removable Flashcards
Clinical indications for RPDs:
- Missing large number of teeth on both sides of the arch
- Remaining teeth are not suitable abutments for fixed bridge 3. Implants are contraindicated
- Patient preference
- Financial limitations
- Need for an immediate or temporary prosthesis
- Failed fixed bridgework
- Need to replace existing RPD
Clinical contraindications for RPDs:
- Missing small number of teeth on one side of the arch
- Remaining teeth are not suitable as abutments for RPD
- Implant placement may be possible with careful planning
- Patient expectations are not realistic
- Non-compliant patient / poor oral hygiene
- Aesthetic demands impossible to satisfy
- Several unsuccessful previous attempts to provide satisfactory RPD
Anatomical features of the partially dentate maxilla:
- Labial / buccal sulci
- Labial / buccal frena
- Incisive papilla
- Rugae
- Residual alveolar ridge
- Palatine raphe
- (Palatine torus)
- Palatal gingival remnant
- Vibrating line / soft & hard palate junction
- Fovea palatini
- Maxillary tuberosity
- Hamular notch
Anatomical features of the partially dentate mandible:
- Labial / buccal / lingual sulci Labial / buccal / lingual frena
- Genial tubercles (Mandibular tori)
- Residual alveolar ridge
- Buccal shelf
- Mylohyoid ridge
- Retromylohyoid fossa
- Retromolar pad
Q: Why is it so important to know all the anatomical features of the partially dentate arch?
- Anatomical landmarks that will guide us to setting up the artificial teeth
- Anatomical structures that determine / limit denture extension
- Anatomical features to avoid!
The Kennedy classification system of partially edentulous arches:
- Class I: bilateral edentulous areas located posterior to the remaining teeth
- Class II: unilateral edentulous area located posterior to the remaining teeth
- Class III: unilateral edentulous area bounded by remaining teeth
- Class IV: single, bilateral edentulous area located anterior to the remaining teeth
Top 5 hazards in the Dental Laboratory:
Maximal intercuspal position (ICP):
the complete intercuspation of the opposing teeth independent of condylar position, sometimes referred to as the best fit of the teeth regardless of the condylar position
Retruded contact position (RCP):
Guided occlusal relationship occurring at the most retruded position of the condyles in the joint cavities. A position that may be more retruded than the centric relation position.
- Retruded position (RP): same as RCP when there are no tooth contacts (edentulous cases or partially dentate with no occluding pairs of teeth)
What is risk management?
“Risk management is something you do to provide the best possible care for your patients; it is not about avoiding a lawsuit”.
negligence or malpractice:
The person who suffers an injury is entitled to receive damages from the person or people responsible. In health care/dentistry, the most prominent tort liability is negligence or malpractice.
In order for negligence to exist, the following four elements must be found:
- A duty (standard of care) was owed by the dentist to the patient.
- The dentist violated the applicable standard of care.
- The plaintiff suffered a compensable injury.
- Such injury was caused in fact and proximately caused by the substandard conduct.
Difficulties:
The designs of dentures are often left to the dental laboratory, which has to make the most limited information provided by impressions and records of dubious quality.
Risk analysis related to human factor:
▪Tooth loss is associated with many risk factors; some are related to behavior
▪Oral hygiene, attendance, compliance, dietary habits, smoking may all contribute to tooth loss through caries and/or periodontal disease
▪For long term success of any Prosthodontic treatment it is first necessary to reduce the risk of further tooth loss, by modifying the patients’ behavior
Failure of appropriate evaluation of prosthesis foundation:
Avoiding damage by RPD to the remaining tissues:
general rules:
TFO:
Trauma from occlusion (TFO) is a separate entity not related to periodontics. However, both conditions may be present simultaneously.
Definition:
- When occlusal forces exceed the adaptive capacity of tissues, tissue injury results. The resultant injury is termed as trauma from occlusion. It is also referred by WHO as “damage in the periodontium caused by stress on the teeth produced directly by the teeth of the opposing jaw”
Informed consent:
Consent in dentistry is described by Dental Protection* as a communication process by which patients can give their voluntary and continuing permission for specific treatment based upon a reasonable knowledge of the purpose, nature, likely effects, consequences, risks, alternatives and costs of that treatment. Removable dentures require teamwork and the result benefits from effective communication.
Hygienic Principles:
- The advantages of hygienic design are universally accepted.
- They are backed by evidence in the literature and should be considered a medico-legal requirement.
- Avoid unnecessary coverage of the gingival tissues. Where this is not possible, it is advisable to design the denture elements so that they impinge as little as possible on the gingival tissues.
Continuing Care:
The stability of the finished treatment should be observed over a period of time, together with the patient’s anility to maintain the denture environment. Once the patient is comfortable, there should be follow-up at three, six and twelve months to assess the interval for monitoring and maintenance in the future. Where possible, it is sensible to include the cost for follow-up visits in the original fee of the treatment.
Informed Consent:
- A dentist has a legal, ethical and moral duty to respect patient decision
- Disclose all information that enables the patient to evaluate all options available and weigh the risks
- Withholding information creates legal exposure
- Contributes to better treatment outcomes and reduces malpractice risk
Falsification of Records:
- NOTHING destroys your credibility like altering a record!
- Generally sufficient to show actual malice
- Sends the wrong signal to jurors, can shatter credibility
- Creates the presumption of negligence
- Can lead to criminal charges (spoliation)
- Infers gross malpractice
Confidentiality:
- Verbal and written communications
- Protected Health Information (PHI) should not be disclosed without patient’s permission
- HIPAA requires a signed Notice of Privacy Practices or authorization as appropriate
- Violation could incur liability
Mouth preparation for removable partial dentures:
Mouth preparations are identified as those procedures that are accomplished to prepare the mouth for reception of prosthesis.
More specifically they are the procedures that change or modify existing oral structures of conditions to
- Facilitate placement and removal of prosthesis
- Facilitate its efficient physiologic function
- Enhance its long term success
Mouth preparation for removable partial dentures:
objectives:
- Establishing state of health in supporting and contiguous tissues
- Eliminating interferences or obstructions
- Establishing acceptable occlusal plane
- Alteration of natural tooth form for requirements of form and function of prosthesis
Palatal papillary hyperplasia:
- Poorly fitting prosthesis worn for prolonged periods
- Inadequate oral hygiene
- Inadequate prosthesis hygiene
Treatment:
- Tissue rest
- Tissue conditioners
- Surgery
Epulis fissuratum:
Ill fitting prosthesis
Treatment:
- Removal of irritation
- Tissue conditioners
- Surgery
Denture stomatitis:
- Trauma from occlusion
- Ill fitting prosthesis
- Poor oral hygiene
- Continuous wearing of prosthesis
Treatment:
*
Exostosis and undercuts:
- Prevents proper extension of denture
- Undercuts are minimized by changing path of insertion
- Surgical correction
Frena:
- Maxillary labial frenum
- Problems while replacing anterior teeth
- Mandibular frenum
- Compromise rigidity and placement of major connectors
- Frenectomy
Periodontal diseases that require treatment:
- Pocket depths in excess of 3mm
- Furcation involvement
- Gingivitis
- Potential abutment teeth with less than 2mm of attached gingiva
- Pulling of frena on attached gingiva
Elimination of gross occlusal interferences:
➢Selective grinding is indicated when associated with pathologic condition
➢Deflective contacts in centric path of closure are removed
➢Balancing or non-chewing side interferences should be removed
Correction of occlusal plane:
Discrepencies in occlusal plane is due to:
➢Infra erupted teeth
➢Super erupted teeth
➢Tipped molars
➢Mesially drifted teeth
Treated Pulpless Teeth:
Criteria to be followed to use them as abutment
➢Canals have been filled to apex with what appears radio graphically to be well condensed filling material
➢No radioluscency at apex
➢Tooth has been clinically asymptomatic since therapy was accomplished
Abutment tooth with pulpitis:
ENDODONTIC TREATMENT SHOULD BE CONSIDERED !
➢Abutment tooth healthy from standpoint
➢Favorable crown root ratio
➢Prosthesis itself is satisfactory
➢When mouth is in state of good health
Preparation of abutment teeth: Objectives:
➢Directs stress along long axis of tooth
➢Eliminating interference by recontouring of teeth
➢Creating retention by simple alteration procedures
➢Allows placement and removal of prosthesis without having it transmitting wedging types of stress against teeth with which it comes in contact
Preparation of guiding planes:
➢Flat surface created should be 2-4mm in occluso- gingival height
➢Reduction should follow curvature of proximal surface
Lingual surfaces:
➢Occlusogingival height should be 2-4mm
➢Provides maximum resistance to lateral stresses
Anterior abutment teeth:
➢Provides parallelism, ensures stabilization
➢Minimize wedging action between teeth
➢Increase retention through frictional resistance
➢Decrease undesirable space between denture and abutment teeth
Preparation of rest seat:
OCCLUSAL REST:
➢Outline form of occlusal rest is triangular with base of triangle at marginal ridge and apex towards center of tooth
➢Apex of triangle and external margins of preparation should be rounded
Extension:
- Extension of rest seat preparation should vary from 1/3 to 1⁄2 the mesiodistal diameter of tooth
- Buccolingual extent should be half the distance between buccal and lingual cusp tips
- Floor must be spoon shaped
Angle:
Angle formed by inclination of floor of rest and vertical projection of proximal surface of tooth must be less than 90 degrees
In amalgam restorations:
➢Less desirable as amalgam alloy tends to flow under constant pressure
➢Rest seats are prepared using no.4 round bur
➢Care must be taken not to weaken proximal portion
of amalgam restoration
Rest seat preparation for embrassure clasp:
➢Preparation extends over occlusal embrasure of two approximating posterior teeth from mesial fossa of one tooth to distal fossa of other tooth
➢Small round diamond stone is used to establish out line form for normal occlusal rest in each of approximating fossa
➢Contact point between teeth should not be broken
Lingual rest seat:
➢Outline form is half-moon shaped
➢Forms a smooth curve from one marginal ridge to other crossing centre of tooth incisally to cingulum
➢Rest seat is v shaped
- Mandibular canines: are poor candidates for placing lingual rests
Incisal rest seat:
➢Least desirable rests on anterior teeth
➢Used only on enamel surface
➢Usually placed near incisal angles of canine
Preparation:
- First cut is made vertically 1.5-2mm deep in form of notch and 2.3mm inside proximal angle of tooth
Oral factors that affect diet and nutritional status:
Xerostomia
Xerostomia affects almost one in five older adults. Xerostomia is associated with difficulties in chewing and swallowing, all of which can adversely affect food selection and contribute to poor nutritional status. The use of drugs with hypo salivary side effects may have deleterious influence on denture bearing tissues.
Oral factors that affect diet and nutritional status:
other factors:
- Age-related changes in taste and smell may alter food choice and decrease diet quality in some people. Factors contributing to this reported decreased function may include health disorders, medications, oral hygiene, denture use and smoking.
- Presence of natural teeth: The presence of natural teeth and well-fitting dentures were associated with higher and more varied nutrition intakes and greater dietary quality, in the oldest old population.
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Chewing ability
The effect of dentures on chewing ability is that denture wearers tend to use more strokes and chew longer, to prepare food for swallowing.
Masticatory efficiency in complete denture :
Masticatory efficiency in complete denture wearers is approximately 80% lower than in people with intact natural dentition
Oral manifestations of dietary deficiencies:
- Vitamin A: decreased salivary flow; dryness and keratosis of oral mucosa; decreased taste acuity
- Vitamin K: increased blood clotting time following surgery; spontaneous bleeding of gingival tissues
- Niacin: exfoliation of the filiform papillae with a red sore tongue; burning sensation of the tongue and oral mucosa
- Riboflavin: angular cheilitis; red ‘pebbly’ tongue
- Folic acid: smooth red tongue; possible gingival inflammation; possible erosions of the tongue and buccal mucosa
- Vitamin C: easily abraded tissues; delayed healing
- Water: dehydration of oral tissues with resulting xerostomia and related problems
Q: How is ‘good’ masticatory function determined?
- Masticatory ability: an individual’s own assessment of the masticatory function
- Masticatory efficiency: the number of strokes or the time required to reduce food to a certain particle size
- Masticatory performance: indicated by the particle size and distribution of food when chewed for a given number of strokes or time
- Occlusal force measurements: measure functional forces when biting or chewing
- Electromyography: records muscle activity during chewing and maximal biting
Masticatory ability:
- Patients with short dental arch (SDA): few complaint about masticatory ability
- Patients with asymmetric SDA: unilateral chewing is prevalent (side with most teeth)
- They also tend to chew longer and swallow larger food particles
- NO EVIDENCE that wearing an RPD improves chewing comfort
- Instead, dentures do cause some discomfort and are not always used for mastication!
- Increasing age, decreasing number of teeth and impaired masticatory ability are linked, but the relationship seems to be strong only for patients with ˂ 20 teeth
Desirable occlusal contact relationships for RPDs:
✓Aim: to develop a harmonious occlusal relationship with the remaining natural teeth in order to:
1. Restore normal function without introducing a disturbance to the masticatory system
- Enhance the stability of the RPD
Maximum
Intercuspation (MIP):
CR:
The Intercuspal Position:
- Intercuspal Position (ICP), also known as Habitual Bite, Habitual Position or Bite of Convenience , is defined at the position where the maxillary and mandibular teeth fit together in maximum interdigitation, or are maximally meshed together. Some dentists call this position “centric occlusion”, but we prefer to avoid this term as it means different things to different people.
- It can also cause confusion with the term “centric relation”, which is an important but verydifferent concept.
CR:
ICP:
determined by?
Centric relation is determined by the temporomandibular joints (TMJs) but ICP is determined by the positions of the teeth, and because the two do not usually coincide the difference is important.
Physiology of ICP:
- Physiologically, ICP is the relationship of the mandible to the maxilla when the teeth reach the end of the chewing cycle. It is here, at the most closed position of the mandible, that the teeth apply maximum force. It is here that the teeth have closed through the food bolus to break up the food into smaller pieces, and it is also here that the mandible is stabilised, allowing swallowing to take place.
- However, there is a sensitive feedback system to regulate the amount of force applied to the teeth by the jaw muscles. Typically, these forces will:
- vary between 350 and 700 N (10 N approximates to 1 kg) for the maximum biting force
- be about one-third of this during chewing
- be several times higher in the molar than incisor regions.
ICP importance:
The fundamentally important point about ICP is that, (because it is tooth determined), it is a consistent and stable position in case there are enough teeth to define it.
Major connectors:
- The component that connects the parts of the RPD on one side of the arch to those on the other side
- All other parts of the RPD are directly or indirectly attached to the major Connector
- Provides cross arch stability to resist functional forces
Q: What is cross arch stability?
A: resistance against dislodging or rotational forces obtained by using natural teeth on the opposite side of the dental arch from the edentulous space
Free gingival margin (FGM):
- 6mm
Why is that?
- Because of blood supply or deep vascularity of the gingival crevice
In the maxillary arch-the border of the major connector should be at least 6mm from the gingival crevice of the teeth.
In the mandibular arch-it should be at least 3-4 mm from the gingival margin.
Palatal strap:
- Most commonly used in Kennedy Class II cases
- May be rigid without being too bulky, by curving antero- posteriorly and laterally
- Should not extend beyond the occlusal rests at either end
Palatal plate:
- Defined as such when covering more than half of the palate
- Requires close tissue adaptation
- Aim to replicate the natural soft tissue contours of the palate
- As thin as possible
- May be extended posteriorly with addition of acrylic post palatal seal
U-shaped connector:
- Best avoided!
- Not as rigid as alternative options
- Poor support
- Bulk necessary to enhance rigidity may interfere with tongue movements and not be well tolerated
Lingual bar:
- Usually the first choice
- Requires minimum of 7-8mm height between lingual sulcus (when floor of the mouth is raised) and gingival margins
- 3-4mm clearance to gingival margins for hygiene + 4mm bar height
- Half pear shape cross section, tapers towards the tissues superiorly, thicker inferiorly
- Trimmed and polished at inferior border to reduce risk of traumatizing tongue and soft tissues in function
- Excessive trimming may weaken the bar and result to fracture
- Relief necessary to avoid impinging on soft tissues, particularly in Kennedy Class I cases
Sublingual bar:
- Characteristics and Location:
- The sublingual bar is essentially the same half- pear shape as a lingual bar, except that the bulkiest portion is located to the lingual and the tapered portion is toward the labial.
- The superior border of the bar should be at least 3 mm from the free gingival margin of the teeth.
- The inferior border is located at the height of the alveolar lingual sulcus when the patient’s tongue is slightly elevated.
- This necessitates a functional impression of the lingual vestibule to accurately register the height of the vestibule.
Continuous bar +/- lingual bar:
- Indicated when the alignment of the anterior teeth would necessitate excessive blocking out of interproximal undercuts
- Also when there is a need for indirect retention but prefer to avoid lingual plate
May be preferable when the anterior teeth are planned for crown placement to avoid interference with tongue movement (as the bar will lay into milled ledges)
Requirements of rests:
Tooth supported RPDs:
- Rigid framework transfers occlusal forces to abutment teeth through the occlusal rests
- This is regardless of the edentulous span
- Residual ridge does not contribute to support of the prosthesis
- Ridge shape, degree of resorption and resiliency of the mucosa are not important considerations
- The denture base in the saddles should prevent food entrapment and offer support for the facial tissues (e.g. lips), but an under extended base in these cases is usually not detrimental
Tooth & mucosa supported RPDs:
- Are dependent on the residual ridge for part of the support
- No tooth support and no direct retention at the distal end
- Indirect retention becomes an important consideration
- Some movement of the prosthesis must be accepted
Conclusion:
- Maintaining a distal abutment tooth should be our priority!
snowshoe principle’:
This principle is based on the distribution of forces to as large an area as possible. Like in a snow shoe which is designed to distribute forces on the entire base area of the shoe, a partial denture should cover maximum area possible within the physiologic limits so as to distribute the forces over a larger area.
- In a given constant occlusal force, a broader denture bearing area decreases the stress unit area under the denture base
- It decreases tissue displacement and reduces denture base movement
Q: How can you minimize the possible need for chairside adjustments at placement?
Q: Why do you think there may be a need to reline a RPD?
Q: What other factors may affect the rate of residual ridge resorption?
Q: Do you think the closed mouth impression technique is indicated in these cases?
