Marc Schmitter

Enamel wear caused by monolithic zirconia crowns after 6 months of clinical use

The purpose of this study was to evaluate enamel wear caused by monolithic zirconia crowns and to compare this with enamel wear caused by contralateral natural antagonists. Twenty monolithic zirconia crowns were placed in 20 patients requiring full molar crowns. For measurement of wear, impressions of both jaws were made at baseline after crown cementation and at 6-month follow-up. Mean and maximum wear of the occlusal contact areas of the crowns, of their natural antagonists and of the two contralateral natural antagonists were measured by the use of plaster replicas and 3D laser scanning methods. Wear differences were investigated by the use of two-sided paired Students t-tests and by linear regression analysis. Mean vertical loss (maximum vertical loss in parentheses) was 10 (43) μm for the zirconia crowns, 33 (112) μm for the opposing enamel, 10 (58) μm for the contralateral teeth and 10 (46) μm for the contralateral antagonists. Both mean and maximum enamel wear were significantly different between the antagonists of the zirconia crowns and the contralateral antagonists. Gender and activity of the masseter muscle at night (bruxism) were identified as possible confounders which significantly affected wear. Under clinical conditions, monolithic zirconia crowns seem to be associated with more wear of opposed enamel than are natural teeth. With regard to wear behaviour, clinical application of monolithic zirconia crowns is justifiable because the amount of antagonistic enamel wear after 6xa0months is comparable with, or even lower than, that caused by other ceramic materials in previous studies.

Accuracy of the newly formulated vinyl siloxanether elastomeric impression material

STATEMENT OF PROBLEMnA newly formulated vinyl siloxanether elastomeric impression material is available, but there is little knowledge of its accuracy in relation to existing materials.nnnPURPOSEnThe purpose of this in vitro study was to assess the accuracy of disinfected vinyl siloxanether impressions and compare the accuracy to a common vinyl polysiloxane and a polyether impression system.nnnMATERIAL AND METHODSnImpressions were made from a modified dentoform master model containing a simulated crown preparation. Dimensional changes (mm) between the master model and working casts (type IV gypsum) were assessed. The following were evaluated: vinyl polysiloxane in a 1-step, dual-viscosity technique (VPS Dual), polyether as monophase material (PE Mono), and vinyl siloxanether in a 1-step, dual-viscosity (VSE Dual), and monophase technique (VSE Mono). Measurements of the master model and working casts, including anteroposterior (AP) and cross-arch (XA) dimensions, were made with a measuring microscope. The simulated crown preparation was measured in mesiodistal (MDG, MDO), buccolingual (BLG, BLO), and occlusogingival dimensions (OGL, OGB). Disinfection involved immersion for 10 minutes in potassium peroxomonosulfate, sodium benzoate, tartaric acid solution, or no disinfection (control) (n=8). A multivariate GLM statistical approach (MANOVA) was used to analyze the data (alpha=.05). Pearsons correlation test was used for related dimensions.nnnRESULTSnThe AP and XA dimensions of working casts were larger than the master for the disinfected condition and control. Whether disinfected or not, the working dies were shorter in height (OGB, OGL), larger in the buccolingual dimension (BLO, BLG), somewhat larger in the MDO dimension, and somewhat smaller in the MDG dimension compared to the prepared tooth of the master model, resulting in an irregular or oval profile. There were significant differences among the impression systems for each dimension except AP. Differences between the disinfected and nondisinfected conditions were significant (P=.03) with respect to dimensions of the gypsum working cast, but not for dimensions of the working die (P=.97). In general, differences relative to the master were small and of minor clinical significance considering marginal gaps of crowns smaller than 150-100 mum are considered clinically acceptable.nnnCONCLUSIONSnVSE monophase impressions and VSE dual-viscosity impressions demonstrated acceptable accuracy for clinical use with immersion disinfection, since the results for VSE were comparable to the results for PE and VPS materials, and the differences as compared to the master model were small.

Implants placed in combination with an internal sinus lift without graft material: an analysis of short‐term failure

AIMnInvestigation of the short-term survival of implants placed in combination with an internal sinus lift (ISL) without graft material.nnnMATERIAL AND METHODSnThirty-six patients received 92 screw-shaped dental implants in combination with an ISL. No bone grafts or bone substitutes were used. Forty-four patients with 77 implants in the native posterior maxilla served as controls. X-rays taken after implant placement and 6 months later were evaluated for the presence of bone gain at the apical aspect of the implants. Kaplan-Meier survival curves and Cox regression analysis were used to estimate survival curves and to isolate risk factors for implant failures.nnnRESULTSnWithin a mean observation period of 1.2 years (minimum 9 months; maximum 3.7 years), four failures were recorded in the experimental group and two in the controls. The probability of survival was above 94% for both groups. Six-nine months after surgery, bone gain was observed in 29 out of 92 implants. Comparison of the experimental group and controls revealed no effect of ISL and membrane perforation on the probability of survival.nnnCONCLUSIONSnPromising short-term outcomes were observed for implants with ISL without graft material; for a substantial proportion of implants, apical bone gain was observed in the first 6-9 months.

Three-body wear of resin denture teeth with and without nanofillers

STATEMENT OF PROBLEMnThe wear behavior of newly developed denture teeth with nanofillers may be different from teeth with other chemical formulations.nnnPURPOSEnThe purpose of this study was to examine the 3-body wear resistance of 11 different commercially available resin denture teeth.nnnMATERIAL AND METHODSnThe materials tested were conventional (SR Orthotyp PE, Orthognath) and cross-linked acrylic resin teeth without inorganic fillers (Premium 8, SR Postaris DCL, Trubyte Portrait, Artiplus), composite resin teeth with inorganic fillers (SR Orthosit PE, Vitapan), and composite resin teeth (experimental materials) with inorganic nanofillers (NC Veracia Posterior, e-Ha, Mondial). Human enamel and a ceramic denture tooth (Lumin Vacuum) were used as reference materials. The 3-body wear test was performed in a wear machine developed by the Academic Center for Dentistry Amsterdam (ACTA), with millet suspension acting as an abrasive medium (n=10, test load: 15 N, slip rate: 20%, number of cycles: 100,000). Wear was determined with the aid of a profilometer. Data were analyzed with the Kruskal-Wallis test and Mann-Whitney U test using the closed testing approach (significance level for familywise error rate, alpha=.05).nnnRESULTSnNone of the acrylic and composite resin materials tested in this study demonstrated the 3-body wear resistance of ceramic teeth or human enamel. Teeth with inorganic fillers demonstrated significantly lower wear values than conventional or cross-linked acrylic resin teeth without fillers. Composite resin teeth with traditional fillers showed significantly lower wear than composite resin teeth with nanofillers.nnnCONCLUSIONSnDenture teeth with and without inorganic fillers differed significantly with regard to the degree of wear generated in the ACTA wear simulator. The incorporation of nanofillers did not improve the wear resistance compared to teeth with traditional fillers.

In vitro fracture load of monolithic lithium disilicate ceramic molar crowns with different wall thicknesses

ObjectivesThe objective of this in vitro study was to assess the effect of wall thickness on the fracture loads of monolithic lithium disilicate molar crowns.Material and methodsForty-eight extracted molars were prepared by use of a standardized preparation design. Lithium disilicate crowns (e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) of different wall thicknesses (du2009=u20090.5, 1.0, and 1.5xa0mm; nu2009=u200916 for each series) were then constructed and milled (Cerec MC-XL, Sirona, Bensheim, Germany). After placement of the teeth in acrylic blocks (Technovit, Heraeus Kulzer, Hanau, Germany), the crowns were adhesively luted (Multilink, Ivoclar Vivadent). In each series, eight crowns were loaded without artificial aging whereas another eight crowns underwent thermocycling (10,000xa0cycles, THE-1100, SD Mechatronik) and chewing simulation (1.2xa0million cycles, Willytec CS3, SD Mechatronik, Fmaxu2009=u2009108xa0N). All specimens were loaded until fracture on one cusp with a tilt of 30° to the tooth axis in a universal testing machine (Z005, Zwick/Roell). Statistical assessment was performed by use of SPSS 19.0.ResultsCrowns with du2009=u20091.0 and 1.5xa0mm wall thickness did not crack during artificial aging whereas two of the crowns with du2009=u20090.5xa0mm wall thickness did. The loads to failure (Fu) of the crowns without aging (with aging) were 470.2u2009±u200980.3xa0N (369.2u2009±u2009117.8xa0N) for du2009=u20090.5xa0mm, 801.4u2009±u2009123.1xa0N (889.1u2009±u2009154.6xa0N) for du2009=u20091.0xa0mm, and 1107.6u2009±u2009131.3xa0N (980.8u2009±u2009115.3xa0N) for du2009=u20091.5xa0mm. For aged crowns with du2009=u20090.5xa0mm wall thickness, load to failure was significantly lower than for the others. However, differences between crowns with du2009=u20091.0xa0mm and du2009=u20091.5xa0mm wall thickness were not significant.ConclusionsFracture loads for posterior lithium disilicate crowns with 0.5 mm wall thickness were too low (Fuu2009<u2009500xa0N) to guarantee a low complication rate in vivo, whereas all crowns with 1.0 and 1.5 mm wall thicknesses showed appropriate fracture resistances Fuu2009>u2009600xa0N.Clinical relevanceThe wall thickness of posterior lithium disilicate crowns might be reduced to 1xa0mm, thus reducing the invasiveness of the preparation, which is essential for young patients.

Clinical assessment of enamel wear caused by monolithic zirconia crowns

The purpose of this study was to measure enamel wear caused by antagonistic monolithic zirconia crowns and to compare this with enamel wear caused by contralateral natural antagonists. Twenty monolithic zirconia full molar crowns were placed in 20 patients. Patients with high activity of the masseter muscle at night (bruxism) were excluded. For analysis of wear, vinylpolysiloxane impressions were prepared after crown incorporation and at 6-, 12-, and 24-month follow-up. Wear of the occlusal contact areas of the crowns, of their natural antagonists, and of two contralateral natural antagonists (control teeth) was measured by use of plaster replicas and a 3D laser-scanning device. Differences of wear between the zirconia crown antagonists and the control teeth were investigated by means of two-sided paired Students t-tests and linear regression analysis. After 2 years, mean vertical loss was 46 μm for enamel opposed to zirconia, 19-26 μm for contralateral control teeth and 14 μm for zirconia crowns. Maximum vertical loss was 151 μm for enamel opposed to zirconia, 75-115 μm for control teeth and 60 μm for zirconia crowns. Statistical analysis revealed significant differences between wear of enamel by zirconia-opposed teeth and by control teeth. Gender, which significantly affected wear, was identified as a possible confounder. Monolithic zirconia crowns generated more wear of opposed enamel than did natural teeth. Because of the greater wear caused by other dental ceramics, the use of monolithic zirconia crowns may be justified.

Influence of bone augmentation procedures on the short-term prognosis of simultaneously placed implants.

OBJECTIVESnThe purpose of this study was to investigate the effect of simultaneous bone-augmentation procedures, and their combination, on the survival of dental implants and on the incidence of complications.nnnMATERIAL AND METHODSnWithin a retrospective analysis, 958 implants placed in 404 patients (mean age 58.18) were selected from a prospective clinical study. In 304 cases of reduced bone width, bone spreading (nxa0=xa0217) with hand osteotomes, or bone splitting (nxa0=xa015), or guided bone regeneration (nxa0=xa072) combined with autogenous bone grafts were also performed. Eighty-eight implants were placed in combination with simultaneous internal sinus floor elevation without using graft material. For 194 additional implants, several augmentation procedures were combined because of extensive bone deficits. Three-hundred and seventy-two conventionally placed implants served as controls. Implant failures and complications were recorded after a mean observation period of 2.1xa0years (maximum 6.9xa0years).nnnRESULTSnSeventeen failures and nine additional implant-related complications were observed. After 4xa0years, Kaplan-Meier curves revealed a probability of survival without complication of 97.5% for conventionally placed implants, and 95.8% for implants placed in combination with a single augmentation technique. If several augmentation techniques were combined, success decreased to 94.1%. Complication-free survival differences between combined augmentation techniques and conventionally placed implants were significant (Pxa0=xa00.004). Age, gender, and location showed no effect on implant survival.nnnCONCLUSIONSnIt can be concluded that simultaneous bone-augmentation techniques slightly reduce short-term prognosis for dental implants. This effect was more pronounced when advanced defects required the combination of several augmentation procedures.

Retention behavior of double-crown attachments with zirconia primary and secondary crowns

OBJECTIVEnTo investigate whether adequate retention of zirconia conical crown (CC) attachments can be achieved, and to investigate their long-term retention.nnnMETHODSnSixteen individual zirconia primary crowns were produced with convergence angles of 1° or 2° (eight of each). After determination of the convergence angles of the primary crowns, monolithic zirconia secondary crowns were manufactured. To evaluate the retention behavior of all-zirconia CC, the crowns were fitted with forces from F=12.5-100 N. Force magnitudes during the loosening process (L) were then measured. L/F ratios were recorded and the coefficient of friction (μ0) was calculated. Long-term retention was tested with up to 50,000 cycles of denture integration at a speed of 30 mms(-1) and a fitting force magnitude of 53 N.nnnRESULTSnEven when primary crowns were manufactured with the utmost care, the real convergence angles were greater than the nominal angles of the standardized burs (1° and 2°) by 0.28° (SD 0.11°). Without mechanical aging, mean L/F was 0.632 (SD 0.038) for 1° samples and 0.526 (SD 0.022) for 2° samples, indicative of high retentive forces of up to 63.2% of the fitting forces. When all the test results were used, best-fitting curves gave μ0=0.117 for new samples and μ0=0.126 for samples after 50,000 integration cycles.nnnSIGNIFICANCEnWhen the correct milling and sintering parameters are chosen, the retention behavior of zirconia CCs is adequate and stable. This innovative type of attachment is appealing because of the beneficial properties of zirconia and the efficient CAD/CAM-based manufacture.

Two-Body Wear of CoCr Fabricated by Selective Laser Melting Compared with Different Dental Alloys

AbstractThe purpose of this study was to assess the two-body wear of cobalt–chromium (CoCr) samples fabricated by selective laser melting (SLM) in contrast to cast samples and enamel. The following materials were chosen for comparison with SLM-CoCr: a CoCr alloy for use in the lost-wax technique, four gold alloys with different hardness, titanium (grade 1), and human enamel. Seven specimens of diameter 12xa0mm and thickness 1xa0mm were produced from each material and polished with emery paper. Al2O3 ceramic balls served as antagonists in the biaxial chewing simulator. Multiple chewing cycles were applied with a static load of 50xa0N. Wear was analysed laser-optically by the use of cast replicas. Statistical analyses were performed with Kruskal–Wallis test and subsequent post hoc Mann–Whitney U tests at a significance level of 0.05. SLM-CoCr showed less wear than any of the other materials. The difference was statistically significant between SLM-CoCr (vertical loss −54.4xa0±xa06.9xa0µm after 300,000 cycles) and cast CoCr (vertical loss −117.2xa0±xa018.6xa0µm after 300,000 cycles). Greatest vertical wear was observed for titanium. SLM-CoCr exhibits a great resistance to wear and might represent an alternative for the manufacture of prosthetic restorations even in occlusal loading areas.n Clinical relevance Clinical investigations on wear of SLM-CoCr are needed to assess its in vivo behaviour.

Clinical effect of different shade guide systems on the tooth shades of ceramic-veneered restorations

PURPOSEnThe objective of this study was to investigate whether a systematically arranged shade guide system (Vita 3D-Master) allows clinicians to achieve a better shade match of a restoration, as compared to a conventional shade guide with a design based on empirical values (Vita Classical).nnnMATERIALS AND METHODSnFifty-nine restorations in 42 patients being treated by student clinicians were assessed. Using 1 of the 2 shade systems assigned randomly, each student independently determined the tooth shade. With the aid of a visual rating scale, the accuracy of the shade match of the finished restoration was assessed.nnnRESULTSnAll restorations whose shades had been determined with the 3D-Master could be placed without any further shade corrections. In contrast, almost 17% of restorations determined with the conventional system required subsequent shade modifications. The match of the shades selected with the 3D-Master was judged significantly better by the clinicians.nnnCONCLUSIONnWithin the limitations of the study, clinicians with less clinical experience who use a system that guides them through the shade-taking procedure in a relatively systematic manner will be more successful in selecting the correct tooth shade and in avoiding shade corrections. Clinical assessment of the restoration shades showed significant differences between the shade guide with a systematic design and that based on empirical values.