Spot the screw-access

Ashley Watson • September 15, 2020

How to make screw-down restorations look as good as cementable ones

We all know that screw-down restorations are the best right?

There are more mechanical problems with screw-down restorations (SDR's) when you compare them to cementables and it is really difficult to hide the restorative material that you fill the access cavity with.

Sure cementables have problems biologically in the longer-term if you don't get that perfect seal, or leave a generous helping of cement behind in the sulcus, but it is so much easier to get a good looking result at the fit appointment, and most labs charge less for a cementable!

But you can't ignore that research that keeps reminding you to screw your restorations down.

I am a very keen supporter of screw-down restorations. It is very rare that I turn to cementable solutions and I have to be sure that I won't want to remove the restoration at a later date. I fit everything cementable to implants with Tempbond and still I have problems removing them later on, and patients hate that impact hammer when you are removing them.

So I try to do everything screwed-down.

In the early days you could moan more about how the screws would loosen, fracture and porcelain from around the access channel would fracture. I think you would have to accept that most connections with retaining screws are now so strong when used correctly that this rarely is the case. Sure, you will see patients who have had a loose restoration for the last few months, and "Just need it tightened...", (cue a one hour talk about loose component stress and how difficult it is to get replacement screws for that copy implant that was so cheap to place abroad!), but if you follow a few simple rules you will have very few issues with your own restorations.

Rules about Screw-Retained Restorations

Plan for screw-retained restoration - Have a thought about where that screw channel is going to exit the occlusal platform and try to avoid working side contacts, this will avoid those annoying porcelain fractures and excessive wear of your screw-access restoration.
Use Genuine Compatible Parts - Copyright and Patents prevent even milling the same parts and if the bits don't fit on a microscopic level you will get wear, and this can be really difficult to recover from if you tulip-fracture the implant itself!
"Torque the torque or walk the walk" - If you ignore the advice of an engineer beware the walk of shame when that screw fractures, especially if you are "just doing a tighten". Choose your torque device carefully and make sure it is calibrated if possible. Torque devices can wear and over time will give incorrect values. Make sure you are using the correct values for the system you are using, and that the screws your lab are supplying are genuine. Most premium systems have colour coding but you should make yourself very familiar with the parts catalogue.
Ask for a one-piece screw-down crown - Don't revert to the old days unless you have to. Keep the restoration simple, you shouldn't need a connecting device or abutment to screw your crown to. The less margins for bacterial ingress the better.
Go for Zirconia - If you haven't started using zirconia yet, prepare to be wowed! This material looks great because of its translucency, is as strong as a metal base if handled correctly, and the wear is amazing. The best way to use these is with a variobase (tibase). When you have a lab, that is switched on, they can receive a CAD file and mill a pre-drilled block of zirconia, with a long access hole that allows the light to pass through the occlusal 2/3rds of the restoration. This passage of light means that you can pretty much get the shade of the filling material wrong and it will still look natural. This is the secret to hiding the access hole! Gone will be the days of searching for the most opaque and light material that will lift the value of the dark cylinders inside a metal restoration access. The height of the abutment will worry you at first, but you have to trust the engineers and researchers on this one, the design allows for good retention and support and the zirconia crown can cope with the stresses thereafter. We used to do some eMax crowns like this and we did see failures, but zirconia doesn't seem to be the same, but remember rule 2 "Use Genuine Compatible Parts", or prepare to be disappointed.

If you have a genuinely forward thinking laboratory, they won't mind you suggesting this and it may even make their job easier. It's a great way to bring the cost of the restoration down. Great communication could mean that they don't need to pour or print models, and you may be able to supply them with the parts which could add to your leverage with your implant supplier.

Getting the best out of your lab means putting a bit of work in yourself, but that is another blog topic!

Please do post your experiences / thoughts I would love to hear them.

Newer Post >

ID Blog

Keep Calm and Carry On with the Carry On! - Dealing with a power outage

By Ashley Watson • September 27, 2021

There are plenty of things you can do without power, and I don’t mean just handing out antibiotics because the guidelines have been relaxed to meet the need of the current government failings! My trip to Ghana with 30 undergraduates taught me this. Prepare yourself for action: 1. Buy a head torch and a really good hand torch that your nurse can hold 2. Stock up on cotton swabs 3. Make sure you have a go to temporary filling material that is sedative where possible 4. Don’t back yourself into any corners you can’t retreat from When your dental unit stops working the most annoying thing to fail is not the chair or the handpiece, its not even the suction, because even if you get the last wheeze of air from your compressor, if you can’t see what you are doing it is useless. I found that a head-torch or better still your loupes with a light are a dentist’s best friend in these situations. Because head torches were designed for making a cup of tea in a tent, if your nurse can hold a good quality hand torch as well this helps. Moisture control need not be an issue if you have enough sterile swabs and cotton rolls and you are a master in the art without suction. Saliva is easily soaked up or spat into a spittoon and in the worst scenario where a patient is bleeding, pressure and a reassuring manner can slow even the most persistent sites. It’s unlikely that you are going to be worrying about keeping patients waiting so you have all the time in the world to look after the patient in the chair. Whenever you work, you will have an end goal in mind, but remember your training and don’t cut away all your options too early in the preparation. It’s much easier to put on a temporary crown with two interproximal slices rather than just the occlusal reduction, so rethink your protocols, and build in some provision for temporisation at every stage. Even if you are in the middle of an extraction you don’t have to finish if you have an emergency power outage. I often think dentists make a mistake spending hours trying to find a root tip or chasing a brittle, dilacerated monster. If you give up after a maximum of 20 minutes, the patient rarely gets as much pain healing if you leave them alone, than if you successfully retrieved the root. After six weeks the gum would have healed over so a grateful surgeon can go in retrieve the last bit and will have some tissue to raise a flap and cover it all up again afterwards. So, in summary, when an extraction doesn’t go your way; drain any infection, remove all the irritating sharp supragingival dentine and then give up! I have had to escort a patient from the chair midway through an implant procedure and dump them on the gilded streets of London because of a fire alarm and evacuation, but thanks to a neat flap and plenty of swabs this wasn’t a problem. Keeping calm in the weirdest situations can almost be amusing for you and the patients. The patient in the chair will appreciate that you are doing your best in difficult times, and the patients waiting will understand as long as they are kept informed. The most important thing is that you have a plan which will keep you calm and the patients will feel reassured they are in the right place. Don’t be too quick to send everyone home either, you’ll be surprised how much you can do for someone in pain even without power, and it won’t be long before the power comes back on!