Carola Kolbeck

Influence of substructure design and spacer settings on the in vitro performance of molar zirconia crowns

OBJECTIVES The aim of this study was to evaluate the in vitro behaviour of all-ceramic zirconia molar crowns in regard to different core designs and marginal fit. METHODS Identically shaped methacrylate molars were prepared according to the ceramic restoration directives resulting in a 1-mm deep circular shoulder preparation. They were embedded in polymethylmethacrylate resin after covering their roots with a polyether layer to simulate periodontal mobility. The crown cores were made of yttria-stabilized zirconia veneered with a corresponding veneering ceramic. The crowns were divided into 5 groups (n=8) which differed in core design and cement gap thickness: #1: simple core, 40 microm cement; #2: core with minimal occlusal support, 40 microm cement; #3: core with optimized cusp support, 40 microm cement; #4: core with optimized cusp support, 30 microm cement; #5: core with optimized cusp support, 10 microm cement. All crowns were cemented with zinc oxide phosphate cement and thermo mechanically loaded (1.2 x 10(6) x 50N; 6000x5 degrees C/55 degrees C) with identical metal ceramic restorations as antagonists. Crown failures were monitored and described. Area and direction of the chipping failures of the veneering ceramic were documented by means of scanning electron micrographs. RESULTS All core designs showed chipping during chewing simulation with different numbers (defect areas). #1: 6 chippings (8.1mm(2)); #2: 2 chippings (3.5mm(2)); #3: 2 chippings (2.1mm(2)); #4: 3 chippings (5.7 mm(2)); #5: 3 chippings (7.3mm(2)). CONCLUSIONS An optimized core design reduced number and surface area of occurring chippings. A variation of the gap thickness showed no significant influence on the in vitro performance.

Wear performance of substructure ceramics and veneering porcelains

AIM The aim of this in vitro study was to compare the two-body wear resistance of substructure zirconia and veneering porcelain versus steatite and human enamel antagonists, respectively. MATERIALS AND METHODS Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists (enamel cusps). A pin-on-block design with a vertical load of 50 N for 1.2 × 10(5) cycles; (f=1.6 Hz; lateral movement: 1mm, mouth opening: 2mm) was used for the wear test. For quantification of the wear resistance, wear tests were performed with standardized steatite spheres. Human enamel was used as a reference. Five zirconia ceramics and four veneering porcelains were investigated. One zirconia ceramic was tested with superficial glaze, which was applied after polishing or sandblasting, respectively. Surface roughness R(a) (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D-Profilometer (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures were used for evaluating wear performance of both, ceramics and antagonists. RESULTS No wear was found for zirconia substructures. Veneering porcelain provided wear traces between 186.1±33.2 μm and 232.9±66.9 μm (steatite antagonist) and 90.6±3.5 μm and 123.9±50.7 μm (enamel). Wear of the steatite antagonists varied between 0.812±0.256 mm(2) and 1.360±0.321 mm(2) for zirconia and 1.708±0.275 mm(2) and 2.568±0.827 mm(2) for porcelain. Enamel generally showed wear, cracks or even fractures at the ridge, regardless whether opposed by zirconia or porcelain/glaze. Enamel was polished, when opposed to zirconia, or plowed, provoked and grinded, when opposed to porcelain/glaze. CONCLUSION The results of the wear test with steatite or enamel antagonists indicated no measurable wear on zirconia surfaces. Porcelain showed higher wear than zirconia, but comparable or lower wear than an enamel reference. Antagonistic wear against zirconia was found to be lower than wear against porcelain.

In vitro examination of the fracture strength of 3 different fiber‐reinforced composite and 1 all‐ceramic posterior inlay fixed partial denture systems

PURPOSE This in vitro study was carried out to examine the fracture strength of metal- free posterior inlay fixed partial dentures (IFPDs). The 3-unit IFPDs were made of either a polyethylene fiber-reinforced composite, 3 glass fiber-reinforced composites, or an all-ceramic material. MATERIALS AND METHODS Eight IFPDs were fabricated of each material in accordance with the manufacturers instructions and luted to extracted human molars with a dual-cure adhesive system. The molars were positioned in PMMA resin 10 mm apart mesiodistally. Inlay cavity preparations with enamel finishing lines were used. After thermal cycling and mechanical loading in an artificial oral environment, the cemented IFPDs were mechanically loaded until failure. Visual and radiologic examinations were done out to discern the different forms of fracture. Median and 25%/75% percentile values were calculated. Statistical analysis was performed using the Mann-Whitney U test and the Kruskal-Wallis test (p< or =0.05). RESULTS With a median (and 25%/75% percentile) fracture strength of 368 N (234 N/424 N), the FibreKor/Conquest Sculpture showed significantly lower values than the Connect/BelleGlass [898 N (736 N/1033 N)], Vectris/Targis [723 N (692 N/806 N)], Everstick/Sinfony [634 N (532 N/673 N)], and Empress2 [520 N (385 N/706 N)]. CONCLUSIONS Assuming maximum chewing forces of > or =500N in posterior areas, all systems showed sufficient fracture strength in most cases and warrant further investigation for potential clinical use.

Self-adhesive resin cement versus zinc phosphate luting material: A prospective clinical trial begun 2003

OBJECTIVES The literature demonstrates that conventional luting of metal-based restorations using zinc phosphate cements is clinically successful over 20 years. This study compared the clinical outcomes of metal-based fixed partial dentures luted conventionally with zinc phosphate and self-adhesive resin cement. METHODS Forty-nine patients (mean age 54+/-13 years) received 49 metal-based fixed partial dentures randomly luted using zinc phosphate (Richter & Hoffmann, Berlin, Germany) or self-adhesive resin cement (RelyX Unicem Aplicap, 3M ESPE, Germany) at the University Medical Center Regensburg. The core build-up material was highly viscous glass ionomer; the finishing line was in dentin. The study included 42 posterior, 5 anterior crowns and two onlays. Forty-seven restorations were made of precious alloys, 2 of non-precious alloys. The restorations were clinically examined every year. The clinical performance was checked for plaque (0-5; PI, Quigley-Hein), bleeding (0-4; PBI; Mühlemann) and attachment scores. The examination included pulp vitality and percussion tests. STATISTICS Means of scores, standard deviation, cumulative survival and complication rates were calculated using life tables. RESULTS The mean observation time was 3.16+/-0.6 years (min: 2.0; max: 4.5 years). During that time no restoration was lost, no recementation became necessary. One endodontic treatment was performed in the self-adhesive composite group after 2.9 years. At study end bleeding (1.44 RelyX Unicem vs. 1.25 zinc phosphate) and plaque (1.64 RelyX Unicem vs. 1.0 zinc phosphate) scores showed no statistically significant difference. SIGNIFICANCE The self-adhesive resin cement performed clinically as well and can be used as easily as zinc phosphate cement to retain metal-based restorations over a 38-month observation period.

The two main theories on dental bruxism

Bruxism is characterized by non-functional contact of mandibular and maxillary teeth resulting in clenching or grating of teeth. Theories on factors causing bruxism are a matter of controversy in current literature. The dental profession has predominantly viewed peripheral local morphological disorders, such as malocclusion, as the cause of clenching and gnashing. This etiological model is based on the theory that occlusal maladjustment results in reduced masticatory muscle tone. In the absence of occlusal equilibration, motor neuron activity of masticatory muscles is triggered by periodontal receptors. The second theory assumes that central disturbances in the area of the basal ganglia are the main cause of bruxism. An imbalance in the circuit processing of the basal ganglia is supposed to be responsible for muscle hyperactivity during nocturnal dyskinesia such as bruxism. Some authors assume that bruxism constitutes sleep-related parafunctional activity (parasomnia). A recent model, which may explain the potential imbalance of the basal ganglia, is neuroplasticity. Neural plasticity is based on the ability of synapses to change the way they work. Activation of neural plasticity can change the relationship between inhibitory and excitatory neurons. It seems obvious that bruxism is not a symptom specific to just one disease. Many forms (and causes) of bruxism may exist simultaneously, as, for example, peripheral or central forms.

The bond strength of the resin-to-zirconia interface using different bonding concepts

OBJECTIVES This study investigated the shear bond strength (SBS) and the tensile bond strength (TBS) of the zirconia-to-resin interface using different cement bonding concepts. METHODS Coplanar zirconia specimens were bonded to CoCr-cylinders measuring 5 mm in diameter and 3 mm in height. All bonding areas were first sandblasted with 110 μm Al(2)O(3) (0.28 MPa, 10 s). SBS and TBS were determined after 24 h and 90 d of water storage as well as after 12,000 thermal cycles (TC, 5°/55 °C, 17 d). The bonding concepts consisted of the application of a silane coupling agent, tribological silica coating (Rocatec system), cements or primers containing phosphone, mono-phosphate, or di-phosphate, and a combination of silica coating and primer. RESULTS Bond strength higher than 10 MPa was considered clinically sufficient. SBS measured with each bonding concept surpassed this value, except control and MaxCem after 90 d. In contrast, TBS values were rather different. The application of a silane coupling agent alone showed very low values in the TBS test. Silica coating was only sufficient after 90 d of water storage and when combined with phosphate-esters or phosphone-containing primers. Bonding agents based on di-phosphates or phosphones showed stable TBS values of less than 10 MPa under different aging conditions. The predominant mode of failure was adhesive failure at the ceramic surface. CONCLUSIONS None of the investigated bonding concepts of the zirconia-to-resin interface provided clinically sufficient tensile bond strength. SBS values were inadequate for a sufficient ranking.

Changes of cement properties caused by mixing errors: The therapeutic range of different cement types

OBJECTIVE The hypothesis was that low grade variations of mixing ratios of luting agents have negligible influence, while high grade variations cause severe property changes independent from the cement type used. MATERIAL AND METHODS A zinc oxide phosphate, carboxylate, glass ionomer, resin-modified glass ionomer, dual-curing composite and self-adhesive composite cement were mixed using various mixing ratios. Beside the recommended ratio, samples were mixed with ratios between 10 and 25% (low grade) up to 60% (high grade) variation of powder/liquid, respectively base/catalyst pastes. The samples underwent a Vickers hardness, flexural strength and three-body abrasion test. Their extent of cure reaction was characterized using differential scanning calorimetry. RESULTS This study indicates that dual-curing composite cements and resin-modified glass ionomers have a wide therapeutic range, followed by zinc oxide phosphate, carboyxlate and classical glass ionomer cements. Dual-curing composite cement showed less property changes, if they were exclusively light-cured in contrast to dark-curing. The classic glass ionomer and the carboxylate cements reacted more sensible to higher liquid content than higher powder content, while zinc oxide phosphate cement was lower sensitive to higher powder content. The investigated self-adhesive composite cement reacted very sensitive even to low grade mixing errors. CONCLUSIONS . Most of the established luting agents seem to tolerate low grade mixing errors, while this is not the case for recently developed self-adhesive composite cement.

Fracture force of tooth–tooth‐ and implant–tooth‐supported all‐ceramic fixed partial dentures using titanium vs. customised zirconia implant abutments

OBJECTIVES Tooth-coloured customised implant abutments and full ceramic supraconstructions thereon can be made of zirconia by computer-aided manufacturing (CAM). The aim of this study was to examine the potential limits of zirconia three-unit fixed partial dentures made on customised zirconia implant abutments in implant-tooth supported cases. MATERIAL AND METHODS Rigidly mounted implants (XiVE-S diameter 3.8 mm; length 11 mm; Friadent, Germany) were placed in PMMA-moulds pairwise with human molars at a distance of 10 mm in groups #1 and #2. Control group #3 consisted of two molars without implant involvement. Beforehand all molar roots were covered with polyether (Impregum: 3 M Espe, Germany) to simulate periodontal mobility. The abutments in #1 were individually fabricated from CerconBase and luted on experimental titanium bases (both: DeguDent, Germany). In #2, industrially prefabricated titanium abutments (Friadent) were used. All molar teeth were provided with a circumferential chamfer preparation. Three-unit fixed partial dentures were fabricated from CerconBase/CerconKiss in a CAM-process (Material/devices: DeguDent) for all test groups (n=8/group). All fixed partial dentures were cemented with RelyXUnicem (3 M Espe), thermomechanically loaded (TCML=1.2 x 10(6) x 50 N; 6000 x 5 degrees /55 degrees) and fracture tested in a Universal Test Machine (UTM 1446: Zwick, Germany). RESULTS None of the dentures failed during TCML, and the Cercon abutments showed no damage either to the bonding surface to titanium or to the ceramic itself. Two fixation screws in group #1 broke towards the end of TCML. Fracture test result (Median and 25-/75-Percentiles) were: #1 1190 (1046/2008), #2 991 (832/1402), #3 1331 (1224/1428). CONCLUSIONS All restoration alternatives showed sufficient fracture resistance for posterior regions.

Fracture resistance of fiber-reinforced composite restorations with different framework design.

Objectives. Veneer fracture and bond deficiency between framework and veneer are typical failures of fiber-reinforced inlay fixed partial dentures (FPD). An eccentric load point on the pontic was used in this study to investigate the fracture resistance of FPDs with different framework designs. As null hypothesis, it was assumed that fracture resistance was not influenced by the fiber framework supporting the veneer. Methods. Four groups of Vectris/Adoro FPDs (4×n=10 each) were manufactured. Beams (25 mm length) of Vectris Pontic (parallel aligned) with (a) rectangular (3×3) sectional view and (b) circular sectional view (⊘ 3 mm) were directly veneered using Adoro. (c) Circular beams like “b” were modified, i.e. those on the upper side were coated with two layers of the cross-sectioned fiber mat Vectris frame. (d) Vectris Pontic fibers were “anatomically” placed in the pontic area and wrapped using Vectris Frame. The frameworks were constructed in a vacuum/pressure process. All FPDs were mounted in a restrained-end apparatus and thermally cycled and mechanically loaded (TCML: 6000×5°C/55°C; 1.2×106×50 N, 1.66 Hz). After TCML, the FPDs were loaded to fracture. Results. All FPDs surpassed TCML, with no visible damage to the veneer or framework. Without transversal enlargement of the framework, additional cross-sectioned fiber mats alone did not improve resistance to fracture (a: 573±158 N (mean, standard deviation given); b: 737±66 N; c: 694±93 N; d: 902±149 N). Fracture lines occurred only in the veneer; the fiber frameworks were never affected. Conclusions. Anatomical enlargement of the fiber framework at the pontic area (height, width) to support the veneer material improves the fracture resistance of fiber-reinforced FPDs.

Outcomes of temporomandibular joint disorder therapy: observations over 13 years

Objective. To evaluate the outcome of temporomandibular joint (TMJ) disorder therapy with different kinds of splints. Methods. One-hundred-and-twenty-nine patients with TMJ disorders and meeting the primary selection criterion of reporting pain in the TMJ region were clinically evaluated. Magnetic resonance imaging of the TMJ was performed at baseline 1993–94. A protrusion splint was used whenever joint clicking could be eliminated by protrusion. In the other cases, a pivot or a Michigan splint was inserted. Re-evaluation of the patients after 12 months included a clinical examination. After 5 and 13 years, all patients were examined by means of a questionnaire. Results. Pain was significantly reduced in the case of more than two-thirds of the patients 1 year after the first consultation. After 5 and 13 years, the percentages of patients with reported pain had increased only slightly. However, the therapy did not reduce joint noises or mouth opening. The prevalence of joint noises was reduced to less than a quarter after 1 year, but during the next 13 years increased to the former level. Initially, one-third of the patients had mouth-opening reduction. This proportion dropped to one-third of these cases after 1 year, but increased to 40% after 13 years. Conclusions. Treatment using splints reduced pain in approximately two-thirds of the patients, but with no difference between the three types of splints used.