Enamel-dentin crown fractures bonded with various bonding agents Munksgaard EC, Hojtved L, Jorgensen EHW, Andreasen FM, Andreasen JO. Enamel-dentin crown fractures bonded with various bonding agents. Endod Dent Traumatol 1991; 7: 1?>-11. Abstract -^ A method is described, by which the fracture strength of bonded, previously fractured incisors can be measured. The study employed incisors from sheep, which could be obtained in suitable numbers and with limited variation in size. The incisors were fractured parallel to the incisal edge. The mean fracture area + SD of central incisors was 8.45 ± 0.89 mm" and of lateral incisors 6.50 ± 0.64 mm^. The enamel area constituted about 30% of the total fracture area. Acid etching of the enamel and bonding of the fractures with an unfilled resin yielded a fracture strength, which was approximately 38% ofthe fracture strength of fractured teeth restored with acid etching of enamel, Gluma treatment of dentin and bonding with the unfilled resin. Teeth restored in this way, but using the dentin bonding agent Tenure or Scotchbond2 instead of Gluma, exhibited mean fracture strengths which were not significantly different from that obtained when Gluma was employed as the bonding agent. The mean fracture strength by using one of the three bonding agents in combination with acid etching of enamel was about 8 MPa, which is approximately 50% ofthe fracture strength of intact teeth.
Traumatic injuries with loss of fragments of teeth in the incisor region is common, especially among children. Such enamel-dentin fragments can be bonded to the remaining tooth by dimethacrylatebased resins, when the enamel is acid etched (1). In addition, the dentin bonding agent Gluma can be used to ensure bonding of the dentin part of the fractures (2). This study indicates that incisors restored in this way can withstand normal chewing forces for a period of at least two years. However, new traumatic injuries will often lead to loss of bonding, and a half-life of about 2.5 years with this type of restoration has been observed (unpublished results; presented in June 1988 at Nordic Pedodontic Society, Bergen, Norway). In order to increase the longevity of this type of restoration, it would probably be beneficial to use bonding systems which, compared to the above mentioned system, imply an increase in strength and fracture toughness of the bond between the fragments and the remaining tooth substance. The purpose of this study was to develop a labora-
E. G. Munksgaard', L Hojtved^ L H. W. Jergensen^ J. 0. Andreasen^ F. M. Andreasen^ Departments ot ^Dental Materials and Technology, ^Pediatric Dentistry & Oral Maxillofaeial Surgery, Royal Dental College, ^Oral Medicine and Oral Surgery, University Hospital (Rigshospitalet), Copenhagen, Denmark
Key words: crown fractures; dentin bonding; fracture strength. F. M. Andreasen, Dept. of Pediatric Dentistry, Royal Dental College. 20 Norre Alle, DK-2200 Copenhagen N, Denmark. Accepted September 27, 1990
tory model suitable fbr testing the strength of the fractured incisors restored with bonding agents and resins, and to test the strength of teeth restored with a number of different dentin bonding systems.
Material and methods Central and lateral incisors from sheep having approximately the same age were obtained from a local slaughterhouse and stored in a tight plastic bag at -80°C until use. The teeth were extracted from the jaws, rinsed with water and stored in 1% chloramine-T until use. The following bonding systems were used: Gluma (Bayer AG, Leverkusen, FRG), Scotchbond2 (3M Co., St. Paul, MN, USA), Tenure two-step procedure (Den-Mat Corp., Santa Maria, CA, USA), NCS (Microbond, Austenal Dental, Holland; designed for bonding porcelain veneers), Clearfil New Bond (Kuraray Co., Osaka, Japan). Pekalux was obtained from Bayer AG and Silux from 3M Co. 73
Munksgaard et al. Table 2. Area of fractured surfaces of incisors from sheep, The numbers in each group are 12.
Fracturing, bonding and debonding
Small notches on the two approximal surfaces were placed with a diamond wheel 2.5 mm from the incisal edge. By using a narrow forceps (4 mm wide) the teeth were fractured at the notches parallel with the incisal edge. The incisal fragment was held by a piece of sticky wax and the two fracture surfaces where treated with a bonding system and a light-curable unfilled resin or composite as indicated below and in Table 1. The fracture surfaces were bonded under a dissecting light microscope ( x 8) to ensure correct fragment alignment. The resin was light-cured for 60 s orally + 60 s facially. Excess polymerized resin was removed with a scalpel. After water storage for one week at room temperature, in some instances after thermal cychng (see below), the root ofthe restored tooth was embedded in a plaster block (2.7 x 1.3x4 cm) in such a way that the long axis ofthe tooth was aligned with the central axis ofthe plaster block. The crown of the tooth was kept moist during curing of the plaster. The block containing the restored tooth was mounted in an Instron Testing Machine. The tooth was fractured along the original fracture line with a spade placed parallel to the fracture Hne, 2.5 mm from the incisal edge and 1 mm from the original fracture hne and at a speed of 1 mm/min. The force at which the tooth was fractured was noted and the fracture strength calculated in MPa using the mean area of fracture surface of a central or lateral incisor, see below and in Table 2. The mean fracture area of 12 central and 12 lateral incisors was determined in a microscope ( x 10) equipped with drawing equipment. The total area ofthe fracture surface as well as the enamel and the dentin areas were determined by cutting out and weighing the drawings. Bonding systems
The two fracture surfaces of a tooth were treated identically. Between 8 and 20 teeth were used in each experimental group, see Table 1. Gluma was used in several experiments. In the normal Gluma procedure (a) enamel was etched with 35% phosphoric acid for 30 s, rinsed with water for 20 s, air dried for 5 s; the dentin was
Table 1. Description of the etching solufions, primers, bonding agents, and unfilled resins or composite used in the experiments.
Name
Pretreatment of: enamel dentin
Gluma H3PO4 Cleanser Tenure Conditioner Scotchbond2 H3PO, Primer NCS H3PO,
74
Final treatment bonding agent resin/comp. Gluma bond A+B Adhesive resin + liquid
Resin L Visar Seal Resin L Luting comp.
Type Central incisor Lateral incisor
Enamel and dentin, ± SD, mm^
Enamel, ±SD, mm^
Enamel, ± SD, %
8.45 ±0.89 6.50 ±0.64
2.52 ±0.31 2.12 ±0.26
29.8 ±12.3 32.6 ±12.3
treated with 0.5 M EDTA (Gluma Cleanser) for 20 s, rinsed for 10 s and air dried for 5 s. Gluma Bond was applied for 20 s, air dried for 5 s, and the unfilled resin (Resin L) was then applied and used as indicated above. In one experiment (b) the phosphoric acid etching was omitted and in another experiment (c) the Cleanser and the Gluma bond treatments were omitted. Additional experiments were performed according to normal Gluma procedure, but with the following changes or additions: - Resin L was replaced with Resin L containing 40% Pekalux (d). - Thermal cycling was performed after curing (e). The cycling was performed for six h between two water baths and one cycle included 15 sec at 10°C and 15 s at 55°C. A double chamfer (f) extending 0.5 mm on both sides of the fracture line and 0.5 mm deep was made with a small round bur. The space was restored and cured with Silux diluted with Silux Enamel Bond (1:1) after acid-etching. - Resin L was replaced with the liquid + resin phase ofthe NCS-system followed by NCS luting composite (g). In experiment (h) Clearfil New Bond was applied before the resin. Tenure and Scotchbond2 were used instead of Gluma in bonding experiments similar to some of those described above. The two bonding systems were used according to the manufacturers' recommendations (Table 1). The final bond with the Tenure system was estabhshed with Visar Seal (i) and with Scotchbond2 with Resin L (j). Teeth restored as above with Scotchbond2 and with Tenure were thermal-cycled as described above (experiment (k) and (1) respectively). In addition, experiments with the Tenure system were performed in which NCS luting cement replaced Visar Seal (m). NCS Bond was used (n) according to manufacturer's specifications using acid etching and the supplied dentin bonding agent (Table 1). Resin L was not used, as the bonding system contained a suitable unfilled resin. Each experimental group usually comprised 8 incisors. However, there were the following exceptions: 12 were used in experiments (a) and (c); 15 in experiment (g) and 16 in experiment (m). As a control, 12 incisors were supphed with not-
Bended enamel-dentin crewn fractures ches as above, embedded in plaster and fractured in the Instron testing machine. The results within each group were calculated as mean + SD. statisticai anaiysis The fracture forces obtained from fracturing the restored teeth in experiments (a), (b) and (c), as well as in (a) and those from experiments (d), (e), (f), (g), (h), (i), Cj), (k), (1), (m), (n) and the control group were tested by Newman-Keuls' multiplerange test (3) at a 5% level of significance. Results The results from the measurements of the fracture area of 12 lateral and 12 central incisors are given in Table 2. Fig. 1 shows the mean fracture strength + SD of restored fractured incisors. The three groups of fractured incisors were restored according to method (a), (b), and (c), respectively. The statistical analysis by Newmann-Keuls' multiple-range test showed that the mean value of the results from
group (a) was significantly different from the mean values of the results from group (b) or group (c). The mean fracture strength from the latter two groups did not differ significantly. Fig. 2 presents the mean fracture strength ± SD of restored fractured incisors and of intact teeth. The restorations were performed by the methods indicated on the figure referring to the methods described in Material and methods. The statistical analysis by Newmann-Keuls' multiple-range test revealed no significant difference between the mean fracture strength of the results from the various experimental groups. However, the mean fracture strength of intact teeth was significantly different from the mean values ofthe results from the experimental groups. The mean fracture strength of the results from all the experimental groups was 8.0 MPa which was 50% ofthe mean fracture strength of intact teeth (16.1 MPa).
Discussion Incisors from sheep seemed to be suitable for use to measure the fracture strength of bonded fractured
(c) ACID
(b) EDTA + GLUMA
(a) ACID + EDTA + GLUMA
0
8
10
12
FRACTURE STRENGTH, MPa Fig. 1. Fracture strength ± SD of combined fractured incisors restored either with (a) acid etching / Gluma Cleanser / Gluma Bond / Resin L; with (b) Gluma Cleanser / Gluma Bond / Resin L or with (c) acid etching / resin L. The mean fracture strength representing teeth m group (a) was significantly different from the mean strength ofthe teeth of groups (b) and (c), the mean of which did not differ significantly. Black bars represent the means and hatched bars the SD's.
7S
Munksiaard et al.
INTACT TEETH (n) NCS (m) TENURE + NCS
(I) SCOTCHB. 2 + THERMOCYCL. (k) TENURE + THERMOCYCL (j) SCOTCHBOND 2 (i) TENURE (h) GLUMA + CLEARFILL (g) GLUMA + NCS (f) GLUMA + DOUBLE CHAMF. (e) GLUMA + THERMOCYCL. (d) GLUMA + MICROFIL (a) GLUMA I
T
I
I
I
I
I
I
I
I
0 2 4 6 8 10 12 14 16 18 20
FRACTURE STRENGTH, MPa Fig. 2. Fracture strength ± SD of intact teeth from sheep and of combined fractured incisors restored according to the methods (a), (d), (e), (f), (g), (h), (i), (j), (k), (1), (m) or (n) as indicated in Materials and methods. The variations in mean fracture strength between the teeth restored according to the various restoration methods are not statistically significant. The mean fracture strength of intact teeth is significantly different from that ofthe other means. Black bars represent the means and hatched bar the SD's.
teeth. Such incisors can be obtained in sufficient numbers and with a limited variation in size. As seen in Table 2, a coefficient of variation of the fracture areas of about 10% was obtained. The measurement was obtained by applying a force at a speed of 1 mm/min and did therefore not imitate the circumstances surrounding accidental trauma. On the other hand, the obtained results provided the relative fracture strength of a restored tooth. The enamel area of the incisor from sheep (Table 2) was about 30% ofthe fracture surface. The contribution to the fracture strength of acid etching in proportion to the strength obtained by acid etching as well as by dentin priming can be calculated from the results presented in Fig. 1. Here the mean representing experiment (c) in proportion to the mean representing experiment (a) is 38%. This proportion is not far from the 30% enamel area. The difference between the two proportions agreed well with a higher bond strength between composite resins and acid etched enamel compared to the strength between composite resins and Gluma treated dentin (4).
A fracture strength of the restored teeth of about 50% of the strength of intact teeth was obtained (Fig. 2). No differences were seen between the fracture strength of the teeth restored with the various bonding agents or combinations of agents. An overall mean of 8 MPa was obtained with a coefficient of variation of 34% and with a range of 23 to 44%,. Although slightly higher (4, 5), this coefficient of variation agreed with previously found variations when measuring bond strength between composite resins and Gluma-treated dentin. This relatively high variation will probably hide any potential differences between the results. It was concluded that, when bonding fractured incisors the use ofthe dentin bonding agents Gluma, Tenure and Scotchbond2 in combination with acid etching of enamel and an unfilled resin will restore the incisors to about 50% of the original fracture strength of the teeth. The bond can withstand temperature changes as seen by comparing the results representing restored teeth that were thermocycled to those representing restored teeth that were not thermocycled.
Bended enamel-dentin crewn fractures Acknowledgement - This project was supported by funds from TNL (Tandlaegernes Nye Landsforening).
3.
BRUNING JL,
KiNTZ BL. Computional handbook of statistics. Glenview: Scoot, Foresman, 1977. 4. MUNKSGAARD EC, ASMUSSEN E . Methacrylate-bonding to dentin. In: THYLSTRUP A, LEACH S A , QVIST V. eds. Dentine and dentine reactions in the oral cavity, Oxford: I R L Press, 1987:
References 1. SiMONSEN RJ. Restoration of a fractured central incisor using original tooth fragments. J Am Dent Assoc 1982; 105: 648-50. 2. ANDREASEN FM, RINDUM JL, MUNKSGAARD EC, ANDRE.ASEN
209-218. 5.
EC, ASMUSSEN E . Bond strength between dentin and restorative resins mediated by mixtures of HEMA and glutaraldehyde. J Dent Res 1984; 63: 1087-9. MUNKSGAARD
JO. Bonding of enamel-dentin crown fractures with GLUMA and resin. Endod Dent Traumatol 1986; 2: 277-80.
77
Traumatic injuries with loss of fragments of teeth in the incisor region is common, especially among children. Such enamel-dentin fragments can be bonded to the remaining tooth by dimethacrylatebased resins, when the enamel is acid etched (1). In addition, the dentin bonding agent Gluma can be used to ensure bonding of the dentin part of the fractures (2). This study indicates that incisors restored in this way can withstand normal chewing forces for a period of at least two years. However, new traumatic injuries will often lead to loss of bonding, and a half-life of about 2.5 years with this type of restoration has been observed (unpublished results; presented in June 1988 at Nordic Pedodontic Society, Bergen, Norway). In order to increase the longevity of this type of restoration, it would probably be beneficial to use bonding systems which, compared to the above mentioned system, imply an increase in strength and fracture toughness of the bond between the fragments and the remaining tooth substance. The purpose of this study was to develop a labora-
E. G. Munksgaard', L Hojtved^ L H. W. Jergensen^ J. 0. Andreasen^ F. M. Andreasen^ Departments ot ^Dental Materials and Technology, ^Pediatric Dentistry & Oral Maxillofaeial Surgery, Royal Dental College, ^Oral Medicine and Oral Surgery, University Hospital (Rigshospitalet), Copenhagen, Denmark
Key words: crown fractures; dentin bonding; fracture strength. F. M. Andreasen, Dept. of Pediatric Dentistry, Royal Dental College. 20 Norre Alle, DK-2200 Copenhagen N, Denmark. Accepted September 27, 1990
tory model suitable fbr testing the strength of the fractured incisors restored with bonding agents and resins, and to test the strength of teeth restored with a number of different dentin bonding systems.
Material and methods Central and lateral incisors from sheep having approximately the same age were obtained from a local slaughterhouse and stored in a tight plastic bag at -80°C until use. The teeth were extracted from the jaws, rinsed with water and stored in 1% chloramine-T until use. The following bonding systems were used: Gluma (Bayer AG, Leverkusen, FRG), Scotchbond2 (3M Co., St. Paul, MN, USA), Tenure two-step procedure (Den-Mat Corp., Santa Maria, CA, USA), NCS (Microbond, Austenal Dental, Holland; designed for bonding porcelain veneers), Clearfil New Bond (Kuraray Co., Osaka, Japan). Pekalux was obtained from Bayer AG and Silux from 3M Co. 73
Munksgaard et al. Table 2. Area of fractured surfaces of incisors from sheep, The numbers in each group are 12.
Fracturing, bonding and debonding
Small notches on the two approximal surfaces were placed with a diamond wheel 2.5 mm from the incisal edge. By using a narrow forceps (4 mm wide) the teeth were fractured at the notches parallel with the incisal edge. The incisal fragment was held by a piece of sticky wax and the two fracture surfaces where treated with a bonding system and a light-curable unfilled resin or composite as indicated below and in Table 1. The fracture surfaces were bonded under a dissecting light microscope ( x 8) to ensure correct fragment alignment. The resin was light-cured for 60 s orally + 60 s facially. Excess polymerized resin was removed with a scalpel. After water storage for one week at room temperature, in some instances after thermal cychng (see below), the root ofthe restored tooth was embedded in a plaster block (2.7 x 1.3x4 cm) in such a way that the long axis ofthe tooth was aligned with the central axis ofthe plaster block. The crown of the tooth was kept moist during curing of the plaster. The block containing the restored tooth was mounted in an Instron Testing Machine. The tooth was fractured along the original fracture line with a spade placed parallel to the fracture Hne, 2.5 mm from the incisal edge and 1 mm from the original fracture hne and at a speed of 1 mm/min. The force at which the tooth was fractured was noted and the fracture strength calculated in MPa using the mean area of fracture surface of a central or lateral incisor, see below and in Table 2. The mean fracture area of 12 central and 12 lateral incisors was determined in a microscope ( x 10) equipped with drawing equipment. The total area ofthe fracture surface as well as the enamel and the dentin areas were determined by cutting out and weighing the drawings. Bonding systems
The two fracture surfaces of a tooth were treated identically. Between 8 and 20 teeth were used in each experimental group, see Table 1. Gluma was used in several experiments. In the normal Gluma procedure (a) enamel was etched with 35% phosphoric acid for 30 s, rinsed with water for 20 s, air dried for 5 s; the dentin was
Table 1. Description of the etching solufions, primers, bonding agents, and unfilled resins or composite used in the experiments.
Name
Pretreatment of: enamel dentin
Gluma H3PO4 Cleanser Tenure Conditioner Scotchbond2 H3PO, Primer NCS H3PO,
74
Final treatment bonding agent resin/comp. Gluma bond A+B Adhesive resin + liquid
Resin L Visar Seal Resin L Luting comp.
Type Central incisor Lateral incisor
Enamel and dentin, ± SD, mm^
Enamel, ±SD, mm^
Enamel, ± SD, %
8.45 ±0.89 6.50 ±0.64
2.52 ±0.31 2.12 ±0.26
29.8 ±12.3 32.6 ±12.3
treated with 0.5 M EDTA (Gluma Cleanser) for 20 s, rinsed for 10 s and air dried for 5 s. Gluma Bond was applied for 20 s, air dried for 5 s, and the unfilled resin (Resin L) was then applied and used as indicated above. In one experiment (b) the phosphoric acid etching was omitted and in another experiment (c) the Cleanser and the Gluma bond treatments were omitted. Additional experiments were performed according to normal Gluma procedure, but with the following changes or additions: - Resin L was replaced with Resin L containing 40% Pekalux (d). - Thermal cycling was performed after curing (e). The cycling was performed for six h between two water baths and one cycle included 15 sec at 10°C and 15 s at 55°C. A double chamfer (f) extending 0.5 mm on both sides of the fracture line and 0.5 mm deep was made with a small round bur. The space was restored and cured with Silux diluted with Silux Enamel Bond (1:1) after acid-etching. - Resin L was replaced with the liquid + resin phase ofthe NCS-system followed by NCS luting composite (g). In experiment (h) Clearfil New Bond was applied before the resin. Tenure and Scotchbond2 were used instead of Gluma in bonding experiments similar to some of those described above. The two bonding systems were used according to the manufacturers' recommendations (Table 1). The final bond with the Tenure system was estabhshed with Visar Seal (i) and with Scotchbond2 with Resin L (j). Teeth restored as above with Scotchbond2 and with Tenure were thermal-cycled as described above (experiment (k) and (1) respectively). In addition, experiments with the Tenure system were performed in which NCS luting cement replaced Visar Seal (m). NCS Bond was used (n) according to manufacturer's specifications using acid etching and the supplied dentin bonding agent (Table 1). Resin L was not used, as the bonding system contained a suitable unfilled resin. Each experimental group usually comprised 8 incisors. However, there were the following exceptions: 12 were used in experiments (a) and (c); 15 in experiment (g) and 16 in experiment (m). As a control, 12 incisors were supphed with not-
Bended enamel-dentin crewn fractures ches as above, embedded in plaster and fractured in the Instron testing machine. The results within each group were calculated as mean + SD. statisticai anaiysis The fracture forces obtained from fracturing the restored teeth in experiments (a), (b) and (c), as well as in (a) and those from experiments (d), (e), (f), (g), (h), (i), Cj), (k), (1), (m), (n) and the control group were tested by Newman-Keuls' multiplerange test (3) at a 5% level of significance. Results The results from the measurements of the fracture area of 12 lateral and 12 central incisors are given in Table 2. Fig. 1 shows the mean fracture strength + SD of restored fractured incisors. The three groups of fractured incisors were restored according to method (a), (b), and (c), respectively. The statistical analysis by Newmann-Keuls' multiple-range test showed that the mean value of the results from
group (a) was significantly different from the mean values of the results from group (b) or group (c). The mean fracture strength from the latter two groups did not differ significantly. Fig. 2 presents the mean fracture strength ± SD of restored fractured incisors and of intact teeth. The restorations were performed by the methods indicated on the figure referring to the methods described in Material and methods. The statistical analysis by Newmann-Keuls' multiple-range test revealed no significant difference between the mean fracture strength of the results from the various experimental groups. However, the mean fracture strength of intact teeth was significantly different from the mean values ofthe results from the experimental groups. The mean fracture strength of the results from all the experimental groups was 8.0 MPa which was 50% ofthe mean fracture strength of intact teeth (16.1 MPa).
Discussion Incisors from sheep seemed to be suitable for use to measure the fracture strength of bonded fractured
(c) ACID
(b) EDTA + GLUMA
(a) ACID + EDTA + GLUMA
0
8
10
12
FRACTURE STRENGTH, MPa Fig. 1. Fracture strength ± SD of combined fractured incisors restored either with (a) acid etching / Gluma Cleanser / Gluma Bond / Resin L; with (b) Gluma Cleanser / Gluma Bond / Resin L or with (c) acid etching / resin L. The mean fracture strength representing teeth m group (a) was significantly different from the mean strength ofthe teeth of groups (b) and (c), the mean of which did not differ significantly. Black bars represent the means and hatched bars the SD's.
7S
Munksiaard et al.
INTACT TEETH (n) NCS (m) TENURE + NCS
(I) SCOTCHB. 2 + THERMOCYCL. (k) TENURE + THERMOCYCL (j) SCOTCHBOND 2 (i) TENURE (h) GLUMA + CLEARFILL (g) GLUMA + NCS (f) GLUMA + DOUBLE CHAMF. (e) GLUMA + THERMOCYCL. (d) GLUMA + MICROFIL (a) GLUMA I
T
I
I
I
I
I
I
I
I
0 2 4 6 8 10 12 14 16 18 20
FRACTURE STRENGTH, MPa Fig. 2. Fracture strength ± SD of intact teeth from sheep and of combined fractured incisors restored according to the methods (a), (d), (e), (f), (g), (h), (i), (j), (k), (1), (m) or (n) as indicated in Materials and methods. The variations in mean fracture strength between the teeth restored according to the various restoration methods are not statistically significant. The mean fracture strength of intact teeth is significantly different from that ofthe other means. Black bars represent the means and hatched bar the SD's.
teeth. Such incisors can be obtained in sufficient numbers and with a limited variation in size. As seen in Table 2, a coefficient of variation of the fracture areas of about 10% was obtained. The measurement was obtained by applying a force at a speed of 1 mm/min and did therefore not imitate the circumstances surrounding accidental trauma. On the other hand, the obtained results provided the relative fracture strength of a restored tooth. The enamel area of the incisor from sheep (Table 2) was about 30% ofthe fracture surface. The contribution to the fracture strength of acid etching in proportion to the strength obtained by acid etching as well as by dentin priming can be calculated from the results presented in Fig. 1. Here the mean representing experiment (c) in proportion to the mean representing experiment (a) is 38%. This proportion is not far from the 30% enamel area. The difference between the two proportions agreed well with a higher bond strength between composite resins and acid etched enamel compared to the strength between composite resins and Gluma treated dentin (4).
A fracture strength of the restored teeth of about 50% of the strength of intact teeth was obtained (Fig. 2). No differences were seen between the fracture strength of the teeth restored with the various bonding agents or combinations of agents. An overall mean of 8 MPa was obtained with a coefficient of variation of 34% and with a range of 23 to 44%,. Although slightly higher (4, 5), this coefficient of variation agreed with previously found variations when measuring bond strength between composite resins and Gluma-treated dentin. This relatively high variation will probably hide any potential differences between the results. It was concluded that, when bonding fractured incisors the use ofthe dentin bonding agents Gluma, Tenure and Scotchbond2 in combination with acid etching of enamel and an unfilled resin will restore the incisors to about 50% of the original fracture strength of the teeth. The bond can withstand temperature changes as seen by comparing the results representing restored teeth that were thermocycled to those representing restored teeth that were not thermocycled.
Bended enamel-dentin crewn fractures Acknowledgement - This project was supported by funds from TNL (Tandlaegernes Nye Landsforening).
3.
BRUNING JL,
KiNTZ BL. Computional handbook of statistics. Glenview: Scoot, Foresman, 1977. 4. MUNKSGAARD EC, ASMUSSEN E . Methacrylate-bonding to dentin. In: THYLSTRUP A, LEACH S A , QVIST V. eds. Dentine and dentine reactions in the oral cavity, Oxford: I R L Press, 1987:
References 1. SiMONSEN RJ. Restoration of a fractured central incisor using original tooth fragments. J Am Dent Assoc 1982; 105: 648-50. 2. ANDREASEN FM, RINDUM JL, MUNKSGAARD EC, ANDRE.ASEN
209-218. 5.
EC, ASMUSSEN E . Bond strength between dentin and restorative resins mediated by mixtures of HEMA and glutaraldehyde. J Dent Res 1984; 63: 1087-9. MUNKSGAARD
JO. Bonding of enamel-dentin crown fractures with GLUMA and resin. Endod Dent Traumatol 1986; 2: 277-80.
77
