[Three-dimensional computer aided design for individualized post-and-core restoration]

OBJECTIVE

To develop a method of three-dimensional computer aided design (CAD) of post-and-core restoration.

METHODS

Two plaster casts with extracted natural teeth were used in this study. The extracted teeth were prepared and scanned using tomography method to obtain three-dimensional digitalized models. According to the basic rules of post-and-core design, posts, cores and cavity surfaces of the teeth were designed using the tools for processing point clouds, curves and surfaces on the forward engineering software of Tanglong prosthodontic system. Then three-dimensional figures of the final restorations were corrected according to the configurations of anterior teeth, premolars and molars respectively.

RESULTS

Computer aided design of 14 post-and-core restorations were finished, and good fitness between the restoration and the three-dimensional digital models were obtained. Appropriate retention forms and enough spaces for the full crown restorations can be obtained through this method.

CONCLUSIONS

The CAD of three-dimensional figures of the post-and-core restorations can fulfill clinical requirements. Therefore they can be used in computer-aided manufacture (CAM) of post-and-core restorations.

[Establishment of database with standard 3D tooth crowns based on 3DS MAX]

The database with standard 3D tooth crowns has laid the groundwork for dental CAD/CAM system. In this paper, we design the standard tooth crowns in 3DS MAX 9.0 and create a database with these models successfully. Firstly, some key lines are collected from standard tooth pictures. Then we use 3DS MAX 9.0 to design the digital tooth model based on these lines. During the design process, it is important to refer to the standard plaster tooth model. After some tests, the standard tooth models designed with this method are accurate and adaptable; furthermore, it is very easy to perform some operations on the models such as deforming and translating. This method provides a new idea to build the database with standard 3D tooth crowns and a basis for dental CAD/CAM system.

Misfit of suprastructures on implants processed by electrical discharge machining or the Cresco method

OBJECTIVE

To assess the accuracy of fit of frameworks on implants processed with electrical discharge machining (EDM) or the Cresco technique (Astra Tech).

METHOD AND MATERIALS

On 12 identical master casts with implants at positions 9(21), 11(23), and 13(25), high-gold alloy frameworks were produced by standard casting procedure. Six frameworks were used for the Cresco technique (group CRE) by employing specific fixed partial denture supports. The remaining 6 frameworks were cast with prefabricated gold copings and served as control. The finished frameworks were screwed onto implant 25 of the corresponding master cast. Dimensions of the marginal gaps were measured at 4 locations on each implant under the scanning electron microscope, applying the replica technique. Subsequently, the control group was processed by EDM (SAE EDM 2000) (group EDM) and analyzed alike. Statistical analysis of the results was performed with Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

The mean marginal gaps were measured as follows (CRE/EDM/control): position 25: 0.0 microm/1.0 +/- 1.6 microm/1.5 +/- 2.1 microm; position 23: 5.2 +/- 5.6 microm/18.7 +/- 29.3 microm/23.6 +/- 30.7 microm; and position 21: 36.0 +/- 21.6 microm/40.7 +/- 31.0 microm/46.0 +/- 41.1 microm. The only statistically significant difference was found at location 23 between group CRE on one side and both group EDM and control on the other side. The strong increase of misfit for group CRE from location 23 to location 21 indicates that laser welding is the crucial parameter in this technique.

CONCLUSION

The Cresco technique has a potential to reduce the marginal gap between implants and suprastructures.

[Resilient attachments--biological treatment solution for unilateral partials]

The attachments recommended for a unilateral free-end distal extension partial denture assure the comfort for the patient because don't need a cross arch stabilization. One of the most used resilient attachment is represented by FM Hinge (New Anchorvis), an extracoronal, hinge resilient distal extension attachment. It is formed by two elements: a metallic female, designed for adhering into the framework of the denture base and a male, made of fully combustible plastic high fusing for casting to precious and semiprecious alloys. The retention of the denture is due to the friction achieved through the male and female elements. The attachment should also be resilient to transfer stress to the ridge and away from the abutment teeth. Resilient attachments represent a functional, aesthetic and biological solution in unilateral extended edentation.

Study on CAD&RP for removable complete denture

This study explored a method for fabricating removable complete denture aided by CAD&RP technology. 3D crossing section scanner and laser scanner were respectively applied to obtain the surface data of artificial teeth, edentulous models and rims made in clinic. The vertical and horizontal relations of models were recorded before scanning with a special device. A 3D graphic database of artificial teeth, which can be aligned with parameters, was established. Special CAD software developed by ourselves was applied to the 3D integrated design process including automatic setting up artificial teeth, semiautomatic designing aesthetic and individualized artificial gingiva and base plate, automatic constructing individualized virtual flasks according to the finished CAD digital models of removable complete denture. At last, 3DP technology was used to make the individualized physical flasks. In this study, AMT and classic denture materials were effectually combined to achieve making removable complete denture aided by CAD/RP technology.

Accuracy of computer-aided oral implant surgery: a clinical and radiographic study

PURPOSE

Computer-aided oral implant surgery offers several advantages over the traditional approach. The purpose of this study was to evaluate the in vivo accuracy of computer-aided, template-guided oral implant surgery by comparing the three-dimensional positions of planned and placed implants.

MATERIALS AND METHODS

Oral implant therapy was performed in two treatment centers on eligible patients using computerized tomography (CT)-based software planning and computer-aided design/computer-assisted manufacture stereolithographic templates. A second CT scan was obtained after surgery. Preoperative and postoperative CT images were compared (planned vs actual implant positions), and the accuracy of this type of image-guided therapy was assessed.

RESULTS

Twenty-five adult patients were included in this retrospective study; 17 (11 partially and eight fully edentulous arches) were treated in center 1, and eight (six partially and two fully edentulous arches) in center 2. Of the 104 implants inserted with the computer-aided method, 100 integrated, giving a cumulative survival rate of 96% (mean follow-up, 36 months). There were no major surgical complications. With regard to accuracy, 89 implants were available for comparison; mean lateral deviations at the coronal and apical ends of the implants were 1.4 mm and 1.6 mm, respectively. Mean depth deviation was 1.1 mm and mean angular deviation was 7.9 degrees. There was a statistically significant correlation in the accuracy of any implants placed with the same guide. There was no difference in accuracy data from the two private centers; nor could a learning curve be demonstrated.

CONCLUSIONS

Based upon this clinical study of 25 patients, the following observations were made: (1) computer-aided oral implant surgery used in two treatment centers provided a high likelihood (96%) of implant survival, and (2) deviations from planned implant positions existed in the coronal and apical portions of the implants as well as with implant angulation. Mean deviations were less than 2 mm in any direction and less than 8 degrees.

Computer-guided flapless surgery: immediately loaded implant-prosthetic rehabilitation

The aim of this study was to show the operative procedure and the advantages coming from computer guided flapless surgery. This case report describes the use of stereolithographic surgiguides in order to insert 6 mandibular and 6 maxillary implants by a computer guided flapless surgery. These implants have been immediately loaded with cross arch screwed temporary prostheses. The definitive rehabilitation was realized with 2 fixed cross arch metal-ceramic prostheses that were cemented by AGC caps. The computer science technology allows to execute complex implant-prosthetic treatments in a shorter time, at low risk, with high esthetical and functional predictability and patient' satisfaction.

Complex all-ceramic rehabilitation of a young patient with a severely compromised dentition: a case report

A young patient with dentinogenesisimperfecta and a dentition severely compromised by discolorations,abrasion, and breakage of enamel on several teeth was prosthodontically treated with CAD/CAM-manufactured all-ceramic restorations. To reduce treatment risk, preparations were limited paragingivally. Maxillary anterior teeth and premolars were restored with adhesively luted ceramic crowns. All other teeth were treated with zirconia-based restorations luted with a self-etching resin-based material. Considering the deficient pretreatment situation, the use of tooth-colored restoration and luting materials yielded a satisfying functional and good esthetic result. The patient is highly satisfied, even though 3 minor chippings occurred shortly after the completion of treatment

Micro-CT evaluation of the marginal fit of different In-Ceram alumina copings

The aim of the study was to evaluate the marginal fit of different In-Ceram alumina ceramic cores manufactured by four different techniques. Four groups of four In-Ceram alumina core specimens (Vita), each 0.6 mm in thickness, were fabricated from a master die using four different techniques: Group SL, the slip-cast technique (In-Ceram system); Group CL, the copy-milling technique (Celay system); Group CR, a CAD/CAM system (Cerec inLab system) and Group WO, the electro-deposition dipping technique (Wol-Ceram). After the core specimens were fitted on the master die, they were scanned with the use of a microtomography device (1072 micro-CT, Sky- Scan). Datasets were processed by software (TView v1.1, SkyScan) and 10 vertical sections from each core were generated. On these microtomographic cross-sections the marginal gap (MG) and the absolute marginal discrepancy (MD) were measured in microscale (microm). The slip-cast and the electro-deposition dipping techniques presented the best results of MG with 22 microm and 35 microm, respectively (alpha<5%). The CAD/CAM system presented an MG of 55 microm. In addition, the slip-cast and the electro-deposition dipping techniques presented the best results of MD with 50 microm and 60 microm, respectively (alpha<5%). The slip-cast technique and the Wol-Ceram system presented the best marginal fit, followed by Cerec inLab, which presented clinically acceptable results. Microtomography analysis seemed to be a reliable method of evaluating the marginal fit of dental restorations.

A comparison of fabrication precision and mechanical reliability of 2 zirconia implant abutments

PURPOSE

Studies have described the reliability of zirconia as an implant abutment material. The purpose of this in vitro study was to compare the precision and fracture strength of 2 different zirconia abutments angled at 30 degrees and loaded to failure in a standardized testing device.

MATERIALS AND METHODS

Twenty-nine Atlantis abutments in zirconia (AAZ) and 29 Nobel Biocare Procera AllZirkon abutments of comparable interface were measured for key interface feature statistical differences (analysis of variance; alpha = 95%). Each specimen was fixed to a regular-platform Brånemark System implant and mounted in an Instron machine. Increasing incremental loads were applied until failure. A 2-tailed t test for independent specimens and unequal variances was employed (alpha = 95%). The Weibull method determined the probability of failure of each abutment sample (alpha = 95%). Fractography by scanning electron microscopy determined the flaws at the fracture origins.

RESULTS

Metrology inspection indicated that the AAZ showed no measurable dimensional differences of 4 key interface features. The mean failure load of the AAZ (831 N) was greater than the AllZirkon (740 N; P < .00006). The Weibull distribution showed that the AAZ would be more likely to survive intraoral occlusal loads (P < .0005).

CONCLUSIONS

Both types of zirconia abutments demonstrated failure loads that exceed maximum human bite force. In vitro, the AAZ outperformed the AllZirkon in survivability. The clinical use of zirconia abutments is indicated when esthetics may be of concern.

A novel post-and-core restoration system--results of three years of clinical application of the "Wuerzburg Post"

The Wuerzburg Post is a new post-and-core restoration system designed to eliminate the weak parts of post-and-core restorations and the associated problems, respectively. In contrast to conventional posts, the Wuerzburg Post is a short and thick post, which no longer relies on cementation or luting for retention in the root, but on stress-free positive locking, which it achieves by means of a post which can be spread into a predefined and form-congruent undercut cavity. The second key feature is an annular groove which runs in the dentin, girded by a corresponding structure, ensuring regular force transmission and stress dissipation, as opposed to the classic ferrule design. There are two versions: one with a machined core which can be prepared like a classic build-up to support crowns and bridges, and another one with a 2.25 mm ball end to connect to common dies which can be integrated into removable prostheses. As the system utilizes prefabricated parts made from Titanium, a precise fit is ensured, enabling the user to restore teeth quickly and easily. Over the course of the past three years, 129 posts were inserted, most commonly on upper and lower incisors and canines. The main application was restoration of fractured telescopes. During the observation period, five failures were observed. Two of the failiures did not cause significant damage to the tooth, and were subsequently immediately repairable. The survival rate amounts to over 95% after three years under risk.

The effect of preparation design on the marginal stress of resin-bonded metal-free crowns: a finite element study

The aim of this study was to evaluate the stress distribution at the marginal edge of metal-free crowns using 2 different materials (ceramic and hybrid composite) and 4 different preparation designs (knife edge, chamfer, heavy chamfer, rounded shoulder). All marginal preparation designs for hybrid composite crowns showed lower compression and tensile stress than the ceramic crowns. The rounded shoulder preparation provided more even stress distribution than the knife-edge preparation. Heavy chamfer was an acceptable preparation design for ceramic crowns. The chamfer preparation was preferred for hybrid composite crown.

Smile design and advanced provisional fabrication

Cosmetic reconstruction is much more predictable when superb provisionals are used as a blueprint for the final restoration. This article provides details for a technique that can be used to fabricate indirect multilayered composite provisional restorations for porcelain veneers and complex full-arch cases.

Clinically based diagnostic wax-up for optimal esthetics: the diagnostic mock-up

A diagnostic wax-up can enhance the predictability of treatment by modeling the desired result in wax prior to treatment. It is critical to correlate the wax-up to the patient to avoid a result that appears optimal on the casts but does not correspond to the patient's smile. This article reviews the applications and techniques for clinically based diagnostic wax-up, and focuses on the diagnostic mock-up philosophy as a means to obtain predictable esthetics and function.