A narrative review of cracks in teeth: Aetiology, microstructure and diagnostic challenges.

OBJECTIVES: To summarize the available evidence of crack formation in teeth and to discuss the limitations of the current clinical diagnostic modalities for crack detection in teeth. BACKGROUND: Cracks are a common clinical finding in teeth and yet clinicians still struggle to identify the full extent and orientation of cracks for their appropriate timely management. The biomechanics of crack development can be due to multiple factors and can differ from an unrestored tooth to a restored or endodontically treated tooth. DATA & SOURCES: This narrative review has been designed following the guidelines published by Green et al. 2006 [1] Published literature in the English language that addresses the objectives of this review up to July 2022 was sourced from online databases and reference lists. The relevance of the papers was assessed and discussed by two reviewers. A total of 101 publications were included in this narrative review. CONCLUSIONS: The initiation and development of cracks in teeth are likely linked to an interplay between the masticatory forces and fracture resistance of the remaining tooth structure. From the identified literature, the quality and quantity of remaining tooth structure in a restored or endodontically-treated tooth affects the biomechanics of crack development compared to an unrestored tooth. The extent, orientation, and size of the cracks do affect a clinician's ability to detect cracks in teeth. There is still a need to develop reliable diagnostic tools that will accurately identify cracks in teeth beneath restorations to enable effective monitoring of their propagation and provide appropriate interventions. CLINICAL SIGNIFICANCE: The development and propagation of cracks in an unrestored tooth differ greatly from a restored and endodontically treated tooth; mainly linked to the quantity and quality of the remaining tooth structure and the forces acting on them. Identifying the extent of cracks in teeth remains challenging for early clinical intervention.

Was the Coronavirus Disease 2019 Pandemic Associated with an Increased Rate of Cracked Teeth?

INTRODUCTION: There is lack of data on whether the coronavirus disease 2019 (COVID-19) pandemic was associated with changes in the etiology of pathosis in endodontic patients. The aim of this study was to determine the rate of cracks and other etiologic factors during the period of March 16th to May 31st in 2020 (COVID-19 initial outbreak) and 2021 (COVID-19 ongoing pandemic) compared with figures from the same period in 2019 (pre-COVID era) in 2 endodontists' practices. METHODS: The etiologies of patients' chief complaints were determined from records of 2440 teeth (740 in 2019, 651 in 2020, and 1049 in 2021). Changes in the proportion of etiologic factors among all 3 periods were analyzed. The association between the rate of cracked teeth and patients' age and sex was determined using a logistic regression model. RESULTS: The rates of all etiologies collectively during the studied periods showed a significant change (P < .0001). The rate of cracks significantly increased in 2020 (11.8%) (P = .0001) and 2021 (8%) (P = .0018) compared with 2019 (4.3%). The rate of persistent infections decreased in 2020 (22.3%) (P = .0013) and then increased in 2021 (27.5%) (P = .0153) compared with 2019 (30%). Cracked teeth were associated with the age group of 40-60 years (odds ratio [OR] = 1.882; 95% confidence interval [CI], 1.063-3.330) in 2020 and with age ranges of 40-60 years (OR = 2.051; 95% CI, 1.120-3.759) and >60 years (OR = 2.038; 95% CI, 1.050-3.956) and male sex (OR = 1.599; 95% CI, 1.019-2.510) in 2021. CONCLUSIONS: The rate of cracked teeth increased during the initial outbreak of the COVID-19 pandemic and 1 year later. This study provided evidence on the association between the COVID-19 pandemic and changes in the rate and presentation of endodontic etiologic factors.

Review of Cracked Tooth Syndrome: Etiology, Diagnosis, Management, and Prevention.

Cracked tooth syndrome refers to a series of symptoms caused by cracked teeth. This article reviews the current literature on cracked tooth syndrome from four aspects, etiology, diagnosis, management, and prevention, to provide readers integrated information about this. The article begins with an introduction to the odontiatrogenic factors and then covers the noniatrogenic factors that induce cracked tooth syndrome. While the former discusses inappropriate root canal therapy and improper restorative procedures, the latter covers the topics such as the developmental and functional status of cracked tooth syndrome. This is then followed by the description of common clinical diagnosis methods, the prospects of new technologies, and summaries of current clinical management methods, including immediate management and direct and indirect restoration. In the final section, preventive methods and their importance are proposed, with the aim of educating the common population.

Repair of teeth with cracks in crowns and roots: An observational clinical study.

AIM: This retrospective observational study investigated the survival rate of teeth with radicular cracks that were restored using composite materials. METHODOLOGY: The study was approved by the Ethical Committee of Sistema Sanitario Nazionale (prot. N°2370CELazio1), Clinicaltrials.gov identifier: NCT04430205. Between 1991 and 2019, 87 teeth with radicular cracks (87 patients [46 men, 41 women, mean age 50.2 years]) were treated with adhesive composite restorations. Forty-five cracks were observed in the maxillary posterior teeth (molars and premolars), 40 in the mandibular posterior teeth and only two cracks in the anterior teeth, both in maxilla. Based on the depth of the crack, teeth were categorized as proximal radicular cracked teeth (PRCT), in which the fracture line was restricted within the pulpal floor or the coronal one-third of the root and deep radicular cracked teeth (DRCT), in which the fracture line extended to the middle and apical thirds of the root canal up to the apex. Bone loss/recovery was evaluated radiographically at 1-year follow-up. All patients were treated using surgical microscopy by the same operator. Logistic regression analysis was performed to determine independent predictors of extraction. Kaplan-Meier survival curves were used to analyse PRCT and DRCT. RESULTS: Among 87 cracked teeth, 66 were molars, 19 premolars and 2 incisors. Fifty-two were DRCT, 35 were PRCT, 46 had a periodontal probing defect. Patients were followed up for a mean of 66.9 months (standard deviation 44.6, min 1 to max 172). Lack of probing depth was a significant protective factor against extraction (odds ratio [OR] 0.027, 95% confidence interval [CI] 0.003-0.27, p < .05), whereas further bone loss (OR 10.63, 95% CI 2.08-54.36, p < .05) was a risk factor for extraction. More than 50% of teeth treated with the adhesive protocol were functional (46 of 87 teeth [χ2 test], p < .05) at 5-year follow-up. Among the PRCT group, a 78% survival rate at 5 years was found, while among the DRCT group, a 58% survival rate was found. CONCLUSION: Composite resin restorations resulted in tooth survival in >50% of patients; 85.4% of PRCT and 61.5% of DRCT were functional after 5 years of follow-up.

Oral Functional Behaviors and Tooth Factors Associated with Cracked Teeth in Asymptomatic Patients.

INTRODUCTION: A cracked tooth may occur due to excessive applied force or tooth weakness. However, there is scant information concerning the cracked tooth risk factors. This study aimed to explore the oral functional behaviors and tooth factors associated with posterior cracked teeth. METHODS: Fifty-six patients underwent their oral functional behavior assessment via a questionnaire. The intraoral parameters at the patient level (remaining teeth, occluding tooth pairs, overbite, overjet, and occlusal guidance type) and tooth level (remaining marginal ridge number, restored surface number, restorative materials, and cuspal inclination) were examined. The posterior teeth were stained with methylene blue dye and inspected for cracks using a microscope. The correlations between each patient-level parameter and the cracked tooth number/subject were determined using linear regression analysis. The cracked teeth were matched with their contralateral noncracked teeth, and binary regression analysis was used to analyze the association between tooth-level parameters and a cracked tooth. Multivariate regression analysis was performed if more than 1 parameter had a P value ≤.1. RESULTS: One hundred thirty-five cracked teeth were found. Eating hard food was significantly related to the cracked tooth number (P < .05). In molars, the occlusal surface restoration and cuspal inclination were significantly related to a cracked tooth, except the mesiobuccal cusp. In the multivariate analysis, the distolingual cusp inclination significantly predicted a cracked tooth (P < .05). In premolars, the lingual cusp inclination was associated with a cracked tooth (P < .05). CONCLUSIONS: Eating hard food, occlusal surface restoration, and steep cuspal inclination were associated with posterior cracked teeth.

Effect of Root Canal Preparation Techniques on Crack Formation in Root Dentin.

INTRODUCTION: The aim of this study was to assess the frequency of root crack formation caused by the use of manual instrumentation, 2 rotary systems, and 1 reciprocating system using light-emitting diode transillumination. METHODS: One hundred fifty mandibular premolars were randomly divided into 5 groups (n = 30): control 1, no intervention; control 2, instrumented with hand files; group 3, instrumented with ProTaper Universal rotary files (Dentsply Maillefer, Ballaigues, Switzerland); group 4, instrumented with OneShape rotary files (Micro-Mega, Besancon, France); and group 5: instrumented with the WaveOne reciprocal system (Dentsply Maillefer, Ballaigues, Switzerland). After root canal preparations, the roots were sectioned at 3, 6, and 9 mm from the apex with water irrigation. The slices were inspected under a stereomicroscope with light-emitting diode transillumination from the buccal, lingual, mesial, and distal directions at ×40 magnification to determine the presence/absence of cracks (dentinal defects). The chi-square test was used to analyze the data. RESULTS: There was a significant difference among the groups in crack frequency (P < .05). The 2 single systems had significantly higher cracks than the other 3 groups. At 3 mm from the apex, there were significantly more cracks in groups 4 and 5 than in groups 1, 2, and 3 (P < .05). At 6 mm from the apex, no significant difference was noted (P > .05). At 9 mm from the apex, the frequency of cracks in group 3 was significantly higher (P < .05). CONCLUSIONS: According to the results, using rotary instrumentation can result in some dentinal defects, and single-file systems, regardless of motion type, can cause significantly higher crack formation in the apical third of root canals.

Evaluation of XP-endo Shaper, Reciproc Blue, and ProTaper Universal NiTi Systems on Dentinal Microcrack Formation Using Micro-Computed Tomography.

INTRODUCTION: The purpose of the present study was to evaluate the frequency of dentinal microcracks observed after root canal preparation with XP-endo Shaper (XP), Reciproc Blue (RB), and ProTaper Universal (PTU) instruments using micro-computed tomographic (µCT) analysis. METHODS: Thirty extracted mandibular first and second molars with mesial roots having 2 separate canals with an angle between 10°and 20° were randomly assigned to 3 experimental groups (n = 10) according to the different nickel-titanium systems used for root canal preparation: XP, RB, and PTU. The specimens were scanned using µCT imaging before and after root canal preparation. Then, preoperative and postoperative cross-sectional images of the teeth were evaluated to identify the presence of dentinal defects. For each group, the number of microcracks was determined as a percentage rate. The McNemar test was used to determine significant differences before and after instrumentation. The level of significance was set at P ≤ .05. RESULTS: No new dentinal microcracks were observed in the XP and RB groups. The PTU system significantly increased the percentage rate of microcracks compared with preoperative specimens (P < .05). CONCLUSIONS: Root canal preparations with XP and RB systems might not induce the formation of new dentinal microcracks on the mesial roots of mandibular molars. Further assessments are suggested for the examination of the morphology of microcracks after the use of these instruments.

Cracked tooth syndrome in irradiated patients with head and neck cancer.

OBJECTIVES: The aim of this study was to assess the presence of enamel craze lines (ECLs), part of the spectrum of the so-called cracked tooth syndrome, on the surface of teeth irradiated in vivo. STUDY DESIGN: Forty teeth extracted from patients with head and neck cancer were paired, matched, and equally divided into 4 groups: noncarious irradiated (G1); noncarious control (G2); radiation-related caries (RRC) (G3), and carious control (G4). Samples were examined for ECL detection with a fiberoptic transillumination device and photographed, and ECL mean size, number, and patterns of topographic distribution in tooth crown were determined. Groups were compared accordingly: G1 versus G2; G3 versus G4. RESULTS: We analyzed 538 ECLs, of which 30.1% were found in noncarious irradiated teeth, 19.3% in noncarious controls, 27.6% in RRC, and 23% in carious controls. Non-carious irradiated teeth presented higher quantities of ECL than non-carious control (P < 0.05). Higher incidences of ECLs were identified in specific enamel topographies of anterior G1 and G3 samples (P <.05). There was no correlation between ECL size/numbers and radiation isodose delivery to teeth. CONCLUSIONS: Increased incidence of ECLs may indicate weakened enamel structure in irradiated teeth, and this may play a role in the onset and progression of RRC.

Cracked Teeth and Poor Oral Masticatory Habits: A Matched Case-control Study in China.

INTRODUCTION: Previous studies have suggested that masticatory forces are associated with cracked teeth, but it is not clear which specific poor oral masticatory habits may be more likely to cause cracks. The aim of this study was to quantitatively assess risk factors for cracked teeth among poor oral masticatory habits and create a model for individualized risk predictions. METHODS: We enrolled 35 patients with cracked teeth matched to 70 controls without cracked teeth by age, sex, position of the affected tooth, presence/absence of systemic disease, and diagnosis of symptomatic irreversible pulpitis from the Stomatology Hospital of Tianjin Medical University, Tianjin, China. Odds ratios (ORs) were calculated using conditional logistic regression analysis. RESULTS: Thermal cycling eating habits (OR = 3.296; 95% confidence interval [CI], 1.684-6.450), eating coarse foods (OR = 2.727; 95% CI, 1.340-5.548), chewing on hard objects (OR = 2.087; 95% CI, 1.041-4.182), and unilateral mastication (OR = 2.472; 95% CI, 1.255-4.869) were independent risk factors for cracked teeth. The corresponding risk scores were 2.182, 1.691, 1.467, and 1.589, respectively. The area under the receiver operating characteristic curve and its 95% CI were 0.920 (0.868-0.973); the sensitivity and specificity were 0.943 and 0.800, respectively. CONCLUSIONS: Thermal cycling eating habits were strongly associated with cracked teeth, whereas eating coarse foods, chewing on hard objects, and unilateral mastication were also independent risk factors for cracked teeth. These findings yield insights into ways to promote the prevention of risky behaviors for cracked teeth.

Cracked tooth syndrome mimicking trigeminal autonomic cephalalgia: A report of four cases.

BACKGROUND: This report describes four cases of cracked tooth syndrome secondary to traumatic occlusion that mimicked trigeminal autonomic cephalalgias. All patients were referred by general practitioners to the Orofacial Pain Clinic at Nihon University Dental School for assessment of atypical facial pain. CLINICAL PRESENTATION: Case 1: A 51-year-old woman presented with severe pain in the maxillary and mandibular left molars. Case 2: A 47-year-old woman presented with sharp, shooting pain in the maxillary left molars, which radiated to the temple and periorbital region. Case 3: A 49-year-old man presented with sharp, shooting, and stabbing pain in the maxillary left molars. Case 4: A 38-year-old man presented with intense facial pain in the left supraorbital and infraorbital areas, which radiated to the temporoparietal and maxillary regions. All cases mimicked trigeminal autonomic cephalalgias, a group of primary headache disorders characterized by unilateral facial pain and ipsilateral cranial autonomic symptoms. Trigeminal autonomic cephalalgias include cluster headache, paroxysmal hemicrania, hemicrania continua, and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing/short-lasting neuralgiform headache attacks with cranial autonomic features. Pulpal necrosis, when caused by cracked tooth syndrome, can manifest with pain frequencies and durations that are unusual for pulpitis, as was seen in these cases. CONCLUSION: Although challenging, differentiation of cracked tooth syndrome from trigeminal autonomic cephalalgias is a necessary skill for dentists.

Cracked Teeth: Distribution, Characteristics, and Survival after Root Canal Treatment.

INTRODUCTION: The aims of this study were to analyze the distribution and characteristic features of cracked teeth and to evaluate the outcome of root canal treatments (RCTs) for cracked teeth. The prognostic factors for tooth survival were investigated. METHODS: Over the 5-year study period, 175 teeth were identified as having cracks. Data were collected regarding the patients' age, sex, tooth type, location and direction of cracks, probing depth, pulp vitality, type of restoration, cavity classification, opposing teeth, and previous endodontic treatment history. Cracked teeth were managed via various treatment methods, and the 2-year survival rate after RCT was analyzed using the Kaplan-Meier method in which significance was identified using the log-rank test. Possible prognostic factors were investigated using Cox multivariate proportional hazards modeling. RESULTS: One hundred seventy-five teeth were diagnosed with cracks. Most of the patients were aged 50-60 years (32.0%) or over 60 (32.6%). The lower second molar was the most frequently (25.1%) affected tooth. Intact teeth (34.3%) or teeth with class I cavity restorations (32.0%) exhibited a higher incidence of cracks. The 2-year survival rate of 88 cracked teeth after RCT was 90.0%. A probing depth of more than 6 mm was a significant prognostic factor for the survival of cracked teeth restored via RCT. The survival rate of root-filled cracked teeth with a probing depth of more than 6 mm was 74.1%, which is significantly lower than that of teeth with probing depths of less than 6 mm (96.8%) (P = .003). CONCLUSIONS: Cracks were commonly found in lower second molars and intact teeth. RCT was a reliable treatment for cracked teeth with a 2-year survival rate of 90.0%. Deep probing depths were found to be a significant clinical factor for the survival of cracked teeth treated with RCT.

Correlation between cuspal inclination and tooth cracked syndrome: a three-dimensional reconstruction measurement and finite element analysis.

BACKGROUND/AIM: This paper explored the correlation between cuspal inclination and tooth cracked syndrome by measuring and reconstructing the cuspal inclinations of cracked maxillary first molars through three-dimensional (3D) finite element analysis (FEA). MATERIAL AND METHODS: The cuspal inclinations of 11 maxillary left first molars with cracked tooth syndrome and 22 intact controls were measured by 3D reconstruction. The mean values of each group were used to construct two 3D finite element models of maxillary first molar for comparing stress distribution under the loads of 200N at 0°, 45°, and 90°, respectively, to the tooth axis. RESULTS: There was statistically significant difference in the cuspal inclination between the incompletely fractured group and the intact control group ( P  < 0.001), which was 5.5-6.7 degrees steeper. The model from the mean cuspal inclinations of the incompletely fractured molars showed the maximum tensile stress of 5.83, 10.87, and 25.32 MPa, respectively, in comparison with 5.40, 8.49, and 22.76 MPa for the model of the control group. Besides, the tensile stress was mainly at the center groove and cervical region of the molar model. CONCLUSIONS: Steeper cuspal inclinations resulted in an increment in tensile stress that was mainly at the center groove and cervical region of the molar model under equivalent loads. Higher unfavorable tensile stress was generated with the increasing horizontal component load on the cuspal incline. This indicates an effective reduction of cuspal inclination to the compromised teeth for dentists.

The reduction in fatigue crack growth resistance of dentin with depth.

The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.

12-year survival of composite vs. amalgam restorations.

Information about the long-term clinical survival of large amalgam and composite restorations is still lacking. This retrospective study compares the longevity of three- and four-/five-surface amalgam and composite restorations relative to patients' caries risk. Patient records from a general practice were used for data collection. We evaluated 1949 large class II restorations (1202 amalgam/747 composite). Dates of placement, replacement, and failure were recorded, and caries risk of patients was assessed. Survival was calculated from Kaplan-Meier statistics. After 12 years, 293 amalgam and 114 composite restorations had failed. Large composite restorations showed a higher survival in the combined population and in the low-risk group. For three-surface restorations in high-risk patients, amalgam showed better survival.

Cracked teeth: a review of the literature.

Although cracked teeth are a common problem for patients and dentists, there is a dearth of evidence-based guidelines on how to prevent, diagnose, and treat cracks in teeth. The purpose of this article is to review the literature to establish what evidence exists regarding the risk factors for cracked teeth and their prevention, diagnosis, and treatment.

Cracked tooth syndrome. Part 1: aetiology and diagnosis.

Symptomatic, incompletely fractured posterior teeth can be a great source of anxiety for both the dental patient and dental operator. For the latter, challenges associated with deriving an accurate diagnosis together with the efficient and time effective management of cases of cracked tooth syndrome are largely accountable for the aforementioned problem. The aim of this series of two articles is to provide the reader with an in-depth insight into this condition, through the undertaking of a comprehensive literature review of contemporarily available data. The first article will provide details relating to the background of cracked tooth syndrome including the epidemiology, patho-physiology, aetiology and diagnosis of the syndrome, together with a consideration of factors which may influence the prognostic outcome of teeth affected by incomplete, symptomatic fractures. The second article will focus on the immediate and intermediate management of cracked teeth, and also provide a detailed account of the application of both direct and indirect restorations and restorative techniques used respectively in the management of teeth affected by this complex syndrome.

Aspects of wear and tear of tooth structure.

Lifestyle factors and the increased longevity of the dentition due to greater life expectancy have resulted in greater wear and tear (cracking) of teeth. Often there exists interplay between damage and repair. An understanding of these mechanisms of damage and repair will assist the clinician in correct diagnosis and treatment planning. Preventive strategies as well as interdisciplinary measures are required for optimal outcomes. However, are some of our restorative interventions causing further damage to tooth structure?

A review of the diagnosis and management of the cracked tooth.

UNLABELLED: A cracked tooth is a common presentation in general dental practice. It may be difficult to diagnose, owing to the variations in the clinical presentation.The symptoms that result from a cracked tooth have given rise to the term Cracked Tooth Syndrome (CTS).This article reviews and discusses the clinical signs, symptoms and the management of CTS. An early diagnosis is important to relieve pain, restore function and improve the prognosis for the tooth. The prognosis can be unpredictable and this needs to be understood by patients before embarking on definitive treatment. CLINICAL RELEVANCE: Cracked tooth syndrome is a common occurrence in general dental practice and may be difficult to diagnose, especially as to the extent and direction of the crack. Awareness of cracked tooth syndrome is therefore important in providing the correct treatment and patient management.

Cracked tooth syndrome: characteristics and distribution among adults in a Nigerian teaching hospital.

This study highlighted the characteristics and distribution of cracked tooth syndrome (CTS) and the associated factors in adult attendees in the University of Nigeria Teaching Hospital. Three hundred seventy patients aged 18 years to 77 years with CTS-like conditions were included and studied over 12 months. The following information was recorded: suspected tooth and the dental arch, restorative status of the tooth, age and sex of the patient, results of bite test and transillumination, and the pulpal and periapical status of the tooth. CTS was seen most often in the 41 to 50 years age band (36.4%), in molars (63.6%), and in the maxillary arch (51.5%). Also, it was more frequent in men (55.8%). About 82% of CTS occurred in amalgam-restored teeth. All cases had a positive response to the bite test and a normal response to the electric pulp test. Only 10% gave a positive history of masticatory accident as against none with history of bruxism habits. It was concluded that patients with unexplained pain in a vital, amalgam-restored tooth (especially in maxillary molars), with or without a history of a masticatory accident, may have a cracked or fractured tooth.

Calculation of contraction stresses in dental composites by analysis of crack propagation in the matrix surrounding a cavity.

OBJECTIVES: Polymerization contraction of dental composite produces a stress field in the bonded surrounding substrate that may be capable of propagating cracks from pre-existing flaws. The objectives of this study were to assess the extent of crack propagation from flaws in the surrounding ceramic substrate caused by composite contraction stresses, and to propose a method to calculate the contraction stress in the ceramic using indentation fracture. METHODS: Initial cracks were introduced with a Vickers indenter near a cylindrical hole drilled into a glass-ceramic simulating enamel. Lengths of the radial indentation cracks were measured. Three composites having different contraction stresses were cured within the hole using one- or two-step light-activation methods and the crack lengths were measured. The contraction stress in the ceramic was calculated from the crack length and the fracture toughness of the glass-ceramic. Interfacial gaps between the composite and the ceramic were expressed as the ratio of the gap length to the hole perimeter, as well as the maximum gap width. RESULTS: All groups revealed crack propagation and the formation of contraction gaps. The calculated contraction stresses ranged from 4.2 MPa to 7.0 MPa. There was no correlation between the stress values and the contraction gaps. SIGNIFICANCE: This method for calculating the stresses produced by composites is a relatively simple technique requiring a conventional hardness tester. The method can investigate two clinical phenomena that may occur during the placement of composite restorations, i.e. simulated enamel cracking near the margins and the formation of contraction gaps.