Biomedical subjects

R G Luthardt

Publications and source records attributed to R G Luthardt.

8 recordsLinked to original sources

PubMed2005

Effects of prosthetic treatment for shortened dental arches on oral health-related quality of life, self-reports of pain and jaw disability: results from the pilot-phase of a randomized multicentre trial.

A multi-centre randomized clinical trial is under way at 14 university dental schools in Germany to compare prosthodontic treatments for the shortened dental arch (SDA). One of the aims of this pilot-study was to measure the effect of two treatment options of the SDA on oral health-related quality of life and on the Research Diagnostic Criteria (RDC) for temporomandibular disorders (TMD). Thirty-four patients participated in the pilot-study. Inclusion criteria were: all molars were missing and the presence of at least both canines and one premolar in each quadrant. Participants were randomly assigned to receive either removable partial dentures including molar replacement (RPD_group) or retain a premolar occlusion (PROC_group). The Oral Health Impact Profile (OHIP-49) and the RDC for TMD were completed by participants before treatment (pre-treatment), 6 weeks (6 wks), 6 months (6m) and 12 months (12 m) after treatment. At the 12-month follow up, data of 10 women and 11 men (mean age: 62 +/- 10 years) were available. Medians of the OHIP total-scores were as follows: RPD (n = 10), 43.5 (pre-treatment), 18.2 (6 wks), 13.3 (6m), 14.7 (12 m). PROC (n = 11): 31.8 (pre-treatment), 27.1 (6 wks), 8.8 (6m), 8.3 (12 m). Significant differences were shown for RPD_group between pre-treatment and 6m/12 m and for PROC_group between pre-treatment and 6m. There were no significant differences between treatment groups at any time. Within each group, an improvement of life-quality was observed. No significant difference could be reported between the two therapy concepts. This may be due to the low sample size within the pilot study.

Aged↗

PubMed2005

Accuracy of intraoral data acquisition in comparison to the conventional impression.

The achievable accuracy is a decisive parameter for the comparison of direct intraoral digitization with the conventional impression. The objective of the study was therefore to compare the accuracy of the reproduction of a model situation by intraoral digitization vs. the conventional procedure consisting of impression taking, model production, and extraoral digitization. Proceeding from a die model with a prepared tooth 16, the reference data set of the teeth 15, 16 and 17 was produced with an established procedure by means ofextraoral digitization. For the simulated intraoral data acquisition of the master model (Cerec 3D camera, Sirona, Bensheim), the camera was fastened on a stand for the measurement and the teeth digitized seven times each in defined views (occlusal, and in each case inclined by 20 degrees, from the mesio-proximal, disto-proximal, vestibular and oral aspect). Matching was automated (comparative data sets B1-B5). A clinically perfect one-step putty-and-wash impression was taken from the starting model. The model produced under defined conditions was digitized extraorally five times (digi-SCAN, comparative data sets C1-C5). The data sets B1-B5 and C1-C5 were assigned to the reference data set by means of best-fit matching and the root of the mean quadratic deviation (RMS; root mean square) calculated. The deviations were visualized, and mean positive, negative and absolute deviations calculated. The mean RMS was 27.9 microm (B1-B5) or 18.8 microm (C1-C5). The mean deviations for the prepared tooth were 18 microm/-17 microm (B1-B5) and 9 microm /-9 microm (C1-C5). For tooth 15, the mean deviations were 22 microm/-19 microm (B1-B5) and 15 microm/-16 microm (C1-C5). The intraoral method showed good results with deviations from the CAD starting model of approx. 17 microm, related to the prepared tooth 16. On the whole, in this in-vitro study, extraoral digitization with impression taking and model production showed higher accuracy than intraoral digitization. Since the inaccuracies in the conventional impression under real clinical conditions may be higher than the values determined above, a comparison under clinical conditions should be performed subsequently.

Bicuspid↗

PubMed2002

Reliability and properties of ground Y-TZP-zirconia ceramics.

Yttria-stabilized zirconia ceramics is a high-performance material with excellent biocompatibility and mechanical properties, which suggest its suitability for posterior fixed partial dentures. The hypothesis under examination is that the strength and reliability of Y-TZP zirconia ceramics are affected by the inner surface grinding of crowns, and vary with the grinding parameter. Flexural strength, surface roughness, and fracture toughness were determined on samples machined by face and peripheral grinding with varied feed velocities and cutting depths. Results have been compared with those on lapped samples. Analysis of variance and Weibull parameter were used for statistical analysis. It was found that inner surface grinding significantly reduces the strength and reliability of Y-TZP zirconia compared with the lapped control sample. Co-analysis of flexural strength, Weibull parameter, and fracture toughness showed counteracting effects of surface compressive stress and grinding-introduced surface flaws. In conclusion, grinding of Y-TZP needs to be optimized to achieve the CAD/CAM manufacture of all-ceramic restorations with improved strength and reliability.

Algorithms↗

PubMed2001

Burs with guide pins for standardized tooth preparation.

OBJECTIVE: The aim of this study was to develop and test self-limiting diamond burs to ease precise chamfer preparation and to fulfill the special requirements of computer-aided design/computer-aided manufacturing and all-ceramic restorations. METHOD AND MATERIALS: Rounded cylinder (based on ISO 881) and torpedo (based on ISO 879) diamond burs with a polished guide pin, 0.5 mm in length and 0.15 mm in radius, at the front end were developed in cooperation with an industrial partner. The in vitro testing involved a total of 140 human teeth. Experimental variables were the quality of the finish line, the microhardness of the enamel, and the thermal alteration of the dentin. Conventional diamonds served as a control. RESULTS: No mechanical or thermal damage related to the bur design was found in the hard tissues that had potentially been in contact with or in close proximity to the guide pin. Microhardness of the enamel at the finish line was significantly higher when prepared with burs with a guide pin compared to conventional burs. The results of using the guide pin might indicate the beneficial effect of reduced vibration. CONCLUSION: The guide pins of the self-limiting diamond burs reduce, rather than increase, the risk of hard tissue damage at the preparation margin. No adverse effects were found. Clinical use is justified.

Body Temperature↗

PubMed2000

Clinical performance and periodontal outcome of temporary crowns and fixed partial dentures: A randomized clinical trial.

STATEMENT OF PROBLEM: Different materials (autopolymerizing, dual curing, and light initiated) are used for fabricating provisional restorations during prosthetic treatment. Randomized clinical trials that have evaluated these provisional materials have not been published. PURPOSE: This clinical trial compared the handling, fitting, plaque adherence, gingivitis, color stability, and the subjective assessment of the provisional materials by the patient and the dentist for 2 autopolymerizing (Protemp, Luxatemp), 1 dual-curing (Provipont), and 1 light-initiated (Triad-VLC) material for the manufacturing of temporary crowns and fixed partial dentures. MATERIAL AND METHODS: Thirty subjects in need of 2 similar fixed prosthetic restorations (single crowns ¿20, three-quarter crowns ¿2, connected crowns ¿9, or fixed partial dentures ¿30) were treated with 1 temporary restoration of Protemp II (control) and one randomly selected from Luxatemp, Provipont, or Triad-VLC materials. The mean time of treatment was 37.5 days (minimum 2 days, maximum 156 days). All restorations were manufactured intraorally with a vacuum-formed template. RESULTS: Mechanical and retentive characteristics revealed a high level of clinical reliability. Plaque adherence of the teeth with temporary restorations was significantly increased (P =.0039) compared with the untreated mesial reference teeth. CONCLUSION: The advantageous mechanical properties of the light-curing and dual-curing materials reviewed in dental literature were clinically offset by disadvantages in handling.

Chi-Square Distribution↗

PubMed1999

Zirconia-TZP and alumina--advanced technologies for the manufacturing of single crowns.

All-ceramic crowns based on Zirconia-TZP-frameworks should have advantages in comparison to copings of Alumina (PROCERA-AllCeram) because of their mechanical properties. Zirconia-TZP-frameworks were manufactured after optical digitising using a modified Precident-DCS-System. The mean fracture strength and the vertical marginal discrepancy of Zirconia-TZP-frameworks and Alumina-copings (PROCERA-AllCeram) were determined. Additionally the bonding strength of suitable veneering ceramics on pre-treated Zirconia-TZP surfaces was examined using the scratch test and the shear bonding strength. The results show that the bonding between Zirconia-TZP and the veneering ceramics as well as the precision of fit of the veneered crowns are comparable with established systems.

Aluminum Oxide↗

PubMedDate not supplied

Accuracy of mechanical digitizing with a CAD/CAM system for fixed restorations.

PURPOSE: Most research on the accuracy of dental computer-aided design/manufacturing (CAD/CAM) systems focuses on the marginal gap. A detailed analysis of the various components of CAD/CAM systems (digitizer, software, and milling machine) using this approach is nearly impossible. The purpose of this study was to determine the accuracy of the manual mechanical digitizer of the Precident-DCS system. MATERIALS AND METHODS: Gauge blocks were aligned to the coordinate planes of the digitizer to determine the point and length measurement uncertainty. The values for each measuring point were compared for statistical differences concerning first versus second operator, pressure, and mode of sensing using analysis of variance. The measurement uncertainty was given by 95th percentiles. RESULTS: The mean one-dimensional point measurement uncertainty in the Y direction was 11 microm for the first, 8 microm for the second, and 37 microm for both operators. The three-dimensional point measurement uncertainty in the Y direction was 10 microm for the first, 33 microm for the second, and 60 microm for both operators. The point measurement uncertainty was significantly influenced by the pressure during sensing and by the operator as well. There were significant differences between the first and second recordings. The length measurement uncertainty in the Y direction for a gauge block of 20 mm was 52 microm for both operators. CONCLUSION: The reliability of the manually guided Precident-DCS digitizer is limited because of the significant influence of the operator and the mode of sensing (one or three dimensional). Compared with an automatic digitizing system, the measurement uncertainty of the manually guided digitizer exceeds the values published in the literature.

Analysis of Variance↗

PubMedDate not supplied

Matching point clouds: limits and possibilities.

In computer-aided production of fixed dental restorations, the process chain always starts with digitizing, independent of the type of further (data) processing, the material used, and the kind of restoration to be produced. The quality of the digitized data, followed by the influences of further data processing and the production parameters, decisively influence the fitting accuracy of the dental restoration to be fabricated. The accuracy with which individually measured 3D data sets in the form of point clouds can be matched for further processing in one common system of coordinates was the object of the present study. Casts of the maxilla and mandible were digitized in several partial measurements comprising two to three teeth in each case, using an optical three-coordinate measuring system. The individual segments were sequentially aligned to surfaces that were created on the basis of partial point clouds. The mean deviation between surfaces and point clouds was between 1.90 microns and 18.24 microns. The accuracy of the alignment was determined by the RMS (root mean square) error, and was on average 14.2 microns (SD 7 microns) for the maxilla and 17.2 microns (SD 9.4 microns) for the mandible. Combining a larger number of smaller segments did not improve the result, since the errors of the individual registrations are summed in sequential matching. In this study, the errors arising in matching are not negligible and can possibly negatively influence the quality (fitting accuracy) of the restoration produced on the basis of the matched data records.

Analog-Digital Conversion↗