Prosthodontics PDF Past Paper

Prosthodontics 1 General Considerations In Prosthodontics we will review general considerations, occlusion and articulators, edentulous anatomy, pre-pr...

Prosthodontics 1 General Considerations In Prosthodontics we will review general considerations, occlusion and articulators, edentulous anatomy, pre-prosthetic surgery, complete dentures, phonetics, support stability & retention, denture processing, Kennedy classi cation, connectors, rest & proximal plates, clasps design, tooth preparation, pontic & connector design, impression materials, gypsum materials, metal alloys, mechanical properties, provisionals crowns, types of crowns, shade selection, dental cements, lab fabrication of crowns Prosthodontics is the branch of dentistry Prognosis of a Bridge focusing on the design, manufacture and Patients with poor prognosis for a dental tting of arti cial replacements for teeth and bridge can exhibit the following characteristics: other parts of the mouth. Equal or less than half alveolar bone support around abutment tooth Connectors not strong 1 Bridge ‣ Lock and key mechanism for bridge to connect to abutment teeth Anatomy & De nitions ‣ Comprise of a tenon (male component) Abutment = a speci c tooth that the and mortise (female component) bridges latches onto Pier (intermediate abutments) Retainer = a speci c crown that sits on top ‣ More occlusal force on pier abutment can of the abutment lead to torquing of abutment Pontic = fake tooth in between retainers Single retainer cantilever Connector = between retainer & pontic ‣ Not ideal for posterior cantilever due to Cantilever = fake tooth only supported on heavy occlusal forces one side by a retainer Multiple-splinted abutment teeth Pier = abutment tooth that has no adjacent teeth in proximal contact Figure 1.02 Nonrigid Connector Figure 1.01 Bridge anatomy INBDE Booster | Booster PrepTM fi fi fi fi fi fi Prosthodontics 2 The following teeth should never be Ante’s Law considered as an abutment tooth: Ante’s Law states that the total periodontal 1. Compromised periodontal teeth surface area of the abutment teeth should be 2. Endodontically treated teeth greater than or equal to the surface area of the ‣ Less internal dentin after RCT thus it is a teeth they are replacing. weaker tooth The following scenario in the image below illustrates this law Crown to Root Ratio Crown to root ratio refers to ratio of the length of the clinical crown to the length of the clinical root. The ratios can indicate to tooth to be ideal to having poor prognosis of an abutment tooth. Crown: Root Ratio Indication Figure 1.03 Ante’s law 1:2 Ideal 2:3 Realistic The blue outline demonstrates the PDL space of the abutment teeth of the bridge 1:1 Minimum The PDL space of the imaginary teeth are 2:1 Poor (contraindicated) in red Blue area ≥ red area for these teeth to be appropriate as abutment teeth INBDE Pro Tip: It is important to know the differences between Splinting clinical and anatomical crown and root. Used when the periodontal surface area of the abutment tooth is insuf cient to attach Clinical Anatomical a bridge and Ante’s Law can not be obeyed Above the Distribute occlusal forces across multiple Crown Above the CEJ gingiva teeth Central and lateral incisors must be Below the Root Below the CEJ splinted together when canines are gingiva replaced ‣ Prevents lateral drifting of the bridge INBDE Booster | Booster PrepTM fi Prosthodontics 3 Root Shape Complete Denture (CD) Overall, root shape will dictate the amount of Complete dentures are used when all teeth are PDL space available of the abutment teeth that missing will support the bridge. Upper denture should be used with caution Preferred characteristics when only mandibular anterior teeth ‣ Broad roots available ‣ Divergent ‣ Combination syndrome ‣ Curved ‣ Multiple Non-preferrable characteristics ‣ Round roots ‣ Fused ‣ Conical ‣ Single Figure 1.05 Complete denture INBDE Pro Tip: Remembering desirable root characteristics can Overdenture relate to how easy or dif cult certain teeth are Classic implant placement = 4 implants in to extract. Teeth that are more dif cult to maxilla, 2 implants in mandible extract have roots that exhibit desirable traits for an abutment tooth. 2 Other Denture Types Removable Partial Dentures (RPD) Figure 1.06 Overdenture Removable partial dentures (RPD) are indicated over bridges in certain scenarios Alternative option for edentulous patients Bridge or implant is too costly Cement-Retained Implant Distal extension Inexpensive ‣ All of teeth distal to a certain point are Used for minor angle correction missing More chair time, less propensity to loosen Bone loss around potential abutment as a screw retained implant spaces Excess cement can cause peri-implantitis Long Span of edentulous teeth ‣ Important to clean implant area after cementation Figure 1.07 Cement-retained implant Figure 1.04 Removable partial denture INBDE Booster | Booster PrepTM fi fi Prosthodontics 4 Screw-Retained Implant Easy to remove the crown to clean it and place it back on Screw may loosen while chewing Figure 1.08 Screw-retained implant INBDE Booster | Booster PrepTM Prosthodontics 5 Occlusion & Articulators 1 Alginate Maximum Intercuspation (MI) Condylar position irrelevant Complete interdigitation of teeth Alginate is the most universally used Sometimes referred to as centric occlusion impression material for diagnostic casts Alginate powder components (CO) ‣ Insoluble calcium alginate produced by a ‣ When CO = MI (rare) chemical reaction between salts ‣ Setting rate controlled by trisodium phosphate More volume = less dimensional change ‣ Alginate should be thick enough to capture anatomy of patient’s teeth Remove tray from patients mouth after 2-3 minutes seating in patient’s mouth Figure 2.02 Maximum Intercuspation Pour impression with stone within 15 minutes ‣ Cast sets within 30-60 minutes CR vs. MI MI and CR rarely match and most people 2 Maxillo-Mandibular Relations (MMR) slide from CR into MI Casts are mounted in either: There are two main relationships where the ‣ MI for single xed procedures or when MI maxilla and mandibular relationships can relate can be maintained to each other. ‣ CR for restoring multiple teeth or when MI can not be maintained or determined Centric Relation (CR) CR is the most reliable and reproducible Teeth position irrelevant jaw relationship in the mouth At the articulation between the condyles and the thinnest portion of the upper and lower discs in the most anterior-superior position against the articular eminences Figure 2.01 Centric Relation Figure 2.03 Maxilo-mandibular relations INBDE Booster | Booster PrepTM fi  Prosthodontics 6 Bimanual Manipulation 4 Articulators Positioning a patient in CR position can be achieved through bimanual manipulation The facebow record transfer the relationship of method. It is an accurate method to obtain CR the maxilla and the rest of the skull to the interocclusal records. articulator. The interocclusal record is used to mount the mandibular cast, on the articulator, 1. With patient lying back relative the maxillary cast. There are many ‣ Hold the posterior mandible with nger different types of articulators used in clinic, but ‣ Hold chin with thumbs there are some parts common to all of them 2. Deprogram the jaw that represent different parts of masticatory ‣ Patient relaxes their jaw as much as system. possible Upper area = maxilla 3. Recognize rst CR tooth contact and Lower area = mandible repeat until a consistent rst tooth contact Hinge axis = TMJ is identi ed 4. Keep anterior teeth slightly apart in CR Non-adjustable Articulator with acrylic resin jig Cannot entirely represent the movements 5. Lastly, measure an interocclusal record of of mandible posterior teeth with PVS ‣ Only opens and closes Much shorter distance between hinge and 3 Facebow Record teeth thus can cause premature contacts A facebow record aims to replicate the Semi-adjustable Articulator articulator relationship of maxillary arch to the Includes Bennett angle (15º) and skull and the mandible to the hinge axis of the Horizontal condylar inclination (30º) TMJs of the patient. The facebow record is taken on the patient with their interocclusal record in the mouth The facebow record is then transferred onto an articulator Figure 2.05 Semi-adjustable articulator Fully Adjustable Articulator Pantograph – most complex articulator Figure 2.04 Arbitrary face bow that is used to record mandibular border movements INBDE Booster | Booster PrepTM fi fi fi fi Prosthodontics 7 Mounting Casts 4. Anterior guidance Casts made with the alginate impression ‣ Involves both incisal and canine guidance are better mounted with wax records Casts made with elastomeric materials are That following are important to note when better mounted with ZOE paste or analyzing the different forms of guidance. elastomeric materials (PVS) Condylar and incisal guidance may or may not work in harmony with each other During protrusive movement, both the incisal and condylar guidance supply clearance for all posterior teeth During lateral movement, canines on the working side and condyle on balancing Figure 2.06 Mounting casts side supply clearance for posterior teeth on the balancing area Disclusion Disclusion describes how the teeth separate Guide table from one another in order to protect the teeth Custom incisal guides tables, are made from wearing or receiving too much occlusal from acrylic resin, and are preferred over force. mechanical guide tables as they move in curves and can follow patients lingual 1. Incisal guidance anatomy. ‣ Determines anterior occlusion During restorative treatments, anterior ‣ Occludes between incisal edges of lower guidance should be protected because incisors & lingual slopes of upper incisors they can modify the “guiding” teeth - Varies between patients ‣ Shown by pin and guide table on the articulator 2. Condylar guidance ‣ Determines posterior occlusion ‣ Slope of articular eminence - Varies between patients ‣ Shown by horizontal condylar inclination Figure 2.08 Guide table (HCl) on articulator Mutual Protection 3. Canine guidance Mutual protection demonstrates the following ‣ During lateral movements, posterior concepts teeth disclude as contact is solely Front teeth preserve the back teeth between upper and lower canines o During protrusive and lateral movements, anterior teeth disclude back teeth Back teeth preserve the front teeth o Back teeth possess at occlusal surface and rigid roots to preserve front teeth from bite forces Figure 2.07 Canine guidance INBDE Booster | Booster PrepTM fl  Prosthodontics 8 Edentulous Anatomy 1 Maxillary Edentulous Anatomy Coronoid Notch – distobuccal side of There are several important anatomical impression/denture landmarks in discussing the anatomy of the ‣ Patient moves in lateral excursion during maxilla impression to capture anterior process of the coronoid notch Alveolar Ridge Buccal and Labial Frenum – thin fold of mucous membrane with enclosed muscle bers that control the movement of mobile tissue Buccal Vestibule – area between the cheek and the lips Labial Vestibule – area between the lips and alveolar ridge Vibrating Line – boundary spanning from Figure 3.01 Max. Edentulous Anatomy hamular notch to hamular notch ‣ Often 2mm away from fovea palatini (pits in the palate) Pterygomandibular Raphe – brous tissue ‣ When patient says “ah”, the vibrating line that links superior pharyngeal constrictor will divide the vibrating tissue to the non- muscle and buccinator vibrating tissue on the palate ‣ Captured in the impression if the patient Hamular Notch – notch/ ssure at junction opens wide (pterygomandibular raphe of maxilla and hamular process of sphenoid moves forward) bone ‣ Distal to the most distal process of the alveolar ridge Posterior Palatal Seal ‣ Marks the area that a denture suf ciently compresses the soft palate with enough suction ‣ Master cast of maxilla is slightly carved around the area of the vibrating line to create more acrylic thickness to make up for polymerization shrinkage of denture Figure 3.02 Pterygomandibular raphe material = creates an ideal posterior palatal seal INBDE Booster | Booster PrepTM fi fi fi fi  Prosthodontics 9 2 Mandibular Edentulous Anatomy 1. Anterior region – from lingual frenum to premylohyoid fossa Like the maxilla, the mandible has important ‣ Sublingual gland located above landmarks to locate when making mylohyoid muscle prosthodontics. ‣ shorter ange of the denture and touches the mucosa of the oor of the Alveolar Ridge – less broad and wide than mouth the maxilla 2. Middle region – from premylohyoid fossa Buccal Frenum – attached to orbicularis to distal end of mylohyoid ridge oris and buccinator ‣ Flange medially de ected away from Labial Frenum – at the midline, attached to mandible due to medial contraction of orbicularis oris mylohyoid muscle and prominence of Lingual Frenum – attached to genioglossus mylohyoid ridge Buccal Vestibule - attached to buccinator 3. Posterior region – reaches the Labial Vestibule – attached to mentalis retromylohyoid fossa Masseteric Notch – distobuccal area on ‣ Although mylohyoid located higher the impression/denture posteriorly, ange is higher and denture ‣ Masseter muscle - contracts when the is deeper because the bers are vertically mouth closes on resistance directed ‣ Analogous to the coronoid notch of ‣ S-form of lingual sulcus due to laterally maxilla de ected ange toward the ramus of the Retromolar Pad – determines distal mandible extension of edentulous ridge ‣ Limited denture extension due to ‣ Should be covered by denture for superior constrictor & palatoglossus retention and support since it has muscles attachments from the following muscles: - Superior pharyngeal constrictor Buccal shelf – lateral to posterior alveolar - Pterygomandibular raphe ridge - Buccinator ‣ Supports denture - Temporalis ‣ Attachment to buccinator muscle Alveololingual Sulcus – between ‣ Perpendicular to occlusal forces mandibular alveolar ridge and tongue ‣ Runs posterior to lingual frenum ‣ Follows an ‘S’ shaped pattern ‣ Divided into 3 regions: - Anterior - Middle - Posterior Figure 3.03 Buccal shelf INBDE Booster | Booster PrepTM fl fl fl fl fl fi fl  Prosthodontics 10 Pre-Prosthetic Surgery 1 Pre-Prosthetic Surgeries Papillary Hyperplasia Multiple papillary projections of the palate Pre-prosthetic surgeries are carried out prior caused by the following: to creation of a denture for better outcomes ‣ Candidiasis (most common cause) and long-term results for the patient. There are - Treat with -statin or -azole many types of these kinds of conditions where ‣ wearing dentures for too long surgeries may be permitted before the nal ‣ local irritation denture is made. ‣ ill- tting denture ‣ poor oral hygiene Treatment Frenectomy When the frenum attaches too far into the ‣ Tissue conditioner alveolar ridge, interfering with seating of ‣ Leave dentures out at night the denture ‣ Soak dentures in 1% bleach and rinse Lingual < buccal < labial (least to most ‣ Brush irritated area lightly with soft brush common) ‣ OHI Epulis Fissuratum Hyperplastic tissue reaction, commonly in vestibule Causes – overextended ange or ill- tting denture Tissue conditioner used for treatment and adjusts denture ange Figure 4.01 Frenectomy May require surgery if response is severe Free Gingival Graft (FGG) Combination Syndrome Required for overdenture teeth Speci c bone resorption pattern in the Expands range of keratinized tissue anterior edentulous maxilla when only around implants or teeth opposing mandibular anterior teeth ‣ Tissue is rmer and not as sensitive as present non-keratinized mucosa Papillary hyperplasia in hard palate ‣ Easier to maintain oral hygiene Multiple tuberosity overgrowth Bone loss below the partial dentures Fibrous (Pendulous) Tuberosity Extrusion of lower anterior teeth Commonly occurs when large tuberosities touch retromolar pads INBDE Pro Tip: Interferes denture fabrication by restricting Questions about Papillary Hyperplasia, Epulis interarch space ssuratum, and Combination Syndrome are Requires surgical excision of bone and/or common questions on the INBDE. brous tissue for correction INBDE Booster | Booster PrepTM fi fi fi fi fi fl fl fi fi  Prosthodontics 11 Hypermobile Ridge Paget’s Disease Mobile edentulous ridges, commonly Etiology is unknown observed in maxilla Poor tting dentures require to be Tissue conditioner used to treat in amed periodically remade tissue ‣ Due to deformities forming Electrosurgery or laser surgery used when Deformities led by bone resorption & tissue conditioner is ineffective repair ‣ Removes tissue ‣ Risk of eliminating the vestibule – not ideal Vestibuloplasty Raises the relative height of the alveolar process = Raises the base of denture area Useful for Apically repositioning the alveolar mucosa, and the mylohyoid, mentalis, and buccinator muscles ‣ Insert into the mandible Lingual vestibuloplasty is more traumatic and rarely done Alveoloplasty Primarily used for spiny, sharp, or extremely irregular ridges Reshaping alveolar bone with surgery Tori (mandibular) removal - When it hinders posterior palatal seal or forms an undercut - Tori are easily irritated as well Retained Root Tips Residual root tips (non-RCT) are risk factors They can be left if they have no PARL and have intact lamina dura Bone Augmentation Horizontal > Vertical Hydroxyapatite – biocompatible bone substitute Bone-grafts – sources (iliac crest of hip & rib) INBDE Booster | Booster PrepTM fi fl  Prosthodontics 12 Complete Dentures 1 Vertical Dimension Excessive VDO Excessive VDO occurs when the interocclusal Vertical Dimension of Rest (VDR) space is less than 2mm. There are many issues Height between nose and chin @ rest associated with excessive VDO. Physiological Rest Position (PRP) - Muscles of mastication fatigue Clicking noise of posterior teeth during elevator and depressor muscles are in a state of equilibrium speaking Typically 3mm space between upper and Both excessive trauma to supporting lower premolars tissues and display of mandibular teeth Unable to wear dentures Gagging Vertical Dimension of Occlusion (VDO) Height between nose and chin during Insuf cient VDO occlusion Insuf cient VDO occurs when the interocclusal Used to illustrate the relationship of the space is more than 4mm and has a long maxilla and mandible during occlusion in distance of closing. The following are MI associated with insuf cient VDO: Angular cheilitis – fungal infection of the Interocclusal Space corners of the mouth VDR - VDO Aging appearance of lower 1/3 of face Ideal distance = 2-4 mm ‣ overlapping corners of mouth, thin lips, VDR = VDO + 3mm wrinkles, chin too near the nose Decreased occlusal force 2 Intraoral Examination CR Record For an edentulous patient, taking a record in centric relation provides the clinician with the ability to increase or decrease the VDO when making a denture. The record provides a radius of mandible Figure 5.01 Interocclusal space arc of closure Facebow carries the relationship between the maxilla and mandibular hinge axis to the articulator INBDE Booster | Booster PrepTM fi fi fi Prosthodontics 13 Protrusive Record Balanced Occlusion Protrusive record shows the anterior-inferior Balanced occlusion is a type of occlusion condyle path in translational movement of the where there is both anterior and bilateral condyles posterior contacts (tripodization) in centric Christensen’s phenomenon – distal gap and eccentric movements. between the maxilla and mandibular teeth Helps sustain the seating of dentures during the mandible protrusion Anterior guidance inhibited for complete ‣ Cause - downward and forward denture occlusion movement of condyles down to their ‣ Avoids the dislodging of denture bases articular eminences On the balancing side ‣ Often results in a posterior open bite ‣ maxillary lingual cusps contact lingual incline of mandibular buccal cusps On the working side ‣ maxillary lingual cusps contact facial incline of mandibular lingual cusps + mandibular buccal cusps contact lingual incline of maxillary buccal cusps Figure 5.02 Protrusive record 3 Occlusion Plane of Occlusion Interpupillary line – theoretical line Figure 5.03 Balanced occlusion between pupils of the eyes Camper’s line – theoretical line from ala of nose to tragus of ear Bennett Maxillary occlusal wax rim must be parallel Bennett angle – created due to to both lines nonworking condyle moving anteriorly & ‣ Fox plane (metal instrument) used for medially relative to the sagittal plane measurement ‣ 15º on average Bennett movement – lateral movement of Lingualized Occlusion both condyles toward the working side Lingualized occlusion occurs when only the Bennett shift – lateral movement of palatal cusps of the maxillary posterior teeth mandible toward the working side during contact the mandibular posterior teeth. lateral excursions Eliminates the destabilizing buccal forces on the dentures INBDE Booster | Booster PrepTM Prosthodontics 14 Factors that Favor Disclusion Factors that favor disclusion (no eccentric contacts) of posterior dentition when entering and leaving MI Horizontal movement: Steep incisal guidance Ant Guidance Lateral movement: Steep Figure 5.04 Benett canine guidance Compensating Curves Horizontal movement: Steep Curve of Spee – the curve of the horizontal condylar mandibular occlusal plane recognized from Post Guidance inclination the beginning of the tip of lower cuspid Lateral movement: Less and following the buccal cusps of the Bennett movement/side shift posterior dentition and stopping at the terminal molar. Cusp Anatomy Short and shallow inclines ‣ More mesial inclination distally ‣ Flatter curve = faster separation of teeth Tooth Less curve of Spee (disclusion) Arrangement Less curve of Wilson Curve of Wilson – mediolateral curve that Less parallel to orientation of follows posterior cusp tips to ensure proper Occlusal Plane the condylar path loading into the long axis of each tooth ‣ More lingual inclination distally ‣ Flatter curve = faster separation of teeth (disclusion) INBDE Pro Tip: Factors that favor eccentric occlusion on posterior teeth are the direct opposite of the factors that favor disclusion. If you know one, you know the other. Figure 5.05 Compensating curves INBDE Booster | Booster PrepTM  Prosthodontics 15 Phonetics 1 Sibilant/Linguoalveolar Sounds 3 Linguodental Sounds Sibilant or Linguoalveolar sounds begin with a Linguodental sounds begin with the th- sound. s-, z-, sh-, ch- or j- sound. Upper and lower teeth contact with the tip Lingual surface or anterior palate of teeth of the tongue contact with the tip of the tongue Labiolingual position of anterior teeth can Can be heard when counting through 60s be identi ed Determines vertical overlap and length of ‣ If tongue is not visible= teeth need to be anterior teeth reset more backward Lisp (s- instead of sh-) = arch too wide ‣ If tongue more anterior than the teeth = Whistling sounds = arch too narrow teeth need to be reset more forward Uses closest speaking area (s sounds) to establish vertical dimension during 4 Bilabial Sounds pronunciation of s-sound ‣ Interincisal separation = 1-1.5mm Bilabial sounds begin with a b-, p- or m- sounds. 2 Labiodental Sounds Both lips contact Sounds could also be produced during Labiodental or fricative sounds are insuf cient lip support by teeth or by the pronunciations that usually begin with a f-, v-, labial ange or ph- sound. Maxillary incisors contact the wet/dry line 5 Guttural Sounds of the lower lip Useful for identifying the position of the Guttural sounds begin with a g- or k- sound. incisal edges of maxillary anterior teeth on Back of tongue and throat contact dentures Ask the patient to counting through 40s to hear fricative sounds INBDE Pro Tip: The linguoalveolar and labiodental sounds are the most important to know for the exam. INBDE Booster | Booster PrepTM fi fl fi  Prosthodontics 16 Support, Stability & Retention 1 Support, Stability & Retention Cohesion Attraction of similar molecules Demonstrated by attraction between saliva Support Support refers to resistance to vertical seating molecules Thick and ropy saliva is unfavorable forces Structures providing the most support to Thin and watery saliva are favorable the upper ridge (due to resistance to allowing for better retention resorption): ‣ Creates a thin and undisturbed lm layer of saliva between the denture and soft ‣ Alveolar ridge tissue ‣ Palate Structures providing the most support to the lower ridge: Adhesion Attraction of dissimilar molecules ‣ Retromolar pad Saliva to tissues and saliva to denture base ‣ Buccal shelf These supporting structures are what the ‣ Intimate contact of denture base to denture base sits on tissues creates the best seal Stability Surface Tension Adhesion and cohesion forces that Stability refers to the resistance to horizontal dislodging forces. maintain lm layer integrity Stability in the upper and lower upper Water molecules are prefer to attach to ridges is determined by the following: each other to the surroundings ‣ Depth of vestibule ‣ Allows for the creation of the peripheral seal that is resistant to dislodgment ‣ Ridge height ‣ For dentures the ange will provide the stability 3 Denture Extension Issues Retention Retention refers to the resistance to vertical Too long dental ange dislodging forces. ‣ Can result in an ulcer or sore spot from continued wearing 2 Peripheral Seal ‣ Treat by relieving the denture followed by re-evaluation Achieved by the peripheral seal by the Too far back denture extension denture ‣ Denture teeth can extend onto the ramus In order to understand the peripheral seal, we ‣ Causes denture dislodgment need to understand some molecular concepts. INBDE Booster | Booster PrepTM fi fl fl fi Prosthodontics 17 Underextension Too short dental ange = less surface area = lack of retention INBDE Pro Tip: The alveolar ridge is the best indicator of denture success (wide & broad preferred). INBDE Booster | Booster PrepTM fl Prosthodontics 18 Denture Materials & Processing 1 Pink Acrylic (Gums) 2 Denture Teeth Heat-Cured Acrylic There are two main options for denture teeth Heat-cured acrylic – material cures by thermal material. reaction. 1. Porcelain PMMA = polymer (powder) ‣ More stain and wear resistant (more ‣ Salts of iron, cadmium, or organic dyes = esthetically pleasing) pigment ‣ Brittle ‣ Benzoyl peroxide = initiator ‣ Mechanical retention is necessary MMA = monomer (liquid) ‣ May wear opposing teeth ‣ Hydroquinone = inhibits MMA 2. Acrylic monomers from polymerization on its ‣ Better retention own - Due to bonding with acrylic resin of the ‣ Dimethyl-p-toluidine = activator (breaks denture base down benzoyl peroxide into its radical form) ‣ Glycol dimethacrylate = cross-linking agent during curing Figure 8.01 Heat-cured acrylic Denture Processing Polymerization shrinkage always occurs, but excessive shrinkage can occur if more monomer is used ‣ Monomers bonded together take up less space than unbonded monomers Ideal ratio = 1:3 (monomer : polymer) Porosity happens due to underpacking with resin during the processing phase or rapid heating INBDE Booster | Booster PrepTM  Prosthodontics 19 Kennedy Classi cation 1 Kennedy Classi cation #6 Other edentulous areas are referred as modi cations Kennedy classi cation is used to classify the #7 Extent of modi cation does not matter patient’s pattern of edentulism. Class IV cannot have any modi cations #8 by de nition Class I Bilateral distal extension Examples Class II Unilateral distal extension Example Classi cation Kennedy Class III Class III Mod 1 Unilateral edentulous space with natural teeth remaining both anterior and posterior to it. Class IV Single edentulous space that crosses the Kennedy Class II midline which is located anterior to the Mod 3 remaining natural dentition. 2 Applegate’s Rules Kennedy Class III Applegate’s rules can be used to assign Mod 2 Kennedy classi cation without any confusion. Rule #1 Classi cation follows extraction #2 Missing third molars are not considered Kennedy Class I Mod 1 #3 Abutment third molars are considered Missing second molars are not #4 considered The most posterior edentulous area #5 determines the classi cation INBDE Booster | Booster PrepTM fi fi fi fi fi fi fi fi fi fi fi  Prosthodontics 20 Connectors 1 Major Connector Thickest central component of the metal framework Primary function - gives rigidity to the denture Combines all other components of the metal framework Not located on movable tissue ‣ Palate (maxilla) ‣ Lingual aspect of mandibular alveolar Figure 10.01 Complete palatal plate (left), Horseshoe complete palatal plate (right), ridge (mandible) Palatal stap (bottom) All major connectors should cross the midline at a right angle Maxillary Major Connector Beading There are several different designs for maxillary This concept is exclusive for maxillary major major connectors. connectors and has the scribing of a 0.5mm 1. Complete palatal plate rounded groove in the cast at the borders ‣ Most rigid of the major connector ‣ Indications Adds strength and maintains tissue contact - periodontally compromised teeth, to prevent food impaction - when all posterior teeth are missing bilaterally Mandibular Major Connector - abby ridges There are different designs for mandibular - shallow vault major connectors. 2. Horseshoe Complete palatal plate 1. Lingual Bar ‣ Least rigid ‣ Depth of lingual vestibule ≥7mm ‣ Solely used if there is a large palatal torus 2. Lingual Plate 3. Palatal Strap ‣ Depth of lingual vestibule Ceramic Material CTE Composite 30 (un lled resin worst) Amalgam 25 Gold 14 (best) Tooth 11.4 Porcelain 6 Desirable Mechanical Properties In summary, desirable mechanical properties of a restorative material include the following: CTE close to the CTE of tooth High elastic modulus ‣ Does not ex easily High yield strength ‣ avoids permanent deformation Casting accuracy ‣ Gold is more accurate than base metal Corrosion resistance ‣ More noble = more corrosion resistance Minimal wear of opposing dentition ‣ Porcelain has poor wear resistance compared to metals Biologic compatibility INBDE Booster | Booster PrepTM fi fi fl Prosthodontics 37 Provisional Crowns Crown Fabrication Steps: Mold There are mainly 3 different ways to mold the 1. Crown preparation on tooth contour of the tooth during fabrication of the 2. Impression of crown prep provisional restoration. 3. Gypsum 4. Provisional crown 1. Prefabricated Crown 5. Permanent crown ‣ Stainless steel – commonly used in 6. Cementation of permanent crown pediatrics ‣ Polycarbonate *Note a digitally scanned tooth prep can ‣ Aluminum eliminate the impression and gypsum steps as well as eliminate the need for a provisional crown by providing a same day crown. A provisional crown is a temporary crown Figure 19.01 Prefabricated crown meant to provide functionality and esthetics during the interim period while the nal prothesis is being fabricated. 2. Putty or shim The provisional crown should still abide ‣ Used to take impression of the tooth by the three principles of tooth before crown prep is performed or with preparation (biologic, mechanical, diagnostic wax up esthetic). ‣ Filled tooth impression with temporary crown material - Place on patients mouth to set (direct) - Place on cast to set (indirect) 1 Provisional Crown Fabrication Method There are two different methods of making a provisional crown. 1. Direct = created within patient’s mouth ‣ Faster process, no lab time ‣ More chairside time Figure 19.02 Putty/shim ‣ More common method 2. Indirect = created outside of patient’s 3. Cellulose acetate crown form mouth ‣ Comes in different sizes and shapes ‣ Usually created in the lab on a cast model ‣ Trimmed to custom t the margins of the ‣ Avoids chemical and pulpal irritation to tooth without impinging of soft tissue tissues ‣ Filled with temporary crown material ‣ Less chairside time INBDE Booster | Booster PrepTM fi fi  Prosthodontics 38 Material Bis-Acryl Composite – direct ‣ Less polymerization shrinkage ‣ Minimal irritation ‣ Lower strength than PMMA PEMA ‣ Not common PMMA ‣ Indirect method ‣ Strong ‣ Easy to repair ‣ Exothermic reaction – easily irritates pulpal tissues (hence indirectly) Removing Provisional Crown Once the permanent crown is fabricated, the provisional crown needs to me removed and the tooth prep cleaned before cementation. Con rmation of occlusion dif cult with anesthesia ‣ Try to avoid delivering local anesthesia unless the patient is sensitive Eugenol (provisional cement) prevents polymerization of permanent resin cement ‣ Use explorer, excavator or wet cotton pellet to remove as much as possible of Eugenol before placing resin cement during crown cementation INBDE Booster | Booster PrepTM fi fi  Prosthodontics 39 Metal-Ceramic & All Ceramic Crowns 1 Metal-Ceramic Crown Adhesive Failures – failure occurs between different material Metal-Ceramic crowns have a layer of metal ‣ In oxide-metal layer if metal is surrounded by a thick layer of porcelain. contaminated Require monomolecular oxidative layer ‣ In porcelain-oxide layer if porcelain is for porcelain to bond/attach to metal alloy contaminated ‣ Dark color presents an esthetic challenge ‣ In porcelain-metal layer if oxide does not form Porcelain Layers Long-span PFM bridges A metal-ceramic crown is often without ‣ Fractures due to exure forces porcelain on the lingual side and only has porcelain layering on the buccal side for esthetics 2 All-Ceramic Crowns Chamfer margin on lingual and shoulder margin on buccal All-ceramic crowns are mainly used for their Occlusal contacts ≥1.5mm away from esthetic principles. There are two different porcelain-metal junction types. 1. Glass in ltrated ceramics – can be The porcelain can be layered for different bonded to the tooth effects on each layer. ‣ Using hydro uoric acid etch and silane 1. Opaque porcelain – covers dark oxide coupling agent (allows bonding) with minimum thickness (0.1mm), creates ‣ More esthetic porcelain-metal bond 2. Ceramics with no glass content- do not 2. Body/dentin porcelain – constitutes most bond of the crown ‣ Attached to the tooth with luting cement 3. Incisal/enamel porcelain – most ‣ Stronger, but less esthetic translucent layer Metal-Ceramic Failures 3 Porcelain Veneers There can be several reasons for failure of a metal ceramic crown. Porcelain veneers only cover the facial side of Cohesive Failures – failure occurs within a tooth. They are purely esthetic in function. the same material ‣ Oxide layer is too thick Porcelain veneer tooth prep is as follows. ‣ Voids or inclusion in porcelain-porcelain Intra-enamel preparation layering Incisal reduction = 1-2mm ‣ Does not occur in metal-metal Facial reduction = 0.5mm Gingival third reduction = 0.3mm INBDE Booster | Booster PrepTM fi fl fl Prosthodontics 40 4 Maryland bridge (resin bonded bridge) A Maryland bridge consists of teeth made of porcelain or PFM with metallic wings on one or both sides that attach to natural teeth. Debonding with resin-bonded bridge is more likely in comparison More removal of tooth structure needed with conventional bridge INBDE Booster | Booster PrepTM  Prosthodontics 41 Shade Selection 1 Color Theory Fluorescence – releasing visible light under UV light ‣ Tooth vs composite can uoresce at different shades Munsell Color System ‣ Material with higher uorescence tends There are 3 main ways to describe color. to match teeth more better 1. Hue – color family Opalescence – observed when a 2. Chroma – color saturation translucent object appears blue when 3. Value – lightness or darkness under re ected light and red-orange under ‣ Ideal for shade selection of crown transmitted light ‣ Shorter wavelengths scatter in the tooth ‣ Longer wavelengths go through the tooth Shade Selection and Color Shade selection should be conducted in a certain order to best match the adjacent teeth. 1. Value – found in middle third of the crown 2. Chroma – found in cervical third of crown 3. Hue – found in incisal third of crown 2 Characterization Characterization of a tooth refers to the reproduction of natural defect on a crown. There are several ways this can be achieved. Figure 21.01 Munsell Color System Staining – loss of uorescence, ↑ metamerism, ↓ value ‣ 0 (black) to 100 (white) ‣ Affects color of tooth Effect of Light Source Glazing – melting porcelain surface to ll in The light source that is present is crucial to defects selecting the best shade. There are 3 concepts ‣ Mainly affects surface texture related to how light can affect how we Porcelain can get darker by adding more perceive color. color (stain), but reversing is not possible Metamerism – Difference of color ‣ When in doubt, pick a shade with less appearance with different lighting saturation and higher value because you ‣ Ex. color looks different under direct can correct it later on sunlight vs indirect sunlight vs artificial light ‣ Ideal light – 5500K (kelvin) and 100% CRI (color rendering index) ‣ Important to stay consistent in light source when shade matching INBDE Booster | Booster PrepTM fl fl fl fl fi Prosthodontics 42 3 Crown Delivery The following is the general order of steps of what to evaluate in the crown before it is cemented. 1. Shade (esthetics) 2. Proximal contacts 3. Margins 4. Fit 5. Retention and resistance form 6. Occlusion 7. Contour 8. Cement INBDE Booster | Booster PrepTM  Prosthodontics 43 Dental Cements 1 Types of Cements INBDE Pro Tip: From 1-6 on the dental cements list, technique Dental cements or luting agents that connect sensitivity increases while solubility decreases. the underlying tooth structure to the prosthesis. There are mainly 6 types of 2 Crown and Cements Armamentarium cements. 1. Zinc Oxide Eugenol Crowns made of different materials should be ‣ Inhibits polymerization of resin paired with certain cements over other ‣ Temporary/provisional cement cements. ‣ Base and accelerator mixed ‣ Eases pulp 2. Zinc Polycarboxylate Crown Cement ‣ Powder and liquid Zirconia Luting cement ‣ Minimal pulp irritation (ceramic but no silica) (GI or RMGI) ‣ Chelation to calcium = weak bond to tooth Metal Luting cement (PFM or full gold) (GI or RMGI) 3. Zinc Phosphate ‣ Phosphoric acid disturbs pulp Lithium Disilicate Resin cement ‣ Exothermic reaction (emax) (dual cure) ‣ No chemical bond to tooth = luting agent Feldspathic porcelain Resin cement 4. Glass Ionomer (veneers) (light-cure) ‣ Powder and liquid ‣ Releases uoride Out of all the zinc cements, only zinc oxide ‣ Attaches to enamel and dentin 5. Resin Modi ed Glass Ionomer eugenol is used today as a temporary cement. ‣ Stronger & lower solubility than Glass Ionomer (GI) Resin cement and Crowns - Due to addition of resin Resin cement requires additional steps in the cementation process. ‣ Ex. RelyX Luting Plus 6. Resin 1. Dentin or etched enamel applied with primer and bonding agents ‣ Binds to dentin & most compressive strength 2. The crown is etched with hydro uoric acid and then line it with silane coupling agent ‣ Chemical, light cure, or dual cure varieties - Dual cure (RelyX Unicem and RelyX 3. Fill with resin cement Ultimate) – have light and chemical cure 4. Seat the crown on the tooth component - Light cure (RelyX Veneer cement) is more color stable than dual cure cement and chemical cure cements INBDE Booster | Booster PrepTM fl fi fl  Prosthodontics 44 Lab Processing of Crowns 1 Die Creation 1. Casting After the master cast of a patient’s dentition Casting – metal is melted into the investment has been created. Then, a die is created for the tooth receiving the crown 2. Recovery Die - a positive reproduction of the tooth Recovery – breaking the investment to recover prep the metal cast framework Ditching a die – cleans away any stone below the margin to expose the tooth prep 3. Quenching Die spacer – thin painted on layer that Quenching – immediately placing hot cast accounts for the cement layer metal into the cool water ‣ Provides space for cement Process allows cast to be more malleable for nishing 2 Crown Processing Steps After die creation, there are a series of steps for producing the crown. 1. Waxing Waxing - creates a positive of the crown 2. Spruing Spruing – a pathway for metal to ow into the prosthesis as it is being casted 3. Investing Investing – Use investment material to create a negative by covering the wax Figure 23.01 Crown processing steps Investment material ‣ Phosphate-bonded investments  PFM ‣ Gypsum-bonded investments  gold ‣ Silica-bonded investments  base metal 4. Burnout Burnout – wax positive is melted INBDE Booster | Booster PrepTM fi fl Prosthodontics 45 3 Porosity Issues Several errors can arise during lab processing of the crown. Heating too fast can cause porosity of acrylic Inadequate condensing of porcelain can cause the porosity of porcelain Sprue being too short can cause back- pressure porosity of metal ‣ A short sprue does not allow gas to leave which subsequently blocks uids from entering Sprue too thin can cause shrinkage porosity of metal INBDE Booster | Booster PrepTM fl