The Orthodontic-Periodontal Risk Assessment (OPRA) in developing Periodontal Disease

a. Periodontal anchorage teeth preservation

Orthodontic movement of teeth alters the homeostatic environment in both a healthy and reduced (healed) periodontium. During orthodontic treatment, it would be desirable to move only the teeth that are planned to be moved, and avoid placing additional stress on the other teeth, especially if there is already reduced periodontal support.

Orthodontic appliances commonly incorporate all teeth in both dental arches, as dental arches must be coordinated. As a result, position of all teeth changes in order to facilitate this. The orthodontic management of segments with reduced residual periodontium presents considerable difficulties with regards to the force intensity and direction of movement. Errors are often made, creating periodontal disorder as seen in occlusal trauma.

Careful planning and selection of teeth to be moved will help avoid unwanted and undesirable movement on the teeth we do not want to move or stress with high-risk force systems. Despite decreasing the magnitude of force application in teeth with reduced periodontal support, there will still be a vertical extrusive effect (due to the “cone effect”) [18] as well as unpredictable movements (due to the sudden change in position of the Center of Resistance). Physiologic bone resorption on the already thin and fragile cortical bone in periodontally-compromised dentitions can occur in orthodontic tipping movements due to the concentration of tensile and compressive stresses on the alveolar margins and root apex [19].

With the introduction of mini-screws in orthodontics [20, 21], undesirable forces and movement of anchor units have been reduced. Mini-screws, mini-plates or conventional implants are recommended for better control of three-dimensional tooth movements [22]. Through time and development, the use of these anchoring devices have become more specific, limiting the extension of orthodontic appliances as well as minimizing the duration of treatment. Thus with the use of TADs, it is now possible to avoid unnecessary biological stimuli or round-tripping movements on compromised anchor teeth without undermining efficacy on the reactive unit (teeth that need to be moved).

b. Cleansability of Device

This is based on the assumption that the increase in bacterial mass on tooth surfaces can easily lead to the worsening of periodontal health - gingivitis and recurrence of periodontitis [23, 24].

The most widespread orthodontic device is the fixed multi-bracket appliance. A single wire (with or without loops) or several wires involving different sectors of the arch can be inserted into the brackets. Maintenance of oral hygiene with fixed metal appliances is very difficult and without proper hygiene, the increase in bacterial load around the brackets leads to a higher gingival bleeding index [25,26,27]. Greater oral hygiene problems including plaque deposits were also found with the lingual bracket system [28].

Previous reports show that clinical periodontal parameters partly normalized in three months following the removal of fixed appliances [11]. However, it can sometimes take between six months to two years post-treatment for levels of supra- and subgingival Colony Forming Units (CFU) to reach pre-treatment values. It is worthwhile noting that these studies were conducted on patients with an average age of fourteen years [8,29, 30], but we know that the peak in incidence of severe chronic periodontitis is around 38–40 years of age [31]. From a biological point of view, it is easier for the periodontium of younger patients to revert back to a healthy condition after debonding.

Clear aligners and other types of minimally invasive appliances have recently appeared in the orthodontic landscape. It has been shown that clear aligners simplify oral hygiene measures for both the individual and professional [32]. Minimally invasive orthodontics use wires with or without brackets bonded in a limited area within the dental arches by which precise forces through a statistically determined system can be applied [33, 34].

c. Treatment Time

It is best to minimize the duration of orthodontic treatment in patients susceptible to periodontitis as orthodontic treatment is considered a sterile inflammatory process. Not only do orthodontic devices lead to a greater accumulation of biofilm, but they also result in a biofilm composition change towards periodonto-pathogenic bacteria. Therefore, a prolonged period of orthodontic therapy becomes a co-factor in the risk for periodontal recurrence [35].

The duration of orthodontic therapy also represents the period in which the periodontium of a patient susceptible to periodontal disease is exposed to mechanical stimuli – further activating the inflammatory mediators implicated in orthodontic tooth movement. The duration of treatment is associated with the complexity of the initial malocclusion, the effectiveness of the orthodontic appliances chosen and the desired treatment outcomes.

In conventional orthodontic therapy, the goal is to obtain an Angle Class I occlusion, in line with the Andrew’s Six Keys of Occlusion [36]. The achievement of this treatment outcome is one of the most used reference parameters by orthodontic institutions around the world where the ideal occlusion is perceived as the most aesthetic and most stable. Meta-analysis has shown that the average duration of orthodontic treatment is approximately 24.9 months [37] with no major differences between adolescents and adults [38]. In the context of fixed devices, treatment which include dental extractions are often of longer duration than those without dental extractions [39]. In reality, this concept is changing, as many studies have shown that post-orthodontic stability is not guaranteed [40]. For this reason, orthodontic treatment outcomes involving a compromised occlusion may need to be considered, as long as the occlusion is stable. In the orthodontic-periodontal interface, longer treatment durations are associated with greater periodontal stimulus from prolonged orthodontic forces and pro-inflammatory factors within the periodontium.

d. Accuracy of Force Systems

Different orthodontic appliances create different force vectors on the periodontium [41]. Ideally, knowledge of the magnitude and direction of the force systems acting on the teeth will lead to treatment with more predictable outcomes [42, 43], however in reality, it is not possible to know or maintain the applied force vector for most orthodontic appliances between appointments. As a result, there is an automatic variability in orthodontic force systems, capable of changing the direction of dental movement (the phenomenon of “dental fluctuation”) [44], leading to treatment not completely identical to the programmed alignment (“indiscriminate alignment”) [44]. Among these variables, we can mention the anchorage value deriving from the occlusion and the musculature of the patient, the soundness of the residual periodontium and the occlusal sensitivity of the patient to the occlusal changes occurring during tooth movements. Swinging movement of the teeth (jiggling) linked to the unpredictable creation of occlusal prematurities in patients with a reduced vertical pattern results in tooth mobility very similar to those present in secondary occlusal trauma [45]. This method of managing orthodontic movements is the prerogative of a group of techniques that we could classify as “continuous arch techniques”. The name is inspired by the fact that there is often only a single wire engaging all the brackets of each arch. Clear aligners work with a similar force system treating entire dental arches with a single device with the same characteristics of elasticity.

An alternative to this approach is the “segmented arch technique” [46,47,48]. This is characterized by brackets on all teeth connected by different wire segments (also with different Load/Deflection characteristics). With a segmented arch approach, we tend to differentiate the active units (teeth to be moved) from the reactive units (teeth that are stationary), using carefully applied forces for more predictable movements.

A third method of working with more calculated, accurate and longer-lasting force systems, allowing extremely delicate movements is the Statically Determined System [49]. A statistically determined system implies “that the law of statics (equilibrium) is sufficient to solve” and they provide us with the most predictable knowledge of force systems [41, 44,45,46,47,48,49]. Therefore, this force system could be the most suitable for teeth or groups of teeth with very small residual periodontium.

e. Gingival Phenotype

Gingival phenotypes are distinguished into three categories - thin, medium or thick but currently, a simple method to identify gingival phenotype in patients does not exist. The available evidence indicates that subjects with thin and narrow gingiva tend to have more gingival recession compared with those with thick and wide gingiva. [50, 51]. This risk is increased with orthodontic therapy and may be clinically apparent over time after orthodontic treatment [2]. To prevent gingival recession, many authors have suggested modifying the gingival phenotype prior to, or during orthodontic treatment.

The benefits of phenotype modification therapy involving soft tissue augmentation (PhMT-s) during orthodontic treatment remain undetermined due to the limited number of studies available in the literature, however, PhMT via corticotomy with particulate bone grafting (PhMT-b along with corticotomy-assisted orthodontic therapy - CAOT) may provide clinical benefits. Augmenting periodontal phenotypes expand the scope of incisor movement [52]. Furthermore, Kao et al. suggests that Bone phenotype modification therapy (PhMT) should be pursued prior to orthodontic treatment in patients with thin phenotype when the necessary orthodontic tooth movement will compromise the bony housing. Similarly, soft tissue PhMT may be needed to perform CAOT (Corticotomy-assisted orthodontic therapy), or in conjunction with bone grafting. Thus, there are clinical situations in which both bone and soft tissue augmentation are necessary [51]. A study also explored the labial gingival thickness using CBCT imaging and found a moderate association with the underlying bone radiographically [53].

It is important to clinically assess and record findings regarding the gingival phenotype prior to commencing orthodontic treatment as it is not only to reduce the risk of gingival recession, but also to be aware of the alveolar bone housing and the boundaries of orthodontic tooth movement.

f. Patient susceptibility to periodontitis

Periodontitis is a complex, chronic inflammatory disease as a result of an imbalance of the oral microbiota and the host response leading to inflammation and destruction of the periodontium in susceptible individuals [54]. Although bacterial presence is essential, there are also other contributing factors such as individual susceptibility, certain systemic diseases (i.e. diabetes), smoking and the presence of excessive occlusal stress. These can all act as co-factors for the disease onset and progression [55, 56]. In recent years, there has been greater attention from the international scientific consensus on occlusal aspects and masticatory dysfunction, where these factors are now included and characterize the staging of the new periodontal classification [57]. In addition to periodontopathogenic bacterial elimination and lifestyle changes, therapeutic strategies must also focus on controlling malpositioning of the dental elements and abnormal occlusal forces. At each stage of inter-disciplinary treatment, the lack of control can affect treatment outcome [58].

In 2018 a new Classification scheme for periodontal and peri-implant diseases was proposed as part of the World Workshop on Classification of Periodontology [1, 54], establishing the stage, extension, complexity and severity of periodontitis through the attribution of the grade, risk of progression and susceptibility of the disease. This new classification incorporates many factors that were previously evaluated in other procedures (Periodontal Risk Assessment) [56], designed to monitor and evaluate health and/or disease characteristics of the patient. In order to reflect on the intrinsic periodontal characteristics of the orthodontic patient, this periodontal parameter has also been included in the synoptic table. The work of Heitz-Mayfield et al 2020 [59] placed the least compromised values (with the least risk of progression [1A]) towards the center of the polygon and those with greater impairment of the periodontal status (with an increased risk of progression ([4C]) towards the external part. We propose to quantify the six discussed variables to create a functional diagram which will help clinicians in their treatment with regards to the orthodontic-periodontal interface (Figure 1).

Scores for the Orthodontic-Periodontal Risk Assessment In order to make the following graph more availabe and easier to reproduce, a numerical scale from 1 to the 10 has been chosen, attributing the value 10 to a maximum risk, the value 5 to an average risk and the value 1 to a minimum risk.

Choosing the appropriate orthodontic strategy

To establish an individualized therapeutic plan, it is essential to know the periodontal status of patients at the initial consultation appointment. From this information we can develop a Preliminary Orthodontic Treatment Plan (Figure 3), evaluating the occlusal relationships and identifying factors that may hinder the normal conduct of therapy. Examples include:

• - the presence or absence of tooth mobility [71]
• - the presence or absence of parafunctions (wear facets or muscle pain)

We should firstly state our “ideal orthodontic goal”. This will be dependent on the patient’s periodontal status. In this phase, any necessary stabilization of hypermobile elements with the use of a splint, as well as occlusal adjustments in patients with increased tooth mobility [72] is carried out. This may allow for any necessary non-surgical periodontal therapy to be performed more easily and reduce the risk of worsening periodontal health [73].

Orthodontic treatment should only commence following the active phase of periodontal therapy and then determining the most appropriate orthodontic strategy using the value of the OPRA (Figure 3).

Example: when a patient needs correction of the anterior deepbite, if posterior anchorage will compromise the posterior dentition (due to teeth with poor residual periodontal support), clinicians can opt for the exclusion of these sectors by using skeletal anchorage (temporary anchorage devices).

If more than one treatment method is available to treat a malocclusion, clinicians should choose the shorter treatment option as well as one that facilitates easier oral hygiene.

Timing of orthodontic tooth movements

The literature remains unclear and somewhat controversial on the exact timing to start tooth movement after periodontal therapy [74]. However, there is clear clinical evidence showing tooth movement enhancing the rate of inflamed connective tissue attachment destruction for teeth with infra bony pockets [75, 76] and thus orthodontic treatment should only be performed on periodontally-stable patients.

It is also important to note that there are variations in the maturation and healing following different periodontal procedures. These range from a few days for Resective Surgery (ORS), to six months for Scaling, Root Planing and Access Flap (AF), and up to one year for Regenerative Surgery (GTR and EMD) [71, 77,78,79].

Maintaining good periodontal control during orthodontic therapy

The presence of orthodontic appliances induces a change in the normal saprophytic bacterial flora towards more pathogenic species [80] and increases the difficulty for patients to maintain good oral hygiene [81]. During orthodontic treatment, there are simultaneously areas of bone neo-apposition and bone resorption in the periodontium around teeth that are being moved. In the absence of plaque and inflammation, bony apposition and resorption is defined as a sterile pseudo-inflammatory process. The mediators RANK, RANKL, OPG, IL-1 / IL-6, MMPs that regulate these movements also intervene during the inflammatory processes of bone lysis as a result of the inflammatory response [35].

There is a need to formulate an individualized professional plaque control program for patients undergoing orthodontic treatment to avoid the recurrence of periodontal disease (Figure 3). Our experience leads us to suggest regular 30-minute hygiene appointments once a month, especially for patients with Grade B and C periodontitis. The following procedures should be carried out:

• - Periodontal re-examination
• - Supra and subgingival instrumentation
• - Reinforcement of oral hygiene motivation

During these monthly evaluations, if periodontal parameters such as Full Mouth Bleeding Score (FMBS) are greater than ten percent and probing depths of orthodontically-involved teeth show increased values, there is a risk of periodontitis progression [82]. We will implement a procedure defined by us as “STOP and GO” whereby the orthodontic treatment is stopped, motivational oral hygiene is reinforced, and professional re-instrumentation is performed by the dental hygienist. Orthodontic treatment only restarts when the periodontal parameters return to ideal conditions. This will make it possible to establish an individualized interdisciplinary procedure with extreme precision, reducing the risk of recurrence or unexpected clinical events. Following treatment, patients should be placed on individualized maintenance programmes that include three month recalls in patients with high PRA and six month recalls in patients with low PRA [83].