Comparison of measured and predicted mesiodistal tooth-widths of 13-17 year old Kenyans: a descriptive cross-sectional study to develop a new prediction equation for use in the mixed dentition in a Kenyan population

doi:10.21203/rs.3.rs-1660919/v1

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Comparison of measured and predicted mesiodistal tooth-widths of 13-17 year old Kenyans: a descriptive cross-sectional study to develop a new prediction equation for use in the mixed dentition in a Kenyan population

https://doi.org/10.21203/rs.3.rs-1660919/v1

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Background: The Tanaka and Johnson equation is commonly used in mixed dentition analysis. However, the analysis is based on Caucasian population making clinical decisions challenging when used in different ethnic groups. This study developed a prediction equation based on a Kenyan population.

Design: A descriptive cross-sectional study done in 68 13-17 year old Kenyans of African descent in two boarding secondary schools. Alginate impressions were taken, study models obtained, and mesiodistal tooth-widths measured on upper and lower study models from the first molar to the contralateral first molar. Descriptive, paired t-tests and independent t-tests were conducted and Pearson product-moment correlation coefficients calculated (p<0.05).

Results: The mean age was 13.78 years (SD ±0.70), females were 59%. The mesiodistal tooth-widths of the permanent canines and premolars were different between males and females (p˂0.1). The Tanaka and Johnston equation significantly under-estimated the mesiodistal tooth-widths of the permanent canines and premolars (p˂0.05). The addition of lower first permanent molars to the permanent lower incisors provided higher correlation coefficients than the Tanaka Johnston equation.

Conclusions: A new equation that includes the permanent lower incisors and first permanent molars as predictor teeth seems to be more suitable for mixed dentition analysis for this Kenyan population. A larger study is needed to validate these findings.

Mixed-dentition

prediction equation

Tanaka and Johnston

Kenyan population

Mixed dentition analysis is carried out to estimate the mesiodistal tooth-widths of unerupted permanent teeth for the purpose of making orthodontic treatment plans for the growing child (1, 2). The methods used to estimate the space of the unerupted permanent canines and premolars include, among others, radiographic analysis, regression/prediction equations (using dental casts) or a combination of the two methods (3). Although radiographic assessments are among the most accurate methods, such analyses require standardization and specialized equipment, which may not be widely available (4). Prediction equations, mathematical formulae used to estimate the mesiodistal tooth-widths of unerupted canines and premolars, are commonly used because no special equipment is needed and can be easily applied (3). These analyses usually employ erupted lower permanent incisors as the predictor teeth (5), being the Tanaka and Johnston the most frequently utilized (1, 6).

The Tanaka and Johnston analysis is based on Caucasian populations (1, 6–8). In this analysis, the combined mesiodistal tooth-widths of maxillary permanent canines and premolars in one quadrant is calculated by dividing the sum of the lower permanent incisors by two and adding eleven millimeters. In the case of the lower dental arch, the mandibular permanent canines and premolars in one quadrant is calculated by dividing the sum of the lower permanent incisors by two and adding ten and a half millimeters. While it continues to be used worldwide, racial and ethnic differences have shown challenges when the Tanaka and Johnston analysis is applied to other populations besides Caucasians (9, 10).

The aim of this study was to develop an analysis tool that better predicts space for the Kenyan population. We hypothesized that there is a significant difference in the actual and calculated values of the sum of mesiodistal tooth-widths of the permanent canines and premolars using the Tanaka and Johnston equation compared to our analysis. We also hypothesized that the use of the lower permanent first molars in the estimate would give more accurate predicted mesiodistal tooth-widths of the permanent canines and premolars (11). Results from this pilot study will be used in a larger project aimed at validating our proposed space analysis equation to be used by Kenyan oral health providers.

The aim of this study was to develop a new prediction equation to be used in the mixed dentition stage based on a Kenyan population.

This was a descriptive cross-sectional study carried out in sixty-eight (68) 13–17-year-old Kenyans of African descent, attending two boarding secondary schools; Starehe Boys’ Centre and Starehe Girls’ Centre. Accounting for up to 10% of missing data and with a power of 80%, a study population of 68 subjects provided us the ability to detect effect sizes of 0.01 mm. Starehe Boys’ Centre is located about 3 km from Nairobi’s central business district in a low socio-economic status neighborhood. Starehe Girls’ Centre is located about 15 km from Nairobi’s central business district in a peri-urban area. Students from the entire country are enrolled in these two schools. Prior collaboration between the principal investigator (PI) and the school’s leadership facilitated inclusion of these two schools in the pilot study. The age range of 13–17 years was chosen to allow only children in permanent dentition to be included. Initially, the study participants were selected through the school records that were used to identify the age, and thereafter a table of random numbers was then utilized to randomly select the participants to obtain the required sample size. Initial examinations were conducted among 400 boys and 200 girls, as a result of the greater student population in the Starehe Boys’ Centre. Only the study participants who fulfilled the inclusion criteria, which were 1) Kenyans of African descent, 2) fully erupted permanent incisors, canines, premolars and molars teeth without morphological anomalies, 3) free of dental caries, 4) without clinical interproximal restorations, 5) without crown fractures, and 6) otherwise healthy, were included in the study.

Data collection

The PI was calibrated by an experienced orthodontist from the University Of Nairobi School Of Dental Sciences. Calibration was conducted using five pairs of study models of teeth in permanent dentition obtained from the Department of Pediatric Dentistry, University of Nairobi School of Dental Sciences. The data collection instrument, digital vernier caliper (Masel, USA), was first calibrated by the Kenya Bureau of Standards before use in this study. The intra-class coefficient to check for intra-examiner variation was 0.9 and for inter-examiner variation during calibration was 0.9 (Kappa score).

Dental impressions for data collection were completed in the health clinic of the girls’ school under natural light with the study participants seated on a normal chair. Similarly, same procedures were repeated for the boys’ school but on a dental chair in the dental clinic (available at the school premises). Irreversible hydrocolloid (alginate, Blueprint-Dentsply DeTrey GmbH (12), Germany) impressions were obtained for both maxillary and mandibular arches using metallic dentate impression trays. Following the manufacturer’s recommendations, dental impressions made were rinsed under tap water, wrapped with moist gauze, and sealed in a polythene bag until they were poured in the dental laboratory of the School of Dental Sciences, University of Nairobi (12). Transportation of the impressions took approximately one hour, and samples were cast within 15 minutes of being received. This time frame was consistent with the manufacturer’s instructions to pour sealed alginate impressions (12). A trained dental technician cast the impressions using type III dental stone using the recommended powder to water ratio, while vibrating the impression tray to eliminate air bubbles (12). Each participant’s pair of study casts was then given a serial number corresponding to the serial number on the data capture form.

Following guidelines by Ngesa (13), we measured mesiodistal tooth-widths in a Kenyan population, each tooth was measured twice under natural light to the nearest 0.01 mm according to the digital vernier caliper utilized and the average value was then recorded. To minimize fatigue, only 3 pairs of dental casts were measured each hour. The PI conducted all measurements, including measuring twice five randomly selected casts for each gender one week apart to check for intra-examiner variability. Mesiodistal tooth-widths for both maxillary and mandibular arches were measured from the distal contact point of the first permanent molar to the distal contact point of the contralateral first permanent molar. A digital vernier caliper (MASEL, USA) was used to measure the mesiodistal tooth-widths. The beaks of the digital vernier caliper were placed perpendicular to the occlusal plane at the contact points of each tooth as described by Hunter and Priest (14). Each tooth was measured twice to the nearest 0.01 mm and the average measurement was then entered in the data capture form which also contained the age and sex of the participant.

Data analysis

Data capture paper forms were utilized to collect data for each study participant, and then transferred to a Microsoft Excel file. Each study subject received a study ID number. De-identified data was then coded and transferred to Statistical Package for Social Sciences (SPSS) software for analysis. Demographic data was analyzed with descriptive statistics. Paired t-test assessed statistically significant differences between the measured sum of mesiodistal tooth-widths of the permanent canines and premolars with the values expected when using the Tanaka and Johnston equation. Correlation coefficients were calculated to evaluate associations between the lower permanent incisors (predictor teeth) and the combined sum of mesiodistal tooth-widths of the permanent canines and premolars in one quadrant. Correlation coefficients were also calculated for the lower permanent incisors and first mandibular molars (predictor teeth) and the combined sum of mesiodistal tooth-widths of the mandibular permanent canines and premolars for both quadrants as described by Melgaco et al (11). Based on the correlation coefficients obtained, new prediction equations were formulated using the higher correlation coefficients. Higher correlation coefficients above 0.6 demonstrate a better association between the predictor teeth and the teeth whose mesiodistal tooth-widths are being predicted (3). The level of significance was p ≤ 0.05.

The majority of our study population was female (59%) with a mean age of 13.78 years (SD: ± 0.70) and a median age of 14 (IQR: 1) (Table 1). Size of posterior teeth varied by sex with boys having statistically significant larger mandibular and maxillary canines and premolars than girls (p < 0.01). We did not find significant difference for the mandibular incisors (p = 0.27) (Table 2).

Table 1

Demographics of the study population.
Sex	N (%)
Males	28 (41%)
Females	40 (59%)
Age: Mean (SD)	13.78 (± 0.70)
Age: Median (IQR)	14 (1)
^∗ SD: standard deviation, IQR: interquartile

Table 2

Mean mesiodistal tooth-widths in millimeters (mm) by sex of the study population.
Teeth measurements	Females Mean (mm ± SD)	Males Mean (mm ± SD)	p-value
Mandibular canines and premolars	20.90 ± 1.26	21.94 ± 1.63	< 0.01*
Maxillary canines and premolars	21.18 ± 1.16	22.25 ± 1.16	< 0.01*
Mandibular incisors	21.24 ± 1.35	21.66 ± 1.63	0.27
Independent T-test, *p ≤ 0.05

Measurements of our female study maxillary (p < 0.001) and mandibular (p = 0.19) canines and premolars were consistently smaller than values predicted by Tanaka Johnston. Among males, there were statistically significant differences between the measured values of permanent canines and premolars in our study population and those predicted by the Tanaka and Johnston equation mandible and maxilla (p = 0.05; 0.03; respectively) (Table 3).

Table 3

Comparison of measured sum of mesiodistal tooth-widths (in mm) with predicted values
Dental arch and teeth		Actual (measured) ± SD	Tanaka and Johnston ± SD	*p value
Females	Mandibular canines and premolars	20.90 ± 1.26	21.12 ± 0.82	0.19
Females	Maxillary canines and premolars	21.18 ± 1.16	21.62 ± 0.82	0.00
Males	Mandibular canines and premolars	21.94 ± 1.63	21.33 ± 0.68	0.05
	Maxillary canines and premolars	22.25 ± 1.16	21.83 ± 0.68	0.03
Paired T-test, *p ≤ 0.05 is significant, SD; standard deviation

Higher correlation coefficients (r) were obtained when the first permanent mandibular molars were added to the mandibular incisors and used as predictor teeth. The r values for the mandibular arch for females and males were 0.674 (compared to 0.550) and 0.652 (compared to 0.339), respectively. Similarly, the r values of the maxillary arch for females and males were 0.718 (compared to 0.630) and 0.725 (compared to 0.578), respectively (Table 4).

Table 4

Correlation coefficients of different groups of predictor teeth
FEMALES	Predictor teeth	Correlation coefficient (r) values
		Mandibular arch
	Four mandibular incisors	0.550
	Four mandibular incisors and two first mandibular permanent molars	0.674
		Maxillary arch
	Four mandibular incisors	0.630
	Four mandibular incisors and two first mandibular permanent molars	0.718
MALES		Mandibular arch
	Four mandibular incisors	0.339
	Four mandibular incisors and two first mandibular permanent molars	0.652
		Maxillary arch
	Four mandibular incisors	0.578
	Four mandibular incisors and two first mandibular permanent molars	0.725

The aim of this study was to pilot an analysis equation that better predicts dental space among the Kenyan population. Our study hypothesized that there was a difference between actual mesiodistal tooth-widths of the permanent canines and premolars and the values obtained using the Tanaka and Johnston prediction equation, a commonly used orthodontic tool. Our findings showed that the Tanaka and Johnston equation, based on a Caucasian population (8), significantly underestimated the mesiodistal tooth-widths of the permanent canines and premolars for both, male and females African children (1, 2). We also demonstrated that the addition of the measurement of the first permanent mandibular molar provides a more accurate estimation of teeth (2, 11).

The results of our study corroborate prior research on the Tanaka and Johnston equation used in non-Caucasian populations. Overestimation of the mesiodistal tooth-widths of permanent canines and premolars was observed by Alzubir et al. in a Sudanese population as well as by Buwembo et al. among Ugandans (6, 15). In addition, over or underestimated predictions were observed among several Indian studies (7, 9, 10, 16–18) while Bherwani and Fida showed that the Tanaka and Johnston equation was not applicable in a Pakistani population (19). Sherpa et al. demonstrated same findings in a Chinese population (20), and Giri et al. and Gyawali et al. in Nepalese populations (9, 21). Over and underestimated predictions were also identified by Brito et al. in a Brazilian population (22), Mahmoud et al. in a Malay population (23), Asiry et al. in a Saudi population (24), and Bughaighis et al. in a Libyan population (25).

The importance of this study is in developing a space analysis tool specific to this Kenyan population. The developed equation appears to be more accurate than the Tanaka and Johnston equation and is therefore, more useful to clinicians in making decisions during mixed dentition space analysis. Notably, in determining whether to do extraction or non-extraction therapy and when to start early or interceptive orthodontic treatment. In addition, this study provides reference for future studies that will develop prediction equations for the mixed dentition period.

Our project has several limitations. Compared to other similar studies (2, 6, 11, 13, 15, 20, 26) the sample size was low (68 subjects). Further, we concentrated recruitment at only two schools limiting variability in several relevant factors, including but not limited to sociodemographic characteristics. Finally, the alginate impressions were not poured immediately or within 15 minutes and this could have led to dimensional changes on the study models. However, findings from this this pilot study provide relevant preliminary data to be corroborated in a larger study that validates our equation prediction at populational level.

This study demonstrates the discrepancy of the Tanaka and Johnston equation in predicting space in a Kenyan African community, and the need to validate a new prediction equation with high correlation coefficients for the Kenyan population. Further studies are needed to validate our findings with the aim of providing an accurate tool to predict space in a growing African child.

Ethical approval and consent to participate: Ethical approval was obtained from the University of Nairobi-Kenyatta National Hospital ethics review committee. The ethical approval number is P252/6/2011. Informed consent was obtained from the principals of the two schools because they were the legal guardians of the study participants. All methods were carried out in accordance with relevant guidelines and regulations.

Consent for publication: not applicable.

Availability of data and materials: the datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests: the authors declare that they have no competing interests.

Funding: this study was fully funded by the corresponding author.

Authors’contributions: NK conceptualized, designed, coordinated data collection and analysis of the larger study, drafted the initial manuscript, reviewed and revised it prior to submission. JLN and PM assisted in the design and planning of the study, made inputs into the data collection, analysis plan, reviewed and revised the drafts of the larger study and for this manuscript. ALS and AKM conceptualized and designed the initial draft of this manuscript, verified the data acquisition and analysis adapted from the original larger study, BJ reviewed and revised the manuscript. Prior to submission of this manuscript, all the authors read and approved it.

Acknowledgements: the students, parents and teachers of Starehe Boys’ and Girls’ Centres who agreed to part of this study. Prof GP Pokhariyal of the Department of Mathematics, University of Nairobi who helped with statistical analysis. Lynly Beard, librarian at the University of Washington Health Sciences library who helped with gathering and organizing reference material.

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No competing interests reported.

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Comparison of measured and predicted mesiodistal tooth-widths of 13-17 year old Kenyans: a descriptive cross-sectional study to develop a new prediction equation for use in the mixed dentition in a Kenyan population

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