Influence of preoperative degree of tooth loosening and thickness of wire on the rigidity of wire composite splint.

Context: A wire composite splint (WCS) is most commonly used in clinical practice for the management of luxation dental injuries (LDIs). Wire thickness and adhesive point dimensions influence the rigidity of WCS. However, the influence of presplint tooth mobility on the rigidity of splint is not yet addressed. Aim: The aim of this study is to identify the optimal thickness of WCS that achieves physiologic mobility in teeth with varying degrees of loosening (DoL) in a simulated LDI model. Settings and Design: In vitro study. Materials and
Methods: Three typodont models with resin teeth were used. Right central incisor (Tooth 11) was simulated as an injured tooth and adjacent right lateral and left central incisor teeth (12 and21) acted as uninjured teeth. Each typodont model was modified to reproduce DoL 1, 2, and 3 in tooth 11 and categorized as Groups I, II, and III, respectively. The simulated injured tooth 11 was splinted with adjacent teeth 12 and 21 using 0.3, 0.5, and 0.8 mm WCS. Postsplinting DoL was assessed with Periotest. Statistical Analysis Used: Two-way ANOVA and post hoc Tukey test were used for intragroup and intergroup comparisons of pre- and postsplinting Periotest values (PTVs). Friedman's two-way ANOVA and Kruskal-Wallis test were used for the intragroup and intergroup comparison of splint effect.
Results: Irrespective of the thickness of WCS, the postsplint PTVs corresponding to DoL 0 for simulated injured right central incisor tooth (11) were not achieved in Groups II and III. In three study groups, there was no statistically significant difference in the splint effect produced by 0.3 mm versus 0.5 mm WCS or 0.5 mm versus 0.8 mm WCS for tooth 11. Conclusions: The postsplint DoL for a luxated tooth is affected by both the degree of presplint tooth mobility and the thickness of the wire. Copyright:

INTRODUCTION

Effective management of luxation dental injuries (LDI) involves repositioning and splinting the traumatized tooth for varying periods depending upon the severity of the damage. A splint sufficiently protects the injured teeth against further accidental trauma or ingestion and allows pulpal and periodontal healing.[1] It is classified traditionally as rigid, semi-rigid, or flexible based on an injured tooth's mobility after splinting.[2] A rigid splint completely immobilizes a luxated tooth and ostensibly promotes ankylosis and replacement resorption. A flexible splint allows functional movement that facilitates periodontal regeneration and prevents ankylosis.[3] However, excessive occlusal forces during the initial healing phase can also contribute to severe root or bone resorption.[4] Thus, an ideal splint must be rigid enough to maintain the tooth in the socket but flexible enough to allow periodontal stimulation during the function.[5] International Association of Dental Traumatology and American Association of Endodontists guidelines recommend the use of passive and flexible splint for teeth with luxation injuries without any associated dentoalveolar fractures.[67] Titanium trauma splint (TTS), nylon fishing lines, and orthodontic wire with a diameter of <0.4 mm are considered flexible splints.[38] Although TTS is regarded as the standard of care for splinting, its use is limited owing to its cost. The acid-etch wire composite splint (WCS) remains a cost-effective alternative that can be fabricated from readily available materials in dental clinics. Therefore, it is the most commonly used splint in clinical practice.

The in vitro study models are extensively used in dental traumatology to evaluate rigidity and splint effect objectively. The majority of published studies have simulated an avulsed tooth in their experiments.[89] However, the degree of tooth mobility varies appreciably between various luxation injuries. The splint effect of a particular thickness of WCS on an injured tooth may vary depending upon the severity of damage and can lead to suboptimal tooth mobility and unexpected outcome. The literature is lacking on the influence of the preoperative degree of tooth loosening on the splint effect of different thickness of wires in wire-composite splints. Consequently, the present study was designed with a specific aim to identify the optimal thickness of WCS that achieves physiologic mobility in teeth with varying degrees of loosening (DoL) in a simulated LDI model. The null hypothesis was that presplint DoL has no influence on the post splint DoL achieved by the WCS.

MATERIALS AND METHODS

This in vitro study was conducted on three typodont models (API, Ashoo Sons, New Delhi, India) containing acrylic resin teeth. All resin teeth except right central incisor (tooth 11) were screwed in the socket and served as uninjured teeth with normal mobility. The socket of the right central incisor (tooth 11) was enlarged 2 mm circumferentially up to the entire root length to simulate an injured tooth with increased mobility. The root surface of right central incisor (tooth 11) was circumferentially wrapped with three coat of 0.075 mm Teflon tape (Swimline Hydrotools, Edgewood) to simulate periodontal ligaments.[10]

The Periotest was used to measure the mobility of teeth in the experimental model. Periotest is a dynamic device designed to provide objective measurement of tooth mobility by assessing damping characteristics of periodontium. The device has an electronically controlled tapping rod with a pressure sensitive tip. The tip is positioned parallel and at a distance 0.6–2 mm from the tooth surface. When activated, the tapping road percusses the tooth for a total of 16 times in 4 s. The control unit measures the duration of tip contact with the tooth and provides a digital readout of the Periotest value (PTV), which ranges from 8 to + 50. The clinical degree of loosening of tooth and corresponding PTVs are presented in Table 1.

Table 1

Reference range of Periotest values and degree of loosening

Clinical degree of loosening	PTV
0	−8-+09
I	+10-+19
II	+20-+29
III	+30-+50

PTV: Periotest value

Typodont model was stabilized in the holder, and a reproducible point was marked at 2 mm from the incisal edge on each tooth. The Periotest (Medizintechnik Gulden, Bensheim, Germany) tapping rod was held parallel to the labial surface at the marked point to measure the mobility of the teeth. The Periotest measurements were repeated seven times for each tooth. Three study groups were predefined based on the degree of loosening (DoL) of the simulated injured tooth, i.e., right central incisor (tooth 11), as determined by PTV.

Group I (DoL 1): Prefabricated fastening mechanism of tooth 11 was unscrewed three turns to simulate the DoL1, median PTV 17 (16–17)

Group II (DoL 2): Prefabricated fastening mechanism of tooth 11 was unscrewed until the DoL 2 was achieved, median PTV 28 (28–28)

Group III (DoL 3): The fastening mechanism was removed from the tooth 11 and was gently repositioned in its socket. The periotest readings confirmed the DoL 3, median PTV 41 (39.5–42).

Splinting protocol

In each group, the simulated injured right central incisor tooth (11) was splinted with adjacent teeth right lateral incisor (12) and left central incisor (21) using three different sizes of stainless-steel wires (0.3 mm, 0.5 mm, and 0.8 mm diameter) in WCS. The buccal surfaces of the resin teeth to be splinted were roughened with air abrasion and etched with 37% phosphoric acid for 15 sec, rinsed with water, and air-dried. A layer of bonding agent (One coat 7, Coltene, Whaledent Pvt. Ltd.,) was applied on the etched surface and light-cured for 20 s. Stainless steel wire (Dentaurum SS true form preformed wires) was adapted and fixed to the teeth with flowable light cure composite resin (Brilliant Everglow Flow composites, Coltene, Whaledent Pvt. Ltd.,) with an adhesive point dimension of 3 mm. Pre- and postsplinting tooth mobility was assessed in each group using the Periotest. The Periotest measurements were repeated seven times for each tooth, and consecutive PTVs per tooth were recorded. The postsplint PTVs were subtracted from presplint PTVs to calculate the splint effect (ΔPTV).

Statistical analysis

The data were recorded in a Microsoft Excel sheet and imported to IBM SPSS statistics version 25 software (IBM Corporation, New York, USA) for the statistical analysis. The data of pre- and postsplint PTVs and splint effect (ΔPTV) was not normally distributed (Shapiro–Wilk test P < 0.05). The log transformation of PTV data was done to achieve normality. The two-way ANOVA was used to compare thickness of wire and degree of tooth mobility on PTVs and if interaction was present, then comparisons were done using post hoc Tukey test taking each combination of wire and degree of tooth mobility as independent group. For the splint effect, Friedman's test followed by multiple comparisons using sign rank test and the Kruskal–Wallis test were employed for within-group and between-group comparisons, respectively. The significance level was set at <0.05.

RESULTS

Presplint periotest values

The presplint PTVs for simulated uninjured right lateral incisor and left central incisor (teeth 12 and 21) were within the reference range for DoL0, and there was no statistically significant difference (P > 0.05) between the study groups [Table 2]. The simulated injured right central incisor (tooth 11) exhibited presplint PTVs within the reference range of DoL 1, 2 and 3 for Groups I, II, and III, respectively [Table 3], with a significant difference (P < 0.05) between presplint PTVs among Groups IVs. II, II Vs. III, and I Vs. III.

Table 2

Presplint Periotest values of uninjured teeth in the three study groups

Descriptive statistics	Tooth 12			Tooth 21
	Group I	Group II	Group III	Group I	Group II	Group III
Mean	3.7143	3.5714	3.7143	3.7143	3.0000	3.1429
SD	0.4879	0.5345	0.9511	0.9511	0.0000	0.3779
Median	4.0000	4.0000	4.0000	3.0000	3.0000	3.0000
Q 25	3.0000	3.0000	3.0000	3.0000	3.0000	3.0000
Q 75	4.0000	4.0000	4.0000	5.0000	3.0000	3.0000
Mean log	1.2904	1.263002	1.278053	1.316834	1.098612	1.139709
SD	0.1485	0.1537	0.2974	0.2525	0	0.1087
P	>0.05			>0.05

SD: Standard deviation

Table 3

Descriptive statistics for pre- and postsplint Periotest values of simulated injured tooth (11) in three study groups

Descriptive statistics	Group I				Group II				Group III
	No splint	0.3 mm WCS	0.5 mm WCS	0.8 mm WCS	No splint	0.3 mm WCS	0.5 mm WCS	0.8 mm WCS	No splint	0.3 mm WCS	0.5 mm WCS	0.8 mm WCS
Mean	16.7143	14.7143	13.1429	8.0000	27.7143	20.7143	18.5714	13.0000	41.0000	26.7143	25.7143	14.4286
SD	0.7559	0.9511	0.3779	0.0000	0.7559	1.3801	2.3704	1.1547	1.8257	0.4879	2.4976	0.5345
Median	17.0000	14.0000	13.0000	8.0000	28.0000	21.0000	19.0000	13.0000	41.0000	27.0000	26.0000	14.0000
Q 25	16.0000	14.0000	13.0000	8.0000	28.0000	20.0000	17.0000	12.0000	39.0000	26.0000	25.0000	14.0000
Q 75	17.0000	16.0000	13.0000	8.0000	28.0000	22.0000	20.0000	14.0000	42.0000	27.0000	27.0000	15.0000
Mean log	2.82	2.69	2.57	2.07	3.32	3.02	2.91	2.56	3.71	3.28	3.24	2.66
SD	0.04457	0.0657	0.0302	0	0.0280	0.0692	0.1380	0.0919	0.0442	0.0184	0.1015	0.0368

SD: Standard deviation, WCS: Wire composite splint

Postsplint periotest values and splint effect

The two-way ANOVA test using interaction model showed significant interaction between wire thickness and study group for PTVs [Figure 1]. Multiple comparisons were made using post hoc tukey test.

Figure 1

Estimated marginal means by the model with interaction terms (w0 = Presplint, W1 = 0.3 mm wire composite splint, W2 = 0.5 mm wire composite splint, W3 = 0.8 mm wire composite splint, g = group)

Injured teeth

Only the application of 0.8 mm WCS reduced mobility within the reference range of DoL0 in group I. Irrespective of the thickness of WCS, the postsplint PTVs corresponding to DoL 0 could not be achieved in Groups II and III [Figure 2]. The splint effect (ΔPTV) increased with an increase in the thickness of WCS (0.8 mm > 0.5 mm > 0.3 mm) in all study groups [Table 4]. Pairwise comparison within groups revealed no statistically significant difference between splint effect produced by 0.3 mm versus 0.5 mm WCS and 0.5 mm versus 0.8 mm WCS. The splint effect produced by 0.8 mm WCS was significantly (P < 0.05) higher than 0.3 mm WCS for all study groups [Figure 3].

Figure 2

Pre and postsplint degree of loosening of an injured tooth

Table 4

Descriptive statistics for splint effect (∆ Periotest values) of three wire composite splint on simulated injured tooth (11) in three study groups

Descriptive statistics	Group I			Group II			Group III
	0.3 mm WCS	0.5 mm WCS	0.8 mm WCS	0.3 mm WCS	0.5 mm WCS	0.8 mm WCS	0.3 mm WCS	0.5 mm WCS	0.8 mm WCS
Mean	2.0000	3.5714	8.7143	7.0000	9.1429	14.7143	14.2857	15.8571	26.5714
Median	2.0000	4.0000	9.0000	7.0000	9.0000	14.0000	14.0000	15.0000	26.0000
SD	1.2909	0.9759	0.7559	1.4142	2.6726	1.3801	1.8898	3.0237	1.9023
Q 25	1.0000	3.0000	8.0000	6.0000	7.0000	14.0000	12.0000	14.0000	25.0000
Q 75	3.0000	4.0000	9.0000	7.0000	11.0000	16.0000	16.0000	18.0000	28.0000

SD: Standard deviation, WCS: Wire composite splint

Figure 3

Horizontal splint effect of different wire composite splint on injured tooth 11

Uninjured teeth

The postsplint PTVs of right lateral incisor and left central incisor (teeth 12 and 21) were within the DoL 0 irrespective of the wire used in the three study groups. There was no significant difference between the splint effect of different thicknesses of WCS used in three study groups for right lateral incisor (tooth 12). The 0.8 mm and 0.5 mm WCS produced significantly (P = 0.015) more splint effect than 0.3 mm WCS for left central incisor (tooth 21), only in Group III [Figure 4].

Figure 4

Horizontal splint effect of different wire composite splint on uninjured teeth (12 and 21)

DISCUSSION

LDIs are classified into concussion, subluxation, extrusion, lateral luxation, and intrusion, depending upon the nature and extent of the injury. Determination of optimal splint stability is essential to ensure favorable periodontal healing in a luxated tooth. As the degree of tooth mobility differs based on the severity of LDI, we suggest that it should be one of the determinants for splint selection.

Various experimental models have been employed in the literature for the evaluation of splint rigidity. Studies using sheep mandible,[11] human cadavers,[8] and healthy volunteers[12] had the advantage of using splint in teeth with natural PDL. However, the results of splint rigidity and splint effect on healthy uninjured teeth cannot represent the clinical scenario of increased mobility after luxation injury. Thus, various in vitro models with extracted teeth mounted in acrylic resin or irreversible hydrocolloid, resin teeth in typodont, stainless steel teeth in the aluminum base were developed to simulate an injured tooth.[113] In this study, the typodont model was used to assess the splint rigidity.[14] It is reported that the mobility of healthy incisors in adults has numeric values of 1–4 PTVs, which corresponds to DOL 0.[15] Therefore, the fastening mechanism of uninjured teeth was adjusted to obtain PTVs similar to physiologic mobility. The tooth mobility in an injured tooth can be simulated by partial unscrewing, removal of fastening mechanism, and enlargement of the socket.[11617] In the present study, all these methods were employed to achieve varying DoL in the LDI model. Teflon tape was used to simulate periodontal ligaments[10] because of its resiliency and ease of application over the root surface in contrast to autopolymerizing silicon used in previous studies.[18] Three coatings of 0.075 mm thick Teflon tape were used to reproduce the average dimensions of PDL.

Tooth mobility can be measured by static or dynamic methods.[19] Periotest is a dynamic method to measure the mobility of the tooth or implant based on the dampening characteristics of surrounding tissues (periodontal ligament or bone). It is an easy, reliable, reproducible, and objective method with high patient acceptability.[1120] It was proposed to be used as a diagnostic and prognostic device to assess the state of the periodontium of a traumatized tooth.[1521] The periotest reference range of tooth mobility given by manufacturers was utilized to simulate LDI models with varying DoL. Since there is no reference range of vertical PTVs available corresponding to DoL 0–3, only horizontal PTVs were studied for this experiment. The rigidity of composite wire splint is determined by adhesive point dimensions, thickness, and extension of wire.[82223] The aim of the experiment was to determine the optimum thickness of WCS required to reduce mobility within physiological limits based on preoperative mobility of the traumatized tooth. Hence, the adhesive point dimensions were kept constant, and the injured tooth was splinted with one adjacent tooth on both sides.

The thickness of wires (0.3 mm, 0.5 mm, and 0.8 mm) was the only variable tested for in WCS in each type of simulated injury. The study results reiterate the fact that splint rigidity increases with the thickness of WCS.[8] The thickness of 0.3 mm wire corresponds to the flexible splint (up to 0.4 mm) recommended for the management of luxation injuries.[7] However, the results of a clinical study to evaluate the effect of WCS on lateral tooth mobility of traumatized teeth reported that the clinically used splint was unable to restore the mobility of hypermobile teeth within the normal range.[24] Similar findings were observed in the present study where the use of 0.3 mm wire in WCS was insufficient to reduce the mobility of the tooth within physiologic limits. The application of 0.5 and 0.8 mm WCS was also unable to achieve the DoL 0 in Groups II and III Figure 2. These results contradict the observations from a cadaveric study that stainless steel wire with a diameter of 0.4 mm can be considered as a clinical threshold between flexible and rigid splint.[8] Since the experiment was performed after extraction and reimplantation of teeth in the cadaveric model to simulate only avulsion injury, the findings cannot be recommended for generalized use in various type of luxation injury.

The traumatic luxation injury can cause damage to the protective layers of the root, such as the precementum and predentine. It results in the formation of areas of necrosis to which the osteocytes are attracted and lead to bone deposition. Insufficient stabilization can cause secondary trauma, delay periodontal healing, and prolong the splint duration,[25] whereas complete immobilization increases the risk of root resorption and ankylosis. However, the stabilization of the teeth within physiologic limits allows controlled movement and induces functional stress or strain of low magnitude.[13] These functional stimuli can depress osteogenesis and enhance fibrous healing.[26] The masticatory stimulus promotes blood circulation, repopulation of fibroblasts in necrotic areas, and maturation of collagen fibers.[132728] These findings emphasize the need to use a splint that can provide optimal stability.

An ideal splint should stabilize an injured tooth but at the same time should not have a negative impact on the adjacent uninjured teeth. In the present study, no statistically significant difference was demonstrated in the mobility of uninjured teeth with the use of 0.3 mm, 0.5 mm and 0.8 mm WCS for Groups I and II. This finding was in concurrence with previous studies.[1724] However, a significant reduction in the postsplint mobility of the adjacent uninjured tooth (21) was also observed with the application of 0.5 mm and 0.8 mm WCS. It could be attributed to the excessive rigidity of these wires and suggests that a longer splinting duration with these WCS can have a detrimental effect on the teeth.

Based on the findings of this study, it can be interpreted that the postsplint DoL of a simulated injured tooth was influenced by both the presplint DoL and wire thickness in WCS. Hence, the null hypothesis of the study was rejected.

CONCLUSION

It can be concluded that the degree of tooth loosening after luxation injury should be considered before splint selection. Usage of a >0.4 mm wire in WCS can be suggested to stabilize the injured tooth with a higher degree of mobility. The use of the in vitro resin model is the limitation of the study as it cannot truly replicate the physioelastic behavior of supporting periodontal tissue. Further clinical studies are needed to validate the in vitro findings of the current study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.