Scientifica implantology

Numeri Uno, 2014;18: 6-9

A MINIMALLY INVASIVE TECHNIQUE: IMPLANTS WITH A REDUCED DIAMETER AND CAD/CAM TECHNIQUES FOR LONG-TERM TEMPORARY SOLUTIONS

J Prosthodont. 2015 Oct 5. doi: 10.1111/jopr.12374. [Epub ahead of print]

The zirconia manufactured by Sweden & Martina and used in implantoprosthetic rehabilitations has yielded excellent results in terms of limited antagonist wear of both natural teeth and composite teeth after one year of functional use.

Numeri Uno 22; 2015, 29-31

REHABILITATION OF A SINGLE ELEMENT IN AN AREA OF HIGH AESTHETIC VALUE WITH SEVERE PERIODONTAL IMPAIRMENT

Journal of Applied Oral Sciences, accepted on 2012, December, 20th

This study analysed the fracture conditions of individual zirconia abutments produced with intentionally thin walls, designed to create extreme test conditions. The morphology of the abutments was both axial and highly tilted. The fracture modes were studied and the bending moments applied to cause them. The results of the tests, conducted in conditions much more severe than in normal clinical practice, indicated the safety of using zirconia abutments with a titanium reinforcement at the level of the connection and a PEEK ring to absorb the closure between the titanium screw and the zirconia abutment.

NumeriUno, 8, 04-05, 2009

In this clinical case, the single-model technique allowed rehabilitating the patient with one surgery and a minimal number of sessions for finalising the screwed prosthesis, obtained with the CAD-CAM Echo protocol on Kohno implants.

Numeri Uno, 4 (4-6):04-05, 2009

USE OF CAD/CAM TECHNOLOGY FOR TREATING CEMENT-RETAINED SINGLE-TOOTH PROSTHESIS IN THE AESTHETIC ZONE

This clinical case demonstrates how the use of the CAD-CAM Echo technique allows obtaining aesthetic results by creating abutments entirely in zirconium oxide on which a zirconium-ceramic crown was cemented.

Numeri Uno, 6, 04-05, 2009

ZIRCONIUM PROSTHESIS ON IMPLANTS AND NATURAL ELEMENTS

The implementation of the Echo prosthetic protocol allowed obtaining an entire meso-structure in zirconium with excellent functional and aesthetic characteristics; the structure is also suitable for maintaining the morphostructural integrity of the remaining teeth.

Numeri Uno, 2014;18: 6-9

A MINIMALLY INVASIVE TECHNIQUE: IMPLANTS WITH A REDUCED DIAMETER AND CAD/CAM TECHNIQUES FOR LONG-TERM TEMPORARY SOLUTIONS

In recent years, the changed socioeconomic conditions of the population and the evolution of the technologies available to dentists have led to the formulation of treatment plans increasingly characterized by minimal invasiveness.
In particular, in the area of implants there has been a significant development important of techniques that are alternatives to bone regeneration, to guarantee patients the same results with notable reductions in treatment times and costs, together with less discomfort due to fewer surgical procedures.
With regard to this, we present a case in which it was decided to treat an elderly patient with an immediate post-extraction technique, using implants with a small diameter on account of the poor bone volumes.

NumeriUno, 2014;18: 16-19

PRECISION IN LASER SINTERED CO-CR ALLOYS WITH CERAMIC CASINGS PART 2

The results obtained in the protocols illustrated in the previous number led us to continue our efforts in larger jobs, with results that were initially encouraging, but that later showed signs of unexpected torsions. In some larger jobs, during the repeated firing sessions, the arch had to be readjusted, since imprecisions appeared due to the release of internal tensions. In some cases, firing for stabilization before ceramic application mitigated the problem. In jobs on milled posts without perfect closure, this could even be acceptable, but on natural teeth it would definitely not be. We need to verify exactly how, when and to what extent these problems occurred, and how we could rectify them, or at least understand their limits.
In agreement with Sweden & Martina we devised a small study to clarify this situation. We constructed a model with four milled posts, and on this we produced three types of arch, so as to determine which was most controllable. The three ferrules were adjusted cold to assess precision both on the single posts and on the entire assembly, and they were then annealed in a ceramic furnace, performing a series of firings as if they were to be ceramicized, with checks every time they were taken out of the furnace and readjustments if necessary. In greater detail, ferrule A was normally adjusted when cold, always requiring further readjustments after the various firings, and becoming stabilized around the sixth firing. The precision after the firings was very good on one side and poor on the other.
Ferrule B gave the best results, with precision when cold, becoming stabilized after four firings, and finally with good precision.
Ferrule C was the most disappointing. The stabilizer bar that we expected to provide stabilization instead caused a series of torsions that made it unusable after just two firings.
Cold adjustment was already very difficult, and even more so after the first firing.

Conclusions:

• it is evident that a structure fabricated with a series of fusions contains tensions that tend to be released during annealing;
• it was noted that a particular design of the structure mitigates this contraindication (a robust linguopalatal band);
• it was determined that these distortions emerged only on very extended structures;
• experience teaches that with up to 2/3 of a complete ferrule, distortions can be controlled if an adequate design is chosen.

The precision when cold of laser-sintered Co-Cr is of a quality that is higher and above all predictable. It is only extended ferrules that show distortions after firing, with particular characteristics: all the ferrules tended to curve inwards at the level of the more distal elements. The use of a very long firing time for stabilization (e.g. 15/20 minutes at 980°/1000°C) could probably further mitigate this contraindication.
To verify if absolute stability could be achieved in such extensive jobs, we decided to experiment with a series of annealing processes on two Co-Cr arches milled from solid metal. Two structures were prepared, exploiting the previous scans, one with a stabilizer bar and one without.
The two structures were then subjected to the same treatment as the previous laser-sintered versions, with extremely positive results. No differences of precision were found between the arch with and the bar without the stabilizer bar, and only cold adjustment required a little extra work. We can conclude with these considerations: for normal routine jobs, laser-sintered Co-Cr is able to provide excellent solutions for all needs for precision in bridge structures, until a particularly sharp curve is reached, and our advice is not to exceed 2/3 of the arch. A milled element gives greater guarantees in all jobs calling for a complete ferule. Considering that as regards dental technology, these techniques are still very recent, and that therefore notable progress will be made with the many experiences of our colleagues, I believe that very soon we will be able to achieve constant dimensional stability even with the laser-sintered Co-Cr technique.


Stabilization firings
Before consigning the job, a cycle of “distension” firings was performed in an argon atmosphere, consisting in:

• First firing from 0 to 450°C in 60 minutes, maintaining this temperature for 45 minutes. Heating up to 750°C in 45 minutes, maintaining this temperature for 60 minutes.
• Furnace off and cooling down to 600°C, then opening the furnace.
• Cooling down to 300°C, closure of the argon flow, extraction of the pieces.

This firing certainly optimizes the properties of the metal, but in dimensional terms it is absolutely insufficient.
Various experiences and a number of tests led us to consider a more incisive firing to be more advantageous: 1000°C for 10 minutes in a vacuum. This firing almost completely releases all the tensions, giving the piece 95% stability. Small corrections will be necessary as work proceeds, but these will be only minor, very similar to those to be encountered with fused precious metals.

NumeriUno, 2013; 17: 9-11

PRECISION IN LASER SINTERED CO-CR ALLOYS WITH CERAMIC CASINGS PART 1

The new CAD/CAM technologies have brought a veritable revolution in the field of dentistry and dental technology in particular. In addition to new materials, such as zirconium, these technologies also offer solutions for more conventional materials like titanium and the cobalt-chrome. This latter can be worked not only by milling, but also using laser sintering systems, building up the component with the addition of microscopic spheres that are fused together by a numerically-guided laser beam.
In the search for a material that could replace the precious metal, which has by now reached intolerable price levels, at least for routine jobs, and that could maintain the long-consolidated characteristics of precision and reliability in casting techniques, the choice of this system seemed to us to be economically viable and interesting in terms of practicality. We were persuaded to explore this technique by the fact that there is no need to change the ceramic casing, that we are thus able to exploit the experience of over forty years with ceramics on base metals, and last but not least, that there is the possibility of working on pieces again with lasers and other types of welding. Our initial experiences were not particularly satisfactory in terms of precision, but all other aspects gave excellent results. But good results without precision are not good results!
The situation was frustrating. We started from the consideration that every material has its prerogatives, and these do not always coincide with conventional ways of working. Very often it can be wiser to adapt to the characteristics of new technologies than to try to adapt these technologies to our habits.
So reconsidering the problem, we found that laser-sintered edges have a “teardrop” shape that is not a defect, but is instead a specific characteristic of this technology. It would therefore be impossible to achieve precision in this area. Precision, if attainable, must be “upstream” from these teardrop edges, which must be positioned beyond the preparation during scanning to allow the teardrop shape to be eliminated.
The technique to achieve this level of precision is extremely simple:

• Locate the closure line beyond the preparation.
• Remove the “teardrop” edge.
• Finish off by trimming away excess material until the closure edge.

Clearly, the more the preparation is vertical, the greater will be the possibility of achieving high precision. Having obtained this result, we decided to verify whether this precision could be maintained on larger jobs as well. We used a step-by-step process on a small bridge of three elements to document this further experience and further develop the technique.
After these results, the construction of laser-sintered bridges became a massive part of our laboratory’s daily routine, resolving the problems encountered at the outset.
In the second part of this study, we will discuss particularly extensive cases, with the problems they present and strategies to resolve these problems.