Crown Height and its Relation to Arch Width, Arch Length and Arch Perimeter in Ideal Occlusion

Introduction: To investigate crown height for sexual dimorphism and its relation to arch length, arch perimeter and arch width (Inter canine, Inter premolar, Intermolar) groups of maxilla and mandible. Material and Methods: Cross sectional study was done the data were collected from 128 subjects (64 males and 64 females with mean age 19.4 ± 1.9 SD). Arch perimeter, arch length, crown height, and width of arch of both maxilla and mandible were acquired by digital calliper (Mitutoyo, Japan). Total variables measured were 4,855. Sex differences in the crown height were explored. Analysis of variance (ANOVA) was applied for evaluating the differences if any between arch perimeter, arch length, and arch width groups. Results: Noteworthy larger mean values in males than females for crown height (p ≤ 0.05) for maxillary as well mandibular arches. No substantial differences were observed in average vs. large, average vs. small, large vs. small groups of arch length, arch perimeter and arch width (Inter canine, Inter premolar, Intermolar) groups (p ≤ 0.05) for both maxillary and mandibular arches. Conclusions: Our results specified sexual disparities in the height of crown. Crown height has no substantial relation to different arch perimeter, arch length, and arch width groups of both maxilla and mandible. Hence it might be useful for orthodontic case investigation and treatment of various malocclusion groups.


Introduction
Variations in tooth size and tooth size ratio have been connected with diverse ethnic foundations and occlusion status [1]. Sexual dimorphism in crown dimension has a relation and is influenced by humanoid sex genes and hormones [2]. Hereditary and ecological factors have strong effects on the human teeth [3]. In orthodontic diagnosis and treatment planning, great importance has been attached to evaluating the tooth size and its discrepancies on the global population [4]. For the achievement of pleasant smile and proper interdigitation, the preadjusted fixed orthodontic brackets should be ideally positioned. Thus, the crown height is of extreme value in orthodontic bonding. The teeth crown height has significant relation to facial stature, both can be swayed by orthodontic treatment [5] Therefore, during orthodontic planning to design a smile the macro, mini and micro-esthetics should be deliberated afore [6][7][8][9][10]. The crown height of incisors has tremendous effect on the smile of a patient, and leads an imperative part in facial charm [11]. Linear measurements have been incorporated into various dental model analyses to help the clinician for designing the most appropriate treatment plan [12]. Some studies have investigated race and sex differences. Other authors have suggested no significant differences in the tooth size ratio with different malocclusion [13].
However, the crown height was investigated in relation to facial height [14], facial appearances [15] and smile. According to our knowledge till date no one investigated the crown height in relation to the arch length, width, perimeter in normal occlusion. Current study goal was to explore the crown height of both maxilla and mandible, correspondingly to reconnaissance the following objectives for the first time in Pakistani population. a) To evaluate crown height in relation to arch perimeter groups.

Methods
Cross sectional study was done, the dental and oral examinations were carried out by careful selection of subjects from Pakistani population. University Sains Malaysia ethical committee ethical approval, bearing letter # (USM/JEPeM/140376), before commencement of the study participants gave informed consent. The design and conduction of this study was in accordance with STROBE guideline (Strengthening the Reporting of Observational studies in Epidemiology), being applied in current manuscript [16][17][18][19][20].

Sample Size Calculation
Size of the sample was calculated at a power of 80%, using estimated standard deviations 0.60mm [21], biologically significant mean difference 0.3mm, with equal sizes of sample [22]. Size of sample calculated was 64 females and 64 males, total 128 participants with mean age.
The inclusion as well the exclusion criteria:

Inclusion Criteria
a) All patient's origin was Pakistan determined by interviews, having common paternities plus ancestors without multi-ethnic marriages.

Arch Dimensions Measurements
Arch width of maxillary and mandibular variables (Figure 2a) a) Maxillary and mandibular inter canine widths were obtained between tips of cusp. b) Maxillary as well as mandibular interpremolar widths were obtained between cusp tips of first maxillary premolars [26].

c)
Maxillary and mandibular intermolar widths were obtained between the mesiobuccally cusp tips the of first molars of maxillary and mandibular respectively [27].

Arch Length, Arch Perimeter Measurements
Arch Length: Arch length was obtained using triangular shaped lines amongst the mesiobuccally cusp tips of first permanent molars and central point between incisors of each respective arch ( Figure 2b).
Arch Perimeter: Arch perimeter was measured as a segmental sum of linear lines on the left and right side of respective arches (Figure 2c).

Arch Length, Arch Perimeter and Arch Width Grouping:
The participants were additionally grouped accordingly: The numbers of subjects for small, average and large arch length groups in the maxilla and mandible were 46, 44 and 38 respectively. b) Arch perimeter groups (small, average and large).
The number of subjects for small, average, and large arch perimeter groups in the maxilla and mandible were 44, 45 and 39 respectively.

c)
Arch widths group (small, average and large) The number of subjects for small, average, and large arch width groups in the maxilla and mandible were 44, 45 and 39 respectively for (intercanine, interpremolar and intermolar width). These groupings were determined on data values of the Mean ±2 SD, >2 SD and <2 SD grouped in the average, large and small group, correspondingly (Alam et al.).

Error Study
20% of dental casts were randomly selected for interobserver errors. There was 2 weeks' time interval approximately between the first and second readings. The ME (method error) was analyzed by the Dalhberg's formula: ME = (Σ (x1-x2)2/ 2(28)) 1/2. x1 being first and x2 being second measurement and n is the number of repeated measurements [9].

Statistical Analyses
Data verification and analysis was done statistically by use of IBM SPSS (Statistics Version 22.0, Armonk, NY: IBM Corp.) confidence level being set at 5% (P < 0.05) for significance test. Application of independent t tests for comparing mean values amongst males and females crown height in relation to all variables. Evaluation of values difference for arch width, length and perimeter was done with ANOVA (Analysis of variance).

Discussion
Current research investigated the crown height in relation with arch perimeter, length and width groups (intercanine, interpremolar and intermolar) for the first time [12]. investigates only mesiodistal size of tooth and size of tooth ratio in relation to these groups via CBCT acquisitions. In orthodontic diagnosis as well as treatment planning, the evaluation of tooth size and tooth size discrepancy is an indispensable step and this investigation is generally determined by conventional plaster study model analysis [10]. The crown height is of extreme value in the orthodontic bonding, the wrong bracket position can have adverse consequences on the ideal treatment goals. Current study reveals the crown height database which can be used as norms for the placement of preadjusted fixed orthodontic brackets. The responsibility of the orthodontist is to visualize the macro, mini and micro-esthetics to design a pleasant smile. The crown height has great part in facial charm.
The crown height has importance in relation to placement of orthodontic brackets bonding, also has effect on the facial height of the patient. Current study revealed the crown height of male is significantly greater than female (Tables 1-2) which are in accordance with other investigators. Our research investigates the class I ideal occlusion with ideal overjet, overbite and proper interdigitation to arch perimeter, length and width groups (intercanine, interpremolar and intermolar). The research results showed no significant difference to these groups of ideal occlusions ( Tables  3-12). Other study investigated the ideal occlusion in relation to tooth size ratios and found significant difference to these groups [12] but the Crown height has no significant difference to various arch groups. Crown height is a valuable landmark for the orthodontists to manage open or deep bite cases. Thus, the current study provides, the norms, database for the crown height of Pakistani population. Therefore, orthodontics can use crown height as a reference guide for the purpose of orthodontic intrusion and extrusion. For the Pakistani population the tooth was investigated in mesiodistal, buccolingual and diagonal dimension. Crown height of maxilla and mandible revealed for first time sexual disparities in Pakistani population. These norms shall be supportive in orthodontics clinical treatment planning, prosthodontics, periodontology and restorative dentistry. Furthermore, the norms will be of great value in forensic dentistry, and dental anthropology. As the human teeth and arch size have lots of variations in size in relation to culture, race and sex. Therefore, such investigations need to be carried out on other population.