Pattern waxes and inaccuracies in fixed and removable partial denture castings

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.

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.

Intaglio Surface Adaptation of Removable Partial Denture Framework Fabricated by Various Data Acquisition Techniques and Fabrication Approaches

OBJECTIVES

 The aim of this study was to compare intaglio surface adaptation of the removable partial denture framework among various data acquisition techniques and fabrication approaches using three-dimensional comparison by metrology software.

MATERIALS AND METHODS

 The partial edentulous typodont model with five digital superimposition landmarks was duplicated and scanned for the digital reference model. Three approaches were the conventional lost-wax (group I; LWT, n = 5), intraoral digital impressions combined with PolyJet printing and lost-wax (group II; IP-LWT, n = 5), and extraoral digital impressions combined with PolyJet printing and lost-wax (group III; EP-LWT, n = 5). Each framework was scanned and superimposed with the reference model. The misfits at 53 locations were measured.

STATISTICAL ANALYSIS

 Data were statistically analyzed by one-way analysis of variance, followed by Tukey's honestly significant difference for pairwise comparisons (p < 0.05).

RESULTS

 Significant differences were found between three approaches at the reciprocal arm, terminal part of the retentive arm, rest, and major connector (p < 0.05). In the LWT group, the reciprocal arm and palatal vault region of major connector had the lowest misfits, but the highest misfit was found in the midline region (p < 0.001). In the IP-LWT group revealed the most excessive contact at the terminal part of the retentive arm (-0.111 ± 0.038 mm, p = 0.031), with the highest misfit at the rest area (p < 0.001).

CONCLUSION

 A difference in adaptation was found in several removable partial denture framework components among three approaches. The LWT group had a better adaptation than other groups. Nevertheless, a clinically acceptable adaptation was seen in all three approaches.

Comparative clinical evaluation of removable partial denture frameworks fabricated traditionally or with selective laser melting: A randomized controlled trial

STATEMENT OF PROBLEM

The clinical efficacy of selective laser melting (SLM) for fabricating removable partial dentures (RPDs) is not well established.

PURPOSE

The purpose of this clinical study was to compare the performance of SLM-fabricated frameworks with that of those fabricated via traditional lost wax casting.

MATERIAL AND METHODS

A double-blind, randomized, crossover design was used to compare cobalt chromium partial denture frameworks (n=29) fabricated by using SLM or traditional methods. The time taken for adjustments and the clinical fit and stability of the adjusted frameworks were appraised. The accuracy of the frameworks was assessed by measuring the space between the occlusal rest seat and the corresponding rest seat. Statistical comparisons between the 2 frameworks were carried out by using a linear mixed-effect model for repeated measurements (α=.05).

RESULTS

Frameworks fabricated by using both SLM and traditional techniques had an acceptable fit based on subjective clinical evaluation. The overall mean ±standard deviation space between the occlusal rest and rest seat for SLM frameworks (273.7 ±44.5 μm) was comparable with that of traditional frameworks (242.2 ±44.5 μm). The clinical fit adjustment time, 7.76 ±6.43 minutes for SLM and 5.49 ±6.39 minutes for traditionally fabricated frameworks, was statistically similar (P=.067).

CONCLUSIONS

Dentures fabricated via SLM and traditional techniques had comparable accuracy of fit and clinical fitting time.

Modern partial dentures - part 1: novel manufacturing techniques

While the conventional fabrication of removal partial dentures through the lost-wax technique is a time-tested technique, it is recognised as a 'complicated, error-prone, time-consuming and expensive process'. This has financial implications and can lead to increased chair time for the patient and dentist, resulting from low precision and ill-fitting frameworks. The use of computer-aided design and computer-aided manufacture brings removable prosthodontics into the digital era and opens up a host of benefits to the practitioner and laboratory technician. This paper introduces the benefits and downsides to adopting a digital workflow, and looks at the various alternative manufacturing techniques, which allow the clinician and technician to streamline their processes and make use of novel denture materials.

Effect of storage time and framework design on the accuracy of maxillary cobalt-chromium cast removable partial dentures

Statement of Problem:

Inaccuracies in the fit of palatal major connectors may be related to distortion of the wax pattern due to prolonged storage time and faulty major connector design.

Purpose:

This in vitro study was carried out to find out the effect of storage time and major connector design on the accuracy of cobalt-chromium cast removable partial dentures (RPDs).

Materials and Methods:

A brass metal die with a Kennedy Class III, modification 1, the partially edentulous arch was used as a master die. Thirty-six refractory casts were fabricated from the master die. The refractory casts were divided into three groups (Group I: Anterior-posterior palatal bar, Group II: Palatal strap and Group III: Palatal plate) based on the design of maxillary major connector and subdivided into four groups (sub Group A: 01 h, sub Group B: 03 h, Sub Group C: 06 h, and sub Group D: 24 h) based on the storage time. For each group, 12 frameworks were fabricated. The influence of wax pattern storage time and the accuracy of the fit palatal major connector designs on the master die were compared. Casting defects (nodules/incompleteness) of the frameworks were also evaluated before finishing and polishing. Repeated measures analysis of variance was used to analyze the data.

Results:

The gap discrepancy was least in sub Group A (01 h) followed by sub Group B (03 h) and C (06 h) and most in sub Group D (24 h). Statistically significant differences (P < 0.05 in all locations L1–L5) in the fit of the framework were related to the design of the major connector. The gap discrepancy was least in Group I (anterior-posterior palatal bar) followed by Group II (palatal strap) and most in Group II (palatal plate).

Conclusions:

It is recommended that the wax patterns for RPD to be invested immediately on completion of the wax procedure. The selection of a major connector design is crucial for an accurate fit of RPD.

Surface roughness and internal porosity of partial removable dental prosthesis frameworks fabricated from conventional wax and light-polymerized patterns: a comparative study

STATEMENT OF PROBLEM

Surface roughness and internal porosity are 2 potential risk factors that threaten the biocompatibility and long-term mechanical stability of cast partial removable dental prostheses frameworks.

PURPOSE

The purpose of this study was to investigate the influence of the material, of conventional wax patterns, and the recently introduced light-polymerized patterns on the initial surface roughness and internal porosity of the cobalt-chromium castings of partial removable dental prostheses.

MATERIAL AND METHODS

Twenty-eight identical partial removable dental prosthesis frameworks were fabricated on a cast of a maxillary Kennedy Class III modification 1 partially edentulous patient. Fourteen frameworks were fabricated from each pattern material. The initial surface roughness, Ra (μm), of the resultant castings was measured with a profilometer. Radiographs of the castings were made on dental occlusal films with a dental x-ray unit with the following exposure conditions: tube voltage 70 kV; exposure time 1.0 seconds; tube current 7 mA; and source-film distance 35 cm. The number and size of porosities in the 3 main components (clasp units, major connectors, denture base meshwork) were assessed. Statistical analysis was conducted with the independent sample t test for surface roughness and the Mann Whitney test for internal porosity (α=.05).

RESULTS

The statistical analysis of mean surface roughness and internal porosity revealed no significant difference between the 2 groups.

CONCLUSIONS

The surface roughness and internal porosity of frameworks fabricated from conventional wax and Liwa patterns were comparable, with no significant differences between the 2 pattern materials.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.