Periodontium soft and hard dental tissues between and

Periodontium • soft and hard dental tissues between and including the tooth and alveolar bone (AB) • figure 14 -1 • cementum • AB • periodontal ligament (PDL) • gingiva? ? (minor role)

Cementum • attaches the tooth to the AB – by anchoring the PDL and AB to the tooth • should NOT be visible in the healthy patient • thickest at the tooth apex • in multirooted teeth – thicker in the interradicular area • thinnest at the cementoenamel junction (CEJ) • no innervation • avascular – receives nutrition from the PDL • forms throughout the life of the tooth • 65% mineral, 23% organic, 12% water • mineral – hydroxyapatite (most similar to that seen in bone • apposition of cementum over the root dentin creates the dentinocemental junction or DCJ

Formation • • see previous lectures but to remind you: – disintegration of Hertwig’s root sheath is followed by cementogenesis – allows direct contact of the cells of the dental sac with the root dentin – cementoblast differentiation results (cementoblasts) – the differentiating cementoblasts disperse to cover the root and undergo cementogenesis – results in the formation of unmineralized cementoid – many CBs become entrapped in the mineralizing cementoid = cementocytes – once the cementoid reaches full thickness it begins to mineralize – initially around the cementocytes – • now called cementum – the cementocytes are located in lacunae – similar to bone – connected by canaliculi – unlike bone they do not contain nerves/vessels • also they do NOT radiate out but are directed toward the PDL • the cellular processes of the cementocytes take up nutrients that have diffused from the PDL into the cementum • see figures 14 -2 and 14 -11

Microscopic appearance • • • figure 14 -2 and 14 -11 made of a matrix + cells matrix – consists of Sharpey’s fibers – portion of collagen fibers from the PDL that partially insert into the outer part of the cementum at a 90 angle and into the alveolar bone – these function as a ligament between the tooth and AB – Figure 14 -2 • fibers – collage fibers made by the cementoblasts – non-organized – but they do run parallel to the DCJ • cells – cementoblasts – Figure 14 -7 – located in lacunae and connected by canaliculi

Cementoenamel Junction (CEJ) • 3 patterns may be present – 1) 60% show cementum overlapping the enamel at the CEJ – Figure 14 -8 – 2) 30% show an end-on-end meeting of cementum and enamel – 3) 10% show a definitive gap between the cementum and enamel • can result in dental hypersensitivity as the gingiva recedes exposing the underlying root dentin • “new study” – 1993 – 76% edge to edge, 14% overlap and 10% gap with no exposed dentin

Repair of Cementum • resorption occurs by the odontoclasts – results in the formation of reversal lines with a a scalloped appearance – occurs at a rate less than bone • repair – apposition of cementum by CBs at the adjacent PDL creates arrest lines – smooth growth rings (like a tree) – these can be prominent due to trauma from occlusal trauma or to tooth movement as well as the shedding of primary teeth and eruption of the permanent dentition – unlike bone – the cementum is not continuously remodelled and repaired

Types of Cementum • Acellular – – – • first layers that are laid at the DCJ formed at a slow rate no embedded cementocytes seen once continuous layer covers the root many layers are found covering the cervical 1/3 rd of the tooth near the CEJ – Figure 14 -3 Cellular – – – or secondary cementum last layers deposited – over the acellular layers mainly at the apical 1/3 rd of the tooth deposited at a faster rate – therefore the presence of many cementocytes at the periphery are CBs - found within the PDL • allow for the future production of more secondary cementum • therefore the width of these layers changes with the life span of each tooth • especially at the apex

Alveolar bone • part of the maxilla and mandible • point of attachment for the cementum – via the periodontal ligament • same composition as regular bone • but is remodelled at a higher rate • also remodelled at a higher rate when compared to the cementum – allows for tooth movement • when stained – alveolar bone shows areas of arrest lines and reversal lines – as seen in all bone tissue (figure 14 -13) • 60% mineralized, 25% organic, 15% water • mainly hydroxyapatite – similar to dentin and enamel • very similar to that seen in cementum

• each jaw is composed of two types of bone tissue – – different physiological functions these can lead to different clinical considerations • • – density of alveolar bone can determine the efficacy of local anesthesia and the spread of dental infection can also determine the most convenient areas of bony fracture during extraction 1. alveolar bone • • • or alveolar process or alveolar ridge contains the roots of the teeth divided into the – a. alveolar bone proper » lining of the tooth socket or alveolus (Figure 14 -15) » compact bone » bone is also called the cribriform plate because of the many holes through which Volkmann’s canals pass (from the alveolar bone into the PDL) » also called bundle bone because Sharpey’s fibers insert into this bone (Sharpey’s fibers = portion of the fibers of the PDL) » these fibers are inserted at a 90 angle into the ABP – but are fewer in number than those found at the cemental surface » consists of plates of compact bone that surround the tooth » varies in thickness from 0. 1 to 0. 5 mm » known in radiographs as the lamina dura (figure 14 -17) » most cervical rim = alveolar crest (figure 14 -18) – slightly apical to the CEJ in healthy patients » the crests of neighboring teeth are uniform in height » can see portions of the alveolar crest between teeth on radiographs also ( Figure 14 -17) – b. supporting alveolar bone » has the same components as ABP » spongy or cancellous bone » considered to be comprised of cortical and trabecular bone – different arrangement of bony plates, different locations » cortical bone is made up of cortical plates found on the facial and lingual surfaces ( Figure 14 -15) » trabecular bone is located between the ABP and the plates of the cortical bone ( Figure 14 -15 C – cross section of mandible)

– the alveolar bone between two neighboring teeth = interdental septum (Figure 14 -15) or interdental bone • made up of ABP and trabecular (spongy) bone • easily seen on periapical and bite wing radiographs (Figure 14 -17) – the alveolar bone between the roots of the same tooth = interradicular bone or interradicular septum • both ABP and trabecular (spongy) bone • only a portion can be seen on radiographs – 2. basal bone • apical to the roots of the teeth • forms the body of the maxilla and mandible

• alveolar bone can be resorbed with age – edentulous • the underlying basal bone is less affected with age – because it does not need the presence of teeth to remain viable • loss of teeth + alveolar bone can results in loss in the vertical dimension of the face – figure 14 -22 – “Popeye” facial appearance – can also affect the teeth and jaw line up – functional consequences – dental implants can prevent this loss • core of titanium that is surgically implanted into the alveolar bone • implant can become integrated into the surrounding bone • no movement – poor insertion of the PDL • after tooth extraction the clot is replaced with immature bone • later remodelled as mature secondary bone – very similar process to fracture repair in skeletal bone

Periodontal ligament • part of the periodontium that provides for the attachment of the teeth to the surrounding alveolar bone by way of the cementum – Figure 14 -25 • PDL appears as the periodontal space (0. 4 to 0. 5 mm) in radiographs – between the lamina dura of the ABP and the cementum (Figure 14 -17) • fibrous connective tissue - Figure 14 -26 • transmits occlusal forces from the teeth to the bone – allowing for a small amount of movement • wider at the apex and cervical portion – narrows between these two points

• components – made of matrix containing cells and fibers – also a vascular supply, lymphatics and nervous innervation – enter the apical foramen to supply the pulp • vascular supply is for the supply of nutrition for the cells of the PDL and surrounding cementum and alveolar bone • the nerve supply provides an efficient propriception mechanism – allows the sensation of even the most delicate forces applied to the teeth • afferent and autonomic sympathetic (regulates blood vessel diameter) • afferent fibers transmit pain, touch, pressure and temperature – cells • participate in the formation and resorption of the hard tissues of the periodontium • most common cell is the fibroblast – similar to other fibrous connective tissues • also has cementoblasts along the cemental surface and osteocytes at the periphery of the ABP • also has odontoclasts and osteoclasts for resorption of cementum and bone • balance between the “clasts” and “blasts” maintain a certain level of AB and cementum – depending on the need and environment adjacent to the PDL • also has epithelial rests of Malassez – figure 14 -26 – disintegration of Hertwig’s root sheath during tooth formation – fibers – all are collagenous in structure • made up of multiple bundles of principal fibers

PDL: Fibers • principal fibers – organized into groups or bundles • designed to resist the forces generated during mastication - because the PDL fibers are anchored in both the cementum and AB – 1) alveolodental ligament – 5 fiber groups – Figure 14 -27 • each of these have their own orientation – as such they resist specific forces • a) alveolar crest group – O: in the alveolar crest of the ABP » I: fans out and inserts into the cementum at various angles » F: resists tilting, intrusive, extrusive and rotational forces • b) horizontal group: O: from the ABP » I: into the cementum in a horizontal manner » F: resists tilting and rotational • c) oblique group: most numerous – covers the apical 2/3 rd of the root – Figure 14 -28 » O: ABP » I: more apically into the cementum – in an oblique manner » F: resists intrusive/inward forces and rotational • d) apical group: O: radiates from the apical region of the cementum » I: ABP » F: resists extrusive/outward forces and rotational • e) interradicular group – multirooted teeth only » O & I: runs from the cementum of one root to the cementum of the adjacent root » F: works with the alveolar crest group to resist intrusive, extrusive and rotational forces

– 2) interdental ligament -or the transseptal ligament • I: mesiodistally into the cementum of the neighboring teeth – over the alveolar crest group fibers (Figure 14 -27) • therefore travels from cementum to cementum without any bony attachment • F: resists rotational forces and holds teeth in interproximal contact • Figure 14 -31 – 3) gingival ligament – some clinicians disagree • Figure 14 -32 • support the marginal gingival tissues and do NOT support the tooth during mastication or speech • separate but adjacent fiber groups within the lamina propria of the marginal gingiva – a) circular ligament – lamina propria, encircles the tooth (pulling of purse strings) – b) dentogingival ligament – inserts into the cementum at the root and extends into the lamina propria, has one mineralized attachment to the cementum – c) alveologingival ligament – extend from the AC and radiate into the lamina propria, role in attachement of the gingiva to the AB – d) dentoperiosteal ligament – course from the cementum near the CEJ across the alveolar crest