Part 2 book “Handbook of research on computerized occlusal analysis technology applications in dental medicine” has contents: The clinical applications of computerized occlusal analysis, new occlusal concepts based on computerized occlusal analysis.
Section The Clinical Applications of Computerized Occlusal Analysis 523 Chapter 11 Orthodontic T-Scan Applications Julia Cohen-Levy, DDS, MS, PhD Private Practice, France ABSTRACT This chapter reviews T-Scan use in Orthodontics, defines normal T-Scan recordings for orthodontically treated subjects versus untreated subjects, and explains T-Scan use in the case-finishing process After orthodontic appliance removal changes in the occlusion result from “settling,” because teeth can move freely within the periodontium Despite a post treatment, visually “perfect” Angle’s Class I relationship, ideal occlusal contacts often not result solely from tooth movement Creating simultaneous and equal contacts following fixed appliance removal can be accomplished using T-Scan data to optimize the end-result occlusal contact pattern The software’s force distribution and timing indicators (the and 3-Dimensional ForceViews, force percentage per tooth and arch half, the Center of Force, and the Occlusion and Disclusion Times) aid in obtaining an ideal occlusal force distribution during casefinishing Several case reports highlight combining lingual orthodontic treatment with Orthognathic surgery, where each presented case utilized T-Scan data during active treatment and retention INTRODUCTION The dental occlusion develops progressively, under the guidance of functional and genetic influences throughout the differing stages of dental arch morphogenesis, and then subsequently through a variety of adaptations made notably to the Temporomandibular joint and the masticatory muscles When dealing with complex malocclusions, Orthodontists modify all dental contacts to achieve a new position of occlusal equilibrium, and take responsibility for its functional integration Fully aware of these implications, they devote special attention to the quality of the final occlusion of their treated cases, whatever the therapeutic occlusal philosophy is that they ascribe to follow It is uniformly understood and agreed upon, that at the completion of orthodontic treatment the occlusal contacts of all teeth should demonstrate simultaneous contact timing and be of equal force intensity, thereby creating a uniform and symmetrical distribution of masticatory force It has been recommended that the anterior teeth be DOI: 10.4018/978-1-4666-6587-3.ch011 Copyright © 2015, IGI Global Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited Orthodontic T-Scan Applications slightly less loaded than the posterior teeth (Roth, 1970; Dawson, 2006) In Orthodontics, and other dental medicine disciplines as well, such as Prosthodontics and Periodontics, the assessment of occlusal quality has relied mostly on the visual inspection of occlusal contacts, by using: • • • The intercuspation of stone dental casts Subjectively Interpreting articulating paper marks Listening to oral patient “feel” feedback Alternative, but more time-consuming occlusal indicator techniques have been described, that are often employed within research studies These alternative occlusal indicator methods are: • • Observing imprints in high fluidity impression materials Analyzing force distribution statically within pressure sensitive wax - Dental Prescale 50H (Fuji Photo Film Corporation, Tokyo, Japan) and its analyzing apparatus (Occluzer ™ FPD703, Fuji Photo Film Corporation, Tokyo, Japan) After the patient imprints the above static dental material indicators, the indicators require digital scanning, followed later by computer processing to retrieve and analyze their force data Unfortunately, their effectiveness in generating force distribution representations is offset by the significant chair time used to complete data retrieval Furthermore, neither of these techniques gives the clinician information about the “timing” of the contacts They offer no indication as to the location of the first contact, the sequence of contacts from 1st contact through until maximum intercuspation, nor the distribution of contacts within the maximum intercuspated position Therefore with these methods, the clinician does not have the required tools to properly evaluate the 524 ‘simultaneity’ or ‘timing’ of the post orthodontic occlusal contact result Orthodontic End-Result Occlusal Function Several questions have arisen about orthodontic treatment completion and the established endresult occlusal function: • • • Should Orthodontists assume that achieving ideal positional tooth-to-tooth relationships is enough to obtain a measurably balanced occlusion? Do the occlusal contacts spontaneously improve the overall occlusal force balance resultant from settling, after appliance removal? Is post treatment occlusal force distribution of the teeth symmetrically obtained when a pre treatment dental asymmetry has been corrected, orthodontically? The T-Scan III (T-Scan III Version 7, Tekscan Inc S Boston, MA, USA) is an occlusal analysis system available to Orthodontists, that records in real-time, the contact force distribution as it changes functionally throughout the progression of occlusal contacts from 1st contact through until maximum intercuspation during closure, and quantifies the time durations of any frictional occlusal surface engagements that posterior teeth make in protrusive or lateral excursions This very detailed occlusal analysis can be played back in increments of 0.01 seconds, or when in the much faster Turbo-mode, 0.003 second-long increments This chapter will initially review the literature describing orthodontic norms and post-orthodontic functional occlusion Then, the clinical use of the T-Scan III system in Orthodontics will be explained by highlighting the force distribution indicators for closure contacts leading to maximum intercuspation (the 2-Dimensional and 3-Dimensional ForceViews; the percentage of force per Orthodontic T-Scan Applications tooth, arch-half, quadrant; the COF trajectory path and the symmetry of its final position), and detailing within dynamic mandibular excursive function, the Disclusion Times Computer-aided orthodontic case finishing and follow-up protocols employing the T-Scan III are illustrated within case studies, which discuss how best to improve the quality of a post-orthodontic occlusal contact pattern end-result Figure 1a Ideal ‘Class I’ molar relationships according to Angle BACKGROUND Occlusal Finishing in Orthodontics According to the American Board of Orthodontists (Casko, Vaden, Kokich, Damone, James, Cangialosi, Riolo, Owens, & Bills, 1998; Dykhouse, Moffitt, Grubb, Greco, English, Briss, Jamieson, Kastrop, & Owens, 2006), occlusal finishing quality can be evaluated on stone dental casts, by visually assessing the proper alignment of incisal borders and marginal ridges, the buccolingual inclinations of the individual teeth, the occlusal relationships (achieving Angle’s Class I is considered ideal), the overjet, and the occlusal contacts Interproximal contacts should be tight with complete space closure Class I is considered the normal antero-posterior relationship of the mandible to the maxilla Following Angle’s classification (Angle, 1899), the mesio-buccal cusp of the permanent maxillary first molar ideally should occlude within the buccal groove of the permanent mandibular first molar, between the mesial and mid-buccal cusp (Figure 1a) Andrews added other “keys” to achieve an ideal occlusion, among which were a mesial angulation of the maxillary first molar crown, so that the distal buccal cusp of the maxillary first molar is placed in close contact with the mesial cusp of the mandibular 2nd molar (Andrews, 1972) (Figure 1b) Figure 1b Ideal ‘Class I’ molar relationships according to Andrews, where there is a recommended mesial angulation of the maxillary first molar crown In 1969, Ricketts highlighted the major role of the maxillary second premolar position (Ricketts, 1969) He also recommended there be a special inclination of the canines, attained with a positive torque value, in order to free the mandible in excursive movements He additionally described an ideal contact distribution for the Class I patient that contained a theoretical “24 points” of occlusion per half-arch, in maximal intercuspation In 525 Orthodontic T-Scan Applications Figure 2a Maxillary ideal contacts to be obtained in a Class I occlusion with no extractions, as described by Ricketts Note the actual contacts illustrated by the blue articulating paper marks versus the ideal contacts noted in dark blue There are less blue paper marks showing contacts than is the presented ideal Figure 2b Mandibular ideal contacts to be obtained in a Class I occlusion with no extractions, as described by Ricketts Note the actual contacts illustrated by the red articulating paper marks versus the ideal contacts noted in dark red There are less red paper marks showing contacts than is the presented ideal 526 Orthodontic T-Scan Applications this proposed ideal contact pattern, the “centric point” contacts were to be placed on the lingual cusp tips of the maxillary posterior teeth, the buccal cusp tips of mandibular posterior teeth, within the central fossa and upon the marginal ridges of the posterior teeth, and the incisal edges of mandibular anterior teeth were to make contact with lingual surfaces of the maxillary anterior teeth (Figures 2a and b) When wisdom teeth are present, a maximum of 30 occlusal contact points could be obtained And, if first premolars were removed during orthodontic treatment, then only 21 points of contact could be established Conversely, Tweed and Merrifield (Tweed & Merrifield, 1986) stated that at the end of edgewise orthodontic treatment, a slight posterior open-occlusion should be left to allow for an overcorrection This posterior “open bite” is created during the leveling phase with directional force mechanics, by sequential tip back bends in the orthodontic wire applied to maxillary first and second molars A “transitional occlusion” remains at appliance removal, which is characterized by a disclusion of the second molars and the distal cusps of the first molars (Figure 3) This Figure The sequential tip-back on the maxillary molars to create a slight posterior open-occlusion at the completion of edgewise orthodontic treatment arrangement was suggested to allow the muscles of mastication to affect the greatest force on the primary chewing table located within the midarch area (Klonz, 1996) During this “denture recovery” phase that followed orthodontic appliance removal, it has been postulated that the noncontacting teeth would spontaneously come into ideal contact, resultant from applied pressure from the surrounding muscles and the periodontium With the development of straight wire appliances in Orthodontics, different authors described for each tooth, their own bracket prescription for proper angulation and torque values Differences according the type of appliance employed are significant, especially for the maxillary anterior teeth Below are three differing author’s recommendations that describe the maxillary canines: • • • According Andrews (Andrews, 1989) and Roth (Roth, 1970), the canines should be inclined towards the palatal (with negative torque, of -7° and -2° values, respectively) According McLaughlin, Benett and Trevisi (McLaughlin, Bennett & Trevisi, 2001), who described the widely used MBT™ straight-wire technique, the canines should be straight with 00 torque value According to Ricketts (Ricketts, 1978) and Hilgers (Hilgers, 1987), the canines should be inclined towards the buccal with a positive torque value of +7° In relation to the malocclusion type or the facial pattern, where reinforced anchorage may or not be required, most authors advocated some variability in the incisor’s torque values Several sets of pre-adjusted brackets then were created that all demonstrated different levels of torque, for different treatment needs The chosen orthodontic appliance design will have a major consequence on the morphology of the anterior guidance because the slope of the 527 Orthodontic T-Scan Applications Figure 4a Visible maxillary incisor negative torque in maximum intercuspation Figure 4b Influence of maxillary incisor’s negative torque on the amount of mandibular opening present in protrusion Significant posterior tooth separation is achieved with negative torque and a flat mandibular curve of Spee Figure 5a Visible maxillary incisor positive torque in maximum intercuspation Figure 5b Influence of maxillary incisor’s positive torque on the amount of mandibular opening during protrusion Lesser posterior tooth separation is achieved with positive torque vs negative torque, combined with a flat mandibular curve of Spee maxillary lingual surfaces guide the mandibular teeth Maxillary incisor and canine torque, together with the overjet and overbite measurements, directly influences the amount of vertical mandibular opening that occurs during protrusive and lateral movements Slavicek in the early 1980’s suggested that the anterior guidance should not be too sharp, so as to avoid distalizing the mandible constrain free movement of the mandible (Slavicek, 1982; Slavicek, 1988) 528 Despite the differences in orthodontic appliance type used, and any major variability in patient occlusal morphology, most authors describe an occlusal scheme that was to be representative of an ‘ideal’ functional occlusion, which should be present at orthodontic treatment completion When an excellent static occlusion was achieved, it has been assumed in Orthodontics, that a balanced Orthodontic T-Scan Applications functional occlusion was also obtained, except in cases of major sagittal divergence or significant tooth-size discrepancies Additionally, it has also been assumed that when excellent static occlusion was achieved orthodontically, the lateral excursive and protrusive movements also functioned properly Nevertheless, despite these assumptions made on visual inspection of the final contacts, some authors have suggested that this is not always the case (King, 2010; Morton & Pancherz, 2009) Is There a Need for Computerized Occlusal Analysis in Orthodontic Case-Finishing? Does Achieving an Ideal Angle’s Class I Result, Ensure a Balanced Occlusion? In order to achieve functional occlusal equilibrium, several occlusal functional features should be achieved (Timm, Herremans, & As, 1976; Morton & Pancherz, 2009; Clark & Evans, 2001; Clark & Evans, 1998): • • • • • Bilateral, symmetrical occlusal contacts developed in the retruded contact position (RCP) Coincidence between the retruded contact position and the intercuspal contact position, or only a short slide of < 1mm should exist between the two positions Contacts on the working side during lateral mandibular movements that may be limited to the canines (canine protection), or may extend posteriorly to include one or more pairs of adjacent posterior teeth (group function) Teeth in group function should be in precise harmony with anterior and condylar guidance No contact should be present between opposing posterior teeth on the non-working side during lateral excursions In a post treatment stone cast analysis performed on 37 patients, where the casts were evaluated immediately after orthodontic appliance removal, most subjects had only unilateral contacts present upon initial closure in the retruded axis position, and exhibited a slide between the retruded contact position and the intercuspal position In addition, most subjects demonstrated non-working side contact between opposing second molars at the end of treatment (Clark & Evans, 1998) In a similar study performed on 230 patients the authors found non-working side contact was present in 30% of subjects, posterior contacts on protrusion present in 20% of the subjects, and RCP-ICP prematurities in 18% of the subjects (Milosevic & Samuels, 2000) The influence of the appliance type and the experience of the orthodontist, have been suggested as critical factors in obtaining varying orthodontic end-results In a recent study using articular ribbon (8 microns thick), patients treated with edgewise appliances were found not to exhibit ideal functional occlusal contact relationships, despite being finished in Class I canine and molar relationships However, most individuals who underwent straight-wire appliance orthodontic treatment better demonstrated a mutually protected occlusion (Akhoundi, Hashem, & Noroozi, 2009) Do Contacts Spontaneously Improve With Time by the ’Settling’ of the Occlusion? Settling, or the reinstatement of functional occlusion, has been likened to a tooth’s physiologic eruption process, and considered as an adaptation phenomenon that occurs once the teeth are freed from the stresses exerted by the orthodontic appliances Settling must be accounted for, both in the orthodontic finishing process and in the retention phase, where settling can allow occlusal contacts to improve Some authors suggest functional occlusal relationships be examined after retention has ceased, rather than prolong active orthodontic treat- 529 Orthodontic T-Scan Applications ment attempting to achieve “ideal” functional occlusal goals (Clark & Evans, 2001) But, is there definitive published evidence that Nature spontanenously improves the occlusion following orthodontic treatment? Lyotard’s study was the first to quantitatively assess the short-term occlusal changes that took place from a total absence of retention following multi-bracket orthodontic treatment in a group of adolescents (Lyotard, Hans, Nelson, & Valiathan, 2010) This study reported that an improvement to the buccolingual inclination and leveling of the marginal ridges was observed, while the overjet and the irregularity index tended to worsen As a consequence, a lack of retainer cannot be recommended Nevertheless, the chosen type of retainer can potentially influence the occlusion, as well (fixed anterior retainers, Hawley plates, thermoformed splints with full or partial coverage), depending upon the amount of relative vertical tooth movement allowed by the type of retainer employed (Baỗiftỗi, Uysal, Sari, & Inan, 2007; Aslan, Dinỗer, Salmanli, & Qasem, 2013; Hoybjerg, Currier, & Kadioglu, 2013) Conversely, other studies that analyzed the settling process found that no spontaneous improvements occurred in dynamic occlusal contacts (Dinỗer, Meral, & Tỹmer, 2003) Although the number of contacts in centric occlusion increased significantly during the retention period, no significant difference was observed with regard to the location of the contacts In a more recent study, the authors were able to establish that at debanding, nearly half of their subjects (44.3%) presented with unsatisfactory functional occlusion, and after years of retention 34.7% of subjects still presented with interferences in protrusion and lateral excursions, where many subjects demonstrated a > mm discrepancy between maximum intercuspation and Centric Relation The occlusion remained comparable to that which was observed at orthodontic bracket 530 removal in 72.3% of cases, while the occlusion improved in only 20% of patients, and worsened in 10% of the cases (Morton & Pancherz, 2009) In conclusion, it seems that the settling process does exist, but its result is unpredictable (Greco, English, Briss, Jamieson, Kastrop, Castelein, DeLeon, Dugoni, & Chung, 2010) The increase in number of contacts continues to evolve beyond months folowing appliance removal, and can extend for up to 21 months (Gazit & Lieberman, 1985; Razdolsky, Sadowsky, & BeGole, 1989) Most authors agree that orthodontic treatment should not be terminated before a proper dynamic evaluation is accomplished It has also been recommended that a 6-month period of observation should pass, prior to performing any proposed occlusal equilibration because the most significant occlusal alterations from settling, take place primarily in the first months following orthodontic appliance removal (Bauer, Behrent, Olivier, & Bushang, 2010) Evaluating ‘Visually Perfect’ Contact Distribution with the T-Scan III System In the last few years, a few studies have been undertaken with orthodontic subjects that were recorded with the T-Scan III Computerized Occlusal Analysis System (Tekscan, Inc S Boston, MA, USA), to assess the post orthodontic contacts present in both maximum intercuspation and during lateral movements In a clinical edgewise therapy study where 14 adolescents were compared to a control group with normal occlusion, the authors found no differences in contact surfaces on the back teeth between the groups (An, Wang, & Bai, 2009) However, they did find a more anterior Center of Force in the treated group, implying the anterior teeth received more occlusal force following edgewise treatment, than did the control untreated subjects This finding could indicate that edgewise Orthodontic T-Scan Applications treatment resulted in Tweed’s ‘recovery phase intermediate occlusion’ where there is a purposeful 2nd molar disclusion in closure (Figure 3), or that during the incisor retraction phase of tooth movement, a lack of maxillary incisor torque control resulted in increased load on the anterior teeth One published study about the occlusal changes that took place during the 12 month period following orthodontic treatment, reported that there was an overall dynamic occlusion improvement, where the Disclusion Times during protrusion, and the right and left lateral excursive movements, were reduced significantly over time (He, Li, Gao & An, 2010) They divided the sample into groups; a “no interference group”, and an “interference group”, and concluded “the presence of occlusal interferences affected the self-improvement process, and increased the chance of post-treatment disorders of the Stomatognathic system, such as mandibular abnormal movements” In another dynamic occlusion, post orthodontic treatment study, when compared to a control group of young adults with normal occlusions, the orthodontic patients had a high prevalence of posterior occlusal interferences, mostly located on the second molars such that their Disclusion Times were also longer (p < 0.01) (An, Wang, & Bai, 2011) In a sample of dental students (young adults), previously orthodontically treated during childhood, Le found numerous prematurities present that were mainly located in the second molar region (Le, 2013) She suggested that orthodontic treatment was possibly completed before the second molars were fully erupted into the mouth, or that because these teeth are difficult to reach clinically, the pre-adjusted orthodontic bracket or tube might not have been correctly bonded, resulting in a poor 3- Dimensional tooth position control In a study made on a sample of adult patients, whose adaptation potential was known to be reduced because adult subjects have no residual growth potential, the authors found an increase in contact surface occurred during retention, without any change occurring in the contact locations (Cohen-Levy & Cohen, 2011) Moreover, most subjects demonstrated overall symmetry improvement during settling, with a tendency over passing time towards 50% of the force being supported on each side (Figure 6) But some patients did develop a significant functional asymmetry, where these patients demonstrated an extremely unequal right side-left side arch-half force imbalance, without exhibiting any significant dysfunctional symptoms (Figure 7) The existence of a possible asymmetry in occlusal force distribution, recorded in the maximal intercuspation position, was previously described by a Japanese team (Mizui, Nabeshima, Tosa, Tanaka, & Kawazoe, 1994), using the T-Scan II system (Tekscan Inc S Boston, MA, USA) The authors noted there was a difference between patients that were affected by TMD (n = 5) and those of an asymptomatic control group (n = 60) In the control group, the duration and distribution of contacts were symmetrical with the Center of Force clustered around the first molar In the TMD group, the force and duration of contacts were asymmetrical, with Center of Force appearing in varied locations This study did not command a great deal of academic impact because of numerous study design methodological flaws (low subject numbers, failure to randomize groups and maintain their anonymity, and an unclear definition of the subject inclusion/exclusion factors) However, similar results were found in another, more recent T-Scan study that reported TMD subjects demonstrated a significantly higher frequency of premature contacts (half of the studied subjects; 16 out of 32 subjects), and greater bilateral asymmetry in the occlusal force distribution, than compared to the control subjects (Wang & Yin, 2012) 531 ... the control subjects (Wang & Yin, 20 12) 531 Orthodontic T-Scan Applications SECTION II Treating an Unbalanced Static Occlusion during Orthodontic Case-Finishing and Retention Evaluating Occlusal. .. information about the “timing” of the contacts They offer no indication as to the location of the first contact, the sequence of contacts from 1st contact through until maximum intercuspation, nor... position of occlusal equilibrium, and take responsibility for its functional integration Fully aware of these implications, they devote special attention to the quality of the final occlusion of