3: Alginate Impressions

Case 3
Alginate Impressions

Review of Symptoms

  • Vital signs
    • Blood pressure: 122/78 mmHg
    • Pulse: 72 beats/min
    • Respiration: 14 Breaths/min

Medical History

The medical history reveals no significant findings. The patient is not taking any medications.

Social History

The patient has a prior history of smoking. Patient quit smoking five years ago. She drinks two to three glasses of red wine on weekends, and drinks two cups of coffee daily.

Extraoral Examination

No significant findings.

Intraoral Examination

No abnormal findings with respect to intraoral structures, mucosa, and gingiva. Periodontal charting was completed and reveals five areas of probing depths 4 mm or greater, #2 distal with a reading of 5 mm, #14, distal with a reading of 5 mm, #15 distal with a reading of 5 mm, and #18 mesial and distal with a reading of 4 mm.

Patient completed orthodontic treatment 30 years ago and only wore retainer for first year after completion of treatment. She is not interested in retreatment.

Dental examination reveals a Class III distal composite on tooth #8 with a slight open margin and recurrent caries, tooth #9 reveals a large Class IV mesial‐facial‐incisal composite with open margins and recurrent caries, as well as a Class III distal composite with an open margin and recurrent caries. Tooth #9 also presents with a composite overhang on the mesial and distal surfaces.

The patient’s oral hygiene is fair. She brushes twice daily, but flosses occasionally.


2 mm maxillary overjet Class (II) occlusion

Radiographic Examination

Anterior periapical was prescribed for tooth #8, #9. Posterior periapical of teeth #2, # 14, #15, and #18, molar and premolar bitewings were also prescribed but not shown (Figure 8.3.1).

Image described by caption.

Figure 8.3.1: Radiographic image teeth #8 and #9.

Diagnosis and Prognosis

The patient’s general oral health is fair. Localized inflammation is present in the areas of teeth #2, #14, #15, and #18 with slight localized bone loss on interproximal surfaces of teeth #2, #14, and #15.

Tooth #8 has caries, which has extended into dentin and can be seen on the radiograph.

Teeth present with yellow extrinsic stain due to age, coffee, and wine.

Dental Hygiene Diagnosis

Problems Related to Risks and Etiology
2 mm overjet Lack of orthodontic intervention and malocclusion
Bleeding on probing Localized periodontal disease, poor oral hygiene management
4–5 mm periodontal pockets on teeth #2, #14, #15, #18 Localized periodontal disease, poor oral hygiene management
Generalized staining Coffee and wine, biofilm accumulation, poor oral hygiene management

Planned Interventions

Clinical Educational/counseling Oral Hygiene Instructions
Evaluate soft and hard tissue for evidence of smoking
Localized scaling and root planing with 4 to 8 week periodontal re‐evaluation
Alginate impressions for fabrication of whitening trays
Refer to Doctor of Dental Surgery (DDS) for tooth #8, redo of existing Class III composite, tooth #9 redo of existing Class IV and Class III composites, possible future laminates
Encourage continued smoking cessation
Stress importance of maintaining recare visits
Discuss homecare technique for whitening trays
Instruct patient that whitening should be done before redo of composites, since composite restorations will not whiten. If sensitivity should occur, recommend dentifrice containing evidence based desensitizing agents (potassium nitrate, calcium sulfate)
Soft bristle brush/ Modified Bass technique
Emphasize importance of flossing
Wear whitening trays for 1 hour, once a day for 14 days
Do not eat or drink for half an hour after, avoid anything that can stain a white t‐shirt

Discussion: Alginate

Alginate is an elastic hydrocolloid impression material made from seaweed. It is also comprised of sodium alginate, calcium sulfate, and retarders. It is used to take primary or preliminary impressions. This colloidal material forms a gel when the powder is mixed with water. It solidifies into an elastic mass capable of producing a negative reproduction of the oral cavity (an impression) (Poling et al. 2008). Alginate is also referred to as an irreversible hydrocolloid because once it is mixed a chemical reaction occurs, known as gelation. Therefore, it can never return to its original state of powder and water. Alginate impressions are taken to obtain diagnostic study models, which are the positive reproductions of the teeth and surrounding structures. They are also used to fabricate bleaching trays and mouth guards. Alginate is the most universally utilized impression material in dentistry.

The following are characteristics of an ideal alginate impression material:

  • cost effective,
  • easy to mix,
  • adequate flow properties,
  • non‐toxic or irritating,
  • sufficient strength to avoid tearing material upon removal from the mouth, and
  • acceptable working and setting times.

Taking Alginate Impressions

Positioning of Patient and Selection of Trays

Patient should be seated in an upright position.

Trays are selected, keeping in mind that proper fitting trays will allow the clinician to obtain all structures, including teeth and soft tissues. The tray should cover maxillary tuberosities and retromolar pads. The tray should also allow for room between the anterior teeth and anterior portion of tray approximately a space of 4 mm to allow for proper definition of anterior teeth.

Trays should be sprayed with a very light layer of alginate impression adhesive and allowed to dry for two to three minutes.

While waiting for adhesive to dry, have the patient rinse out well with a nonalcohol‐based rinse to remove any debris.

Manipulation of Alginate Material

Alginate material comes in canisters and single‐use packets. If using alginate in a canister, the canister should be turned gently upside down to fluff material before opening. If using premeasured single‐use package, the bag may be lightly shaken before tearing open.

Alginate is mixed as a 1 : 1 ratio. Typically, three scoops of powder to three measures of water are used for a maxillary impression and two scoops of powder to two measures of water are used for a mandibular impression.

Proper mixing is critical: powder should be added to the bowl first and then cool water.

The first step is to incorporate the water and powder so powder particles are wet. This should be done quickly. Next, the mixture should be spatulated against one side of the bowl with the flat portion of the buffalo spatula, turning the spatula over at times to ensure a smooth bubble free mix (Poling et al. 2008) (see Figure 8.3.2).

A spatula placed inside a bowl containing a mixture for impression.

Figure 8.3.2: Proper spatulation technique.

Alginate setting time can be changed by altering the mixing time or water: powder ratio. However, due to nonconformities in mixing time or proportions of material utilized, certain properties of the gel can be effected and diminish. The best way to alter gelation time is to change the temperature of the water in the mix. The higher the temperature of the water the shorter the gelation time of the alginate.

Taking the Impression

The mandibular impression is always taken first to introduce the patient to the procedure as it is easier and less likely to cause gagging (Poling et al. 2008) (see Figure 8.3.3).

Image described by caption.

Figure 8.3.3: Placement of mandibular tray.

The material is scooped up and loaded into the tray from the lingual portion of the tray (it should only take two‐three portions of material to fill tray).

The clinician stands at about 8.00 o’clock, in front of the patient and retracts the patient’s cheek with index and middle finger, the tray is inserted into the patient’s mouth sideways, and seated in posterior area first and then anterior. Soft tissues, lips and cheeks, should then be maneuvered over tray gently.

The maxillary impression is taken with the clinician standing at about 10.00–11.00 o’clock, beside and slightly behind the patient. The procedure for taking the impression is repeated (see Figure 8.3.4).

Image described by caption.

Figure 8.3.4: Placement of maxillary tray.

Patient should rinse and all alginate should be removed from the patient’s face.

Alginates should be rinsed immediately, disinfected with a broad spectrum disinfectant, and then wrapped in damp paper towels and preferably stored in a sealed plastic bag for no longer than 30 minutes (Demajo et al. 2016; Hiraguchi and Hirose 2016; Iwasaki and Iwasaki 2016; Walker et al. 2010).

Alginate should be poured immediately as it is subject to deformation, which can include imbibition, an uptake of water that results in swelling, or syneresis, a loss of water that results in shrinkage (Rohanian et al. 2014).

Criteria of an Ideal Alginate Impression

Surface texture; moist, elastic, strong (proper thickness of material), and without voids.

The maxillary impression is aligned with the maxillary facial upper midline, the mandible, with the mandibular dental midline, most often between central incisors the borders of the impression should be rolled, round and thick, one‐quarter thickness of alginate material covering the borders of the tray and extending into all vestibular spaces and including soft tissue attachments, such as frenula, maxillary tuberosity, hard palate, and retromolar pads, and detail of the gingival margin, no distortion, and no tray visible, including the borders of the tray (Figure 8.3.5).

Maxillary and mandibular impressions on trays.

Figure 8.3.5: Acceptable maxillary and mandibular impressions.

The Future of Impressions

Technology is advancing in our greater world, as we move into a more digital arena in all aspects of our lives. The same holds true in dentistry; digital impressions are taking the place of conventional alginate impressions. Two types of systems are available today: Computer aided design/computer aided manufacture (CAD/CAM) and dedicated three‐dimensional digital impressions (3D). These systems are used for restorative dentistry, implant dentistry, and orthodontics. While there are many systems available, the one thing is common is that they all provide potential for greater accuracy, precision, speed, and patient comfort when compared to traditional impressions. CAD/CAM dental systems are able to supply data obtained from digital scanning of teeth directly into milling systems which carve restorations out of ceramic or composite blocks, for example, CEREC. There are also dedicated 3D digital dental impression scanners, for example, iTero, that utilize lasers and imaging technology to capture tooth and gingival structure. Conventional impression success depends on many factors; material, tray selection, and technique. Each step involves potential risk of human and material error. Using digital scanners eliminates these problems; however, digital scanners have their own types of errors that can occur. A few systems use powders to coat the abutment teeth prior to scanning. This helps to eliminate reflection and allow for accurate measurements. The powder also adds thickness of 13–85 μm to the surfaces. Other scanners do not use the powder because their software is able to interpret the shiny surfaces of the abutment teeth. Either system can be affected by saliva, blood, poor soft‐tissue isolation, humidity, and patient movement (Renne et al. 2017).

Take‐Home Hints

  1. Utility wax may be placed around the border of the impression tray. This enhances patient comfort and promotes proper fit of tray so that all oral structures are obtained in the impression
  2. Before placing your impression tray, take a small scoop of alginate with your fingers and place on anterior facial surfaces, and posterior occlusal surfaces. This will help you achieve good detail of these areas and help to prevent voids
  3. For patients with overactive gag reflex do the following: instruct patient to breathe deeply through the nose and focus on an object about 2–3 ft away or raise one leg and lower up and down as if exercising. These simple procedures help to take the patient’s focus off the tray in their mouth and can help to minimize gagging.

Jul 18, 2020 | Posted by in Dental Hygiene | Comments Off on 3: Alginate Impressions

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