Desarrolladas por Andrews Se usan como base para evaluar una oclusión normal y a su vez un tx ordontico. En resumen son 6 llaves de la olcusion. I: relación. results Spanish to English, (Tech/Engineering), plano de crujía (6) . English, (General/ Other), plano preciosista · (highly) detailed shot, Ross Andrew Parker. Revisiting Two of the Keys to Normal Oclusion. (Crown Inclination . Andrews words “The six keys to normal occlusion contribute individually and collectively to the .. Las 6 llaves de la oclusión de Andrews en 32 modelos.

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Vega 4 and J. Introduction In the second half of the last century, Lawrence F.

The six keys to normal occlusion.

Andrews studied a series of casts, of non-orthodontic subjects with ideal patterns of dental occlusion, and established The six keys to normal occlusion. These were the basis to program the tooth movement directly on the bracket and not in wire bending, and were also the origin of the straight-wire, or preadjusted, appliance of current use in orthodontics. However, until now, the postulates of Andrews never have been contrasted using the scientific method and a proper statistical analysis.

Moreover, some orthodontists have the suspect that the criteria of Andrews are not universal and applicable to the whole population since he do not distinguished agedependent changes, ethnical group, sex, or left-right asymmetry. The critical analysis of the Andrews work is the goal of this Chapter, but we have centered our efforts in the date related to Crown angulation the mesiodistal tip and Crown inclination labiolingual or buccolingual inclination which are of capital importance to perform accurately functional and aesthetic orthodontic treatments.

Historical context The use of the fixed appliance in orthodontic is directly linked to the proposal and guides of Edward H. Angle to move the teeth to the so-called occlusion line, defined as “the line, shape and position, must be teeth in balance if there is a normal occlusion”. Angle described in detail the relationships between maxillary and mandible, and maxillary-mandible and teeth, and especially the teeth among them, in order to achieve an ideal occlusion Angle, b; see the Special Edition of These recommendations required the designing of special devices for three-dimensional control of teeth in order to reach the occlusion line and allow teeth to be correctly aligned in.

Furthermore, according to Angle the alignment of the teeth, both crown and root, would result in the expansion of both the maxillary and mandible arches. This was also one of the main objectives to design the Angle s devices. Nevertheless, these postulates are still under discussion Canut, ; Peck, InAngle developed the E arch appliance formed by a thick gold wire placed for labial and some stainless steel tape on the first molar adjusted at pressure.

This type of arch expanded both maxillary and mandible arches sagittally and transversely, and allowed a movement of simple inclination of the crown through a few ligatures that surrounded the tooth and conformed to the arch. In the early 20th century with the development of metallurgy emerged the possibility of banding all the teeth and welding devices for the control of rotations. InAngle introduced the first appliance with individual tooth action and fullbanding, the so-called pin and tube appliance, which welded small vertical tubes in the bands to introduce a stem attached to the wire.

This device facilitated the labiolingual as mesiodistal expansion of the maxillary, and its drawback was the requirement for adjustment and accuracy in addition to the skill by the clinician Bravo, Unfortunately one of the problems posed by this device was its inestability Graber and Vanarsdall, Later, inAngle designed a bracket, called ribbon arch appliance wire-band, containing a rectangular wire fixed by a few pins and placing the wider side on the tooth.

This device properly controlled the labiolingual as well as vertical placement of teeth, by facilitating the correction of giroversions. However, it was difficult to place on the cusp and the looseness of the wire in the slot prevented mesiodistal control. Another substantial contribution of Angle was the frontal slot bracket, as opposed to the ribbon arch appliance of vertical opening, which featured great advantages, especially the ease to introduce the wire and the possibility to control the premolars and the adjustment of mesiodistal movement.

In he presented the bracket ” with a horizontal slot. It was made in gold and was called soft bracket, as it opened easily and distorting see for a review the Special Edition of Angle s work, Over the basis of this model Steiner developed the bracket ” hard bracketmore resistant to deformation which allowed to control teeth movement at the three levels through bends as tip, torque and in-out.


This would become the prototype of the contemporary brackets. Previously to the emergence of the straight wire, Angle already proposed to place the brackets to mesial or distal from the teeth to help to correct teeth rotations Angle, aand a posterior angulation of the brackets to get proper root movements see Meyer and Nelson, Later, Lewis joined segments “arms” linked to the brackets, in contact with the wires for controlling rotations. Thereafter, Holdaway proposed that the buccal aspect of the brackets could be angulated depending on the degree of severity of the malocclusion.

Twenty years later the original idea of Lewis, with some modifications, was adapted by Gottlieb et al. On the other hand Jarabak and Fizell minted the well-known phrase “building treatment into the appliance” which proposed to incorporate angles within the bracket, and these authors presented at the meeting of the American Association of Orthodontist in the first bracket model combining crown angulation and crown inclination Wahl, Revisiting Two of the Keys to Normal Oclusion Crown Inclination and Crown Angulation in the Andrews Series 55 All together the work of all these authors consisted in eliminating bends in the wire to be incorporated into the bracket.

All this led to the evolution of the bracket of edgewise to the bracket of straight wire incorporating the information in the slot of the bracket Figure 1. Scanning electron microscopy of one bracket of standard edgewise appliance from a frontal Alateral Band oblique C view.

Scanning electron microscopy of one straight wire bracket from a frontal Dlateral Eand oblique F view. The absence of information in the slot of the bracket of standard edgewise appliance in comparison with the bracket of the straight-wire appliance can be observed.

Andrews From Andrews published a series of five studies, which resulted in the development of a new concept for the ocusion treatment: The First study had as purpose the completion of a thesis for obtaining the certification of the American Board of Orthodontics.

It consisted of the static analysis of the occlusion in post-orthodontic treatment casts. He found that there were features common to all them: However, other parameters were not common at all. He deduced that the optimal positioning of the teeth should sustain in studies of optimal natural dentures see Andrews, In order to perform the Second study, Andrews selected casts of non-orthodontic, untreated, patients with supposedly ideal occlusions, from which arose a few assumptions that should determine the occlusal objectives after orthodontic treatment.

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The compilation of the cases was carried out between and with the help of various Orthodontists, among them Brodie Andrews, These casts have in common, in addition to lack of orthodontic treatment, a correct teeth alignment and oxlusion as well as a seemingly an “excellent” occlusion.

The concept was, in essence, that if it is know what is right it can identify and quantify what’s wrong in a direct and methodical manner. Over the casts Andrews conducted a series of marks: These features would be referred to as The llafes keys to normal occlusion” and were published in in the American Journal of Orthodontics Andrews, The Six Keys would assess the occlusal situation without using measuring instruments, as in the keys II and III referring to the crown angulation and crown plaves, respectivelyAndrews do not use units but simply the positive or negative sign he used terms such pclusion lightly positive, generally negative, etc.

According to Andrews the Six Keys are interdependent components of the structural system of optimal occlusion and serve as a basis to assess the occlusion. They consisted of a series of significant characteristics shared by all of the non-orthodontic normal teeth, and were the following: Key IIcrown inclination the labiolingual or buccolingual inclination of the qndrews axis of the crown: In the own Andrews words The six keys to normal ocusion contribute individually and collectively to the total scheme of occlusion and, therefore, are viewed as essential to successful orthodontic treatment.

The casts analyzed by Andrews showed similarities in values of crown angulation, crown inclination, shape, and size for the different types of teeth. But this was not enough for the design of the new device.

Therefore, in a further study attempted to determine the shape, ve and position of each tooth in the arch. For the Fourth study, Andrews made new measurements over the casts see Andrews, The measurements made in this case were: So, he doubled the casts and removed the occlusal halves of the crown. On these surfaces he defined a line that joins the portion more vestibular of contact points and oclusiob most prominent portions of each clinical crown.

He denominated this line as the embrasure line.

The values obtained were incorporated into the design of the bracket to eliminate the first order bends. These measurements, except bracket size and curve of Spee, were averaged for each tooth type, and the results served as norms for the design of the new appliance: After describing outcomes, Andrews concludes that the study reveals essential data on the position with the exception of the inclination of the incisorsmorphology and relative vestibular prominence of each tooth in the arch.


The differences in the inclination of the incisors were attributed to disharmonies between the maxillary bones. The Fifth, and final, study consisted of comparison of casts post-treatment in terms of occlusion, with the casts from non-treated subjects with optimal occlusion.

This study was focused to the design of a new device able to include the “six keys”. The conclusion was that very few of the analyzed casts presented all the “six keys” Andrews, a.

Therefore, he considered necessary the establishment of some premises of treatment, including common objectives, coupled with a new device. The straight wire appliance of Andrews was the first completely pre-adjusted orthodontic appliance. As the closure of the spaces after premolar extractions produces undesirable side effects rotation, inclinationAndrews subsequently introduced different brackets for cases with extractions.

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Moreover, when designing their brackets, Andrews differentiated between treatments in which the translation of teeth is necessary and that no, the so-called brackets. In a short oclsion the new straight-wire appliance was adopted by the American universities and most of the orthodontists Andrews, b, Some year later Roth, designed brackets with information at the three levels, varying the characteristics described by Andrews. It is based on light forces and sliding mechanics maintaining the advantages of the prescriptions of Andrews and Roth, but eliminating certain limitations.

The introduction of straight-wire appliance in orthodontics led llavex a great controversy initially, but soon was accepted by all American orthodontic companies since it easily consent to control dental positions with the placement of llsves. Since then, others have developed new appliances, also fully programmed pre-adjusted see for a review and references Proffit et al.

The Andrew s series: Llqves values for crown angulation and crown inclination revisited The first step of our work was to collect the individual values for crown angulation and crown inclination contained in the text and annex from Andrews book Straight-Wire, The Concept and Appliance Andrews,confirm that the descriptive statistical are exact, and apply to them a descriptive statistical analysis using the actual current methods.

When we try to validate the Andrews statistical design the following questions and laa troubles emerge when analyze the series of casts that are the basis of the Andrews work: The origin of the sample: The type of clustering of the data: The variability between the data in the same group: Therefore, our second step was the verification of the validity of the Andrew s design by contrast of hypothesis.

It was carried out a Student t test of paired data to know whether or not there are significant differences in the crown angulation and crown inclination between the right and left hemi-arch with respect of their average values.

The null hypothesis was that there are no significant differences in the crown angulation or crown inclination of teeth with respect to the side p 0. Descriptive statistics in the Ocluson s series Surprisingly, several andrewa in the basic descriptive statistics count, average, standard deviation, minimum and maximum values were detected for crown angulation but not for.

Thus, there is an error between the source single data and statistic results appearing in his publication. Moreover, in comparing these basic descriptive statistics with those obtained by us, applying the some probes on the Andrews data, it can be observed again that do not match for crown angulation Table 1.

Thus, there is an error between the source single data and statistic results appearing in his publication, and the statistics are llaved well calculated.

Basic descriptive statistics of Andrews data after revisited by us blackand after the descriptive statistical study we have carried out red. Values are expressed oclusino degrees, and the observed differences are highlighted in bold. Revisiting Two of the Keys to Normal Oclusion Crown Inclination and Crown Angulation in the Andrews Series 59 As Llavrs considered the data together then we analyzed if there are differences between left and right teeth.

Student t test for crown angulation of right vs left arch. Significant differences are highlighted in bold. Maxillary Mandible Tooth t fd p t df p values df: Student t test for crown inclination for right vs left arch.