CHAPTER 7 Stage I
The aims of the first stage are simply directed at correcting the anterior teeth, with the exception of centrelines, which generally do not require consideration until Stage II. However, the method of carrying out Stage I may vary considerably, depending on the type of malocclusion, the skeletal pattern, age of patient and the degree of available space.
Since the Tip-Edge appliance has the capability of combining the treatment advantages of both Begg and straight-wire concepts, it has the flexibility to proceed in either mode, while exploiting the advantages of differential tooth movement. Anchorage may therefore be derived from a number of possible sources.
The principles of variable anchorage with Class II traction were first demonstrated by Dr Begg, and an evolved version of this works well with Tip-Edge in the treatment of most Class II malocclusions, particularly those with increased overbite, and is dramatically effective in difficult deep bite cases. The reason for using Class II intermaxillary elastics in preference to headgear, wherever suitable, is ease of wear for the patient, leading to better compliance. Also, it is appropriate to say here that the side effects commonly attributed to Class II intermaxillary traction, such as clockwise rotation of the occlusal plane, opening of the mandibular angle and elongation of the upper incisors, while no doubt true with conventional fixed appliances, can be avoided with the use of such light forces as Tip-Edge allows, in correctly selected cases.
Class I and Class III cases, without deep overbites, will frequently be treated by purely horizontal mechanics. Moreover, the high mandibular angle Class II facial type may require particular caution, avoiding any potentially extrusive mechanics, such as vigorous anchor bends, which might risk the deleterious side effects mentioned above. In extreme situations, the intrusive forces which can be derived from headgear can be used to advantage with Tip-Edge which, being a light anchorage technique, is highly responsive. However, whichever way any case is approached, the objectives of the first stage always stay the same.
Because the maximum difficulty malocclusion, with large overjet, increased overbite and crowding, uses the method least familiar to most orthodontists, this will be described here. It is very effective in the treatment of the majority of Class II division 1 and division 2 cases.
A clinical case at the outset of treatment (Fig. 7.1) illustrates a Class II malocclusion with upper and lower anterior crowding and an increased overbite. Four first premolars have been extracted to gain the necessary space for overjet reduction and alignment. The mechanical principles in Stage I are therefore designed to align both anterior segments, concurrent with correction of overjet and overbite. To achieve this, .016 inch high tensile stainless main archwires are used, to control the molars and overall arch width, and also to begin overbite reduction. Simultaneously, upper and lower sectional nickel–titanium ‘underarches’ provide the additional local flexibility for the alignment of the instanding incisors, in the initial treatment visits. It should be stressed at this point that an underarch runs through the main archwire slot and never, in the Plus bracket, through the deep tunnels. In instanding teeth (such as, in this case, the upper left central and lateral incisors) it will be the only archwire engaged. Elsewhere, in the aligned units, it shares the slot with the main archwire, running beneath it.
Fig. 7.1 Start of Stage I. In this severely misaligned upper arch, engagement to the main archwire is only possible with three anterior teeth, and the rotated upper right canine has a wire ligature safety tie through the vertical slot to prevent accidental disengagement. Beneath the .016 inch main archwires, the nickel–titanium underarches are .014 inch (upper) and .012 inch (lower).
Vertical control of the incisor segments is by means of anchorage or ‘tip-back’ bends, placed 2 mm mesial to the upper and lower first molar round tubes. These will induce intrusion to both upper and lower labial segments as well as mesial root movement to the molars, so preventing loss of anchorage. It will be noted that the premolars are omitted from the appliance during overbite reduction. This is because the intrusive effect of the anchor bends mesial to the molars needs to be passed directly to the anterior teeth, without any vertical interference from the premolars in mid-segment.
Overjet reduction proceeds concurrently, by means of light (50 grams) Class II elastics, worn full-time, from the ‘cuspid circle’ hooks mesial to both upper canines, to the archwire ends distal to the lower first molar tubes.
It is seldom appreciated just how little force is required to move teeth, if the brackets allow them to tip. This answers a frequently raised question: why are the canines not retracted first, in extraction cases? There is seldom need for this, since the canines are free to tip distally into the space available, and can slide along the archwire, without bracket binding, to permit decrowding of the incisors. This they do readily, in response to the instanding lateral incisors seeking space for themselves in the line of the arch. In the upper arch, control of the overjet is taken care of by the intermaxillary elastics, but even in the lower anterior segment, little transient proclination will result from rapid initial alignment. This is in marked contrast to conventional bracket systems, in which simultaneous bracket engagement on all crowded incisors will provoke proclination of the anterior segment, which may prove difficult to retrieve. The culprit is the canine which, if bodily controlled by an edgewise type bracket, effectively acts as an ‘anchorage unit’.
After one or sometimes two treatment visits, the incisors will be aligned and the overjet and overbite partially reduced (Fig. 7.2). The nickel–titanium underarches have served their purpose and/>