Innovative Crown & Bridge Technique --
The H&H Impression Technique
Continued
H&H Hydraulic and Hydrophobic Properties Work Together
The physical properties of the high- and low-durometer materials used in the H&H Technique are the key to understanding the logic behind this method. The high durometer of the first-step material permits the material to set to a rigid, plaster-like state. It is this rigidity that allows no rebound of the first-step material and creates a hydraulic force that promotes the surge of low-viscosity material into the sulcus and subgingival margins during the second step of the procedure. The hydraulic force of the rigid, high-durometer material displaces the soft gingival tissue to allow the flow of the hydrophobic low-viscosity impression material in the second step of the H&H Technique (Figure 7a-e). Due to this hydraulic and hydrophobic action of the materials, the gingival retraction cord is not required.
Figure 7. A - E Graphics demonstrating the dynamics of hydraulic and hydrophobic properties working together in the H&H Technique.
 Figure 7a |
 Figure 7b |
 Figure 7c |
 Figure 7d |
 Figure 7e |
Contraindications
There are four instances in which use of the H&H Impression Technique would be contraindicated. For clinical cases involving mobile teeth, use of a material with a high durometer would cause excessive stress on the teeth during withdrawal of the impression due to the rigid set of the material. Secondly, patients exhibiting maxillary or mandibular tori or anatomical undercuts would present a challenge when disengaging the final impression from the arch. A third clinical situation that would contraindicate use of the H&H Technique is that of severely malposed or inclined teeth, in which case the patient may have difficulty with complete occlusion into the material during the second step of the technique. Finally, any extreme spatial discrepancy between the maxillary and mandibular arch could present a problem selecting a dual arch tray to accommodate the physical abnormality.
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