Top-down design and fabrication with digital technology of removable partial dentures incorporating custom abutments: A dental technique.

A novel design of removable partial dentures (RPDs) is described wherein custom abutments are incorporated into the RPD framework. The artificial teeth and custom abutments are designed by using a computer-aided design (CAD) software program. Subsequently, the RPD framework is designed and merged to the custom abutments in the CAD software program to form a single unit. This modified framework is additively manufactured in metal by using a 3D printer. Thereafter, the framework is adapted to the definitive cast and scanned by using a laboratory scanner. The scanned file is imported into the CAD software program, and the artificial teeth are redesigned. After fabricating each artificial tooth from a polymethylmethacrylate disk and artificial tooth and denture-base assemblies from a wax disk, the RPD is injection molded. This RPD design and fabrication workflow enables a top-down approach by prioritizing the shape and arrangement of the artificial teeth and facilitates their replacement.

Comparative assessment of marginal and internal gaps of cast-free monolithic zirconia crowns fabricated from 2 intraoral scanners: A prospective, double-blind, randomized clinical trial.

STATEMENT OF PROBLEM: Despite the introduction of intraoral scanners (IOSs) with dual camera triangulation, only a few comparative clinical studies have evaluated their clinical performances in the digital workflow for cast-free restorations. PURPOSE: The purpose of this clinical trial was to assess the clinical efficacy of 2 different technology-based IOSs by evaluating the marginal and internal gaps of cast-free monolithic zirconia crowns fabricated by using a fully digital workflow. MATERIAL AND METHODS: A prospective randomized clinical trial was conducted in 35 participants requiring a single-unit restoration. One crown was fabricated from the scan data obtained with a confocal microscopy-based IOS (Group T), while the other was made with the scan data obtained from an IOS using dual camera triangulation (Group I). A replica technique was used to assess the marginal and internal gaps. The buccolingual and mesiodistal cross-sections were measured, and noninferiority trials were performed. RESULTS: A total of 39 teeth from 35 participants were restored with a single-unit crown. The marginal and axial wall gaps of the crowns in Group I was not inferior to that of the crowns in Group T (upper limit confidence interval [CI] <30). In contrast, the gap of the crowns at the line angle in Group T was inferior to that of the crowns in Group I (lower limit CI <-30). From an occlusal space perspective, the gap of the crowns in Group I was inferior to that of the crowns in Group T (upper limit CI >30). Twenty-five crowns were selected from Group I, and 14 crowns were selected from Group T for definitive placement. CONCLUSIONS: The marginal gap of the crown fabricated by using the scan data obtained from the dual camera triangulation-based IOS was noninferior to that obtained from the confocal microscopy-based IOS and was within the clinically applicable limit.

Comparison of tissue displacement in edentulous arches among three-dimensional files obtained through different impression-making methods: A retrospective study.

PURPOSE: To retrospectively compare and analyze differences in tissue displacement of edentulous arches among three-dimensional (3D) files obtained using various impression-making techniques. MATERIALS AND METHODS: Fourteen patients who underwent prosthodontic treatment for edentulous arches at Yonsei University Dental Hospital between June 2020 and April 2023 were included in the study. Three types of 3D files were used for the evaluation of each arch: a 3D scan file of a definitive cast (Group DEF), a preliminary cast (Group PRE), and an intraoral scan file (Group IOS). The files were superimposed on a reference 3D scan file of the definitive cast group through best-fit matching using metrology software. Seventeen measurement points (MP1-4, RC1-6, TB1-2, and PPS1-5 for the maxilla and RP1-2, RC1-7, BS1-4, and LS1-4 for the mandible) were selected for both the maxillary (n = 13) and mandibular arches (n = 6). The deviation considering the direction (DD) between the three groups and the absolute deviation (AD) between the three groups were recorded. Kruskal-Wallis and post-hoc Mann-Whitney tests were used for statistical analyses (α = 0.05 and α = 0.0167, respectively). RESULTS: Concerning the DD values, at the RC4 point of the maxillary arch, Group PRE exhibited significantly higher values than Groups IOS (p = 0.006) and DEF (p < 0.001), and at the RC5 point of the maxillary arch, Group IOS exhibited significantly lower values than Groups PRE (p = 0.016) and DEF (p < 0.001). Group IOS showed significantly lower DD values in the mandibular arch than Group DEF at the RP2 and RC3 points (p < 0.167). The AD values in Groups PRE and IOS significantly differed from those in Group DEF (all p < 0.001) at all measurement points but did not exhibit significant differences between each other (p > 0.05). CONCLUSIONS: Different impression-making methods yielded different amounts of tissue displacement. The tendency of 3D files regarding tissue displacement varied at certain residual ridge crest areas and retromolar pad areas. The absolute amount of tissue displacement observed in the intraoral scan data was comparable to that observed in the preliminary casts.

Lack of keratinized mucosa increases peri-implantitis risk.

DESIGN: A systematic appraisal and statistical aggregation of primary studies in humans. DATA SOURCES: The researchers utilized PubMed (Medline) and Scopus databases as the primary data sources for this study. They performed a comprehensive literature search based on free keywords and Medical Subject Heading (MeSH) terms to enhance the search accuracy. The database search was concluded on November 13, 2022. Furthermore, a meticulous examination of the references cited in the selected studies was conducted to identify additional relevant articles that could be incorporated into the analysis. STUDY SELECTION: The systematic review focused on partially or fully edentulous patients receiving dental implants and aimed to determine if the lack of keratinized mucosa at the implant site increased the risk of peri-implantitis compared to patients with adequate keratinized mucosa. Human studies with a minimum of 100 implants, cross-sectional, cohort, or case-control designs, and a follow-up period of at least one year were included. Studies lacking a clear case definition or information on peri-implantitis and those that did not investigate keratinized mucosa as a risk indicator were excluded. DATA EXTRACTION AND SYNTHESIS: Two reviewers independently utilized a systematic review screening website (Rayyan, Qatar Computing Research Institute, Qatar Foundation) to select potential articles, and conflicts were resolved through discussion or consultation with a third reviewer. The data extraction process involved recording information from the included articles, such as study design, patient and implant numbers, prosthesis type (fixed or removable), follow-up duration, peri-implantitis case definition, prevalence at patient and implant levels, keratinized mucosa cutoff value, odds ratio (OR) of peri-implantitis considering keratinized mucosa, and conclusions on the potential effect of keratinized mucosa from each study. The Newcastle Ottawa scale (NOS) and a modified version of NOS were used, respectively, to assess the quality of cohort and cross-sectional studies. Studies scoring below 6 out of 9 points were classified as low quality. For the meta-analysis, the relationship between peri-implantitis and keratinized mucosa was evaluated using the odds ratio (OR) and standard error (SE). Heterogeneity was assessed through the Chi2 test and I2 index, determining whether a random-effects or fixed-effects model should be applied. Subgroup and cluster analyses were conducted based on specific criteria, and forest plots and funnel plots were generated to visualize results and identify potential study bias. Sensitivity analysis was performed to verify the robustness of the meta-analysis, with statistical significance set at p < 0.05. The Review Manager (RevMan) software facilitated data analysis. The GRADE rating system was used to determine the level of evidence, considering factors such as bias risk, imprecision, inconsistency, indirectness, and publication bias. The certainty of the evidence was evaluated based on the overall outcomes of analyzed subgroups. RESULTS: Twenty-two primary studies were identified, and a meta-analysis was conducted on 16 cross-sectional studies. The prevalence of peri-implantitis ranged from 6.68% to 62.3% at the patient level and from 4.5% to 58.1% at the implant level. The overall analysis revealed a significant association between the lack of keratinized mucosa and a higher prevalence of peri-implantitis (OR = 2.78, 95% CI 2.07-3.74, p < 0.00001). Subgroup analyses with a consistent case definition of peri-implantitis (MBL ≥ 2 mm) showed similar results (OR = 1.96, 95% CI 1.41-2.73, p < 0.0001). Studies focusing on fixed prostheses only demonstrated that the lack of keratinized mucosa was associated with an increased prevalence of peri-implantitis (OR = 2.82, 95% CI 1.85-4.28, p < 0.00001). Among patients under regular implant maintenance, the absence of keratinized mucosa significantly raised the occurrence of peri-implantitis (OR = 2.08, 95% CI 1.41-3.08, p = 0.0002). Studies adjusting for other variables also confirmed a higher risk of peri-implantitis with inadequate keratinized mucosa (OR = 3.68, 95% CI 2.32-5.82, p = 0.007). Although some publication bias was observed, the certainty of evidence based on the GRADE system was judged to be "moderate." CONCLUSIONS: The lack of keratinized mucosa increased the risk of peri-implantitis, emphasizing the need to consider it during dental implant placement. Inadequate data on patient-specific factors and the predominance of cross-sectional studies influenced the evidence quality (i.e., moderate). Future studies with consistent methodologies shall confirm these findings and identify additional risk indicators to improve implant dentistry practices.

Comparative evaluation of digitally fabricated complete dentures versus conventional complete dentures: A randomized, single-blinded, cross-over clinical trial.

STATEMENT OF PROBLEM: Clinical trials comparing outcomes associated with digital complete dentures (CDs) fabricated from intraoral scan data with those of CDs fabricated by using the conventional workflow are lacking. PURPOSE: The purpose of this randomized clinical trial was to evaluate the clinical performance of and patient satisfaction associated with digitally versus conventionally fabricated CDs. MATERIAL AND METHODS: Eight participants requiring CDs were enrolled in this study. Two sets of CDs were fabricated for each participant. One set was fabricated by using a digital workflow, which involved digital scanning with an intraoral scanner, whereas the other set was made by using the conventional workflow. The participants were given 1 set of CDs for 1 month and another set for the next month. The order of placing CDs was randomly selected for each participant. The internal adaptation, masticatory force, and masticatory efficiency of the CDs in each group were evaluated for objective analysis. Additionally, a questionnaire was provided to the participants, and the responses were evaluated for subjective satisfaction analysis. All parameters were analyzed by using t tests (α=.05). RESULTS: The internal adaptation did not statistically significantly differ between the conventional and digital CDs with regard to the maxillary arches (P=.406) and mandibular arches (P=.412). The average masticatory force (P=.051) and maximum masticatory force (P=.110) likewise did not statistically significantly differ between the 2 types of CDs. Masticatory efficiency, expressed via the mixing ability index, was statistically better for conventional CDs than the digital CDs (P=.009). No statistically significant differences were observed between the 2 types of CDs in terms of overall patient satisfaction as assessed by using the study questionnaire (P=.172 for maxillary CD and P=.161 for mandibular CD). However, the conventional CDs were statistically significantly better than the digital CDs with regard to subjective satisfaction with pronunciation ability (P=.006). CONCLUSIONS: The digital CDs were inferior to the conventional CDs in terms of masticatory efficiency and pronunciation. However, internal adaptation and overall patient satisfaction were comparable between conventional and digital CDs. This finding suggests that intraoral scanning and additively manufactured CDs may be suitable for edentulous patients, at least for interim use.

Accuracy of impression-making methods in edentulous arches: An in vitro study encompassing conventional and digital methods.

STATEMENT OF PROBLEM: Studies evaluating the accuracy of edentulous arch impressions encompassing conventional and digital methods are lacking. PURPOSE: The purpose of this in vitro study was to evaluate 8 impression-making methods for edentulous arches and to determine the effects of using a 3-dimensionally printed polyetheretherketone (PEEK) scanning aid on the accuracy of intraoral scanners. MATERIAL AND METHODS: Three sets of edentulous arch typodonts were scanned with an industrial scanner as a reference. Subsequently, a scanning aid for the edentulous arch was individually designed on each reference scan dataset by using a 3-dimensional modeling software program and fabricated in PEEK with a 3-dimensional printer. Each typodont was scanned with 2 intraoral scanners 12 times, with and without the assistance of a scanning aid for the edentulous arch. Impressions were made with 4 different conventional impression materials (irreversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane)-12 times for each typodont-the casts were poured and digitized with a tabletop scanner. Each scan data set was superimposed over the corresponding scan data set, and the original and absolute distance values from the paired surface points were obtained to measure the trueness and precision. These were expressed by using the mean, median, root mean square, and (90 percentile-10 percentile)/2 of the absolute distance value (NMT) concepts, based on the raw data extraction protocol. A repeated-measures ANOVA followed by a post hoc Bonferroni test was conducted (α=.05). RESULTS: The impression-making methods did not show statistically significant differences (P>.05) for either trueness or precision, particularly when the median values of the original and absolute distance values from the paired surface points were chosen as the standard values. One of the intraoral scanners used exhibited significantly superior outcomes to conventional impression materials when scanned with the scanning aid for the edentulous arch for both trueness and precision when the mean, root mean square, and NMT concepts were applied (P<.05). CONCLUSIONS: Intraoral scanners demonstrated accuracy comparable with that of conventional impression materials for making edentulous arch impressions, regardless of the concepts used to express the trueness and precision. The PEEK-based scanning aid for the edentulous arch did not improve the accuracy of the intraoral scanners; however, its application resulted in higher accuracy compared with that of conventional impression materials.

A Comparative Study of the Accuracy of Dental CAD Programs in Designing a Fixed Partial Denture.

PURPOSE: Error testing at each stage of prosthetic manufacturing remains relatively underdeveloped for computer-aided design/computer-aided manufacturing methods, and no experimental studies have validated the computer-aided design programs. This study aimed to test the accuracy and trueness of the computer-aided design of a three-unit fixed prosthesis. MATERIALS AND METHODS: Three computer-aided design programs (Exocad, Dental System™, and inLab 16) were tested on the designs of a three-unit fixed partial denture, and a three-dimensional analysis program was used to calculate the internal clearance error for the computer-aided design prostheses. The Kruskal-Wallis and Dunn's post hoc tests were used to reveal significant differences in trueness between the three computer-aided design programs (α < 0.05). RESULTS: Dental System™ showed the lowest mean error values for #24 and #26 at the mesial margin (both 0 µm), mesial wall (0.10, 0.12 µm, respectively), occlusal surface (-0.05, 0.10 µm), distal wall (0.23, -0.02 µm), and distal margin (both 0 µm). In sum, except for the mesial margin and distal margin site of tooth #26, the mean error value of Dental System™ was statistically the lowest, followed by those of Exocad and inLab 16 (p < 0.003). CONCLUSIONS: The accuracy of computer-aided design differed according to the type of computer-aided design program. Dental System™ achieved the best trueness at the margins, axial walls, and occlusal surface, followed by Exocad and inLab 16.

Fabrication of a removable partial denture combining conventional and digital techniques.

This article describes a combined conventional and digital workflow for fabricating removable partial dentures (RPDs). After scanning the dental cast and RPD framework assembly, artificial teeth and denture base regions were designed using computer-aided design software. The artificial teeth and denture base assembly was milled as a single structure by using a wax disk and then placed on the RPD framework. The artificial teeth were additionally milled from a polymethyl methacrylate disk. Conventional procedures were followed for denture investment until the wax elimination procedure, after which the assembly was replaced with the artificial teeth in the cope of the flasks, and the denture resin material was injected to process the RPD. This technique enabled the RPD to be fabricated in the same form as the design state.

Influence of shoulder coverage difference of abutment on stress distribution and screw stability in tissue-level internal connection implants: A finite element analysis and in vitro study.

STATEMENT OF PROBLEM: Tissue-level internal connection implants are widely used, but the difference in abutment screw stability because of the shoulder coverage formed by the contact between the shoulder of the implant collar and the abutment remains unclear. PURPOSE: The purpose of this finite element analysis (FEA) and in vitro study was to investigate stress distribution and abutment screw stability as per the difference in shoulder coverage of the abutment in tissue-level internal connection implants. MATERIAL AND METHODS: Abutments were designed in 3 groups as per the shoulder coverage of the implant collar, yielding complete coverage (complete group), half coverage (half group), no coverage (no group) groups. In the FEA, a tightening torque of 30.0 Ncm was applied to the abutment screw, a force of 250 N was applied to the crown at a 30-degree angle, and the von Mises stresses and the stress distribution patterns were evaluated. In the in vitro study, the groups were tested (n=12). A total of 200 000 cyclic loads were applied at 250 N, 14 Hz, and at a 30-degree angle. Removal torque values and scanning electron microscopy (SEM) images were assessed. Removal torque values were analyzed by ANOVA and paired t tests. RESULTS: The maximum von Mises stress of the abutment screw was the lowest in the complete group, slightly higher in the half group, and highest in the no group. High stresses were concentrated in 1 location in the implant abutment connection area of the no group. The removal torque values after loading were significantly lower in the no group than in the complete group (P=.047). The SEM images revealed concentrated structural loss and wear in 1 location of the no group. CONCLUSIONS: FEA and in vitro studies confirmed that the shoulder coverage of the abutment in the tissue-level internal connection implant helped improve screw stability. Cyclic loading reduced the removal torque of the abutment screw.

Denture-reversing technique for assessing the soft tissue dimensional changes according to artificial tooth position in completely edentulous patients.

A digital workflow to assess the soft tissue dimensional changes in completely edentulous patients is described. Diagnostic casts obtained at 2 time points and the complete denture were scanned by using a desktop scanner. The denture scan was inverted by using a metrology software program to obtain the soft tissue contour. Using this reversed file as a reference, the file and 2 scan files obtained at different time points were aligned individually with the best fit alignment function. The scanned denture file and the 2 realigned scan files were imported into the same software. A plane vertical to the occlusal plane was determined such that it moved anteroposteriorly. The distance between the contours of the 2 realigned files was measured by selecting a point and a vector based on the artificial tooth positions of the denture. This technique of using a reversed denture file may provide a quantitative evaluation of soft tissue changes and further aid in determining appropriate intervals for denture relining or rebasing.

Tissue surface adaptation of CAD-CAM maxillary and mandibular complete denture bases manufactured by digital light processing: A clinical study.

STATEMENT OF PROBLEM: Clinical studies evaluating the tissue surface adaptation of complete denture bases fabricated by digital light processing (DLP) are lacking. PURPOSE: The purpose of this clinical study was to assess the tissue surface adaptation of complete denture bases generated by the DLP technique and to compare the adaptation with that of denture bases manufactured by 5-axis milling (MIL) and pack-and-press (PAP) method. MATERIAL AND METHODS: A total of 9 participants with 12 edentulous arches (7 maxillary and 5 mandibular) were included in this study. For each edentulous arch, the complete denture bases with occlusion rims were prepared by 3 different techniques (PAP, MIL, and DLP). A virtual denture base with occlusion rim was designed by means of a digital subtraction tool and served to fabricate the DLP and MIL denture bases. The complete denture bases were placed intraorally with an indicator applied to the intaglio surfaces. The thickness of the indicator was measured within the denture-bearing areas and anatomic landmarks of the edentulous arch to obtain the absolute tissue surface adaptation (ATA) value. The relative tissue surface adaptation (RTA) value was calculated from the differences between the ATA values of DLP or MIL techniques and those of the PAP technique. The Kruskal-Wallis test and the McNemar test were used for statistical analysis (α=.05). RESULTS: No statistically significant differences were found among the 3 denture base fabrication techniques with respect to the ATA values of either arch (P>.05). In terms of the RTA values for the maxillary arch, the DLP base was significantly different from the MIL base in the RC and P areas (both P<.05). The DLP base exhibited a higher frequency of negative RTA values than the MIL base. Regarding the RTA values for the mandibular arch, no significant differences were detected between the DLP and MIL denture bases (P>.05). CONCLUSIONS: The DLP and MIL denture bases demonstrated clinically acceptable tissue surface adaptation to both edentulous the maxilla and mandible. The DLP denture base was likely to exhibit intimate tissue adaptation in the stress-bearing areas of maxillary arches compared with the PAP denture base. The maxillary MIL denture base was likely to exhibit small gaps between the supporting tissue and denture base. Both DLP and MIL mandibular denture bases were likely to show intimate adaptation on the lingual slope compared with the PAP base.

Effects of Scanning Strategy and Scanner Type on the Accuracy of Intraoral Scans: A New Approach for Assessing the Accuracy of Scanned Data.

PURPOSE: This study aimed to determine the most reliable scanning strategy and scanner type, using a new protocol for assessing the accuracy (trueness and precision) of intraoral scan data. MATERIALS AND METHODS: Five different maxillary and mandibular typodont pairs (n = 10) and 2 intraoral scanners were used for the study. A reference scan for each arch was obtained with an industrial scanner. Scanning strategies were classified into 2 continuous methods-continuous scan in horizontal direction (CH group) and continuous scan with vertical rotation in anterior region (CV group)-and 1 segmental method (S group). In the CH group, the scanner head was maintained mostly in a horizontal position. In the CV group, the scanners were rotated 180° around the anterior tooth region to allow smooth scanning through the area. The intraoral scan data were individually superimposed over their corresponding reference scan data. Raw data of the distances between paired surface points were extracted from the superimposed pairs of datasets, with (original distance values) or without consideration (absolute distance values) of the value signs. Trueness values were calculated using absolute distance values, while precision values were obtained from original distance values. Data were analyzed with a 2-way repeated-measures analysis of variance using α = 0.05 as the level of significance. RESULTS: The CV group produced significantly inferior outcomes compared to the CH and S groups in terms of trueness (p < 0.001, F = 24.67), whereas no significant differences were observed among the 3 scanning strategies with respect to precision (p = 0.451, F = 0.83). Scanner type did not produce significant differences in terms of either trueness (p = 0.058, F = 4.72) or precision (p = 0.742, F = 0.12). CONCLUSIONS: The segmental approach for scanning the region of interest first and continuous scanning with the scanner head held mostly in a horizontal position are both acceptable as full-arch scanning strategies. However, vertical rotation of intraoral scanners should be minimized.

Digital workflow to provide an immediate interim restoration after single-implant placement by using a surgical guide and a matrix-positioning device.

This article describes a workflow based on a top-down approach to provide a fixed-type immediate interim restoration after placing a single implant using a digitally driven surgical guide and a matrix-positioning device. A characteristic of the technique is that both the surgical guide and the matrix-positioning device are fabricated from a single diagnostic virtual trial restoration designed on computer-aided design (CAD) software. This workflow may shorten the time required for chairside placement of an interim restoration and enhance esthetics when rehabilitating anterior teeth.

Integration of intraoral digital scans with a 3D facial scan for anterior tooth rehabilitation.

This article describes a digital technique that combines intraoral digital scans with a 3-dimensional facial scan to predict the outcome of prosthodontic treatment of anterior teeth at the treatment planning phase. This approach may increase patient acceptance of the definitive treatment, as the altered facial appearance is visualized with definitive prosthodontic restorations, thereby improving communication before treatment begins.

Accuracy of Three Digitization Methods for the Dental Arch with Various Tooth Preparation Designs: An In Vitro Study.

PURPOSE: To evaluate the accuracy of three digitization methods for the maxillary dental arch. MATERIALS AND METHODS: A maxillary typodont with various tooth preparation designs was used as the reference model. The scanned data were classified into direct scanning (DS), cast scanning (CS), and impression scanning (IS) groups according to the techniques applied for digitization (n = 10/group). An intraoral scanner was used for the DS group. Impressions obtained with polyether impression material were scanned with a tabletop scanner for the IS group. For the CS group, the definitive casts fabricated from the obtained impressions were scanned with the same tabletop scanner. The accuracy (trueness and precision) of the produced virtual dental casts was evaluated with specialized software. The full-arch and individual abutment deviations were measured with regard to root mean square error (RMSE) values. Data were analyzed with statistical software with an α = 0 . 05 . RESULTS: The RMSE values for both trueness and precision were lowest in the IS group, followed by the CS and DS groups, with statistically significant differences among the groups (p < 0.05). The trueness of individual abutments was significantly higher in the IS group than in the DS group. In addition, the trueness of individual abutments was affected by the location of the abutments in the DS group, whereas it did not differ between individual abutments in the CS and IS groups. CONCLUSIONS: These findings suggest that the IS method is an accurate digitization technique for the creation of a virtual dental cast.

Evaluation of the fit of zirconia copings fabricated by direct and indirect digital scanning procedures.

STATEMENT OF PROBLEM: Intraoral scanners are effective for direct digital scans when dental restorations are fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM); however, if the abutment tooth cannot be dried completely or the prepared margin is placed subgingivally, accurate digital images cannot always be guaranteed. PURPOSE: The purpose of this in vitro study was to compare the internal and marginal discrepancies of zirconia copings fabricated directly using an intraoral scanner with those fabricated indirectly with impression scanning. MATERIAL AND METHODS: Forty-five resin dies fabricated with a 3-dimensional (3D) printer were divided into 3 groups: direct scanning (DS), impression scanning (IMP), and lost-wax casting (LW). For the DS group, a resin die was scanned with an intraoral scanner (Trios; 3Shape), whereas for the IMP group, impressions made with polyether were scanned with a cast scanner (D700; 3Shape). The zirconia copings were fabricated in the same way in the DS and IMP groups. For the LW group, impressions were made in the same way as in the IMP group, and Ni-Cr alloy copings were fabricated using LW. The marginal and internal discrepancies of the copings were measured by cementing them onto resin dies, embedding them in acrylic resin, and sectioning them in a buccolingual direction. The cement layer was measured, and the Kruskal-Wallis test was used to detect significant differences (α=.05). A nonparametric Friedman test was also performed to compare the measurements of each group by location (α=.05). RESULTS: The mean marginal discrepancies in the DS, IMP, and LW groups were 18.1 ±9.8, 23.2 ±17.2, and 32.3 ±18.6 µm (mean ±standard deviation), respectively. The mean internal discrepancies of the DS, IMP, and LW groups in the axial area were 38.0 ±9.1, 47.0 ±16.3, and 36.5 ±15.8 µm, and those in the occlusal area were 36.7 ±16.9, 33.4 ±21.6, and 44.5 ±31.9 µm, respectively. No statistically significant differences were found in marginal or internal discrepancies among groups (P>.05). CONCLUSIONS: Within the limitations of this study, the zirconia copings fabricated with CAD-CAM using different digitization methods and Ni-Cr copings fabricated using the lost-wax technique and casting produced clinically acceptable marginal and internal discrepancies. No significant differences were found among the DS, IMP, and LW groups.

Treatment of a mandibular discontinuity defect by using a fibula free flap and an implant-supported fixed complete denture fabricated with a PEKK framework: A clinical report.

This clinical report describes the rehabilitation of a patient with a history of mandibulectomy that involved the use of a fibula free flap and an implant-supported fixed complete denture. A recently introduced material, polyetherketoneketone (PEKK), was used as the framework material for the prosthesis, and the treatment produced favorable esthetic and functional results.

Effects of Alendronate on Bone Remodeling Around Osseointegrated Implants in Rats.

OBJECTIVE: To determine the effects of alendronate on bone remodeling around osseointegrated implants in rats. MATERIALS AND METHODS: The maxillary first molars were extracted from 36 male Sprague-Dawley rats, and replaced with customized implants. They were then administered twice-weekly subcutaneous injections of either alendronate (alendronate group) or saline (control group) after allowing a 4-week period for osseointegration. They were killed at 4, 8, or 12 weeks after the commencement of the injection protocol, and the implant sites were evaluated comprehensively by microcomputed tomographic, histologic, and biochemical assessments. RESULTS: It was hard to find statistically significant differences from microcomputed tomographic analyses. In addition, inconsistent variations were derived from histologic data. However, biochemical data showed statistically significant differences; serum osteocalcin level was statistically significantly lower in the alendronate group than in the control group at 8 weeks after the commencement of injections. In addition, serum osteocalcin level in the alendronate group was statistically significantly lower at 8 and 12 weeks after the initial injection point than at preinjection. CONCLUSIONS: The results suggest alendronate might affect bone remodeling activity around osseointegrated implants negatively, and serum osteocalcin could serve as an accessory tool to evaluate this effect.

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.