Introduction
Class II and III malocclusions, associated with decreased vertical dimension of the face, pose significant challenges for the clinician aiming for optimal treatment outcomes and maintaining the corrected occlusion after treatment. While orthodontists and patients typically focus on correcting sagittal and transverse discrepancies and intra-arch deviations, achieving a successful clinical outcome primarily depends on accurate diagnosis and effective management of the vertical dimensions of face and occlusion.
Malocclusions with decreased vertical dimension exhibit distinctive craniofacial skeletal growth and soft tissue characteristics. , They are associated with strong and broad pterygoid and masseter muscles, unique wear patterns on the teeth, and require special considerations regarding anchorage and retention. These features influence the selection of treatment plans, the objectives of treatment and the methods used to achieve goals for optimum outcomes, whether through extraction or non-extraction approaches, surgical or non-surgical techniques or restorative rehabilitation.
A decreased vertical dimension malocclusion manifests clinically as a deep bite involving dental, dentoalveolar or skeletal components or a combination thereof. The bite may express from a mild increase in overbite to a traumatic bite pattern where the mandibular incisors traumatise the palatal tissues of the maxillary incisors and the maxillary incisors traumatise the labial gingiva in the mandibular anterior region.
A skeletal deep bite occurs due to variation in the inclination of maxillary and mandibular jaw bases or a combination of both, resulting in a decreased vertical dimension, which is the focus of this chapter.
A low-angle case or a patient with decreased vertical dimensions can be associated with features of class I, class II division 1, class II division 2 or even a class III malocclusion.
Clinical evaluation of the patient with decreased vertical dimensions
Fundamentals of facial proportions of thirds of the face given by Frakas and Munro, , help the clinician diagnose vertical dimension problems. For example, does a patient have a disproportionately long lower facial height because of vertical maxillary excess or due to excessive chin height? Conversely, is a short facial height caused by vertical maxillary deficiency or a short chin height? A careful determination of the vertical proportions of the face is therefore the first step in the diagnosis of a vertical dimension problem.
Subjects with decreased facial dimensions have distinctly reduced proportions of the lower third of the face when compared with the upper third and middle third. The reduced lower third might be contributed by the decreased upper one-third of the lower third (vertical maxillary deficiency) or a decreased lower two-thirds of the lower third (vertical chin deficiency).
Individuals with decreased vertical dimensions present with unique extraoral, intraoral, facial soft tissue and radiographic characteristics ( Fig. 88.1 ). These subjects present with a brachycephalic head form, an euryprosopic facial form, wide-set eyes, prominent cheekbones, bulbous forehead, less prominent glabella and supraorbital ridges. Body type is generally endomorphic with an advanced skeletal age and upright posture.
Facial, dental, and cephalometric characteristics associated with decreased vertical dimensions of the face.
A 19-year-old female presenting with typical features of the face, skeleton and occlusion associated with decreased vertical dimensions (A) Facial features include a prominent chin, inset lips, decreased incisor show on smiling, a flat mandibular lower border and reduced vertical dimensions of the anterior face, particularly the anterior lower one-third, giving an aged appearance. (B) Cephalogram and OPG depict anti-clockwise rotation of the mandible, deep bite and parallel Sassouni planes. The typical features of the patient are a lack of vertical eruption of the buccal segment teeth, reduced gonial angle and lack of antegonial notch, broad and long vertical ramus and a well-developed condyle and coronoid process. (C) Intraoral photographs reveal traumatic deep bite with supra-erupted mandibular incisors, an increased cure of Spee, an almost 180 degrees inter-incisal angle and severe mandibular incisor labial gingival recession.
The lips are thin, everted and prominent, with little or no show of teeth at repose. The nasal apertures are large, and the mento labial sulcus is deep. The heavy masseter muscles with a predominantly vertical direction of pull and strong temporalis muscles on the lateral profile contribute to a horizontal growth type. The chin is prominent (macrogenia), straight or usually dished-in soft tissue profile, and a short nose.
The intraoral features include maxillary and mandibular dental alveolar retrusion with a deep overbite. The palatal vault is flat with wide dental arches and potentially small teeth. Mandibular incisors may show crowding. Alternatively, they may even present with a spaced dentition. These patients often present with significant occlusal wearing away of the posterior dentition, palato-incisal and labio-incisal surfaces of the maxillary and mandibular anterior teeth, respectively. They typically have infra-erupted posterior teeth and increased freeway space. Strong sling musculature and increased biting force are associated features of decreased vertical dimension and short face patterns.
Diagnosis and treatment planning
Cephalometric features
The immediate and distinct impression on a lateral cephalogram ( Fig. 88.1 B) of these patients is the seemingly parallel Sassouni planes (Sella-Nasion, Frankfort’s horizontal, palatal, occlusal and mandibular) that do not converge at a posterior point. Typical mandibular structural features include a small gonial angle with no ante-gonial notching, a broad and long ramus, a large coronoid process and a low mandibular plane angle with mandibular growth predominantly expressed horizontally. , , The anterior and posterior facial heights are generally equal, and even within the anterior facial height, the lower anterior facial height is small. They present with a small cranial base angle, which in turn is responsible for the upward and backward position of the naso-maxillary complex, an upward and forward position of the mandible and a large pharyngeal space with a posterior tongue position. The subjects with this type of malocclusion are classified as horizontal growers with anti-clockwise growth rotation of the mandible.
Condylar growth direction and mandibular rotation in decreased vertical dimension
In order to plan and execute treatment effectively in patients with decreased vertical dimensions of the face, it is crucial to understand this malocclusion from the perspective of growth and development, especially concerning condylar growth and mandibular rotation. Vertical malocclusions result from the interplay of many different aetiological factors during growth. These factors include growth of the maxilla and mandible, function of the lips and tongue and dentoalveolar development with the eruption of teeth.
Schudy, in 1964, discussed vertical growth versus anteroposterior growth as related to function and treatment. The vertical dimension and the development of a deep or open bite are influenced by the interaction of environmental factors and familial patterns that determine the posterior facial height and those that determine the anterior facial height. Anterior facial height (AFH) is determined by the sutural descent of the naso-maxillary complex and the vertical eruption of the upper and lower posterior teeth. In contrast, the posterior facial height (PFH) is determined by condylar vertical growth and lowering of the articular fossa with a small contribution from the growth of the cranial base. When vertical condylar growth exceeds vertical growth increments at the sutures and dentoalveolar growth (i.e. eruption of teeth in the jaws), forward or anterior rotation of the mandible occurs. In contrast, if sutural increments and dentoalveolar growth are greater than vertical condylar growth, it results in posterior or backward rotation of the mandible. The balance between AFH and PFH determines the displacement of the chin during the growth period and is an expression of rotation of the mandible during growth.
Studies by Bjork, Bjork and Skieller , have shown that the most common direction of condylar growth is vertical, with some anterior component. Patients with a pronounced short lower anterior facial height generally exhibit a more extreme upward and forward condylar growth (anti-clockwise mandibular rotation). These individuals generally have a deep vertical overbite with a deep mento-labial sulcus, and a strong over-closed appearance. In contrast, patients with long-face syndrome have a more posteriorly directed growth pattern of the mandibular condyle. These subjects who are backward growth rotators (clockwise mandibular rotation) have increased anterior facial height and a more posterior chin position, and in extreme cases, an anterior open bite may develop.
Bjork’s studies also demonstrated that the fulcrumming point for anterior or forward mandibular rotation is usually located at the incisors. If proper incisal contact is lacking due to lip dysfunction, a finger-sucking habit or a severe sagittal jaw discrepancy, the patient will often develop a skeletal deep bite due to the growth pattern. The fulcruming point is then located further distally along the occlusal plane. Such growth-related skeletal deep bites often develop early in age, remain reasonably unchanged during the juvenile growth period and further deepen during the pubertal growth spurt when growth intensity is at its greatest. In such cases, whereas the genetically determined mandibular growth pattern, in general, cannot be influenced by treatment, the occlusal relationships can be influenced by the orthodontist by early intervention. When posterior (clockwise) rotation occurs, the fulcruming point is located near the mandibular condyles.
Interaction of the sagittal and vertical dimensions in causing chin projection
In individuals with a growth pattern that results in decreased vertical dimensions, forward mandibular rotation tends to allow more horizontal expression of mandibular growth and increases sagittal chin projection. This trend is conducive for class II correction and worsens class III correction ( Fig. 88.2 B).
The figures illustrate two cases demonstrating the backward and forward rotation of the mandible. Profile photographs and superimpositions of two boys of similar age who underwent orthodontic treatment.
(A) The top row indicates a mandible that has backwardly rotated during growth resulting in very less chin projection. (B) The bottom row reveals a forwardly rotating mandible and increased chin projection with growth.
In individuals with a growth pattern that results in increased vertical dimensions, backward mandibular rotation expresses mandibular growth in a vertical direction and does not improve sagittal chin projection. This tendency compromises attempts for class II correction but facilitates class III correction ( Fig. 88.2 A).
Soft tissue considerations in treatment planning for decreased vertical dimension malocclusions
Patients with decreased vertical dimensions generally have very inset dentoalveolar portions with less teeth display at rest and during smiling ( Fig. 88.1 A). Further, this display of anterior teeth becomes even lesser with age-related soft tissue changes. , These patients have a prominent soft tissue chin and nose, a dished-in lip profile, redundant soft tissues and exaggerated facial folds due to the decreased lower anterior facial height. All these features pose a big challenge in treatment planning when the clinician has to address crowding or proclination in these patients. Treatment modalities that end up retracting the anterior teeth excessively can result in loss of lip support and decreased teeth display, which can affect aesthetics negatively.
Management
Management approaches are influenced by the type and severity of deep bite and reduced vertical dimensions, age of the patient, remaining growth potential, patient cooperation and desire for the treatment.
Growth modulation in skeletal class II and class III malocclusions with reduced vertical dimension
Early intervention in skeletal Class II patients with a decreased vertical dimension in the form of interception of deleterious habits and improvement in the relative sagittal position of the mandible can prevent the development of a deleterious deep bite by the establishment of an anterior fulcrumming point during forward mandibular rotation, as explained earlier.
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Growth modulation for skeletal class II in patients with decreased vertical dimensions could include cervical pull headgear in cases with maxillary prognathism or a mandibular advancement appliance such as a Twin Block in cases with mandibular deficiency. Extrusion of the maxillary molars with a cervical pull headgear and guided eruption of the posterior teeth through selective trimming of the interocclusal blocks in the mandibular advancement appliance helps in counteracting the forward rotating tendency of the mandible and increases the lower anterior facial height. Further these patients often respond very well to a fixed functional appliance for mandibular advancement integrated with fixed appliance therapy. , , The prognosis for chin projection with treatment is generally good in these patients.
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Skeletal class III malocclusion with decreased vertical dimension in growing patients can be addressed with a reverse pull headgear applied to a bonded rapid maxillary expansion (RME) appliance or skeletal anchors (miniplates) in the maxilla in older children. These miniplates are generally placed in the zygomatic buttress area or lateral to the piriform aperture. The downward and forward vector of pull on the maxilla, along with the reciprocal effect of restraining the chin with a reverse pull headgear that results in maxillary protraction along with a downward and backward rotation of the mandible, can address the major problem areas in these patients, namely stimulating the growth of a vertically and sagittally deficient maxilla, redirecting the growth of the mandible in a caudal direction and eliminating a mandibular forward path of closure if present. These changes are conducive to increasing the lower anterior facial height and to bring about a sagittal Class III correction.
Non-extraction treatment plan considerations in decreased vertical dimension malocclusions
A non-extraction treatment plan ( Fig. 88.3 ) although a challenge, must be considered as the first option. Arch length is gained by proclining the incisors when they are retroclined to start with, increasing arch circumference and interproximal enamel reduction to address crowding.
A case study of a severe deep bite and low facial heights treated with a fixed appliance in a non-extraction approach.
(A) Facial photographs, (B) radiographs, and (C) intraoral photographs of a 14-year-old female patient with a class II division 2 malocclusion (ANB 5 degrees) with decreased vertical dimension (FMA 11 degrees), a traumatic deep bite, severely retroclined maxillary and mandibular incisors and an exaggerated curve of Spee.
Retention records show stability of results achieved over a 2-year period.
Retention involved a maxillary wrap around retainer with an anterior bite plane in addition to fixed lingual bonded retainers for the maxillary and mandibular anterior teeth.
In growing patients, relative intrusion of lower incisors, which is achieved by preventing eruption of the incisors while growth provides vertical space into which the posterior teeth erupt is used to level the curve of Spee. Deep bite is corrected by active intrusion of incisors, prevention of eruption of mandibular incisors, extrusion of premolars and molars, proclination of retroclined incisors or a combination thereof. It is vital that upper lip to maxillary incisor relation at rest and smiling and age-related changes in this relation be taken into consideration when planning maxillary incisor intrusion. Intrusion of maxillary and mandibular incisors can be accomplished with utility arches, anchor/tip back bends, Burstone segmental arches, intrusion arches or TADs (temporary anchorage devices). Absolute (true) intrusion of the incisors is possible using skeletal anchorage from median or paramedian mini screw implants (MSI) placed apical to the anterior teeth. , It is important to involve the second molars early in treatment for the leverage afforded by these teeth in levelling the curve of Spee when continuous arch wires are used.
An important treatment goal in patients with decreased vertical dimension is to increase maxillary incisor display during rest and smiling and to increase the vertical dimension of the lower third of the face. A non-extraction treatment plan maximises this possibility ( Fig. 88.3.ii ). Buccal uprighting of the mandibular posterior teeth (flattening the curve of Wilson) also aids in increasing the vertical dimension in non-extraction treatment plans.
