JOURNAL OF DENTISTRY AND DENTAL MEDICINE (ISSN:2517-7389)

The aim of this review is to discuss the longitudinal tooth fractures in terms of definition and classification, aetiologies, incidence, diagnosis and management as well as to assess literatures including critical appraisal. Electronic library search was undertaken between January 2017 to March 2017 through different well Known journals such as International Endodontic Journal (IEJ), Journal of Endodontics (JOE), Journal of Endodontics, Oral Surgery Oral Med icine Oral Pathology Oral Radiology Endodontology (OOOOE) and Australian Dental Journal (ADJ).

Longitudinal tooth fracture is defined as a fracture that occurs over time with a vertical direction. Mainly, cracks and fractures can be divided into either incomplete and/or complete. In 2008, a classification of longitudinal tooth fracture was established to be from the least severe to the most. Longitudinal tooth fracture categorized into (a) craze line; (b) fractured cusp; (c) cracked tooth; (d) split tooth; and (e) vertical root fracture. The incidence of longitudinal tooth fracture is increasing due to many factors including that diagnosis of longitudinal tooth fracture is improved; therefore, it is not difficult to be identified and reported. Moreover, doing restorative procedures on teeth with no enough dentin support and placing restorations that eventually create wedging/displacing forces and cause longitudinal tooth fracture.

Longitudinal tooth fractures are findings; they are not considered to be pulpal or periapical diagnosis. Clinical signs and symptoms, results of objective tests such as a selective biting test aid detection of longitudinal tooth fracture. In addition, radiographic findings assist also to diagnose some types of longitudinal tooth fracture. There were numerous studies that used different imaging modalities and compared them to each other in order to evaluate their diagnostic accuracy. In fact, three-dimensional imaging modalities produce an image with high accuracy than the two-dimensional ones. However, some recent studies that have some limitations concluded that there was no statistical difference between the sensitivity or specificity of both 2D and 3D imaging modalities to detect vertical root fractures certainly.

Management of longitudinal tooth fracture is complex and challenging in some cases; however, some cases are severely fractured and the tooth is considered to be non-restorable; therefore, tooth or root extraction is the required treatment approach. Management of longitudinal tooth fracture varies based on the fracture extent as well as on tooth vitality and the associated symptoms. An essential initial step to be followed which is the removal of any existent restoration in order to assess tooth restorability and check for cracks and fractures. For instance, if the affected tooth is non-vital, severely symptomatic or a fracture is extended to the pulp, a root canal treatment is required. In addition, an orthodontic band to be placed in order to hold the segments together and to prevent the increase of the existing fracture during the root canal procedure. On the contrast, if the tooth is vital and asymptomatic. A bonded composite resin restoration to be placed in the assessment cavity and a cusp coverage restoration such as an onlay or a crown to be on the top eventually. Regarding vertical root fracture (VRF), the predictable treatment approach is either to extract the tooth or remove the fractured root by either hemisection or root amputation in multirooted teeth. Prevention of the different types of longitudinal tooth fracture can be achieved by following some preventive measures that can increase the fracture resistance ultimately.

Longitudinal tooth fractures; Vertical Root Fracture; Split tooth; Cracked tooth; Fractured cusp; Craze lines

In 1996, a longitudinal tooth fracture term was firstly introduced by Rivera. The reason behind using the term longitudinal fractures is that they represent vertical extensions of cracks or fractures over distance and time (1). Therefore, the definition of a longitudinal tooth fracture is a combination of two meanings or components. The first implies distance (length), particularly in the vertical (occlusal￾cervical) plane. The second indicates that these fractures occur over a period of time (2).

According to the American Association of Endodontists (AAE) in 2008, a longitudinal tooth fracture is classified into five classifications from the least severe to the most: (a) craze line; (b) fractured cusp; (c) cracked tooth; (d) split tooth; and (e) vertical root fracture (3). There are many terms that have been used for tooth fractures and this show the confusion about this complex condition (4). Therefore, in order to lower this confusion throughout researchers and clinicians, these five classifications aid to provide global definitions (5). The term crack differs from the term fracture. Crack means an incomplete break in a substance, while fracture is a complete or incomplete break in a substance (1).

There are many reasons behind the increase in the incidence of longitudinal tooth fractures. First of all, patients when they age, treatment modalities for their teeth that include restorative procedures (e.g. loss of marginal ridges) are their first treatment of choice rather than teeth extraction. A fracture happens once a force exceeds the dentine or enamel elastic limit (6, 7). Secondly, due to the improvement in diagnosing longitudinal tooth fractures, they can be more identified and their incidence is increased (1).

Generally, longitudinal tooth fractures occur as a result of occlusal displacing forces and/or dental procedures. These forces exceed the dentin strength (weaken dentin) and eventually lead to a longitudinal tooth fracture. These types of fractures are more common in posterior teeth although they can occur in all teeth (8). Bader et al identified the incidence rate for complete tooth fracture and that was based on 143 complete fractures identified during 14 days from a candidate population of 74,503 adults. Complete fracture rates of 5.0 and 4.4 per 100 adults per year for all teeth and for posterior teeth, respectively (9). In a recent study, it was found that 175 teeth out of 1977 teeth were diagnosed over a five-year period as cracked teeth (8.9%) (10). Vertical Root Fracture (VRF) is another common type of fracture. According to many studies that were conducted on certain participants who had extraction of root canal treated teeth because of VRF, the prevalence of VRF was reported and found to be as the main reason of teeth extraction.

Longitudinal tooth fractures are considered findings; they are not pulpal or periapical diagnosis. The diagnosis of these fractures is developed and there are many clinical tests that help in identifying these fractures such as trans-illumination, biting devices, staining and magnification improve the longitudinal tooth fracture diagnosis in addition to radiographic findings (1).

Treatment options for these fractures vary according to the fracture type. For instance, no treatment is needed for craze lines but other fractures require a treatment. Moreover, the prognosis of the fracture also depends on the fracture type and extent that ranges from hopeless to very good prognosis (1). For instance, teeth with extensive fracture have a poor prognosis and extraction is the possible treatment option (11).

Craze lines

Craze lines are a longitudinal defect in anterior teeth and also a defect that extends over marginal ridges in posterior teeth. These craze lines occur naturally and confined to enamel structure. When they occur on marginal ridges of posterior teeth, they can be confused with cracked teeth (12).

Fractured cusp

Fractured cusp is defined as either complete or incomplete fracture that starts from the crown and extends subgingival with both mesio￾distal and facio-lingual direction. On molar teeth, both buccal and lingual cusps may be involved (Figure 1) (13). Fortunately, fractured cusp is considered as the least devastating fracture type as well as the easiest to diagnose and manage (1). 

Incidence: Fractured cusp is more common than the other types of longitudinal tooth fracture. Teeth without cusp protection with extensive caries or large restorations are the more common teeth to have this type of fracture (14).

Mandibular cusps fracture is more common than maxillary cusps fracture, also nonfunctional cusps fracture is more often to occur than the functional cusps fracture. In 1985, hundred and eighteen cusp fractures were observed in an in vivo study (clinical survey). Mandibular molars presented 59 cusp fractures, eleven (19%) occurred on the functional buccal cusps, while 48 (81%) were on the nonfunctional lingual cusps. On the other hand, Maxillary molars presented 32 cusp fractures, 14 (44%) were on the functional lingual cusps while eighteen (56%) occurred on the nonfunctional buccal cusps (15).

Etiology: Longitudinal tooth fractures occur by occlusal wedging forces and/or dental procedures. In fractured cusp, there is usually a history of extensive deep interproximal caries or a subsequent large Class II restoration (1). Extensive caries or large restorations cause inadequate dentine support of the cusp (16); hence, a cusp fracture occurs.

Cracked tooth

Cracked tooth is an incomplete fracture started from the crown with subgingival extension, usually directed mesio-distally.

Incidence: Kang et al analyzed the distribution and characteristic features of cracked teeth and evaluated the outcome of root canal treatments (RCTs) for cracked teeth; the incidence of cracked teeth was stated. Out of 1977 teeth were examined over a five-year period, 175 teeth were diagnosed as cracked teeth (8.9%). According to AAE classification, of 175 cracked teeth, 25 were fractured cusps (14.3%), 111 were cracked teeth (63.4%), 21 were diagnosed with VRF (12.0%), and 18 were diagnosed with split tooth (10.3%). Cracks were more prevalent amongmen (61.1%) than women. The lower second molar was most frequently cracked (25.1%).

The majority of patients with cracked teeth were in the age ranges of 50–59 years (32.0%) and > 60 years (32.6%) (10). This study has some limitations. Although the title of this study is “Cracked teeth”, the results included all types of tooth fractures. In addition, this study was conducted on a specific population, those patients who visited the Department of Conservative Dentistry at Ewha Womans University Dental Hospital, Seoul, Korea. Therefore, the results of this study do not reflect the prevalence of cracked tooth on the whole population.

Etiology: Cracked teeth depend on both time and patient habits such as patients who chew hard on hard substances. Therefore, these forces exceed dentin strength and cracked teeth may occur. According to inconclusive evidence, another suggested cause is that differences in expansion and contraction of restorations versus tooth structure may weaken and crack dentin (17).

Split tooth

The end-result of a long-term progression of a cracked tooth is a split tooth (18) (Figure 2). The term split tooth means a complete fracture initiated from the crown with subgingival extension, usually directed mesio-distally. Both marginal ridges and proximal surfaces are involved (1).

Incidence: The incidence of split tooth is increasing as the incidence of cracked tooth (19).

Etiology: Both cracked and split teeth have the same causes. Split tooth may be more common in root canal treated teeth and this is because caries, restorations, or overextended access preparations compromise the strength of these teeth. In summary, the causes of split tooth include wedging forces on existing restorations and new traumatic forces that exceed the elastic limits of the remaining intact dentin.

Vertical Root Fracture (VRF)

Vertical Root Fracture (VRF) is either complete or incomplete fracture initiated on the root at any level with facio-lingual direction usually. This fracture may include one or both proximal surface (facial or/and lingual) (Figure 3) (20).

Incidence: Vertical Root Fracture (VRF) is a common fracture type to occur (21). Vire et al. evaluated extracted teeth which had been endodontically treated over a 1-year period. The reason for extraction was VRF in 4.3 % of the 116 extracted teeth (22). Fuss et al. researched a total of 564 permanent teeth which were extracted over 6 months. VRF was 10.9 % among 147 endodontically treated teeth (23). Moreover, Yoshino et al. investigated the prevalence, by gender, of vertical root fracture (VRF) as the main reason for the extraction of permanent teeth in dental clinics in Tokyo, Japan. The results of this study showed that 736 teeth were extracted from 626 patients during the 6-month period. A total of 233 teeth were extracted by VRF (31.7 %), and 93.6 % of these were endodontically treated teeth. In females, the percentage of extractions due to VRF (34.7 %) was higher than males (29.4 %) (24).

Etiology: Vertical Root Fracture (VRF) occurs due to wedging forces within the canal such as condensation (lateral and vertical) of the root canal filling (25) as well as post placement and cementation (26). Different condensation techniques for gutta-percha have revealed many fracture potentials (27, 28); however, larger canal preparations can cause higher stresses when these condensation forces are applied (28).