Dynamic resistance of teeth: technical considerations and applications of an experimental device

Tooth fracture by impact is the most common cause of fracture in human incisors. We have designed an experimental system to measure the dynamic fracture force of teeth in vitro, and initial results obtained from a sample of healthy, recently removed human incisors are reported. The method was reproducible and reliable, and the results provide a baseline for studies evaluating the effect of endodontic procedures on the dynamic fracture force of teeth.     

Fracture strength of composite fixed partial denture using bovine teeth as a substitute for human teeth with or without fiber-reinforcement

This study evaluate the use of bovine teeth as a substitute for human teeth on fracture strength tests of composite fixed partial dentures (Cpd), with and without fiberglass reinforcement (Fg). Eighty teeth were selected, being 40 bovine incisors, 20 human premolars and 20 molars. Bovine incisors were ground to get a platform, simulating an occlusal surface of human molar. Teeth in pairs were embedded in polystyrene resin, simulating the periodontal ligament and divided in 4 groups: B-Cpd-Fg: bovine teeth restored with Cpd with Fg; B-Cpd-NFg: bovine teeth restored with Cpd without Fg; H-Cpd-Fg: human teeth restored Cpd with Fg; and H-Cpd-NFg: human teeth restored with Cpd without Fg. The Cpd were adhesively fixed and submitted to an axial compression load at the pontic center with a crosshead speed of 0.5 mm/min until fracture. Failure modes were assessed and classified. Data were subjected to two-way ANOVA and Tukey's HSD test (α=0.05). The tooth type had no influence on fracture strength and fracture mode. The inclusion of fiberglass increased significantly the fracture strength. The failure modes were more reparable in groups with fiber-reinforcement. Bovine teeth can be used as a substitute for human teeth in these types of fracture strength tests.     

An evaluation of various materials and tooth preparation designs used for reattachment of fractured incisors

Abstract – Background/Aim: The present study was undertaken to evaluate and compare the fracture strength of various restorative materials and designs used in the reattachment of anterior fractured teeth. Materials and method: Sound human maxillary central incisors were selected for the study. These teeth were fractured using universal testing machine so as to obtain Ellis class II fracture with intact fragment. The fractured fragment was reattached to the tooth using three restorative materials namely, bonding agent, resin luting cement and nano‐composite, and designs incorporated were simply bonding the fragment to the tooth and other one included a chamfer along the fractured line. The reattached teeth were again fractured and the mean fracture strength values recorded. Results and Conclusion: A combination of nano‐composite (best material) and chamfer preparation (best design) gave the highest mean fracture strength values.     

三种方式修复严重缺损的上颌中切牙抗折性能研究

目的：比较三种方式修复严重缺损的上颌中切牙的抗折性能,探讨保存残根残冠更合理的修复方式。方法：36颗上颌中切牙随机分为3组,根管治疗后平齐唇侧釉牙本质界垂直与牙体长轴截冠。分别行铸造镍铬合金桩核、铸造镍铬合金桩树脂核及玻璃纤维桩树脂核＋金属全冠修复。在万能测试机进行力学测试,记录最大载荷和断裂模式。结果：3组的抗折强度分别为292.06±155.51N、439.89±89.55N和284.98±133.56N,铸造镍铬合金桩树脂核组明显高于另外2组,差异具有统计学意义。铸造镍铬合金桩均导致牙根垂直折裂,玻璃纤维桩10颗桩折,2颗桩折合并唇侧颈1/3折裂。结论：无箍作用时应充分利用树脂与牙体的粘结作用,高强度的铸造镍铬合金桩较玻璃纤维桩能更好地抵抗外力,结合高强度的树脂核强度更大。     

Influence of post placement in the fracture resistance of endodontically treated incisors veneered with direct composite

STATEMENT OF PROBLEM: Veneer preparations are considered to weaken endodontically treated maxillary incisors. Prefabricated posts have been controversially indicated to reinforce endodontically treated teeth before final restoration. PURPOSE: This in vitro study evaluated whether (1) veneer preparation in enamel or in enamel/dentin weakens endodontically treated maxillary incisors, (2) bonding of direct composite veneer restores the original strength of the unprepared teeth, and (3) use of prefabricated metal posts increases fracture resistance of prepared and restored teeth. MATERIAL AND METHODS: Ninety extracted human maxillary central incisors were submitted to conventional root canal treatment. Specimens were randomly divided into 8 experimental groups (veneer preparation in enamel or dentin with/without post and with/without direct composite veneer restoration) and a control group (n = 10). Specimens were loaded to fracture, and the data were analyzed statistically. RESULTS: Statistical analysis revealed that a conservative veneer preparation does not significantly reduce maxillary incisors' fracture resistance. For prepared incisors, bonding of direct composite veneer restored their original strength, and the use of posts did not increase their fracture resistance. CONCLUSION: Conservative veneer preparations involving enamel and enamel/dentin did not significantly reduce the fracture resistance of endodontically treated maxillary incisors. In addition, restoration of the intraenamel preparations with direct composite resulted in teeth more resistant to fracture than teeth having restorations in dentin. The use of posts did not improve fracture resistance of endodontically treated maxillary incisors reduced and veneered with direct composite.     

Proclination of lower incisors: a design to maximize food penetration and minimize torque

Human upper and lower incisors are both tilted forward in the sagittal plane. Previous theoretical and in vitro studies have investigated how proclination may help the teeth either to penetrate or to fracture food more effectively or both. We study the proclination of lower incisors in relation to efficiency and to the protection it may offer from potentially damaging torque forces. Lateral cephalographs from 57 normal human subjects were traced. In one study, a line was drawn joining the centre of the condyle to the tip of the lower incisor. The results showed the lower incisor is oriented so that it is closely parallel to the arc of a circle centred at the condyle. In another study, lines were drawn joining the tips of upper and lower incisors at different openings. Each line showed the direction of the force that must be used to bite an object held between the tips of the incisor teeth. Its direction was compared with the direction of the long axis of the lower incisor when the mandible was graphically rotated open. The results showed the long axis of the lower incisor is closest to the direction of the bite force at 12 degrees and 15 degrees of jaw openings (roughly 20-25 mm incisal separation). This is the opening where the maximum incisal force is normally produced. The findings suggest that to reduce the torque, lower incisors implanted or relocated during orthodontic treatment should be oriented parallel to the closing arc.     

Fracture behavior of human mandibular incisors following endodontic treatment and porcelain veneer restoration

PURPOSE: Because of existing controversy, the present study investigated the individual and combined effects of endodontic treatment and porcelain veneer restoration on the fracture behavior of human mandibular incisors. MATERIALS AND METHODS: Forty extracted intact human mandibular incisors were assigned to four groups of ten with a similar range of labiolingual widths at the cementoenamel junctions. Group A consisted of intact teeth; group B consisted of endodontically treated teeth; group C teeth were restored with labial porcelain veneers; and those of group D were endodontically treated and had labial porcelain veneers. All teeth were subjected to a slow continuous loading test at 30 degrees to the long axis of the teeth and 1 mm below the incisal edge on the labial side. RESULTS: Fracture forces were 415 +/- 220 N, 370 +/- 89 N, 420 +/- 128 N, and 448 +/- 156 N for groups A, B, C, and D, respectively. Root fracture was the most common mode of failure. There were no statistically significant differences between the groups in terms of fracture forces and modes of failure. CONCLUSION: Human mandibular incisors with endodontic treatment and/or porcelain veneer restorations were able to withstand the same magnitude of oblique loading as intact teeth. Endodontic treatment and/or porcelain veneer restoration did not affect the mode of failure of mandibular incisors.     

Shear bond strength of restorations applied to un-complicated crown fractures: an in vitro study

Abstract – Background: Study was designed to evaluate shear bond strengths of different restorative techniques of uncomplicated enamel‐dentin fractures in permanent incisors. Material and Methods: Forty human mandibular incisors were divided into four groups. One‐third of their anatomical crowns from the incisal edges were cut off in three groups, representing an uncomplicated enamel‐dentin fracture. Intact teeth in group 1 were used as control. In group 2, edge fragments were reattached by flowable composite (Filltek Flowable Supreme XT). In group 3, teeth were restored with universal resin composite (Filtek Z 250). In group 4, pre‐impregnated glass fiber sheet (everStickNet) was positioned onto fractured surface, and then restorations were completed with resin composite. Three‐step etch‐and‐rinse adhesive system (Adper Scotchbond Multi Purpose) was used in all test groups. Shear bond strengths of all samples were determined in universal testing machine, and data were analyzed with Kruskal–Wallis followed by Mann–Whitney U tests. Failure types were observed by light microscope. Results: Shear bond strength of sound teeth was significantly higher than those of restored teeth (P < 0.05). Mean shear bond strengths of the reattached teeth were lower than the other two restoration types; however, differences were not statistically significant (P > 0.05). Conclusions: Load‐bearing capacity of restored teeth was not as high as sound teeth in the uncomplicated crown fracture. However, shear bond strength of different types of restorations seems close to each other.     

Evaluation of the effect of different ferrule designs on the fracture resistance of endodontically treated maxillary central incisors incorporating fiber posts, composite cores and crown restorations

AIM: The purpose of this study was to evaluate the fracture resistance of endodontically treated maxillary central incisors restored with quartz fiber posts, composite cores, and crowns when different types of ferrule designs were incorporated. METHODS AND MATERIALS: Sixty maxillary incisors were divided into six groups: Group 1 (control): teeth with root canal treatments having a full crown prosthesis; Group 2: teeth with a 2 mm circumferential ferrule; Group 3: teeth with a 2 mm ferrule only in the vestibular region; Group 4: teeth with a 2 mm ferrule only in the palatal region; Group 5: teeth with a 2 mm ferrule in the vestibular and palatal region, having cavities in both proximal areas; and Group 6: teeth with no ferrule. The teeth in the experimental groups were restored with quartz fiber posts-composite cores and full metallic crowns. All experimental teeth were subjected to an increasing compressive force with a crosshead speed of 1 mm/min, until fracture occurred. RESULTS: The median fracture values of groups were as follows: Group 1: 574.4 N, Group 2: 472.4 N, Group 3: 474.3 N, Group 4: 480.7 N, Group 5: 463.1 N, and Group 6: 297.9 N. A statistically significant difference was found between Group 1 and Group 6 (p< 0.01). CONCLUSION: It was concluded different ferrule designs did not have any influence on the fracture resistance of teeth with fiber posts. The results of this study indicate fiber posts can safely be used for their reinforcing properties. Furthermore, there is no significant change in the resistance of teeth with fiber posts regardless of which ferrule design is incorporated. The property of these types of posts is an additional advantage in clinical practice.     

Impact fracture characteristics of intact and crowned human central incisors

Dynamic fracture energies and patterns of fracture in extracted human central incisors were determined for groups of intact controls, groups with Vita Dur N® crowns, Vita Hi Ceram® crowns, Dicor® crowns and porcelain veneers. Teeth were struck on their middle labial surfaces by a pendulum impact device.
The mean fracture energy for teeth with Dicor crowns was significantly lower than for all other groups ( P <0.05). Control tooth crowns fractured obliquely in an apicaldirection. Vita Dur N® and Dicor® crowns, shattered, the underlying tooth usually fracturing in the plane of the impact force. Vita Hi Ceram® crowns chipped at the site of impact and some fractures were located in the roots. Gold crowns remained cemented and fracture occurred at the crown/root junction, or in the root. Porcelain veneers fractured at the site of impact but remained cemented. Dicor® crowns were less fracture resistant than other restoration types tested. Porcelain veneers and full gold crowns stiffened teeth which led to more root fractures than the porcelain crowns.     

Influence of core material on fracture resistance and marginal adaptation of restored root filled teeth

Aim To investigate ex vivo the influence of direct placement core materials on the fracture strength and marginal adaptation of root filled maxillary central incisors restored with glass fibre‐reinforced posts, various core materials and all‐ceramic crowns. Methodology Forty‐eight human maxillary incisors were root filled. Posts were placed and teeth restored with composite cores and crowns (n = 8). Six core materials were examined after thermal cyclic and mechanical loading (TCML). Fracture force was determined under static loading. The marginal adaptation at the interfaces between cement‐tooth and cement‐crown were categorized as ‘intact margin’ or ‘marginal gap’ using scanning electron microscopy. Statistical analysis was undertaken with the Mann–Whitney U‐test (α = P ≤ 0.05). Results Median fracture strength varied between 204 N (low viscous experimental core) and 1094 N (Multicore). No difference in fracture resistance was found with varying viscosity of the core material. The layering technique improved the fracture performance (P = 0.059) to a minor degree. Crowns with dedicated core materials (Rebilda 1063 N; Multicore 1094 N) had a significantly higher fracture resistance than crowns with a conventional restorative material (Tetric Ceram 509 N). Significantly poorer marginal adaptation before TCML was found for the layering technique at the tooth–cement interface and for all experimental cores after TCML. At the crown–cement interface significant differences in marginal adaptation could be determined between Multicore‐layered core (P = 0.002) and Multicore‐Rebilda (P = 0.001) after TCML. Conclusions The fracture strength of post and core restorations was dependent on the core material and bonding system. Marginal adaptation was influenced by the method of application of the core material and by TCML.     

下颌切牙Empress 2瓷贴面与全瓷冠牙预备体及全瓷修复复合体的抗折裂研究

目的比较下颌切牙Empress 2瓷贴面和全瓷冠牙预备体及修复体粘接后复合体的抗折强度。方法选择人离体下颌切牙50颗,随机分为5组。A组为瓷贴面牙体预备组,B组为全瓷冠牙体预备组,C组为瓷贴面修复组,D组为全瓷冠修复组,E组为完整下颌切牙（对照组）。采用标准化牙体预备过程,Empress 2铸瓷系统及树脂粘接技术完成瓷贴面-牙体和全瓷冠-牙体复合体。使用Instron万能试验机测试5组牙齿的抗折裂载荷值,采用方差分析进行统计学分析。结果A、B、C、D、E组的抗折裂载荷值分别为：（576.11±91.53）、（204.13±85.88）、（451.50±116.81）、（386.16±117.75）、（566.05±121.37）N。经统计学分析,B组抗折裂载荷值低于其他组（P<0.01）;A、E组间的差异无统计学意义,其值最高,高于其他组（P<0.05）;C、D组间的差异也无统计学意义,其值低于A、E组,但高于B组（P<0.05）。结论下颌切牙瓷贴面预备后,牙体抗折能力无明显降低。下颌切牙Empress 2瓷贴面与全瓷冠粘接后,2种复合体的抗折裂能力无明显区别。     

Combination injuries 3. The risk of pulp necrosis in permanent teeth with extrusion or lateral luxation and concomitant crown fractures without pulp exposure

Abstract – Aim: To analyze the influence of a crown fracture without pulp exposure on the risk of pulp necrosis (PN) in teeth with extrusion or lateral luxation. Material and methods: The study included 82 permanent incisors with extrusion from 78 patients (57 male, 21 female) and 179 permanent incisors with lateral luxation from 149 patients (87 male, 62 female). A total of 25 teeth with extrusion and 33 teeth with lateral luxation had suffered a concomitant crown fracture (infraction, enamel fracture or enamel‐dentin‐fracture). All the teeth were examined and treated according to a standardized protocol. Statistics: The risk of PN was analyzed separately for teeth with immature and mature root development by the Kaplan–Meier method, the log‐rank test and Cox regression (lateral luxation only). The level of significance was set at 5%. Risk factors included in the analysis were gender, age, crown fracture, and response to electric pulp test at the initial examination. Results: A concomitant crown fracture significantly increased the risk of PN in teeth with lateral luxation. For teeth with immature root development (hazard ratio: 10 [95% confidence interval (CI): 1.1–100] P = 0.04), the overall risk increased from 4.7% (95% CI: 0–10.8) to 40% (95% CI: 2.8–77.2). For teeth with mature root development [hazard ratio: 2.4 (95% CI: 1.4–4.2) P < 0.001], the overall risk increased from 65.1% (95% CI: 55.2–75.1) to 93% (95% CI: 85.5–100). In teeth with extrusion and mature root development, the overall risk of PN increased from 56.5% (95% CI: 37.7–75.4) to 76.5% (95% CI: 58.9–94) in case of a concomitant crown fracture, but the difference was not statistically significant (P > 0.05). Conclusion: A concomitant crown fracture without pulp exposure significantly increased the risk of PN in teeth with lateral luxation. This risk factor may be used to identify teeth at increased risk of PN following lateral luxation injury.     

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

Abstract 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 ineisal edge. The strength was equivalent to that of intact teeth supplied with Dicor veneers (26.7 ± 6.3 MPa). While fracture strengths of teeth which were initially restored by fragment reattachment and then supplied with veneers exceeded that of intact teeth when veneer preparation was limited to enamel, they were reduced to the half of (hat of intact teeth (i.e. the same strength as teeth initially restored by fragment reattachment and no veneering) if the preparation extended into dentin. In the present experimental model, ii would appear that laminate veneers alone might be used to restore lost incisal edges of crown fractured anterior teeth.     

Location of the centers of resistance for anterior teeth during retraction using the laser reflection technique

The location of the centers of resistance for various symmetric units of the anterior maxillary dentition for a lingually directed force was studied in two dry human skulls. The units investigated were composed of two incisors, four incisors, and six anterior teeth. In addition, the effect of change in force magnitude on the location of the centers of resistance of these units was investigated. The laser reflection technique was used to study both the direction and magnitude of the initial displacement of the consolidated teeth under loading. The results indicated that the center of resistance shifted apically with the incorporation of a greater number of teeth into an anterior segment. With a unit of six anterior teeth, the apical shift of the center of resistance was the greatest. Increasing force levels had little effect on the location of the center of resistance of a given unit. This phenomenon was observed in both the skulls tested, suggesting that general trends may exist in the displacement characteristics of the dentition when subject to controlled force systems.     

Effect of chamfer design on load capacity of reattached incisors

ObjectiveThis study aimed to evaluate the effect of different chamfer preparations on the load capacity of reattached fractured incisors under lingual loading.MethodsEighty #8 typodonts were randomly assigned to four groups (n = 20 each). They were sectioned to simulate crown fracture, and reattached with a self-etch adhesive and a resin composite. The preparation for each group was: (1) no chamfer; (2) buccal chamfer; (3) lingual chamfer; and (4) circumferential chamfer. Forty-eight human lower incisors were grouped and prepared similarly (n = 12 each). These teeth were tested for their load capacity under a lingual load on a universal testing machine. Finite element models were used to examine the stresses on the reattached surfaces to help interpret the experimental results.ResultsThe buccal chamfer did not increase the load capacity when compared with the no-chamfer group. Lingual and circumferential chamfers respectively increased the fracture load by 36.9% and 32.3% in typodonts, and 78.5% and 33.3% in human incisors. The increase was statistically significant (p < 0.05). A higher fracture load tended to be accompanied by a larger area of deflected cohesive fracture. Finite element analysis showed that lingual and circumferential chamfers reduced the fracture-causing tensile stress at the lingual margin of the reattachment interface by approximately 70% and 60%, respectively, in human upper incisors.SignificanceIt was the joint design, and not the size of the bond area, that affected the load capacity of reattached incisors. Among the preparations considered, only those with a lingual chamfer could increase the load capacity of reattached incisors under a lingual load.     

Fracture resistance of human incisors and premolars: morphological and patho-anatomical factors

Abstract – 305 extracted human front teeth and premolars were investigated for their dynamic resistance to fracture. Morphological factors, such as the anatomical class of tooth and root lengths, and patho-anatomical factors, such as infractions, occlusal and cervical abrasions, composite and amalgam restorations and damage resulting from previous traumatic impacts, were taken into consideration. A comparison of stability after a defined impact stress showed that maxillary canines and premolars had the highest resistance to fracture; this differs significantly from the resistance of maxillary and mandibular incisors. The root length correlates directly with fracture energy and therefore to stability. Composite restorations with an adhesive joint were found to increase the resistance of a tooth to fracture, but amalgam restorations had a weakening effect. Cervical wedge-shaped defects of the tooth cause considerable destabilization, but occlusal abrasion and infractions have only a moderate weakening influence. Previous traumatic stress reduces the resistance to fracture of a tooth by up to 85%. The fracture patterns generated were very similar to clinically observed tooth fractures, indicating the results to be clinically relevant.     

Dental injuries and attention‐deficit/hyperactivity disorder in children

The purpose of this study was to determine the relationship between attention‐deficit/hyperactivity disorder (ADHD) and traumatic dental injuries in children. A total of 194 children aged 7–15 years participated in this study. Fifty‐seven traumatic injuries to permanent teeth were observed in 33 children. Although a statistically significant difference was not found (p= .848), the rate of incidence was higher in the group with ADHD (17.5%) than in the control group (16.5%). The maxillary right central incisors accounted for nearly half of all injured teeth, while the maxillary central incisors represented the most frequently injured teeth. Enamel fracture was the most common type of dental injury observed. The incidence of enamel fracture was higher in the control group (66.7%) than in the subjects with ADHD (43.3%). There was a significant association between the occurrence of traumatic dental injury and the presence of an overjet greater than 3 mm (p= .020).     

Influence of attachment and bone loss on the mobility of incisors and canine teeth

Abstract

Objective. The purpose of this clinical study was to evaluate the correlation between tooth mobility (TM), crown-to-root ratio (CRR) and clinical attachment loss (CAL) in periodontally-compromised participants. Materials and methods. While slowly biting on a load cell, the mobility of the upper incisors and canine teeth of 20 volunteers was measured using a photogrammetric measurement technique. An automated software program recorded the force-related three-dimensional TM at 3-N intervals. CAL was assessed clinically and CRR values were assessed radiographically. For each contralateral pair of teeth (central, lateral incisor, canine) and for each main level of force, the Pearson product-moment correlation coefficient between TM and CRR and between TM and CAL was computed. Correlations were considered statistically significant at p < 0.05. Results. Statistically significant positive correlations were found between TM and CRR for incisors and canines for each main level of force, whereas canines had the lowest correlation. Statistically significant positive correlations were also found between TM and CAL for the central and lateral incisors at each main level of force. Canines showed no significant correlation between CAL and TM, regardless of force level. Conclusion. The loss of attachment and bone seem to have more influence on the mobility of incisors than canines.     

Dynamometric assessment of the mechanical resistance of porcelain veneers related to tooth preparation: a comparison between two techniques

STATEMENT OF PROBLEM: There is little agreement regarding a palatal extension of the preparation for porcelain veneers, as it represents a more invasive technique than a preparation limited to the facial surface of a tooth. PURPOSE: The purpose of this study was to detect the stress in maxillary anterior teeth restored with porcelain veneers and compare the resistance to fracture of porcelain veneers prepared using different preparation designs. MATERIAL AND METHODS: Forty-five maxillary anterior teeth were restored with porcelain veneers and divided into 9 groups as follows: Ca, canines with no preparation; Ca-Ch, canines with palatal chamfer preparation; Ca-W, canines with window preparation; LI, lateral incisors with no preparation; LI-Ch, lateral incisors with palatal chamfer preparation; LI-W, lateral incisors with window preparation; CI, central incisors with no preparation; CI-Ch, central incisors with palatal chamfer preparation; CI-W, central incisors with window preparation. Shear-flexural fracture tests were performed. The fractured specimens were subjected to scanning electron microscope (SEM) analysis. Data were statistically analyzed with univariate analysis of variance and the Tukey post hoc test for multiple comparisons (alpha=.05). RESULTS: The following mean fracture load values (N) were recorded: Ca, 395 +/- 6; Ca-Ch, 310 +/- 8; Ca-W, 322 +/- 8; LI, 309 +/- 8; LI-Ch, 242 +/- 6; LI-W, 225 +/- 8; CI, 298 +/- 8; CI-Ch, 255 +/- 8; CI-W, 221 +/- 6. The SEM analysis showed that both adhesive and cohesive fractures were primarily concentrated at the cervical region. Statistical analysis showed that both the type of tooth and the design of the preparation significantly influenced the resistance to fracture of the restored teeth (P<.001). CONCLUSION: The chamfer preparation is recommended for central incisors, whereas the window preparation showed better results for canines. Both preparations can be adopted in the restoration of lateral incisors.