The accuracy of a high-precision digitizer for CAD/CAM of crowns

Comparison of the learning curve of intraoral scanning with two different intraoral scanners based on scanning time

BACKGROUND

The appearance of intraoral scanners (IOSs) in dental offices was an important milestones for the digital innovations in dentistry. Knowing the learning curve for intraoral scanning is crucial, because it can serve as a guideline for clinicians before buying a new IOS. The aim of the present in vivo study was to determine the learning curve required by dental students for intraoral scanning with the 3Shape Trios 4 IOS and the CEREC Primescan IOS, based on scanning time.

METHODS

A total of 20 dental students with no previous experience in intraoral scanning participated in the present study. 10 students scanned with Trios 4® IOS (TRI) and 10 students took digital impressions with Primescan® IOS (CER). Every student created 15 digital impressions from patients. Prior to taking the impressions, theoretical and practical education was provided. The total scanning time included the upper and lower arches as well as bite registration, for which average values were calculated. Statistical analysis was performed using the Stata package with a mixed-effects generalized least squares regression models.

RESULTS

The average total scanning times were the following: TRI - 205 s for the 1st impression, 133.6 s for the 15th, CER - 289.8 s for the 1st impression, 147 s for the 15th. The model-based estimate of the difference between the two in case of TRI was 57.5 s, and in CER was 144.2 s which is a highly significant improvement in both cases (P < 0.0001). The slope of the scanning time vs. learning phase curve gradually approached flatness, and maintained a plateau: TRI - from the 11th measurement and CER - from the 14th measurement onward.

CONCLUSIONS

Given the limitations of the present study, we found difference between the learning curve of scanner types which are operate various principle of imaging. In case of the TRI fewer digital impressions (11 repeating) were sufficient to reach the average scanning time of an experienced user than using CER (14 repeating).

TRIAL REGISTRATION

The permission for this study was given by the University Ethics Committee of Semmelweis University (SE RKEB number: 184/2022).

In vitro Comparison of the Accuracy (Precision and Trueness) of Seven Dental Scanners

Statement of the Problem:

The mechanisms of operation of dental scanners are based on different technologies. Considering these differences, there are many types of scanners available in the market.

Purpose:

This in vitro study aimed to compare the accuracy (precision and trueness) of seven commonly used dental scanners.

Materials and Method:

In this in vitro experimental study, the accuracy of 7 common extra oral scanners (Sirona ineos inLab, Sirona X5, Dentium, Imes Icore 350I, Amann Girrbach, 3shape D700, and 3Shape E3) were evaluated. Each of scanners performed 7 scans of implant abutment of SIC (SIC MAX.GH1). Data from each scanner were then compared to data received from 3Shape Trios intra oral scanner as a reference. For evaluating the accuracy of each scanner, trueness and precision was evaluated. Collected data were analyzed using Kruskal Wallis and Bonferroni tests via SPSS version 22.

Results:

Descriptive statistics showed the best trueness was for 3Shape E3 scanner with the average of 35.37µm and the worst trueness belonged to Sirona x5 scanner with the average of 51.75µm. Furthermore, the best precision was achieved for 3Shape E3 scanner with the average of 35.34, while the lowest precision was detected in 3Shape D700. The scanners had statistically significant differences with each other in terms of trueness and precision (p<0.05).

Conclusion:

Based on the results of this study, the extra oral scanner, 3shape E3, had the best trueness and precision. The lowest amount of trueness among the studied scanners was for the extra oral scanner, Sirona x5, and the lowest precision was for scanner 3shape D700.

Dentistry 4.0 Concept in the Design and Manufacturing of Prosthetic Dental Restorations

The paper is a comprehensive but compact review of the literature on the state of illnesses of the human stomatognathic system, related consequences in the form of dental deficiencies, and the resulting need for prosthetic treatment. Types of prosthetic restorations, including implants, as well as new classes of implantable devices called implant-scaffolds with a porous part integrated with a solid core, as well as biological engineering materials with the use of living cells, have been characterized. A review of works on current trends in the technical development of dental prosthetics aiding, called Dentistry 4.0, analogous to the concept of the highest stage of Industry 4.0 of the industrial revolution, has been presented. Authors’ own augmented holistic model of Industry 4.0 has been developed and presented. The studies on the significance of cone-beam computed tomography (CBCT) in planning prosthetic treatment, as well as in the design and manufacture of prosthetic restorations, have been described. The presented and fully digital approach is a radical turnaround in both clinical procedures and the technologies of implant preparation using computer-aided design and manufacturing methods (CAD/CAM) and additive manufacturing (AM) technologies, including selective laser sintering (SLS). The authors’ research illustrates the practical application of the Dentistry 4.0 approach for several types of prosthetic restorations. The development process of the modern approach is being observed all over the world. The use of the principles of the augmented holistic model of Industry 4.0 in advanced dental engineering indicates a change in the traditional relationship between a dentist and a dental engineer. The overall conclusion demonstrates that it is inevitable and extremely beneficial to implement the idea of Dentistry 4.0 following the assumptions of the authors’ own, holistic Industry 4.0 model.

Accuracy of digitization obtained from scannable and nonscannable elastomeric impression materials

STATEMENT OF PROBLEM

Elastomeric impression materials have been marketed for optimizing direct digital acquisition without requiring a stone cast. The trueness and precision of the digitization of these new elastomeric impression materials are unclear.

PURPOSE

The purpose of this in vitro study was to compare the trueness and precision of digital dental casts obtained from the direct digitization of 2 types of vinylsiloxanether (VSXE) impression materials by using a laboratory laser scanner.

MATERIAL AND METHODS

Thirty-eight elastomeric impressions were made of a master die with a similar morphology to a premolar crown preparation. The impression materials were Identium (IDE) and Identium Scan (SCAN), designed for direct digitalization. Each impression was digitalized by using an optical scanner to create digital casts. A computer-aided design (CAD) reference model of trueness (CRM) was created and aligned to each digital cast for digital 3-dimensional discrepancy analysis.

RESULTS

The mean ±standard deviation global trueness of IDE was 53 ±16 μm and that of SCAN was 46 ±3 μm. SCAN digital casts showed higher precision (58 ±5 μm) than IDE (69 ±18 μm) (P<.05). At the margin of the preparation and at the axial surfaces, SCAN models showed higher trueness (3 ±6 μm and 1 ±5 μm) than IDE (15 ±10 μm and 2 ±37 μm), respectively.

CONCLUSIONS

Scannable impressions could be digitalized with higher global precision than conventional elastomeric materials. Higher trueness could be achieved in specific impression locations such as gingival areas or axial walls of preparations, where the light emitted by the scanner was not blocked.

Evaluation of the Effect of Fluoride-containing Luting Cements on Titanium and Its Effect on the Shear Bond Strength

Context:

The most appropriate luting agent for titanium crowns is yet to be determined. Commonly used cements for luting titanium restorations give off leachable ions which may cause surface interaction with the titanium.

Aims:

The purpose of this study was to determine the shear bond strength of four grades of commercially pure titanium and Ti 6Al 4V with different cements and to examine for any surface physical changes.

Settings and Design:

The three luting cements, i.e., zinc polycarboxylate cement, glass ionomer cement, and zinc phosphate cement, were used to evaluate their effect on titanium. Ni Cr was used as a control.

Methods and Material:

The metal rods were milled to discs of 6 mm diameter and 4 mm height. Freshly extracted maxillary first molars, mounted in resin blocks, were sliced horizontally at occlusal third of the tooth. The discs were cemented to the sliced surface of the tooth with the three luting cements. The models were subjected to the shear bond strength test. Statistical analysis used: The data collected were analyzed statistically with one way ANOVA. A representative specimen of each group was observed under a scanning electron microscope.

Results:

The mean values ranged from 0.31 to 15.6 MPa. The shear bond strength values of the zinc polycarboxylate cement group were significantly high (P < 0.05). Corrosion of the titanium alloy luted with zinc polycarboxylate cement was observed.

Conclusions:

Cementation with zinc polycarboxylate cement provided high shear bond strength, but showed corrosion on titanium.

Discrepancy of complete-arch titanium frameworks manufactured using selective laser melting and electron beam melting additive manufacturing technologies

STATEMENT OF PROBLEM

Titanium frameworks for implant-supported prostheses can be additively manufactured using different powder-based fusion technologies, including selective laser melting (SLM) and electron beam melting (EBM). Some manufacturers have developed a technique that combines the printing of the framework with the subsequent machining of the implant interface. Whether these technologies produce frameworks with acceptable accuracies is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the discrepancy obtained from the digitizing procedures of the definitive cast, the implant-prosthesis discrepancy, and the distortion of the manufacturing processes in the fabrication of titanium frameworks for implant-supported complete-arch prostheses manufactured using SLM and EBM additive manufacturing technologies.

MATERIAL AND METHODS

A completely edentulous mandibular definitive cast with 4 implant analogs and a replica of a screw-retained interim restoration was obtained. A standard tessellation language (STL) file of the framework design was prepared using dental software (Exocad). Six frameworks were manufactured using either SLM (3D Systems) or EBM (Arcam) technologies. Discrepancy (μm) was measured at the x- (mesiodistal), y- (buccolingual), and z- (occlusogingival) axes by using the formula 3D=x²+y²+z² three times by best-fit superimposure of the definitive cast STL file, the definitive cast titanium framework, and the framework STL file by using a coordinate measuring machine (CMM) controlled by software (Geomagic). The Kruskal-Wallis and Mann-Whitney U statistical tests were used (α=.05).

RESULTS

The digitizing procedures of the definitive cast showed a mean accuracy of 3 ±3 μm. Except for the z-axis (P<.05), no significant differences were observed between the SLM and EBM technologies for implant prosthesis discrepancy for the x- or y-axis (P>.05). The most favorable results were obtained in the z-axis, representing the occlusogingival direction. Three-dimensional discrepancy measurements in all comparisons ranged between (60 ±18 μm and 69 ±30 μm) and were not statistically significant (P>.05). The highest discrepancy was observed in the y-axis (37 to 56 μm), followed by the x- (16 to 44 μm) and z- (6 to 11 μm) axes (P<.05).

CONCLUSIONS

The titanium frameworks analyzed for a complete-arch implant-supported prosthesis fabricated using either the SLM or EBM additive technologies showed a clinically acceptable implant-prosthesis discrepancy, where similar discrepancies on the x-, y-, and z-axes were found between the additive manufacturing technologies. Both technologies showed comparable abilities to manufacture the STL file additively on the x-, y-, and z-axes.

Fabricating a custom zirconia post-and-core without a post-and-core pattern or a scan post

Due to the increased esthetic demands, custom zirconia post-and-cores have recently become popular. A post-and-core pattern with acrylic resin or wax is scanned using a laboratory scanner for the design of a definitive post-and-core restoration. This procedure requires additional time and material handling experience. If a scan post is used for an intracanal digital scan, substantial initial investments for hardware and software are required. This article introduces an alternative technique for fabricating a custom zirconia post-and-core with a conventional impression. By using this technique, a properly fitted zirconia post-and-core is quickly and easily fabricated with less human error.

Influence of Different Luting Agents on the Marginal Discrepancy of Procera® AllCeram Alumina Crown Copings – An Experimental Study

Two maxillary first molars and two central incisor typhodont teeth were prepared with 0.8 mm chamfer, 2.0 mm occlusal reduction, and 6 degree taper. The prepared teeth were duplicated 9 times to obtain 36 die stone models and divided into three groups (n = 12). Luting agents tested were zinc phosphate, glass ionomer and resin cement. Procera®AllCeram 0.6 mm coping was fixed with a calibrated finger force of 50 N. The absolute marginal discrepancy was measured using the scanning electron microscope on four axial walls with 4 measurements on each wall to obtain a total of 16 readings for one tooth. Mann Whitney U test was applied to find significant differences between luting cements and Kruskal Wallis tests among groups. Results The absolute marginal discrepancies of cements were in reducing order zinc phosphate (AZ) 53 μm; resin (AR) 44.5 μm, glass ionomer (AG) 29 μm. There was a significant difference among luting cements AG V/s AZ (p = 0.001) and AR V/s AG (p = 0.003), except AR V/s AZ (p = 0.213). All axial surfaces except mesial showed a significant difference. Conclusion The study concluded that different luting media have a definite effect over the final fit of AllCeram coping. Absolute marginal discrepancy was within the accepted level of 100 μm. Distal axial surface demonstrated a wider gap among all the luting agents.

The accuracy of the CAD system using intraoral and extraoral scanners for designing of fixed dental prostheses

The accuracy of prostheses affects clinical success and is, in turn, affected by the accuracy of the scanner and CAD programs. Thus, their accuracy is important. The first aim of this study was to evaluate the accuracy of an intraoral scanner with active triangulation (Cerec Omnicam), an intraoral scanner with a confocal laser (3Shape Trios), and an extraoral scanner with active triangulation (D810). The second aim of this study was to compare the accuracy of the digital crowns designed with two different scanner/CAD combinations. The accuracy of the intraoral scanners and extraoral scanner was clinically acceptable. Marginal and internal fit of the digital crowns fabricated using the intraoral scanner and CAD programs were inferior to those fabricated using the extraoral scanner and CAD programs.

Marginal and internal fit of metal copings fabricated with rapid prototyping and conventional waxing

STATEMENT OF PROBLEM

Given the limitations of conventional waxing, computer-aided design and computer-aided manufacturing (CAD-CAM) technologies have been developed as alternative methods of making patterns.

PURPOSE

The purpose of this in vitro study was to compare the marginal and internal fit of metal copings derived from wax patterns fabricated by rapid prototyping (RP) to those created by the conventional handmade technique.

MATERIAL AND METHODS

Twenty-four standardized brass dies were milled and divided into 2 groups (n=12) according to the wax pattern fabrication method. The CAD-RP group was assigned to the experimental group, and the conventional group to the control group. The cross-sectional technique was used to assess the marginal and internal discrepancies at 15 points on the master die by using a digital microscope. An independent t test was used for statistical analysis (α=.01).

RESULTS

The CAD-RP group had a total mean (±SD) for absolute marginal discrepancy of 117.1 (±11.5) μm and a mean marginal discrepancy of 89.8 (±8.3) μm. The conventional group had an absolute marginal discrepancy 88.1 (±10.7) μm and a mean marginal discrepancy of 69.5 (±15.6) μm. The overall mean (±SD) of the total internal discrepancy, separately calculated as the axial internal discrepancy and occlusal internal discrepancy, was 95.9 (±8.0) μm for the CAD-RP group and 76.9 (±10.2) μm for the conventional group. The independent t test results showed significant differences between the 2 groups. The CAD-RP group had larger discrepancies at all measured areas than the conventional group, which was statistically significant (P<.01).

CONCLUSIONS

Within the limitations of this in vitro study, the conventional method of wax pattern fabrication produced copings with better marginal and internal fit than the CAD-RP method. However, the marginal and internal fit for both groups were within clinically acceptable ranges.

Repeatability and reproducibility of individual abutment impression, assessed with a blue light scanner

PURPOSE

We assessed the repeatability and reproducibility of abutment teeth dental impressions, digitized with a blue light scanner, by comparing the discrepancies in repeatability and reproducibility values for different types of abutment teeth.

MATERIALS AND METHODS

To evaluate repeatability, impressions of the canine, first premolar, and first molar, prepared for ceramic crowns, were repeatedly scanned to acquire 5 sets of 3-dimensional data via stereolithography (STL) files. Point clouds were compared and the error sizes were measured (n=10, per type). To evaluate reproducibility, the impressions were rotated by 10-20° on the table and scanned. These data were compared to the first STL data and the error sizes were measured (n=5, per type). One-way analysis of variance was used to assess the repeatability and reproducibility of the 3 types of teeth, and Tukey honest significant differences (HSD) multiple comparison test was used for post hoc comparisons (α=.05).

RESULTS

The differences with regard to repeatability were 4.5, 2.7, and 3.1 µm for the canine, premolar, and molar, indicating the poorest repeatability for the canine (P<.001). For reproducibility, the differences were 6.6, 5.8, and 11.0 µm indicating the poorest reproducibility for the molar (P=.007).

CONCLUSION

Our results indicated that impressions of individual abutment teeth, digitized with a blue light scanner, had good repeatability and reproducibility.

Three-dimensional evaluation of the repeatability of scans of stone models and impressions using a blue LED scanner

In this study, we evaluated the repeatability of scans of stone models and impressions of abutment teeth using a blue LED scanner and compared the findings between different abutment teeth types. For the stone models as well as impression of the canines, premolars, and molars, we generated 10 color-difference-maps and reports for each tooth type (n=10 per tooth type). One-way analysis of variance (ANOVA) and independent t-tests were performed to evaluate the repeatability of scans of the stone models and impressions obtained from a blue LED scanner. Our results indicate a high repeatability of scans of stone models and impressions of abutment teeth using the blue LED scanner and suggest a possible clinical advantage for scanning impressions of different abutment teeth types.

Accuracy of 3D white light scanning of abutment teeth impressions: evaluation of trueness and precision

PURPOSE

This study aimed to evaluate the accuracy of digitizing dental impressions of abutment teeth using a white light scanner and to compare the findings among teeth types.

MATERIALS AND METHODS

To assess precision, impressions of the canine, premolar, and molar prepared to receive all-ceramic crowns were repeatedly scanned to obtain five sets of 3-D data (STL files). Point clouds were compared and error sizes were measured (n=10 per type). Next, to evaluate trueness, impressions of teeth were rotated by 10°-20° and scanned. The obtained data were compared with the first set of data for precision assessment, and the error sizes were measured (n=5 per type). The Kruskal-Wallis test was performed to evaluate precision and trueness among three teeth types, and post-hoc comparisons were performed using the Mann-Whitney U test with Bonferroni correction (α=.05).

RESULTS

Precision discrepancies for the canine, premolar, and molar were 3.7 µm, 3.2 µm, and 7.3 µm, respectively, indicating the poorest precision for the molar (P<.001). Trueness discrepancies for teeth types were 6.2 µm, 11.2 µm, and 21.8 µm, respectively, indicating the poorest trueness for the molar (P=.007).

CONCLUSION

In respect to accuracy the molar showed the largest discrepancies compared with the canine and premolar. Digitizing of dental impressions of abutment teeth using a white light scanner was assessed to be a highly accurate method and provided discrepancy values in a clinically acceptable range. Further study is needed to improve digitizing performance of white light scanning in axial wall.

Accuracy of 3D scanners in tooth mark analysis

The objective of this study was to compare the accuracy of contact and laser 3D scanners in tooth mark analysis. Ten dental casts were scanned with both 3D scanners. Seven linear measurements were made from the 3D images of dental casts and biting edges generated with DentalPrint© software (University of Granada, Granada, Spain). The uncertainty value for contact 3D scanning was 0.833 for the upper dental cast and 0.660 mm for the lower cast; similar uncertainty values were found for 3D-laser scanning. Slightly higher uncertainty values were obtained for the 3D biting edges generated. The uncertainty values for single measurements ranged from 0.1 to 0.3 mm with the exception of the intercanine distance, in which higher values were obtained. Knowledge of the error rate in the 3D scanning of dental casts and biting edges is especially relevant to be applied in practical forensic cases.

Marginal Fit of Implant-Supported All-Ceramic Zirconia Frameworks

This study evaluated the effect of fabrication techniques and cyclic loading on the vertical marginal fit of implant-supported fixed partial denture (FPD) frameworks. Thirty implant-supported 3-unit FPD frameworks were fabricated on a model system, divided into 3 equal groups (n = 10). The first group (control) was constructed from base metal alloy; the other 2 test groups were constructed from all-ceramic zirconia using a computer-aided design/computer-aided manufacturing (CAD/CAM) Cerec 3 system and a copy milling (Zirkonzahn) system. A cyclic load of 200 N was applied to each framework for up to 50,000 cycles. Linear measurements were made in micrometers of the vertical gap between the framework and the implant-supported abutment at 16 predetermined points before and after cyclic loading. The frameworks were viewed using scanning electron microscopy to inspect any fractographic features. One-way analysis of variance was performed to compare the marginal discrepancy values of the control and the 2 test groups and for each group; a t test was applied to determine whether significant changes in the fit were observed after cyclic loading (α = 0.05). The CAD/CAM group showed significantly higher marginal gap mean values (80.58 μm) than the Zirkonzahn and control groups (50.33 μm and 42.27 μm, respectively) with no significant difference. After cyclic loading, the CAD/CAM group recorded the highest marginal gap mean value (91.50 ± 4.260 μm) followed by control group (72.00 ± 2.795 μm); the Zirkonzahn group recorded the lowest marginal gap (65.37 ± 6.138 μm). Cyclic loading significantly increased the marginal gap mean values in the control group only. A marginal chip was observed in one of the CAD/CAM ceramic frameworks. Within the limitations of this study, the fabrication technique influenced the marginal fit of the implant-supported 3-unit FPD frameworks. Cyclic loading failed to change the fit of all-ceramic zirconia frameworks, whereas significant changes were found in the metal frameworks.

A review of dental CAD/CAM: current status and future perspectives from 20 years of experience

In this article, we review the recent history of the development of dental CAD/CAM systems for the fabrication of crowns and fixed partial dentures (FPDs), based on our 20 years of experience in this field. The current status of commercial dental CAD/CAM systems developed around the world is evaluated, with particular focus on the field of ceramic crowns and FPDs. Finally, we discuss the future perspectives applicable to dental CAD/CAM. The use of dental CAD/CAM systems is promising not only in the field of crowns and FPDs but also in other fields of dentistry, even if the contribution is presently limited. CAD/CAM technology will contribute to patients' health and QOL in the aging society.

Computer aided analysis of digitized dental stone replicas by dental CAD/CAM technology

OBJECTIVES

To determine the reproducibility of digitized dental stone replicas compared to the master model and the reliability of the computer aided analysis.

METHODS

Four master dies, prepared for complete crowns were fabricated in presintered yttria-stabilized tetragonal zirconia (Y-TZP). Eight vinyl polysiloxane impressions (PROVIL novo; Heraeus Kulzer) were taken of each die and stone replicas were poured in type IV stone (Vel-Mix Stone; Kerr). The master dies and the stone replicas were digitized in a touch-probe scanner (Procera Forte; Nobel Biocare AB), to create triangulated surface-models. The point-cloud from the first of the repeated digitizations of each master die was used as CAD-reference-models (CRM). Discrepancies between the points in the triangulated surface-models and the corresponding CRM were measured by a matching-software (CopyCAD 6.504 SP2; Delcam Plc). The distribution of the discrepancies was analyzed and presented in color-difference-maps.

RESULTS

The precision of the measuring method, presented as the repeatability coefficient, ranged between 7 and 16 microm (entire surface), whereas the analysis of the stone replicas revealed a precision (repeatability coefficient) ranging from 19 to 26 microm. The accuracy of the replica to master (the mean discrepancy) ranged from 0.5 to 2.0 microm (95% confidence interval 1.5-2.9 microm).

SIGNIFICANCE

The greatest precision of the measurement was seen in the jacket surface of the die. The size of the stone replicas varied and the repeatability coefficient was on average 15 microm (2-25 microm) greater for the replica-to-master alignment than the repeated digitizations of the master.

Maxillary zirconia implant fixed partial dentures opposing an acrylic resin implant fixed complete denture: A two-year clinical report

The fabrication of fixed implant-supported prostheses for edentulous patients may be performed using all-ceramic or acrylic resin materials. This clinical report describes the fabrication and 2-year follow-up of maxillary zirconia implant fixed partial dentures opposing a mandibular acrylic resin screw-retained fixed complete denture.

Accuracy of dental digitizers

The need for proper validation and verification methodology for CAD/CAM systems is imminent. CAD/CAM systems consisting of an optical impression system, design software and a fabrication machine have to perform to a certain level, whereby manufacturers need to prove the effectiveness of the system as a whole. However, especially when dental surface digitization devices are used as open, stand-alone applications in dental outsourcing, a reliable standard test for comparison is necessary.

PURPOSE

This study evaluates a proposed test method to be used to quantify "digitizing quality" with respect to accuracy and reproducibility of two dental surface digitization devices. Comparability of the characteristics should be ensured.

METHOD

Two laser light section scanners: DentaScope II and D200 were evaluated by means of the 'Sphere Test', that involves repeated measurements of a precision ball (radius: 6mm) according to a pre-defined protocol. The surface information was received as unmatched, overlapping point clouds and statistically processed with a newly developed software package. The standard deviation of all points as well as a measure for undercutting the equator were determined.

RESULTS

The standard deviation for the radius for D and S were 7.7 (+/-0.8) and 13.9 (+/-1.0) microm respectively. The equator undercut elevations were -2.0 degrees and -0.25 degrees for scanner D and S respectively.

CONCLUSION

Scanner D had a significantly higher accuracy than S (p<0.05), corresponding with the smaller pixel distance of the sensor. Both devices show adequate accuracy and reproducibility and have an adequate ability to detect the equator. The test is also suitable for calibration purposes.

A three-dimensional evaluation of a laser scanner and a touch-probe scanner

STATEMENT OF PROBLEM

The fit of a dental restoration depends on quality throughout the entire manufacturing process. There is difficulty in assessing the surface topography of an object with a complex form, such as teeth, since there is no exact reference form.

PURPOSE

The purpose of this study was to determine the repeatability and relative accuracy of 2 dental surface digitization devices. A computer-aided design (CAD) technique was used for evaluation to calculate and present the deviations 3-dimensionally.

MATERIAL AND METHODS

Ten dies of teeth prepared for complete crowns were fabricated in presintered yttria-stabilized tetragonal zirconia (Y-TZP). The surfaces were digitized 3 times each with an optical or mechanical digitizer. The number of points in the point clouds from each reading were calculated and used as the CAD reference model (CRM). Alignments were performed by registration software that works by minimizing a distance criterion. In color-difference maps, the distribution of the discrepancies between the surfaces in the CRM and the 3-dimensional surface models was identified and located.

RESULTS

The repeatability of both scanners was within 10 microm, based on SD and absolute mean values. The qualitative evaluation resulted in an even distribution of the deviations in the optical digitizer, whereas the dominating part of the surfaces in the mechanical digitizer showed no deviations. The relative accuracy of the 2 surface digitization devices was within +/- 6 microm, based on median values.

CONCLUSION

The repeatability of the optical digitizer was comparable with the mechanical digitization device, and the relative accuracy was similar.

Precision of fit and clinical evaluation of all-ceramic full restorations followed between 0.5 and 5 years

Currently CAD-CAM systems are rapidly gaining importance in dental practice as some of their products aim to combine aesthetics with strength and are free of metals. This study reports on the crown adaptation, marginal fit and clinical behaviour of 300 all-ceramic full coverage restorations (Procera, Gothenburg, Sweden) placed in one clinical centre and followed up to 5 years. The marginal fit and coping adaptation before and after luting was determined by direct measurement as well as after sectioning in a laboratory study. Three hundred all-ceram restorations were installed in 165 patients between 1994 and 1998. Before the end of 2000, patients were recalled to assess their restorations, using the California Dental Association quality evaluation index, their own appreciation, as well as the reaction towards the periodontium. The in vitro data revealed a mean marginal adaptation of 30 microm, before and after luting of the Al(2)0(3)-coping onto the tooth. However, at the deepest part of the chamfer, the distance increased to 135 microm. In the clinical study only one restoration fractured, while in 6% small porcelain infractions occurred. After polishing the latter, no persistent patient complaints remained. At the last recall visit 1.8% of the margins were rated unacceptable. Dentists rated 72 and 78% of the restorations excellent for surface, colour and anatomic form respectively. Eighty-seven per cent of the patients rated their restorations more than 7/10 on an ordered analogue scale for aesthetics as well as for function.

Measurements of Soft Tissue Volume in Association with Single-Implant Restorations: A 1-Year Comparative Study after Abutment Connection Surgery

BACKGROUND

Patients with buccal defects due to tooth extraction seem to regain some of the contour at the time of abutment surgery and connection of single-implant crown restorations. It can then be assumed that different abutment systems could restore the buccal contour to different degrees.

PURPOSE

To measure changes in buccal tissue volume after placing restorations with single-implant crowns using two different abutment systems and to measure soft tissue change during the 1 year after single-implant treatment.

MATERIALS AND METHODS

Eighteen patients were provided with single-implant restorations in the central incisor area. Nine patients in each group were treated with single-implant crowns supported by either CeraOne abutments (Nobel Biocare AB, Göteborg, Sweden) or customized Procera ceramic abutments (Nobel Biocare AB). Study casts were made before abutment connection, at crown placement, and after 1 year. After the casts were scanned, they were analyzed with a computer, using the model before abutment as a reference. In the area of the single implant, sagittal projections provided images of the models that allowed measurements between the contours at the different situations. Radiography and photography for measuring papillary volume were also performed.

RESULTS

All patients exhibited increased "buccal volume" after abutment connection and crown placement (p < .01). A trend to greater increase was observed for the Procera group. Both groups also showed a reduction of buccal tissue 1 year later (p < .05-.01), leaving on average more volume in the Procera group. The papillae recovered spontaneously, and no relationship was observed between the presence of papilla and underlying bone support (p > .05).

CONCLUSIONS

The buccal tissue increased significantly after placement of the abutment cylinder and the implant crown. This increase of buccal contour was reduced after 1 year. Furthermore, no relationship was established between the presence of papillae and the distance between the contact point and the underlying bone crest.

Optical modeling of extraoral defects

In order to reduce the stress caused to patients by conventional methods of modeling using computed tomography (CT) or magnetic resonance imaging (MRI), an optical modeling process has been developed for extraoral defects and body areas. The selected body part is digitized using optical 3-coordinate measuring technology, providing an extensive data record. This is adapted for further use by equalizing the point clouds to obtain a Computer Aided Design (CAD) model, which is converted to a physical model by means of a stereolithographic process. With this technology, the patient's physical and psychological stress may be reduced. This article describes a technique for optical modeling of an ocular prosthesis.

Fit of implant frameworks: an in vitro comparison between two fabrication techniques

STATEMENT OF PROBLEM

It has been suggested that a precise fit between the implant and the framework cylinder is necessary to ensure a satisfactory long-term clinical outcome.

PURPOSE

The purpose of this study was to compare the precision of fit between implant abutments and framework cylinders in frameworks fabricated by the Procera system and those fabricated from cast gold-alloy.

MATERIAL AND METHODS

A total of 19 frameworks, 14 made with the Procera system (type 1) and 5 made of a cast gold-alloy (type 2), were fabricated. A total of 95 implants, 70 type 1 and 25 type 2 frameworks, were evaluated. Three replicas of the space between the implant abutments and the framework cylinders of the master cast were made for each test specimen. The replicas were cut with a scalpel in 2 axial directions: buccal-lingual and right-left. For the purpose of measurement, a microscope with a precision of +/- 0.5 microm was used at original magnification x30. The Student t test was used to determine whether there were significant differences between the framework designs.

RESULTS

The buccal-lingual measurements for the type 1 and type 2 frameworks showed mean values of 28.1 microm (SD 9.8) and 42.0 microm (SD 1.8) on the buccal side, respectively, and 25.6 microm (SD 11.2) and 51.6 microm (SD 10.9) on the lingual side, respectively. For the right-left view, the mean measurements were 26.6 microm (SD 8.4) and 49.2 microm (SD 11.4) on the right side, respectively, and 27.4 microm (SD 8.5) and 44.4 microm (SD 6.5) on the left side, respectively. The total mean value for type 1 frameworks was 26.9 microm (SD 9.3); that for type 2 frameworks was 46.8 microm (SD 8.8).

CONCLUSION

Within the limitations of this experiment, it was demonstrated that the fit of frameworks made with the Procera system was significantly better than that of the frameworks made with cast gold-alloy (P<.01).

Use of zinc phosphate cement as a luting agent for Denzir trade mark copings: an in vitro study

BACKGROUND: The clinical success rate with zinc phosphate cemented Procera crowns is high. The objective with this study was to determine whether CADCAM processed and zinc phosphate cemented Denzir copings would perform as well as zinc phosphate cemented Procera copings when tested in vitro in tension. METHODS: Twelve Procera copings and twenty-four Denzir copings were made. After the copings had been made, twelve of the Denzir copings were sandblasted on their internal surfaces. All copings were then cemented with zinc phosphate cement to carbon steel dies and transferred to water or artificial saliva. Two weeks after cementation, half of the samples were tested. The remaining samples were tested after one year in the storage medium. All tests were done in tension and evaluated with an ANOVA. RESULTS: Sandblasted and un-sandblasted Denzir copings performed as well as Procera copings. Storage in water or artificial saliva up to one year did not decrease the force needed to dislodge any of the coping groups. Three copings fractured during testing and one coping developed a crack during testing. The three complete fractures occurred in Procera copings, while the partly cracked coping was a Denzir coping. CONCLUSION: No significant differences existed between the different material groups, and the retentive force increased rather than decreased with time. Fewer fractures occurred in Denzir copings, explained by the higher fracture toughness of the Denzir material. Based on good clinical results with zinc phosphate cemented Procera crowns, we foresee that zinc phosphate cement luted Denzir copings are likely to perform well clinically.

Fabrication of a digitally scanned, custom-shaped abutment: a clinical report

A procedure for the creation of a custom, anatomic implant abutment copy milled with digitally scanned information has been described. The definitive restoration was a custom-machined abutment with a ceramic crown that had an aluminous oxide core.

Marginal fit and short-term clinical performance of porcelain-veneered CICERO, CEREC, and Procera onlays

STATEMENT OF PROBLEM

Onlay preparations are very complex surfaces for computer surface digitization, CAD, and CAM of all-ceramic onlay cores.

PURPOSE

This study tested the hypothesis that onlays can be fabricated with CICERO, CEREC, and Procera core technologies.

MATERIAL AND METHODS

Fifteen mandibular and 10 maxillary molars were prepared for onlays in 17 patients (11 women and 6 men). The onlay design was experimental. Molars were prepared with deep gingival chamfers in the proximal boxes and around the functional cusps. The nonfunctional cusps were prepared with broad bevels. Eight stone dies of preparations were measured with a laser beam (CICERO), 10 dies with a light beam (CEREC), and 7 dies with a contact probe (Procera). Two onlay cores were produced for the same stone die. One core was used to analyze fit on the stone die, and the other core was porcelain veneered for optimizing anatomy, esthetics, and fit of the onlay and cemented. The fit of the onlay core on the stone die and the cement width on a stone cast were measured by a microscopic digital imaging system. The onlays were evaluated for function every 6 months for 2 years.

RESULTS

Measurements of the margins by the CICERO system were (1) precise (error <4%) and (2) accurate with an SD of less than 9 microm. The proposed onlay preparation design met the requirement that all points of the surface be visible from a single point of view for optical 3-dimensional mapping by the CEREC system. For the surface measurements by the Procera contact probe, the orientation of the sapphire tip toward the preparation surface was critical, and it was necessary to apply wax to smooth internal edges. The marginal gaps of the CICERO, CEREC, and Procera cores on the stone dies were 74 microm (SD 15), 85 microm (SD 40), and 68 microm (SD 53), respectively. The cement width was 81 microm (SD 64). No fractures occurred.

CONCLUSION

Marginal gaps for the onlay cores were no more than 85 microm. The cement width of the semicomputer-produced onlays of 81 microm was a favorable measurement value for a clinically acceptable, strong all-ceramic onlay. However, this value as well as anatomy and esthetics of the onlay depended on the craftsmanship of the porcelain veneering by the dental technician.

Procera all-ceramic crowns: a new approach to an old problem?

Increasing patient expectations regarding the appearance of restorations continue to test the ingenuity and skill of the dental team. To this end the quest for sufficiently strong, metal-free, all-ceramic restorations to function in all areas of the mouth continues apace. We report on a possible solution to this problem that uses computer-aided design/computer-aided milling (CAD/CAM) technology coupled with a novel, densely sintered, ceramic material. In this article we offer suggestions for case selection, preparation design, and luting procedures, and in addition illustrate these with a number of completed cases.

Five-year clinical evaluation of Procera AllCeram crowns

STATEMENT OF PROBLEM

Esthetic demands of patients and practitioners for an all-ceramic crown in both anterior and posterior regions of the dental arches has prompted the development of the Procera AllCeram crown. Long-term clinical trials that evaluate the strength and naturalness of the Procera AllCeram crown are lacking.

PURPOSE

This prospective study was initiated to evaluate the clinical performance of 100 Procera AllCeram crowns after 5 years in service.

MATERIAL AND METHODS

One hundred Procera AllCeram crowns were fabricated for 58 patients (20 men and 38 women). Patients were treated by 4 general dental practitioners. Crown placement involved both the anterior and posterior regions of the dental arches. Crowns were examined at baseline and once a year during the 5 years that followed and evaluated at each appointment with the California Dental Association's quality assessment system.

RESULTS

Of the 97 crowns remaining in the study after 5 years, only 3 crowns had experienced a fracture through the veneering porcelain and the aluminum oxide coping material. Two additional crowns were replaced as a result of fractures of only the veneering porcelain. One crown was replaced as a result of recurrent caries. All remaining crowns were ranked as either excellent or acceptable for surface/color, anatomic form, and marginal integrity.

CONCLUSION

The 5-year clinical observations and ranking with the California Dental Association's quality assessment criteria supported the conclusion that Procera AllCeram crowns may be used in all areas of the mouth.

Computer-assisted milling of dental restorations using a new CAD/CAM data acquisition system

BACKGROUND

Recent technologic innovations have created possibilities for restorative dentistry, such as computer-aided design and computer-aided manufacturing (CAD/CAM).

PURPOSE

This article presents a new CAD/CAM process that has been developed for the fabrication of dental restorations.

METHODS

This process uses an improved imaging technique, successfully applied in other industries. Imaging is accomplished with 2-dimensional line grids projected onto an object, which allows for a mathematical reproduction of prepared and unprepared tooth surfaces, including those that are outside the direct line of light. The relative position of the sensor to the surface of the object is controlled automatically.

CONCLUSIONS

This system, which is undergoing clinical testing, allows the generation of various types of highly accurate dental restorations (inlays, onlays, crown, and fixed partial dentures) from a number of different materials. Acquired digitized data points are directly translated from the sensor to the electronic controls of the milling machine to provide various manufacturing possibilities, including copy milling and accurate reproduction of occlusal tooth surfaces in various materials.

AllCeram crowns for single replacement implant abutments

Clinicians who are comfortable with traditional porcelain fused to metal restorations may find the thickness of veneering porcelain addition to the CeraOne single tooth ceramic cap disconcerting. When using a premanufactured ceramic cap to fit the space of the final restoration, substantial amounts of "unsupported" veneer porcelain may be required to achieve tooth contact to adjacent or opposing dentition. A potential problem of weak, unsupported veneer porcelain has been addressed by a modification of an existing manufacturing process. By using CAD/CAM technology, a custom-designed Procera AllCeram coping can be created for the implant abutment that eliminates any concerns regarding the resultant design of the underlying ceramic cap substructure.

Accuracy of machine milling and spark erosion with a CAD/CAM system

A method for manufacturing crowns and fixed partial dentures based on CAD/CAM has been developed as an alternative to the lost wax technique and the casting of an alloy. In this process two steps are included: milling and spark erosion. The computer-assisted design (CAD) relies heavily on the accuracy of the milling and spark erosion processes to achieve a clinically acceptable restoration. These two processes must be able to produce the crown data generated in the CAD files. This study evaluated the accuracy of the Procera CAD/CAM system in creating specific geometric bodies that were compared with the known dimensions in the CAD files for these bodies. The manufacturing errors of milling (ellipse +/- 6.5 microm, square +/- 3.4 microm, and cylinder +/- 5.8 microm) and spark erosion (ellipse +/- 8.6 microm and square +/- 10.4 microm) were determined. The accuracy of this manufacturing process demonstrated that this system was capable of producing a crown with a clinically accepted range for marginal opening gap dimension of less than 100 microm.