- Email: [email protected]
Three-way tray technique
Three-way tray technique Background.—Use of a 3-way tray to obtain a master and opposing arch impression plus an interocclusal record saves time and money, making it a popular choice. Although these impressions, properly prepared, can be as accurate as or more accurate than complete-arch impressions, it is vital that the patient close properly into maximum intercuspation position (MIP). In non-ideal occlusion, the MIP can be extremely difficult to discern. Three-way tray usage was described, along with how these trays can be used improperly. Indications and Contraindications.—Three-way tray impressions should only be used for single units or multiple units in carefully selected circumstances. The multiple units must be adjacent or short-span fixed partial dentures. For the master casts to be stable, enough teeth must be present in both arches, ideally, teeth on each side of the restored tooth or teeth. Adjacent teeth must be stable occlusally and proximally. The 3-way tray technique is designed to achieve a final treatment position in MIP. It requires that the patient have canine disocclusion. If these guidelines are not followed, the occlusion of the final restoration will require extensive modification before it will benefit the patient. Quadrant 3-way trays cannot capture tooth contours on the contralateral side of the arch so that crowns can accommodate the path of insertion for removable partial dentures. The number of functional contacts with the opposing arch is generally inadequate in patients with free-end distal extension. Considerable adjustment will be needed if the 3-way tray technique is used for restorations in patients with complex occlusal schemes. Other challenging situations include unstable anterior contacts between the incisors and canines and deep vertical overlaps.
Fig 1.—Anterior triple tray (DTW anterior impression tray, Patterson Dental Supply, St Paul, Minn). Note the lack of support of the impression material lingual to the anterior teeth. (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2008.)
The strength of the impression material used with 3-way trays and the ability to support the die stone when casts are poured can become an issue. Removing the tray behind the posterior-most teeth or across an arch can leave the impression material inadequate to support the impression material on the lingual surface (Fig 1). The impression can become distorted, producing an inaccurate die. Selecting a Tray and Impression Material.—Trays can be plastic, metal, or metal-reinforced plastic. Plastic ones tend to be too flexible and can deform during the impression process. A rigid tray minimizes distortion. The tray’s length and width must be appropriate for the patient. The tray should not touch the buccal or lingual surfaces
Fig 3.—Tray contact with soft tissue through impression material results in distortion of the tray. (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907911, 2008.)
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Issue 3
2009
143
of the alveolar ridges (Fig 3) because the sides may be forced apart when the patient occludes, then rebound and distort the impression. The tray’s anterior extent must be sufficient to include the canines, which help determine the vertical component of lateral excursive movements. Seating of the tray can be compromised by tori, bony exotoses, and third molars. The patient must be able to close into MIP with no interference. Flexure error in the tray cannot be compensated for by elastomeric impression material. The impression material should be relatively rigid; heavy-body polyether and vinyl-polysiloxane are quite acceptable. Machine or syringe mixing can overcome the technique’s sensitivity to hand mixing, diminish the risk of contamination, and minimize ledges, drags, and pulls. The mixing should be accomplished quickly and completely for a more uniform result. Cartridges should be bled to ensure the catalyst and base flow uniformly, remain uncontaminated, and do not produce set material that sticks in the mixing tip or is improperly mixed. Caveats.—To obtain an accurate impression, the tissue at the gingival margin must be displaced vertically to expose the margin of the preparation and horizontally to allow sufficient space for the impression material. The hard and soft tissues being imaged must be clean and dry with no bleeding. Seating pressure alone cannot provide adequate tissue retraction for margin exposure. Standard tissue retraction techniques are needed. The material is placed immediately after mixing. Operators with small hands may do well to inject the material into a separate intraoral unidose syringe that is easier to manipulate and has been developed for this purpose
Fig 4.—Syringes for injecting light-body impression material. Top to bottom, Regular syringe with mixing tip (Dentsply), Digit Targeted Delivery system (Dentsply), and COE syringe (GC America). (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2008.)
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Dental Abstracts
(Fig 4). Voids are minimized by fitting the injection tip directly onto the mixing syringe. Low-viscosity material permits better flow and more accurate marginal accuracy and tissue coverage. The syringe tip is immersed in the impression material as it is placed in the retracted tissue sulcus; use of a stirring motion ensures that the tissue coverage is adequate. Using tray adhesives prevents the impression material from separating in the tray. The tray is properly aligned, then slowly seated intraorally. Alignment is maintained as the patient closes into MIP. When the tray is correctly positioned, it is held steady until the impression material sets completely, then removed. Standard Technique.—Syringe light-body wash material onto the prepared tooth. Fill the 3-way tray with heavy-body impression material on both sides; to be sufficient there should be a 2- to 3-mm thick wall of impression material around the prepared tooth. Seat the tray in the patient’s mouth and have him or her close into MIP. Place Mylar ribbon between the indicated teeth on the opposite side to ensure the patient achieves MIP. Pre-impression Techniques.—Pretreatment matrix, a putty or heavy-body impression material, is used for the impression and the provisional restorations, so less material is needed for pre-impression techniques. A twostep process is followed. First, fabricate a pretreatment matrix, then either wash the site with light-body material or use a laminar flow technique. If the wash impression technique is used, confirm that the matrix permits space for the wash material. Place light-body impression material around the tooth; reseat the tray. Apply pressure to force impression material into the sulcus around the tooth, but do not overfill. Provide a vent for excess material, which will distort the tray. If the laminar flow technique is used, apply the pre-impression material around the site, then inject light-body impression material. Use impression material to wash out the area around the prepared tooth. Modify the pre-impression matrix by drilling two access holes through the impression material on the buccal aspect of the prepared dental site. Make one access hole at the mesial line angle and one at the distal line angle. Reseat the pre-impression material intraorally, having the teeth fully occluded into MIP. Insert the tip of the syringe containing light-body impression materials into the mesial hole and inject material until clean material extrudes from the distal hole (Fig 5). Discussion.—Excellent results can be achieved using the 3-way tray technique if cases are selected appropriately. Rigid cast and impression materials yield the best results. Tray-tissue contact must be avoided, with meticulous attention to detail throughout the process. Success is determined by the skill and diligence of the operator.
Clinical Significance.—Both dentists and patients benefit from the use of the 3-way tray technique. It saves time, uses 50% less material than a complete-arch impression, and is 60% faster than full-arch techniques. Patients have to endure the impression materials in their mouths only once. Especially for patients who gag easily, closed-mouth impressions are 80% more comfortable than open-mouth ones. The best results recognize the limitations of the technique and stay within the abilities of the operator and dental technician.
Fig 5.—Injection of impression material using the laminar technique. Arrows show flow of light-body material around teeth and out vent hole. (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2008.)
Reprints available from IJ Pesun, Dept of Restorative Dentistry, Univ of Manitoba, D227B-780 Bannatyne Ave, Winnipeg MB R3E 0W2 Canada; e-mail: [email protected]
Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2009
EXTRACTS GET YOUR ZZZS Sleep may protect against the common cold. Researchers at Carnegie Mellon University paid 153 volunteers to report their sleep habits for 2 weeks, have cold viruses sprayed up their noses, and then wait 5 days in a hotel room to see what happened. One hundred thirty-five were infected, but only 54 got sick. People who normally slept 8 hours were much less likely to develop colds than those who slept fewer than 7 hours or who slept fitfully. Even considering the effects of stress, smoking, drinking, and lack of exercise, sleep and cold resistance were linked. Sleeping fitfully for more than 8% of the time in bed raised the chances of getting a cold by 5 times compared to tossing and turning only 2% of the time. Sheldon Cohen, the lead researcher, summed it up: ‘‘The longer you sleep, the better off you are, the less susceptible you are to colds.’’ [CK Johnson: Preventing Colds May Be as Easy as Vitamin ZZZ. Archives of Internal Medicine, January 2009; reported by Reuters Health at http://www.reutershealth.com.]
Volume 54
Issue 3
2009
145
Fig 1.—Anterior triple tray (DTW anterior impression tray, Patterson Dental Supply, St Paul, Minn). Note the lack of support of the impression material lingual to the anterior teeth. (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2008.)
The strength of the impression material used with 3-way trays and the ability to support the die stone when casts are poured can become an issue. Removing the tray behind the posterior-most teeth or across an arch can leave the impression material inadequate to support the impression material on the lingual surface (Fig 1). The impression can become distorted, producing an inaccurate die. Selecting a Tray and Impression Material.—Trays can be plastic, metal, or metal-reinforced plastic. Plastic ones tend to be too flexible and can deform during the impression process. A rigid tray minimizes distortion. The tray’s length and width must be appropriate for the patient. The tray should not touch the buccal or lingual surfaces
Fig 3.—Tray contact with soft tissue through impression material results in distortion of the tray. (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907911, 2008.)
Volume 54
Issue 3
2009
143
of the alveolar ridges (Fig 3) because the sides may be forced apart when the patient occludes, then rebound and distort the impression. The tray’s anterior extent must be sufficient to include the canines, which help determine the vertical component of lateral excursive movements. Seating of the tray can be compromised by tori, bony exotoses, and third molars. The patient must be able to close into MIP with no interference. Flexure error in the tray cannot be compensated for by elastomeric impression material. The impression material should be relatively rigid; heavy-body polyether and vinyl-polysiloxane are quite acceptable. Machine or syringe mixing can overcome the technique’s sensitivity to hand mixing, diminish the risk of contamination, and minimize ledges, drags, and pulls. The mixing should be accomplished quickly and completely for a more uniform result. Cartridges should be bled to ensure the catalyst and base flow uniformly, remain uncontaminated, and do not produce set material that sticks in the mixing tip or is improperly mixed. Caveats.—To obtain an accurate impression, the tissue at the gingival margin must be displaced vertically to expose the margin of the preparation and horizontally to allow sufficient space for the impression material. The hard and soft tissues being imaged must be clean and dry with no bleeding. Seating pressure alone cannot provide adequate tissue retraction for margin exposure. Standard tissue retraction techniques are needed. The material is placed immediately after mixing. Operators with small hands may do well to inject the material into a separate intraoral unidose syringe that is easier to manipulate and has been developed for this purpose
Fig 4.—Syringes for injecting light-body impression material. Top to bottom, Regular syringe with mixing tip (Dentsply), Digit Targeted Delivery system (Dentsply), and COE syringe (GC America). (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2008.)
144
Dental Abstracts
(Fig 4). Voids are minimized by fitting the injection tip directly onto the mixing syringe. Low-viscosity material permits better flow and more accurate marginal accuracy and tissue coverage. The syringe tip is immersed in the impression material as it is placed in the retracted tissue sulcus; use of a stirring motion ensures that the tissue coverage is adequate. Using tray adhesives prevents the impression material from separating in the tray. The tray is properly aligned, then slowly seated intraorally. Alignment is maintained as the patient closes into MIP. When the tray is correctly positioned, it is held steady until the impression material sets completely, then removed. Standard Technique.—Syringe light-body wash material onto the prepared tooth. Fill the 3-way tray with heavy-body impression material on both sides; to be sufficient there should be a 2- to 3-mm thick wall of impression material around the prepared tooth. Seat the tray in the patient’s mouth and have him or her close into MIP. Place Mylar ribbon between the indicated teeth on the opposite side to ensure the patient achieves MIP. Pre-impression Techniques.—Pretreatment matrix, a putty or heavy-body impression material, is used for the impression and the provisional restorations, so less material is needed for pre-impression techniques. A twostep process is followed. First, fabricate a pretreatment matrix, then either wash the site with light-body material or use a laminar flow technique. If the wash impression technique is used, confirm that the matrix permits space for the wash material. Place light-body impression material around the tooth; reseat the tray. Apply pressure to force impression material into the sulcus around the tooth, but do not overfill. Provide a vent for excess material, which will distort the tray. If the laminar flow technique is used, apply the pre-impression material around the site, then inject light-body impression material. Use impression material to wash out the area around the prepared tooth. Modify the pre-impression matrix by drilling two access holes through the impression material on the buccal aspect of the prepared dental site. Make one access hole at the mesial line angle and one at the distal line angle. Reseat the pre-impression material intraorally, having the teeth fully occluded into MIP. Insert the tip of the syringe containing light-body impression materials into the mesial hole and inject material until clean material extrudes from the distal hole (Fig 5). Discussion.—Excellent results can be achieved using the 3-way tray technique if cases are selected appropriately. Rigid cast and impression materials yield the best results. Tray-tissue contact must be avoided, with meticulous attention to detail throughout the process. Success is determined by the skill and diligence of the operator.
Clinical Significance.—Both dentists and patients benefit from the use of the 3-way tray technique. It saves time, uses 50% less material than a complete-arch impression, and is 60% faster than full-arch techniques. Patients have to endure the impression materials in their mouths only once. Especially for patients who gag easily, closed-mouth impressions are 80% more comfortable than open-mouth ones. The best results recognize the limitations of the technique and stay within the abilities of the operator and dental technician.
Fig 5.—Injection of impression material using the laminar technique. Arrows show flow of light-body material around teeth and out vent hole. (Courtesy of Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2008.)
Reprints available from IJ Pesun, Dept of Restorative Dentistry, Univ of Manitoba, D227B-780 Bannatyne Ave, Winnipeg MB R3E 0W2 Canada; e-mail: [email protected]
Pesun IJ, Swain VL: Three-way trays: Easy to use and abuse. J Can Dent Assoc 74:907-911, 2009
EXTRACTS GET YOUR ZZZS Sleep may protect against the common cold. Researchers at Carnegie Mellon University paid 153 volunteers to report their sleep habits for 2 weeks, have cold viruses sprayed up their noses, and then wait 5 days in a hotel room to see what happened. One hundred thirty-five were infected, but only 54 got sick. People who normally slept 8 hours were much less likely to develop colds than those who slept fewer than 7 hours or who slept fitfully. Even considering the effects of stress, smoking, drinking, and lack of exercise, sleep and cold resistance were linked. Sleeping fitfully for more than 8% of the time in bed raised the chances of getting a cold by 5 times compared to tossing and turning only 2% of the time. Sheldon Cohen, the lead researcher, summed it up: ‘‘The longer you sleep, the better off you are, the less susceptible you are to colds.’’ [CK Johnson: Preventing Colds May Be as Easy as Vitamin ZZZ. Archives of Internal Medicine, January 2009; reported by Reuters Health at http://www.reutershealth.com.]
Volume 54
Issue 3
2009
145