Comparison of occlusal settling, patient compliance, and retention ability between hawley’s and van der linden retainers – A randomized controlled trial

Introduction

The success of orthodontic treatment is determined by facial esthetics, occlusion, and stability. After active orthodontic tooth movement, the teeth might be in an inherently unstable position and have a tendency to return to their pre-treatment position; this is termed as ‘Relapse’. "Retention is the toughest drawback in orthodontia; in reality, it's the problem." was declared by Oppenheim;1 still holds true in several cases.

The post-treatment period can be divided into retention and post-retention phases. During the retention phase, the reorganization of elastic supra-crestal fibers can take up to 232 days.2 The post-retention phase begins after the retention phase and lasts for the rest of the patient's life. During this period, teeth bear varied forces- neuromuscular forces, dentoalveolar development, and growth.3

Retainers utilized for orthodontic retention may either be fixed or removable. Hawley retainers and Van der Linden retainers fall under the category of removable retainers.4 The Hawley’s retainer is one of the most popular and commonly used removable retainers which was designed by Charles Hawley in 1919 and has been used widely for nearly a century.5 Due to the plentitude of advantages like occlusal settling, ease of modification and durability Hawley's retainer has stood strongly against the test of time. The Van Der Linden retainer was designed by Van Der Linden in 2003, which offers complete control over the maxillary anterior teeth, with a contoured labial bow and closed loops on canines. Van der Linden has emphasized on good versatility and occlusal settling ability of this retainer.6

There is insufficient evidence in terms of clinical effectiveness comparison between Hawley’s retainer and Van Der Linden’s retainer. In most studies, retainers are compared either for retention ability or occlusal settling, or patient compliance. There is an inadequacy of studies that were intended to consider all these aspects to be studied on the same sample. We have attempted to open new horizons in this direction by comparing both retainers based on retention ability, patient compliance, and occlusal stability. In this study, we checked the hypothesis to compare occlusal settling, patient compliance, and retention ability of maxillary Hawley’s and Van Der Linden retainers at the time of retainer delivery, after 3 months and 6 months of retention.

Materials and Methods

Statistical analysis

The data of the study were analyzed using SPSS version 20, statistics packages. In each case, the level of significance was set at α = 0.05. The data were inspected for normality and found to be normally distributed. Descriptive statistics were computed to give the basic features of the data. Independent sample t-test and pair t-test were conducted for comparison between the two groups.

Figure 1

Consort flow chart

Figure 2

Hawley’s retainer

Figure 3

Van der linden retainer

Figure 4

Figure 5

Bite registration with “True” and “Near” contacts.

Figure 6

Questionnaire

Table 1

Descriptive statistics of the changes in true and near occlusal contacts of both the retainers at the time of retainer delivery (T0), at 3 months (T1), and at 6 months (T2) of retainer delivery.

Number Of Occlusal Contacts		Mean		Standard deviation		Minimum		Maximum
		HL	VL	HL	VL	HL	VL	HL	VL
Retainer delivery (T0)	True contacts Ant.	3.28	2.94	0.88	0.86	2.00	2.00	5.00	5.00
	True contacts Post.	8.22	7.69	1.07	0.75	5.00	7.00	10.00	10.00
	Total True contacts	11.50	10.64	1.42	1.22	8.00	9.00	14.00	14.00
	Near contacts Ant.	4.47	4.36	0.61	0.76	3.00	3.00	5.00	6.00
	Near Contacts Post.	11.94	12.39	1.31	1.38	10.00	10.00	15.00	15.00
	Total Near Contacts	16.42	16.75	1.48	1.57	14.00	14.00	20.00	20.00
	Total contacts	27.92	27.39	1.98	2.06	24.00	23.00	34.00	32.00
After 3 months (T1)	True contacts Ant.	3.94	3.42	0.47	0.65	3.00	2.00	5.00	5.00
	True contacts Post.	11.33	10.44	0.96	0.77	10.00	9.00	14.00	13.00
	Total True contacts	15.28	13.86	0.97	1.05	14.00	12.00	18.00	17.00
	Near contacts Ant.	4.42	4.19	0.55	0.47	3.00	3.00	5.00	5.00
	Near Contacts Post.	13.72	11.86	0.66	1.10	13.00	10.00	15.00	15.00
	Total Near Contacts	18.14	16.06	0.99	1.12	17.00	14.00	20.00	19.00
	Total contacts	33.42	29.92	1.44	1.54	31.00	28.00	38.00	33.00
After 6 months (T2)	True contacts Ant.	4.31	3.78	0.52	0.59	3.00	2.00	5.00	5.00
	True contacts Post.	14.06	11.50	0.79	0.65	11.00	10.00	15.00	12.00
	Total True contacts	18.39	15.28	0.96	0.81	16.00	13.00	20.00	17.00
	Near contacts Ant.	4.06	3.39	0.41	0.49	3.00	3.00	5.00	4.00
	Near Contacts Post.	10.89	11.14	0.78	0.59	10.00	10.00	13.00	12.00
	Total Near Contacts	14.89	14.53	0.82	0.74	13.00	13.00	17.00	16.00
	Total contacts	33.31	29.81	1.35	1.01	31.00	27.00	37.00	32.00

Table 2

Statistical significance of the difference in change in occlusal contacts between both groups.

HL vs VL	Contacts	t	Sig. (2-tailed)	Mean Difference	95% Confidence Interval of the Difference
					Lower	Upper
Retainer delivery	True contacts Ant.	1.62	0.11	0.33	-0.08	0.74
	True contacts Post.	2.42	0.22	0.53	0.09	0.96
	Total True contacts	2.75	0.01	0.86	0.24	1.49
	Near contacts Ant.	0.68	0.50	0.11	-0.21	0.44
	Near Contacts Post.	-1.40	0.17	-0.44	-1.08	0.19
	Total Near Contacts	-0.93	0.36	-0.33	-1.05	0.39
	Total contacts	1.11	0.027	0.53	-0.42	1.48
After 3 months	True contacts Ant.	3.94	0.00	0.53	0.26	0.80
	True contacts Post.	4.34	0.00	0.89	0.48	1.30
	Total True contacts	5.95	0.00	1.42	0.94	1.89
	Near contacts Ant.	1.84	0.07	0.22	-0.02	0.46
	Near Contacts Post.	8.71	0.00	1.86	1.43	2.29
	Total Near Contacts	8.36	0.00	2.08	1.59	2.58
	Total contacts	9.96	0.00	3.50	2.80	4.20
After 6 months	True contacts Ant.	4.01	0.00	0.53	0.27	0.79
	True contacts Post.	14.94	0.00	2.56	2.21	2.90
	Total True contacts	14.79	0.00	3.11	2.69	3.53
	Near contacts Ant.	6.23	0.00	0.67	0.45	0.88
	Near Contacts Post.	-1.53	0.12	-0.25	-0.58	0.08
	Total Near Contacts	1.97	0.05	0.36	-0.01	0.73
	Total contacts	12.47	0.00	3.50	2.94	4.06

Table 3

Descriptive statistics of changes in little's irregularity index, inter canine width (ICW), and Inter molar width (IMW) of both the retainers at the time of retainer delivery (T0), at 3 months (T1), and 6 months (T2) of retainer delivery.

	Mean(mm)		Standard deviation(mm)		Minimum(mm)		Maximum(mm)
Retainer delivery	HL	VL	HL	VL	HL	VL	HL	VL
LII	0.25	0.22	0.44	0.42	0.00	0.00	1.00	1.00
ICW	26.21	25.22	0.86	0.97	24.24	24.24	28.05	28.05
IMW	35.22	34.31	0.60	0.57	33.69	33.95	36.25	36.26
After 3 months
LII	0.14	0.33	0.35	0.53	0.00	0.00	1.00	2.00
ICW	26.25	26.30	0.91	0.99	24.46	23.52	28.11	28.11
IMW	35.29	35.32	0.68	0.74	33.71	33.41	36.95	36.81
After 6 months
LII	0.11	0.28	0.32	0.51	0.00	0.00	1.00	2.00
ICW	26.19	28.48	0.91	0.81	24.31	25.31	28.19	27.96
IMW	35.35	36.41	0.75	0.79	33.67	33.66	36.94	36.72

Table 4

Shows the statistical significance of the difference in change in LII, ICW, and IMW of both retainers.

HL vs VL	t	Sig. (2-tailed)	Mean Difference	95% Confidence Interval of the Difference
				Lower	Upper
Retainer delivery
LII	0.27	0.79	0.03	-0.17	0.23
ICW	-0.06	0.95	-0.01	-0.44	0.42
IMW	-0.67	0.51	-0.09	-0.37	0.18
After 3 months
LII	-1.82	0.07	-0.19	-0.41	0.02
ICW	-0.19	0.85	-0.04	-0.49	0.41
IMW	-0.21	0.84	-0.03	-0.37	0.30
After 6 months
LII	-1.66	0.01	-0.17	-0.37	0.03
ICW	-1.39	0.04	-0.28	-0.69	0.12
IMW	-0.32	0.03	-0.06	-0.42	0.30

Table 5

Shows descriptive statistics of responses to questions asked to each participant through the questionnaire to assess patient compliance, which was assessed at 3 months and 6 months of retention.

Questions		After 3 months			After 6 months
	response	HL (n=36)	VL(n=36)	HL vs VL (p-value)	HL(n=36)	VL(n=36)	HL vs VL (p-value
Difficult to insert/remove the retainer	yes	8.3	5.6	0.033	2.8	2.8	0.047
	no	91.7	94.4		97.2	97.2
Wire components of retainer hurt	yes	7.3	13.9	0.012	5.6	8.3	0.124
	no	92.7	86.1		94.4	91.7
Retainer affects your speech	yes	2.8	11.1	0.256	5.6	8.3	0.28
	no	97.2	88.9		94.4	91.7
Feel embarrassed to wear the retainer	yes	9.6	5.6	0.008	8.3	2.8	0.039
	no	90.4	94.4		91.7	97.2
Overall experience with retainer	good	83.3	75	0.019	88.9	77.8	0.028
	neutral	11.1	22.2		8.3	16.7
	bad	5.6	2.8		2.8	5.6

Results

Total observations of seventy-two participants [36 in the VL group & 36 in the HL group] were considered for appraisal of results and statistical analysis.  The average age of the participants was 27.1 years in both groups.

Epresents the descriptive statistics of the occlusal contacts of the retainer. At T0 the mean total true contacts for HL were above VL. At T2 the mean total true contacts Grew in both groups. On considering total near contacts, it was found that the mean total near contacts for HL dipped at T2, whereas the pattern of decline is the same for VL. However, taking into consideration total contacts, results are suggestive of a greater increase for HL than VL.

Table 2 shows the difference between the occlusal contacts of HL and VL respectively. At T1 the average total true contacts and average total contacts differ significantly for HL and VL, where both were slightly in favor of HL. In addition, both at T1 and T2, the mean difference between HL and VL was found to be statistically and significantly different indicating all the contacts were in favor of HL compared to VL. Both at T1 and T2, the average true contacts were almost thrice as higher for HL as compared to that of VL.

The retention ability of retainers was calculated by LII, ICW, and IMW at each time. 

Table 3 shows the descriptive statistics of the index of retainer for HL and VL separately. Considering T0, it was found that the average LII, ICW, and IMW were Minutely higher for HL as contrasted to that of VL. Whereas at T2, the pattern changed slightly, indicating the average LII, ICW, and IMW was found to be exceeding in VL. 

Table 4 shows the difference between the index of HL and VL respectively. On considering T0 and at T1, it was found that the values of LII, ICW, and IMW were not significantly different for both groups. Whereas at T2 they were statistically and significantly different between HL and VL and were slightly in favor of HL. 

There were 5 questions in the questionnaire. Participants had to answer in affirmation or in negative for the initial 4 questions whereas in terms of good, bad, or neutral for the last question.

Assessment of patient compliance was done at T1 and T2. Table 5 depicts that in 6 months difficulty or the laboriousness in wearing the retainer diminished in both retainers. This decline was also found to be statistically significant at a 5% level.

Wire components of both retainers hurt during T1, but at T2 it was noticed more in VL.  In the case of the Effect of retainer on speech production, VL was more comfortable than HL. With time embracement while wearing a retainer decreased. Most of the respondents had a good overall experience with the retainers, which increased at T2. Participants were feeling comfortable as they started using retainers. So, the ratio of participants replying in "Neutral" and "Bad" abated from T1 to T2. 

Discussion

There are varied types of retainers available to the orthodontist, including removable and fixed, and it may be onerous to decide on a universal protocol of retention. The recent Cochrane review concluded that there was insufficient evidence on which to base the clinical practice of retention in orthodontics.7

With the time of a century, Hawley's retainer has proven its retention ability, efficiency for occlusal settling, and patient compliance. But, in a recently conducted systematic review by Jaber et al. They noticed greater changes in LII, and a greater proportion of maxillary anterior teeth rotation was observed with Hawley’s retainers.8 This led us to search for an alternate removable retainer that can substitute this well-known retainer. Recently introduced Van Der Linden retainer was selected to check for its effectiveness against Hawley’s retainer.

Our Inferences showed that total contacts increase with the wearing of retainers. But the ratio of true contacts increased more in comparison with near contacts. This means inter digitations of upper and lower dentition increased as patients wore retainers, although the change was more prominently seen in Hawley's retainer. The same results were obtained in the study done by Sauget et al.7 who compared occlusal contacts with the use of Hawley and clear overlay retainers. He stated that with Hawley’s retainer, there was a marked increase in occlusal contacts on posterior teeth but no change on anterior teeth.9

We also assessed and compared the retention ability of retainers by measuring the ability of retainers to maintain LII, ICW, and IMW. In our study, we noticed that Hawley's retainer was able to retain the dentition in its position, as there were no significant changes noticed during 3 months and 6 months of follow-up. On the contrary, Van Der Linden showed changes in these parameters. Although, these changes were not so significant they were more than Hawley's retainer. This suggested that Hawley's retainer had more retention ability. In our study, we noticed the change in LII of 0.14mm and 0.06mm in Hawley's and Van Der Linden’s retainer respectively during 6 months of retention. LII was changed by 0.25mm in a single-centered randomized controlled trial conducted by H. Rowland10 who compared the effectiveness of Hawley and vacuum-formed retainers (VFRs). 

For the assessment of patient compliance, we had taken the feedback of patients in form of responses to a questionnaire consisting of 5 questions. The questions were based on inconveniences in wearing the retainer, harm from wire components, effect on speech as well as social embarrassment while retainer wear, and overall experience. In most of the responses, we noticed that the comfort level of patients increased as they started wearing retainers and got adapted to them. In most of the responses, patients were feeling comfortable with Hawley's retainer, except for feeling embarrassed while wearing the retainer which decreased more with the Van Der Linden retainer during 6 months of retention. In contrast to our study, M. Pratt et al.11 noticed less patient compliance with Hawley’s retainers when they compared it with VFRs in their questionnaire-based study to assess patient compliance with orthodontic retainers.

In the matter of selecting retainers, other factors such as aesthetics, ease of fabrication, and cost should be taken into account. Overall, in the case of retention ability, occlusal settling and patient compliance Hawley's retainer was more effective than Van Der Linden’s retainer. But, Van Der Linden’s retainer is better than Hawley's retainer in the matter of palatal acrylic coverage Otherwise, Hawley's retainer has given satisfactory results since the last century.

Conclusion

Source of Funding

None.

Conflict of Interest

None.