Fracture resistance of reattached fragments using three different techniques with emphasis on vertical grooves and fiber-reinforced composite post: A novel technique.

BACKGROUND: The aim of this study was to evaluate and compare relatively less explored fragment reattachment methods following traumatic injury.
MATERIALS AND METHODS: Eighty sound permanent maxillary incisors were selected and mounted in acrylic blocks. Teeth were sectioned using the diamond disc and randomly divided into 4 groups (n = 20), Group A, B, C, D. In Group A, after reattachment with composite, a 1 mm-depth circumferential chamfer was placed in the fracture line using a diamond disc bur and filled with composite. In Group B, two vertical grooves 1 mm deep, 1 mm wide, and 4 mm length were placed on the labial surface perpendicular to the fracture line and filled with two fiber-reinforced composite (FRC) posts and composite. In Group C, dentin is removed from the fragment and filled with composite. In Group D, the teeth were intact which served as control group. The force required to fracture the reattached teeth were recorded in Newton's using an onscreen calibration tool of the universal testing machine.
RESULTS: Teeth in Groups A, B, C required lesser force to fracture when compared with the teeth of the Group D. When compared to Group D, Group A showed a fracture resistance of 36%, Group B 62%, and Group C 32%.
CONCLUSION: This study proves that reattachment by vertical grooves with FRC posts showed highest fracture resistance and it is the most preferred method. So far no attempt has been made to reattach fractured fragment using vertical grooves and reinforcing with FRC posts.

INTRODUCTION

One of the most difficult and perplexing problems faced in the pediatric dentistry is injuries to the anterior teeth. The functional and esthetic disturbances that accompany such injuries necessitates that these should be treated without delay.[1] Large number of techniques has been employed to treat coronal fractures which include crowns of pure steel, orthodontic bands, resin held by pins, and porcelain crowns.[2] When the fractured fragment is intact, with adequate and correctly preserved margins fragment reattachment is the first choice of treatment as it is simple, cost-effective, and esthetic.[34]

Apart from the material used, the design of preparation also governs the fracture strength of the reattached tooth.[5] Many operative procedures have been suggested, from no additional tooth preparation to circumferential bevel, internal dentin groove, external over contour, and superficial over contour of composite on the fracture line.[67]

A thorough literature search by the authors did not reveal any study which used a fiber-reinforced composite (FRC) post, in grooves on the exterior surface of the tooth, to reattach a fractured tooth fragment. Hence, a study was conducted with the aim of comparing this method with a few other methods such as placing a chamfer and internal dentine groove.

MATERIALS AND METHODS

Eighty permanent maxillary incisors, extracted because of periodontal reasons, were collected for this study. Teeth were cleaned from adherent tissue using a sickle scaler and stored in normal saline (0.9%) at room temperature till the beginning of the experiment. All teeth were randomly distributed into 4 groups (n = 20); Group A, B, C, D.

Standardized aluminum jigs were taken and teeth were embedded in each jig using self-cure acrylic. All teeth were embedded in the center of acrylic till the level of cementoenamel junction and parallel to long axis of aluminum jig.

Of the 80 teeth, 20 teeth were kept as a control that is Group D. These were stored in normal saline. For the three groups where the fragment was to be reattached, a standardized section through the middle third of the crown was done using a diamond disk to simulate an Ellis and Davey Class II fracture. Only 33 teeth out of 60 could be neatly sectioned into two pieces. Hence, they were included in 3 groups, each with 11 teeth.

The detailed procedures of fragment reattachment for each group are described below:

Group A

Tooth fragments and remaining tooth structures were etched using 37% phosphoric acid gel for 15 s. Etchant was washed and air dried for 20 s. A 5th generation adhesive system (Prime and Bond NT, Dentsply, CAULK) was applied on remaining tooth structure and light cured for 20 s.

Dental composite (A3 shade Tetric Dental Hybrid Composite Ivoclar Vivadent Inc.,) was applied on the fractured surfaces, and the fragment was positioned correctly (direct bonding). Light curing was done in four stages: 20 s mesial buccal half, 20 s distal buccal half, 20 s mesial lingual half, and 20 s distal lingual half using light curing unit (Optilux 400 set at 450 Mw cm2).

Then, a 1 mm-deep circumferential chamfer was placed on the fracture line using a diamond bur with a depth marker. The chamfer was restored using the same composite [Figure 1A].

Figure 1

Different methods of reattachment (A) circumferential chamfer technique (B) vertical grooves with fiber reinforced composite post technique (C) internal dentin groove technique

Group B

In this group, after etching and application of adhesive system, a small layer of composite was applied to the fractured area of tooth. Tooth fragment was positioned correctly, excess material was removed from labial and lingual surfaces, and light curing was done, exactly as in Group A.

Then two vertical grooves, each 1 mm deep, 1 mm wide, and 4 mm in length were placed on the labial surface perpendicular to the fracture line using a high-speed depth orientation diamond bur. Then acid etching of these grooves was done and adhesive was applied, FRC posts (No. 0., Quartz, [VIVA] of 4 mm were made by sectioning a longer FRC post with a diamond disc. Two posts on the labial surface were placed in the grooves. Dental composite was applied to fill the gap between the FRC post and tooth surface and light cured [Figure 1B].

Group C

Complete removal of the dentinal portion from the fragment was done using a high-speed aerator diamond disc bur. Etching and adhesive application was done. The area where dentin was removed was filled with A3 shade dental composite and curing was done [Figure 1C].

Group D

This was the control group. The teeth were not sectioned.

The acrylic blocks containing all specimens (n = 53) were mounted in the universal testing machine (Instron). The load was applied to each tooth in a labial to lingual direction by means of a reinforced stainless-steel wedge at a speed of 1 mm/min. The force required to fracture the tooth was recorded in Newtons (N) using an onscreen calibration tool.

Fractured surfaces of all the teeth were photographed using a digital camera Canon 550D with EF-S 60 mm macro lens and flash MR-14EX at 1:1 magnification. The surface area of the fractured surface of crowns, embedded in the blocks, was measured using AutoCAD software in mm2. The pressure required to fracture teeth was calculated dividing the Force (N) by area of the fractured surface (mm2). The results were tabulated into Microsoft Excel sheet and subjected to statistical analysis (SPSS - Statistical Package for the Social Sciences UNICOM Systems, Inc).

RESULTS

For the statistical analysis of the data one-way ANOVA followed by Tukey's multiple post hoc tests was used. All the teeth in Groups A, B, C required lesser force to fracture when compared with the teeth of the Group D. The force necessary to fracture the teeth in Group A and Group C was significantly inferior to the force necessary to fracture the teeth in Group D (P < 0.05), but not when compared with Group B (P = 0.159) [Table 1]. The statistical analysis showed no significant difference between force needed to fracture the teeth in Group B and Group D [Table 2]. Comparison of four groups with respect to force, surface area, and pressure is shown in [Graphs 1ߝ3].

Table 1

Comparison of four groups A, B, C, D with respect to force (n) scores by one way ANOVA

Table 2

Pair wise comparison of four groups A, B, C, D with respect to force (n) scores by Tukeys multiple post-hoc procedures

Graph 1

Comparison of four Groups A, B, C, D with respect to force (n) scores

Graph 3

Comparison of four Groups A, B, C, D with respect to pressure (n/mm2) scores

Comparison of four Groups A, B, C, D with respect to surface area (mm2) scores

DISCUSSION

In our study, only maxillary incisors were included because the incidence of trauma is more in these teeth.[89]

Various methods of obtaining tooth fragment are placing small notches on two proximal surfaces, fracturing the teeth using narrow forceps or a blunt instrument without making notches. Badami and Reis have shown that the surface of a sectioned tooth is different from a naturally occurring fractured one, as the fracture produces fragments with a good fitting.[10] In this study, the teeth were cut in a standardized manner with a mounted disc. The cut was made in the middle third of the crown so as to enable better handling of the tooth fragment during reattachment. Using a disc results in smooth surfaces, which is an advantage as the number of defects in the adhesive interface is lower and allows to standardize the mode of “fracture” that would have been otherwise random.[10]

Therefore, in this study, the approximation between the tooth and the fragment was not perfect and sometimes even presented a small gap. Hence, the results obtained in this study would be an underestimation of what could be achieved clinically using these techniques. A limitation or drawback of this study is that if the teeth were fractured with a narrow forceps, following small notches, there could be thinning out of tooth at different levels and it would be more clinically applicable.

If the approximation was accurate, vertical grooves with FRC posts in Group B would have shown more strength.

Amount of dentin removed in the circumferential chamfer and internal dentin groove groups were standardized using a diamond disc bur of diameter 4mm Figure 1A, 1B. A standard depth of 1 mm dentin was removed for chamfer and dentinal groove using the same bur thereby reducing the operative error. The bur was inserted sideways till its full depth of 1 mm[Figure 3].

Figure 3

Diagram of the bur used to make standard size of grooves

After fragment reattachment teeth were fractured using universal testing machine. The force was applied at standardized speed of 1 mm/min by a stainless steel wedge. This standardized speed was in accordance with a study done by Farik and Munksgaard who stated that fracture strength of intact and fragment bonded teeth tend to decrease when high crosshead speeds were employed.[11]

The results of this study are in accordance with many studies like Demarco et al., who confirmed that no material and technique was able to attain the fracture strength of the sound natural teeth.[12] According to Davis et al., the enamel margins of tooth and fragment were beveled circumferentially before reattaching the fragment to obtain a better retention and enhancement of the finishing line with resin composite. Its placement altered the enamel prism orientation, allowing more effective enamel acid etch. However, this technique required additional enamel preparation, and in certain cases, the precise fit between segments was lost, which made the correct positioning of the fragment more difficult. As the precise, fit was affected in the bevel technique, in our study, we opted for circumferential chamfer technique in the fracture line.[13]

In Group C, dentin was removed from the fragment as part of the bonding preparation. The placement of internal dentin groove in the tooth fragment is suggested as it provides space for resin composite thus reinforcing bonding. According to Diangelis and Jungbluth complete dentin removal from the fragment before bonding increases the bond strength and prevents the eventual darkening of the devitalized dentin fragment.14 In cases of thin friable fragments, this method of internal dentine removal is not done since the fragment itself may disintegrate while attempting this.

Group B presented a resistance against fracture almost equal to 62% of the whole tooth. This could be attributed to the reinforcement of adhesion by the placement of fiber-reinforced posts in the region of the fracture line. This method could be clinically effective, as the value of resistance against fracture was almost equal to control group and a more conservative preparation of the coronal buccal surface was achieved. When the failure occurred, it most frequently involved adhesive type of fracture involving resin enamel interface and a cohesive type fracture within the body of resin. However, there was no fracture within vertical posts. Even though when high amount of force was applied it caused the fracture of reattached fragment leaving the posts intact [Figure 2]. Esthetically, the shade of the dental composite, which is used to fill the gap between the FRC post and the tooth surface, can be matched with the tooth color and a little more composite can be added on top to mask the FRC post. The color of the FRC post is translucent. We, however, did not attempt this in our study as we used only a single tube of composite for the entire study.

Figure 2

Fractured tooth showing fragment with posts intact

Since self-threaded pins are hazardous to pulpal health and in many cases, result in direct esthetic failure of the restoration, fiber-reinforced posts were used in our study.[15]

Surface area calculated showed that teeth of Group D have least surface area followed by Group C and Group B. Maximum surface area was calculated in Group A. The least surface area calculated in the Group D can be attributed to the fact that amount of force applied to teeth was consumed in the formation of cracks apart from fracturing teeth into fragments. As the area calculated was only the fractured surface, the area available in the Group D would be an underestimation.

Group D required highest pressure to fracture the teeth followed by Group B and Group A. Least pressure was required for the teeth of Group C. As the pressure is calculated by the formula, force per unit area, the value shown in control (Group D) could be an overestimated result. This is because surface area of Group D calculated was an underestimated value.

Fracture strength of fragment reattached teeth is mainly determined by reattachment technique. Vertical grooves with posts have a positive effect on the fracture strength. Fragment reattached with this technique could approximate the fracture strength of about 62% of that achieved by sound teeth. The circumferential chamfer technique and the internal dentin groove technique were able to guarantee a resistance of the restoration equal to at least 36% and 32% of that of a whole tooth. Among the various latest techniques and materials used for the fragment reattachment, our study which included vertical grooves with FRC posts has a definitive place in dentistry.

CONCLUSION

The reattachment of fractured tooth fragments offers an excellent restorative option for clinicians and patients because it restores tooth function, esthetics, requires less time in the dental office, and represents a cost-effective approach. Among the various techniques and materials used for the fragment reattachment, our study which included vertical grooves with fiber-reinforced composite posts shows the highest fracture resistance. This can be considered as an alternate method of reattachment when the fragment is intact, with adequate size and appropriately preserved margins.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.