Heike Rudolph

Three-dimensional fit of CAD/CAM-made zirconia copings

OBJECTIVES CAD/CAM-technologies aim for a standardized, accurate production of dental restorations out of high strength materials (zirconia). The three-dimensional internal fit of CAD/CAM-manufactured zirconia copings was evaluated in vitro to verify the realizability of this aim. METHODS The analysis was based on ceramic master dies of prepared teeth and corresponding virtual CAD surfaces. Five copings per die were manufactured with two different CAD/CAM-technologies: milling and grinding. The internal fit was determined by a three-dimensional replica technique by optical digitization and computer-assisted analysis. RESULTS Mean internal gaps were 134/84μm (SD 78/28) for molar and 93/69μm (SD 56/35) for premolar copings (milling/grinding) using a digitizable silicone for the replicas representing the cement space; they were statistically significant regarding tooth and CAD/CAM-system (p<0.001). SIGNIFICANCE All zirconia copings showed an internal accuracy of fit where the gap widths ranged within the current clinical recommendations. However, there still is room for improvement and further standardization of CAD/CAM-technologies.

Accuracy of intraoral and extraoral digital data acquisition for dental restorations

ABSTRACT The computer-aided design (CAD) and computer-aided manufacturing (CAM) process chain for dental restorations starts with taking an impression of the clinical situation. For this purpose, either extraoral digitization of gypsum models or intraoral digitization can be used. Despite the increasing use of dental digitizing systems, there are only few studies on their accuracy. Objective This study compared the accuracy of various intraoral and extraoral digitizing systems for dental CAD/CAM technology. Material and Methods An experimental setup for three-dimensional analysis based on 2 prepared ceramic master dies and their corresponding virtual CAD-models was used to assess the accuracy of 10 extraoral and 4 intraoral optical non-contact dental digitizing systems. Depending on the clinical procedure, 10 optical measurements of either 10 duplicate gypsum dies (extraoral digitizing) or directly of the ceramic master dies (intraoral digitizing) were made and compared with the corresponding CAD-models. Results The digitizing systems showed differences in accuracy. However, all topical systems were well within the benchmark of ±20 µm. These results apply to single tooth measurements. Conclusions Study results are limited, since only single teeth were used for comparison. The different preparations represent various angles and steep and parallel opposing tooth surfaces (incisors). For most digitizing systems, the latter are generally the most difficult to capture. Using CAD/CAM technologies, the preparation angles should not be too steep to reduce digitizing errors. Older systems might be limited to a certain height or taper of the prepared tooth, whereas newer systems (extraoral as well as intraoral digitization) do not have these limitations.

Comparison of an analog and digital quantitative and qualitative analysis for the fit of dental copings

BACKGROUND Precision in fit is crucial for dental crowns and bridges. Most analyses of fit are based on analog 2D techniques. Aim of this in-vitro study was to compare an analog and a digital quantitative and qualitative analysis for the fit of CAD/CAM fabricated dental copings. METHODS A prepared steel canine served as master die. CAD surface models, varying in data density, were purposely enlarged in height (Ez), circumference (Exy) and both of these aspects at once (Exyz). Two titanium copings for each variation were produced. The silicone-replica-technique was applied to analyze the fit by means of a 2D analog light microscope measurement (LMM) and a 3D computer-assisted measurement using an optical digitizing system (ODKM97), respectively. RESULTS In most cases, restorations based on the low data density showed a better fit than those based on high data density. Original size low density data showed the lowest marginal and axial values in the quantitative 2D analyses (LMM and ODKM97). The 3D measurements (ODKM97) revealed best fit of the low density original size specimens, whereas the Ez specimens showed the highest values. Noticeable variations in fit were detected marginally and axially depending on the specific measurement point (mesial, distal, oral, or buccal) for both measurement systems. DISCUSSION The analog 2D replica technique revealed a loss of information due to the necessary cutting process. By contrast, the digital computer-based method provided 3D quantitative and qualitative results without data loss over the complete surface.

Retrospective study to determine the accuracy of template-guided implant placement using a novel nonradiologic evaluation method

OBJECTIVES With a novel, noninvasive method for determining three-dimensional accuracy, the realized implant position relative to the planned implant position was analyzed retrospectively. Additional postoperative cone beam computed tomography was thus dispensable. STUDY DESIGN Twelve cases with distal extension situations (DESs) or single tooth gaps (STGs) were evaluated. The data sets of the planned implant position were superimposed on the actually achieved implant position, retrieved from digitizing the implant impression. The deviations were measured and statistically analyzed. RESULTS The mean deviation was 5° in the DES group and 4° in the STG group for the implant axes, 1 mm (DES) and 0.9 mm (STG) at the implant neck, and 1.6 mm (DES) and 1.5 mm (STG) at the implant apex. The mean height discrepancy was 0.5 mm (DES) and 0.5 mm (STG). No significant differences (P > .05) were found between the DES and STG groups. CONCLUSIONS The innovative, noninvasive evaluation method is suitable and sufficiently accurate for the assessment of larger cohorts. The results of our study showed a sufficiently high degree of accuracy when using a virtual planning program for which no radiopaque template is needed when performing cone beam computed tomography.

Performance of dental impression materials: Benchmarking of materials and techniques by three-dimensional analysis.

Among other factors, the precision of dental impressions is an important and determining factor for the fit of dental restorations. The aim of this study was to examine the three-dimensional (3D) precision of gypsum dies made using a range of impression techniques and materials. Ten impressions of a steel canine were fabricated for each of the 24 material-method-combinations and poured with type 4 die stone. The dies were optically digitized, aligned to the CAD model of the steel canine, and 3D differences were calculated. The results were statistically analyzed using one-way analysis of variance. Depending on material and impression technique, the mean values had a range between +10.9/-10.0 µm (SD 2.8/2.3) and +16.5/-23.5 µm (SD 11.8/18.8). Qualitative analysis using colorcoded graphs showed a characteristic location of deviations for different impression techniques. Three-dimensional analysis provided a comprehensive picture of the achievable precision. Processing aspects and impression technique were of significant influence.

Er:YAG Laser Activation of Sodium Hypochlorite for Root Canal Soft Tissue Dissolution

The aim of this in vitro study was to investigate the effect of Er:YAG laser irradiation on the ability of sodium hypochlorite (NaOCl) to dissolve soft tissue during endodontic procedures.Background and Objective The aim of this in vitro study was to investigate the effect of Er:YAG laser irradiation on the ability of sodium hypochlorite (NaOCl) to dissolve soft tissue during endodontic procedures. Materials and Methods Two acrylic glass plates, each containing a semi-canal, were bolted together to form a complete canal. This geometry permitted one semi-canal to be filled with fine liver sausage of bovine origin dyed by methylene blue and the other with NaOCl (4.00–4.99% available chlorine; Sigma–Aldrich Corporation, St. Louis, MA), which was then activated by Er:YAG laser irradiation (KEY Laser 3; KaVo, Biberach, Germany) using a plain-ended fiber tip and a range of output energy and repetition rate. To achieve relatively low output energy from high input energy, the laser beam was attenuated by placing glass slides in the beam path. The resultant images acquired were analyzed using pixel-based analysis. Samples were statistically analyzed (two-way ANOVA, P < 0.05, univariate, bifactorial; IBM SPSS Statistics 19, SPSS Inc., Chicago, IL). Results Both output energy and repetition rate significantly influenced the tissue dissolution ability of NaOCl (P < 0.05). Conclusion Within the limitations of this in vitro study, we conclude that laser activation of NaOCl at 200 mW output power leads to effective soft tissue dissolution. This finding can be of use to endodontists pursuing effective soft tissue dissolution from their irrigants. Lasers Surg. Med. 45:339–344, 2013.

Randomized controlled trial comparing direct intraoral digitization and extraoral digitization after impression taking.

This study aimed to evaluate the correspondence of intraoral digitization (ID) with extraoral digitization (ED) after impression taking. One-stage putty-and wash impressions and ID were carried out in a randomized order for 10 subjects. The impressions were used to make casts, which were then subjected to ED. ID datasets were aligned to create computer-aided design reference models. Deviations between ID and ED were calculated. The mean positive and negative deviations were 37.7 and -48.4 µm, respectively, for one quadrant. The results showed that the ID system is well suited for the acquisition of single-tooth restorations and is of limited suitability for the acquisition of small multiple unit restorations.

Alveolar Ridge Preservation as a Way to Reduce the Need for Bone Augmentation: Implementation of a New, Non-invasive Method of Measuring Bone Preservation: Study Protocol of a Randomized Controlled Clinical Trial and Feasibility Testing Results

Introduction: The efficacy of alveolar ridge preservation (ARP) in preserving the bone after tooth extractions and before rehabilitation with an implant-supported restoration is examined. A new, non-invasive measurement method to determine the extent of bone preservation is presented. This measurement method is based on a 3D comparison of the condition immediately after extraction with the data of a cone-beam computed tomography (CBCT) eight weeks after extraction. Method: The study is a single-center, randomized, controlled parallel-group clinical investigation. 88 patients who required extraction of a maxillary tooth participated in the study. In 44 patients (intervention group), the socket is filled with a combination of a collagen plug and a collagen membrane introduced in the empty socket immediately after tooth removal (ARP). The 44 patients (control group) experience unassisted socket healing the hyporeflective space. Primary endpoints are (1) bone loss after tooth extraction; (2) the preservation of the alveolar ridge (soft tissue and bone); (3) the need for augmentation during the subsequent implant treatment; and (4) the question whether ARP is more costeffective than the therapy with unassisted socket healing. Patients will be followed for 5 years. Discussion: The extent of bone resorption after tooth extraction significantly influences the subsequent implant placement. Preserving the bone as well as possible is of great importance for the stability, prosthetically correct position and long-term functional success of the implantological treatment. A new, non-invasive method, without additional, study-related X-ray exposure, presented here for the first time, the change in volume of the bone bed can be analyzed. The preliminary results of this feasibility test report a median value of buccal and palatal bone loss of 6.2 mm (control)/4.4 mm (test) and 2.5 mm (control)/2.8 mm (test), respectively. These values are comparable to studies that also determined bone resorption by CBCT.

Echinococcus cysts affecting oromaxillofacial structures – a systematic review

OBJECTIVES Cystic echinococcosis is a worldwide spread zoonosis and humans become accidental intermediate hosts. Any tissue can be affected. However, oromaxillofacial cystic echinococcosis is very uncommon and has never been studied systematically and no evidence-based treatment recommendations are available. Aim of this paper is to summarize the current knowledge and clinical experience with oromaxillofacial manifestations of cystic echinococcosis. MATERIALS AND METHODS PubMed database was accessed with a comprehensive, complex search strategy. Medical Subject Headings terms, wildcard search, truncated search terms and Boolean operators were used. No filters to restrict the results were set. Two evaluators jointly assessed the results in terms of defined criteria. RESULTS The search strategy retrieved 538 results in total. After evaluation 83 publications presenting 108 cases on oromaxillofacial cystic echinococcosis were included. Parotid gland, mandibular region and maxillary region were most commonly affected. Median patient age was 22 years (range 2.5 months to 81 years). Surgical treatment was performed in 97 cases. CONCLUSIONS In cases of oromaxillofacial cystic echinococcosis a thorough evaluation of the patients for further cysts is essential. Therapeutic treatment options are surgical or minimally invasive intervention and drug treatment with benzimidazoles. The diagnosis can be difficult and often require a multidisciplinary approach.

Performance of Fast-Setting Impression Materials in the Reproduction of Subgingival Tooth Surfaces Without Soft Tissue Retraction

PURPOSE Fast-setting impression materials may be prone to inaccuracies due to accidental divergence from the recommended mixing protocol. This prospective randomized clinical trial aimed to assess three-dimensional (3D) deviations in the reproduction of subgingival tooth surfaces and to determine the effect of either following or purposely diverging from the recommended mixing procedure for a fast-setting addition-curing silicone (AS) and fast-setting polyether (PE). MATERIALS AND METHODS After three impressions each were taken from 96 participants, sawcut gypsum casts were fabricated with a standardized procedure and then optically digitized. Data were assessed with a computer-aided 3D analysis. RESULTS For AS impressions, multivariate analysis of variance revealed a significant influence of the individual tooth and the degree to which the recommended mixing protocol was violated. For PE impressions, the ambient air temperature and individual tooth showed significant effects, while divergence from the recommended mixing protocol was not of significance. CONCLUSIONS The fast-setting PE material was not affected by changes in the recommended mixing protocol. For the two fast-setting materials examined, no divergences from the recommended mixing protocol of less than 2 minutes led to failures in the reproduction of the subgingival tooth surfaces.