Computer generated complete dentures guideline and errors

This article summarizes “Errors associated with digital preview of computer-engineered complete dentures and guidelines for reducing them: A technique article” by Abdulaziz AlHelal, BDS, MS, Brian J. Goodacre, DDS, Mathew T. Kattadiyil, BDS, MDS, MS, and Rajesh Swamidass, DDS (J Prosthet Dent 2018;119:17-25)

Interest in computer-engineered complete dentures (CECDs) has increased in the past 3 years. The main advantages of CECDs are a reduced number of visits, improved fit and retention, and electronic archiving for easy refabrication.

A systematic review of CECDs reported clinical complications associated with the 2-visit protocol. Even clinical studies that included a trial placement appointment with CECDs observed similar clinical complications. Another systematic review of clinical studies reported that difficulty in reading the digital previews of CECDs could result in some of these complications.

The purpose of this technique article was to help avoid common errors as a result of digitally previewing the CECD design by providing a systematic checklist. This checklist can also serve as an educational tool for dental students and dental technicians who are learning to fabricate CECDs.

Occlusal view evaluation

  1. Evaluate tooth arrangement in relation to arch form. The tooth arrangement should follow the arch form and be aligned with the alveolar ridge by following removable prosthodontic principles. (Fig. 1) The lingual cusps of the mandibular teeth should ideally fall within the Pound triangle unless otherwise indicated . (Fig. 2A)
  2. Evaluate the distance from the most posterior point of the incisive papilla to the labial surface of the central incisors in relation to the provided records (approximately 10 to 12 mm). If measurements fall within this range, the incisor tooth position can be considered acceptable.

[Fig. 1] . Digital previews for fabrication of maxillary CECD. Anterior teeth were evaluated, followed by posterior teeth, and then both in relation to maxillary edentulous ridge. Anatomic landmarks: incisive papilla, maxillary tuberosities, and pterygomaxillary fissures in relation to tooth arrangement, and denture base evaluated following removable prosthodontic principles. CECD, computer-engineered complete denture.

[Fig. 2] Preview for CECDs prior to design approval. A, Preview of mandibular CECD having tooth arrangement within Pound triangle. B, Grid view mode for maxillary CECD corresponding to mandibular CECD in A. View allows measuring distance from incisive papilla to labial surface of anterior incisors, represented in millimeters. Grid view mode not provided by all manufacturers. CECD, computer-engineered complete denture.

[Fig. 3] Different occlusal relationships based on MR records. A, Class I relationship with anatomic teeth (lingualized occlusion). B, Class II relationship with nonanatomic teeth (monoplane occlusion). C, Parallel maxillary and mandibular edentulous arches, indicating appropriate OVD. D, Unavoidable violation of posterior teeth position above retromolar pad with single CECD because of existing maxillary occlusal plane. E, Virtual preview of definitive CECD for same clinical situation as D. F, Error during preview of another mandibular CECD with insufficient space for second molar. Second molar placed on ascending ramus and above retromolar pad needs to be virtually removed before fabrication. CECD, computer-engineered complete denture; MR, maxillomandibular relationship. OVD, occlusal vertical dimension.

[Fig. 4] A, Incorrect tooth arrangement. Anterior teeth placed anterior to alveolar ridge, second molars placed over tuberosities, and teeth midline shifted to left side compared with anatomic landmarks (incisive papilla and mid palatine suture). B, CECDs show virtual discrepancy with tooth arrangement related to maxillary and mandibular right canines compared with left side. C, Maxillary virtual denture base posterior extension in relation to clinical records. D, Proper posterior denture base extension including pterygomaxillary fissures for the same clinical situation shown in C. CECD, computer-engineered complete denture.

Lateral view evaluation

  1. Evaluate the previewed horizontal and vertical overlap of the anterior teeth. Confirm the previewed horizontal and vertical overlap based on conventional removable prosthodontic principles and confirm a shallow incisal guidance.
  2. Evaluate the previewed occlusal relationship (class I, II, or III). (Fig. 3 A, B) Maxillary and mandibular alveolar ridge parallelism has been reported to indicate appropriate occlusal vertical dimension. (Fig. 3C)
  3. Evaluate the posterior aspect of the mandibular occlusal plane to correspond with the distal third of the retromolar pads. (Fig. 3 D, E)
  4. Evaluate the most posterior mandibular denture teeth positions (both sides) to ensure they are not positioned on the ascending part of the ramus, on an inclined plane. (Fig. 3F)
  5. Evaluate the most posterior maxillary denture teeth position to the maxillary tuberosities (both sides). The teeth should not be located on the maxillary tuberosities unless a specific request was made. (Fig. 4A)
  6. Ensure proper occlusion between maxillary and mandibular teeth. (Fig. 4B)

Frontal view evaluation

  1. Evaluate the relationship of the midline of the previewed teeth (maxillary and mandibular) to ensure it coincides with the midline marked on the record. Also, reevaluate steps 3 and 5. Evaluate the frontal virtual preview of the CECD for symmetrical tooth arrangement (unless otherwise requested), appropriately inclined occlusal plane, and normal relationships to other anatomic landmarks.
  2. Evaluate requested tooth type and morphology for requested occlusal scheme: lingualized, bilateral balanced occlusion or monoplane (anatomic or nonanatomic). (Fig. 3 A, B)

Denture base evaluation

  1. Evaluate the posterior maxillary denture base extension. Ensure extension to cover pterygomaxillary fissures. (Fig. 4 C, D) Evaluate posterior palatal seal dimensions if requested.
  2. Evaluate posterior mandibular denture base extension. Ensure coverage of retromolar pads and buccal shelf areas.
  3. Evaluate denture border thickness for both maxillary and mandibular denture bases. Compare previewed denture base extension to the provided image of impression border extensions or virtual arch impression scan.

Prosthetic space evaluation

  1. Evaluate the previewed distance from the crest of the alveolar ridge to the occlusal surface of the denture teeth. Ensure sufficient available prosthetic space for the denture base and the acrylic resin teeth, which will help in the selection of CECD type. (monolithic or bonded) In a reduced prosthetic space consider the use of monolithic CECDs, which occupy less space without compromising strength. (Fig. 5 A, B)

Additionally, evaluate the prosthetic space for planned computer-engineered complete overdentures (CECO) and immediate computer-engineered complete dentures (ICECDs) clinical situations. In a CECO clinical situation, assure sufficient prosthetic space for the desired type of attachments as requested; consider increasing the denture base contours allowing sufficient denture base thickness. Similarly, with ICECDs, prosthetic space is critical to avoid a thin denture base which is more prone to fracture.

[Fig. 5] A, Showing virtual intaglio surface view of ICECD with insufficient prosthetic space. B, Mandibular ICECD fractured at an area with insufficient prosthetic space with bonded ICECD type.

[Fig. 6] Tooth colored trial placement prosthesis is used for objective evaluation as precaution.

Esthetic (teeth and festooning) evaluation

  1. Evaluate the denture tooth size (width and height), shade, form, and custom tipping or rotation if requested. Confirm compliance with conventional prosthodontic principles regarding tooth arrangement and festooning to delineate ideal tooth embrasures.
  2. Evaluate proper festooning and gingival zenith level (affected by tooth height) compared with the provided records showing the highest location of the upper lip during smiling. At this stage, customized festooning (contours, stippling, and rugae) should be confirmed to provide superior esthetic characterization for the definitive CECD. (Fig. 1) Ensure shade for the denture base has been selected and noted.
  3. When in doubt, a trial placement prosthesis is recommended to provide an objective evaluation of the definitive prosthesis before its fabrication. (Fig. 6)

Digital designing can be performed in the office or delegated to dental laboratory technicians. Digital previews should be used to evaluate the design prior to approval for manufacturing. The proposed list serves as a digital preview guide in the fabrication of CECDs, maintaining prosthodontic design principles and reducing complications.

Careful and sequential digital previewing with proper guidelines could reduce CECD complications. Unfortunately, not all manufacturers currently offer digital previews. Even though trial prostheses are offered by many companies, digital preview provides advantages by avoiding this step and the need for remakes. CECD clinical studies completed in academic settings that included manufacturers offering digital previews have reported that the digital previews were difficult to evaluate. These difficulties in digital previewing demand the use of a trial prosthesis, thus adding additional appointments. The use of a checklist can offer a more objective fabrication for a better treatment outcome.

Difficulty in reading digital previews can result in additional appointments and costly remakes of CECDs. This step-by-step checklist for objectively previewing CECDs is expected to reduce this complication.

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