C H A P T E R                                        3                Design Criteria for           Restorative Dental Mat...
26                                   CRAIG’S RESTORATIVE DENTAL MATERIALS   As discussed in Chapter 2, restorative materia...
3.   DESIGN CRITERIA FOR RESTORATIVE DENTAL MATERIALS                             27plan, build steps, refining the restora...
28                                               CRAIG’S RESTORATIVE DENTAL MATERIALSmaterial developments that are enhanc...
3.    DESIGN CRITERIA FOR RESTORATIVE DENTAL MATERIALS                                 29posterior fixed dental prosthesis,...
30                                   CRAIG’S RESTORATIVE DENTAL MATERIALS    Some diagnoses of a clinical situation may ha...
3.   DESIGN CRITERIA FOR RESTORATIVE DENTAL MATERIALS                                  31for indirect restorations. When t...
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  1. 1. C H A P T E R 3 Design Criteria for Restorative Dental Materials O U T L I N EDesign Cycle Creating the PlanEvidenced Used in Product Design Building the RestorationEvidence-Based Dentistry Patient Evidence Laboratory (In Vitro) Evidence 25
  2. 2. 26 CRAIG’S RESTORATIVE DENTAL MATERIALS As discussed in Chapter 2, restorative materials some regions might have proximal restorations withare exposed to chemical, thermal, and mechanical varying degrees of marginal adaptation. The devel-challenges in the oral environment. The combination opment of a new dental floss product might startof forces, displacements, bacteria, biofilm, fluids, with the problem of a potential customer who has athermal fluctuations, and changing pH contribute to two-surface posterior restoration with an overhang.the degradation of natural and synthetic biomateri- Current floss products on the market shred or tearals. Each patient has a unique combination of these when flossing in such a region. This main observationfactors. When considering a new or replacement is analyzed and deemed significant, because manyrestoration for a patient, the performance history of people with this problem and similar problems couldthe patient’s existing restorations can provide insight be helped by a design change to this dental floss.into the prognosis of the new restoration. The perfor- Multiple and varied ideas are generated to addressmance of materials in controlled conditions, in vitro the problem: (1) the dental floss cross section couldand in vivo, is also useful when selecting materials be a ribbon rather than a rope to ease the floss overand predicting their service life. Making the final the overhang; (2) the floss could be a single strandmaterials choices involves a complex decision-mak- rather than a braid of multiple strands to reduce theing process that can be informed by principles of number of surfaces on the floss that could catch; orproduct design. (3) the floss could be made of a different material or a slippery coating could be added to reduce friction. (Note that all of these designs have been presented to DESIGN CYCLE consumers at one time or another.) Based on these possible design changes, a plan is Considering many factors and integrating many made that incorporates a method or combination ofspecifications into one final product is a require- methods that appear to be most promising in regardment of any object that requires fabrication. In prod- to addressing the observed problem. All of the pos-uct design, a cyclical approach of analyzing and sibilities could have merit, but by selecting thosethen testing problems is used to determine the best that address the observed problem most directly, onedesign for the final production piece. Three catego- can test the solutions most directly. In this example,ries of problem-solving are used in the design cycle: we will say that the floss will be formed as a ribbonobserve, plan, and build. Then the steps are repeated cross section and a change of material will be madeas the time, number of problems, and difficulty of to reduce friction. The new floss is built and tested inproblems allow (Figure 3-1). simulated and actual environments. To illustrate how this process can be applied to One cycle of our design process for a new den-the design of a materials-sensitive product for dental tal floss has been completed. We hope to find inhygiene, we use the simple example of dental floss. our testing that we solved the observed problem.The job this product needs to accomplish is removal That would be an effective solution. What we mayof interproximal plaque and debris. All interproxi- observe through testing our built product, however,mal regions and surfaces are not the same. Some is that the material is too slippery to remove plaqueinterproximal contacts are tight, others are open, and effectively, or the ribbon is too wide to stay flat when drawn through the interproximal contact and into the gingival sulcus. Based on these observations, a Observe new plan is made, a new product version is created, and we find that we have completed another design cycle. We repeat this process creating more refined versions of the product that provide more exacting solutions to the observed problems. We also observe use of the product in as broad a range of consumer groups as possible to ensure the product addresses the needs of the target market. The design cycle for developing new products can Build Plan be used in the planning of restorations as well. When selecting materials for a restoration, one observes the patient’s oral and medical condition and prioritizes the observed problems. The observation data are integrated with valid materials performance data to create a plan of treatment. A restoration is built andFIGURE 3.1 The design cycle: Observe, Plan, Build, …. tested for occlusion, compatibility, esthetics, feel, andRepeat. so forth. Adjustments are made in recurring observe,
  3. 3. 3. DESIGN CRITERIA FOR RESTORATIVE DENTAL MATERIALS 27plan, build steps, refining the restoration to satisfyboth patient and clinician. Scientific evidence EVIDENCE USED IN PRODUCT DESIGN The entire design cycle is based on evidence.Observation provides evidence about the historyof performance of existing materials and solu- Clinician Patient needs,tions and identifies the job that new solutions experience and conditions andmust perform. The thoroughness of the observa- expertise preferencestion phase depends on the skills and experience ofthe designer. In the plan phase, material propertiesand characteristics and test data for performanceof materials in controlled conditions are added tothe observation data. The build phase integrates FIGURE 3.2 The elements of evidence-based dentistry.knowledge of the job or problem with the skill andexperience of the designer and considers varia- abfractions may indicate heavy occlusal contacttions in the operating conditions and properties accompanied by bruxing or occlusal interferences.and known performance of the materials. With- Erosion on anterior teeth suggests elevated levels ofout this systematic and integrative approach, the dietary acids, and generalized wear without occlu-design process would be haphazard and wasteful. sal trauma could involve a systemic disorder suchThe evidence-based design cycle just described is as gastroesophageal reflux disease (GERD). Any ofanalogous to evidence-based decision making in these conditions would compromise the longevity ofhealth care and evidence-based dentistry. restorative therapy. Unusually harsh environments require careful restoration design and selection of materials, sometimes different from the norm. EVIDENCE-BASED DENTISTRY The options for material to be selected then need to be considered in accord with the problems and The American Dental Association (ADA) defines needs exhibited by the patient. These data are foundevidence-based dentistry as an approach to oral health in the scientific literature. The integration of patientcare that requires the judicious integration of sys- data and materials data helps make a more fully con-tematic assessments of clinically relevant scientific sidered plan for treatment.evidence relating to the patient’s oral and medicalcondition and history, along with the dentist’s clini-cal expertise and the patient’s treatment needs and Laboratory (In Vitro) Evidencepreferences (http://ebd.ada.org). This approach is When searching for scientific evidence, the bestpatient centered and tailored to the patient’s needs available evidence, usually compiled from a reviewand preferences. Our goal is to practice at the inter- of the scientific literature, provides scientific evi-section of the three circles (Figure 3-2). dence to inform the clinician and patient. The high- est level of validity is chosen to minimize bias. These studies are typically meta-analyses of randomizedPatient Evidence controlled trials (RCTs), systematic reviews, or indi- Patient needs, conditions, and preferences are vidual RCTs. Lower levels of evidence are found inconsidered throughout the diagnostic and treatment case studies, cohort studies, and case reports. Labo-planning process. Observation of patient needs and ratory studies are listed as “other evidence” becausemedical/dental history occurs first. In this phase, a clinical correlation can be made only as an extrap-performance of prior and existing restorations, in olation of the laboratory data. The listing of benchterms of success or failure, should be noted. This or laboratory research as “other evidence” shouldis often a good indicator of conditions in the oral not be construed as meaning that bench research isenvironment and the prognosis of success of similar not valid. The hierarchy of evidence as presentedmaterials in this environment. The patient’s facial for evidence-based data (EBD) is based on humanprofile and orofacial musculature is a good indicator clinical data, for which bench data can only be aof potential occlusal forces. Wear patterns on occlusal surrogate.surfaces are indicators of bruxing, clenching, occlu- When searching for scientific evidence, the bestsal forces, and mandibular movements. Cervical available, or most valid, data should be chosen. New
  4. 4. 28 CRAIG’S RESTORATIVE DENTAL MATERIALSmaterial developments that are enhancements to for implementing successful materials choices in aexisting products are not required to undergo clini- treatment plan. The elements of EBD and materialcal testing by the Food and Drug Administration properties should be considered as a system to pro-(FDA). Published laboratory or in vitro studies are vide the best patient-centered care. The observed evi-often the only forms of scientific evidence available dence in an assessment of the patient, the analyzedfor materials. This does not mean that no evidence evidence of the laboratory data, the experience of theis available. It is simply an indication that laboratory clinician, and the needs and wants of the patient arestudies should be admitted into evidence for making all related and all impact the prognosis of the resto-the clinical decision (Table 3-1). ration. Although it might be tempting to categorize Researchers in dental materials science have a patient’s needs by age, gender, or general clinicalsought to correlate one or two physical or mechani- presentation, careful data gathering, planning, andcal properties of materials with clinical performance. analysis provides the best solution. This assessmentAlthough it is possible to use laboratory tests to rank is the basis for the complex process of oral rehabilita-the performance of different formulations of the tion (Figure 3-3).same class of material, the perfect clinical predictorremains elusive. Often the comparison of laboratory-based materials studies is difficult because of an CREATING THE PLANincomplete description of methods and materials.Researchers in dental materials are encouraged to The plan phase integrates elements of evidence-provide a complete set of experimental conditions in based decision making and a consideration oftheir publications to enable the comparison of data material properties and performance. The processamong studies. This process will facilitate systematic of treatment planning is familiar to clinicians, butreviews of laboratory studies that can be used as a the practice of designing restorations with materialsource of scientific evidence when clinical studies are properties in mind might not be done routinely. Tonot available. begin, performance requirements are analyzed. The Every patient is unique, including the patient’s environment in which the restoration will serve isoral environment and general physiology. This pro- used as a modifier to the performance requirements.vides a unique set of circumstances and challenges For example, when treatment planning a three-unitTABLE 3.1 Assessing the Quality of Evidence Treatment/Prevention/Study Quality Diagnosis Screening PrognosisLevel 1: good- Validated clinical decision rule SR/meta-analysis or RCTs SR/meta-analysis ofquality, patient- SR/meta-analysis of high-quality with consistent findings good-quality cohort studiesoriented evidence studies High-quality individual Prospective cohort study High-quality diagnostic cohort RCT† with good follow-up study* All-or-none study‡Level 2: limited- Unvalidated clinical decision rule SR/meta-analysis of SR/meta-analysis of lowerquality patient- SR/meta-analysis of lower quality lower quality clinical quality cohort studies or withoriented evidence studies or studies with inconsis- trials or of studies with inconsistent results tent findings inconsistent findings Retrospective cohort study Lower quality diagnostic cohort Lower quality clinical trial or prospective cohort study study or diagnostic case-control Cohort study with poor follow-up study Case-control study Case-control study Case seriesLevel 3: other Consensus guidelines, extrapolations from bench research, usual practice, opinion,evidence disease-oriented evidence (intermediate or physiologic outcomes only), or case series for studies of diagnosis, treatment, prevention, or screeningFrom Newman MG, Weyant R, Hujoel P: J. Evid. Based Dent. Pract. 7, 147-150, 2007.*High-quality diagnostic cohort study: cohort design, adequate size, adequate spectrum of patients, blinding, and a consistent, well-defined referencestandard.†High-quality RCT: allocation concealed, blinding if possible, intention-to-treat analysis, adequate statistical power, adequate follow-up (greaterthan 80%).‡In an all-or-none study, the treatment causes a dramatic change in outcomes, such as antibiotics for meningitis or surgery for appendicitis, whichprecludes study in a controlled trial.SR, Systematic review; RCT, randomized controlled trial.
  5. 5. 3. DESIGN CRITERIA FOR RESTORATIVE DENTAL MATERIALS 29posterior fixed dental prosthesis, the usual consider- because the design of the restoration will determineations will include the length of the span, location, the amount and shape of the tooth reduction.condition of the abutments, opposing occlusion, When creating a plan, the goal is to be succinct,periodontal support of the abutments, parafunc- which is difficult to do considering a goal of thetional habits, oral hygiene, existing restorations in observe phase is to be comprehensive in the gather-the abutment teeth, shape of the edentulous area, ing of data. Some pieces of information will be extra-and esthetic concerns. Other elements for the inte- neous to the treatment problem and can conceal thegrative plan and design are the three-dimensional best plan of treatment. There will be synergistic andgeometry of the edentulous area, potential occlusal contradictory materials solutions for the possibleforce that can be generated, history of other restora- plans of action. There will be features and constraintstions in the region, the cause of tooth loss, and poten- presented by each possible materials choice. Priori-tial materials and their properties. Tooth preparation tization of this information will guide the clinicianoccurs after the restoration is conceptually designed toward the solutions that will be most effective. Data collection 1. Patient information 2. Chief complaint 3. Medical and dental history Observe 4. Physical evaluation 5. Clinical examination 6. Radiographic examination 7. Performance of existing restorations/materials 8. Risk assessment Data integration and system analysis Plan Summary of significant and relevant data and conclusions Patient modifiers 1. Patient conditions and activation level 2. Patient preferences Problem list 3. Materials performance Diagnoses 1. Medical/systemic 2. Oral Clinician modifiers 1. Clinician experience Integrative treatment objectives 2. Materials handling Treatment design Treatment plan Scientific evidence 1. Procedure options 1. Procedures 1. Systematic reviews 2. Restoration and prep 2. Restoration & prep design 2. Clinical trials design options 3. Selected materials 3. Laboratory studies 3. Materials options 4. Rationale 4. Forecasted outcomes 5. Prognosis Definitive Provisional treatment treatment Build Performance review, maintenance, and preventionFIGURE 3.3 A process diagram that illustrates the integration of clinical decision making, evidence, and the design cycle.
  6. 6. 30 CRAIG’S RESTORATIVE DENTAL MATERIALS Some diagnoses of a clinical situation may have a constraints. Each step of the cycle offers opportu-strong basis in the care that was previously provided. nities to prioritize the features and constraints ofA patient may have an upper posterior tooth that is materials for the case and select those that best fit theexhibiting an excessive amount of wear. A lower pos- occlusal scheme. In every design cycle, the solutionterior crown with a porcelain occlusal surface could and problem become more convergent and the qual-be the culprit. Porcelain was chosen for esthetic rea- ity of the final product or service increases.sons. However, the hard porcelain occlusal surface isabrading the upper tooth, resulting in severe occlu-sal wear of the enamel surface. This prognosis could BUILDING THE RESTORATIONbe addressed by restoring the upper tooth, and/orby changing the restoration on the lower tooth to a Building is the next phase. The building requiredsofter material or less abrasive material. Because the for the restoration may be directly applied to thepreservation of natural tooth material is a high prior- tooth or may require several iterative steps to createity, replacement of the lower crown with a material the final product, including a laboratory procedure.that is more harmonious with the occlusal scheme In many intracoronal restorations and some veneers,would provide the best service for the patient. The the restoration is applied directly to the tooth andimportance of a systems approach to observation typically completed in one visit. These are referredand planning is illustrated here, where all factors are to as direct procedures. For these procedures, finalto be considered together, followed by prioritization. material decisions are made prior to any “building” Prioritization is also an opportunity to provide procedures. The plan of treatment must include alleducation and to enhance the patient’s level of acti- materials selections. Fine adjustments are made byvation. It is not uncommon for patients to be unaware adding and/or removing material based on assess-of serious oral problems. For example, interproximal ment of the occlusion, questioning the patient aboutcaries or oral lesions might not be evident to the tactile feel, and evaluating the esthetics and harmonypatient, whereas a single discolored anterior tooth of the restoration with the rest of the dentition andcan be very noticeable. Although the patient’s desire oral environment.for care could be the discolored tooth, prioritizing Some restorative materials are more sensitive tothe care and first acting to treat the immediate dan- technique variations than others. For example, place-ger of infection and disease progression helps the ment of resin composite restorations in posteriorpatent’s overall oral health. The priorities and expec- teeth requires more steps than for an amalgam. Eachtations can be altered so that the most serious issues of these steps require a specified level of precision,are addressed first. that when totaled, equate to a more complex process. The patient may arrive with a materials-specific An error in any step could affect the success of thetreatment in mind, such as a ceramic veneer on the restoration. Clinical expertise therefore is an impor-discolored tooth mentioned earlier. If the tooth is in tant factor when developing a treatment plan andmalocclusion or potentially abutting an opposing selecting restorative materials, particularly when thenatural enamel surface, a ceramic material could be restoration is a direct application to the tooth. Thean unwise choice because of the potential for chip- handling properties of a material are an importantping or wear of the opposing tooth. In this case, com- consideration that is often difficult to measure andposite is a better choice for longevity of the natural describe.dentition. Discussion of the materials available and In indirect restorations that require severalthe potential plans of action can shift the patient’s appointments and a laboratory procedure, prototyp-understanding of the problem to include the unique ing occurs before building. Prototyping can also benature of the case, the desire for a long-lasting, natu- done with direct restorations, for example, by sim-rally colored restoration, and the materials that are ulating the shape and color of a composite veneerbest suited for the case to meet the patient’s initial without curing the material. For indirect restora-goal. The planning then shifts away from the prede- tions, prototyping is done routinely. Creating modelstermined material specification of a ceramic veneer. of the final restoration is helpful because that allowsIncluding the patient in prioritizing his or her care the clinician and patient to discuss and agree onprovides an immediate and personal feedback loop treatment outcomes. This early discussion reducesthat can be incorporated into the planning phase. surprises when the final restoration is delivered to The materials used are both features and con- the patient. The use of models is also an excellentstraints of a restoration. Composites, ceramics, and aid for designing tooth preparations that optimallymetals offer features and constraints that allow their transfer occlusal force through the restoration to theapplications to vary slightly in different treatments. tooth and supporting tissues.The observe, plan, build…repeat cycle is a process that The concept of prototyping is also useful in theaids the identification and analysis of features and fabrication of provisional or transitional restorations
  7. 7. 3. DESIGN CRITERIA FOR RESTORATIVE DENTAL MATERIALS 31for indirect restorations. When the provisional resto- these elements are considered together, an integra-ration accurately simulates the final design in form tive treatment plan and design can be achieved thatand appearance, the patient and clinician can dis- provides the optimal outcome for the patient. Thecuss design outcomes, expectations, and required iterative cycle of design also provides many oppor-modifications. Esthetics is particularly important tunities for discussion between the clinician andto simulate as accurately as possible because of its patient to facilitate agreement on expectations wellsubjectivity. Color, shape, size, and position are all ahead of the delivery of the final restoration.important factors to evaluate to ensure the patient’s Chapter 4 presents concepts of material science,satisfaction with the restoration. Provisional res- including the physical and mechanical properties oftorations also act as important diagnostic aids for materials. A good understanding of the fundamentalstudying occlusion, occlusal forces, parafunctional properties of materials enables the clinician to designhabits, oral hygiene, and soft tissue response. Analy- treatment and prepare oral tissues to best distributesis of the performance of carefully fabricated tran- forces in the oral environment.sitional restorations can provide many clues foroptimal design and fabrication of the permanent Bibliographyrestoration. The transitional restoration is the placefor testing and making iterative modifications to design American Dental Association: ADA Center for Evidence-Based Dentistry. http://ebd.ada.org/. Accessed August 28,concepts before the permanent restoration is fabri- 2011.cated. Observations of occlusal wear facets, cracks, Ashby MF: Materials Selection and Process in Mechanicaldislodgements, discoloration, and discomfort from Design. 1999, Butterworth Heinemann, Oxford.the provisional restoration are all indicators of condi- Ashby MF, Johnson K: Materials and Design, the Art andtions that might be beyond the usual design limits. Science of Materials Selection in Product Design, 2002,Studying the cause of these events can help specify Butterworth Heinemann, Oxford.material properties for the dental laboratory. Bader JD: Stumbling into the age of evidence, Dent Clin Material selection is best made during planning North Am 53(1):15, 2009.and design rather than after tooth preparation. Mate- Brown T: Design thinking, Harv Bus Rev 86(6):84, 2008.rial options for a particular restorative scenario will Forrest JL: Introduction to the basics of evidence-based den- tistry: concepts and skills, J Evid Based Dent Practdiffer in their mechanical and physical properties. 9(3):108, 2009.For example, casting alloys for a fixed dental pros- Forrest JL, Miller SA: Translating evidence-based decisionthesis differ in their stiffness, hardness, malleabil- making into practice: EBDM concepts and finding theity, and corrosion resistance. Higher stiffness alloys evidence, J Evid Based Dent Pract 9(2):59, 2009.will transfer more occlusal stress to the abutments, Martin R: How successful leaders think, Harv Bus Revwhereas lower stiffness alloys will deform and cause 85(6):60, 2007.the prosthesis to deflect. Corrosion resistance is Miller SA, Forrest JL: Translating evidence-based decisionimportant when patients have diets high in acids and making into practice: appraising and applying the evi-consume foods and fluids with high staining poten- dence, J Evid Based Dent Pract 9(4):164, 2009.tial. In another example, ceramics might satisfy the Newman MG, Weyant R, Hujoel P: JEBDP improves grading system and adopts strength of recommendationesthetic requirements of the restoration, but might taxonomy grading (SORT) for guidelines and systematicnot be suitable for the high occlusal loads of patients reviews, J Evid Based Dent Pract 7:147–150, 2007.who brux and clench. Sakaguchi RL: Evidence-Based Dentistry: Achieving a The concepts of the design process—observe, plan, Balance, J Am Dent Assoc 141(5):496–497, 2010.build…repeat—integrate well with evidence-based Vossoughi S: Designing the ‘care’ into health care, Businessdecision making and materials selection. When all of Week Nov 21, 2007.