Assessing the Validity and Reliability of Tooth Widths and Bolton Ratios Obtained from Digital Models and Plaster Models.

Aim: The aim of the study is to compare and evaluate the validity and reliability of tooth widths and Bolton ratios measured from digital models obtained from intraoral scanners and plaster models derived from alginate and polyvinyl siloxane impression materials. Materials and
Methods: Alginate and polyvinylsiloxane impression was taken for 40 subjects, orthokal stone was poured and grouped as Group I and Group II, respectively. Intraoral scanning was done using Trios Pod 3shape for the same patients, digital models were obtained and grouped as Group III. OrthoAnalyzer software was used for obtaining measurements in digital models and Aerospace Vernier calipers in plaster models. The validity and reliability of the three groups were quantified and compared.
Results: Validity measurements showed significant differences between tooth widths and Bolton ratios obtained from digital models and plaster models indicating higher accuracy for plaster models whereas reliability coefficients were excellent for digital models indicating better reproducibility of values.
Conclusion: The study shows significant differences in accuracy on measuring with vernier calipers and Orthoanalyzer software showing plaster models are still better than digital models for measuring tooth widths and bolton ratios. Copyright:

INTRODUCTION

The relationship between maxillary and mandibular tooth sizes is an important part of diagnosis and treatment planning for an individual. A good posttreatment occlusion relies on an appropriate relationship between maxillary and mandibular teeth.[1] Study model analysis has been the gold standard for diagnostic procedure for many years. Various methods have been used for measuring and analyzing study models.

Bolton's analysis, introduced in 1958 by W. A Bolton, has proven to be an extremely useful tool in a clinical setting. Based on a study of models of 55 random patients with perfect occlusion, he developed an overall and anterior ratio of the mesiodistal width of all permanent teeth up to the first molar.[2]

Although plaster models provide a three-dimensional view of occlusion, digital models are easier to retrieve, not subjected to physical damage and show negligible storage space.[3]

Thus, the aim of this study is to assess the validity and reliability of mesiodistal widths and Bolton's ratios using models taken by intraoral scanners and alginate and polyvinyl siloxane impression materials.

MATERIALS AND METHODS

Alginate and polyvinyl siloxane impression was taken for 40 subjects and orthokal stone was poured. These orthokal models were grouped as I and II. The same patient's dentition was scanned using Trios Pod 3 shape intraoral scanner and transferred to Dell Optic 7040 computer to process into digital models and grouped as Group III.

Models under Group I and Group II were analyzed manually with aerospace digital Vernier caliper [Figure 1], and models under Group III were analyzed using Orthoanalyser Software [Figure 2].

Figure 1

Mesiodistal width of an alginate model is calculated using a Digital Vernier caliper (Aerospace)

Figure 2

Segmentation of maxillary model: Marking set points using 3Shape OrthoAnalyzer 2015 1.6.1.1 software in a Dell Optiplex 7040 computer system

The Bolton's anterior ratio and overall ratio for the models were calculated using the formula:

Sum of mesiodistal width of mandibular 6/sum of maxillary 6 × 100 = Anterior Ratio (%)

Sum of mesiodistal width of mandibular 12/sum of maxillary 12 × 100 = Overall Ratio (%)

In this study, validity is the extent to which measurements of the digital models agree with the plaster models. Measurements made with calipers were considered to be true values. Reliability is the extent to which measurements were repeatable under identical conditions. It was gauged by the concordance between replications.

Statistical analysis

Validity analysis is done by overall comparison between three different groups using analysis of variance with a P < 0.05. To analyze the reliability intraclass correlation coefficient was calculated between two time intervals and R value was set based on:

<0.2– slight correlation; negligible relationship

0.2-0.4-low correlation; weak relationship

0.4-0.7-Moderate correlation; substantial relationship

0.7-0.9-High correlation; marked relationship.

RESULTS

In the present analysis, models of 40 subjects poured from alginate and polyvinyl siloxane impression and digital models scanned by intraoral scanners were analyzed for validity. Significant differences were seen in the tooth widths obtained from caliper method and orthoanalyser software as shown in Table 1. Teeth measured using digital models showed 0.023 mm and 0.025 mm greater width than alginate derived models and polyvinyl siloxane derived models, respectively. Bolton ratios measured from models derived from alginate and orthoanalyzer software also showed a significant difference as shown in Table 2 whereas no significant difference in overall ratios between models derived from polyvinyl siloxane and digital models as shown in Table 3. Reliability was analyzed by calculating the intraclass correlation coefficient of the three groups in two intervals of time as shown in Table 4.

Table 1

Comparison of tooth widths between three different groups for validity using analysis of variance

Teeth	Mean±SD			ANOVA
	ALG	PVL	OAS	F	P
16	9.85	9.82	10.10	4.52	0.013*
15	6.64	6.61	6.90	3.09	0.049*
14	6.96	6.99	7.28	6.87	0.002*
13	7.83	7.80	8.10	4.17	0.018*
12	6.89	6.85	7.15	2.91	0.058*
11	8.68	8.67	8.94	4.17	0.113
21	8.72	8.66	8.94	2.91	0.116
22	7.01	7.02	7.31	2.22	0.0611
23	7.76	7.73	7.99	2.19	0.074
24	7.03	6.94	7.26	2.85	0.016*
25	6.2	6.38	6.69	2.66	0.006*
26	9.9	9.95	10.20	4.29	0.040*
36	10.71	10.66	10.95	5.36	0.142
35	6.82	7.09	7.10	3.31	0.461
34	7.22	7.44	7.48	1.98	0.414
33	6.823	6.763	7.17	0.77	0.020*
32	6.06	6.03	6.31	0.89	0.067
31	5.33	5.46	5.69	4.06	0.041*
41	5.53	5.52	5.80	2.77	0.007*
42	6.02	5.99	6.33	3.28	0.004*
43	6.82	6.80	7.07	5.83	0.082
44	7.17	7.15	7.39	2.55	0.176
45	6.59	6.99	6.88	1.76	0.014*
46	10.50	10.7	11.02	4.40	0.139

*P<0.05. SD: Standard deviation, ANOVA: Analysis of variance, ALG: Alginate, PVL: Polyvinyl siloxane, OAS: OrthoAnalyzer Software

Table 2

Comparison between Group I and Group III for overall and anterior Bolton’s ratios

	Alginate versus orthoanalyzer software
	Difference			SD	P
	Mean	Lower limit	Upper limit
OBR	0.32	0.12	0.52	0.290	0.0001a
ABR	0.27	0.95	0.45	0.328	0.001a

*P<0.001. SD: Standard deviation, OBR: Overall bolton ratio, ABR: Anterior bolton ratio

Table 3

Comparison between Group II and Group III for overall and anterior Bolton’s ratios

	Orthoanalyzer software versus polyvinyl siloxane
	Difference			SD	P
	Mean	Lower limit	Upper limit
OBR	0.62	−1.11	2.35	0.714	0.032*
ABR	0.90	−0.86	2.68	0.731	0.034

*P<0.05. SD: Standard deviation, OBR: Overall bolton ratio, ABR: Anterior bolton ratio

Table 4

Intraclass correlation coefficient between two time intervals

Groups	Average mean		R	Inference
	Time 1	Time 2
Mesiodistal tootd widtds
Group I	7.477	7.554	0.90	Good
Group II	7.500	7.348	0.98	Excellent
Group III	7.789	7.789	0.99	Excellent
Overall Bolton ratio
Group I	91.88	92.00	0.90	Good
Group II	92.13	92.23	0.98	Excellent
Group III	92.25	92.25	0.99	Excellent
Anterior Bolton ratio
Group I	77.65	77.97	0.90	Good
Group II	78.00	78.26	0.98	Excellent
Group III	79.22	79.22	0.99	Excellent

DISCUSSION

Intermaxillary tooth size ratio has a prominent part in diagnosing and treatment planning. Any discrepancies in this relationship can predict if the treatment can be proceeded as extraction or nonextraction.[4] An adequate relationship between the maxillary and mandibular teeth is important for perfect interdigitation overjet and overbite during treatment completion.

Initial analysis on tooth size was given by Neff, Ballard, Black, and Lundstorm but a classic and most popular method for determining tooth size abnormality was given by Bolton who calculated the mesiodistal widths of maxillary and mandibular teeth from 55 patients with ideal occlusion, to give the overall and anterior ratios. Since Bolton's analysis is the most common and reliable method, this study compares the tooth widths and Bolton's ratio using Vernier calipers and digital softwares.[5]

Digital models are a product of recent advancements in computers and have shown to have many advantages such as instant accessibility of information, accuracy in treatment planning, negligible storage space.[6] In this study, 40 patients were selected and alginate and polyvinyl siloxane impression, intraoral scanning using Trios Pod 3 shape was performed. Mesiodistal dimensions for every tooth was calculated using the gold standard method of Vernier caliper and Orthoanalyzer software.

Validity is the extent to which measurements of the orthoanalyzer software agrees with measurements derived from Vernier calipers. The results of this study showed significant differences in Bolton's ratios and the mesiodistal widths measured between the digital models and plaster models. This was in accordance with a study done by Gustavo Adolfo et al. who studied the validity of values obtained from Cecile 3 digital models. He found that plaster and Cecile 3 digital models presented difference in mesiodistal width, intercanine distance, intermolar distance, overjet, and overbite.[7]

Reliability is defined as the extent to which measurements taken from digital models and plaster models are repeatable under identical conditions. The results showed that the tooth widths and Bolton ratio derived from the two models at two different time intervals were not significantly different from each other. This was in accordance with the study conducted by Kazuo Hayashi et al. who studied the accuracy and reliability of SureSmile Orascanner with Vivid910 scanner and R700 scanner[8] that showed reliability values with no significant difference when compared with the gold standard values.

SUMMARY AND CONCLUSION

The current study concluded that values obtained from the Orthoanalyzer software were higher with relation to tooth width and Bolton's Ratio compared to caliper measurements showing that plaster models are still the most reliable method for measuring tooth widths and Bolton's ratios.

On the other hand, digital models showed excellent reliability values compared to plaster models derived from alginate and polyvinyl siloxane.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.