Paul Weigl

Advanced biomaterials used for a new telescopic retainer for removable dentures.

Telescopic retainers with conical ceramic abutment crowns and electroplated gold copings define a new retainer for removable dentures exhibiting favorable tribological properties that could offer clinical advantages. The objective of this study was to evaluate the clinical effects of this retainer. To do so, a novel treatment modality was developed based on intraoral bonding of the copings to the framework in order to be able to realize, in a clinical setting, the retainer function based on a precision fit. A total of 32 patients wearing 33 dentures (16 mandibular, 17 maxillary; period of risk [months]: minimum = 3; maximum = 58; mean = 27.6), supported by 147 abutments (83 natural teeth, 64 implants) with ceramic abutment crowns (IPS Empress 1, IPS Empress 2, InCeram, Procera, CerAdapt; CeraBase) were followed at 6-month intervals. The ceramic abutment crowns showed low plaque accumulation (mean PI = 17.3%). The gingival tissues around natural abutments were generally free of inflammation; so was the mucosa around the implants (mean SBI = 4.9%). Denture adhesion and occlusion did not change, and there were no rocking movements. The mobility (as determined by Periotest) of 29 teeth was reduced in a highly significant manner within 6 months (t test, p < 0.001). Osseointegration was preserved for all implants. One abutment loosened. Six Empress 1 ceramic copings failed (94.6% Kaplan-Meier survival rate), and one abutment tooth was lost (99.2% survival rate). All patients reported problem-free handling, no rocking movements, and constant adhesion. The adhesive strength of one denture was too low at insertion. 94% of the patients experienced no problems with oral hygiene. The retainer examined has relevant clinical advantages and meets geriatric requirements for removable dentures.

Surface roughness of zirconia for full-contour crowns after clinically simulated grinding and polishing

The aim of this study was to evaluate the effect of controlled intraoral grinding and polishing on the roughness of full-contour zirconia compared to classical veneered zirconia. Thirty bar-shaped zirconia specimens were fabricated and divided into two groups (n=15). Fifteen specimens (group 1) were glazed and 15 specimens (group 2) were veneered with feldspathic ceramic and then glazed. Prior to grinding, maximum roughness depth (Rmax) values were measured using a profilometer, 5 times per specimen. Simulated clinical grinding and polishing were performed on the specimens under water coolant for 15 s and 2 N pressure. For grinding, NTI diamonds burs with grain sizes of 20 µm, 10 µm, and 7.5 µm were used sequentially. The ground surfaces were polished using NTI kits with coarse, medium and fine polishers. After each step, Rmax values were determined. Differences between groups were examined using one-way analysis of variance (ANOVA). The roughness of group 1 was significantly lower than that of group 2. The roughness increased significantly after coarse grinding in both groups. The results after glazing were similar to those obtained after fine grinding for non-veneered zirconia. However, fine-ground veneered zirconia had significantly higher roughness than venerred, glazed zirconia. No significant difference was found between fine-polished and glazed zirconia, but after the fine polishing of veneered zirconia, the roughness was significantly higher than after glazing. It can be concluded that for full-contour zirconia, fewer defects and lower roughness values resulted after grinding and polishing compared to veneered zirconia. After polishing zirconia, lower roughness values were achieved compared to glazing; more interesting was that the grinding of glazed zirconia using the NTI three-step system could deliver smooth surfaces comparable to untreated glazed zirconia surfaces.

Machinability of IPS Empress® 2 framework ceramic

Using ceramic materials for an automatic production of ceramic dentures by CAD/CAM is a challenge, because many technological, medical, and optical demands must be considered. The IPS Empress 2 framework ceramic meets most of them. This study shows the possibilities for machining this ceramic with economical parameters. The long life-time requirement for ceramic dentures requires a ductile machined surface to avoid the well-known subsurface damages of brittle materials caused by machining. Slow and rapid damage propagation begins at break outs and cracks, and limits life-time significantly. Therefore, ductile machined surfaces are an important demand for machine dental ceramics. The machining tests were performed with various parameters such as tool grain size and feed speed. Denture ceramics were machined by jig grinding on a 5-axis CNC milling machine (Maho HGF 500) with a high-speed spindle up to 120,000 rpm. The results of the wear test indicate low tool wear. With one tool, you can machine eight occlusal surfaces including roughing and finishing. One occlusal surface takes about 60 min machining time. Recommended parameters for roughing are middle diamond grain size (D107), cutting speed v(c) = 4.7 m/s, feed speed v(ft) = 1000 mm/min, depth of cut a(e) = 0.06 mm, width of contact a(p) = 0.8 mm, and for finishing ultra fine diamond grain size (D46), cutting speed v(c) = 4.7 m/s, feed speed v(ft) = 100 mm/min, depth of cut a(e) = 0.02 mm, width of contact a(p) = 0.8 mm. The results of the machining tests give a reference for using IPS Empress(R) 2 framework ceramic in CAD/CAM systems.

Influence of femtosecond laser treatment on shear bond strength of composite resin bonding to human dentin under simulated pulpal pressure.

This in vitro study evaluated the influence of femtosecond laser (fs-laser)-generated patterns on shear bond strength (SBS) of composite resin bonded to human dentin under simulated pulpal pressure. Laser treatment was used to produce two different patterns on dentin surfaces. Three test groups and a control group without laser treatment under pulpal pressure were investigated. Dentin discs of 800 nm thickness were cut from 60 extracted caries-free human molars. Using a perfusion machine, the discs were exposed to Ringer solution on their basal surfaces. Clearfil SE Bond/Herculite XRV system was used. The samples were stored in distilled water and thermocycled. Bonding failures caused by a test set-up to challenge SBS were analyzed by scanning electron microscope (SEM). An 80 μm-sized cube-shaped pattern caused more cohesive failures in dentin or resin compared with the 160 μm-sized cube-shaped pattern. Weibull statistics demonstrated a significant difference between the two laser patterns, but only the test group with small-sized laser pattern was significantly different from the control group. The Weibull moduli ranged from 4.3 to 9.6 (control group). The 160 μm-sized pattern enhanced the bonding quality and avoided dentin weakening. It was concluded that fs-laser treatment in a 160 μm-sized cube-shaped pattern enabled a simplified bonding procedure by dispensing the primer without affecting SBS, compared with the control group.

Processing HIP-zirconia with ultra-short laser pulses

Creating individual complex three dimensional structures in HIP-zirconia by conventional mechanical machining, e.g. milling, is time consuming and subject to significant loss in bending strength due to microcracking during the milling process. Utilizing ultra-short laser pulses, individual complex three dimensional microstructures can be created very precisely without significant damage to the structure. This advantage is used to process HIP-zirconia in order to create dental restorations. To evaluate efficiency and quality, different laser parameters such as pulse duration, pulse energy and ablation strategies were studied. The maximum ablation rate was found at 400 fs.

Precise machining of ceramic dental prosthesis with ultra-short laser pulses using online depth profiling

Creating individual dental prostheses in hot isostatic pressed (HIP) zirconia by conventional mechanical machining, e.g. milling, is time consuming and subject to significant loss in bending strength due to microcracking during the milling process.Ultra-short laser pulses offer a possibility in machining ceramic with negligible damage to the surface of the ceramic.Dental prosthesis are three dimensional objects requiring five axis milling machines when manufacturing high strength ceramic conventionally. During milling only a certain amount of bulk material is removed, dependent only on the movement of the milling cutter. Using ultra-short laser pulses to accomplish the same task needs careful monitoring of the material ablated, especially the ablation depth.To process high strength ceramics, ultra-short laser pulse systems presently have small ablation rates compared to conventional milling machines. To overcome this drawback and to speed up the process of manufacturing dental prostheses, a special ablation strategy was developed. Large amounts of material are simply cut away. To avoid damage by ablating too deep into the bulk material, the depth has to be monitored carefully.Creating individual dental prostheses in hot isostatic pressed (HIP) zirconia by conventional mechanical machining, e.g. milling, is time consuming and subject to significant loss in bending strength due to microcracking during the milling process.Ultra-short laser pulses offer a possibility in machining ceramic with negligible damage to the surface of the ceramic.Dental prosthesis are three dimensional objects requiring five axis milling machines when manufacturing high strength ceramic conventionally. During milling only a certain amount of bulk material is removed, dependent only on the movement of the milling cutter. Using ultra-short laser pulses to accomplish the same task needs careful monitoring of the material ablated, especially the ablation depth.To process high strength ceramics, ultra-short laser pulse systems presently have small ablation rates compared to conventional milling machines. To overcome this drawback and to speed up the process of manufacturing dental prostheses, a special ablati...

In-vitro performance and fracture strength of thin monolithic zirconia crowns

PURPOSE All-ceramic restorations required extensive tooth preparation. The purpose of this in vitro study was to investigate a minimally invasive preparation and thickness of monolithic zirconia crowns, which would provide sufficient mechanical endurance and strength. MATERIALS AND METHODS Crowns with thickness of 0.2 mm (group 0.2, n=32) or of 0.5 mm (group 0.5, n=32) were milled from zirconia and fixed with resin-based adhesives (groups 0.2A, 0.5A) or zinc phosphate cements (groups 0.2C, 0.5C). Half of the samples in each subgroup (n=8) underwent thermal cycling and mechanical loading (TCML)(TC: 5℃ and 55℃, 2×3,000 cycles, 2 min/cycle; ML: 50 N, 1.2×106 cycles), while the other samples were stored in water (37℃/24 h). Survival rates were compared (Kaplan-Maier). The specimens surviving TCML were loaded to fracture and the maximal fracture force was determined (ANOVA; Bonferroni; α=.05). The fracture mode was analyzed. RESULTS In both 0.5 groups, all crowns survived TCML, and the comparison of fracture strength among crowns with and without TCML showed no significant difference (P=.628). Four crowns in group 0.2A and all of the crowns in group 0.2C failed during TCML. The fracture strength after 24 hours of the cemented 0.2 mm-thick crowns was significantly lower than that of adhesive bonded crowns. All cemented crowns provided fracture in the crown, while about 80% of the adhesively bonded crowns fractured through crown and die. CONCLUSION 0.5 mm thick monolithic crowns possessed sufficient strength to endure physiologic performance, regardless of the type of cementation. Fracture strength of the 0.2 mm cemented crowns was too low for clinical application.

Immediate placement of dental implants into infected versus noninfected sites in the esthetic zone: A systematic review and meta-analysis

Statement of problem. Immediate implantation has been established to shorten waiting time before definitive restoration, offering the ability to deliver a predictable esthetic and functional outcome for patients. However, this approach remains controversial for a tooth with a periodontal or periapical lesion. Purpose. The purpose of this systematic review was to analyze the treatment outcomes of immediate implant placement into extraction sockets with or without infection of periodontal or periapical origin in the esthetic zone and to provide treatment protocols based on current studies. Material and methods. An electronic search was performed in PubMed, ISI Web of Knowledge, and the Cochrane Library between January 2009 and October 2017. A subsequent manual search included all clinical studies published in the English language and excluded any reviews or animal studies. An article quality assessment scale, Newcastle‐Ottawa Scale (NOS), was used to evaluate the quality of studies enrolled. The implant survival rate was expressed as risk ratio, whereas bone level changes and gingiva level changes were expressed as mean differences in millimeters with 95% confidence intervals. The meta‐analysis was conducted by using commercial software. Results. The search initially found 1171 references. The manual search of the reference lists of identified articles yielded additional papers. Altogether, 9 studies were identified within the selection criteria, with NOS scores between 5 and 8. Compared with the healthy sites, immediate implant placement in infected sites in the esthetic zone showed similar survival rates (97.6% vs. 98.4%, respectively; risk ratio [RR], 0.99; 95% confidence interval [CI], 0.97 to 1.00; P=.138). No statistically significant differences were found in bone level changes (mean difference [MD], 0.03; 95%CI, −0.09 to 0.14; P=.667) or in gingiva level changes (MD, −0.06; 95% CI, −0.13 to 0.01; P=.070) between the 2 groups. Conclusions. Meta‐analysis showed that immediate implant placement into infected sites and noninfected sites in esthetic zone had similar survival rates, bone level changes, and gingiva level changes.

The micromechanical behavior of implant-abutment connections under a dynamic load protocol

BACKGROUND The implant-abutment connection (IAC) is known to be a key factor for the long-term stability of peri-implant tissue. PURPOSE The aim of the present in vitro study was to detect and measure the mechanical behavior of different IACs by X-ray imaging. MATERIALS AND METHODS A total of 20 different implant systems with various implant dimensions and IACs (13 conical-, 6 flat-, and 1 gable-like IAC) have been tested using a chewing device simulating dynamic and static loading up to 200 N. Micromovements have been recorded with a high-resolution, high-speed X-ray camera, and gap length and gap width between implant and abutment have been calculated. Furthermore, X-ray video sequences have been recorded to investigate the sealing capacity of different IACs. RESULTS Out of the 20 implant systems, eight implant systems with a conical IAC showed no measurable gaps under static and dynamic loading (200 N). By contrast, all investigated implant systems with a flat IAC showed measurable gaps under dynamic and static loading. X-ray video sequences revealed that a representative conical IAC had sufficient sealing capacity. CONCLUSION Within the limits of the present in vitro study, X-ray imaging showed reduced formation of microgaps and consecutive micromovements in implants with conical IAC compared to flat IACs.

Combining contour detection algorithms for the automatic extraction of the preparation line from a dental 3D measurement

Due to the increasing demand for high-quality ceramic crowns and bridges, the CAD/CAM-based production of dental restorations has been a subject of intensive research during the last fifteen years. A prerequisite for the efficient processing of the 3D measurement of prepared teeth with a minimal amount of user interaction is the automatic determination of the preparation line, which defines the sealing margin between the restoration and the prepared tooth. Current dental CAD/CAM systems mostly require the interactive definition of the preparation line by the user, at least by means of giving a number of start points. Previous approaches to the automatic extraction of the preparation line rely on single contour detection algorithms. In contrast, we use a combination of different contour detection algorithms to find several independent potential preparation lines from a height profile of the measured data. The different algorithms (gradient-based, contour-based, and region-based) show their strengths and weaknesses in different clinical situations. A classifier consisting of three stages (range check, decision tree, support vector machine), which is trained by human experts with real-world data, finally decides which is the correct preparation line. In a test with 101 clinical preparations, a success rate of 92.0% has been achieved. Thus the combination of different contour detection algorithms yields a reliable method for the automatic extraction of the preparation line, which enables the setup of a turn-key dental CAD/CAM process chain with a minimal amount of interactive screen work.