Innovative Crown & Bridge Technique --
The H&H Impression Technique

Continued

The technique described exemplifies impression-taking for a full crown. Prior to preparing the tooth, a dual-arch tray is selected for the patient with appropriate try-in to be certain that the tray does not impinge on any anatomical structures and exhibits a passive fit. The dentist should have the patient open and close several times with the empty tray in place until the patient feels comfortable with this practice. It is essential that the patient occlude completely down into Maximum Intercuspation (MI) without interference from the impression tray (Figure 1).

Figure 1 Try-in of empty, dual-arch tray with patient occluded in Maximum Intercuspation (MI).

Following this try-in procedure, the dentist may proceed with preparing the tooth and subgingival margins.

The H&H Technique

Following tooth preparation, the dentist extrudes the high durometer material onto both sides of the dual arch tray while the clinical assistant uses the air-water syringe and suction to rinse and dry the prepared tooth and control saliva. The dentist coaches the patient to completely bite down as the material-filled tray is inserted into the patient's mouth. This directs the patient into MI (Figure 2).

Figure 2 Both sides of the dual-arch fray have been filled high-durometer impression material and inserted in the mouth. Patient is occluded in MI.

Due to the high viscosity of the first-step, high-durometer material, an impression of the prepared teeth, adjacent teeth, and opposing teeth is produced without exceptional detail.

Once the high-durometer material is set, the dentist stabilizes the impression and tray by applying gentle pressure directed at the opposing arch and asks the patient to open (Figure 3).

Figure 3 The high durometer material is set. The patient opens while the impression is held against the opposing arch to make ready for the low durometer material.

When using the H&H technique, the impression and tray are not removed from the mouth until the final low durometer material is applied and set. With the patient's mouth open and the impression and tray secured on the opposing arch, the clinical assistant rinses and dries the prepared tooth as well as the impression of the prepared tooth. The dentist extrudes a small amount of the low-durometer material into the coronal half of the impression of the prepared tooth (Figure 4) while the clinical assistant turns attention to rinsing and drying the prepared tooth.

Figure 4 A small amount of the low-durometer material is extruded into one-half of the corona portion of the prepared tooth. The low durometer material is not placed on the prepared tooth directly, nor is it placed anywhere else on the impression.

The dentist encourages the patient to completely bite down into the material to reach MI (Figure 5).

Figure 5 Final step of the H&H technique. The patient is held in MI.

It is important to note that only a thin film of the low-durometer material should be applied in the coronal half of the impression of the prepared tooth.

The principle objective of the low-durometer material is to flow into the sulcus and engulf the subgingival margin to yield an accurate impression. When the low-durometer material has completely set, the dentist stabilizes the impression and tray against the arch that contains the prepared tooth and instructs the patient to open wile still maintaining pressure against the arch that contains the prepared tooth. The impression and tray are gently rocked and removed from the mouth.

An accurate impression is obtained with clear delineation of the subgingival margins (Figure 6).

Figure 6 Close view of the vinyl polysiloxane impression. Note the definition and fine detail of the subgingival margins of the tooth preparation.

Best results are obtained when the high durometer material shows through the low durometer material on the occlusal aspect of the impressed area of the prepared tooth. This indicates the patient gained complete closure into MI and the impression was completely seated.

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