A systematic review of digital removable partial dentures. Part II: CAD/CAM framework, artificial teeth, and denture base

Metal framework reinforcement in implant overdenture fabricated with a digital workflow and the double milling technique: A dental technique

An implant-supported overdenture is a cost-effective option that enhances both appearance and function. Advances in computer-aided design and computer-aided manufacturing (CAD-CAM) technology have simplified the procedures for denture fabrication, reducing time and costs while increasing patient satisfaction. However, fractures in overdentures are often caused by misalignment of the occlusal registration, excessive force, material wear, and insufficient space between the denture base and the attachment. Reinforcing the overdenture with a metal framework enhances mechanical strength, stability, and durability. A novel technique with a double milling procedure of a single resin disk using a digital workflow for a maxillary overdenture reinforced with a selective laser melting metal framework should increase the mechanical strength and accuracy of the implant overdenture.

Digital workflow for fabricating an implant-supported overdenture with the custom disk method

Although methods have been developed to fabricate complete digital dentures, a digital workflow of fabrication methods for complete dentures with metal frameworks such as implant overdentures has not yet been established. The purpose of this dental technique article was to provide a comprehensive description of implant overdenture fabrication techniques using a digital workflow originally devised by applying the custom disk method. In this method, the custom disk was made of resin and contained prefabricated artificial teeth. Both the denture base and the artificial teeth in the custom disk were milled together. This described technique focuses on a 4-implant-supported overdenture with metal reinforcement for an edentulous maxilla. The aim was to establish a standard that can be widely adopted not only for implant overdentures but also for complete dentures that contain a metal framework. Advantages of this technique include that it enables the application of the custom disk method to the fabrication of implant overdentures with a metal framework as a reinforcement. In this technique, a metal framework is integrated into a resin-based complete denture fabricated by using the custom disk method, providing a better fit of the denture base and precise positioning of the artificial teeth.

Analysis of Peri-Implantitis Photothermal Therapy Effect According to Laser Irradiation Location and Angle: A Numerical Approach

In recent years, dental implants have become increasingly popular around the world. However, if the implant is not properly managed, inflammation may occur, and the implant itself may need to be removed. Peri-implantitis is a common inflammation that occurs in dental implants, and various laser treatments have recently been studied to eliminate it. In this study, the situation of removing peri-implantitis using photothermal therapy, one of the various laser treatments, was analyzed theoretically and numerically. The temperature distribution in the tissue for various laser irradiation locations, angles, and power was calculated based on heat transfer theory, and the degree of thermal damage to tissue was analyzed using the Arrhenius damage integral. In addition, the thermally damaged region ratio of inflamed and normal tissue was analyzed using the Arrhenius thermal damage ratio and normal tissue Arrhenius thermal damage ratio to confirm the trend of treatment results for each treatment condition. The results of the study showed that if only the thermal damage to the inflamed tissue is considered, the laser should be angled vertically, and the laser should be applied to the center of the inflamed tissue rather than close to the implant. However, if the thermal damage to the surrounding normal tissue is also considered, it was found that the laser should be applied at 1.0 mm from the right end of the inflamed tissue for maximum effect. This will allow for more accurate clinical treatment of peri-implantitis in the future.

Seating accuracy of removable partial denture frameworks fabricated by different digital workflows in comparison to conventional workflow

PURPOSE

To evaluate the seating accuracy of removable partial denture (RPD) frameworks fabricated by two digital workflows involving selective laser melting (SLM) in comparison to the conventional workflow.

MATERIALS AND METHODS

A Kennedy class III modification 1 partially edentulous mandibular arch was used as a master model. Three RPD framework groups were included: (1) a conventional workflow group with conventional impression and casting (CC), (2) a partial digital workflow group with conventional impression and digital fabrication (CD), and (3) a complete digital workflow group with digital impression and digital fabrication (DD). A total of 10 frameworks were produced for each group. The marginal gaps at the occlusal rests, retention arms, and reciprocating arms were measured by a traveling microscope. The data were analyzed with the one-way analysis of variance test.

RESULTS

At the framework level, the most superior fit was observed for the CD group (79.5 µm) followed by DD (85.3 µm) and CC (114.2 µm) groups. The CD and DD groups were significantly superior to CC (p < 0.001). This fit pattern was consistent for the retention and reciprocating arms, while the occlusal rest fit was similar among all the groups.

CONCLUSIONS

The SLM frameworks had a promising seating accuracy in comparison to conventional frameworks. The type of impression, conventional or digital, did not affect the accuracy of SLM frameworks. The differences observed in the present study are likely to be of minimal clinical significance.

Rehabilitation of Combined Hard and Soft Palate Defects with a Soft Relining Prosthesis: A Clinical Report

It remains a significant challenge in prosthetic rehabilitation for combined hard and soft palate defects on account of two primary reasons. At first, conventional impressions can hardly get an accurate analogue and usually bring about a terrible experience for the patients. Secondly, conventional hard denture base resins used in obturator prostheses exhibit limitations in marginal sealing, undercut retention, and elastic buffering when in contact with the soft palate. This article presents a case where combined hard and soft palate defects were successfully and rapidly reconstructed by using digital intraoral impression technology and denture soft reline material.

Patient-reported outcomes and framework fit accuracy of removable partial dentures fabricated using digital techniques: A systematic review and meta-analysis

PURPOSE

This review aimed to summarize the evidence on patient-reported outcomes and clinical performance of digitally fabricated removable partial dentures (RPDs) compared to traditionally fabricated dentures.

METHODS

Three databases were systematically searched (PubMed, CENTRAL, and Wiley online library) for clinical studies comparing digitally and conventionally fabricated RPDs regardless of data acquisition methods used for fabrication. The Cochrane Collaboration risk of bias assessment tool 2 and the Oxford Center for Evidence-based Medicine tool were used to assess risk of bias, and level of evidence, respectively. Descriptive narrative analysis was used to summarize data on patient-reported outcomes, as there were inadequate studies to pool data in a meta-analysis. A random-effects model was used to analyze the data of framework fit accuracy.

RESULTS

Ten randomized controlled trials were included in the systematic review, and 4 were included in the meta-analysis. Two studies showed that digitally fabricated RPDs are associated with higher patient satisfaction than conventionally fabricated RPDs (with a mean difference of 12.5 mm on a 100-satisfaction scale, p = .008). The pooled standardized mean difference for framework fit accuracy was 0.49 (p = 0.02) in favor of conventionally fabricated RPDs, which showed that conventionally fabricated RPDs have a quantitatively better fit compared to digitally fabricated RPDs. However, clinical evaluation studies showed that both frameworks have clinically acceptable fit.

CONCLUSIONS

Current evidence shows that digitally fabricated RPDs are associated with higher patient satisfaction compared to conventionally fabricated RPDs. However, the scarcity of literature here warrants the generalization of this conclusion. Both digitally and conventionally fabricated metal RPD frameworks showed acceptable fit clinically.

An in vitro evaluation of bond strength and failure behavior between 3D-printed cobalt-chromium alloy and different types of denture base resins

OBJECTIVES

This study aimed to evaluate the shear bond strength and failure behavior between cobalt-chromium (Co-Cr) alloy and different types of denture base resins (DBRs) over time.

METHODS

Seventy-two disk-shaped specimens (8 mm in diameter and 2 mm in thickness) were manufactured using a selective laser melting technology-based metal 3D printer. Three types of DBRs were used: heat-cure (HEA group), cold-cure (COL group), and 3D-printable (TDP group) DBRs (n = 12 per group). Each DBR specimen was fabricated as a 5 mm × 5 mm × 5 mm cube model. The specimens of the TDP group were manufactured using a digital light processing technology-based 3D printer. Half of the DBRs were stored in distilled water at 37 °C for 24 h, whereas the remaining half underwent thermocycling for 10,000 cycles. Shear bond strength was measured using a universal testing machine; failure modes were observed, and metal surfaces were evaluated using energy dispersive spectrometry.

RESULTS

The shear bond strength did not differ between the DBR types within the non-thermocycled groups. Contrarily, the TDP group exhibited inferior strength compared to the HEA group (P = 0.008) after thermocycling. All three types of DBRs exhibited a significant decrease in the shear bond strength and an increased tendency toward adhesive failure after thermocycling.

CONCLUSIONS

The bond strength between 3D-printable DBRs and Co-Cr alloy was comparable to that of heat-and cold-cure DBRs before thermocycling. However, it exhibited a considerable weakening in comparison to heat-cure DBRs after simulated short-term use.

CLINICAL SIGNIFICANCE

The application of 3D-printable DBR in metal framework-incorporated removable partial dentures may be feasible during the early phase of the treatment. However, its application is currently limited because the bond strength between the 3D-printable DBR and metal may weaken after short-term use. Further studies on methods to increase the bond strength between these heterogeneous materials are required.

Effect of Reinforcement Bar on Trueness of Printed Titanium Kennedy I Removable Partial Denture Frameworks by Selective Laser Melting

OBJECTIVE

The addition of reinforcement bars is a commonly used method to improve the fabrication trueness of selective laser melting removable partial denture alloy frameworks. However, the effects of different reinforcement bar designs on the trueness of the entire framework remain unclear. This study investigated the trueness of removable partial denture frameworks of pure titanium fabricated by selective laser melting under different reinforcement bar settings.

METHOD

A virtual framework was designed based on the Kennedy Class I partially edentulous model using computer-aided design software. Frameworks with different reinforcement bar settings (Ti-A without reinforcement bar, Ti-B with a single horizontal bar joining the lingual bar, Ti-C with two more bars at the anterior region, Ti-D with another horizontal bar at the anterior region, and Ti-E with one more bar at the posterior region, n = 5) were printed using pure titanium powder using a direct metal laser melting machine. The fabricated frameworks were scanned, and their fabrication trueness was compared with the designed virtual framework using one-way ANOVA.

RESULTS

The overall mean discrepancies for Ti-A, Ti-B, Ti-C, Ti-D, and Ti-E were 0.111, 0.047, 0.073, 0.068, and 0.047 mm, respectively. For the group of Ti-A set with no reinforcement bars, larger discrepancies were observed compared with the other four groups (P < .05). Groups Ti-B and Ti-E showed better trueness of the RPI clasps, rests, and distal ends (P < .05).

CONCLUSIONS

Adding reinforcement bars improved the printing trueness of the pure titanium frameworks, and different settings resulted in various degrees of improvement. Setting a single reinforcement bar to join the lingual bar or an additional reinforcement bar at the distal end significantly enhanced the printing trueness of the RPI clasps, rests, and distal ends.

Effect of wall thickness on shape accuracy of hollow zirconia artificial teeth fabricated by a 3D printer

PURPOSE

This study aimed to analyze how the wall thickness of 3D-printed hollow zirconia teeth affects shape accuracy.

METHODS

Datasets with measurement points were created for different artificial teeth resembling the mandibular right first molar (Geomagic Design X, 3D Systems). Reference distances were 9.8 mm for mesio-distal direction (M-D), 10.9 mm for bucco-lingual direction (B-L), 7.0 mm for MB-BB and DB-BB, and 4.5 mm for ML-LB and DL-LB. The outer geometry was identical for all artificial teeth with wall thicknesses of 0.30, 0.50, 0.75, and 1.00 mm. Twenty zirconia teeth were fabricated using a 3D printer (CeraFab 7500 Dental, Lithoz) for each group and sintered before support removal. After performing analog distance measurements using a micrometer screw, the digital distance measurements and angular deviations between measurement points on 3D scans were analyzed. Possible effects were investigated using nonparametric ANOVA, followed by Tukey's honest significant difference (HSD) test for multiple comparisons.

RESULTS

The shape accuracy was acceptable for artificial teeth with wall thicknesses of ≥0.5 mm. The largest distance deviation was observed for a wall thickness of 0.3 mm. In particular, DB-BB showed a median deviation of >56.2 µm, which is significantly larger than that for other test groups, ranging from 7.4-9.5 µm (P < 0.05). In most cases, angular deviations were the largest for teeth with 0.3-mm wall thickness (11.6°) and remained below 5.0° for the other test groups.

CONCLUSIONS

Acceptable accuracy was obtained for artificial teeth with wall thicknesses of at least 0.5 mm.

Digitally designed and milled implant-retained maxillofacial prosthesis for velopharyngeal closure in a patient with a nonsurgically treated cleft palate: A clinical report

An implant-retained maxillofacial overdenture with a pharyngeal speech aid prosthesis was fabricated for a patient with a nonsurgically treated cleft palate who was unable to achieve velopharyngeal closure. Computer-aided design and computer-aided manufacturing were used to fabricate a metal-reinforced prosthesis using the Ivotion Denture System and subtractive manufacturing with geographic guides. Magnetic attachments were incorporated to improve the retention and stability of the prosthesis. Masticatory function, deglutition, and esthetics were found to be improved at the 6-month follow-up.

Evaluation of Surface Roughness of Acrylic Denture Bases Polished Using Algishine, a Novel Polishing Material: An In Vitro Study

Introduction Surface roughness (Ra) significantly impacts the aesthetic and functional qualities of dental prosthetics. Traditional polishing involves pumice, a material routinely used in dental practice. This study introduces Algishine as a potential cost-effective eco-friendly alternative. Materials and methods A 3D design software (Geomagic) created a Standard Tesselation Language (STL) file of 10 mm x 10 mm x 2 mm. 30 STL file outputs were generated. The output was milled in wax. This was then flasked and processed. 30 acrylic resin specimens were fabricated and divided into two groups. Group A was polished using traditional pumice, and Group B was polished using Algishine. The Ra of each sample was measured using surface profilometry, with three readings per sample averaged for each group. Results Kruskal-Wallis test was performed to compare the two groups with the pre-testing samples, which showed p<0.05; indicating that there was a significant difference between the two groups. The average Ra value for unpolished acrylic was 7.105, while the specimens polished with pumice showed an Ra value of 2.218; specimens polished with novel material Algishine showed an Ra value of 1.743. This illustrates that Algishine achieves surface smoothness significantly superior to commonly used polishing agent and pumice. Discussion The results of our study demonstrate that Algishine, a novel polishing material derived from recycled alginate, effectively reduces the Ra of acrylic resin. This finding has significant implications, both clinically and environmentally. The primary clinical benefit of a smoother acrylic resin surface is the enhanced aesthetic appearance and increased patient comfort. A polished surface reduces plaque accumulation, thereby decreasing the risk of oral infections and improving the longevity of the dental prosthesis. The results show that Algishine achieves surface smoothness comparable to or better than pumice indicating that it can maintain, if not enhance, these clinical outcomes. Dental professionals can confidently use Algishine, knowing it meets the high standards required for patient care. Conclusion Algishine effectively reduces the Ra of acrylic resin, suggesting it is a viable, eco-friendly alternative to traditional pumice for dental polishing procedures. This indicates potential benefits in maintaining clinical outcomes while promoting environmental sustainability.

Evaluation of Shear Bond Strengths of 3D Printed Materials for Permanent Restorations with Different Surface Treatments

The development of high-filled 3D printing resin necessitates a bonding protocol for dental indirect restorations to achieve optimal bond strength after cementation. This study evaluates shear bond strengths of high-filler 3D printed materials for permanent restorations with various surface treatments. Rodin Sculpture 1.0 (50% lithium disilicate fillers) and 2.0 Ceramic Nanohybrid (>60% zirconia and lithium disilicate fillers) were tested, with Aelite All-Purpose Body composite resin as control. Samples were prepared, post-cured, and sandblasted with alumina (25 µm). Surface roughness was analyzed using an optical profilometer. Two bonding protocols were compared. First, groups were treated with lithium disilicate silane (Porcelain Primer) or zirconia primer (Z-Prime Plus) or left untreated without a bonding agent. Beam-shaped resin cement (DuoLink Universal) specimens were bonded and stored in a 37 °C water bath. Second, additional sets of materials were coated with a bonding agent (All-Bond Universal), either followed by silane application or left untreated. These sets were then similarly stored alongside resin cement specimens. Shear bond tests were performed after 24 h. SEM images were taken after debonding. One-Way ANOVA and post hoc Duncan were performed for the statistical analysis. Rodin 1.0 exhibited increased adhesive failure with silane or zirconia primer coating, but significantly improved bond strengths with bonding agent application. Rodin 2.0 showed consistent bond strengths regardless of bonding agent application, but cohesive failure rates increased with bonding agent and filler coating. In all groups, except for Rodin 1.0 without bonding agent, silane coating increased cohesive failure rate. In conclusion, optimal shear bond strength for high-filler 3D printing materials can be achieved with silane coating and bonding agent application.

Bonding Efficiency between Artificial Teeth and Denture Base in CAD/CAM and Conventional Complete Removable Dentures

A common challenge encountered with both traditional and digitally produced dentures involves the extraction of artificial teeth from the denture base. This narrative review seeks to present an updated perspective on the adherence of synthetic teeth for denture base materials, employing diverse methods. Dental technicians often employ chemical approaches and mechanical techniques (including abrasion, laser treatment, and abrasive blasting) to augment the retention of denture teeth. However, the efficacy of these treatments remains uncertain. In certain instances, specific combinations of Denture Base Resin (DBR) materials and artificial teeth exhibit improved performance in conventional heat-cured dentures following these treatments. The primary reasons for failure are attributed to material incompatibility and inadequate copolymerization. As new denture fabrication techniques and materials continue to emerge, further research is imperative to identify optimal tooth-DBR combinations. Notably, 3D-printed tooth-DBR combinations have demonstrated reduced bond strength and less favorable failure patterns, while utilizing milled and traditional combinations appears to be a more prudent choice until advancements in additive manufacturing enhance the reliability of 3D-printing methods.

Accuracy of Mandibular Removable Partial Denture Frameworks Fabricated by 3D Printing and Conventional Techniques

Herein, we used digital superimposition to evaluate the accuracy of metal frameworks for mandibular removable partial dentures fabricated using three techniques. Thirty master casts of a mandibular dentiform were categorized into three groups (n = 10) based on the framework manufacturing method: selective laser melting-based metal three-dimensional (3D) printing (SLM), digital light projection-based resin 3D printing and subsequent casting (RPC), and conventional casting (CON). The master casts were scanned twice, initially after preparation and subsequently after attaching silicone using the frameworks. These scan files were digitally superimposed to measure the silicone thickness. Statistical analysis was conducted using SPSS Statistics (Version 23.0, IBM Corp., Somers, NY, USA). One-way ANOVA and a post hoc Tukey's multiple comparison tests were performed to determine differences among the three groups (α = 0.05). The RPC group exhibited significantly higher overall and mean internal discrepancies at rest and tissue stops than the SLM and CON groups, which exhibited statistically insignificant differences. Thus, SLM fabrication resulted in comparable accuracy to that achieved by CON, whereas sequentially performing resin 3D printing and casting induced inferior accuracy. However, all frameworks across the three groups were clinically acceptable.

CAD-CAM denture teeth made on cast metal removable partial denture frameworks

Once the fit of the cast metal framework on a removable partial denture (RPD) has been verified, the manufacturer's prefabricated denture teeth are typically secured on the cast metal framework to prepare for a wax evaluation. Although prefabricated denture teeth are available in different tooth forms and sizes, they require modification to fit an edentulous space. In arches with severe space discrepancy, it may be inefficient and time-consuming to make modifications to prefabricated denture teeth. The technique described uses digital technology to fabricate custom denture teeth on a cast metal framework and establish harmonious occlusion. An edentulous space with more than a single tooth replacement is designed as a splinted fixed partial denture with a connector. The designed teeth are milled in the double-cross-linked polymer to prepare for a wax evaluation, and once verified, the RPD is processed by using heat polymerization. Modifications are made to the milled denture teeth after wax elimination to reduce the likelihood of acrylic resin bond failure.

Suitability and Trueness of the Removable Partial Denture Framework Fabricating by Polyether Ether Ketone with CAD-CAM Technology

The object of the study was to evaluate the suitability and trueness of the removable partial denture (RPD) framework fabricated by polyether ether ketone (PEEK) with the CAD-CAM technology in vitro. Four different types of dentition defects were selected. In each type, five PEEK RPD frameworks were fabricated by the CAD-CAM technology, while five Co-Cr RPD frameworks were made by traditional casting. The suitability of the framework was evaluated by silicone rubber film slice measurement and the three-dimensional image overlay method. The trueness of the PEEK framework was detected by the three-dimensional image overlay method. Data were statistically analyzed with the use of an independent samples t-test (α = 0.05). The suitability values by silicone rubber film slice measurement of the PEEK group were lower than those of the Co-Cr group in four types, with the differences indicating statistical significance (p < 0.05) in type one, type two, and type four. The suitability values using the three-dimensional image overlay method showed no statistical differences (p > 0.05) between the two groups in four types. The trueness values of the PEEK group were within the allowable range of clinical error. The suitability and trueness of the PEEK RPD framework fabricated by CAD-CAM technology met the requirements of the clinical prosthesis.

Fatigue life prediction considering variability for additively manufactured pure titanium clasps

PURPOSE

This study aims to develop a numerical prediction method for the average and standard deviation values of the largely varied fatigue life of additively manufactured commercially pure titanium (CPTi grade 2) clasps. Accordingly, the proposed method is validated by applying it to clasps of different shapes.

METHODS

The Smith-Watson-Topper (SWT) equation and finite element analysis (FEA) were used to predict the average fatigue life. The variability was expressed by a 95% reliability range envelope based on the experimentally determined standard deviation.

RESULTS

When predicting the average fatigue life, the previously determined fatigue parameters implemented in the SWT equation were found to be useful after conducting fatigue tests using a displacement-controlled fatigue testing machine. The standard deviation with respect to stroke and fatigue life was determined for each clasp type to predict variability. The proposed prediction method effectively covered the experimental data. Subsequently, the prediction method was applied to clasps of different shapes and validated through fatigue tests using 22 specimens. Finally, the fracture surface was observed using scanning electron microscopy (SEM). Many manufacturing process-induced defects were observed; however, only the surface defects where the maximum tensile stress occurred were crucial.

CONCLUSIONS

It was confirmed that the fatigue life of additively manufactured pure titanium parts is predictable before the manufacturing process considering its variability by performing only static elasto-plastic FEA. This outcome contributes to the quality assurance of patient-specific clasps without any experimental investigation, reducing total costs and response time.

A digital workflow for designing and manufacturing metal frameworks and removable partial dentures: A novel dental technique

The purpose of this technical report is to demonstrate a fully digital workflow for designing and fabricating metal frameworks and removable partial dentures. After obtaining a digital cast of the dental arch with bilateral distal extension defect, computer-aided design software and 3D printing technology are used for the design and fabrication of the removable partial denture frameworks, denture teeth, and denture bases, instead of the traditional workflow. The assembly of the three components is facilitated through a meticulously structured framework. The technology, which prints metal frameworks, denture bases, and denture teeth through different processes with different materials, achieves full 3D printing technology for making removable partial dentures.

[Current Status and Analysis of the Clinical Application of Digital Technology in Oral Medicine]

With the increasing maturity and popularization of digital technology in oral medicine, its application has now expanded to various clinical subspecialties of oral medicine. Digitalization has become one of the important development directions of oral medicine. What is the current development status of digital technology in oral medicine? In what ways is digital technology applied across various clinical specialties of oral medicine? Dentists are particularly concerned about these issues in their clinical work and research. In this paper, all the digital technologies applied in oral medicine are organized and categorized from a technical perspective. In this paper, we focused on presenting three-dimensional data acquisition technology, dental computer-aided design technology, dental computer-aided processing technology, and oral surgery implementation technology. Their technical principles, technical characteristics, applications in oral medicine, a secondary discipline of medicine, and the development status of domestically-developed technology are described and reviewed in detail. The other technologies such as oral digital materials, oral virtual simulation teaching, and oral multi-source data management are briefly discussed. We intend to provide references for dentists to apply digital technology in clinical practice and research.

Clinical evaluation of removable partial dentures with digitally fabricated metal framework after 4 years of clinical service

This case report describes the clinical outcomes of three patients who received removable partial dentures with a completely digitally designed and manufactured metal framework. The initial intraoral impressions were prepared, and the resulting standard tessellation language files were sent to a dental laboratory, where the alloy framework was designed using inLab software and printed using a 3D printer or milled directly from a Co-Cr disc. The quality of fit of the framework was evaluated intraorally to confirm the laboratory design. The acrylic teeth were set, and the definitive partial dentures were delivered after the acrylic resin bases were processed. The follow-up time was 4 years. No complications or failures related to the components of the partial dentures were observed.

Digital workflow to produce 3D-printed incisal facial indirect restoration with lingual rest seats to support a removable partial denture

A technique for fabricating lingual rest seats and indirect incisal restorations using a digital workflow is described. After intraoral scanning, the incisal edge position of the restoration and lingual rest seats for a subsequent removable partial denture (RPD) were designed digitally. Adaptation was evaluated with trial restorations, and definitive restorations were printed from a 3-dimensional resin (Varseo Smile Crown Plus Bego; Wilcos). The restorations were cemented with a heated composite resin (Tetric N; Ivoclar AG) polymerized for 40 seconds. The RPD was fabricated and delivered following a conventional technique. This standard, rapid, cost-effective, and straightforward approach allows a controlled and standardized process to obtain lingual rest seats and incisal restorations simultaneously, providing support for a successful Kennedy Class I RPD.

A survey on utilization and barriers of digital removable prostheses in the US dental education

PURPOSE

Gaining knowledge on the extent of digital technology implementation in dental education and the barriers to it will help inform future directions to promote the use of such technology and will enhance dental education. This study aimed to investigate the utilization of digitally fabricated removable prostheses and the potential obstacles to implementing such technology in US dental schools.

METHODS

A survey was developed and distributed to the restorative dentistry department chairs and postdoctoral prosthodontic program directors. The survey delivery protocol included follow-up emails 1 week, 3 weeks, and 4 weeks after the initial email. The collected data were analyzed descriptively.

RESULTS

The response rate was 85% and 45% for predoctoral and postdoctoral prosthodontic programs, respectively. The results showed that 88.06% of the predoctoral programs and 95.65% of the postdoctoral prosthodontic programs implement digital complete dentures in the curriculum; however, the digital removable partial dentures implementation rate was recorded at 70.77% in predoctoral programs and 61.9% in postdoctoral prosthodontic programs.

CONCLUSIONS

Dental schools are challenged by cost, design software limitations, IT and laboratory support, and faculty training. Multifaceted support is instrumental in further implementing digital removable prosthodontics into dental education.

Effect of Surface Textures and Fabrication Methods on Shear Bond Strength Between Titanium Framework and Auto-Polymerizing Acrylic Repair Resin

The aim of the study was to evaluate the effect of airborne particle abrasion (using different sizes of alumina particles) on the shear bond strength (SBS) between cast and milled titanium metal frameworks and auto-polymerizing acrylic repair resin. Forty flat cylindrical titanium disks were divided into two main divisions: cast and milled titanium. The two divisions were further subdivided into four groups based on metal surface treatment. Three particle sizes of aluminum oxide air abrasive powders (50µm, 110µm, and 250µm) were used for metal surface treatment by airborne particle abrasion. One group was the control group with no surface treatment. Auto-polymerizing acrylic repair resin was applied to all titanium disks. The specimens were subjected to SBS testing using a universal testing machine (Instron Corporation, Norwood, Massachusetts, United States). Surface evaluation was performed using a scanning electron microscope. One-way ANOVA was used for statistical analysis. The results showed a significant increase in SBS after airborne particle abrasion of both milled and cast titanium groups (p<0.001). The SBS was directly proportional to the size of the aluminum oxide particles. The milled titanium group showed higher SBS values than the cast group when the surface was not treated with alumina particles (p < 0.001) and when the surface was treated with the smaller particle sizes of 50 µm, whereas the cast group demonstrated higher SBS values than the milled group (p < 0.01) when the particle size was increased to 110 µm and 250 µm. It could be concluded that SBS between titanium metal frameworks and auto-polymerizing repair acrylic resin was directly related to the size of the alumina airborne particle abrasives. The fabrication method of the titanium framework also influenced the SBS as the untreated milled frameworks demonstrated favorable SBS values compared to the untreated cast frameworks.

Fabrication of milled removable partial dentures using a custom plate with prefabricated artificial teeth

PURPOSE

Although digital removable partial dentures have been previously described, there have been no reports on how to fabricate them in one piece. This study proposes a new method for fabricating patient-specific digital removable partial dentures using a custom plate.

METHODS

First, a gypsum model was scanned using a laboratory scanner and a removable partial denture was designed using computer-aided design (CAD) software based on standard tessellation language data. The metal clasp was fabricated from Ti-6Al-4V using a 3D printer. For custom plate fabrication, a resin plate frame was designed using computer-aided design (CAD) software and fabricated using a 3D printer. An artificial tooth and metal clasp were fixed on the base surface of the frame, an auto-polymerizing resin was poured into the frame for the denture base, and the artificial tooth and metal clasp were packed to form a custom plate. The plate was cut using a milling machine. Subsequently, the support attached to the denture was removed and polished for complete fabrication of the denture.

CONCLUSIONS

Our novel removable partial denture fabrication method is more efficient than the conventional method. The obtained removable partial dentures demonstrated satisfactory accuracy.

Comparison of the fatigue life of pure titanium and titanium alloy clasps manufactured by laser powder bed fusion and its prediction before manufacturing

PURPOSE

In this study, the fatigue properties of additively manufactured titanium clasps were compared with those of commercially pure titanium (CPTi) and Ti-6Al-4V (Ti64), manufactured using laser powder-bed fusion.

METHODS

Fourteen specimens of each material were tested under the cyclic condition at 1 Hz with applied maximum strokes ranging from 0.2 to 0.5 mm, using a small stroke fatigue testing machine. A numerical approach using finite element analysis (FEA) was also developed to predict the fatigue life of the clasps.

RESULTS

The results showed that although no significant differences were observed between the two materials when a stroke larger than 0.35 mm was applied, CPTi had a better fatigue life under a stroke smaller than 0.33 mm. The distributions of the maximum principal stress in the FEA and the fractured position in the experiment were in good agreement.

CONCLUSIONS

Using a design of the clasp of the present study, the advantage of the CPTi clasp in its fatigue life under a stroke smaller than 0.33 mm was revealed experimentally. Furthermore, the numerical approach using FEA employing calibrated parameters for the Smith-Watson-Topper method are presented. Under the limitations of the aforementioned clasp design, the establishment of a numerical method enabled us to predict the fatigue life and ensure the quality of the design phase before manufacturing.

Annual review of selected scientific literature: A report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The Scientific Investigation Committee of the American Academy of Restorative Dentistry offers this review of the 2022 dental literature to briefly touch on several topics of interest to modern restorative dentistry. Each committee member brings discipline-specific expertise in their subject areas that include (in order of the appearance in this report): prosthodontics; periodontics, alveolar bone, and peri-implant tissues; dental materials and therapeutics; occlusion and temporomandibular disorders; sleep-related breathing disorders; oral medicine and oral and maxillofacial surgery; and dental caries and cariology. The authors focused their efforts on reporting information likely to influence the daily dental treatment decisions of the reader with an emphasis on innovations, new materials and processes, and future trends in dentistry. With the tremendous volume of literature published daily in dentistry and related disciplines, this review cannot be comprehensive. Instead, its purpose is to update interested readers and provide valuable resource material for those willing to subsequently pursue greater detail on their own. Our intent remains to assist colleagues in navigating the tremendous volume of newly minted information produced annually. Finally, we hope that readers find this work helpful in managing patients.

A Feasible and Innovative Method of Investing Wax Pattern for Removable Partial Dentures: An In Vitro Study

Background A dental prosthesis called a removable partial denture (RPD) is used to fill the gaps left by one or more lost teeth. It serves as an option to fixed bridges and restorations supported by implants. This research was on a simple and effective method of investing RPD wax pattern and an in vitro investigation into the creation of a cutting-edge RPD technique. Methodology The method outlines the straightforward steps for waxing an RPD and validating the precision of the cast framework. The use of a laminated paper ring rather than a metallic one for investing the wax patterns is the main distinction between the novel method and the traditional ringless technique. Results A total of 30 samples were considered for investigation, with 15 in the traditional and 15 in the experimental group. The innovative wax pattern investment method exhibited a higher mean geometric orientation (9.23 ± 0.42) compared to traditional investment casting (8.90 ± 0.37 mm). Conversely, the dimensional accuracy mean was lower for the innovative wax pattern investment method (0.28 ± 0.03 mm) compared to traditional investment casting (0.31 ± 0.05 mm). The p-value was less than 0.001 for both parameters, signifying that the differences between the means of the two methods were statistically significant. The statistical power (1-β) was the probability of rejecting the null hypothesis when it was false. The statistical power was 0.999 for both geometric orientation and dimensional accuracy, indicating that the study had a very high power to detect differences between the two methods. Conclusions This innovative method does away with the requirement for a commercially available plastic ring, reduces the price and time needed for RPD manufacturing, and offers decent marginal accuracy. However, it has some restrictions, such as the challenge of cutting and preparing the paper ring after investing, which could lower the finished product's quality.

Fit accuracy in the rest region of RPDs fabricated by digital technologies and conventional lost-wax casting: a systematic review and meta-analysis

BACKGROUND

Digital technologies have recently been introduced into the fabrication of removable partial dentures (RPDs). However, it is still unclear whether the digitally fabricated RPDs fit better than conventionally cast ones in the rest region. The aim of this study was to evaluate the fit accuracy in the rest region of RPDs fabricated by digital technologies and compare it to those made by conventional lost-wax (CLW) technique.

METHODS

A comprehensive search was conducted in Cochrane Library, PubMed, EMbase, Web of Science and SpringerLink. Studies published up to August 2022 were collected. Two authors analyzed the studies independently and assessed the risk of bias on the modified methodological index for non-randomized studies (MINORS) scale. The mean values of gap distance between rests and corresponding rest seats of each study were extracted as outcome. A random-effects model at a significance level of P < 0.05 was used in the global comparison and subgroup analysis was carried out.

RESULTS

Overall, 11 articles out of 1214 complied with the inclusion criteria and were selected, including 2 randomized controlled trials (RCTs), 1 non-randomized clinical trial and 8 in vitro studies. Quantitative data from Meta-analysis revealed that fit accuracy in the rest region of RPDs fabricated with CLW showed no statistically significant difference with digital techniques (SMD = 0.33, 95%CI (-0.18, 0.83), P = 0.21). Subgroup analysis revealed a significantly better fit accuracy of CLW-fabricated RPDs in the rest region than either additive manufacturing (AM) groups or indirect groups (P = 0.03, P = 0.00), in which wax or resin patterns are milled or printed before conventional casting. While milled RPDs fit significantly better than cast ones in the rest region (P = 0.00). With digital relief and heat treatment, hybrid manufactured (HM) clasps obtained better fit accuracy in the rest region (P < 0.05). In addition, finishing and polishing procedure had no significant influence in the fit accuracy in all groups (P = 0.83).

CONCLUSIONS

RPDs fabricated by digital technologies exhibit comparable fit accuracy in rest region with those made by CLW. Digital technologies may be a promising alternative to CLW for the fabrication of RPDs and additional studies are recommended to provide stronger evidence.

TRIAL REGISTRATION

CRD42020201313.

Environmental sustainability related to dental materials and procedures in prosthodontics: A critical review

This article aims to review the status, challenges, and directions of environmentally sustainable oral healthcare by focusing on the dental materials and procedures used in prosthodontics. Sustainable development is a global priority and requires a systemic, integrative approach from all sectors of society. The oral healthcare sector is responsible for substantial greenhouse emissions throughout its value chain, including raw material extraction, industrial production, supply distribution, clinical practice, and management of waste. Of all dental specialties, prosthodontics has been one of the main generators of carbon emissions by fabricating a single product such as dentures or crowns in multiple steps. Dental prosthetic procedures involve chemicals and materials such as polymers, ceramics, metals, gypsum, and wax, which are often used in large quantities and for a single use. Thus, environmental risks and socioeconomic burdens can result from residuals and improper disposal, as well as waste and the embedded costs of unused materials retained by manufacturers, retail suppliers, dental laboratories, and dental clinics. To mitigate the environmental impact generated by conventional prosthodontics, we urge awareness and the adoption of sustainable good practices in the daily routine of dental clinics and laboratories. Capacity building and investment in a circular economy and digital technology can reduce the carbon footprint of prosthetic dentistry and improve the quality of life for present and future generations.

Different Polymers for the Base of Removable Dentures? Part I: A Narrative Review of Mechanical and Physical Properties

Even before considering their introduction into the mouth, the choice of materials for the optimization of the prosthesis depends on specific parameters such as their biocompatibility, solidity, resistance, and longevity. In the first part of this two-part review, we approach the various mechanical characteristics that affect this choice, which are closely related to the manufacturing process. Among the materials currently available, it is mainly polymers that are suitable for this use in this field. Historically, the most widely used polymer has been polymethyl methacrylate (PMMA), but more recently, polyamides (nylon) and polyether ether ketone (PEEK) have provided interesting advantages. The incorporation of certain molecules into these polymers will lead to modifications aimed at improving the mechanical properties of the prosthetic bases. In the second part of the review, the safety aspects of prostheses in the oral ecosystem (fragility of the undercuts of soft/hard tissues, neutral pH of saliva, and stability of the microbiota) are addressed. The microbial colonization of the prosthesis, in relation to the composition of the material used and its surface conditions (roughness, hydrophilicity), is of primary importance. Whatever the material and manufacturing process chosen, the coating or finishes dependent on the surface condition remain essential (polishing, non-stick coating) for limiting microbial colonization. The objective of this narrative review is to compile an inventory of the mechanical and physical properties as well as the clinical conditions likely to guide the choice between polymers for the base of removable prostheses.

Fully digital workflow for duplicating clasp-retained removable partial dentures using three-dimensional printing: A clinical report

This clinical report describes a fully digital workflow for replicating removable partial dentures (RPDs). The artificial teeth and denture base of existing dentures were duplicated and applied to new dentures with a redesigned framework. After the components of RPDs had been separated from the scan data of the existing dentures, they were fabricated using 3-dimensional printing and assembled to create a new denture.

Adhesion of Conventional, 3D-Printed and Milled Artificial Teeth to Resin Substrates for Complete Dentures: A Narrative Review

BACKGROUND

One type of failure in complete or partial dentures is the detachment of resin teeth from denture base resin (DBR). This common complication is also observed in the new generation of digitally fabricated dentures. The purpose of this review was to provide an update on the adhesion of artificial teeth to denture resin substrates fabricated by conventional and digital methods.

METHODS

A search strategy was applied to retrieve relevant studies in PubMed and Scopus.

RESULTS

Chemical (monomers, ethyl acetone, conditioning liquids, adhesive agents, etc.) and mechanical (grinding, laser, sandblasting, etc.) treatments are commonly used by technicians to improve denture teeth retention with controversial benefits. Better performance in conventional dentures is realized for certain combinations of DBR materials and denture teeth after mechanical or chemical treatment.

CONCLUSIONS

The incompatibility of certain materials and lack of copolymerization are the main reasons for failure. Due to the emerging field of new techniques for denture fabrication, different materials have been developed, and further research is needed to elaborate the best combination of teeth and DBRs. Lower bond strength and suboptimal failure modes have been related to 3D-printed combinations of teeth and DBRs, while milled and conventional combinations seem to be a safer choice until further improvements in printing technologies are developed.

Mechanical properties and accuracy of removable partial denture frameworks fabricated by digital and conventional techniques: A systematic review

STATEMENT OF PROBLEM

Providing a removable partial denture (RPD) can be a complex, time-consuming, and error-prone procedure. Computer-aided design and computer-aided manufacturing (CAD-CAM) techniques have shown promising clinical outcomes; however, the influence of manufacturing techniques on the properties of RPD components is unclear.

PURPOSE

The purpose of this systematic review was to determine the accuracy and mechanical properties of RPD components fabricated with conventional and digital methods.

MATERIAL AND METHODS

This study followed the guidelines of the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA) and was registered on the international prospective register of systematic reviews (PROSPERO) database (CRD42022353993). An electronic search was conducted on PubMed/MEDLINE, Scopus, Web of Science, and the Cochrane Library in August 2022. Only in vitro studies comparing the digital with the lost-wax casting technique were included. The quality of the studies was assessed by using the methodological index for nonrandomized studies (MINORS) scale.

RESULTS

Of the 17 selected studies, 5 evaluated the accuracy of RPD components as well as the mechanical properties, 5 studies evaluated only the component accuracy, and another 7 evaluated only the mechanical properties. The accuracy was similar regardless of the technique, with discrepancies within clinically acceptable values (50 to 426.3 μm). The surface roughness was higher for 3D-printed clasps and lower for milled clasps (P<.05). The metal alloy significantly influenced the porosity, with the highest number of pores obtained by casting for Ti clasps and by rapid prototyping for Co-Cr clasps.

CONCLUSIONS

In vitro studies showed that the digital technique provided similar accuracy to that of the conventional technique within a clinically acceptable range. The manufacturing technique influenced the mechanical properties of RPD components.

Retentive Forces and Deformation of Fitting Surface in RPD Clasp Made of Polyether-Ether-Ketone (PEEK)

BACKGROUND

Polyetheretherketone (PEEK) has provided the option to fabricate RPDs with aesthetics unlike metal RPDs, but little attention has been paid to its suitability, especially towards the retentive forces and deformation of the clasp. This study aimed to examine the retentive forces and the fitting surface (inner surface) deformation of clasps made from PEEK and compare it with cobalt-chromium (Co-Cr) clasp.

METHODS

Forty-two circumferential clasps (14 Co-Cr and 28 PEEK) were fabricated and divided into two groups with clasp undercuts (0.25 mm and 0.5 mm) with thicknesses of 1 mm and 1.5 mm. Each was examined for retentive forces after cycle test on its abutment for 360 cycles. Initial and final retentive forces were recorded. The fitting surface deformation was determined using 3-Matic research analysis software.

RESULTS

The results revealed that highest mean initial retentive force was of Co-Cr clasps with 0.50 mm undercut 22.26 N (±10.15 N), and the lowest was the 1 mm PEEK clasps with 0.25 mm undercut 3.35 N (±0.72 N) and highest mean final retentive force was the Co-Cr clasps with 0.50 mm undercut 21.40 N (±9.66 N), and the lowest was the 1 mm PEEK clasps with 0.25 mm undercut 2.71 N (±0.47 N). PEEK clasps had a lower retentive force than Co-Cr clasps with 0.50 undercut. PEEK clasps (1.5 mm) at 0.25 mm undercut had the least deformation (35.3 µm). PEEK showed significantly less deformation (p ≤ 0.014) than Co-Cr.

CONCLUSION

The deformation of PEEK clasps fitting surface was lower than Co-Cr clasps and retentive forces were close to the Co-Cr clasps, suggesting the use of PEEK as an aesthetic clasp option for RPD framework.

Clinical Applications of Polyetheretherketone in Removable Dental Prostheses: Accuracy, Characteristics, and Performance

The high-performance thermoplastic polyetheretherketone (PEEK) has excellent mechanical properties, biocompatibility, chemical stability, and radiolucency. The present article comprehensively reviews various applications of PEEK in removable dental prostheses, including in removable partial dentures (RPDs) (frameworks and clasps), double-crown RPDs, and obturators. The clinical performance of PEEK in removable dental prostheses is shown to be satisfactory and promising based on the short-term clinical evidence and technical complications are scarce. Moreover, the accuracy of RPDs is a vital factor for their long-term success rate. PEEK in removable dental prostheses is fabricated using the conventional lost-wax technique and CAD/CAM milling, which produces a good fit. Furthermore, fused deposition modeling is considered to be one of the most practical additive techniques. PEEK in removable prostheses produced by this technique exhibits good results in terms of the framework fit. However, in light of the paucity of evidence regarding other additive techniques, these manufacturers cannot yet be endorsed. Surface roughness, bacterial retention, color stability, and wear resistance should also be considered when attempting to increase the survival rates of PEEK removable prostheses. In addition, pastes represent an effective method for PEEK polishing to obtain a reduced surface roughness, which facilitates lower bacterial retention. As compared to other composite materials, PEEK is less likely to become discolored or deteriorate due to wear abrasion.

Does Multifunctional Acrylate's Addition to Methacrylate Improve Its Flexural Properties and Bond Ability to CAD/CAM PMMA Block?

This study investigated the effects of a multifunctional acrylate copolymer-Trimethylolpropane Triacrylate (TMPTA) and Di-pentaerythritol Polyacrylate (A-DPH)-on the mechanical properties of chemically polymerized acrylic resin and its bond strength to a CAD/CAM polymethyl methacrylate (PMMA) disk. The methyl methacrylate (MMA) samples were doped with one of the following comonomers: TMPTA, A-DPH, or Trimethylolpropane Trimethacrylate (TMPTMA). The doping ratio ranged from 10 wt% to 50 wt% in 10 wt% increments. The flexural strength (FS) and modulus (FM) of PMMA with and without comonomer doping, as well as the shear bond strength (SBS) between the comonomer-doped PMMA and CAD/CAM PMMA disk, were evaluated. The highest FS (93.2 ± 4.2 MPa) was obtained when doped with 20 wt% of TMPTA. For TMPTMA, the FS decreased with the increase in the doping ratio. For SBS, TMPTA showed almost constant values (ranging from 7.0 to 8.2 MPa) regardless of the doping amount, and A-DPH peaked at 10 wt% doping (8.7 ± 2.2 MPa). TMPTMA showed two peaks at 10 wt% (7.2 ± 2.6 MPa) and 40 wt% (6.5 ± 2.3 MPa). Regarding the failure mode, TMPTMA showed mostly adhesive failure between the CAD/CAM PMMA disk and acrylic resin while TMPTA and A-DPH showed an increased rate of cohesive or mixed failures. Acrylate's addition as a comonomer to PMMA provided improved mechanical properties and bond strength to the CAD/CAM PMMA disk.

The Use of Acrylate Polymers in Dentistry

The manuscript aimed to review the types of acrylate polymers used in dentistry, as well as their chemical, physical, mechanical, and biological properties. Regarding their consistency and purpose, dental acrylate polymers are divided into hard (brittle), which includes acrylates for the production of plate denture bases, obturator prostheses, epitheses and maxillofacial prostheses, their repairs and lining, and soft (flexible), which are used for lining denture bases in special indications. Concerning the composition and method of polymerization initiation, polymers for the production of denture bases are divided into four types: heat-, cold-, light-, and microwave-polymerized. CAD/CAM acrylate dentures are made from factory blocks of dental acrylates and show optimal mechanical and physical properties, undoubtedly better monomer polymerization and thus biocompatibility, and stability of the shape and colour of the base and dentures. Regardless of the number of advantages that these polymers have to offer, they also exhibit certain disadvantages. Technological development enables the enhancement of all acrylate properties to respond better to the demands of the profession. Special attention should be paid to improving the biological characteristics of acrylate polymers, due to reported adverse reactions of patients and dental staff to potentially toxic substances released during their preparation and use.

Where Is the Artificial Intelligence Applied in Dentistry? Systematic Review and Literature Analysis

This literature research had two main objectives. The first objective was to quantify how frequently artificial intelligence (AI) was utilized in dental literature from 2011 until 2021. The second objective was to distinguish the focus of such publications; in particular, dental field and topic. The main inclusion criterium was an original article or review in English focused on dental utilization of AI. All other types of publications or non-dental or non-AI-focused were excluded. The information sources were Web of Science, PubMed, Scopus, and Google Scholar, queried on 19 April 2022. The search string was “artificial intelligence” AND (dental OR dentistry OR tooth OR teeth OR dentofacial OR maxillofacial OR orofacial OR orthodontics OR endodontics OR periodontics OR prosthodontics). Following the removal of duplicates, all remaining publications were returned by searches and were screened by three independent operators to minimize the risk of bias. The analysis of 2011–2021 publications identified 4413 records, from which 1497 were finally selected and calculated according to the year of publication. The results confirmed a historically unprecedented boom in AI dental publications, with an average increase of 21.6% per year over the last decade and a 34.9% increase per year over the last 5 years. In the achievement of the second objective, qualitative assessment of dental AI publications since 2021 identified 1717 records, with 497 papers finally selected. The results of this assessment indicated the relative proportions of focal topics, as follows: radiology 26.36%, orthodontics 18.31%, general scope 17.10%, restorative 12.09%, surgery 11.87% and education 5.63%. The review confirms that the current use of artificial intelligence in dentistry is concentrated mainly around the evaluation of digital diagnostic methods, especially radiology; however, its implementation is expected to gradually penetrate all parts of the profession.

Influence of molding angle on the trueness and defects of removable partial denture frameworks fabricated by selective laser melting

PURPOSE

To examine the effect of molding angle on the trueness and defects associated with removable partial denture (RPD) frameworks fabricated by selective laser melting (SLM).

METHODS

A plaster model of a partially edentulous mandibular arch classified as Kennedy class II modification 1 was used. After obtaining the 3D data of the model (design data), a framework was designed using CAD software. Based on the design data, three different molding angle conditions (0°, 45°, and -45°) were set in the CAM software. The frameworks were fabricated by SLM under each condition, and 3D data were captured (fabrication data). The design and fabrication data were superimposed using 3D inspection software to verify the shape errors. The number of support structures was then measured. To examine the internal defects, micro-computed tomography (µCT) was performed for void analysis. Surface roughness was measured using a laser microscope.

RESULTS

The overall shape errors of the RPD framework were smaller under the 0° condition compared with the others, and the largest number of support structures was observed at 0°. Many internal defects were observed in the large components of the framework at 45° and -45°. The surface roughness was the smallest at -45°.

CONCLUSION

The trueness and defects associated with the RPD frameworks were affected by the difference in the SLM molding angle.

Removable partial dentures retained by hybrid CAD/CAM cobalt-chrome double crowns: 1-year results from a prospective clinical study: CAD/CAM cobalt-chrome double crowns: 1-year results

OBJECTIVES

Computer-aided design and manufacturing (CAD/CAM) has been successfully used to replace conventional steps in the fabrication of double crowns, creating hybrid-workflows that might facilitate the wider application of these restorations in the future. However, in-vivo data are still lacking.

METHODS

A prospective clinical trial was designed in which 20 patients (median age = 69 years; n women = 10) with 73 abutment teeth who needed a double-crown-retained removable partial denture (RPD) were consecutively recruited. While most of the work steps were done conventionally, gypsum models were digitized with a laboratory scanner to allow CAD/CAM fabrication of primary crowns and secondary structures. DentalDesigner software (3Shape) was used in combination with milling unit PrograMillPM7 and Co-Cr- blanks (Ivoclar-vivadent). Connectors were milled from wax, transferred to Co-Cr using lost-wax technique and bonded to the secondary crowns. Clinical follow-ups were scheduled 6 and 12 months after prosthesis insertion. Outcome parameters were complication-free survival of RPDs and abutment teeth after one year.

RESULTS

After 12 months, complication-free survival was 74% and 91% for the RPDs and abutment teeth, respectively. Complications comprised decementations (n = 5), abutment tooth fractures (n = 2), fracture of denture teeth (n = 1), and loss of abutment teeth (n = 1). These complications were easily manageable, resulting in 1-year survival of 100% for CAD/CAM RPDs.

CONCLUSIONS

First data on short-term complication rates of CAD/CAM double-crown-retained RPDs appear promising. To gather further evidence, prospective clinical trials over a longer follow-up time and with larger patient groups are required.

CLINICAL SIGNIFICANCE

Hybrid CAD/CAM double-crown retained RPDs showed a successful clinical application after one year of follow-up. Further research is needed to evaluate their performance in comparison to conventional manufacturing methods.

Retentive force and fitness accuracy of cobalt-chrome alloy clasps for removable partial denture fabricated with SLM technique

PURPOSE

Evaluating the fitness accuracy and retentive force of cobalt-chrome (Co-Cr) alloy clasps fabricated using the selective laser melting (SLM) technique.

METHODS

Premolar and molar abutment models with a 0.5-mm undercut depth, 1.5-mm-thick occlusal rest seats, and guiding planes were designed and fabricated using a milling machine. On these models, Akers clasps with 0.25- and 0.5-mm undercut depths were designed and fabricated with SLM and a traditional lost wax casting method. Based on the manufacturing methods, abutment types, and undercut depths, the clasps were divided into eight groups (10 per group). The fitness accuracy of the clasps was evaluated by measuring the gap distance between the clasps and abutments using a silicone film method. The initial retentive force and changes in retention up to 7,200 insertion/removal cycles of the clasps were also measured. The data were analyzed using multiple linear regression, paired t-tests, and one-way ANOVA (α=0.05).

RESULTS

For both the SLM and cast clasps, the fitness accuracy of the rest was greater than that of the clasp tip and shoulder. No significant difference was found in the fitness accuracy between the SLM and cast clasps, regardless of the abutment type and undercut depth before or after insertion/removal cycles (p>0.05). There was also no significant difference in the initial retentive force between the SLM and cast clasps (p>0.05). After 7,200 insertion/removal cycles, the SLM clasp exhibited a greater residual retentive force (p<0.05).

CONCLUSION

The SLM technique for manufacturing the clasps of removable partial dentures has promising clinical applications.

Flexural and fatigue properties of polyester disk material for milled resin clasps

To evaluate the flexural and fatigue properties of a polyester disk material used in milled resin clasps of removable partial dentures, experimental polyester disk (mPE), injection-molded polyester (iPE), and polymethyl methacrylate disk (mPMMA) were examined by three-point bending tests and cyclic fatigue tests at 0.75 or 1.50 mm deflection. The mPE exhibited significantly higher flexural strength than the iPE (p<0.05). Meanwhile, the mPMMA displayed higher flexural modulus and strength than the polyesters. The mPE exhibited a significantly lower residual strain than the iPE at the cyclic 0.75 mm deflection (p<0.05); however, microcracks were observed in the mPE at the 1.50 mm deflection. The mPMMA showed a high residual strain at the 0.75 mm deflection and fractured within 1,000 cycles at the 1.5 mm deflection. The higher flexural strength and lower residual strain of the mPE compared with the iPE suggest the advantages of milled resin clasps within a limited deflection.