Influence of surface finishing and printing layer orientation on surface roughness and flexural strength of stereolithography-manufactured dental zirconia.

OBJECTIVE: To evaluate the effect of surface finishing and printing layer orientation on the surface roughness and flexural strength of three-dimensionally (3D) printed 3 mol% yttria-stabilized zirconia manufactured by stereolithography (SLA). METHODS: Ninety bar-shaped zirconia specimens (1 mm x 1 mm x 12 mm) were 3D-printed via SLA. After debinding and sintering, they were randomly divided according to the printing layer orientation: parallel (PR) or perpendicular (PD) to the tensile surface for bending test. Each group was submitted to a surface finishing protocol (n=15/group): unpolished (subgroup 0), with polished tensile surface (subgroup 1), and with polished lateral and tensile surfaces (subgroup 3). Roughness of tensile surface was determined using a contact sensor and surface morphology was analyzed under Scanning Electron Microscopy (SEM). Flexural strength, apparent elastic modulus, and Weibull parameters were assessed using a 3-point bending test. Fractured specimens were examined to identify failure origins. Finite element analysis was used to evaluate tensile stress peaks and failure risk. RESULTS: PR orientation exhibited higher strength, higher apparent elastic modulus, higher maximum principal stress peaks, and lower failure risk. For both layer orientations, groups with polished lateral and tensile sides (PR3 and PD3) were the strongest. SEM revealed that polishing led to changes in defect type, location, and size. SIGNIFICANCE: SLA zirconia shows different mechanical properties according to surface roughness and defects. Orienting the printed layers parallel to the tensile side improves its mechanical performance. Polishing can significantly improve its flexural strength. It is necessary to reduce the final product's surface roughness and large pores for its best performance.

Effect of glazing technique and firing on surface roughness and flexural strength of an advanced lithium disilicate.

OBJECTIVE: The objective of this study was to investigate the effects of glazing technique and firing on the surface roughness and flexural strength of an advanced lithium disilicate (ALD) and lithium disilicate (LD). METHODS: Eight groups of bar-shaped specimens (1 mm × 1 mm × 12 mm, N=160, 20/group) were manufactured from ALD (CEREC Tessera, Dentsply Sirona) and LD (IPS e.max CAD, Ivoclar). The specimens were then submitted to various posttreatments: crystallization (c), crystallization followed by a second firing (c-r), crystallization with glaze in one step (cg), and crystallization followed by a glaze layer firing (c-g). Surface roughness was measured by means of a profilometer, and flexural strength was determined using a three-point bending test. Surface morphology, fractography, and crack healing analysis were conducted using scanning electron microscopy. RESULTS: Refiring (c-r) did not affect the surface roughness (Ra) while applying glaze at both cg and c-g procedures increased the roughness. ALDc-g (442.3 ± 92.5 MPa) promoted higher strength than ALDcg (282.1 ± 64.4 MPa), whereas LDcg (402.9 ± 78.4 MPa) was stronger than LDc-g (255.5 ± 68.7 MPa). Refiring completely closed the crack in ALD, but it had a limited effect on LD. CONCLUSIONS: Two-step crystallization and glazing improved ALD strength compared to the one-step protocol. Refiring and one-step glazing do not increase LD's strength, while two-step glazing has a negative effect. CLINICAL RELEVANCE: Besides both materials being lithium-disilicate glass ceramics, the glazing technique and firing protocol affected their roughness and flexural strength differently. A two-step crystallization and glazing should be the first choice for ALD, while for LD, glazing is optional and when necessary, should be applied in one-step.

[Dental materials and oral care products that can cause contact allergies]. / Tandheelkundige materialen en mondverzorgingsproducten die contactallergieën kunnen geven.

Various restorative and prosthetic materials, dental implants, medicines and cosmetic materials, such as toothpaste and denture cleaning products, are used in oral care. In principle, these materials can cause contact allergies, which can manifest as lichenoid reaction, cheilitis and angioedema. It is usually a local reaction of the oral mucosa and surrounding tissues, but a systemic reaction can also occur elsewhere in the body. If a patient develops complaints from dental materials that could be due to an allergy, it makes sense to investigate this allergologically, although these do not yet show full specificity or sensitivity. After a positive allergological examination, it is possible to examine more specifically whether the patient's complaints match the test result and it can be decided whether it is sensible to replace the dental material and, if so, which material could be an alternative. After removal of the causative allergens, the complaints should disappear completely.

[Series: Education and the dentist in 2025. Harmonisation of dental curricula in a European and Dutch perspective]. / Serie: Onderwijs en de tandarts anno 2025. Harmonisatie van de opleidingen tandheelkunde in Europees en Nederlands perspectief.

Coinciding with an increasing tendency of professionals to cross national borders, there is also an increasing need to harmonise curricula. In dentistry in Europe, this tendency is undiminished. By defining international curriculum requirements for dentists, international harmonisation can be strengthened. In the Netherlands, too, harmonisation with European standards has taken place in establishing final achievement levels for dentistry curricula, as defined in a national framework. In a working environment where oral health professionals are confronted with rapid change, for example, in the division of responsibilities, future caregivers should have an optimal educational preparation for their competences, skills and expertise.

Restoration of severely damaged endodontically treated premolars: The influence of the endo-core length on marginal integrity and fatigue resistance of lithium disilicate CAD-CAM ceramic endocrowns.

OBJECTIVES: To explore fatigue limits of ceramic endocrowns for premolars. METHODS: Forty-eight devitalized premolars were cut at the CEJ. They were restored with standardized CAD-CAM lithium disilicate reinforced ceramic restorations (IPS e.max CAD, Ivoclar-Vivadent) and divided into four Groups (n=12): overlays (Group A, no endo-core, negative control), endocrowns with an endo-core of 2mm (Group B), 4mm (GroupC) and crowns with post and core (Group D, positive control). All specimens were first submitted to thermo-mechanical cyclic loading (TCML)(1.7Hz, 49N, 600000 cycles, 1500 thermo-cycles). Margins were analysed before and after the loading. Survived specimens were then submitted to cyclic isometric stepwise loading (5Hz, 200N to 1200N) until completion of 105000 cycles or failure. In case of fracture, fragments were analysed using SEM and failure mode was determined. Results of stepwise loading were statistically analysed by Kaplan-Meier life survival analysis and log rank test (p=0.05). RESULTS: All the specimens survived the TCML test except four specimens of Group A (early restorations' debonding). No difference in percentages of closed margins was found between endocrowns (Groups B, C) and crowns (Group D). After the stepwise test, differences in survival within the groups were not statistically significant. Most of restorations experienced non-reparable fracture. CONCLUSIONS: Endocrowns with both 2-mm and 4-mm long endo-cores displayed outcomes after fatigue equivalent to classical crowns. Results of this study discourage the use of flat overlays with only adhesive retention. CLINICAL SIGNIFICANCE: When restoring extremely destroyed devitalized premolars, adhesive strategies should be coupled to a macro-mechanical retention in the root.

Adhesive Cementation Promotes Higher Fatigue Resistance to Zirconia Crowns.

OBJECTIVE: The aim of this study was to investigate the influence of the cementation strategy on the fatigue resistance of zirconia crowns. The null hypothesis was that the cementation strategy would not affect the fatigue resistance of the crowns. METHODS AND MATERIALS: Seventy-five simplified molar tooth crown preparations were machined in glass fiber-filled epoxy resin. Zirconia crowns were designed (thickness=0.7 mm), milled by computer-aided design/computer-aided manufacturing, and sintered, as recommended. Crowns were cemented onto the resin preparations using five cementation strategies (n=15): ZP, luting with zinc phosphate cement; PN, luting with Panavia F resin cement; AL, air particle abrasion with alumina particles (125 µm) as the crown inner surface pretreatment + Panavia F; CJ, tribochemical silica coating as crown inner surface pretreatment + Panavia F; and GL, application of a thin layer of porcelain glaze followed by etching with hydrofluoric acid and silanization as crown inner surface pretreatment + Panavia F. Resin cement was activated for 30 seconds for each surface. Specimens were tested until fracture in a stepwise stress fatigue test (10,000 cycles in each step, 600 to 1400 N, frequency of 1.4 Hz). The mode of failure was analyzed by stereomicroscopy and scanning electron microscopy. Data were analyzed by Kaplan-Meier and Mantel-Cox (log rank) tests and a pairwise comparison (p<0.05) and by Weibull analysis. RESULTS: The CJ group had the highest load mean value for failure (1200 N), followed by the PN (1026 N), AL (1026 N), and GL (1013 N) groups, while the ZP group had the lowest mean value (706 N). Adhesively cemented groups (CJ, AL, PN, and GL) needed a higher number of cycles for failure than the group ZP did. The groups' Weibull moduli (CJ=5.9; AL=4.4; GL=3.9; PN=3.7; ZP=2.1) were different, considering the number of cycles for failure data. The predominant mode of failure was a fracture that initiated in the cement/zirconia layer. Finite element analysis showed the different stress distribution for the two models. CONCLUSION: Adhesive cementation of zirconia crowns improves fatigue resistance.

Fatigue behavior of resin-modified monolithic CAD-CAM RNC crowns and endocrowns.

OBJECTIVE: To evaluate the influence of different types of modifications with resin on fatigue resistance and failure behavior of CAD-CAM resin nano ceramic (RNC) restorations for maxillary first premolars. METHODS: Sixty standardized resin composite root dies received CAD-CAM RNC endocrowns (n=30) and crowns (n=30) (Lava Ultimate, 3M Espe). Restorations were divided into six groups: full anatomic endocrowns (group A) and crowns (group D), buccal resin veneered endocrowns (group B) and crowns (group E) and buccal resin veneered endocrowns (group C) and crowns (group F) with a central groove resin filling. A nano-hybrid resin composite was used to veneer the restorations (Filtek Supreme, 3M Espe). All specimens were first submitted to thermo-mechanical cyclic loading (1.7Hz, 49N, 600000 cycles, 1500 thermo-cycles) and then submitted to cyclic isometric stepwise loading (5Hz) until completion of 105000 cycles or failure after 5000 cycles at 200N, followed by 20000 cycles at 400N, 600N, 800N, 1000N and 1200N. In case of fracture, fragments were analyzed using SEM and modes of failure were determined. Results were statistically analyzed by Kaplan-Meier life survival analysis and log rank test (p=0.05). RESULTS: The differences in survival between groups were not statistically significant, except between groups D and F (p=0.039). Endocrowns fractured predominantly with a mesio-distal wedge-opening fracture (82%). Partial cusp fractures were observed above all in crowns (70%). Analysis of the fractured specimens revealed that the origin of the fracture was mainly at the occlusal contact points of the stepwise loading. SIGNIFICANCE: Veneering of CAD-CAM RNC restorations has no influence on their fatigue resistance except when monolithic crowns are modified on their occlusal central groove.

Ceramic Inlays: Effect of Mechanical Cycling and Ceramic Type on Restoration-dentin Bond Strength.

This study aimed to evaluate the bond strength between dentin and five different ceramic inlays in permanent maxillary premolars, with and without mechanical cycling. One hundred permanent maxillary premolars were prepared and divided into 10 groups (n=10) according to the ceramic system (IPS e.Max Press; IPS e.Max CAD; Vita PM9; Vita Mark II; and Vita VM7) and the mechanical cycling factor (with and without [100 N, 2 Hz, 1.2×10(6) cycles]). The inlays were adhesively cemented, and all of the specimens were cut into microbars (1×1 mm, nontrimming method), which were tested under microtensile loading. The failure mode was classified and contact angle, roughness, and microtopographic analyses were performed on each ceramic surface. The mechanical cycling had a significant effect (p=0.0087) on the bond strength between dentin and IPS e.max Press. The Vita Mark II group had the highest bond strength values under both conditions, with mechanical cycling (9.7±1.8 MPa) and without (8.2±1.9 MPa), while IPS e.Max CAD had the lowest values (2.6±1.6 and 2.2±1.4, respectively). The adhesive failure mode at the ceramic/cement interface was the most frequent. Vita Mark II showed the highest value of average roughness. IPS e.max Press and Vita Mark II ceramics presented the lowest contact angles. In conclusion, the composition and manufacturing process of ceramics seem to have an influence on the ceramic surface and resin cement bond strength. Mechanical cycling did not cause significant degradation on the dentin and ceramic bond strength under the configuration used.

Fatigue Resistance of Y-TZP/Porcelain Crowns is Not Influenced by the Conditioning of the Intaglio Surface.

OBJECTIVES: The objective of this study was to investigate the effects of treatments of the intaglio surface of Y-TZP frameworks and luting agents on the fatigue resistance of all-ceramic crowns. METHODS: A research design was chosen that attempted to reduce the likelihood of Hertzian cracking and to increase the probability of fracture initiation at the intaglio surface of the framework. Ninety identical preparations were machined in a dentin-like epoxy composite. Each preparation was restored with a Y-TZP framework made by a CAD/CAM system and veneered using feldspathic ceramic. Prior to cementation the intaglio surface of the ceramic was treated using one of four treatments: 1) cleaning with isopropyl alcohol; 2) application of an overglaze; 3) sandblasting with 125 µm aluminum oxide powder; and 4) sandblasting with 30 µm silica powder (CJ). One of three luting cements were used: 1) zinc phosphate; 2) glass ionomer; and 3) adhesive resin cement (PN). All three cements were tested against frameworks that were alcohol cleaned. Only the PN cements were tested against frameworks that had been sandblasted or glazed. Altogether, six groups of 15 specimens each were tested. Fatigue resistance was evaluated using stepwise loads at 1.4 Hz until failure: 5000 cycles at maximum load of 200 N, followed by 10,000 cycles at maximum loads of 800, 1000, 1200, and 1400 N. The cement thickness and failure modes were analyzed using a stereomicroscope and scanning electron microscopy. The results were analyzed using the Kaplan-Meier and Mantel-Cox log rank tests (5%), a one-way analysis of variance, Tukey multiple comparison test, and Weibull nonparametric test. RESULTS: The predominant failure mode was chipping of the veneer. The crowns cemented with the adhesive resin cement exhibited chipping failure at higher mean loads than did crowns cemented with cements that usually do not bond strongly with dentin. When the adhesive cement was used, glazing and sandblasting intaglio framework surface treatments exhibited lower mean loads at chipping than did crowns whose intaglio surface was only cleaned with alcohol. Weibull analysis indicated that all specimens had a high ratio of late-to-early failures. CONCLUSIONS: The fatigue experiment produced a pattern of failures that is very similar to that observed in clinical trials of Y-TZP crowns that are veneered with feldspathic porcelain. Crowns cemented with an adhesive resin cement exhibited chipping at a significantly higher mean load than those cemented with luting cements that do not usually form strong bonds with dentin. When cemented with adhesive resin cement, glazing or sandblasting the intaglio surface of the framework significantly reduced the mean fatigue loads at which chipping of veneers occurred, as compared to crowns whose intaglio surface had only been cleaned with alcohol. For this cement glazing or sandblasting the intaglio surface of the crown is not recommended.

The effect of a fiber reinforced cavity configuration on load bearing capacity and failure mode of endodontically treated molars restored with CAD/CAM resin composite overlay restorations.

OBJECTIVES: To evaluate the fracture strength and the mode of failure of endodontically treated molars restored with CAD/CAM overlays with fiber reinforced composite build-up of the pulp chamber. METHODS: 40 Devitalized molars were cut over the CEJ and divided into five groups (n=8). The pulp chamber area was filled with: group 0 (control), no resin build-up; group 1, hybrid composite build-up (G-aenial posterior, GC); group 2, as in group 1 but covered with 3 nets of bi-directional E-glass fibers (EverStickNET, Stick Tech Ltd.); group 3, a FRC resin (EverX posterior, GC); group 4, as in group 3 but covered by the bi-directional fibers. The crowns were restored with CAD-CAM composite restorations (Lava Ultimate, 3M ESPE). Maximum fracture loads were recorded in Newton and data were analyzed using Kruskal-Wallis test (p<0.05). Fragments were analyzed using SEM. RESULTS: The mean static loads in Newton were: group 0: 2448 (546); group 1: 2817 (873); group 2: 2128 (952); group 3: 2429 (1091); group 4: 2577 (833). No significant differences were found between the groups (p>0.05). All specimens fractured in a catastrophic way, under the CEJ. The main crack evolved in the corono-apical direction. In groups 2 and 4 secondary fracture paths with apico-coronal direction were detected close to the bi-directional fibers' layer. CONCLUSIONS: For the restoration of endodontically treated molars, the incorporation of FRCs did not influence the load-bearing capacity of the tooth-restoration complex. The SEM analysis showed a low ability of the bi-directional fibers net in deviating the fracture but this effect was not sufficient to lead more favorable fracture patterns, over the CEJ. CLINICAL SIGNIFICANCE: The use of FRCs to reinforce the "core" of devitalized molars against vertical fractures under static loads seems useless when the thickness of the CAD/CAM composite overlay restoration is high.

[Monitoring steam sterilisation processes in the dental office]. / Het monitoren van stoomsterilisatieprocessen in de mondzorgpraktijk.

In dental offices, steam sterilisation is used to sterilise instruments and in that way to prevent the cross-contamination of patients and the dental team. In order to ensure that the sterilisation process has been executed successfully, every sterilisation process has to be monitored. The monitoring of every load in the steam steriliser is necessary and often even required, either directly (by legislation) or indirectly (by harmonised standards). The complete monitoring protocol consists of controls of the installation, the exposure, the loading, the packaging and, finally, the 'track and trace' of the instruments. For examining the installation, a steam penetration test, such as the Bowie and Dick test, can be carried out.

In vitro evaluation of temperature changes in the root canal induced by ultrasonic scalers.

OBJECTIVE: To evaluate in vitro the thermal effects induced by four different ultrasonic scalers on the temperature in the root canal during ultrasonic scaling. METHODS: An extracted lower central incisor provided with a thermocouple in the root canal and a tube, entering the tooth incisally and exiting it apically to simulate an artificial bloodstream, was placed in a model of the lower jaw with soft artificial gingiva. Tested ultrasonic scaler systems included: EMS PM-600, Satelec P-max, Dürr Vector and Dentsply Cavitron. The tooth was scaled with each system at full water supply of 21°C. Furthermore, the amount of water supply was determined to maintain during scaling a constant temperature in the root canal. Finally, thermal changes due to scaling without water were assessed. RESULTS: Except for the Vector all scaler systems showed a temperature decrease in the root canal. The Vector with water/polish suspension showed a trend towards an increase in temperature. To maintain a constant temperature in the root canal the Cavitron needed twice the amount of water compared with PM-600 and P-max. Without water, all scaling systems induced a temperature increase. CONCLUSION: For safe ultrasonic scaling, care should be taken that the cooling water has room temperature and that, dependent on the scaler system, the proper amount of water is supplied.

The influence of varying layer thicknesses on the color predictability of two different composite layering concepts.

OBJECTIVE: Optical properties of teeth are mimicked by composite layering techniques by combining a relatively opaque layer (dentin) with more translucent layers (enamel). However, the replacing material cannot always optically imitate the tooth when applied in the same thickness as that of the natural tissues. The natural layering composite system is available in 2 concepts: (1) dentin (D) and enamel (E) have the same shade but with different translucencies; (2) D and E have different shades where E is always the same high translucent shade. The objective was to evaluate the influence of varying thicknesses of E and D composites on the overall color and on the translucency for both concepts. METHODS: For each concept three composite brands were tested; Concept 1: Clearfil Photo Bright (Kuraray), Herculite XRV Ultra (Kerr), Venus Diamond (Heraeus Kulzer); Concept 2: Amaris (VOCO), CeramX Duo (DENTSPLY) and Point4 (Kerr). Two specimens of each shade (A1-A3) per composite were made of standardized thicknesses with a poly-acrylic mold and Teflon cover, making 36 specimens of wedge-like dimension. The L*a*b* values were measured three times against a white and black background (n=216). Student's t-tests revealed significant levels between the average ΔE* values of the 3 areas for each composite. RESULTS: Statistically significant differences (p<0.05) were found for all thicknesses and for all shades between the concepts. Concept 2 showed greater variations in ΔE* with increased thicknesses. SIGNIFICANCE: Concept 2 composites are more sensitive to layer thickness changes, which implicates less predictability in a daily clinical routine.

[Systemic reactions to orally applied metal alloys]. / Systemische reacties op in de mond toegepaste metaallegeringen.

Orally applied metal alloys can cause undesirable physical effects. A distinction needs to be made in this respect between local and systemic reactions and toxic and immunological reactions. A case is presented which illustrates this problem. In this case, the application of orthodontic appliances was probably the trigger for an exacerbation of nickel allergy. The oral exposure to nickel resulted in hand eczema. The patient was also exposed to nickel by single-unit fixed dental prostheses, a removable dental prosthesis, and food, as a result of which removal of the orthodontic appliances did not result in complete healing. Therefore, the single-unit fixed dental prostheses also had to be removed and food had to be prepared henceforward in nickel free pans.

Palladium-induced Th2 cytokine responses reflect skin test reactivity.

Recently, a crucial role of Th2 responses in nickel allergic contact dermatitis (ACD) was demonstrated. As palladium allergy is an issue of growing interest, the diagnostic potential of Th2 parameters for palladium sensitization was investigated. Palladium (Na(2) [PdCl(4)])-induced lymphocyte proliferation (LPT), Th1 and Th2 cytokine production were correlated with skin test (ST) reactivity in 16 positive and 21 negative controls. Furthermore, the diagnostic potential of these assays was evaluated using receiver operating characteristics (ROC) analysis. For comparison, same experiments were carried out for nickel (NiSO(4)). Correlation coefficients between palladium ST reactivity and IFN-γ, LPT, IL-5, and IL-13 were 0.34, 0.51, 0.69, and 0.78, and overall test accuracies were 68%, 81%, 89%, and 95%, respectively. Both palladium- and nickel-mediated Th2 responses tightly correlate with ST reactivity, supporting recent findings on the crucial role of Th2 involvement in ACD. Therefore, these assays may have great potential as diagnostic tools for future in vitro sensitization testing.

Clinical success and survival of indirect resin composite crowns: results of a 3-year prospective study.

OBJECTIVES: The aim of this study was to test the new resin composite "NECO" as a material for indirect restorations clinically. METHODS: Forty-five patients were selected, of which 12 men and 33 women, with a mean age of 53. A total of 91 post-canine indirect resin composite NECO (Heraeus Kulzer, GmbH) restorations were placed, of which 86 full crowns and 5 onlays. Restorations were cemented with either resin cement (2bond2) or resin modified glass ionomer cement (Fuji Plus). The restorations were evaluated 1-2 weeks (baseline), 6 months, 1, 2, and 3 years after placement. At these recalls, success and survival data of the abutment teeth were documented. Survival was defined as the restoration being in situ, and success as the restoration in situ without complications. RESULTS: After 3 years in service, the restorations showed success and survival rates of 84.8 and 91.6%, respectively. Cementation with Fuji Plus showed a trend (p=0.054) toward higher success (93.1%) and survival (100%) rates compared to cementation with 2bond2 cement which showed success and survival rates of 81.4 and 87.9% respectively. Restorations on vital teeth resulted in success and survival rates of 86.8 and 95.3% respectively, while restorations on endodontically treated teeth showed success and survival rates of 82.6 and 87.5%. This difference was not statistically significant (p=0.296). SIGNIFICANCE: Three-year success and survival rates of NECO restorations were 84.8 and 91.6%, respectively. The design of the preparation and restoration should take the material properties into account in order to enhance the clinical performance.

Data comparison between two dental spectrophotometers.

OBJECTIVES: The objective of this study was to clinically test whether the data from two different spectrophotometers, based on spot and surface measurements, can be compared. METHODS: Under standardized clinical conditions two devices (Vita Easyshade and Spectro Shade-Micro) were used to record the color of three areas (cervical, middle, and incisal) per tooth for three upper maxillary anterior teeth in 102 participants. Each position was measured three times to attain an average for the CIE L*a*b* coordinates and to attain the corresponding Vita Classical shade tab integrated in the software of both devices. Vita tabs were also described as L*a*b* values using earlier published translations so that color differences (ΔE) could be calculated between them. RESULTS: The regression analysis between the two devices showed that the independent correlation coefficients of the L*a*b* values are low. Yet when the suggested shade codes are compared with Vita colors instead of L*a*b*, 40% of the cases were equal and 51% were clinically acceptable. SIGNIFICANCE: According to this study the two devices do not give a comparable shade selection output, and thus the exchange of L*a*b* values between the two spectrophotometers cannot be recommended.

A comparison of finite element analysis with in vitro bond strength tests of the bracket-cement-enamel system.

The aim of this study was to determine the in vitro shear bond strength (SBS) and tensile bond strength (TBS) of 45 metal brackets bonded with Transbond XT to bovine enamel. The SBS was determined by loading the short and the long sides of the bracket base. Testing took place after storage of the specimens for 72 hours in water at 37°C. Fractures were analysed with the adhesive remnant index (ARI) and scanning electron microscope (SEM). The stresses in the system were analysed with finite element (FE) analysis models of the experimental set-up to identify the initial fracture point and the stress distribution at fracture. Statistical analysis of bond strengths was performed using analysis of variance (ANOVA) and the Tukey's post hoc test (P < 0.05). The ARI scores were analysed using Kruskal-Wallis one-way ANOVA on ranks. ANOVA showed significant differences between the three experiments. Loading the short side of the bracket resulted in the highest average bond strength. Tensile loading gave the lowest results. FE models supported the bond strength findings and SEM. FE analysis revealed peak stresses in the cement during loading, confirming that shear testing is sensitive to loading angles. The stress distribution over the bracket-cement-enamel system is not homogeneous during loading. Fractures are initiated at peak stress locations. As a consequence, the size of the bonding area is not predictive of bond strength. The bracket design and the mode of loading may be of greater relevance.

[Burning mouth caused by denture material]. / Behandeling van mondbrandklachten.

A 60-year-old man with an edentulous maxilla was referred by his dentist to an allergy clinic with complaints of burning mouth and bad taste. In the majority of cases, it is hard or impossible to detect the cause of burning mouth. In this case, ultimately the complaint could be solved by eliminating exposure to possible allergenic components of denture base resins.