What is a cryptocracked tooth? Occultly cracked teeth, also known as incomplete fissures or microfissures, refer to small, non-physiological cracks on the surface of the tooth crown that are often not easily detected. The cracks often penetrate into the dentin structure and cause painful symptoms such as hot and cold stimulation or chewing discomfort. They are more common clinically, but are easily overlooked, so clinicians should pay sufficient attention to them. The most frequent occlusion occurs in the maxillary molars, followed by the mandibular molars and maxillary premolars, and the first molars are significantly more than the second molars, especially the proximal mid-palatal cusp, which is the main working cusp during the chewing movement of the upper and lower jaws and bears the greatest jaw force, and has the most suitable cusp corresponding to the central fossa of the mandibular molars. Although the maxillary molars have oblique crests, due to the unevenly worn high and steep cusps and the close occlusal relationship, they are also prone to occlusion at the proximal and distal sockets of the jaw surface and at the sulcus fissure between the two buccal cusps. The maxillary molar occlusion often overlaps with the proximal and distal mesiolingual sulcus, and the mandibular molar occlusion often overlaps with the proximal and distal mesiolingual developmental sulcus and crosses the marginal ridge to the adjacent surface. The etiology of occluded tooth fracture may be related to the following factors: the presence of fossae and grooves, which are weak links in the physiological structure of teeth, makes them have low cracking strength, and these places are precisely where the stress is concentrated when the teeth are subjected to normal jaw force, so they themselves are prone to occluded fracture. I. Endogenous causes The defects of the hard tissue structure of the tooth, the deep sulcus fissure or the presence of a large enamel plate between the enamel columns are the endogenous causes of the occult fracture. External causes (1) Treatment surgery to remove too much tooth tissue, thus weakening the tooth’s ability to withstand external forces. (2) Developed masticatory muscles or chewing hard and brittle foods and foreign bodies often lead to the occurrence of occluded fissures in the posterior teeth. (3) Differences in the coefficient of thermal expansion and coefficient of polymerization of filling materials can also weaken the strength of dentin and lead to the occurrence of occult fractures. There are two different views on the age of occurrence of occult fractures: one believes that it is mainly concentrated between 4O and 6O years of age, which is related to the fact that with age, teeth are also worn down and have sharp edges [1]. Another view is that it is predominant in young adult males between 35 and 50 years of age, which may be related to a preference for hard objects with too much force. Clinical manifestations of cryptoconjugation: Early cryptoconjugation often presents with fixed biting pain and transient and sharp cold stimulation pain, which is terminated by avoidance of occlusion. With the further development of the crypt fracture, the fracture reaches the pulp and the pulp becomes infected or even necrotic due to exposure. Clinically, crypt fissures may show a variety of symptoms such as pulpitis, pulp necrosis, and apical inflammation. In addition to the hot and cold pain, the characteristic chewing pain is often the main symptom of patients visiting the clinic, i.e. patients suddenly feel a penetrating soreness or sharp pain when chewing or feel the teeth are “soft” and dare not chew, at this time through careful examination can often find the hidden fissure. Early detection and timely treatment of occluded fissures can prevent them from deepening and maintain the function of the teeth. If there is long term bite discomfort or deep excitation pain, and no sensitive point or deep cavity can be found, and there is still discomfort after χ adjustment, the existence of cryptocclusion should be considered. Diagnosis method Exclude the tooth pain caused by carious disease and periodontal disease and make the diagnosis. (1)Bite jaw test: Place a cotton swab on the tip of the suspected tooth and ask the patient to bite the jaw, if there is obvious pain, the tooth may have occult fissure. (2) Staining method: the tooth surface will be dried and stained with 2.5% tincture of iodine when the fissure is clearly visible. (3) Prying method: Place the probe on the hidden fissure with pressure or pry with force to appear painful. (4) The affected teeth are taken x-ray to exclude root fracture. Diagnostic criteria for early cryptocclusion The crown is intact, and a cryptocclusion is visible on the cemental surface that anastomoses with the developmental sulcus and extends beyond the marginal ridge or has secondary caries; the affected tooth may be asymptomatic or have a history of occlusal discomfort or occasional soreness caused by biting on a specific site; the vitality of the pulp is normal or slightly sensitive, and there is no complication of endodontic disease. Treatment and restoration method The following comprehensive treatment is adopted for the teeth diagnosed as occult crack or fracture: I. Jaw adjustment: Jaw adjustment is the first step of treatment, any occult cracked teeth need occlusal adjustment. For teeth with cracks that cannot be restored with permanent crowns, the high and steep cusps and sharp marginal ridges should be reduced to eliminate occlusal trauma. For teeth with deep cracks that require dental treatment, the occlusion can be lowered or even made contactless. The degree of occlusal adjustment can depend on the thickness of the crown restoration to be made. Second, filling treatment: for teeth with cracks that only reach the superficial layer of dentin and do not affect the pulp, grind out the cracks to prepare the cavity and fill it directly with posterior glass ions, for those with cracks that reach the deep layer of dentin, cover with Ca(OH) and fill with posterior glass ions, without full crown restoration. The composite resin filling with strong adhesion and high anti-cracking strength is used for early cryptocracks, which helps to prevent the expansion of the cryptocracks. The preparation of small bevels on the cavity edge can improve the occlusal resistance of the cryptocracked tooth in addition to increasing the resin retention area. Crown restoration 1. For teeth with obvious occluded cracks or even fractures and lesions affecting the pulp or root tip, a shallow horizontal groove is prepared in the middle 1/3 of the buccal-palatal (lingual) surface of the crown and fixed with wire ligatures to make it fit closely with the tooth surface. 2. Patients with deeper occult fractures and fast progression of the disease present with obvious symptoms of pulpitis or subjective sensation of living pulp teeth at the time of consultation, but the pulp is found to be partially necrotic when endodontic treatment is performed. Therefore, perfect root canal treatment before full crown restoration is very necessary to avoid the symptoms of pulpitis and periapical inflammation after crown restoration, which will increase the patient’s pain, i.e., effective and perfect root canal treatment, after observing no obvious clinical symptoms for 2 weeks, full crown restoration will be given in time. 3. Full crown production should be fully reduced to reduce the joint force, so as to avoid excessive joint force and affect the service life of the affected tooth. The quality of full crown restoration is also one of the factors affecting the efficacy of the treatment. The crown edge should be tightly fitted, reducing the slope of the tooth tip and reducing the role of the horizontal splitting force, i.e., the splitting force. Increase the drainage sulcus and use point contact for occlusion. Increase the friction by grinding a reticular pattern on the inner wall of the crown and use resin bonding agent for adhesion. Underfitting of the full crown neck to the dentition, poor shape, adjacent relationship and too high occlusal surface can affect the efficacy. 4. A few cryptocrazed teeth split during treatment by abruptly biting hard objects; therefore, perfect root canal treatment along with plastic temporary crown protection is essential. In addition, it is also necessary to do transitional treatment with plastic nail crowns before formal crown restoration to observe the soft tissue reaction on both sides of the fracture, and after the patient has been restored with plastic crowns for 1-2 months without any discomfort, then crown restoration is performed. Fourth, after completing the treatment regardless of when the symptoms appear require patients to follow up in a timely manner, early detection and timely treatment. Asymptomatic patients are followed up after 1 year of treatment. Evaluation criteria (1) success: clinically asymptomatic, normal masticatory function, no percussion pain, no fistula formation, x-ray shows no abnormality at the periapical and root bifurcation. (2) Basic success: Occasional discomfort of the affected tooth, basic normal sensation and function of the affected tooth, normal percussion or slight discomfort, x-ray shows no lesion at the periapical and root bifurcation or no obvious change of the original periapical lesion, there may be a small shadow in the root bifurcation area. (3) Failure: discomfort of the affected tooth, pain, inability to chew, redness and swelling of the gums, even apical periapical infection, alveolar abscess or tooth fracture, tooth loosening II. Above, percussion pain is obvious, and x-ray shows enlarged shadows in periapical and root bifurcation areas. In conclusion, a comprehensive treatment method should be adopted for cryptoconstructed teeth. Preventing tooth fracture during treatment is the prerequisite, perfect treatment of pulpal or periapical disease is the basis, and timely full-crown restoration can enable long-term preservation of the affected tooth. As long as the effective and perfect root canal treatment can be carried out early and timely, and the crown restoration can be done properly and early, the phenomenon of tooth splitting can be effectively avoided.