rationale for the use of t-scan occlusal analysis in

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Rationale for the Use of T-Scan Occlusal Analysis in Orthodontics

Svetlana Koval, BDS, MDS, DMDa and Robert B. Kerstein, DMDb

a. Private Practice Dentistry of South Florida, Deerfield Beach, FL USA b. Former Assistant Clinical Professor, Dept. of Restorative Dentistry, Tufts University School of Dentistry, Boston, MA USA

Corresponding author: Svetlana Koval [email protected]

Abstract

Ideal static occlusal relationships do not necessarily result in ideal functional occlusal relationships. Current Orthodontic

outcome indexes assess and satisfy aesthetic and morphologic endpoints but do not measure or determine any functional

occlusal relationships, or report on the quality of the occlusal contacts that follow tooth movement. The T-Scan 10

Computerized Occlusal Analysis system can measure the occlusal contact distribution, can diagnose both static and dynamic

functional occlusal relationships following orthodontic treatment, and can aid in the diagnosis of TMD/Occluso-muscle

disorder patients. Comprehensive evidence supports the use of T-Scan analysis as an outcome measure in conjunction with

the well-accepted means of registering occlusion (articulating paper, shimstock, occlusal wax, stone dental casts). This

manuscript presents a rationale and a treatment protocol for the use of T-Scan in Orthodontics. It details T-Scan

implementation during the initial examination, the active treatment appointments in extraction and non-extraction

orthodontic treatment, before debonding the fixed orthodontic appliances, and during the settling and retention stages. T-

Scan occlusal force and timing data sets can guide tooth movement decision making to improve functional occlusal contact

interrelationships, optimize the occlusal balance and the functional posterior disclusion, speed up orthodontic treatment, and

increase the long-term stability of the orthodontic outcome to prevent relapse.

Key Words: Orthodontics, Dental Occlusion, T-Scan, Temporomandibular Disorders, Malocclusion

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28 December 2020 Vol. 3 No. 1 Advanced Dental Technologies & Techniques Koval S & Kerstein RB

Introduction

Orthodontic treatment aims at improving both the aesthetic

appearance of a patient, and the functional characteristics

of the patient`s occlusion. There are several occlusal

schemes which are considered ‘acceptable’ when studied in

the general population: Canine-protected Occlusion, Group

Function, and Balanced Occlusion. The latter is

characterized by the presence of working and balancing

interferences on both sides during lateral movements.1

Orthodontic treatment outcomes have been graded by two

occlusal indexes. The Peer Assessment Rating (PAR)2 has

eleven components, assessing buccal occlusion visually for

the quality of the intercuspation. Introduced in 1998 by the

American Board of Orthodontists, the Objective Grading

System (OGS) has eight criteria,3 with one criterion

assessing static occlusal contacts on hand-articulated casts.

Efforts to classify and measure dynamic occlusion include

Shimstock use to detect occlusal contacts at different

distances from the intercuspal position out to the most

lateral and protrusive positions.4 This method, along with

visually observing articulating paper marks and wax bite

records, depend upon an operator`s Subjective

Interpretation.5-7

The concept of treating orthodontic patients to specific

Gnathologic standards has been discussed in the literature

and deemed unnecessary, alternatively suggesting that the

Maximum Intercuspal Position (MIP) is the most

appropriate musculo-skeletally balanced position for the

patient.8 Some authors suggest that it is not valuable to

prolong treatment time for the patient to attempt to create a

shorter RCP-MIP slide.9 The same study suggested that

Group Function was acceptable.9 Alternatively, a study by

Haralur and coauthors suggested that an RCP-MIP slide of

more than 2 mm had a significant association with TMD

symptoms.10

The prevailing idea of finishing orthodontic treatment with

the maximum number of contacts in static occlusion (MIP)

raises the question, are the contacts marked with

articulating paper considered ‘favorable’ and advantageous

for the patient? A study conducted by Lepley has shown

that higher forces tend to occur in the larger contact and

near contact areas,11 and that higher forces are associated

with fewer discrepancies in marginal ridge positions and

interproximal contact positions, when assessed by the OGS

criteria.3 But do these findings indicate that a better

orthodontic alignment results in better masticatory

performance? Or, do the higher forces ‘hide’ within the

larger contact or near contact areas? Lepley and coauthors

found the highest forces were responsible for supporting the

Vertical Dimension of Occlusion (VDO), indicating that the

orthodontically treated occlusion contains contact areas

with differing occlusal force levels. T-Scan data measures

256 differing force levels as they change across time,12

clearly illustrating the sequence of rising forces, and which

teeth experience more applied force over longer periods of

time.

Modern articulating paper studies revealed that articulating

paper markings are not reliable indicators of differing

occlusal force levels.5, 6, 13, 14 However, emerging evidence

indicates that the T-Scan 10 Computerized Occlusal

Analysis System (Tekscan, Inc. S. Boston, MA, USA) is a

reliable alternative method of making an occlusal

assessment.15 T-Scan timing data sets have been correlated

to several occlusal index parameters.16 Lee and Lee showed

a statistically significant correlation existed between the

PAR and OGS indexes and the Occlusion Time (OT),

which assesses the quality of the occlusal simultaneity. The

better the index (lower PAR; higher OGS), the shorter

duration was the OT, indicating the better the occlusion was

at the end of orthodontic treatment, the shorter was the OT.

Also determined was the larger the overjet (assessed by the

PAR), the longer was the OT.16 Of note was that OGS had

nearly twice as many measured parameters statistically

correlated with the T-Scan III system measurements, than

did the PAR index.16

Qadeer and Yang compared closure occlusal force

parameters in non-orthodontic and in post-orthodontic

patients. They found statistically significant differences in

the distribution of forces existed between the non-

orthodontic and post-orthodontic groups.17 Further, the

orthodontically treated subject’s posterior quadrants had

significantly more contact areas than did the anterior

quadrants. And, 2nd molars in both the non-orthodontic and

post-orthodontic subjects received greater occlusal forces

than all other teeth.17

In another study by Qadeer and Abbas,18 excursive occlusal

force and timing parameters were measured in both non-

orthodontic and post-orthodontic patients:

• The Disclusion Time (DT, which assesses the

duration of occlusal surface friction present in a

lateral excursive movement)

• The presence of working and non-working side

interferences

• The Occlusal Scheme (canine guidance, group

function, balanced occlusion)

• The presence of TMD signs and symptoms

Their Results found statistically significant differences in

the DT between the 2 groups, with the post-orthodontic

group having twice the duration of DT compared to the




non-orthodontic group. But the presence of working side

interferences was higher in the non-orthodontic group (72%

on the working side; 27% on the balancing side), whereas

in the post-orthodontic group, a more equal distribution of

working to non-working side interferences was found (54%

- 46%, respectively).

The percentage of differing Occlusal Schemes in the non-

orthodontic group were:

• 4% anterior guidance

• 60% canine guidance

• 36% group function

In the post-orthodontic group, the percentage of differing

Occlusal Schemes were:

• 4% anterior guidance

• 24% canine guidance

• 72% group function

Importantly, 72% of subjects in the post-orthodontic group

presented with one or more TMD signs/symptoms, while

only 32% of non-orthodontic subjects presented with one

or more TMD signs/symptoms.18 The authors explained the

higher DT in the post-orthodontic subjects resulted from

orthodontic treatment creating a much better posterior

interdigitation, which lead to more working and balancing

posterior interferences in lateral movements.

These findings suggest that the orthodontic treatment

created fewer working interferences, but increased the

percentage of balancing interferences, and that the post-

orthodontic group had a higher prevalence of TMD signs

and symptoms. The inference can be made that group

function and non-working contacts combined are

associated with TMD signs/symptoms, as group function

and non-working contacts are both known major

components of prolonged Disclusion Time.7 These recent

findings are contrary to the frequently advocated opinion

that there lacks an association between occlusion and TMD.

However, that flawed conclusion was made in studies

where the occlusion was assessed with articulating paper

markings alone.1, 9, 19

Studies by Cohen-Levy and Cohen determined that during

the Retention Phase following lingual orthodontic

treatment, repeated T-Scan measurements of the static

occlusion made over a 2-year period of observation,

reflected a general improvement in the right side-left side

occlusal balance. However, some cases maintained a

persistent, uneven distribution of the occlusal contacts

between the right and left sides of the arch.20, 21

Based upon existing, modern measured occlusion

orthodontic evidence,17, 18, 20, 21 the Specific Aims of this

manuscript are to demonstrate the rationale for the use of

T-Scan digital occlusion analysis at different stages of

orthodontic treatment

Suggested T-Scan Implementation Points During

Orthodontic Treatment

Initial assessment - Collection of baseline occlusal force

and timing data prior to orthodontic intervention.

Active Treatment Appointments - T-Scan data can be

used to guide elastic application and wire adjustments in:

• Non-extraction cases

• Extraction cases

• Distalization cases

Prior to Debonding of Fixed appliances - T-Scan data can

be used to guide the:

• Final adjustments to correct mandibular position

• Final adjustments to improve teeth interdigitation

and functional movements.

Retention Phase and Follow-up appointments - T-Scan

data can be used to assess occlusal stability over multiple

post treatment visits.

Stability and Relapse - T-Scan data can be used to guide

the initiation of relapse intervention.

Use of Fixed Retainers on Both Arches - T-Scan data can

be used to guide occlusal adjustments made to retainers

I. Initial Orthodontic Assessment

The prevalence of clinical signs of Temporomandibular

Disorders (TMD) in non-patient populations have been

reported in a few epidemiological studies,22, 23 as being

higher than the prevalence of symptoms reported by actual

TMD patients. This indicates the importance of making an

objective diagnosis of Temporomandibular Disorders

(TMD) before the start of any dental intervention.

In one study, neither the type of malocclusion, nor the

presence of occlusal interferences within the functional

movements, were shown to have a clear association with

the presence of TMD.19 Somewhat older studies that

compared TMD prevalence in orthodontically treated to

non-treated individuals, reported no TMJ signs/symptoms

differences between treated and non-treated individuals.24-

26 The above mentioned studies employed the Helkimo

index,27 where the presence of jaw pain in both the static

occlusal position and in lateral movements was one of the




clinical signs of TMD. This group of studies suggest there

is equal prevalence of TMD in orthodontically treated and

non-treated subjects. One of these papers found that in non-

orthodontic patient populations, the frequency and severity

of Temporomandibular Disorders (TMD) signs and

symptoms tended to increase, beginning in the second

decade of life.25 Therefore, the awareness of whether there

are TMD symptoms prior to initiating any orthodontic

intervention is crucial.

T-Scan studies involving patients with TMD have

repeatedly shown a significant correlation exists between

both increased Occlusion Time 28 and prolonged Disclusion

Time, and the presence of TMD symptoms.29-32 The

Occlusion Time (OT) is the elapsed time in seconds,

measured from the 1st tooth contact until the last tooth

contacts, as a patient closes all their teeth together from

completely open (no tooth contact) to the beginning of

static intercuspation.12 Static intercuspation always occurs

before the patient achieves maximum intercuspation force

levels (MIP). The Occlusion Time describes the degree of

bilateral time-simultaneity present in a patient's occlusion

and is ideal when the OT < 0.2 seconds in duration.12

The Disclusion Time (DT) is the elapsed time in seconds of

an excursive movement made in one direction (right, left,

or forwards), beginning with all teeth in complete

intercuspation through until only canines and/or incisors

are in contact.33 The Disclusion Time describes the

capability of a patient’s Anterior Guidance mechanism to

functionally separate posterior teeth. Both the Occlusion

Time and the Disclusion Time are occlusal function

parameters that cannot be detected with articulating paper

alone.

The previously mentioned 2013 Haralur study reported the

T-Scan measured increased Occlusion Times in a TMD

subject group, as well as longer left, right, and protrusive

Disclusion Times in the TMD group.10 The association

between pain emanating from static occlusion and lateral

mandibular movements, has been shown in T-Scan studies

where subjects presented with prolonged Disclusion

Times.29-32 Therefore, an initial measured digital occlusal

analysis with T-Scan is designed to establish an occlusal

function force and timing baseline, before any intervention

is performed on the patient (Figures 1a-c).

Figure 1 A. – Frontal retracted view of the patient in MIP, at the initial data collection appointment. There appears to be good visual

inter-arch interdigitation. B. – The Right-side retracted view of the patient in MIP. C. – Left side retracted view of the patient in MIP

The Goals of T-Scan Data Acquisition

It is important that each Multi-bite, MIP/CO, right, left and

protrusive excursive movements should be recorded as

separate, individual functional movements.

When Multi-bite and MIP/CO data sets are recorded

(Figures 1d-g), special attention should be given to the

Occlusion Time (the A-B period in the Force vs. Time

Graph), when the earliest contacts appear in the 2-D Force

View window, and the Vertical Opening time (VOT),

which is when the patient opens out of MIP. The VOT is

denoted in the C-D period within the Force vs. Time Graph)

(Figure 1h).

T -Scan data sets show the progression of changes in forces

across time (e.g. Figures 1d-g). So, all the T-Scan Figures

in this manuscript are series of T-Scan time-moments

frames that illustrate changing forces as more and more

teeth come in to contact towards MIP, or as teeth disengage

in lateral excursions. Each data set grouping describes how

different contacts in the course of orthodontic treatment,

can influence the occlusal force profile at any given

moment.

The A-B period (where the OT is recorded) should be

analyzed for the presence and location of any Force Outlier

occlusal contacts, which are very rapidly rising contact

forces. More-often-than-not, the highest contact forces tend

to exist on the molars.34 Teeth with Force Outlier contacts

should be marked with articulating paper to locate these

rapidly rising high force contacts, intraorally (Figures 1d-

g).35




Figure 1d. The earliest low-force fast rising contacts (known as Force Outliers) at 6.48% of Total Force, as the patient begins to close into MIP. The Force Outliers occur on #s26 and 27 on the left side, and #s15, 16, and 17 on the right side.

Figure 1e. 0.355 seconds later, moderate force rises continue on Force Outliers #s 16, 17, 26, and 27, at 25.47% of Total Force. The left posterior forces are rising faster

than those on the right side.

Figure 1f. 0.154 seconds later at 64.48% of total Force, the 4 Force Outliers now reach high forces, making up 70.7% of the total occlusal force distribution.




These contacts can be compared to those which disappear latest from the 2-D Force View window, when the patient opens

out of MIP (Figure 1h).

Figure 1g. 0.14 seconds later in MIP at 83.89% of Total Force, the 4 Force Outliers reach near-maximal forces (pink columns), with markedly less occlusal force distributed

anterior to #s 16, 17, 26, and 27. The COF Icon rests in the posterior left with a 54.9% left - 45.1% right occlusal force imbalance.

Figure 1h. The last contacts to remain forceful when the patient opens out of MIP (between C-D) are the same contacts on the same teeth that were the earliest to rise quickly during initial closure (#s 16, 17, 26, and 27; Figure 1d). These contact areas maintained the force during both the closure into MIP, and when the patient opened

out of MIP.

Both Multi bite and MIP/CO recordings are made to

analyze the left side - right side arch-half occlusal force %

imbalance. Multi-bite recordings also verify the

reproducibility of the Occlusion Time, the VOT, and the

reproducibility of the mandibular position, assessed by the

presence of stable interarch contacts or alternatively by the

presence of a so-called “dual bite.” Alternatively, left and

right laterotrusive recordings and Protrusive recordings, are

made to capture the presence of excursive occlusal surface

friction and measure the duration of each excursion’s

corresponding Disclusion Times.29, 36

Figures 2d-f illustrate the MIP/CO closure contact

sequence observed during fixed appliance orthodontic

treatment, of the patient shown in Figures 2a-c. Visually

there appears reasonable interdigitation, but the T-Scan

analysis clearly detects that only 4-5 occlusal contact

regions evolve around the arch, with some contacts

exhibiting very high force concentrations (yellow, orange,

and pink force zones). The closure OT is quite prolonged =

0.48 seconds (Timing Pane), indicating the patient cannot

easily fit these few maxillary and mandibular contacts

together.




Figure 2 A. Another patient’s maxillary occlusal view with the patient in fixed appliances being observed during a follow-up check appointment – B. Mandibular occlusal

view with the patient in fixed appliances showing good arch form being developed along with the maxillary arch form (Figure 2a) – C. The frontal retracted view of the patient in MIP with fixed appliances. Once again, there appears to be good visual interocclusal interdigitation, which does not accurately describe the true occlusal contact

pattern.

Figure 2d - Early in the closure into MIP there are only four points of contact at 6.16% of Total Force during this Class II correction. The visual assessment in Figure 2c does not reveal there is a marked lack of occlusal interdigitation.

Figure 2e. 0.068 seconds later at 33.66% of total Force, the same four contacts remain as the only solid occlusal stops. At this point in the closure tooth #13 contains the fastest rising contact forces, and draws the COF icon towards the anterior right teeth when it should be moving posteriorly towards the midline of the arch.




Figure 2f. 0.349 seconds later at 74.37% of Total Force nearing the completion of the closure into MIP. The left anterior teeth # 21 and # 22 now become overly forceful

and pull the COF icon towards the left anterior slightly, while # 13 worsens to be the most forceful tooth. The 4 original contacts are still predominant (Figure 2d), while the middle of the arch bilaterally does not make any occlusal contact.

Excursive movement recordings illustrate the presence or

absence of, and the quality of the Canine guidance, is one

aim of full-arch orthodontic treatment in young patients.37

Laterotrusive movement recordings illustrate which teeth

contact during right and left excursive movements, detail

the presence and duration of working and nonworking side

contacts, quantify the Disclusion Time durations of any

frictional contacts, and can determine if occluding 3rd

molars should be extracted because they prolong the

Disclusion Times. All of these excursive functional

elements can be isolated within the Force vs. Time graph

the C-D period).29

Figures 2g-m illustrate the left and right excursive

movement contact sequences. These recordings were made

after 6 more months of tooth movement took place in the

same patient shown in Figures 2a-f. The ongoing fixed

appliance treatment improved the MIP occlusal contact

volume, as there are now widespread MIP occlusal contacts

present that were absent in Figure 2f. However, even with

more contact throughout, the OT is still quite slow (OT =

0.73 sec.), suggesting the patient cautiously closed into the

T-Scan sensor (Figure 2g).

Figure 2g. 6 months later following further tooth movement and Class II elastic use, the MIP position at 89.86% of Total Force, (just before C) there are widespread

occlusal contacts that were absent in Figure 2f. The COF trajectory travels near the midline, illustrating an overall balanced closure contact sequence on the way into MIP.




Figure 2h. 0.086 seconds into the left lateral excursion, where a working side group function controls the movement, as in the Force vs Time Graph, the orange posterior left quadrant line rises to the right of C because of the palatal rising forces on #26, while the balancing side drops to low force (the blue right posterior quadrat line drops

towards the x axis). The COF trajectory travels straight towards #25 instead of moving anteriorly towards #23, which indicating the presence of a prolonged working side

group function. Although #s 21-23 are in contact, they cannot disclude the posterior left teeth.

Figure 2i. 0.193 seconds later in the left excursion, the working side group function persists while the non-working side has been nearly discluded. The COF trajectory travels further towards #25 as the posterior forces have dropped but the excursive contacts are still maintained.

Figure 2j. 0.69 seconds later in the left excursion, the anterior guidance surface on #23 is still unable to disclude both the working side 1st and 2nd molars and the non-

working side 2nd molar. The Disclusion Time for the entire excursion = 0.88 seconds, which is twice as long known physiologic durations (< 0.4 seconds).




Figure 2k. The patient makes a very low closure into MIP as the Total Force curve in the Force vs Time graph rises very slowly from A-C, indicating the patient had

difficulty fitting their teeth together before making complete interdigitation. The Occlusion Time is very prolonged = 0.66 seconds (3x longer than physiologic; < 0.2 seconds). The weak slow closure resulted in poor occlusal balance of 65.1% left – 34.9% right.

Figure 2l. 0.117 seconds into the right excursion, there are both working and balancing contacts present, with the COF trajectory moved right anteriorly towards #13. This

indicates the right anterior guidance is more effective than the left.

Figure 2m. 0.093 seconds later in the right excursion, just prior to posterior disclusion. The Disclusion Time = 0.22 seconds, indicating the working side interferences

during right lateral movement on teeth #s16 and 17 disclude quickly, and are within the physiologic range of < 0.4 seconds.




Follow-up Appointments for Non-Extraction Cases

Studies that have related orthodontic treatments with

Temporomandibular Disorders (TMD) have all been

categorized as:23

• Papers that show TMD signs and symptoms are

prevalent in orthodontically treated populations

• Papers that researched the impact of orthodontic

treatment on the development of TMD signs and

symptoms

• Papers comparing different types of appliances and

their impact on the development of TMD signs and

symptoms

• Papers showing a relationship between extraction

orthodontic treatment and the development of

TMD

• Papers showing that undergoing orthodontic

treatment can induce a preventative effect on the

development of TMD signs and symptoms

This collection of studies led to the conclusion that there is

no association between the prevalence of TMD signs and

symptoms, and undergoing orthodontic treatment. Further,

a separate study by Rendell concluded that orthodontic

treatment does not cause the onset of TMD signs/

symptoms, and if TMD signs/symptoms are ongoing during

orthodontic treatment, their severity and frequency does not

change during the duration of treatment.38 However, in

clinical practice, it is not uncommon for patients to report

the onset of TMD symptoms while undergoing the process

of orthodontic treatment.

One study used the Herbst appliance to make Class II

corrections, showed the orthodontic treatment increased

muscle tenderness. But by the end of the study time frame,

the number of subjects exhibiting muscle symptoms was

equal to those at the start of treatment.39 Silverman also

stated that intermaxillary elastic use can potentially induce

TMD signs/symptoms by excessively increasing the

Vertical Dimension of Occlusion (VDO).8 Because TMD

signs/symptom can readily appear during orthodontic

treatment, close monitoring of a patient`s mid-tooth

movement status with the T-Scan technology, is advised,

and is readily accomplished.

Considerations for T-Scan use during follow-up

appointments:

Orthodontic biomechanics in non-extraction cases includes

inter-arch appliances that are attached to teeth directly, or

to orthodontic wires engaged into attachments on certain

teeth. Direct force application to teeth, tends to displace

them in the direction of the applied force.

During Interarch Elastic Use (Figures 2a-c) record

MIP/CO, protrusive, and both laterotrusive movements.

I. Record MIP/CO - Detect any Force Outliers on

molar teeth which serve as elastic attachments

(Figures 2d - f) and evaluate the Occlusion Time.

This is important because usually in Class II elastic use,

lower molars tend to extrude with their distal cusps rising

above the occlusal plane, such that molar extrusion will

often produce only 4 points of contact (upper - lower central

incisors; upper - lower first molars) (Figures 2d and e).

Further, attention should be paid to the marginal ridge

positions of the lower 1st and 2nd molars (especially if they

serve as attachments), because Force Outlier contacts often

are present on their distal marginal ridges. And, in cases

with the Occlusion Time > 0.2 seconds, additional wire

adjustments should be made on the molar teeth, to lessen

the overall time required for the patient to reach MIP.

II. Record laterotrusive movements - To ensure that

upper and lower canines occupy the correct

positions to ensure the Disclusion Time (DT) > 0.4

seconds (Figures 2g - m).

To manage detected excessive forces on posterior teeth

during the lateral movements, wire adjustments should be

incorporated. Engaging more teeth into the anchor unit on

the mandible will redistribute vertical forces more evenly,

and prevent unwanted super-eruption.

Follow-up Appointments - Extraction and Molar

Distalization Cases

A well-published lawsuit about the Orthodontic treatment

of a Class II Division 2 malocclusion, that resulted in a 7

mm anterior open bite end-point, was legally decided in

favor of the patient. This decision was based on the

assumption that the extraction treatment of 2 upper

premolars was associated with the development of TMD

signs and symptoms, while the patient`s predilection to

Temporomandibular Disorders (TMD) was not well-

diagnosed before the commencement of intervention. The

patient did not demonstrate any signs and symptoms of

TMD before treatment, but began complaining during the

course of her orthodontic treatment.




The explanation for the development of TMD symptoms

during premolar extraction orthodontics has been

researched, to determine whether the extractions were the

cause of TMD, whether patient growth was the cause, or if

there were any other possible causes. Sadowsky and

coauthors demonstrated there was no difference in the

frequency of TM joint sounds between patients treated with

and without premolar extractions.40 The authors stated that

the frequency of TM joint sounds was less after orthodontic

treatment, which suggests there is an association between

occlusion and TMD signs and symptoms. A study by

Luppanapornlarp and Johnston reported there was no

association between TMD and premolar extraction.41

However contrarily, Dibbets & van der Weele showed there

was a higher prevalence of TMD signs/symptoms 15 years

after premolar extraction orthodontics, when compared to

10 years’ post-treatment. The authors surmised that growth

patterns rather than the extraction protocol might be

responsible for the increased occurrence of symptoms

following orthodontic treatment.42 Lastly, a retrospective

study by Staggers rejected the assumption that 4 premolar

extraction treatment decreased the Vertical Dimension of

Occlusion (VDO), instead showing that the VDO actually

increased due to growth.43 With the evidence being

equivocal regarding the anecdotal development of TMD

symptoms during the course of orthodontic treatment,

combined with the indirect association of TMD signs and

symptoms and occlusion reported in many T-Scan based

studies,5, 31, 44-47 close monitoring of the occlusion with the

T-Scan should be provided throughout the active phase of

orthodontic treatment.

Distalization Case Management with T-Scan

Despite that distalization is usually considered to be a non-

extraction treatment option, the mechanics of tooth

movement in extraction and distalization cases does

incorporate sagitally-directed tooth movement in the

posterior segments of the arch (Figures 3a-e). Sagittal tooth

movements generally cause positional changes of the main

supporting cusps, which can lead to changes in the Vertical

Dimension of Occlusion (VDO), and often cause new

prematurities to be perceived within 2-3 days after

appliance activation. Sometimes during distalization in

severe cases, the mesiopalatal cusp of the upper first molar

can cause acute pain and periodontal abscess formation in

its opposing lower molar.

Figure 3 A. Frontal view of patient with fixed appliances undergoing lower molar distalization using mini-screws bilaterally – B. Right side retracted view of the lower

molar distalization showing the employed hardware – C. Left side retracted view of the lower molar distalization showing the employed hardware




Figure 3 D. Periapical radiograph of the mini-screw in the area of # 31- E. Periapical radiograph of the mini-screw in the area of #17

During Distalization:

I. MIP/CO is recorded - to determine the presence of any contacts with excessive force, and for any rapidly rising

Force Outlier contacts (Figures 3f - h).

II. The Clench-and-Grind movement is recorded - to reveal any painful contacts. The patient is asked to first clench

his/her teeth together into the T-Scan sensor, and then to grind repeatedly to both sides, back and forth.

Figure 3f. The early closure contacts in the 2nd closure to MIP, the contacts are widespread and of low force. The 1st closure is very low with the OT being prolonged (OT

= 0.89 seconds). The 2nd closure is more physiologic with a slightly prolonged OT = 0.40 seconds




Figure 3g - 0.186 seconds later in the 2nd closure, more contacts evolve midway towards MIP. To avoid Force Outliers forming on the 2nd molars during the distalization,

the load was transferred to #s 14 and 24, by using occlusal buildups on those 2 premolars.

Figure 3h. 0.112 seconds later in the 2nd closure nearing MIP, the highest intensity forces have formed on the premolar buildups #s 14 and 24.

Figure 3i. Early contacts in the right excursion after additional buildups were placed on #s 16 and #26, the patient began experience pain on #16. The excursive data shows there is a moderately forceful palatal working side interfering contact evolving on #16 (light blue column).




Usually, painful contact is revealed in the T-Scan data as an

extremely high and forceful contact, visible in the grinding

movement. After locating and adjusting the contact, the

patient should feel immediate relief (Figures 3i - l).

Figure 3j. 0.125 seconds later in the right excursion, the #16 palatal working side contact discludes the entire right side, causing the COF trajectory to move directly

posterior. This contact is the reason the patient experienced pain on #16, even though the DT = 0.36 seconds.

III. Both the right and left lateral excursive movements should be recorded - to be sure that the DT is short (< 0.4

seconds per excursion).

Figure 3k. After adjusting the #16 palatal working side contact, a new T-Scan right excursive recording shows that early in the corrected excursion, the forces on #16 stay low while forces go up on the premolar #15.

To maintain the DT closer to 0.4 seconds during any sagittal

posterior tooth movements, additive procedures can be

incorporated that enhance the contour of the palatal side of

the ipsilateral canine. And, to resolve a painful tooth

problem during distalization, occlusal buildups that may

have been placed earlier on the molar teeth to facilitate

sagittal tooth movement, can be adjusted. Finally, in cases

where no molar occlusal buildups are employed, additional

occlusal buildups can be placed onto premolars and 2nd

molars to relieve a painful tooth.

Extraction Mechanics

If en-masse mechanics is preferred, the canine position

should be checked prior to performing any space closure.

This ensures the canine has proper inclination to create

sound posterior disclusion in the right and left lateral

movements. Despite the initial situation (excessive

crowding, or excessive buccal tipping of the upper incisors

requiring possible tooth extraction), the mandible tends to




Figure 3l – 0.358 seconds later in the corrected right excursion, the load stays reduced on #16 and the anterior guidance contacts can engage, rather than being discluded by #16 (Figure 3j). The patient felt immediate relief once #16 palatal was relieved from controlling the right excursion.

completely use the available space for performing all

border movements. Therefore, the canine guidance should

be obvious during this stage of treatment, although the

posterior segments can still contain working and non-

working side contacts. Then when the extraction site is

nearly healed, more obvious canine guidance should be

visually apparent. But until the extraction full space closure

is complete, no straight wire additional bends should be

incorporated in the posterior regions.

I. After complete space closure is achieved, an

MIP/CO recording is made - to assess the

occlusal contact distribution, the right side-left side

occlusal force % imbalance, the Occlusion Time,

the presence of any Force Outliers, and the VOT.

II. To verify canine contact correctness, the

laterotrusive movements should be recorded - The

DT should approach < 0.4 seconds.

At this point in orthodontic treatment, the MIP/CO contact

distribution gives insight into the necessity of further

vertical tooth movement. When there are only a few

existing contacts between the opposing arches, there likely

will be molar Force Outliers present, along with prolonged

Occlusion Time during the closure into MIP (A-B > 0.2

seconds). And if space closure remains incomplete, a

Detailing Phase of tooth movement should be undertaken,

to address these remaining occlusal issues.

Prior to Debonding of Fixed Appliances

The question of whether the ‘ideal’ occlusal relationships

should be achieved before or after debonding is crucial to

treatment planning. Improper tooth alignment combined

with deflective interferences have been shown to be

contributory to orthodontic relapse.8 In order to avoid

unwanted tooth movements and relapse, proper tooth

positions should be checked during the course of treatment.

Occlusal interferences that are detected before debonding

might aid in determining the need for further canine and

incisor movements that could idealize the final incisor and

canine positions, so they can better disclude the posterior

teeth.

Two goals of completed orthodontic treatment are:

• To decrease the amount of non-axial occlusal

forces

• To redistribute the occlusal load between as many

teeth as possible.

But as teeth change their positions during orthodontic

treatment teeth, the likelihood that a horizontal force will

act against inclined occlusal surfaces when patients

swallow and/or function, is significantly increased.48, 49

Rothner also advocated that Occlusal Equilibration50 could

mitigate the occlusal trauma that can lead to periodontal

breakdown, stating (incorrectly in 1948) that all centric

contacts, regardless of the area, experience the same load.49

Both the adjusted amount of tooth structure requiring

correction, and the relative differing occlusal contact force

levels that exist around the post-orthodontically treated

arch, can be easily improved by using T-Scan data sets to

guide the final movements to optimize tooth position and

orientation.

A Case Report51 involving the use of T-Scan to optimize a

patient`s occlusion prior to debonding, illustrated how the




T-Scan detected an increased time-duration of applied

occlusal force on a pair of antagonists, that were

subjectively reported by the patient to cause “continuous

discomfort” during function. Although the patient was

satisfied with the aesthetic outcome of the orthodontic

treatment, the T-Scan diagnosed and treated the causative

occlusal contacts responsible for the patient`s ongoing

occlusal discomfort.51

The Detailing Stage (Figures 4a-d) is when the maximum

amount of contact between the opposing arches should be

developed.

Figure 4 A. Beginning the Detailing Phase by observing the anterior interdigitation from the infra- incisal view with the arch wires removed. The anterior incisal

overlap appears adequate as do the anterior interarch contacts – B. A close-up of the anterior right quadrant with arch wire and elastics in place illustrating the incisal overlap and appropriate canine-canine contact – C. The right-side retracted view of the patient in MIP – D. The left side retracted view of the patient in MIP

The T-Scan should be used in the following ways:

I. Make MIP/CO and Multi-bite recordings – to

assess the MIP contact occlusal force distribution,

and all of the below closure into MIP T-Scan

occlusal parameters described in Figures 4e-g:

a. No molar contacts should be the sole first

contact at A.

b. No persistent contacts should be present on any

molar tooth during the opening phase (during

the VOT between C-D).

c. The Center of Force Trajectory (COF) should

demonstrate a simultaneous closure path,

starting near the midline close to the anterior

teeth, and concluding near to the posterior teeth

while staying near to the arch midline.

d. The Right side -Left side balance should be

very near to 50%-50%, with all the MIP

contacts evenly distributed around the arch

(Figure 4h)




Figure 4e. The 3 earliest contacts at 4.1% of Total force showing both canines and #27 are in contact.

Figure 4f. 0.118 seconds later at 65.25% of Total Force, the entire dentition is in occlusion with widespread moderate force levels and a fairly centered Center of Force.

Figure 4g – 0.08 seconds later at 89.32% of Total Force in MIP, there is good occlusal balance bilaterally with only #s14 and 27 exhibiting elevated occlusal force levels.




It is important to note that even if there is a high degree of

right side-left side occlusal balance (near to 50%

bilaterally), sometimes only a few occlusal contacts may be

present around the arch immediately following debanding.

Therefore, subtle adjustments made to the occlusion guided

by the T-Scan can improve the overall closure

interdigitation. Figures 4h - j detail the optimized closure

sequence into MIP that resulted from T-Scan guided

corrections made to the debanded data displayed in Figures

4e-g.

Figure 4h. After minor adjustments were made to the occlusion shown in Figures 4e-g, at 9.33% of Total Force multiple low force early contacts are widely distributed throughout the arch.

Figure 4i. 0.103 seconds later at 42.2% of Total Force (midway into MIP), all teeth are in contact with low-moderate forces throughout and near equal right side - left side

force y (53.1% left-46.9 % right).

Also, during the Detailing Phase, the protrusive and lateral

movements are of great importance. If there are tight

contacts present on the canines with no other anterior teeth

in contact, any excessive palatal tipping should be

overcome to provide more freedom for anterior mandibular

positioning, and to develop additional solid anterior

contacts that will guide straight protrusion.

I. Record the Protrusive Guidance - to assess the

DT, which should not exceed 0.4 seconds

(Figures 4k-n).




Figure 4j. 0.095 seconds later at 82.57% of Total Force in MIP, solid posterior contacts are present with a centered Center of Force, and equal forces shared bilaterally (49.2% left – 50.8 % right). Occlusal adjustments should be performed on #s17 and 27 to moderate some of the high forces (pink columns) prior to entering the Retention

Phase.

Figure 4k. The MIP contacts at 91.8% of Total Force, just before the patient commenced a protrusive excursion (at C). In MIP there are widespread occlusal contacts with

a force distribution imbalance of 56.5% left - 43.5% right. The COF trajectory starts early on the left side, and is then pulled towards the midline by the late rising high force contacts on the right molars. It settles in MIP slightly left of the arch midline.

Figure 4l. 0.107 seconds into the protrusive excursion at 29.02% of Total Force, where tooth #17 maintains a significant high force and controls the early protrusive

movement. In the Force vs Time Graph, the blue posterior right quadrant line rises to the right of C, because of this major mesiobuccal #17 force concentration. The COF

trajectory travels straight towards #15, indicating a prolonged protrusive interference exists in the posterior right quadrant. The anterior contacts established by tooth movement (see Figure 4a), cannot protrusively disclude the posterior right 2nd molar.




Figure 4m. 0.39 seconds later at 12.92% of Total Force in the protrusive excursion, the working side group function persists while the non-working side has been nearly

discluded. The COF trajectory shifted anteriorly and travels towards #s11-21. The posterior forces have dropped, but #s 15, 16, 17, 26 and 27 are still in low force contact.

Figure 4n. 0.61 seconds later at 6.9% of Total Force in the protrusive excursion at D, when the anterior guidance surfaces on #s11, 21, and 22 evenly (the columns are near-equal heights) share the posterior disclusion. The protrusive DT = 0.21 seconds, which is a physiologic duration (< 0.4 seconds).

Establishing Canine guidance is one important goal of

orthodontic treatment. It can be easily achieved in most

Class I and Class II cases. However, in Class III cases

canine extrusion can be an option to establish Canine

guidance, which can negatively impact the anterior

aesthetics with a reverse smile curve. This option should be

communicated with the patient during the initial treatment

planning stages.

I. Record the left and right lateral excursions

- High quality canine guidance is best

characterized by a DT < 0.4 seconds (see prior

Figures 2k-m; 3k-l).

Articulating Paper can be used to help assess the contact

path of the guiding contacts controlling each lateral

excursion. The right and left lateral excursions should be

guided by mesial canine fossae, with paper marks

extending from the upper canine palatal ridge to the mesial

marginal ridge of the mesial lingual fossa. In cases where

no sufficient guidance can be achieved, or the DT exceeds

0.4 seconds, additional tooth movement should be




incorporated. In most cases, these will be rotational upper

canine bends.

Retention Phase

The Retention Phase has two major aspects of concern:

• The longevity of the anterior alignment

• Changes in the number of contacts in the posterior

segments.

The problem of stability of anterior alignment has been

addressed in many longitudinal studies that followed

orthodontic outcomes at 3, 5, and 10-year intervals. Most

studies agree that in an average patient, the maxillary

anterior segment does not need dual retention, in that

removable retention is sufficient.52-55 Canuto and coauthors

reported that in 30% of treated subjects, there was a relapse

causing maxillary irregularity during the post-retention

period,54 but the degree and nature of relapse was not

necessarily associated with some initial outcome tooth

position irregularities. The generally accepted theory

behind a maxillary anterior relapse is based on an

association between posterior occlusal forces, and the

periodontal reflex of the anterior teeth.56, 57

Occlusal improvements during the so called “Settling

Stage”, has a less discussed opposing view. This

contradictory thinking suggests, there can be the evolution

of both functional and non-functional occlusal contacts

during Settling.

The commonly believed as being undesirable occlusal

interferences present at the end of tooth movement are:58

• Non-working side interferences with a lack of

working side contacts

• Posterior interferences in protrusive movements

• Extensive retruded contact position-intercuspal

position slides

Longitudinal studies performed during Settling reported at

the 24-month recall, 72% of the patients showed no changes

in their functional occlusion, such that it appeared the

functional occlusion did not significantly change after fixed

orthodontic appliance removal.56-58 The authors considered

functional occlusion to be ‘satisfied’ when:

• either canine guidance or group function existed,

with or without balancing side interferences,

• when an RCP-ICP slide < 2 mm, and

• there were no posterior interferences in the

protrusive movement.

However, the studies on Disclusion Time Reduction show

that not only balancing interferences are problematic, but

often working side interferences contribute to increased

DT.29, 36 Therefore, working side interferences should also

be avoided at the end of orthodontic treatment.

Durbin and coauthors in their study of occlusal contacts

following orthodontic treatment stated, “that newly gained

occlusal contacts could either contribute to improved

interdigitation or constitute a basis for a relapse.” 59 This

study found a gain in the total number of occlusal contacts

in MIP occurred over a three-month retention period, with

a major gain in the posterior segments. However, the

anterior regions showed a decrease in the number of

contacts. The assumption was made by the authors that

anterior teeth were not supposed to move during the

retention phase. The authors explained the anterior contact

decreased from either an incomplete Class II correction, or

from retainer interferences. The authors also found a

negative correlation between the number of contacts at

debonding and the number of contacts found at 3-month

retention stage. The increase in contacts and their potential

impact on the functional occlusion might be avoided, if the

contacts and their relative forces were made even, and the

DT reduced to < 0.4 seconds, before finishing the

orthodontic treatment.

The behavior of first and second molars is of particular

importance, as both contribute to the majority of the final

occlusal contacts. Sultana and coauthors found a gradual

increase in the occlusal force and occlusal area on first

molar teeth occurred during the first months of retention.

Whereas the second molar exhibited the highest increase in

occlusal forces and occlusal area over the second year of

retention, after retention was completed.60 This agrees with

Lepley’s findings where higher forces were associated with

larger occlusal areas.11

Two case reports described the Disclusion Time duration as

an indicator that frictional posterior contacts caused

maxillary anterior teeth spacing.61, 62 Disclusion Time

Reduction (DTR) improves a patient`s laterotrusive

movements by decreasing the amount of excursive

frictional interferences, while also lowering the muscle

activity levels required to perform the movement.7, 29-33, 36,

44-46, 63 Silverman considered these excursive frictional

interferences a potential cause of orthodontic relapse.8

Two comprehensive studies by Cohen-Levy and Cohen 20,

21 describe the outcome implications of utilizing T-Scan




data sets when optimizing orthodontic case-finishing and

retention outcomes. In patients that wore lingual bracket

appliances, the authors described using differing T-Scan

software tools to guide the case-finishing in adult patients

with restorations present in their posterior teeth (Force

Percentage per tooth, the Center of Force Trajectory and

Icon, and the Occlusion Time). The overall goal of

achieving symmetrical contact distribution with a centered

Center of Force and no fast-rising Force Outliers on any

tooth, can be achieved using T-Scan data to assess the

patient`s occlusion. When necessary, changes can be made

to occlusal surfaces of worn teeth, or to existing restorations

to relieve forceful contacts.

In conclusion, orthodontic “Settling”, is dependent on the

number of contacts developed before fixed appliance

debonding, with the majority of contacts being “co-

developed” during the first three months of retention. Later,

the second molar teeth tend to align and erupt after retention

is completed. Retention appliances should be planned

according to the overall orthodontic biomechanics, whereas

fixed orthodontic retainers placed on both arches provide

more space for proper posterior interdigitation.

During the Retention Phase, the T-Scan should be used in

the following ways:

I. MIP/CO recordings are made at every

retention follow-up appointment – to assess

the distribution and number of contacts

present, as well as right side - left side % force

balance

The Disclusion Time tends to remain constant during the

retention period unless new restorations are introduced. To

avoid unwanted tooth movements during retention, T-Scan

excursive recordings should be made during each follow-

up appointment.

II. Protrusion, and right and left laterotrusion

recordings are also made - to detect changes

in the DT from excursive working and

nonworking side contacts that evolved during

Settling, which require adjustment to prevent

relapse.

Summary

The ideal static occlusal relationships, as defined by both

the OGS and PAR indexes traditionally define the quality

of the orthodontic treatment outcome. Although the

majority of visual characteristics of both indexes satisfy the

aesthetic component of the orthodontic treatment goals,

neither gives any insight into the functional occlusal

relationships that follow tooth movement. When measured

with T-Scan during and after orthodontic treatment, the

functional occlusal relationships can be improved through

interventional tooth movements guided by T-Scan data sets.

This force and timing-based targeted orthodontic tooth

movement approach, renders overall treatment to be more

efficient, while decreasing patient discomfort and

optimizing occlusal ‘Settling’ to prevent relapse.

Author Statements:

Svetlana Koval: Conceptualization, methodology, writing

of the original draft.

Robert Kerstein: Review and editing of the original draft,

visualization, supervision.

Conflict of Interest:

Robert Kerstein is a clinical consultant to Tekscan, Inc.,

South Boston, MA USA.

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Citation Koval S, Kerstein RB. Rationale for the Use of T-Scan Occlusal Analysis in Orthodontics. Adv Dent

Tech. 2020 Dec;3(1):26-50. Epub

Received September 10, 2020

Published December 12, 2020

Funding none

Conflicts Robert B. Kerstein, DMD is a Clinical Consultant to Tekscan, Inc., South Boston, MA USA.


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