Lab Solutions

How to Accurately Gauge Occlusal Reduction
The most common error seen on the lab floor is insufficient occlusal reduction. Frequently this occurs when the occlusal portion of a posterior crown preparation is prepared flat, or parallel to the floor. While there may be enough reduction at the cusp tips, the flat occlusal table leaves no room for properly developed occlusal anatomy. As a result, many laboratories will call the doctor and ask to place a metal occlusal in an attempt to solve this problem, which may be an unacceptable option to the patient. The best way to accurately gauge this reduction is to remember the proper amount of reduction in the central groove area is approximately the same depth as the pulpal floor of an average Class 1 amalgam preparation. I often find it helpful to remove the old occlusal amalgam first and follow by reducing the occlusal surface to match that depth. Then the slope of my reductions match the slope of the pre-operative cusps. Using a football shaped diamond, such as a 379-023 bur, will also help prevent flat occlusal tables.

Michael C. DiTolla, DDS, FAGD
Director of Clinical Education
Glidewell Laboratories

Why don’t crowns always fit the model?
Q: What is the reason for crowns not fitting well when very clean impressions with clear margins were sent to the lab?
A: The working model is used quite extensively throughout the process including waxing, casting, fitting the coping or framework, porcelain build-up and grinding in the porcelain. This can result in the wearing down of the working model and die. The crown should however, fit the solid model well.

Bob Cullivan
Quality Control Manager
Trident Dental Laboratories

Causes of Incorrect Centric Relation
During the try-in of a full or partial denture, with the use of thin articulating paper, the doctor must determine the correct centric relation before the case is processed. Each denture tooth on the articulator and in the mouth must catch the paper and prevent it from pulling out. Incorrect centric relation is caused by an incorrect bite, mounting or opposing model.

1. Incorrect bite– patient bite to the side, protruded the mandible or both.

2. Incorrect mounting– stone behind the tuburosity contacting stone behind retromolar pad or bubbles on occlusal or incisal surfaces of model prevented necessary closure when mounting.

3. Inaccurate opposing model– If during the impression procedure to produce the opposing, the partial patient was wearing got displaced or the impression was off, no matter how many resets you have the correct centric relation will not be established.

Arivid Saunaitis
President
Kromex Dental Laboratory, Inc.

Can Flexite or Valplast be repaired?
Q: Can a thermoplastic partial, like Flexite or Valplast, be repaired, or relined? Or can I add a tooth?
A: Yes. It can be done in a laboratory and in our facility we have specially designed equipment just for this purpose. Actually, all our lab needs to repair these appliances are two new models from the doctor and the old appliance to be sent with the case. Here’s a word of advice–do not take a pickup impression with the partial in place because it will get buried in the impression material.

Robert Gonzalez
Laboratory Manager
Continental Dental Labs

Occlusal Plane Visualization Tool
Here is a tip I suggest to my clients who have difficulty trimming their occlusal rims to depict the correct occlusal plane angle .ie. parallel to the floor.

The defining and communication of the occlusal plane angle from the doctor to the technician is crucial for the natural arrangement of denture teeth. On many occasions, it is difficult for the doctor to determine if the wax rim has been trimmed intraorally to correctly depict the plane as parallel to the floor. An easy way to determine this is to have the patient stand and slightly open their mouth with the base-plates in place. The doctor would then place a tongue depressor across the rim in the anterior incisor area and have the patient close down gently on the depressor. The doctor is then free to stand back and evaluate the plane with the depressor extensions in place to aid in his/her visualization. Once the plane is correct, the depressor can be left in place to aid the technician in determining plane parallelism during articulation.

Thomas Zaleske
Matrix Dental Laboratory
Specializing in Removable Prosthodontics

Communicate subtle character traits with The Ladder
Communicating characterizations like hypocalcification, degree of translucency, texture and facial anatomy, etc., just got easier. A new system called The Ladder offers digitally enhanced pictures that are organized by character traits in a swatch fan. It is very quick, easy to use and standardized, unlike many of the books where you randomly search through hundreds of pages. The Ladder's organizational design allows you to focus on just the traits you are trying to match. There are for example 3 swatches for hypocalcification, with 4 centrals on each in graduated levels of character, and each has a specific name or code to clearly communicate to the lab the desired level and placement of hypocalcification. Additional information on this system is available upon request.

David French, BA,
Senior Technical Advisor
Burbank Dental Laboratory Inc.

Use Flexible Occlusal Clearance Guides
Q: Is there a better way to communicate the amount of occlusal clearance needed?
A: Because preparation guidelines can vary significantly from restoration to restoration, we recommend using flexible occlusal clearance guides to verify the amount of clearance you, the clinician, is providing to the laboratory. Flexible occlusal clearance guides are incredibly easy to use and slide smoothly between the prepared area and the opposing so that you can tell right away if you have provided the .5mm to 2.0mm required in today's aesthetic restorations.

Glenn Bonagura
Vice President Sales and Marketing
MicroDental Laboratories

Unexpected implant patient–What to do?
Situation: Your next patient arrives with metal implant healing cuffs. Your team member, as surprised as you, has neither a screwdriver nor appropriate impression posts on the tray. You ask yourself what do I do now?

Sound familiar? We hope not. Every day offices across the country face the same uncomfortable and unexpected situation. Despite the best intentions of all involved, somehow, the communication link from the implant surgeon to the restorative dentist has been interrupted.

Begin the restorative phase of implant dentistry with study models, a centric relation bite and a note about the intraoral implant parts.

To obtain the correct impression post, you must know exactly what is in the mouth. Obtain the implant type/size and catalog numbers of healing abutment or prosthetic abutment from the surgeon. Send this information along with a study model, opposing model and bite to the lab for evaluation and custom tray fabrication. With this detail in hand, your laboratory can begin the planning stage, outline appointment protocol, provide estimate for restorative costs, and generally make your next appointments go smoothly.

Larry Zenk
Vice President and Direct Sales Director
Keller Laboratories, Inc.

Pink Opaque for Stained Dentition
Darkly stained teeth have always been difficult to treat cosmetically. Tetracycline-stained dentition and the single nonvital tooth are among the most difficult teeth to treat esthetically with minimally invasive procedures such as porcelain veneers.

Using pink opaque, by bonding it to the patient’s dentition prior to taking your impression, is an effective way to treat darkly stained dentition reliably and with natural results. The result of applying this material creates a neutral background, to your preparation, which results in the ability to create a very translucent veneer and the ability to use a clear resin for bonding. You no longer have to be concerned with opacity in your veneers or trying to mask the discolored dentition with opaque resin during bonding.

Gary Materdomini
DaVinci Dental Studios, Inc.

Prescribe for a Successful Restoration
What to send to your laboratory in order to receive a successful restoration:

1. A complete prescription providing as much information as possible. Include restoration type, design, patient age, shade and expectations.
2. A full-arch impression that has been inspected to insure the margins are clear, readable and that the tray has not been bitten into or exposed.
3. A model of approved temporaries. Be sure to either measure temporaries to determine if enough clearance has been provided for the prescribed restoration or use a Flexible Clearance Guide when prepping.
4. Photographs that have been taken with the shade tabs in the mouth.
5. A stick bite registration. When taking a bite registration, use either a heavy body polyvinyl or blue mousse and isolate to the prepped teeth only. This will help eliminate high occlusions and chair side adjustments.

When provided with these five materials, we are able to consistently provide our clients with predictable, quality restorations, minimizing the chair time necessary for insertion.

Heather Voss DeZak, CDT
Operations Manager
BonaDent Dental Laboratory