Fracture resistance of fragmented incisal edges restored with fiber-reinforced composite

PURPOSE: The aim of this study was to determine the static load-bearing capacity of fractured incisors restored with the conventional adhesive-composite technique or by using fiber-reinforced composites (FRC). MATERIALS AND METHODS: Twelve extracted sound maxillary incisors per group were prepared by cutting the incisal (one-third) part of the crown horizontally. Restorations were made using three techniques. Group A (control group) was restored by reattaching the original incisal edge to the tooth. Group B was restored using particulate filler composite (PFC). Group C was restored with PFC and FRC by adding a thin layer of FRC on the palatal surface of tooth. The bonding system used was the conventional etch system with primer and adhesive. All restored teeth were stored in water at room temperature for 24 h before they were statically loaded until fracture in a universal testing machine. Data were analyzed using ANOVA (p = 0.05). Failure modes were visually examined. RESULTS: Group A (reattaching fractured incisal edge) revealed the lowest load-bearing values, whereas preparation of the new incisal part with PFC revealed 148% higher load-bearing values compared to Group A. Group C (teeth restored with FRC) revealed a 254% higher load-bearing capacity than the control group. ANOVA revealed that the restoration technique significantly affected load-bearing capacity (p < 0.001). The failure mode in Groups A and B was debonding of the restoration from the adhesive interface, while in group C, 50% of the teeth fractured below the cementoenamel junction. CONCLUSION: These results suggest that an incisally fractured tooth restored with a combination of PFC and FRC provide the highest load-bearing capacity.     

Fatigue strength of fragmented incisal edges restored with a fiber reinforced restorative material

AIM: The aim of this study was to determine the compressive fatigue limits (CFLs) of fractured incisor teeth restored using either a conventional adhesive-composite technique or using fiber-reinforced composites (FRCs). METHODS AND MATERIALS: Fifteen extracted sound upper incisor teeth were prepared by cutting away the incisal one-third part of their crowns horizontally. The teeth were restored using three techniques. Group A (control group) was restored by reattaching the original incisal edge to the tooth. Group B was restored using particulate filler composite (PFC). Group C was restored with PFC and FRC by adding a thin layer of FRC to the palatal surface of the teeth. The bonding system used was a conventional etch system with primer and adhesive. All restored teeth were stored in water at room temperature for 24 h before they were loaded under a cyclic load with a maximum controlled regimen using a universal testing machine. The test employed a staircase approach with a maximum of 103 cycles or until failure occurred. Data were analyzed using analysis of variance (ANOVA) (p=0.05). Failure modes were visually examined. RESULTS: Group A (reattaching fractured incisal edge) revealed the lowest CFL values, whereas the creation of a new incisal edge with PFC revealed a 152% higher CFL value compared to Group A. Group C (teeth restored with FRC) revealed a 352% higher CFL than the control group. ANOVA revealed the restoration technique significantly affected the compressive fatigue limit (p<0.001). The failure mode in Group A and B was debonding of the restoration from the adhesive interface. While in Group C, the sample teeth fractured below their cemento-enamel junctions. CONCLUSION: These results suggested an incisally fractured tooth restored with the combination of PFC and FRC-structure provided the highest CFL.     

纳米树脂直接修复离体切牙切角缺损后整体抗折性能的体外实验研究

目的：：检测纳米树脂直接修复离体切牙切角缺损后牙齿的整体抗折性能。方法：搜集30颗完整离体中切牙,分为A、B、C 3组,每组10颗。 A、B 2组为实验组,对实验组离体切牙用磨除法制备近中切角缺损模型。对缺损模型进行根管治疗及牙体预备,2组皆预备唇侧贴面及舌侧鸠尾,对A组切缘进行2 mm磨除。用纳米树脂对2组牙齿进行分层分色直接充填修复,完成抗折试件的制备。 C组作为对照组,不进行任何处理。冷热循环2000次试验后以万能材料试验机检测试件的断裂载荷,观察断裂模式,将3组结果进行对比。结果：A,B,C 3组的平均断裂载荷分别为(466.93±171.68) N,(444.5±173.00) N及(474.77±97.55) N(P>0.05)。30个试件中,仅对照组中发生1个不利断裂。结论：纳米树脂直接修复离体切牙切角缺损后与天然牙的抗折性能相近,断裂模式皆为有利断裂。切端磨除不影响整体抗折性能。     

Influence of cavosurface configuration and composite resin type on impact fracture resistance of Class IV restorations

The fracture behaviours of intact maxillary central incisor teeth, and teeth restored by five different composite resins utilising uninstrumented fractured etched margins and bevelled etched margins, were determined by a pendulum impact method. It was established that: 1. Intact teeth fractured in a predictable manner when struck by a pendulum hammer at predetermined points on the labial surfaces close to incisal angles. 2. The impact resistance of teeth with bevelled margin restorations was significantly greater than that of teeth restored using the uninstrumented fractured margins. 3. Differences in impact resistance between intact teeth and teeth restored with bevelled margins were not significant. 4. There was no significant difference in fracture energy between any of the composite resin materials in either the uninstrumented joint or bevelled joint modes. 5. For all restorations placed on uninstrumented margins, the fracture paths were at or near the adhesive interface; no restorations failed cohesively. 6. Fracture paths in the bevelled joint mode were variable, with fracture occurring either entirely in enamel, or entirely in composite resin, or at the interface.     

In vitro fracture resistance of fiber reinforced cusp-replacing composite restorations.

OBJECTIVES: To assess the fracture resistance and failure mode of fiber reinforced composite (FRC) cusp-replacing restorations in premolars. METHODS: Forty-five extracted sound upper premolars were randomly divided into three groups. Identical MOD cavities with simulated buccal cusp fracture and height reduction of the palatal cusp were prepared. In Group A two layers of resin impregnated woven continuous FRC (EverStick Net) were applied. In Group B one layer of unidirectional continuous FRC (EverStick) was used. In Group C no fibers were applied (control). Subsequently, all teeth were restored with resin composite (Clearfil Photo Posterior), subjected to thermocycling (6000 x 5-55 degrees C) and static load tests. Load until fracture was registered for each tooth. Simultaneously, fracture propagation was monitored using acoustic emission analysis (AE). Failure modes were visually assessed. RESULTS: Weibull analysis revealed a characteristic strength and Weibull modulus (m) at 2364.8 N for Group A (m=8.9), 2437.9 N for Group B (m=5.9) and 2160.3N for Group C (m=13.6). Fracture loads were not significantly different (ANOVA, p>0.05). Teeth with FRC showed less fractures below the cemento-enamel junction (CEJ) (38% and 23% for Groups A and B, respectively) than teeth without FRC (93%) (chi-square, p<0.05). The control group showed the least AE energy signals. SIGNIFICANCE: The results suggest that glass FRC does not increase fracture load of premolars with cusp-replacing restorations. However, FRC has a beneficial effect on the failure mode. Woven fibers give more consistent results than unidirectional fibers.     

Evaluation of tooth‐fragment reattachment: a clinical and laboratory study

Abstract – Purpose: To evaluate the restoration of fractured teeth by reattaching tooth fragment to its tooth remnant in a group of children and adolescents, and to compare the results with those of a laboratory study. Materials and Methods: The clinical study was conducted on 43 fractured incisors: 22 uncomplicated crown fractures (Group A) and 21 complicated crown fractures (Group B). The 43 incisal fragments: 23 were kept dry for 47 h and 20 were kept wet for 24 h by the patients before they were reattached. The fragments were kept in 0.9% saline solution for 30 min before reattachment. The fragments in Group A were reattached using a dentin bonding agent, a flowable and a hybrid resin composite, whereas the fragments in Group B were reattached to the tooth remnant after a pulpotomy was performed. The laboratory study was conducted on 56 extracted incisors. Teeth were divided equally into four groups: Group I – Uncomplicated crown fracture + wet medium; Group II – Uncomplicated crown fracture + dry medium; Group III – Complicated crown fracture + wet medium, and Group IV – Complicated crown fracture + dry medium. The fragments were then reattached in a manner that was similar to that used in the clinical study. The restored teeth were then re‐fractured. All data were analyzed statistically. Results:  In the clinical study, the restored teeth were followed up for 2 years. Neither the type of trauma nor the storage medium had any significant effect on the survival, color, and bond strength of the restored teeth when assessed in the clinical and laboratory study. The color disharmony that was encountered initially in restored teeth resolved significantly on its own accord within 12 months after reattachment of the fragment. Conclusion:  Fragment reattachment can be used to treat fractured teeth successfully in children and adolescents.     

Evaluation of success in the reattachment of coronal fractures

Abstract –  The aim of this study was to evaluate clinically and radiographically the restored teeth using reattachment technique of fractured fragment to the remaining tooth. This study was conducted on 11 children (six girls and five boys; age range: 8–13 years). Before the treatment, the teeth were evaluated clinically and radiographically. The broken incisal part was directly reattached to the remaining tooth part with flowable resin composite. Thereafter, with the purpose of obtaining optimal esthetics and function, along the fracture line an external 'double chamfer' in the shape of a V was created and then covered with resin composite. During the follow-up (1–24 months) after the treatment, the teeth were evaluated clinically and/or radiographically with regard to periodontal, pulpal, coronal, color harmony of the fragments, and occlusion. In addition, the restored teeth were assessed in terms of parental–patient ratings of satisfaction. Both clinically and radiographically, no pathology was reported and all the restorations were successful. Moreover, the mean scores of parental–patient satisfaction were reported as 'satisfied, very-satisfied.'     

Treatment of crown fractured incisors with laminate veneer restorations. An experimental study.

A method is described by which crown fractured incisors are restored with cast ceramic (Dicor) laminate veneers after initial treatment with either reattachment of the original crown fragment with a dentin bonding agent, with a composite resin build-up or no treatment (i.e. the veneer alone is used to restore the incisal edge). In order to elucidate the effect of the fragment/composite-tooth bonding interface on fracture strength of the restored teeth, the fracture strengths of the various treatment groups were compared to that of intact teeth supplied with Dicor laminate veneers. In an experimental investigation using central and lateral incisors from sheep, it was found that fracture strength (16.6 +/- 4.2 MPa) equal to that of intact incisors (16.1 +/- 2.6 MPa) could be achieved using laminate veneers made of porcelain on fractured teeth whose crown fragments were reattached using a dentin bonding agent (5). In the present investigation, using the same experimental model but using cast ceramic (Dicor) laminate veneers, the fracture strength of the restored incisors was significantly increased (21.0 +/- 3.7 MPa), exceeding that of intact teeth. The fracture strength of intact teeth was also exceeded in veneered incisors which were initially restored with a conventional composite resin build-up (20.2 +/- 5.6 MPa). However, the greatest fracture strength (28.2 +/- 8.9 MPa) was achieved when a Dicor laminate veneer alone was used to restore the fractured incisal edge.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of thickness of flowable resins on marginal leakage in class II composite restorations

Despite limited scientific evaluation, there is an increased use of low elastic modulus flowable resin composite (FRC) as a stress-relieving gingival increment in Class II restorations. This study compared marginal leakage in preparations with gingival margins in enamel or dentin/cementum (sub-CEJ and supra-CEJ) after FRC was used as a gingival increment to hybrid resin composite used alone. In addition, the extent of leakage around restorations with or without the use of FRC gingival increments when light curing the resin composites from occlusal direction only or buccal, lingual and occlusal directions was compared. Sixty extracted human molars were prepared with two identical Class II (MO and OD) preparations (30 were 1 mm sub-CEJ and 30 were 1 mm supra-CEJ) and randomly assigned to six groups. After etching, dentin-bonding agent was applied to all prepared tooth surfaces according to the manufacturer's specifications. One of three different thicknesses of FRC (0.5 mm, 1 mm or 2 mm) was placed on the gingival floor, cured and a hybrid resin composite was placed occlusally to complete the restoration. The control preparation on each tooth was restored in the same manner, except that a hybrid resin composite was used for both the gingival and occlusal increments. The restored teeth were thermocycled (300 cycles), then immersed in 50% silver nitrate prior to the hemi-section and measured for leakage under a light microscope. The data were evaluated using paired measures analysis of variance (ANOVA). Most of the occlusal margins showed no leakage, while almost every gingival margin demonstrated some silver nitrate penetration regardless of whether it was located sub or supra-CEJ, although significantly less leakage was found in restorations with supra-CEJ margins (p=0.0001). Among supra-CEJ restorations, there was a pronounced reduction in leakage as FRC thickness increased (p=0.0005). In the teeth restored with the gingival-margin located supra-CEJ, the 2 mm thickness FRC gingival increment showed significantly less leakage (p<0.01) compared with the 0.5 mm thickness of FRC gingival increment. The direction of the curing light did not affect the extent of leakage (p>0.05). The use of FRC material as a gingival increment sub-CEJ in posterior hybrid resin restorations produced no significant difference in leakage (p>0.05). The results of this study indicated that restorations located supra-CEJ (with gingival margins in enamel) with 2 mm thick FRC gingival increments demonstrated significantly less leakage than did those with 0.5 mm FRC. When the margin of the restoration was located sub-CEJ (in dentin/cementum), neither the thickness nor the presence of FRC as a gingival increment significantly influenced the marginal leakage.     

Direct restoration of severely damaged incisors using short fiber-reinforced composite resin

OBJECTIVES: The aim of this in vitro study was to evaluate the static load-bearing capacity and the failure mode of endodontically treated maxillary incisors restored with complete crowns made of experimental composite resin (FC) with short fiber fillers, with and without root canal posts. Further aim was to evaluate the effect of fiber-reinforced composite resin (FRC) on the failure mode of the restoration. MATERIAL AND METHODS: The experimental composite resin (FC) was prepared by mixing 22.5 wt.% of short E-glass fibers (3mm in length) and 22.5 wt.% of semi-interpenetrating polymer network (IPN) resin with 55 wt.% of silane treated silica fillers. The clinical crowns of 30 human extracted maxillary incisors were sectioned at the cemento-enamel junction. Five groups of direct complete crowns were fabricated (n=6); Group A: made from particulate filler composite resin (PFC) (Grandio Caps, VOCO, control), Group B: PFC with fiber post (everStick, StickTeck), Group C: made from PFC with everStick fiber post and FRC-substructure, Group D: made from FC, Group E: made from FC with FRC-substructure. The root canals were prepared and posts were cemented with resin cement (ParaCem Universal). All restored teeth were stored in water at room temperature for 24h before they were statically loaded with speed of 1.0 mm/min until fracture. Data were analyzed using ANOVA (p=0.05). Failure modes were visually examined. RESULTS: ANOVA revealed that restorations made from experimental fiber composite resin had higher load-bearing capacity (349N) (p<0.05) than the control restorations (173N). No significant difference was found in load-bearing capacity between restorations reinforced with FRC-substructure and those without (p>0.05). CONCLUSIONS: Restorations made from short glass fiber containing composite resin with IPN-polymer matrix showed better load-bearing capacity than those made with either plain PFC or PFC reinforced with fiber post.     

Fracture resistance of composite resin restorations and porcelain veneers in relation to residual tooth structure in fractured incisors

Abstract – The aim of the present study was to investigate whether there is a direct correlation between the amount of residual tooth structure in a fractured maxillary incisor and the fracture resistance of composite resin restorations or porcelain veneers after cyclic loading. Sixty human‐extracted maxillary central and lateral incisors were mounted in an acrylic block with the coronal aspect of the tooth protruding from the block surface. The teeth were assigned to two groups: 2‐mm incisal fracture and 4‐mm incisal fracture. Then, the teeth were further divided into two different restoration subgroups, porcelain laminate veneer and composite resin restoration, therefore obtaining four groups for the study (n = 15). The specimens were subjected to 1000 cycles of thermocycling and were mechanically tested with a custom‐designed cyclic loading apparatus for 2 × 106 cycles or until they failed. The specimens that survived the cyclic loading were loaded on the incisal edge along the long axis of the tooth with a flat stainless steel applicator until they fractured using a universal testing machine to measure the failure load. Two‐way anova was used to assess the significance of restoration, amount of fracture, and interaction effect (α = 0.05). During the cyclic loading, for the composite resin group, two specimens with 2‐mm fracture and three specimens with 4‐mm fracture failed. For the porcelain veneer group, two specimens with 2‐mm fracture and one specimen with 4‐mm fracture failed. The 2‐way anova did not show statistical significance for restoration (P = 0.584), amount of fracture (P = 0.357), or interaction effect (P = 0.212). A composite resin restoration and a porcelain veneer could perform similarly for replacing a fractured incisor edge up to 4 mm. Other factors such as esthetic and/or cost would be considerations to indicate one treatment over the other.     

Optimization of resilience and stress distribution in porcelain veneers for the treatment of crown-fractured incisors

The present study was conducted to define, when restoring extensive loss of dentin, the configuration of the restoration that will best reproduce the biomechanical properties of the intact original tooth in terms of resilience and stress distribution. The treatment of 1/3-crown fractures and 2/3-crown fractures was investigated using different designs of facial porcelain veneers with and without underlying composite buildup. The stress distribution and tooth compliance were assessed in a numeric model reproducing a 2-dimensional buccolingual cross section of an incisor. A 50-N facial force was applied to simulate an incisal impact situation. The facial surface tangential stresses were calculated, and the maximum displacement (horizontal direction) at the most incisal node of the enamel surface was also recorded and used to calculate the tooth compliance (i.e., displacement/load or resilience) for each test condition. Tensile stresses were generated on the facial surface of the porcelain laminates with a similar pattern for all test conditions, the cervical part of the crown being the most quiescent area. Substantial differences appeared in the incisal half of the crown, the lowest stresses being observed for extensively fractured teeth restored without composite buildup (facial peaks at approximately 33 MPa). Fractured teeth restored with minimal veneers and a "dentin-like" composite buildup showed stress patterns similar to the intact tooth (facial peaks at approximately 50 MPa). The natural tooth gave the highest tooth compliance or flexibility. All restorative designs featured increased tooth stiffness. However, the original tooth compliance was almost restored when composite was used to replace the missing dentin, with the porcelain acting only as a facial and incisal enamel substitute. When restoring crown-fractured incisors, tooth compliance and stress distribution can be modulated by the combination of composite and ceramics. Optimized configurations can be reached to reproduce the original biomechanical behavior of the intact tooth. The use of ceramic alone generates low stress concentrations, but also less compliant restored teeth.     

复合树脂嵌体修复后牙体抗力的三维有限元研究

目的:对直接树脂和间接树脂嵌体修复后牙体的抗力进行三维有限元研究。方法:通过2种加载方式(中央窝垂直加载和2功能面上与牙长轴呈45°加载),研究4种材料(Tescera间接树脂、Renew通用树脂、陶瓷和Co-Cr合金)嵌体修复后牙体应力分布的变化。对照组:备洞未充填的缺损牙体和完整牙体。结果:4种材料嵌体均可以提高缺损牙的抗力,改善缺损牙体内部的应力分布。2种树脂嵌体修复后的牙体应力分布与完整牙体相似;陶瓷、Co-Cr合金则改变了牙本质原有的应力分布。结论:复合树脂嵌体修复能提高缺损牙体的抗力;复合树脂不同固化处理对牙体抗力无明显影响。     

Fracture resistance of teeth restored with class II bonded composite resin

The purpose of this study was to determine whether composite resin bonded to enamel or to both enamel and dentin can increase the fracture resistance of teeth with Class II cavity preparations. Extracted maxillary pre-molars with MOD slot preparations were restored with composite resin bonded to enamel (P-30 and Enamel Bond) or composite resin bonded to enamel and dentin (P-30 and Scotch-bond). Teeth in a control group were prepared but left unrestored. All teeth were loaded occlusally in a universal testing machine until they fractured. Means of forces required to fracture teeth in each of the three groups were statistically compared (one-way ANOVA and Bonferroni t test). Teeth restored with combined enamel- and dentin-bonded composite resins were significantly more resistant to fracture than were similarly prepared but unrestored teeth and also than teeth restored with enamel-bonded composite resin (p less than 0.05). A significant difference was not demonstrated between the enamel-bonded group and the unrestored group. Further testing is needed to determine the durability of the bonds between tooth and restoration in the clinical setting.     

Post-endodontic restorations with adhesively luted fiber-reinforced composite post systems: a review

PURPOSE: To review the literature on adhesive luting of fiber-reinforced composite posts (FRC) to provide evidence for the clinical procedure of restoring endodontically treated teeth using FRC posts. METHODS: Data focusing on bonding behavior between root canal dentin, luting agent, and FRC post in vitro as well as in vivo performance of teeth restored with FRC posts were reported. These data were identified by searches of "PubMed", "Scopus", and "Cochrane Library" databases with the terms "post-endodontic restoration", "fiber post", "adhesive luting", "root canal dentin", "clinical study", and "pre-treatment fiber post". Papers published up to September 2007 were selected, and most relevant references were chosen. Cross-referencing of significant papers identified additional relevant articles. RESULTS: FRC posts seem to have become increasingly popular for the restoration of endodontically treated teeth. Compared to metal posts, FRC posts revealed reduced fracture resistance in vitro, along with a usually restorable failure mode. Bonding behavior among FRC post, luting agents, and root canal dentin demonstrated varying results. Bond strengths between FRC posts and resin cements can be enhanced by using various pre-treatment procedures; however, bonding to root canal dentin still seems to be challenging. Most clinical studies investigating survival rates of teeth restored with FRC posts revealed promising results, but risk factors (e.g., the loss of coronal tooth structure) have not been studied intensively. In addition, randomized controlled clinical long term trials are scarce.     

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??Objective    To evaluate microleakage of incisally fractured incisors restored with nanofilled composite resins.  Methods    Twelve previously extracted incisors were assigned to two groups ??A and B?? equally according to the size of tooth. The teeth were cut obliquely from the mesial incisal angle to simulate uncomplicated tooth fracture. Labial reduction of 0.5mm and dovetails in the lingual surfaces were prepared. Additional 2mm of the incisal edge were cut horizontally in group A. The teeth in both groups were restored with nanofilled composite resins using a multilayer technique. Thermal and mechanical cycling was used to simulate oral temperature and aging effect. Level of microleakage was assessed. Statistical analyses were conducted between the two groups. Results    Eleven of the twelve samples revealed microleakage??and one case had the leakage up to the medullary shaft wall. Difference between the two groups revealed no statistical significance. Conclusion    According to the results of this study??microleakage still exists when using nanofilled composite resins to restore incisally fractured incisors. Whether to reduce 2mm of incisal edge or not does not affect level of microleakage.     

Combined technique with glass‐fibre‐reinforced composite post and original fragment in restoration of traumatized anterior teeth – a case report

Abstract – Dentoalveolar trauma is frequently encountered by dental practitioners. In some instances, saving a child’s traumatized permanent teeth can create difficulties for the child, the parents and the dentist. Reattachment of a crown fragment is a conservative treatment that should be considered for crown fractures of anterior teeth. This case describes the clinical reattachment of an original tooth fragment. A 10‐year‐old male presented at the Department of Pediatric Dentistry with a complex crown fracture of the left maxillary central incisor 1 day after the trauma occurred. Following endodontic treatment, a glass‐fibre‐reinforced composite root canal post (FRC Postec^®; Ivoclar Vivadent AG, Schaan, Liechtenstein) was inserted to increase retention and distribute stress along the root. The dental restoration was completed using the original fragment and a dual‐cured resin composite (Variolink^® II; Ivoclar Vivadent AG). Clinical and radiographic examinations at 1‐year recall showed the glass‐fibre‐reinforced composite root canal post and restoration to be in place, indicating the success of the treatment in maintaining the fractured tooth. Thus, we conclude that reattachment of a tooth fragment using a dual‐cured resin composite and a glass‐fibre‐reinforced composite root canal post is an alternative method for the rehabilitation of fractured teeth that offers satisfactory aesthetic and functional outcomes.     

Resistance to fracture of endodontically treated premolars restored with glass ionomer cement or acid etch composite resin

MOD cavity preparations in 64 endodontically treated premolars were restored using four different methods. Copper rings were filled with commercial hard-setting cement and the teeth were placed into the cement up to the level of the cementoenamel junction. The teeth were grouped according to restorative method, mounted in an Instrom T.T. machine, and the buccal walls subjected to a slowly increasing compressive force until fracture occurred. The force of fracture of the walls of each tooth was recorded and the results in the various groups compared. All teeth fractured in a similar manner irrespective of the restorative method used. The resistance to fracture of the teeth was the same when they were restored with glass ionomer cement as a base over which an amalgam or composite resin was placed or with acid-etched resin. When the entire cavities were filled with glass ionomer cement the resistance to fracture of the teeth decreased significantly compared with the acid etch resin technique.     

Re-attachment of anterior fractured teeth: fracture strength using different techniques

Fracture of anterior teeth by trauma is a common problem in children and teenagers. Complex metal-ceramic crowns with considerable loss of remaining sound structure are no longer necessary due to adhesive techniques, such as composite restorations and re-attachment techniques. This study compared the fracture strength of sound and restored anterior teeth using a resin composite and four re-attachment techniques. A "one bottle" adhesive system (One-Step, BISCO) and a dual cure resin cement (Duo-Link, BISCO) were applied. Thirty-five sound permanent lower central incisors were fractured by an axial load applied to the buccal area and randomly divided into five groups. The teeth were restored as follows: 1) bonded only = just bonding the fragment; 2) chamfer-group = after bonding, a chamfer was prepared on the enamel at the bonding line and filled with composite; 3) overcontour group = after bonding, a thin composite overcontour was applied on the buccal surface around the fracture line; 4) internal dentinal groove = before bonding, an internal groove was made and filled with a resin composite; 5) resin composite group = after a bevel preparation on the enamel edge, the adhesive system was applied and the fractured part of the teeth rebuilt by resin composite. Restored teeth were subjected to the same loading in the same buccal area. Fracture strength after restorative procedure was expressed as a percentage of the original fracture strength and the results analyzed by Kruskal-Wallis statistical analysis. The mean percentages of fracture strength were: Group 1: 37.09%, Group 2: 60.62%, Group 3: 97.2%, Group 4: 90.54% and Group 5: 95.8%. It was concluded that the re-attachment techniques used in Groups 3 and 4, as well as the composite restored group (Group 5), were statistically similar and reached the highest fracture resistance, similar to the fracture resistance of sound teeth.     

Impact strength of teeth restored by fragment-bonding

The objective of this in vitro study was to investigate the impact strength of anterior teeth that have been fractured and restored by bonding with a dentin-bonding agent and a composite resin. Twenty sheep central incisors were divided into two groups, 10 in each. One group (intact teeth) served as the control and the teeth in the other group were fractured and then bonded with a bonding agent and a low-viscous composite resin. The specimens were tested in a modified impact-testing machine (pendulum type). The mean impact strength of the intact teeth was 30.6 +/- 2.16 KJ/m2 and of the bonded teeth was 30.2 +/- 1.86 KJ/m2. Statistics revealed that the two means were not significantly different. The results related well with the fracture strength obtained by loading intact and bonded teeth at constant but low speed until fracture. It was concluded that bonding fragments to the remaining tooth structure may restore the tooth to its original strength, measured at modest velocities of the applied force. In other words, reattaching the original coronal fragment of traumatised fractured anterior teeth restored with One-Step dentin bonding system and AEliteflo composite resin would withstand a second trauma to the same extent as intact teeth.