INTRODUCTION

Deep bite malocclusions present with decreased lower anterior facial height (LAFH), and are seen in Class I, Class II Division 1, and Class II Division 2 Angle classifications. The first and third groups are characterized by retroclined lower incisors and an increased interincisal angle.^1,2 While the majority of anterior overbite malocclusions are associated with a decreased gonial angle, a decreased mandibular plane angle, and maxillary plane clockwise rotation,² there are cases with dolichocephalic growth patterns that exhibit increased incisor overbite.^3–5 The anterior (counter clockwise) rotation of the mandibular plane does not necessarily affect the development of an anterior overbite.⁶ Some authors have shown that anterior overbites can be related to Temporomandibular Disorders,^7,8 while others were unable to find any association.^9–11

T-Scan digital occlusal analysis has been used to analyze the progression of orthodontic treatment,^12,13 by assessing reactive tooth movements with objective mid-treatment occlusal measurements.^12,14 T-Scan occlusal analysis measures the Right side-to-Left side occlusal imbalance,¹⁵ the distribution of force in the anterior region of the dental arches,¹⁶ and the first occurring contact during the closure cycle,¹⁷ which are frequently utilized findings that evaluate progress and finishing of orthodontic treatment. T-Scan records occlusal function across time, as a patient occludes or excurses into a digital sensor that is attached to a computer via a USB cable. The T-Scan High-Definition Novus sensor (Novus HD, Tekscan Inc. S. Boston, MA USA) is a Mylar-encased, arch-shaped pressure-measuring grid-based printed electronic circuit, that fits into the patient’s mouth between occluding teeth. The large HD recording sensor contains 2200 sensel electronic force measurers and the small HD sensor contains 1500 electronic sensels. When a patient occludes upon a sensor with opposing teeth making approximating contact, the teeth compress together the upper and lower sensor surfaces, which results in a change in the electronic resistance in each of the occlusally-loaded sensels, registering up to 256 relative occlusal contact force levels. The force output data is displayed as a dynamic occlusal video in 3D and 2D ForceView windows, with a Force vs. Time graph located below on the T-Scan desktop.

The 2D ForceView can be divided into four quadrants to facilitate a more detailed force distribution analysis, with the corresponding quadrant-colored lines being displayed for analysis in the Force vs. Time graph.

This Case Report employs T-Scan data to describe and explain the changes in occlusal load distribution before, during and after orthodontic treatment of a Class II Division 2 anterior overbite patient.

CASE STUDY

A 28-year-old female presented with requests to better align her front teeth (Figures 1a-e). The clinical and radiographic examinations revealed she was skeletal Class I and a dentoalveolar bilateral Class II, with an anterior overbite, and a brachycephalic growth pattern. She demonstrated 4 mm of overjet and 5 mm of overbite, with mild-to-moderate upper anterior crowding and mild lower anterior crowding (Table 1).

Figure 1a.The extraoral photographs show there existed slight facial asymmetry with an obtuse left mandibular angle, a short lower third of the face, an evident mento-labial fold, and a retrognathic profile.

Figure 1b.A superimposed lateral cephalometric tracing before treatment illustrating a nearly normal interincisal angle (130 degrees) from lower incisor proclination (107 degrees), a full cusp Class II molar relationship, dual occlusal planes, an exaggerated curve of Spee, an anterior overbite, and a small basal angle (the angle between the maxillary and mandibular bases). Note the dual curve in the cervical region of the spine, where cervical lordosis is combined with kyphosis at the C6-C7 level. The hyoid bone is inferior to the base of C3 and the Gnathion, and the pharyngeal airway width at C2 is minimal, with a posterior-inferior tongue position (Table 1).

Figure 1c.A pretreatment panoramic radiograph illustrating the presence of three third molars and asymmetric condylar head positions, with the left condyle being closer to the eminent slope’s apex, compared to the right condyle which is closer to the eminent slope’s base.

Figure 1d.The occlusal views of the patient prior to treatment show moderate crowding, signs of attrition, and labially tipped lower incisors.

Figure 1e.The labial views of the teeth prior to the onset of treatment. The molar Class II is evident on both sides, with an upper molar anterior shift equal to a full cusp’s mesiodistal width. There is also a 4 mm Class II canine relationship bilaterally, and an anterior overbite of > 60%, with coincident upper and lower midlines.

Digital occlusal measurements were recorded using T-Scan version 9 (Tekscan Inc. S. Boston, MA, USA), that assessed the Occlusion Time (OT), the Disclusion Time (DT), the Percentage of Force by quadrant (anterior right and left; posterior right and left), the Anterior/Posterior Force Ratio, and the Right side-to-Left side force percentage imbalance. The data was gathered by recording a multi-bite patient self-closure into maximum intercuspation (MIP) and a series of excursive movements (anterior, right, and left latero-trusive) (Figures 2a- 2c). The Occlusion Time (OT) is time elapsed from first contact until both arches fully intercuspate, and is visualized in the A-B time duration within the Force-Time graph (Figure 2a). The curved black line within the Force vs. Time graph represents the changing total force of all occluding teeth between both arches. The pretreatment OT values (Timing Table) of three consecutive closure movements equaled 0.32, 0.10, and 0.11 seconds respectively. The Right-side-to-Left-side imbalance was equal to 42.4 % Right 57.6 % Left. The initial quadrant force percentages equaled 6.6 % (right anterior), 16.9 % (left anterior), 35.9 % (right posterior), and 40.7 % (left posterior). The total anterior force percentage equaled 23.5%, with an Anterior-Posterior force ratio equal to 31%.

Figure 2a.The Multi-bite recording pre-treatment, showing the % force distribution between quadrants. The 2 anterior quadrants hosted 23.5% of occlusal force, with the remainder (76.5%) being hosted by the posterior quadrants, resulting in a 31% Anterior-Posterior force ratio. The Right side-to-Left side is imbalanced favoring the left side (57.6% left - 42.4% right).

Figure 2b.A pretreatment left lateral excursion to measure the Disclusion Time. Despite that the Disclusion Time = 0.37 sec. (Timing Table), the tooth #2 non-working right side interference = 26.6.% force, and tooth #12 maintains a working side interference = 7.4% force, until they are fully discluded by the distal slope of tooth #11, with significant support from teeth #s 9 and 10.

Figure 2c.The right lateral excursion with a Disclusion Time = 0.25 sec., although a balancing interference remains on tooth #15 = 48.7% force. The disclusion of both the right and left excursions is facilitated by the increased anterior overbite, illustrated by the presence of 51.3% force on #7 during the right excursive movement.

The Disclusion Time (DT) is the time elapsed from the initial excursive commencement until all posterior contacts bilaterally are discluded from all molars and premolars. The DTs of the left and right lateral excursions equaled 0.37 and 0.25 seconds, respectively (Figures 2b and 2c)

It must be noted that although this left lateral movement’s Disclusion Time was within physiologic limits (= 0.37 seconds), both working (#12) and non-working contacts (#2) were present in this excursion.

Esthetic braces (ORMCO, Brea, California, USA) were bonded to the upper teeth, and metal braces (3M Unitek, Monrovia, California, USA) were bonded onto the lower teeth using a standard bonding protocol. A Class II dentoalveolar correction was planned with upper molar de-rotation and Class II elastic use (3/16, 6 oz,, 3M Unitek, Monrovia, California, USA). Treatment progress from Class II elastic use with correction to the antero-posterior relationship can be seen in Figures 3a and 3b.

Figure 3a.Occlusal views of the well-aligned arches document the mid-treatment progress.

Figure 3b.3 labial views of treatment progress from Class II elastic wear and Class II molar and canine corrections. The upper incisor gingival levels are now well aligned, and the crowding has been resolved. The anterior overbite has been resolved by correcting the curve of Spee by leveling and aligning the second molars to create a single occlusal plane.

Progress with respect to the occlusal force profile can be seen in newly recorded T-Scan data (Figure 4).

Figure 4.T-Scan force profile changes from wearing Class II elastics, showing the Right side-to-Left side balance has improved, but with a significant undesirable change in the A/P ratio. At this stage in treatment 84.3% of the total occlusal force was located in the 2 anterior quadrants, with only 15.7% force in the posterior quadrants. The total A/P ratio = 537%.

The Figure 4 centric occlusion recording was made to evaluate the contact distribution within the arches, the timing of closure into MIP occlusion, the Right side-to-Left side imbalance, and the Anterior/Posterior Force ratio. The OT was prolonged measuring 0.46 seconds, indicating the patient struggled to quickly fit her teeth into MIP. The Right side-to-Left side imbalance = 53.2% right- 46.8% left, with contact forces mainly located in the anterior segments, which hosted more than 80% of total load.

At the completion of active tooth movement and bracket debonding, final patient photographs were obtained (Figure 5a), as were the final occlusal views (Figure 5b). Both Class I molar and canine relationships were achieved along with 2 mm of overbite and 2 mm of overjet (Figure 5c).

Figure 5a.Post treatment, the patient has a more even mandibular angle outline and a straightened profile.

Figure 5b.The final occlusal views of the patient show the crowding was fully resolved, and the marginal ridges were leveled.

Figure 5c.The final labial views of the patient. Class I molar and canine relationships were achieved, with 2 mm of overbite and 2 mm of overjet.

At debonding, T-Scan multi-bite and right and left excursive movement recordings were made, that detailed the end of tooth movement occlusal force profile and timings (Figures 6a, 6b and 6c)

Figure 6a.The final post-treatment multi-bite illustrates bilateral zones of occlusal force, with solid interdigitation of many contacts compared to the Class II elastic data. The anterior quadrants hosted less than 10% total force, with the load being distributed between teeth #s 11, 10, 7, and 6. The Right side-to-Left side balance was almost ideal (= 49.2% right - 50.8% left). The OT duration vacillates between 0.31-1.2-0.36 seconds, as the patient demonstrates an inconsistent capability to close into her new MIP.

Figure 6b.The post treatment left excursion Disclusion Time evaluation. Short duration working and balancing side interferences exist (on teeth #15 and #2, respectively) before approaching complete posterior disclusion. The dominance of the left side anterior guidance is further challenged by the balancing interference on #2 (elevated posterior right quadrant blue line in the Force vs. Time graph after C), and the working-side interference on tooth #15 (elevated posterior left orange line in the Force vs. Time after C). Both interferences reach 0% force at complete disclusion (at D).

Figure 6c.The post treatment right excursion Disclusion Time evaluation shown at the moment of complete posterior disclusion (at D in the Force vs. Time Graph), with the right excursion guided by tooth #7. After C (excursive commencement), all four quadrants maintain various contact forces (blue, red, orange, and green quadrant lines are elevated) throughout the C-D time segment that describes the elapsed time of the right excursive movement. The Center of Force (COF) trajectory (the red-white diamond followed by the red-white tracing) changes its’ direction several times moving from the center of the 2D graph in a downward-right direction (indicating the presence of the right-side posterior interferences), then moving upward-right, and finally upward-left. This COF trajectory path indicates consecutive posterior working and balancing interferences are involved in the right excursion, that eventually dissipate when the anterior guidance contacts on #7 completely control the right excursion (at D).

The comparison from before to after tooth movement T-Scan recordings show the A/P ratio decreased from 32% to 10.5%, the anterior quadrants decreased in force %, the Disclusion Times (DT) approached physiologic normal¹⁸ (0.55 sec Right DT; 0.38 sec Left DT) with both excursions demonstrating short duration working side and balancing side contacts that rapidly discluded. And the Right side-to-Left side imbalance was nearly equal (49.2% right- 50.8% left) (Table 2).

Discussion

There is emerging evidence that using the T-Scan Digital Occlusal Analysis System is a reliable alternative method for making an occlusal assessment.¹⁹ Data acquired from T-Scan was found to correlate with several orthodontic occlusal index parameters.²⁰ Lee and Lee showed a significant correlation exists between 2 orthodontic indexes and the OT. The authors used the Peer Assessment Rating (PAR) Index that measures crowding and spacing in the maxilla and mandible, the buccal segment occlusion (anteroposterior, vertical, and transverse), the overjet (including anterior crossbite), the overbite, any edge-to-edge relationships, the presence of an open bite, any midline discrepancy, and the presence of impacted teeth. Further, the authors also employed the Objective Grading System (OGS), which was introduced by the American Board of Orthodontics as an alternative treatment outcome index.²⁰ The better the index (lower for PAR and higher for OGS), the smaller was the OT. The better was the occlusion, the faster was the OT. This study also found that that the larger was the PAR overjet, value the worse was the OT (longer). Of note was that the OGS had nearly twice as many measured parameters significantly correlated with T-Scan measurements than did the PAR index.²⁰

The goal of the described treatment in this Case Report was to correct the Class II molar and canine relationships to Class I, with the simultaneous correction of the increased overbite and the related crowding. Changes in the occlusal relationships improved the A/P ratio (the proportion of the total anterior percentage load to the total posterior percentage load). The A/P ratio is potentially important in assessing orthodontic treatment efficiency in anterior overbite cases. The latter presents with greater values at the beginning of treatment, as was shown in this Case Report. The occlusal plane inclination before treatment (Figure 1b; Table 1) may be the factor most associated with an increased A/P ratio. Further research is needed to support this contention.

The pre-treatment characteristics of the differing Angle Classifications have been previously described by Koval and coauthors,²¹ where the degree of Right side-to-Left side imbalance was similar in all Angle Classifications. But Class II had a significantly higher A/P ratio compared to Class 1 and Class II. The average Class I A/P ratio = 9.5%,and in Class II = 18.7%. Based on the notion that the aim of ideal orthodontic treatment is to correct occlusal relationships to Angle Class I, orthodontic treatment should aim to achieve ≤> 9.7% A/P ratio.

T-Scan studies involving patients with TMD have determined there exists a significant correlation between increased Occlusion Times²² and prolonged Disclusion Times and the presence of TMD symptoms.^23–26 The Occlusion Time describes the degree of bilateral time-simultaneity present when a patient’s closes into MIP, and is ideal when it is ≤ 0.2 seconds in duration.²⁷ The Disclusion Time (DT) is the elapsed time measured from the beginning of an excursive movement made in one direction (right, left, or forwards) from all teeth in complete intercuspation, through until only canines and/or incisors are in contact.²⁸ The Disclusion Time describes the capability of a patient’s Anterior Guidance mechanism to functionally separate posterior teeth.

It has been previously described that Class II Division 2 non-extraction treatment carried out with Class II elastics, develops four-point contact, which corresponds to the sites where occlusal force is applied. The direction of force when using intermaxillary elastics extends in all three planes, including a vertical component that causes teeth to extrude, a sagittal component that causes mesio-distal tipping, and a transverse component that causes buccal tipping. Depending on the length of treatment and the strength of the elastic force, the resulting incisor relationship can be either edge-to-edge or slightly deeper. This inadvertently creates excessive anterior contact forces, as was shown in this presented Case Report in Figure 4. Importantly, the posterior contact points developed by Class II elastic wear, transferred into working and balancing side interferences that will often result in increased DT.

Several case reports^12,14,29 describe the use of the DT measurement as an indication there exists posterior frictional contacts that may cause spacing between the maxillary anterior teeth. Disclusion Time Reduction (DTR) improves a patient`s laterotrusive movements by decreasing the amount of frictional interferences present, which are referred to by Silverman,⁸ as a potential cause of orthodontic relapse.

A comprehensive study by Cohen-Levy and Cohen³⁰ described the implications of T-Scan data in optimizing orthodontic case-finishing and retention outcomes. In particular, these authors described in patients that wore lingual bracket appliances, the clinical implication of Force Percentage per tooth, the location of the Center of Force, the Occlusion Time when case-finishing adult patients whom had restored posterior teeth, and the presence of wear facets. The overall goals of achieving symmetrical contact distribution with the Center of Force centered and no Force Outlier contacts present on any teeth, can be achieved only with T-Scan data assessing the existing patient`s occlusion. And when necessary, making adjustments to the occlusal surfaces of worn teeth or to existing restorations, to relieve forceful contacts.

CONCLUSIONS

This Case Report described using T-Scan digital occlusion measurements before, during, and after orthodontic treatment with an Angle Class II division 2 anterior overbite malocclusion patient. Orthodontic intervention with fixed brackets and elastics were able to measurably improve the Right side-to-Left side balance, measurably decrease the A/P ratio, and measurably achieve Disclusion Time durations in the right and left excursive movements that approached the normal physiologic value (≤ 0.50 seconds/excursion).

Funding

No funding was received from any source for this project.

Conflicts of Interest

SK reported none. RBK is a consultant to Tekscan but receives no monetary or other compensation because of sales of their products.