Fabrication of a 3D Printing Definitive Obturator Prosthesis: a Clinical Report

Abstract

Introduction

Digital technologies related to imaging and manufacturing provide the clinician with a wide variety of treatment options. Stereolithography (SLA) offers a simple and predictable way for an accurate reconstruction of congenital or acquired defects.

Clinical case

A 65-years old cancer patient with non- keratinized squamous cell carcinoma of left maxillary sinus came for a prosthetic clinical evaluation. A bilateral maxillectomy was performed and the treatment plan included definite obturator prosthesis for the upper arch. CT data and 3D planning software were used to create a 3D printing plastic model of the defect. A wax pattern of the hollow bulb was fabricated and cured with heat-cured silicone soft liner. A final impression was obtained with the hollow bulb placed intraorally. The master cast was duplicated and the new cast was invested and reflasked. The flasks were opened, wax was boiled out and some space was created in the internal part of the obturator. Transparent heat cured acrylic resin was sandwiched with, at the inner part of the bulb, improving the retention between the acrylic denture base and the silicone based soft lining material. The patient was then placed on a 6-month recall. The five-year follow up consists of a chair side relining, when needed, of the definite removable prostheses.

Conclusion

Maxillofacial surgery patients may develop postoperative complications such as trismus and pain. In these cases, the combination of digital technology and conventional techniques provide an accurate prosthetic restoration.

Introduction

The obturator is a maxillofacial prosthesis used to close a congenital or acquired tissue opening, primarily of the hard palate and/or contiguous alveolar/soft tissue structures (1). In Maxillofacial Prosthetics, the anatomical structures that have to be rehabilitated most of the time impede the clinician to make a detailed impression or even the patient himself/herself is under psychological pressure or pain.

Impression taking procedure has to consider a diversity of soft and hard tissues, mobility, undercuts and the distortion of impression material related to weight and consistency (2). At the present time, compared to the previous decades, a need for the rehabilitation of such patients has increased. There has been an increase of oral cancer patients of 15% in the U.S.A. during the last 40 years, (3). These numbers reveal the need for a more accurate, demanding and personalized treatment planning.

The CAD-CAM technology has been developed as an alternative tool for designing and manufacturing in dentistry since 1980. Although there are numerous systems available on the market, the main sequence is primarily produced by a scanner that converts human anatomy into digital data following a specific software program that can edit the digitized data and give information to a fabrication machine (4).

Finally, the CAM technology uses the combined data and fabricates the final restoration. There are two methods for fabrication: one is cut back from a certain material block (subtractive technique) and the other is layering the restoration (additive technique). Stereolithography (SLA) is the extension of CAD CAM technology in order to produce 3D prototype models. Originally it emerged from Rapid Prototyping (RP) technology combined with laser technology and nowadays it gives dentistry the possibility to create customized 3D models for each patient adjusted to his needs and anatomical structures. The use of stereolithographic models may progressively replace traditional milled models in the management of craniofacial anomalies (5). SLA, as a manufacturing method, has many applications, however, it must be carefully selected. The advantages of SLA is that light sensitive polymers are used to fabricate models, which allows a brief fabrication time and gives the ability to create complex anatomical structures with low cost materials. However, SLA has a small range of materials in use and the polymers may cause skin sensitization because the models cannot be sterilized (6).

All these manufacturing technologies became more accessible imaging technology had been improved. CT and CBCT are widely used in dentistry and provide volumetric data that can be used immediately and in a very accurate way (7). Fourie et al. used CBCT to detect whether soft tissue imaging is reliable. Their findings revealed that there is a deficiency in surface detail, however, they concluded that CT is a reliable and accurate method (8).

Using the data from the CT scan in order to create a 3D model for RPDPs or obturators without an intraoral scanning or impression making of the surged area is not a commonly used technique. This clinical report provides a combined concept of conventional and digital technology for obturator fabrication.

Clinical case

A 65-year- old male patient with a history of a tumor of the left maxillary sinus was referred for a prosthetic treatment. A bilateral maxillectomy was performed 6 months prior to the surgical resection which extended from the posterior border of the ramus and angle of the mandible the anatomical level of the posterior frontal surface, in the left visceral skull. A thorough intra-oral examination showed that the palatal defect was large (dimensions 10.4 x 10.5 cm) (Figure 1). Moreover, the two remaining roots of the right central incisor and canine were found. The mandibular arch was dentate and it had many overerupted carious teeth requiring a multidisciplinary treatment approach.

Figure 1.

Pre-operative condition of palatal defect

The histological examination demonstrated the features of a non-keratinized squamous cell carcinoma of moderate differentiation (Stage T₄N₁M₀).

Subsequently, the patient presented with severe trismus and pain in the facial and mucosal area which interfered with speaking, nutrition and functioning. Those two post operation symptoms complicated further the prosthetic restoration plan. Following intra oral examination, data collection and discussion of treatment options, the treatment plan was agreed consisting of definite obturator prosthesis for the upper arch. The remaining roots of central incisor and canine had a RCT and composite restorations in order to avoid extraction and the risk of osteonecrosis. Post-surgical maxillary defects predispose the patient to hypernasal speech, fluid leakage through the nose and compromise the masticatory ability and deglutition (9).

Visualization and communication of pathology involved a 3 dimensional (3D) measurement of a remarkably large palatal defect using a computerized tomography (CT) data and a 3D planning software (SimPlant v14, Materialise Dental N.V., Leuven, Belgium) (Figure 2). The MIMICS software (SimPlant v14, Materialise Dental N.V., Leuven, Belgium) was utilized for a 3D processing of the DICOM images and the preparation of the STL file for manufacturing the model. 116 CT images in a DICOM format were processed and a relevant STL file was developed.

Figure 2.

Simplant software view of maxillary defect

A 3D-printing Solido SD300 (Solidmodel, Acton, USA) was the rapid manufacturing technology used for building the precise anatomical model within the limits of the defect. It was developed from virtual planning data input. This specific 3D printing machine is cutting thin the layers of PVC plastic (Solidmodel, Acton, USA) which are glued together layer by layer until the complete anatomical model is fabricated (Figure 3). The duration of the process was about 10-12 hours.

Figure 3.

A 3D printing anatomical model of defect

Laboratory process

At the beginning, a wax pattern of the hollow bulb was fabricated using the plastic anatomical model. The wax pattern was invested in stone (Silky Rock, Whip-mix Corp. Whipmix, Louisville, USA) and then boiled out from the mold (Figure 4). The space created, was packed with a heat cured silicone soft liner (Molloplast-B, Detax GmGh and Co., Ettlingen, Germany) for approximately 10 min under bench pressure (100 kPa), into the dummy blank and then heated up to 100⁰ C in a water bath, followed by curing in boiling water at 100⁰ C for 2 h according to the manufacturer’s recommendations. A separating agent was applied to the stone surfaces of dental flasks for insulation.

Figure 4.

An invested wax pattern of a hollow bulb

Preliminary impressions were obtained using a stock tray with a silicone hollow bulb intraorally. The master cast was used to create a special tray. Border molded impression was obtained through the border molding process by utilizing impression compound (Impression compound, type 1 Kerr Corp. CA, USA) and medium body vinyl polysiloxane (Episil, Dreve, Unna, Germany (Figure 5 and 6). The next step included the fabrication of a working cast using Type IV (Whip-mix Corp. Whipmix, Louisville, USA) dental die stone (Figure 7). Subsequently, the duplication of the master cast using laboratory silicone (Prestige. Duplex, Vanini Dental Industry, Grassina, Italy) was made with wax pouring inside the silicone obturator and the sealing of the area in terms of a cap (Figure 8). After the silicone curing, a new working cast was invested and reflasked. The model had the borderline of the obturator and the sealant imprinted, hence the gap between the denture and the obturator was preserved (Figure 9).

Figure 5.

An intraoral application of the hollow bulb.

Figure 6.

The final impression with the silicone hollow bulb in situ.

Figure 7.

Fabrication of a working cast. The retention groove of the hollow bulb can be detected on its borders.

Figure 8.

Duplication of the master cast and the silicone obturator.

Figure 9.

A new working model created with the wax sealant imprinted.

After the whole procedure had been completed, the flasks were opened, the wax was boiled out from molds and mold space was created in the internal part of the obturator. Transparent heat cured acrylic resin (Vertex, Vertex Denta, Zeist, The Netherlands) was sandwiched with, at the inner part of the bulb, improving the retention between the acrylic denture base and the silicone hollow bulb (Figure 10). The dental flask was placed under bench pressure and the acrylic resin was allowed to cure for 7h at 70⁰ C followed by 1 h at 100⁰ C, according to the manufacturer’s instructions in a water bath (Interlab Products, Hull, UK). A base plate with occlusal rims was used to record the jaw relationship. Selection and arrangement of anterior and posterior teeth was made. The final curing cycle included the dental flask within a water bath at 74⁰ C for 90 min and 100⁰ C for 60 min (Figure 11). After the obturator prosthesis was successfully inserted in the patient’s mouth, pressure areas during functional movements were located with pressure indicator silicone (Fit Checker II, GC America Inc, USA) and relieved especially in large undercuts that composed the anatomical borders of the defect.

Figure 10.

Fabrication of the transparent heat cured acrylic denture base.

Figure 11.

Direct relining of the definite 3D printing obturator prosthesis with RTV soft lining materials.

Additionally, occlusal adjustments of the new prosthesis and the opposite natural dentition were made carefully. The patient was advised about oral hygiene procedures focusing on the effective cleaning of natural teeth, the obturator prosthesis and the acquired palatal defect. Postinsertion appointments were scheduled at intervals of 2 days, 1 week, 1 month, 6 months and once a year after placement of the prosthesis (2). After 6 months in patient’s recall, a direct relining using a chairside silicone soft liner (Tokuyama Sofreliner, Tokuyama Dental Corporation, Taitou-Ku Tokyo, Japan) improved the fitting of the complete denture and the accuracy of its borders.

Five years after the initial placement of the 3D printing obturator prosthesis, no clinical symptoms were observed (Figure 12).

Figure 12.

A 5 year- follow up of the maxillary 3D printing obturator prosthesis.

Discussion

Squamous cell cancer of the head and neck (SCC) is diagnosed in nearly 400.000 patients per year. Staging of SCC has not been evaluated as a finding of importance related to the treatment planning and therapeutic strategies (10). Patients surged for oral cavity cancer develop postoperative complications such as trismus and pain which occur quite frequently. Trismus is well recognized in patients who have also received radiotherapy with the reported incidence of 33.9%. An unmanaged trismus converts into chronic trismus, followed by a gradual fibrosis of the muscles. Chronic postoperative pain is confirmed and its occurrence ranges from 4.2% to 6.5%. Those two symptoms affect the Quality of Life measurements and complicate the clinical management. However, prosthetic rehabilitation of oral cavity permits patients to overcome postoperative difficulties and bring back natural function (speech, nutrition, mastication) (11), (12) (13). Trismus complicates prosthodontics procedures during rehabilitation phase and disturbs materials accuracy, especially during the impression session. In order to overcome this problem, Cheng et al. made a primary impression for a microstomic patient creating intraorally a silicone tray. Subsequently, a custom tray was created and the impression was by using putty and medium viscosity silicone. The difficulty with this technique is that dimension distortion may occur due to gypsum thermal expansion (14). Vojvodic et al. used a two steps impression technique (alter cast impression technique). The primary impression was made to construct the metal framework which was used as a custom tray for the defect impression. The altered cast technique is well documented in the literature. The use of this impression technique has the following advantages: more accurate impression and less discomfort for the patient (15).

In this clinical case, the patient was in great pain and had severe trismus as postoperative symptoms. During the impression making stage, the clinicians decided to overcome this problem by resorting to imaging and digital technology. Digital technologies such as RP and SLA as shown by Williams et al are more accurate and more adequate methods when complex anatomical structures have to be restored (13), (16), (17), (18). The preciseness of the last generation of CTs combined with digital analyzing programs and 3D rapid prototyping can lead to a more reliable result. In maxillofacial prosthetic cases, where only the RP mold is fabricated, the process is shortened and multiple pouring is allowed from a single mold. Cone-beam computed tomography (CBCT) can be used to provide primary reconstruction as a primary cast combined with SLA and construct parts or complete removable prostheses reducing the chair side pain and anxiety of surgically treated patients. However, the clinicians should consider the procedure cost, the accuracy of the manufacturing system and materials used.

Conclusion

There is evidence that pain and trismus are frequent postoperative complications. In this clinical case, digital technology was used to overcome the two symptoms. A combination of conventional techniques and SLA is an alternative for the clinician to make an accurate prosthetic restoration, thus reducing treatment time, patient discomfort and anxiety.