Follow-up assessment of the complete denture rehabilitation was performed for the first fifteen subjects (65 ± 13 years, 48 to 81 years old, 7 women and 8 men). They included eight Class II subjects. The subjects’ complete dentures underwent minor corrections during the follow up sessions. For two subjects, the vertical dimension was observed as overestimated during the template wear try-out period and corrected. This series of clinical cases could be used to establish a preliminary comparison with conventional complete dentures (Table
1) and pave the way to interesting future prospects.
Table 1
Assessment of digital complete denture versus conventional denture based on the first fifteen rehabilitations
Facilitating system? | Number of clinical sessions | Decrease |
Repeatability of recordings | Better |
Systematic procedure reliability | Verified |
Suitability for All Angle Class | Designed only for CL I |
Material durability | Maybe, follow-up studies needed |
Occlusal Accuracy? | Occlusion Transfer | Better |
Profitable system? | Cost /efficiency ratio | Maybe, socio-economic studies needed |
Physiological interest? | Functional Training | Yes, temporary usable template (Prior final validation) |
Data digitization? | Data backup/storage | Yes |
However, this procedure still presented some limitations. Indeed, the scan and modeling phase still brought about great difficulties. On one hand, the scan surface was not sufficient enough to totally register the impression components: it was not possible to scan trigon and para-lingual areas simultaneously, or tuberosity and para-tuberosity areas. On the other hand, the fixation method (with fixating paste) of the impression tray on the magnetized scanner plates remained artisanal. These recurring episodes induced an important working time delay (4 or 5 time more) compared to a classic straightforward scan and design phase, and remained longer compared with the time required for traditional impressions treatment.
In addition, the designing phase was far from matching the manual work of a skilled laboratory prosthesis technician, as it was not possible, for example, to choose to remove one or several teeth depending on the wanted result, to finish waxing of the polished functional edges, to have adaptable thickness, minimal and distinct on different parts of the tray, to specify the position of the teeth mounting plan, or to choose the type of mounting with the different exploitable correction curves. New updates should correct these problems.
Discussion
This first study was performed to evaluate and to validate the clinical and laboratory processes and their potential integration into a daily practice. The evaluation of the treatment success was not a primary goal; to this end, follow-up controls must be planned for each patient over time.
The Complete Removable Denture is the last prosthetic procedure to switch to digital techniques whose advantages are mainly observed in the laboratory stages; however, it is not possible to measure the depressibility of the oral mucosa using optical cameras, thus conventional impression techniques are still necessary. However, the complete innovative Wieland® system allows standardizing procedures and fewer sessions for the practitioner. A central point intra-oral recording system can be used to ensure complete reproducibility of the inter-arch ratio. This new system is beneficial for producing complete dentures, a domain of prosthetics that is often neglected and sometimes frustrating, as the results obtained do not always live up to the expectations of the practitioner or dental technician.
A recent study showed that the milling process is more advantageous in terms of retention compared to the conventional polymerization procedure [
10]. The absence of polymerization prevents distortions of the bases and teeth displacement. The teeth positioning key allows precise occlusion placement, programmed by the software. The virtual mounting of the posterior teeth is therefore ideally suited to the morphology of the prosthetic teeth, facilitating the integration of a bilateral balanced occlusion concept. This constitutes a major improvement in comparison to manual positioning. Also, this logistic evolution facilitates the dental laboratory step in which occlusal concepts and denture mountings require highly specific technical skills. Until now, these competences in the domain of complete dentures were considered as less important than implant or esthetic treatments.
As in other disciplines, the CAD/CAM procedure for complete dentures should increase the level of realizations. However, the investment in both learning and equipment remains considerable for dental laboratories. In this sense, investing in the Zenotec Select Hybrid is an alternative solution for extending prosthetic work (fixed and prosthetic implants). Virtual modeling requires training as 3D visualization on screen could be disconcerting and cause difficulties when reading the final result, especially during the wax finishing step. Cutting the mandibular impression, in particular in the retromolar pad area, is delicate as its contact surface must be optimal for ideal fitting. Indeed, removing a tooth next to the second molar is impossible, making it difficult to mount dentures in the case of Class II subjects. According to the supplier, this digital procedure is only intended to treat Angle Class I subjects. However, in the dental hospital unit, numerous Class II subjects were treated: the possibility of removing a premolar represents a crucial improvement of the software. As of today, the only available option to treat patient with an Ackermann class different from class I is either the removal of the second molar or changing the size of the prosthetic teeth without using matching tables between the anterior teeth and the posterior teeth. One improvement of the software would be to allow removal of one or multiple teeth to facilitate treatment of class II and III patients or to set up an overjet.
The correct positioning of the plate for recording the Gothic Arch is indispensable, which is facilitated by the snap-in system procedure. The height of the occlusal rim, determined by the measurements recorded with the Centry Tray, is undervalued to avoid interference between the two arches. The orientation of the occlusal rim is adjusted using the values recorded with the UTS CAD. One of the limiting factors is the arcade shape which does not allow the snap-fit system to be placed on the rim because only one Gnathometer dimension is available today. Severe class II or too narrow arcades will require a traditional recording system of the inter-arcade relationship.
From a clinical point of view, if all the favorable conditions of realization are met, patients will require professional guidance for the registration of their mandibular movements.
Nonetheless, the capacity of the CAD/CAM procedure to deal with any individual tooth, with mounting assistance and simultaneous machining of several dentures without polymerization is an improvement leading to fewer errors encountered during the realization of Removable Dentures [
3‐
5].
From the practitioner’s point of view, the digital denture procedure is timesaving since the clinical step of functional impression and recording of the inter-arch ratio are coupled. However there are difficulties in recording occlusion with the intra-oral central point with some patients. In addition, the practitioner must ensure that trays and retro-molar pads or tuberosity do not interfere with the recording. If difficulties occur, conventional recording can be carried out instead.