The BASIC Anatomical Impression

One of the keystones of the BASIC implant system is the CASE SELECTION Model-Tomographic ™, a diagnostic entity. Its importance centers around providing the doctor information about the patients existing buccal-lingual (B/L) bone volume and anatomical configuration of a proposed implant placement site without having to utilize the radiographic CAT SCAN or surgical exposure. Secondly because it is actual – constructed from the patients anatomical cast – rather than virtual-computer generated – the BASIC 3D channel drilling guide stent can easily and inexpensively be fabricated using this Tomographic entity in the dental office or in a certified dental laboratory.

The anatomical cast of the proposed implant site is one of the five patient records that are utilized in the BASIC system protocol. As we all know usually dental impressions center around diagnostic study casts or prosthetics. An anatomical impression on the other hand is a hybrid. It must accurately impress the dentition of the quadrant or arch in which the implant proposed site occurs and it must attain an accurate impress of the soft tissue and hard anatomy configuration short of surgical exposure. Probably the closest we come to this form of impression is the free end partial denture impression. But even in this exercise we are possibly more concerned with accurate dentition reproduction on the master cast then soft and hard tissue features. However our interest now must center around placing the implant body in an acceptable site in the most accurate way possible and this outcome depends heavily on attaining an excellent anatomical cast.

The soft tissue, as we all know, about a proposed site can be of the fixed or loose type. Often this loose type will hang as a drape of tissue, not conforming to the bone contour and will therefore give us poor anatomical hard tissue information when the usual static impression is made. One example of this draping is found in the posterior lingual region of the mandible. This condition naturally hides the true shape and extent of the sub-mandibular fossa, a most critical area of concern when placing posterior mandibular implants. Another area of importance is the maxillary anterior apical regions. The often hidden depressions occurring here will limit facial bone volume greatly resulting in poor implant placement angulation if pursued without bone regeneration. For these reasons it is important to palpate first all proposed site regions to recognize pertinent undercuts and depressions and then to address these conditions with a simple, accurate impression protocol. It became a challenge to say the least. We spent a good length of time investigating flexible flanges, mold-able flanges, short flanges, no flanges, specially designed trays, no trays at all, and back to my favorite, balloon equipped flanges. All of these trials in the end proved deficient in some aspect: too expensive, too complex and time consuming, difficult to learn an use practically, caused discomfort and worst of all were just not accurate in the final analysis.

But all was not lost because a number of doctors, laboratory people, impression material companies advised us to return to BASIC thinking and just alter somewhat tried and true techniques. This worked so well that a very practical, almost intuitive protocol was developed to allow for simple, very accurate anatomical impressions to be taken. So with easily adjusted appropriate trays and excellent vinyl polysiloxane materials the challenge was, we believe met.

Impression protocol:

1. Materials
   1. Impressions
      1. Heavy Body – Hydrophilic vinyl polysiloxane comparable or Examix NDS ( G.C. America)
      2. Type O Putty – Vinyl Polysiloxane comparable or Exaflex (G.C. America)
      3. Vinyl Polysiloxane adhesive (All)
   2. Impression Trays – disposable Comparable or COE® (G.C. America)
   3. Vinyl Gloves* your choice of manufacturer. *Reason: In the manufacturing of all medical gloves, except vinyl, the chemistry involves a cross linking with sulfur. This element can adversely impact the set and accuracy of A and B kneaded parts of vinyl polysiloxane putty materials.
2. Technique steps
   1. The proposed site is visualized for adequate M/D prosthetic space. Amount of attached keratinized gingival tissue. Inter-occlusal space for an appropriate prosthetic.
   2. The proposed site is palpated to determine extent of anatomical contours, undercuts, exostosis, fossas, depressions, resorptions, swellings, tenderness, etc.
   3. An appropriate full arch or quadrant impression tray (COE® or comparable) is chosen for adequate site and adjacent tooth crown coverage without excess soft tissue impingement.
   4. If mandibular posterior, maxillary anterior or other important arch areas the tray is adjusted chair side with appropriate instruments to create space (facial or lingual flange adjustment) allowing the use of ancillary putty impression material.Example: Mandibular tray adjustment allowing putty use in the posterior molar area.
      
      
   5. Next the adjusted tray (in this example a full arch which is preferred) is adequately filled with the heavy body impression material and seated carefully. Meanwhile the A&B putty components are being kneaded together to a complete homogeneous color and placed to the adjusted lingual flange area. Usually one spoon full of each A&B (Blue and yellow in G.C. material) is more then enough. The mixed putty mass is placed within 5 to 10 seconds after the heavy body material and tray is positioned. The putty is pressed to the side of the tray, into the heavy body overflow, and then index finger (only with vinyl gloves) pressed into the sub-mandibular fossa area so that the drape of lingual loose tissue is intimately pushed against the lingual cortical plate of the fossa depression. The sub- mandibular salivary gland must carefully be pushed down as the drape of tissue is positioned against the lingual cortical plate. Carefully practice this on initial palpation. It would appear something similar to this diagram of the cross section (transverse) of the implant site:
      
      

This impression protocol will work extremely well in all areas of the two arches where any depressions, fossas, or undercuts are palpated and exist as long as the appropriate tray (for size and configuration) is adjusted to allow for finger pressurized use of the putty material. The accuracy is truly remarkable and along with accurate bone soundings with acupuncture needle use, formulation of a precise Model-Tomographic™ is greatly enhanced and implant channel directional risk is diminished almost to a non-factor.