, Hai-Yang Yu2, Jing Zheng1, Lin-Mao Qian1 and Yu Yan3
(1)
Tribology Research Institute, Southwest Jiaotong University, Chengdu, People’s Republic of China
(2)
West China College of Stomatology, Sichuan University, Chengdu, People’s Republic of China
(3)
Institute of Advanced Materials and Technology, University of Science and Technology, Beijing, People’s Republic of China
Abstract
Being the hardest organ in body, human teeth have a very unique structure. To understand the wear behavior of human teeth, the properties of materials and structures need to be evaluated. There are several quantitative and qualitative methods to measure or assess these properties. This chapter reviews evaluation techniques to understand their unique properties for both mammal and human teeth. Chapter 6 gives a more detailed discussion on artificial dental materials.
Being the hardest organ in body, human teeth have a very unique structure. To understand the wear behavior of human teeth, the properties of materials and structures need to be evaluated. There are several quantitative and qualitative methods to measure or assess these properties. This chapter reviews evaluation techniques to understand their unique properties for both mammal and human teeth. Chapter 6 gives a more detailed discussion on artificial dental materials.
2.1 Clinical Evaluation Methods and Diagnosis
A number of systems for the classification and measurement of tooth surface loss have been reported in the literature.
Scott presented an ordinal dental attrition scoring technique for molar teeth involving a quadrant system [1]. Molar teeth were divided into four sections and each section scored on a 1–10 scale, as described in Table 2.1. The sum of the four quadrants is the score for that tooth. Such wear score categories were quickly learned and proven useful in the analysis of dental wear data.
Table 2.1
Attrition scoring technique
|
Score
|
Description
|
|---|---|
|
0
|
Wear facets invisible or very small.
|
|
1
|
Wear facets large, but large cusps still present and surface features (crenulations, noncarious pits) very evident. It is possible to have pinprick-size dentin exposures or “dots” that should be ignored. This is a quadrant with much enamel.
|
|
2
|
Any cusp in the quadrant area is rounded rather than being clearly defined as in 2. The cusp is becoming obliterated but is not yet worn flat.
|
|
3
|
Quadrant area is worn flat (horizontal), but there is no dentin exposure other than a possible pinprick-size “dot.”
|
|
4
|
Quadrant is flat, with dentin exposure one fourth of quadrant or less. (Be careful not to confuse noncarious pits with dentin exposure.)
|
|
5
|
Dentin exposure greater: More than one fourth of quadrant area is involved, but much enamel is still present. If the quadrant is visualized as having three “sides,” the dentin patch is still surrounded on all three “sides” by a ring of enamel.
|
|
6
|
Enamel is found on only two “sides” of the quadrant.
|
|
7
|
Enamel on only one “side” (usually outer rim), but the enamel is thick to medium on this edge.
|
|
8
|
Enamel on only one “side” as in 8, but the enamel is very thin, just a strip. Part of the “edge” may be worn through at one or more places.
|
|
9
|
No enamel on any part of quadrant: dentin exposure complete. Wear is extended below the cervicoenamel junction into the root.
|
A few years after Scott’s scoring system, Eccles developed a classification system for erosion due to nonindustrial causes; it indicates the severity and site of a lesion on each tooth [2]. Three types of lesions and four kinds of surfaces were possible, as listed in Table 2.2. Eccles believed that this may be of value in describing the condition and as a guide to treatment.
Table 2.2
Classification of erosion due to nonindustrial causes
|
Class
|
Type of lesion
|
|---|---|
|
I
|
Superficial: enamel only
|
|
II
|
Locallized: <1/3 into dentin
|
|
III
|
Extensive: >1/3 into dentin
|
|
Letter
|
Surface denoted
|
|---|---|
|
a
|
Labial
|
|
b
|
Lingual or palatal
|
|
c
|
Occlusal or incisal
|
|
d
|
Multisurface
|
Around the same time as Scott [1], a method was presented for quantitative measurement based upon the samples of modern and prehistoric hunter-gatherers and agriculturalists. An eight-stage system of occlusal wear was fully described, shown here in Table 2.3. Through an analysis of molar wear, Smith [6] believed that a change in the wear plane angle should be an early sign of a change in diet, and that flatness of molar wear appeared to be a good indicator of change in food or food preparation.
Table 2.3
Descriptions of stages of occlusal surface wear
|
Molars
|
Premolars
|
Diagnostic criteria
|
|
|---|---|---|---|
|
1
|
Unworn to polished or small facets (nondentin exposure)
|
Unworn to polished or small facets (nondentin exposure)
|
Unworn to polished or small facets (nondentin exposure)
|
|
2
|
Moderate cusp removal (blunting)
Thinly enameled teeth may show cusp tip dentin, but human permanent molars show no more than one or two pinpoint exposures
|
Moderate cusp removal (blunting)
|
Point or hairline of dentine exposure
|
|
3
|
Full cusp removal and/or some dentin exposure, pinpoint to moderate
|
Full cusp removal and/or moderate dentin patches
|
Dentin line of distinct thickness
|
|
4
|
Several large dentin exposures, still discrete
|
At least one large dentin exposure on one cusp
|
Moderate dentin exposure no longer resembling a line
|
|
5
|
Two dentinal areas coalesced
|
Two large dentin areas (may be slight coalesced)
|
Large dentin area with enamel rim complete
|
|
6
|
Three dentinal areas coalesced, or four coalesced with enamel island
|
Dentinal areas coalesced, enamel rim still complete
|
Large dentin area with enamel rim lost on one side or very thin enamel only
|
|
7
|
Dentin exposed on entire surface Enamel rime largely intact
|
Full dentin exposure, loss of rim on at least one side
|
Enamel rim lost on two sides or small remnants of enamel remain
|
|
8
|
Severe loss of crown height, breakdown of enamel rim; crown surface takes on shape of roots
|
Severe loss of crown height, crown surface takes on shape of roots
|
Complete loss of crown, no enamel remaining; crown surface takes on shape of roots
|
Human tooth wear occurs so slowly that traditionally it has needed months or years to be measurable. Teaford and Tylenda [3] proposed that microscopic changes in wear patterns on human teeth detected in a matter of days could be used as indicators of rates of wear. Particularly, they emphasized that the creation of new wear features on a surface may only be a good indicator of a certain type of wear (e.g., abrasion) and not others (e.g., erosion). Through their approach, clinicians could modify their procedures in response to changes in tooth use.
A system was introduced by Johansson et al. [4] for the longitudinal evaluation of the severity and the rate of tooth wear based upon clinical observations. Five scales were used for grading the severity and four scales for scoring the progression of occlusal wear, as indicated in Tables 2.4 and 2.5, respectively. The advantage of this system is that it is simple and reliable for clinical treatment.
Table 2.4
Ordinal scale used for grading severity of occlusal wear
|
Score
|
Diagnostic criteria
|
|---|---|
|
0
|
No visible facets in the enamel. Occlusal/incisal morphology intact
|
|
1
|
Marked wear facets in the enamel. Occlusal/incisal morphology altered
|
|
2
|
Wear into the dentin. The dentin exposed occlusally/incisally or adjacent tooth surface. Occlusal/incisal morphology changed in shape, with height reduction of the crown
|
|
3
|
Extensive wear into the dentin, large dentinal area (>2 mm2) exposed occlusally/incisally or adjacent tooth surface. Occlusal/incisal morphology totally lost locally or generally. Substantial loss of crown height
|
|
4
|
Wear into secondary dentin (verified by photographs)
|
Table 2.5
Scale used for scoring progression of occlusal wear
|
Score
|
Diagnostic criteria
|
|---|---|
|
0
|
No definite change in previously recorded area(s)
|
|
1
|
Visible change, such as an increase of the facets area(s), without any measurable reduction of crown length; occlusal/incisal morphology changed in shape compared to the first examination
|
|
2
|
Measurable reduction of crown length, <1 mm
|
|
3
|
Marked reduction of crown length, >1 mm
|
A similar diagnostic criteria on tooth erosion was presented by Millward et al. [5], given in Table 2.6, through an investigation involving the clinical examination of 101 children and an assessment of their dietary habits. It provided a similar method as that proposed by Eccles [2]. Three kinds of tooth erosion, such as none or mild, moderate, and severe erosion, corresponding to different criteria and different tooth surfaces were classified for the children.
Table 2.6
Diagnostic criteria for tooth wear index. B buccal or labial, L lingual or palatal, O occlusal, I incisal
|
Score
|
Diagnostic criteria
|
Surfaces
|
|---|---|---|
|
0
|
No loss of enamel surface characteristics
|
B, L, O, I
|
|
1
|
Loss of enamel surface characteristics
|
B, L, O, I
|
|
2
|
Loss of enamel, visible dentin on less than one third of the surface area
|
B, L, O
|
|
Loss of enamel with visible dentin
|
I
|
|
|
3
|
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