1. Which is better: roll on-roll up design (self-controlled positioning) or a tilting chair that can lay flat?
  2. Why not choose dental chairs that can go flat?
  3. What convinced Dr. Beach to design the dental table?
  4. What is the concept of proprioceptive derivation?
  5. Why is pd considered the core of ergonomics?
  6. Why categorically condemn the use of tilting dental chairs?
  7. Why are dental chairs an ergonomic risk?
  8. What is wrong with using elbow rests?
  9. Why is the pd working height so high?
  10. Why don’t patients like to be tilted backwards?
  11. Doesn’t pd begin with a pd posture?
  12. Why should health care providers learn about pd and zero concept?
  13. How does one derive the optimal working position, instrument location, etc. for the dental operator?
  14. How does a dental patient get out of a pd treatment position?
  15. What about handicapped patients?
  16. Which is pd, the 3rd finger rest or the 4th finger rest?
  17. Isn’t it bad for MSK health to work from static positions?
  18. What about left handed operators?

Which is better: roll on-roll up design (self-controlled positioning) or a tilting chair that can lay flat?

The roll on-roll up design with no hand or computerized positioning of instrument holders and layout supports is best. Patient body tilters must be compared with self-controlled positioning to separate stations for upright patients and horizontal patients for precise procedures. Patients are upright for first meetings, informed consent, x-rays-brief exams-prosthetic options, and it is best that they stand for self-care exercises, i.e. tooth brushing exercise. Most important, self-controlled positioning directs to 0 points for patient care, and everything used for care reduces chance of error in patient care. Self-controlled or hand aided positioning prevails at home, sitting at tables, rolling on or rolling up from beds etc. We assume self-controlled positioning is most natural to people. This assumption prevails in physicians’ clinics. Why are dentists different?

Why not choose dental chairs that can go flat?

The xyz0 (point of origin for the positions of everyone and everything in the treatment area is centered under the patient pelvis. The chair is basically designed for the seated position with body tilting devices. The patient seat is the wrong 0 point for specifying human centered acts, space, installations and everything we use in a complete treatment area for mouth care. This 0 point with the body tilting function becomes a chair centered base of judgment for everything we do and everything we use in treatment areas. This 0 point is also prone to position error with its effect on treatment method, informed consent and spontaneous interaction with patients. If patients controlled dental chair tilts very few would go back to the best position for treatment, because mechanized positioning is an unpleasant experience – especially to dentist instruments. Even when the chair is flat, the chair shape for buttocks and hinge joints remain, when patient mouths shift up or down to the best treatment position for operators. A support designed for a fixed position at the full rest horizontal provides the best potential to design for comfort during treatment. Chair related equipment must be positioned, after the patient is positioned. Handles and finger switches are covered with disposables or disinfected to be compatible with use of gloved hands. Why not eliminate all of this? Each positioning step is subject to error that makes treatment method prone to error.

What convinced Dr. Beach to design the dental table?

Dr. Beach personally decided to stop using dental chairs based on self-awareness with a sim mouth at home after a long day in the clinic. The balanced head, loosely hanging elbows, seat above knee height, mouth height at his heart height, free legs, a foot controller position with the leg at 30 degrees, and fixed positions of all instrument supports adjacent to the mouth were derived in one evening from self-awareness in open space. He cared for no other dentists; it was only for himself and his patients that he originally conceived of the dental table. After getting what he wanted with more engineering effort than he anticipated, others took him seriously. Dr. Beach had introduced high speed handpieces to a school and saw remaining caries and cutting of adjacent teeth routinely from checking both graduate dentists and undergraduates. It became clear to him that these errors were based on compromised finger control and views of operating points due to dental chair habits. He began to observe error in the use of almost all instruments from ‘reclined’ dental chair habits. He then took the stance of patients in the aim to stop the use of dental chairs with instrument supports and lights positioned by hand. Extra advantages of stabilized patient positioning include the benefits to dentists’ bodies, confidence in a principle for treatment method, improved relations with coworkers, and a lifelong understanding of human-centered organization for total clinics.

What is the concept of proprioceptive derivation?

Proprioceptive derivation (pd) in health care is the process of deriving the best positioning of the operator’s body, patient’s body, assistant’s body, instruments, equipment, and physical space for optimal ergonomic functioning. In dentistry, pd involves an innate introspective process to derive more natural body positioning for performing dental procedures while also considering patient positioning, instrument and equipment design, as well as the layout of the environment in which the dental procedures are performed.The process of applying proprioceptive feedback allows the participant (the self-appraiser) to decide for him or herself the best use of the body for clinical practice. The individual uses feedback from the proprioceptive neurons to discern the least physical effort and most efficient way to perform procedures in the mouth. In using the pd process, the eyes are masked to avoid distractions from visual clues and to focus attention on all muscles of the body while specific dental procedures are mimed. Past operating positioning habits and previous experience with dental instruments and equipment are disregarded.

Why is pd considered the core of ergonomics?

The outcome of applying pd results in skillful use of the body and ensures that human performance is measurable and verifiable. It reflects the essential principle of ergonomic functioning-using the least human effort needed to resist the effects of gravity that contribute to body disorders, errors in procedures and outcomes due to fatigue, stress, and strain, and the waste of material resources. Understanding pd as the core of ergonomics is most useful because it links the proprioceptively perceived body positions and movement with body space, body contacts and measurements of anything such as the length of a needle, diameter of an instrument handle or the angle and xyz location of the most frequently used handpiece in its holder in relation to the mouth.

Why categorically condemn the use of tilting dental chairs?

1. GEPEC data revealed that patients signaled they are most comfortable after 20-30 degree tilts. Patients need to be told that the dental chair needs to be further declined for the best position for their treatment. Avoid this hassle and have the patient go directly to the treatment position optimum for access to their mouth. The machine manipulation of patients’ bodies contradicts the daily living conditions of human beings with self positioning everywhere except for the disabled who are normally assisted by hands — not machines. 2. The main reason to reject dental equipment with a rotation axis between the patient pelvis and upper body is that positioning of the upper body of the patient is prone to routine position error that leads to error in treatment method and most important error in judgment of lifetime patterns for patient care including communication and clinic management. Some tilting dental chairs may qualify for a “needs improvement” rating by GEPEC. However, almost all dental chairs on the market today have a rating of “Unacceptable.” 3. The 9’oclock position of the operator common with dental chair use is not valid because it sets the instrument placement vectors at 90 degrees from the operator’s midsagital (zy) plane with its significant control handicap. Instrument placement vectors are best set in an operator’s sagittal (zy) plane for optimum control vectors from fingers and hands for safety in treatment method. Position error with compromised treatment method can be seen everywhere in dental chair clinics by anyone aware of the reference balanced upright and full rest positions for best use of human bodies.

Why are dental chairs an ergonomic risk?

A tilted dental chair forces the operator to the 9 o’clock position where neutral joint positions are not possible because of the patient’s shoulder and chest.This is one reason why dental chair users treat patients in a variety of awkward positions.The 9 o’clock seated operator position increases body tension especially from body twists and side leans of the head. A second reason is patient centered operators set dental chair equipment in wrong places and adjust their bodies for reach, stabilization, and sighting. For evidence see dentists and dental students in any dental chair clinic. A third reason is that dental chair manufacturers encourage stomach level placement of the operating point that directs forward leaning, promotes the use of elbow rests, and the opportunity for slouching.

What is wrong with using elbow rests?

Elbow rests distract the focus of attention on the operation and are another unnecessary expense.

Why is the pd working height so high?

As a norm, human eyes and the positioning of the human arm have evolved to best see fine detail at the finger tips in the midline of the body at arm pit level +- 12 cm.. This range is close to the level of the heart, however, the arm pit is easier to locate. Anecdotal evidence indicates those who are sightless from birth intuitively prefer this range when fine finger control is necessary. These observations reflect the isolation of the use of vision from the feel for position to maintain optimal finger control. Dental manufacturer recommendations for stomach level treatment has evolved because of object-centered thinking.

Why don’t patients like to be tilted backwards?

Patients do not like to be tilted backwards because they do not have eyes in the back of their head and their semicircular canals indicate an alarming condition out of their control. Patient’s automatically think something bad is happening to them the way their body is conditioned from everyday life.

Doesn’t pd begin with a pd posture?

First of all, there is no such thing as a pd posture. The balanced upright trunk and head is a given for optimum finger control and associated views by the way humans have developed. It is simply self sensed from proprioceptive feedback -it is not derived from pd. It is true that pd begins with balanced upright bodies. However, balanced upright bodies not postures are visually appraised by others. Most important is what we sense from self assessment of tissue stretch which includes the cilia in the inner ear. We dentists want to know the best use of our bodies in patient care which is expressed through our fingers and tongue -our most flexible body parts.

Why should health care providers learn about pd and zero concept?

When a clinic owner obtains information on how to work, how to organize/administrate their clinic, or design and equip their clinic the most reliable source for their decision is their own proprioception coupled with logic, zero concept, for minimal waste of effort, decisions, and manufactured resources. The benefits of this approach to health care are great.

How does one derive the optimal working position, instrument location, etc. for the dental operator?

Pd tests are strictly feel-based and involve miming health care procedures with masked eyes in open space (that is, in areas unrestricted by objects). Masked eyes reduce sensory input so that the individual’s self-appraisal of how s/he performs imagined dental procedures focuses on perceiving any strain associated with body position and paths of motion. This includes establishing the best position for the operating point in the patient’s mouth to ensure optimal precision of the dental operation being “performed.” Once the operating point is determined, the paths of motion for locating instrument supports, holders, monitors, switches and other technologies are identified in relationship to the operating point, again through masked miming procedures. This involves assessing the strain in the body, particularly of the eye, neck, and foot muscles, in regard to the frequency, duration, and time that it takes to access whatever equipment, instruments, switch, monitor, or materials that are needed to perform the operation. The appraisal process next considers procedures from both the patient’s and assistant’s perspectives by having the dental care provider assume these roles. Participant appraisers do this, still masked, to better understand the stresses and strains and motion paths experienced during procedures from both the patient’s and the assistant’s points of view. In summary, the primary conclusions derived by this method include – positions for the operator’s body, limbs, and fingers while in use and at rest; – the points on the body, including fingertips and feet, that come in contact with patients and objects for stable control and sightings of the operating points. – human supports and material objects that account for pd body space, paths of motion of body parts, and location of instrument supports. Importantly, the pd process is human-centered rather than object-centered because it focuses on discerning the safest and most efficient way to perform dental procedures from the operator’s, the patient’s, and the assistant’s perspectives.

How does a dental patient get out of a pd treatment position?

Human beings want to have control of their bodies after the age of two years old. Dental patients are not helpless unless they are completely sedated. Nearly 100% of dental patients sleep in a bed at night. Getting out of a pd treatment position is no different that getting out of bed. If a patient needs assistance the action of clinic personnel would be no different than what he/she were to offer someone in their own home: a steady hand or arm assist.

What about handicapped patients?

Human beings relate best to flat surfaces for security and stability against gravity. Pd clinic surfaces are flat making them more accommodating to the handicapped compared to wavy surfaced dental chairs. Direct transfers from gurneys and wheel chairs are easier. Handicapped patients that can not lay on their backs including pregnant women can lay on their sides for treatment. Pd space and locations of instruments accommodates dental operators who are handicapped and in wheel chairs.
Video (Thai language)

Which is pd, the 3rd finger rest or the 4th finger rest?

The closer the finger rest point to the operating point, the finer finger control becomes. The 3rdfinger rest enables the operator to have better control than the 4th finger rest because the 3rdfinger during treatment stabilizes the instrument. It is impossible to stabilize an air turbine without the 3rd finger contact. The same applies to any other instrument including an explorer, an excavator or a scaler. It is more natural to use the 3rd finger than the 4th finger to locate the instrument to the operating point. When the 4th finger is used as a finger rest, the 3 fingers which hold an instrument do not have a contact with tooth surface, so that stronger force may be applied to a tooth during treatment. In other words, the 3rd finger rest enables the operator to have a feather (light) touch easily. It is also better to minimize the number of fingers inserted in the mouth during treatment. A disadvantage of the 3rd finger rest is the extent of movement of the controlled object is limited. This, however, translates into the finer control that is achieved with the 3rd finger rest.

Isn’t it bad for MSK health to work from static positions?

No, only static positions from non-pd positions. Avoid non-pd static positions. Adopt static pd positions when fingers are directed to operating points.

What about left handed operators?

Dental work is mostly finger work. The hand in general dentistry is only engaged in efforts of force such as with extractions by elevators and forceps. Humans have evolved with equal dexterity of fingers. Otherwise, they could not type or play musical instruments including the piano with repeated accuracy. It is true if one has not used certain fingers for a task that they will feel awkwardness. However, this is overcome with practice. Approximately 13-15 % of the human population has been reported to be left dominant. Of this population about 8 % are naturally ambidextrous. The rest need to determine if the use of primarily their right fingers in oral care is better for the administration of clinics in the United States and getting along with assistants who need to learn to work from the opposite side of the patient. Dental students in Asia, where left armed units are not offered in schools, have for years worked only with the right fingers There is always the option to pay additional costs for convertible units and expect dental assistants to work equally well from both sides of the patient. The impact of convertible units in the administration of large clinics and the training skill of dental assistants need to be considered before electing this alternative. The few, if any, strongly left fingered dentists can work with one-sided handpiece holders with minor inconvenience of a midplane transfer. Surgical, endodontic, materials related, anesthetic, and prosthetic instruments and devices are all picked up by left fingers or by an assistant and placed in the operator’s right or left fingers or hand. GEPEC specifies a small right side tray because very few instruments are picked up with the operator’s right fingers.

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