Erwin Jonke

Cytotoxicity and shear bond strength of four orthodontic adhesive systems.

The objective of this study was to compare the cytotoxicity of four orthodontic bonding systems, Light Bond, Enlight, Concise, and Transbond, and to evaluate their shear bond strength (SBS). These orthodontic bonding materials were applied to metal brackets (Mini Diamond). Glass specimens were used as controls in all experiments. Only Concise was a chemically cured system, the other systems were light cured. The specimens were added to L-929 fibroblast cultures immediately after fabrication or after pre-incubation for 7 days. The incubation time was 72 hours and the cells were counted by flow cytometry. One hundred and fifty-seven freshly extracted human third molars were used for testing the SBS in a universal testing machine. Statistical significance was determined using analysis of variance followed by post hoc comparisons for multiple-level alpha control. Pairwise comparisons showed a significant difference only between Light Bond and Concise (P = 0.0126). The highest SBS was obtained with Light Bond (23.23 +/- 1.53 MPa) followed by Transbond (20.39 +/- 1.18 MPa) and Enlight, (20.32 +/- 1.06 MPa). Concise (17.87 +/- 1.04 MPa) showed the lowest SBS. The cytotoxicity of all light-cured systems for fresh specimens was comparable, whereas the chemically cured system, Concise, was significantly more cytotoxic. After 7 days of pre-incubation, all systems were significantly less cyotoxic than fresh specimens (P < 0.001). Brackets alone were not cytotoxic. All bonding systems showed a clinically satisfactory bond strength higher than 10 MPa, with the chemically cured system showing the lowest SBS.

Shear bond strength of fluoride-releasing orthodontic bonding and composite materials

Several fluoride-releasing bonding materials are available for orthodontic bracket placement. These are supposed to prevent white spot lesions during therapy. The objectives of this in vitro study were to evaluate the shear bond strength (SBS) and failure mode of a recently introduced fluoride-releasing adhesive, as well as the comparison with established orthodontic adhesives. Sixty bovine mandibular incisors were randomly allocated to three groups (n = 20): stainless steel brackets were bonded with Transbond Plus Color Change Adhesive, Transbond XT, or Light Bond. A universal testing machine was used to determine the SBS at a crosshead speed of 1 mm/minute. After debonding, the adhesive remnant index (ARI) was used to assess the adhesive remaining on the brackets. One-way analysis of variance comparing the three experimental groups showed no differences between the bonding systems for mean SBS (P = 0.27). ARI scores showed more residual adhesive on the teeth bonded with the Transbond systems (P < 0.01). As the fluoride-releasing bonding system provided sufficient mean bond strength in vitro (19.9 MPa), it may be used as an additional prophylactic measure in orthodontic therapy. However, the clinical effectiveness of its fluoride release may be questionable, as the amount of fluoride required from a bonding material to be caries preventive is still unknown.

Rebonding performance of different ceramic brackets conditioned with a new silane coupling agent

The objective of this study was to investigate the rebonding effect of a new silane coupling agent on various ceramic brackets bonded to ceramic specimen. Different ceramic brackets (Fascination 2, Clarity SL, and In-OvationC) were assigned to three groups: rebonding with new silane coupling agent, rebonding with conventional silane coupling agent, or regular bonding as control (n = 16). Bracket adhesion was calculated with a shear test in a universal testing machine. The bracket-composite-ceramic interface was evaluated using the adhesive remnant index score. One-way analysis of variance was applied for inferential statistics. Rebonding with the new silane coupling agent resulted in high shear bond strengths (SBSs; mean values: 37.44-41.24 MPa) and ceramic specimen fractures. Rebonding with the conventional silane coupling agent resulted in significantly (P < 0.001) lower clinically adequate SBS (mean values: 20.20-29.92 MPa) with the least ceramic specimen fractures. Regularly bonded ceramic brackets resulted in clinically adequate to high SBS (mean values: 17.06-41.56 MPa) depending on their bracket base design. Rebonded ceramic brackets showed sufficient SBS to ceramic specimen surfaces. However, increased bracket adhesion was associated with a risk of ceramic specimen surface damage. Therefore, ceramic brackets rebonded with the new silane coupling should be debonded cautiously using alternative debonding methods.

Secular trends in the European male facial skull from the Migration Period to the present: a cephalometric study

Secular trends in the facial skull over three Central European samples spanning more than 13 centuries were examined. Data were 43 conventional cephalometric landmark points for samples dating from 680 to 830 AD (29 male Avars), from the mid-19th century (49 adult Hapsburg Monarchy males), and from the 20th century (54 living Austrian young adult males). Analyses by standard methods of geometric morphometrics demonstrated shape differences by data and by size, with a strong interaction of these with sample, in that group mean differences were different for small and large individuals (allometry is different from period to period). The oldest sample, from the Migration Period, exhibited allometric features that may possibly be Turkic. There are implications for the orthodontist interested in growth trends or growth predictions in ethnically mixed patient samples.

Left/right asymmetries and open/closed differences of interdental forces in the mandible

The aim of the present investigation was to study the variation in interdental forces between mandibular canines and lateral incisors of 19 volunteers (9 males and 10 females) aged 20-26 years for four configurations (mandible open/closed and left/right side). These forces were derived by pulling a stainless steel matrix strip between these teeth, six times per configuration, and registering the time variation with a high-resolution transducer. The repeated median smoothing algorithm was applied to find the maximum of each curve and a bootstrap method estimated the 95 per cent confidence intervals (CIs) for all 76 configurations. Seventy-six per cent of all paired force differences were found to be significant. Asymmetry phenomena were observed: the interdental forces differed significantly between the left and right sides and also between the open and closed position of the mandible. The interdental forces (4-21 N) showed a pattern modulated by volunteer-specific features: in 91 per cent of the configurations, the interdental forces were larger when the mouth was open. This observed pattern contributes to the instability observed in clinical practice, thus necessitating permanent fixed lower retainer wear.