- Email: [email protected]
Esthetic parameters of mandibular anterior teeth
Esthetic parameters of mandibular Lewis Lorton, D.D.S., M.S.D.,”
and Peter Whitbeck,
anterior teeth
D.D.S.*
Walter Reed Army Medical Center, Washington, D.C.
R
eplacement of lost mandibular anterior teeth with a fixed partial denture is one of the most demanding tasks in prosthodontics. Aside from the obvious difficulties with any fixed prosthetic procedure, there is the additional problem of esthetics. Since lower anterior fixed prostheses are a relatively uncommon restoration, the esthetic factors, which are important and should be controlled, are not well understood. A recent sl:udy by Cade’ indicated that as the age of the patient increased, the mandibular teeth were displayed more and more during speaking. The mandibular anterior teeth were displayed at least as much as the maxillary teeth when the patient was speaking or resting. Vig and Brundo’ considered the degree of visibility of the mandibular central incisor versus the maxillary central incisor and found that the mandibular incisor became more visible than the maxillary central in patients 40 to 49 years of age. The inference that may be drawn from these studies is that the dentist should know the determining factors of the esthetics of a lower fixed partial denture if the goals of esthetics and naturalness are to be met.
RESEARCH METHODOLOGY One hundred ten sets of diagnostic casts were selected from a pool of dental casts. The patients were from a military population with a high percentage of retired personnel. The sample was made up mainly of persons 35 to 70 years of age. Selection criteria were that the casts could be well articulated, that no more than one posterior tooth in any quadrant be missing and unreplaced, and that no anterior teeth be missing.
The opinions expressed herein are those of the authors and are not to be construed as those of the U.S. Army Medical Department. *Lieutenant CSolonel, US. Army Institute of Dental Research. **Colonel, U.S. Army Regional Dental Activity.
These criteria were based on the desire to survey a selection of dentitions which exhibited good dental health and would express a normal range of age- and health-induced changes.
EVALUATION TECHNIQUE
PARAMETERS
AND
A questionnaire consisting of 37 questions was designed to record the arrangement of mandibular anterior teeth as viewed anteriorly, the curve of the incisal edge, the condition and contour of the incisal edges in various teeth, the relative height and placement of contact areas, diastemas, and/or the overlap of anterior teeth and rotation of canines. Both authors evaluated all sets of casts and consensus decisions were made about each question. Results were coded, and suitable cross-tabulations performed. RESULTS Maxillomandibular relationships were classified at the molar and incisor areas. Table I indicates the relative percentage of occurrence of each category. Table II indicates the cross-tabulations comparing molar to incisor positions. The tables confirm that, in general, the molar relationship is repeated at the anterior teeth in Class III molar relationships where Class I incisor relationships may be seen frequently. When viewed from the occlusal, the arrangement of the mandibular six anterior teeth was curved, 69.5%; straight, 17.5%; and irregular, 13.6%. The contour of the mandibular anterior teeth was generally unrelated to the shape of the maxillary arch (Table III). The square maxillary arch showed a distribution that was significantly different from the others. A straight line arrangement of lower anterior teeth viewed occlusally is not a common occurrence (17.3%) except when the maxillary arch is square (40%). Occlusal contact of most or all mandibular anteri-
SEPTEMBER
1981
VOLUME
46
NUMBER
3
ESTHETIC
PARAMETERS
Table III. Contour as viewed occlusally
Table I. Class of jaw relation Class
Molar area m
Incisor area (W
56.4 12.7 12.7 18.2
77.3 17.3 5.5
I
II III Not classified due to tooth malposition
Total % Arch form Square OVaI Tapering Tapering oval
Curved 40 72.7 64.3 76.7
Straight 40 12.1 21.4 13.3
69.5
17.5
Total % of incidence
Table II. Cross-tabulation and molar relationships
Table IV. Horizontal
between incisor
mm Incisor relationship (Angle’s classification)
Molar relationship Angle’s Class I
Class II
Class III
Unclassified
60 96.8% 70.6 54.5 2 14.3 2.4 1.5 5 57.1 9.4 7.3 15 75 17.6 13.6
2 3.2% 10.5 1.8 12 85.7 63.2 10.9 0 0 0 0 5 25 26.3 4.5
Row total 0 0 0 0 0 0 0 0 6 42.9 100 5.5 0 0 0 0
from
62 56.4%
14 12.7%
14 12.7%
85 77.3%
19 17.3%
6 5.5%
20 18.2%
DENTISTRY
and vertical overlap
Horizontal overlap m
Vertical overlap (3
7.3 1.8
12.7 0.9
13.6
15.5
29.1
24.5
25.4
20.9
9.1
13.7
5.4
5.5
0.9
3.6
4.5
1.5
1.5 0.9
0.9 0.9
Zorn/’
to
9
110 100%
or teeth with maxillary anterior teeth occurred 84.5% of the time. Contact of the incisors only occurred 2.7% of the time; there was no contact 12.7% of the time. The frequency of contact was not found to be related to the shape of the arch. Seventy-five percent or more of the facial surface of the mandibular canines was visible in 78% of all casts from a point on the level of the occlusal plane and directly anterior to the midpoint of the lower cast when viewed at a standard distance. Horizontal and vertical overlap was measured in millimeters (Table IV). The mean horizontal overlap was 3.507 mm, and mean vertical overlap was 3.5 mm. The distribution is leptokurtic, which indicates
OF PROSTHETIC
13.6
FornA6
In each category the top figure is the count. The second number is the percentage of that row. The third number is the percentage of the column (vertical). The fourth number is the percentage of the entire sample.
THE IOURNAL
of incidence 4.5% 30% 38.2% 27.3%
ZomA5
More than Column total
0
Irregular 20 15.2 14.2 10
that the distribution was clustered more tightly around the mean than normally occurs in a distribdtion curve. Correlation coefficients were calculated for the sample overall and for only those sets of casts with Class I molar relationships. There was no significant correlation between vertical and horizontal overlap. (r’ all classes = 0.0 1; f’ Class I = 0.10) The average thickness of the incisal edges of the mandibular anterior incisors was measured in millimeters (Table V). The average thickness was 1.8 mm; the distribution was also leptokurtic. 4s viewed anteriorly, the incisal edges of the mandibular anterior teeth formed a convex curve 23% of the time. They were straight 56% and concave 21% of the time. The tip of the canine was higher than the adjoining tooth 25..5%, lower 41.8%, and the same height 32.7% of the time. The canine
281
LORTON
Table V. Thickness
of incisal
%
Including-e More than/
Including-More than
> 0.85 1.2
0.9
1.5
33.1
1.8
21.1
2.1
13.8
2.4 -2.4
17.4 8.3
exhibited wear of the incisal edge 67.3% and the incisors 74.5% of the time. Both canines and incisors appeared worn 64% of the time (xif, = 50.63, p = .O). The canine-lateral incisor contact areas were in the incisal third 27.6%, in middle third 53.3%, and gingival third 19% of the time. The lateral incisor to central incisor contact areas were 88.6% incisal and 11.4% middle. The central incisor to central incisor contact was !30.5% incisal and 9.5% middle third. The contact area between canine and lateral incisor was at the same height as the lateral incisorcentral incisor contact area 29.5% of the time. It was lower 70.5% of the time. Tooth overlap occurred between lateral and central incisors in 35% of the casts, and between lateral incisors and canines in 11%. Diastemas occurred in 10%. When the canine did not show signs of incisal wear, the canine-lateral incisor contact was at the same height as the lateral incisor-central incisor contact only 8.8% of the time. The remainder of the time, the canine-lateral incisor contact was lower. When the canine was worn incisally, the contacts were at the same height 39.4% of the time (x&, = 10.35474, p = .0013). When the incisors showed no occlusal wear, only 12% of the lateral incisor-canine contacts were at the same height as the lateral incisor-central incisor contacts. The remainder were lower. When the incisors were worn, 34% of the contacts were at the same height. When the canines were worn, more canine-lateral incisor contacts appeared as the incisal third (36%) than when the canines were not worn (8.8%) (xi,:! = 16.15173,~ = .0003).
282
WHITBECK
DISCUSSION
edge (in
millimeters)
More than.
AND
Determining the proper and/or desired esthetic display for a mandibular anterior fixed prosthesis is not an intuitive skill. The training in esthetic parameters has been, for the most part, confined to the upper arch. Yet, previously cited studies show that as age increases, more of the mandibular anterior teeth is observed.‘, ’ In making decisions about the various parameters which control esthetics, some of the previously mentioned results should be considered by both dentist and dental laboratory technician. Placement of the mandibular anterior teeth can generally be made in accordance with the jaw relationship class as determined in the molar area except in Class III molar relationships where a Class I incisor relationship can be used. All lower anterior teeth are generally in contact. Thus the contour of the incisors usually conforms to the curve of the maxillary anterior teeth. The vertical position or height of the incisal edge of the mandibular anterior teeth can usually be determined by phonetic means. When viewed anteriorly, the incisal edges formed a straight line from canine to canine in 56% of the casts. The remainder formed a convex (23%) or concave (21%) curve. Although the average vertical and horizontal overlap was not statistically different, there was no correlation between the amount of vertical and horizontal overlap in any single occlusion. The incisal edge in mature individuals was rounded or unworn in only 25% of the casts. Thus, the incisal edge of the artifical tooth should have some wear facet or bevel. The average thickness was 1.8 mm, and distribution clustered around this point. In ceramometal restorations, this bevel provides an ideal opportunity for creative staining. Although only 13.6% of the occlusions were classified as irregular in the arrangement of the lower anterior teeth, some degree of overlap occurred between the central and lateral incisors 35% of the time and between lateral incisors and canines 11% of the time. Diastemas occurred 10% of the time. Thus, it is clear that straight and even lower anterior teeth, with unworn incisal edges, are the distinct exception. It is also of interest that the facial surface of lower canines is slightly visible anteriorly. Location of the contact areas is extremely critical to good esthetics. The contact areas of teeth seem to shift as wear occurs. When the canine did not show wear, its contact with the lateral incisor was at the same level as the lateral incisor-central incisor con-
SEPTEMBER
1981
VOLUME
46
NUMBER
3
ESTHETIC
PARAMETERS
tact only 8.8% of the time. When the canine was worn, the contacts were at the same level 34.4% of the time. This same phenomenon occurred with the amount of incisor wear. The canine-lateral incisor contact area is one of the keys to proper esthetics in mandibular fixed prostheses. Proper placement of this contact allows for shaping and definition of the mesioincisal angle of the lower canine and allows this tooth to be visually distinguished from the rest of the lower anterior teeth.
placement of the incisal edge, and incisal contacts. Design factors which must be appreciated and manipulated by the dentist in his prescription and in the fabrication techniques are overlap, incisal wear and facets, and height and variety of contact area. It is these design factors which are crucial to the esthetic success of a mandibular anterior fixed partial denture. Thanks for technical and administrative support to Ms. Pat Scully of U.S. Army Regional Dental Activity, and Ms. Ailene Otterstedt of U.S. Army Institute of De.ltal Research, Walter Reed Army Medical Center.
SUMMARY Designing mandibular anterior fixed prostheses for good esthetics involves many factors. Factors which are, at least in part, functionally or phonetically determined are degree of vertical and horizontal overlap, curve and height of the teeth, anterior
-IHE JOURNAL
OF PROSTHETIC
DENTISTRY
Reprini requestsb: DR. LEWIS Lowolu DIVISION OF CLINICAL OPERATIONS US ARMY INSTITUTE OF DENTAL RESEARCH WALTER REED ARMY MEDICAL CENTER WASHINGTON, DC 20012
283
and Peter Whitbeck,
anterior teeth
D.D.S.*
Walter Reed Army Medical Center, Washington, D.C.
R
eplacement of lost mandibular anterior teeth with a fixed partial denture is one of the most demanding tasks in prosthodontics. Aside from the obvious difficulties with any fixed prosthetic procedure, there is the additional problem of esthetics. Since lower anterior fixed prostheses are a relatively uncommon restoration, the esthetic factors, which are important and should be controlled, are not well understood. A recent sl:udy by Cade’ indicated that as the age of the patient increased, the mandibular teeth were displayed more and more during speaking. The mandibular anterior teeth were displayed at least as much as the maxillary teeth when the patient was speaking or resting. Vig and Brundo’ considered the degree of visibility of the mandibular central incisor versus the maxillary central incisor and found that the mandibular incisor became more visible than the maxillary central in patients 40 to 49 years of age. The inference that may be drawn from these studies is that the dentist should know the determining factors of the esthetics of a lower fixed partial denture if the goals of esthetics and naturalness are to be met.
RESEARCH METHODOLOGY One hundred ten sets of diagnostic casts were selected from a pool of dental casts. The patients were from a military population with a high percentage of retired personnel. The sample was made up mainly of persons 35 to 70 years of age. Selection criteria were that the casts could be well articulated, that no more than one posterior tooth in any quadrant be missing and unreplaced, and that no anterior teeth be missing.
The opinions expressed herein are those of the authors and are not to be construed as those of the U.S. Army Medical Department. *Lieutenant CSolonel, US. Army Institute of Dental Research. **Colonel, U.S. Army Regional Dental Activity.
These criteria were based on the desire to survey a selection of dentitions which exhibited good dental health and would express a normal range of age- and health-induced changes.
EVALUATION TECHNIQUE
PARAMETERS
AND
A questionnaire consisting of 37 questions was designed to record the arrangement of mandibular anterior teeth as viewed anteriorly, the curve of the incisal edge, the condition and contour of the incisal edges in various teeth, the relative height and placement of contact areas, diastemas, and/or the overlap of anterior teeth and rotation of canines. Both authors evaluated all sets of casts and consensus decisions were made about each question. Results were coded, and suitable cross-tabulations performed. RESULTS Maxillomandibular relationships were classified at the molar and incisor areas. Table I indicates the relative percentage of occurrence of each category. Table II indicates the cross-tabulations comparing molar to incisor positions. The tables confirm that, in general, the molar relationship is repeated at the anterior teeth in Class III molar relationships where Class I incisor relationships may be seen frequently. When viewed from the occlusal, the arrangement of the mandibular six anterior teeth was curved, 69.5%; straight, 17.5%; and irregular, 13.6%. The contour of the mandibular anterior teeth was generally unrelated to the shape of the maxillary arch (Table III). The square maxillary arch showed a distribution that was significantly different from the others. A straight line arrangement of lower anterior teeth viewed occlusally is not a common occurrence (17.3%) except when the maxillary arch is square (40%). Occlusal contact of most or all mandibular anteri-
SEPTEMBER
1981
VOLUME
46
NUMBER
3
ESTHETIC
PARAMETERS
Table III. Contour as viewed occlusally
Table I. Class of jaw relation Class
Molar area m
Incisor area (W
56.4 12.7 12.7 18.2
77.3 17.3 5.5
I
II III Not classified due to tooth malposition
Total % Arch form Square OVaI Tapering Tapering oval
Curved 40 72.7 64.3 76.7
Straight 40 12.1 21.4 13.3
69.5
17.5
Total % of incidence
Table II. Cross-tabulation and molar relationships
Table IV. Horizontal
between incisor
mm Incisor relationship (Angle’s classification)
Molar relationship Angle’s Class I
Class II
Class III
Unclassified
60 96.8% 70.6 54.5 2 14.3 2.4 1.5 5 57.1 9.4 7.3 15 75 17.6 13.6
2 3.2% 10.5 1.8 12 85.7 63.2 10.9 0 0 0 0 5 25 26.3 4.5
Row total 0 0 0 0 0 0 0 0 6 42.9 100 5.5 0 0 0 0
from
62 56.4%
14 12.7%
14 12.7%
85 77.3%
19 17.3%
6 5.5%
20 18.2%
DENTISTRY
and vertical overlap
Horizontal overlap m
Vertical overlap (3
7.3 1.8
12.7 0.9
13.6
15.5
29.1
24.5
25.4
20.9
9.1
13.7
5.4
5.5
0.9
3.6
4.5
1.5
1.5 0.9
0.9 0.9
Zorn/’
to
9
110 100%
or teeth with maxillary anterior teeth occurred 84.5% of the time. Contact of the incisors only occurred 2.7% of the time; there was no contact 12.7% of the time. The frequency of contact was not found to be related to the shape of the arch. Seventy-five percent or more of the facial surface of the mandibular canines was visible in 78% of all casts from a point on the level of the occlusal plane and directly anterior to the midpoint of the lower cast when viewed at a standard distance. Horizontal and vertical overlap was measured in millimeters (Table IV). The mean horizontal overlap was 3.507 mm, and mean vertical overlap was 3.5 mm. The distribution is leptokurtic, which indicates
OF PROSTHETIC
13.6
FornA6
In each category the top figure is the count. The second number is the percentage of that row. The third number is the percentage of the column (vertical). The fourth number is the percentage of the entire sample.
THE IOURNAL
of incidence 4.5% 30% 38.2% 27.3%
ZomA5
More than Column total
0
Irregular 20 15.2 14.2 10
that the distribution was clustered more tightly around the mean than normally occurs in a distribdtion curve. Correlation coefficients were calculated for the sample overall and for only those sets of casts with Class I molar relationships. There was no significant correlation between vertical and horizontal overlap. (r’ all classes = 0.0 1; f’ Class I = 0.10) The average thickness of the incisal edges of the mandibular anterior incisors was measured in millimeters (Table V). The average thickness was 1.8 mm; the distribution was also leptokurtic. 4s viewed anteriorly, the incisal edges of the mandibular anterior teeth formed a convex curve 23% of the time. They were straight 56% and concave 21% of the time. The tip of the canine was higher than the adjoining tooth 25..5%, lower 41.8%, and the same height 32.7% of the time. The canine
281
LORTON
Table V. Thickness
of incisal
%
Including-e More than/
Including-More than
> 0.85 1.2
0.9
1.5
33.1
1.8
21.1
2.1
13.8
2.4 -2.4
17.4 8.3
exhibited wear of the incisal edge 67.3% and the incisors 74.5% of the time. Both canines and incisors appeared worn 64% of the time (xif, = 50.63, p = .O). The canine-lateral incisor contact areas were in the incisal third 27.6%, in middle third 53.3%, and gingival third 19% of the time. The lateral incisor to central incisor contact areas were 88.6% incisal and 11.4% middle. The central incisor to central incisor contact was !30.5% incisal and 9.5% middle third. The contact area between canine and lateral incisor was at the same height as the lateral incisorcentral incisor contact area 29.5% of the time. It was lower 70.5% of the time. Tooth overlap occurred between lateral and central incisors in 35% of the casts, and between lateral incisors and canines in 11%. Diastemas occurred in 10%. When the canine did not show signs of incisal wear, the canine-lateral incisor contact was at the same height as the lateral incisor-central incisor contact only 8.8% of the time. The remainder of the time, the canine-lateral incisor contact was lower. When the canine was worn incisally, the contacts were at the same height 39.4% of the time (x&, = 10.35474, p = .0013). When the incisors showed no occlusal wear, only 12% of the lateral incisor-canine contacts were at the same height as the lateral incisor-central incisor contacts. The remainder were lower. When the incisors were worn, 34% of the contacts were at the same height. When the canines were worn, more canine-lateral incisor contacts appeared as the incisal third (36%) than when the canines were not worn (8.8%) (xi,:! = 16.15173,~ = .0003).
282
WHITBECK
DISCUSSION
edge (in
millimeters)
More than.
AND
Determining the proper and/or desired esthetic display for a mandibular anterior fixed prosthesis is not an intuitive skill. The training in esthetic parameters has been, for the most part, confined to the upper arch. Yet, previously cited studies show that as age increases, more of the mandibular anterior teeth is observed.‘, ’ In making decisions about the various parameters which control esthetics, some of the previously mentioned results should be considered by both dentist and dental laboratory technician. Placement of the mandibular anterior teeth can generally be made in accordance with the jaw relationship class as determined in the molar area except in Class III molar relationships where a Class I incisor relationship can be used. All lower anterior teeth are generally in contact. Thus the contour of the incisors usually conforms to the curve of the maxillary anterior teeth. The vertical position or height of the incisal edge of the mandibular anterior teeth can usually be determined by phonetic means. When viewed anteriorly, the incisal edges formed a straight line from canine to canine in 56% of the casts. The remainder formed a convex (23%) or concave (21%) curve. Although the average vertical and horizontal overlap was not statistically different, there was no correlation between the amount of vertical and horizontal overlap in any single occlusion. The incisal edge in mature individuals was rounded or unworn in only 25% of the casts. Thus, the incisal edge of the artifical tooth should have some wear facet or bevel. The average thickness was 1.8 mm, and distribution clustered around this point. In ceramometal restorations, this bevel provides an ideal opportunity for creative staining. Although only 13.6% of the occlusions were classified as irregular in the arrangement of the lower anterior teeth, some degree of overlap occurred between the central and lateral incisors 35% of the time and between lateral incisors and canines 11% of the time. Diastemas occurred 10% of the time. Thus, it is clear that straight and even lower anterior teeth, with unworn incisal edges, are the distinct exception. It is also of interest that the facial surface of lower canines is slightly visible anteriorly. Location of the contact areas is extremely critical to good esthetics. The contact areas of teeth seem to shift as wear occurs. When the canine did not show wear, its contact with the lateral incisor was at the same level as the lateral incisor-central incisor con-
SEPTEMBER
1981
VOLUME
46
NUMBER
3
ESTHETIC
PARAMETERS
tact only 8.8% of the time. When the canine was worn, the contacts were at the same level 34.4% of the time. This same phenomenon occurred with the amount of incisor wear. The canine-lateral incisor contact area is one of the keys to proper esthetics in mandibular fixed prostheses. Proper placement of this contact allows for shaping and definition of the mesioincisal angle of the lower canine and allows this tooth to be visually distinguished from the rest of the lower anterior teeth.
placement of the incisal edge, and incisal contacts. Design factors which must be appreciated and manipulated by the dentist in his prescription and in the fabrication techniques are overlap, incisal wear and facets, and height and variety of contact area. It is these design factors which are crucial to the esthetic success of a mandibular anterior fixed partial denture. Thanks for technical and administrative support to Ms. Pat Scully of U.S. Army Regional Dental Activity, and Ms. Ailene Otterstedt of U.S. Army Institute of De.ltal Research, Walter Reed Army Medical Center.
SUMMARY Designing mandibular anterior fixed prostheses for good esthetics involves many factors. Factors which are, at least in part, functionally or phonetically determined are degree of vertical and horizontal overlap, curve and height of the teeth, anterior
-IHE JOURNAL
OF PROSTHETIC
DENTISTRY
Reprini requestsb: DR. LEWIS Lowolu DIVISION OF CLINICAL OPERATIONS US ARMY INSTITUTE OF DENTAL RESEARCH WALTER REED ARMY MEDICAL CENTER WASHINGTON, DC 20012
283