Clark Twin Block - McNamara Modification

Special Notes

To view prices, please create an account. The photograph shows our standard design. We can customize many of our appliances for your patient's specific needs - please see our auxiliaries and color chart (not applicable for nylon appliances).

LAB APPLIANCE This product is a custom lab appliance. Please choose the "Send us a Case" option on the product page or top menu bar.
Item Number

The Twin Block Technique was developed by Dr. William Clark of Scotland in the early 1980’s. This technique incorporates a different functional orthopedic principle that uses the forces of occlusion as the functional mechanism to correct the malocclusion.

Twin Blocks are worn 24 hours a day, which means the patient eats with the appliance in the mouth, and the forces of mastication are harnessed to maximize the functional response to treatment. Cooperation is excellent because the appliance is not removed for two-three days after it is fitted. There are no aesthetic cheek pads, lip pads, uncomfortable lingual extensions, as well as no anterior wires.

Twin Blocks can be modified to treat a wide range of malocclusions to achieve sagittal and vertical correction of Class II division I, Class II division II, and Class III malocclusions.

Also indicated in treatment of temporomandibular joint dysfunction. McNamara Modification Great Lakes recommends modifications to the Twin Block developed by Dr. James A. McNamara: The upper plate has two expansion screws for stability during transverse development, and occlusal pads that cover the molars. The lower lingual acrylic is extended distally to the last tooth with a lingual support wire, and a labial bow with acrylic is added making the appliance more stable and retentive. The lower plate includes occlusal pads to cover the lower bicuspids. These plates interface at 70° angles and posture the mandible in a forward position. 

Deviations from standard design include:

  • Twin Block Sagittal design
  • Twin Blocks to expand
  • Fixed Twin Blocks - Hybrid design
More Information
Great Lakes Exclusive No
Medicare Accepted No
Removable Yes
Banded No
Bite Required Protrusive
Material Type Acrylic, Duraloy, Stainless Steel
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Mail Traditional Models

Step 1 - Download Prescription

Clark Twin Block - McNamara Modification Rx

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Canadian and International Customers

Ship to:

Great Lakes Dental Technologies
PO BOX 5111
Tonawanda NY 14150-5111

Upload Digital Models

Option 1

Select your scanner to view easy instructions on how to submit a digital model.

Great Lakes also supports DDX, Medit, and Planmeca. If you need assistance, please contact us.

Option 2

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General Requirements


  • Accurate impressions with any type of impression material are acceptable
  • Impressions must adequately reflect all relevant anatomy
  • Impression material must not be separating from the impression tray
  • Consider pouring your models right away if your impressions are moisture, temperature, or time sensitive
  • Impressions sensitive to moisture content should be wrapped in a damp paper towel and placed in a sealed plastic bag if models are not poured immediately
  • Only metal impression trays and those with VPS impression material will be returned
  • The nature of impression materials currently on the market may contribute to common model problems encountered in the laboratory. Have you encountered porosity (bubbles, voids) or poor surface quality? Plaster or stone mixes are water based and they interact with impression surfaces in a water-like manner. Liquids placed on solid surfaces will be either attracted to, or repelled from that surface in varying degrees. Please be aware when selecting impression material if it is hydrophilic or hydrophobic.

Hydrophilic: is attracted to, or can be wetted by water.
Hydrophobic: is when liquid is repelled or fails to bond with liquids.
Vinyl poly siloxane (VPS) options can be hydrophilic or hydrophobic. Alginate is hydrophilic.

  • There are advantages and disadvantages to these impression options but there are products on the market to help reduce the disadvantages. Surfactants and debubblizer sprays can be used to lower surface tension between surfaces making the impression material more hydrophilic and assure a better impression result.
  • Great Lakes carries ACU-flow™ a VPS impression material which is hydrophilic and requires NO surfactant spray for surface tension reduction, eliminating bubble formation. Surfactants must be used properly and excess surfactant should not be allowed to pool in the cusp tips. This can cause loose, sandy-like cusp tips. Excess surfactant needs to be blown out leaving a wet look only before pouring. 

Learn how to take a reliable impression


  • Plaster or stone models are acceptable. Generally, the durability of stone is preferred.
  • Models should be reasonably trimmed, yet sufficiently thick for strength considerations.
  • No horseshoe-shaped models; Models should have a base of at least 7mm in the thinnest area.
  • Bases will be added as necessary (for an additional fee) to models without bases or those lacking adequate base thickness or strength.
  • Please indicate if your model must be duplicated as work models may get damaged during the appliance fabrication process.

Bite Records:

  • Please package bite registrations carefully.
  • Bite records must not be left between models for shipment to the lab.
  • Dedicated packaging should be considered for brittle materials such as Delar wax.
  • Please identify the nature and the intent of each bite record, if more than one is being supplied.
  • Please consider mounting the maxillary model, before sending it to the lab, for those cases requiring mounting. Sending items such as facebows, bite forks, and mounting jigs through the mail often results in unreliable mountings.


We use the following articulators and their accessories in our laboratory:

  • SAM® 1, SAM® 2, SAM® 3 
  • Denar®
  • Panadent
  • Whip Mix
  • Hanau™
  • Stratos 200
  • Artex®
  • Kavo

Wear Instructions

Remove to eat and clean

Care Instructions

Clean using Dentasoak   

Wear Times

Full Time

Appliance Warranty

Wire: 90 days

Acrylic: 1 year

Appliance Protection Program

Great Lakes understands that appliances may be lost or destroyed through the course of treatment. This obviously creates extra expense for your patient. That's why we created our Appliance Protection Program as a type of appliance insurance. This program may also be an asset in furthering the growth of your practice. Contact Laboratory Customer Service for more information.

Program Cost

$32.00 Initial Registration / 25% Replacement Cost*
* Elastodontics and Twin Blocks: $39.50 Initial Registration / 50% Replacement Cost

As an additional service to our Laboratory customer, Great Lakes provides protection against loss or irreparable damage to any appliance fabricated by Great Lakes Laboratory. We believe we have a total service package unequaled anywhere in the lab industry when this program is combined with our existing benefits:

  • Competitive prices
  • Free repair or replacement of broken Biocryl II acrylic plates
  • Free acrylic repairs of any repairable functional appliance fabricated by Great Lakes

Program Terms

  • If the Appliance Protection Program is desired for an individual patient, it must be noted on the original prescription accompanying models and wax bite registration to the Laboratory.
  • An appliance protection fee per individual appliance will be applied to the original invoice.
  • Your document number will be noted on the original invoice. This, along with the fee charged is your record of purchase of the program.
  • If the appliance is damaged beyond repair, the damaged appliance, original construction models, set up, and original construction bite must be forwarded to Great Lakes with new models and wax bite registration if applicable. Please note on the new prescription that this remake was insured, and provide the document number noted on the original invoice.
  • If the appliance is lost, the original construction models, set up, and original construction bite must be forwarded to Great Lakes with the new models and wax bite registration if applicable.
  • Please note on the new prescription that this remake was insured and provide the document number noted on the original invoice.
  • Upon fabrication of a replacement appliance, a charge of 25% of the original appliance price will be applied, 50% for Elastodontics and Twin Blocks.
  • Because this program is designed to offer protection against loss or irreparable damage, design changes of any type will not be included in this program.
  • This program provides protection against loss or irreparable damage to an original appliance for a period of one year or one remake.
  • Not Available on Positioners or The Klearway Appliance

Important Information

Certificates of Protection are valid only if original construction models, set up, and original construction bite registration if applicable, are returned at time of replacement.

Great Lakes Laboratory reserves the right to determine irreparable damage and/or any other individual circumstances regarding the terms of this program.