DTUS1310

can cause bleeding of the tissues from the bur abrasion as opposed to a counter-clockwise movement where the bur would be rolling on the gingival tissues creating less damage. A modern device that creates no damage to adjacent gingival tis- sues is a sonic handpiece (SF1LM from Komet) that uses special sonic tips to prepare and finish margins. Unlike the rotation cutting action of traditional burs and handpieces, this instrument vibrates back and forth so there is no cutting effect on gingival tissues. Lasers If bleeding occurs with any tech- nique, the fastest approach to con- trol bleeding, crevicular fluids and tissue management is the use of various types of lasers. tLasers can be used to remove excess tissues or to trough around margins within seconds to expose tooth structure and create a dry field. The ability of lasers to stop cre- vicular fluids and bleeding makes for the driest field possible for impression taking, and nothing else is available in the dental mar- ket that can achieve this type of result. The availability of inexpen- sive diode lasers from companies such as Discus and AMD LASERS are, for the first time, making it affordable for every office to uti- lize this technology and to simplify the impression taking process for everyone, including the patient. Impression trays Impression trays have also gone through their fair share of enhancements and developments over the years. The metal, perfo- rated trays and Rim-Lock border trays have given way to disposable plastic versions of the same. The advent of the overwhelm- ingly popular triple tray has laid claim to approximately 85 percent of all current impressions sent to dental laboratories. These trays have been imple- mented like many other tech- niques and materials to cut down on overhead on both impression trays and materials because one simple triple tray catn not only take the impression of the pre- pared tooth, but also the opposing teeth and register a bite reference. The downside to this technique is the lack of ideal jaw move- ment that can be reproduced with the models that are created, the absence of cross-arch stabilization and the inability to create an accu- rate interocclusal record. This can create dental restora- tions that may need more adjust- ment when it comes time to deliver. Custom trays made from tradi- tional acrylic or modern materials such as Triad (Dentsply Caulk), although seemingly extinct in most offices, still provide the best impression results, but another modern material may soon take over. The HEATWAVE mouldable custom tray (Clinician’s Choice) comes in a variety of sizes and is anatomically shaped to provide an excellent fit straight out of the box, but the difference is that it can be customized further. When placed in a hot water bath the tray becomes pliable and can be custom molded to fit even more precisely. Additionally, the abil- ity to use less impression material with a custom tray and to create an ideal impression due to better adaptation on the first attempt pro- vides a substantial savings of both time and money. If someone does not have the modern digital impression devices, he or she is fortunate to still have the ability to choose from numer- ous types of advanced impression materials. Polyethers, polyvinyls, blends and smart wetting sur- factants are all various materials available to practitioners. Polyethers, having been known for their affinity to moisture (hydrophilic), and the polyvinyls, typically having been more mois- ture sensitive (hydrophobic), have changed. Many of the polyvinyls are get- ting extremely good results via improvements in their chemistry over recent years. The bulk of the market sales come from poly- vinyl impression materials. They are available in various viscosi- ties, such as putties, heavy bodies, medium bodies and light and extra light bodies, which makes it easy to find a viscosity to meet anyone’s preferences. Furthermore, most companies offer variations in setting and working time for those that want speed for individual teeth or those that need a longer setting time so they can impress full arches. The most common technique that has been shown to provide the best results is a heavy tray material with a low viscosity wash material placed around the tooth that flows into the gingival sulcus capturing the marginal detail. Impression guns and volumix- ers such as Pentamix (3M ESPE) or Volume Mixer (Kerr Corporation) have simplified the mixing process to achieve accurate material dis- pensing and proper mixing for bet- ter physical properties compared to hand mixing techniques. The most recent additions are surface modifiers that allow for better adaptation of impression materials to the tooth structure above and below the gum line. These materials allow for better surface adaptation via decreased surface tension (B4, Dentsply Caulk). Impression technique Start the indirect impression tech- nique by preparing the tooth struc- ture in a clockwise manner to reduce tooth structure quickly, but staying away from the gingival margin. After breaking the inter- proximal contacts, place your first retraction cord. Continue preparing the tooth and margins to ideal in a counter clockwise direction, so as not dam- age gingival tissues, or use a sonic handpiece. If a second cord is desired, it can be placed and margins can be refined again if necessary. Based on tissue tension, pocket depth and margin visibility, one can first rinse and then remove, one or both cords. The advantage of leaving one cord in is that it holds the tissues away from the margins and allevi- ates most bleeding issues. Bleeding typically occurs due to previously irritated tissues, bur trauma, cord packing trauma or epithelial tears due to the cord not being moistened before removal. Should bleeding occur, chemi- cal coagulants can be implement- ed quickly to resolve most bleed- ing issues. A laser could be used as an alternative to retraction cords and chemical coagulants to expe- dite the process. An impression can then be cap- tured either with a digital impres- sion device or a heavy body and wash material using the impres- sion tray of your choice. However, a full-arch custom tray will typi- cally achieve the best results. Upon retrieval from the mouth, the impression needs to be evalu- DENTAL TRIBUNE | May 2010 Clinical 15 AD g DT page 16 Fig. 1: Dual cord technique where the remaining cord came out in the impression. Fig. 2: Ideal margin detail after obtaining proper tissue retraction.