Abstract
Precise analysis of occlusal contacts and occlusal force is a problem in functional diagnostics that has not yet been satisfactorily resolved, despite the fact that the deleterious consequences of an unbalanced occlusion are widespread and can be severe. In clinical practice, the present-day analysis of the occlusion is reduced to depicting force with color-marking foils that leave ink marks upon the teeth. However, these foils only indicate the localization of contacts, but do not describe reliably the occlusal force relationships. Precise analysis that incorporates time resolution and plots the distribution of forces within the occlusion is not possible when employing the traditional occlusal indicator methods. A detailed occlusal force and timing analysis can only be provided by performing a computer-assisted analysis, using the T-Scan III system (Tekscan, Inc. S. Boston, MA, USA), which records changing relative occlusal force levels and real-time occlusal contact sequence data with High Definition (HD) recording sensors. This chapter demonstrates the accuracy and reliability of this computer-based occlusal measurement method that reliably describes the time-dependent distribution of occlusal force evolution.
TopIntroduction
A smooth and functional occlusion is basic and central to all sub-disciplines of dentistry, including orthodontics (Andrews, 1972). In conservative restorative dentistry, the presence of a harmonious and smooth occlusion is considered essential to the physiological function of the Stomatognathic system, and is deemed essential to protect against excessive loading and fracture of inserted restorations and dental implants. In orthodontics, harmonious occlusal relationships are required to ensure the stability of achieved treatment outcomes. It is a vital element of therapeutic dentistry to accurately and realistically record and analyze the occlusal relationships of examined patients, by the use of occlusal indicators (foils, papers, silk ribbon) or instrumental occlusal diagnostics. This chapter will focus mainly on the reproducibility and reliability of methods. What follows is an analytical presentation of the temporal sequence of occlusal force buildup that can be observed with the T-Scan III occlusal analysis system (Tekscan, Inc. S. Boston, MA USA). This topic will be discussed against the background of the available literature regarding the conventional, non-digital, occlusal indicator diagnostic methods.
Key Terms in this Chapter
Increasing Participation: This term describes the increasing numbers of teeth that make occlusal contact during the temporal sequence of the occlusal force buildup, as each differing occlusal contact changes relative occlusal force levels.
Conventional Occlusal Indicators: These are the color-marking foils, articulating papers, and silk ribbons, which are used by clinicians to identify occlusal contacts in daily clinical practice. The range of thickness of these commercially available occlusal indicators lies between 8–200 microns. While indicators of this type disclose the location of contacts, they provide no information about the relative occlusal force of the occlusal contacts. Given a mere 21% reliability of there existing an association between occlusal markings and occlusal contact force levels, any force level conclusions drawn from conventional indicators have been described as being “tantamount to clinical guessing”. Due to this inadequate representation of the relative occlusal force levels, the usefulness of conventional indicators should be confined to “contact locators” solely, and not as occlusal force descriptors (these indicators have been incorrectly advocated in many published papers and occlusion textbooks, to be capable of describing occlusal force).
GEDAS: A computer assisted diagnostic procedure comparable to the DPS. Like the Dental Prescale System, GEDAS involves two separate steps, and does not offer the direct transfer of the measured occlusal relationships to be easily displayed within an analysis software. First, an extra hard silicone interocclusal record is made. After hardening, the silicone record is removed and is scanned optically together with a calibration object.
Repeatability: The second statistical term according to Bland and Altman, that describes the precision of the repeated measurements. Repeatability, Also known as the Reproducibility , the variation of the measured values in repeated investigations, involving a factor of 2.77.
Temporal Sequence: The temporal sequence describes the continous development of occlusal contacts and occlusal force, that results between the first tooth contact (T1 - initial antagonistic tooth contact) and complete intercuspation (T15 - 0.15 seconds after T1,that can be divided into 15 individual time increments). The force and timing changes that occur between T1 and T15 have not been adequately described within the literature, such that how force evolves over time while sequential occlusal contacts occur during closure, has been overlooked by clinicians and researchers. Although a distinction is often made between “static occlusion“ (that which occurs without mandibular movement), and “dynamic occlusion“ (that which occurs with mandibular movement in a lateral or mediotrusive direction), these definitions are based on starting the movememts from complete intercuspation (MIP). However, the very important time period when occlusal force builds up between the initial tooth contact, through the progressive increase in the numbers of occlusal contacts, to finally end in complete intercuspation, has not been adequately studied due to a lack of capable measuring tools. However, because the T-Scan technology records incremental time, the temporal sequence of occlusal force build up can be readily recorded and displayed in fractional time increments,for analysis.
Non-Measurable True Value: Also known as the Systematic Error , it describes that all true values can only be “estimated”, even when using suitable measurement instruments that demonstrate proper measurement precision and low measurement error. For example, measuring the thickness of a crown margin using a caliper gauge would result in better precision and smaller measurement error than would using a ruler. Although the ruler is a measurement tool, for crown margin measurement, a ruler would be far less precise and would demonstrate a greater measurement error than would the caliper. Therefore, the caliper gauge would be the best device to “estimate” the true thickness of the crown margin.
Measurement Error: This statistical term describes the accuracy of a single measurement according to the “true value factor of 1.96. Described by Bland and Altman, this biostatistic is a method of data plotting used in analyzing the agreement between two different assays.
Occlusal Force Buildup: The process of occlusion is dynamic starting from no force when the patient is open, until where the maximum occlusal force is generated at the point of maximum intercuspation, where the highest numbers of occlusal contacts occur. The occlusal force levels within the entire dental arch, rise in a logistic growth curve, where different growth curves can often be correlated to functional disorders.
T-Scan III HD Recording Sensor: The HD recording sensor has a thickness of 100 microns, which is within the range of other commercially available occlusal indicator films, articulation papers, and silk ribbons (8–200 microns). The sensor is compriosed of a gridwork of conduction paths (sensels) that are embedded in a double-sided mylar matrix. Force exerted on the sensor surface by intetrcuspating teeth leads to sequential voltage drops that occur within the conduction paths. These voltage changes are measured and digitized by the T-Scan software and then displayed both as percentages, and as color-coded, relative occlusal force levels describing 256 levels of masticatory force. The software then displays the relative occlusal force data as it occurs in sequence in 0.01- 0.003 second-long increments, that areplayed back as a continuous, or stop-action movie.
Dental Prescale System (DPS): A computer assisted diagnostic device, that when used intraorally, can estimate occlusal force. It involves a two-stage process where first, the patient occludes into a pressure-sensitive wax wafer that changes color locally, depending on the pressure levels exerted throughout differing sites on the wafer. The second step involves computer scanning of the imprinted wax wafer, to analyzes the observed color changes . The Dental Prescale System does not provide any information about the timing of the occlusal contact sequence, or the temporal sequence of occlusal force buildup.