Zirconia crowns - the new standard for single-visit dentistry?

Zirconia crowns combine the advantages of metal restorations, such as minimally invasive tooth preparation and ease of cementation, with those of full ceramic crowns, such as low thermal conductivity and tooth color. With the introduction of a high-speed sintering procedure, it is possible to produce and cement zirconia crowns and small monolithic bridges in a Cerec Single Visit procedure. This new procedure is compared to established chairside methods.

New Design for Rapid Prototyping of Digital Master Casts for Multiple Dental Implant Restorations

Aim

This study proposes the replacement of all the physical devices used in the manufacturing of conventional prostheses through the use of digital tools, such as 3D scanners, CAD design software, 3D implants files, rapid prototyping machines or reverse engineering software, in order to develop laboratory work models from which to finish coatings for dental prostheses. Different types of dental prosthetic structures are used, which were adjusted by a non-rotatory threaded fixing system.

Method

From a digital process, the relative positions of dental implants, soft tissue and adjacent teeth of edentulous or partially edentulous patients has been captured, and a maser working model which accurately replicates data relating to the patients oral cavity has been through treatment of three-dimensional digital data.

Results

Compared with the conventional master cast, the results show a significant cost savings in attachments, as well as an increase in the quality of reproduction and accuracy of the master cast, with the consequent reduction in the number of patient consultation visits. The combination of software and hardware three-dimensional tools allows the optimization of the planning of dental implant-supported rehabilitations protocol, improving the predictability of clinical treatments and the production cost savings of master casts for restorations upon implants.

[Translucency of dental zirconia ceramics sintered in conventional and microwave ovens]

OBJECTIVE

To evaluate the effect of microwave sintering on the translucency of zirconia and to compare these effect with those of conventional sintering. The relationship between the microstructure of specimens and translucency was investigated.

METHODS

A total of 10 disc-shaped specimens were fabricated from 2 commercial brands of zirconia, namely, Zenostar and Lava. Each group included 5 discs. Conventional sintering was performed according to the manufacturers' specifications. The maximum temperature for Zenostar was 1,490 °C, whereas that for Lava was 1,500 °C. The dwelling time was 2 h. The sintering temperature for microwave sintering was 1,420 °C, heating rate was 15 °C · min⁻¹, and dwelling time was 30 min. After sintering, the translucency parameter (TP) of the specimens were measured with ShadeEye NCC. The sintered density of the specimens was determined by Archimedes' method. The grain size and microstructure of the specimens were investigated by scanning electron microscopy.

RESULTS

Density and translucency slightly increased by microwave sintering, but no significant difference was found between microwave and conventional sintering (P > 0.05). Small and uniform microstructure were obtained from microwave sintering. The mean TP of Lava was significantly higher than that of Zenostar (P < 0.001).

CONCLUSION

The translucency of zirconia sintered by microwave sintering is similar to that of the zirconia sintered by conventional sintering.

Evaluation of Temperature and Stress Distribution on 2 Different Post Systems Using 3-Dimensional Finite Element Analysis

BACKGROUND The mouth is exposed to thermal irritation from hot and cold food and drinks. Thermal changes in the oral cavity produce expansions and contractions in tooth structures and restorative materials. The aim of this study was to investigate the effect of temperature and stress distribution on 2 different post systems using the 3-dimensional (3D) finite element method. MATERIAL AND METHODS The 3D finite element model shows a labio-lingual cross-sectional view of the endodontically treated upper right central incisor and supporting periodontal ligament with bone structures. Stainless steel and glass fiber post systems with different physical and thermal properties were modelled in the tooth restored with composite core and ceramic crown. We placed 100 N static vertical occlusal loading onto the center of the incisal surface of the tooth. Thermal loads of 0°C and 65°C were applied on the model for 5 s. Temperature and thermal stresses were determined on the labio-lingual section of the model at 6 different points. RESULTS The distribution of stress, including thermal stress values, was calculated using 3D finite element analysis. The stainless steel post system produced more temperature and thermal stresses on the restorative materials, tooth structures, and posts than did the glass fiber reinforced composite posts. CONCLUSIONS Thermal changes generated stresses in the restorative materials, tooth, and supporting structures.

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.

Prevention of distal extension cantilever fracture in mandibular overdentures

OBJECTIVES

Fractures of distal bar extensions, supporting a mandibular overdenture, do occur with significant functional and economic consequences for the patient. This study therefore aims to evaluate the effect of different bar cross-sectional shapes and surfaces, bar extension lengths and the placement of a support rib under the distal bar extension on fracture resistance.

MATERIALS AND METHODS

The 2nd moment area and static strength were calculated for 11 frequently used bar designs using finite element analysis (FEA). For two specific designs (Ackermann round Ø 1.8mm and Dolder-Y macro, the former with and without a support rib) additional physical static and fatigue strength tests were included.

RESULTS

The FEA static strength data corresponded well to the 2nd moment area (a similar ranking when maximum allowed force was considered). The application of a rib support (Ackermann Ø 1.8mm) and limitations of the bar extension length (6mm for the Ackermann Ø 1.8mm, 8mm for the Dolder-Y macro) allowed the bars to exceed 5 × 10(6) cycles of 120 and 250N, respectively, before fracture. The region of highest stresses in FEA corresponded well with the locations of the fractures observed in static- and fatigue-testing.

CONCLUSIONS

With some simple guidelines/modifications, the number of bar extension fractures can be reduced significantly.

CLINICAL SIGNIFICANCE

This study focusses on distal bar extensions which improve the positioning of an implant supported overdenture. By combining laboratory testing and finite element simulations we aim to: (1) explain why fractures occur (dependent on physical characteristics of the bar), and (2) give clinical guidelines on how to prevent such fractures.

Evaluation of the Marginal Fit of CAD/CAM Crowns Fabricated Using Two Different Chairside CAD/CAM Systems on Preparations of Varying Quality

PURPOSE

This study evaluated the marginal gap of crowns fabricated using two new chairside computer-aided design/computer-aided manufacturing systems on preparations completed by clinicians with varying levels of expertise to identify whether common preparation errors affect marginal fit. The null hypothesis is that there is no difference in the mean marginal gaps of restorations of varying qualities and no difference in the mean marginal gap size between restorations fabricated using the PlanScan (D4D, Richardson, TX, USA) and the CEREC Omnicam (Sirona, Bensheim, Germany).

MATERIAL AND METHODS

The fit of 80 lithium disilicate crowns fabricated with the E4D PlanScan or CEREC Omnicam systems on preparations of varying quality were examined for marginal fit by using the replica technique. These same preparations were then visually examined against common criteria for anterior all-ceramic restorations and placed in one of four categories: excellent, good, fair, and poor. Linear mixed modeling was used to evaluate associations between marginal gap, tooth preparation rating, and fabrication machine.

RESULTS

The fit was not significantly different between both systems across all qualities of preparation. The average fit was 104 μm for poor-quality preparations, 87.6 μm for fair preparations, 67.2 μm for good preparations, and 36.6 μm for excellent preparations.

CONCLUSION

The null hypothesis is rejected. It can be concluded that preparation quality has a significant impact on marginal gap regardless of which system is used. However, no significant difference was found when comparing the systems to each other.

CLINICAL SIGNIFICANCE

Within the limitations of this in vitro study, it can be concluded that crown preparation quality has a significant effect on marginal gap of the restoration when the clinician uses either CEREC Omnicam or E4D PlansScan.

Microcomputed tomography marginal fit evaluation of computer-aided design/computer-aided manufacturing crowns with different methods of virtual model acquisition

This in vitro study used microcomputed tomography to evaluate the marginal fit of crowns fabricated using a chairside computer-aided design/computer-aided manufacturing (CAD/CAM) system with different methods of virtual model acquisition. Crowns were fabricated to fit in a cast containing a single human premolar. Four methods of virtual model acquisition were used: Group 1 (control), digital impressioning of a typodont; Group 2, digital impressioning of a powdered typodont; Group 3, digital impressioning of a regular impression; and Group 4, digital impressioning of a master cast. Statistically significant differences were found between the marginal gap of Group 2 and the other groups (P < 0.05); no differences were found among Groups 1, 3, and 4. The results showed that crowns fabricated using the chairside CAD/CAM system exhibited significantly smaller vertical misfit when a thin layer of powder was applied over the typodont before digital impressioning.

[Application of spark erosion technology in manufacture of implant prosthesis]

OBJECTIVE

To evaluate the influence of the implant-supported porcelain bridges made from non-precious metals using spark erosion techniques, and to discuss the feasibility and details of making the implant restoration by spark erosion technique.

METHODS

The study included 12 patients (9 males and 3 females) with 92 units implant-supported non-precious porcelain bridge from Sep. 2011 to Feb. 2013. All the patients received implant treatment in Department of Oral Implantology, Peking University School and Hospital of Stomatology. The total of 52 implants, were from Nobel Biocare implant system, Camlog implant system and Ankylos implant system. The implant analogs were connected in sequence with a copper wire to guarantee conductivity. The implant electrodes represented one electrode and the superstructure the other. During spark-erosion machining, the cast holding the implant electrodes and the prosthetic framework were moved toward one another, causing an electrical erosion of the protruding elements.

RESULTS

After the spark-erosion machining, the minimum gap between the framework and abutment was 0.21 mm, which was two units bridge. The maximum was 2.59 mm, which was 11 units bridge with 6 implants. The average gap was 0.68 mm. After the spark-erosion machining, the bridge fitted well with the passive position stability.

CONCLUSION

The method of making implant-supported non-precious porcelain bridge reduces costs on patients. Spark erosion has the potential to provide implant framework with an excellent fit. The patients are satisfied with the clinical results.

Fracture resistance and microleakage of endocrowns utilizing three CAD-CAM blocks

This study assessed marginal leakage and fracture resistance of computer-aided design/computer-aided manufacturing (CAD/CAM) fabricated ceramic crowns with intracoronal extensions into the pulp chambers of endodontically treated teeth (endocrowns) using either feldspathic porcelain (CEREC Blocks [CB], Sirona Dental Systems GmbH, Bensheim, Germany), lithium disilicate (e.max [EX], Ivoclar Vivadent, Schaan, Liechtenstein), or resin nanoceramic (Lava Ultimate [LU], 3M ESPE, St Paul, MN, USA).). Thirty extracted human permanent maxillary molars were endodontically treated. Standardized preparations were done with 2-mm intracoronal extensions of the endocrowns into the pulp chamber. Teeth were divided into three groups (n=10); each group was restored with standardized CAD/CAM fabricated endocrowns using one of the three tested materials. After cementation with resin cement, specimens were stored in distilled water at 37°C for one week, subjected to thermocycling, and immersed in a 5% methylene-blue dye solution for 24 hours. A compressive load was applied at 35 degrees to long axis of the teeth using a universal testing machine until failure. Failure load was recorded, and specimens were examined under a stereomicroscope for modes of failure and microleakage. Results were analyzed using one-way analysis of variance and Bonferroni post hoc multiple comparison tests (α=0.05). LU showed significantly (p<0.05) higher fracture resistance and more favorable fracture mode (ie, fracture of the endocrown without fracture of tooth) as well as higher dye penetration than CB and EX. In conclusion, although using resin nanoceramic blocks for fabrication of endocrowns may result in better fracture resistance and a more favorable fracture mode than other investigated ceramic blocks, more microleakage may be expected with this material.

Strength analysis of a three-unit dental bridge framework with the Finite Element Method

PURPOSE

The aim of the study was to analyse the strength of a prosthetic bridge with variable geometry in the connectors between the span and the retention elements on the pillar teeth crowns.

METHODS

Research was carried using the Finite Elements Method (FEM) on a model of the bridge in the anterior teeth arch in the field 21-22-23, obtained using a contact scanner and computer aided design (CAD) system, with four different cross-sectional areas of the connectors: 4.0, 5.0, 5.5, and 6.0 mm2. For that purpose, the impact of the properties of selected metal alloys on the deflection of the prosthesis was analysed.

RESULTS

On the basis of the analyses, it was found that when the loading force acted obliquely, the stress was 19% higher compared to the stress with a loading vertical force. In the case of connectors with the smallest cross-sectional area, the stress exceeded permissible value (with safety factor n = 2) for one of the alloys.

CONCLUSIONS

Deflection of the bridges tested changed depending on the connector cross-section and the elastic modulus of the selected material.

Ceramic dental biomaterials and CAD/CAM technology: state of the art

PURPOSE

Ceramics are widely used as indirect restorative materials in dentistry because of their high biocompatibility and pleasing aesthetics. The objective is to review the state of the arts of CAD/CAM all-ceramic biomaterials.

STUDY SELECTION

CAD/CAM all-ceramic biomaterials are highlighted and a subsequent literature search was conducted for the relevant subjects using PubMed followed by manual search.

RESULTS

Developments in CAD/CAM technology have catalyzed researches in all-ceramic biomaterials and their applications. Feldspathic glass ceramic and glass infiltrated ceramic can be fabricated by traditional laboratory methods or CAD/CAM. The advent of polycrystalline ceramics is a direct result of CAD/CAM technology without which the fabrication would not have been possible.

CONCLUSIONS

The clinical uses of these ceramics have met with variable clinical success. Multiple options are now available to the clinicians for the fabrication of aesthetic all ceramic restorations.

New-design dental implants: a 1-year prospective clinical study of 344 consecutively placed implants comparing immediate loading versus delayed loading and flapless versus full-thickness flap

PURPOSE

This study compared the 1-year success rates of immediately loaded dental implants to delayed loaded implants, regardless of the surgical technique (flapless or conventional full-thickness flap) and regardless of extraction time. It also examined whether the surgical technique had an influence on the success rate of the immediately loaded implants.

MATERIALS AND METHODS

A total of 344 dental implants, some with a new expanded winged-thread design, were placed in 155 patients; 53% of the implants were immediately loaded. Of the immediately loaded implants, 68.9% were placed with a flapless surgical technique and 88% were placed in extraction sites. Pocket depth, mobility, bleeding on probing, presence of erythema, pain, or radiolucency around the implants, as well as clinical findings, were recorded. Implants were followed from placement through definitive restoration. Descriptive, univariate, and multivariate analyses using clustered marginal approach of the Cox proportional hazards model were applied.

RESULTS

Of the 344 implants in the study, 10 (2.9%) failures were recorded, 7 of which were immediately loaded; however, there was no significant difference in failure rates between the immediate and delayed loading groups. Seven of the implants that failed were placed with a flapless (extraction site) technique; however, there was no significant difference in the failure rates between the flapless versus full-thickness flap technique in immediately loaded implants.

CONCLUSIONS

The clinical success of immediately loaded implants after 1 year showed no difference from the success rate of delayed loaded implants. The implantation procedure (flapless versus conventional flap) or extraction time also had no influence on the success rate of the immediately loaded implants.

An overlay partial denture to restore worn mandibular anterior teeth

Restoring worn anterior mandibular teeth is a challenge, especially when teeth are small, esthetics are a concern, the long-term prognosis is questionable, and/or patient finances are an issue. This article describes an alternate treatment for a patient with a collapsed bite, missing posterior mandibular teeth, an ill-fitting complete maxillary denture with poor esthetics, and irregular, worn mandibular anterior teeth.

Additive manufacturing technology (direct metal laser sintering) as a novel approach to fabricate functionally graded titanium implants: preliminary investigation of fabrication parameters

PURPOSE

This article describes the preliminary findings of the mechanical properties of functionally graded titanium with controlled distribution of porosity and a reduced Young's modulus on the basis of a computeraided design (CAD) file, using the rapid-prototyping, direct metal laser sintering (DMLS) technique.

MATERIALS AND METHODS

Sixty specimens of Ti-6Al-4V were created using a DMLS machine (M270) following the standard for tensile testing of metals. One group was fabricated with only 170 W of laser energy to create fully dense specimens (control group). The remaining specimens all featured an outer fully dense "skin" layer and a partially sintered porous inner "core" region. The outer "skin" of each specimen was scanned at 170 W and set at a thickness of 0.35, 1.00, or 1.50 mm for different specimen groups. The inner "core" of each specimen was scanned at a lower laser power (43 or 85 W).

RESULTS

The partially sintered core was clearly visible in all specimens, with somewhat greater porosity with the lower laser power. However, the amount of porosity in the core region was not related to the laser power alone; thinner skin layers resulted in higher porosity for the same power values in the core structure. The lowest Young's modulus achieved, 35 GPa, is close to that of bone and was achieved with a laser power of 43 W and a skin thickness of 0.35 mm, producing a core that comprised 74% of the total volume.

CONCLUSION

Additive manufacturing technology may provide an efficient alternative way to fabricate customized dental implants based on a CAD file with a functionally graded structure that may minimize stress shielding and improve the long-term performance of dental implants.

Prosthodontic management of implant therapy

Implant-supported dental restorations can be screw-retained, cement-retained, or a combination of both, whereby a metal superstructure is screwed to the implants and crowns are individually cemented to the metal frame. Each treatment modality has advantages and disadvantages. The use of computer-aided design/computer-assisted manufacture technologies for the manufacture of implant superstructures has proved to be advantageous in the quality of materials, precision of the milled superstructures, and passive fit. Maintenance and recall evaluations are an essential component of implant therapy. The longevity of implant restorations is limited by their biological and prosthetic maintenance requirements.

[Marginal fit changes in implant-supported prosthetic bars by electroerosive processing]

The aim of the study was to evaluate the marginal fit changes in implant supported prosthetic bars by electroerosive processing. The experimental model included 9 bars supported by 2, 4 and 6 implant analogues (3 bars for each number of supports). Marginal gap size was assessed by digital microscopy before and after electroerosive processing conducted in 3 stages (10, 8 and 5 minutes long). Electroerosive processing proved to be useful tool for marginal fit correction.

Achieving optimal outcomes with all-zirconia crowns

All-zirconia crowns are enjoying an unprecedented popularity. Dental laboratories are acquiring new equipment and adopting novel techniques, some of which require a learning curve. As a result, some crowns fabricated by computer-aided design/computer-aided manufacturing technology may come back to the dentist with unsatisfactory features. Dentists should carefully examine each crown under magnification prior to delivery to the patient. The dentist and dental laboratory should establish a close partnership with clear communication to yield the most favorable outcome for the patient.

Prosthetic rehabilitation of an edentulous patient with cleft palate

It is difficult today to find older patients without their cleft palate prosthetically rehabilitated. This case report presents the rehabilitation by conventional dental prostheses of a cleft palate patient who had no prior treatment. A 52-year-old male presented himself to have his fissured palate obturated and occlusion restored. He reported difficulties in swallowing food and liquids, along with a severe speech disability. The patient's medical history revealed diabetes mellitus type II, hypertension, low vision due to macular atrophic lesions, and xerostomia. The upper and lower arches were completely and partially edentulous, respectively. The treatment plan involved a conventional denture to be placed in the upper arch, and a removable partial denture to be placed in the lower arch.

A critically appraised topic review of computer-aided design/computer-aided machining of removable partial denture frameworks

A critically appraised topic (CAT) review is presented about the use of computer-aided design (CAD)/computer-aided machining (CAM) removable partial denture (RPD) frameworks. A systematic search of the literature supporting CAD/CAM RPD systems revealed no randomized clinical trials, hence the CAT review was performed. A PubMed search yielded 9 articles meeting the inclusion criteria. Each article was characterized by study design and level of evidence. No clinical outcomes research has been published on the use of CAD/CAM RPDs. Low levels of evidence were found in the available literature. Clinical research studies are needed to determine the efficacy of this treatment modality.

Simple method for fabricating a cast partial framework obturator for lifelike appearance: a case report

Defects can form after tumors in the maxillary region are resected surgically. Maxillofacial defects can affect a patient's physical, psychological, and social status. Surgery reduces the residual teeth and tissue's ability to provide optimal cross-arch support, stability, and retention. The design of the obturator can improve the esthetics of the prosthesis and give it a more lifelike appearance. This case report describes the fabrication of a cast metal framework design for a partial obturator prosthesis in a maxillectomy patient.

A technique for fabricating a milled titanium complete-arch framework using a new CAD/CAM software and scanner with laser probe

By using traditional casting procedures, accurately fitting of complete-arch frameworks that are screwed on multiple implants is difficult to achieve. The introduction of computer-aided design and manufacturing (CAD/CAM) techniques for fabricating custom 1-piece titanium frameworks simplifies this challenge and reduces time spent by the restorative dentist. This report presents a milled titanium complete-arch mandibular framework using a new planning software and a new scanner using non-contact laser probe, which eliminates the need for wax pattern fabrication.

Digital data management for CAD/CAM technology. An update of current systems

Abstract - Computer-aided design/computer-aided manufacturing (CAD/CAM) technology continues to rapidly evolve in the dental community. This review article provides an overview of the operational components and methodologies used with some of the CAD/CAM systems. Future trends are also discussed. While these systems show great promise, the quality of performance varies among systems. No single system currently acquires data directly in the oral cavity and produces restorations using all materials available. Further refinements of these CAD/CAM technologies may increase their capabilities, but further special training will be required for effective use.