Discussion
Extreme residual ridge resorption is a challenging clinical situation for the fabrication of complete dental prostheses and there are no clinical reports of CAD/CAM workflows for complete prosthesis solving this complicated situation. This workflow combines traditional and novel techniques in order to fabricate digital complete dentures in patients presenting extreme alveolar ridge atrophy. Due to the short height of the ridge, it was decided to make the conventional final impression following the functional impression technique using her current complete dentures. Making the final impression using the patient’s existing denture as the impression tray has been shown to be a successful approach for atrophic ridges.31,32 Conventional mounted master casts and can be either scanned by the clinician or simply mail them to the dental laboratory. Once the digital file is created, the computerized designs of the complete removal dentures are made, and the clinician can access online and have full control of the tooth shape, shade and arrangement, denture plate color and anatomical features. After the dentist approves all the features, the company ships the restorations in short time.
Wearing complete denture for several years may have adverse effects on the alveolar ridge bone as well as on the keratinized mucosa, and unstable denture wearing may cause adverse undesirable such as extreme alveolar atrophy of alveolar ridge.33-39 Mandibular atrophic ridge sometimes can be so advanced that the short mandibular height40 makes it almost impossible to deliver a stable and well-functioning complete dentures with conventional techniques, and as a result it leads to chewing difficulties, pain, sore spots and poor oral health-related to quality of life.41,42 Unfortunately, due to high costs involving implant therapy, complete dentures still the first choice of treatment for patients with financial constraints, so it is imperative to have a well-fitting prosthesis in order to improve the patients’ quality of life.
Milled complete dentures can be either fabricated all in one piece with base plate and teeth together or separated as this case report whereas the denture based is milled from a puck and the milling of the teeth from another puck. Milling both pieces separated provides higher esthetic results because there are multi-chromatic discs offering shade degradation to give high esthetics to milling of teeth. Moreover, in a situation whereas the patients break the teeth, there could be an option merely to mill the teeth and bond them to the existing plate without the need of milling a new entire base plate.
There are numerous techniques for the final impressions making in the edentulous arches.43-47 This clinical situation was complex because the patient had been wearing the existing complete dentures for the last 15 years and the residual alveolar ridges in the mandible were excessively reabsorbed and atrophied. Due to the short height of the ridge, it was decided to make the conventional final impression following the functional impression technique using her current complete dentures. Making the final impression using the patient’s existing denture as the impression tray has been shown to be a successful approach for atrophic ridges.48,49Unfortunately, the patient needs to wait in the dental clinic while the clinicians pours the impression and fabricate the conventional master cast.
Milled complete dentures, including the teeth, are made out of prepolymerized resin acrylic pucks and teeth are bonded to the plate using a proprietary bonding mechanism in the milled recesses. This resin puck is produced under higher pressure and heat, so polymerization shrinkage does not happen and the porosity decreases and the adherence of Candida Albicans to the base plate decrease.14Polymerization shrinkage absence in the complete milled dentures results in a highly accurate denture fitting and improvement of retention.50,51 The CAD/CAM company (AvaDent Digital Dental Solutions, Scottsdale, Arizona, USA) offers all the tooth shades and shapes that are available in conventional denture fabrication for the milled prosthesis. Moreover, the digital construction of the complete dentures allows the designer to define the minimal thickness of the denture base and to include anatomic features on the denture base plate. The company provides the clinician the opportunity to logging into their website to modify the teeth set-up before milling the final prosthesis.52-56 The Avadent®(AvaDent Digital Dental Solutions, Scottsdale, Arizona, USA) order form demands the clinician to select the type of occlusal scheme, tooth shade, denture base colour, the set-up of position of the anterior teeth, and optional anatomical details for the denture base. The type of occlusal schemes offered are the anatomical, lingualized and flat-on-flat, which resembles the options provided by traditional denture teeth companies. The denture base color options include light shade, original, standard, medium and extra dark; these shades could be selected to match the patient’s gingival color.
The anterior teeth position and arrangement are also available options for the clinician and patient, it offers the regular set-up, and other options such as flared out central incisors, rotated lateral incisors, palatalized lateral incisors, with small overlap among them, and with small diastemas between all anterior teeth. The extra anatomical options for the denture base include the root prominence, stippling, rugae, gingival staining, frenum depth to match impression, posterior palatal seal, buccal roll and engraving the patients name on the base. The company (AvaDent Digital Dental Solutions, Scottsdale, Arizona) also offers a wide variety of teeth shape and shades including the designs of the traditional denture teeth.
Trying to incorporate new technology or clinical techniques can be challenging because clinician needs to become familiar with the software and operating equipment by the dental laboratories to maximize the dental care options for patient care. Due to the investment in novel equipment, laboratory costs may be increased compared with conventional methods.57 The laboratory companies may offer the clinical non-color trial dentures before the milling of the final prostheses however those trial dentures also have extra costs and its try-in will require an additional appointment for the patient. A previous study comparing the trueness fit of the intaglio surface of conventional and CAD/CAM dentures demonstrated significant improvements for the conventional prosthesos.58 However, as technology improves, newer studies have shown improvements of the CAD/CAM prosthesis.18
Several studies have indicated that prosthodontic management of anthropic mandibular ridges can be very challenging.59,60 The present case report successfully combines the advantage of CAD/CAM technology and traditional clinical recording methods for the construction of complete dentures in atrophic alveolar ridges. The presented workflow is completely functional because the clinician does not need to have either an intra-oral or laboratory scanner to offer CAD/CAM dentures to patients. Following this protocol, the clinician can do conventional final impressions, jaw relation records and mounting, then it can be either sending those mounted records to the laboratory in order to fabricate CAD/CAM dentures. If the dental office has a laboratory scanner, the records could be scanned and the STL file would be sent to the company. The combination of this workflow provides the necessary critical information of maxillomandibular relationship with conventional techniques and the improved material properties and fit of the milled dentures.