Dear Editor,
I read with interest the recent article from Dias et al, Comparison between conventional and computerized methods in the assessment of an occlusal scheme. J Oral Rehabil. 2020 Feb;47(2):221-8. The actual occlusion placed on an oral appliance (OA) is a critical concept and often not verified in studies, obscuring the evidence on the effect of occlusion from OA therapy. Several points in this study bear further discussion.
When the T-Scan III sensor is used as described by the authors in maximum clench on an occlusal appliance (OA), there is a uniform elevation of the flat occlusal surface. Where the opposing cusps contact the sensor, it compresses to 60 μm. The concern of deflective jaw movement by uneven, asynchronous incline contacts are eliminated by the congruence of the flat sensor and flat OA surfaces against opposing cusp tips. The flat OA model of investigation represents the best-case analysis of using digital occlusal analysis on concern of sensor thickness.1 At maximum intercuspation clench on a flat surface, there is virtually no clinical difference whether the full-arch occlusal indicator is 24 u ribbon or 60 μm sensor. The authors acknowledge this, “the occlusal recordings were performed over the flat posterior surface of mandibular appliances, thus avoiding the influence of occlusal anatomy.” The authors then contradict this, “An excessive thickness increases the number and size of the contacts; it can induce an altered response and potentially lead to mandibular deflection.” and “The computerized assessment has a potentially important limitation related to the sensor thickness, which may influence the analysis of the occlusal scheme.” These cautions are not valid for this flat OA study model which is the topic of the article.
The authors also criticize the T-Scan sensor stiffness, “recording contacts on a rigid and thick sensor may not necessarily be viewed as the most suitable strategy to appreciate the real intercuspation.” This statement is also not valid for their flat OA study model. Adjusting the occlusion on a flat OA involves the hard OA surface against the cusp tips of teeth with normal mobility of up to 100 u (authors reference #33) or more on teeth with occlusal trauma. This is a soft interface in that adjustment of the OA acrylic relieves pressure in the periodontal ligament and reduces tooth mobility. The rigidity of the sensor is an advantage since a flexible or soft sensor would allow more indent of rigid teeth versus mobile teeth and reduce the accuracy of the occlusal recording.
It is important to understand that the T-Scan III is not used in the same way as the ink ribbon and should not be compared as if it is. The sensor records the location, relative force and duration of occlusal contact, but does not mark the teeth. The clinician uses very thin ink ribbon to mark the teeth and the T-Scan III sensor interprets these marks. The closure contact markings on all sites of the OA in this study are ideally small dots representing a single contact per tooth against the opposing cusp tip. The clinical difficulty is not correcting the shape or location of these dots as that is done easily during gross adjustment. The challenge is creating multiple, simultaneous and even intensity closure contacts. Ink ribbon or patient feedback doesn’t give any information that allows the clinician to accomplish a precise, programmed occlusion. The T-Scan III immediately displays location, duration and intensity of the tooth contacts.
The T-Scan III sensor records contact at 0.003 second intervals during the described closure and will show initial light contacts that often do not even register with ink ribbon. This allows the clinician to analyze and document the actual occlusion from initial light contact to maximum clenching. The authors’ references 1, 9, 13, 27 and those articles’ reference sections indicate they are aware of many studies that consistently show that ink ribbon cannot determine the location, duration and force of occlusal contact, which is the objective assessment of occlusion for both in vivo and in vitro studies. Ink ribbon marking is material dependent, subjectively assessed, inaccurate and can misguide the clinician during adjustment procedures to the detriment of the patient. Ink ribbon only shows whether there was contact or not.2 The authors do not refute these studies.
The authors could not demonstrate a high correlation between the software analysis of digital photographs and visual assessment of the ink marks, showing a further problem with ink mark interpretation in clinical practice. They did not recommend the additional time and equipment of sequential photographs to compensate for this problem and better guide the adjustment of the OA. By comparison, the T-Scan III gives the patient and clinician immediate 2D and 3D views of the actual occlusion that is clear and unambiguous. The only advantage of ink ribbon compared to the T-Scan III is cost. As with many technologies, long term use and better patient care mitigate the initial cost.
The authors compared the areas of ink marks, software analyzed mark areas and T-Scan III occlusal contact areas. The reader should ask what is the clinical significance of these areas since the T-Scan III does not function as tooth marking. The authors do not attribute clinical significance to these areas nor indicate which unequal area is incorrect or which modality is more accurate. The authors did not compare a quantified occlusal interference using the T-Scan III and ink ribbon that would have indicated accuracy of detecting occlusal contacts. The authors own reference 28 states that “The T-Scan III showed a high degree of reliability when used to perform consecutive measurements.” and reference no.13 states, “the computerized occlusal analysis system is the only occlusal indicator that demonstrates the ability to provide quantifiable force and time variance in real-time.”
The authors reference and summarize studies that show ink ribbon fails to correctly assess the occlusal contact area and intensity but conclude that “relying on articulation foils to evaluate occlusal contacts may still be viewed as the best available clinical method.” There is no validity to this statement for the flat OA study model, no data presented to support it and no refutation of their own contradictory references. The authors suggest not using the T-Scan III by repetitively confusing possible sensor distortion of the occlusion when opposing, uneven, asynchronous tooth inclines contact on natural teeth with the flat OA model where this does not occur. The authors provide no evidence showing sensor distortion of the occlusion in the flat OA model and do not refute their references that endorse digital occlusal analysis. There is not a pittance of validity to their recommendation not to use the T-Scan III as the standard for occlusal analysis.
Sarinnaphakorn et al showed that occlusal problems persisted on ink ribbon adjusted OAs and that T- Scan III was able to predictably correct them and create a programmed therapeutic occlusion.3 Clinicians need to know that OA ribbon marking does not ensure that an optimal occlusion has been achieved.
Efficacy research requires that the most consistent and accurate methodology is used. Digital occlusal analysis surpasses ink ribbon marking in every aspect and is clearly the reference standard.4 Research that inaccurately uses ink ribbon or visual inspection to determine a test or control occlusion is not valid. Their introductory comment that “based on suggestions that the role of dental occlusion features is less important than believed in the past in the etiology of temporo-mandibular disorders (TMD), bruxism or functional impairment” exemplifies this problem. It is based on studies using surrogate features of the occlusion and ink ribbon determined occlusion status that have no validity.5 Current literature reviews with digital occlusal analysis studies on diagnosis and treatment of occlusal problems demonstrates the opposite conclusion; there exists a direct correlation between occlusal status and the comfort and function of masticatory muscle.
Clinical dental research directly influences the clinician’s diagnosis and treatment of occlusal problems. Digital occlusal analysis of flat OAs shows the patient and dentist the actual location, duration and relative force of occlusal contacts that are unobtainable with ink ribbon marking. Providing a precise, programmed therapeutic occlusion on OAs is clinically achievable when the occlusal contacts are displayed by digital occlusal analysis. The authors’ references show that research must accurately document the actual OA occlusion with digital occlusal analysis for the study conclusion to be valid.
Conflict of Interest Statement
The author reported no conflict of interest.