hi everyone in this video we'll be talking about posterior onlys we'll be discussing only
preparation provisional restoration conventional and digital impression taken and finally only
cementation and bonding protocols so just before we get started we'd like to thank dr kushal
guardia who is a consultant in restorative dentistry and a specialist in periodontology
prosthodontics endodontics restorative dentistry and has a special interest in dental implantology
dr guardia has been kind enough to provide us with this content from ace courses and while this video
is only a summary the full webinar is available to students completely free of charge on the
ace courses website sign up in the description with the advances in adhesive materials in the
last few decades were quickly moving towards more conservative dentistry and with that only should
be preferred over full coverage crowns in most scenarios dr guardia says that he rarely finds
the need to place a crown over an only and usually only places them when there is a need to replace
the old crown you can pause the video now to have a look at the different preparation finishes and
their corresponding appropriate materials there are generally speaking four categories of onlays
and so four different preparation designs we can prepare a tooth for an mod gold only and ammo the
emax only an adhesive emax only or a heat treated gold only the first two are for conventional
cementation and the last two are to be bonded for an mod gold only we need retention and resistance
form we need boxes the minimum depth and width of your isthmus and on the functional cusp we
need the protection from a chamfer and on the non-functional cusp we need a butt finish with a
little bevel for an mod emax only you would need to do this if you didn't have the 90 remaining
enamel that you would need for an adhesive emax only the prep is almost identical to an mod gold
only but the difference is that all the edges need to be round so that you can reduce any
points of stress you'll also need a much heavier chamfer on the functional cusp and a butt finish
on the non-functional cusp the obvious advantage here is that it would be more aesthetic than gold
for an adhesive emax only you'll need at least 90 percent of the enamel remaining
around the tooth and there is no specific preparation design for this type of restoration
and it depends on the presentation of the tooth and where it's fractured here are a few different
design examples but again we need rounded edges and no sharp angles finally for bonded heat
treated gold on lays the preparation is very similar to adhesive only preps but you don't
need as much reduction for the chamfers around the edges you want to do your occlusion reduction and
if there's any old restorations you can remove them and incorporate that space into the only
also try to make your chamfer follow the contour of the tooth for a more aesthetic result as shown
by one of dr guardia's photographs on the screen now it's also important to note that
when you're preparing a tooth which is in the visible aesthetic zone when the patient smells
especially an upper premolar it's really easy to see the buckle margin between the only and
the tooth if you prepare to the middle of the buckle wall instead do an ultra conservative
preparation it'll be less obvious and this would be acceptable because on the upper
the buckle is the non-functional cusp and so less forces will be acting in that area so it
doesn't need as much reinforcement by a larger preparation however if you have a patient with
a crack in the buccal cusp then you should prepare the tooth a bit more aggressively to avoid crack
propagation and fracture before we move on to the next section we'd really appreciate it if
you guys give this video a like it really helps our channel grow and reach more people thank you
once you've prepared the tooth you should always place a resin seal in the same appointment
this is known as immediate dentine sealing and you might see it written as ids
you etch for two to three seconds to identify the dentine from the enamel and you'll see the dentine
will go glossy and enamel will go frosty and then you quickly wash and dry it then you selectively
etch the glossy dentine for 10 seconds or 20 seconds if it's sclerotic to roughen the surface
of the dentine and not the enamel this increases the surface area and then you wash and dry it then
you prime and bond and this can be a two-in-one or can be done separately depending on the generation
of bonding system that you're using as shown on the screen now you want to use a micro brush to
massage it into the dentine for 20 seconds and then like cure it for 20 seconds then you apply
an oxygen inhibiting layer like glycerin and light cure again for 20 seconds through the glycerin and
then wash that off this is done because the very top layer of resin is inhibited by oxygen in the
air this process is known as ids and it helps with sensitivity and bonding because the hybrid layer
starts to mature over the two weeks that your weight for your only to be made and therefore
massively increases the bond strength this of course will mean the restoration will last longer
than it would have otherwise now that you've made this strong hybrid layer between the dentine and
adhesive resin you can make your provisional restoration you can do this with any of the
materials on the screen now and the reason you should make your temp before taking the impression
is because the temp can tell you a lot about your preparation and what the final only will be like
if it's too thin in areas for example then at this stage you can adjust the preparation before taking
the impression once you're happy with your temp you can use some glycerin or vaseline to make sure
your temporary doesn't get stuck onto the tooth the cement will depend on if the restoration will
be held in mechanically or adhesively bonded if it's mechanically held you want to use a
non-eugenol zinc oxide cement like non-neutrino temp bond if you want something a little bit
stronger you can use polyeth this can also be used for cementing adhesive temporary restorations an
alternative for adhesive restorations can be spot etching the enamel applying flowable composite
then locking the temporary restoration with flowable in the interproximal areas to hold
it in place if you opt for this option make sure not to use any prime or bond so that the temp can
be easily flicked off at the next appointment before you cement the provisional in you need
to take your impression this can be done by either using polyvinyl siloxane or an intraoral
scanner and the use of retraction cord is not usually needed unless you have an aspect which
is subgingival once the impression has been taken you would then need to finish the visit
by cementing the temporary inn after waiting a couple weeks for the fabrication of your only
on your next visit you want to start by removing your temporary restoration you can do this by
getting an instrument in the margin and levering it off so it pings off you could also tighten
a sig villain matrix band to create pressure coronally and it can come off just like that
you could also use an ultrasonic scaler and if all of these methods don't work you can carefully
cut it with the back then you want to try the only in and check your margins interproximal
contact static and dynamic occlusion and make any necessary adjustments once you're happy with the
restoration if you're not bonding you can then cement the on lay in remove any excess and check
the occlusion the examples of cements you can use for mechanically retained onlays are aquasem
polyf fujiplus or zinc phosphate if you're bonding an emax only then the process isn't as
straightforward you need to add a few extra steps and it must be always done under rubber dam we'll
need to start by preparing the only for bonding and this is done by etching the fit surface of the
only for 60 seconds with a 9 buffered hydrofluoric acid this is a less concentrated version of the 5
hydrofluoric acid the lab would have used then we need to wash it off for 20 seconds
and clean the debris that it leaves by brushing 35 phosphoric acid onto it with a micro brush for
another 60 seconds and rinsing it again with water for another 20 seconds this is done to remove
the crystalline debris and if you skip this step the bond strength may reduce by about 50 percent
and if you want to take it a step further you can leave the restoration for five minutes in
an ultrasonic bath filled with 95 alcohol at this stage you may need to apply a primer to the fit
surface of the restoration depending on the cement you're going to use and which bonding system it
requires we spoke a little bit about the different generations of bond earlier but the idea is that
some do all of the steps in one go and other systems require each step to be done separately if
you're using a self-adhesive resin cement you can skip this step but it's really important to follow
the manufacturer's instructions or the only will really quickly fail if it's bonded incorrectly
now that the restoration has been prepared we need to prepare the tooth itself we need to reactivate
the bond that we placed when we did the immediate dentin sealing on the tooth preparation surface at
the last visit we do this by sandblasting the preparation surface with 50 microns aluminium
oxide and washing it off for 30 to 60 seconds then you want to etch the enamel for 30 seconds
and the denting for 15 seconds and prime and bond the surface but it's really important that you
don't light cure the bond at this stage now the emax restoration and the tooth are ready to be
joined together by the cement and there are so many to choose from you can use a self-adhesive
resin cement like relyx adiocure resin cement like panavia or heated composite make sure you research
the protocol for the one you decide to use to ensure the best bond strength once you've cemented
it in you can put pressure on the only for about three minutes and remove your excess cement using
a sharp probe super floss ptfe tape normal floss with a couple of knots or even a teepee brush you
can get really creative in how you want to remove this excess cement finally you want to apply a
layer of vaseline glycerin or ky jelly and cure through it to make sure you don't get an oxygen
inhibiting layer forming show your passion in the mirror and i'm sure they'll be really impressed
with the results okay guys we hope you found that video useful and if you did we'd really appreciate
it if you gave this video a like and subscribe to the channel there are more videos like this
coming soon in line with the ace courses webinars created by dr guardia for the full webinar make
sure you check out the ace courses website which is completely free for students to use it has
webinars covering the inclusion tooth surface loss perio and so much more there's a link in
the description to sign up if you haven't done so already we'll see you guys in the next video see y