Foundation Complete Denture Prothetics 2024/25 PDF

FOUNDATION COMPLETE DENTURE PROSTHETICS 2024/25 Disclaimer: Advanced Diploma of Den...

FOUNDATION COMPLETE DENTURE PROSTHETICS 2024/25 Disclaimer: Advanced Diploma of Dental Technology Some diagrams and information are from the internet. This is used for teaching purposes only. Prepared by PS Cheung ASSESSMENT Continuous assessment Practical Assessment 20% Written test & Speed test 10% Examination Practical 35% Written 35% 2  AIMS OF UNIT Understand the design of complete dentures Understand the principles of occlusion, retention and stability Understand the principles of articulation Understand the finishing procedures of acrylic resin dentures Be able to design and construct a Class I complete denture to a satisfactory standard 3  AIMS OF UNIT Be capable of recognising and correcting occlusal errors which may occur during processing Understand the clinical procedures for obtaining recordings for the replacement of fitting surfaces and be able to perform appropriate laboratory reline and rebase procedures on complete dentures Be able to understand the principles and use appropriate techniques involved in repairing dentures Be able to understand the principles and use appropriate techniques to repair dentures. 4  CONTENT Introduction Complete Denture Procedures Edentulous Anatomical Landmarks Denture Outline Denture contour affected by musculature Key Concepts In Prosthodontics Skeletal jaw relation & facial profile 5 INTRODUCTION 6 Definitions of key Terms Prosthetics: the field of study and research of the replacements for missing parts of the human body. Prosthodontics: The branch of dentistry pertaining to the restoration and maintenance of oral function, comfort, appearance, and patient health. Prosthesis: An artificial replacement of an absent part of the human body. What is a denture? Dentures (also known as false teeth假牙) are prosthetic devices constructed to replace missing teeth; they are supported by the surrounding soft and hard tissues in the oral cavity. What is a complete denture? Complete(Full) denture is a denture worn by a patient who is missing all teeth in a single arch either the maxillary or mandibular arch What are the other kinds of dentures? 1. Removable partial dentures/ prosthetics devices are for patients who are missing some of their teeth in a single arch 2. Fixed partial dentures, also known as “crown and bridge” dentures, are made from crowns that are fitted on the remaining teeth What is the meaning of ‘Edentulous’? Edentulous refers to a lack of teeth. Edentulous space is an area of the mouth without teeth. An edentulous patient is a patient who has complete loss of dentition (teeth).  Reasons for tooth loss Traumatic injuries創傷 Caries蛀牙 Periodontal diseases牙周病 Cysts囊腫, malignancies惡性腫瘤, and tumors腫瘤 Radiation therapy for tumors 腫瘤放射治療 Severely misaligned teeth Iatrogenic extraction醫源性拔牙 Congenitally missing teeth先天性缺牙 Failure to erupt (impacted teeth)  Residual alveolar ridge Alveolar ridge is the bone that surrounds the teeth and provides support for them. Residual ridge is the bone that remains after tooth loss and can also experience resorption over time.  Residual alveolar ridge Various changes take place in the alveolar ridge after tooth extraction or loss. The empty socket fills with clots and is gradually replaced with new bone The bone reorganizes around the socket The mucoperiosteum骨膜heals and covers the healing socket The remodelling process results in a rounded ridge is called residual alveolar ridge  Residual alveolar ridge Rate of resorption alveolar bone is gradually absorbed throughout life most rapid in the first year, can be as high as 4.5 mm after healing of residual ridge, annual rate reduction in height is about 0.1-0.2mm in mandible mandible annual rate of reduction is 4X higher than maxilla  Residual alveolar ridge Rate of resorption Maxilla upwards and inwards looks smaller Mandible downwards and outwards looks wider Objectives of Complete denture Aesthetic - restoration of facial appearance Restoration Function of Mastication Improve speech Maintenance of the health of temporomandibular joint(TMJ) Preservation of oral structure/anatomy Psychological comfort of patient CD PROCEDURES 18 Complete denture step-by-step The procedure for providing dentures consists of five key stages: Straight forward, simple scheme Clinical procedure Laboratory procedure 1.) Primary impression > Manufacturing of custom trays 2.) Secondary impression > Manufacturing of registration rims 3.) Interocclusal registration > Set up of teeth 4.) Try-in > Processing of denture 5.) Fitting (Delivery of dentures)  Clinic 2nd visit Clinic 1 st visit Primary impression is taken from patient’s mouth by stock tray.  Clinic 2nd visit Laboratory 1 st step Pour the working impression and fabricate special/custom trays.  Clinic 2nd visit Clinic 2 nd visit Final impression is taken from the patient’s mouth by special/custom trays.  Clinic 2nd visit Laboratory 2 nd step Pour the working models and fabricate wax rims for bite registration  Clinic 2nd visit Clinic 3 rd visit Interocclusal registration with wax rims and marking references  Clinic 2nd visit Laboratory 3 rd step Mounting up the models with jaw relation record and setting up artificial teeth  Clinic 2nd visit Clinic 4 th visit Denture wax try-in  Clinic 2nd visit Laboratory 4 th step Processing of denture  Clinic 2nd visit Clinic 5 th visit Fitting(Delivery of denture) Complete denture step-by-step Complicated scheme (production lab workflow) (Permanent base + using semi-adjustable articulator) Clinical procedure Laboratory procedure 1.) Primary impression > Manufacturing of customized tray 2.) Secondary impression > Manufacturing of permanent base + registration rims 3.) Bite registration + facebow taking > Set up of teeth in flat plane 4.) Aesthetic try-in + lateral & protrusion bite registration > Set up (balanced) 5.) Final try-in > processing of denture 6.) Fitting (Delivery of dentures) 7.) Review > Check record if necessary  Clinic 2nd visit Clinic 1 st visit Primary impression is taken from patient’s mouth by stock tray.  Clinic 2nd visit Laboratory 1 st step Pour the working impression and fabricate special/customized tray.  Clinic 2nd visit Clinic 2 nd visit Final impression is taken from the patient’s mouth by special/customized tray.  Clinic 2nd visit Laboratory 2 nd step Pour the working models and fabricate permanent base plate with wax rims for bite registration  Clinic 2nd visit Clinic 3 rd visit Bite registration + Facebow taking  Clinic 2nd visit Laboratory 3 rd step Mounting up the models with facebow jaw record and setting up artificial teeth in flat plane  Clinic 2nd visit Clinic 4 th visit Denture wax aesthetic try-in and lateral & protrusion bite registration  Clinic 2nd visit Laboratory 4 th step Set up teeth in balanced occlusion  Clinic 2nd visit Clinic 5 th visit Final Try in  Clinic 2nd visit Laboratory 5 th step Processing of denture  Clinic 2nd visit Clinic 6 th visit Fitting(Delivery of denture)  Clinic 2nd visit Clinic 7 th visit Review – check record if necessary 42 EDENTULOUS ANATOMICAL LANDMARKS 43 ANATOMICAL LANDMARKS Maxilla Frenum Labial frenum Buccal vestibule are folds of mucous membranes and do not contain significant muscle fibers. High frenum attachments will compromise denture retention and may Buccal frenum require surgical excision (frenectomy). 44  ANATOMICAL LANDMARKS Maxilla Buccal vestibule Labial frenum Buccal vestibule Properly filling with the denture flange greatly enhances stability and retention. Buccal frenum 45  ANATOMICAL LANDMARKS Maxilla Incisive papilla Incisive papilla is a fibrous tissue pad over the nasopalatine canal. Pressure in this area can disrupt blood flow and compress the nerve, causing pain or a burning sensation. It is important to Canine eminence relieve the denture in this region. 46  ANATOMICAL LANDMARKS Maxilla Canine eminence Incisive papilla This important bone supports dentures. A square arch prevents denture rotation, making it the best for stability. Canine eminence 47  ANATOMICAL LANDMARKS Maxilla Tuberosity is a crucial primary support area for dentures, providing resistance to horizontal Tuberosity movements. Posterior Palatal Seal Area 48  ANATOMICAL LANDMARKS Maxilla Rugae Raised areas of dense connective tissue in the anterior 1/3 of the palate. This area resists anterior displacement of the denture and is a secondary support area. 49  ANATOMICAL LANDMARKS Maxilla Hamular Notch This narrow cleft runs from the tuberosity to the pterygoid muscles. The pterygomandibular ligament connects to the pterygoid hamulus at the medial pterygoid plate of the sphenoid bone. The hamular notch is essential for maxillary denture design, as improper moulding can cause soreness and reduce retention. 50  ANATOMICAL LANDMARKS Maxilla Fovea palatine Two small depressions in the mucosa on either side of the midline. This location of the relief area aids and acts as an ideal guide for the posterior border of the maxillary denture. 51  ANATOMICAL LANDMARKS Maxilla Midline palatal suture Extends from the incisive papilla to the distal end of the hard palate. The overlying mucosa is tightly attached and thin; relief is required to prevent soreness. The underlying bone is dense and often raised, forming a torus palatinus. 52  ANATOMICAL LANDMARKS Maxilla Hard palate Extends from the incisive papilla to the distal end of the hard palate. The overlying mucosa is tightly attached and thin; relief is required to prevent soreness. The underlying bone is dense and often raised, forming a torus Hard palate palatinus. 53 ANATOMICAL LANDMARKS Maxilla 54  ANATOMICAL LANDMARKS Ideal maxillary ridge Abundant keratinized attached tissue Square arch U-shaped in cross-section Moderate palatal vault Absence of undercuts Frenal attachments distal from crestal ridges as much as possible Well-defined hamular notch 55  ANATOMICAL LANDMARKS Mandibular Labial frenum Historically and functionally the same as in the maxilla, mucous membrane without significant muscle fibres. Denture outline should be avoided. 56  ANATOMICAL LANDMARKS Mandibular Buccal frenum Historically and functionally the Buccal frenum same as in the maxilla. Denture outline should be avoided. 57  ANATOMICAL LANDMARKS Mandibular Labial Vestibule Limited inferiorly by the mentalis muscle, internally by the residual ridge and labially by the lip. 58 ANATOMICAL LANDMARKS Mandibular Mentalis Elevates the skin of the chin and protrudes the lower lip. It determines the length and thickness of the labial flange extension for lower dentures. 59 ANATOMICAL LANDMARKS Mandibular Buccal shelf The area between the buccal frenum and the anterior border of masseter boundaries which is a primary stress-bearing area supporting the denture 60 ANATOMICAL LANDMARKS Mandibular Retromolar pad The retromolar pad is a stable structure on the bearing surface of a mandibular denture. It contains glandular tissue, loose alveolar connective tissue, and fibres from the buccinator, superior constrictor, and temporal tendon. This area does not resorb under denture pressure, making it a primary support region for dentures. 61 ANATOMICAL LANDMARKS Mandibular Pear shaped pad Refers to the residual scar of the third molar and retromolar papilla Mucosa is firm, stippled and has a dull appearance Anterior to retromolar pad 62 ANATOMICAL LANDMARKS Mandibular Pear shaped pad Associated with Buccinator, Superior Constrictor, Temporalis and firmly bound Masticatory mucosa. 63 ANATOMICAL LANDMARKS Mandibular Lingual frenum is a small fold of mucous membrane that overlies the genioglossus muscle. e it must be Lingual frenum molded well in the impression to prevent displacement of the denture or ulceration of the tissue 64 ANATOMICAL LANDMARKS Mandibular Sublingual folds form by the superior surface of the sublingual glands and the ducts of the submandibular glands. 65 ANATOMICAL LANDMARKS Mandibular Retromylohyoid fossa located behind the mylohyoid muscle and the mandibular alveolar ridge. Recording the shape of the retromylohyoid fossa is important for providing border seal and a stabilizing effect for complete mandibular dentures 66 ANATOMICAL LANDMARKS Mandibular Retromylohyoid space lies at the distal end of the alveolingual sulcus. It is bounded medially by the anterior tonsillar pillar, posteriorly by the retromylohyoid curtain, laterally by the mandible and pterygomandibular raphe, anteriorly by the lingual tuberosity of the mandible, and inferiorly by the mylohyoid muscle. 67  ANATOMICAL LANDMARKS Mandibular Pterygomandibular raphe It is a union of the buccinator and superior constrictor muscles, extending from the hamular process to the retromolar pad. This structure is stretched during the opening of the mouth. 68  ANATOMICAL LANDMARKS Mandibular Masseter grove The action of the masseter muscle reflects the buccinator muscle in a superior and medial direction. The distobuccal flange of the denture should be contoured to allow freedom for this action. 69 ANATOMICAL LANDMARKS Mandibular Mental foramen The anterior opening of the mandibular canal is found between the first and second premolars on the mandible's outer surface. 70 ANATOMICAL LANDMARKS Mandibular Alveolingual sulcus It is extended from the lingual frenum to the retromylohyiod curtain and bounded externally by the residual ridge and internally by the tongue. This space is filled by the lingual flange of the denture. 71  ANATOMICAL LANDMARKS Mandibular External oblique line/ridge The dense bone ridge outside the buccal shelf extends from above the mental foramen, running superiorly and distally to connect with the anterior border of the ramus. This ridge is the attachment site for the buccinator muscle and guides the lateral termination of the mandibular buccal flange. 72  ANATOMICAL LANDMARKS Mandibular Mylohyoid ridge is sharp and irregular and runs along the lingual surface of the mandible. It starts near the inferior border and rises towards the posterior body, ending just distal to the lingual tuberosity. The thin mucosa covering this ridge may become traumatized and should be relieved. 73  ANATOMICAL LANDMARKS Mandibular Torus mandibularis is a bony prominence on the lingual side, near the premolar region. It is covered by a thin mucosa. It is found in 6-8% of the population; 80% of these cases are found bilaterally. It has to be relieved or surgically removed as decided by its size and extent. 74  ANATOMICAL LANDMARKS Mandibular Genial tubercles Two bony structures are located on the anterior lingual side of the mandible. In cases of severe bone resorption, they may shift higher, necessitating surgical correction. The superior tubercle attaches to the genioglossus muscle, while the inferior tubercle connects to the geniohyoid muscle. 75 ANATOMICAL LANDMARKS 76  ANATOMICAL LANDMARKS Ideal mandibular ridge Well-defined retromolar pad Blunt mylohyoid ridge Deep retromylohyoid space Low frenum attachment interference Absence of undercuts Adequate residual alveolar ridge height Abundant keratinized mucosa 77 Complete denture impression is a negative registration of the entire denture bearing, stabilizing and border seal areas present in the edentulous mouth. Wax-boxed impression 78 Complete denture impression Landmarks of a maxillary impression 79 Complete denture impression Landmarks of a mandibular impression 80 81 DENTURE OUTLINE 82  DENTURE OUTLINE 1. Denture periphery – Posterior border – Buccal sulcus – Labial sulcus 2. Denture form 83 UPPER DENTURE PERIPHERY thin flange under the nose, and lip support is gained lower down the flange and from the teeth. the labial edges of the upper central incisors should be between 5.5 - 12 mm from the centre of the incisive papilla. The denture flange is wider from the first premolars backwards to increase the suction by pressing on the cheeks. The denture fully covers the tuberosites, and the post- dam border is just in front of the fovea palatini. 84 UPPER DENTURE PERIPHERY Posterior border Commences from the hamular notch Non-movable tissues close to the foveae 85 UPPER DENTURE PERIPHERY Posterior border Hamular notches Posterior denture border Overextension causes extreme pain, ulcers, displacement Under extension - non-retentive Must be captured in impressions 86 UPPER DENTURE PERIPHERY Posterior border Vibrating line An imaginary line drawn across the posterior part of the palate that determine the junction the movable and immovable tissue can be identified by asking the patient to say ‘ah’. It extends from one hamular notch to the other hamular notch, usually lying 2mm in front of the fovea palatinae. 87 UPPER DENTURE PERIPHERY Posterior border Pterygomandibular raphe - Behind hamular notches – occasionally significant - patient open mouth as wide as possible - Can displace denture – requires relief in extreme cases 88 UPPER DENTURE PERIPHERY Pterygomaxillary seal – extends across the hamular notch and 3-4 mm anterolaterally to end in the mucogingival junction on the posterior part of the maxillary ridge. Post-palatal seal – extends between the two maxillary tuberosities. 89 UPPER DENTURE PERIPHERY Buccal sulcus Sulcus on the buccal side of the tuberosity Height – the attachment of the buccinator muscle Descends following the buccinator attachment to the root of the zygoma Across the buccal frenum 90 UPPER DENTURE PERIPHERY Labial sulcus Shape and depth affected by the levator anguli oris muscle The upper incisive muscle Labial frenum 91 LOWER DENTURE PERIPHERY is thinner in the front and widens towards the back. proper support is essential, with primary support from the buccal shelves and retromolar pads, while the remaining ridge provides secondary support. The denture ends at the mylohyoid muscle insertion, except for a slight extension (2-3 mm) distal to tooth number 6 into the retromylohyoid area. fully cover the retromolar pad at the back for stability and suction. 92 LOWER DENTURE PERIPHERY Posterior border Sweeps outwards from the pterygomandibular raphe Downwards and outwards from the retromolar pad to the first molar region Follows the attachment of the buccinator muscle 93 LOWER DENTURE PERIPHERY The denture border should be contoured to accommodate the interaction of the buccinator and masseter muscles. 94 LOWER DENTURE PERIPHERY Posterior border Retromolar pad - Posterior border of the denture base should terminate on the pad - Compressible soft tissue – affects comfort and denture peripheral seal 95 LOWER DENTURE PERIPHERY Posterior border Retromolar pad – The interior surface of the denture base is in close contact with the mucosa above the retromolar pad. 96 LOWER DENTURE PERIPHERY Posterior border sinew string – is a. frenum or wrinkle-like entity of buccal mucosa. – is usually found along the distal surface of the lower second molar to the third. – denture border should avoid it The denture flange should be designed in this way if sinew string is present. 97 LOWER DENTURE PERIPHERY Posterior border sinew string – Under tension, a mucosal sinew string forms at the buccal root of the retromolar pad – The sinew string located behind the second molar is visible in only 10 to 20% of edentulous patients. It is thought to help pull the buccal mucosa inward during swallowing, closing the space behind the second molar. 98 LOWER DENTURE PERIPHERY Buccal border – Runs forward sweeping sharply is not encroaching on the modiolus; keep as narrow as possible in the region – Curves outwards and downwards in the canine region not too deep into incisive muscle 99 LOWER DENTURE PERIPHERY Labial border – Full extension of the periphery in the incisor region – Mid-line at the periphery should allow room for the labial frenum 100 LOWER DENTURE PERIPHERY Lingual posterior border – Crest of the ridge in the retromolar area – Runs downloads and slightly forwards- affected by the form of palatoglossus muscle – The depth to which the periphery descends depends on the degree of resorption 101 LOWER DENTURE PERIPHERY Lingual posterior border – Rubs forwards along the floor of the mouth – limited by constrictor muscle – Rises slightly to cross the narrow posterior edge of the mylohyoid muscle 102 LOWER DENTURE PERIPHERY Lingual posterior border – Runs forward and follows a gentle curve dictated sublingual gland – Reaches the first premolar region it descends again for a short distance and then rises to clear the lingual frenum 103 MAXILLARY DENTURE FORM Polished buccal surface Concave downwards and outwards Avoid excessive thickness of buccal flange in the second molar region 104 MANDIBULAR DENTURE FORM Polished buccal surface concave downloads and upwards Lingual side – concave sloping outwards and upwards to present no area which overhangs the tongue 105 PERIPHERAL PHYSIOLOGICAL STRUCTURES (MAXILLARY) Labial frenum Labial mucosa membrane reflection area Buccal frenum Buccal mucosa membrane reflection area Fovea palatine Greater palatine foramen 106 PERIPHERAL PHYSIOLOGICAL STRUCTURES (MANDIBULAR) Labial frenum Labial mucosa membrane reflection area Buccal frenum Buccal mucosa membrane reflection area Distal extension of the alveo-lingual area Lingual frenum 107 108 109 DENTURE CONTOUR AFFECTED BY MUSCULATURE 110  Oral cavity 111  MUSCLES ACTIVITIES : Mastication咀嚼 Deglutition吞嚥 Speech 112 112 DENTURE CONTOUR AFFECTED BY MUSCULATURE Correct denture contour increase: Retention Function Comfort Aesthetics of a denture 113 DENTURE CONTOUR AFFECTED BY MUSCULATURE Muscle function is important in several important stages of making complete dentures. Groups of muscle studies are related to complete dentures: Muscles of mastication Muscles of facial expression Muscles of soft palate Muscles of the tongue 114 DENTURE CONTOUR AFFECTED BY MUSCULATURE Muscles of mastication Masseter Temporalis Medial Pterygoid Lateral Pterygoid 115 DENTURE CONTOUR AFFECTED BY MUSCULATURE Masseter The fibres extend from the zygomatic arch downwards and backwards to the outer surface of the ramus of the mandible. The primary action of this powerful muscle is to elevate the mandible. When the masseter contracts, it exerts pressure on the buccinator, which, in turn, shapes the distobuccal corner of the mandibular impression. 116 DENTURE CONTOUR AFFECTED BY MUSCULATURE Muscles of facial expression Modiolus Mentalis Buccinator Orbicularis Oris Incisivus Labii Superioris Incisivus Labii Inferioris 117 DENTURE CONTOUR AFFECTED BY MUSCULATURE Modiolus located laterally and slightly superior to the mouth's corner is a concentration of fibres from extrinsic perioral muscles that connect with the intrinsic fibres of the orbicularis oris muscle. This area significantly impacts the labial flange thickness of the maxillary denture. 118 118 DENTURE CONTOUR AFFECTED BY MUSCULATURE Buccinator provides support and mobility of the soft tissues of the cheek. the muscle fibres contract in a line parallel to the plane of occlusion. as a person ages, tension is lost in this muscle, predisposing誘發them to cheek biting. DENTURE CONTOUR AFFECTED BY MUSCULATURE Mentalis elevates the skin of the chin and turns the lower lip outward. Dictates the length and thickness of the labial flange extension of the lower denture. Incisivus Labii Superioris & Inferioris their action on the vestibular fornix is similar to that of the mentalis muscle. 120 DENTURE CONTOUR AFFECTED BY MUSCULATURE Orbicularis Oris is the sphincter括約肌muscle of the mouth. has no skeletal attachments, and is a composite muscle composed not only of intrinsic固有的fibres but also of extrinsic外在fibres of many muscles that converge at the modiolus. 121 DENTURE CONTOUR AFFECTED BY MUSCULATURE Muscles of the soft palate Tensor Veli Palatini Levator Veli Palatini Musculus Uvulae Palatoglossus Palatopharyngeous 122  LABIAL CONTOUR Orbicularis oris muscle acts less force on the labial surface than the periphery area Permit a more natural anterior position of teeth Incorrectly positioned surface may prevent the surrounding muscles from adopting their normal resting or functional positions, Backward and Upward displacement of the lower denture if lower teeth are placed too forward – pressure from the lip Extension of the upper and lower labial flanges affected by four incisivus muscles and mentalis muscle 123 124  BUCCAL CONTOUR Buccinator muscles contract, the modiolus is drawn backwards, and the cheeks are drawn in towards the teeth The pressure is exerted by the cheek which presses the dentures towards their supporting tissues 125 125  BUCCAL CONTOUR At rest, the passive muscles rest against the buccal flanges Suitably shaped buccinator assists in the stability of the dentures Buccal surface of a maxillary denture which inclined inward and directs a lateral force from the contracting buccinator muscle so that the force would have its greatest superior component and thus tend to seat the denture 126 LOWER BUCCAL CONTOUR Concave, to face up and out, permitting the cheek to cradle in against the flange and give the desired inferior component of forces Overextension causes de-stabilization and trauma to mucosa The contraction of masseter muscle: − Forces the buccinator muscle in a medial direction in the area of the retromolar pad − This action can be recorded in the impression, and the denture border can be contoured to accommodate the action − If not done, this muscle interaction will displace the mandibular denture and force it in an anterior direction 127 LOWER BUCCAL CONTOUR Modiolus A Chiasma of facial muscles held together by fibrous tissue Aid the orbicularis oris and buccinator muscles in their functions associated with mastication, speech and deglutition Masticatory functions pull the modiolus medially, applying forces against the teeth or denture flanges in the premolar area, which can displace them from the tissue. 128 LOWER BUCCAL CONTOUR It is important in moving the mouth, facial expression and in dentistry. It derives its motor nerve supply from the facial nerve, and its blood supply from labial branches of the facial artery. 129 LINGUAL AND PALATAL CONTOUR The flanges and palatal surface should be conformed to the shape, which avoids impairing the tongue movements and assists in stability The alveolar palatal surface of the denture should be concave, permitting the greater superior component of tongue force The lingual flange of the lower denture should be slightly concave and face in and up 130 LINGUAL AND PALATAL CONTOUR The occlusal surface of the mandibular teeth to be at a level slightly below the greatest convexity of the sides of the tongue If the occlusal plane is too high than the tongue will tend to displace the denture in its efforts to reach up on the occlusal surface 131 132 133  KEY CONCEPT IN PROSTHODONTICS 134 Retention, Stability and Support Four kinds of displacing forces:  Muscular  Masticatory  Mechanical  Gravitational 135  MUSCULAR FORCES Most powerful displacing forces The muscles surrounding the oral cavity and the tongue These forces are used to grind the food to bolus and swallow These movements are powerful, and unless the dentures are very firmly seated Liable to be moved about with the food during mastication During the opening of the mouth, the muscles of the cheeks tense 136   MASTICATORY FORCES Denture rotates when subjected to masticatory load Depends on the amount of retention on the side of the denture opposite to that of the applied load Depend on the periphery seal and, to a certain extent, on the ability of the buccinator to grasp the denture 137   MECHANICAL FORCES Reduce displacement forces by proper technique and design Unbalanced occlusal contact Tooth contact on one side of the dental arch is not balanced by contact on the other side Tipping of the dentures takes place, causing breaking of the border seal with consequent loss of retention Occlusal interference Interference and locking of the cusps of the teeth as the lower moves across the upper in chewing This inference tends to displace both dentures from their seating. 138  GRAVITATIONAL FORCE Gravity will lead to the falling of the upper denture The weight of the denture depends on the materials used The thickness of the denture base 139 Retention, Stability and Support Retention: Resistance to vertical displacement away from the bearing surfaces Stability: Resistance to lateral displacement Support: Factors of the bearing surfaces that absorb or resist forces of occlusion 140 Retention, Stability and Support The success of complete denture treatment mainly depends on the retention, stability, and support of the dentures. - Good retention allows the denture to stay in place when the jaws are apart, such as during laughing and speaking. - Good stability prevents the dentures from shifting when the jaws come together, as in chewing or swallowing. - Good support prevents the dentures from sinking into the tissue under the load of mastication. 141 Retention, Stability and Support Retention The ability of a denture to resist removal along its path of insertion and withdrawal Resists vertical movement away from the tissue 142 FACTORS AFFECTS RETENTION  Physical forces  Physiological structures  Mechanical aids  Anatomical factors 143   PHYSICAL FORCES Adhesion Cohesion Surface Tension Capillary Action / Attraction Atmosphere pressure (Suction) Gravity 144   PHYSICAL FORCES Adhesion The physical attraction existing between dissimilar bodies in close contact This force acts most powerfully at right angles to the surfaces is proportional to the area of the surfaces in contact 145   PHYSICAL FORCES Cohesion The apparent force of attraction existing between similar bodies in close contact A denture base is made accurately to fit the mucosa membrane on which it rests, and intervening between the two surfaces is saliva – similar to the film experiment 146  PHYSICAL FORCES Adhesion and Cohesion 147   PHYSICAL FORCES Surface Tension Tension/resistance to separation possessed by the film of liquid between two well-adapted surfaces Found in the film of saliva between the denture base and the mucosa Molecules on the inside attract the surface molecules inward, resulting in potential energy called surface tension 148   PHYSICAL FORCES Adhesion, Cohesion and Surface Tension Factors affect those physical forces The shape of the mouth Its surface area The closeness of the denture to the tissues The direction of the displacing forces 149   PHYSICAL FORCES Adhesion, Cohesion and Surface Tension Lower denture has a very small surface area; its adhesion effect is less The viscosity of saliva is important in the phenomenon of cohesion. A thin film of saliva resists flow much more readily than a thicker film Viscous saliva increases the thickness of the saliva film reduces retention 150   PHYSICAL FORCES Capillary Action / Attraction is a force (developed because of surface tension) that causes the surface of a liquid to become elevated or depressed when it is in contact with a solid It is what causes a liquid to rise in a capillary tube The denture base is sufficiently close to the mucosa, the space filled with a thin film of saliva acts like a capillary tube and helps retain the denture This force, like the other, is directly proportional to the area of the basal seat covered by the denture base 151   PHYSICAL FORCES Atmosphere pressure can act to resist dislodging forces applied to dentures if the dentures have an effective seal around their borders. This resistance force has been called “suction.” 152   PHYSICAL FORCES When a perpendicular force is exerted on a properly extended complete denture to dislodge it, pressure between the prosthesis and mucosa drops below the outside pressure, thus resisting displacement. Retention due to atmospheric pressure is directly proportionate to the area covered by the denture base. 153   PHYSICAL FORCES Effective atmospheric pressure the periphery of a denture should bed into the soft tissues in the sulci and slightly displace the buccal and labial mucosa to produce a facial seal Proper border molding with physiological, selective pressure techniques is essential for taking advantage of this retentive mechanism. The pressure acting on the fitting surface of the denture is less than that acting on the non-fitting surface 154   PHYSICAL FORCES Aspects influence the amount of retention obtained: A. Border seal B. Area of fitting surface C. Accuracy of fit D. Balanced occlusion 155 A. BORDER SEAL The periphery border of the denture at all points should be formed so that the tissues when at rest or under muscular tension, will remain in close contact with their periphery border preventing the ingress of air between the denture and tissues Posterior border of upper denture – sometimes post- dam is used post-dam – a border seal is obtained by cutting a groove in the posterior border of the working cast 156  A. BORDER SEAL Post Dam also known as a posterior palatal seal is the raised posterior border of a maxillary removable complete denture that places pressure within physiological limits on the posterior palatal seal area of the soft palate to aid in its retention 157  A. BORDER SEAL Post Dam Depth Width 0.5mm 1.5mm 1mm 158 B. AREA OF FITTING SURFACE Degree of physical retention is proportional to the area of the fitting surface Ensure maximum extension of the dentures so that the optimum retention 159 C. ACCURACY OF FIT The thinner the saliva film between the denture and underlying mucosa, the greater the forces of retention Therefore, the fitting surface of the dentures is as accurate as possible A poor fit will increase the thickness of the saliva film and increase the possibility of air bubbles occurring within the film The bubbles reduce the retention The bubbles also move to the periphery when displacement forces are acted. This will break the periphery seal. 160 D. BALANCED OCCLUSION A perfectly balanced occlusion of the teeth will aid in the stability of the dentures and maintaining the border seal. No interference and group function 161 162 162  PHYSIOLOGICAL STRUCTURES dentures are foreign objects the muscles may initially expel in the mouth. the wearer learns to distinguish between food and the dentures. This process requires conscious effort, but eventually it becomes subconscious. the wearer learns to control and stabilize the dentures using the tongue and cheeks. older patients may struggle to develop the necessary skills, which can lead to failure even if the dentures are technically suitable. 163  PHYSIOLOGICAL STRUCTURES Tongue While the tongue resting on the lower denture, it prevents the tendency to rise and counterbalance to a large degree, stabilizing masticatory forces Can also be unconsciously trained to prevent the posterior border of the upper denture from dropping while the front teeth are incising 164  PHYSIOLOGICAL STRUCTURES Muscular cheeks Trained to press downwards on the buccal flanges of the lower denture while still carrying out their function of placing food between the teeth Lips Trained, again unconsciously, to press downwards on the labial flanges of the lower 165   MECHANICAL AIDS Devices which aid in holding complete dentures permanent use should only be employed as a last method They require a high degree of skill in construction - Springs - Rubber suction discs - Magnets - Subperiosteal implants 166 SPRINGS Made of coiled stainless steel or gold-plated base metal Have their ends attached to swivels in the premolar areas on both sides of the upper and lower dentures Dentures are thus permanently attached to each other Are held in occlusion for insertion into the mouth. The dentures are released and forced apart by the action of the spring and held in place 167 RUBBER SUCTION DISC It is buttoned on a stud sunk into the fitting surface of a denture Partial vacuum created within the perimeter of this disc holds the upper denture suspended from the hard palate cause a constant irritation on palate epithelium 168 MAGNET (REPELLING) Small steel magnets embedded beneath the denture base Arranged with similar poles opposite each other, has been advocated The repulsion effect thus keeps the dentures apart and in place 169 IMPLANTS Subperiosteal implant Embed substructure in the alveolar and superstructure in the denture A high degree of skill and specialist experience Suitable for patients with insufficient retention problem Magnet, snap, screw type Excellent result but expensive 170   ANATOMICAL FACTORS Arch size: Retention increases with an increase in the size of the denture-bearing area. The size of the maxillary denture- bearing area is about (24 cm²) & that of the mandible is about (14 cm²). Arch form: Squared, ovoid, tapered, and the best one is the squared. 171   ANATOMICAL FACTORS Ridge form: The crest is high and flat from recent extraction, but there is no space for teeth placement. Flat one is difficult and has no retention and stability, so in taking the impression, try to extend it beyond the mylohyoid area to gain more stability and retention. Ridge with undercut is more common in the upper (bilateral maxillary tuberosity), so we do surgery on one side and block out the other. We have to change the insertion path. 172   ANATOMICAL FACTORS Ridge form: Knife ridge is difficult and causes lacerations and pain, so we do relief. Flabby ridge fibrous tissue is movable and lacks a proper seal, leading us to either adjust the impression technique or perform surgical correction. Parallel-walled alveolar ridges enhance retention. 173   ANATOMICAL FACTORS Volt form: U-shaped → good in retention and stability. V-shaped → have retention but no stability, and any pressure on it could break the seal. Flat-shaped → not enough depth, so no retention and stability. 174   ANATOMICAL FACTORS Arch relationship: most edentulous patients have class III → because of the pattern of bone resorption of the ridges. Almost no protrusive movement, only opening and closing. class II has a small surface area, and it is difficult to get occlusal contact. 175   ANATOMICAL FACTORS Interarch distance: Small interarch space, more retention Tongue: If too big → it could interfere with a denture, so dislodging of the lower and upper. Mucosa: We need it to be firm, compressible and even thick. not be thick and flabby." 176 Retention, Stability and Support Stability Neither denture should rock when finger pressure is applied alternately to either side of the occlusal surfaces in the first molar region. Horizontal displacement should not result in a shift of the centre line of more than 2 mm. 177  STABILITY Its quality of being firm, steady, and constant in position when forces are applied to it To resistance against horizontal movement and Forces that tend to alter the relationship between the denture base and its supporting function in a horizontal or rotatory direction 178  STABILITY Affected by: 1. The size and form of the basal seat 2. The quality of the final impression 3. The form of the polished surfaces 4. The proper location and arrangement of the artificial teeth 179  STABILITY The size and form of the basal seat Vertical height of the residual ridge - the residual ridge should have sufficient vertical height to obtain good stability. Highly resorbed ridges offer the least stability. 180  STABILITY The size and form of the basal seat Vault shape - a steep palatal vault may enhance stability by providing a greater surface area of contact and long inclines approaching a right angle to the direction of force. 181  STABILITY The size and form of the basal seat Vault shape - U-shaped: ideal for both retention and stability. - V-shaped: retention is less as the peripheral seal is easily broken. - Round: reduced resistance to lateral and rotator force 182  STABILITY The quality of the final impression An accurate impression has maximum coverage and increased stability. Impressions should be recorded in the stress-bearing areas under stress and relief with no or minimum pressure. (border molding) 183  STABILITY The form of the polished surfaces should be harmonious with the oral structures should not interfere with the action of the oral musculature. The area which is situated laterally and slightly above the corner of the mouth is known as the muscular node or the (modiolus), which is a concentration of many fibers of this group of muscles. 184  STABILITY The form of the polished surfaces the labial flange of the maxillary denture should be reduced in thickness to not affect the upper denture's stability. The first mandibular premolar should be positioned on the crest of the residual ridge to avoid interfering with the modiolus. The activation of the masseter muscle pushes the buccinator muscle against the denture border in the retromolar pad area. 185  STABILITY The proper location and arrangement of the artificial teeth Occlusal plane: should be oriented parallel to the ridge If the occlusal plane is higher than that level of the tongue it will interfere with the stability at the denture because the tongue will move too far high to bring the bullous of food between the teeth from the lingual vestibule which lead to dislodgment of the denture. 186  STABILITY The proper location and arrangement of the artificial teeth Occlusal plane: should be oriented parallel to the ridge If the occlusal plane is higher than that level of the tongue it will interfere with the stability at the denture because the tongue will move too far high to bring the bullous of food between the teeth from the lingual vestibule which lead to dislodgment of the denture. 187 Retention, Stability and Support Support Denture support is the resistance to the forces of chewing, occlusal forces, and other pressures applied towards the area where the denture rests. To achieve effective support for the denture, impression procedures are utilized to ensure optimal extension and functional loading of the supporting tissues. 188  SUPPORT The resistance to vertical components of masticatory forces and to occlusal or other forces applied in the direction towards the basal seat The maxillary and mandibular bones and their covering mucosa The effective area of the bone and mucosa may vary the efficiency of the support 189  SUPPORT Supporting tissue Should be in a healthy state exhibiting a round and smooth alveolar bone and mucosa with no sharp or prominent Consists of - Alveolar bone - Periosteum (骨膜) - Submucosa (黏膜下層) - Mucosa (黏膜)  SUPPORT a keratinized outer layer mucosa that varies in thickness the submucosa, attached to the periosteum of the supporting bone, is crucial for denture support. a thick, healthy submucosal layer improves resilience, whereas a thin or inflamed layer can cause trauma and instability. maintaining the height of the alveolar ridge is vital for patients with complete dentures. By reducing pressure in areas susceptible to resorption and directing forces to more resilient regions, we can preserve a healthy residual ridge. 191  SUPPORT Supporting tissue problems Buried roots, unerupted teeth Irregular crest of the bony alveolar ridge Torus palatinus or mandibularis genial tubercles Mental foramen and dehiscence of the mandibular canal - Pressure on the superior dental vessels and nerves 192 193 SKELETAL JAW RELATION & FACIAL PROFILE 194 ANGLE’S CLASSIFICATION In orthodontics, Angle’s classification – a means to differentiate malocclusion Class I, Class II, and Class III of malocclusion with modifications such as divisions and subdivisions In Angle’s classification, the mesiodistal position of the first maxillary and mandibular permanent molars is primarily considered It also takes into consideration the dental arches and jaws and the facial profile In cases where the first molars were missing, the Canine relationship is used 195  ANGLE’S CLASSIFICATION Angle’s Class I: Neutroclusion Molar Relationship: The mesiobuccal cusp of the maxillary first permanent molar occludes with the mesiobuccal groove of the mandibular first permanent molar. Canine Relationship: The maxillary canine's mesial incline occludes with the mandibular canine's distal incline. The distal incline of the maxillary canine occludes the mesial incline of the mandibular first premolar. 196  ANGLE’S CLASSIFICATION Angle’s Class I: Neutroclusion Line of Occlusion: Altered in the maxillary and mandibular arches. – Individual tooth irregularities (crowding/spacing/other localized tooth problems). – Inter-arch problems (open bite/deep bite/crossbite). Mesognathic: normal, straight face profile with flat facial appearance. 197  ANGLE’S CLASSIFICATION Angle’s Class II: Distoclusion (overjet) Molar relationship: the mesiobuccal groove of the mandibular first molar is positioned distally when occluded with the mesiobuccal cusp of the maxillary first molar, which usually rests between the first and second molar. Canine Relationship: the mesial incline of the maxillary canine occludes anteriorly with the distal incline of the mandibular canine, with the mandibular canine's distal surface positioned posterior to the maxillary canine's mesial surface by at least a premolar's width. 198  ANGLE’S CLASSIFICATION Angle’s Class II: Distoclusion Line of occlusion: It needs to be specified but irregular, depending on the facial pattern, overcrowded teeth and space needs. Retrognatic: convex face profile resulting from a mandible that is too small or maxilla that is too large. 199  ANGLE’S CLASSIFICATION Angle’s Class II: Distoclusion Class II Malocclusion has 2 subdivisions to describe the position of anterior teeth: Class II Division 1: The molar relationships are like that of Class II, and the maxillary anterior teeth are protruded. Teeth are proclaimed, and a large overjet is present. Class II Division 2: The molar relationships are Class II, where the maxillary central incisors are retroclined. The maxillary lateral incisor teeth may be proclaimed or normally inclined. Retroclined and a deep overbite exists. 200  ANGLE’S CLASSIFICATION Angle’s Class III: Mesioclusion (negative overjet) Molar Relationship: The mesiobuccal cusp of the maxillary first permanent molar occludes distally (posteriorly) to the mesiobuccal groove of the mandibular first molar. Canine Relationship: Distal surface of the mandibular canines are mesial to the mesial surface of the maxillary canines by at least the width of a premolar. Mandibular incisors are in complete crossbite. 201  ANGLE’S CLASSIFICATION Angle’s Class III: Mesioclusion Line of occlusion: It needs to be specified but irregular, depending on the facial pattern, overcrowded teeth and space needs. Prognathic: concave face profile with prominent mandible is associated with Class III 202 ANGLE’S CLASSIFICATION 203  SKELETAL JAW RELATION Three classes of skeletal jaw relationships: class I, class II and class III Normal Class I Abnormal Class II Class III 204  SKELETAL CLASS I Normal skeletal jaw relationship resulting also a normal alveolar ridge relationship in centric relation In the anterior region, the upper ridge is slightly labial to the lower ridge In the posterior region, the interalveolar crest line between two ridges forms an 80-degree angle to a horizontal plane, i.e. the crest of the lower ridge is slightly buccal to that of the upper ridge The facial profile gives a neutral and normal appearance with no prominence on either the upper or lower jaw contour 205  SKELETAL CLASS II Anterior region: the upper ridge is located much further labially than the lower ridge Posterior region: the crest of the lower ridge is placed lingual to that of the upper ridge The inter-crest line between the two ridges forms an obtuse angle to the horizontal plane. It is called maxillary protrusion or retrognathism Facial profile: retrognathic facial profile. The severity of the retrognathism depends on the severity of the Class II relationship. An edentulous patient previously having Class II division 1 jaw relationship, there will be pronounced upper facial contour and reduced chin 206  SKELETAL CLASS III Anterior region: the upper ridge is located in the same line as or lingual to the lower ridge Posterior region: the crest of the lower ridge is placed much further buccally than that of the upper arch The inter-crest line between the two ridges forms an acute angle to the horizontal plane. It is also called the mandibular protrusion or prognathism Facial profile: prognathic facial profile with a prominent chin and long-face appearance 207  SUMMARY Skeletal jaw relationship classification Class Molar relation Types of occlusion Development of Ridge Profile mandible I Normal Neutroclusion Normal 80 Normal II Distal Distoclusion Underdeveloped Obtuse Retrognathis m III Mesial Mesioclusion Overdevelop Acute Prognathism 208