DPRWorld.com
Learn More

 

Wednesday, August 20, 2008
[ Login ]
Top 10
Emailed Articles
1. Emmott on Technology: Digital radiography, part 1
2. DPR Survey Exclusive: The 2007 Dental Equipment Survey Report
3. The DPR 100: Top 10 High-Tech Products
4. DPR Exclusive: Cosmetic Dentistry Survey
5. Practice Innovations: LED curing lights
6. Chairside Confidential: Alginate impressions
7. Infection Control Report: Is dental water drinkable?
8. Emmott on Technology: Office Hardware Shopping Planner
9. Infection Control Report: Sterilization, Part 2
10. Infection Control Report: Sterilization, Part 1

Chairside Confidential | Alginate impressions

Improving the alginate impression

Recognizing problems and finding solutions will help increase the quality of alginate impressions in your practice.

By Gordon J. Christensen, DDS, MSD, PhD

This monthly column is co-sponsored by DPR and The Scottsdale Center for Dentistry.

Do you realize how many alginate impressions (Fig. 1) are made in your practice? Someone in
gordon
Dr. Christensen is a leading clinician and educator. He is the founder and director of Practical Clinical Courses, an international continuing education organization for dentists, and has presented more than 45,000 hours of continuing education to thousands of dentists and team members. A Diplomate for the American Board of Prosthodontists, he has published hundreds of books and articles and is a co-founder of Clinical Research Associates (now named CLINICIANS REPORT). He is a consultant, advisor, evaluator, and speaker. He graduated from the University of Southern California School of Dentistry.
every general practice and most specialty practices makes numerous alginate impressions every day. Usually, that task is delegated to assistants and sometimes to hygienists. Some dentists make alginate impressions, especially for areas of fixed or removable prosthodontics.
Today’s alginates are excellent (Figs. 2 and 3), but are the impressions? There’s a good chance many of your alginate impressions could be significantly improved by learning to solve typical deficiencies, having staff education sessions, and then following up with frequent repeat sessions as employees come and go.
In this article, I will explain how to improve the quality of your alginate impressions—and thus all subsequent procedures.

Alginate impressions are key
Consider the frequency and importance of techniques requiring alginate impressions:
• Diagnostic casts
• Casts for making provisionals
• Working and opposing casts for fixed and removable prostheses
• Orthodontic casts
• Casts for occlusal splint and mouthguard construction
• Casts for fabricating bleaching trays
• Casts to make trays for preventive chemical application to teeth
• Impressions for many aspects of removable partial and complete dentures

Common errors and solutions
Every dentist has observed errors when critiquing alginate impressions. These errors can easily be prevented with minimal effort, but prevention requires continual staff education. The following error categories and explanations include potential solutions for correction or prevention.

Problem: Leaving plaque and other debris on the teeth before the impression
It is common to see alginate impressions made without first cleaning superficial plaque, calculus, and food debris from teeth. It is easy to visualize the negative challenges associated with leaving these materials on the teeth. The inaccuracies transfer to the subsequently made casts. Restorations, dentures, trays, and other appliances made from these casts don’t fit well, have unacceptable occlusion, or exhibit other problems.
Solution: Remove major calculus accumulations and perform a simple rubber cup prophylaxis with water-moistened flour of pumice before making the impression. Thoroughly rinse the mouth.
 
Fig. 1 Typical full-arch diagnostic alginate impressions made by a dental assistant.
 
Fig. 2 The alginate Jeltrate Plus from Dentsply Caulk.
 
Fig. 3 An alginate reinforced with silicon dioxide particles, Triphasix Alginate from Parkell,  makes a smooth mix.
 
Fig. 4 Typical perforated trays are still the “gold standard” for accuracy. However, they can be difficult to clean.
 
Fig. 5 Plastic trays need large holes and/or adhesive.
 
Fig. 6 A double-arch alginate tray records the interocclusal relationship.
 
Fig. 7 The Cadco Alginator II, a popular mechanical alginate mixer.
Fig. 8 Use a surfactant, such as Almore, when pouring the alginate to decrease bubbles.
 

Problem: Leaving mucous and liquid debris in the mouth
If alginate impressions are placed without first rinsing out liquid debris from the mouth, the debris becomes incorporated into the unset alginate, resulting in a visually rough surface on the cast. Inaccuracies in the cast are transferred to inaccuracies in subsequent restorations.
Solution: This challenge can easily be overcome by rinsing the mouth before making the impression.

Problem: Inadequate trays
Metal trays, perforated or rim lock, produce the most stable, accurate, and predictable alginate impressions¹ (Fig. 4). However, many dentists and staff members prefer not to use metal trays. Disposable plastic trays (Fig. 5) are popular, especially among staff, because they don’t have to be cleaned. Plastic trays are acceptable if they are rigid and have many large holes. Research shows that large holes (3-mm diameter) located close together provide good retention of the alginate to the tray².
A useful alginate double-arch tray (Fig. 6) allows diagnostic casts to be made easily if there are not enough teeth to provide stability without making occlusion rims. Maxillary and mandibular teeth impressions can be made at the same time. The impressions are poured, the stone is allowed to set, and the casts are mounted without separating the tray from the casts, thereby correctly orienting the unstable casts.
If trays are rigid plastic or metal with only a few holes, alginate adhesive may be used for retention³. Every dentist has seen set alginate separate from the tray on removal from the mouth, severely compromising clinical accuracy.
Solution: Although I prefer metal trays, plastic trays, when used properly, can be very acceptable.

Problem: Not mixing thoroughly
Hand mixing alginate impressions is still the most common method to incorporate alginate powder and water. Such mixes can be homogeneous and smooth with a vigorous and thorough mix. Anything else results in a lumpy, non-homogeneous, rough alginate mix with minimal potential to make accurate impressions. As with the previously mentioned challenges, a non-homogeneous mixture results in a rough and inaccurate cast and the inevitable consequences.
Solution: Mechanical mixing reduces void formation and improves surface detail reproduction.4 There are many excellent alginate mechanical mixing devices on the market, including Cadco Alginator II (Fig. 7) from Dome Inc. (www.domeortho.com), Dentsply Raintree Essix TurboMAX Alginate Auto Mixer (www.essix.com), and the Whip Mix Combination Mixer (www.whipmix.com). If room temperature water and a measured amount of alginate powder are used, each product produces an excellent, homogeneous, and smooth mix with predictable work and setting times.

Problem: No border molding
I suspect that in many offices, almost all alginate impressions are made without an attempt to accomplish the well-known lip, tongue, and cheek manipulations that mold the impression borders. Why is this important? If final trays are to be made from diagnostic casts, an accurate representation of the muccobuccal fold must be created.
Solution: Teach the respective staff member to make the same mouth manipulations as the dentist for border molding complete or removable partial dentures. Spraying a surfactant lightly on the impression before pouring the stone reduces bubbles (Fig. 8).

Problem: Not placing alginate in the grooves of the posterior teeth
Most alginate impressions are placed without rubbing any mixed alginate on the occlusal surfaces before seating the impression, resulting in trapped air bubbles. These bubbles become negative holes in the occlusal surfaces of the alginate impression and resultant positive bubbles on the occlusal surfaces of the casts.
Unless the bubbles are carefully picked off the occlusal surfaces of the casts, whether the casts are working casts or opposing casts, the result will be restorations that are too high.
Solution: Immediately before placing the impression, firmly and thoroughly rub a small amount of mixed, unset alginate material on the occlusal surfaces of all the posterior teeth.

Problem: Taking the impression out too soon or leaving it in too long
Most alginate impressions are made by placing the impression in the mouth with little or no pre-impression cleaning; they are immediately removed after the initial gel. Leaving the impression in the mouth for a short time after the initial gel provides a more accurate impression.5
Solution: Leave alginate impressions in at least 2 minutes after the initial gel, allowing for maturation of the chemical set of the alginate and a more accurate impression.

Problem: Leaving tongue space open in the mandibular impression
When the mandibular alginate impression is made, the tongue lies in the center of the impression and creates a large void. The resultant cast usually has a large irregular piece of stone in the center where the tongue was, which is unsightly and often impedes restoration fabrication.
Solution: Make the lower impression first; most agree it is less objectionable for patients than the maxillary impression. After making the mandibular impression and the unset maxillary impression is in place, use leftover material to fill the void on the mandibular impression to create a smooth area of stone where the tongue was located (Fig. 1).

Problem: Leaving debris, mucous, or saliva in the impression before pouring
Leaving extraneous material on the impression’s surface results in a cast with a “fur-like” appearance. The inaccuracies produced can negatively affect many aspects of oral therapy.
Solution: Wash the impression with an air-water syringe to remove contaminants. Then dry it with an air stream only to the point that the water “shine” is just disappearing. The impression will be adequately dried but not dehydrated.

Problem: Improper storage
Many dentists and staff members make alginate impressions, moisten a paper towel, wrap the impression in the towel, and pour the impression when they get time. This leads to either imbibition (soaking up excess moisture) or syneresis (drying out), and the obvious inaccuracies in the impression and the cast.6
Solution: When the impression has been properly washed and minimally dried, place it in a resealable plastic bag along with a few drops of water. Seal the bag and pour it as soon as possible.

SUMMARY
Alginate impressions are common in most offices and are typically made by staff members. Many could be better, thus providing more accurate casts and treatment planning, better fitting provisional and final restorations, orthodontic appliances, occlusal splints, bleaching and fluoride trays, and many other oral therapies.

References available upon request.
 

DPR is proud to present the second installment of Chairside Confidential. Each month, a different member of The Scottsdale Center for Dentistry’s esteemed faculty will share practical tips, solutions, philosophies, and insights. The goal is to provide readers with helpful information they can apply in the operatory to enhance patient care, maximize productivity, and minimize stress.
The Center’s faculty comprises many great minds and thought leaders in dentistry with unparalleled expertise in every aspect of dentistry, from implants and removables to radiography and oral surgery.
We look forward to bringing you this column along with news about the Center’s upcoming initiatives and educational opportunities.

About the Scottsdale Center
The Scottsdale Center for Dentistry has a comprehensive, straightforward mission: “…to increase the clinical skills, basic scientific knowledge, financial productivity, practice enjoyment, and self-esteem of participants by providing high-quality, pragmatic, ethical, evidence-based, affordable, patient-centered continuing education for all areas of the dental profession.”
courses
Esthetic Dentistry with Frank Spear, DDS, MSD and Harald Heymann, DDS, MEd
April 28-29

Upcoming courses by Dr. Gordon J. Christensen:
Faster, Easier, Higher Quality Dentistry
May 29-30

Enjoyable, Profitable, Fixed Prosthodontics (Hands-on)
June 16-17

Practical Esthetic Restorative Dentistry (Hands-on)
July 10-11

Complex Dentistry for the Typical Practice (Hands-on)
Nov. 3-4

For more information or to register, call 866-781-0072 or visit www.scottsdalecenter.com.

Correction: Dr. Harald Heymann’s class on anterior direct composites listed in last month’s column was a misprint—see www.scottsdalecenter.com for a full course schedule.
1 of 1
Browse By Category