The Periodontal-Endodontic Relationship, What Do We Know?

Diagnosis and management of periodontal-endodontic lesions are often complicated by the close interrelationship between periodontal tissues and dental pulps. Communications between both biological entities may occur through the apical foramen, accessory canals or exposed dentinal tubules, allowing bi-directional spread of infection and/or inflammation. Endodontic and periodontal lesions may occur distinctly or in tandem. Infected pulps may provoke an inflammatory response in adjoining periodontal tissues, and induce tissue destruction, and likewise, periodontal infection may elicit progressive pulpal pathoses. Solely periodontal or solely endodontic lesions are often clinically recognizable as distinct pathologies. However reported pain from pulpal or periodontal tissues may be similar, especially in combined lesions in which both endodontic and periodontal infection co-exist. When combined lesions develop, signs and symptoms such as toothache, tooth mobility, increased probing pocket depths and localized swelling may develop concurrently. As such, appropriate diagnostic tests and detailed clinical examination are required to differentiate periodontal, endodontic and combined pathologies and to arrive at correct diagnoses. Successful treatment outcomes for any periodontal and/or endodontic lesion depend on correct diagnosis and timely implementation of appropriate therapies. In this chapter, available evidence on periodontal-endodontic lesions will be reviewed with classification, clinical presentations, prognoses and treatment modalities discussed collectively

N-Carbethoxy-N′-(3-phenyl-1H-1,2,4-triazol-5-yl)thiourea

The title compound {systematic name: ethyl N-[N-(3-phenyl-1H-1,2,4-triazol-5-yl)carbamothio­yl]carbamate}, C12H13N5O2S, exists in the 3-phenyl-5-thio­ureido-1H-1,2,4-triazole tautomeric form stabilized by intra­molecular hydrogen bonding between the endocyclic NH H atom and the thio­ureido S atom. The mol­ecular structure is also stabilized by intra­molecular N—H⋯O=C hydrogen bonds arranged in an S(6) graph-set motif within the carbethoxy­thio­urea moiety. The mean planes of the phenyl and 1,2,4-triazole rings make a dihedral angle of 7.61 (11)°. In the crystal, the mol­ecules form two types of inversion dimers. Inter­molecular hydrogen bonds are arranged in R 2 2(6) and R 2 2(8) graph-set motifs, together forming a network parallel to (111)

7-Dimethyl­amino-2-phenyl-1,2,4-triazolo[1,5-a][1,3,5]triazin-5-amine methanol solvate1

7-Dimethyl­amino-2-phenyl-1,2,4-triazolo[1,5-a][1,3,5]triazin-5-amine crystallized with one mol­ecule of methanol to give the title compound, C12H13N7·CH3OH. The triazolo[1,5-a][1,3,5]triazine heterocyclic core is essentially planar as are both amino groups that are involved in π-electron delocalization with the triazolo[1,5-a][1,3,5]triazine nucleus. The methyl groups of the dimethyl­amino fragment are involved in the formation of weak intra­molecular C—H⋯N hydrogen bonds with the N atoms of the heterocyclic system. The crystal packing is stabilized by inter­molecular N—H⋯N hydrogen bonds between the triazolo[1,5-a][1,3,5]triazine mol­ecules. The methanol solvent mol­ecule also participates in the formation of the crystal structure via inter­molecular O—H⋯N, N—H⋯O and weak C—H⋯O hydrogen bonds, linking the layers of triazolo[1,5-a][1,3,5]triazine mol­ecules

4-Amino-2,8-dimethyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-one1

In the title compound, C8H9N5O, the mean planes through the pyrimidine and triazine rings form a dihedral angle of 2.83 (16)°. The amino group adopts a trigonal-planar configuration and forms an intra­molecular resonance-assisted N—H⋯O=C hydrogen bond with the carbonyl group. In the crystal, mol­ecules are linked via inter­molecular N—H⋯N hydrogen bonds into chains of C 2 2(6)[R 2 2(6)] motif. The molecules form two types of sheet parallel to (201) and (01), respectively

2-Phenyl-7-(4-pyridyl­methyl­amino)-1,2,4-triazolo[1,5-a][1,3,5]triazin-5(4H)-one1

In the title compound, C16H13N7O, the 1,2,4-triazolo[1,5-a][1,3,5]triazine heterocyclic system is essentially planar (r.m.s. deviation = 0.0375 Å). The attached benzene ring lies almost in the mean plane of 1,2,4-triazolo[1,5-a][1,3,5]triazine [dihedral angle = 1.36 (23)°], while the pyridine ring is turned out of this plane by the amino­methyl bridge [dihedral angle = 69.22 (9)°]. The amino group H atom is involved in intra­molecular hydrogen bonding with a triazole N atom. In the crystal, mol­ecules are connected via C(=O)NH⋯N hydrogen bonds into C(11) chains parallel to [100]. The amino group H atom acts as a hydrogen-bond donor, forming an NH⋯O=C hydrogen bond with the carbonyl O atom, which links the mol­ecules into C(6) chains running along [011] and [01]

3-Pyridin-2-yl-1H-1,2,4-triazol-5-amine

In the title compound, C7H7N5, the non-H atoms are almost coplanar (r.m.s. deviation = 0.050 Å), with the N atom of pyridine ring oriented to the N—N(H) side of the 1,2,4-triazole ring. The mean planes of the pyridine and 1,2,4-triazole rings form a dihedral angle of 5.58 (7)°. The N atom of the amino group adopts a pyramidal configuration. The mol­ecules are linked into a two-dimensional network parallel to (10) by N—H⋯N hydrogen bonds

3-Phenyl-1H-1,2,4-triazol-5-amine–5-phenyl-1H-1,2,4-triazol-3-amine (1/1)

In the title compound, C8H8N4·C8H8N4, two tautomers, viz. 3-phenyl-1,2,4-triazol-5-amine and 5-phenyl-1,2,4-triazol-3-amine, are crystallized together in equal amounts. The 3-phenyl-1,2,4-triazol-5-amine mol­ecule is essentially planar; the phenyl ring makes a dihedral angle of 2.3 (2)° with the mean plane of the 1,2,4-triazole ring. In the 5-phenyl-1,2,4-triazol-3-amine tautomer, the mean planes of the phenyl and 1,2,4-triazole rings form a dihedral angle of 30.8 (2)°. The π-electron delocalization of the amino group with the 1,2,4-triazole nucleus in the 3-phenyl-1,2,4-triazol-5-amine mol­ecule is more extensive than that in the 5-phenyl-1,2,4-triazol-3-amine tautomer. The mol­ecules are linked into a two-dimensional network parallel to (100) by N—H⋯N hydrogen bonds

4,4-Dimethyl-3,4-dihydro­pyrido[2′,3′:3,4]pyrazolo­[1,5-a][1,3,5]triazin-2-amine ethanol monosolvate1

In the title compound, C10H12N6·C2H5OH, the planarity of the heterocyclic system is slightly distorted at the triazine ring (r.m.s. deviation = 0.1191 Å), which adopts a conformation best described as inter­mediate between a flattened twisted boat and a half-boat with the tertiary Csp 3 atom at the bow. In the crystal, mol­ecules form centrosymmetric dimers connected by N⋯H—O and O⋯H—N hydrogen bonds between the amino group H atom, the ethanol solvent mol­ecule and the triazine N atom, making an R 4 4(12) graph-set motif. The other H atom of the amino group and the H atom on the endocyclic N atom form N⋯H—N hydrogen bonds with the N atoms of the pyrazole and pyridine rings, respectively, linking the mol­ecules into C(7)C(7) chains with the R 2 2(8) binary graph-set motif running along [010]

A monoclinic polymorph of N-eth­oxy­carbonyl-N′-(3-phenyl-1H-1,2,4-triazol-5-yl)thio­urea

The title compound, C12H13N5O2S {systematic name: ethyl N-[N-(3-phenyl-1H-1,2,4-triazol-5-yl)carbamothio­yl]carbamate}, is a monoclinic polymorph (space group P21/c) which crystallizes with three similar independent mol­ecules in the asymmetric unit. The triazole ring makes dihedral angles of 6.6 (2), 8.4 (2) and 10.6 (2)° with the phenyl ring in the three independent molecules. The structure was previously reported [Dolzhenko et al. (2010a ▶). Acta Cryst., E46, o425] as a triclinic polymorph crystallizing in space group P . Mol­ecules in both polymorphs possess two S(6) rings generated by intra­molecular N—H⋯S and N—H⋯O hydrogen bonds, resulting in similar mol­ecular geometries. However, the two polymorphs differ in the crystal packing. In contrast to the dimers of the triclinic polymorph, mol­ecules of the monoclinic polymorph are connected by inter­molecular N—H⋯S and N—H⋯N hydrogen bonds, forming pseudosymmetric trimers arranged in sheets parallel to (302)

4-Carbethoxy-1-[4-(N,N-dimethylamino)benzoyl]thiosemicarbazide

The mol­ecular structure of the title compound, C13H18N4O3S, (systematic name: ethyl N-{2-[4-(dimethyl­amino)benzo­yl]hydrazinethio­carbon­yl}carbamate) is stabilized by intra­molecular N—H⋯O=C hydrogen bonding arranged in an S(6) graph-set motif. In the crystal, inversion dimers connected via inter­molecular N—H⋯S=C hydrogen bonds [R 2 2(8) graph-set motif] form sheets parallel to the (21) plane. Dimers are also formed by the mol­ecules via weak inter­molecular N—H⋯S=C hydrogen bonds [R 2 2(10) graph-set motif] connecting the sheets