By Dr Theodoros Tasopoulos
Many denture wearers who require replacement dentures may have been wearing the same set for a long time. For that reason, especially for the elderly, adapting and controlling a new set of dentures may pose a diffi culty, as they can diff er in shape from the existing one.
However, it is now possible to reproduce the polished surfaces of the existing dentures thanks to a novel, simple method of the fully digital copy denture technique.
A 78-year-old healthy female patient was referred to our private dental practice for replacement of her existing implant-retained
overdenture on the lower jaw (Fig. 1).
Clinical examination showed general deterioration of the denture base material. Dental history revealed multiple excessive fractures
and repairs on the existing denture, which appeared as a result of flexural fatigue for over 10 years.
Additionally, the artificial teeth were worn down and slightly discoloured. The patient was generally satisfied with her overdenture
but wishes to improve its retention.
After reviewing treatment options, the patient decided to have a new implant-retained lower overdenture with a polyether ether
ketone (PEEK) framework insert to reinforce the milled poly methyl methacrylate (PMMA) denture base resin.
Firstly, the entire surface of the lower denture was scanned chairside (TRIOS 4 intraoral scanner, 3Shape). This scan generated an STL file format and was sent directly to a 3D printer (Fig. 2).
A duplicate of the patient’s existing prosthesis was printed. The 3D printed denture replica was trimmed in the midline. Two equal pieces came out from the acrylic model (Fig. 3), and the half of the copy denture was seated intraorally onto locator abutment (Fig. 4). A pre-preparation intraoral scan was obtained with the half of the 3D printed copy denture in situ (Fig. 5).
Subsequently, digital impression of the opposite dentition and bite registration of the jaws were scanned (TRIOS 4, 3Shape) (Fig. 6). Moving to the final step, the pre-preparation scan was edited and the area of the 3D printed denture was deleted (Fig.7).
Definite intraoral impression of the lower jaw was made from rescanning (capturing) only the relevant region (Fig. 8), while the alignment of pre-preparation and final impression scan was done using the three-point method available in 3Shape Dental System.
Then, the milled trial copy denture (ProArt CAD try-in, Ivoclar Digital) was produced (Fig. 10).
The monoblock try-in denture utilising the ProArt CAD try-in replaces the conventional wax teeth try-in, allowing the clinician and the patient to evaluate the main clinical parameters such as the aesthetics, phonetics, occlusion, and maxillomandibular relation (Fig. 11).
Moreover, the clinical assessment included the fit of the denture, flange extensions, and retention of the denture base. Following the milling process, the trial denture was covered with a thin layer of pink wax.
While creating the STL file of the definite denture base, CAD software designs automatically and accurately the cavities for the teeth (Fig. 12). Permanent denture teeth were also selected from available libraries and milled from a 20mm thick tooth-coloured disc (SR Vivadent CAD, Ivoclar Digital).
Once approved, the denture base was milled from a PMMA puck (IvoBase CAD, Ivoclar Digital). Finally, a PEEK reinforced mesh was
also constructed, utilising CAD/CAM technology (Fig. 13).
Then, the definite implant-retained overdenture was seated on the patient’s mouth (Fig. 14). Intaglio surface of the mandibular
overdenture was evaluated with pressure indicating paste, showing excellent adaptation with underlying tissues immediately after the final delivery of the prosthesis and before any adjustments1,2,3.
Using the direct technique, processing of the locator denture attachment metal housings and inserts into the denture was
employed (Fig. 15). Definite prosthesis (Fig. 16) was again seated in patient’s mouth.
The selected final inserts were set into place, providing sufficient retention. Occlusion was verified (Fig. 17) and the patient was
instructed on proper home maintenance and given advice for the required recall visits.
The fully digital protocol for denture duplication followed in this case demonstrates an easy and predictable way to assist patients
who feel comfortable with the fit and/or aesthetics of their existing denture.
Moreover, the laboratory now has an STL file of the milled denture, so this overdenture can be replicated at any time without additional patient visits. Modern literature clearly supports the high accuracy of edentulous arch scans.
Intraoral scanners (TRIOS 4, 3Shape) are based on mucostatic impressions, and denture retention is obtained mainly by the intimate contact of the surface of the denture base with the underlying tissues under the principle of surface tension1,2,3.
- Lo Russo L, Caradonna G, Troiano G, Salamini A, Guida L, Ciavarella D. Three-dimensional differences between intraoral scans and conventional impressions of edentulous Jaws: A clinical study. J Prosthet Dent 2019; (Epub ahead of print).
- Tasaka A, Yuuki U, Tomoharu M, Takao K; Takuya; Homma T, Matsunaga S, Abe S, Yoshinari S, Yajima M, Sakurai Y, Yamashita K, Shuichiro. Applying intraoral scanner to residual ridge in edentulous regions: in vitro evaluation of inter-operator validity to confirm trueness. BMC Oral Health 2019; 19 (1): 1-10.
- Lo Russo L, Ciavarella D, Salamini A, Guida L. Alignment of intraoral scans and registration of maxillo-mandibular relationships for the edentulous maxillary arch. J Prosthet Dent 2019; 121 (5): 737-740.
This article was published in Dental Asia March/April 2021 issue.
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