# Risk Factors Associated with Cusp Fractures in Posterior Permanent Tenth--A Cross-Sectional Study
## 4 Discussion
Proximal box preparation significantly weakens the entire dental structure and further potentiates fractures due to the marginal ridge loss. Cavity preparation has been reported as one of the numerous risk factors for dental fractures [5, 6, 7, 10, 11, 12, 13, 15], yet more than 500 million restorations are annually placed worldwide [19]. Dentistry coexists with these paradoxical data since restorative interventions in the management of dental caries is often unavoidable. Besides, placing this relevant information together with the other 49 described risk factors for tooth fractures may be leading the practitioner to underestimate the relevance of cavity preparation, not knowing what really matters and believing that, due to restoration, the tooth is recovering. However, this is not what actually occurs. Lower molars were the most fractured teeth, followed by upper molars and upper premolars. This could be explained by the tooth eruption chronology since the lower 1 st permanent molars are the first posterior teeth to erupt and thus they could be affected earlier by caries, receiving restorations and becoming more vulnerable to fractures. Generally, patients did not refer symptomatology before experiencing fractures (85%) and, consequently, the presence of symptoms cannot be taken as an indication to start preventive measures. However, these data reinforce the importance of frequent dental visits since the absence of sensitivity alone cannot be considered relevant for the diagnosis; clinical observation of the presence of cracks or fracture lines is also relevant, among others indicators [2,13,17,21,29]. Here, when symptoms were present (15%), they were often inaccurate. However, pain during mastication was the most frequently reported, followed by nonspecific pain and after-cold stimulus. Although endodontic treatment is not a fracture determinant, it might be associated with its severity since the present is more subgingival. In vital teeth, fractures often reach the level of the bone crest, whereas in nonvital teeth, they are usually subgingival since the fracture line may propagate to the root portion. Fractures begin at the dihedral of the cavity preparation involving the pulp wall and its surrounding ones, mainly buccal and lingual, and the deeper the pulp wall, the more subgingival the fractures tend to be [6]. Although endodontic treatment is not a fracture determinant, it might be associated with its severity, since the present is more subgingival. Usually, teeth that require root canals have undergone successive structure losses, numerous cavity preparations, and restoration placements. These factors really weaken the structure integrity and not necessarily the pulp removal and endodontic access as an isolated cause. [PERSON] et al. (1989) [18] stated that accessing the pulp chamber reduces dental stiffness by only 5%, whereas the preparation of a mesial-oclusal-distal cavity reduces it by up to 63%. [PERSON] and [PERSON] (1990) [19] observed retrospectively that the survival of endodontically treated teeth restored with amalgam was 74% (teeth with mesial-oclusal/distal-occlusional preparation), 38% (mesial-oclusal-distal), and only 28% of upper premolars (mesial-oclusal-distal) remained intact after 20 years. These data suggest, as do the findings in this study, that cavity preparation is an important factor for dental fractures in comparison to endodontic treatment itself. Individual and multifactorial variations such as sex, age, race, cusp height, pit and fissure depth, enamel thickness, tooth size, structure loss (i.e., cavity preparation, caries, and cervical lesions), restorative material, type of food, occlusal contact, and parafunctional habits have been cited as failure predictors [1,2,5, 6, 7, 11, 13, 14, 15]. Nevertheless, some of these can be considered as possible confounding factors, such as the restoration size and restorative material. In a case-control study, [PERSON] et al.