Retrospective evaluation of treatment time and efficiency of a predictable cantilever system for orthodontic extrusion of impacted maxillary canines.

INTRODUCTION: Orthodontic extrusion of impacted maxillary canines requires careful biomechanical planning and the use of physiologic force. The aim of this study was to evaluate the time needed for orthodontic extrusion of impactions of different severities, using a device that can predictably apply forces under 0.6 N. METHODS: Twenty-two patients who were consecutively treated were selected retrospectively, and a total of 30 impacted canines were studied. Indexes of impaction were used to measure severity on pretreatment panoramic radiographs. Statistical analysis was used to detect interactions between treatment time, complexity of impaction, age, and sex. RESULTS: Treatment time was highly dependent on the patient's age; the shortest treatment time was observed in 11- to 12-year old patients. On the other hand, the severity of impaction had no effect on treatment time. CONCLUSIONS: Applying physiologic force with the proposed device resulted in a short treatment time, which depended on the patient's age more than the impaction complexity. Few complications were associated with use of this device. Future prospective studies are needed to replicate these findings and confirm the recommended use of this device.

Predictable method to deliver physiologic force for extrusion of palatally impacted maxillary canines.

INTRODUCTION: Orthodontic treatment of palatally impacted maxillary canines raises many difficulties; to minimize complications, careful planning of orthodontic extrusion and the use of physiologic force are crucial. The aim of this study was to quantitatively evaluate a simple and reproducible system for orthodontic extrusion of impacted canines that can provide the correct amount of force. METHODS: Ten specimens were constructed, consisting of a cantilever made with a 0.6-mm or 0.7-mm stainless steel wire modeled around a transpalatal bar with 3, 5, or 7 loops in the shape of a helical torsion spring. A mechanical testing machine was used to measure the force produced by the cantilever at 3, 6, 9, 12, and 15 mm of activation. RESULTS: The force values ranged from 1.24 ± 0.13 N for the 0.7-mm wire with 3 loops to 0.48 ± 0.04 N for the 0.6-mm wire with 7 loops. The forces measured for the 0.6-mm wire with 3 loops and the 0.7-mm wire with 7 loops were similar at 15 mm of deflection. CONCLUSIONS: The proposed system has a simple and robust design, is easy to construct and manage, and can provide the desired amount of force by changing the wire diameter and number of loops.

Microtensile Bond Strength of Etch-and-Rinse Adhesives in Different Hydroabrasion Conditionings.

The aim of the present study was to in vitro evaluate the effect of dentin conditioning with hydroabrasion on the microtensile bond strengths of three adhesive systems, compared to the standard etch-and-rinse technique. Sixty extracted human third molars were collected, and their midcoronal occlusal dentin was used for the microtensile bond strength test. Teeth were randomly assigned to three groups according to the adhesive system used: ExciTE F DSC, ENA Bond, and Scotchbond Universal. Specimens from each group were further divided into four subgroups: control specimens were treated with standard adhesive procedures; hydroabraded (HA) specimens were subjected to preventive hydroabrasion with three different intensity levels. After bonding procedures, composite crowns were incrementally built up. After thermocycling, specimens were subsequently sectioned into 1 × 1 mm sticks, and microtensile bond strengths were measured. Data were statistically analyzed. Failure mode analysis was performed. There were no significant differences in terms of bond strength between standard adhesion protocols and adhesion with HA preconditionings. On the other hand, the type of adhesive used had a significant effect on the tensile bond strength. Subgroups treated with hydroabrasion at higher intensity showed a slightly increased frequency of cohesive fractures. In conclusion, hydroabrasion can be used for dentin cavity preparation or finishing, since it does not seem to affect the bonding effectiveness.

Dimensional variability of orthodontic slots and archwires: an analysis of torque expression and clinical implications.

BACKGROUND: The loss of third-order information in pre-adjusted brackets due to torsional play is a problem in clinical orthodontics. The aim of this study was to evaluate the impact of slot height, archwire height, width and edge bevel's radius on the torsional play for three brackets/archwire systems. METHODS: Ninety brackets with a 0.022 × 0.028 in. slot with McLaughlin-Bennett-Trevisi prescription from three different manufacturers were selected, and the slot's height and depth were measured using a profile projector. Sixty stainless-steel rectangular archwires from three different manufacturers were sectioned and observed with a SEM to measure their height, width, and radius of edge bevel. The recorded data were used to calculate the theoretical torsional play between different slot-archwire combinations. One-way ANOVA was used to compare the measurements within different bracket types and among different manufacturers. RESULTS: Slot height was usually oversized. Archwire's height was usually undersized, but oversized wires were also observed. The radius edge bevel was the most variable parameter. A certain degree of torsional play is always present that differs from one bracket type to another of the same producer and that can even be doubled from one manufacturer to another. CONCLUSIONS: Due to production tolerance, differences between the nominal values and the real dimensions of any components of a slot/archwire system are common. This results in a torsional play that limits torque expression. The archwire's edge bevel plays an important role in torque expression, and clearer information should be provided by the manufacturers regarding this aspect.

In Vitro Shear Bond Strength of Orthodontic Brackets after Enamel Conditioning with Acid Etching and Hydroabrasion.

The purpose of this study was to evaluate the shear bond strength and adhesive remnant index ARI) of orthodontic brackets following enamel conditioning with acid etching, hydroabrasion, and with both procedures. Thirty extracted human premolars were divided into three groups and received either acid etching, hydroabrasion or both procedures. Orthodontic brackets were bonded with composite resin. Shear bond strength was tested with a tensile machine, then the teeth were observed under a stereomicroscope to evaluate ARI scores. The enamel morphology after each conditioning method was evaluated with scanning electron microscope imaging. A one-way ANOVA and a Kruskal-Wallis H test were used to compare the bond strength and the ARI scores among the three groups. Hydroabrasion alone produced shear bond strength values below clinical acceptability, while the combination of acid etching and hydroabrasion produced the highest values. The ARI scores in the hydroabrasion group were significantly different from the other groups. Hydroabrasion followed by acid etching was effective in increasing the shear bond strength of orthodontic brackets. Further in vivo studies are needed to confirm the cost and benefits of this technique.

Does muscular activity related to vertical facial divergence influence the time needed for orthodontic extrusion of palatally impacted maxillary canines? A retrospective study.

BACKGROUND: The aim of the present study was to evaluate if the different muscular activity correlated to different degrees of facial divergence has an effect on the time needed to extrude a palatally impacted maxillary canine. MATERIAL AND METHODS: Twenty-six patients were retrospectively selected, all treated with a specific cantilever appliance that allows extrusion of the impacted canine applying a physiologic amount of force below 0.6 N in a predictable way. For all the patients, pre-treatment cephalometric tracings were used to evaluate facial divergence through the FMA angle, the angle between the maxillary and mandibular plane, and the angles between the occlusal plane and either the maxillary and mandibular plane. Linear bivariate regression was calculated to evaluate if facial divergence can predict the time needed for canine extrusion. RESULTS: The linear regression model was not able to predict extrusion time from variables explaining the facial divergence. CONCLUSIONS: Palatally impacted maxillary canines can be treated with the application of physiologic extrusion force regardless of patients' facial divergence and muscular activity. Key words:Impacted canines, cantilever, facial divergence, muscular activity.

Expansion of permanent first molars with rapid maxillary expansion appliance anchored on primary second molars.

BACKGROUND: To evaluate how the amount of expansion of the primary second molars, the patient's age, and the skeletal maturation stage influence the amount of expansion at the level of the permanent first molars. MATERIAL AND METHODS: Fifty-five patients aged between 6 and 11 years with a cervical vertebral maturation stage of CS1 or CS2 were retrospectively selected. The intermolar width was measured before and after expansion to evaluate the amount of expansion achieved at the level of the primary second molars and the permanent first molars. Stepwise multiple linear regression was used to evaluate how the amount of primary molars expansion, the patient's age, and the cervical vertebral maturation stage predict the amount of permanent molar expansion. RESULTS: A significant regression equation was found, and for every 1 mm of primary molar expansion, 0.91 mm of permanent molar expansion can be expected. An age between 6 and 11 years and the CS1 or CS2 skeletal maturation stage were not significant predictors of permanent molar expansion. CONCLUSIONS: A rapid maxillary expansion appliance anchored on primary second molars is effective in expanding the permanent molars to correct a transverse maxillary deficiency in prepubertal patients, transferring the risks associated with the large forces used to the primary teeth. Key words:Maxillary expansion, transversal deficiency, primary molars.