10Jun

The Bigger Picture continued….After bite alignment procedures:

by Dr. McBride

After bite alignment procedures, if needed, an appropriate material would be recommended to give the teeth repaired the best chance of never needing repair again.  This is important because each time a tooth is repaired, the nerve within it is traumatized and these traumas, like x-rays, are cumulative.  Following is a typical history of incidents that occur during the lifetime of a tooth.  First the tooth has a cavity (decay) which traumatizes the nerve (pulp) as bacteria enter it even with a moderate sized decay.  Then the decay is drilled out along with some healthy tooth structure to provide undercuts so that the filling won’t fall out, as mercury amalgam fillings have absolutely no adhesive qualities – they actually just sit in the tooth.   And then they expand and contract at a different rate than the tooth, which cracks from internal expansion that eventually causes tooth structure to break away as seen with this tooth.

Fortunately, the pulp issue inside the tooth has healing resources - a blood supply and a lymphatic system - that counteract the inflammatory process from the bacterial invasions (decays) and trauma of the removal process.  The plot thickens though, as the process continues with the tooth breaking from being weakened from a previous filling(s) and/or has another decay and needs repairing again – more trauma to the pulp. Small decays to be filled or mercury amalgam fillings to be replaced can be restored with direct bonded tooth-colored restorations in one appointment.  However, when a large amount of tooth structure is missing from decay or the presence of large mercury amalgam fillings, especially in back teeth where the pressure is greatest, this type of filling material has less of a longevity factor as its strength factor is limited compared to laboratory processed materials.  Also, if the bonding material replaces a large biting area of a back tooth where the opposing tooth contacts only the material and not much surrounding biting tooth surface, it can wear away from chewing forces causing a bite to change through the opposing tooth’s erupting into the void created by the wear. One feature of mercury amalgam fillings is that they wear similarly to that of tooth structure.  I’ve seen them replaced with bonding materials and although the mercury was now absent, the materials that replaced it presented other types of problems such as teeth sensitivity, bite shifting, etc. A tooth with large and/or multiple fillings will eventually need a protective restoration of some type, and this adds more trauma to the pulp.  Here is where the philosophy of the dental practice enters, which can vary considerably from dentist to dentist.  The type of protective restoration most frequently placed is a porcelain crown.  Yet, the most frequently root canalled teeth are those with porcelain crowns.  This is because, along with the accumulated traumas earlier described, a porcelain crown requires that 35 – 40% additional healthy tooth structure be removed circumferentially as well from top down to make room for the porcelain and  underlying metal or zirconium materials fabricated within it that give it strength.  This causes a lot of pulp/nerve trauma, as the surface of the tooth at its neck area just above the gum needs to be cut into deep enough around its base to provide strength of material.  This area - 360 degrees around the base of the tooth - is especially close to its nerve.