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May I start by thanking all the writers from the Royal College of Physicians and Surgeons of Glasgow for the excellent, heavyweight last issue of Dental Update. I am sure that readers will have appreciated the wealth of information that it contained. Thanks are due to the Dental Dean of the College for persuading so many of his Fellows and Members to write for us.
The International Association for Dental Research holds several meetings per annum, at which researchers present their research, either by way of a research poster or a 15-minute oral presentation. This year, their ‘General Session’ was held in San Francisco and over 4,000 research abstracts were presented. Of course, it is not possible to attend all the sessions, given that 10 or more are occurring at the same time, so it is for the attendees to attend the sessions in which they have a particular interest or expertise. For me, that means attending the sessions on dental materials and their clinical application. Here is a synopsis of some that I felt were of relevance to the readers of Dental Update. My colleague from Birmingham, Dr Katarzyna Gurzawska, attended the sessions on oral surgery/implantology, so she has summarized the papers of relevance to you in Part 2, which will be published in the next issue.
Readers of Dental Update will be aware of the great advances in adhesive dentistry that have facilitated the contemporary approach to the treatment of toothwear using adhesive resin composite restorations placed at an increased occlusal vertical dimension (OVD). While clinicians from the UK have been in the forefront of this, clinicians from Nijmegen in The Netherlands have also been carrying out clinical research in this field. Their paper (number 3022) is therefore of note, because of the large number of restorations involved, namely, 705 anterior direct-placement composites placed at an increased OVD in ‘severe tooth wear patients’ and followed up for a maximum of 4.5 years. After a mean time of 3.5 years, the overall survival of these restorations was 94% (annual failure rate of 2%). Interestingly, significantly more failures were reported when, in anterior teeth, the palatal and buccal veneer restorations were placed on a different day! Survival rate was not influenced by gender, age, location of the restoration or, interestingly, bite force. This represents another confirmation that the direct composite method is now the treatment of choice in toothwearology.
One of the perceived problems related to direct placement posterior composite restorations has been the Class II cavity where there is no enamel at the bottom of the proximal box, so a paper (3024) describing the performance of 68 such restorations, observed for 12 years, is bound to be of interest. The restorations were placed in 30 patients and 27 attended the 12-year review, a terrific recall rate. The overall success rate was 97%, and this was independent of the two materials used (Grandio [VOCO] and Tetric Ceram [Ivoclar]). As would be expected over 12 years, tooth integrity decreased due to enamel cracks and ‘chippings’ and there were visible signs of wear in 90% of the restorations. If there is a flaw in the work, it was that all the restorations were placed by one dentist but, against that, they were all placed in the real world of private dental practice. Notwithstanding this, this is a good endorsement of resin composite Class II restorations in deep boxes.
The three-step total etch Dentine Bonding Agents have been considered a gold standard (at least until the introduction of the Universal Dentine Bonding Agents recently described in Dental Update1), so the paper (505) entitled ‘Are three-step total-etch adhesives still up to the challenge?’ caught my eye! This work described 95 testing sessions in which up to 40 GDPs per session made dentine to enamel test cylinders under pseudo-scientific conditions, sometimes known as ‘The Battle of the Bonds’. Overall, 23,000 shear bond tests were carried out, with the results indicating that some of the newer self-etch adhesive systems yielded shear bond strengths which were 20% better than the best etch and rinse systems. The author concluded that ‘the belief that etch and rinse systems perform better on dentine appears to have been overruled by new products that appeared in the early 2010s’, the only caveat being that the test was a shear test, not everyone's favourite in the world of dental materials science!
Bulk-fill resin composites are the new material on the block, so it was not a surprise to see a variety of papers on these. In one laboratory study (3228), on the effect of high intensity lights on polymerization, anxieties were raised that bulk-fill composites cured with high irradiance and short exposure time might not have adequate depth of cure and degree of polymerization, and that long exposure times always produced best cure and polymerization. There is a lesson here, given that, when placing bulk-fill composites in bulk, there is only one light cure cycle, so it has to be in the right place and for adequate time! In another in vitro study (3229), a large variety (n = 11) of bulk-fill composite materials were tested for marginal adaptation in conservative Class II cavities in plastic teeth, with the results indicating that flowable composites provided better marginal adaptation than sculptable composites. On the other hand, a study (2604) assessed microleakage, in which 48 extracted human molar teeth were prepared for Class II slot preparations (of 5 mm depth) and filled with three dual-cured, bulk-fill materials, one light-cured bulk-fill restorative and a conventional composite cured in increments or in bulk. The results indicated that three of the four bulk-fill materials produced less microleakage than the conventional composite cured in bulk. An alternative conclusion could, however, be – don't try to cure conventional composites in bulk!!
Lastly, on the subject of resin-based dentistry, from time to time there are rumours that resin-based sealants may contain bisphenol A as an unreacted monomer in the manufacturing process, with this material known to be oestrogenic. It was therefore comforting to see the results of a presentation (2611) from the American Dental Association: they tested 12 sealants, with the results indicating that, relative to human daily exposure of bisphenol A (6.020 ng/day), the contribution from dental sealants was limited to 0.001% during the first 24 hours after placement and was well below the level set by the Environmental Protection Agency. They concluded that ‘exposure from dental sealants can be considered safe’.
On the subject of prevention, just when we thought that we had heard the last of ozone in the treatment of caries following a series of negative systematic reviews, 2 it was a surprise to read the presentation by Professor Lynch (now of the University of Nevada, Las Vegas, USA) reporting the results of the treatment of 10 deep carious cavities, 5 in a ‘traditional’ way and 5 using ozone for 10 seconds on ‘deep leathery caries on the pulpal floor’. Results from this trial indicated that 2 of the 5 teeth treated in a traditional manner required root canal treatment after three months, compared with none in the ozone group. The conclusion that ‘less root canal treatment was needed in the ozone group’ seemed statistically bold in view of the small numbers of teeth and patients in the study, but we will all watch this space.
Presently trending is translucent/monolithic zirconia. Readers will be aware that zirconia possesses great strength characteristics but has, until recently, been somewhat opaque and thereby less than ideal for monolithic crowns in the aesthetic zone. In addition, the use of translucent zirconia obviates worries about chipping of the veneering ceramic used in the past. Another worry has been whether zirconia crowns abrade the opposing dentition. In that regard, results of an in vitro two-body wear test (0666) indicated no changes in the translucent zirconia surface when it was placed against a variety of substrates. On the same subject, but this time a clinical study (674) involving 30 patients randomized to monolithic zirconia (Lava Plus, 3M ESPE) or porcelain fused to metal (PFM) full crowns and using a scanner to measure wear, no significant difference was noted between the wear of zirconia vs PFM and zirconia vs enamel. Regarding the margin design for monolithic zirconia crowns, one paper (487) researched the effect of a light chamfer (0.3 mm) or a shoulder (0.8 mm) on in vitro fracture strength, with the results indicating no statistical difference between the two groups. Message – laboratory data suggest that minimal preparation margins may perform well for monolithic zirconia.
The high strength of zirconia should make it ideal as a bridge framework, so it was interesting to see the report of 99 zirconia-based Cercon® Smart (DeguDent, Dentsply International) 3- and 4-unit bridges placed in 75 patients at the University of Goettingen, Germany and recalled at 10 years (3023). The recall was 76%, 51 bridges remaining in function, 24 being classified as total failures and, in 50 bridges, some form of clinical intervention was needed to maintain the bridge in function. The problems were mainly technical, such as chipping of the veneering ceramic, rather than biological. The authors, correctly, comment that studies of this duration are rare but that such prolonged observation times are needed to determine the long-term success of restorations.
With what material should we lute zirconia-based restorations? One study (2543), on 30 zirconia specimens, used 12 variables of materials containing silane and/or the resin 10-MDP and other adhesive systems. The results indicated that the use of an MDP-containing silane alone, or associated with an MDP-containing universal adhesive, resulted in the highest mean bond strengths to zirconia at 24 hours. A related study (2545) reported similar results for a lithium-disilicate ceramic after one year's storage of the specimens in water.
Now, the shape of things to come! Readers may be aware of the staggering advances in 3D-printing (from a recent article in Dental Update),3 so a paper (1005) using this technique in combination with a TRIOS scanner provoked considerable interest. The study examined print speeds, with partial and complete dentures being fabricated from PMMA filaments and tested for strength and accuracy of fit. The authors concluded that a combination of digital imaging and 3D printing offered an economical route with a rapid turnaround time in generating dental prostheses.
Finally, UK readers who feel that they might enjoy attending the IADR to view all the latest dental research may be interested to know that the 2018 meeting will be held right on their doorstep, at Excel, London between 25th and 28th July.