THE AMALGAM-RESIN DEBATE: INDICATIONS FOR PLACEMENT OF RESIN VS AMALGAM
My regional dental school recommends that composites be used posteriorly only for the smallest restorations, no more than ¼ the inter-cuspal width, with no more than incipient interproximal damage. As restoration size increases, the more they believe amalgam should be employed. The greater the amount of tooth structure is missing, the more, in their view, is amalgam the preferred material. Caries-inhibition of amalgam is played out as the indication for this choice, while the real reasons for poor performance in resins is incorrect and fundamentally unsound composite technique.
In the outlook developed by this Handbook, that view is 180 degrees wrong. Please read the entirety of what follows.
THE EFFECTIVENESS OF THE SMALL CLASS II AMALGAM
- It is in the tiniest of restorations that amalgam belongs. A small restoration in amalgam is scarcely an esthetic imposition – it is unobtrusive. It is unlikely to promote cusp fracture in later years, the end-point of their service life. Experienced clinicians know that fracture is serious; it sometimes dooms the tooth to extraction.
- A small amalgam is unlikely to impose significant staining of tooth structure and hence permanent disfigurement of the smile. The box walls can be meticulously prepared with hand instruments, absolutely limiting proximal extension and iatrogenic damage to the adjacent tooth. Such a mini-amalgam can last for 40 years, a very efficient dental intervention. Small amalgam, thumbs up.
- A proximal box for an amalgam restoration is inherently narrower than an equivalent resin restoration. There are two reasons:
- Because resin restorations require rod-end bonding, and hence beveled box walls See enamel axiom #2 and enamel axiom #3, a conservative resin box cannot be achieved with hand instruments, which can only cleave enamel rods along their planes, and cannot create a beveled margin. Burs must be used to cut enamel rods to a bevel. The extension thus must be at least the thickness of rotary disc or the diameter of the smallest bur tip used. See Outside-Inwards cutting for the method used in this Handbook to safely open beveled but minimal proximal boxes.
- As well, resin box walls require proximal extension for access of burs or discs for final finishing, they require more extension than that required for amalgam where the finest piano-wire explorer tip can remove excess amalgam from box margins.
- In terms of cariology, if small composite boxes are not extended to break contact, they fail early. Why?
- Because enamel rods on the box walls are not properly beveled and therefore weakly bonded
- There is not sufficient space to visualize the extent of caries
- The gingival margin is not extended onto sound tooth structure
- The gingival margin has unsupported enamel rods, being neither a butt margin nor an apically inclined margin, but is rather an occlusally inclined margin, the rods of which do not terminate in dentin and hence have no cohesive connection to the dentin.
These realities combine to make a dysfunctional restoration, the outcome of which contradicts the minimally invasive intention. Early failure and short lifespan are not credible treatment, regardless of what we think we are doing.
Once large amounts of tooth structure go missing
- More and more restorative material becomes part of the smile, disfiguring if amalgam, inconspicuous if effectively treated in resin. Composite in large restorations becomes more relevant to the New Goals of Dental Treatment;
- To preserve and promote the appearance of the patient
- to avoid systemic ill-health
- To deliver treatment without emotional or physical trauma
- To respect the economic well-being of the patient
- The tooth becomes progressively weaker.A bonded restoration exhibits higher strength.“Resistance to cusp fracture in class II prepared and restored premolars”by Gelb, MN, Barouch E, Simonsen RJ.J Pros Dent 1986 (55) 184-185 Abstract: “While both amalgam and composite restorations may restore some strength, only etched and bonded composite restorations return the tooth to a fracture strength as high as or higher than that of sound, unrestored teeth.”
The findings of this now-dated study are even more valid today with out improved resins, dentin adhesives, and curing lights.
When replacing large amounts of missing tooth structure, to restore strength,prevent fracture, and maintain appearance, adhesion needs to be called into play. Big composite, thumbs up.
Sadly, I often re-restore failed and under-extended composite boxes placed by a new grad following their dysfunctional university training. Even more regrettably, at the same time, I restore the adjacent tooth which has been damaged by rotary instruments attempting to avoid opening the proximal box.
Every week I restore a tooth with a cusp fractured secondary to long-service amalgam. Conversely, I never need to re-restore a large composite due to cusp fracture.
These failure points are very prevalent; large amalgam = cusp fracture, small composite = caries recurrence.
My regional school is not known as an eminent restorative school, it is cloaked in the comfortable dogma of old ways, discouraging innovation and closing doors to progressive influences. Their graduates sometimes hardly know how to hold a handpiece. I know this because they have been my study club members for years, both operative and didactic. Sorry, Ivory Tower, the world changed and you got left behind.
While this is an important scientifically-based outlook, This Handbook is not a debate of materials, people, institutions, or beliefs; it is a matter of method. Amalgam is a wonderfully practical material. So is gold. Resin can achieve spectacular results. All the dental materials at our disposal, used properly, can play an effective part in dental treatment.
When you have finished understanding the methods that follow, no dogma will be necessary. The clinical choices are open. You can safely prepare proximal boxes and not damage adjacent teeth, restore teeth rationally with resin and expect excellent lifespan. I will get off my podium now and start the journey. Please join me, with an open mind, because you have not heard this before.