To me, the creative part of dentistry usually involves capturing an entire maxillary or mandibular arch when traditional techniques – whether with elastomeric materials or digital capture – are unable to provide the necessary detail.
A sectional impression technique is a general way to describe many applications where we are limited only by our creativity. Three relatively common situations where a sectional impression can be beneficial include:
1. A partially edentulous patient missing nearly all of their posterior teeth
2. A soon-to-be edentulous patient with extremely mobile teeth
3. A patient with dental implants with limited opening potential in what might be considered microstomia
Partially edentulous – missing posterior teeth
A restorative treatment plan is identified for the patient maintaining the ability to select a path that makes sense whether teeth are removed or the remaining teeth are maintained. The outlines of the desired position of the teeth are helpful in identifying the challenges and/or compromises that are critical in the decision making process in terms of how to proceed.
A sectional impression technique for this patient allows the opportunity to focus on the edentulous areas prior to capturing the remaining natural teeth. An accurate recording of the soft tissue and associated landmarks provides information helpful for the variety of treatment options that exist for this patient. Specifically, it is helpful to know the thickness of the soft tissues relative to the supporting alveolar bone when creating a surgical guide in conjunction with a CBCT image for the placement and, in particular, the depth of the dental implants. When the goal is to transition a patient into a situation where all of the natural teeth are to be removed, the edentulous areas are the only consistent reference points.
The initial impression of the edentulous posterior segments for this patient creates a customized and highly stable record basis that transfers well between the patient and the master working-model when mounting on the articulator.
1. Make a preliminary impression and models.
2. Construct the initial custom tray in the form of a “record base” in the edentulous segments, making sure to create index grooves for use as a reference when making an interocclusal record.
3. Place a spacer over the initial custom tray and create a second full-arch custom tray (although a stock tray could work as well) that fits over the remaining natural teeth and over at least the index grooves of the initial tray.
4. Make an impression of the edentulous posterior segments extending into the vestibular border areas as well as around the lingual/palatal aspect of the remaining natural teeth to help retain the sectional impression.
5. Evaluate with the initial sectional impressions in the patient’s mouth to make sure the posterior extension of the tray is not touching the opposing arch or tray, shorten the tray(s) as needed and make an interocclusal record making use of the index grooves.
6. Remove the sectional impression trays, remove the interocclusal record and replace the sectional impression trays in the patient's mouth to prepare for the final impression.
7. Make the final impression over the initial sectional impression in order to relate the remaining natural dentition with the edentulous posterior segments.
8. Make the master working model first, then remove the sectional piece recording the edentulous spaces to mount the upper and lower models.
Highly mobile teeth – immediate denture impression
Many patients with advanced periodontal disease have responded well to treatment and maintenance over time. This patient presents with visibly mobile teeth and has elected to proceed with a restorative dental treatment plan that includes the removal of all remaining teeth. When the teeth are mobile, can the tooth position on the master model be accurate for use as a reference point when placing denture teeth? The other question is, when the teeth are mobile, how many chances do I have to make the impression?
The identification and transfer of landmarks in the final impression are critical in the evaluation of tooth position on the working model. Specifically, it is hard to know if the teeth moved facially or palatally during the impression process.
A sectional impression, whether with irreversible hydrocolloid (alginate) or vinyl polysiloxane (silicone) or a combination of impression materials, can be useful to customize a stock tray to record the landmarks of the palatal surface of the maxillary arch. The tray can be modified with boxing wax to extend the flange areas and to support the palatal area of the impression as well. The modification with wax is most helpful when working with alginate (irreversible hydrocolloid) to help maintain the accuracy of the transfer of information to the master working model.
1. Select a stock impression tray, modify the flange extensions and palatal height with boxing wax and evaluate intraorally.
2. Make an initial impression with the goal being to record the palatal vault area as well as to index the occlusal/incisal aspect of the natural teeth to serve as a reference point when re-inserting the impression.
3. Evaluate and adjust the initial impression as well as wax extensions to prepare for the final impression.
4. Make a decision on whether or not to place wax at the cervical embrasures to minimize the amount of impression material that could potentially lock in around a mobile tooth.
5. Make a final impression using the previously formed index or reference point created by the palatal vault and the occlusal/incisal aspect of the remaining dentition.
Limited Opening and/or Microstomia – Dental Implant Impression
This patient has been managing with pemphigus vulgaris (PV) and as a result presents with advanced periodontal disease particularly evident in the lower arch, resulting in a hopeless prognosis. Minor trauma as a result of wearing a denture would certainly result in epithelial separation, acantholysis or bullae (fluid-filled elevation greater than 1 cm in diameter) formation.
The restorative treatment plan includes a mandibular fixed hybrid (fixed-detachable); however, the challenge in restoring this patient with PV is compounded by a limited ability to open her mouth. Traditionally, an open-tray final impression involves placing the implant specific impression abutments and connecting with a rigid material such GC Pattern Resin LS (low shrinkage).
The challenge is how to insert an impression tray, loaded with impression material, up and over the impression abutments placed in the mouth. This can be painful or simply impossible in a scenario where the patient simply cannot open wide enough to accommodate, particularly with a time-sensitive material.
The final impression for the definitive restoration in this patient was completed with a sectional impression technique. The first component was made to capture the edentulous areas in the posterior segments of the mandibular arch as well as the lingual aspect of the impression abutments. A visual evaluation can be completed to assure the appropriate capture of information prior to proceeding. The second component was made to capture the facial aspect of the impression abutments and to connect to the first component of the custom tray. The modified open-tray technique allowed for primarily an anterior path of removal after releasing impression abutments.
Limited by Our Creativity
The sectional impression technique has been modified and adapted for traditional impressions for edentulous patients working with stock trays. The technique can also be applied to edentulous patients with fibrous and highly mobile segments in the anterior maxilla by creating a window through the first impression and capturing the anterior segment in a second impression. The techniques can be applied for patients requiring obturators as a result of a hemi-maxillectomy where trismus and limited opening can be included.
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Douglas G. Benting, DDS, MS, FACP, Spear Visiting Faculty and Contributing Author. www.drbenting.com