Effect of implant divergence on the accuracy of definitive casts created from traditional and digital implant-level impressions: an in vitro comparative study

PURPOSE

The purpose of this research was to compare the accuracy of definitive casts created with digital and conventional methods for implants with internal-octagon connections placed parallel or at different angles (15, 30, or 45 degrees).

MATERIALS AND METHODS

Four customized epoxy resin master casts were fabricated with two-implant analogs placed in the posterior mandible with different degrees of divergence. For the conventional (control) group, 10 traditional impressions were taken on each master cast with custom trays, open-tray impression copings, and polyvinyl siloxane; definitive stone casts were poured with type IV dental stone. For the digital group, 10 digital impressions were taken on each master cast with two-piece scannable impression copings and an intraoral digital scanner; definitive milled polyurethane casts were fabricated by the manufacturer. All four master casts and 80 control and test casts were scanned and digitized, and the data sets were compared. Any deviations in measurements between the definitive and corresponding master casts were analyzed statistically.

RESULTS

The amount of divergence between implants did not affect the accuracy of the stone casts created conventionally; however, it significantly affected the accuracy of the milled casts created digitally. A decreasing linear trend in deviations for both distance and angle measurements suggested that the digital technique was more accurate when the implants diverged more. At 0 and 15 degrees of divergence, the digital method resulted in highly significantly less accurate definitive casts. At 30 and 45 degrees of divergence, however, the milled casts showed either no difference or marginal differences with casts created conventionally.

CONCLUSION

The digital pathway produced less accurate definitive casts than the conventional pathway with the tested two-implant scenarios. To ensure passive fit of definitive prostheses, verification devices and casts may be used when materials are produced digitally.

Comparison of the marginal fit of lithium disilicate crowns fabricated with CAD/CAM technology by using conventional impressions and two intraoral digital scanners

STATEMENT OF PROBLEM

Conventional impression materials and techniques have been used successfully to fabricate fixed restorations. Recently, digital pathways have been developed, but insufficient data are available regarding their marginal accuracy.

PURPOSE

The purpose of this in vitro study was to compare the marginal gap discrepancy of lithium disilicate single crowns fabricated with computer-aided design and computer-aided manufacturing (CAD/CAM) technology by using both conventional and 2 digital impression techniques.

MATERIAL AND METHODS

One typodont maxillary right central incisor was prepared for a ceramic crown. Ten impressions were made by using each method: conventional with polyvinyl siloxane impression material, Lava COS (3M ESPE), and iTero (Cadent) intraoral scanning devices. Lithium disilicate (e.max CAD) crowns were fabricated with CAD/CAM technology, and the marginal gap was measured for each specimen at 4 points under magnification with a stereomicroscope. The mean measurement for each location and overall mean gap size by group were calculated. Statistically significant differences among the impression techniques were tested with F and t tests (α=.05).

RESULTS

The average (±SD) gap for the conventional impression group was 112.3 (±35.3) μm. The digital impression groups had similar average gap sizes; the Lava group was 89.8 (±25.4) μm, and the iTero group was 89.6 (±30.1) μm. No statistically significant difference was found in the effects among impression techniques (P=.185) CONCLUSIONS: Within the limitations of this study, digital and conventional impressions were found to produce crowns with similar marginal accuracy.

Maxillary and Mandibular Rehabilitation in the Esthetic Zone Using a Digital Impression Technique and CAD/CAM-fabricated Prostheses: A Multidisciplinary Clinical Report

Interdisciplinary treatment planning is necessary in certain clinical situations to optimize esthetic treatment outcomes. Patients presenting with severe wear of their anterior teeth from iatrogenic influences pose a particularly difficult problem in terms of esthetic treatment planning. Collaboration of practitioners from the disciplines of orthodontics, periodontics, and restorative dentistry is essential for the treatment of patients with complex esthetic dental needs. Careful assessment of clinical situations and corresponding specialty consultations are of utmost importance to achieve more predictable and esthetic treatment outcomes. The purpose of this clinical case is to report to the readership a novel digital fabrication of computer-aided design/computer-aided manufacturing milled acrylic provisional restorations and final lithium disilicate definitive restorations after orthodontic and periodontal therapy with virtual master impressions, casts, and articulation.

Dental student perception and assessment of their clinical knowledge in educating patients about preventive dentistry

In today's dental school curricula, an increasing amount of time is dedicated to technological advances, and preventive dentistry topics may not be adequately addressed. Freshman (D1) students participated in a new Introduction to Preventive Dentistry course, which consisted of didactic lectures, active learning breakout sessions and case-based studies. The goal of this study was to determine if D1 dental students completing the course had a better knowledge and comfort level with basic preventive dentistry concepts and caries risk assessment than the upcoming graduating senior dental students. Following the completion of the course, D1 students were administered a survey that assessed their comfort level describing preventive dentistry topics to patients. This was immediately followed by an unannounced examination over the same topics. Senior (D4) students, who had not taken a formal course, reported statistically significant higher comfort levels than D1 students. However, the D4s scored significantly lower in all of the examination areas than the D1 students. Higher scores in D1s may have been due to recent exposure to the course material. However, the basic nature of the content-specific questions should be easily answered by novice practitioners educating their patients on oral disease prevention. As the current data shows lower content-specific scores of basic preventive dentistry knowledge amongst graduating D4 students, this may indicate a need for more guidance and education of students during the patient care. This study showed that implementation of a formalised course for D1 students can successfully ameliorate deficiencies in knowledge of preventive dentistry topics.

Digital workflow for virtually designing and milling ceramic lithium disilicate veneers: a clinical report

Laminate veneers have been routinely used to restore and enhance the appearance of natural dentition. The traditional pathway for fabricating veneers consisted of making conventional polyvinyl siloxane impressions, producing stone casts, and fabricating final porcelain prostheses on stone dies. Pressed ceramics have successfully been used for laminate veneer fabrication for several years. Recently, digital computer-aided design/computer-aided manufacturing scanning has become commercially available to make a digital impression that is sent electronically to a dental laboratory or a chairside milling machine. However, technology has been developed to allow digital data acquisition in conjunction with electronically transmitted data that enables virtual design of restorations and milling at a remote production center. Following the aforementioned workflow will provide the opportunity to fabricate a physical cast-free restoration. This new technique has been reported recently for all-ceramic IPS e.max full-coverage pressed-ceramic restorations. However, laminate veneers are very delicate and technique-sensitive restorations when compared with all-ceramic full-coverage ones made from the same material. Complete digital design and fabrication of multiple consecutive laminate veneers seems to be very challenging. This clinical report presents the digital workflow for the virtual design and fabrication of multiple laminate veneers in a patient for enhancing the esthetics of his maxillary anterior teeth. A step-by-step process is presented with a discussion of the advantages and disadvantages of this novel technique. Additionally, the use of lithium disilicate ceramic as the material of choice and the rationale for such a decision is discussed.

The influence of digital fabrication options on the accuracy of dental implant-based single units and complete-arch frameworks

PURPOSE

To compare the accuracy and reproducibility of digital versus conventional dental impressions and fabrication techniques for single units and full-arch implant frameworks.

MATERIALS AND METHODS

A total of 24 samples, divided into four groups, were created using conventional and digital implant impression/fabrication techniques: group 1 (conventional single implant), group 2 (digital single implant), group 3 (conventional complete arch), and group 4 (digital complete arch). All impressions were made at the abutment level. Marginal fit measurements were made using an optical microscope at two points (buccal and lingual) for each sample. Statistical analysis was performed using F and t tests (α = .05).

RESULTS

For single implants, the conventional impression/fabrication pathway resulted in a mean marginal discrepancy of 24.1 μm compared to 61.43 μm for the digital impression/fabrication pathway. For full-arch frameworks, the conventional impression/fabrication pathway resulted in a mean marginal discrepancy of 135.1 μm compared to 63.14 μm for the digital technique.

CONCLUSION

The conventional pathway resulted in a smaller marginal discrepancy for single-implant frameworks. In contrast, the digital pathway resulted in a smaller marginal discrepancy for full-arch implant frameworks.

A direct technique to fabricate an intraoral shield for unilateral head and neck radiation

A radiation oncologist may ask the prosthodontist to fabricate an intraoral shield when ipsilateral fields are used for patients with head and neck cancer. A technique for its fabrication is described that can be accomplished with materials and equipment that are readily available in the dental office. Baseplate wax is used intraorally to fabricate a pattern, which is duplicated with irreversible hydrocolloid material. Autopolymerizing acrylic resin is then used to make the shield. This simple technique can be completed in a single visit.

Oral rehabilitation of an edentulous patient using two-segment le fort I repositioning and implant-supported fixed prostheses

Anteroposterior (AP) deficiencies present a restorative treatment challenge. Complex, multidisciplinary planning is necessary for the success of the treatment. This clinical report describes an approach to managing a complex complete oral rehabilitation of an edentulous patient with skeletal transverse and AP deficiencies with a history of facial trauma to the left zygomaticomaxillary complex. This was further complicated by a hopeless remaining dentition and pneumatization of the maxillary sinuses. Treatment included initial bony augmentation of the vertically and horizontally deficient maxilla, dental implant placement, provisional restoration in a Class III malocclusion with bilateral posterior crossbite, and Le Fort I osteotomy with transverse widening and advancement to correct the skeletal deficiency. Definitive restoration was accomplished with implant-supported fixed prostheses that provided ideal facial balance and occlusion.

Implementation of a laboratory quality assurance program: the Louisville experience

Remakes, or the refabrication of dental prostheses, can occur as a result of inherent inaccuracies in both clinical and laboratory procedures. Because dental schools manage large numbers of predoctoral dental students with limited familiarity and expertise as related to clinical prosthodontic techniques, it is likely these schools will experience an elevated incidence of laboratory remakes and their ramifications. The University of Louisville School of Dentistry, not unlike other dental schools, has experienced remakes associated with both fixed and removable prosthodontic procedures. Limitations in faculty standardization and variable enforcement of established preclinical protocols have been identified as variables associated with the high percentage of remakes documented. The purpose of this study was to introduce the implementation of a new multidepartmental quality assurance program designed to increase consistency and quality in both information provided to commercial dental laboratories and the prostheses returned. The program has shown to be advantageous in terms of cost-effectiveness and treatment outcomes. A statistically significant decrease in remake percentages has been recorded from inception of this program in December 2010 until December 2012. Furthermore, this program has resulted in more consistent communication between the dental school and commercial dental laboratories, among faculty members, and between faculty and students.

Fabrication of a fixed multipurpose template retained by existing dental implants

This report describes the use of a multipurpose template stabilized with existing implants to provide accurate information for immediate implant placement, to facilitate impression making, and to record maxillomandibular relationships for the fabrication of an interim immediate implant-supported fixed prosthesis.