A comparative evaluation of fracture resistance using different techniques for the reattachment of fractured maxillary central incisor – an <i>in vitro </i>study :Saini Rashmi, Saini V Kumar, Tanta Dental Journal

ORIGINAL ARTICLE
Year : 2022 | Volume : 19 | Issue : 3 | Page : 110--116

A comparative evaluation of fracture resistance using different techniques for the reattachment of fractured maxillary central incisor – an in vitro study

Saini Rashmi¹, Saini V Kumar²,
¹ Department of Conservative Dentistry and Endodontics, Sardar Patel Post Graduate Institute of Dental And Medical Sciences, Lucknow, Uttar Pradesh, India
² Department of Nuclear Medicine, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

Correspondence Address:
Saini Rashmi
BDS, MDS (Conservative Dentistry and Endodontics), MRA 92A, Block 12, SGPGI, Lucknow, Uttar Pradesh
India

Abstract

Objective To comparatively evaluate fracture resistance of different techniques for the reattachment of fractured maxillary central incisors. Materials and Methods Sixty intact freshly extracted permanent maxillary central incisors were selected and randomly divided into four groups of 15 each one of control (I) and three experimental groups (II, III, IV) according to the technique of reattachment. The incisal third of the experimental groups were sectioned horizontally. Group I: the teeth were kept intact without sectioning. Group II: an internal dentinal groove (1 mm deep and 1 mm wide). Group III: a pinhole (1.5 mm depth and 1.5 mm diameter). Fractured fragments in group II and group III were reattached using composite resin. Group IV: two vertical grooves (1 mm deep, 1 mm wide, and 4 mm length) with fiber-reinforced composite post (Everstick, GC America). After 24 h of restoration, all samples in each group were then subjected to thermocycling at 5±1 and 55±1°C for 500 cycles each cycle. All the samples were mounted on the universal testing machine (instron). The force was then applied at an angle of 45° of each tooth in a labial to palatal direction at a cross-head speed of 1 mm/min until fractured occurred and the obtained values were subjected to statistical analysis. Results The results showed that the mean fracture resistance of group I was the highest followed by group III, group IV, and group II the least (group II < group IV < group III < group I). Comparing the mean fracture resistance of four groups, analysis of variance showed significantly different fracture resistance among the groups (F = 22.93, P < 0.001). Conclusion No material and technique can restore the strength of intact tooth. However, reattachment techniques can be considered as an alternate method, when the fractured fragment is available with adequate size and appropriately preserved margins.

How to cite this article:
Rashmi S, Kumar SV. A comparative evaluation of fracture resistance using different techniques for the reattachment of fractured maxillary central incisor – an in vitro study.Tanta Dent J 2022;19:110-116

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Rashmi S, Kumar SV. A comparative evaluation of fracture resistance using different techniques for the reattachment of fractured maxillary central incisor – an in vitro study. Tanta Dent J [serial online] 2022 [cited 2023 Mar 29 ];19:110-116
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Full Text

Introduction

Traumatic injuries are the most difficult and perplexing problems in dentistry [1]. Dental traumas not only cause damage to the dentition, but also have a physical as well as psychological impact on the individual [2]. Children and teenagers are becoming more likely to sustain dental trauma as a result of contact sports, automobile accidents, outdoor sports, and falls [3]. Maxillary central incisors are frequently involved (95%) because of their protrusion and position taken during the eruptive process [4].

In traumatized teeth, uncomplicated crown fractures are most prevalent (51%), consisting of enamel and enamel-dentin fractures without pulp exposure. Numerous treatment modalities have been proposed for management of fractured crowns, such as resin crowns, stainless steel crowns, porcelain laminate veneers, porcelain fused to metal crowns, all ceramic crowns, and composite build-ups have been used with varying degrees of success [5]. While restorative materials can mimic natural dental structures, appearance, and function, no restorative material is able to replicate the natural structures, appearance, and function of the dental structure [6]. Thus, reattaching fractured tooth fragments is one valid conservative treatment option for anterior teeth in the present demanding situation [7]. Therefore, when a fractured fragment is available, immediate restorative treatment may be the best option [8].

It has been proposed that many techniques can be utilized for the reattachment of simple fragments, such as circumferential bevels, labial chamfers, internal dentinal grooves, v-shaped enamel notch, use of dental pins, circumferential or lingual composite overcontours, vertical groove technique, or bonding without additional preparation [8]. There are many factors that can affect the choice of reattachment technique, but studies have shown that new dental trauma or nonphysiological usage of the restored tooth is the leading cause of reattachment treatment failure [9]. Therefore, in search of increasing the longevity of treatment outcomes, newer materials and techniques were advocated that could improve the durability of the reattached tooth [2]. There is a lack of consensus on techniques for reattachment having better strength. Therefore, the present in-vitro study was formulated to evaluate and compare the fracture resistance of reattached teeth using three different techniques (internal dentinal groove, pin-holes, and vertical groove with fiber-reinforced post technique).

Materials and methods

Study samples consisted of 60 intact human maxillary central incisors freshly removed from the mouth for periodontal reasons. The teeth were cleaned and scaled thoroughly to remove hard and soft tissues remnants. Teeth were than autoclaved at a temperature 240°C at 20 psi for 40 min and stored in 0.9% normal saline till the experimentation.

Teeth were randomly divided into four groups (n = 15/group) according to the technique of reattachment.

Group I (control group): sound teeth.

Group II: internal dentinal groove.

Group III: pin-holes.

Group VI: vertical grooves with fiber-reinforced.

All the teeth in experimental groups (II, III, and IV) were marked at the junction of the incisal and middle third of the crown. Thereafter, a standardized sectioning was performed perpendicular to the long axis of the teeth using a diamond disc at 30 000 rpm to simulate an Ellis and Davey class II fracture (a fracture involving enamel and dentin) [Figure 1]a and [Figure 1]b.{Figure 1}

All the teeth in the control group (unsectioned or intact) and experimental groups were embedded into the molds (24 mm height × 24 mm width) using acrylic resin up to the cement–enamel junction such that the long axis of the tooth was aligned with the central axis of the block [Figure 1]c.

Reattachment procedure

Group I (control group)

In this group sectioning of tooth was not carried out and samples were left untreated without any further preparation.

Group II (internal dentinal groove)

Prior to performing the reattachment of a fractured fragment, an internal dentinal groove (1 mm deep and 1 mm wide) was prepared within the dentin of the fragment (obtained from previously done sectioning of teeth, as mentioned) 1 mm away from the dentino–enamel junction with a #2 carbide bur using a high-speed hand piece under a water cooling system [Figure 2]a.{Figure 2}

Group III (pin-holes)

In this group, prior to performing reattachment of a fractured fragment, a pinhole (1.5 mm in depth and 1.5 mm in diameter) was prepared bilaterally in the dentin of the tooth fragment, 1 mm away from the dentino–enamel junction using a #4 round carbide bur with a high speed hand piece under water cooling system.

The pin-holes were joined with shallow dentin grooves created with a #1 round carbide bur (diameter 0.8 mm) [Figure 2]b. The prepared fragment was measured by a periodontal probe (GDC, India). Thereafter, in samples of group II and group III, two coats of dentin bonding agent (3M ESPE, single bond universal, Germany) were applied on the fractured fragment and tooth remnant with the help of an applicator tip, which were gently air dried with the three way syringe and light cured (Elipar, 3M, USA) for 20 s.

After application of the bonding agent, a thin film of bulk-fill composite resin (Tetric N–Ceram, Ivaclar, Vivadent, Switerland) was applied on the fractured fragment and the tooth fragment by a Teflon-coated composite instrument, after which the fragment was repositioned on the tooth remnant under firm pressure and excess material was removed using the same instrument. After fragment repositioning, each mesial and distal half of the buccal and palatal surfaces were separately cured for 20 s according to the manufacturer's instructions. All samples were finished with Sof-Lex (3M ESPE, Germany).

Group IV (vertical grooves with fiber-reinforced post)

In this group, after the application of the adhesive system, a small layer of composite was applied on the fractured fragment and positioned correctly to the remaining tooth structure. Light curing was done, exactly as in group II and group III.

Two vertical grooves, each 1 mm deep, 1 mm wide, and 4 mm in length, were prepared on the palatal side perpendicular to the fracture line 2 mm away from the midline using a #2 round carbide bur with a high speed hand piece under water cooling system. From the total length (i.e. 4 mm) of each groove, half the groove (i.e. 2 mm) was placed in the reattached fragment and half the remaining tooth structure (i.e. 2 mm) in the remaining tooth structure [Figure 2]c. Thereafter, the adhesive system (3M, ESPE single bond universal, Germany) was applied within the prepared grooves and the fiber reinforced composite post (Everstick, GC America) of 0.9 mm in diameter was taken out of the foil bag, the required 4 mm length was cut from the silicon strip, and two posts were placed within the prepared grooves on the palatal side. Bulk-fill composite resin (Tetric N–Ceram, Ivaclar) was applied to fill the gap between the post and tooth surface, and light cured.

Thermocycling procedure

During the study period, the samples were stored in normal saline at room temperature to prevent dehydration. After 24 h of restoration, all the samples were subjected to thermocycling at 5±1 and 55±1°C for 500 cycles each, with a dwell time of 15 s between the baths in order to stimulate the conditions in the oral cavity.

Debonding procedure

The acrylic blocks containing samples were mounted on the universal testing machine (Instron, USA). The force was then applied at a 45° angle to each tooth in a labial-palatal direction with a stainless steel wedge with a tip size of 4 mm2 and a cross-head speed of 1 mm/min until fractured [Figure 3] and [Figure 4]. Thereafter, values were noted and the data was subjected to statistical analysis using analysis of variance (ANOVA), Tukey's honestly significant difference post-hoc test, Shapiro–Wilk's test, and Levene's test.{Figure 3}{Figure 4}

Statistical analysis

Data were summarized as mean ± SD. Groups were compared by one factor ANOVA and the significance of mean difference between (inter) the groups was done by Tukey's honestly significant difference post-hoc test after ascertaining normality by Shapiro–Wilk's test and homogeneity of variance between groups by Levene's test. A two-tailed (α=2). P value less than 0.05 was considered statistically significant.

Results

The outcome measure of the study was fracture resistance assessed in force and measured in Newton (N). The fracture resistance (N) of four groups is summarized in [Table 1] and also depicted in [Graph 1] which showed that the mean fracture resistance of group I were the highest, followed by group III, group IV, and group II the least (group II, group IV, group III, group I).[INLINE:1]{Table 1}

Comparing the mean fracture resistance of four groups, ANOVA showed significantly different fracture resistance among the groups (F = 22.93, P < 0.001) [Table 2].{Table 2}

Tukey test showed significantly different and higher fracture resistance of group I as compared to both group II (304.98 ± 34.03 vs. 205.14 ± 22.50, mean diff = 99.84, q = 10.70, P < 0.001) and group IV (304.98 ± 34.03 vs. 246.05 ± 38.73, mean diff = 58.93, q = 6.31, P < 0.001) but not differ with group III (304.98 ± 34.03 vs. 287.73 ± 45.43, mean diff = 17.24, q = 1.85, P > 0.05) that is found to be statistically the same [Table 2] and [Graph 2].[INLINE:2]

Similarly, further, comparing the difference in mean fracture resistance of group II with other groups (group III and group IV), Tukey test showed significantly different and higher fracture resistance of both group III (205.14 ± 22.50 vs. 287.73 ± 45.43, mean diff = 82.60, q = 8.85, P < 0.001) and group IV (205.14 ± 22.50 vs. 246.05 ± 38.73, mean diff = 40.91, q = 4.38, P < 0.05) as compared to group II [Table 2] and [Graph 3].[INLINE:3]

Further, comparing the difference in mean fracture resistance of group III with group IV, Tukey test showed significantly different and higher fracture resistance of group III as compared to group IV (287.73 ± 45.43 vs. 246.05 ± 38.73, mean diff = 41.69, q = 4.47, P < 0.05) [Table 2] and [Graph 4].[INLINE:4]

Discussion

The major objective of restorative dentistry is to restore teeth in a way that allows conservation of healthy dental tissues, esthetics, function, and durability. Uncomplicated coronal fractures are most common among children and teenagers, resulting from accidental trauma or sports injuries [10]. When the fractured fragment is still available, repositioning and bonding it immediately to the tooth remains is the first restorative immediate treatment option that should be performed [11].

In this present study, only maxillary central incisors were included because there are a greater number of incidences of trauma/fracture to these teeth [4]. In the current study, the teeth were sectioned in a standardized manner with a mounted disc, as the aim was to compare reattachment techniques. In an attempt to obtain an equal amount of area for adhesion, all of the teeth were cut at the junction of the middle and incisal third of the crown. Sushma et al.[12] reported that using a disc results in a smooth surface and allows standardization of the mode of 'fracture,' which is an advantage as the number of defects in the adhesive interface results in a better approximation between the fractured tooth and the cut tooth surface. Thereafter, teeth were embedded in acrylic resin blocks to simulate the support given to healthy teeth by the alveolar bone and to reduce stresses caused by unrealistic bending movements [2],[13].

So the amount of dentin removed in the internal dentin groove group was standardized using a # 2 round carbide bur with a diameter of 1 mm. A standard depth of 1 mm of dentin was removed for the dentinal groove using the same bur for the entire group. Similarly, in pin-holes technique #4, a round carbide bur was used for the preparations, which had a diameter of 2 mm.

In this study, the thermocycling procedure was carried out at 5 and 55° for 500 cycles with a 15 s dwell time between each cycle to simulate short-term ageing of dental material [14],[15]. After the reattachment procedures, the samples were subjected to the universal testing machine for the evaluation of their fracture resistance. The cross-head speed used to fracture the specimens in this study was 1 mm/min, as recommended by the ISO standard (ISO/TS 11405:2003-Dental Materials-Testing of adhesion to tooth structure). The force was applied in a labial to lingual direction because 80% of traumatized incisors fracture in an oblique fashion from labial to lingual aspects with the fracture line proceeding in an apical direction. Here, the compressive load was applied to the incisal third of teeth at 45° using a universal strength testing machine to simulate impact from a fall [12],[14],[16].

In the current study, the control sound group had the highest fracture strength followed by pin-holes, vertical grooves with fiber-reinforced post, and internal dentinal groove, and the difference was significant. The fracture load values obtained for group I (intact teeth) were the highest amongst all the tested groups. The reason for this high fracture resistance may be the higher mechanical strength of sound or intact teeth [17],[18]. The results of this study are in accordance with many studies like Demarco et al. [19] and Sushma et al. [12] who confirmed that no material or technique was able to attain the fracture strength of sound natural teeth.

In this study, group II (internal dentinal groove technique) showed the least fracture resistance among all the tested groups. This could be due to the fracture resistance of the reattached teeth being directly proportional to the surface area of adhesion [18]. Therefore, the lower values of group II might be due to the presence of a lower surface area for adhesion. Similar values were reported by Karre et al. [20] and Beltagy [21].

According to this study, group III (pin-holes technique) showed the highest fracture resistance among the experimental groups. This may be due to the two vertical slots on both (mesial and distal) sides with a horizontal channel were created on fractured fragments in the pinhole design. This channel filled with composite acts as a horizontal resin bar and two vertical resin slots provide additional retention, both opposing to each other, resulting in the distribution of load to a larger area [22]. Thus, the increase in surface area of adhesion in this group enhances the retention and distribution of forces, resulting in increased fracture resistance [20],[23]. Therefore, the greater surface area is present for adhesion in group III, which provides additional retention and better resistance against the applied forces, and here nearly similar higher values of fracture resistance were noted, which was in accordance with the previous study done by Beltagy [21] using the internal dentinal groove, pin-holes techniques for reattachment.

Results of group IV showed higher fracture load values than group II. The reason for this fracture resistance may be that the reinforcing glass fibers present in the everstick post cause stress transfer from the matrix to the fibers, which act as stress absorbers and prevent the crack propagation [24],[25]. The results of fracture load obtained in this group were in accordance with the study conducted by Karre et al. [20] But lower than group III may be due to the additional stress introduced by the preparation of the vertical groove for the placement of fiber-reinforced composite post in the fracture segment line [26],[27].

In the modern era of evidence, re-fixation procedures have proven beneficial in patients with clinical crown fractures due to alveolar damage. Reattaching the fragment can provide a great, durable esthetic appearance. This is a more conservative and simple procedure that also restores dental function. Reattaching the tooth fragment allows the tooth to be restored with minimal damage to the rest of the tooth structure. Therefore, it is preferable to reattach a tooth fragment rather than to restore a broken tooth. This is an extensive and widely used procedure.

Conclusion

Within the limitations of this in vitro study, it can be concluded that tooth preparations and different techniques for reattachment have an influence on the fracture resistance of teeth. However, no reattachment technique or material was able to achieve the strength of an intact tooth.

In addition to restoring tooth function, esthetics and requiring less time in the dental office, reattachment of fractured tooth fragments is an excellent restorative option for both clinicians and patients. Therefore, reattachment techniques can be considered as an alternate method when the fractured fragment is available.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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