Treatment of the Canted Occlusal Plane

The canted occlusal plane problem has not being addressed as a real issue in the clinical orthodontics. In the past, its clinical consideration was minimal, if any, and doing correction in this area was often associated with complications. One reason is that the clinical technique was complex and required complete cooperation from the patient’s side. Orthodontists seldom integrated the correction of the occlusal plane, especially the canted one, into the actual treatment plan. If it was considered a significant issue within the therapy and part of the chief complaint, such as face asymmetry, facial esthetic, jaw function, and temporomandibular dysfunction (TMD) problems, the procedure of choice most of the time was orthognathic surgery treatment. In the first author’ practice, by conducting “orthodontics and dentofacial orthopedics”, an attempt to minimize the need of surgery by using temporary anchorage devices (TADs) is routinely utilized. The term “orthodontics and dentofacial orthopedics” refers to the movement of teeth together with their supporting alveolar bone so that by camouflage surgery is avoided. A good number of patients would decline treatment when surgical intervention is the only option.

The use of TADs is presented in this chapter as a possible alternative in doing orthodontic treatment without or limited surgical intervention in problems involved the canted occlusal plane. By using this concept, a new dimension in orthodontics for treating the canted occlusal plane is presented according to the limitations of camouflage therapy based on the envelope of discrepancy (Graber et al. 2011) (Figure 12.3.1). The concept presented in this chapter focuses on the middle range of motion using TADs for producing the orthopedic effect (Anka and Grummons 2009). By using this concept, a deviated mandible can be corrected to a certain degree thus, minimizing the asymmetry of the face and the jaws as well as by rehabilitating the oral function. The challenge is great especially if considering that form follows function (Kondo 2007). On the other hand, the question remains whether the function will follow if a change of the structure will be attempted. Unfortunately, the answer is negative unless the deviated function is corrected by efficient oral rehabilitation which is necessary for stability. Therefore, with all treatments of asymmetries with a canted occlusal plane primarily involved, the practice of myofunctional therapy is recommended to be part of the overall treatment plan.

By performing orthodontic procedures for the correction of an occlusal problem often the skeletal problem becomes less apparent (Raghuraj et al. 2015). Since it is not possible to change the underlying structures, a camouflage treatment could be used to manage the problem. In such cases, search and assessment regarding etiology becomes the first priority based on a detailed classification of the malocclusion and the skeletal relationships (Moyers et al. 1980; White et al. 1976; Proffit 1986; Graber 1963). Making identification of the cause of malocclusion simple, it can be divided into three main categories in which treatment should be directed to the tissues involved.

Firstly, diseases and syndromes: Crouzon syndrome, Apert syndrome, hemangioma, plexiform neurofibromas, torticollis, premature closure of cranial sutures, craniosynostosis, scoliosis, etc.

Secondly, posture: Respiratory problems that affect posture, tongue trust related to swallowing and sucking, sitting and/or sleeping on one side, etc.

Thirdly, growth: Hypoplasia, hyperplasia, cleft lip and palate, skeletal heredity, etc.

It seems that is feasible to deal mostly with the malocclusions related to the second category only, namely posture. Sometimes it can be difficult to correct this kind of problem, as patients are reluctant to change their habits. As an example, when it comes to their appearance, they like their hairstyle, which they prefer to let the hair dropped on the side of the head that may or may not cover one of the eyes. This habit will first affect the symmetry of the left and right eyes; then the maxilla bone might tilt to one side, effect the occlusal plane, and head posture can sometimes be severely affected (Chihiro et al. 2015). However, when this problem is explained by the doctor to the patient, his/her reaction can vary, and the treatment outcome will differ as well. The problem of the canted occlusal plane mostly begins with asymmetry of the mandible, which will force the maxilla to adapt and will result in a deviation of both jaws (Kheir and Kau 2016). In the etiological category of disease, it can sometimes involve more complex problems such as scoliosis (Saccucci et al. 2011). Scoliosis can trigger one‐sided chewing thus causing unilateral posterior crossbite. Adolescent idiopathic scoliosis is defined as a spinal curve or curves of 10° or more in about 2.5% of most populations. However, in only about 0.25%, the curve does progress to the point that treatment is justified (Visscher et al. 2001). It is recommended to treat patients with scoliosis during a young age so that the problem can be identified early and be treated efficiently. After orthodontic treatment for deep overbite has finished and an excellent posterior occlusal relationship has been achieved, posttreatment radiographic evaluation revealed a normal‐appearing spine (Saccucci et al. 2011). Physical exercises have been described as giving the patient significantly improved posture. Abnormal scoliotic and kyphotic curves in the spine have been also associated with general health problems such as headaches, backaches, and limited range of back motion. Following various types of rehabilitation dental treatments, all these symptoms disappeared, and the spine on posttreatment radiographic examination appeared normal (Saccucci et al. 2011).

It is quite understandable that many of the cases with canted occlusal plane will involve a multidisciplinary approach of dental and medical disciplines due to their complex nature and three‐dimensional manifestations of malocclusion. The deviated direction of the maxillary and mandibular bones that affects the occlusal plane of the upper and lower dentition can be of Roll, Yaw, and Pitch movement and combinations (Figure 12.3.2). The role of orthodontist in correcting or camouflaging the asymmetry can be limited depending on the Roll, Yaw, and Pitch characteristics and severity of the problem.

The Yaw movement is probably the biggest obstacle in dealing with the camouflage treatment at the contemporary clinical approach of dentoalveolar orthopedics. The problem involves the skeletal deformation or asymmetry of the maxilla and mandible expressed between two or more maxillary or mandibular movements. Camouflage treatment depends on the impact of the combined action of the treatment of the maxilla and mandible toward the cranial base. Among the mentioned three movements, the Yaw movement will make the configuration of the two jaws so that deformity can be beyond the ability of correction with conventional orthodontics and even with the assistance of TADs. In these cases, observation of the three‐dimensional CT images show that the landmarks Porion are not located in the exact mesialdistal location thus, directly influencing the left and right part of the maxilla as well as the molar location.

The limitation of Roll motion correction may vary depending on the case, but the most common modification is up to 3° (Kheir and Kau 2016). However, the absence of a good number of cases and statistical data prevents from determining how much influence can take place occlusally. The correction of the Roll will affect the TMJ region and the adaptation ability of the joint toward the changes of the position of the occlusal plane. Precautions should be taken in correcting the cant of the occlusal plane by extruding and intruding the four quadrants of the posterior occlusal planes involved which are the main causes of the canted problems (Figure 12.3.3). Many cases with canted occlusal plane already present symptoms of TMD and joint adaptation may not be expected. In these cases, treatment should be designed in such a way to improve TMD symptoms and conditions as well as to correct the canted occlusal plane.

Assessment of the canted occlusal plane by means of CBCT has been recommended (Kheir and Kau 2016), but it seems that at present the standardization of the method is not easily achievable. Since the occlusal plane is projected in the three dimensions of space its superimposition before and after treatment to show the differences of the correction is not feasible yet. The necessity of easing superimposing the plane of two periods (before and after treatment) to the cranial base of the skull will be appropriate to understand the effect of orthopedic outcome. The three‐dimensional evaluation will also assist to follow the direction and how the occlusal plane has moved and corrected.

The next problem is knowing the adaptive ability of the TMJ structure to endure a compression or distraction, which happens when the canted occlusal plane is altered. For the movement of the correction of the canted occlusal plane, it is wise to consider all four quadrants of posterior teeth (Figure 12.3.3).

Sometimes, it is possible to intrude or extrude one quadrant for the correction of the canted occlusal plane that may help decreasing the asymmetry. Still, the maneuver will be depending on the condyle adaptation ability of the new environment. The spaces and structures between the condyle and fossa namely mandibular fossa anatomical configuration, disc, and the bilaminar zone are the structures that might influence the success of the treatment. Therefore, the treatment plan should be adapted to each case according to their temporal articular mandibular condition. In doing the correction of the canted occlusal plane, it is also recommended to do a functional analysis of the TMJ by using axiograph or other jaw tracking devices, and combine its findings with the radiographic findings regarding the articular structures of the TMJs. Clinical evaluation of the position of the mandible in rest and in maximum intercuspation is also required. These clinical findings are significant in determining whether there is a functional change due to occlusal interferences. The functional shift caused by occlusal interferences may be contralateral to the side of the problem, and care should be taken if any change due to treatment may worsen the situation. Any occlusal interference must be detected and related to the actual asymmetrical condition (Bishara et al. 1994). The TMJ problem will affect the mandibular position toward the maxilla, and the joint condition must first be addressed to avoid a wrong or incomplete diagnosis. Management of TMD symptoms must come first before starting the camouflage treatment. The treatment of the canted occlusal plane is needed not only for esthetic reasons but also for restoring function and associated problems such as TMD. An association between craniofacial asymmetry and unilateral TMJ sounds in adult patients has been documented (Yáñez‐Vico et al. 2013).

Interestingly, the laypersons’ perception toward the canted occlusal plane is not to the degree of the actual tilting as orthodontists assess on the frontal cephalometric radiographs. However, people do accept canted occlusal planes up to 3–4° (Olivares et al. 2013).

Correction of the camouflage treatment takes place in the dentoalveolar region and not in the basal bone itself since dentoalveolar bone changes are relatively straightforward and predictable. However, correction of the deviated basal bone that caused the canted occlusal plane may not be easy, but still can be done if the volume of the alveolar bone allows the dental movement in such a way to camouflage and to restore oral masticatory function. When tilting of the occlusal plane is severe, for example 3° or more, distraction osteogenesis of the condylar neck area is also a choice to correct the asymmetric mandible, if indicated (Grayson and Santiago 1999).

Clinical analysis of the face is essential because asymmetry needs to be documented and reviewed all times, and with the aim to change the structures, if possible. After a thorough overall analysis of the face takes place, personalization of the treatment can be done using all the data collected (Meneghini and Biondi 2012).

In the frontal cephalometric radiograph, the Mid‐Sagittal Reference Line is the first variable to primarily identify the deviation between the left and right sides of the face, and afterward to assess and measure the asymmetry in detail (Figure 12.3.4). It should be noted that this variable is primarily a two‐dimensional measurement, and it will be challenging to interpret a three‐dimensional problem especially when the interpupillary line is not perpendicular to the upper median line of the head because the left and right eyes are not symmetrical toward the median line. It should be noted that in prosthodontic work, the interpupillary line guides the arrangement of upper anterior teeth. The occlusal plane of the upper anterior teeth must be parallel to the interpupillary line. However, in orthodontic patients, these two lines are not necessarily parallel to each other (Bhuvaneswaran 2010). This finding has been presented in several reports (Kokich et al. 1999; Rifkin 2000; Kavitha 2019; Revilla‐León et al. 2019) and for this reason the midline of the face (maxilla) should be selected when the interpupillary line is not parallel (Figure 12.3.5).

The use of the line N‐ANS as orientation baseline is preferable and by drawing a line from the left orbital rim perpendicular to the N‐ANS an interpupillary line can be formed. The search for an orientation baseline in studying head asymmetry presents great difficulty in cases with a deviated nasal septum (Figure 12.3.6). The maxillary bone differences of left and right side will make the case a complex one and the deviation of the maxilla to one side and the asymmetrical structure of the temporal bones will affect the location of Porion (Figure 12.3.7).

Dealing with asymmetry cases, an aim should be to avoid further deterioration thus, giving to the patient a better quality of life rather than correcting the entire entity, which may be related to hereditary or acquired etiological factors. The challenge is what orthodontic and dentoalveolar orthopedic procedures should be used in dealing with this kind of asymmetry, which often is mainly characterized by the canted occlusal plane.

Biomechanics for the Correction of the Canted Occlusal Plane

The introduction of TADs in clinical practice almost 20 years ago has significantly contributed to the development of camouflage treatment for the management of face asymmetries, especially in the correction of the canted occlusal plane. The use of TADs provides a semi‐fixed anchorage that can be placed in strategic locations that might be difficult or impossible in the past, resulting in a predictable and reliable way of bone‐borne anchorage. TADs’ use and design can be of various types, varying from single‐standing TADs to extended bone‐borne plates, so that the technique and the biomechanics have provided many options in correcting the occlusal plane.

The Trans‐Palatal Arch (TPA) Plus Hooks

This device is a modification of the trans‐palatal arch (TPA) with hooks. The following case is an example of understanding its function and how it works to correct the canted occlusal in combination with TADs.

The patient is a 16Y2M female with TMD symptoms, including reciprocal clicking on her right TMJ, mandibular deviation to her right side upon opening and closing the mandible, limited opening to 30 mm, and masticatory muscles painful to palpation, especially on the left and right lateral and medial pterygoid muscles. MRI reveals an anterior disc displacement of the right TMJ (Figure 12.3.8).

Patient underwent TMD splint therapy for 1 month, with fair‐to‐good response resulting in relief of the dysfunction symptoms. The patient’s lower right first molar presented poor prognosis and its preservation was problematic. Her dentist asked if the second molar could move orthodontically in such a way as to replace it. Un‐face extraoral and intraoral photographs of the patient appear in Figure 12.3.9. Patient presented with a Class III molar relationship in both sides. The upper second molar lingual cusps caused occlusal interferences during lateral excursions. Treatment began with the extraction of upper second premolars, the lower right first molar, and the lower left second premolar. Resin was placed on the upper first molars to reduce occlusal interferences and ease the alignment of the second molars (Figure 12.3.10). The course of treatment and the result of the use of TPA with hooks is presented in Figure 12.3.11. The method has successfully corrected the canted occlusal plane as seen in the frontal cephalometric radiographs (Figure 12.3.12), the un‐face photographs (Figure 12.3.13) and the intraoral photographs (Figure 12.3.14). This case finished using fixed appliances. Although every case has different characteristics and treatment outcomes, the 3° of correction of the inclination of the occlusal plane should be noted. Perhaps the limit of correction of the canted occlusal plane lies significantly on the condyle adaptation coping with the drastic changes induced by the therapy. In this case, the opening and closing movements of the mandible were improved and showed no limitation. Temporomandibular functional evaluation after orthodontic treatment reveals that clicking was still present, without pain, and no ongoing muscle tenderness anymore.

The TPA plus hooks has been successfully used after the Benefit plate (PSM Medical Solutions, Gunningen, Germany) was integrated into the system. The arms provide maneuvering of the force in different directions using coil springs or elastics (Figure 12.3.15). This maneuverability adds flexibility in moving and guiding the occlusal plane in an oral environment involving deviated oral function and TMD problems. However, when increasing the vertical height of the bite, the masticatory force encountered will be difficult to predict and measure. Therefore, adjustment of force direction during the treatment, when necessary, may be required.

The placement of single‐standing screw‐type TADs was the standard procedure before the Benefit system was available. The location chosen as the implantation area is the alveolar bone between the first molars and the second premolars, about 5–10 mm below the cervical region of the palatal alveolar bone. The selection of the site for placement depends on the quality and quantity of the alveolar bone in this area. This location is considered a safe site for the implantation with regards to the distance from the lingual root of the first molar and the root of the second premolar since there is enough length that the clinician can reassure the safety of the procedure, even without a surgical guide. The anatomical limitations of tooth movement also need to be taken into account in the treatment plan. The lateral side of palatal alveolar bone placement provides ample distance between the implanted TAD’s screw since it is far away from the roots. There will be minimum or no risk for any collusion between the screws and the roots as the dentition moves mesially or distally. Therefore, it is essential to calculate and observe the distance of the en‐masse movement of the treatment plan before the therapy commences. The range of limitation for the en‐masse movement depends on the anatomy of the occlusal view available in the posterior area distally to the upper second molars, as seen in Figure 12.3.16. The third molars should be removed to provide enough space when there is a need to distalize the dentition. Although theoretically, the upper dentition could move at a considerable distance, the anatomical configuration of the most backward cortical wall of the maxilla will prevent this movement since the outer cortical bone will run in a curve inward. Therefore, the maxillary intermolar width will constrict with further posterior movement. The lateral aspect of a radiograph repeatedly shows that the nasal floor is stacking between the roots of the molars (Figure 12.3.17). If there is a desire to further move the tooth or teeth distally the risk of perforating the sinus floor or blunting the apexes is high. The need for distalizing the molars will vary significantly between individuals. Therefore it is essential to thoroughly assess the CBCT or panoramic radiographic images of the patient before making the final treatment plan. It should be noted that in the mandible the situation is opposite with the intermolar width to increase with distal movement and, on the other hand, the cortical bone of the lingual side not to permit the mesialization of the posterior teeth (Figure 12.3.18). The differences of the intermolar widths in the maxilla and the mandible during distalization of the dentition are apparent.

When upper and lower teeth move distally, at one point, the relationship between upper and lower posterior molars will gradually become end‐to‐end thus leading to crossbite. When a Class III molar relationship of skeletal etiology is corrected by moving the lower molars distally, this crossbite phenomenon frequently happens. Depending on the age and maturity of the palatal bone, the Alt‐RAMEC protocol to expand and advance forward the maxillary bone orthopedically may be used (Liou and Tsai 2005). This procedure might help avoid the crossbite of the posterior teeth and keep the correct relation of the molars as expansion of the maxilla and distalization of the lower dentition take place to compensate each other. Therefore, it becomes obvious that calculation of the space in need is necessary for the treatment plan of the mesial and distal movements related to the widths of the maxilla and mandible to maintain proper molar relations and good interdigitation. Each anatomical structure should be understood when moving teeth mesial or distally, as it will change the intermolar width and may cause a disturbance in occlusion.