Accuracy and surface roughness of Co-Cr partial denture frameworks with different digital fabrication methods.

STATEMENT OF PROBLEM: Traditional removable partial denture (RPD) manufacture is being phased out in favor of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques and rapid prototyping (RP), which provide more efficient methods of producing RPD frameworks. However, studies comparing the accuracy and surface roughness of these approaches on RPD frameworks are still scarce. PURPOSE: The purpose of this in vitro study was to evaluate the accuracy and surface roughness of class I cobalt chromium (Co-Cr) removable partial denture frameworks digitally constructed using 2 different CAD-CAM technologies: direct milling (DM) and selective laser melting (SLM). MATERIAL AND METHODS: An educational maxillary stone cast was scanned to create a resin model after rest seat preparation. The resin model was scanned, and an RPD framework was digitally designed. Sixteen frameworks were constructed (n=8). Two groups were defined. In the direct milling (DM) group, the standard tessellation language (STL) file of the RPD framework was used to mill the design from a Co-Cr blank directly. In the selective laser melting (SLM) group, the STL file of the RPD framework was used to print the design from Co-Cr powder using the selective laser melting technique. Geomagic Control X software program was used to measure the accuracy of the fabricated frameworks. Surface roughness was tested using optical profilometry. An unpaired t test was used to compare the 2 groups (α=.05). RESULTS: The DM group showed significantly higher mean ±standard deviation accuracy (189 ±9 µm) (P<.001) compared with the SLM group (456 ±122 µm). Regarding the surface roughness, the DM group (0.157 ±0.001 mm) showed significantly lower surface roughness (P<.001) compared with the SLM group (0.256 ±0.001 mm). CONCLUSIONS: The direct milling fabrication technique enabled the fabrication of Co-Cr RPD frameworks with higher accuracy and less surface roughness when compared with the 3-dimensionally printed SLM technique.

Evaluation of Accuracy and Position of Milled and 3D-Printed Teeth in Digital Complete Dentures.

PURPOSE: To compare the accuracy of milled versus 3D-printed complete denture bases and teeth and to assess the position of the teeth in relation to the corresponding denture bases. MATERIALS AND METHODS: Two different manufacturing techniques were used in this study. In Group A, 10 complete dentures were digitally designed and fabricated by milling prepolymerized blocks of polymethyl methacrylate (PMMA). In Group B, 10 complete dentures were digitally designed and fabricated using a 3D-printing technique. The accuracy of the maxillary and mandibular denture bases and teeth and the positions of the teeth in relation to the corresponding denture bases were evaluated using Geomagic Control X software (Oqton). Data were presented as mean and SD values. Statistical analysis of the resultant data was performed using Student t test. The significance level was set at P ≤ .05. RESULTS: With regard to denture bases, lower surface deviation values were found in the maxillary and mandibular milled denture bases (Group A), with values of 0.158 ± 0.024 and 0.117 ± 0.022, respectively. However, regarding the denture teeth, lower surface deviation values were found for printed teeth (Group B), with values of 0.18 ± 0.016 for the maxillary teeth and 0.153 ± 0.02 for the mandibular teeth. For positioning of the teeth in relation to the corresponding denture bases, the values were 0.4 ± 0.08 for the maxillary teeth and 1.003 ± 0.027 for the mandibular teeth. CONCLUSIONS: The milling technique yields complete denture bases with superior accuracy, whereas printing technology produces denture teeth with better accuracy and positioning in the corresponding denture bases.

Effect of different digital technology on the adaptation and retention of Co-Cr partial denture frameworks.

PURPOSE: To evaluate the overall adaptation and retention of class I cobalt-chromium (Co-Cr) removable partial denture (RPD) frameworks using three different computer-aided design and computer-aided manufacturing (CAD-CAM) technologies: Indirect wax milling with lost wax technique (LWT), direct milling, and selective laser melting (SLM) technique. MATERIALS AND METHODS: An educational maxillary stone model (Kennedy class I) was scanned after preparing rest seats to create a resin model. The resin model was scanned, and the RPD framework was digitally designed and saved as a standard tessellation language (STL) file. Twenty-four Co-Cr RPD frameworks were then constructed and divided into three groups (n = 8) based on fabrication technique: Group A (indirect wax milling with LWT), Group B (direct milling), and Group C (selective laser melting). In Group A, the STL file was used to mill the design from castable resin blanks which were then cast by the LWT. In Group B, the STL file was used to mill the design from the Co-Cr blank directly. Finally in Group C, the STL file was used to print the design from Co-Cr powder using SLM 3D printed technique. Geomagic Control X software was used to measure the overall adaptation of the fabricated RPD frameworks, Retention was also tested using a universal testing machine. One-way Analysis of Variance (ANOVA) test was used to compare the three groups then the Tukey HSD post-hoc test was used for pair-wise comparisons. The significance level was set at p ≤ 0.05. RESULTS: Regarding the overall adaptation, Group B (0.71 ± 0.02 mm) showed significantly higher adaptation than Group A (0.96 ± 0.06 mm) and Group C (1.05 ± 0.16 mm). Regarding retention, Group B (2.03 ± 0.34 N) showed significantly higher retention than Group A (1.00 ± 0.13 N) and Group C (0.78 ±0.17 N). CONCLUSION: Based on the findings of this in vitro study, Co-Cr RPD frameworks fabricated by direct milling technique revealed the best adaptation and retention.

A Comparison of Denture Base Retention and Adaptation Between CAD/CAM and Conventional Fabrication Techniques.

PURPOSE: To assess the retention and adaptation of milled and printed denture bases in comparison to conventional ones. MATERIALS AND METHODS: A total of 24 completely edentulous patients were selected. For each patient, three maxillary denture bases were constructed according to different fabrication techniques, thus defining the three groups for comparison: group 1 consisted of denture bases constructed by a conventional technique, group 2 consisted of denture bases milled from prepolymerized blocks of PMMA, and group 3 consisted of denture bases fabricated by a 3D printing technique. A digital force gauge was used for measuring the retention of the denture bases intraorally, while Geomagic Control X 64 software was used to evaluate the adaptation of the denture bases with their corresponding master casts. Repeated-measures analysis of variance was used for comparison among the groups, followed by pairwise comparison with post hoc Bonferroni correction. The significance level was set at α = .05. RESULTS: Statistical analysis showed significant differences among the three groups regarding retention and adaptation. The highest values of retention and adaptation of denture bases were found in group 2 (milling group). CONCLUSION: Within the limitations of this study, the following could be concuded: milled denture bases demonstrated better retention and adaptation than the conventional heat-polymerized and printed denture bases, and the printed denture bases showed better adaptation but similar retention to conventional heat-polymerized denture bases.

Assessment of tooth positions of printed complete dentures with different designs and tooth positioning techniques.

PURPOSE: To evaluate the accuracy of tooth positions in printed complete dentures with different designs and teeth positioning techniques. MATERIALS AND METHODS: Five different designs of complete dentures and teeth positioning techniques were evaluated in this in vitro study. In Group I, the denture bases and teeth were designed as a single piece. In groups II and III, the denture bases were designed separately, and the denture teeth were designed as separate teeth. In groups IV and V, the denture bases were designed separately, and the denture teeth were designed as a single piece. Teeth positioning keys were designed for groups III and V. The dentures of all groups were scanned, and the data were imported to the surface matching software to evaluate the accuracy of the teeth positions. Statistical analysis was done using One -way ANOVA of Variance. The significance level was set at p ≤ 0.05. RESULTS: The results showed that the highest deviations of the positions of the canines (0.0781 ± 0.0154 mm) and the first molars (0.0611 ± 0.0055 mm) were found in Group II. On the other hand, Group I showed the least deviations of the positions of the canines (0.0287 ± 0.0054 mm) and molars (0.0354 ± 0.005 mm). CONCLUSIONS: The most accurate tooth positions are obtained in monolithic printed complete dentures. Fewer deviations in tooth positions occur when denture teeth are designed as a single piece.

Evaluation of the Accuracy and Adaptation of BioHPP Removable Partial Denture Frameworks Constructed by Milling vs the Pressing Technique.

PURPOSE: To evaluate the accuracy and adaptation of BioHPP removable partial denture frameworks constructed from milling vs the pressing technique. MATERIALS AND METHODS: This in vitro study was applied on an educational maxillary stone model with bilateral bounded saddles. Two different manufacturing techniques were used, and thus two groups were defined: (1) the pressed group, in which 20 BioHPP frameworks were constructed by milling a castable resin that was pressed into BioHPP using the lost wax technique; and (2) the milled group, in which 20 BioHPP frameworks were constructed directly by milling the BioHPP blanks. The accuracy of the frameworks was evaluated using Geomagic Control X software, and the gap distance was captured using a stereomicroscope. RESULTS: The milled group showed higher values of accuracy than the pressed group in the x, y, and z axes, and according to Student t test, this difference was statistically significant in the x and z axes. Regarding the adaptation of the frameworks, the milled group showed lower adaptation values than the pressed group. Student t test showed that this difference was statistically significant regarding adaptation of the major connector. However, there was no statistically significant difference concerning adaptation of the denture bases between the two groups. CONCLUSION: Within the limitations of this study, it could be concluded that: (1) the milling technique could be used to fabricate BioHPP RPD frameworks with higher accuracy than the pressing technique; and (2) the pressing technique showed less gap distance (ie, better adaptation) at the area of the major connector.

Evaluation of accuracy and position of milled and printed teeth in digital complete dentures.

PURPOSE: To compare the accuracy of milled vs printed complete denture bases and teeth and to assess the position of the teeth on the corresponding denture bases. MATERIALS AND METHODS: Two different manufacturing techniques were used in this study. In group A, 10 complete dentures were digitally designed and fabricated by milling prepolymerized blocks of polymethyl methacrylate. In group B, 10 complete dentures were digitally designed and fabricated using the 3D printing technique. The accuracy of the maxillary and mandibular denture bases and teeth and the position of the teeth on the corresponding denture bases were evaluated using Geomagic Control X software. Data were presented as mean and SD values. Statistical analysis of the resultant data was performed using Student t test. The significance level was set at P ≤ .05. RESULTS: The results revealed lower surface deviations of the maxillary and mandibular milled denture bases (group A) with values of 0.158 ± 0.024 and 0.117 ± 0.022, respectively. Lower surface deviations of the printed teeth (group B) were found with values of 0.18 ± 0.016 for the maxillary teeth and 0.153 ± 0.02 for the mandibular teeth, and for position of teeth on the corresponding denture bases, the values were 0.4 ± 0.08 for the maxillary teeth and 1.003 ± 0.027 for the position of the mandibular teeth. CONCLUSION: The milling technique yields complete denture bases with superior accuracy, while printing technology provides denture teeth with better accuracy and positioning on the corresponding denture bases.

Subtractive versus additive indirect manufacturing techniques of digitally designed partial dentures.

PURPOSE: The purpose of this in vitro study was to evaluate the accuracy of digitally designed removable partial denture (RPD) frameworks, constructed by additive and subtractive methods castable resin patterns, using comparative 3D analysis. MATERIALS AND METHODS: A Kennedy class III mod. 1 educational maxillary model was used in this study. The cast was scanned after modification, and a removable partial denture framework was digitally designed. Twelve frameworks were constructed. Two groups were defined: Group A: six frameworks were milled with castable resin, then casted by the lost wax technique into Co-Cr frameworks; Group B: six frameworks were printed with castable resin, then casted by the lost wax technique into Co-Cr frameworks. Comparative 3D analysis was used to measure the accuracy of the fabricated frameworks using Geomagic Control X software. Student's t-test was used for comparing data. P value ≤ .05 was considered statistically significant. RESULTS: Regarding the accuracy of the occlusal rests, group A (milled) (0.1417 ± 0.0224) showed significantly higher accuracy than group B (printed) (0.02347 ± 0.0221). The same results were found regarding the 3D comparison of the overall accuracy, in which group A (0.1501 ± 0.0205) was significantly more accurate than group B (0.179 ± 0.0137). CONCLUSION: In indirect fabrication techniques, subtractive manufacturing yields more accurate RPDs than additive manufacturing.