Comparative Study of Tooth Size and Arch Dimensions in Class I Crowded, Proclined Malocclusion and Class I Normal Occlusion.

AIM: The objectives are to compare the extent and to find whether it is arch dimension or tooth size that contributes to a greater extent to malocclusions such as dental crowding and proclination.
MATERIALS AND METHODS: A total of 90 pretreatment models were selected and divided into three groups, namely uncrowded (Group-A), crowded (Group B), and proclination (Group-C). Measurements obtained were: (1) The largest mesiodistal width of each tooth on each arch (except the second and third molars), (2) Buccal inter-canine and inter-molar widths, (3) Lingual inter-canine and inter-molar widths, (4) Arch perimeters, and (5) Arch length.
RESULTS: The mesiodistal teeth dimensions were higher in crowded and proclination group. Both inter canine width and inter molar width of maxilla were reduced in crowded group. Maxillary and mandibular arch perimeter and arch lengths were higher proclination group. Copyright:

INTRODUCTION

The prevalence of dental crowding has shown a steady rise in the modern population. An effective treatment mode to eliminate malocclusion involves clear understanding of its etiology. Etiology of malocclusion is multifactorial. It is evident from two large scale epidemiological studies conducted by the United States public health services that class I malocclusion with crowding or proclination form the single large group of malocclusions. There is complex interrelationship between mesiodistal crown widths, various arch dimensions, and primary dental crowding as reported in previous studies. Among various studies reported so far correlating malocclusion with tooth size-arch dimension discrepancy, studies exploring level of contribution of each of factors such as arch length, arch width, and teeth dimensions in causing malocclusion are incongruous, not throwing adequate light to unravel the query. The purpose of this study therefore, was to locate which of the following factors, namely, arch dimension such as inter canine alveolar widths (buccal and lingual), intermolar alveolar widths (buccal and lingual), arch perimeter, arch length, and mesiodistal tooth dimensions contribute maximum to malocclusions such as crowding and proclination. This study compares the extent and to find whether it is arch dimension or tooth size that contributes to a greater extent to malocclusions such as dental crowding and proclination. This study compares the mesiodistal tooth dimensions and arch dimensions such as arch widths in canine and molar region, arch perimeter, arch length between crowded, proclined and uncrowded dentition.

MATERIALS AND METHODS

Samples were obtained from the records available in the Department of orthodontics, Tamil Nadu Government dental college and hospital, Chennai. A total of 90 pretreatment models were selected from records of 90 patients. The samples were divided into three groups, namely: Group A, Group B, and Group C. Each group consisted of 30 models. The age group of samples was between 18 and 24 years. Patient pretreatment records were checked for following inclusion criteria and patient models were selected. The models should have permanent dentition with normal size, shape and form of the teeth with bilateral Angle's Class I molar relationship. The models should not have any anterior or posterior open bite. The models should not have anterior or posterior crossbite. Models with missing teeth, supernumerary teeth and proximal restorations on the teeth were excluded from the study. Grouping was done in following order, Grouping: Group A)– Uncrowded group, (30 samples): Well aligned maxillary and mandibular arches. If spacing or crowding were present, they were <2 mm. Normal overjet and overbite relationship. Group B-Crowded group (30 samples): Crowding of 5 mm or more in both upper and lower arches. Group C-Proclination group (30 samples): Proclined upper and lower dental arches with acceptable alignment of teeth.

Digital Vernier caliper (Aerospace, china) [Figure 1] to measure the mesiodistal width of tooth , buccal intercanine width, lingual intercanine width, buccal intermolar alveolar width and lingual intermolar alveolar width. The caliper was calibrated to 0.1 mm for measurements. Scanner (Hp G2410 Scanjet flatbed scanner) to scan the models. The following measurements were obtained: (1) The largest mesiodistal width of each tooth on each arch (except the second and third molars), (2) Buccal inter-canine and inter-molar widths, (3) Lingual inter-canine and inter-molar widths, (4) Arch perimeters, (5) Arch length. For measuring buccal intercanine and intermolar width mesiodistal center points at the cervical margins on buccal side of canines and first molars on either side were marked. A point was marked 5 mm apical to the above-mentioned point. Using digital caliper, the buccal inter-canine and inter-molar arch widths[12] [Figure 2] were measured as the distance between the two apical points on buccal side of both canine and molar regions of the right and left sides, respectively. Lingual inter-canine and inter-molar widths' were measured as the distance between midpoints on the lingual cervical region of canines and molars on either side, respectively, using digital caliper. Arch perimeters: An arch perimeter is a line drawn from the distal surface of the first permanent molar around the arch over the contact points and incisal edges in a smooth curve to the distal surface of the first permanent molars on the opposite side. To draw the curve, dental casts with contact point markings were scanned by Hp G2410 Scanjet flatbed scanner and arch perimeters were measured using Auto-CAD software (Autodesk Inc., san Rafael, CA, USA) [Figure 3] from scanned copies of dental casts. (5) Arch length: A line touching distal surfaces of first molars on either side was drawn. The perpendicular distance between this line and midpoint between incisal edges of central incisors was measured as the arch length.

Figure 1

Digital vernier calliper

Figure 2

Buccal inter canine width

Figure 3

Arch length measurement

Data analysis

All the data obtained were analyzed using SPSS® software (SPSS Inc., Chicago, IL, USA), and the one-way ANOVA test was used to compare the groups and Tukey HSD post hoc Tests for multiple pair-wise comparisons between each group was done.

RESULTS

On comparison of collective mesiodistal teeth width of total 12 teeth in maxillary and mandibular arches between Group A, B, and C, which revealed that the mesiodistal tooth dimensions were significantly higher in crowded (Group B) and proclination group (Group C) [Table 1]. Study revealed that inter canine width and inter molar width of maxilla were significantly reduced in crowded (Group B) than uncrowded (Group A) and proclination group (Group C) Tables 2 and 3. Maxillary and mandibular arch perimeter significantly increased in proclination (Group C) group than crowded (Group B) and uncrowded (Group A) group. Maxillary and mandibular arch length also significantly increased in proclination (Group C) group than crowded (Group B) and uncrowded group (Group A) [Table 4].

Table 1

One-way ANOVA test for comparison of mean values of maxillary and mandibular total 12 teeth between groups

Group	Maxillary 12 teeth			Mandibular 12 teeth
	A	B	C	A	B	C
Mean	91.97	98.38	99.19	84.29	90.38	90.53
SD	1.690	1.788	1.788	2.419	2.550	2.681
P	<0.001			<0.001

SD: Standard deviation

Table 2

One-way ANOVA test for comparison of the mean values of buccal and lingual inter canine widths of maxillary and mandibular arches between groups

Group	Maxillary buccal intercanine width			Mandibular buccal intercanine width			Maxillary lingual intercanine width			Mandibular lingual intercanine width
	A	B	C	A	B	C	A	B	C	A	B	C
Mean	38.11	34.82	37.81	31.87	29.55	31,59	26.20	23.74	25.93	19.81	19.58	19.61
SD	1.330	0.967	1.254	1.527	1.293	1.406	0.725	1.031	0.793	0.792	0.933	0.820
P	<0.001			<0.001			<0.001			0.538

SD: Standard deviation

Table 3

The comparison of buccal and lingual inter molar widths of maxillary and mandibular arches between groups

Group	Maxillary buccal intermolar width			Mandibular buccal intermolar width			Maxillary lingual intermolar width			Mandibular lingual intermolar width
	A	B	C	A	B	C	A	B	C	A	B	C
Mean	60.59	57.22	60.05	57.34	57.00	57.00	35.75	33.40	35.64	33.16	32.64	32.95
SD	2.240	1.057	2.152	1.694	1.873	1.661	1.347	1.210	1.351	1.158	1.483	1.222
P	<0.001			0.678			<0.001			0.235

SD: Standard deviation

Table 4

The comparison of arch perimeter and arch length of both maxillary and mandibular arches between groups

Group	Maxillary arch perimeter			Mandibular arch perimeter			Maxillary arch length			Mandibular arh length
	A	B	C	A	B	C	A	B	C	A	B	C
Mean	99.30	98.53	104.2	90.23	89.53	93.52	36.42	37.13	42.27	32.49	31.76	36.08
SD	2.499	2.281	1.590	2.114	2.072	1.102	1.388	1.082	1.339	0.813	1.275	1.254
P	<0.001			<0.001			<0.001			<0.001

SD: Standard deviation

DISCUSSION

A meticulous treatment planning is the key stone for successful orthodontic treatment results. Since tooth size–arch dimension discrepancy is the most common etiology of dentoalveolar malocclusion, an understanding of the same is essential while planning treatment. Moorrees and reed[3] pointed out that a harmonious relationship between mesiodistal tooth dimension and arch length results in satisfactory alignment and optimum occlusion of teeth. Disproportion between these elements results in crowding or spacing in the dental arch. Purpose of this study was to determine whether it is the mesiodistal teeth dimensions or the arch dimension such as inter canine alveolar widths (buccal and lingual), intermolar alveolar widths (buccal and lingual), arch perimeter and arch length contribute maximum to malocclusions such as crowding and proclinations. In this study, it was found that the combined mesiodistal teeth width of total (first molar to first molar) teeth in the maxillary and mandibular dental arches were significantly greater in crowded group when compared with normal group. These findings correlate with study results of Fastlicht,[4] Lundstrom,[5] Doris et al.,[6] and Lombardi[7] who found that the group with crowded arches consistently had teeth with larger mesio-distal dimension than in those with less or no crowding. Some researchers including Norderval et al.,[8] Peck and Peck[9] found the same correlation with crown dimension and crowding, but others Mills,[10] Howe et al.,[1] Radnzic[11] found no correlation with findings of Lundstrom. Results of Doris et al.[6] study on tooth size comparison on crowded and noncrowded dental arches revealed a significant relationship between tooth size and arch alignment. They stated that, in maxillary arch, lateral incisors and second premolars showed significant difference between crowded and noncrowded groups. In the mandibular arch, canines, first and second premolars showed significant differences in mesiodistal tooth size between crowded and noncrowded groups. Therefore, one can use measurement of tooth mass as another aid in diagnosing border line case. Howe et al.,[1] Randzic,[11] Forsberg,[12] and Gilmore and Little[13] did not find any significant correlation between mesio distal tooth size and crowding. They stated that crowding was related to dental arch dimension such as arch width, arch perimeter rather than mesio distal tooth dimension. Howe et al.[1] examined the extent to which tooth size and jaw size contributed to dental crowding. Based on the study, Howe et al. did not find any significant difference in mesiodistal crown dimension in crowded and noncrowded groups. Instead they found that, dental arch dimension of two groups significantly differ. Buccal and lingual arch widths were significantly higher in noncrowded group. Based on their study, Howe suggested that subjects with crowding were more likely to have smaller dental arches than subjects with little or no crowding. Findings of the present study also contradict those of Shah et al.[14] Their study examined orthodontically untreated subjects with varying degrees of crowding and found no difference in “crown shape” (defined as the MD/BL Ratio) Radnzic[11] carried out a study on primary dental crowding and found significant correlation between arch length and arch perimeter and to a lesser extent arch width to primary dental crowding or spacing which supports the findings of Mills,[10] Mckeown[15] and Howe et al.[1] Mills[10] did a study to determine if well-aligned dental arches in young adult males differ from crowded dental arches in width, length, or tooth size. He stated that, mean arch width in the second premolar region would make a good index of group scores for tooth crowding. His findings did tend to support the suggestion of Howe et al. that, lack of arch width in the premolar area may be an important factor in malalignment. His findings did not show a relation of tooth size or arch length, mesial to second molar, to alignment. Looking at the problem of dental crowding in a different way, McCann and Burden[16] investigated the role of tooth size in the etiology of bimaxillary dental protrusion. They found that individuals exhibiting bimaxillary protrusion had 5.7% larger teeth than those without protrusion. In the present study tooth dimensions, as well as arch dimensions were analyzed and the results of the study corroborate with their findings. While evaluating width of the maxillary alveolar arch in canine and molar region, it was significantly reduced in crowded group than uncrowded and proclined group. In mandibular arch, mandibular buccal intercanine width was significantly reduced in crowded group in comparison with other two groups. In this study, no significant difference was found in both maxillary and mandibular arch width between the proclination and uncrowded group. Maxillary and mandibular arch perimeters and arch length were not significantly different between crowded and uncrowded group. The proclination group had significantly higher arch perimeter and arch length than crowded and normal group. This may be due to greater mesio-distal dimensions of teeth which occupy a greater circumference of arch than a normal occlusion. The present study suggests that tooth size to a greater extent and maxillary arch dimensions to a lesser extent in crowded group contribute to crowding of dental arches. The greater tooth size and larger arch length contribute to proclination of dental arches in the proclination group. This shows that mesio distal tooth size mainly contribute to malocclusion such as crowding and proclination of dental arches.

CONCLUSION

The mesiodistal teeth dimensions were significantly higher in crowded and proclination group. Both inter canine width and inter molar width of maxilla were significantly reduced in crowded group than uncrowded and proclination groups. Maxillary and mandibular arch perimeter and arch lengths were significantly increased in proclination group than crowded and uncrowded group.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.