Dental Clinical Articles

Posted: 30 March 2011

Crown and Bridge: The State of the Art

Author: Martin Docking

Martin Docking of Dental Precision talks to Moira Crawford about how the world of dental ceramics is changing.

Martin Docking is a dental technician and a clinical technician with real passion. Together with his wife Lucy, he set up his own dental lab, Dental Precision, based in St Agnes on the north coast of Cornwall back in 1995, and the firm has gone from strength to strength. Now employing a staff of 19, his reputation attracts and maintains a client base, from all over the UK and Ireland, of like-minded dentists who are at the top of their game and expect only the best in quality and service.

Restoring dental implants and crown and bridge work are the mainstay of Dental Precision and the company is keen to share its knowledge and expertise with their dentists. ‘Communication is essential to a good relationship so keeping my clients informed on the latest trends and materials is important. Feedback we received at a recent event with 10 practices highlighted that dentists have so much to think about every day, their clients’ needs, their employees, the general running of the practice, CQC, marketing, new techniques and equipment... that when it comes to their laboratory they need to be able to trust their technicians to keep them abreast of changes and advise them of how to achieve the best product from the lab,’ Martin commented.

One aspect of this is to keep an eye on the developments in the industry - finding out about the latest materials and how they might benefit his clients and their patients.

The Rise and Fall of Gold

‘Traditionally porcelain bonded to gold has been the restoration of choice for around 95% of GDPs in the UK, but the introduction and acceptance of new materials coupled with the increase in the price of gold has been very significant in a change of thinking,’ Martin stated. ‘If I was asked two years ago if I would use non precious alloy in my laboratory, I would have said absolutely not, but how things have changed! The introduction from several CAD-CAM companies of machined frameworks milled out of nickel-free chrome has revolutionised the market; being light in weight, strong, and very cost effective, non-precious alloys also give a great ceramic bond. The last two years have given me and my clients a very positive view of non-precious alloys, as they are fulfilling all the criteria that the expensive gold-based alloys were but at a significantly lower cost. Many dentists still have a fear, as I did, that these materials, being cheaper, would be inferior but they have the advantages detailed above and they etch very well so luting is possible. Some claim that gold looks better in the mouth but trends are changing and the desire to have visible gold showing is no longer there for the majority of patients.’

Martin recommends that dentists who wish to take a new look at the cost reduction and other advantages that non-precious alloys can offer, speak with their technicians about the products they would like to use to ensure the best combination of metal and ceramic. But Martin believes there are good and bad non-precious alloys and you must also be mindful of the materials that are used alongside them.

Zirconia

About eight years ago zirconia came to prominence in the UK dental market but has it been the new generation material it promised to be?

‘We have had great success with zirconia and also some real issues,’ Martin explained. ‘Zirconia is very strong, tooth coloured and light weight with fantastic biocompatibility, so in theory it should be perfect for creating frameworks for crowns and bridges, from single units to full mouth reconstruction. The ceramic can be sintered directly to the structure or pressed on with some ceramic systems and we have achieved some beautiful results. However, we have also had some real issues with delamination of the sintered ceramic.

‘If a problem presents itself in our laboratory a full investigation is carried out and we review our processes, techniques and occulsal loading to analyse the root cause; during such investigations we noticed that even with a carefully designed framework and well supported ceramic, we still had a few cases that delaminated from the zirconia framework.

‘Zirliners and other pre ceramic bonding layers were tried with some success but still some delamination occurred. I had read reports from America stating that this problem would appear in the UK and many clinicians in America had reduced their use of it. The conclusion we came to in my laboratory was that the zirconia was so hard at about 900 MPa that the ceramic bond was insuffcient,’ added Martin.

‘Zirconia has a place in dentistry with implant abutments and interestingly on the next generation of implants that combine titanium and zirconia,’ he explained. ‘Crowns made completely from zirconia are now being marketed which are full contour zirconia that is stained and tinted and these are proving successful on posterior teeth with limited occlusal space, replacing conventionally prescribed full gold crowns. Something to bear in mind if you plan to start using full zirconia crowns is that you will need a lot of time and sharp burs if you need to cut them off.’

IPS E.MAX

If you have not used IPS e.max from Ivoclar yet, you will be in for a treat,’ said Martin with a big smile. ‘Quite simply e.max allows my technicians to deliver outstanding aesthetics with the most predictable shade matching even with difficult combination cases.’

‘A nano-fluoroapatite layering ceramic gives beautiful natural opalescence and life to crowns, anterior bridges, veneers, inlay and onlays. A range of ingots with different opacities gives my ceramists the ability to mask out post and cores, implant abutments, etc, or to use the bleaching ingots to match the most demanding aesthetic patients.’

Posteriorly full anatomical-pressed e.max can be stained and or layered and the material can also be conventional cemented or luted. ‘With a flexural strength of about 400 MPa it is plenty strong enough to withstand normal posterior loading and with the many thousands that we have completed over the last few years we have not had any failures,’ said Martin. ‘e.max makes up about 70% of our crown and bridge work at present and we are confident that this will increase.’Figures 1 - 4 show before and after examples of e.max in use.

Passion

But all of the materials in the world are only as good as the people who work with them. ‘What we value most at Dental Precision are the skills and the passion that our team delivers,’ said Martin. ‘They have the desire to improve standards constantly and are always investigating and evaluating new materials and techniques. We work for the most discerning dentists who are looking to go to the next level of excellence and who want to work closely with their laboratory to achieve this.’

‘Communication is the key; photography, diagnostic wax ups, detailed prescriptions and talking directly to the technician who is making the restoration will ensure great results,’ said Martin.