal of tooth structures. So you've gone from this small cavity and now
you've reduced significantly more of the tooth because the restorative technique calls for that
because it needs extension for prevention to get a good marginal seal, it requires a minimum
amount of reduction so that the material is not too thin so it won't fracture and break
and it also requires additional tooth structure removal to retain the restoration which means
to keep the restoration in place, you need to remove extra tooth structure. Well because it's
a non-bonded filling and because you've removed so much additional tooth, what happens over time
is cracks develop, the filling, the silver filling does restore the cavity, but it doesn't regain the
strength and the properties that an intact natural tooth does so now the biomechanics are altered
which means every time you are chewing on the tooth or every time the patient is using the tooth,
there's going to be stress concentrations in unnatural areas especially around the
silver fillings, around the marginal ridges and what happens is this leads to cracks. Sometimes
these cracks lead to symptoms, sometimes they go unnoticed, but eventually these turn into fractures.
Cusp fractures around silver fillings are very common so traditional restorations, which start
with silver fillings typically carry on for many years and eventually lead to fractures
known as cusp fractures, sometimes with pain, sometimes without pain. At this point,
the tooth must be restored and since there's significant tooth structure
already missing, it becomes very common now to attempt to restore the tooth with a crown
because now it becomes important to not only restore the fractured cusp, replace the existing
filling that was there, but also now it becomes important to try to address the strength that
was not restored in the first treatment so now you'd place a crown. However, unfortunately,
this requires again more removal of intact tooth structure. Typically a crown removes up to 75 percent
of coronal tooth structure so you've removed 75 percent of the tooth structure that is present above the alveolar
bone and at this point, this is meaning that the tooth is very likely to have additional failures.
Crowns do have significant complications long-term, significantly higher chance of complications
leading to root canals for a variety of reasons including poor marginal seal, sensitivity,
the cumulative loss of tooth structure contributes to this. For one reason or another a root canal
treatment typically will occur with a higher chance on a crown tooth versus an intact tooth
or an unrestored tooth. So you do the root canal and now you take a look at how much tooth structure is
remaining here and you see that there isn't much room left for mechanical retention so the crown
relied on mechanical retention, the silver filling relied on mechanical retention which means having
enough tooth structure to hold the restoration in place, but by this point, you don't have much
tooth structure left because you've removed more and more throughout the process so now
the most common solution is to place a post and core. A post and core serve only one purpose.
The purpose of a post and a core is to retain the crown so you're placing a post and core
so that the crown has something to again hold on to and now you have your crown restoration,
you have very little remaining coronal tooth structure, but you have a crown restoration.
However, as this crown is used, stresses again transmit through the tooth in a very unnatural way,
the biomechanics of a tooth restored with a post and core are nothing like an intact tooth. Stresses
concentrate around the post in the root and this is not what happens in a normal intact tooth
and what happens is the chance of an unrestorable or catastrophic failure is high and that means, for
example, having a vertical root fracture something that's not treatable or restorable and when
that happens, you're unable to restore the tooth. Therefore, you have to look at replacement options
including an implant as the most uh ideal solution. Other options for replacing a tooth that's been
lost are a bridge, but that involves damage to the adjacent teeth and compromising those, you
can also have a removable partial denture or you cannot restore the tooth at all, but all
these occur because as you've done the restorative treatments over time, you haven't respected that
the importance of the tooth goes beyond filling the cavity or placing the crown, it also involves
restoring the strength and the biomechanics of the tooth and the rigidity and these things have been
studied and understood and bonded restorations are able to help us restore teeth more faithfully.
Amalgam silver fillings are not bonded and they don't do that. Sometimes composite filling still
behaves as a non-bonded restoration if it has a poor bond or it's not restoring the properties
of the tooth because it's very large, it has a low modulus of elasticity, there's a variety
of reasons that translate to the tooth having an altered biomechanics and when that happens,
you will expect that the tooth will experience higher chance of complications and failures and
it will have a higher chance of ultimately being lost. So in biomimetic dentistry, the goal is to
interrupt this cycle to prevent the series of steps that result in losing teeth. So from the very
first time the tooth is treated with this cavity, if a conservative composite restoration is placed
that doesn't involve removing additional tooth structure, then you can have more of the tooth
stay intact, more of the strength of the tooth maintained and because it's a bonded restoration,
it can regain some of the stiffness that's been lost from the cavity or even the preparation. So
first, first time you intervene with a biomimetic restoration, it becomes very important to try to
make that restoration last as long as possible. As you proceed through treatments, avoiding full
coverage crowns with partial inlays or onlays also has a dramatic role in minimizing the incidence of
root canals and subsequent post and core and using an adhesive approach is one of the key methods to
prevent the tooth cycle of death. So biomimetic dentistry prevents the tooth cycle of death in a
variety of ways. In biomimetic dentistry, there are three major pillars that we appreciate and respect
and apply to every restoration. One is to mimic the properties and structure of natural teeth,
two is to preserve tooth structure and pulp vitality and then three is to restore the strength,
stiffness, and structural integrity of the intact natural tooth. When you apply biomimetic dentistry
and you aim to mimic the tooth and preserve intact tooth structure and regain the strength
and stiffness of a natural intact tooth, you dramatically minimize the occurrence of
these complications. The tooth cycle of death can be prevented in a large majority of cases and that's
good for patients, it's good for dentists, and that's why biomimetic dentistry has a huge advantage
and it's also why biomimetic dentistry is the most logical choice for all restorative dentistry.