Functional Evaluation for 3D Printed Complete Dentures

• Introduction In recent years, advances in digital technology have led to a growing body of research on digital complete dentures. For example, in challenging single-arch complete denture cases involving an irregular opposing occlusal plane, digital technology can simplify conventional procedures, including adjustment of the opposing dentition and accurate transfer of the adjusted occlusal scheme to the definitive denture. Digital denture workflows can effectively reduce the number of patient visits. Moreover, the number and duration of clinical adjustments required after denture delivery do not differ significantly between digital and conventional dentures. Digital denture fabrication methods can generally be divided into two categories: additive manufacturing and subtractive manufacturing. Additive manufacturing, commonly known as three-dimensional (3D) printing, offers several advantages, including convenience, rapid production, and relatively low cost. Its disadvantages include comparatively weaker material properties and limited esthetics because of the relatively uniform color of printed dentures. Subtractive manufacturing involves milling the denture from a prefabricated material block. Because these materials are industrially polymerized in advance, they generally have greater strength and dimensional stability than 3D-printed materials. However, milling results in greater material waste and higher manufacturing costs.

Several studies have evaluated the adaptation of 3D-printed dentures. Comparisons involving different printing techniques and printing orientations have demonstrated that the adaptation of 3D-printed dentures is comparable to that of dentures fabricated using the conventional pack-and-press technique. An intraoral clinical study also demonstrated that digitally fabricated dentures, whether produced through 3D printing or milling, provide sufficient accuracy and intraoral adaptation for clinical use.

During the processing of conventional complete dentures, substantial material deformation may occur during flasking and polymerization. This deformation can cause displacement of the artificial teeth and result in occlusal discrepancies. A clinical study by Saurabh et al. reported that digitally fabricated dentures resulted in less displacement of the artificial teeth and required fewer adjustments after fabrication than conventional dentures.

Digital technologies for removable denture fabrication continue to evolve, with ongoing improvements in both accuracy and material strength. Nevertheless, additional studies are required to clarify the differences in their actual clinical performance.

In that study, intraoral scanning was used to obtain impressions for digital denture fabrication. For edentulous ridges, impressions obtained exclusively through intraoral scanning may provide less adequate border extension than conventional impressions made using custom trays. This is because the oral mucosa and surrounding soft tissues are mobile, making the scanning conditions fundamentally different from those encountered during the fabrication of fixed prostheses. Therefore, complete dentures fabricated solely from intraoral scans may have less favorable border extension and peripheral sealing than conventionally fabricated dentures, potentially resulting in reduced stability and masticatory efficiency.

In another intraoral clinical study, a custom tray was fabricated following a preliminary impression using the conventional workflow. Border molding and a definitive impression were subsequently performed intraorally. After the master cast was produced and the artificial teeth were arranged, the denture setup was scanned to create a standard tessellation language (STL) file. The same digital file was then used to fabricate both a 3D-printed denture and a milled denture. After the patients had worn each denture for a specified period, the two dentures were compared. Patient satisfaction with both digital dentures was greater than that with their existing dentures. The digital dentures also demonstrated favorable intraoral stability, comfort, esthetics, speech, and occlusal performance.

These findings indicate that the quality of digital dentures is sufficiently stable and acceptable for clinical use. However, the intraoral performance of the definitive denture depends on obtaining an accurate and complete impression and recording the maxillomandibular relationship precisely. Although conventional procedures can provide a complete definitive impression, they do not reduce the number or duration of clinical procedures. Therefore, it is important to investigate how digital technologies can be integrated into the conventional complete denture workflow to obtain complete and accurate impressions, reduce the number of patient visits, and produce definitive dentures whose clinical performance is comparable to that of conventionally fabricated dentures.

• Study Objective The objective of this study is to compare the clinical performance of digitally fabricated and conventionally fabricated complete dentures. After each participant has worn both types of dentures for a specified period, their performance will be evaluated using objective clinical assessments and subjective patient-reported outcome measures. The study will determine whether digitally fabricated complete dentures provide superior or comparable clinical performance to conventional complete dentures.
• Study Design This study is designed as a randomized, single-blinded crossover clinical trial. Participants will be randomly allocated to two groups, with an anticipated enrollment of five participants per group and a total sample size of 10 participants.

Group 1: Participants will first wear conventionally fabricated complete dentures for six weeks and will subsequently wear digitally fabricated 3D-printed complete dentures for six weeks. Questionnaires and clinical performance assessments will be administered after each six-week intervention period.

Group 2: Participants will first wear digitally fabricated 3D-printed complete dentures for six weeks and will subsequently wear conventionally fabricated complete dentures for six weeks. Questionnaires and clinical performance assessments will be administered after each six-week intervention period.

Clinical Procedures Conventional complete denture workflow

At the first visit, preliminary impressions will be obtained using alginate, and diagnostic casts will be produced. Custom acrylic resin impression trays will subsequently be fabricated using autopolymerizing resin (Ostron, GC Co.).

At the second visit, border molding will be performed using the custom trays and thermoplastic border-molding compound (Peri Compound, GC Co.). Definitive impressions will then be obtained using a silicone impression material (Exadenture, GC Co.), and the master casts will be produced. Record bases and occlusion rims will subsequently be fabricated on the master casts.

At the third visit, the record bases and occlusion rims will be used to determine the occlusal vertical dimension and record the centric relation. The master casts will then be mounted on an articulator, and the artificial teeth will be arranged.

At the fourth visit, the trial dentures will be evaluated intraorally to assess esthetics, speech, and occlusion. If no problems are identified, the dentures will be processed using the conventional flasking and heat-polymerization technique.

At the fifth visit, the definitive dentures will be adjusted and delivered. Follow-up adjustments will be performed 24 hours, three days, and one week after denture delivery. After the participant has worn the dentures for six weeks, clinical performance assessments will be conducted, and fabrication of the second set of dentures will begin.

Digital complete denture workflow

At the first visit, preliminary impressions will be obtained using alginate, and diagnostic casts will be produced. The casts will be digitized using a 3Shape scanning system. Record bases will then be designed digitally and fabricated using a 3D printer (NextDent 5100) and a printable material (NextDent Try-In). Wax occlusion rims will subsequently be fabricated on the printed record bases.

At the second visit, the record bases and occlusion rims will be used to determine the occlusal vertical dimension. Border molding and peripheral sealing will be performed using a thermoplastic border-molding compound. A definitive closed-mouth impression will then be obtained using a silicone impression material while the participant occludes at the predetermined vertical dimension. The dental midline and occlusal plane will be marked on the occlusion rims, and facial photographs will be obtained.

After the master casts are produced from the definitive impressions, they will be scanned to create STL files. The facial photographs will be integrated into the denture design software to assist with the digital arrangement of the artificial teeth. After completion of the design, the definitive complete dentures will be fabricated directly using a 3D printer and NextDent Denture 3D+ material.

At the third visit, the dentures will be evaluated intraorally, the occlusion will be adjusted, and the definitive dentures will be delivered. Follow-up adjustments will be performed 24 hours, three days, and one week after denture delivery. Clinical performance assessments will be conducted after the participant has worn the dentures for six weeks. At the end of the study, each participant will be allowed to select the set of dentures that they prefer to continue wearing.

Inclusion criteria

• Participants must be 20 years of age or older.
• Participants must be completely edentulous in both the maxilla and mandible, with at least three months having elapsed since the most recent tooth extraction.
• Participants must have sufficient cognitive ability to understand the study procedures and be able to read and complete the study questionnaires.
• Participants must voluntarily agree to participate in all study procedures after receiving and understanding the study information.

Exclusion criteria

• Individuals who are unable to read or complete the study questionnaires.
• Individuals with temporomandibular disorders that impair normal mouth opening and closing or prevent them from performing movements according to the investigators' instructions.
• Individuals with maxillary or mandibular defects resulting from congenital conditions or surgical procedures.
• Individuals whose physical or psychological health is considered unsuitable for study participation, as determined by the investigator or primary contact.