A Novel Design of a Pick-up–Type Impression Coping

A dental impression is a negative imprint of an oral structure used to produce a positive replica of the structure for use as a permanent record or in the production of a dental restoration or prosthesis.¹ Impression-taking is a challenging procedure in implant dentistry, because accuracy is essential to produce an implant restoration with a passive fit,¹ which is related to long-term success of the implant treatment.²

Traditionally, there have been two implant impression techniques used for transferring impression copings from the implant to the impression: the transfer and the pick-up impression techniques.³ The transfer technique uses tapered copings and a closed tray to make an impression. These copings are connected to the implants, and an impression is made and separated from the mouth. The copings are removed and connected to the implant analogs. The coping-analog assemblies are then manually reinserted into the impression before the definitive cast is fabricated (Figure 1 through Figure 4).⁴

Alternatively, the pick-up impression technique uses square copings and a tray with openings (open tray), allowing the coronal ends of the impression coping screw to be exposed. The copings are unscrewed from the implant so they may be removed along with the impression. The implant analogs are then connected to the copings to fabricate the definitive cast (Figure 5 through Figure 7).¹

Several studies have analyzed the differences between these two types of impression copings.⁵ Most of these studies have demonstrated that the pick-up type has shown better reproducibility than the transfer type, especially when a greater number of implants was involved.⁶ The pick-up impression technique is believed to be more accurate because the impression copings are maintained within the impression when removed from the mouth; thus the potential for error and distortion that may occur when manually placing the copings in the impression, as with the transfer technique, is eliminated.^1,7-12

A current trend with pick-up impressions is the use of impression copings that are rhomboidal in shape so as to improve the stability of the coping in the impression material. This design is useful in multi-unit impressions in which several impression copings become strongly locked into the impression material to increase stability and decrease errors. This type of impression coping, however, oftentimes is unable to engage the implant if the implant is placed with limited mesiodistal distance where a narrow interproximal space prevents proper fit of the impression coping. Thus, this article is intended to compare various pick-up impression copings and propose a new impression coping design for the purpose of making an accurate impression easily with no discrepancies regardless of implant/tooth proximity.

In February 2017, a 54-year-old male patient presented to the Ashman Department of Periodontology and Implant Dentistry at New York University College of Dentistry. His chief complaint was the absence of tooth No. 20. He desired a fixed restoration. The patient was a nonsmoker with an unremarkable medical history, reported taking no medications, had no known drug allergies, and consumed alcohol only occasionally. Intraoral examination showed a healthy periodontal status and good oral hygiene. The treatment plan was to place an implant in the location of tooth No. 20. A periapical x-ray of the area was taken and a surgical guide was made from an ideal wax-up.

After administration of local anesthesia (Lidocaine Hydrochloride 2% with Epinephrine 1:100,000, Septodont, septodontusa.com), a mid-crestal incision was performed in the area of No. 20 with intrasulcular incisions around teeth Nos. 19 and 21. A full-thickness flap was then reflected. An osteotomy was performed at the No. 20 site, and a 4.1 mm x 10 mm implant (Straumann^® Bone Level, Straumann, straumann.com) was placed in the osteotomy. Because of the poor bone quality the implant was placed slightly distal to ideal position (Figure 8). Primary flap closure was achieved with four interrupted chromic gut 4-0 sutures (Henry Schein Dental, henryschein.com).

The patient was scheduled for second-stage surgery 3 months later for placement of a healing abutment. He stated there were no changes in his medical history. Following local anesthesia infiltration, a crestal incision was made and a full-thickness flap was elevated to expose the implant for removal of the implant cover screw. A healing abutment was placed and two single interrupted resorbable 4-0 chromic gut sutures (Henry Schein Dental) were used to close the flap.

Two weeks later the patient presented for impression-taking of the implant. The plan was to take an open-tray impression; however, when attempting to place the pick-up impression it was noted that the conventional-shaped impression coping did not completely engage the implant because the coping was too wide for the narrow interproximal space that was present (Figure 9 and Figure 10). To overcome this problem a modified coping for the impression was designed to fit the narrow mesiodistal space. The traditional pick-up impression coping was trimmed at two corners to form a new shape using a slow-speed hand motor and acrylic bur (Figure 11 through Figure 13). This modified coping design fit well and completely engaged the implant.

The impression coping was polished and finished with a polishing bur before being placed in the patient's mouth. A successful and accurate impression was then taken using the newly designed impression coping. Impressions were taken using polyether material and sent to the laboratory for fabrication of a porcelain-fused-to-metal crown, which was screw-retained. The crown was returned from the laboratory and fitted 4 weeks later. The fit was verified clinically and by radiograph (Figure 14 through Figure 16). The patient reported complete satisfaction with the function and esthetics of this single-crown fixed restoration.

Generally, there are two types of impression copings: transfer and pick-up. Reproducibility of these impression copings varies. Some studies show pick-up impression copings provide better accuracy than the transfer type when used for two or more different implant types.¹³ Open trays should be used for pick-up impressions. Pick-up impressions, however, are more technique sensitive than transfer impressions and generally cannot be used when mesiodistal distance is limited. In order to engage or release the retaining screw of the pick-up coping, sufficient vertical and horizontal space in the mouth is necessary.

On the other hand, transfer copings generally are easier to use and can be utilized in limited mesiodistal space, but are less accurate.¹⁴ This method uses tapered copings with a closed tray to create an impression.

The pick-up and transfer copings come in various shapes and sizes, with pick-up impression copings generally being wider. The shape of a pick-up impression coping is designed to hold the impression material with greater accuracy and more stability as compared to a transfer impression coping.

Despite the various advantages of using an open-tray impression, including increased accuracy and minimized potential for error due to the impression coping being maintained within the impression upon removal from the mouth, sometimes lack of mesiodistal and/or vertical space may contraindicate the use of an open-tray technique. Hence, in such situations use of a transfer or closed-tray technique may be a better option.

Recent developments in optical techniques have shown increased benefits for both patient and dentist as digital data (position and angle) are extracted directly.¹⁵ The use of digital technology can overcome some of the errors associated with traditional impression-taking, such as impression material shrinkage, coping shape inconsistencies, and limited interproximal space, as well as cast production. Digital systems such as intraoral scanners have proven to be highly accurate and capable of increasing overall efficiency, and with the use of intraoral digital impressions laboratory products become more consistent and accurate.¹⁶ A rigid protocol that includes slow zigzag scanning and calibration must be followed to obtain a complete intraoral dental arch digital size. This requires that clinicians be experienced with this type of system, as accuracy is directly related to operator experience.¹⁷ Ultimately, the dentist and laboratory technician are responsible for recognizing and interpreting errors to determine their effect on the desired treatment outcome.¹⁷ Generally, the more experience they have with the system, the better.

In the present case report, an attempt was made to use a conventional pick-up impression coping that proved insufficient in engaging the implant due to narrow interproximal space. To overcome this dilemma a new impression coping design was created. The modified shape of the new impression coping made insertion and engagement in a narrow mesiodistal space feasible. While this new impression coping design appears to offer better reproducibility than the transfer type and may be used in limited mesiodistal space, additional studies are necessary to examine its use in multiple implant arrangements with various angulations and depths so that the present results may be verified.

Accurate impressions are necessary to create well-fitting esthetic and functional restorations. The shape of the novel impression coping presented allows it to engage the implant in cases where there is limited available space either mesiodistally or buccolingually, facilitating a more precise impression and accurate fabrication of a correctly fitted crown.

Motoharu Unozawa, DDS
Resident, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York

Stuti Muchhala, BDS
Resident, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York

Arvin Kadempour, DDS
Adjunct Clinical Professor, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York; Private Practice, New York, New York

Stuart J. Froum, DDS
Adjunct Clinical Professor and Director of Clinical Research, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York; Private Practice, New York, New York