In the short term, as long as dentinal tubules are not exposed and if the dimensional changes in the composite are within a clinically acceptable range, the chances of post cure sensitivity are low. Of course, we are talking about in normal occlusion, because if the occlusion is off, that is a separate issue in itself.
So, the long-term success relates to more the reaction of the restorative material when it is put under the strain and stress of everyday use. So, a margin that can sustain its seal over a long period of time with minimal routine maintenance is the ideal margin.
The materials in their body, for the most part, will hold together as the basic principles of cavity design are taken into consideration at cavity prep such as resistance and retention form.
So, we focus on the factors that we can modify during preparation, placement, curing and finish as it relates to a marginal seal and its integrity.
Margins must allow for the coming together of the composite with the tooth surface in a setting that allows enough material thickness to sustain under pressure of use. The two designs commonly used are a 90-degree margin that abuts with the composite and the second is the bevel margin that lets the composite overlap the enamel surface and attains more surface area for the enamel bond and allows for an intimate contact between the two surfaces. Both situations require however the manipulation of the composite material so that there are no gaps between the composite and the tooth surface. Historically with metal or alloy materials we were able to burnish and adapt the margins into a nicely adept margin. With composite, we have a micromechanical bond with the tooth surface. If the margin is supported and not put under undue elements, we can expect a marginal seal that stands for a longer period of time than a margin that is either exposed to new decay conditions and or undue stress on the hybrid zone.
The C-Shape system allows the clinician to really pack the composite irrespective of cavity design (class 1 or 2 or 3 etc.) into the cavity and be able to get more of the material into the space in a uniform way that allows a more intimate relation between the composite and the cavity wall surface and the margins. So that when the material is cured there is relatively less dimensional changes. This allows for a tighter, less strained bond in the hybrid zone. Less sensitivity can be expected. In bulk fill or incremental fill techniques, either way, the ability of the instrument system to nicely layer and pack and compound the material against the tooth surface gives a tighter reaction as well as less dimensional change.
When there is plenty of enamel thickness, like the occlusal surface or cuspal areas, the bonding is more forgiving; but in areas such as the gingival floor where the enamel thickness is minimal, the proper technique is critical to achieving the optimal marginal seal.
In this situation, the C-Shape system allows the compressing of the material down into the cavity in a uniform way. Under pressure, that allows for a denser material in the given space that is going to develop the micromechanical bond. As a result, the strength of this bond is increased by default.
When working with composite the voids that we try to avoid are of different sizes and location. Large voids, of course, can be detrimental to the longevity of the filling. Smaller voids, particularly those at the composite tooth interface, can be hard to detect and avoid. These can also be more uncomfortable for the patient and can, of course, shorten the life of the restoration as our patients put them to use. Anytime we can achieve a more solid restoration that is denser in its composition and can become one with the tooth surface exposed to it in the prepared cavity, we can have a restoration that will stand up better to function. The C-Shape instrument system lets us do just that spending less time and being more confident of the result. Its design lets the clinician pack in the composite almost like a piston, and the gliding motion, particularly if you use bond as a lubricant, can help you achieve a burnishing effect. The composite can have the opportunity to become almost one with the tooth.
The composite filling material exhibits some level of shrinkage as it cures. The contracts towards the bonded surface and really assimilates if you will. This is not an ideal property and we would like there to be more stability and to that end, attempts have been made (e.g. placing filling material in small increments, making more dense composites with more fillers, packable composites, and different varieties and brands) that market themselves as more and more stable. One common theme that we noticed is that most of these products are denser and heavier in the body. One of the nice things about the C-Shape system is that it allows us to pack in significantly more composite material in the same space without wasting composite. The tips are large enough to cover a significant amount or all of the cavity surface, and when pushed in it squeezes out the composite under pressure. This ensures a more densely packed in filling and a more finely adept margin of the composite. And some people like to dip the tip in bond from the well and sort of burnish the filling with a wet tip of C-Shape instrument this helps the seal more and takes away the stickiness of composite and lets the instrument only push in and not pull out the filling. More densely packed the composite is in the cavity less will there be room for dimensional change.
This principal is one in particular where a balance is very critical. Too much flow usually is accompanied with more dimensional change and less strength in composite (not always, but mostly) the exception being the newer composites that claim less shrinkage with flowable and I don’t have any reliable data on those. A material that is too viscous is going to be more stable as far as shrinkage is concerned but is going be hard to be adapted intimately with the cavities’ prepared surface. In this instance, the C-Shape can be a very valuable tool in that it allows the operator to really be able to push the composite in the cavity repeatedly do really pack it in and get some extrusion of material that indicates the voids have been removed and the material is packed in tight with the walls and margins. Now when you cure it there isn’t much room for dimensional change. And the margins can be more predictably sealed, with less chance of short-term failure.
This is a very important point in that it refers to the stoutness of the filling if you will. The more densely packed the material in the cavity the stronger its substance of structure. Some benefits come along with this situation:
An overall harder, stronger filling.
Less shrinkage of the material as it cures.
Increased marginal integrity due to increased strength and increased contact.
Longer lasting filling.
The angle that the restoration makes with the tooth surface is important because we have at least a couple of options and the advantages and disadvantages of both should be considered.
Let’s take a look at the 90-degree angle. The most obvious benefit is the ease of preparation. And once the prep is done placing composite has a clean and sharp surface to abut against as we seal the margin of the restoration. The C-Shape instrument can help achieve a tighter seal and hence better restoration at this junction particularly. The burnishing motion the can be done with a wet tip particularly can be really helpful to establish a nice seal at the junction of tooth and composite.
The second option we are going to talk about is the bevel at the margin. This is a bit more technique sensitive but gives more surface area for enamel bond to a composite which is a stronger bond. Gives a more forgiving marginal seal and a more intimate relation between the composite and enamel.
These concepts in the real world do overlap and breaking them down for academic purposes can seem repetitive but it is important we understand why something is happening. And when more than one factor is contributing to the same objective then the chances of failure is decreased.
For example, if the filling material is dense and you pack it in well into the cav ity and you can burnish it in the cavity and along the margins (not just the workable margins but also the margins you cannot get to directly, for example, the gingival floor in the class two cavity) then you have two things going your way. If now you were able to get most of the anatomy close to normal occlusion before curing. You have one more factor in favor of a more comfortable filling.
"Composites are easier to place since there is no pull back"- Dr. G. Felen
"Works very well! It makes resins much more efficient to complete"- K. Ducote (dental student)
"I can't believe how much I love the instrument. I'm ready to order more!"- I. Renieris
"I have added it to my composite placement instruments."- C. Kerbaugh