The Accuracy of Post and Core Fabricated with Digital Technology.

PURPOSE: To compare the accuracy of post and cores created with three different fabricating techniques: direct conventional, machine milling, and three-dimensional (3D) printing. MATERIALS AND METHODS: Thirteen extracted single root central incisors were selected. Root canal treatment and tooth preparation for crown were performed on all teeth. Post space preparation of 11 mm was created using prefabricated fiber post drill to standardize post space width and length. Root canal impressions were performed on all teeth using polyvinyl siloxane impression material. Each impression was then three dimensionally scanned using an extraoral lab scanner. The scanned impressions were used to design digital files of post and cores with 3Shape CAD software. The digitally designed post and cores were used to fabricate 3D printed and milled post and core resin patterns. The same teeth were used to fabricate post and core with conventional technique (direct duplication of root canal with resin pattern). All posts were then scanned before being invested and then cast using base metal educational alloy. The metal post and cores were tried in with sample teeth and manually adjusted until found to be clinically acceptable. The post and cores were scanned in different stages to perform digital volume measurement using Geomagic Control software to determine accuracy. Pairwise comparisons were accomplished using exact version of the sign test (α = 0.05). RESULTS: These three techniques of post and core fabrication showed different results in the various stages of fabrication. The accuracy of 3D printed resin pattern (26.89 ±11.09 mm3 ) was found to be inferior compare to milled resin pattern (28.20 ±11.41 mm3 , p = 0.0002). However, dimensional stability of the 3D printed resin pattern before and after casting (0.56 ±0.95 mm3 ) was found to be superior to milled resin pattern (0.79 ±0.89 mm3 ) and direct resin pattern (2.51 ±1.38 mm3 , p = 0.00002). All three techniques showed significant volume reduction after adjustment (p = 0.0002). In the final stage, the adjusted metal post and core fabricated with three different techniques showed no statistical different in accuracy (p = 0.15). CONCLUSION: Digitally fabricated post and cores have the same degree of accuracy as those fabricated using the gold standard direct conventional post and core technique.

Teaching the Design and Fabrication of RPD Frameworks With a Digital Workflow: A Preclinical Dental Exercise.

Introduction: The conventional method for teaching removable partial denture (RPD) design using a pencil drawing on a solid cast has always been the basis for teaching RPD design in most dental schools at both the undergraduate and graduate levels. This does not apply to RPD fabrication technology, as more laboratories have recently adopted more efficient and versatile digital techniques to design and fabricate RPD frameworks. Methods: At the University of Iowa College of Dentistry, we created a pilot workshop to assess the efficiency of a new approach to teaching RPD design utilizing this new digital RPD technology as a teaching tool for graduate prosthodontics residents. Three first-year prosthodontics residents were enrolled in the workshop, which involved learning the new digital workflow of designing RPD. Results: This new teaching approach very successfully achieved its educational goals. The residents reported that the digital RPD teaching approach enriched their knowledge and deepened their understanding of RPD design. Discussion: The technique garnered significant interest from the students and seemed to also increase their understanding of the steps involved in RPD fabrication as well as the different components of the RPD.

Comparison of the Accuracy of Implant Position Using Surgical Guides Fabricated by Additive and Subtractive Techniques.

PURPOSE: To evaluate the accuracy of implant position using surgical guides fabricated by additive and subtractive techniques. MATERIALS AND METHODS: A partially edentulous standardized mandibular implant model with different bone densities and soft tissue was duplicated and a diagnostic wax-up was performed for the #30 area. A reference radiographic guide was fabricated and cone beam computed tomography (CBCT) was made with the reference radiographic guide in place. A surgical guide was designed using BlueSky Plan 4 software and a reference implant was placed in the #30 region. The STL file of the surgical guide was exported and specimens (n = 15) were fabricated by two different techniques: additive (3D printing) and subtractive (milling). The standardized mandibular model was surface-scanned and duplicated with printed dental model resin (n = 30). Each surgical guide was used to place an implant in thirty duplicate printed models. Differences in implant position as compared to the reference were measured from digital scans with scan bodies in place. The angular deviations, differences in depth, coronal and apical deviations were measured using GeoMagic Control X software. Results were analyzed by Wilcoxon-Mann-Whitney test and PERMANOVA (Permutational Multivariate Analysis of Variance). Intraclass correlation was used to assess measurement reproducibility with Bonferroni adjustment for multiple testing as needed (α = 0.05). RESULTS: There were no significant differences in accuracy of implant placement using guides fabricated using additive vs subtractive techniques. The mean angular deviations between the reference and actual position of implant in mesio-distal cross-section were 0.780 ± 0.80° for printed group and 0.77 ± 0.72° for the milled group. The differences in bucco-lingual cross-section were 1.60 ± 1.22° in in printed group and 1.77 ± 0.76° in the milled group. The differences in depth (mm) were measured at the top of the scan body at four locations: mesial, distal, buccal and lingual. The mean differences in depth for the group that used printed surgical guides were (mesial) 0.37 ± 0.29 mm, (distal) 0.32 ± 0.23 mm, (buccal) 0.24 ± 0.23 mm, and (lingual) 0.25 ± 0.17 mm. The mean differences in depth for the group that used milled surgical guides were (mesial) 0.51 ± 0.33 mm, (distal) 0.40 ± 0.32 mm, (buccal) 0.22 ± 0.23 mm, and (lingual) 0.23 ± 0.12 mm in those four aspects, respectively. The mean coronal deviation showed 0.32 mm in the printed group and 0.27 mm in the milled group. For the apical deviation, the results of this study showed mean apical deviation 0.84 mm in the printed group and 0.80 mm in the milled group. CONCLUSIONS: Results indicate that 3D-printed surgical guides are statistically as accurate as milled guides for guided-implant surgery with the benefits of high accuracy, ease of fabrication, less waste compared to subtractive techniques, and reduction of laboratory time thereby increasing cost-effectiveness.

The Use of CAD/CAM Technology for Fabricating Cast Gold Survey Crowns under Existing Partial Removable Dental Prosthesis. A Clinical Report.

The fabrication of a survey crown under an existing partial removable dental prosthesis (PRDP) has always been a challenge to many dental practitioners. This clinical report presents a technique for fabricating accurate cast gold survey crowns to fit existing PRDPs using CAD/CAM technology. The report describes a technique that would digitally scan the coronal anatomy of a cast gold survey crown and an abutment tooth under existing PRDPs planned for restoration, prior to any preparation. The information is stored in the digital software where all the coronal anatomical details are preserved without any modifications. The scanned designs are then applied to the scanned teeth preparations, sent to the milling machine and milled into full-contour clear acrylic resin burn-out patterns. The acrylic resin patterns are tried in the patient's mouth the same day to verify the full seating of the PRDP components. The patterns are then invested and cast into gold crowns and cemented in the conventional manner.

Integrating conventional and CAD/CAM digital techniques for establishing canine protected articulation: A clinical report.

Canine protected articulation is widely accepted for patients requiring extensive oral rehabilitation. Computer-aided design and computer-aided manufacturing (CAD/CAM) restorations have been primarily designed in occlusion at the maximum intercuspal position. Designing a virtual articulator that is capable of accepting excursive occlusal records and duplicating the mandibular movements is a challenge for CAD/CAM technology. Modifying tooth shape using composite resin trial restorations to produce esthetic results and later scanning the modified teeth to create milled crowns is becoming a popular use of the CAD/CAM technology. This report describes a technique that combines conventional and CAD/CAM prosthodontic techniques for milling crowns for canine teeth that are designed to establish or improve canine protected articulation. This technique involves designing and fabricating interim restorations based on diagnostic waxing, scanning the designs intraorally, and storing them in software as pretreatment digital records. The scanned designs are then applied to the digital representation of the prepared teeth to fabricate the definitive restorations.

A Single Visit Direct Technique to Provisionally Restore Occlusion for a Full-Mouth Rehabilitation: A Clinical Report.

Attrition of the dentition can negatively affect esthetics and function. When reconstructing patients with attrition who require restoration at increased occlusal vertical dimension (OVD), it is necessary to first evaluate the OVD using a removable interim prosthesis to ensure that the patient will tolerate the new position. The transition to fixed interim prostheses has to be carefully planned to achieve the desired OVD. One approach is to prepare all teeth in a single day and place full-arch interim prostheses; however, this can be tiring for the patient and prosthodontist. An alternative approach is to prepare one arch and place interim prostheses, while using composite resin in the opposing arch to maintain the newly established OVD. A diagnostic wax-up at the proposed OVD is completed and duplicated in stone. A vacuform matrix is loaded with composite resin and applied to the unprepared etched teeth of the opposing arch to restore form and occlusion until full contour interim prostheses are placed at a later visit.

Preclinical Course in Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) Digital Dentistry: Introduction, Technology and Systems Evaluation, and Exercise.

INTRODUCTION: Computer-aided design and computer-aided manufacturing (CAD/CAM) technology is an innovative digital system capable of scanning prepared teeth that are intended to receive crowns, bridges, and inlays and then effectively designing and fabricating restorations. Many dental schools are currently implementing this innovative CAD/CAM technology as part of their curricula and at University of Florida College of Dentistry we created a hands-on elective. METHODS: The 5-week course requires 2- to 3-hours of time per week for the lectures and labs. The sessions cover an introduction to digital dentistry, technology and systems evaluation, an exercise for scanning, designing, milling, and finishing a single unit ceramic restoration, and a final exam. The students also gave presentations about systems and materials used. The classroom exercises included small-group learning and class debate sessions. RESULTS: In 2015, two 5-week sessions included a total of 16 participants (8 each). The overall course satisfaction from the combined two rounds was 4.7 out of 5. Comments for the course have been generally positive, indicating that the course was a successful introduction to CAD/CAM technology. Students' comments showed that they were very impressed by the new technology and interested in implementing it in their practices. DISCUSSION: This exercise in the comparison between CAD/CAM and conventional technology resulted in a deeper understanding of digital dentistry systems and ensured that students were prepared in their clinical reasoning to apply their education in real-world decision making after graduation. By integrating this new technology in a core curriculum, preclinical, prosthodontic sophomore course and as a junior elective course, students were provided with the hands-on experience needed to utilize CAD/CAM effectively in patient care.

Impression Making and Lab Work Authorization Forms in Fixed Prosthodontics: A Preclinical Exercise.

INTRODUCTION: Making a final impression using a custom tray for fixed prosthodontics is a widely accepted procedure that is taught in many dental schools. As such, achieving competency in impression making and lab communication is a new Commission on Dental Accreditation curriculum requirement for all dental schools in the US. METHODS: This resource presents an instructional slide show on the clinical steps required in fabricating a custom tray using a visible light-cured resin, making a successful impression, and writing a work authorization form for the fabrication of a fixed dental prosthesis. The presentation also contains a brief overview of alternative techniques and materials used as well as basic points for self-evaluation for the custom tray and the final impression. This activity was conducted as a small-group team-based learning exercise in a preclinical setting, where a self-assessment form was provided for students to evaluate their work. RESULTS: Examiners indicated that students who completed this exercise had a deeper understanding of the sequencing of steps involved in the construction of a fixed partial denture as well as better lab communication skills compared to students from previous classes who did not participate in the exercise. DISCUSSION: The preclinical setting provided students with a relaxed atmosphere for fabricating a custom tray using visible light-curing material. This exercise is part of a larger preclinical exercise that takes students through all the steps involved in the fabrication of a fixed dental prosthesis, from impression making to the evaluation of the framework made by the lab.

A conservative approach to rebasing an implant-retained fixed complete denture.

After years of service, the acrylic resin base of an implant-retained fixed complete dental prosthesis may need to be replaced because of the wear of the acrylic resin teeth. The most common methods used by dental laboratories to remove the acrylic resin from the metal framework are either burning with a flame or grinding. Both of these methods risk exposing the dental laboratory technician to hazardous by-products and damaging or contaminating the metal framework or the gold cylinders. This article presents a safe approach to removing acrylic resin while preserving the integrity of the framework. The technique involves heating the prosthesis to beyond the glass transitional temperature of the acrylic resin to allow the resin to be safely peeled off the framework.